Exhibit
10.13  AMENDED AND
RESTATED EMPLOYMENT AGREEMENT  THIS AMENDED AND
RESTATED EMPLOYMENT AGREEMENT dated as of January 3, 2008 (the Agreement)
is by and between Sirtris Pharmaceuticals, Inc. (the Company), a Delaware
corporation with its principal place of business at 200 Technology Square,
Cambridge, Massachusetts, and Michael Jirousek (the Executive).  WHEREAS, the
Company and the Executive are parties to a certain Employment Agreement dated August 30,
2006 (the Previous Agreement) pursuant to which the Executive has been
serving the Company as its Senior Vice President, Research; and  WHEREAS, the
Company and the Executive desire to make certain changes to the terms and
conditions of the Executives employment;  NOW, THEREFORE, in
consideration of the mutual covenants and promises contained herein and other
good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the Company offers and the Executive accepts employment
upon the following amended and restated terms and conditions:  1.Position and Duties.  (a)           The Company.
Upon the terms and subject to the conditions set forth in this Agreement, the
Company hereby offers and the Executive hereby accepts employment with the
Company to serve as its Senior Vice President, Research, reporting to the Chief
Executive Officer of the Company.  The
Executive shall be employed for an undefined term, commencing on the effective
date thereof, and on an at-will basis. The Executives rights upon the
termination of employment shall be governed by the terms of Sections 4 and 5
hereof. The period of this agreement is hereafter referred to as the term of
this Agreement or the term hereof. During the term hereof, the Executive
shall be employed by the Company on a full-time basis and shall perform the
duties and responsibilities of his position and such other duties and
responsibilities on behalf of the Company and its Affiliates, reasonably
related to that position, as may be designated from time to time by the Board
of Directors of the Company (the Board) or by its Chair or other designee.
During the term hereof, the Executive shall devote his full business time and
his best efforts, business judgment, skill and knowledge exclusively to the
advancement of the business and interests of the Company and its Affiliates and
to the discharge of his duties and responsibilities hereunder.  The Executive shall not engage in any other
business activity or serve in any industry, trade, professional, governmental
or academic position during the term of this Agreement, except as may be
expressly approved in advance by the Chief Executive Officer in writing.  2.              Compensation
and Benefits.  During the
Executives employment, as compensation for all services performed by the
Executive for the Company and subject to his


performance of his duties
and responsibilities for the Company, pursuant to this Agreement or otherwise,
the Company will provide the following pay and benefits:  (a)           Base Salary.   From the period of the date hereof until December 31,
2008, the Company will pay the Executive a base salary at the rate of Two
Hundred Ninety Thousand Dollars ($290,000) per year.  Such amount shall be payable in accordance
with the ordinary payroll practices of the Company for its executives, as in
effect from time to time, and subject to adjustment from time to time by the
Board in its discretion.  (b)Bonus Compensation.  The Executive shall be considered annually by
the Board for a bonus with a target of 35% of the Base Salary earned, which
percentage shall be subject to adjustment from time to time by the Board in its
discretion.  The amount of the bonus
shall be determined by the Board, based on its assessment, in its discretion,
of the Executives performance and that of the Company against appropriate
goals established annually by the Company after consultation with the
Executive.  Any bonus or incentive
compensation paid to the Executive shall be in addition to the Base Salary.Any bonus due
to the Executive hereunder will be payable not later than two and one-half
months following the close of the Companys fiscal year or the close of the
calendar year, if later, in which occurs the later of the two following
dates:  (i) the date on which the
Executive first has a legally binding right (whether or not vested) to the
bonus; and (ii) if the Executives right to the bonus is subject to one or
more vesting conditions, the first date on which the Executives right to the
bonus is no longer subject to any substantial risk of forfeiture.  The foregoing rules shall be construed
and applied to ensure that any bonus payable to the Executive qualifies as a short-term
deferral under Section 409A of the Internal Revenue Code, as amended
(including the regulations thereunder, Section 409A).  Without limiting the generality of the
foregoing, for purposes of these rules the terms legally binding right
and substantial risk of forfeiture shall have the meaning assigned to them
under Treas. Regs. § 1.409A-1(b)(1) and § 1.409A-1(d),
respectively.  (c)           Stock Options.
The Company previously granted to the Executive on the date the Executive
commenced employment with the Company pursuant to the Previous Agreement, an
option to purchase 900,000 shares of the common stock of the Company at $0.21
per share (the Option).  The Option
shall continue to vest on the schedule set forth in the Previous Agreement,
restated here as follows:  twenty-five
percent (25%) of the shares subject to the Option vested on August 30, 2007
and the remaining seventy-five percent (75%) of the shares subject to the
Option shall vest at the rate of 6.25% per quarter on the hire anniversary date
of each of the next twelve (12) quarters after August 30, 2007, provided
that the Executive is still employed by the Company on such dates.  The Option and all other options and
restricted stock granted to the Executive by the Company shall be subject to
any applicable stock option plan, stock certificate and shareholder and/or option
holder and restricted stock agreements and other restrictions and limitations
generally applicable to equity held by Company executives or otherwise required
by law.  The Executive shall not be
eligible to receive any stock options, restricted stock or other equity of the Company,
however, whether under an equity incentive plan or otherwise, except as
expressly provided in this Agreement or as otherwise expressly authorized for
him individually by the Board. Further, prior to issuing the Option or any
other stock options to the Executive, the Company may require that the  2


Executive provide
such representations regarding the Executives sophistication and investment
intent and other such matters as the Company may reasonably request.  (d)           Participation in Employee
Benefit Plans.  The Executive
will be entitled to participate in all Employee Benefit Plans from time to time
in effect for employees of the Company generally, except to the extent such
plans are duplicative of benefits otherwise provided the Executive under this
Agreement (e.g., severance pay) or under any other
agreement.  The Executive participation
will be subject to the terms of the applicable plan documents and generally
applicable Company policies.  The Company
may alter, modify, add to or delete its Employee Benefit Plans at any time as
it, in its sole judgment, determines to be appropriate, without recourse by the
Executive. For purposes of this Agreement, Employee Benefit Plan shall have
the meaning ascribed to such term in Section 3(3) of ERISA, as
amended from time to time.  (e)           Vacations.  During the term hereof, the Executive shall
be entitled to earn vacation at the rate of three (3) weeks per year (or
such greater amount as is generally made available to the Companys executive
officers), to be taken at such times and intervals as shall be mutually agreed
by the Executive and Chief Executive Officer.  
Vacation shall otherwise be governed by the policies of the Company, as
in effect from time to time.  In
addition, during the term hereof, the Executive shall be entitled to receive
paid holidays (currently 11 per year) in accordance with the Companys holiday
schedule.  (f)            Business Expenses.  The Company will pay or reimburse the
Executive for all reasonable business expenses incurred or paid by the
Executive in the performance of his  duties and responsibilities for the Company,
subject to any maximum annual limit and other restrictions on such expenses set
by the Company and to such reasonable substantiation and documentation as it
may specify from time to time.  Any such
reimbursement that would constitute nonqualified deferred compensation subject
to Section 409A shall be subject to the following additional rules:  (i) no reimbursement of any such expense
shall affect the Executives right to reimbursement of any other such expense
in any other taxable year; (ii) reimbursement of the expense shall be
made, if at all, not later than the end of the calendar year following the
calendar year in which the expense was incurred; and (iii) the right to
reimbursement shall not be subject to liquidation or exchange for any other
benefit.  3.Confidential Information, Non-Competition
and Proprietary Information.The
Executive previously executed the Companys Confidentiality, Non-Competition
and Proprietary Information Agreement.  
It is understood and agreed that breach by the Executive of the
Confidential Information, Non-Competition and Proprietary Information Agreement
shall constitute a material breach of this Agreement.  4.             Termination
of Employment.   The Executives
employment under this Agreement shall continue until terminated pursuant to
this Section 4.  (a)           The Company may terminate the Executives
employment for Cause upon written notice to the Executive setting forth in
reasonable detail the nature of the Cause. 
The following, as determined by the Board in its reasonable judgment,
shall constitute Cause for  3


termination:  (i) the Executive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 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
Executives conviction of a felony.  (b)           The Company may terminate the
Executives employment at any time other than for Cause upon written notice to the
Executive.  (c)           The Executive may terminate his
employment hereunder for Good Reason by providing notice to the Company of the
condition giving rise to the Good Reason no later than thirty (30) days
following the occurrence of the condition, by giving the Company thirty (30)
days to remedy the condition and by terminating employment for Good Reason
within thirty (30) days thereafter if the Company fails to remedy the
condition.   For purposes of this
Agreement, Good Reason shall mean, without the Executives consent, the
occurrence of any one or more of the following events: (i) material
diminution in the nature or scope of the Executives responsibilities, duties
or authority, provided that neither shall constitute Good Reason: (x) the
Companys failure to continue the Executive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 Executives responsibilities, duties or authority that
is reasonably related to a diminution of the business of the Company or any of
its Affiliates, other than any such diminution resulting from the sale or
transfer of any or all of the assets of the Company or any of its Affiliates;(ii) a reduction in the Executives base salary other
than one temporary reduction of not more than 120 days and not in excess of 20%
of the Executive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 Executive the salary or benefits in accordance
with Section 2 hereof after thirty (30) days notice during which the
Company does not cure such failure; or (iv) relocation of the Executives
office more than thirty-five (35) miles from the location of the Companys
principal offices as of January 1, 2008.  (d)           The Executive may
terminate his employment with the Company other than for Good Reason at any
time upon one months notice to the Company, unless such termination would
violate any obligation of the Executive to the Company under a separate
severance agreement.  (e)           This Agreement shall automatically
terminate in the event of the Executives death during employment.  The Company may terminate the Executives
employment, upon notice to the Executive, in the event the Executive becomes
disabled during employment and, as a result, is unable to continue to perform
substantially all of his material duties and responsibilities under this Agreement
for one-hundred and twenty (120) days during any period of three hundred and
sixty-five (365) consecutive calendar days. 
If any question shall arise as to whether the Executive is disabled to
the extent that the Executive is unable to perform  4


substantially all
of his material duties and responsibilities for the Company and its Affiliates,
the Executive shall, at the Companys request and expense, submit to a medical
examination by a physician selected by the Company to whom the Executive or the
Executives guardian, if any, has no reasonable objection to determine whether the
Executive is so disabled and such determination shall for the purposes of this
Agreement be conclusive of the issue.  If
such a question arises and the Executive fails to submit to the requested
medical examination, the Companys determination of the issue shall be binding
on the Executive.  5.             Severance Payments and Other Matters Related to
Termination.  (a)           Termination pursuant to Section 4(b),
4(c) or 4(e).  Except as
provided in Section 5(c) below,  (i) in
the event of termination of the Executives employment by the Company other
than for Cause pursuant to Section 4(a) of this Agreement, or in the
event of termination of the Executives employment by the Executive for Good
Reason pursuant to Section 4(c) of this Agreement, (a) all
unvested options and restricted stock which, by their terms, vest only based on
the passage of time(disregarding any acceleration of the vesting of such
options based on individual or Company performance) shall vest as of the date
of termination (notwithstanding anything to the contrary in Section 2(c) of
this Agreement) with respect to an additional one year of vesting (except that
with respect to restricted stock, a minimum of 25% of such unvested shares
shall vest); and (b) the Company will continue to pay the Executives base
salary, at the rate in effect on the date of termination, for a period of
twelve (12) months from the date of termination and pay a pro-rata portion (for
the period from January 1 of the year of termination through the date of
termination) of the target cash bonus for the year in which the Executive is
terminated; or  (ii) in the event of
the Executives termination of employment as a result of the Executives death
or disability at any time pursuant to Section 4(e) of the Agreement, (a) all
unvested options and restricted stock which, by their terms, vest only based on
the passage of time (disregarding any acceleration of the vesting of such
options based on individual or Company performance) shall vest as of the date
of termination (notwithstanding anything to the contrary in Section 2(c) of
this Agreement) with respect to an additional one year of vesting (except that
with respect to restricted stock, a minimum of 25% of such unvested shares
shall vest); (b) to the extent the Companys benefits do not include
disability insurance benefits that will continue the Executives base salary at
100% of the amount of such base salary for the period of twelve (12) months
from the date of termination, the Company shall pay such amount at the time
that the Executives base salary would be otherwise paid as shall equal the
amount by which 100% of the Executives base salary exceeds the disability
insurance benefits, if any, actually paid to him; and (c) the Company
shall pay him a pro-rata portion (for the period from January 1 of the
year of termination through the date of termination) of the target cash bonus
for the year in which the Executive is terminated.  If the Executive is
participating in the Companys group health plan and/or dental plan at the time
the Executives employment terminates (whether such termination is as described
in (i), (ii) or (iii) above), and the Executive exercises his right
to continue participation in those plans under  5


the federal law
known as COBRA, or any successor law, the Company will pay or, at its option,
reimburse the Executive, for the full premium cost of that participation for twelve
(12) months following the date on which the Executives employment with the
Company terminates or, if earlier, until the date the Executive becomes
eligible to enroll in the health (or, if applicable, dental) plan of a new
employer.  The Company will also pay the
Executive on the date of termination any base salary earned but not paid
through the date of termination, any vacation time accrued but not used to that
date and any business expenses incurred by the Executive but un-reimbursed on
the date of termination, provided that such expenses and required
substantiation and documentation are submitted within sixty (60) days of
termination and that such expenses are reimbursable under Company policy.  In addition, the Company will pay the
Executive any bonus which has been awarded to the Executive, but not yet paid
on the date of termination of his employment. 
Subject to the Companys discretion, the portion of any of the Executives
base salary to be paid pursuant to i(b) and ii(b) above that does not
constitute nonqualified deferred compensation within the meaning of Section 409A,
will either be paid in a lump sum or in accordance with normal payroll
practices. Any portion of any of the Executives base salary to be paid pursuant
to i(b) and ii(b) above that constitutes nonqualified deferred
compensation within the meaning of Section 409A shall be paid in a lump
sum.  Any obligation of
the Company to provide the Executive severance payments or other benefits under
this Section 5(a) is conditioned on the Executives signing an
effective release of claims in the form provided by the Company (the Employee
Release) following the termination of the Executives employment, which
release shall not apply to (i) claims for indemnification in the Executives
capacity as an officer or director of the Company under the Companys
Certificate of Incorporation, By-laws or agreement, if any, providing for
director or officer indemnification, (ii) rights to receive insurance
payments under any policy maintained by the Company and (iii) rights to
receive retirement benefits that are accrued and fully vested at the time of the
Executives termination.  Any severance
payments to be made in the form of salary continuation pursuant to the terms of
this Agreement shall be payable in accordance with the normal payroll practices
of the Company, and will begin at the Companys next regular payroll period
following the effective date of the Employee Release, but shall be retroactive
to the date of termination. The Executive agrees to provide the Company prompt
notice of the Executives eligibility to participate in the health plan and, if
applicable, dental plan of any employer. 
The Executive further agrees to repay any overpayment of health benefit
premiums made by the Company hereunder.  (b)           Termination other than pursuant to
Section 4(b), 4(c) or 4(e). 
In the event of any termination of the Executives employment, other
than a termination by the Company pursuant to Section 4(b) of this
Agreement, a termination by the Executive for Good Reason pursuant to Section 4(c) of
this Agreement or a termination as a result of the Executives death or
disability pursuant to Section 4(e) of this Agreement, the Company
will pay the Executive any base salary earned but not paid through the date of
termination and pay for any vacation time accrued but not used to that
date.  In addition, the Company will pay
the Executive any bonus which has been awarded to the Executive, but not yet
paid on the date of termination of the Executives employment. The Company
shall have no other obligation to the Executive under this Agreement.  6


(c)           Upon a Change of
Control.  (i)            If a Change of Control (as defined
in Section 6 hereof) occurs, twenty-five percent (25%) of the Executives
stock options and restricted stock which, by their terms, vest only based on
the passage of time (disregarding any acceleration of the vesting of such
options based on individual or Company performance) shall vest as of the date
of such Change of Control, provided that no more than one hundred-percent
(100%) of the total shares may vest at any time. If, within one year following
such Change of Control or otherwise in connection with such Change of Control,
the Company or any successor thereto terminates the Executives employment
other than for Cause, or the Executive terminates his employment for Good
Reason, then, in lieu of any payments to the Executive or on the Executives
behalf under Section 5(a) hereof, (i) all of the Executives
then remaining unvested options and restricted stock which, by their terms,
vest only based on the passage of time (disregarding any acceleration of the
vesting of such options based on individual or Company performance) shall automatically
vest as of the date of termination (notwithstanding anything to the contrary in
Section 2(c) of this Agreement) and (ii) the Company shall pay,
within thirty (30) days of such termination, (x) a lump sum payment equal
to the Executives then-current annual base salary for a period of twelve (12)
months; and (y) pay a pro-rata portion (for the period from January 1
of the year of termination through the date of termination) of the target cash
bonus for the year in which the Executive is terminated; and  (ii)           The Company and the Executive agree
that in the event it shall be determined that any of the payments or benefits
received or to be received by the Executive in connection with a Change of
Control or Executives termination from employment would be subject to the
excise tax imposed by Section 4999 of the Code, together with any interest
or penalties imposed with respect to such excise tax (the Excise Tax), then
Executive shall be entitled to promptly receive from the Company an additional
lump sum cash payment (the Gross-Up Payment) in an amount such that, after
payment by the Executive of all taxes related to such payments and benefits,
including any income taxes and Excise Tax imposed upon the Gross-Up Payment,
Executive retains an amount of the Gross-Up Payment equal to the Excise Tax
imposed upon such payments and benefits.  (d)           Except for any right the Executive
may have under applicable law to continue participation in the Companys group
health and dental plans under COBRA, or any successor law, benefits shall
terminate in accordance with the terms of the applicable benefit plans based on
the date of termination of the Executives employment, without regard to any
continuation of base salary or other payment to the Executive following
termination.  (e)           Provisions of this Agreement shall
survive any termination if so provided in this Agreement or if necessary or
desirable to accomplish the purposes of other surviving provisions, including
without limitation the Executives obligations under Section 3 of this
Agreement and under the Confidentiality, Non-Competition and Proprietary
Information Agreement.  The obligation of
the Company to make payments to the Executive or on the  7


Executives behalf under Section 5
of this Agreement is expressly conditioned upon the Executives continued full
performance of the Executives obligations under Section 3 hereof, under
the Confidentiality, Non-Competition and Proprietary Information Agreement to
be executed herewith, and under any subsequent agreement between the Executive
and the Company or any of its Affiliates relating to confidentiality,
non-competition, proprietary information or the like.  (f)            In the event the Executive remains
in the employ of the Company or any of its Affiliates following termination of
this Agreement, by the expiration of the term or otherwise, then such
employment shall be at will.  6.             Definitions.For purposes of this agreement,
the following definitions apply:  Affiliates
means all persons and entities directly or indirectly controlling, controlled
by or under common control with the Company, where control may be by management
authority, equity interest or otherwise.  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.  Person means an
individual, a corporation, an association, a partnership, an estate, a trust
and any other entity or organization, other than the Company or any of its
Affiliates.  7.             Conflicting Agreements.
The Executive hereby represents and warrants that his signing of this Agreement
and the performance of his obligations under it will not breach or be in conflict
with any other agreement to which the Executive is a party or is bound and that
the Executive is not now subject to any covenants against competition or
similar covenants or any court order that could affect the performance of the Executives
obligations under this Agreement.  The
Executive agrees that he will not disclose to or use on behalf of the Company
any proprietary information of a third party without that partys consent.  8.             Withholding; Other Tax
Matters.  Anything to the
contrary notwithstanding, (a) all payments required to be made by the
Company hereunder to Executive shall be subject to the withholding of such
amounts, if any, relating to tax and other payroll deductions as the Company
may reasonably determine it should withhold pursuant to any applicable law or
regulation, and (b) to the extent any payment hereunder shall be required
to be delayed until six months  8


following separation from
service to comply with the specified employee rules of Section 409A
it shall be so delayed (but not more than is required to comply with such
rules).  9.             Assignment.  Neither the Executive nor the Company may
make any assignment of this Agreement or any interest in it, by operation of
law or otherwise, without the prior written consent of the other; provided,
however, that the Company may assign its rights and obligations under this
Agreement without the Executives consent to one of its Affiliates or to any
Person with whom the Company shall hereafter affect a reorganization,
consolidate with, or merge into or to whom it transfers all or substantially
all of its properties or assets.  This
Agreement shall inure to the benefit of and be binding upon the Executive and
the Company, and each of our respective successors, executors, administrators,
heirs and permitted assigns.  10.           Severability.  If any portion or provision of this Agreement
shall to any extent be declared illegal or unenforceable by a court of
competent jurisdiction, then the remainder of this Agreement, or the
application of such portion or provision in circumstances other than those as
to which it is so declared illegal or unenforceable, shall not be affected
thereby, and each portion and provision of this Agreement shall be valid and enforceable
to the fullest extent permitted by law.  11.           Waiver.No waiver of any provision hereof
shall be effective unless made in writing and signed by the waiving party.  The failure of either party to require the
performance of any term or obligation of this Agreement, or the waiver by
either party of any breach of this Agreement, shall not prevent any subsequent
enforcement of such term or obligation or be deemed a waiver of any subsequent
breach.  12.           Arbitration.  (a)           Any
dispute, controversy or claim between the parties arising out of this Agreement
shall be settled by arbitration conducted in Cambridge, Massachusetts in
accordance with the American Arbitration Association National Rules for
the Resolution of Employment Disputes (the Rules) and the laws of the
Commonwealth of Massachusetts.  (b)           In
the event that a party requests arbitration (the Requesting Party), it shall
serve upon the other party (the Non-Requesting Party), within ninety (90)
days of the date the Requesting Party knew, or reasonably should have known, of
the facts on which the controversy, dispute or claim is based, a written demand
for arbitration stating the substance of the controversy, dispute or claim, the
contention of the party requesting arbitration and the name and address of the
arbitrator appointed by it.  The
Non-Requesting Party, within twenty (20) days of such demand, shall accept the
arbitrator or appoint a second arbitrator and notify the other party of the
name and address of this second arbitrator so selected, in which case the two
arbitrators shall appoint a neutral umpire. 
Upon the appointment of such neutral umpire, each of the two partisan
arbitrators appointed by the parties shall withdraw from the case, and the neutral
umpire shall preside over the matter as sole decisionmaker.  In the event that the two partisan
arbitrators fail in any instance to appoint a third arbitrator within twenty
(20) days of the appointment of the second arbitrator, either arbitrator or any
party to the arbitration may apply to the American Arbitration Association for
appointment of the neutral umpire in accordance with the Rules.  9


Should the Non-Requesting Party (upon whom a demand
for arbitration has been served) fail or refuse to accept the arbitrator
appointed by the other party or to appoint an arbitrator within twenty (20)
days, the single arbitrator shall have the right to decide alone, and such
arbitrators decision or award shall be final and binding upon the parties.  (c)           The
function of the arbitrator shall be to determine the interpretation and
application of the specific provisions of this Agreement to the issues
submitted to arbitration.  There shall be
no right in arbitration to obtain, and no arbitrator shall have any authority
to award or determine, any change in, addition to, or detraction from, any of
the provisions of this Agreement.  The
decision of the arbitrator shall be in writing; shall set forth the basis for
the decision; and shall be rendered within thirty (30) business days following
the hearing. The decision of the arbitrator acting within the scope of his/her
authority shall be final and binding upon the parties and may be enforced and
executed upon in any court having jurisdiction over the party against whom
enforcement of such award is sought.  (d)           The
parties involved in the dispute shall divide equally the administrative
charges, arbitrators fees and related expenses of the arbitration, but each
party shall pay its own legal fees incurred in connection with such
arbitration.  (e)           Nothing
contained herein, however, shall limit the right of the Company to seek
equitable or other relief from any court of competent jurisdiction for
violation of the Confidentiality, Non-Competition and Proprietary Information
Agreement.  13.           Miscellaneous.  This Agreement, together with the
Confidentiality, Non-Competition and Proprietary Information Agreement, sets
forth the entire agreement between the Executive and the Company and replaces
all prior communications, agreements and understandings, written or oral, with
respect to the terms and conditions of the Executives employment.  This Agreement may not be modified or
amended, and no breach shall be deemed to be waived, unless agreed to in
writing by the Executive and an expressly authorized representative of the
Board.  The headings and captions in this
Agreement are for convenience only and in no way define or describe the scope
or content of any provision of this Agreement. 
This Agreement may be executed in two or more counterparts, each of
which shall be an original and all of which together shall constitute one and
the same instrument. This is a Massachusetts contract and shall be governed and
construed in accordance with the laws of the Commonwealth of Massachusetts,
without regard to the conflict-of-laws principles thereof.  14.           Notices.  Any notices provided for in this Agreement
shall be in writing and shall be effective when delivered in person, consigned
to a reputable national courier service for overnight delivery or deposited in
the United States mail, postage prepaid, and addressed to the Executive at the Executives
last known address on the books of the Company or, in the case of the Company,
to it by notice to the Chairman of the Board of Directors, c/o Sirtris
Pharmaceuticals, Inc. at its principal place of business, or to such other
address(es) as either party may specify by notice to the other actually
received.  [Remainder of page intentionally
left blank.]  10


IN WITNESS WHEREOF, this Agreement has been executed as a
sealed instrument by the Company, by its duly authorized representative, and by
the Executive, as of the date first above written.   THE EXECUTIVE
  
  THE COMPANY/s/ Michael Jirousek
  
  By:
  /s/ Christoph WestphalMichael JirousekTitle:
  Chief Executive Officer  11