Exhibit 10.15  Garen Bohlin Name of Employee  SIRTRIS PHARMACEUTICALS, INC. Amended and Restated 2004 Incentive
Plan  Restricted Stock Award Agreement  Sirtris Pharmaceuticals, Inc. 200 Technology Square Cambridge, MA 02139  Ladies and Gentlemen:  The undersigned (i) acknowledges
that he has received an award (the Award) of restricted stock from Sirtris
Pharmaceuticals, Inc. (the Company) under the Amended and Restated 2004
Incentive Plan (the Plan), subject to the terms set forth below and in the Plan;
(ii) further acknowledges receipt of a copy of the Plan as in effect on
the date hereof; and (iii) agrees with the Company as follows:  1.             Effective Date.  This Agreement
shall take effect as of January 2, 2008, which is the date of grant of the
Award.  2.             Shares Subject to Award.  The
Award consists of 55,000 shares (the Shares) of common stock of the Company (Stock). 
The undersigneds rights to the Shares are subject to the restrictions
described in this Agreement and the Plan (which is incorporated herein by
reference with the same effect as if set forth herein in full) in addition to
such other restrictions, if any, as may be imposed by law.  3.             Meaning of Certain Terms.  Except
as otherwise expressly provided, all terms used herein shall have the same
meaning as in the Plan.  The term vest as used herein with respect to
any Share means the lapsing of the restrictions described herein with respect
to such Share.  4.             Nontransferability of Shares. 
The Shares acquired by the undersigned pursuant to this Agreement shall not be
sold, transferred, pledged, assigned or otherwise encumbered or disposed of
except as provided below and in the Plan.  5.             Accelerated Vesting of Unvested Shares Upon
Termination Without Cause or for Good Reason.  If the undersigned
is terminated by the Company without Cause (as defined below), the undersigned
terminates his employment for Good Reason (as defined below) or the undersigneds
employment terminates as a result of the undersigneds death or disability, to
the extent there are any unvested Shares, 
all of the unvested Shares shall vest with respect to an additional one
year of vesting (provided that a minimum of 25% of such unvested Shares shall
vest).  For the purposes of this
Agreement, the term Cause shall mean: (i) the undersigneds willful
failure to perform, or gross negligence in the performance of, his material
duties and responsibilities to the Company and its affiliates which is not
remedied within thirty (30) days of written notice thereof; (ii) material
breach by the undersigned of any material provision of this Agreement or any
other agreement with the Company or any of its affiliates which is not remedied
within thirty (30) days of written notice thereof; (iii) fraud,
embezzlement or other dishonesty with respect to the Company and any of its
affiliates, taken as a whole, which, in the case of such other dishonesty,
causes or could reasonably be expected to cause material


harm to the Company and any
of its affiliates, taken as a whole; or (iv) the undersigneds conviction
of a felony.  For the purposes of this
Agreement, the term Good Reason shall mean, without the undersigneds
consent, theoccurrenceof any one or
more of the following events: (i) material diminution in the nature or
scope of the undersigneds responsibilities, duties or authority, provided that
in the absence of a Change of Control neither of the following shall constitute
Good Reason:(x) the Companys failure to continue the undersigneds
appointment or election as a director or officer of any of its affiliates nor (y) any
diminution in the nature or scope of the undersigneds responsibilities, duties
or authority that is reasonably related to a diminution of the business of the
Company or any of its affiliates; (ii) a reduction in the undersigneds
base salary other than one temporary reduction of not more than 120 days and
not in excess of 20% of the undersigneds base salary in connection with and in
proportion to a general reduction of the base salaries of the Companys executive
officers; (iii) failure of the Company to provide the undersigned the
salary or benefits in accordance with the Employment Agreement dated January 3,
2008 by and between the Company and the undersigned after thirty (30) days
notice during which the Company does not cure such failure; or (iv) relocation
of the undersigneds office more than thirty-five (35) miles from the location
of the Companys principal offices as January 1, 2008.  6.             Accelerated Vesting of Unvested Shares After a Change
of Control.  If a Change of Control (as defined
below) occurs before the undersigneds employment terminates, then 25% of the
unvested Shares will immediately become vested. 
If, within one year following a Change of Control or otherwise in
connection with a Change of Control, the Company or any successor thereto
terminates the undersigneds employment other than for Cause or the undersigned
terminates his employment for Good Reason, then all of the unvested Shares that
vest based only on the passage of time will immediately become vested.  For the purposes of this Agreement, the term Change
of Control shall mean: (i) the acquisition of beneficial ownership (as
defined in Rule 13d-3 under the Exchange Act) directly or indirectly by
any person (as such term is used in Sections 13(d) and 14(d) of the
Exchange Act), of securities of the Company representing a majority or more of
the combined voting power of the Companys then outstanding securities, other
than an acquisition of securities for investment purposes pursuant to a bona
fide financing of the Company; (ii) a merger or consolidation of the
Company with any other corporation in which the holders of the voting
securities of the Company prior to the merger or consolidation do not own more
than 50% of the total voting securities of the surviving corporation; or (iii) the
sale or disposition by the Company of all or substantially all of the Companys
assets other than a sale or disposition of assets to an affiliate of the
Company or a holder of securities of the Company.  7.             Forfeiture Risk.  If the
undersigned ceases to be employed by the Company and its subsidiaries for any
reason other than as specified in Section 5 or 6 above, any then
outstanding and unvested Shares acquired by the undersigned hereunder shall be
automatically and immediately forfeited.  With respect to any Shares that
are forfeited under this Section 7 or Section 5 above, the
undersigned hereby (i) appoints the Company as the attorney-in-fact of the
undersigned to take such actions as may be necessary or appropriate to
effectuate a transfer of the record ownership of any such shares that are
unvested and forfeited hereunder, (ii) agrees to deliver to the Company,
as a precondition to the issuance of any certificate or certificates with
respect to unvested Shares hereunder, one or more stock powers, endorsed in
blank, with respect to such Shares, and (iii) agrees to sign such other
powers and take such other actions as the Company may reasonably request to
accomplish the transfer or forfeiture of any unvested Shares that are forfeited
hereunder.  8.             Retention of Certificates.  Any
certificates representing unvested Shares shall be held by the Company. 
If unvested Shares are held in book entry form, the undersigned agrees that the
Company may give stop transfer instructions to the depository to ensure
compliance with the provisions hereof.   2


9.             Vesting of Shares.  The shares
acquired hereunder shall vest in accordance with the provisions of this Section 9
and applicable provisions of the Plan, as follows: 20% of the Shares on January 1,
2010, an additional 30% of the Shares on January 1, 2011, and an
additional 50% of the Shares on January 1, 2012, provided that, the
portion of the Shares that would otherwise vest on January 1, 2012 (the Final
Tranche) will vest as follows, if earlier than January 1, 2012:  (a) one-half of the Final Tranche (25%
of the total number of Shares) shall vest upon completion of a Board approved
corporate partnership for a SIRT1 activator that the Board determines to be significant
for this purpose and (b) one-half of the Final Tranche (25% of the total
number of the Shares) shall vest upon positive clinical efficacy data for a
Sirtris NCE SIRT1 activator as demonstrated by safely meeting the primary
efficacy endpoint of a Sirtris-sponsored Phase 2a or 2b clinical trial in Type
2 diabetes, obesity or a metabolic syndrome.  Notwithstanding the foregoing, no shares shall vest on
any vesting date specified above unless the undersigned is then, and since the
date of grant has continuously been, employed by the Company or its
subsidiaries.  10.           Legends.  Any certificates
representing unvested Shares shall be held by the Company, and any such
certificate shall contain legend substantially in the following form:  THE TRANSFERABILITY OF THIS CERTIFICATE AND THE SHARES
OF STOCK REPRESENTED HEREBY ARE SUBJECT TO THE TERMS AND CONDITIONS (INCLUDING
FORFEITURE) OF THE AMENDED AND RESTATED 2004 INCENTIVE PLAN AND A RESTRICTED
STOCK AWARD AGREEMENT ENTERED INTO BETWEEN THE REGISTERED OWNER AND SIRTRIS
PHARMACEUTICALS, INC.  COPIES OF SUCH PLAN AND AGREEMENT ARE ON FILE IN
THE OFFICES OF SIRTRIS PHARMACEUTICALS, INC.  As soon as practicable following the vesting of any
such Shares the Company shall cause a certificate or certificates covering such
vested Shares to be issued and delivered to the undersigned without the first
legend set forth above referencing the Restricted Stock Award Agreement. 
If any Shares are held in book-entry form, the Company may take such steps as
it deems necessary or appropriate to record and manifest the restrictions
applicable to such Shares.  11.           Dividends, etc..  The undersigned
shall be entitled to (i) receive any and all dividends or other
distributions paid with respect to those Shares of which he is the record owner
on the record date for such dividend or other distribution, and (ii) vote
any Shares of which he is the record owner on the record date for such vote; provided, however, that any property (other
than cash) distributed with respect to a share of Stock (the associated share)
acquired hereunder, including without limitation a distribution of Stock by
reason of a stock dividend, stock split or otherwise, or a distribution of
other securities with respect to an associated share, shall be subject to the
restrictions of this Agreement in the same manner and for so long as the
associated share remains subject to such restrictions, and shall be promptly
forfeited if and when the associated share is so forfeited; and further provided, that the
Administrator may require that any cash distribution with respect to the Shares
other than a normal cash dividend be placed in escrow or otherwise made subject
to such restrictions as the Administrator deems appropriate to carry out the
intent of the Plan.  References in this Agreement to the Shares
shall  refer, mutatis mutandis,
to any such restricted amounts.  12.           Sale of Vested Shares.The
undersigned understands that he will be free to sell any Share once it has
vested, subject to (i) satisfaction of any applicable tax withholding
requirements with respect to the vesting or transfer of such Share; (ii) the
completion of any administrative steps (for example, but without limitation,
the transfer of certificates) that the Company may reasonably impose; and (iii) applicable
requirements of federal and state securities laws.   3


13.           Certain Tax Matters.  The
undersigned expressly acknowledges the following:  a.The
undersigned has been advised to confer promptly with a professional tax advisor
to consider whether the undersigned should make a so-called 83(b) election
with respect to the Shares.  Any such election, to be effective, must be
made in accordance with applicable regulations and within thirty (30) days
following the date of this Award.  The Company has made no recommendation
to the undersigned with respect to the advisability of making such an election.  b.The award
or vesting of the Shares acquired hereunder, and the payment of dividends with
respect to such Shares, may give rise to wages subject to withholding. 
The undersigned expressly acknowledges and agrees that his rights hereunder are
subject to his promptly paying to the Company in cash (or by such other means
as may be acceptable to the Company in its discretion, including, if the
Administrator so determines, by the delivery of previously acquired Stock or
shares of Stock acquired hereunder or by the withholding of amounts from any
payment hereunder) all taxes required to be withheld in connection with such
award, vesting or payment.  Very truly yours,/s/ Garen Bohlin(Signature of Employee)  Dated: January 2, 2008  The foregoing Restricted
Stock
Award Agreement is hereby accepted:  SIRTRIS
PHARMACEUTICALS, INC.   By
  /s/ Christoph Westphal   4