Document:

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                                                                    Exhibit 10.3

                           SYNTA PHARMACEUTICALS CORP.
                          DIRECTOR COMPENSATION POLICY*

     The Board of Directors of Synta Pharmaceuticals Corp. (the "Company") has
approved the following policy which establishes compensation to be paid to
non-employee directors of the Company, effective January 1, 2005, to provide an
inducement to obtain and retain the services of qualified persons to serve as
members of the Company's Board of Directors. Each such director will receive as
compensation for his or her services (i) a stock option grant upon his or her
initial appointment or election to the Board of Directors of the Company and
(ii) an annual fee payable in cash and/or stock, all as further set forth
herein.

APPLICABLE PERSONS

     This Policy shall apply to each director of the Company who (a) is not an
employee of the Company or any Affiliate and (b) does not receive compensation
as a consultant to the Company or any Affiliate unless such compensation is
received solely for services provided as a member of the Scientific Advisory
Board (each, an "Outside Director"). Affiliate shall mean a corporation which is
a direct or indirect parent or subsidiary of the Company, as determined pursuant
to Section 424 of the Internal Revenue Code of 1986, as amended.

STOCK OPTION GRANT UPON INITIAL APPOINTMENT OR ELECTION AS A DIRECTOR

     NUMBER OF SHARES

     Each new Outside Director on the date of his or her initial appointment or
election to the Board of Directors, shall be granted a non-qualified stock
option to purchase 22,000 shares** of the Company's common stock under the
Company's then applicable stockholder-approved stock plan (the "Stock Plan"),
subject to automatic adjustment in the event of any stock split or other
recapitalization affecting the Company's common stock.

     VESTING PROVISION

     Such option shall vest as to 25% of such grant on the first anniversary of
the date of grant of the option and as to an additional 6.25% of such grant on
the last day of each calendar quarter of the Company thereafter, provided such
Outside Director continues to serve as a member of the Board of Directors.
However, in the event of termination of service of an Outside Director, such
option shall vest to the extent of a pro rata portion through the Outside
Director's last day of service based on the number of days accrued in the
applicable period prior to his or her termination of service.

*  Amended as of April 13, 2005.

** Reflects the 1-for-2.75 reverse stock split to be effected prior to the
   Company's initial public offering.

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     EXERCISE PRICE AND TERM OF OPTION

     Each option granted shall have an exercise price per share equal to the
Fair Market Value (as defined in the Stock Plan) of the shares of common stock
of the Company on the date of grant of the option, have a term of ten years and
shall be subject to the terms and conditions of the Stock Plan. Each such option
grant shall be evidenced by the issuance of a non-qualified stock option
agreement.

     EARLY TERMINATION OF OPTION UPON TERMINATION OF SERVICE

     If an Outside Director:

     a.   ceases to be a member of the Board of Directors for any reason other
          than death or disability, any then vested and unexercised options
          granted to such Outside Director may be exercised by the director
          within a period of three months after the date the director ceases to
          be a member of the Board of Directors and in no event later than the
          expiration date of the option; or

     b.   ceases to be a member of the Board of Directors by reason of his or
          her death or disability, any then vested and unexercised options
          granted to such director may be exercised by the director (or by the
          director's personal representative, or the director's survivors)
          within a period of one year after the date the director ceases to be a
          member of the Board of Directors and in no event later than the
          expiration date of the option.

ANNUAL FEE

     Each Outside Director shall be compensated on an annual basis for providing
services to the Company. Except as otherwise set forth in this Policy, director
compensation shall be paid for the period from July 1 through June 30 of each
year. Each Outside Director shall receive compensation consisting of one of the
following combinations of cash and/or a grant of common stock, subject to
certain contractual restrictions, under the Stock Plan, at the election of each
Outside Director, as follows:

       -  $40,000 cash,
       -  $30,000 cash and such number of shares of the Company's common stock
          as is equal to $10,000 on the date of grant of the shares,
       -  $20,000 cash and such number of shares of the Company's common stock
          as is equal to $20,000 on the date of grant of the shares,
       -  $10,000 cash and such number of shares of the Company's common stock
          as is equal to $30,000 on the date of grant of the shares, or
       -  such number of shares of the Company's common stock as is equal to
          $40,000 on the date of the grant of the shares.

     The number of shares to be received by an Outside Director shall be
calculated by dividing the total dollar amount that the Outside Director has
elected to be paid in shares of common stock by the Fair Market Value (as
defined in the Stock Plan) of the shares of common

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stock of the Company on the last business day prior to the date of grant of the
shares (rounded down to the nearest whole number so that no fractional shares
shall be issued).

     ELECTION

     Each Outside Director shall make an election on the form provided by the
Company, indicating the combination of his or her annual compensation, prior to
each annual meeting of stockholders. If the Company does not schedule an annual
meeting of stockholders to be held on or before June 30th of any year, each
Outside Director shall make his or her election by June 15th of the applicable
year.

     CASH PAYMENTS

     Any cash portion to be paid to an Outside Director shall be paid quarterly
in arrears as of the last day of each calendar quarter. If an Outside Director
dies, resigns or is removed during any quarter, he or she shall be entitled to a
cash payment on a pro rata basis through his or her last day of service.

     RESTRICTED STOCK GRANTS

     Shares of common stock shall be granted at the first meeting of the Board
of Directors following each annual stockholders meeting, or if no such meeting
of the Board of Directors shall occur before June 30 of the applicable year, by
unanimous written consent dated June 30 of that year. The shares shall be
subject to a lapsing repurchase right such that the shares shall be subject to
forfeiture to the Company if such Outside Director does not continue to serve as
a member of the Board of Directors as of the end of the applicable quarter as
follows: the repurchase right shall lapse as to 25% of each such grant on each
of September 30, December 31, March 31 and June 30 thereafter, provided such
Outside Director continues to serve as a member of the Board of Directors as of
the applicable date.

     INITIAL ANNUAL FEE UPON INSTITUTION OF POLICY

     On the date of adoption of this Policy, each Outside Director then serving
shall be entitled to receive compensation prorated for the period from January
1, 2005 through June 30, 2005. Each Outside Director shall make an election on
or before January 14, 2005 as to the combination of cash and/or stock to be
received. The Board of Directors shall, by unanimous written consent dated
January 18, 2005, grant any shares to be issued as part of such compensation.
The shares to be issued shall be subject to a lapsing repurchase right such that
the Company's repurchase right shall lapse as to 50% of each such grant on each
of March 31, 2005 and June 30, 2005, provided such Outside Director continues to
serve as a member of the Board of Directors as of the applicable date.

     INITIAL ANNUAL FEE FOR NEWLY APPOINTED OR ELECTED DIRECTORS

     Each Outside Director who is first appointed or elected to the Board of
Directors after the date of the adoption of this Policy shall receive his or her
first year's annual fee prorated in accordance with the terms of this Policy
from the beginning of the next calendar quarter after his or her initial
appointment or election through the following June 30. Each such Outside
Director

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shall make an election prior to the beginning of the next calendar quarter after
his or her initial appointment or election as to the combination of cash and/or
stock. The Board of Directors shall, by unanimous written consent dated the date
of the first day of such quarter, grant any shares to be issued to such Outside
Director as part of such compensation. Any such shares shall be subject to a pro
rata lapsing repurchase right as of the last day of each quarter remaining in
such initial period, provided such Outside Director continues to serve as a
member of the Board of Directors as of the end of the applicable quarter.

     PURCHASE PRICE AND OTHER PROVISIONS APPLICABLE TO ALL STOCK GRANTS

     Shares granted shall have a purchase price equal to the par value of the
common stock on the date of grant and shall be subject to the terms and
conditions of the Stock Plan. The terms of such grant shall be evidenced by a
restricted stock agreement to be entered into between the Company and the
Outside Director. In addition, in the event of termination of service of an
Outside Director, the Company's lapsing repurchase right shall be deemed to have
lapsed to the extent of a pro rata portion of the shares through the Outside
Director's last day of service based on the number of days accrued in the
applicable period prior to his or her termination of service.

BOARD COMMITTEE COMPENSATION

     Each Outside Director shall also receive an annual fee of $5,000 for each
Committee of the Board of Directors on which such individual serves. However,
the Chairman of each Committee, other than the Audit Committee, shall receive an
annual fee of $10,000, and the Chairman of the Audit Committee shall receive an
annual fee of $15,000 for services as Chairman. Payment shall commence effective
January 1, 2005 and shall be made quarterly in arrears on the last day of each
calendar quarter and upon death, resignation or removal, payment shall be made
pro rata through the last day of service.

EXPENSES

     Upon presentation of documentation of such expenses reasonably satisfactory
to the Company, each Outside Director shall be reimbursed for his or her
reasonable out-of-pocket business expenses incurred in connection with attending
meetings of the Board of Directors, Committees thereof or in connection with
other Board related business.

AMENDMENTS

     The Board of Directors shall review this Policy from time to time to assess
whether any amendments in the type and amount of compensation provided herein
should be adjusted in order to fulfill the objectives of this Policy.

DATED: January 11, 2005, as amended April 13, 2005<Page>

                                                                   Exhibit 10.21

December 20, 2004

Stephen Gansler
[ADDRESS]

Dear Stephen:

On behalf of Synta Pharmaceuticals, I am pleased to offer you the position of
Vice President of Human Resources reporting to Safi Bahcall, the President and
Chief Executive Officer of Synta Pharmaceuticals Corp. (hereinafter "Synta
Pharmaceuticals" or the "Company").

1. START DATE: Your first day of employment will be January 3, 2005.

2. BASE COMPENSATION: Your initial base salary will be $210,000 annually payable
on a semi-monthly basis, from which all applicable taxes and other customary
employment-related deductions will be taken.

3. BONUSES: You will be eligible to receive annual performance based bonuses.
Cash bonuses for fully meeting and exceeding expectations under the Company's
proposed bonus program are expected to be in the 10-20% range, with a full
target level of 20%. Such bonus, if any, will be granted at the discretion of
the Company's Board of Directors.

4. STOCK OPTION: Subject to the approval of the Company's Board of Directors,
you will be granted an incentive stock option to purchase a total of 150,000
shares of the Company's common stock. The shares will vest pursuant to the terms
of the Synta Pharmaceuticals Corp. 2001 Stock Plan (the "Plan") and a formal
stock option agreement that you will receive after the grant is approved. All
stock option grants shall be priced at the fair market value on the grant date,
which will be your first day of employment. Provided that you are still employed
by the Company, the Option shall become exercisable in cumulative installments
of 25% of the Stock Right Shares on the one-year anniversary of your grant date,
and thereafter 6.25% of the Stock Rights Shares upon the end of each following
calendar quarter. In addition, you will be eligible to receive an annual option
grant on the same date as other eligible employees in February/March of 2005.

5. BENEFITS: As an 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. All benefits may be changed or modified from time to
time at the Company's sole discretion.

6. EMPLOYMENT PERIOD: Your employment with the Company will be at-will, meaning
that you will not be obligated to remain employed by the Company for any
specified period of time; likewise, the Company will not be obligated to
continue your employment for any specific period and may terminate your
employment at any time, with or without cause. No provision of this letter shall
be construed to create an express or implied employment contract.

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7. SEVERANCE: In the event the Company terminates your employment without cause,
the Company will make a one-time severance payment to you one week after the
date of termination equal to: 1.5 months of base salary if your employment
period has been between 6 and 12 months, or 3 months of base salary if your
employment period has been 12 or more months. In addition to the one-time
severance payment, the Company will provide for a continuation of health care
coverage for a 12 month period.

     For purposes of this letter, termination "without cause" shall include, but
not be limited to, your resignation following a significant and material
diminution in your title, salary, duties or responsibilities by the Company or a
requirement that you relocate to an office more than 50 miles from Lexington,
MA. The preceding sentence notwithstanding, "cause" shall include (but is not
limited to): (i) any substantial malfeasance or non-feasance of duty, (ii) any
material breach by you of any of the terms of the Confidential Information
Agreement and Non-Competition Agreement between you and the Company, (iii) any
attempt by you to secure any improper personal profit in connection with the
business of the Company or any of its affiliates, (iv) your conviction, or the
entry of a pleading of guilty or nolo contendre by you to, any crime involving
moral turpitude or any felony, or (v) any conduct substantially injurious or
prejudicial to the business of the Company or its affiliates.

     Concurrently with the receipt of your severance payment, and as a condition
to such receipt, you shall execute and deliver to the Company your written
release of the Company from any and all claims and causes of action against the
Company arising in connection with your employment with the Company.

8. CONTINGENCIES: Our employment offer to you is contingent upon (1) your
execution of the standard form of Non-Competition, Confidentiality and
Inventions Agreement (a copy of which is attached hereto as EXHIBIT A); (2) 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; and (3) completion of a satisfactory background check. If any of the
foregoing conditions are not met, this employment offer shall be null and void.

9. JURISDICTION AND WAIVER: In the case of any dispute, this offer of employment
shall be interpreted under 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.

10. ORIENTATION: On your first day of employment, please see Human Resources for
benefits orientation and enrollment at 9:30am.

We are very enthusiastic about the prospect of your joining us as a Synta
Pharmaceuticals employee. Please indicate your acceptance of the foregoing by
signing one enclosed copy of this letter and returning it to Human Resources by
______, 2004. After that date, this offer will lapse.

                                       A-2
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Sincerely,

  /s/ SAFI BAHCALL
-----------------------
Safi Bahcall
President and CEO
SYNTA PHARMACEUTICALS CORP.

Agreed to and accepted:

Name: /s/ STEPHEN M. GANSLER                Date: January 3, 2005
      -----------------------                     ---------------

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                                                                       EXHIBIT A

                           Synta Pharmaceuticals Corp.
                               45 Hartwell Avenue
                               Lexington, MA 02421

December 20, 2004

Stephen Gansler
[ADDRESS]

Dear Stephen:

     This letter is to confirm our understanding with respect to (i) your
agreement not to compete with 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 COMPETITION AND 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 will devote your full time and efforts to the
business of the Company and, during the period of your employment with the
Company (the "Term") and for a period of twelve (12) months following
termination of your employment (whether such termination is voluntary or
involuntary), shall not participate, directly or indirectly, in any capacity, in
any business which is competitive with the Company without the prior written
consent of the Company. You acknowledge and agree that a business will be deemed
competitive with the Company if it conducts research, performs any of the
services or manufactures or sells any of the products provided or offered by the
Company or if it performs any other services and/or engages in the production,
manufacture, distribution or sale of any product similar to services performed
or products produced, manufactured, distributed or sold by the Company within
the Field of Interest (as defined below) at any time during the period of your
employment with the Company.

                                       A-4
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                    (iii)  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 Term and for a period of twelve
(12) months following termination of your employment, 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 within 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) FIELD OF INTEREST. As used herein, the term "Field of Interest"
means the research of, and/or the development, manufacture and sale of, any
therapeutic or diagnostic product that is developed, manufactured or sold by the
Company at any time during the Term, as documented in the bi-weekly scientific
project reports or other scientific planning documents of the company (the
"Scientific Reports") prepared by the Company during the Term. You hereby
acknowledge and agree that the Field of Interest shall be assessed for purposes
of this Agreement as of the date on which your employment with the Company
terminates, which assessment shall include, without limitation, a review of the
applicable Scientific Reports.

            (d) REASONABLENESS OF RESTRICTIONS. You further acknowledge and
agree that (i) the activities which are prohibited by this Section 1 are narrow
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.

            (e) 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.

                                       A-5
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     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.

            (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

                                       A-6
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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 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.

                                       A-7
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     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
of such injunction or 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.

            (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

                                       A-8
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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.

            (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.

                                       A-9
<Page>

            (e) ASSIGNMENT. The Company may 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 party 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.

            (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

                                      A-10
<Page>

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.

     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
                                          President and CEO

Agreed to and accepted:

/s/ STEPHEN M. GANSLER
----------------------
Name:

       [ADDRESS]
------------------------------------

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

Date:  January 3, 2005
     -------------------------------

                                      A-11

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