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                                                                    Exhibit 10.9

                            STOCK EXCHANGE AGREEMENT

     This Stock Exchange Agreement (this "AGREEMENT") is made and entered into
as of September 9, 2002 by and among CxSynta LLC, Keith R. Gollust, and Mountain
Trail Investments, LLC (each a "SELLER" and collectively, "SELLERS"), Principia
Associates, Inc., a Delaware corporation ("PRINCIPIA"), and Synta
Pharmaceuticals Corp., a Delaware corporation ("SYNTA").

                              W I T N E S S E T H:

     WHEREAS, Sellers own all of the outstanding Common Stock , $.01 par value
per share ("PRINCIPIA SHARES"), which shares represent all of the outstanding
capital stock of Principia, and desire to exchange the Principia Shares for
shares of the Common Stock , $.0001 par value per share ("SYNTA SHARES"), of
Synta and warrants for additional shares of Synta Shares;

     WHEREAS, Principia is the owner of thirty seven million four hundred
thousand (37,400,000) shares of the Common Stock, $.01 par value per share (the
"SBR SHARES"), of SBR Pharmaceuticals Corp., a Delaware corporation ("SBR"),
which SBR Shares represent all of the shares of capital stock of SBR owned
beneficially or of record by Principia; and

     WHEREAS, Synta desires to receive, acquire and accept from Sellers, and
Sellers desire to assign, transfer and deliver to Synta, the Principia Shares,
upon the terms and subject to the conditions set forth herein;

     NOW, THEREFORE, in consideration of the mutual covenants and agreements set
forth in this Agreement and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
agree as follows:

                                    ARTICLE I
                         EXCHANGE AND PURCHASE OF SHARES

     Section 1.1    EXCHANGE OF SHARES. At the Closing, subject to the terms and
conditions of this Agreement, Sellers, as the legal and beneficial owners of the
Principia Shares, shall transfer, assign convey and deliver, or cause to be
transferred, conveyed and delivered, the Principia Shares to Synta, free and
clear of all liens and encumbrances, and Synta shall accept the transfer and
assignment of the Principia Shares.

     Section 1.2    DELIVERY OF PRINCIPIA SHARES. At the Closing, Sellers shall
deliver to Synta stock certificates representing the Principia Shares together
with stock powers duly endorsed by Sellers in favor of Synta, and Principia
shall promptly issue a new stock certificate representing the Principia Shares
in the name of Synta or its designee upon delivery by Synta of the
aforementioned stock certificates and stock powers to the transfer agent for
Principia.

     Section 1.3    ISSUANCE OF SYNTA SHARES. At the Closing, in consideration
for the contribution of the Principia Shares to Synta as set forth in Section
1.1 and 1.2 hereof, Synta shall deliver to Sellers an aggregate of four million
nine hundred thirty nine thousand five hundred eighty one (4,939,500) shares of
Synta Shares, together with three year warrants for the purchase of an aggregate
of nine hundred fifty nine thousand one hundred twenty-six (959,126)

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shares of Synta Shares, in the form attached hereto as EXHIBIT A (collectively,
the "SYNTA WARRANTS"). The number of shares of Synta Shares to be issued to each
Seller and the number of shares of Synta shares subject to the Synta Warrant to
be granted to each Seller is set forth on EXHIBIT B attached hereto.

                                   ARTICLE II
                                     CLOSING

     Section 2.1    CLOSING. The closing of the transactions contemplated hereby
(the "CLOSING") shall take place at the offices of Nixon Peabody LLP, 101
Federal Street, Boston, MA 02110-1832, or at such other place as may be agreed
to by Sellers and Synta, at 10:00 AM (Boston time) on or before September 20,
2002, or on such other date as may be agreed upon in writing by Sellers and
Synta if subsequent to September 20, 2002 (the "CLOSING DATE").

                                   ARTICLE III
                    REPRESENTATIONS AND WARRANTIES OF SELLERS

Each of the Sellers hereby severally represents and warrants to Synta as
follows:

     Section 3.1    TITLE TO SHARES. Such Seller owns of record and
beneficially, free and clear of all encumbrances, and has good title to the
number of Principia Shares as set forth on EXHIBIT B attached hereto. Such
Seller is not a party to any agreement, trust or other arrangement that in any
way restricts such Seller's ability to perform its obligations under this
Agreement, including, without limitation, voting or transferring such Seller's
Principia Shares.

     Section 3.2    NO CONFLICT. The execution, delivery and performance of this
Agreement by such Seller does not and will not (a) conflict with or violate any
law or governmental order applicable to such Seller or any of such Seller's
respective assets, properties or businesses or (b) conflict with, result in any
breach of, constitute a default (or event which with the giving of notice or
lapse of time, or both, would become a default) under, require any consent
under, or give to others any rights of termination, amendment, acceleration,
suspension, revocation or cancellation of, or result in the creation of any
encumbrance on any of the Principia Shares owned by such Seller pursuant to, any
note, bond, mortgage or indenture, contract, agreement, lease, sublease,
license, permit, franchise or other instrument or arrangement to which such
Seller is a party or by which any of the Principia Shares owned by such Seller
is bound or affected, which would adversely affect the ability of such Seller to
carry out its obligations under, and to consummate the transactions contemplated
by, this Agreement.

     Section 3.3    GOVERNMENTAL CONSENTS AND APPROVALS. The execution, delivery
and performance of this Agreement by such Seller does not and will not require
any consent, approval, authorization or other order of, action by, filing with
or notification to, any governmental authority.

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     Section 3.4    LITIGATION. No action, suit, investigation or proceeding by
or against such Seller is pending or, to the knowledge of each Seller,
threatened before any court, arbitrator or administrative agency, which could
reasonably be expected to affect the legality, validity or enforceability of
this Agreement or the consummation of the transactions contemplated by this
Agreement.

     Section 3.5    SECURITIES ACT. The Synta Shares and Warrant issued by Synta
to such Seller pursuant to this Agreement are being acquired by such Seller for
investment only and not with a view to any public distribution thereof, and such
Seller will not offer to sell or otherwise dispose of the Synta Shares or
Warrant so acquired by him in violation of any of the registration requirements
of the Securities Act of 1933, as amended, or any applicable state blue sky
laws.

     Section 3.6    NO BROKER. No broker, finder or investment banker is
entitled to any brokerage, finders or other fee or commission in connection with
the transactions contemplated by this Agreement based upon arrangements made by
or on behalf of Sellers.

                                   ARTICLE IV
                   REPRESENTATIONS AND WARRANTIES OF PRINCIPIA

     Principia hereby represents and warrants to Synta as follows:

     Section 4.1    ORGANIZATION, GOOD STANDING AND AUTHORITY OF PRINCIPIA.
Principia is a corporation duly organized, validly existing and in corporate
good standing under the laws of the State of Delaware. Principia has full
corporate power and authority to enter into this Agreement. The execution and
delivery of this Agreement, and the consummation of the transactions
contemplated hereby, have been duly authorized by the Board of Directors of
Principia and no other proceedings or actions on the part of Principia are
necessary to authorize this Agreement and the transactions contemplated hereby.
This Agreement constitutes the valid and binding obligation of Principia,
enforceable in accordance with its terms.

     Section 4.2    CAPITAL STOCK OF PRINCIPIA. The authorized capital stock of
Principia consists of Two Million One Hundred (2,000,100) shares of Principia
Shares. As of the date hereof, One Million Three Hundred Thousand (1,300,000)
shares of Principia Shares are issued and outstanding, all of which are validly
issued, fully paid and nonassessable. None of the issued and outstanding shares
of Principia Shares were issued in violation of any preemptive rights. There are
no options, warrants, convertible securities or other rights, agreements,
arrangements or commitments of any character relating to the Principia Shares or
obligating Principia to issue, sell or assign the Principia Shares, or any other
interest in, Principia Shares. There are no outstanding contractual obligations
of Principia to repurchase, redeem or otherwise acquire any shares of Principia
Shares or to provide funds to, or make any investment (in the form of a loan,
capital contribution or otherwise) in, any other person.

     Section 4.3    FINANCIAL STATEMENTS. The unaudited balance sheet of
Principia as of August 31, 2002 and the related statement of income for the
period then ended, complete and correct copies of which have been delivered to
Synta, fairly present the financial position of Principia as at such date and
the results of operations of Principia for the period then ended, in each case
in accordance with U.S. generally accepted accounting principles ("GAAP")
consistently applied for the period covered (subject to the normal year-end
adjustments).

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     Section 4.4    NO MATERIAL ADVERSE CHANGE. Since August 31, 2002, there has
been no material adverse change in the properties, business, prospects, results
of operations or financial condition of Principia.

     Section 4.5    NO DEFAULT; NO CONFLICT WITH OTHER INSTRUMENTS. Principia is
not in default under or in violation of any provision of its Certificate of
Incorporation or By-Laws. To its knowledge, based upon the representations made
in the Stock Purchase Agreement, Principia is not in default under or in
violation of any material indenture, mortgage, deed of trust, note, debenture,
or any material agreement, lease, or other instrument or contract to which it is
a party or by which it or any of it properties or assets is bound or any
judgment, decree, order, statute, rule or regulation to which it is subject or
by which it or any of its properties or assets is bound. To its knowledge, based
upon the representations made in the Stock Purchase Agreement, the execution,
delivery and performance of this Agreement, and the consummation by Principia of
the transactions contemplated hereby do not and will not constitute a default
under any of (a) the terms, conditions or provisions of the Certificate of
Incorporation or By-Laws of Principia or (b) any material indenture, mortgage,
deed of trust, note, debenture, agreement, lease or other material instrument or
material contract or any such judgment, decree, order, statute, rule or
regulation with respect to which Principia is a party or subject or result in
the creation of any lien, charge or encumbrance on any of the properties or
assets of Principia.

     Section 4.6    SUBSIDIARIES; OWNERSHIP OF SBR SHARES. Principia has no
subsidiaries other than SBR. To its knowledge, Principia has good and marketable
title to the SBR Shares free and clear of any and all restrictions, liens,
charges, encumbrances, options and adverse claims or rights whatsoever, except
as provided by applicable federal and state securities laws. To its knowledge,
based upon the representations made in the Stock Purchase Agreement, Principia
owns ninety-eight and eight-tenths percent (98.80%) of the issued and
outstanding capital stock of SBR and all the issued and outstanding shares of
capital stock of SBR are duly authorized, validly issued, fully paid and
nonassessable.

     Section 4.7    ORGANIZATION, GOOD STANDING AND AUTHORITY OF SBR. Based upon
the representations made in the Stock Purchase Agreement (as defined in Section
7.1 of this Agreement), SBR is a corporation duly organized, validly existing
and in corporate good standing under the laws of the State of Delaware and has
the requisite power and authority to own all of its properties and assets and to
carry on its business as it is now being conducted. Based upon the
representations made in the Stock Purchase Agreement, SBR is duly qualified to
do business and is in corporate good standing in each jurisdiction in which it
owns or leases property or engages in any activity which would require it to
qualify to do business as a foreign corporation, except such jurisdictions where
the failure to so qualify would not have a material adverse effect on the
business, condition (financial or otherwise), results of operations, rights,
properties, assets or prospects of SBR.

     Section 4.8    CERTIFICATE AND BY-LAWS, ETC., OF SBR. Based upon the
representations made in the Stock Purchase Agreement, Principia has delivered to
Synta true, accurate and complete copies of the Certificate of Incorporation and
By-Laws of SBR and such Certificate of Incorporation and By-Laws are in full
force and effect.

     Section 4.9    NO DEFAULT; NO CONFLICT WITH OTHER INSTRUMENTS. To
Principia's knowledge, based upon the representations made in the Stock Purchase
Agreement, SBR is not,

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and by reason of the consummation of the transactions contemplated by this
Agreement will not be, in default under or in violation of any material
indenture, mortgage, deed of trust, note, debenture, or any material agreement,
lease, or other material instrument or material contract to which it is a party
or by which it or any of its properties or assets is bound or any judgment,
decree, order, statute, rule or regulation to which it is subject or by which it
or any of its properties or assets are bound. To Principia's knowledge, based
upon the representations made in the Stock Purchase Agreement, the consummation
of the transactions contemplated by this Agreement will not result in the
creation of any lien, charge or encumbrance on any of the properties or assets
of SBR or on the SBR Shares.

     Section 4.10   CAPITAL STOCK OF SBR. Based upon the representations made in
the Stock Purchase Agreement, the authorized capital stock of SBR consists of
forty million (40,000,000) shares of Common Stock, $.01 par value per share
("SBR COMMON STOCK"). Based upon the representations made in the Stock Purchase
Agreement, thirty seven million eight hundred fifty five thousand two hundred
(37,855,200) shares of SBR Common Stock are issued and outstanding, all of which
are validly issued, fully paid and nonassessable, and seven hundred two thousand
three hundred thirty four (702,334) shares of SBR Common Stock are reserved for
issuance pursuant to stock options granted pursuant to SBR's 1997 Stock Option
Incentive Plan. Based upon the representations made in the Stock Purchase
Agreement, none of the issued and outstanding shares of SBR Common Stock was
issued in violation of any preemptive rights. Based upon the representations
made in the Stock Purchase Agreement, except for the aforementioned stock
options issued under the SBR Stock Option Incentive Plan, there are no options,
warrants, convertible securities or other rights, agreements, arrangements or
commitments of any character relating to the SBR Shares or obligating either
Principia or SBR to issue, sell or assign the SBR Shares or any SBR Common
Stock, or any other interest in, SBR. Based upon the representations made in the
Stock Purchase Agreement, there are no outstanding contractual obligations of
SBR to repurchase, redeem or otherwise acquire any shares of SBR Common Stock or
to provide funds to, or make any investment (in the form of a loan, capital
contribution or otherwise) in, any other person.

     Section 4.11   LITIGATION. Based upon the representations made in the Stock
Purchase Agreement, (a) no action, suit, investigation or proceeding is pending
or, to Principia's knowledge, threatened before any court, arbitrator or
administrative agency against or affecting Principia or SBR, (b) no action,
suit, investigation or proceeding is pending or, to Principia's knowledge,
threatened before any court, arbitrator or administrative agency against or
affecting Principia or SBR that could have the effect of delaying or hindering
the transactions contemplated in this Agreement and (c) to Principia's
knowledge, neither Principia nor SBR is in default with respect to any judgment,
order, writ, injunction or decree of any court or any administrative agency.

     Section 4.12   REQUIRED CONSENTS AND APPROVALS. Except for the
authorization of Principia's Board of Directors and stockholders, the execution
and delivery of this Agreement by Principia does not, and the performance of
this Agreement by Principia will not, require any consent, approval, order,
authorization, registration, qualification or designation from any governmental
authority or pursuant to any agreement or other instrument by which Principia,
or any of its respective properties or assets, is bound except (a) for such
consents, approvals, orders, authorizations, registrations, qualifications or
designations that have already been obtained and are in full force and effect on
the date hereof, and (b) where the failure to obtain such consents,

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approvals, orders, authorizations, registrations, qualifications or designations
would not prevent or delay the consummation of the transactions contemplated by
this Agreement, or otherwise prevent Principia from performing its obligations
under this Agreement.

                                    ARTICLE V
                      REPRESENTATIONS, WARRANTIES OF SYNTA

     Synta represents and warrants to Sellers as follows:

     Section 5.1    ORGANIZATION, GOOD STANDING AND AUTHORITY OF SYNTA. Synta is
a corporation duly organized, validly existing and in corporate good standing
under the laws of the State of Delaware and has the requisite power and
authority to own, lease and operate all its properties and assets and to carry
on its business as it is now being conducted. Synta is duly qualified to do
business and is in corporate good standing in each jurisdiction in which it owns
or leases property or engages in any activity which would require it to qualify
to do business as a foreign corporation, except such jurisdictions where the
failure to so qualify would not have a material adverse effect on the business,
condition (financial or otherwise), results of operations, rights, properties,
assets or prospects of Synta.

     Section 5.2    AUTHORIZATION. Synta has full corporate power and authority
to enter into this Agreement and to carry out its obligations hereunder. The
execution and delivery of this Agreement, and the consummation of the
transactions contemplated hereby have been duly authorized by the Board of
Directors of Synta and no other proceedings or actions on the part of Synta are
necessary to authorize this Agreement and the transactions contemplated hereby.
This Agreement constitutes a valid and binding obligation of Synta, enforceable
in accordance with its terms.

     Section 5.3    CERTIFICATE AND BY-LAWS, ETC., OF SYNTA. Synta has delivered
to Principia true, accurate and complete copies of the Certificate of
Incorporation and By-Laws of Synta. Such Certificate of Incorporation and
By-Laws are in full force and effect.

     Section 5.4    NO DEFAULT; NO CONFLICT WITH OTHER INSTRUMENTS. Synta is not
in default under or in violation of any provision of its Certificate of
Incorporation or By-Laws. Synta is not in default under or in violation of any
material indenture, mortgage, deed of trust, note, debenture, or any material
agreement, lease, or other instrument or contract to which it is a party or by
which it or any of it properties or assets is bound or any judgment, decree,
order, statute, rule or regulation to which it is subject or by which it or any
of its properties or assets is bound. The execution, delivery and performance of
this Agreement, and the consummation by Synta of the transactions contemplated
hereby do not and will not constitute a default under any of (a) the terms,
conditions or provisions of the Certificate of Incorporation or By-Laws of Synta
or (b) any material indenture, mortgage, deed of trust, note, debenture,
agreement, lease or other material instrument or material contract or any such
judgment, decree, order, statute, rule or regulation with respect to which Synta
is a party or subject or result in the creation of any lien, charge or
encumbrance on any of the properties or assets of Synta.

     Section 5.5    CAPITAL STOCK OF SYNTA. The authorized capital stock of
Synta consists of one hundred million (100,000,000) shares of Synta Common
Stock. As of the date hereof, thirty

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one million eight hundred twenty six thousand seven hundred thirty eight
(31,826,738) shares of Synta Common Stock are issued and outstanding, all of
which are validly issued, fully paid and nonassessable, and two million two
hundred eighty four thousand five hundred fifty (2,284,550) shares of Synta
Common Stock are reserved for issuance pursuant to stock options granted
pursuant to Synta's 2001 Stock Plan. None of the issued and outstanding shares
of Synta Common Stock was issued in violation of any preemptive rights. Except
for the aforementioned stock options issued under the Synta 2001 Stock Plan,
there are no options, warrants, convertible securities or other rights,
agreements, arrangements or commitments of any character relating to the Synta
Common Stock or obligating Synta to issue or sell any Synta Common Stock, or any
other interest in, Synta. There are no outstanding contractual obligations of
Synta to repurchase, redeem or otherwise acquire any shares of Synta Common
Stock or to provide funds to, or make any investment (in the form of a loan,
capital contribution or otherwise) in, any other person. Upon consummation of
the transactions contemplated by this Agreement and issuance of the Synta Shares
in the name of each Seller in the stock records of Synta, assuming the exercise
of the Synta Warrants (but excluding Synta Shares, if any, owned by the Sellers
prior to the Closing Date), the Sellers will own in aggregate fourteen and
seventy-five hundredths percent (14.75%) of the issued and outstanding capital
stock of Synta, as calculated on a fully-diluted basis, free and clear of any
and all mortgages, pledges, liens, security interests, charges, claims,
equitable interests, encumbrances, restrictions on transfer, conditional sale or
other title retention device or arrangement, transfer right for the payment of
any liability, or restriction on the creation of the foregoing. Upon
consummation of the transactions contemplated by this Agreement, the Synta
Shares will be fully paid and nonassessable. All the issued and outstanding
shares of capital stock of Synta are duly authorized, validly issued, fully paid
and nonassessable.

     Section 5.6    LITIGATION. There are no actions, suits, or proceedings
pending, or to the knowledge of Synta threatened, against Synta by any person
which question the validity, legality or propriety of the transactions
contemplated by this Agreement.

     Section 5.7    REQUIRED CONSENTS AND APPROVALS. Except for the
authorization of Synta's Board of Directors and stockholders, the execution and
delivery of this Agreement by Synta does not, and the performance of this
Agreement by Synta will not, require any consent, approval, order,
authorization, registration, qualification or designation from any governmental
authority or pursuant to any agreement or other instrument by which Synta or any
of its properties is bound except (a) for such consents, approvals, orders,
authorizations, registrations, qualifications or designations that have already
been obtained and are in full force and effect on the date hereof, and (b) where
the failure to obtain such consents, approvals, orders, authorizations,
registrations, qualifications or designations would not prevent or delay the
consummation of the transactions contemplated by this Agreement or otherwise
prevent Synta from performing its obligations under this Agreement.

     Section 5.8    SECURITIES ACT. The Principia Shares transferred and
assigned to Synta pursuant to this Agreement are being acquired for investment
only and not with a view to any public distribution thereof, and Synta will not
offer to sell or otherwise dispose of the Principia Shares so acquired by it in
violation of any of the registration requirements of the Securities Act of 1933
or any applicable state blue sky laws.

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     Section 5.9    NO BROKER. No broker, finder or investment banker is entitle
to any brokerage, finders or other fee or commission in connection with the
transactions contemplated by this Agreement based upon arrangements made by or
on behalf of Synta.

                                   ARTICLE VI
                              CONDITIONS TO CLOSING

     6.1  CONDITIONS OF SYNTA'S PERFORMANCE. The performance by Synta of its
obligations under this Agreement shall be subject to the fulfillment, as
determined by Synta, in its reasonable judgment, of each of the conditions
specified below:

     (a)  each of the Sellers shall have performed and complied in all material
respects with his or its obligations under this Agreement required to be
performed by him or it at or prior to the Closing.

     (b)  the representations and warranties of each of the Sellers and
Principia shall be true and correct in all material respects when made and as of
the Closing with the same effect as though made at and as of the Closing;

     (c)  Synta shall have received from Principia:

          (i)    a certificate, duly executed by an authorized officer,
certifying that the representations and warranties of Principia set forth in
this Agreement are true and correct in all material respects when made and as of
the Closing with the same effect as though made at and as of the Closing; and

          (ii)   satisfactory evidence that the representatives of Principia
executing and delivering this Agreement are authorized to do so.

     (d)  Synta shall have received from each of the Sellers: a certificate,
duly executed by such Seller, certifying that the representations and warranties
of such Seller set forth in this Agreement are true and correct in all material
respects when made and as of the Closing with the same effect as though made at
and as of the Closing;

     (e)  Synta shall have received the written resignation of each member of
the Board of Directors of Principia and each of the officers of Principia.

     6.2  CONDITIONS OF SELLERS' PERFORMANCE. The performance by each of the
Sellers of his or its obligations under this Agreement shall be subject to the
fulfillment, as determined by such Seller, in his or its reasonable judgment, of
each of the conditions specified below:

     (a)  Synta shall have performed and complied in all material respects with
its obligations under this Agreement required to be performed by it at or prior
to the Closing; and

     (b)  the Sellers shall have received from Synta:

          (i)    a certificate, duly executed by an authorized officer of Synta,
certifying that the representations and warranties of Synta set forth in this
Agreement are true and correct in

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all material respects when made and as of the Closing with the same effect as
though made at and as of the Closing; and

          (ii)   satisfactory evidence that the representatives of Synta
executing and delivering this Agreement are authorized to do so.

                                   ARTICLE VII
                                OTHER AGREEMENTS

     Section 7.1    PURCHASE OF SBR SHARES BY SYNTA. Promptly following the
Closing, Synta shall cause SBR to be merged with and into Principia, and in
connection therewith Synta shall have Principia give notice to each of the other
stockholders of SBR that Principia will purchase, for a purchase price of
$.3267973 per share, all of the shares of the SBR Shares owned by such other
stockholders of SBR substantially on the terms contemplated by Section 6.14 of
the Stock Purchase Agreement dated as of July 31, 2002 pursuant to which
Principia purchased the SBR Shares (the "STOCK PURCHASE AGREEMENT"). A copy of
the Stock Purchase Agreement has been provided to Synta previously.

     Section 7.2    INDEMNIFICATION OF SELLERS. Synta hereby covenants and
agrees to indemnify, protect, defend and save harmless each Seller from and
against any and all damages, losses, liabilities, obligations, penalties,
claims, litigation, demands, judgments, suits, actions, proceedings, costs,
disbursements and expenses (including, without limitation, attorneys' expenses
and disbursements) of any kind or nature whatsoever (a "Loss") which may at any
time be imposed upon, incurred by or asserted or awarded against any Seller (an
"Indemnitee") relating to, resulting from or arising out of the Stock Purchase
Agreement or Principia's acquisition of the SBR Shares, provided such Loss was
not due to the Indemnitee's willful misconduct. Indemnitee shall give to Synta
notice in writing as soon as reasonably practicable under the circumstances of
the commencement of any action, suit or proceeding or of any claim threatened to
be made against Indemnitee for which Indemnitee proposes to demand
indemnification under this Section 7.2. Failure to notify Synta shall not
relieve Synta from any liability which it may have to Indemnitee if such failure
does not materially adversely affect Synta or its ability to defend any such
action, suit or proceeding. With respect to any action, suit or proceeding as to
which Indemnitee gives notice, Synta shall have the right to assume control of
the defense, compromise or settlement thereof, including at its own expense,
employment of counsel reasonably satisfactory to Indemnitee, provided that the
outcome includes the complete general release of the Indemnitee. In the event
Synta does not notify Indemnitee in writing that it intends to assume control of
such defense within thirty (30) days after Indemnitee has given Synta notice
thereof, Indemnitee may undertake such defense. Synta shall not be liable to
indemnify Indemnitee under this Agreement for any amounts paid in settlement of
any action, suit or proceeding or claim threatened to be made against Indemnitee
effected without Synta's prior written consent. Synta shall not settle any
action, suit or proceeding or threatened claim without Indemnitee's prior
written consent. Neither Synta nor Indemnitee will unreasonably withhold its or
his consent to any proposed settlement. Synta shall not be obligated to
indemnify any Indemnitee for any consequential or other indirect damages of any
kind other than as set forth in this Section 7.2.

                                  ARTICLE VIII

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                                OTHER PROVISIONS

     Section 8.1    GOVERNING LAW AND JURISDICTION. This Agreement and the
rights and obligations of the parties hereunder shall be governed by and
construed according to the laws of the State of Delaware without regard to
choice of law principles.

     Section 8.2    NOTICES. Unless otherwise provided herein, all notices
required or permitted by the terms hereof shall be in writing. Any written
notice shall become effective when received. All notices and other
communications hereunder shall be deemed to have been duly given if hand
delivered or mailed, by certified or registered mail, return receipt requested,
postage prepaid, by overnight delivery service or by facsimile (with receipt
confirmed and hard copy to follow) to the respective parties at the following
addresses, or at such other address for a party as shall be specified in a
notice given in accordance with this Section:

     If to Sellers, to:

          CxSynta LLC
          c/o Caxton Corporation
          731 Alexander Road, Bldg. 2
          Princeton, NJ  08540
          Attn: Scott Bernstein, Esq.
          Facsimile:  (609) 419-9040

          Keith R. Gollust
          c/o Gollust Management, Inc.
          500 Park Avenue, Suite 510
          New York, NY  10022
          Facsimile:

          Mountain Trail Investments, LLC
          865 South Figueroa St., Suite 700
          Los Angeles, CA  90017
          Attn:  Jonathan D. Jaffrey
          Facsimile:

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     if to Principia, to:

          Principia Associates, Inc.
          731 Alexander Road, Bldg. 2
          Princeton, NJ  08540
          Attn: Scott Bernstein, Esq.
          Facsimile: (609) 419-9040

     and, if to Synta, to:

          Synta Pharmaceuticals Corp.
          45 Hartwell Avenue
          Lexington, MA  02421
          Attn: Dr. Safi R. Bahcall
          Facsimile: (781) 274-8228

     with a copy to:

          Nixon Peabody LLP
          101 Federal Street
          Boston, MA  02110-1832
          Attn: Michael K. Barron, Esq.
          Facsimile: (866) 947-1784

     Section 8.3    AMENDMENT AND ALTERATION. No amendment or alternation of the
terms of this Agreement shall be valid or binding unless made in writing signed
by an authorized representative of each of the parties to this Agreement
specifically referring to this Agreement.

     Section 8.4    BINDING AGREEMENT/ASSIGNMENT. This Agreement and all of the
provisions hereof shall be binding upon and inure to the benefit of the parties
hereto and their respective heirs, successors, permitted assigns and legal
representatives; PROVIDED, HOWEVER, that neither this Agreement nor any of the
rights, interests or obligations hereunder shall be assigned by any of the
parties hereto without the prior written consent of each of the other parties,
which consent shall not unreasonably be delayed, conditioned or withheld.

     Section 8.5    COUNTERPARTS; COPIES. This Agreement may be executed
simultaneously in two or more counterparts, each of which shall be deemed an
original, but all of which together shall constitute one and the same
instrument. For purposes of this Agreement, any copy, facsimile or
telecommunication or other reliable reproduction of a writing, transmission or
signature may be substituted and used in lieu of the original writing,
transmission or signature for any and all purposes for which the original
writing, transmission or signature could be used, provided that receipt of such
copy, facsimile telecommunication or other reproduction shall have been
confirmed by the sending party.

     Section 8.6    EXPENSES. Except as otherwise specified in this Agreement,
each party hereto shall bear its or his own expenses incurred in connection with
the negotiation, execution and performance of this Agreement.

<Page>

     Section 8.7    CERTAIN RULES OF CONSTRUCTION. The headings in the Sections
and paragraphs of this Agreement are inserted for convenience only and shall not
constitute a part of this Agreement or in any way modify, amend or affect its
provisions. This Agreement is the result of negotiations between the parties and
shall not be deemed or construed as having been drafted by any one party.

     Section 8.8    TAX CONSEQUENCES. Synta, Principia and the Sellers are each
relying on the advice of their own tax advisors as to the tax effects of the
transactions contemplated by this Agreement. No party is making any
representation or warranty regarding the tax effects of such transactions to any
other party; PROVIDED, HOWEVER, that the parties shall cooperate and take such
actions and execute and deliver such documents and instruments as may be
necessary to insure that the transactions contemplated hereby qualify as a
tax-free reorganization pursuant to all applicable federal, state, local or
foreign tax laws.

     Section 8.9    INTEGRATION. This Agreement represents the entire agreement
among the parties hereto with respect to the subject matter hereof and
supersedes any prior agreements, negotiations, discussions or understandings
with respect to the subject matter hereof.

     Section 8.10   EXCLUSIVITY. Sellers will not, for the period beginning on
the date hereof until the earlier to occur of the Closing or December 31, 2002,
directly or indirectly (a) solicit or initiate the submission of proposals or
offers from any person other than Synta for, (b) participate in any discussions
other than with Synta pertaining to, or (c) furnish any information to any
person other than Synta relating to, any acquisition or purchase of all or
substantially all of the material assets of, or any equity interest in Principia
(including without limitation the Principia Shares or), SBR, the SBR Shares, or
a merger, consolidation or business combination involving Principia or SBR.

     Section 8.11   FURTHER ASSURANCES. Each party hereto shall do and perform
or cause to be done and performed all further acts and things and shall execute
and deliver all other agreements, certificates, instruments and documents as any
other party hereto reasonably may request in order to carry out the intent and
accomplish the purposes of this Agreement and the consummation of the
transactions contemplated hereby.

     Section 8.12   SURVIVAL. The representations and warranties of the parties
hereto contained in this Agreement shall survive until the first anniversary of
the date of the Closing. The right to indemnification set forth in Section 7.2
shall not be affected by this Section 8.12.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK.]

<Page>

     IN WITNESS WHEREOF, Synta and Principia have caused this Agreement to be
executed by their respective duly authorized officers, under seal, as of the
date first set forth above.

                                            SELLERS

                                            CxSYNTA LLC

                                            By:     /S/ PETER D'ANGELO
                                               ---------------------------------

                                            Print Name:   Peter D'Angelo
                                                       -------------------------

                                            Title:  PRESIDENT
                                                  ------------------------------


                                                    /S/ KEITH R. GOLLUST
                                            ------------------------------------
                                            Keith R. Gollust


                                            MOUNTAIN TRAIL INVESTMENTS, LLC

                                            By:     /S/ RICHARD N. FOSTER
                                               ---------------------------------

                                            Print Name:   R.N. Foster
                                                       -------------------------

                                            Title:  PARTNER
                                                  ------------------------------


                                            PRINCIPIA ASSOCIATES, INC.

                                            By:     /S/ BRUCE KOVNER
                                               ---------------------------------

                                            Print Name:   Bruce Kovner
                                                       -------------------------

                                            Title:  CHAIRMAN
                                                  ------------------------------


                                            SYNTA PHARMACEUTICALS CORP.

                                            By:     /S/ SAFI BAHCALL
                                               ---------------------------------

                                            Print Name:   Safi Bahcall
                                                       -------------------------

                                            Title:  CHIEF EXECUTIVE OFFICER
                                                  ------------------------------


             Signature Page to Stock Exchange and Purchase Agreement

<Page>

                                    EXHIBIT A

                              FORM OF SYNTA WARRANT

<Page>

THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE OF THIS WARRANT HAVE
NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AND, ACCORDINGLY, MAY NOT
BE OFFERED FOR SALE, SOLD OR OTHERWISE TRANSFERRED EXCEPT (i) UPON EFFECTIVE
REGISTRATION UNDER THE SECURITIES ACT OF 1933 AND ANY APPLICABLE STATE
SECURITIES LAW, OR (ii) UPON ACCEPTANCE BY THE COMPANY OF AN OPINION OF COUNSEL
IN SUCH FORM AND BY SUCH COUNSEL, OR OTHER DOCUMENTATION, AS SHALL BE
SATISFACTORY TO COUNSEL FOR THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

                                   Right to Purchase ______ Shares of
                                   Common Stock of Synta Pharmaceuticals Corp.


                           SYNTA PHARMACEUTICALS CORP.

                          Common Stock Purchase Warrant

          SYNTA PHARMACEUTICALS CORP., a Delaware corporation (the "COMPANY"),
hereby certifies that, for value received, _______________________ is entitled,
subject to the terms set forth below, to purchase from the Company at any time
or from time to time after 12:00 midnight on __________, 2002 and before 5:00
P.M., Boston time, on ___________, 2005 up to _________________________________
(_______) fully paid and nonassessable shares of Common Stock, par value $0.0001
per share ("COMMON STOCK"), of the Company, at a purchase price per share of
$0.50 (such purchase price per share, as adjusted from time to time as herein
provided, is referred to herein as the "PURCHASE PRICE"). The number and
character of such shares of Common Stock and the Purchase Price are subject to
adjustment as provided herein. The term "COMPANY" shall include Synta
Pharmaceuticals Corp., and any corporation which shall succeed or assume the
obligations of the Company hereunder.

          1.   EXERCISE OF WARRANT. This Warrant may be exercised from time to
time in whole or in part by the holder hereof by surrender of this Warrant, with
the form of notice of exercise at the end hereof duly executed by such holder,
to the Company at its principal office, accompanied by payment, if applicable,
in cash or by certified or official bank check payable to the order of the
Company, in the amount obtained by multiplying the number of shares of Common
Stock for which this Warrant is then exercisable by the Purchase Price then in
effect. This Warrant shall expire and be of no further force or effect on
____________, 2005.

          2.   DELIVERY OF STOCK CERTIFICATES, ETC., ON EXERCISE. As soon as
practicable after the exercise of this Warrant, the Company will cause to be
issued in the name of and delivered to the holder hereof, and/or the designee or
designees specified by the holder on the notice of exercise, a certificate or
certificates for the number of fully paid and nonassessable shares of Common
Stock to which such holder and/or any such designee(s) shall be entitled on such
exercise, plus, in lieu of any fractional share to which such holder would
otherwise be entitled, cash equal to such fraction multiplied by the then
current market value of one full share, together with any other stock or other
securities and property (including cash, where applicable) to which such holder
is entitled upon such exercise pursuant to

<Page>

Section 1 or otherwise. In the event of a partial exercise of this Warrant by
the holder hereof, on surrender for exchange of this Warrant, properly endorsed,
to the Company, the Company at its expense will issue and deliver to or on the
order of the holder thereof a new Warrant of like tenor, in the name of such
holder, calling in the aggregate on the face thereof for the number of shares of
Common Stock representing the balance of the shares of Common Stock represented
hereby following such exercise and delivery of shares of Common Stock.

          3.   NET ISSUE EXERCISE. Notwithstanding any provisions herein to the
contrary, if the fair market value of one share of the Company's Common Stock
(or whatever securities are issuable upon exercise of this Warrant at the time)
is greater than the Purchase Price (at the date of calculation as set forth
below), then, in lieu of exercising this Warrant for cash, the holder may elect
a "NET ISSUE EXERCISE", pursuant to which the holder will receive shares equal
to the value (as determined below) of this Warrant (or the portion thereof being
exercised), in which event the Company shall issue to the holder and/or the
holder's designee(s) a number of shares of Common Stock computed using the
following formula:

                   X = Y(A-B)
                       -----
                         A

     Where:                    X =  the number of shares of Common Stock to be
                               issued to the Holder;

                               Y = the number of shares of Common Stock
                               purchasable under the Warrant or, if only a
                               portion of the Warrant is being exercised, the
                               portion of the Warrant being exercised;

                               A = the fair market value of one share of the
                               Company's Common Stock (at the date of such
                               calculation); and

                               B = Purchase Price in effect (at the date of such
                               calculation).

For purposes of the above calculation, the fair market value of one share of
Common Stock shall be determined by the Company's Board of Directors in good
faith. To exercise this Warrant pursuant to this Section 3, the holder must
surrender this Warrant at the principal office of the Company together with the
properly endorsed Form of Subscription and notice of such election.


          4.   REORGANIZATION. CONSOLIDATION. MERGER, ETC.

          (a)  In case at any time or from time to time, the Company shall, (i)
effect a reorganization of the capital stock of the Company, (ii) consolidate
with or merge into any other person, (iii) sell all or substantially all of its
assets or have all or substantially all of its stock sold (or converted into
other property by virtue of a reverse merger) or (iv) dissolve or liquidate
(each a "MAJOR TRANSACTION") then, in each such case, the Company will use best
efforts to ensure that the acquiring entity (as applicable) assumes this Warrant
or issues a comparable substitute warrant so that the holder of this Warrant, on
the exercise of this Warrant or such substitute warrant, shall receive, in lieu
of the Common Stock issuable on such exercise prior to such transaction, the
stock and other securities and property (including cash) to which such holder
would have been entitled upon consummation of such transaction if such holder
had so exercised this Warrant, immediately prior thereto, all subject to further
adjustment thereafter as

                                        2
<Page>

provided in Section 5. In each such case, appropriate adjustment (as determined
in good faith by the Board of Directors of the Company) shall be made in the
application of the provisions herein set forth with respect to the rights and
interests thereafter of the holder of this Warrant to the end that the
provisions set forth herein (including those relating to adjustments of the
Purchase Price) shall thereafter be applicable, as near as reasonably may be, in
relation to any shares or other property deliverable upon the exercise hereof as
if this Warrant had been exercised immediately prior to such transaction.

          (b)  Notwithstanding the foregoing or anything in this Warrant to the
contrary, in connection with a Major Transaction, if the Company, despite its
best efforts, is not successful in obtaining the assumption or substitution of
this Warrant, the Company will give notice to the holder that this Warrant will
terminate if not exercised prior to or simultaneously with the closing or
consummation of such Major Transaction. Any such notice shall be in writing,
shall describe with specificity the consideration to be received in such Major
Transaction and shall be given in accordance with Section 7 at least thirty (30)
days before the closing or consummation of such Major Transaction. If the holder
fails to exercise this Warrant prior to simultaneously with the closing or
consummation of such Major Transaction, this Warrant shall terminate and be of
no further force or effect.

     5.   ADJUSTMENT FOR STOCK SPLIT OR STOCK DIVIDEND. In the event that the
Company shall (a) declare a dividend or issue additional shares of the Common
Stock (or other securities convertible into shares of Common Stock) in any other
type of distribution on outstanding Common Stock, (b) subdivide its outstanding
shares of Common Stock, or (c) combine its outstanding shares of the Common
Stock into a smaller number of shares of the Common Stock, then, in each such
event, the Purchase Price shall, simultaneously with the happening of such
event, be adjusted by multiplying the then Purchase Price by a fraction, the
numerator of which shall be the number of shares of Common Stock (which number
shall not include the shares of Preferred Stock (or other security of the
Company convertible into Common Stock) on an as-converted basis) outstanding
immediately prior to such event and the denominator of which shall be the number
of shares of Common Stock (which number shall not include the shares of
Preferred Stock (or other security of the Company convertible into Common Stock)
on an as-converted basis) outstanding immediately after such event, and the
product so obtained shall thereafter be the Purchase Price then in effect. The
Purchase Price, as so adjusted, shall be readjusted in the same manner upon the
happening of any successive event or events described herein in this Section 5.
The holder of this Warrant shall thereafter, on the exercise hereof as provided
in Section 1 or otherwise, be entitled to receive that number of shares of
Common Stock determined by multiplying the number of shares of Common Stock
which would otherwise (but for the provisions of this Section 5) be issuable on
such exercise by a fraction of which (x) the numerator is the Purchase Price
which would otherwise (but for the provisions of this Section 5) be in effect,
and (y) the denominator is the Purchase Price in effect on the date of such
exercise. Upon any adjustment of the Purchase Price or any increase or decrease
in the number of shares purchasable upon the exercise of this Warrant, the
Company shall give written notice thereof to holder in accordance with Section 7
below. The notice shall be signed by the Company's chief financial officer and
shall state the Purchase Price resulting from such adjustment and the increase
or decrease, if any, in the number of shares purchasable at such price upon the
exercise of this Warrant, setting forth in reasonable detail the method of
calculation and the facts upon which such calculation is based.

     6.   CERTAIN EVENTS. If any change in the outstanding Common Stock of the
Company or any other event occurs as to which the other provisions of this
Warrant are not strictly applicable or if strictly applicable would not fairly
protect the purchase rights of the holder in accordance with such provisions,
then the Board of Directors of the Company shall make an adjustment in the
number and class of shares available under this Warrant, the Purchase Price or
the application of such provisions, so the holder upon

                                        3
<Page>

exercise for the same aggregate purchase price would obtain the total number,
class and kind of shares as it would have owned had this Warrant been exercised
prior to the event and had the holder continued to hold such shares until after
the event requiring adjustment.

     7.   NOTICES. Any notice pursuant to this Warrant by the Company or by the
holder shall be in writing and shall be deemed to have been duly given: (a) on
the date of delivery if delivered by hand, (b) on the date of delivery or
refusal indicated on the return receipt if delivered or mailed by certified
mail, return receipt requested, postage prepaid, (c) on the date of delivery if
sent by nationally recognized overnight delivery service, or (d) on the date of
transmission if sent by facsimile (with receipt confirmed and hard copy to
follow):

          (i)  If to the holder, addressed to _________________________________
Attention: ____________. Facsimile: (__)________.

          (ii) If to the Company, addressed to it at Synta Pharmaceuticals
Corp., 45 Hartwell Avenue, Lexington, MA 02421, Attention: Dr. Safi R. Bahcall.
Facsimile: (530) 323-7045.

A party may from time to time change the address to which notices to it are to
be delivered or mailed hereunder by notice in accordance herewith to the other
party.

     8.   RESERVATION OF STOCK, ETC., ISSUABLE ON EXERCISE OF WARRANT. The
Company will at all times reserve and keep available, solely for issuance and
delivery on the exercise of this Warrant, all shares of Common Stock from time
to time issuable on the exercise of this Warrant. The Company covenants and
agrees that all shares of Common Stock that may be issued upon the exercise of
the rights represented by this Warrant will, upon issuance, be duly authorized,
validly issued, fully paid and nonassessable and free from all preemptive rights
of any stockholder and free of all taxes, liens and charges with respect to the
issue thereof.

     9.   REPLACEMENT OF WARRANT. On receipt of evidence reasonably satisfactory
to the Company of the loss, theft, destruction or mutilation of this Warrant
and, in the case of any such loss, theft or destruction of this Warrant, on
delivery of an indemnity agreement or security reasonably satisfactory in form
and amount to the Company or, in the case of any such mutilation, on surrender
and cancellation of such Warrant, the Company at its expense will execute and
deliver, in lieu thereof, a new Warrant of like tenor.

     10.  NO IMPAIRMENT. The Company will not avoid or seek to avoid the
observance or performance of any of the terms of the Warrant, but will at all
times in good faith assist in the carrying out of all such terms and in the
taking of all such action as may be necessary or appropriate in order to protect
the rights of the holder of this Warrant against impairment.

     11.  NEGOTIABILITY, ETC. This Warrant may not be assigned or transferred
without the prior written consent of the Company (which consent shall not be
unreasonably withheld).

     12.  BINDING EFFECT ON SUCCESSORS. This Warrant shall be binding upon any
corporation succeeding the Company by merger, consolidation or acquisition of
all or substantially all of the Company's assets. All of the obligations of the
Company relating to Common Stock issuable upon the exercise of this Warrant
shall survive the exercise and termination of this Warrant. All of the covenants
and agreements of the Company shall inure to the benefit of the permitted
successors and assigns of the holder.

                                        4
<Page>

     13.  MISCELLANEOUS. This Warrant and a certain Stock Exchange Agreement
dated ____________ constitute the full and entire understanding and agreement
between the parties with respect to the subject matter hereof. This Warrant and
any term hereof may be changed, waived or discharged only by an instrument in
writing signed by the party against which enforcement of such change, waiver,
discharge or termination is sought. This Warrant shall be construed and enforced
in accordance with and governed by the laws of the State of Delaware without
regard to its choice of law principles. The headings in this Warrant are for
purposes of reference only, and shall not limit or otherwise affect any of the
terms hereof. This Warrant is being executed as an instrument under seal. The
invalidity or unenforceability of any provision hereof shall in no way affect
the validity or enforceability of any other provision.

The Company has caused this Warrant to be signed by its duly authorized officer
as of _____________________


                                             SYNTA PHARMACEUTICALS CORP.


                                             By:
                                                -------------------------

                                             Print:
                                                   ----------------------

                                             Title:
                                                   ----------------------

                                        5
<Page>

                               NOTICE OF EXERCISE
                      (To be signed only on exercise of Warrant)

TO: SYNTA PHARMACEUTICALS CORP.

1.   The undersigned, the holder of the within Warrant, hereby irrevocably
elects to exercise this Warrant for, and to purchase thereunder, _____________
shares of Common Stock, $.0001 par value per share ("COMMON STOCK"), of SYNTA
PHARMACEUTICALS CORP., and herewith makes payment of $_____________ therefor.

OR

2.   The undersigned, the holder of the within Warrant, hereby irrevocably
elects to convert ___% of the value of the Warrant pursuant to the provisions of
Section 3 of the Warrant.

     Please issue a certificate or certificates representing said number of
shares of Common Stock in the name of the undersigned or in the name(s) of the
undersigned and/or the undersigned designees as specified below:

<Table>
<Caption>
        Name                     Address                  # Shares/%
--------------------------------------------------------------------------------
        <S>                      <C>                      <C>

</Table>


Dated:
      -------------------------        -----------------------------------------
                                       (Signature must conform to name of holder
                                       as specified on the face of the Warrant)


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

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

<Page>

                                    EXHIBIT B

                             PRINCIPIA STOCKHOLDERS

<Table>
<Caption>
                           No. of Principia                                           No. of Synta Shares
         Name                   Shares              No. of Synta Shares            subject to Synta Warrant
         ----                   ------              -------------------            ------------------------
<S>                            <C>                       <C>                                <C>
CxSynta LLC                    500,000                   1,899,808                          575,476

Keith R. Gollust               300,000                   1,139,884                          115,095

Mountain Trail                 500,000                   1,899,808                          268,555
Investments, LCC
</Table>