8-K

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT
Pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported):  July 18, 2008

OPTIMER PHARMACEUTICALS, INC.

(Exact name of registrant as specified in its charter)

Delaware	001-33291	33-0830300
(State or other jurisdiction of incorporation)	(Commission File Number)	(IRS Employer Identification No.)

10110 Sorrento Valley Road, Suite C

San Diego, CA  92121
(Address of principal executive offices, including zip code)

Registrant’s telephone number, including area code: (858) 909-0736

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

o    Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o    Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o    Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o    Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 1.01   Entry into a Material Definitive Agreement.

On July 18, 2008, Optimer Pharmaceuticals, Inc. (“Optimer”) entered into a common stock purchase agreement with certain institutional investors relating to a registered direct offering of 1,443,396 shares of Optimer’s common stock. Under the terms of the transaction, Optimer will sell the common stock at $8.48 per share to the institutional investors for gross proceeds of approximately $12.2 million. The closing of the offering is expected to take place on July 25, 2008. A copy of the common stock purchase agreement is attached as Exhibit 99.1 hereto and is incorporated herein by reference.

The common stock will be issued pursuant to a prospectus supplement to be filed with the Securities and Exchange Commission in connection with a shelf takedown from Optimer’s registration statement on Form S-3 (File No. 333-149935) which became effective on April 7, 2008. The purchasers in the offering include funds affiliated with ProQuest Investments.  Alain B. Schreiber, M.D., one of Optimer’s directors, is a Managing Partner at ProQuest Investments.

Proceeds from the offering will be used in the further development of Optimer’s ongoing programs, as well as for other general corporate purposes.

On July 21, 2008, Optimer issued a press release announcing the offering. A copy of the press release is attached as Exhibit 99.2 hereto and is incorporated herein by reference. A copy of the opinion of Cooley Godward Kronish LLP relating to the legality of the issuance and sale of the shares in the offering is attached as Exhibit 5.1 hereto.

Item 9.01   Financial Statements and Exhibits.

(d) Exhibits.

Exhibit No.	Description
5.1	Opinion of Cooley Godward Kronish LLP.
23.1	Consent of Cooley Godward Kronish LLP (included in its opinion filed as Exhibit 5.1 hereto).
99.1	Common Stock Purchase Agreement.
99.2	Press release of Optimer Pharmaceuticals, Inc. dated July 21, 2008.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

	OPTIMER PHARMACEUTICALS, INC.
Dated: July 21, 2008	By:	/s/ John D. Prunty
		John D. Prunty   Chief Financial Officer (Duly Authorized Officer   and Principal Financial and Accounting Officer)

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EX-5.1

Exhibit 5.1

Barbara L. Borden

(858) 550-6064

bordenbl@cooley.com

July 18, 2008

Optimer Pharmaceuticals, Inc.

10110 Sorrento Valley Road, Suite C

San Diego, CA  92121

Ladies and Gentlemen:

You have requested our opinion with respect to certain matters in connection with the offering by OPTIMER PHARMACEUTICALS, INC., a Delaware corporation (the “Company”), of 1,443,396 shares of the Company’s common stock, par value $0.001 (the “Shares”), pursuant to a Registration Statement on Form S-3 (Registration Statement No. 333-149935) (the “Registration Statement”), filed with the Securities and Exchange Commission (the “Commission”) under the Securities Act of 1933, as amended (the “Act”), the prospectus dated April 7, 2008 (the “Base Prospectus”), and the prospectus supplement relating to the Shares filed with the Commission pursuant to Rule 424(b) of the Rules and Regulations of the Act (the “Prospectus Supplement”).  (The Base Prospectus and Prospectus Supplement are collectively referred to as the “Prospectus.”)  All of the Shares are to be sold by the Company as described in the Registration Statement and Prospectus.

In connection with this opinion, we have examined and relied upon the Registration Statement, the Prospectus, the Company’s Restated Certificate of Incorporation, its Restated Bylaws, as amended, and the originals or copies certified to our satisfaction of such records, documents, certificates, memoranda and other instruments as in our judgment are necessary or appropriate to enable us to render the opinion expressed below. We have assumed the genuineness and authenticity of all documents submitted to us as originals, and the conformity to originals of all documents submitted to us as copies thereof and the due execution and delivery of all documents where due execution and delivery are a prerequisite to the effectiveness thereof.

On the basis of the foregoing, and in reliance thereon, we are of the opinion that the Shares, when sold in accordance with the Registration Statement and Prospectus, will be validly issued, fully paid and nonassessable.

We consent to the reference to our firm under the caption “Legal Matters” in the Prospectus and to the filing of this opinion as an exhibit to the Registration Statement.

Very truly yours,

Cooley Godward Kronish LLP

By:	/s/ Barbara L. Borden
		Barbara L. Borden

4401 EASTGATE MALL, SAN DIEGO, CA 92121  T: (858) 550-6000  F: (858) 550-6420  WWW.COOLEY.COM

EX-99.1

Exhibit 99.1

OPTIMER PHARMACEUTICALS, INC.
COMMON STOCK
PURCHASE AGREEMENT

THIS COMMON STOCK PURCHASE AGREEMENT (the “Agreement”) is made as of the 18th day of July, 2008, by and among Optimer Pharmaceuticals, Inc., a Delaware corporation (the “Company”), and the investors, severally and not jointly, listed on the signature pages hereto (the “Investors”).

THE PARTIES HEREBY AGREE AS FOLLOWS:

1.Purchase and Sale of Stock.

1.1Sale and Issuance of Common Stock.

(a)On or prior to the Closing (as defined below), the Company shall have authorized the sale and issuance to the Investors of an aggregate of 1,443,396 shares of the Company’s common stock, $0.001 par value (the “Common Stock”), at a purchase price of $8.48 per share (the “Per Share Purchase Price”).

(b)Subject to the terms and conditions of this Agreement, each Investor, severally and not jointly, agrees to purchase at the Closing, and the Company agrees to sell and issue to such Investor at the Closing, that number of shares of the Company’s Common Stock set forth opposite such Investor’s name on the signature pages hereto, at the Per Share Purchase Price (the “Stock”).

1.2Closing.  The purchase and sale of the Stock shall take place at the offices of Cooley Godward Kronish LLP located at 4401 Eastgate Mall, San Diego, California at 7:00 a.m., on July 25, 2008, or at such other time and place as the Company and the Investors may mutually agree upon orally or in writing (which time and place are designated as the “Closing”).  At the Closing, the Company shall cause its transfer agent to deliver to each Investor, via electronic book-entry or in the form of a stock certificate, the Stock such Investor is purchasing hereunder against payment of the purchase price therefor by wire transfer of immediately available funds to the following account:

Silicon Valley Bank

3003 Tasman Drive

Santa Clara, California 95054

Account Name: Optimer Pharmaceuticals, Inc.

Account No.: **********

ABA/Routing No.: *********

SWIFT Code: ********

2.Representations and Warranties of the Company.  The Company hereby represents and warrants to each Investor that:

2.1The Company meets the requirements for use of Form S-3 under the Securities Act of 1933, as amended (the “Securities Act”), and has filed with the Securities and Exchange Commission (the “Commission”) a registration statement on such Form (Registration File No. 333-149935), which became effective as of April 7, 2008 for the registration under the Securities Act of the Stock.  Such registration statement meets the requirements set forth in Rule 415(a)(1)(x) under the Securities Act and complies with said Rule. The Company will file with the Commission pursuant to Rule 424(b) under the Securities Act, and the rules and regulations (the “Rules and Regulations”) of the Commission promulgated thereunder, a supplement to the Base Prospectus (as defined below) relating to the offer to sell and proposed sale of the Stock and the plan of distribution thereof.  Such registration statement, including the exhibits thereto, as amended at the date of this Agreement, is hereinafter called the “Registration Statement”; the prospectus filed with the Commission on April 7, 2008 and related to the Registration Statement is hereinafter called the “Base Prospectus”; and the supplemented form of prospectus, in the form in which it will be filed with the Commission pursuant to Rule 424(b) (including the Base Prospectus as so supplemented) is hereinafter called the “Prospectus Supplement.”  Any reference herein to the Registration Statement, the Base Prospectus or the Prospectus Supplement shall be deemed to refer to and include the documents incorporated by reference therein (the “Incorporated Documents”) pursuant to Item 12 of Form S-3 which were filed under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), on or before the date of this Agreement, or the issue date of the Base Prospectus or the Prospectus Supplement, as the case may be; and any reference herein to the terms “amend,” “amendment” or “supplement” with respect to the Registration Statement, the Base Prospectus or the Prospectus Supplement shall be deemed to refer to and include the filing of any document under the Exchange Act after the date of this Agreement, or the issue date of the Base Prospectus or the Prospectus Supplement, as the case may be, deemed to be incorporated therein by reference.  All references in this Agreement to financial statements and schedules and other information which is “contained,” “included,” “described,” “set forth” or “stated” in the Registration Statement, the Base Prospectus or the Prospectus Supplement (and all other references of like import) shall be deemed to mean and include all such financial statements and schedules and other information which is or is deemed to be incorporated by reference in the Registration Statement, the Base Prospectus or the Prospectus Supplement, as the case may be.  No stop order suspending the effectiveness of the Registration Statement or the use of the Base Prospectus or the Prospectus Supplement has been issued, and no proceeding for any such purpose is pending or has been initiated or, to the Company’s knowledge, is threatened by the Commission.

2.2The Registration Statement (and any further documents to be filed with the Commission) contains all exhibits and schedules as required by the Securities Act.  Each of the Registration Statement and any post-effective amendment thereto, at the time it became effective, complied in all material respects with the Securities Act and the Exchange Act and the applicable Rules and Regulations and did not and, as amended or supplemented, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading.  The Base Prospectus and the Prospectus Supplement, each as of its respective date, comply in all material respects with the Securities Act and the Exchange Act and the applicable Rules and Regulations. 

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Each of the Base Prospectus and the Prospectus Supplement, as amended or supplemented, did not and will not contain as of the date thereof any untrue statement of a material fact or omit to state a material fact necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading.  The Incorporated Documents, when they were filed with the Commission, conformed in all material respects to the requirements of the Exchange Act and the applicable Rules and Regulations and none of such Incorporated Documents, when they were filed with the Commission, contained any untrue statement of a material fact or omitted to state a material fact necessary to make the statements therein, in light of the circumstances under which they were made, not misleading; and any further documents so filed and incorporated by reference in the Base Prospectus or Prospectus Supplement, when such documents are filed with the Commission, will conform in all material respects to the requirements of the Exchange Act and the applicable Rules and Regulations, as applicable and will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in light of the circumstances under which they are made, not misleading.  Notwithstanding the foregoing, the Company makes no representations or warranties as to information, if any, contained in or omitted from the Prospectus Supplement or any amendment thereof or supplement thereto in reliance upon and in conformity with information furnished in writing to the Company by or on behalf of the Investor specifically for use in the Registration Statement or the Prospectus Supplement, which information the parties hereto agree is limited to the Investor’s Information as defined in Section 4.1.  No post-effective amendment to the Registration Statement reflecting any facts or events arising after the date thereof which represent, individually or in the aggregate, a fundamental change in the information set forth therein is required to be filed with the Commission.  There are no documents required to be filed with the Commission in connection with the transaction contemplated hereby that have not been filed as required pursuant to the Securities Act or will not be filed within the requisite time period.  There are no contracts or other documents required to be described in the Base Prospectus or Prospectus Supplement, or to be filed as exhibits or schedules to the Registration Statement, which have not been described or filed as required.

2.3The Company has delivered, or will as promptly as practicable deliver, to the Investor complete conformed copies of the Registration Statement and of each consent and certificate of experts filed as a part thereof, and conformed copies of the Registration Statement (without exhibits) and the Base Prospectus and the Prospectus Supplement, as amended or supplemented, in such quantities and at such places as the Investor reasonably requests.  Neither the Company nor any of its directors and officers has distributed and none of them will distribute, prior to the Closing, any offering material in connection with the offering and sale of the Stock other than the Base Prospectus, the Prospectus Supplement, the Registration Statement, copies of the documents incorporated by reference therein and any other materials permitted by the Securities Act.

3.Representations and Warranties of the Investor.  Each Investor, severally and not jointly, hereby represents and warrants to the Company that:

3.1(i)The Investor has full right, power and authority to enter into this Agreement and to consummate the transactions contemplated hereby and has taken all necessary action to authorize the execution, delivery and performance of this Agreement, and (ii) this Agreement constitutes a valid and binding obligation of the Investor enforceable against the

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Investor in accordance with its terms, except as enforceability may be limited by applicable bankruptcy, insolvency, reorganization, moratorium or similar laws affecting creditors’ and contracting parties’ rights generally and except as enforceability may be subject to general principles of equity (regardless of whether such enforceability is considered in a proceeding in equity or at law).

3.2The Investor, in connection with its decision to purchase the Stock, relied only upon the Base Prospectus, the Prospectus Supplement, the Incorporated Documents, and any representations and warranties of the Company contained herein.

3.3The Investor acknowledges, represents and agrees that no action has been or will be taken in any jurisdiction outside the United States by the Company that would permit an offering of the Stock, or possession or distribution of offering materials in connection with the issue of the Stock in any jurisdiction outside the United States where action for that purpose is required.

3.4The Investor understands that nothing in this Agreement or any other materials presented to the Investor in connection with the purchase and sale of the Stock constitutes legal, tax or investment advice.  The Investor has consulted such legal, tax and investment advisors as it, in its sole discretion, has deemed necessary or appropriate in connection with its purchase of the Stock.

4.Miscellaneous.

4.1Investor’s Information.  The parties hereto acknowledge and agree that, for all purposes of this Agreement, “Investor’s Information” means solely the statements concerning the Investor contained under the heading “Plan of Distribution” in the Prospectus Supplement.

4.2Successors and Assigns.  Except as otherwise provided herein, the terms and conditions of this Agreement shall inure to the benefit of and be binding upon the respective successors and assigns of the parties.  Nothing in this Agreement, express or implied, is intended to confer upon any party other than the parties hereto or their respective successors and assigns any rights, remedies, obligations, or liabilities under or by reason of this Agreement, except as expressly provided in this Agreement.

4.3Governing Law.  This Agreement shall be governed by and construed under the laws of the State of California as applied to agreements among California residents entered into and to be performed entirely within California.

4.4Counterparts; Facsimile.  This Agreement may be executed in two or more counterparts, each of which shall be deemed an original, but all of which together shall constitute one and the same instrument.  Facsimile signatures shall be as effective as original signatures.

4.5Titles and Subtitles.  The titles and subtitles used in this Agreement are used for convenience only and are not to be considered in construing or interpreting this Agreement.

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4.6Notices.  Unless otherwise provided, any notice required or permitted under this Agreement shall be given in writing and shall be deemed effectively given upon personal delivery to the party to be notified or upon deposit with the United States Post Office, by registered or certified mail, postage prepaid and addressed to the party to be notified at the address indicated for such party on the signature page hereof, or at such other address as such party may designate by 10 days’ advance written notice to the other parties.

4.7Finder’s Fee.  Each party represents that it neither is nor will be obligated for any finders’ fee or commission in connection with this transaction.  The Investor agrees to indemnify and to hold harmless the Company from any liability for any commission or compensation in the nature of a finders’ fee (and the costs and expenses of defending against such liability or asserted liability) for which the Investor or any of its officers, partners, employees, or representatives is responsible.  The Company agrees to indemnify and hold harmless the Investor from any liability for any commission or compensation in the nature of a finders’ fee (and the costs and expenses of defending against such liability or asserted liability) for which the Company or any of its officers, employees or representatives is responsible.

4.8Amendments and Waivers.  Any term of this Agreement may be amended and the observance of any term of this Agreement may be waived (either generally or in a particular instance and either retroactively or prospectively), only with the written consent of the Company and the Investor.

4.9Severability.  If one or more provisions of this Agreement are held to be unenforceable under applicable law, such provision shall be excluded from this Agreement and the balance of the Agreement shall be interpreted as if such provision were so excluded and shall be enforceable in accordance with its terms.

4.10Entire Agreement.  This Agreement and the other documents referred to herein constitute the entire agreement among the parties and no party shall be liable or bound to any other party in any manner by any warranties, representations, or covenants except as specifically set forth herein or therein.

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IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the day and year first above written.

OPTIMER PHARMACEUTICALS, INC.
By:	/s/ John D. Prunty
Name:	John D. Prunty
Title:	Chief Financial Officer
Address:		10110 Sorrento Valley Road
		Suite C
		San Diego, California 92121

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the day and year first above written.

INVESTOR		SHARES OF COMMON STOCK
ProQuest Investment IV, L.P.		628,931
By:	/s/ Pasquale DeAngelis
Name: Pasquale DeAngelis
Title: Managing Member of the General Partner
ProQuest Investment III, L.P.		314,465
By:	/s/ Pasquale DeAngelis
Name: Pasquale DeAngelis
Title: Managing Member of the General Partner

IN WITNESS WHEREOF, the parties hereto have executed this Agreement as of the day and year first above written.

INVESTOR		SHARES OF COMMON STOCK
Chung Chia Company Limited		500,000
By:	/s/ Hsu Tsui-Hua
Name: Hsu Tsui-Hua
Title: Director

EX-99.2

Exhibit 99.2

Optimer Pharmaceuticals to Raise $12.2 Million in Registered Direct Offering

SAN DIEGO– July 21, 2008 – Optimer Pharmaceuticals, Inc. (Nasdaq: OPTR) today announced that it has received commitments from selected investors to purchase an aggregate of 1,443,396 shares of Optimer’s common stock at a purchase price of $8.48 per share pursuant to an effective shelf registration statement.

The closing of this offering is expected to take place on July 25, 2008.  Proceeds from the transaction will be used in the further development of Optimer’s ongoing programs, as well as for other general corporate purposes.

Copies of the final prospectus supplement and accompanying base prospectus can be obtained from the Corporate Communications Manager, Optimer Pharmaceuticals, Inc., 10110 Sorrento Valley Road, Suite C, San Diego, CA 92121.

The press release shall not constitute an offer to sell or the solicitation of an offer to buy nor will there be any sale of these securities in any state in which to offer, solicitation or sale would be unlawful prior to registration statement or qualification under the securities laws of any such state.

About Optimer Pharmaceuticals

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative anti-infective products for the treatment of serious infections. Optimer has two late-stage anti-infective product candidates. OPT-80 is being developed for the treatment of Clostridium difficile infection, the most common hospital-acquired diarrhea. Prulifloxacin is an antibiotic being developed for the treatment of travelers’ diarrhea, a form of infectious diarrhea. Additional information regarding Optimer can be found at http://www.optimerpharma.com.

Forward-looking Statements

Statements included in this press release that are not a description of historical facts are forward-looking statements, including without limitation all statements related to the expected closing of the offering and Optimer’s receipt and use of the offering proceeds.  Words such as “believes,” “anticipates,” “plans,” “expects,” “intend,” “will,” “goal” and similar expressions are intended to identify forward-looking statements. The inclusion of forward-looking statements should not be regarded as a representation by Optimer that any of its plans will be achieved. Actual results may differ materially from those set forth in this release due to the risks and uncertainties inherent in Optimer’s business including, without limitation, risks relating to: whether the investors will fulfill their obligations to purchase the shares in the offering, the timing, progress and likelihood of success of Optimer’s product research and development programs, the timing and status of Optimer’s preclinical and clinical development of potential drugs and other risks detailed in Optimer’s filings with the Securities and Exchange Commission.

Contacts

Optimer Pharmaceuticals, Inc.

Christina Donaghy, Corporate Communications Manager

John D. Prunty, Chief Financial Officer & VP Finance

858-909-0736

Porter Novelli Life Sciences

Jason I. Spark, Vice President

619-849-6005