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                                                                   EXHIBIT 10.13

                       RESTRICTED STOCK PURCHASE AGREEMENT
                              (Ganesh Venkataraman)

     This Restricted Stock Purchase Agreement dated as of June 13, 2001 (this
"Agreement") is made by and between Mimeon, Inc., a Delaware corporation (the
"Company"), and Ganesh Venkataraman (the "Purchaser").

     1.   DEFINITIONS. As used in this Agreement, the following terms shall have
the following meanings:

          QUALIFIED OFFERING: A firm commitment underwritten public offering of
the Company's Common Stock pursuant to an effective registration statement under
the Securities Act of 1933, as amended (the "Act"), in which the price per share
is at least $5.00 (subject to equitable adjustment in the event of stock splits
and the like) and the aggregate gross proceeds to the Company from such offering
are not less than $10,000,000.

          QUALIFIED SALE: The sale of all or substantially all of assets or
issued and outstanding capital stock of the Company, or merger or consolidation
involving the Company in which stockholders of the Company immediately before
such merger or consolidation do not own immediately after such merger or
consolidation capital stock or other equity interests of surviving corporation
or entity representing more than fifty percent in voting power of capital stock
or other equity interests of such surviving corporation or entity outstanding
immediately after such merger or consolidation.

          SERVICE: Service as an employee, officer or director of, or a
consultant or advisor to, the Company or its successors.

          SHARES: The shares of Common Stock issued to Purchaser hereunder and
any other securities of the Company which may be issued in exchange for or in
respect of such shares of Common Stock, whether by way of stock split, stock
dividend, combination of shares, reclassification, recapitalization,
reorganization or any other means.

          UNVESTED SHARES: Any Shares that are not Vested Shares.

          VESTED: Released from the Company's Repurchase Option (as defined in
Section 5(a)).

          VESTED SHARES: Any Shares that have vested in accordance with
Section 5(b).

     2.   PURCHASE AND SALE OF SHARES. The Company hereby sells to Purchaser,
and Purchaser hereby purchases from the Company, 380,400 shares of the Company's
common stock, $0.0001 par value per share ("Common Stock"), for a purchase price
per share of $0.0001, and an aggregate purchase price of $38.04. The Company
acknowledges receipt from Purchaser of $38.04 in cash, in full payment of such
purchase price. Purchaser and the Company hereby agree that the fair market
value of the Shares on the date hereof is $0.0001 per share.

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     3.   REPRESENTATIONS OF PURCHASER. Purchaser understands that the Shares
are not registered under the Act, and represents to the Company, and agrees that
the Company is entitled to rely on such representations, as follows:

          (a)  Purchaser understands that the Shares have not been registered
under the Act, or registered or qualified under the securities or "Blue Sky"
laws of any jurisdiction, and are being sold pursuant to exemptions contained in
the Act and exemptions contained in other applicable securities or "Blue Sky"
laws. Purchaser understands further that the Company's reliance on these
exemptions is based in part on the representations made by Purchaser in the
Agreement. In this connection, Purchaser represents and warrants that the offer
and sale of the Shares were made solely in Massachusetts.

          (b)  Purchaser understands the term "accredited investor" as used in
Regulation D promulgated under the Act and represents and warrants to the
Company that he is an "accredited investor" for purposes of acquiring the
Shares. The nature and amount of Purchaser's investment in the Shares is
consistent with Purchaser's investment objectives, abilities, and resources.
Purchaser understands that the Shares are an illiquid investment, which will not
become freely transferable by reason of any "change of circumstances" whatever.
Purchaser has adequate means of providing for Purchaser's current needs and
possible contingencies and has no need for liquidity in Purchaser's investment.

          (c)  Purchaser is acquiring the Shares for Purchaser's own account for
investment, and not for, with a view to, or in connection with the resale or
distribution thereof. Purchaser has no present intention to sell, hypothecate,
distribute or otherwise transfer the Shares or any portion thereof or any
interest therein.

          (d)  Purchaser understands that the Shares will constitute "restricted
securities" within the meaning of Rule 144 promulgated under the Act and that,
as such, the Shares must be held indefinitely unless they are subsequently
registered under the Act or unless an exemption from the registration
requirements thereof is available. Purchaser has been advised that Rule 144,
which permits the resale, subject to various terms and conditions, of small
amounts of such "restricted securities" after they have been held for one year,
does not now apply to the Company, because the Company is not now required to
file, and does not file, current reports under the Securities Exchange Act of
1934, and because information concerning the Company substantially equivalent to
that which would be available if the Company were required to file such reports
is not now publicly available. The Company may become a reporting entity at some
future date, but no assurance can be given that it will do so.

          (e)  In connection with Purchaser's acquisition of the Shares,
Purchaser accepts the condition that the Company may maintain "stop transfer"
orders with respect to the Shares and that each certificate or other document
evidencing the Shares will bear conspicuous legends in substantially the form
set forth in Section 7 of this Agreement.

          (f)  Purchaser has consulted Purchaser's attorney or accountant with
respect to Purchaser's purchase of the Shares. Purchaser has fully investigated
the Company and its business and financial condition and has knowledge of the
Company's current activities. Purchaser acknowledges that the Company has
granted Purchaser and Purchaser's attorney or

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accountant access to all information about the Company which they have requested
and has offered each of them access to all further information which they deemed
relevant to an investment decision with respect to the Shares. Purchaser and
Purchaser's attorney or accountant have had the opportunity to ask questions of,
and receive answers from, representatives of the Company concerning such
information and the Company's financial condition and prospects.

     4.   RESTRICTIONS ON TRANSFER. The following restrictions on transfer of
the Shares shall apply:

          (a)  SECURITIES LAWS. Except for purchases of Unvested Shares by the
Company as contemplated by Section 5, no Shares, nor any interest therein, may
be sold, assigned, pledged or otherwise transferred at any time or under any
circumstances unless (i) the Shares proposed to be transferred have been
registered under the Act and qualified under applicable state securities laws,
or (ii) the Company has received, or agreed to waive, an opinion of counsel
acceptable to the Company to the effect that such transfer may be effected
without registration under the Act or qualification under the securities laws of
relevant states and the proposed transferee has made such representations and
agreements as the Company shall require to .assure compliance with the Act and
such laws.

          (b)  TERMINATION OF REPURCHASE OPTION. Except for purchases of
Unvested Shares by the Company as contemplated by Section 5, no Shares, nor any
interest therein, may be sold, assigned, pledged or otherwise transferred until
the Repurchase Option shall have terminated with respect to such Shares.

          (c)  RIGHT OF FIRST OFFER. In the event that at any time Purchaser
desires to sell, assign or otherwise transfer any of the Vested Shares then held
by Purchaser, he shall first offer the Vested Shares desired to be transferred
to the Company by giving written notice of the proposed transfer. The notice
shall state the number of Vested Shares proposed to be transferred, the name of
the person or persons to whom it is proposed to transfer the Vested Shares, the
price at which the Vested Shares are intended to be transferred and all other
terms of the transaction, which must be bona fide. Such notice shall constitute
an offer by Purchaser to the Company for the Company to purchase such Vested
Shares on such terms and at a price per Vested Share equal to the price stated
in the notice. The Company may accept the offer as to all, but not less than
all, of the Vested Shares offered by notifying Purchaser in writing within 30
days after receipt of such notice of its acceptance of the offer. If the offer
is accepted, Purchaser shall sell the offered Vested Shares to the Company on
the terms and at the price per Vested Share as aforesaid, free of all
encumbrances, and shall deliver the certificates representing such Vested
Shares, duly endorsed in blank by Purchaser or with duly executed stock powers
attached thereto, all in form suitable for the transfer of such Vested Shares to
the Company, within 30 days of the date of acceptance of the offer to sell,
against payment therefor at the same price per vested Share and according to the
same terms as were offered by the proposed transferee. If within the applicable
time period Purchaser does not receive notice of the Company's intention to
purchase the offered Vested Shares, the offer shall be deemed to have been
rejected. In such event, Purchaser may transfer title to the offered Vested
Shares within 90 days from the date of his written notice to the Company of his
intention to sell, but such transfer shall be made only to the proposed
transferee or transferees and at the proposed price and on such other terms as
stated

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in such notice. Vested Shares that are so transferred to such transferee or
transferees shall remain subject to this Section 3 and as a condition to any
transfer Purchaser shall obtain a written agreement from the transferee by which
the transferee agrees to be bound by this Section 3.

          (d)  PERMITTED TRANSFERS. Any portion or all of the Vested Shares may,
without compliance with the provisions of Section 4(c), be transferred by
Purchaser to a member of his immediate family or to a family partnership or
family trust, or on Purchaser's death may be transferred to Purchaser's estate
or to those entitled to a distribution of the Vested Shares under the laws of
descent and distribution, provided that Shares that are so transferred shall
remain subject to this Section 4 and as a condition to any transfer Purchaser
shall obtain a written agreement from the transferee by which the transferee
agrees to be bound by this Section 4.

          (e)  REMEDIES. No sale, assignment, pledge or other transfer of Shares
shall be effective or given effect on the books of the Company unless all of the
applicable provisions of this Section 4 have been duly complied with. If any
transfer of Shares is made or attempted in violation of the foregoing
restrictions, or if Shares are not offered to the Company as required hereby,
the Company shall have the right to purchase such Shares from the purported
owner thereof or his transferee at any time before or after the transfer, as
herein provided. In addition to any other legal or equitable remedies which it
may have, the Company may enforce its rights by actions for specific performance
(to the extent permitted by law) and may refuse to recognize any transferee as
one of its stockholders for any purpose, including, without limitation, for
purposes of dividend and voting rights, until all applicable provisions hereof
have been complied with.

          (f)  LOCK-UP. Purchaser agrees that for a period of up to 180 days
from the effective date of any registration of securities of the Company (upon
request of the Company or the underwriters managing any underwritten offering of
the Company's securities), he will not sell, make any short sale or loan of,
grant any option for the purchase of, or otherwise dispose of any Shares held by
him without the prior written consent of the Company or such underwriters, as
the case maybe.

          (g)  TERMINATION OF RESTRICTIONS. Sections 4(c) and 4(d) shall
terminate upon the earlier to occur of: (i) immediately prior to the
consummation of a Qualified Sale; or (ii) the closing of a Qualified Offering.

     5.   REPURCHASE OF UNVESTED SHARES.

          (a)  REPURCHASE OPTION.

               (i)   In the event of the termination of Purchaser's Service by
Purchaser or the Company for any reason, with or without cause, the Company
shall upon the date of such termination (the "Termination Date") have an
irrevocable, exclusive option (the "Repurchase Option") for a period of 90 days
from such date to repurchase all or any portion of the Unvested Shares at the
per share repurchase price of $0.0001 per share, appropriately adjusted in the
event of a stock dividend, stock split, recapitalization, combination of shares
or similar event occurring subsequent to the date of this Agreement.

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               (ii)  Unless the Company notifies Purchaser within 90 days from
the of termination of Purchaser's Service that it does not intend to exercise
its Repurchase Option with respect to some or all of the Unvested Shares, the
Repurchase Option shall be deemed automatically exercised by the Company as of
the 90th day following such termination, provided that the Company may notify
Purchaser that it is exercising its Repurchase Option as of a date prior to such
90th day. Unless Purchaser is otherwise notified by the Company pursuant to the
preceding sentence that the Company does not intend to exercise its Repurchase
Option as to some or all of the Unvested Shares to which it applies at the time
of termination, execution of this Agreement by Purchaser constitutes written
notice to Purchaser of the Company's intention to exercise its Repurchase Option
with respect to all Unvested Shares to which such Repurchase Option applies. The
Company, at its choice, may satisfy its payment obligation to Purchaser with
respect to exercise of the Repurchase Option by either (A) delivering a check to
Purchaser in the amount of the purchase price for the Unvested Shares being
repurchased, or (B) in the event Purchaser is indebted to the Company, canceling
an amount of such indebtedness equal to the purchase price for the Unvested
Shares being repurchased, or (C) by a combination of (A) and (B) so that the
combined payment and cancellation of indebtedness equals such purchase price,
provided that the Company shall use good faith efforts to satisfy its payment
obligation to Purchaser within 15 days after Company's notice of exercise of the
Repurchase Option (or deemed exercise), and that if such check is not delivered
or such cancellation is not effective within such 15 days from such date, the
amount of the Company's unsatisfied payment obligation shall bear interest at a
rate of nine percent (9%) per annum until the Company has satisfied its payment
obligation under this paragraph (ii). In the event of any deemed automatic
exercise of the Repurchase Option pursuant to this Section 5(a)(ii) and
Purchaser is then indebted to the Company, the amount of such indebtedness equal
to the purchase price of the Unvested Shares being repurchased shall be deemed
automatically canceled as of the date of Company's notice of exercise of the
Repurchase Option (or deemed exercise). As a result of any repurchase of
Unvested Shares pursuant to this Section 5(a), the Company shall become the
legal and beneficial owner of the Unvested Shares being repurchased and shall
have all rights and interest therein or related thereto, and the Company shall
have the right to transfer to its own name the number of Unvested Shares being
repurchased by the Company, without further action by Purchaser.

          (b)  VESTING.

               (i)   The Shares will become vested as follows:

                     (A)  one sixteenth (1/16) of the Shares shall vest on
September 13, 2001; and

                     (B)  an additional one sixteenth (1/16) of the Shares shall
vest on the last day of each consecutive three-month period thereafter until
100% of the Shares have become vested; PROVIDED, however, that the vesting of
Shares on any such vesting date shall be conditioned upon Purchaser's continuing
Service with the Company from the date hereof through such vesting date.
Fractional shares shall be rounded down to the nearest whole share.

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               (ii)  Notwithstanding Section 4(b)(i), all Shares shall be deemed
to have vested immediately prior to the consummation of a Qualified Sale.

     6.   CUSTODY OF CERTIFICATES. In order to facilitate the exercise of the
Repurchase Option, the Company or its counsel shall hold all certificates
representing Unvested Shares, together with an adequate number of undated and
otherwise blank stock powers executed by Purchaser. The Company shall have the
right to cause transfers of Unvested Shares to be effected pursuant to Section
5. After any Shares become Vested Shares, the Company shall, upon request of
Purchaser, deliver to Purchaser a certificate or certificates representing such
Vested Shares. After the Company sends Purchaser a notice that it does not
intend to exercise its Repurchase Option as to certain Unvested Shares, the
Company shall, upon request of Purchaser, deliver to Purchaser a certificate or
certificates representing such Unvested Shares.

     7.   LEGENDS. Each certificate representing Shares shall prominently bear
legends in substantially the following forms:

     These securities have not been registered under the Securities Act of 1933.
     They may not be sold, offered for sale, pledged or hypothecated in the
     absence of a registration statement in effect with respect to the
     securities under such Act or an opinion of counsel satisfactory to the
     Corporation that such registration is not required.

     The securities represented by this certificate have been acquired for
     investment and have not been registered or qualified under the securities
     or "Blue Sky" laws of any jurisdiction. They may not be offered or sold
     without an opinion of counsel to the Corporation to the effect that the
     proposed transaction will be exempt from registration, qualification, and
     filings in all applicable jurisdictions.

     The Corporation is authorized to issue more than one class or series of
     stock. The powers, designations, preferences and relative participating,
     optional or other special rights, and the qualifications, limitations or
     restrictions of such preferences and/or rights of each class of stock or
     series of any class set forth in the Certificate of Incorporation of the
     Corporation. The Corporation will furnish a copy of the Certificate of
     Incorporation of the Corporation to the holder of this certificate without
     charge upon request

     The securities represented by this certificate are subject to restrictions
     on transfer and repurchase rights pursuant to the terms of a Restricted
     Stock Purchase Agreement, as amended from time to time, between the owner
     of this certificate and the Corporation. The Corporation will furnish a
     copy of this agreement to the holder hereof without charge upon written
     request.

     8.   MISCELLANEOUS.

          (a)  ENTIRE AGREEMENT. This Agreement constitutes the entire agreement
between the parties with respect to the subject matter hereof and supersedes all
prior agreements, negotiations, representations and proposals, written or oral,
relating to such subject matter.

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          (b)  AMENDMENTS. Neither this Agreement nor any provision hereof may
be changed or modified except by an agreement in writing executed by Purchaser
and on behalf of the Company.

          (c)  BINDING EFFECT OF THE AGREEMENT. This Agreement shall inure to
the benefit of, and be binding upon, the Company, Purchaser and their respective
estates, heirs, executors, transferees, successors, assigns and legal
representatives.

          (d)  PROVISIONS SEVERABLE. In the event that any provision of this
Agreement shall be determined to be invalid, illegal or otherwise unenforceable
by any court of competent jurisdiction, the validity, legality and
enforceability of the other provisions of this Agreement shall not be affected
thereby. Any invalid, illegal or unenforceable provision of this Agreement shall
be severed, and after any such severance, all other provisions hereof shall
remain in full force and effect.

          (e)  NOTICES. All notices under this Agreement shall be effective (i)
upon personal or facsimile delivery, (ii) two business days after deposit in the
United States mail as registered or certified mail postage fully prepaid, or
(iii) one business day after pickup by any overnight commercial courier service,
in each case sent or addressed to the Company at its principal office and to
Purchaser at his record address as carried in the stock records of the Company
or at such other address as he may from time to time designate in writing to the
Company.

          (f)  CONSTRUCTION. A reference to a Section shall mean a Section of
this Agreement unless otherwise expressly stated. The titles and headings herein
are for reference purposes only and shall not in any manner limit the
construction of this Agreement which shall be considered as a whole. The words
"include," "includes" and "including" when used herein shall be deemed in each
case to be followed by the words "without limitation." Whenever the context may
require, any pronouns used herein shall include the corresponding masculine,
feminine or neuter forms, and the singular form of names and pronouns shall
include the plural and vice-versa.

          (g)  NO EMPLOYMENT AGREEMENT. This Agreement shall not be construed as
an agreement by the Company to employ Purchaser, nor is the Company obligated to
employ Purchaser by reason of this Agreement or the issuance of the Shares to
Purchaser.

          (h)  SECTION 83(b) ELECTION. Purchaser will furnish to the Company a
copy of any election made by Purchaser under Section 83(b) of the Internal
Revenue Code of 1986, as amended, with respect to his acquisition of the Shares.

          (i)  APPLICABLE LAW. This Agreement shall be construed and enforced in
accordance with the laws of The Commonwealth of Massachusetts, without regard to
its principles of conflicts of laws. Purchaser consents to jurisdiction and
venue in any state or federal court in The Commonwealth of Massachusetts for the
purposes of any action relating to or arising out of this Agreement or any
breach or alleged breach hereof, and to service of process in any such action by
certified or registered mail, return receipt requested.

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          (j)  DISPOSITION OF SHARES; PURCHASE BY NOMINEE OR DESIGNEE. Any
Shares that the Company elects to purchase hereunder may be disposed of by it in
such manner as it deems appropriate with or without restrictions on the transfer
thereof, and the Company may require their transfer to a nominee or designee as
part of any purchase of the Shares from Purchaser.

          (k)  WITHHOLDING TAXES. Purchaser acknowledges and agrees that the
Company has the right to deduct from payments of any kind otherwise due to
Purchaser any federal, state or local taxes of any kind required by law to be
withheld with respect to the purchase of the Shares by Purchaser.

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     IN WITNESS WHEREOF, the parties hereto have executed this Restricted Stock
Purchase Agreement as of the date first above written.

                                          MIMEON, INC.

                                          By:   /s/ Ganesh Venkataraman
                                             ----------------------------------
                                          Name:
                                          Title:


                                           /s/ Ganesh Venkataraman
                                          -------------------------------------
                                          Ganesh Venkataraman

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