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                                                                   Exhibit 10.18

November 29, 2002

Wendy E. Rieder, Esq.
[ADDRESS]


Dear Wendy:

     We are pleased to make the following employment offer to you at Synta
Pharmaceuticals Corp. (hereinafter "Synta Pharmaceuticals" or the "Company"). We
are looking forward to working with you. The terms of your employment are
detailed below.

Position:                     Your position will be Vice President of
                              Intellectual Property and Legal Affairs, and you
                              will work at our office located at 45 Hartwell
                              Avenue, Lexington, Massachusetts. If you continue
                              with the Company, your position and assignments
                              will be subject to change. Synta Pharmaceuticals
                              is a dynamic organization with ever-changing
                              needs, and we will place you where we believe your
                              talents and abilities can be best utilized. As a
                              Synta Pharmaceuticals employee, we expect that you
                              will perform any and all duties and
                              responsibilities normally associated with your
                              position in a satisfactory manner and to the best
                              of your abilities at all times. You will be
                              expected to devote all of your working time to the
                              performance of your duties at the Company
                              throughout your employment. Notwithstanding the
                              above, you shall be permitted to continue as a
                              member of the Board of Directors of Microbiotix,
                              Inc. Your employment at all times remains at-will,
                              as discussed below.

Salary:                       Your initial base pay shall be $150,000 annually;
                              payable at a semimonthly rate of $6,250.00, from
                              which all applicable taxes and other customary
                              employment-related deductions will be taken.
                              Additionally, you will qualify to receive annual
                              performance-based bonuses. Bonuses for fully
                              meeting and exceeding expectations will be granted
                              in the 10%-20% range. Any such bonus will be
                              granted at the discretion of the Company's Board
                              of Directors.

Stock Option:                 Subject to the approval of the Company's Board of
                              Directors, you will be granted an incentive stock
                              option to purchase 300,000 shares of the Company's
                              common stock pursuant to the terms of the Synta
                              Pharmaceuticals Corp. 2001 Stock Plan (the "Plan")
                              and formal stock option agreement. All stock
                              option grants shall be priced at the fair market
                              value on the grant date and are subject to a
                              vesting schedule. Please refer to the Plan and to
                              your stock option agreement for further
                              information concerning this aspect of your
                              compensation.

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Benefit Plans:                As a full-time employee, you will be eligible to
                              participate in certain Company-sponsored benefit
                              plans to the same extent as, and subject to the
                              same terms, conditions and limitations applicable
                              to, other employees of the Company of similar rank
                              and tenure. The Company will provide you with
                              detailed information on its current benefits,
                              holiday schedule, and vacation and sick leave
                              policies on your start date. All benefits, of
                              course, may be changed or modified from time to
                              time and the provision of any benefits to you in
                              no way changes or impacts your status as an
                              at-will employee. Company agrees to award you
                              short term disability benefits for maternity
                              leave, notwithstanding the length of employment
                              requirement stated in the Company's employee
                              handbook.

Severance:                    In the event that the Company terminates your
                              employment without cause after the first year of
                              employment following the Transition Period, the
                              Company will make a one-time severance payment to
                              you on the date of termination equal to 3 months
                              base pay. If such termination occurs during the
                              first year of employment following the Transition
                              Period, the severance payment will be
                              appropriately prorated. For the purposes of this
                              section, "cause" means (i) an act of dishonesty
                              demonstrating lack of integrity or moral
                              turpitude, (ii) willful or persistent inattention
                              to the services and duties required in connection
                              with your employment, including failure to comply
                              with all applicable laws and regulations after
                              notice and failure to cure within 30 days or (iii)
                              conviction of any felonious criminal act.

Starting Date:                Your first day of employment under this offer of
                              employment will be December 15, 2002.

Transition Period:            During the time between the Starting Date until
                              January 15, 2003 (the "Transition Period"), you
                              will receive a reduced salary equal to 50% of your
                              base pay in recognition of the fact that you will
                              be completing work undertaken for your previous
                              employer. However, you will be considered a full
                              time employee of Synta Pharmaceuticals during this
                              Transition Period.

Nature of Relationship:       No provision of this letter shall be construed to
                              create an express or implied employment contract,
                              or a promise of employment for any specific period
                              of time. Your employment with Synta
                              Pharmaceuticals is at-will employment which may be
                              terminated by you or the Company at any time for
                              any reason with or without advance notice.

     Our employment offer to you is contingent upon (i) your execution of the
form of Non-Competition, Confidentiality and Inventions Agreement which is
attached hereto as EXHIBIT A, and (ii) your ability, as required under federal
law, to establish your employment eligibility as a U.S. citizen, a lawful
permanent resident of the U.S. or an individual specifically authorized for
employment by the Immigration and Naturalization Service.

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     This letter constitutes our entire offer regarding the terms and conditions
of your prospective employment with Synta Pharmaceuticals. It supersedes any
prior agreements, or other promises or statements (whether oral or written)
regarding the offered terms of employment. The terms of your employment shall be
governed by the laws of the Commonwealth of Massachusetts. By accepting this
offer of employment, you agree that any action, demand, claim or counterclaim in
connection with any aspect of your employment with the Company, or any
separation of employment (whether voluntary or involuntary) from the Company,
shall be resolved in a court of competent jurisdiction in Massachusetts by a
judge alone, and you knowingly waive and forever renounce your right to a trial
before a civil jury.


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                                        3
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     If you accept the above-described offer, please sign and return the
original copy of this letter; the second copy is for your records. We look
forward to you joining Synta Pharmaceuticals. If you have any questions, please
feel free to call me.


                                          Sincerely,

                                          SYNTA PHARMACEUTICALS CORP.

                                          /s/ SAFI BAHCALL
                                          -----------------------------
                                          Safi Bahcall, Ph.D.
                                          Chief Executive Officer

Agreed to and accepted:

Name: /s/ WENDY E. RIEDER                 Date:1/14/03
     ---------------------                     -------

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                                    EXHIBIT A

Synta Pharmaceuticals Corp.
45 Hartwell Avenue
Lexington, MA 02421

November 29, 2002

Wendy E. Rieder, Esq.
[ADDRESS]


Dear Wendy:

     This letter is to confirm our understanding with respect to (i) your
agreement not to solicit customers or employees of Synta Pharmaceuticals Corp.
or its subsidiaries or affiliates (collectively, the "Company") and (ii) your
agreement to protect and preserve information and property which is confidential
and proprietary to the Company (the terms and conditions agreed to in this
letter shall hereinafter be referred to as the "Agreement"). You hereby
acknowledge and agree that you are an "at-will" employee and that no provision
of this Agreement shall be construed to create an express or implied employment
contract, or a promise of employment for a specific period of time, and the
Company expressly reserves the right to end your employment at any time, with or
without notice or cause.

     In consideration of your employment by the Company, the mutual promises and
covenants contained in this Agreement, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby mutually
acknowledged, we have agreed as follows:

1.   PROHIBITED SOLICITATION.

     (a)  CERTAIN ACKNOWLEDGMENTS AND AGREEMENTS.

          (i)     We have discussed, and you recognize and acknowledge the
competitive and proprietary aspects of the business of the Company.

          (ii)    You further acknowledge and agree that, during the course of
your employment with the Company, the Company will furnish, disclose or make
available to you confidential and proprietary information related to the
Company's business and that the Company may provide you with unique and
specialized training. You also acknowledge that such confidential information
and such training have been developed and will be developed by the Company
through the expenditure by the Company of substantial time, effort and money and
that all such confidential information and training could be used by you to
compete with the Company.

     (b)  NON-SOLICITATION. During the period in which you are employed by the
Company ("Term") and for a period of twelve (12) months following termination of
your employment,

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whether such termination is voluntary or involuntary, you shall not, without the
prior written consent of the Company:

               (i)     either individually or on behalf of or through any third
party, solicit, divert or appropriate or attempt to solicit, divert or
appropriate, any customer of the Company with which you had any contact at any
time during the Term, located anywhere in the world (the "Restricted Territory")
with the effect or intention of reducing or limiting the amount of business the
customer does with the Company; or

               (ii)    either individually or on behalf of or through any third
party, directly or indirectly, solicit, entice or persuade or attempt to
solicit, entice or persuade any employees of or consultants to the Company
(other than your spouse), who have been employees or consultants of the Company
at any time during the Term, or who are employees at the time of the
solicitation, to leave the services of the Company.

     (c)  REASONABLENESS OF RESTRICTIONS. You further acknowledge and agree that
(i) the activities which are prohibited b y this Section I are n arrow and
reasonable in relation to the skills which represent your principal salable
asset both to the Company and to your other prospective employers, and (ii)
given the global nature of the Company's business, including its need to market
its services and sell its products in a large geographic area in order to have a
sufficient customer base to make the Company's business profitable, the
geographic, length of time and substantive scope of the provisions of this
Section 1 are reasonable, legitimate and fair to you.

     (d)  SURVIVAL OF ACKNOWLEDGMENTS AND AGREEMENTS. Except as expressly set
forth hereunder, your acknowledgments and agreements set forth in this Section 1
shall survive the termination of your employment with the Company for the
periods set forth above.

2.   PROTECTED INFORMATION.

     (a)  CONFIDENTIALITY OBLIGATIONS. You shall at all times, both during the
Term and thereafter, maintain in confidence and shall not, without the prior
written consent of the Company, use, except in the course of performance of your
duties for the Company, disclose or give to others any Confidential Information
of the Company. As used herein, the term "Confidential Information" shall mean
any information which is disclosed to or developed by you during the course of
performing services for, or receiving training from, the Company, and is not
generally available to the public, including but not limited to confidential
information concerning business plans, customers, future customers, suppliers,
licensors, licensees, partners, investors, affiliates or others, training
methods and materials, financial information, sales prospects, client lists,
Company Inventions (as defined in Section 3), or any other scientific,
technical, trade or business secret or confidential or proprietary information
of the Company or of any third party provided to you during the Term. In the
event anyone not employed or otherwise engaged by the Company seeks information
from you in regard to any such Confidential Information or any other secret or
confidential work of the Company, or concerning any fact or circumstance
relating thereto, you will promptly notify the chief executive officer of the
Company.

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     (b)  LIMITED EXCEPTIONS. The restrictions in Section 2(a) hereof shall not
apply to information that, as can be established by competent written records:
(i) was publicly known at the time of the Company's communication thereof to
you; (ii) becomes publicly known through no fault of yours subsequent to the
time of the Company's communication thereof to you; (iii) was in your possession
free of any obligation of confidence at the time of the Company's communication
thereof to you; or (iv) is developed by you independently of and without
reference to or use of any of the Company's Confidential Information. In the
event that you are required by law, regulation or court order to disclose any of
the Company's Confidential Information, you shall (i) first notify the Company
of such disclosure requirement and (ii) furnish only that portion of the
Confidential Information that is legally required and will exercise all
reasonable efforts to obtain reliable assurances that confidential treatment
will be accorded the Confidential Information.

3.   OWNERSHIP OF INTELLECTUAL PROPERTY IDEAS.

     (a)  PROPERTY OF THE COMPANY. As used in this Agreement, the term
"Inventions" shall mean all ideas, discoveries, creations, manuscripts and
properties, innovations, improvements, know-how, inventions, designs,
developments, apparatus, techniques, methods, biological processes, cell lines,
laboratory notebooks and formulae, whether patentable, copyrightable or not,
including all rights to obtain, register; perfect and enforce any of the
foregoing. You hereby agree that any Inventions which you may conceive, reduce
to practice or develop during the Term in connection with the business
activities of the Company or otherwise within the Field of Interest, alone or in
conjunction with any other party, whether during or out of regular business
hours, and whether at the request or upon the suggestion of the Company, or
otherwise (collectively, the "Company Inventions"), shall be the sole and
exclusive property of the Company. You hereby assign to the Company all of your
right, title and interest in and to all such Company Inventions and hereby agree
that you shall not publish any of the Company Inventions without the prior
written consent of the Company.

     (b)  COOPERATION. During the Term, you agree that, without further
compensation, you will disclose promptly to the Company in writing, all Company
Inventions you conceive, reduce to practice or develop during the Term (or, if
based on or related to any Confidential Information of the Company obtained by
you during the Term, within one (1) year after the termination of your
employment). You further agree that you will fully cooperate with the Company,
its attorneys and agents in the preparation and filing of all papers and other
documents as may be reasonably required to perfect the Company's rights in and
to any of such Company Inventions, including, but not limited to, joining in any
proceeding to obtain patents, copyrights, trademarks or other legal rights of
the United States and of any and all other countries on such Company Inventions;
PROVIDED, THAT, the Company will bear the expense of such proceedings (including
all of your reasonable expenses). You further agree that any patent or other
legal right covering any Company Invention so issued to you, personally, shall
be assigned by you to the Company without charge by you. You further acknowledge
that all original works of authorship made by you, whether alone or jointly with
others within the scope of your employment and which are protectable by
copyright are "works made for hire" within the meaning of the United States
Copyright Act, 17 U.S.C. Section 101, as amended, the copyright of which shall
be owned solely, completely and exclusively by the Company. If any Company
Invention is considered to be work not included in the categories of work
covered by the United States Copyright Act, 17 U.S.C. Section

                                       A-3
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101, as amended, such work shall be owned solely by, or hereby assigned or
transferred completely and exclusively to, the Company. If the Company is unable
because of your mental or physical incapacity or for any other reason, after
reasonable effort, to secure your signature on any document or documents needed
to obtain or enforce any patent, copyright, trademarks or any other rights
covering Inventions or original works of authorship assigned by you to the
Company as required above, you hereby irrevocably designate and appoint the
Company and its duly authorized officers and agents as your agent and
attorney-in-fact, to act for and in your behalf and stead to execute and file
any application or assignment and to do all other lawfully permitted acts to
further the prosecution and issuance to the Company of patents, copyright
registrations, trademark registrations or similar protections covering the
Inventions with the same legal force and effect as if executed by you.

4.   PROVISIONS NECESSARY AND REASONABLE/BREACH/ATTORNEYS' FEES. You agree that
(i) the provisions of Sections 1, 2 and 3 of this Agreement are necessary and
reasonable to protect the Company's Confidential Information, Company
Inventions, and goodwill and (ii) in the event of any breach of any of the
covenants set forth herein, the Company would suffer substantial irreparable
harm and would not have an adequate remedy at law for such breach. In
recognition of the foregoing, you agree that in the event of a breach or
threatened breach of any of these covenants, in addition to such other remedies
as the Company may have at law, without posting any bond or security, the
Company shall be entitled to seek and obtain equitable relief, in the form of
specific performance, and/or temporary, preliminary or permanent injunctive
relief, or any other equitable remedy which then may be available. The seeking o
f such injunction o r order shall not affect the Company's right to seek and
obtain damages or other equitable relief on account of any such actual or
threatened breach. In the event the Company takes any court action with respect
to your breach or threatened breach of this Agreement, and prevails in such
action, you shall be obligated to reimburse the Company for its reasonable
attorneys' fees and costs incurred in such action.

5.   DISCLOSURE TO FUTURE EMPLOYERS. You agree that you will provide, and that
the Company may similarly provide in its discretion, a copy of the covenants
contained in Sections 1, 2 and 3 of this. Agreement to any business or
enterprise which you may directly, or indirectly, own, manage, operate, finance,
join, control or in which you participate in the ownership, management,
operation, financing, or control, or with which you may be connected as an
officer, director, employee, partner, principal, agent, representative,
consultant or otherwise.

6.   REPRESENTATIONS REGARDING PRIOR WORK AND LEGAL OBLIGATIONS.

     (a)  You represent that you have no agreement or other legal obligation
with any prior employer or any other person or entity that restricts your
ability to engage in employment discussions with, employment with, or to perform
any function for, the Company.

     (b)  You represent that you have been advised by the Company that at no
time should you divulge to or use for the benefit of the Company, any trade
secret or confidential or proprietary information of any previous employer. You
acknowledge that you have not divulged or used any such information for the
benefit of the Company.

                                       A-4
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     (c)  You acknowledge that the Company is basing important business
decisions on these representations, and affirm that all of the statements
included herein are true.

7.   RECORDS. Upon termination of your employment relationship with the
Company, you shall deliver to the Company any property of the Company which may
be in your possession including products, materials, memoranda, notes, records,
reports, or other documents or photocopies of the same.

8.   NO CONFLICTING AGREEMENTS. You hereby represent and warrant that you have
no commitments or obligations inconsistent with this Agreement and you hereby
agree to indemnify and hold the Company harmless against loss, damage, liability
or expense arising from any claim based upon circumstances alleged to be
inconsistent with such representation and warranty.

9.   GENERAL.

     (a)  NOTICES. All notices, requests, consents and other communications
hereunder shall be in writing, shall be addressed to the receiving party's
address set forth below or to such other address as a party may designate by
notice hereunder, and shall be either (i) delivered by hand, (ii) made by telex,
telecopy or facsimile transmission with confirmed receipt thereof (and with a
copy of such telex, telecopy or facsimile, together with a copy of the
confirmation sent to the recipient by regular U.S. mail on the next business
day), (iii) sent by overnight courier, or (iv) sent by registered mail, return
receipt requested, postage prepaid.

If to the Company:

Synta Pharmaceuticals Corp.
45 Hartwell Avenue
Lexington, MA 02421
Attn: Chief Executive Officer

If to you:     To the address set forth on the signature page of this Agreement.

     All notices, requests, consents and other communications hereunder shall be
deemed to have been given either (i) if by hand, at the time of the delivery
thereof to the receiving party at the address of such party set forth above,
(ii) if made by telex, telecopy or facsimile transmission, at the time that
receipt thereof has been acknowledged by electronic confirmation or otherwise,
(iii) if sent by overnight courier, on the next business day following the day
such notice is delivered to the courier service, or (iv) if sent by registered
mail, on the fifth business day following the day such mailing is made.

     (b)  ENTIRE AGREEMENT. This Agreement embodies the entire agreement and
understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior oral or written agreements and understandings
relating to the subject matter hereof. No statement, representation, warranty,
covenant or agreement of any kind not expressly set forth in this Agreement
shall affect, or be used to interpret, change or restrict, the express terms and
provisions of this Agreement.

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     (c)  MODIFICATIONS AND AMENDMENTS. The terms and provisions of this
Agreement may be modified or amended only by written agreement executed by the
parties hereto.

     (d)  WAIVERS AND CONSENTS. The terms and provisions of this Agreement may
be waived, or consent for the departure therefrom granted, only by written
document executed by the party entitled to the benefits of such terms or
provisions. No such waiver or consent shall be deemed to be or shall constitute
a waiver or consent with respect to any other terms or provisions of this
Agreement, whether or not similar. Each such waiver or consent shall be
effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

     (e)  ASSIGNMENT. The Company m ay assign its rights and obligations
hereunder to any person or entity that succeeds to all or substantially all of
the Company's business or that aspect of the Company's business in which you are
principally involved. Your rights and obligations under this Agreement may not
be assigned by you without the prior written consent of the Company.

     (f)  BENEFIT. All statements, representations, warranties, covenants and
agreements in this Agreement shall be binding on the parties hereto and shall
inure to the benefit of the respective successors and permitted assigns of each
p arty hereto. Nothing in this Agreement shall be construed to create any rights
or obligations except among the parties hereto, and no person or entity shall be
regarded as a third-party beneficiary of this Agreement.

     (g)  GOVERNING LAW. This Agreement and the rights and obligations of the
parties hereunder shall be construed in accordance with and governed by the laws
of the Commonwealth of Massachusetts, without giving effect to the conflict of
laws principles thereof.

     (h)  JURISDICTION. Any legal action or proceeding with respect to this
Agreement may be brought in the courts of the Commonwealth of Massachusetts or
of the United States of America. By execution and delivery of this Agreement,
each of the parties hereto accepts for itself and in respect of its property,
generally and unconditionally, the jurisdiction of the aforesaid courts.

     (i)  SEVERABILITY. The parties intend this Agreement to be enforced as
written. However, (i) if any portion or provision of this Agreement shall to any
extent be declared illegal or unenforceable by a duly authorized court having
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 and (ii) if any provision, or part thereof, is
held to be unenforceable because of the duration of such provision or the
geographic area covered thereby, the Company and you agree that the court making
such determination shall have the power to reduce the duration and/or geographic
area of such provision, and/or to delete specific words and phrases
("blue-penciling"), and in its reduced or blue-penciled form such provision
shall then be enforceable and shall be enforced.

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     (j)  HEADINGS AND CAPTIONS. The headings and captions of the various
subdivisions of this Agreement are for convenience of reference only and shall
in no way modify, or affect the meaning or construction of any of the terms or
provisions hereof.

     (k)  NO WAIVER OF RIGHTS. Powers and Remedies. No failure or delay by a
party hereto in exercising any right, power or remedy under this Agreement, and
no course of dealing between the parties hereto, shall operate as a waiver of
any such right, power or remedy of the party. No single or partial exercise of
any right, power or remedy under this Agreement by a party hereto, nor any
abandonment or discontinuance of steps to enforce any such right, power or
remedy, shall preclude such party from any other or further exercise thereof or
the exercise of any other right, power or remedy hereunder. The election of any
remedy by a party hereto shall not constitute a waiver of the right of such
party to pursue other available remedies. No notice to or demand on a party not
expressly required under this Agreement shall entitle the party receiving such
notice or demand to any other or further notice or demand in similar or other
circumstances or constitute a waiver of the rights of the party giving such
notice or demand to any other or further action in any circumstances without
such notice or demand.

     (l)  COUNTERPARTS. This Agreement may be executed in one or more
counterparts, and by different parties hereto on separate counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

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                                       A-7
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     If the foregoing accurately sets forth our agreement, please so indicate by
signing and returning to us the enclosed copy of this letter.

                                          Very truly yours,

                                          SYNTA PHARMACEUTICALS CORP.


                                          By:  /s/ SAFI BAHCALL
                                              -----------------------------
                                              Safi Bahcall, Ph.D.
                                              Chief Executive Officer


Agreed to and accepted:

/s/ WENDY E. RIEDER
--------------------------
Name:


--------------------------


--------------------------
Address:


Date:  1/14/03
     ---------------------

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