Exhibit 10.7.1  FIRST AMENDMENT TO LEASE  FIRST AMENDMENT TO LEASE dated
as of this 7th day of September, 2007 by and between MORTIMER B. ZUCKERMAN AND
EDWARD H. LINDE, Trustees of 91 Hartwell Avenue Trust under Declaration of
Trust dated September 28, 1981 filed with the Middlesex South Registry as
Document No. 616455 as amended by instruments dated December 10, 1984
and April 17, 1991 respectively filed with said Registry District as
Document Nos. 675674 and 844541 but not individually (Landlord) and SYNTA
PHARMACEUTICALS, INC., a Delaware corporation (Tenant).  RECITALS  A.            Landlord and Tenant are parties to that certain Lease
Agreement dated as of January 13, 2005 (the Lease), in connection with
certain premises located at 91 Hartwell Avenue, Lexington, Massachusetts (the Building),
consisting of 13,764 square feet of rentable floor area on the second (2nd)
floor and 8,068 square feet of rentable floor area on the third (3rd)
floor collectively (the Rentable Floor Area of the Premises in the Building
(referred to in the Lease as the Premises or Tenants Space).  B.            Landlord and Tenant now desire to extend the Term of the
Lease for one (1) period of eighteen (18) months upon all of the same
terms and conditions set forth in the Lease except for those terms and
conditions amended herein (the First Amendment).  C.            Capitalized terms used herein and not otherwise defined
herein shall have the meaning set forth in the Lease.  AGREEMENT  NOW THEREFORE, in consideration
of the mutual promises and covenants contained herein and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, Landlord and Tenant hereby agree as follows:  1.             The current Term of the Lease is scheduled to expire on February 29,
2008.  Landlord and Tenant agree that the
Lease is hereby extended for one (1) period of eighteen (18) months
commencing on March 1, 2008 and expiring on August 31, 2009 (First
Extended Term) unless sooner terminated or extended in accordance with the
provisions of the Lease and this First Amendment.  2.             Landlord and Tenant acknowledge and agree that the
extension option contained in both the Reference Data Sheet and Section 2.4.1
of the Lease shall be deleted in its entirety, and Tenant shall have no further
option to extend the Lease Term upon the expiration of the First Extended Term,
except as provided in Section 4 below.    1


3.             (A)          For
the period prior to the First Extended Term, Annual Fixed Rent for the Premises
shall continue to be payable as set forth in the Lease.  (B)           During the First Extended Term,
Annual Fixed Rent shall be paid by Tenant at the annual rate of $502,136.00
(being the product of (i) $23.00 and (ii) the Rentable Floor Area of
the Premises (being 21,832 square feet)).  4.             (A)          For
the purposes of computing Tenants payments for Landlords Operating Expenses,
pursuant to Section 2.6 of the Lease, for the portion of the Lease Term on
and after March 1, 2008, the definition of Base Operating Expenses
contained in Section 2.6 of the Lease shall be deleted in its entirety and
replaced with the following:  BASE
  OPERATING
  EXPENSES:
  
  Landlords
  Operating Expenses (as hereinafter defined in
  Section 2.6) for calendar year 2008, being January 1, 2008
  through December 31,2008.  For the portion of the Lease
Term prior to March 1, 2008, such definition shall remain unchanged.  (B)           For the purposes of computing Tenants
payments for Landlords Tax Expenses, pursuant to Section 2.7 of the
Lease, for the portion of the Lease Term on and after March 1, 2008 the
definition of Base Taxes contained in Section 2.7 of the Lease shall be
deleted in its entirety and replaced with the following:  BASE
  TAXES:
  
  Landlords
  Tax Expenses (as hereinafter defined in Section
  2.7) for fiscal tax year 2008, being July 1, 2007 through June
  30, 2008.  For the portion of
the Lease Term prior to March 1, 2008, such definition shall remain
unchanged for such purposes.  5.             (A)          Tenant
shall have the right to extend the Lease Term upon all the same terms,
conditions, covenants and agreements contained in the Lease and this First
Amendment for one (1) period of fourteen (14) months commencing on September 1,
2009 and expiring on November 30, 2011, (Second Extended Term) on the
conditions, which conditions Landlord may waive by written notice to Tenant,
that at the time of exercise of the Second Extended Term (i) there exists
no Event of Default, (ii) the Lease is still in full force and effect, and
(iii) Tenant has neither assigned the Lease nor sublet any portion of the
Premises. Notwithstanding anything contained herein to the contrary, Landlord
has no obligation to make any additional payment to Tenant with respect to any
construction allowance or the like or to perform any work to the Premises as a
result of Tenant exercising its Second Extended Term option.  (B)           If Tenant desires to exercise its
right to the Second Extended Term, then Tenant shall give written notice to
Landlord, not earlier than November 30, 2008 nor later than   2


February 28,
2009.  Upon the giving of such written
notice, the Lease shall be extended for the Second Extended Term without the
necessity for the execution of any additional documents; and in such event all
references herein to the Lease, the Term of the Lease shall be construed as
referring to the Lease Term, as so extended, unless the context clearly
otherwise requires.  (C)           For
the Second Extended Term, Annual Fixed Rent shall be paid by Tenant at the
annual rate of $529,426.00 (being the product of (i) $24.25 and (ii) the
Rentable Floor Area of the Premises (being 21,832 square feet)) and Base
Operating Expenses and Base Taxes shall be calculated in accordance with Section 4
(B) contained herein.  6.             (A)          Tenant
warrants and represents that Tenant has not dealt with any broker in connection
with the consummation of this First Amendment except for Richard Barry Joyce &
Partners (the Broker); and in the event any claim is made against Landlord
relative to dealings by Tenant with brokers other than the Broker, Tenant shall
defend the claim against Landlord with counsel of Tenants selection first
approved by Landlord (which approval will not be unreasonably withheld) and
save harmless and indemnify Landlord on account of loss, cost or damage which
may arise by reason of such claim.   (B)           Landlord warrants and represents that
Landlord has not dealt with any broker in connection with the consummation of
this First Amendment except for the Broker; and in the event any claim is made
against Tenant relative to dealings by Landlord with brokers other than the
Broker, Landlord shall defend the claim against Tenant with counsel of Landlords
selection and save harmless and indemnify Tenant on account of loss, cost or
damage which may arise by reason of such claim.  7.             As an inducement to Landlord to enter into this First
Amendment, Tenant hereby represents and warrants that: (i) Tenant is not,
nor is it owned or controlled directly or indirectly by, any person, group,
entity or nation named on any list issued by the Office of Foreign Assets
Control of the United States Department of the Treasury (OFAC) pursuant to
Executive Order 13224 or any similar list or any law, order, rule or
regulation or any Executive Order of the President of the United States as a
terrorist, Specially Designated National and Blocked Person or other banned
or blocked person (any such person, group, entity or nation being hereinafter
referred to as a Prohibited Person); (ii) Tenant is not (nor is it
owned, controlled, directly or indirectly, by any person, group, entity or
nation which is) acting directly or indirectly for or on behalf of any
Prohibited Person; and (iii) from and after the effective date of the
above-referenced Executive Order, Tenant (and any person, group, or entity
which Tenant controls, directly or indirectly) has not conducted nor will
conduct business nor has engaged nor will engage in any transaction or dealing
with any Prohibited Person in violation of the U.S. Patriot Act or any OFAC rule or
regulation, including without limitation any assignment of the Lease or any
subletting of all or any portion of the Premises or the making or receiving of
any contribution of funds, goods or services to or for the benefit of a
Prohibited Person in violation of the U.S. Patriot Act or any OFAC rule or
regulation. In connection with the foregoing, it is expressly understood and
agreed that (x) any breach by Tenant of the foregoing representations and
warranties shall be deemed an immediate Event of Default by Tenant under Section 7.1
of the Lease (without the benefit of notice or grace) and shall be covered by
the indemnity provisions of   3


Section 5.7
of the Lease, and (y) the representations and warranties contained in this
subsection shall be continuing in nature and shall survive the expiration or
earlier termination of the Lease.  8.             Except as herein amended the Lease shall remain unchanged
and in full force and effect.  All
references to the Lease shall be deemed to be references to the Lease as
herein amended.         4


EXECUTED as a sealed instrument
as of the date and year first above written.  WITNESS:
  LANDLORD:91 HARTWELL AVENUE
  TRUSTBy:
  Boston Properties
  Limited Partnership,its sole beneficiaryBy:
  Boston
  Properties, Inc.,its general partner/s/ ILLEGIBLE
  
  By:
  /s/ DAVID C. PROVOSTName:
  David C. ProvostTitle:
  Senior Vice President
  Boston Properties  WITNESS:
  TENANT:SYNTA PHARMACEUTICALS,
  INC.By:
  /s/ KEITH EHRLICHName:
  Keith EhrlichTitle:
  Vice President(Hereto duly
  authorized)By:
  /s/ KEITH EHRLICHName:
  Keith EhrlichTitle:
  Treasurer   5