METABASIS THERAPEUTICS, INC. WARRANT TO PURCHASE COMMON STOCK

Exhibit 4.4

THIS WARRANT AND THE UNDERLYING SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE “ACT”).  THEY MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT AS TO SUCH SECURITIES UNDER THE ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

METABASIS THERAPEUTICS, INC.

WARRANT TO PURCHASE COMMON STOCK

April 16, 2008

VOID AFTER APRIL 16, 2013

THIS CERTIFIES THAT , for value received, [                      ], or assigns (the “Holder” ), is entitled to subscribe for and purchase at the Exercise Price (defined below) from Metabasis Therapeutics, Inc., a Delaware corporation, with its principal office at 11119 Torrey Pines Road, La Jolla, California 92037 (the “Company” ) up to [                      ] shares of the common stock of the Company, par value $0.001 per share (the “Common Stock” ).

1.              DEFINITIONS.  As used herein, the following terms shall have the following respective meanings:

(a)           “Exercise Period” shall mean the period commencing with the date that is 180 days after the date hereof and ending five years from the date hereof, unless sooner terminated as provided below.

(b)           “Exercise Price” shall mean $2.69 per share, subject to adjustment pursuant to Section 5 below.

(c)           “Exercise Shares” shall mean the shares of Common Stock issuable upon exercise of this Warrant.

2.              EXERCISE OF WARRANT.  The rights represented by this Warrant may be exercised in whole or in part at any time during the Exercise Period, by delivery of the following to the Company at its address set forth above (or at such other address as it may designate by notice in writing to the Holder):

(a)            An executed Notice of Exercise in the form attached hereto;

(b)            Payment of the Exercise Price either (i) in cash or by check, (ii) by cancellation of indebtedness, or (iii) pursuant to Section 2.1 below; and

(c)            This Warrant.

Certificates for shares purchased hereunder shall be transmitted by the transfer agent of the Company to the Holder by crediting the account of the Holder’s prime broker with the Depository Trust Company through its Deposit Withdrawal Agent Commission system if the Company is a participant in such system, and otherwise by physical delivery to the address

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specified by the Holder in the Notice of Exercise within five business days from the delivery to the Company of the Notice of Exercise, surrender of this Warrant and payment of the aggregate Exercise Price as set forth above.  This Warrant shall be deemed to have been exercised on the date the Exercise Price is received by the Company.  The Exercise Shares shall be deemed to have been issued, and Holder or any other person so designated to be named therein shall be deemed to have become a holder of record of such shares for all purposes, as of the date the Warrant has been exercised by payment to the Company of the Exercise Price.

The person in whose name any certificate or certificates for Exercise Shares are to be issued upon exercise of this Warrant shall be deemed to have become the holder of record of such shares on the date on which this Warrant was surrendered and payment of the Exercise Price was made, irrespective of the date of delivery of such certificate or certificates, except that, if the date of such surrender and payment is a date when the stock transfer books of the Company are closed, such person shall be deemed to have become the holder of such shares at the close of business on the next succeeding date on which the stock transfer books are open.

2.1          Net Exercise .  Notwithstanding any provisions herein to the contrary, if during the Exercise Period the fair market value of one share of the Common Stock is greater than the Exercise Price (at the date of calculation as set forth below), in lieu of exercising this Warrant by payment of cash or by check, or by cancellation of indebtedness, the Holder may elect to receive shares equal to the value (as determined below) of this Warrant (or the portion thereof being canceled) by surrender of this Warrant at the principal office of the Company together with the properly endorsed Notice of Exercise in which event the Company shall issue to the Holder a number of shares of Common Stock computed using the following formula:

X = Y (A-B)

A

For purposes of the above calculation, the “fair market value” of one share of Common Stock shall mean (i) the average of the closing sales prices for the shares of Common Stock on the NASDAQ Global Market or other trading market where such security is listed or traded as reported by Bloomberg Financial Markets (or a comparable reporting service of national reputation selected by the Company and reasonably acceptable to the Holder if Bloomberg Financial Markets is not then reporting sales prices of such security) (collectively, “ Bloomberg ”) for the 10 consecutive trading days immediately preceding such date, or (ii) if the NASDAQ Global Market is not the principal trading market for the shares of Common Stock, the average of the reported sales prices reported by Bloomberg on the principal trading market for the

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Common Stock during the same period, or, if there is no sales price for such period, the last sales price reported by Bloomberg for such period, or (iii) if neither of the foregoing applies, the last sales price of such security in the over-the-counter market on the pink sheets or bulletin board for such security as reported by Bloomberg, or if no sales price is so reported for such security, the last bid price of such security as reported by Bloomberg or (iv) if fair market value cannot be calculated as of such date on any of the foregoing bases, the fair market value shall be as determined by the Board of Directors of the Company in the exercise of its good faith judgment.

2.2           Issuance of New Warrants.   Upon any partial exercise of this Warrant, the Company, at its expense, will forthwith and, in any event within five business days, issue and deliver to the Holder a new warrant or warrants of like tenor, registered in the name of the Holder, exercisable, in the aggregate, for the balance of the number of shares of Common Stock remaining available for purchase under the Warrant.

2.3           Payment of Taxes and Expenses .  The Company shall pay any recording, filing, stamp or similar tax which may be payable in respect of any transfer involved in the issuance of, and the preparation and delivery of certificates (if applicable) representing, (i) any Exercise Shares purchased upon exercise of this Warrant and/or (ii) new or replacement warrants in the Holder’s name or the name of any transferee of all or any portion of this Warrant.

3.                COVENANTS OF THE COMPANY.

3.1          Covenants as to Exercise Shares.   The Company covenants and agrees that all Exercise Shares that may be issued upon the exercise of the rights represented by this Warrant will, upon issuance, be validly issued and outstanding, fully paid and nonassessable, and free from all taxes, liens and charges with respect to the issuance thereof.  The Company further covenants and agrees that the Company will at all times during the Exercise Period, have authorized and reserved, free from preemptive rights, a sufficient number of shares of Common Stock to provide for the exercise of the rights represented by this Warrant.  If at any time during the Exercise Period the number of authorized but unissued shares of Common Stock shall not be sufficient to permit exercise of this Warrant, the Company will take such corporate action as may, in the opinion of its counsel, be necessary to increase its authorized but unissued shares of Common Stock to such number of shares as shall be sufficient for such purposes.

3.2          No Impairment .  Except and to the extent as waived or consented to by the Holder, the Company will not, by amendment of its Certificate of Incorporation or through any reorganization, transfer of assets, consolidation, merger, dissolution, issue or sale of securities or any other voluntary action, avoid or seek to avoid the observance or performance of any of the terms to be observed or performed hereunder by the Company, but will at all times in good faith assist in the carrying out of all the provisions of this Warrant and in the taking of all such action as may be necessary or appropriate in order to protect the exercise rights of the Holder against impairment.

3.3          Notices of Record Date and Certain Other Events.   In the event of any taking by the Company of a record of the holders of any class of securities for the purpose of determining the holders thereof who are entitled to receive any dividend (other than a cash dividend which is the same as cash dividends paid in previous quarters) or other distribution, the

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Company shall mail to the Holder, at least 20 days prior to the date on which any such record is to be taken for the purpose of such dividend or distribution, a notice specifying such date.  In the event of any voluntary dissolution, liquidation or winding up of the Company, the Company shall mail to the Holder, at least 20 days prior to the date of the occurrence of any such event, a notice specifying such date.

4.                REPRESENTATIONS OF HOLDER.

4.1          Acquisition of Warrant for Personal Account.   The Holder represents and warrants that it is acquiring the Warrant solely for its account for investment and not with a view to or for sale or distribution of said Warrant or any part thereof.  The Holder also represents that the entire legal and beneficial interests of the Warrant and Exercise Shares the Holder is acquiring is being acquired for, and will be held for, its account only.

4.2             Securities Are Not Registered.

(a)            The Holder understands that the Warrant and the Exercise Shares have not been registered under the Securities Act of 1933, as amended (the “Act” ) on the basis that no distribution or public offering of the stock of the Company is to be effected.  The Holder realizes that the basis for the exemption may not be present if, notwithstanding its representations, the Holder has a present intention of acquiring the securities for a fixed or determinable period in the future, selling (in connection with a distribution or otherwise), granting any participation in, or otherwise distributing the securities.  The Holder has no such present intention.

(b)        &