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Exhibit 4.5    
    


        THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THEY MAY NOT BE SOLD,
OFFERED FOR SALE, PLEDGED, HYPOTHECATED, OR OTHERWISE TRANSFERRED EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER THE SECURITIES ACT OF 1933, AS AMENDED OR AN OPINION OF COUNSEL
SATISFACTORY TO THE COMPANY THAT REGISTRATION IS NOT REQUIRED.


Issue
Date:             , 2005 


OPTIMER PHARMACEUTICALS, INC.  


 WARRANT TO PURCHASE SERIES D PREFERRED STOCK  


        This Warrant to Purchase Series D Preferred Stock (the "Warrant") is issued to
                         (the "Holder") by Optimer Pharmaceuticals,
 Inc. a Delaware corporation (the
"Company") in exchange for the payment in cash by Holder of $             to the Company. 



        1.    Purchase of Shares.    Subject to the terms and conditions hereinafter set forth, the Holder of this Warrant is
entitled during the Exercise Period, upon surrender of this Warrant at the principal office of the Company (or at such other place as the Company shall notify the Holder hereof in writing), to
purchase, in whole or in part, from the Company up to            fully paid and nonassessable Shares (as defined below), at an exercise price per Share equal to the Exercise Price (as
defined
below). 


        2.    Definitions.    



        (a)   "Act" shall mean the Securities Act of 1933, as amended. 


        (b)   "Exercise Price" shall mean $3.60. 


        (c)   "Exercise Period" shall mean the term commencing on the date of issuance of this Warrant and ending on the expiration of
this Warrant pursuant to Section 14 hereof. 


        (d)   "Shares" shall mean shares of the Company's Series D Preferred Stock. 


        (e)   "Change of Control" shall mean (i) a sale, lease or disposition of all or substantially all of the assets of the
Company, or (ii) a merger or consolidation (in a single transaction or a series of related transactions) of the Company with or into any other corporation or corporations or other entity, or
any other corporate reorganization, where the stockholders of the Company immediately prior to such event do not retain more than fifty percent (50%) of the voting power of and interest in the
successor entity (excluding any transactions if the primary purpose of the transaction is to obtain financing from new or existing investors). 




        3.    Method of Exercise.    While this Warrant remains outstanding and exercisable in accordance with
Section 1 above, the Holder may exercise, in whole or in part, the purchase rights evidenced hereby. Such exercise shall be effected by: 



        (i)    the
surrender of the Warrant, together with a notice of exercise to the Secretary of the Company at its principal offices; and 



        (ii)   the
payment to the Company of an amount equal to the aggregate Exercise Price for the number of Shares being purchased. 




        4.    Net Exercise.    In lieu of cash exercising this Warrant, the Holder of this Warrant may elect to receive shares
equal to the value of this Warrant (or the portion thereof being canceled) by surrender of this Warrant at the principal office of the Company together with notice of such election, in which 







 

event
the Company shall issue to the Holder hereof a number of Shares computed using the following formula: 



	X =	 	Y (A - B)
 A






        Where



        X
— The number of Shares to be issued to the Holder of this Warrant. 


        Y
— The number of Shares purchasable under this Warrant. 


        A
— The fair market value of one Share. 


        B
— The Exercise Price (as adjusted to the date of such calculations). 


        For
purposes of this Section 4, the fair market value of a Share shall mean the average of the closing bid and asked prices of Shares quoted in the
over-the-counter market in which the Shares are traded or the closing price quoted on any exchange on which the Shares are listed, whichever is applicable, as published in the
Western Edition of The Wall Street Journal for the ten (10) trading days prior to the date of determination of fair market value (or such shorter
period of time during which such stock was traded over-the-counter or on such exchange). If the Shares are not traded on the over-the-counter market or
on an exchange, the fair market value shall be the price per Share that the Company could obtain from a willing buyer for Shares sold by the Company from authorized but unissued Shares, as such prices
shall be determined in good faith by the Company's Board of Directors. 


        5.    Certificates for Shares.    Upon the exercise of the purchase rights evidenced by this Warrant, one or more
certificates for the number of Shares so purchased shall be issued as soon as practicable thereafter, and in any event within thirty (30) days of the delivery of the subscription notice. 



        6.    Issuance of Shares; Further Assurances.    The Company covenants that the Shares, when issued pursuant to the
exercise of this Warrant, will be duly and validly issued, fully paid and nonassessable and free from all taxes, liens, and charges with respect to the issuance thereof. In connection with the
exercise of this Warrant, the Holder (including any transferees, successors, and assigns), by acceptance of this Note, agrees to execute all agreements and other documents requested by the Company. 


        7.    Adjustment of Exercise Price and Number of Shares.    The number of and kind of securities purchasable upon
exercise of this Warrant and the Exercise Price shall be subject to adjustment from time to time as follows: 



        (a)    Subdivisions, Combinations and Other Issuances.    If the Company shall at any time prior to the expiration of
this Warrant subdivide the Shares, by split-up or otherwise, or combine its Shares, or issue additional shares of its Shares as a dividend, the number of Shares issuable on the exercise of
this Warrant shall forthwith be proportionately increased in the case of a subdivision or stock dividend, or proportionately decreased in the case of a combination. Appropriate adjustments shall also
be made to the purchase price payable per share, but the aggregate purchase price payable for the total number of Shares purchasable under this Warrant (as adjusted) shall remain the same. Any
adjustment under this Section 7(a) shall become effective at the close of business on the date the subdivision or combination becomes effective, or as of the record date of such dividend, or in
the event that no record date is fixed, upon the making of such dividend. 


        (b)    Reclassification, Reorganization and Consolidation.    In case of any reclassification, capital reorganization,
or change in the capital stock of the Company (other than as a result of a subdivision, combination, or stock dividend provided for in Section 7(a) above), then the Company shall make
appropriate provision so that the Holder of this Warrant shall have the right at any 



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time
prior to the expiration of this Warrant to purchase, at a total price equal to that payable upon the exercise of this Warrant, the kind and amount of shares of stock and other securities and
property receivable in connection with such reclassification, reorganization, or change by a Holder of the same number of Shares as were purchasable by the Holder of this Warrant immediately prior to
such reclassification, reorganization, or change. In any such case appropriate provisions shall be made with respect to the rights and interest of the Holder of this Warrant so that the provisions
hereof shall thereafter be applicable with respect to any shares of stock or other securities and property deliverable upon exercise hereof, and appropriate adjustments shall be made to the purchase
price per share payable hereunder, provided the aggregate purchase price shall remain the same. 


        (c)    Notice of Adjustment.    When any adjustment is required to be made in the number or kind of shares purchasable
upon exercise of the Warrant, or in the Exercise Price, the Company shall promptly notify the Holder of such event and of the number of Shares or other securities or property thereafter purchasable
upon exercise of this Warrant. 




        8.    No Fractional Shares or Scrip.    No fractional shares or scrip representing fractional shares shall be issued
upon the exercise of this Warrant, but in lieu of such fractional shares the Company shall make a cash payment therefor on the basis of the Exercise Price then in effect. 



        9.    Representations of the Company.    The Company represents that all corporate actions on the part of the Company
for the sale and issuance of this Warrant have been taken. 


        10.    Restrictive Legend.    The Shares (unless registered under the Act) shall be stamped or imprinted with a legend
in substantially the following form (in addition to any other applicable legends as set forth in agreements between the original Holder and the Company, including the Company's Amended and Restated
Investors' Rights Agreement dated April 29, 2005, the Company's Amended and Restated Co-Sale Agreement dated April 29, 2005, the Company's Amended and Restated Voting
Agreement dated April 29, 2005): 




THE
SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO, OR IN CONNECTION WITH, THE SALE OR DISTRIBUTION THEREOF, AND HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED. SUCH SHARES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER THE ACT AND ANY APPLICABLE STATE SECURITIES LAWS.
COPIES OF THE AGREEMENT COVERING THE PURCHASE OF THESE SHARES AND RESTRICTING THEIR TRANSFER MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER OF RECORD OF THIS CERTIFICATE TO THE
SECRETARY OF THE COMPANY AT THE PRINCIPAL EXECUTIVE OFFICES OF THE COMPANY. 





        11.    Rights of Stockholders.    No holder of this Warrant shall be entitled, as a Warrant holder, to vote or receive
dividends or be deemed the holder of the Shares or any other securities of the Company which may at any time be issuable on the exercise hereof for any purpose, nor shall anything contained herein be
construed to confer upon the Holder of this Warrant, as such, any of the rights of a stockholder of the Company or any right to vote for the election of directors or upon any matter submitted to
stockholders at any meeting thereof, or to give or withhold consent to any corporate action (whether upon any recapitalization, issuance of stock, reclassification of stock, change of par value,
consolidation, merger, conveyance, or otherwise) or to receive notice of meetings, or to receive dividends or subscription rights or otherwise until the Warrant shall have been exercised and the
Shares purchasable upon the exercise hereof shall have become deliverable, as provided herein. 


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        12.    Expiration of Warrant; Notice of Certain Events Terminating This Warrant.    



        (a)   This
Warrant shall expire and shall no longer be exercisable upon the earliest to occur of: 



        (i)    5:00 p.m.,
California local time, on the fifth anniversary of the issue date set forth on the first page herein; 



        (ii)   Any
Change of Control; or 


        (iii)  The
initial public offering of the Company's Common Stock. 




        (b)   The
Company shall provide at least ten (10) days prior written notice of any event set forth in Section 12(a)(ii) or (iii). 




        13.    Notices.    All notices and other communications required or permitted hereunder shall be in writing, shall be
effective when given, and shall in any event be deemed to be given upon receipt or, if earlier, (a) five (5) days after deposit with the U.S. Postal Service or other applicable postal
service, if delivered by first class mail, postage prepaid, (b) upon delivery, if delivered by hand, (c) one business day after the business day of deposit with Federal Express or
similar overnight courier, freight prepaid or (d) one business day after the business day of facsimile transmission, if delivered by facsimile transmission with copy by first class mail,
postage prepaid, and shall be addressed (i) if to the Holder, at the Holder's address as set forth on the Schedule of Investors to the Purchase Agreement, and (ii) if to the Company, at
the address of its principal corporate offices (attention: President), or at such other
address as a party may designate by ten days advance written notice to the other party pursuant to the provisions above. 


        14.    "Market Stand-Off" Agreement.    The Holder agrees, so long as such Holder owns outstanding voting
equity securities of the Company, in connection with the Company's initial public offering of the Company's securities, upon request of the Company or the underwriters managing any underwritten
offering of the Company's securities, not to sell, make any short sale of, loan, grant any option for the purchase of, or otherwise dispose of any shares of the Company (other than those included in
the registration) without the prior written consent of the Company or such underwriters, as the case may be, for such period of time (not to exceed one hundred eighty (180) days) from the
effective date of such registration as may be requested by the underwriters; provided, that the officers, directors and holders of 1% or more of the
outstanding securities of the Company also agree to such restrictions. 


        15.    Governing Law.    This Warrant and all actions arising out of or in connection with this Agreement shall be
governed by and construed in accordance with the laws of the State of California, without regard to the conflicts of law provisions of the State of California or of any other state. 



        16.    Rights and Obligations Survive Exercise of Warrant.    Unless otherwise provided herein, the rights and
obligations of the Company, of the Holder of this Warrant and of the holder of the Shares issued upon exercise of this Warrant, shall survive the exercise of this Warrant. 


[Remainder
of page intentionally left blank.] 


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        This Warrant to Purchase Series D Preferred Stock is issued as of the date first set forth above. 



	 	 	OPTIMER PHARMACEUTICALS, INC.
	

 	
 	

By:	
 	

 
	 	 	 	 	

	 	 	 	 	Michael N. Chang, Chief Executive Officer





OPTIMER PHARMACEUTICALS, INC.

SIGNATURE PAGE TO WARRANT TO PURCHASE SERIES D PREFERRED STOCK 







EXHIBIT A  


 NOTICE OF EXERCISE  


	TO:
	Optimer
Pharmaceuticals, Inc.

Attention: President 



        1.     The
undersigned hereby elects to purchase                        Shares of Series D Preferred Stock of Optimer Pharmaceuticals,
 Inc. pursuant to the terms of the
attached Warrant. 


        2.     Method
of Exercise (Please initial the applicable blank): 



	              	 	The undersigned elects to exercise the attached Warrant by means of a cash payment, and tenders herewith payment in full for the purchase price of the shares being purchased, together with all applicable transfer taxes,
if any.
	

              	
 	

The undersigned elects to exercise the attached Warrant by means of the net exercise provisions of Section 4 of the Warrant.





        3.     Please
issue a certificate or certificates representing said Shares in the name of the undersigned or in such other name as is specified below: 


                                        
                                          
              

(Name) 


                                        
                                          
              



                                        
                                          
              


(Address) 


        4.     The
undersigned hereby represents and warrants that the aforesaid Shares are being acquired for the account of the undersigned for investment and not with a view to, or
for resale, in connection with the distribution thereof, and that the undersigned has no present intention of distributing or reselling such shares. 



	 	 	

	 	 	(Signature)
	

 	
 	

 
	 	 	

	 	 	(Name)
	

 	
 	

 
	
	 	

	(Date)	 	(Title)













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Exhibit 4.5