WARRANT TO PURCHASE STOCK

Exhibit 10.10

THIS WARRANT AND THE SHARES ISSUABLE HEREUNDER HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAWS, AND MAY NOT BE SOLD, PLEDGED, OR OTHERWISE TRANSFERRED WITHOUT AN EFFECTIVE REGISTRATION THEREOF UNDER SUCH ACT AND LAWS OR, SUBJECT TO SECTION 5.3 HEREOF, AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE CORPORATION AND ITS COUNSEL, THAT SUCH REGISTRATION IS NOT REQUIRED.

WARRANT TO PURCHASE STOCK

Issuer: Sirtris Pharmaceuticals, Inc., a Delaware corporation
Number of Shares: As set forth below
Class of Stock: Series B Convertible Preferred Stock, $0.001 par value per share
Exercise Price: $0.80 per share, subject to adjustment
Issue Date: June 23, 2006
Expiration Date: June 23, 2016

        FOR THE AGREED UPON VALUE of $1.00, and for other good and valuable consideration, the receipt and sufficiency of which are hereby acknowledged, this Warrant is issued to SILICON VALLEY BANK (together with its successors and permitted assigns, "Holder") by Sirtris Pharmaceuticals, Inc., a Delaware corporation (the "Company").

        Subject to the terms and conditions hereinafter set forth, the Holder is entitled upon surrender of this Warrant and a duly executed Notice of Exercise in substantially the form attached hereto as Appendix 1 (the "Notice of Exercise"), at the principal office of the Company, 790 Memorial Drive, Suite 104, Cambridge, Massachusetts 02139 or such other office as the Company shall notify the Holder of in writing, to purchase from the Company up to the amount fully paid and non-assessable shares of the Company's Series B Convertible Preferred Stock, $0.001 par value per share (the "Class") set forth below, at a purchase price per Share of Eighty Cents ($0.80) (the "Exercise Price"). Subject to adjustment as set forth herein, this Warrant shall be exercisable for such number of shares of the Class (the "Shares") as shall equal (a) (i) one and one-third percent (1.33%) multiplied by (ii) the aggregate principal amount of all Equipment Advances (as defined in that certain Loan and Security Agreement of even date herewith among the Company and Silicon Valley Bank (the "Loan Agreement")), made to the Company pursuant to the Loan Agreement, divided by (b) the Exercise Price. This Warrant may be exercised in whole or in part at any time and from time to time until 5:00 PM, Eastern time, on the Expiration Date set forth above, and shall be void thereafter. Until such time as this Warrant is exercised in full or expires, the Exercise Price and the number of Shares are subject to adjustment from time to time as hereinafter provided.

        Notwithstanding the foregoing definition of Class, upon and after the automatic or voluntary conversion, redemption or retirement of all (but not less than all) of the outstanding shares of such Class, including without limitation the Company's initial registered underwritten public offering and sale of its securities ("IPO"), then from and after the date upon which all such outstanding shares have been so converted, redeemed or retired, "Class" shall mean the Company's common stock, $0.001 par value per share ("Common Stock"), and this Warrant shall be exercisable for such number of shares of Common Stock as shall equal the number of shares of Common Stock into which the Shares would have been converted pursuant to the Company's Certificate of Incorporation, as amended, including without limitation the Certificate of Designation, if any, applicable to the same class or series of preferred stock as the Shares (the "Certificate") had the Shares been issued and outstanding immediately prior to such conversion, redemption or retirement, and the Exercise Price shall be the Common Stock conversion price as determined pursuant to the Certificate immediately prior to such conversion, redemption or retirement (all subject to further adjustment as provided herein).

ARTICLE 1.     EXERCISE .

        1.1     Method of Exercise .    Holder may exercise this Warrant by delivering this Warrant together with a duly executed Notice of Exercise to the principal office of the Company. Unless Holder is exercising the conversion right set forth in Section 1.2, Holder shall also deliver to the Company a check for the aggregate Exercise Price for the Shares being purchased.

        1.2     Conversion Right .    In lieu of exercising this Warrant as specified in Section 1.1, Holder may from time to time convert this Warrant, in whole or in part, into a number of Shares determined as follows:

•         where:

        1.3     Fair Market Value .    

•         1.3.1     If shares of the Class (or shares of the Company's stock into which shares of the Class are convertible or exchangeable) are traded on a nationally recognized securities exchange or over the counter market, the fair market value of a Share shall be the closing price of a share of the Class (or the closing price of a share of the Company's stock for which shares of the Class are convertible or exchangeable, multiplied by the number of shares of such stock into which one share of the Class is convertible or exchangeable) reported for the business day immediately preceding the date of Holder's Notice of Exercise to the Company.

          1.3.2     If shares of the Class (or shares of the Company's stock into which shares of the Class are convertible or exchangeable) are not traded on a nationally recognized securities exchange or over the counter market, the Board of Directors of the Company shall determine fair market value in its reasonable good faith judgment.

        1.4     Delivery of Certificate and New Warrant .    Promptly after Holder exercises or converts this Warrant, the Company at its sole expense shall promptly deliver to Holder (i) certificates for the Shares acquired upon such exercise, and (ii) if this Warrant has not been fully exercised or converted and has not expired, a new warrant of like tenor representing the Shares for which this Warrant is still exercisable.

        1.5     Replacement of Warrants .    On receipt of evidence reasonably satisfactory to the Company of the loss, theft, destruction or mutilation of this Warrant and, in the case of loss, theft or destruction, on delivery of an indemnity agreement reasonably satisfactory in form and amount to the Company or, in the case of mutilation, on surrender and cancellation of this Warrant, the Company at its expense shall execute and deliver, in lieu of this Warrant, a new warrant of like tenor.

        1.6     Assumption on Sale, Merger, or Consolidation of the Company .    

•         1.6.1.     "Acquisition" .    For the purpose of this Warrant, "Acquisition" means any sale, assignment, transfer, exclusive license, or other disposition of all or substantially all of the assets of the Company, or any acquisition, reorganization, consolidation, or merger of the Company where the holders of the Company's outstanding voting equity securities immediately prior to the transaction beneficially own less than a majority of the outstanding voting equity securities of the surviving or successor entity immediately following the transaction.

2

•         1.6.2.     Assumption of Warrant .    Upon the closing of any Acquisition (other than an Acquisition in which the consideration received by the Company's stockholders consists solely of cash and/or cash equivalents), and as a condition precedent thereto, the successor or surviving entity shall assume the obligations of this Warrant, and this Warrant shall be exercisable for the same securities and property as would be payable for the Shares issuable upon exercise of the unexercised portion of this Warrant as if such Shares were outstanding on the record date for the Acquisition and subsequent closing. The Exercise Price shall be adjusted accordingly, and the Exercise Price and number and class of Shares shall continue to be subject to adjustment from time to time in accordance with the provisions hereof. Upon the closing of any Acquisition in which the consideration received by the Company's stockholders consists solely of cash and/or cash equivalents, then, to the extent not exercised or converted on or before the closing of such Acquisition, this Warrant shall terminate and be of no further force or effect.

ARTICLE 2.     ADJUSTMENTS TO THE SHARES .

        2.1     Stock Dividends, Splits, Etc .    If the Company declares or pays a dividend on the outstanding shares of the Class, payable in shares of the Class, Common Stock or other securities, or subdivides the outstanding shares of the Class into a greater number of shares of the Class, or subdivides the shares of the Class in a transaction that increases the amount of Common Stock into which such shares are convertible, then upon exercise of this Warrant, for each Share acquired, Holder shall receive, without additional cost to Holder, the total number and kind of securities to which Holder would have been entitled had Holder owned the Shares of record as of the date the dividend or subdivision occurred.

        2.2     Reclassification, Exchange or Substitution .    Upon any reclassification, exchange, substitution, reorganization or other event that results in a change of the number and/or class of the securities issuable upon exercise or conversion of this Warrant, Holder shall be entitled to receive, upon exercise or conversion of this Warrant, the number and kind of securities and property that Holder would have received for the Shares if this Warrant had been exercised immediately before such reclassification, exchange, substitution, reorganization or other event. The Company or its successor shall promptly issue to Holder a new warrant of like tenor for such new securities or other property. The new warrant shall provide for adjustments which shall be as nearly equivalent as may be practicable to the adjustments provided for in this Article 2 including, without limitation, adjustments to the Exercise Price and to the number of securities or property issuable upon exercise of the new warrant. The provisions of this Section 2.2 shall similarly apply to successive reclassifications, exchanges, substitutions, reorganizations or other events.

        2.3     Adjustments for Combinations, Etc .    If the outstanding shares of the Class are combined or consolidated, by reclassification or otherwise, into a lesser number of shares, the Exercise Price shall be proportionately increased and the number of Shares issuable upo