Exhibit 10.20

OMEROS CORPORATION GUARANTY TO
OXFORD FINANCE CORPORATION

Date: August 11, 2006

Oxford Finance Corporation
133 North Fairfax Street
Alexandria, VA 22314

     To induce you to consent to the anticipated merger transaction involving Epsilon Acquisition Corporation, a corporation organized and existing under the laws of the State of Delaware, and Nura, Inc , a corporation organized and existing under the laws of the State of Delaware (collectively, the “Customer”), as well as to enter into, purchase or otherwise acquire, now or at any time hereafter, any promissory notes, security agreements, chattel mortgages, pledge agreements, conditional sale contracts, lease agreements, and/or any other documents or instruments evidencing, or relating to, any loan, extension of credit or other financial accommodation (such merger and loan transaction documents collectively , the “Account Documents” and each an “Account Document”) to Omeros Corporation, a corporation organized and existing under the laws of the State of Washington, but without in any way binding you to do so, the undersigned, for good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, does hereby guarantee to you, your successors and assigns, the due regular and punctual payment of any sum or sums of money which the Customer may owe to you now or at any time hereafter, whether evidenced by an Account Document, on open account or otherwise, and whether it represents principal, interest, late charges, indemnities, an original balance, an accelerated balance, liquidated damages, a balance reduced by partial payment, a deficiency after sale or other disposition of any leased equipment, collateral or security, or any other type of sum of any kind whatsoever that the Customer may owe to you now or at any time hereafter, and does hereby further guarantee to you, your successors and assigns, the due, regular and punctual performance of any other duty or obligation of any kind or character whatsoever that the Customer may owe to you now or at any time hereafter (all such payment and performance obligations being collectively referred to as “Obligations”). Undersigned does hereby further guarantee to pay upon demand all reasonable attorneys’ fees and other costs which may be suffered by you by reason of the default of the undersigned under this Guaranty. As used in this Guaranty, “you” shall mean Oxford Finance Corporation and all its subsidiaries and affiliates.

     This Guaranty is a guaranty of prompt payment and performance (and not merely a guaranty of collection). Nothing herein shall require you to first seek or exhaust any remedy against the Customer, its successors and assigns, or any other person obligated with respect to the Obligations, or to first foreclose, exhaust or otherwise proceed against any leased equipment, collateral or security which may be given in connection with the Obligations. It is agreed that you may, upon any breach or default of the Customer, or at any time thereafter, make demand upon the undersigned and receive payment and performance of the Obligations, with or without notice or demand for payment or performance by the Customer, its successors or assigns, or any other person. Suit may be brought and maintained against the undersigned, at your election, without joinder of the Customer or any other person as parties thereto. The obligations of each signatory to this Guaranty shall be joint and several.

     The undersigned agrees that its obligations under this Guaranty shall be primary, absolute, continuing and unconditional, irrespective of and unaffected by any of the following actions or circumstances (regardless of any notice to or consent of the undersigned): (a) the genuineness, validity, regularity and enforceability of the Account Documents or any other document; (b) any extension, renewal, amendment, change, waiver or other modification of the Account Documents or any other document; (c) the absence of, or delay in, any action to enforce the Account Documents, this Guaranty or any other document; (d) your failure or delay in obtaining any other guaranty of the Obligations (including, without limitation, your failure to obtain the signature of any other guarantor hereunder); (e) the release of, extension of time for payment or performance by, or any other indulgence granted to the Customer or any other person with respect to the Obligations by operation of law or otherwise, (f) the existence, value, condition, loss, subordination or release (with or without substitution) of, or failure to have title to or perfect and maintain a security interest in, or the time, place and manner of any sale or other disposition of any leased equipment, collateral or security given in connection with the Obligations, or any other impairment (whether intentional or negligent, by operation of law or otherwise) of the rights of the undersigned; (g) the Customer’s voluntary or involuntary bankruptcy, assignment for the benefit of creditors, reorganization, or similar proceedings affecting the Customer or any of its assets; or (h) any other action or circumstances which might otherwise constitute a legal or equitable discharge or defense of a surety or guarantor, other than payment in full of the Obligations.

     This Guaranty, the Account Documents and the Obligations may be assigned by you, without the consent of the Undersigned. The Undersigned agrees that if it receives written notice of an assignment from you, the Undersigned will pay all amounts due hereunder to such assignee or as instructed by you. The Undersigned also agrees to confirm in writing receipt of the notice of assignment as may be reasonably requested by assignee. The Undersigned hereby waives and agrees not to assert against any such assignee any of the defenses set forth in the immediate preceding paragraph.

     This Guaranty may be terminated upon delivery to you (at your address shown above) of a written termination notice from the undersigned. However, as to all Obligations (whether matured, unmatured, absolute, contingent or otherwise) incurred by the Customer prior to your receipt of such written termination notice (and regardless of any subsequent amendment, extension or other modification which may be made with respect to such Obligations), this Guaranty shall nevertheless continue and remain undischarged until all such Obligations are indefeasibly paid and performed in full.

     The undersigned agrees that this Guaranty shall remain in full force and effect or be reinstated (as the case may be) if at any time payment or performance of any of the Obligations (or any part thereof) is rescinded, reduced or must otherwise be restored or returned by you, all as though such payment or performance had not been made. If, by reason of any bankruptcy, insolvency or similar laws effecting the rights of creditors, you shall be prohibited from exercising any of your rights or remedies against the Customer or any other person or against any property, then, as between you and the undersigned, such prohibition shall be of no force and effect, and you shall have the right to make demand upon, and receive payment from, the undersigned of all amounts and other sums that would be due to you upon a default with respect to the Obligations.

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     Notice of acceptance of this Guaranty and of any default by the Customer or any other person is hereby waived. Presentment, protest, demand, and notice of protest, demand and dishonor of any of the Obligations, and the exercise of possessory, collection or other remedies for the Obligations, are hereby waived. The undersigned warrants that it has adequate means to obtain from the Customer on a continuing basis financial data and other information regarding the Customer and is not relying upon you to provide any such data or other information. Without limiting the foregoing, notice of adverse change in the Customer’s financial condition or of any other fact which might materially increase the risk of the undersigned is also waived. All settlements, compromises, accounts stated and agreed balances made in good faith between the Customer, its successors or assigns, and you shall be binding upon and shall not affect the liability of the undersigned.

     Payment of all cash amounts now or hereafter owed to the undersigned by the Customer or any other obligor for any of the Obligations is hereby subordinated in right of payment to the indefeasible payment in full to you of all Obligations. Until the Obligations are paid in full, the undersigned hereby irrevocably and unconditionally waives and relinquishes all statutory, contractual, common law, equitable and all other claims against the Customer, any other obligor for any of the Obligations, any collateral therefore, or any other assets of the Customer or any such other obligor, for subrogation, reimbursement, exoneration, contribution, indemnification, setoff or other recourse in respect of sums paid or payable to you by the undersigned hereunder, and, until the Obligations are paid in full, the undersigned hereby further irrevocably and unconditionally waives and relinquishes any and all other benefits which it might otherwise directly or indirectly receive or be entitled to receive by reason of any amounts paid by, or collected or due from, it, the Customer or any other obligor for any of the Obligations, or realized from any of their respective assets.

     THE UNDERSIGNED HEREBY UNCONDITIONALLY WAIVES ITS RIGHT TO A JURY TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF, DIRECTLY OR INDIRECTLY, THIS GUARANTY, THE OBLIGATIONS GUARANTEED HEREBY, ANY OF THE RELATED DOCUMENTS, ANY DEALINGS BETWEEN US RELATING TO THE SUBJECT MATTER HEREOF OR THEREOF, AND/OR THE RELATIONSHIP THAT IS BEING ESTABLISHED BETWEEN US. THE SCOPE OF THIS WAIVER IS INTENDED TO BE ALL ENCOMPASSING OF ANY AND ALL DISPUTES THAT MAY BE FILED IN ANY COURT (INCLUDING, WITHOUT LIMITATION, CONTRACT CLAIMS, TORT CLAIMS, BREACH OF DUTY CLAIMS, AND ALL OTHER COMMON LAW AND STATUTORY CLAIMS). THIS WAIVER IS IRREVOCABLE MEANING THAT IT MAY NOT BE MODIFIED EITHER ORALLY OR IN WRITING, AND SHALL APPLY TO ANY SUBSEQUENT AMENDMENTS, RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO THIS GUARANTY, THE OBLIGATIONS GUARANTEED HEREBY, OR ANY RELATED DOCUMENTS. IN THE EVENT OF LITIGATION, THIS GUARANTY MAY BE FILED AS A WRITTEN CONSENT TO A TRIAL BY THE COURT.

     As used in this Guaranty, the word “person” shall include any individual, corporation, partnership, joint venture, association, joint-stock company, trust, unincorporated organization, or any government or any political subdivision thereof.

     This Guaranty shall be governed by, construed, and interpreted in accordance with the law of the Commonwealth of Virginia, without regard to the choice of law principles thereof.

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     This Guaranty is intended by the parties as a final expression of the guaranty of the undersigned and is also intended as a complete and exclusive statement of the terms thereof. No course of dealing, course of performance or trade usage, nor any paid evidence of any kind, shall be used to supplement or modify any of the terms hereof. Nor are there any conditions to the full effectiveness of this Guaranty. This Guaranty and each of its provisions may only be waived, modified, varied, released, terminated or surrendered, in whole or in part, by a duly authorized written instrument signed by you. No failure by you to exercise your rights hereunder shall give rise to any estoppel against you, or excuse the undersigned from performing hereunder. Your waiver of any right to demand performance hereunder shall not be a waiver of any subsequent or other right to demand performance hereunder.

     This Guaranty shall bind the undersigned’s successors and assigns and the benefits thereof shall extend to and include your successors and assigns. In the event of default hereunder, you may at any time inspect undersigned’s records as related to the Obligations hereunder during normal business hours and upon reasonable advance notice, or at your option, undersigned shall furnish you with the most current independent audit report that has been obtained by the undersigned.

     If any provisions of this Guaranty are in conflict with any applicable statute, rule or law, then such provisions shall be deemed null and void to the extent that they may conflict therewith, but without invalidating any other provisions hereof.

     Each signatory on behalf of a corporate guarantor warrants that he had authority to sign on behalf of such corporation and by so signing, to bind said guarantor corporation hereunder.

     IN WITNESS WHEREOF, this Guaranty is executed the day and year above written.

OMEROS CORPORATION

By:	/s/ Gregory Demopulos
	(Signature)
Title:	Chairman & CEO
	(Officer’s Title)
ATTEST:	/s/ Craig Sherman
	Secretary/Assistant Secretary

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Certified Resolution

     The undersigned hereby certifies that he/she is Secretary of Omeros Corporation, that the following resolution was passed at a meeting of the Board of Directors of said corporation held on July 31, 2006 duly called, a quorum being present, that said resolution has not since been revoked or amended. and that the form of guaranty referred to therein is the form shown attached hereto:

     “RESOLVED that it is to the benefit of this corporation that it execute a guaranty of the obligations of Epsilon Acquisition Corporation, a corporation organized and existing under the laws of the State of Delaware, and Nura, Inc., a corporation organized and existing under the laws of the State of Delaware (“Customer”) to Oxford Finance Corporation (together with its successors and assigns, if any, the “Secured Party”) and that the benefit to be received by this corporation from such guaranty is reasonably worth the obligations thereby guaranteed, and further that such guaranty shall be substantially in the form annexed to these minutes, and further that any Vice President and the Chief Executive Officer (Title of Officers) of this corporation are authorized to execute such guaranty on the behalf of this corporation.”

     WITNESS my hand and the seal of this corporation on this 11 day of August, 2006.

/s/ Craig Sherman

      [Seal] Secretary