Document:

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                                                                  Exhibit 10.24

                           Synta Pharmaceuticals Corp.
                               45 Hartwell Avenue
                               Lexington, MA 02421

April 18, 2005

Safi R. Bahcall, Ph.D.
[ADDRESS]

Dear Safi:

This letter agreement is to confirm our understanding with you with respect to
your employment as President and Chief Executive Officer of Synta
Pharmaceuticals Corp. (hereinafter "Synta Pharmaceuticals" or the "Company"),
reporting directly to the Board of Directors of the Company (the "Board").

1. EFFECTIVE DATE: The effective date of this agreement is the date that you
accept the terms hereof as set forth on the signature page hereto.

2. BOARD MEMBERSHIP: While you continue to serve as President and Chief
Executive Officer, the Board also agrees to nominate you for election as a
director at each annual meeting of stockholders immediately preceding which your
then current term as a director expires.

3. COMPENSATION: Your initial base salary will be $340,000 annually (the "Base
Salary"); payable at a semi-monthly rate of approximately $14,167 (or otherwise
in accordance with the Company's payroll practices as in effect from time to
time), from which all applicable taxes and other customary employment-related
deductions will be taken. The Base Salary may be subject to adjustment from time
to time in the discretion of the Board or the Compensation Committee thereof.

For each fiscal year of the Company during the term of this agreement, the
Board, or the Compensation Committee thereof, may, in its discretion, grant to
you an option to purchase shares of the Company's common stock (the "Common
Stock") under the Company's 2001 Stock Plan (the "Plan"), or any successor plan
then in effect. The exercise price for any such option will be the fair market
value per share of the Common Stock on the date of grant, and the other terms
and conditions of such option will be as set forth in the Plan and in a written
stock option agreement between you and the Company, evidencing such option. Each
option will be an incentive stock option to the extent permissible under
applicable law.

You will be eligible to receive annual performance based bonuses. Such bonus, if
any, will be granted at the discretion of the Board, or the Compensation
Committee thereof.

4. BENEFITS: 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

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limitations applicable to other executive officers of the Company. All benefits
may be changed or modified from time to time at the Company's sole discretion.

5. TERMINATION AND SEVERANCE: Upon termination of your employment for any
reason, you shall receive payment of (a) your Base Salary, as then in effect,
through the date of termination of employment (the "Termination Date"), and (b)
all accrued vacation, expense reimbursements and any other benefits (other than
severance benefits, except as provided below) due to you through the Termination
Date in accordance with established Company plans and policies or applicable
law. In addition, in the event the Company terminates your employment without
cause, you will be entitled to continue to receive your then-current Base Salary
for a period equal to twenty-four (24) months, payable in accordance with the
Company's normal payroll practices.

For purposes of this agreement, termination "without cause" shall include, but
not be limited to, your resignation following a significant material diminution
in your title, salary, duties or responsibilities by the Company. 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.

On the Termination Date, and as a condition to the receipt of the aforementioned
severance payments, you shall execute and deliver to the Company your written
release of the Company and its officers, directors, employees, security holders,
agents, and representatives from any and all claims and causes of action against
the Company arising in connection with your employment with the Company.

6. EMPLOYMENT PERIOD: Subject to the provision of severance payments as set
forth in Section 5, 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.

7. CONTINGENCIES: This agreement and your employment with the Company is
contingent upon your execution of the standard form of Non-Competition,
Confidentiality and Inventions Agreement (a copy of which is attached hereto as
EXHIBIT A).

8. JURISDICTION AND WAIVER: In the case of any dispute, this agreement shall be
interpreted under the laws of the Commonwealth of Massachusetts. By accepting
the terms of this agreement, 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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9. INSURANCE. The Company, in its sole discretion, may apply for and purchase
key person life insurance on your life in an amount determined by the Company
with the Company as beneficiary and one or more other policies of insurance
insuring your life. You will submit to any medical or other examinations and
execute and deliver any applications or other instruments in writing that are
reasonably necessary to effectuate such insurance.

10. REPRESENTATIONS. You hereby represent and warrant to the Company that you
understand this agreement, that you enter into this agreement voluntarily and
that your employment under this agreement will not conflict with any legal duty
owed by you to any other party, or with any agreement to which you are a party
or by which you are bound, including, without limitation, any non-competition or
non-solicitation provision contained in any such agreement. You will indemnify
and hold harmless the Company and its officers, directors, employees, security
holders, agents and representatives against loss, damage, liability or expense
arising from any claim based upon circumstances alleged to be inconsistent with
such representation and warranty.

11. ENTIRE AGREEMENT. This agreement, together with the other agreements
specifically referred to herein, 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 will affect, or
be used to interpret, change or restrict, the express terms and provisions of
this agreement.

12. 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 or to any Company Affiliate. You may not assign your rights and
obligations under this agreement without the prior written consent of the
Company, and any such attempted assignment by you without the prior written
consent of the Company will be void.

Sincerely,

SYNTA PHARMACEUTICALS CORP.

/s/ Keith R. Gollust
----------------------------------
Keith R. Gollust
Chairman of the Board of Directors

Agreed to and accepted:

Name: /s/ Safi R. Bahcall                     Date: April 18, 2005
      ----------------------------                  --------------
      Safi R. Bahcall, Ph.D.

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                                                                     EXHIBIT A

                           Synta Pharmaceuticals Corp.
                               45 Hartwell Avenue
                               Lexington, MA 02421

April 18, 2005

Safi R. Bahcall, Ph.D.
[ADDRESS]

Dear Safi:

         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 twenty-four (24) 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 that may be purchased in lieu
of purchasing services performed or products produced,

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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.

                     (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
twenty-four (24) 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, 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.

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             (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.

         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 chairman of the
board 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

             (c) SURVIVAL OF ACKNOWLEDGMENTS AND AGREEMENTS. Except as expressly
set forth hereunder, your acknowledgments and agreements set forth in this
Section 2 shall survive the termination of your employment with the Company.

         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

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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. ss. 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. ss. 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

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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 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.

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         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: Chairman of the Board

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.

             (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

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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 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

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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/ Keith R. Gollust
                                     ------------------------------------------
                                     Keith R. Gollust
                                     Chairman of the Board of Directors

Agreed to and accepted:

/s/ Safi R. Bahcall
---------------------------------
Name: Safi R. Bahcall, Ph.D.

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

[ADDRESS]
---------------------------------
Address:

Date: April 18, 2005
      --------------

                                       A-8<Page>

                                                                 Exhibit 10.25

                    [SYNTA PHARMACEUTICALS CORP. LETTERHEAD]

                                                April 18, 2005

Lan Bo Chen, Ph.D.
[ADDRESS]

         Re:  CONSULTING AGREEMENT
              --------------------

Dear Lan Bo:

         This letter is to confirm our understanding with respect to (i) your
continued service to Synta Pharmaceuticals Corp. (the "Company") as a
consultant, (ii) your agreement not to compete with the Company, or any present
or future parent, subsidiary or affiliate of the Company (each, a "Company
Affiliate" and collectively with the Company, the "Company Group"), (iii) your
agreement to protect and preserve information and property which is confidential
and proprietary to the Company Group and (iv) your agreement with respect to the
ownership of inventions, ideas, copyrights and patents which may be used in the
business of the Company Group (the terms and conditions agreed to in this letter
are hereinafter referred to as the "Agreement"). In consideration of 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. SERVICES.

         (a) You are hereby engaged by the Company as an independent contractor,
and not as an employee, to provide the following services to the Company (the
"Consulting Services"):

             (i) to serve as Chairman and/or a member of the Company's
Scientific Advisory Board;

             (ii) to carry out various projects which the Chief Executive
Officer or the Board of Directors of the Company may request and assign to you
from time to time; and

             (iii) to bring to the attention of the Company from time to time
information about inventions, scientific developments, research programs,
available chemical compounds or biological entities, ideas, formulations,
business development opportunities, potential employees, scientific contacts and
the like, that may be of interest to the Company in the pursuit of its business
as currently conducted or then anticipated or planned (hereinafter, "Business
Opportunities")

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         (b) You shall maintain sole control and discretion as to the exact
manner of the performance of the Consulting Services, subject to the following:

             (i) The Company and you acknowledge that you currently have, and
may continue to have, a consulting arrangement with Caxton Health Holdings LLC
("CHH"), pursuant to which you will provide services to CHH that include
identifying potential technologies and related opportunities for investment and
development by CHH ("Investment Opportunities"). The Company and you further
acknowledge that, upon occasion, an Investment Opportunity that you identify may
also constitute a Business Opportunity for the Company. You hereby agree that,
if you identify or become aware of any Investment Opportunity that also
constitutes a Business Opportunity for the Company, you will endeavor first to
bring such Business Opportunity to the attention of the Company, by
communicating such opportunity to the Company's Chief Executive Officer,
providing the Company with information reasonably available to you about the
Business Opportunity, and assisting the Company, to the extent requested, in
evaluating the Business Opportunity. Such actions shall hereinafter be referred
to as providing the Company with a "Right of First Evaluation". If, however, in
any instance you believe that it would violate your obligations to CHH if you
were to provide the Company a Right of First Evaluation with respect to a
Business Opportunity that also constitutes and Investment Opportunity, you agree
to promptly notify the Company of such circumstances.

             (ii) You shall satisfy all reasonable deadlines, specifications and
requirements set forth by the Company (in consultation with you).

             (iii) In performing the Consulting Services under this Agreement,
you will (a) use diligent efforts and professional skills and judgment, (b)
perform professional services in accordance with recognized industry standards;
and (c) comply with the Company's policies applicable to consultants, members of
the Scientific Advisory Board, and other personnel and Company representatives,
as in effect from time to time. You also shall comply with all federal, state
and local employment, labor and taxation laws, regulations and rules relating to
the Consulting Services to be performed by you.

         2. TERM. This Agreement shall continue until such time as it is
terminated by you or by the Company (for any reason or no reason at all), in
either case by written notice at least fifteen (15) days in advance (the
"Consulting Term").

         3. COMPENSATION.

                  (a) CONSULTING FEES. While you continue to provide Consulting
         Services to the Company, you will be paid a consulting fee of
         Twenty-Five Thousand Dollars ($25,000.00) per month (the "Consulting
         Fee"). Consulting Fees will be paid to you no later than fifteen (15)
         days following the last day of the month during which such Consulting
         Fees are earned.

                                       2
<Page>

                  (b) REIMBURSEMENT OF EXPENSES. Upon presentation of
         documentation of such expenses reasonably satisfactory to the Company,
         the Company will reimburse you for all ordinary and reasonable
         out-of-pocket business expenses that are reasonably incurred by you in
         furtherance of the Company's business in accordance with the Company's
         policies with respect thereto as in effect from time to time.

         4. TERMINATION. Upon termination of your service to the Company for any
reason or no reason, you shall receive payment of (a) your accrued, but unpaid,
Consulting Fees through the date of termination of your service to the Company
(the "Termination Date"), and (b) all expense reimbursements due to you through
the Termination Date in accordance with established Company policies or
applicable law.

         5. PROHIBITED COMPETITION.

                  (a) CERTAIN ACKNOWLEDGEMENTS AND AGREEMENTS.

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

                           (ii) You acknowledge that a business will be deemed
                  "competitive" with the Company Group if, at the time you enter
                  into a relationship with such business or, at any time within
                  two years thereafter while you have a relationship with such
                  business, it engages in, or is actively planning or
                  developing, any service and/or the research, development or
                  commercialization of any product that is the functional
                  equivalent of, or that has or will likely have the effect of
                  materially displacing sales of services or products which (A)
                  are performed, produced, manufactured, distributed, sold,
                  under research or active development or in active planning by
                  the Company Group at any time while you are providing
                  Consulting Services or (B) are expressly identified in writing
                  as the subject of your Consulting Services hereunder. If the
                  Company requests that you provide Consulting Services that you
                  advise the Company may be competitive with the activities of
                  another business with which you then have a relationship, the
                  Company may at its option (x) terminate the Consulting
                  Services and in connection therewith pay to you any fees and
                  reimbursable expenses due for all Consulting Services rendered
                  through the date of termination, or (y) require you to
                  terminate your services with the competitive business or
                  entity.

                           (iii) You further acknowledge that, while you perform
                  Consulting Services hereunder, the Company Group will furnish,
                  disclose or make available to you Confidential Information (as
                  defined below) related to the business of the Company Group
                  and that the Company Group. You also acknowledge that such
                  Confidential Information has been developed and will be
                  developed by the Company Group through the expenditure by the
                  Company Group of substantial time, effort and money and that
                  all such Confidential Information could be used by you to
                  compete with the Company Group. Further, while you perform
                  Consulting Services hereunder, you will be introduced to
                  customers and others with important relationships to the
                  Company Group. You acknowledge that any

                                       3
<Page>

                  and all "goodwill" created through such introductions belongs
                  exclusively to the Company Group, including, without
                  limitation, any goodwill created as a result of direct or
                  indirect contacts or relationships between yourself and any
                  customers or other third parties doing business with the
                  Company Group.

                           (iv) For purposes of this Agreement, "Confidential
                  Information" means confidential and proprietary information of
                  the Company Group, whether in written, oral, electronic or
                  other form, including but not limited to, information and
                  facts concerning business plans; current or potential
                  customers, suppliers, licensors, licensees, partners,
                  investors, affiliates or others; training methods and
                  materials; financial information; sales prospects; client
                  lists; inventions; or any other scientific, technical or trade
                  secrets of the Company Group or of any third party provided to
                  you or the Company Group under a condition of confidentiality;
                  provided that Confidential Information will not include
                  information that is in the public domain other than through
                  any fault or act by you. The term "trade secrets," as used in
                  this Agreement, will be given its broadest possible
                  interpretation under the law of the Commonwealth of
                  Massachusetts and will include, without limitation, anything
                  tangible or intangible or electronically kept or stored, which
                  constitutes, represents, evidences or records secret,
                  scientific, technical, merchandising, production or management
                  information, or any design, process, procedure, formula,
                  invention, improvement or other confidential or proprietary
                  information or documents.

                  (b) NON-COMPETITION; NON-SOLICITATION. While you perform
         Consulting Services hereunder and for a period of one year following
         the termination of your service to the Company Group hereunder for any
         reason or for no reason, you will not, without the prior written
         consent of the Company:

                           (i) For yourself or on behalf of any other person or
                  entity, directly or indirectly, either as principal, partner,
                  stockholder, officer, director, member, employee, consultant,
                  agent, representative or in any other capacity, own, manage,
                  operate or control, or be concerned, connected or employed by,
                  or otherwise associate in any manner with, engage in or have a
                  financial interest in, any business which is competitive with
                  the business of the Company Group (each, a "Restricted
                  Activity") anywhere in the world, except that (A) nothing
                  contained herein will preclude you from purchasing or owning
                  securities of any such business if such securities are
                  publicly traded, and provided that your holdings do not exceed
                  one percent of the issued and outstanding securities of any
                  class of securities of such business and (B) nothing contained
                  herein will prohibit you from engaging in a Restricted
                  Activity for or with respect to any subsidiary, division or
                  affiliate or unit (each, a "Unit") of an entity if that Unit
                  is not engaged in any business which is competitive with the
                  business of the Company Group, irrespective of whether some
                  other Unit of such entity engages in such competition (as long
                  as you do not engage in a Restricted Activity for such other
                  Unit); or

                           (ii) Either individually or on behalf of or through
                  any third party, directly or indirectly, solicit, divert or

                                       4
<Page>

                  appropriate or attempt to solicit, divert or appropriate, for
                  the purpose of competing with the Company Group, any
                  customers, licensors, licensees, collaborative partners, or
                  other patrons of the Company Group, or any such person or
                  entity with respect to which the Company Group has developed
                  or made a presentation (or similar communication) with a view
                  to developing a business relationship;

                           (iii) Either individually or on behalf of or through
                  any third party, directly or indirectly, (A) solicit, entice
                  or persuade or attempt to solicit, entice or persuade any
                  employee of or consultant to the Company Group to leave the
                  service of the Company Group for any reason, or (B) employ,
                  cause to be employed, or solicit the employment of, any
                  employee of or consultant to the Company Group while any such
                  person is providing services to the Company Group or within
                  six months after any such person has ceased providing services
                  to the Company Group; or

                           (iv) Either individually or on behalf of or through
                  any third party, directly or indirectly, interfere with, or
                  attempt to interfere with, the relations between the Company
                  Group and any licensor, licensee, collaborative partner,
                  customer, vendor or supplier to the Company Group.

                  (c) REASONABLENESS OF RESTRICTIONS. You further recognize and
         acknowledge that (i) the types of employment which are prohibited by
         this Section 5 are narrow and reasonable in relation to the skills
         which represent your principal salable asset both to the Company Group
         and to others and (ii) the time period and the geographical scope of
         the provisions of this Section 5 is reasonable, legitimate and fair to
         you in light of the Company Group's need to effectively pursue its
         business plan and objectives and in light of the limited restrictions
         on the type of activities prohibited herein compared to the types of
         activities for which you are qualified to earn your livelihood.

                  (d) SURVIVAL OF ACKNOWLEDGEMENTS AND AGREEMENTS. Your
         acknowledgements and agreements set forth in this Section 5 will
         survive the termination of this Agreement and the termination of your
         services hereunder for any reason or for no reason.

                  (e) ACKNOWLEDGEMENT REGARDING CHH AFFILIATION. The Company
         acknowledges that your affiliation with CHH is not in violation of this
         Agreement, provided that you (i) maintain the confidentiality of all
         Confidential Information as required by this Agreement, (ii) may not
         engage in a competitive Restricted Activity, individually or in concert
         with others, in connection with your affiliation with CHH, and (iii)
         abide by your obligations set out in Section 1(b)(i) hereof.

         6. PROTECTED INFORMATION. You will at all times, both during the period
while you perform Consulting Services hereunder and after the termination of
this Agreement and the termination of your service to the Company hereunder for
any reason or for no reason, maintain in confidence and will not, without the
prior written consent of the Company Group, use, except as required in the
course of performance of your duties for the Company Group or by court order,
disclose or give to others any Confidential Information. In the event you are
questioned

                                       5
<Page>

by anyone not employed by the Company or by an employee of or a consultant to
the Company not authorized to receive Confidential Information, in regard to any
Confidential Information, or concerning any fact or circumstance relating
thereto, you will promptly notify the Company. Upon the termination of your
service to the Company hereunder for any reason or for no reason, or if the
Company Group otherwise requests, you will return to the Company Group all
tangible Confidential Information and copies thereof (regardless how such
Confidential Information or copies are maintained). The terms of this Section 6
are in addition to, and not in lieu of, any statutory or other contractual or
legal obligation that you may have relating to the protection of the Company
Group's Confidential Information. The terms of this Section 6 will survive
indefinitely any termination of this Agreement and/or any termination of your
service to the Company Group hereunder for any reason or for no reason.

         7. OWNERSHIP OF IDEAS, COPYRIGHTS AND PATENTS.

                  (a) PROPERTY OF THE COMPANY. 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 in any form known or not yet known throughout the world
         (collectively, the "Inventions") which may be used or useful in the
         current or planned business of the Company Group or which in any way
         relates to such business, whether patentable, copyrightable or not,
         which you may conceive, reduce to practice or develop arising out of or
         in connection with your performance of Consulting Services hereunder
         (and, if based on or related to any Confidential Information, within
         one year after termination of such service to the Company Group for any
         reason or for no reason), alone or in conjunction with another or
         others, whether during or out of regular business hours, whether or not
         on the Company Group's premises or with the use of its equipment, and
         whether at the request or upon the suggestion of the Company Group or
         otherwise, will be the sole and exclusive property of the Company
         Group, and you will not publish any of the Inventions without the prior
         written consent of the Company Group. Without limiting the foregoing,
         you also acknowledge that all original works of authorship which are
         made by you (solely or jointly with others) within the scope of your
         services to the Company or which relate to the business of the Company
         Group and which are protectable by copyright are "works made for hire"
         pursuant to the United States Copyright Act (17 U.S.C. Section 101).
         You hereby assign to the Company Group all of your right, title and
         interest in and to all of the foregoing. You further represent that, to
         the best of your knowledge and belief, none of the Inventions will
         violate or infringe upon any right, patent, copyright, trademark or
         right of privacy, or constitute libel or slander against or violate any
         other rights of any person, firm or corporation, and that you will not
         knowingly create any Invention which causes any such violation.

                  (b) COOPERATION. At any time during your service to the
         Company hereunder or after the termination of your service to the
         Company hereunder for any reason or for no reason, you will cooperate
         fully with the Company Group and its attorneys and agents in the
         preparation and filing of all papers and other documents as may be
         required to perfect the Company Group's rights in and to any of such
         Inventions, including, but not limited to, joining in any proceeding to
         obtain letters patent, copyrights, trademarks or other legal rights
         with respect to any such Inventions in the United States and in any and

                                       6
<Page>

         all other countries, provided that the Company Group will bear the
         expense of such proceedings and, if after the termination of your
         services to the Company Group hereunder, shall compensate you at your
         then current per diem rate for your time spent providing such
         cooperation and assistance, as evidenced by time records in reasonable
         detail submitted to the Company. Any patent or other legal right so
         issued to you personally will be assigned by you to the Company Group
         without charge by you.

                  (c) LICENSING AND USE OF INVENTIONS. With respect to any
         Inventions, whenever created, which you have not prepared or originated
         in the performance of your services to the Company Group, but which you
         provide to the Company Group or incorporate in any Company Group
         product or system, you hereby grant to the Company Group a
         royalty-free, fully paid-up, non-exclusive, perpetual and irrevocable
         license throughout the world to use, modify, create derivative works
         from, disclose, publish, translate, reproduce, deliver, perform,
         dispose of, and to authorize others so to do, all such Inventions. You
         will not include in any Inventions you deliver to the Company Group or
         use on its behalf, without the prior written approval of the Company
         Group, any material which is or will be patented, copyrighted or
         trademarked by you or others unless you provide the Company Group with
         the written permission of the holder of any patent, copyright or
         trademark owner for the Company Group to use such material in a manner
         consistent with then-current Company Group policy.

                  (d) PRIOR INVENTIONS. Listed on EXHIBIT 7(d) to this Agreement
         are any and all Inventions in which you claim or intend to claim any
         right, title and interest (collectively, "Prior Inventions"),
         including, without limitation, patent, copyright and trademark
         interests, which to the best of your knowledge will be or may be
         delivered to the Company Group in the course of your service to the
         Company, or incorporated into any Company Group product or system. You
         acknowledge that your obligation to disclose such information is
         ongoing while you perform Consulting Services hereunder.

         8. DISCLOSURE TO FUTURE EMPLOYERS. You will provide, and the Company,
in its discretion, may similarly provide, a copy of the covenants contained in
Sections 5, 6 and 7 of this Agreement to any business or enterprise which you
may, directly or indirectly, own, manage, operate, finance, join, control or in
which you may 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.

         9. RECORDS. Upon termination of your services to the Company Group
hereunder for any reason or for no reason and at any other time requested by the
Company Group, you will deliver to the Company Group any property of the Company
Group which may be in your possession, including products, materials, memoranda,
notes, records, reports, or other documents or photocopies of the same
(regardless of how they are maintained, including whether or not they are in
electronic form).

         10. INSURANCE. While you are performing Consulting Services to the
Company Group hereunder, you shall be solely responsible for securing, paying
for and maintaining any insurances, licenses and/or permits necessary to perform
any of the Consulting Services required under this Agreement, including, but not
limited to, general liability insurance (bodily injury and

                                       7
<Page>

property damage), professional liability insurance and workers' compensation
insurance. Upon request, you will furnish to the Company all applicable
certificates of insurance contemplated by this section.

         11. INDEPENDENT CONTRACTOR STATUS. You and the Company agree that your
Consulting Services are made available to the Company Group on the basis that
you will retain your individual professional status and that your relationship
with the Company Group is that of an independent contractor and not that of an
employee. You acknowledge will not be eligible for any employee benefits, nor
will the Company make deductions from its fees to you for taxes, insurance,
bonds or any other subscription of any kind. The Company will record payments to
you on, and provide to you, an Internal Revenue Service Form 1099, and the
Company will not withhold any employment taxes on your behalf. Payment of all
federal, state and local income, employment and other taxes (including
unemployment insurance, social security taxes and federal, state and local
withholding taxes) are your sole responsibility. You will indemnify and hold
harmless the Company Group and its officers, directors, security holders,
partners, members, employees, agents and representatives against loss, damage,
liability or expense arising from any claim based on your failure to pay any or
all taxes due from you to any applicable taxing authorities.

         12. REPRESENTATIONS AND ACKNOWLEDGEMENTS. You hereby represent and
warrant to the Company that you understand this Agreement, that you enter into
this Agreement voluntarily and that your service to the Company Group under this
Agreement will not conflict with any legal duty owed by you to any other party,
or with any agreement to which you are a party or by which you are bound,
including, without limitation, any non-competition or non-solicitation provision
contained in any such agreement. You will indemnify and hold harmless the
Company Group and its officers, directors, security holders, partners, members,
employees, agents and representatives against loss, damage, liability or expense
arising from any claim based upon circumstances alleged to be inconsistent with
such representation and warranty.

         13. GENERAL.

                  (a) NOTICES. All notices, requests, consents and other
         communications hereunder which are required to be provided, or which
         the sender elects to provide, in writing, will be addressed to the
         receiving party's address set forth above or to such other address as a
         party may designate by notice hereunder, and will be either (i)
         delivered by hand, (ii) sent by overnight courier, or (iii) sent by
         registered or certified mail, return receipt requested, postage
         prepaid. All notices, requests, consents and other communications
         hereunder will be deemed to have been given either (i) if by hand, at
         the time of the delivery thereof to the receiving party, (ii) if sent
         by overnight courier, on the next business day following the day such
         notice is delivered to the courier service, or (iii) if sent by
         registered or certified mail, on the fifth business day following the
         day such mailing is made.

                  (b) ENTIRE AGREEMENT.

                     (i) It is hereby acknowledged that the Company an you have
         entered into an Agreement and Release, dated January 14, 2005 (the
         "Agreement and Release"), arising out of your services to the Company,
         its Affiliates and Predecessors (as such terms

                                       8
<Page>

         are defined therein) during the period prior to the date hereof. The
         Company and you hereby acknowledge and agree that certain provisions of
         the Agreement and Release (E.G., the confidentiality, non-competition,
         non-solicitation and inventions assignment provisions) are
         substantially the same as corresponding provisions of this Agreement,
         except that such provisions of the Agreement and Release are intended
         to be effective and apply to matters arising out of the period of your
         services to the Company, its Affiliates and Predecessors prior to the
         date of this Agreement, and the corresponding provisions of this
         Agreement are intended to be effective and apply to matters arising out
         of the period commencing on the date hereof. The parties agree that
         this Agreement shall not be deemed to supersede the Agreement and
         Release except if, and to the extent that, (A) a provision of this
         Agreement contains substantially equivalent terms to a corresponding
         provision of the Agreement and Release, and (B) the application of such
         provision of this Agreement alone (I.E., without continued
         effectiveness and application of the corresponding provision of the
         Agreement and Release) will provide the same protection to the Company
         Group as would be the case if both the provision in this Agreement and
         the corresponding provision in the Agreement and Release continued to
         be effective and apply. All other terms and provisions of the Agreement
         and Release shall continue in full force and effect.

                     (ii) Subject to subparagraph (i) above, this Agreement,
         together with the other agreements specifically referred to herein,
         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 will
         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 will be
         deemed to be or will 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 will be effective only in the specific
         instance and for the purpose for which it was given, and will not
         constitute a continuing waiver or consent.

                  (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, or to any
         Company Affiliate. You may not assign your rights and obligations under
         this Agreement without the prior written consent of the Company, and
         any such attempted assignment by you without the prior written consent
         of the Company will be void.

                  (f) BENEFIT. All statements, representations, warranties,
         covenants and agreements in this Agreement will be binding on the
         parties hereto and will inure to the

                                       9
<Page>

         benefit of the respective successors and permitted assigns of each
         party hereto. Nothing in this Agreement will be construed to create any
         rights or obligations except between the Company and you, except for
         your obligations to the Company Group as set forth herein, and no
         person or entity (except for a Company Affiliate as set forth herein)
         will be regarded as a third-party beneficiary of this Agreement.

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

                  (h) JURISDICTION, VENUE AND SERVICE OF PROCESS. Any legal
         action or proceeding with respect to this Agreement that is not subject
         to arbitration pursuant to Section 13(i) below will be brought in the
         courts of the Commonwealth of Massachusetts or of the United States of
         America for the District of Massachusetts. 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 exclusive
         jurisdiction of the aforesaid courts.

                  (i) ARBITRATION. Any controversy, dispute or claim arising out
         of or in connection with this Agreement, other than a controversy,
         dispute or claim arising under Section 5, 6 or 7 hereof, will be
         settled by final and binding arbitration to be conducted in Boston,
         Massachusetts pursuant to the national rules for the resolution of
         employment disputes of the American Arbitration Association then in
         effect. The decision or award in any such arbitration will be final and
         binding upon the parties and judgment upon such decision or award may
         be entered in any court of competent jurisdiction or application may be
         made to any such court for judicial acceptance of such decision or
         award and an order of enforcement. In the event that any procedural
         matter is not covered by the aforesaid rules, the procedural law of
         Massachusetts will govern. Any disagreement as to whether a particular
         dispute is arbitrable under this Agreement shall itself be subject to
         arbitration in accordance with the procedures set forth herein.

                  (j) WAIVER OF JURY TRIAL. ANY ACTION, DEMAND, CLAIM OR
         COUNTERCLAIM ARISING UNDER OR RELATING TO THIS AGREEMENT THAT IS NOT
         SUBJECT TO ARBITRATION PURSUANT TO SECTION 13(i) ABOVE WILL BE RESOLVED
         BY A JUDGE ALONE AND EACH OF YOU AND THE COMPANY WAIVE ANY RIGHT TO A
         JURY TRIAL THEREOF.

                  (k) SEVERABILITY. The parties intend this Agreement to be
         enforced as written. However, (i) if any portion or provision of this
         Agreement is to any extent 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, will not be affected thereby, and each portion and
         provision of this Agreement will 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, the geographic area covered thereby, or other aspect or
         scope of such provision, the court making such determination will have
         the power to reduce the duration, geographic area of such provision, or
         other aspect or scope of such

                                       10
<Page>

         provision, and/or to delete specific words and phrases
         ("blue-penciling"), and in its reduced or blue-penciled form, such
         provision will then be enforceable and will be enforced.

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

                  (m) INJUNCTIVE RELIEF. You hereby expressly acknowledge that
         any breach or threatened breach of any of the terms and/or conditions
         set forth in Section 5, 6 or 7 of this Agreement will result in
         substantial, continuing and irreparable injury to the Company Group.
         Therefore, in addition to any other remedy that may be available to the
         Company Group, the Company Group will be entitled to injunctive or
         other equitable relief by a court of appropriate jurisdiction in the
         event of any breach or threatened breach of the terms of Section 5, 6
         or 7 of this Agreement. The period during which the covenants contained
         in Section 5 will apply will be extended by any periods during which
         you are found by a court to have been in violation of such covenants.

                  (n) 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,
         will 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,
         will 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 will 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 will 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.

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

                  (p) OPPORTUNITY TO REVIEW. You hereby acknowledge that you
         have had adequate opportunity to review these terms and conditions and
         to reflect upon and consider the terms and conditions of this
         Agreement, and that you have had the opportunity to consult with
         counsel of your own choosing regarding such terms. You further
         acknowledge that you fully understand the terms of this Agreement and
         have voluntarily executed this Agreement.

                                       11
<Page>

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

                                        Very truly yours,

                                        SYNTA PHARMACEUTICALS CORP.

                                        By: /s/ Safi R. Bahcall
                                            -----------------------------------
                                            Safi R. Bahcall, Ph.D.
                                            President and Chief Executive
                                            Officer

Accepted and Approved:

/s/ Lan Bo Chen                        April 18, 2005
----------------------------------     ----------------------------------
Lan Bo Chen, Ph.D.                     Date

                                       12

<Page>

                                  EXHIBIT 7(d)

                                PRIOR INVENTIONS

                                       13

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