Omeros Corporation - SEC Filing

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TABLE OF CONTENTS

As filed with the Securities and Exchange Commission on December 4, 2019

Registration No. 333-

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

OMEROS CORPORATION
(Exact name of registrant as specified in its charter)


Washington (State or other jurisdiction of incorporation or organization)		91-1663741 (I.R.S. Employer Identification Number)

201 Elliott Avenue West
Seattle, Washington 98119
(206) 676-5000
(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)

Gregory A. Demopulos, M.D.
President, Chief Executive Officer and
Chairman of the Board of Directors
Omeros Corporation
201 Elliott Avenue West
Seattle, Washington 98119
(206) 676-5000
(Name, address, including zip code, and telephone number, including area code, of agent for service)


With copies to:
Peter B. Cancelmo Vice President, General Counsel and Secretary Omeros Corporation 201 Elliott Avenue West Seattle, Washington 98119 (206) 676-5000		Kerry Shannon Burke Matthew C. Franker Covington & Burling LLP One CityCenter 850 Tenth Street, N.W. Washington, D.C. 20001 (202) 662-6000

Approximate date of commencement of proposed sale to the public:
From time to time after the effective date of this registration statement.

If the only securities being registered on this Form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. o

If any of the securities being registered on this Form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ý

If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

If this Form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ý

If this Form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act.


Large accelerated filer ý		Accelerated filer o		Non-accelerated filer o		Smaller reporting company o Emerging growth company o

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of Securities Act. o

CALCULATION OF REGISTRATION FEE

Title of Each Class of Securities to be Registered	Amount to be Registered⁽¹⁾	Proposed Maximum Offering Price per Unit⁽¹⁾	Proposed Maximum Aggregate Offering Price⁽¹⁾	Amount of Registration Fee⁽²⁾




Common Stock, par value $0.01 per share	—	—	—	—

Preferred Stock, par value $0.01 per share	—	—	—	—

Debt Securities	—	—	—	—

Depositary Shares⁽³⁾	—	—	—	—

Warrants	—	—	—	—

Subscription Rights	—	—	—	—

Units⁽⁴⁾	—	—	—	—

Total	—	—	—	—

⁽¹⁾: An indeterminate number and aggregate initial offering price of securities of each identified class are being registered as may from time to time be offered at indeterminate prices, including an indeterminate number or amount of securities that may be issued upon the exercise, settlement, exchange or conversion of securities offered hereunder. Separate consideration may or may not be received for securities that are issuable upon conversion of, or in exchange for, or upon exercise of, convertible or exchangeable securities.
⁽²⁾: The registrant is deferring payment of all of the registration fee and omitting information from the Calculation of Registration Fee table in accordance with Rules 456(b) and 457(r) under the Securities Act. Pursuant to Rule 415(a)(6) under the Securities Act, this registration statement includes $100,000,000 aggregate amount of unsold securities previously registered in the primary offering under Post-Effective Amendment No. 1 to the registrant's Registration Statement on Form S-3 (File No. 333-219959), which was filed by the registrant on March 1, 2019. Pursuant to Rule 415(a)(6) under the Securities Act, the primary offering of the unsold securities under the previous registration statement was deemed terminated upon the filing of this automatic shelf registration statement. The registration fee previously paid by the registrant with respect to such securities will continue to apply to such securities in accordance with Rule 415(a)(6) under the Securities Act.
⁽³⁾: Each depositary share will be issued under a depositary agreement and will be evidenced by a depositary receipt.
⁽⁴⁾: Each unit will represent an interest in two or more other securities registered hereunder, which may or may not be separable from one another.

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PROSPECTUS

By this prospectus, Omeros Corporation may from time to time offer and sell:

Common Stock
Preferred Stock
Debt Securities
Depositary Shares
Warrants
Subscription Rights
Units

From time to time, we may offer and sell the securities described in this prospectus separately or together in any combination, in one or more classes or series, in amounts, at prices and on terms that we will determine at the time of the offering.

This prospectus may not be used to sell securities unless accompanied by a prospectus supplement, which will describe the method and specific terms of the offering, including the amount, price and terms of the applicable offered securities. You should carefully read this prospectus, the information incorporated by reference in this prospectus, the prospectus supplement, including any information incorporated by reference in such prospectus supplement, and any free writing prospectus before you purchase any of the securities offered hereby.

These securities may be offered and sold in the same offering or in separate offerings, to or through underwriters, dealers or agents or directly to purchasers. The names of any underwriters, dealers or agents involved in the sale of our securities, their compensation and any options held by them to purchase additional securities will be described in the applicable prospectus supplement. See "Plan of Distribution."

Our common stock is listed on The Nasdaq Global Market under the symbol "OMER." On December 3, 2019, the closing price of our common stock was $14.37 per share.

Investing in our securities involves significant risks. Before buying our securities, you should carefully consider the risks described under the caption "Risk Factors" beginning on page 3 of this prospectus, in the documents incorporated by reference into this prospectus, and in the applicable prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is December 4, 2019.

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TABLE OF CONTENTS

		Page

About This Prospectus			ii
Forward-Looking Statements			iii
About Omeros			1
Where You Can Find More Information			2
Incorporation by Reference			3
Risk Factors			3
Use of Proceeds			4
Description of Common Stock			5
Description of Preferred Stock			8
Description of Debt Securities			11
Description of Depositary Shares			22
Description of Warrants			25
Description of Subscription Rights			26
Description of Units			27
Plan of Distribution			28
Legal Matters			32
Experts			32

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ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement on Form S-3 that we filed with the United States Securities and Exchange Commission (the "SEC") using an automatic shelf registration process. Under this shelf process, we may, from time to time, offer or sell any combination of the securities described in this prospectus in one or more offerings.

This prospectus only provides you with a general description of the securities that we may offer. Each time we sell securities pursuant to this prospectus, we will describe in a prospectus supplement, which will be delivered with this prospectus, specific information about the offering and the terms of the particular securities offered. The prospectus supplement may also add, update or change the information contained in this prospectus. Before purchasing any securities, you should carefully read both this prospectus and the accompanying prospectus supplement and any free writing prospectus prepared by or on behalf of us, together with the additional information described under "Where You Can Find More Information."

This prospectus does not contain all of the information included in the registration statement. For a more complete understanding of the offering of the securities, you should refer to the registration statement, including its exhibits. Those exhibits may be filed with the registration statement or may be incorporated by reference to earlier SEC filings listed in the registration statement or in subsequent filings that we may make under the Securities Exchange Act of 1934 (the "Exchange Act").

We have not authorized anyone else to provide you with information that is different or in addition to that contained or incorporated by reference in this prospectus supplement, the accompanying prospectus or any free writing prospectus prepared by us or on our behalf. We do not take any responsibility for, and can provide no assurance to the reliability of, any information that others may give. We are not making an offer to sell or soliciting an offer to buy our securities under any circumstance in any jurisdiction where the offer or solicitation is not permitted. You should assume that the information contained in this prospectus, any prospectus supplement or any free writing prospectus prepared by us or on our behalf is accurate only as of the date of the respective document in which the information appears, and that any information in documents that we have incorporated by reference is accurate only as of the date of the document incorporated by reference, regardless of the time of delivery of this prospectus or any prospectus supplement or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

This prospectus, any prospectus supplement and the information incorporated herein and therein by reference includes trademarks, service marks and trade names owned by us or other companies. All trademarks, service marks and trade names included or incorporated by reference into this prospectus supplement or the accompanying prospectus are the property of their respective owners.

Unless the context indicates otherwise, in this prospectus supplement and the accompanying prospectus the terms "Omeros," "we," "us," and "our" refer to Omeros Corporation, a Washington corporation, and its subsidiaries on a consolidated basis.

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FORWARD-LOOKING STATEMENTS

This prospectus, each prospectus supplement and the information incorporated by reference in this prospectus and each prospectus supplement contain forward-looking statements within the meaning of Section 27A of the Securities Act of 1933 (the "Securities Act"), and Section 21E of the Exchange Act, which are subject to the "safe harbor" created by those sections for such statements. Forward-looking statements are based on our management's beliefs and assumptions and on information currently available to our management. All statements other than statements of historical fact are "forward-looking statements." Terms such as "anticipate," "believe," "could," "estimate," "expect," "goal," "intend," "may," "plan," "potential," "predict," "project," "should," "target," "will," "would," and similar expressions and variations thereof are intended to identify forward-looking statements, but these terms are not the exclusive means of identifying such statements. Those statements appear in this prospectus, any accompanying prospectus supplement and the documents incorporated herein and therein by reference, particularly in the sections entitled "Prospectus Summary" and "Risk Factors," and include statements regarding the intent, belief or current expectations of us and our management that are subject to known and unknown risks, uncertainties and assumptions. Examples of forward-looking statements include, but are not limited to, statements regarding:

•: our expectations related to obtaining permanent separate or similar reimbursement for OMIDRIA® (phenylephrine and ketorolac intraocular solution) 1%/0.3% from the Centers for Medicare & Medicaid Services for periods after September 30, 2020, and our expectations regarding reimbursement coverage for OMIDRIA by commercial and government payers;
•: our estimates regarding how long our existing cash, cash equivalents, short-term investments and revenues will be sufficient to fund our anticipated operating expenses, capital expenditures and debt service obligations;
•: our expectations relating to demand for OMIDRIA from wholesalers, ambulatory surgery centers and hospitals, and our expectations regarding OMIDRIA product sales;
•: our plans for the marketing and distribution of OMIDRIA and our estimates of OMIDRIA chargebacks and rebates, distribution fees and product returns;
•: our expectations regarding the clinical, therapeutic and competitive benefits and importance of OMIDRIA and our product candidates;
•: our ability to design, initiate and/or successfully complete clinical trials and other studies for our products and product candidates and our plans and expectations regarding our ongoing or planned clinical trials, including for our lead MASP-2 inhibitor, narsoplimab (also referred to as OMS721), and for our other investigational candidates, including OMS527 and OMS906;
•: with respect to our narsoplimab clinical programs, our expectations regarding: whether enrollment in any or all ongoing and planned Phase 3 and Phase 2 clinical trials will proceed as expected; whether we can capitalize on the financial and regulatory incentives provided by orphan drug designations granted by the U.S. Food and Drug Administration (the "FDA"), the European Commission or the European Medicines Agency (the "EMA"); and whether we can capitalize on the regulatory incentives provided by fast-track and/or breakthrough therapy designations granted by the FDA;
•: our expectations regarding clinical plans and anticipated or potential paths to regulatory approval of narsoplimab by the FDA and/or the EMA in hematopoietic stem cell transplant-associated thrombotic microangiopathy ("HSCT-TMA"), Immunoglobulin A ("IgA") nephropathy, and atypical hemolytic uremic syndrome ("aHUS");

iii

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•: whether and when a Biologics License Application may be filed with the FDA for narsoplimab in any indication and whether the FDA will grant approval for narsoplimab in any indication, and whether any such approval will be accelerated or regular (full) approval;
•: whether and when a marketing authorization application may be filed with the EMA for narsoplimab in any indication and whether the EMA will grant approval for narsoplimab in any indication;
•: our plans for the commercial launch of narsoplimab following any regulatory approval and our estimates and expectations regarding coverage and reimbursement for any approved products;
•: our expectation that we will rely on contract manufacturers to manufacture OMIDRIA for commercial sale and to manufacture our product candidates for purposes of clinical supply and in anticipation of potential commercialization;
•: our ability to raise additional capital through the capital markets or through one or more corporate partnerships, equity offerings, debt financings, collaborations, licensing arrangements or asset sales;
•: our expectations about the commercial competition that OMIDRIA and our product candidates, if commercialized, face or may face;
•: the expected course and costs of existing claims, legal proceedings and administrative actions, our involvement in potential claims, legal proceedings and administrative actions, and the merits, potential outcomes and effects of both existing and potential claims, legal proceedings and administrative actions, as well as regulatory determinations, on our business, prospects, financial condition and results of operations;
•: the extent of protection that our patents provide and that our pending patent applications will provide, if patents are issued from such applications, for our technologies, programs, products and product candidates;
•: the factors on which we base our estimates for accounting purposes and our expectations regarding the effect of changes in accounting guidance or standards on our operating results; and
•: our expected financial position, performance, revenues, growth, costs and expenses, magnitude of net losses and the availability of resources.

Our actual results could differ materially from those anticipated in these forward-looking statements for many reasons, including the risks, uncertainties and other factors described in our filings with the SEC that are incorporated herein by reference. Given these risks, uncertainties and other factors, actual results or anticipated developments may not be realized or, even if substantially realized, may not have the expected consequences to or effects on our company, business or operations. Accordingly, you should not place undue reliance on these forward-looking statements, which represent our estimates and assumptions only as of the date they are made. The events and circumstances reflected in the forward-looking statements may not be achieved or occur and actual results may materially differ from those projected in the forward-looking statements. Except as required by applicable law, we assume no obligation to update or revise any forward-looking statements contained in this prospectus, the accompanying prospectus supplement or any information incorporated by reference herein or therein, whether as a result of any new information, future events or otherwise.

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ABOUT OMEROS

Company Overview

We are a commercial-stage biopharmaceutical company committed to discovering, developing and commercializing small-molecule and protein therapeutics for large-market as well as orphan indications targeting inflammation, complement-mediated diseases, disorders of the central nervous system and immune-related diseases, including cancers.

Our drug product OMIDRIA® is marketed in the United States for use during cataract surgery or intraocular lens replacement to maintain pupil size by preventing intraoperative miosis (pupil constriction) and to reduce postoperative pain. In our pipeline we have multiple Phase 3 and Phase 2 clinical-stage development programs focused on complement-mediated disorders, including HSCT-TMA, IgA nephropathy and aHUS, and substance abuse. In addition, we have a diverse group of preclinical programs, including GPR174, a novel target in immuno-oncology that modulates a new cancer immunity axis recently discovered by us. Small-molecule inhibitors of GPR174 are part of our proprietary G protein-coupled receptor ("GPCR") platform through which we control 54 new GPCR drug targets and their corresponding compounds. We also exclusively possess a novel antibody-generating platform. For OMIDRIA and each of our product candidates and our programs, we have retained control of all commercial rights.

Recent Events

Clinical Findings in Pivotal Trial of HSCT-TMA Patients Treated with Narsoplimab

On December 4, 2019, we announced positive data in our pivotal clinical trial of our investigational complement inhibitor narsoplimab in the treatment of HSCT-TMA, a frequently lethal complication of HSCT. These preliminary data were recently provided to FDA as part of our ongoing interactions with the agency regarding our rolling BLA submission. The single-arm, open-label trial included safety and efficacy endpoints that were established following discussions with FDA. These endpoints were assessed for (i) all patients who received at least one dose of narsoplimab and (ii) patients who received at least four weeks of narsoplimab dosing.

The primary efficacy endpoint in the trial was the proportion of patients who achieved designated "responder" status based on improvement in HSCT-TMA laboratory markers and clinical status. The primary laboratory markers that were evaluated were platelet count and lactate dehydrogenase ("LDH") levels, while improvement in clinical status was evaluated based on organ function and transfusions. Patients who did not fully meet these criteria were considered "non-responders." Among patients who received at least one dose of narsoplimab, 56% achieved responder status, while 68% of patients who received the protocol-specified narsoplimab treatment of at least four weeks of dosing achieved responder status.

Secondary endpoints in the trial were survival rates and change from baseline in HSCT-TMA laboratory markers. Among the responder population, 93% of patients survived for at least 100 days following HSCT-TMA diagnosis, while 81% of patients who received treatment for at least four weeks and 65% of the total treated population achieved this benchmark. Results also included statistically significant improvements in platelet count, LDH and haptoglobin (p < 0.01 for all treated patients, p £ 0.002 for patients who received treatment for at least four weeks and p < 0.001 for responders). In addition, hemoglobin increased in all groups and reached statistical significance (p = 0.041) in responders. Creatinine also improved in all patient groups, but did not reach statistical significance, we believe due to the use of nephrotoxic agents in trial patients.

The treated population had multiple high-risk features that portend a poor outcome, including the persistence of HSCT-TMA despite modification of immunosuppression (which was a criterion for entry into the trial), graft-versus-host disease, significant infections, non-infectious pulmonary complications

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and neurological findings. Patients in the trial had a high expected mortality rate, with 93% of them having multiple risk factors. No signal of any serious safety risk was observed with narsoplimab in the trial. The most common adverse events observed in the trial were nausea, vomiting, diarrhea, hypokalemia, neutropenia and fever, which are all common in stem-cell transplant patients. 21% of patients died during the trial due to causes common in stem cell transplant, with no additional patients discontinuing for adverse events. The data from the patients who died were not excluded from any analyses.

Enrollment of patients in this trial has completed. The details of the endpoints, including the response criteria agreed with FDA, and the number of patients in the trial remain confidential for competitive business reasons.

Preclinical Findings on GPR 174

On November 19, 2019, we announced new findings on GPR174, our preclinical program targeting immuno-oncology. Our studies in mouse models of melanoma and colon carcinoma found that GPR174-deficiency resulted in significantly reduced tumor growth and improved survival of the animals (p=0.006 in melanoma; p=0.03 in colon cancer) versus normal mice. We have presented these findings at the American Association for Cancer Research Conference on Tumor Immunology and Immunotherapy.

Contract Arbitration

On December 3, 2019, we received a demand for arbitration from a former manufacturer in connection with a contract dispute relating to failed or cancelled batches of OMS721 under a 2011 development and manufacturing agreement. The former manufacturer claims it is owed approximately $6.76 million for manufacturing milestones, raw materials and cancellation fees under the agreement, plus interest and legal fees. We dispute that these amounts are owed and intend to seek return of approximately $2.95 million in prior payments to the manufacturer. This dispute does not affect clinical or commercial supplies of narsoplimab or any of our products or other product candidates, which are currently produced by other contract manufacturers.

Corporate Information

We were incorporated in the State of Washington in 1994. Our principal executive offices are located at 201 Elliott Avenue West, Seattle, Washington 98119, and our telephone number is (206) 676-5000.

WHERE YOU CAN FIND MORE INFORMATION

We file annual, quarterly and current reports, proxy statements and other information with the SEC. Our SEC filings are available to the public over the Internet at the SEC's website at www.sec.gov. Our Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, including any amendments to those reports, and other information that we file with or furnish to the SEC pursuant to Section 13(a) 13(c), 14 or 15(d) of the Exchange Act can also be accessed free of charge on our website at www.omeros.com under "Investors and News—Financial Information—SEC Filings." These filings will be available as soon as reasonably practicable after we electronically file such material with, or furnish it to, the SEC.

We have filed with the SEC a registration statement under the Securities Act relating to the offering of these securities. The registration statement, including the attached exhibits, contains additional relevant information about us and the securities. This prospectus does not contain all of the information set forth in the registration statement. You can obtain a copy of the registration statement from the SEC's website at the address listed above. The registration statement and the documents

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referred to below under "Incorporation by Reference" are also available on our website, www.omeros.com. We have not incorporated by reference into this prospectus the information on, or that can be accessed through, our website, and you should not consider it to be a part of this prospectus.

INCORPORATION BY REFERENCE

The SEC allows us to "incorporate by reference" the information we file with it, which means that we can disclose important information to you by referring you to those documents. The information incorporated by reference is an important part of this prospectus, and information that we file later with the SEC will automatically update and supersede this information. The following documents that we have previously filed with the SEC (File No. 001-34475) are incorporated by reference herein:

•: our Annual Report on Form 10-K for the year ended December 31, 2018, filed with the SEC on March 1, 2019;
•: our Quarterly Reports on Form 10-Q for the quarterly periods ended March 31, 2019, June 30, 2019 and September 30, 2019 filed with the SEC on May 9, 2019, August 8, 2019 and November 12, 2019, respectively;
•: our Current Reports on Form 8-K filed with the SEC on February 12, 2019, June 11, 2019, July 31, 2019 and August 8, 2019 (filed under Items 1.01, 2.03 and 9.01); and
•: the description of our common stock contained in Exhibit 99.1 to our Annual Report on Form 10-K for the year ended December 31, 2016, filed with the SEC on March 16, 2017.

All reports and other documents that we subsequently file pursuant to Section 13(a), 13(c), 14 or 15(d) of the Exchange Act prior to the completion of the sales of the securities offered hereby but excluding any information furnished to, rather than filed with, the SEC (unless expressly incorporated by reference herein), will also be incorporated by reference into this prospectus and deemed to be part of this prospectus from the date of the filing of such reports and documents.

This prospectus, as supplemented, may contain information that updates, modifies or is contrary to information in one or more of the documents incorporated by reference in this prospectus. You should rely only on the information incorporated by reference or provided in this prospectus, the accompanying prospectus supplement or any free writing prospectus that we have prepared that relates to a particular offering. We have not authorized anyone else to provide you with different or additional information. You should not assume that the information in this prospectus is accurate as of any date other than the date of this prospectus or the date of the documents incorporated by reference in this prospectus.

We will provide without charge to each person, including any beneficial owner, to whom this prospectus is delivered, upon written or oral request, a copy of any or all documents that are incorporated by reference into this prospectus, but not delivered with the prospectus, other than exhibits to such documents unless such exhibits are specifically incorporated by reference into the documents that this prospectus incorporates. You should direct written requests to: Omeros Corporation, Attn: Legal Department, 201 Elliott Avenue West, Seattle, Washington 98119, or you may call us at (206) 676-5000.

RISK FACTORS

An investment in our securities involves a high degree of risk. The prospectus supplement applicable to each offering of our securities will contain a discussion of the risks applicable to an investment in our securities. Before deciding whether to invest in our securities, you should consider

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carefully the risks described under the heading "Risk Factors" in the applicable prospectus supplement and in any of our filings with the SEC that are incorporated by reference therein.

USE OF PROCEEDS

Unless otherwise indicated in the prospectus supplement, we intend to use the net proceeds from the sale of securities offered under this prospectus for general corporate purposes, including expenses related to funding research and development expenses for our narsoplimab programs and clinical trials, pre-clinical studies, manufacturing and other costs associated with advancing our product candidates toward Marketing Authorization Application, Biologic License Application and New Drug Application submissions. We may also use the net proceeds for working capital, the repayment of debt obligations, acquisitions or investments in businesses, products or technologies that are complementary to our own, and other capital expenditures. We will set forth in the prospectus supplement our intended use for the net proceeds received from the sale of any securities. Pending the use of such proceeds, we intend to invest the net proceeds in short-term, investment grade, interest-bearing instruments.

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DESCRIPTION OF COMMON STOCK

We may issue, separately or together with, or upon conversion, exercise or exchange of other securities, common stock, par value $0.01 per share, as set forth in the applicable prospectus supplement. The following summary of our common stock does not purport to be complete and is subject to, and is qualified in its entirety by reference to, our Amended and Restated Articles of Incorporation (the "Articles of Incorporation"), Amended and Restated Bylaws (the "Bylaws"), and applicable provisions of the Washington Business Corporation Act (the "WBCA"). Therefore, you should carefully consider the actual provisions of our Articles of Incorporation and Bylaws as well as relevant portions of the WBCA.

Authorized and Outstanding Shares

Our authorized capital stock consists of (i) 150,000,000 shares of common stock, par value $0.01 per share, and (ii) 20,000,000 shares of preferred stock, par value $0.01 per share. As of September 30, 2019, 49,525,474 shares of common stock were outstanding and no shares of preferred stock were outstanding. All outstanding shares of common stock are fully paid and nonassessable.

Dividend Rights

Subject to preferences that may be applicable to any outstanding shares of preferred stock, holders of common stock are entitled to receive ratably such dividends as may be declared by the board of directors out of funds legally available therefor.

Voting Rights and Cumulative Voting

The holders of our common stock are entitled to one vote per share on all matters to be voted on by the shareholders. Our Articles of Incorporation provide that shareholders are not entitled to cumulate votes in the election of directors.

Preemptive Rights; Redemption or Sinking Fund

Holders of common stock have no preemptive, conversion or subscription rights. There are no redemption or sinking fund provisions applicable to our common stock.

Liquidation Rights

If we liquidate, dissolve or wind up, holders of our common stock are entitled to share ratably in all assets remaining after payment of liabilities and the liquidation preferences of any outstanding shares of preferred stock.

Listing; Transfer Agent and Registrar

Our common stock is listed on The Nasdaq Global Market under the symbol "OMER." The transfer agent and registrar for our common stock is Computershare Inc. Its address is P.O. Box 505000, Louisville, Kentucky 40233-5000 and its telephone number is 1-866-282-4938.

Warrants

As of September 30, 2019, we had outstanding warrants to purchase an aggregate of 243,115 shares of our common stock. The warrants have a weighted average exercise price of approximately $20.68 per share and will expire in the second quarter of 2023.

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Anti-Takeover Effects of Washington Law and our Articles of Incorporation and Bylaws

Certain provisions of Washington law, our Articles of Incorporation and our Bylaws contain provisions that may delay, defer or discourage another party from acquiring control of us. These provisions, which are summarized below, are expected to discourage coercive takeover practices and inadequate takeover bids. These provisions are also designed, in part, to encourage persons seeking to acquire control of us to first negotiate with our board of directors. We believe that the benefits of increased protection of our potential ability to negotiate with an unfriendly or unsolicited acquiror outweigh the disadvantages of discouraging a proposal to acquire us because negotiation of these proposals could result in an improvement of their terms.

Washington Anti-Takeover Statute

Chapter 23B.19 of the Washington Business Corporation Act, with limited exceptions, prohibits a "target corporation" from engaging in specified "significant business transactions" for a period of five years after the share acquisition by an "acquiring person", unless (a) the significant business transaction or the acquiring person's purchase of shares was approved by a majority of the members of the target corporation's board of directors prior to the acquiring person's share acquisition or (b) the significant business transaction was both approved by the majority of the members of the target corporation's board and authorized at a shareholder meeting by at least two-thirds of the outstanding voting shares (excluding the acquiring person's shares or shares over which the acquiring person has voting control) at or subsequent to the acquiring person's share acquisition. An "acquiring person" is defined as a person or group of persons that beneficially owns 10% or more of the voting securities of the target corporation. "Significant business transactions" include, among other transactions:

•: mergers, share exchanges or consolidations with, dispositions of assets to, or issuances of stock to or redemptions of stock from, the acquiring person;
•: termination of 5% or more of the employees of the target corporation employed in Washington over a five-year period as a result of the acquiring person's acquisition of 10% or more of the shares;
•: allowing the acquiring person to receive any disproportionate benefit as a shareholder; and
•: liquidating or dissolving the target corporation.

After the five-year period, "significant business transactions" are permitted, as long as they comply with the "fair price" provisions of the statute or are approved by a majority of the outstanding shares other than those of which the acquiring person has beneficial ownership. A corporation may not "opt out" of this statute. This statute could prohibit or delay the accomplishment of mergers or other takeover or change in control attempts with respect to us and, accordingly, may discourage attempts to acquire us.

Amendment of Bylaws

Our Articles of Incorporation and Bylaws provide that shareholders can amend or repeal our bylaws only upon the affirmative vote of the holders of our voting stock.

Undesignated Preferred Stock

As discussed below, our board of directors has the ability to issue preferred stock with voting or other rights or preferences that could impede the success of any attempt to effect a change of control. These and other provisions may have the effect of deferring hostile takeovers or delaying changes in control or management.

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Limits on Ability of Shareholders to Act by Written Consent or Call a Special Meeting

Washington law limits the ability of shareholders of public companies from acting by written consent by requiring unanimous written consent for a shareholder action to be effective. This limit on the ability of our shareholders to act by less than unanimous written consent may lengthen the amount of time required to take shareholder actions. As a result, a holder controlling a majority of our capital stock who is unable to obtain unanimous written consent from all of our shareholders would not be able to amend our Bylaws or remove directors without holding a shareholders meeting.

In addition, our Articles of Incorporation provide that, unless otherwise required by law, special meetings of the shareholders may be called only by the chairman of the board, the chief executive officer, the president, or the board of directors acting pursuant to a resolution adopted by a majority of the board members. A shareholder may not call a special meeting, which may delay the ability of our shareholders to force consideration of a proposal or for holders controlling a majority of our capital stock to take any action, including the removal of directors.

Requirements for Advance Notification of Shareholder Nominations and Proposals

Our Bylaws establish advance notice procedures with respect to shareholder proposals and the nomination of candidates for election as directors, other than nominations made by or at the direction of the board of directors or a committee of the board of directors. The Bylaws do not give the board of directors the power to approve or disapprove shareholder nominations of candidates or proposals regarding business to be conducted at a special or annual meeting of the shareholders. However, our Bylaws may have the effect of precluding the conduct of certain business at a meeting if the proper procedures are not followed. These provisions may also discourage or deter a potential acquiror from conducting a solicitation of proxies to elect the acquiror's own slate of directors or otherwise attempting to obtain control of us.

Board Vacancies Filled Only by Directors Then in Office

Only our board of directors may determine the number of directors on our board and fix such number by resolution from time to time. Our Articles of Incorporation provide that vacancies and newly created seats on our board of directors may only be filled by the majority vote of the remaining members of our board of directors. The inability of our shareholders to determine the number of directors or to fill vacancies or newly created seats on our board of directors makes it more difficult to change the composition of our board of directors, but these provisions may promote a continuity of existing management.

Directors May be Removed Only for Cause

Our directors may be removed only for cause by the affirmative vote of the holders of our voting stock at a meeting of shareholders called for such purpose.

Board Classification

Our board of directors is divided into three classes. The directors in each class will serve for a three-year term, with one class being elected each year by our shareholders. This system of electing directors may tend to discourage a third party from making a tender offer or otherwise attempting to obtain control of us, because it generally makes it more difficult for shareholders to replace a majority of the directors.

No Cumulative Voting

Our Articles of Incorporation provide that shareholders are not entitled to cumulate votes in the election of directors.

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DESCRIPTION OF PREFERRED STOCK

We may issue, separately or together with, or upon conversion, exercise or exchange of other securities, preferred stock, par value $0.01 per share, as set forth in the applicable prospectus supplement. The following summary does not purport to be complete and is subject to, and is qualified in its entirety by reference to, our Articles of Incorporation, Bylaws and applicable provisions of the WBCA. Therefore, you should carefully consider the actual provisions of our Articles of Incorporation and Bylaws as well as relevant portions of the WBCA.

General

Under the terms of our Articles of Incorporation, our board of directors is authorized, from time to time and without further shareholder action, to issue of up to 20,000,000 shares of preferred stock in one or more series, and to fix the designations, powers, preferences and rights, and the qualifications, limitations or restrictions applicable to the preferred stock. As of the date of this prospectus, no shares of preferred stock were outstanding and our board of directors has made no provision for the issuance of any series of preferred stock.

The rights, preferences, privileges and restrictions of the preferred stock of each series will be fixed by Articles of Amendment to the Articles of Incorporation relating to that series and will be described in the applicable prospectus supplement. Our board of directors has the discretion to fix the number of shares of any such series and the designation thereof, and to fix and amend the powers, preferences and rights, and the limitations or restrictions granted to or imposed upon any wholly unissued series of preferred stock, including the voting rights, dividend rights, dividend rate, conversion rights, rights and terms of redemption (including sinking fund provisions), redemption prices and liquidation preferences of any such series. Our board of directors has authority to decrease the number of shares of any series of preferred stock that is outstanding, but not below the number of shares of any such series then outstanding. In addition, any such reduction is subject to the powers, preferences and rights, and the qualifications, limitations and restrictions thereof stated in the Articles of Incorporation or the board resolution originally fixing the number of shares of such series.

The issuance of preferred stock will affect, and may adversely affect, the rights of holders of common stock. It is not possible to state the actual effect of the issuance of any shares of preferred stock on the rights of holders of common stock until our board of directors determines the specific rights, preferences and privileges attached to that series of preferred stock. The effects of issuing preferred stock could include one or more of the following:

•: restricting dividends on the common stock;
•: diluting the voting power of the common stock;
•: impairing the liquidation rights of the common stock; or
•: delaying or preventing changes in control or management.

The applicable prospectus supplement will specify the terms of the series of preferred stock being offered, including the following:

•: the number of shares of preferred stock being offered;
•: the designation of the series of preferred stock;
•: the per share purchase price of the preferred stock;
•: the dividend rate or method of determining the dividend rate, if any, including whether the dividend rate is fixed or variable;
•: the date or dates on which dividends will accrue and the dividend payment dates;

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•: whether dividends will be cumulative or non-cumulative and, if cumulative, the dates from which dividends will accrue;
•: the price and the terms and conditions for redemption, if any, including redemption at our option or at the option of the holders, the time period for redemption, and any accumulated dividends or premiums;
•: the liquidation preference, if any, and any accumulated dividends upon the liquidation, dissolution or winding up of our affairs;
•: any sinking fund or similar provision, and, if so, the terms and provisions relating to the purpose and operation of the fund;
•: the terms and conditions, if any, for conversion or exchange of preferred stock for any other class or classes of our securities, including the price or the rate of conversion or exchange and the method, if any, of adjustment;
•: the voting rights of the preferred stock;
•: any exchange on which the preferred stock will be listed;
•: any or all other preferences and relative, participating, optional or other special rights, privileges or qualifications, limitations or restrictions; and
•: the material United States federal income tax consequences relating to the purchase and ownership of the series of preferred stock that is described in the prospectus supplement.

We have no present plans to issue any shares of preferred stock nor are any shares of our preferred stock presently outstanding. Preferred stock will be fully paid and nonassessable upon issuance.

Rank

Unless otherwise specified in the applicable prospectus supplement, the preferred stock will, with respect to distribution rights and rights upon liquidation, dissolution or winding up, rank (i) senior to our common stock and to any series of preferred stock which specifically provides that it will rank junior to the preferred stock being offered, (ii) junior to any series of preferred stock which specifically provides that it will rank senior to the preferred stock being offered and (iii) on parity with any other series of preferred stock.

Dividend Rights

Holders of preferred stock will have the dividend rights set forth in the applicable prospectus supplement. Dividends on any series of preferred stock, if cumulative, will be cumulative from and after the date set forth in the applicable prospectus supplement. Any restriction on the repurchase or redemption of shares of preferred stock while dividends on such shares are in arrears shall be set forth in the applicable prospectus supplement.

Transfer Agent and Registrar

We will appoint a transfer agent and registrar for the preferred stock that will be set forth in the applicable prospectus supplement.

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Certain Anti-Takeover Matters

Refer to "Description of Common Stock—Anti-Takeover Effects of Washington Law and our Articles of Incorporation and Bylaws" for a discussion of provisions of the WBCA and our Articles of Incorporation and Bylaws that may have the effect of delaying, deferring or preventing a change of control.

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DESCRIPTION OF DEBT SECURITIES

We may issue, separately or together with, or upon conversion, exercise or exchange of other securities, debt securities, including debentures, notes, bonds and other evidences of indebtedness as set forth in the applicable prospectus supplement. The debt securities may be either secured or unsecured and will either be senior debt securities or subordinated debt securities. The debt securities will be issued under one or more separate indentures between us and a trustee to be specified in an accompanying prospectus supplement. Senior debt securities will be issued under a senior indenture and subordinated debt securities will be issued under a subordinated indenture. Together, the senior indenture and the subordinated indenture are called indentures in this description. This prospectus, together with the applicable prospectus supplement, will describe the terms of a particular series of debt securities that we may offer from time to time.

The following summary of the material provisions of the indentures and the debt securities does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the provisions of the applicable indenture and certificates evidencing the applicable debt securities. Therefore, you should carefully consider the applicable indenture and the certificate evidencing the applicable debt security that is filed as an exhibit to the registration statement that includes this prospectus. Other specific terms of the applicable indenture and debt securities will be described in the applicable prospectus supplement. If any particular terms of the indenture or debt securities described in a prospectus supplement differ from any of the terms described below, then the terms described below will be deemed to have been superseded by that prospectus supplement. In this description of the debt securities, the words "Omeros Corporation," "we," "us" or "our" refer only to Omeros Corporation and not to our subsidiary, unless we otherwise expressly state or the context otherwise requires.

General

Debt securities may be issued in separate series without limitation as to aggregate principal amount. We may specify a maximum aggregate principal amount for the debt securities of any series.

We are not limited as to the amount of debt securities that we may issue under the indentures. Unless otherwise provided in a prospectus supplement, a series of debt securities may be reopened to issue additional debt securities of such series.

The prospectus supplement relating to a particular series of debt securities will set forth the material terms of the debt securities being offered, including:

•: the title of the debt securities and whether they are senior debt securities or subordinated debt securities;
•: the offering price;
•: the person who shall be entitled to receive interest, if other than the record holder on the record date;
•: the maturity date or dates;
•: the interest rate or rates, if any, which may be fixed or variable, at which the debt securities will bear interest, or the method of determining such rate or rates;
•: the date from which interest will accrue, the interest payment dates and the regular record dates, or the method for calculating the dates and rates;
•: the place or places where payments of principal and interest may be made;

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•: any mandatory or optional redemption provisions or sinking fund provisions and any applicable redemption or purchase prices associated with these provisions;
•: if issued other than in denominations of $1,000 or any multiple of $1,000, the denominations in which the debt securities shall be issuable;
•: if applicable, the method for determining how the principal, premium, if any, or interest will be calculated by reference to an index or formula;
•: if other than U.S. currency, the currency or currency units in which principal, premium, if any, or interest will be payable, whether we or a holder may elect payment to be made in a different currency and the designation of the original currency determination agent;
•: the portion of the principal amount that will be payable upon acceleration of maturity, if other than the entire principal amount;
•: if the principal amount payable at stated maturity will not be determinable as of any date prior to stated maturity, the amount or method for determining the amount which will be deemed to be the principal amount;
•: if applicable, whether the debt securities shall be subject to the defeasance provisions described below under "Satisfaction and Discharge; Defeasance" or such other defeasance provisions specified in the applicable prospectus supplement for the debt securities;
•: any conversion or exchange provisions;
•: whether the debt securities will be issuable in the form of a global security;
•: any subordination provisions applicable to the subordinated debt securities if different from those described below under "Subordinated Debt Securities";
•: any paying agents, authenticating agents, security registrars or other agents for the debt securities, if other than the trustee;
•: any provisions relating to any security provided for the debt securities, including any provisions regarding the circumstances under which collateral may be released or substituted;
•: any deletions of, or changes or additions to, the events of default, acceleration provisions or covenants;
•: any provisions relating to guaranties for the securities and any circumstances under which there may be additional obligors; and
•: any other specific terms of such debt securities.

If we denominate the purchase price of any of the debt securities in a foreign currency or currencies, or if the principal of or premium, if any, or interest on any series of debt securities is payable in a foreign currency or currencies, we will include in the applicable prospectus supplement information on the restrictions, elections, material federal income tax considerations, specific terms and other information with respect to that issue of debt securities and the foreign currency or currencies.

Unless otherwise specified in the prospectus supplement, the debt securities will be registered debt securities. Debt securities may be sold at a substantial discount below their stated principal amount, bearing no interest or interest at a rate which at the time of issuance is below market rates. The U.S. federal income tax considerations applicable to debt securities sold at a discount will be described in the applicable prospectus supplement.

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Exchange and Transfer

Debt securities may be transferred or exchanged at the office of the security registrar or at the office of any transfer agent designated by us.

We will not impose a service charge for any transfer or exchange, but we may require holders to pay any tax or other governmental charges associated with any transfer or exchange.

In the event of any partial redemption of debt securities of any series, we will not be required to:

•: issue, register the transfer of or exchange any debt security of that series during a period beginning at the opening of business 15 days before the day of mailing of a notice of redemption and ending at the close of business on the day of the mailing; or
•: register the transfer of or exchange any debt security of that series selected for redemption, in whole or in part, except the unredeemed portion being redeemed in part.

Initially, we will appoint the trustee as the security registrar. Any transfer agent, in addition to the security registrar initially designated by us, will be named in the prospectus supplement. We may designate additional transfer agents or change transfer agents or change the office of the transfer agent. However, we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

Conversion or Exchange

If any debt securities being offered are convertible into or exchangeable for our common stock or other securities, the relevant prospectus supplement will set forth the terms of conversion or exchange. Those terms will include whether conversion or exchange is mandatory, at the option of the holder or at our option, and the number of shares of common stock or other securities, or the method of determining the number of shares of common stock or other securities, to be received by the holder upon conversion or exchange. These provisions may allow or require the number of shares of our common stock or other securities to be received by the holders of such series of debt securities to be adjusted.

Global Securities

The debt securities of any series may be represented, in whole or in part, by one or more global securities. Each global security will:

•: be registered in the name of a depositary, or its nominee, that we will identify in a prospectus supplement;
•: be deposited with the depositary or nominee or custodian; and
•: bear any required legends.

No global security may be exchanged in whole or in part for debt securities registered in the name of any person other than the depositary or any nominee unless:

•: the depositary has notified us that it is unwilling or unable to continue as depositary or has ceased to be qualified to act as depositary;
•: an event of default has occurred and is continuing with respect to the debt securities of the applicable series; or
•: any other circumstance described in a prospectus supplement has occurred permitting or requiring the issuance of any such security.

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As long as the depositary, or its nominee, is the registered owner of a global security, the depositary or nominee will be considered the sole owner and holder of the debt securities represented by the global security for all purposes under the indenture. Except in the above limited circumstances, owners of beneficial interests in a global security will not be:

•: entitled to have the debt securities registered in their names;
•: entitled to physical delivery of certificated debt securities; or
•: considered to be holders of those debt securities under the indenture.

Payments on a global security will be made to the depositary or its nominee as the holder of the global security. Some jurisdictions have laws that require that certain purchasers of securities take physical delivery of such securities in definitive form. These laws may impair the ability to transfer beneficial interests in a global security.

Institutions that have accounts with the depositary or its nominee are referred to as "participants." Ownership of beneficial interests in a global security will be limited to participants and to persons that may hold beneficial interests through participants. The depositary will credit, on its book-entry registration and transfer system, the respective principal amounts of debt securities represented by the global security to the accounts of its participants.

Ownership of beneficial interests in a global security will be shown on and effected through records maintained by the depositary, with respect to participants' interests, or any participant, with respect to interests of persons held by participants on their behalf.

Payments, transfers and exchanges relating to beneficial interests in a global security will be subject to policies and procedures of the depositary. The depositary policies and procedures may change from time to time. Neither any trustee nor we will have any responsibility or liability for the depositary's or any participant's records with respect to beneficial interests in a global security.

Payment and Paying Agents

Unless otherwise indicated in a prospectus supplement, the provisions described in this paragraph will apply to the debt securities. Payment of interest on a debt security on any interest payment date will be made to the person in whose name the debt security is registered at the close of business on the regular record date. Payment on debt securities of a particular series will be payable at the office of a paying agent or paying agents designated by us. However, at our option, we may pay interest by mailing a check to the record holder. The trustee will be designated as our initial paying agent.

We may also name any other paying agents in a prospectus supplement. We may designate additional paying agents, change paying agents or change the office of any paying agent. However, we will be required to maintain a paying agent in each place of payment for the debt securities of a particular series.

All moneys paid by us to a paying agent for payment on any debt security that remain unclaimed for a period ending the earlier of:

•: 10 business days prior to the date the money would be turned over to the applicable state; or
•: at the end of two years after such payment was due, will be repaid to us thereafter. The holder may look only to us for such payment.

No Protection in the Event of a Change of Control

Unless otherwise indicated in a prospectus supplement with respect to a particular series of debt securities, the debt securities will not contain any provisions that may afford holders of the debt

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securities protection in the event we have a change in control or in the event of a highly leveraged transaction, whether or not such transaction results in a change in control.

Covenants

Unless otherwise indicated in a prospectus supplement with respect to a particular series of debt securities, the debt securities will not contain any financial or restrictive covenants.

Consolidation, Merger and Sale of Assets

Unless otherwise indicated in a prospectus supplement with respect to a particular series of debt securities, we may not consolidate with or merge into any other person, in a transaction in which we are not the surviving corporation, or convey, transfer or lease our properties and assets substantially as an entirety to, any entity, unless:

•: the successor entity, if any, is a corporation, limited liability company, partnership, trust or other business entity existing under the laws of the United States, any State within the United States or the District of Columbia;
•: the successor entity assumes our obligations on the debt securities and under the applicable indenture;
•: immediately after giving effect to the transaction, no default or event of default shall have occurred and be continuing; and
•: certain other conditions specified in the indenture are met.

Events of Default

Unless we indicate otherwise in a prospectus supplement with respect to a particular series of debt securities, the following will be events of default for any series of debt securities under the indentures:

(1): we fail to pay any interest on any debt security of that series when it becomes due and we subsequently fail to pay such interest for 30 days;
(2): we fail to pay principal of or any premium on any debt security of that series when due;
(3): we fail to deposit any sinking fund payment when due;
(4): we fail to perform any other covenant in the applicable indenture and such failure continues for 90 days after we are given the notice required in the indentures; and
(5): certain events including our bankruptcy, insolvency or reorganization.

Additional or different events of default applicable to a series of debt securities may be described in a prospectus supplement. An event of default of one series of debt securities is not necessarily an event of default for any other series of debt securities.

The trustee may withhold notice to the holders of any default, except defaults in the payment of principal, premium, if any, interest, any sinking fund installment on, or with respect to any conversion right of, the debt securities of such series. However, the trustee must consider it to be in the interest of the holders of the debt securities of such series to withhold this notice.

Unless we indicate otherwise in a prospectus supplement, if an event of default, other than an event of default described in clause (5) above, shall occur and be continuing with respect to any series of debt securities, either the trustee or the holders of at least 25% in aggregate principal amount of the outstanding securities of that series may declare the principal amount and premium, if any, of the debt securities of that series, or if any debt securities of that series are original issue discount securities, such

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other amount as may be specified in the applicable prospectus supplement, in each case together with accrued and unpaid interest, if any, thereon, to be due and payable immediately.

If an event of default described in clause (5) above shall occur, the principal amount and premium, if any, of all the debt securities of that series, or if any debt securities of that series are original issue discount securities, such other amount as may be specified in the applicable prospectus supplement, in each case together with accrued and unpaid interest, if any, thereon, will automatically become immediately due and payable without any declaration or other action on the part of the trustee or any holder. Any payment by us on the subordinated debt securities following any such acceleration will be subject to the subordination provisions described below under "Subordinated Debt Securities."

After acceleration, the holders of a majority in aggregate principal amount of the outstanding securities of that series may, under certain circumstances, rescind and annul such acceleration if all events of default, other than the non-payment of accelerated principal, or other specified amounts or interest, have been cured or waived.

Other than the duty to act with the required care during an event of default, the trustee will not be obligated to exercise any of its rights or powers at the request of the holders unless the holders shall have offered to the trustee reasonable indemnity. Generally, the holders of a majority in aggregate principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee or exercising any trust or power conferred on the trustee.

A holder of debt securities of any series will not have any right to institute any proceeding under the indentures, or for the appointment of a receiver or a trustee, or for any other remedy under the indentures, unless:

(1): the holder has previously given to the trustee written notice of a continuing event of default with respect to the debt securities of that series;
(2): the holders of at least a majority in aggregate principal amount of the outstanding debt securities of that series have made a written request and have offered reasonable indemnity to the trustee to institute the proceeding; and
(3): the trustee has failed to institute the proceeding and has not received direction inconsistent with the original request from the holders of a majority in aggregate principal amount of the outstanding debt securities of that series within 60 days after the original request.

Holders may, however, sue to enforce the payment of principal, premium or interest on any debt security on or after the due date or to enforce the right, if any, to convert any debt security (if the debt security is convertible) without following the procedures listed in clauses (1) through (3) above.

We will furnish the trustee an annual statement by our officers as to whether or not we are in default in the performance of the conditions and covenants under the indenture and, if so, specifying all known defaults.

Modification and Waiver

Unless we indicate otherwise in a prospectus supplement, we and the applicable trustee may make modifications and amendments to an indenture with the consent of the holders of a majority in aggregate principal amount of the outstanding securities of each series affected by the modification or amendment.

We may also make modifications and amendments to the indentures for the benefit of holders without their consent, for certain purposes including, but not limited to:

•: providing for our successor to assume the covenants under the indenture;

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•: adding covenants or events of default;
•: making certain changes to facilitate the issuance of the securities;
•: securing the securities, including provisions relating to the release or substitution of collateral;
•: providing for guaranties of, or additional obligors on, the securities;
•: providing for a successor trustee or additional trustees;
•: curing any ambiguities or inconsistencies;
•: permitting or facilitating the defeasance and discharge of the securities; and
•: other changes specified in the indenture.

However, neither we nor the trustee may make any modification or amendment without the consent of the holder of each outstanding security of that series affected by the modification or amendment if such modification or amendment would:

•: change the stated maturity of any debt security;
•: reduce the principal, premium, if any, or interest on any debt security or any amount payable upon redemption or repurchase, whether at our option or the option of any holder, or reduce the amount of any sinking fund payments;
•: reduce the principal of an original issue discount security or any other debt security payable on acceleration of maturity;
•: change the place of payment or the currency in which any debt security is payable;
•: impair the right to enforce any payment after the stated maturity or redemption date;
•: if subordinated debt securities, modify the subordination provisions in a materially adverse manner to the holders;
•: adversely affect the right to convert any debt security if the debt security is a convertible debt security; or
•: change the provisions in the indenture that relate to modifying or amending the indenture.

Satisfaction and Discharge; Defeasance

We may be discharged from our obligations on the debt securities, subject to limited exceptions, of any series that have matured or will mature or be redeemed within one year if we deposit enough money with the trustee to pay all of the principal, interest and any premium due to the stated maturity date or redemption date of the debt securities.

Each indenture contains a provision that permits us to elect either or both of the following:

•: We may elect to be discharged from all of our obligations, subject to limited exceptions, with respect to any series of debt securities then outstanding. If we make this election, the holders of the debt securities of the series will not be entitled to the benefits of the indenture, except for the rights of holders to receive payments on debt securities or the registration of transfer and exchange of debt securities and replacement of lost, stolen or mutilated debt securities.
•: We may elect to be released from our obligations under some or all of any financial or restrictive covenants applicable to the series of debt securities to which the election relates and from the consequences of an event of default resulting from a breach of those covenants.

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To make either of the above elections, we must irrevocably deposit in trust with the trustee enough money to pay in full the principal, interest and premium on the debt securities. This amount may be made in cash and/or U.S. government obligations or, in the case of debt securities denominated in a currency other than U.S. dollars, cash in the currency in which such series of securities is denominated and/or foreign government obligations. As a condition to either of the above elections, for debt securities denominated in U.S. dollars we must deliver to the trustee an opinion of counsel that the holders of the debt securities will not recognize income, gain or loss for U.S. federal income tax purposes as a result of the action.

"Foreign government obligations" means, with respect to debt securities of any series that are denominated in a currency other than United States dollars:

•: direct obligations of the government that issued or caused to be issued the currency in which such securities are denominated and for the payment of which obligations its full faith and credit is pledged, or, with respect to debt securities of any series which are denominated in euros, direct obligations of certain members of the European Union for the payment of which obligations the full faith and credit of such members is pledged, which in each case are not callable or redeemable at the option of the issuer thereof;
•: obligations of a person controlled or supervised by or acting as an agency or instrumentality of a government described in the bullet above, the timely payment of which is unconditionally guaranteed as a full faith and credit obligation by such government, which are not callable or redeemable at the option of the issuer thereof; or
•: any depository receipt issued by a bank as custodian with respect to any obligation specified in the first two bullet points and held by such bank for the account of the holder of such deposit any receipt, or with respect to any such obligation which is so specified and held.

Notices

Notices to holders will be given by mail to the addresses of the holders in the security register.

Governing Law

The indentures and the debt securities will be governed by, and construed under, the laws of the State of New York.

No Personal Liability of Directors, Officers, Employees and Shareholders

No incorporator, shareholder, employee, agent, officer, director or subsidiary of ours will have any liability for any obligations of ours, or because of the creation of any indebtedness under the debt securities, the indentures or supplemental indentures. The indentures provide that all such liability is expressly waived and released as a condition of, and as a consideration for, the execution of such indentures and the issuance of the debt securities.

Regarding the Trustee

The indentures limit the right of the trustee, should it become our creditor, to obtain payment of claims or secure its claims.

The trustee is permitted to engage in certain other transactions with us. However, if the trustee acquires any conflicting interest, and there is a default under the debt securities of any series for which it is trustee, the trustee must eliminate the conflict or resign.

The accompanying prospectus supplement will specify the trustee for the particular series of debt securities to be issued under the indentures.

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Subordinated Debt Securities

The following provisions will be applicable with respect to each series of subordinated debt securities, unless otherwise stated in the prospectus supplement relating to that series of subordinated debt securities.

The indebtedness evidenced by the subordinated debt securities of any series is subordinated, to the extent provided in the subordinated indenture and the applicable prospectus supplement, to the prior payment in full, of all senior debt, including any senior debt securities, in cash or other payment satisfactory to the holders of senior debt.

Upon any distribution of our assets upon any dissolution, winding up, liquidation or reorganization, whether voluntary or involuntary, marshalling of assets, assignment for the benefit of creditors, or in bankruptcy, insolvency, receivership or other similar proceedings, payments on the subordinated debt securities will be subordinated in right of payment to the prior payment in full in cash or other payment satisfactory to holders of senior debt of all senior debt.

In the event of any acceleration of the subordinated debt securities of any series because of an event of default with respect to the subordinated debt securities of that series, holders of any senior debt would be entitled to payment in full in cash or other payment satisfactory to holders of senior debt of all senior debt before the holders of subordinated debt securities are entitled to receive any payment or distribution.

In addition, the subordinated debt securities will be structurally subordinated to all indebtedness and other liabilities of our subsidiaries, including trade payables and lease obligations. This occurs because our right to receive any assets of our subsidiaries upon their liquidation or reorganization, and your right to participate in those assets, will be effectively subordinated to the claims of that subsidiary's creditors, including trade creditors, except to the extent that we are recognized as a creditor of such subsidiary. If we are recognized as a creditor of that subsidiary, our claims would still be subordinate to any security interest in the assets of the subsidiary and any indebtedness of the subsidiary senior to us.

We are required to promptly notify holders of senior debt or their representatives under the subordinated indenture if payment of the subordinated debt securities is accelerated because of an event of default.

Under the subordinated indenture, we may also not make payment on the subordinated debt securities if:

•: a default in our obligations to pay principal, premium, if any, interest or other amounts on our senior debt occurs and the default continues beyond any applicable grace period, which we refer to as a payment default; or
•: a nonpayment default occurs and is continuing with respect to designated senior debt that permits holders of designated senior debt to accelerate its maturity, and the trustee receives a payment blockage notice from us or some other person permitted to give the notice under the subordinated indenture, which we refer to as a non-payment default.

We may and shall resume payments on the subordinated debt securities:

•: in case of a payment default, when the default is cured or waived or ceases to exist; and
•: in case of a nonpayment default, the earlier of when the default is cured or waived or ceases to exist or 179 days after the receipt of the payment blockage notice.

No new payment blockage period may start on the basis of a nonpayment default unless at least 365 days have elapsed from the initial effectiveness of the immediately prior payment blockage notice.

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No nonpayment default that existed or was continuing on the date of delivery of any payment blockage notice to the trustee shall be the basis for a subsequent payment blockage notice.

As a result of these subordination provisions, in the event of our bankruptcy, dissolution or reorganization, holders of senior debt may receive more, ratably, and holders of the subordinated debt securities may receive less, ratably, than our other creditors. The subordination provisions will not prevent the occurrence of any event of default under the subordinated indenture.

The subordination provisions will not apply to payments from money or government obligations held in trust by the trustee for the payment of principal, interest and premium, if any, on subordinated debt securities pursuant to the provisions described under "Satisfaction and Discharge; Defeasance," if the subordination provisions were not violated at the time the money or government obligations were deposited into trust.

If the trustee or any holder receives any payment that should not have been made to them in contravention of subordination provisions before all senior debt is paid in full in cash or other payment satisfactory to holders of senior debt, then such payment will be held in trust for the holders of senior debt.

Senior debt securities will constitute senior debt under the subordinated indenture.

Additional or different subordination provisions may be described in a prospectus supplement relating to a particular series of debt securities.

Definitions

"Designated senior debt" means our obligations under any particular senior debt in which the instrument creating or evidencing the same or the assumption or guarantee thereof, or related agreements or documents to which we are a party, expressly provides that such indebtedness shall be designated senior debt for purposes of the subordinated indenture. The instrument, agreement or other document evidencing any designated senior debt may place limitations and conditions on the right of such senior debt to exercise the rights of designated senior debt.

"Indebtedness" means the following, whether absolute or contingent, secured or unsecured, due or to become due, outstanding on the date of the indenture for such series of securities or thereafter created, incurred or assumed:

•

our indebtedness evidenced by a credit or loan agreement, note, bond, debenture or other written obligation;

•

all of our obligations for borrowed money;

•

all of our obligations evidenced by a note or similar instrument given in connection with the acquisition of any businesses, properties or assets of any kind,

•

our obligations:

•: as lessee under leases required to be capitalized on the balance sheet of the lessee under generally accepted accounting principles, or
•: as lessee under other leases for facilities, capital equipment or related assets, whether or not capitalized, entered into or leased for financing purposes;

•

all of our obligations under interest rate and currency swaps, caps, floors, collars, hedge agreements, forward contracts or similar agreements or arrangements;

•

all of our obligations with respect to letters of credit, bankers' acceptances and similar facilities, including reimbursement obligations with respect to the foregoing;

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•: all of our obligations issued or assumed as the deferred purchase price of property or services, but excluding trade accounts payable and accrued liabilities arising in the ordinary course of business;
•: all obligations of the type referred to in the above clauses of another person and all dividends of another person, the payment of which, in either case, we have assumed or guaranteed, for which we are responsible or liable, directly or indirectly, jointly or severally, as obligor, guarantor or otherwise, or which are secured by a lien on our property; and
•: renewals, extensions, modifications, replacements, restatements and refundings of, or any indebtedness or obligation issued in exchange for, any such indebtedness or obligation described in the above clauses of this definition.

"Senior debt" means the principal of, premium, if any, and interest, including all interest accruing subsequent to the commencement of any bankruptcy or similar proceeding, whether or not a claim for post-petition interest is allowable as a claim in any such proceeding, on, and all fees and other amounts payable in connection with, our indebtedness. Senior debt shall not include:

•: any debt or obligation if its terms or the terms of the instrument under which or pursuant to which it is issued expressly provide it shall not be senior in right of payment to the subordinated debt securities or expressly provide that such indebtedness is on the same basis or "junior" to the subordinated debt securities; or
•: debt to any of our subsidiaries.

"Subsidiary" means an entity more than 50% of the outstanding voting stock of which is owned, directly or indirectly, by us or by one or more of our other subsidiaries or by a combination of us and our other subsidiaries. For purposes of this definition, "voting stock" means stock or other similar interests to us which ordinarily has or have voting power for the election of directors, or persons performing similar functions, whether at all times or only so long as no senior class of stock or other interests has or have such voting power by reason of any contingency.

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DESCRIPTION OF DEPOSITARY SHARES

We may elect to offer fractional interests in shares of preferred stock, in which case we will issue to the public receipts for depositary shares and each of these depositary shares will represent a fraction of a share of the applicable series of preferred stock, as set forth in the applicable prospectus supplement. The following summary of the terms of the depositary shares does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the terms of the depositary shares and preferred stock, as well as the form of the deposit agreement, our Articles of Incorporation and the Articles of Amendment relating to the applicable series of preferred stock that are, or will be, filed with the SEC. Therefore, you should carefully consider the actual provisions of these documents.

General

Each owner of a depositary share will be entitled, in proportion to the applicable fractional interest in shares of preferred stock underlying that depositary share, to all rights and preferences of the preferred stock underlying that depositary share. These rights may include dividend, voting, redemption and liquidation rights.

The shares of preferred stock underlying the depositary shares will be deposited with a bank or trust company selected by us to act as depositary, under a deposit agreement between us, the depositary and the holders of the depositary receipts. The depositary will be the transfer agent, registrar and dividend disbursing agent for the depositary shares. The name and address of the principal executive office of the depositary will be included in the prospectus supplement relating to the issue.

The depositary shares will be evidenced by depositary receipts issued pursuant to the depositary agreement. Holders of depositary receipts agree to be bound by the deposit agreement, which requires holders to take certain actions such as filing proof of residence and paying certain charges.

Dividends and Other Distributions

The depositary will distribute cash dividends or other cash distributions, if any, received in respect of the series of preferred stock underlying the depositary shares to the record holders of depositary receipts in proportion to the number of depositary shares owned by those holders on the relevant record date. The relevant record date for depositary shares will be the same date as the record date for the preferred stock.

In the event of a distribution other than in cash, the depositary will distribute property received by it to the record holders of depositary receipts that are entitled to receive the distribution, unless the depositary determines that it is not feasible to make the distribution. If this occurs, the depositary, with our approval, may adopt another method for the distribution, including selling the property and distributing the net proceeds to the holders.

Liquidation Preference

If a series of preferred stock underlying the depositary shares has a liquidation preference, in the event of our voluntary or involuntary liquidation, dissolution or winding up, holders of depositary shares will be entitled to receive the fraction of the liquidation preference accorded each share of the applicable series of preferred stock, as set forth in the applicable prospectus supplement.

Redemption

If a series of preferred stock underlying the depositary shares is subject to redemption, the depositary shares will be redeemed from the proceeds received by the depositary resulting from the redemption, in whole or in part, of the preferred stock held by the depositary. Whenever we redeem

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any preferred stock held by the depositary, the depositary will redeem, as of the same redemption date, the number of depositary shares representing the preferred stock so redeemed. The depositary will mail the notice of redemption to the record holders of the depositary receipts promptly upon receiving the notice from us and no fewer than 20 nor more than 60 days, unless otherwise provided in the applicable prospectus supplement, prior to the date fixed for redemption of the preferred stock.

After the date fixed for redemption, the depositary shares called for redemption will no longer be outstanding. When the depositary shares are no longer outstanding, all rights of the holders will end, except the right to receive money, securities or other property payable upon redemption.

Voting

Upon receipt of notice of any meeting at which the holders of preferred stock are entitled to vote, the depositary will mail the information contained in the notice of meeting to the record holders of the depositary receipts underlying the preferred stock. Each record holder of those depositary receipts on the record date will be entitled to instruct the depositary as to the exercise of the voting rights pertaining to the amount of preferred stock underlying that holder's depositary shares. The record date for the depositary will be the same date as the record date for the preferred stock. The depositary will try, as far as practicable, to vote the preferred stock underlying the depositary shares in accordance with these instructions. We will agree to take all action that may be deemed necessary by the depositary in order to enable the depositary to vote the preferred stock in accordance with these instructions. The depositary will not vote the preferred stock to the extent that it does not receive specific instructions from the holders of depositary receipts.

Withdrawal of Preferred Stock

Owners of depositary shares will be entitled to receive upon surrender of depositary receipts at the principal office of the depositary and payment of any unpaid amount due to the depositary, the number of whole shares of preferred stock underlying their depositary shares.

Partial shares of preferred stock will not be issued. Holders of preferred stock will not be entitled to deposit the shares under the deposit agreement or to receive depositary receipts evidencing depositary shares for the preferred stock.

Amendment and Termination of the Deposit Agreement

The form of depositary receipt evidencing the depositary shares and any provision of the deposit agreement may be amended by agreement between the depositary and us. However, any amendment that materially and adversely alters the rights of the holders of depositary shares, other than fee changes, will not be effective unless the amendment has been approved by at least a majority of the outstanding depositary shares. The deposit agreement may be terminated by the depositary or us only if:

•: all outstanding depositary shares have been redeemed; or
•: there has been a final distribution of the preferred stock in connection with our dissolution and such distribution has been made to all the holders of depositary shares.

Charges of Depositary

We will pay all transfer and other taxes and governmental charges arising solely from the existence of the depositary arrangement. We will also pay charges of the depositary in connection with:

•: the initial deposit of the preferred stock;
•: the initial issuance of the depositary shares;

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•: any redemption of the preferred stock; and
•: all withdrawals of preferred stock by owners of depositary shares.

Holders of depositary receipts will pay transfer, income and other taxes and governmental charges and other specified charges as provided in the deposit agreement for their accounts. If these charges have not been paid, the depositary may:

•: refuse to transfer depositary shares;
•: withhold dividends and distributions; and
•: sell the depositary shares evidenced by the depositary receipt.

Miscellaneous

The depositary will forward to the holders of depositary receipts all reports and communications we deliver to the depositary that we are required to furnish to the holders of the preferred stock. In addition, the depositary will make available for inspection by holders of depositary receipts at the principal office of the depositary, and at such other places as it may from time to time deem advisable, any reports and communications we deliver to the depositary as the holder of preferred stock.

Neither we nor the depositary will be liable if either we or the depositary are prevented or delayed by law or any circumstance beyond the control of either the depositary or us in performing our respective obligations under the deposit agreement. Our obligations and the depositary's obligations will be limited to the performance in good faith of our or the depositary's respective duties under the deposit agreement. Neither we nor the depositary will be obligated to prosecute or defend any legal proceeding in respect of any depositary shares or preferred stock unless satisfactory indemnity is furnished. The depositary and we may rely on:

•: written advice of counsel or accountants;
•: information provided by holders of depositary receipts or other persons believed in good faith to be competent to give such information; and
•: documents believed to be genuine and to have been signed or presented by the proper party or parties.

Resignation and Removal of Depositary

The depositary may resign at any time by delivering a notice to us. We may remove the depositary at any time. Any such resignation or removal will take effect upon the appointment of a successor depositary and its acceptance of such appointment. The successor depositary must be appointed within 60 days after delivery of the notice for resignation or removal. The successor depositary must be a bank and trust company having its principal office in the United States of America and having a combined capital and surplus of at least $50,000,000.

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DESCRIPTION OF WARRANTS

We may issue warrants for the purchase of common stock, preferred stock, debt securities or any combination thereof. Warrants may be issued independently or together with common stock, preferred stock or debt securities and may be attached to or separate from any offered securities. Each series of warrants will be issued under a separate warrant agreement, the terms of which will be described in the applicable prospectus supplement. The following summary of the terms of the warrants does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the terms of the warrants as well as the form of warrant agreement and the terms of the applicable underlying securities. Therefore, you should carefully consider the actual provisions of these documents.

The particular terms of any issue of warrants will be described in the prospectus supplement relating to the issue. Those terms may include:

•: the number of shares of common stock or preferred stock purchasable upon the exercise of warrants to purchase such shares and the price at which such number of shares may be purchased upon such exercise;
•: the designation, stated value and terms (including, without limitation, liquidation, dividend, conversion and voting rights) of the series of preferred stock purchasable upon exercise of warrants to purchase preferred stock;
•: the principal amount of debt securities that may be purchased upon exercise of a debt warrant and the exercise price for the warrants, which may be payable in cash, securities or other property;
•: the date(s) on which the right to exercise the warrants will commence and the date(s) on which the right will expire;
•: United States federal income tax consequences applicable to the warrants;
•: provision for changes to or adjustments in the exercise price;
•: the terms of any anti-dilution or other adjustment provisions;
•: the terms of any mandatory or optional call provisions;
•: if applicable, the date on and after which the warrants and the common stock, preferred stock or debt securities underlying the warrants will be separately transferable;
•: information with respect to book entry procedures;
•: the identity of the warrant agent; and
•: any additional terms of the warrants, including terms, procedures, and limitations relating to the exchange, exercise and settlement of the warrants.

Holders of equity warrants will not be entitled to:

•: vote, consent or receive dividends;
•: receive notice as shareholders with respect to any meeting of shareholders for the election of our directors or any other matter; or
•: exercise any rights as shareholders of Omeros Corporation.

Debt warrant certificates will be exchangeable for new debt warrant certificates of different denominations. Debt warrants may be exercised at the corporate trust office of the warrant agent or any other office indicated in the prospectus supplement. Prior to the exercise of their debt warrants, holders of debt warrants will not have any of the rights of holders of the debt securities purchasable upon exercise and will not be entitled to payment of principal or premium, if any, or interest on the debt securities purchasable upon exercise.

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DESCRIPTION OF SUBSCRIPTION RIGHTS

We may issue subscription rights to purchase shares of our common stock or preferred stock. These subscription rights may be issued independently or together with any other security offered hereby and may or may not be transferable by the shareholder receiving the subscription rights in such offering. In connection with any offering of subscription rights, we may enter into a standby arrangement with one or more underwriters or other purchasers pursuant to which the underwriters or other purchasers may be required to purchase any securities remaining unsubscribed for after such offering.

The prospectus supplement relating to any offering of subscription rights will include specific terms relating to the offering, including:

•: the price, if any, for the subscription rights;
•: the exercise price payable for each share of common stock or preferred stock upon the exercise of the subscription rights;
•: the number of subscription rights to be offered to each shareholder;
•: the number and terms of the shares of common stock or preferred stock which may be purchased per each subscription right;
•: the extent to which the subscription rights are transferable;
•: any other terms of the subscription rights, including the procedures and limitations relating to the exchange and exercise of the subscription rights;
•: the dates on which the right to exercise the subscription rights shall commence and expire;
•: the extent to which the subscription rights may include an over-subscription privilege with respect to unsubscribed securities or an over-allotment privilege to the extent the securities are fully subscribed; and
•: if applicable, the material terms of any standby underwriting or purchase arrangement that we may enter into in connection with the offering of subscription rights.

The preceding summary of the terms of the subscription rights does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the terms of the subscription rights being offered, as well as any applicable subscription rights certificate and the terms of the securities to which the subscription rights relate. Therefore, you should carefully consider the actual provisions of the subscription right, and subscription agreement and the applicable securities.

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DESCRIPTION OF UNITS

We may issue units comprised of one or more of the other securities described in this prospectus or any prospectus supplement in any combination. Each unit will be issued so that the holder of the unit is also the holder, with the rights and obligations of a holder, of each security included in the unit. The units may be issued under unit agreements to be entered into between us and a unit agent, which may provide that the securities included in the unit may not be held or transferred separately, at any time or times before a specified date or upon the occurrence of a specified event or occurrence.

The applicable prospectus supplement will describe:

•: the designation and terms of the units and of the securities comprising the units, including whether and under what circumstances the securities comprising the units may be held or transferred separately;
•: a description of the terms of any unit agreement governing the units;
•: a description of the provisions for the payment, settlement, transfer or exchange of the units;
•: a discussion of material federal income tax considerations, if applicable; and
•: whether the units if issued as a separate security will be issued in fully registered or global form.

The preceding summary of the terms of the units does not purport to be complete and is subject to, and is qualified in its entirety by reference to, the terms of the units being offered, as well as any applicable unit agreement and the terms of the applicable classes of securities comprising the unit. Therefore, you should carefully consider the actual provisions of the unit, any unit agreement and the applicable securities.

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PLAN OF DISTRIBUTION

We may sell the securities offered under this prospectus from time to time pursuant to underwritten public offerings, negotiated transactions, block trades or a combination of these methods or through underwriters, dealers or agents or directly to one or more purchasers. The securities may be distributed from time to time in one or more transactions at:

•: a fixed price or prices, which may be changed;
•: market prices prevailing at the time of sale;
•: prices related to the prevailing market price; or
•: negotiated prices.

Each time that we sell securities pursuant to this prospectus, we will provide a prospectus supplement or supplements that will describe the method of distribution and set forth the terms and conditions of the offering of such securities, including the following information:

•: the terms of the offering;
•: the names of any underwriters, dealers or agents;
•: the name or names of any managing underwriter or underwriters;
•: the purchase price of the securities;
•: the net proceeds from the sale of the securities;
•: any underwriting discounts, concessions, commissions or agency fees and other items constituting underwriters', dealers' or agents' compensation;
•: any delayed delivery arrangements; and
•: estimated offering expenses.

We may grant to the underwriters options to purchase additional securities at the public offering price, with additional underwriting commissions or discounts, as applicable, set forth in the prospectus supplement. The terms of any option to purchase additional securities will be set forth in the prospectus supplement for those securities.

We may engage in at-the-market offerings into an existing trading market in accordance with Rule 415(a)(4) under the Securities Act. Any at-the-market offering will be through an underwriter or underwriters acting as principal or agent for us.

We may issue to our existing security holders, through a dividend or similar distribution, subscription rights to purchase shares of our common stock or preferred stock, which may or may not be transferable. In any distribution of subscription rights to our existing security holders, if all of the underlying securities are not subscribed for, we may then sell the unsubscribed securities directly to third parties or may engage the services of one or more underwriters, dealers or agents, including standby underwriters, to sell the unsubscribed securities to third parties. The applicable prospectus supplement will describe the specific terms of any offering of our common stock or preferred stock through the issuance of subscription rights, including, if applicable, the material terms of any standby underwriting or purchase arrangement.

Sale Through Underwriters or Dealers

If underwriters are used in the sale, the underwriters will acquire the securities for their own account, including through underwriting, purchase, security lending or repurchase agreements with us. The underwriters may resell the securities from time to time in one or more transactions, including

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negotiated transactions. Underwriters may sell the securities in order to facilitate transactions in any of our other securities (described in this prospectus or otherwise), including other public or private transactions and short sales. Underwriters may offer securities to the public either through underwriting syndicates represented by one or more managing underwriters or directly by one or more firms acting as underwriters. Unless otherwise indicated in the prospectus supplement, the obligations of the underwriters to purchase the securities will be subject to certain conditions, and the underwriters will be obligated to purchase all the offered securities if they purchase any of them. The underwriters may change from time to time any initial public offering price and any discounts or concessions allowed or reallowed or paid to dealers. The prospectus supplement will include the names of the underwriters and the terms of the transaction, including any underwriting discounts or commissions.

If dealers are used in the sale of securities offered through this prospectus, we will sell the securities to them as principals. They may then resell those securities to the public at varying prices determined by the dealers at the time of resale. The prospectus supplement will include the names of the dealers and the terms of the transaction, including any discounts or commissions received.

Direct Sales and Sales Through Agents

We may sell the securities offered through this prospectus directly. In this case, no underwriters, dealers or agents would be involved. Such securities may also be sold through agents designated from time to time. The prospectus supplement will name any agent involved in the offer or sale of the offered securities and will describe any commissions payable to the agent. Unless otherwise indicated in the prospectus supplement, any agent will agree to use its reasonable best efforts to solicit purchases for the period of its appointment.

We may sell the securities directly to institutional investors or others who may be deemed to be underwriters within the meaning of the Securities Act with respect to any sale of those securities. The terms of any such sales will be described in the prospectus supplement.

Delayed Delivery Contracts

If the prospectus supplement indicates, we may authorize underwriters, dealers or agents to solicit offers from certain types of institutions to purchase securities at the public offering price under delayed delivery contracts. These contracts would provide for payment and delivery on a specified date in the future. The contracts would be subject only to those conditions described in the prospectus supplement. The applicable prospectus supplement will describe the commission payable for solicitation of those contracts.

Market Making, Stabilization and Other Transactions

Unless the applicable prospectus supplement states otherwise, all preferred stock, debt securities, depositary shares, warrants, subscription rights and units will be new issues of securities with no established trading market. Unless indicated in the applicable prospectus supplement, we do not expect to list the offered securities on a securities exchange, except for our common stock, which is listed on The Nasdaq Global Market. Any underwriters that we use in the sale of offered securities may make a market in such securities, but may discontinue such market making at any time without notice. Therefore, we cannot assure you that the securities will have a liquid trading market.

Any underwriter may also engage in stabilizing transactions, syndicate covering transactions and penalty bids in accordance with Rule 104 of Regulation M under the Exchange Act. Stabilizing transactions involve bids to purchase the underlying security in the open market for the purpose of preventing or retarding a decline in the price of the securities. Syndicate covering transactions involve purchases of the securities in the open market after the distribution has been completed in order to cover syndicate short positions. Penalty bids permit the underwriters to reclaim a selling concession

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from a syndicate member when the securities originally sold by the syndicate member are purchased in a stabilizing or syndicate covering transaction to cover syndicate short positions.

Stabilizing transactions, syndicate covering transactions and penalty bids may have the effect of raising or maintaining the market price of our securities or preventing or retarding a decline in the market price of our securities. As a result, the price of the securities in the open market may be higher than it would otherwise be in the absence of these transactions. The underwriters may, if they commence these transactions, discontinue them at any time.

Derivative Transactions and Hedging

We, the underwriters or other agents may engage in derivative transactions involving the securities. These derivatives may consist of short sale transactions and other hedging activities. The underwriters or agents may acquire a long or short position in the securities, hold or resell securities acquired and purchase options or futures on the securities and other derivative instruments with returns linked to or related to changes in the price of the securities. In order to facilitate these derivative transactions, we may enter into security lending or repurchase agreements with the underwriters or agents. The underwriters or agents may effect the derivative transactions through sales of the securities to the public, including short sales, or by lending the securities in order to facilitate short sale transactions by others. The underwriters or agents may also use the securities purchased or borrowed from us or others (or, in the case of derivatives, securities received from us in settlement of those derivatives) to directly or indirectly settle sales of the securities or close out any related open borrowings of the securities.

Electronic Auctions

We may also make sales through the Internet or through other electronic means. Since we may from time to time elect to offer securities directly to the public, with or without the involvement of agents, underwriters or dealers, utilizing the Internet or other forms of electronic bidding or ordering systems for the pricing and allocation of such securities, you will want to pay particular attention to the description of that system, which we will provide in a prospectus supplement.

Such electronic system may allow bidders to directly participate, through electronic access to an auction site, by submitting conditional offers to buy that are subject to acceptance by us, and which may directly affect the price or other terms and conditions at which such securities are sold. These bidding or ordering systems may present to each bidder, on a so-called "real-time" basis, relevant information to assist in making a bid, such as the clearing spread at which the offering would be sold, based on the bids submitted, and whether a bidder's individual bids would be accepted, prorated or rejected. For example, in the case of debt security, the clearing spread could be indicated as a number of "basis points" above an index treasury note.

Upon completion of such an electronic auction process, securities will be allocated based on prices bid, terms of bid or other factors. The final offering price at which securities would be sold and the allocation of securities among bidders would be based in whole or in part on the results of the Internet or other electronic bidding process or auction.

General Information

The specific terms of any lock-up provisions in respect of any given offering will be described in the applicable prospectus supplement.

Underwriters, dealers and agents may be entitled, under agreements entered into with us, to indemnification by us against certain liabilities, including liabilities under the Securities Act. Our underwriters, dealers and agents, or their affiliates, may be customers of, engage in transactions with or perform services for us, in the ordinary course of business.

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In compliance with guidelines of the Financial Industry Regulatory Authority, Inc. ("FINRA"), and unless otherwise disclosed in the applicable prospectus supplement, we do not intend for the maximum consideration or discount to be received by any FINRA member or independent broker dealer to exceed 8.0% of the aggregate amount of the securities offered pursuant to this prospectus and any applicable prospectus supplement.

Underwriters, dealers and agents may engage in transactions with us, or perform services for us, in the ordinary course of business for which they receive customary compensation.

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LEGAL MATTERS

The legality of any offered securities will be passed upon for us by Covington & Burling LLP, Washington, D.C., and Keller Rohrback L.L.P., Seattle, Washington. Counsel for any underwriters, dealers or agents will be named in the applicable prospectus supplement.

EXPERTS

Our consolidated financial statements appearing in our Annual Report (Form 10-K) for the year ended December 31, 2018, and the effectiveness of Omeros' internal control over financial reporting as of December 31, 2018, have been audited by Ernst & Young LLP, independent registered public accounting firm, as set forth in its reports thereon (which contain an explanatory paragraph describing conditions that raise substantial doubt about our ability to continue as a going concern as described in Note 1 to the consolidated financial statements) included therein, and incorporated herein by reference. Such consolidated financial statements are incorporated herein by reference in reliance upon such reports given on the authority of such firm as experts in accounting and auditing.

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PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution

The following table sets forth the various costs and expenses (other than the underwriting discounts and commissions) payable by the registrant in connection with the sale of the securities being registered. All amounts are estimates except the SEC registration fee.


SEC registration fee	$	*
Nasdaq Global Market listing fee		**
Printing and engraving costs		**
Legal fees and expenses		**
Accounting fees and expenses		**
Transfer agent fees and expenses		**
Trustee fees and expenses		**
Miscellaneous		**

Total	$	**

*: In accordance with Rules 456(b) and 457(r) under the Securities Act, the registrant is deferring payment of the registration fee associated with this registration statement. Pursuant to Rule 415(a)(6) under the Securities Act, this registration statement includes $100,000,000 aggregate amount of unsold securities previously registered under Post-Effective Amendment No. 1 to the Registration Statement on Form S-3 (File No. 333-219959). The registration fee previously paid with respect to such unsold securities will continue to apply to such securities in accordance with Rule 415(a)(6) under the Securities Act. The balance of the registration fees will be paid at the time of any offering of securities under this registration statement after the unsold securities have been used and therefore is not determinable.
**: These fees are variable based on the securities offered and the number of issuances and accordingly cannot be estimated at this time. The applicable prospectus supplement will set forth the estimated amount of expenses incurred in connection with securities to be offered and sold pursuant to this registration statement.

Item 15. Indemnification of Directors and Officers

Sections 23B.08.510 and 23B.08.570 of the Washington Business Corporation Act (the "WBCA") authorize Washington corporations to indemnify directors and officers under certain circumstances against expenses and liabilities incurred in legal proceedings in which they are involved by reason of being directors or officers. Section 23B.08.560 of the WBCA authorizes a corporation by provision in its articles of incorporation or in a bylaw approved by its shareholders to indemnify or agree to indemnify a director made a party to a proceeding, or obligate itself to advance or reimburse expenses incurred in a proceeding, without regard to the limitations imposed by Sections 23B.08.510 through 23B.08.550 of the WBCA; provided, however, that no such indemnity shall indemnify any director from or on account of (a) acts or omissions of the director finally adjudged to be intentional misconduct or a knowing violation of law, (b) conduct of the director finally adjudged to be in violation of Section 23B.08.310 of the WBCA (relating to unlawful distributions) or (c) any transaction with respect to which it was finally adjudged that such director personally received a benefit in money, property or services to which the director was not legally entitled.

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Article XI of our Articles of Incorporation and Article VII of our Bylaws require that we indemnify and hold harmless, to the fullest extent permitted by the WBCA, any individual made a party to any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative, and whether formal or informal, because that individual is or was a director or officer or is or was serving at our request as a director, officer, partner, trustee, employee or agent of another corporation, partnership, joint venture, trust, employee benefit plan or other enterprise, and that we will reimburse the reasonable expenses incurred by that individual with respect to such proceeding without regard to the limitations of Sections 23B.08.510 through 23B.08.550 and 23B.08.560(2) of the WBCA, or any other limitation that may be enacted in the future to the extent the limitation may be disregarded if authorized by our Articles of Incorporation.

Our practice is to enter into separate indemnification agreements with each of our directors and officers that provide the maximum indemnity allowed to directors and officers by the WBCA. We also maintain directors and officers insurance to insure such persons against certain liabilities potentially arising from their service to us.

The above discussion of the WBCA, our Articles of Incorporation and Bylaws and the other documents described above is not intended to be exhaustive and is qualified in its entirety by the actual provisions of that statute and those documents.

Item 16. Exhibits

			Incorporated by Reference

Exhibit No.		Exhibit Description	Form	File No.	Exhibit No.	Filing Date	Filed Herewith
	1.1	Form of Underwriting Agreement*
	3.1	Amended and Restated Articles of Incorporation of Omeros Corporation	10-K	001-34475	3.1	March 31, 2010
	3.2	Amended and Restated Bylaws of Omeros Corporation	10-K	001-34475	3.2	March 31, 2010
	4.1	Form of Common Stock Certificate	S-1/A	333-148572	4.1	October 2, 2009
	4.2	Form of Senior Indenture	S-3	333-169856	4.1	October 8, 2010
	4.3	Form of Subordinated Indenture	S-3	333-169856	4.2	October 8, 2010
	4.4	Form of Senior Debt Security (included in Exhibit 4.2)	S-3	333-169856	4.3	October 8, 2010
	4.5	Form of Subordinated Debt Security (included in Exhibit 4.3)	S-3	333-169856	4.4	October 8, 2010
	4.6	Form of Articles of Amendment*
	4.7	Form of Preferred Stock Certificate*
	4.8	Form of Deposit Agreement*
	4.9	Form of Depositary Receipt*

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			Incorporated by Reference

Exhibit No.		Exhibit Description	Form	File No.	Exhibit No.	Filing Date	Filed Herewith
	4.10	Form of Warrant Agreement*
	4.11	Form of Warrant*
	4.12	Form of Subscription Rights Agreement*
	4.13	Form of Subscription Rights Certificate*
	5.1	Opinion of Covington & Burling LLP					X
	5.2	Opinion of Keller Rohrback L.L.P.					X
	23.1	Consent of Independent Registered Public Accounting Firm					X
	23.2	Consent of Covington & Burling LLP (included in Exhibit 5.1)					X
	23.3	Consent of Keller Rohrback L.L.P. (included in Exhibit 5.2)					X
	24.1	Power of Attorney (included on signature page hereto)					X
	25.1	Form T-1 Statement of Eligibility of Trustee for Senior Indenture under the Trust Indenture Act of 1939**
	25.2	Form T-1 Statement of Eligibility of Trustee for Subordinated Indenture under the Trust Indenture Act of 1939**
	99.1	Description of Common Stock	10-K	001-34475	99.1	March 16, 2017

*: To be filed by amendment or as an exhibit to a report pursuant to Section 13(a) or 15(d) of the Securities Exchange Act of 1934 and incorporated herein by reference.
**: To be filed separately pursuant to Section 305(b)(2) of the Trust Indenture Act of 1939 and the rules and regulations thereunder.

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Item 17. Undertakings

The undersigned registrant hereby undertakes:

1. To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the U.S. Securities and Exchange Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the "Calculation of Registration Fee" table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided, however, that paragraphs (l)(i), (l)(ii) and (l)(iii) do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the U.S. Securities and Exchange Commission by the registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934 that are incorporated by reference into this registration statement, or that are contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

2. That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

3. To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

4. That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i) Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5) or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(l)(i), (vii) or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration

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statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

5. That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to the registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

(iii) The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

(iv) Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

6. That, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant's annual report pursuant to Section 13(a) or Section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan's annual report pursuant to Section 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in this registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

7. The undersigned registrant hereby undertakes to supplement the prospectus, after the expiration of the subscription period, to set forth the results of the subscription offer, the transactions by the underwriters during the subscription period, the amount of unsubscribed securities to be purchased by the underwriters, and the terms of any subsequent reoffering thereof. If any public offering by the underwriters is to be made on terms differing from those set forth on the cover page of the prospectus, a post-effective amendment will be filed to set forth the terms of such offering.

8. Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the indemnification provisions described herein, or otherwise, the registrant has been advised that in the opinion of the U.S. Securities and Exchange Commission such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its

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counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

9. To file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act in accordance with the rules and regulations prescribed by the U.S. Securities and Exchange Commission under Section 305(b)(2) of the Trust Indenture Act.

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SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Seattle, State of Washington, on December 4, 2019.



		OMEROS CORPORATION
		By:		/s/ GREGORY A. DEMOPULOS, M.D. President, Chief Executive Officer and Chairman of the Board of Directors

POWER OF ATTORNEY

KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints Gregory A. Demopulos, M.D., Michael A. Jacobsen and Peter B. Cancelmo, and each of them severally, as his true and lawful attorney-in-fact and agent, with full power of substitution and resubstitution, for him and in his name, place and stead, in any and all capacities, to sign any and all amendments (including post-effective amendments) to this registration statement, and to file the same with all exhibits thereto, and other documents in connection therewith, with the Securities and Exchange Commission, granting unto said attorneys-in-fact and agents, and each of them, full power and authority to do and perform each and every act and thing requisite and necessary to be done, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or any of them, may lawfully do or cause to be done by virtue hereof.

Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed by the following persons in the capacities and on the dates indicated:

Signature	Title	Date


/s/ GREGORY A. DEMOPULOS, M.D. Gregory A. Demopulos, M.D.	President, Chief Executive Officer and Chairman of the Board of Directors (Principal Executive Officer)	December 4, 2019
/s/ MICHAEL A. JACOBSEN Michael A. Jacobsen	Vice President, Finance, Chief Accounting Officer and Treasurer (Principal Financial Officer and Principal Accounting Officer)	December 4, 2019
/s/ RAY ASPIRI Ray Aspiri	Director	December 4, 2019
/s/ THOMAS F. BUMOL, PH.D. Thomas F. Bumol, Ph.D.	Director	December 4, 2019

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Signature	Title	Date


/s/ THOMAS J. CABLE Thomas J. Cable	Director	December 4, 2019
/s/ PETER A. DEMOPULOS, M.D. Peter A. Demopulos, M.D.	Director	December 4, 2019
/s/ ARNOLD C. HANISH Arnold C. Hanish	Director	December 4, 2019
/s/ LEROY E. HOOD, M.D., PH.D. Leroy E. Hood, M.D., Ph.D.	Director	December 4, 2019
/s/ RAJIV SHAH, M.D. Rajiv Shah, M.D.	Director	December 4, 2019

Exhibit 5.1



	December 4, 2019

Omeros Corporation

The Omeros Building
201 Elliott Avenue West
Seattle, Washington 98119

Ladies and Gentlemen:

We have acted as special counsel to Omeros Corporation, a Washington corporation (the “Company”), in connection with the registration by the Company under the Securities Act of 1933, as amended (the “Securities Act”), of the offer and sale from time to time of (i) shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”), (ii) shares of the Company’s preferred stock, par value $0.01 per share (the “Preferred Stock”), (iii) debt securities, which may be either senior or subordinated and may be issued in one or more series (the “Debt Securities”), (iv) depositary shares, representing a fractional interest in a share of Preferred Stock and evidenced by a depositary receipt (the “Depositary Shares”), (v) warrants to purchase Common Stock, Preferred Stock or Debt Securities (the “Warrants”), (vi) rights to subscribe for and to purchase Common Stock or Preferred Stock (the “Subscription Rights”) and (vii) units comprised of any combination of Common Stock, Preferred Stock, Debt Securities, Depositary Shares, Warrants or Subscription Rights (“Units” and, collectively with Debt Securities, Depositary Shares, Warrants and Subscription Rights, the “Covered Securities”), pursuant to the Company’s Registration Statement on Form S-3 (the “Registration Statement”) filed with the Securities and Exchange Commission (the “Commission”) on the date hereof.

We have reviewed such corporate records, certificates and other documents, and such questions of law, as we have considered necessary or appropriate for the purposes of this opinion. We have assumed that all signatures are genuine, that all documents submitted to us as originals are authentic and that all copies of documents submitted to us conform to the originals.

We have assumed that, at the time of the issuance, sale and delivery of each series of Debt Securities and each issue of Depositary Shares, Warrants, Subscription Rights or Units, as the case may be: (i) the execution, delivery and performance by the Company of the senior indenture in the form of Exhibit 4.2 to the Registration Statement or the subordinated indenture in the form of Exhibit 4.3 to the Registration Statement, as applicable, and any supplemental indenture thereto (any such indenture, together with any applicable supplemental indenture, the “Indenture”), deposit agreement, warrant agreement, subscription agreement or subscription rights certificate, and unit agreement (collectively, the “Documents”), as applicable, and all actions necessary for the issuance of the applicable Covered Securities, and the form and terms thereof, will comply with all requirements and restrictions, if any, applicable to the Company, whether imposed by any agreement or instrument to which the Company is a party or by which it

Omeros Corporation

December 4, 2019

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is bound or any court or other governmental or regulatory body having jurisdiction over the Company; and (ii) the Company will have duly authorized, executed and delivered any such Document and will have duly authorized the issuance of any such Covered Security, and that none of such authorizations will have been modified or rescinded, and there will not have occurred any change in law affecting the validity, legally binding character or enforceability thereof. We have also assumed that the Covered Securities will be offered and sold in compliance with applicable federal and state securities laws and in the manner stated in the Registration Statement and the appropriate prospectus supplement. We have assumed further that the Documents will be governed by and construed in accordance with the law of the State of New York. With respect to any Document executed or to be executed by any party other than the Company, we have assumed that such party has, or will have, duly authorized, executed and delivered the Documents to which it is a party and that each such Document is, or will be, the valid and binding obligation of such party, enforceable against it in accordance with its terms.

We have assumed further that the Company is duly organized, validly existing and in good standing under the law of the State of Washington and has all requisite power, authority and legal right to execute, deliver and perform its obligations under the Covered Securities, the Indenture, and the Documents. With respect to all matters of Washington law, we note that you are relying on an opinion of Keller Rohrback L.L.P., dated as of the date hereof, which opinion is filed as Exhibit 5.2 to the Registration Statement.

Additionally, we have relied as to certain matters on information obtained from public officials, officers of the Company and other sources believed by us to be responsible.

Based upon the foregoing, and subject to the qualifications set forth herein, we are of the opinion that, when, as and if:

1. With respect to the Debt Securities: (i) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act and all prospectus supplements required by applicable law have been delivered and filed as required by such laws; (ii) the Indenture has been duly executed and delivered on behalf of the Company and a trustee qualified to act as such under applicable law (the “Trustee”) and such Indenture has been duly qualified under the Trust Indenture Act of 1939, as amended; (iii) all necessary corporate action has been taken by the Company to authorize, execute and deliver any necessary supplemental indenture and to authorize the form, terms, execution and delivery of the Debt Securities; (iv) any legally required consents, approvals, authorizations and other orders of the Commission and any other regulatory authorities have been obtained; and (v) such Debt Securities have been duly executed by the Company and authenticated by the Trustee in accordance with the Indenture and have been duly issued and delivered against payment therefor in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Debt Securities and the plan of distribution, then, upon the happening of such events, such Debt Securities (including any Debt Securities to be issued by the Company upon the conversion or

Omeros Corporation

December 4, 2019

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exercise of other Covered Securities issued by the Company pursuant to the Registration Statement) will constitute the valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

2. With respect to the Depositary Shares: (i) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act and all prospectus supplements required by applicable law have been delivered and filed as required by such laws; (ii) all necessary corporate action has been taken by the Company to authorize, execute and deliver a deposit agreement; (iii) any legally required consents, approvals, authorizations and other orders of the Commission and any other regulatory authorities have been obtained; (iv) any shares of Preferred Stock underlying the Depositary Shares have been duly and validly authorized and reserved for issuance and sale and any such shares of Preferred Stock have been validly issued and are fully paid and non-assessable; and (v) the depositary receipts evidencing the Depositary Shares have been duly executed and delivered by the depositary in accordance with the applicable deposit agreement and in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Depositary Shares and the plan of distribution, then, upon the happening of such events, the Depositary Shares will be validly issued and will entitle the holders thereof to the rights specified in the deposit agreement, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

3. With respect to the Warrants: (i) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act and all prospectus supplements required by applicable law have been delivered and filed as required by such laws; (ii) all necessary corporate action has been taken by the Company to authorize, execute and deliver a warrant agreement and to authorize the form, terms, execution and delivery of the Warrants and to fix or otherwise determine the consideration to be received for the Warrants; (iii) any legally required consents, approvals, authorizations and other orders of the Commission and any other regulatory authorities have been obtained; (iv) any shares of Common Stock or Preferred Stock or any Debt Securities purchasable upon exercise of such Warrants, as applicable, have been duly and validly authorized and reserved for issuance and sale; and (v) the Warrants have been duly executed and sold by the Company against payment therefor in accordance with any applicable warrant agreement, and in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Warrants and the plan of distribution, then, upon the happening of such events, the Warrants will constitute the valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

Omeros Corporation

December 4, 2019

Page 4

4. With respect to the Subscription Rights: (i) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act and all prospectus supplements required by applicable law have been delivered and filed as required by such laws; (ii) all necessary corporate action has been taken by the Company to authorize, execute and deliver a subscription agreement or subscription rights certificate to the rights agent and to authorize the form, terms, execution and delivery of the Subscription Rights and to fix or otherwise determine the consideration to be received for the Subscription Rights; (iii) any legally required consents, approvals, authorizations and other orders of the Commission and any other regulatory authorities have been obtained; (iv) any shares of Common Stock or Preferred Stock purchasable upon exercise of such Subscription Rights, as applicable, have been duly and validly authorized and reserved for issuance and sale; and (v) the Subscription Rights have been duly executed and sold by the Company against payment therefor in accordance with any applicable subscription agreement or subscription rights certificate, and in accordance with such corporate action and applicable law as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Subscription Rights and the plan of distribution, then, upon the happening of such events, the Subscription Rights will constitute the valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

5. With respect to the Units: (i) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act and all prospectus supplements required by applicable law have been delivered and filed as required by such laws; (ii) all necessary corporate action has been taken by the Company to authorize, execute and deliver a unit agreement and to authorize the form, terms, execution and delivery of the Units and the other Registered Securities underlying the Units; (iii) any legally required consents, approvals, authorizations and other orders of the Commission and any other regulatory authorities have been obtained; (iv) any shares of Common Stock or Preferred Stock or any Debt Securities, Depositary Shares, Warrants or Subscription Rights to be issued pursuant to such Units, have been duly and validly authorized and reserved for issuance and sale; and (v) the Units and the other Registered Securities underlying the Units have been duly executed and sold by the Company against payment therefor in accordance with any applicable unit agreement, and in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Units and the other Registered Securities underlying the Units and the plan of distribution, then, upon the happening of such events, the Units will constitute the valid and binding obligations of the Company, enforceable against the Company in accordance with their terms, subject to bankruptcy, insolvency, fraudulent transfer, reorganization, moratorium and other laws of general applicability relating to or affecting creditors’ rights and to general equity principles.

Omeros Corporation

December 4, 2019

Page 5

Our opinions above are qualified to the extent that the enforcement of any Covered Securities denominated in a currency other than United States dollars may be limited by requirements that a claim (or a foreign currency judgment in respect of such claim) be converted into United States dollars at a rate of exchange prevailing on a date determined pursuant to applicable law.

We express no opinion as to (i) waivers of defenses, subrogation and related rights, rights to trial by jury, rights to object to venue, or other rights or benefits bestowed by operation of law, (ii) releases or waivers of unmatured claims or rights, (iii) indemnification, contribution, exculpation or arbitration provisions, or provisions for the non-survival of representations, to the extent they purport to indemnify any party against, or release or limit any party’s liability for, its own breach or failure to comply with statutory obligations, or to the extent such provisions are contrary to public policy or (iv) provisions for liquidated damages and penalties, penalty interest and interest on interest.

We are members of the bars of the District of Columbia and the State of New York. We do not express any opinion herein on any laws other than the law of the State of New York.

We hereby consent to the filing of this opinion as Exhibit 5.1 to the Registration Statement. We also hereby consent to the reference to our firm under the heading “Legal Matters” in the prospectus constituting part of the Registration Statement. In giving such consent, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act.

	Very truly yours,

	/s/ Covington & Burling LLP

EXHIBIT 5.2

KELLER ROHRBACK L.L.P.

December 4, 2019

Omeros Corporation

201 Elliott Avenue West

Seattle, WA 98119

Ladies and Gentlemen:

We have acted as Washington state counsel to you, Omeros Corporation, a Washington state corporation (the “Company”), in connection with its filing of the Registration Statement on Form S-3 (the “Registration Statement”) under the Securities Act of 1933, as amended (the “Securities Act”), with the United States Securities and Exchange Commission (the “Commission”) on the date hereof.

The Registration Statement relates to the registration by the Company under the Securities Act of the offer and sale by the Company from time to time, pursuant to Rule 415 under the Securities Act, of the following securities:

(i) shares of the Company’s common stock, par value $0.01 per share (the “Common Stock”);

(ii) shares of the Company’s preferred stock, par value $0.01 per share (the “Preferred Stock”);

(iii) debt securities, which may be either senior or subordinated and may be issued in one or more series (the “Debt Securities”);

(iv) depositary shares, representing a fractional interest in a share of Preferred Stock and evidenced by a depositary receipt (the “Depositary Shares”);

(v) warrants to purchase Common Stock, Preferred Stock or Debt Securities (the “Warrants”);

(vi) rights to subscribe for and to purchase Common Stock or Preferred Stock (the “Subscription Rights”); and

(vii) units comprised of any combination of Common Stock, Preferred Stock, Debt Securities, Depositary Shares, Warrants or Subscription Rights (“Units” and collectively with the Debt Securities, Depositary Shares, Warrants and Subscription Rights, the “Covered Securities”).

The Common Stock, Preferred Stock, Debt Securities, Depositary Shares, Warrants, Subscription Rights and Units are collectively referred to herein as the “Securities.”

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Omeros Corporation

KELLER ROHRBACK L.L.P.

December 4, 2019

Page 2

We have reviewed such corporate records, certificates and other documents and such questions of law, as we have considered necessary and relevant for the purposes of this opinion. We have assumed that all signatures are genuine, that all documents submitted to us as originals are authentic and that all copies of documents submitted to us conform to the originals. As to any facts material to our opinion, we have relied as to certain matters on information obtained from public officials, officers of the Company and other sources we believe to be responsible.

Based upon the foregoing and assuming that (a) the Registration Statement and any required post-effective amendments thereto have all become effective under the Securities Act, such effectiveness has not been terminated or rescinded, and comply with all applicable laws at the time the Securities are offered and sold as contemplated by the Registration Statement, (b) a prospectus supplement will have been prepared, delivered and filed with the Commission describing the Securities offered thereby and will comply with all applicable laws, (c) all Securities will be offered and sold in compliance with applicable federal and state securities laws and in the manner stated in the Registration Statement and the appropriate prospectus supplement, (d) any legally required consents, approvals, authorizations and other orders of the Commission and any other governmental or regulatory authorities have been obtained, (e) the truth, accuracy and completeness of the information, representations and warranties contained in the instruments, documents, certificates and records we have reviewed, (f) that a definitive purchase, underwriting, placement agency or similar agreement with respect to any Securities offered will have been duly authorized and validly executed and delivered by the Company and the other parties thereto, and (g) with respect to shares of Common Stock or Preferred Stock offered, that there will be sufficient shares of Common Stock or Preferred Stock authorized under the Company’s organizational documents that are not otherwise reserved for issuance, and further subject to the additional qualifications below, we are of the opinion that:

1. The Company is duly organized and validly existing under the laws of the State of Washington and possesses the requisite corporate power and authority to execute, deliver and perform its obligations under the Covered Securities.

2. With respect to the Common Stock, assuming (a) the Company has taken all necessary corporate action to authorize and approve the issuance of any Common Stock and to fix or otherwise determine the consideration to be received for the shares of Common Stock and the terms of the offer and sale thereof, (b) certificates representing shares of Common Stock shall have been duly executed, countersigned and registered and duly delivered to purchasers against payment therefor, if issued in certificated form, and (c) the Common Stock is duly issued and delivered against payment of the consideration therefor in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of the Common Stock, or is duly issued and delivered upon the conversion, exercise or exchange of any Preferred Stock, Debt Securities, Warrants, Subscription Rights or Units, the Common Stock will be validly issued, fully paid and non-assessable.

Omeros Corporation

KELLER ROHRBACK L.L.P.

December 4, 2019

Page 3

3. With respect to the Preferred Stock, assuming (a) the Company has taken all necessary corporate action to establish the rights, preferences and privileges of, and limitations on, any series of Preferred Stock and to authorize and approve the issuance and sale of the Preferred Stock of such series and to fix or otherwise determine the consideration to be received for the shares of Preferred Stock and the terms of the offer and sale thereof, (b) appropriate Articles of Amendment to the Company’s Amended and Restated Articles of Incorporation with respect to such series of Preferred Stock have been duly filed in accordance with applicable law, (c) certificates representing shares of Preferred Stock shall have been duly executed, countersigned and registered and duly delivered to purchasers against payment therefor, (d) any shares of Common Stock issuable upon conversion of such Preferred Stock, if applicable, have been duly and validly authorized and reserved for issuance, and (e) the Preferred Stock with terms so fixed is duly issued and delivered against payment of the consideration therefor in accordance with such corporate action and applicable law and as contemplated in the Registration Statement and the prospectus supplement setting forth the terms of such series of Preferred Stock, or is duly issued and delivered upon the conversion, exercise or exchange of Debt Securities, Depositary Shares, Warrants, Subscription Rights or Units, the Preferred Stock will be validly issued, fully paid and non-assessable.

4. With respect to the Covered Securities, if the Covered Securities are convertible into Common Stock or Preferred Stock, or if Common Stock or Preferred Stock may be acquired upon exercise, exchange or otherwise upon fulfillment of the terms of the Covered Securities, when (i) the issuance of such Common Stock or Preferred Stock relating to the Covered Securities have been duly authorized by appropriate corporate action, (ii) the Covered Securities have been presented for conversion, exercise, exchange or fulfillment in accordance with the terms thereof, (iii) with respect to Preferred Stock, appropriate Articles of Amendment to the Company’s Articles of Incorporation regarding such series of Preferred Stock have been duly filed in accordance with applicable law, and (iv) certificates representing Common Stock or Preferred Stock, as applicable, shall have been prepared in accordance with the Bylaws and duly executed, countersigned and registered and duly delivered upon conversion, exercise, exchange or fulfillment to the person entitled thereto, if issued in certificated form, in accordance with the terms of such Covered Securities, the Common Stock or Preferred Stock issuable upon conversion, exercise or exchange of the Covered Securities will be validly issued, fully paid and non-assessable.

We have assumed that, at the time of the issuance, sale and delivery of Covered Securities: (i) such Covered Securities, and any agreements or other documents relating thereto, will be duly executed and delivered and will constitute valid and binding obligations of the Company enforceable in accordance with their terms, (ii) the execution, delivery and performance by the Company of any supplemental indentures, and any agreements or other documents relating to the issuance of the Covered Securities, as applicable, and all actions necessary for the issuance of the Covered Securities, and the forms and terms thereof, will comply with all requirements and restrictions, if any, applicable to the Company, whether imposed by any agreement or instrument to which the Company is a party or by which it is bound or any court or other governmental or regulatory body having jurisdiction over the Company, and (iii) there will not have occurred any change in law affecting the legally binding character or enforceability thereof.

Omeros Corporation

KELLER ROHRBACK L.L.P.

December 4, 2019

Page 4

We are members of the bar of the State of Washington. We do not express any opinion herein on any laws other than the Washington Business Corporation Act, applicable provisions of the Washington State Constitution and reported judicial decisions interpreting these laws.

We hereby consent to the filing of this opinion as Exhibit 5.2 to the Registration Statement and to the use of our name under the caption “Legal Matters” in the prospectus contained therein, and in any supplement thereto or amendments thereof. In consenting to such reference, we do not thereby admit that we are in the category of persons whose consent is required under Section 7 of the Securities Act or under the rules and regulations of the Commission thereunder.

	Very truly yours,

	/s/ KELLER ROHRBACK L.L.P.

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Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the reference to our firm under the caption "Experts" in this Registration Statement (Form S-3) and related Prospectus of Omeros Corporation for the registration of common stock, preferred stock, debt securities, depositary shares, warrants, subscription rights, and units and to the incorporation by reference therein of our reports dated March 1, 2019, with respect to the consolidated financial statements of Omeros Corporation, and the effectiveness of internal control over financial reporting of Omeros Corporation, included in its Annual Report (Form 10-K) for the year ended December 31, 2018, filed with the Securities and Exchange Commission.


		/s/ Ernst & Young LLP
Seattle, Washington December 4, 2019

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Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM