Document:

<PAGE>
                                                                    Exhibit 4.11

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A)
COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT, (B) THE COMPANY
HAS BEEN FURNISHED WITH AN OPINION OF COUNSEL REASONABLY ACCEPTABLE TO THE
COMPANY TO THE EFFECT THAT NO REGISTRATION IS REQUIRED FOR SUCH TRANSFER OR (C)
SUCH TRANSFER IS MADE IN ACCORDANCE WITH THE PROVISIONS OF REGULATION S UNDER
THE ACT. HEDGING TRANSACTIONS INVOLVING THESE SHARES MAY NOT BE CONDUCTED UNLESS
IN COMPLIANCE WITH THE ACT.

WARRANT NO. W-6

                      WARRANT TO PURCHASE 119,355 SHARES OF
                                  COMMON STOCK

                                       OF

                              ALTUS BIOLOGICS INC.

                           VOID AFTER DECEMBER 7, 2006

     This certifies that, for value received, SG Cowen Securities Corporation or
its permitted assigns ("Holder"), is entitled, subject to the terms and
conditions of this Warrant, at any time before 5:00 p.m. Eastern Standard Time
on December 7, 2006 (the "Expiration Date") to purchase from Altus Biologics
Inc. a Delaware corporation (the "Company"), up to 119,355 shares of the
Company's Common Shares, each with a par value of $0.01 (the "Warrant Stock"),
at a price of $4.2747100 per share (the "Purchase Price"). The Purchase Price
and the number and character of shares of Warrant Stock purchasable hereunder
are subject to adjustment as provided herein. Unless the context otherwise
requires, the term "Warrant Stock" shall mean the stock and other securities and
property at any time issuable upon exercise of this Warrant. The term "Warrant"
as used herein, shall include this Warrant and any warrants delivered in
substitution or exchange therefor as provided herein.

                                        1
<PAGE>
     1. EXERCISE.

     1.1 Method of Exercise. Subject to the terms and conditions of this
Warrant, the Holder may exercise this Warrant in whole or in part, at any time
or from time to time, on any business day prior to the Expiration Date by
surrendering this Warrant at the principal executive office of the Company,
together with an executed Notice of Exercise in the form attached hereto as
Exhibit 1 and payment in full of the Purchase Price for the number of shares of
Warrant Stock to be purchased upon such exercise of this Warrant.

     1.2 Form of Payment. Payment may be made by (i) check payable to the
Company's order, (ii) wire transfer of funds to the Company, (iii) cancellation
of indebtedness of the Company to the Holder or (iv) any combination of the
foregoing.

     1.3 Partial Exercise. Upon a partial exercise of this Warrant, this Warrant
shall be surrendered by the Holder and the Company shall promptly issue a new
Warrant of like tenor for purchase of the number of remaining shares of Warrant
Stock not previously purchased.

     1.4 No Fractional Shares. No fractional shares may be issued upon any
exercise of this Warrant, and any fractions shall be rounded down to the nearest
whole number of shares. If upon any exercise of this Warrant a fraction of a
share results, the Company shall pay the cash value of any such fractional
share, calculated on the basis of the Warrant Price.

     1.5 Net Exercise Election. The Holder may exercise the Warrant either (i)
by paying to the Company, by cash or check, an amount equal to the aggregate
Exercise Price of the Shares being purchased, or (ii) by electing to receive
Shares equal to the value (as determined below) of this Warrant by surrender of
the Warrant together with notice of such election, in which event the Company
shall issue to the Holder a number of Shares computed using the following
formula:

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

Where: X = the number of Shares to be issued to the Holder.

       Y = the number of Shares under this Warrant (or such lesser number of
       Shares as the Holder elects to purchase, in the case of a partial
       exercise).

       A = the fair market value of one share of Common Stock on the date of
       exercise.

       B = the Exercise Price.

     As used herein, the fair market value of the Common Stock shall mean the
mean between the highest and lowest quoted selling prices on such date on the
securities market where the Common Stock of the Company is traded, or if there
were no sales on the applicable date, on the next preceding date within a
reasonable period (as determined in the sole discretion of the Board of
Directors of the Company) on which there were sales. In the event that there
were no sales in such a market within a reasonable period, the fair market value
shall be as determined in good faith by the Board of Directors. In the event the
Holder disagrees with the fair market value determined by the Board of
Directors, the Company and the Holder shall use their best efforts to

                                        2
<PAGE>
agree upon the selection of an independent appraiser, who will have 30 days in
which to determine the fair market value of the Common Stock, and whose
determination will be final and binding on all parties concerned. All costs of
such determination shall be borne by the Company.

     1.6 Stock Certificates. In the event of any exercise of the rights
represented by this Warrant, as promptly as practicable on or after the date of
exercise and in any event within ten (10) days thereafter, the Company at its
expense shall issue and deliver to the person or persons entitled to receive the
same a certificate or certificates for the number of shares of Warrant Stock
issuable upon such exercise.

     1.7 Taxes. The issuance of the shares of Warrant Stock upon the exercise of
this Warrant, and the delivery of certificates or other instruments representing
such shares, shall be made without charge to the Holder for any tax or other
charge in respect of such issuance.

     2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

     2.1. Valid Issuance. All shares of Warrant Stock issued upon the exercise
of this Warrant shall be validly issued, fully paid and non-assessable, and free
from all taxes, liens and charges in respect of the issue thereof (other than
taxes in respect of any transfer occurring contemporaneously or otherwise
specified herein).

     2.2. Due Authorization. The execution, delivery and performance of this
Warrant have been duly authorized by all requisite corporate action by the
Company, will not violate or result in a breach of any provision of any law,
statute, rule or regulation which would materially and adversely affect the
business, assets, liabilities, financial conditions or operations of the
Company, and will not violate or result in a breach of any provision of any
order of any court or other agency or the Amended and Restated Certificate of
Incorporation of the Company and will not result in the creation or imposition
of any lien, charge or encumbrance of any nature whatsoever upon the properties
or assets of the Company.

     2.3. Binding Obligation; No Consents. This Warrant has been duly executed
and delivered by the Company and constitutes the valid and legally binding
obligation of the Company, enforceable in accordance with its respective terms.
No registration or filing with, or consent or approval of, or other action by,
any Federal, state, foreign or other governmental department, commission, board,
bureau, agency or instrumentality or any third party is necessary for the
execution, delivery and performance of this Warrant or for the issuance of the
shares of Common Shares issuable upon exercise of the Warrant Stock.

     3. TRANSFER.

     3.1 Subject to the terms hereof, including, without limitation, Sections
3.2 and 3.3, the Warrant and all rights thereunder are transferable, in whole or
in part, on the books of the Company maintained for such purpose at its office
designated in Section 8.4 hereof by the registered holder hereof in person or by
duly authorized attorney, upon surrender of the Warrant properly endorsed. Upon
any partial exercise or transfer, the Company will issue and deliver to such
holder a new warrant or warrants with respect to the Shares not so exercised,
converted or transferred. Each taker and holder of the Warrant, by taking or
holding the same, consents and agrees that the Warrant when endorsed in blank
shall be deemed negotiable, and that when the Warrant shall have been so
endorsed, the holder may be treated by the Company and all other

                                        3
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persons dealing with the Warrant as the absolute owner of such Warrant for any
purpose and as the person entitled to exercise the rights represented thereby,
or to the transfer on the books of the Company, any notice to the contrary
notwithstanding; but until such transfer on such books, the Company may treat
the registered holder of the Warrant as the owner for all purposes. The term
"Warrant" as used herein shall include the Warrant and, any warrants delivered
in substitution or exchange therefor as provided herein. The Warrant is
exchangeable for a warrant or warrants for the same aggregate number of Shares,
each new Warrant to represent the right to purchase such number of Shares as the
holder shall designate at the time of such exchange. The Warrant may be
subdivided, at the Holder's option, into several warrants to purchase the Shares
(collectively, also referred to as the "Warrant"). Such subdivision may be
accomplished in accordance with the provisions of this Section 4.

     3.1. RESTRICTIONS ON TRANSFER. Neither the Warrant nor the Shares shall be
transferable except upon the conditions specified in this Section 5.1, which
conditions are intended to insure compliance with the provisions of the
Securities Act of 1933, as amended (the "Securities Act") in respect to the
transfer of the Warrant and the Shares.

     3.1.1. Unless and until otherwise permitted by this Section 5.1, the
Warrant and each certificate or other document evidencing any of the Shares
shall be endorsed with the legends substantially in the following form:

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A)
COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT, (B) THE COMPANY
HAS BEEN FURNISHED WITH AN OPINION OF COUNSEL REASONABLY ACCEPTABLE TO THE
COMPANY TO THE EFFECT THAT NO REGISTRATION IS REQUIRED FOR SUCH TRANSFER [OR (C)
SUCH TRANSFER IS MADE IN ACCORDANCE WITH THE PROVISIONS OF REGULATION S UNDER
THE ACT. HEDGING TRANSACTIONS INVOLVING THESE SHARES MAY NOT BE CONDUCTED UNLESS
IN COMPLIANCE WITH THE ACT.]

The foregoing legend shall be removed from the certificates representing any
Shares, at the request of the Holder, (x) upon any sale pursuant to an effective
registration statement under the Securities Act, Section 4(1) of the Securities
Act or Rule 144 under the Securities Act or (y) at such time as they become
eligible for sale under Rule 144(k) under the Securities Act

THE SHARES OF STOCK REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
VOTING AGREEMENTS AS SET FORTH IN A STOCKHOLDERS' VOTING AGREEMENT, AS AMENDED
FROM TIME TO TIME, BY AND AMONG THE REGISTERED OWNER OF THIS CERTIFICATE, THE
COMPANY AND CERTAIN OTHER STOCKHOLDERS OF THE COMPANY, A COPY OF WHICH IS
AVAILABLE FOR INSPECTION AT THE OFFICES OF THE SECRETARY OF THE COMPANY.

THE SALE OR OTHER DISPOSITION OF ANY OF THE SHARES REPRESENTED BY THIS
CERTIFICATE IS RESTRICTED BY A RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT,
DATED AS OF SEPTEMBER __, 2001 AS AMENDED FROM TIME TO TIME, AMONG CERTAIN OF
THE SHAREHOLDERS OF THIS COMPANY AND THIS COMPANY (THE "AGREEMENT"). A COPY OF
THE AGREEMENT IS AVAILABLE FOR

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INSPECTION DURING NORMAL BUSINESS HOURS AT THE PRINCIPAL EXECUTIVE OFFICE OF
THIS COMPANY.

     3.1.2. Neither the Warrant nor the Shares shall be transferred and the
Company shall not be required to register any such transfer, unless and until
one of the following events shall have occurred:

     (a) (i) they first shall have been registered under the Securities Act, or
(ii) the Company first shall have been furnished with an opinion of legal
counsel, reasonably satisfactory to the Company, to the effect that such sale or
transfer is exempt from the registration requirements of the Securities Act.

     (b) Notwithstanding the foregoing, no registration or opinion of counsel
shall be required for (i) a transfer by a Holder to an affiliate (as such term
is defined in the Securities Act) of such Holder, (ii) a transfer by a Holder
which is a partnership to a partner of such partnership or a retired partner of
such partnership who retires after the date hereof, or to the estate of any such
partner or retired partner, or (iii) a transfer by a Holder which is a limited
liability company to a member of such limited liability company or a retired
member who resigns after the date hereof or to the estate of any such member or
retired member; provided that the transferee in each case agrees in writing to
be subject to the terms of this Section 5 to the same extent as if it were the
original Holder hereunder, or (iv) a transfer made in accordance with Rule 144
under the Securities Act.

     (c) For purposes of this Section 5, "Shares" shall mean the Shares and any
other shares of capital stock of the Company issued in respect of such shares
(as a result of stock splits, stock dividends, reclassifications,
recapitalizations, or similar events).

     3.2. COOPERATION. The Company shall cooperate in supplying such information
as may be reasonably requested by the Holder to complete and file any
information reporting forms presently or subsequently required by the Commission
as a condition to the availability of an exemption, presently existing or
subsequently adopted, from the 1933 Act for the sale of the Warrant or Shares.

     3.3. PERMITTED TRANSFERS. The Holder may, subject to this Section 3 and all
applicable laws and rules, transfer this Warrant and any Shares purchased
hereunder.

     4. ADJUSTMENT OF PURCHASE PRICE AND NUMBER OF SHARES. The number and
character of shares of Warrant Stock issuable upon exercise of this Warrant (or
any shares of stock or other securities or property at the time receivable or
issuable upon exercise of this Warrant) and the Purchase Price therefor, are
subject to adjustment upon occurrence of the following events:

     4.1 Adjustment for Stock Splits, Stock Dividends, Recapitalizations, etc.
The Purchase Price of this Warrant and the number of shares of Warrant Stock
issuable upon exercise of this Warrant shall each be proportionally adjusted to
reflect any stock dividend, stock split, reverse stock split, combination of
shares, reclassification, recapitalization or other similar event altering the
number of outstanding shares of Warrant Stock.

     4.2 Adjustment for Other Dividends and Distributions. In case the Company
shall make or issue, or shall fix a record date for the determination of
eligible holders entitled to receive,

                                        5
<PAGE>
a dividend or other distribution with respect to the Warrant Stock payable in
securities of the Company then, and in each such case, the Holder of this
Warrant, on exercise of this Warrant at any time after the consummation,
effective date or record date of such event, shall receive, in addition to the
shares of Warrant Stock (or such other stock or securities) issuable on such
exercise prior to such date, the securities of the Company to which such Holder
would have been entitled upon such date if such Holder had exercised this
Warrant immediately prior thereto.

     5. CERTIFICATE AS TO ADJUSTMENTS. In each case of any adjustment in either
the Purchase Price or in the number of shares of Warrant Stock, or other stock,
securities or property receivable on the exercise of this Warrant, the Chief
Financial Officer of the Company shall compute such adjustment in accordance
with the terms of this Warrant and prepare a certificate setting forth such
adjustment and showing in detail the facts upon which such adjustment is based,
including a statement of the adjusted Purchase Price. The Company shall
forthwith mail a copy of each such certificate to the Holder of this Warrant.

     6. INTENTIONALLY OMITTED.

     7. NO IMPAIRMENT. The Company shall not, by amendment of its Amended and
Restated Certificate of Incorporation or bylaws, or through reorganization,
consolidation, merger, dissolution, issue or sale of securities, sale of assets
or any other voluntary action, willfully avoid or seek to avoid the observance
or performance of any of the terms of this Warrant, but shall 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. Without limiting the generality
of the foregoing, the Company (a) shall not increase the par value of any shares
of stock issuable upon the exercise of this Warrant above the amount payable
therefor upon such exercise, and (b) shall take all action as may be necessary
or appropriate in order that the Company may validly and legally issue fully
paid and non-assessable shares of Warrant Stock upon the exercise of this
Warrant.

     8. NOTICES OF RECORD DATE. In case:

          (a) the Company shall take a record of the holders of its Warrant
Stock (or other stock or securities at the time receivable upon the exercise of
this Warrant) for the purpose of entitling them to receive any stock dividend;
or

          (b) of any consolidation or merger of the Company with or into another
corporation, or any conveyance of all or substantially all of the assets of the
Company to another corporation in which holders of the Company's stock are to
receive stock, securities or property of another corporation; or

          (c) of any voluntary dissolution, liquidation or winding-up of the
Company; or

          (d) of any redemption or conversion into Common Shares of all
outstanding Warrant Stock;

then, and in each such case, the Company shall mail or cause to be mailed to the
Holder of this Warrant a notice specifying, as the case may be, (i) the date on
which a record is to be taken for the purpose of such dividend, and stating the
amount and character of such dividend, or (ii) the date on which such
consolidation, merger, conveyance, dissolution, liquidation, winding-up,
redemption or conversion is to take place, and the time, if any is to be fixed,
as of which the holders of record of

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Warrant Stock (or such stock or securities as at the time are receivable upon
the exercise of this Warrant) shall be entitled to exchange their shares of
Warrant Stock (or such other stock or securities) for securities or other
property deliverable upon such consolidation, merger, conveyance, dissolution,
liquidation or winding-up.

     9. LOSS OR MUTILATION. Upon receipt by the Company of evidence reasonably
satisfactory to it of the ownership of and the loss, theft, destruction or
mutilation of this Warrant, and of a written indemnity agreement reasonably
satisfactory to the Company, and (in the case of mutilation) upon surrender and
cancellation of this Warrant, the Company shall execute and deliver in lieu
thereof a new Warrant of like tenor.

     10. RESERVATION OF WARRANT STOCK. The Company shall at all times reserve
and keep available for issue upon the exercise of this Warrant such number of
its authorized but unissued shares of Warrant Stock as shall be sufficient to
permit the exercise in full of this Warrant and the conversion of all shares of
Warrant.

     11. NO SHAREHOLDER RIGHTS. This Warrant in and of itself shall not entitle
the Holder to any voting rights or other rights as a shareholder of the Company.

     12. REPRESENTATIONS OF THE HOLDER. The Holder hereby represents and
warrants to the Company that it:

     12.1 Understands that: (a) the Warrant and Warrant Stock are "restricted
securities" under the federal securities laws since the sale of the Warrant and
Warrant Stock has not been registered under the Act; (b) the Warrant and Warrant
Stock may be resold without registration under the Act only in certain limited
circumstances; and (c) the Holder may be required to hold the Warrant and
Warrant Stock indefinitely unless such securities are subsequently registered
under the Act or an exemption from such registration is available.

     12.2 Agrees that the Company may place the legend set forth above on any
stock certificate(s) evidencing the Warrant Shares.

     13. NOTICES. All notices and other communications from the Company to the
Holder shall be mailed by first-class registered or certified mail, postage
prepaid, to the address furnished to the Company in writing by the Holder.

     14. AMENDMENT; WAIVER. This Warrant may be amended or any provision hereof
waived only by an instrument in writing signed by the Company and the Holder.

     15. HEADINGS. The description headings in this Warrant are inserted for
convenience and shall not control or affect the meaning or construction of any
of the provisions hereof.

     16. LAW GOVERNING. This Warrant shall be governed by the laws of the
Commonwealth of Massachusetts without regard to principles of conflicts of laws.

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     IN WITNESS WHEREOF, Company has caused this Warrant to be signed by its
duly authorized officer and issued as of the date set forth below.

Dated: December ___, 2001

                                        ALTUS BIOLOGICS INC.

                                        By:
                                            ------------------------------------
                                            Peter Lanciano
                                            President

                                        8
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                                                                       Exhibit 1

                               NOTICE OF EXERCISE

To: Altus Biologics, Inc.
    625 Putnam Avenue
    Cambridge, MA 02139

     (1) Standard Election. The undersigned Holder elects to purchase _________
shares of Common Shares of _______________ (the "Warrant Stock"), pursuant to
the terms of the attached Warrant, and tenders herewith payment of the purchase
price for such shares in full.

     (2) Net Exercise Election. The undersigned Holder elects to convert the
Warrant into shares of Warrant Stock by net exercise election pursuant to
Section 1.5 of the Warrant. This conversion is exercised with respect to
__________ shares of Common Shares of _______________ (the "Warrant Stock").

     Please issue a certificate or certificates representing such shares of
Warrant Stock in the name specified below:

-------------------------------------
(Name)

-------------------------------------
(Address)

-------------------------------------
(City, State, Zip Code)

-------------------------------------
(Federal Tax Identification Number)

-------------------------------------
(Date)

                                        SG COWEN SECURITIES CORPORATION

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                        9
<PAGE>
                               FORM OF ASSIGNMENT

     FOR VALUE RECEIVED the undersigned Holder of this Warrant hereby sells,
assigns and transfers to the Assignee named below all of the rights of the
undersigned under the Warrant, with respect to the number of shares of Common
Shares set forth below:

<TABLE>
<CAPTION>
Name of Assignee   Address   No. of Shares
----------------   -------   -------------
<S>                <C>       <C>

</TABLE>

and does hereby irrevocably constitute and appoint ________________ Attorney to
make such transfer on the books of ___________________, maintained for the
purpose, with full power of substitution in the premises.

Dated:                                  SG COWEN SECURITIES CORPORATION
       ------------------------------

                                        By:
                                            ------------------------------------
                                        Name:
                                              ----------------------------------
                                        Title:
                                               ---------------------------------

                                       10<PAGE>
                                                                    Exhibit 4.12

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A)
COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT, (B) THE COMPANY
HAS BEEN FURNISHED WITH AN OPINION OF COUNSEL REASONABLY ACCEPTABLE TO THE
COMPANY TO THE EFFECT THAT NO REGISTRATION IS REQUIRED FOR SUCH TRANSFER OR (C)
SUCH TRANSFER IS MADE IN ACCORDANCE WITH THE PROVISIONS OF REGULATION S UNDER
THE ACT. HEDGING TRANSACTIONS INVOLVING THESE SHARES MAY NOT BE CONDUCTED UNLESS
IN COMPLIANCE WITH THE ACT.

================================================================================

Warrant No. W-B __________                                         XXXXXX Shares

                                     Form of
                                     WARRANT
           To Purchase Shares of Series B Convertible Preferred Stock
                                       of
                              ALTUS BIOLOGICS INC.
                            Dated September __, 2001

================================================================================

     WHEREAS, Altus Biologics Inc., a Delaware corporation (the "Company"),
intends to provide the Holder an opportunity to increase its equity interest in
the Company through the acquisition of shares of its Series B Convertible
Preferred Stock, $.0l par value per share ("Series B Stock"), upon the exercise
of a warrant with respect thereto;

     NOW, THEREFORE, in consideration of the foregoing and other good and
valuable consideration, the receipt of which is hereby acknowledged, the Company
certifies and agrees as follows:

     This Warrant certifies that, for value received, ______________ (the
"Holder"), or registered assigns, is entitled to purchase from the Company XXXXX
(as adjusted from time to time pursuant to Section 6 hereof, the "Original
Number") shares of the fully paid and non-assessable Series B Stock of the
Company, at a price of $4.3147358 per share (the "Exercise Price").
Notwithstanding the foregoing, if the Series B Stock shall prior to exercise or
exchange of this Warrant have been converted into Common Stock, $.01 par value
(the "Common Stock") of the Company as a result of mandatory conversion
("Mandatory Conversion Event") of the Series B Stock as set forth in Article IV,
Section E5 of the Amended and Restated Certificate of Incorporation of the
Company (as the same may be further amended, restated or in effect from time to
time, the "Charter"), then from and after the date of the Mandatory Conversion
Event, this Warrant shall be exercisable for that number of shares of Common
Stock that is equal to the Original Number multiplied by the Conversion Factor
(as defined below). The Conversion Factor shall equal the number of shares of
Common Stock that each share of outstanding Series B Stock converted into on the
date of the Mandatory Conversion Event. Upon the occurrence of the Mandatory
Conversion Event, the Exercise Price then in effect (the "Original Exercise
Price") shall be adjusted to a number that is equal to the Original Exercise
Price divided by the Conversion Factor. This Warrant may be exercised at any
time on or before the "Expiration Date" which shall mean the date that is seven
(7) years after the date hereof. This Warrant is issued as of September __, 2001
(the "Issue Date") pursuant to that certain Series B Convertible Preferred Stock
and Warrant Purchase Agreement dated as of September __, 2001. The shares of
capital stock of the Company issuable upon exercise or exchange of this Warrant
are sometimes hereinafter referred to as the "Warrant Shares," and, in
connection therewith, all references herein to Warrant Shares shall mean Series
B Stock until the occurrence of a Mandatory Conversion Event, and upon and at
all times after, the occurrence of a Mandatory Conversion Event, shall mean
Common Stock. As used herein, the term "Warrant Class" shall mean (i) prior to
the occurrence of the Mandatory Conversion Event, the Series B Stock and (ii)
after the occurrence of the Mandatory Conversion Event, the Common Stock.
<PAGE>
     1. EXERCISE OF WARRANT.

     1.1. PROCEDURE. The Holder or any person or entity to whom the Holder has
assigned its rights under this Warrant (collectively referred to as the
"Warrantholder") may exercise this Warrant, at any time or from time to time,
prior to the Expiration Date, on any business day, by surrendering the Warrant,
accompanied by a written notice in the form attached hereto (the "Exercise
Notice"), to the Company at the address designated in Section 8.4 hereof,
exercising this Warrant and specifying the total number of Warrant Shares the
Warrantholder will purchase pursuant to such exercise. This Warrant may be
exercised in whole or in part as to any or all of the Warrant Shares. A
certificate or certificates for the Warrant Shares purchased upon exercise of
this Warrant and, in the event of a partial exercise of this Warrant, a new
Warrant of like tenor representing the balance of Warrant Shares purchasable
hereunder, shall be delivered by the Company to the Warrantholder not later than
ten days after payment is made for the Warrant Shares purchased upon such
partial exercise. No fractions of a share of capital stock will be issued upon
the exercise of this Warrant, but if a fractional share would be issuable upon
exercise, the Company will pay in cash the fair market value thereof as
determined under Section 1.2 below.

     1.2. NET EXERCISE FORMULA. The Warrantholder may exercise this Warrant
either (i) by paying to the Company, by cash or check, an amount equal to the
aggregate Exercise Price of the Warrant Shares being purchased, or (ii) by
electing to receive Warrant Shares equal to the value (as determined below) of
this Warrant by surrender of this Warrant together with notice of such election,
in which event the Company shall issue to the Warrantholder a number of Warrant
Shares computed using the following formula:

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

Where: X = the number of Warrant Shares to be issued to the Warrantholder.

          Y = the number of Warrant Shares under this Warrant (or such lesser
     number of Warrant Shares as the Warrantholder elects to purchase, in the
     case of a partial exercise).

          A = the fair market value of one Warrant Share.

          B = the Exercise Price.

     As used herein, the fair market value of one Warrant Share shall mean:

     (i) After the Mandatory Conversion Event (A) (1) if the Common Stock of the
Company is not then traded on a national securities exchange, the average of the
closing prices quoted on the National Association of Securities Dealers, Inc.
Automated Quotation National Market System, if applicable, or the average of the
last bid and asked prices of the Common Stock quoted in the
over-the-counter-market or (2) if the Common Stock is then traded on a national
securities exchange, the average of the high and low prices of the Common Stock
listed on the principal national securities exchange on which the Common Stock
is so traded, in each case for the twenty (20) trading days immediately
preceding the determination date or, if such date is not a business day on which
shares are traded, the next immediately preceding trading day;

               (B) in all other circumstances, the fair market value per share
of Common Stock as determined by the Company's Board of Directors in good faith
after taking into consideration all factors it deems appropriate, including,
without limitation, recent sale and offer prices of the capital stock of the
Company in private transactions negotiated at arm's length; provided that in the
event the Warrantholder disagrees with the fair market value determined by the
Board of Directors, the Company and the Warrantholder shall use their best
efforts to agree upon the selection of an independent appraiser, who will have
30 days in which to determine the fair market value of the Common Stock, and
whose determination will be final and binding on all parties concerned with all
costs of such determination to be borne by the Company;

     (ii) Prior to the Mandatory Occurrence Event, the fair market value per
share of Series B Stock as determined by the Company's Board of Directors in
good faith after taking into consideration all factors it deems appropriate,
including, without limitation, recent sale and offer prices of the capital stock
of the Company in private

                                       2
<PAGE>
transactions negotiated at arm's length and the privileges and preferences of
the Series B Stock, provided that in the event the Warrantholder disagrees with
the fair market value determined by the Board of Directors, the Company and the
Warrantholder disagrees with the fair market value determined by the Board of
Directors, the Company and the Warrantholder shall use their best efforts to
agree upon the selection of an independent appraiser, who will have 30 days in
which to determine the fair market value of the Series B Stock, and whose
determination will be final and binding on all parties concerned with all costs
of such determination to be borne by the Company.

     1.3. AUTOMATIC EXERCISE. To the extent this Warrant is not previously
exercised, and if the fair market value (as determined in accordance with
Section 1.2 above) of one Warrant Share is greater than the Exercise Price, as
adjusted, this Warrant shall be deemed automatically exercised in accordance
with Section 1.2 hereof (even if not surrendered) immediately prior to the close
of business on the Expiration Date or if such date is not a business day in
Boston, on the business day next preceding the Expiration Date. For purposes of
such automatic exercise, the fair market value of one Warrant Share shall be the
fair market value determined pursuant to Section 1.2 above. To the extent this
Warrant or any portion thereof is deemed automatically exercised pursuant to
this Section 1.3, the Company agrees to notify Warrantholder within a reasonable
period of time of the number of shares of the Company's capital stock, if any,
the Warrantholder is to receive by reason of such automatic exercise. The
Company shall not be required to deliver any share certificates evidencing any
shares of capital stock issuable upon such automatic exercise unless and until
the Company has received the original of this Warrant or a Lost Warrant
Certificate (as defined below).

     1.4. LOST, STOLEN, MUTILATED OR DESTROYED WARRANT. If this Warrant is lost,
stolen mutilated or destroyed, the Company may require the Warrantholder to
provide a certificate ("Lost Warrant Certificate"), which may contain terms as
to indemnity or otherwise as it may require in its reasonable discretion (which
shall, in the case of a mutilated Warrant, include the surrender thereof), issue
a replacement Warrant of like denomination and tenor as the Warrant so lost,
stolen, mutilated or destroyed.

     2. RECORD HOLDER. A Warrant shall be deemed to have been exercised
immediately prior to the close of business on the date of its surrender for
exercise as provided in Section 1.1 above and the person entitled to receive the
Warrant Shares issuable upon such exercise or conversion shall be treated for
all purposes as the holder of such Warrant Shares of record as of the close of
business on such date. In the event of an automatic exercise pursuant to Section
1.3 above, the person entitled to receive the Warrant Shares shall be treated
for all purposes as the holder of such Warrant Shares of record as of the close
of business on the Expiration Date.

     3. PAYMENT OF TAXES. The Company shall pay all taxes and other governmental
charges (other than income taxes) that may be imposed in respect of the issue of
delivery of the Warrant Shares or any portion thereof. The Company shall not be
required, however, to pay any tax or other charge imposed in connection with any
transfer involved in the issue of any certificate for the Warrant Shares or any
portion thereof in any name other than that of the registered holder of this
Warrant surrendered in connection with the purchase of such shares, and in such
case the Company shall not be required to issue or deliver any certificate until
such tax or other charge has been paid or it has been established to the
Company's satisfaction that no tax or other charge is due.

     4. TRANSFER AND EXCHANGE.

     4.1. TRANSFER. Subject to the terms hereof, including, without limitation,
Sections 5.1 and 5.3, this Warrant and all rights thereunder are transferable,
in whole or in part, on the books of the Company maintained for such purpose at
its office designated in Section 8.4 hereof by the registered holder hereof in
person or by duly authorized attorney, upon surrender of this Warrant property
endorsed. Upon any partial exercise or transfer, the Company will issue and
deliver to such holder a new warrant or warrants with respect to the Warrant
Shares not so exercised, converted or transferred. Each taker and holder of the
Warrant, by taking or holding the same, consents and agrees that this Warrant
when endorsed in blank shall be deemed negotiable, and that when this Warrant
shall have been so endorsed, the holder may be treated by the Company and all
other persons dealing with this Warrant as the absolute owner of such Warrant
for any purpose and as the person entitled to exercise the rights represented
thereby, or to the transfer on the books of the Company, any notice to the
contrary notwithstanding; but until such transfer on such books, the Company may
treat the registered holder of this Warrant as the owner for all purposes. The
term "Warrant" as used herein shall include this Warrant and, any warrants
delivered in substitution or exchange therefor as provided herein.

                                       3
<PAGE>
     4.2. EXCHANGE. The Warrant is exchangeable for a warrant or warrants for
the same aggregate number of Warrant Shares, each new Warrant to represent the
right to purchase such number of Warrant Shares as the holder shall designate at
the time of such exchange. The Warrant may be subdivided, at the Warrantholder's
option, into several warrants to purchase the Warrant Shares (collectively, also
referred to as the "Warrant"). Such subdivision may be accomplished in
accordance with the provisions of this Section 4.

     5. TRANSFER OF SECURITIES

     5.1. RESTRICTIONS ON TRANSFER. Neither this Warrant nor the Warrant Shares
shall be transferable except upon the conditions specified in this Section 5.1,
which conditions are intended to insure compliance with the provisions of the
Securities Act of 1933, as amended (the "Securities Act") in respect to the
transfer of this Warrant and the Warrant Shares.

          5.1.1. Unless and until otherwise permitted by this Section 5.1, this
Warrant and each certificate or other document evidencing any of the Warrant
Shares shall be endorsed with the legends substantially in the following form:

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED, AND MAY NOT BE SOLD, PLEDGED OR OTHERWISE TRANSFERRED UNLESS (A)
COVERED BY AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT, (B) THE COMPANY
HAS BEEN FURNISHED WITH AN OPINION OF COUNSEL REASONABLY ACCEPTABLE TO THE
COMPANY TO THE EFFECT THAT NO REGISTRATION IS REQUIRED FOR SUCH TRANSFER OR (C)
SUCH TRANSFER IS MADE IN ACCORDANCE WITH THE PROVISIONS OF REGULATION S UNDER
THE ACT. HEDGING TRANSACTIONS INVOLVING THESE SHARES MAY NOT BE CONDUCTED UNLESS
IN COMPLIANCE WITH THE ACT.

The foregoing legend shall be removed from the certificates representing any
Warrant Shares, at the request of the Warrantholder, (x) upon any sale pursuant
to an effective registration statement under the Securities Act, Section 4(1) of
the Securities Act or Rule 144 under the Securities Act or (y) at such time as
they become eligible for sale under Rule 144(k) under the Securities Act.

THE SHARES OF STOCK REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO CERTAIN
VOTING AGREEMENTS AS SET FORTH IN A STOCKHOLDERS' VOTING AGREEMENT, AS AMENDED
FROM TIME TO TIME, BY AND AMONG THE REGISTERED OWNER OF THIS CERTIFICATE, THE
COMPANY AND CERTAIN OTHER STOCKHOLDERS OF THE COMPANY, A COPY OF WHICH IS
AVAILABLE FOR INSPECTION AT THE OFFICES OF THE SECRETARY OF THE COMPANY.

THE SALE OR OTHER DISPOSITION OF ANY OF THE SHARES REPRESENTED BY THIS
CERTIFICATE IS RESTRICTED BY A RIGHT OF FIRST REFUSAL AND CO-SALE AGREEMENT,
DATED AS OF SEPTEMBER __, 2001 AS AMENDED FROM TIME TO TIME, AMONG CERTAIN OF
THE STOCKHOLDERS OF THIS COMPANY AND THIS COMPANY (THE "AGREEMENT"). A COPY OF
THE AGREEMENT IS AVAILABLE FOR INSPECTION DURING NORMAL BUSINESS HOURS AT THE
PRINCIPAL EXECUTIVE OFFICE OF THIS COMPANY.

          5.1.2. Neither this Warrant nor the Warrant Shares shall be
transferred and the Company shall not be required to register any such transfer,
unless and until one of the following events shall have occurred:

     (a) (i) the Warrant or the Warrant Shares, as the case may be, first shall
have been registered under the Securities Act, or (ii) the Company first shall
have been furnished with an opinion of legal counsel, reasonably satisfactory to
the Company, to the effect that such sale or transfer is exempt from the
registration requirements of the Securities Act.

     (b) Notwithstanding the foregoing, no registration or opinion of counsel
shall be required for (i) a transfer by a Warrantholder to an affiliate (as such
term is defined in the Securities Act) of such Warrantholder, (ii) a transfer by
a Warrantholder which is a partnership to a partner of such partnership or a
retired partner of such

                                       4
<PAGE>
partnership who retires after the date hereof, or to the estate of any such
partner or retired partner, or (iii) a transfer by a Warrantholder which is a
limited liability company to a member of such limited liability company or a
retired member who resigns after the date hereof or to the estate of any such
member or retired member; provided that the transferee in each case agrees in
writing to be subject to the terms of this Section 5 to the same extent as if it
were the original Warrantholder hereunder, or (iv) a transfer made in accordance
with Rule 144 under the Securities Act.

     (c) For purposes of this Section 5, "Warrant Shares" shall mean the Warrant
Shares and any other shares of capital stock of the Company issued in respect of
such shares (as a result of stock splits, stock dividends, reclassifications,
recapitalizations, or similar events).

     5.2. COOPERATION. The Company shall cooperate in supplying such information
as may be reasonably requested by the Warrantholder to complete and file any
information reporting forms presently or subsequently required by the Commission
as a condition to the availability of an exemption, presently existing or
subsequently adopted, from the Securities Act for the sale of this Warrant or
Warrant Shares.

     5.3. PERMITTED TRANSFERS. The Warrantholder may, subject to all applicable
laws and rules, transfer this Warrant and any Warrant Shares purchased
hereunder.

     6. ADJUSTMENTS TO EXERCISE PRICE AND WARRANT SHARES. The Exercise Price in
effect from time to time and the number of Warrant Shares shall be subject to
adjustment in certain cases as set forth in this Section 6.

     6.1. SUBDIVISION OR COMBINATION. In the event the outstanding shares of the
Warrant Class shall be subdivided into a greater number of shares of such class,
the Exercise Price for the Warrant Shares shall, simultaneously with the
effectiveness of such subdivision, be proportionately reduced and the number of
Warrant Shares proportionately increased, and conversely, in case the
outstanding shares of the Warrant Class shall be combined into a small number of
shares of such class, the Exercise Price shall simultaneously with the
effectiveness of such combination, be proportionately increased and the number
of Warrant Shares proportionately reduced. Any adjustment under this paragraph
shall become effective at the close of business on the date the subdivision or
combination becomes effective.

     6.2 DIVIDENDS AND DISTRIBUTIONS.

          6.2.1. In the event the Company at any time, or from time to time
after the Issuance Date shall make or issue, or fix a record date for the
determination of holders of shares of the Warrant Class entitled to receive, a
dividend or other distribution payable in additional shares of shares of the
Warrant Class, then and in each such event the Exercise Price then in effect
immediately before such event shall be decreased as of the time of such issuance
or, in the event such a record date shall have been fixed, as of the close of
business on such record date, by multiplying the Exercise Price then in effect
by a fraction:

     (1) the numerator of which shall be the total number of shares of the
Warrant Class issued and outstanding immediately prior to the time of such
issuance or the close of business on such record date, and

     (2) the denominator of which shall be the total number of shares of the
Warrant Class issued and outstanding immediately prior to the time of such
issuance or the close of business on such record date plus the number of shares
of the Warrant Class issuable in payment of such dividend or distribution;

     provided, however, if such record date shall have been fixed and such
dividend is not fully paid or if such distribution is not fully made on the date
fixed therefor, the Exercise Price shall be recomputed accordingly as of the
close of business on such record date and thereafter the Exercise Price shall be
adjusted pursuant to this paragraph as of the time of actual payment of such
dividends or distributions.

          6.2.2. In the event the Company at any time or from time to time after
the Issuance Date shall make or issue, or fix a record date for the
determination of holders of shares of the Warrant Class entitled to receive, a
dividend or other distribution payable in securities of the Company (other than
shares of the Warrant Class) or in cash or other property (other than cash out
of earnings or earned surplus, determined in accordance with generally accepted
accounting principles), then and in each such event provision shall be made so
that the Warrantholder shall

                                       5
<PAGE>
receive upon exercise hereof, in addition to the number of shares of the Warrant
Class issuable hereunder, the kind and amount of securities of the Company
and/or cash and other property which the Warrantholder would have been entitled
to receive had this Warrant been exercised into shares of the Warrant Class on
the date of such event and had the Warrantholder thereafter, during the period
from the date of such event to and including the date of exercise, retained any
such securities receivable, giving application to all adjustments called for
during such period under this Section 6 with respect to the rights of the
Warrantholder.

     6.3. ADJUSTMENT FOR REORGANIZATION, CONSOLIDATION OR MERGER.

          6.3.1. In case of any reorganization of the Company (or any other
corporation the stock or other securities of which are at the time receivable on
the exercise of the Warrant) after the date on which this Warrant is first
issued (the "Issuance Date"), or in case, after such date, the Company (or any
such other corporation) shall consolidate with or merge into another corporation
or convey all or substantially all of its assets to another corporation, then
and in each such case the Warrantholder, upon exercise of this Warrant as
provided in Section 1 hereof at any time after the consummation of such
reorganization, consolidation, merger or conveyance, shall be entitled to
receive, in lieu of the stock or other securities and property receivable upon
the exercise of this Warrant prior to such consummation, the stock or other
securities or property to which the Warrantholder would have been entitled upon
such consummation if the Warrantholder had exercised or converted this Warrant
immediately prior thereto; in each such case, the terms of this Warrant,
including the exercise provisions of Section 1, shall be applicable to the
shares of stock or other securities or property receivable upon the exercise of
this Warrant after such consummation.

          6.3.2. The Company shall not effect any consolidation, merger or
conveyance of all or substantially all of its assets unless prior to the
consummation thereof, the successor corporation (if other than the Company)
resulting from such consolidation or merger or the corporation into or for the
securities of which the previously outstanding stock of the Company shall be
changed in connection with such consolidation or merger, or the corporation
purchasing such assets, as the case may be, shall assume by written instrument,
in form and substance reasonably satisfactory to the Warrantholder, executed and
delivered in accordance with Section 10.4 hereof, the obligation to deliver to
the Warrantholder such shares of stock, securities or assets as, in accordance
with the foregoing provisions, the Warrantholder is entitled to purchase.

          6.3.3. If a purchase, tender or exchange offer is made to and accepted
by the holders of more than 50% of the voting power of the outstanding shares of
stock of the Company, the Company shall not effect any consolidation, merger or
sale with the Person having made such offer or with any Affiliate of such
Person, unless prior to the consummation of such consolidation, merger or sale
the Warrantholder shall have been given a reasonable opportunity to then elect
to receive either the stock, securities or assets then issuable upon the
exercise of this Warrant or, if different, the stock, securities or assets, or
the equivalent, issued to previous holders of the Common Stock in accordance
with such offer, computed as though the Warrantholder hereof had been at the
time of such offer, a holder of the stock, securities or assets then purchasable
upon the exercise or conversion of the Warrant. As used in this paragraph
6.3.3., the term "Person" shall mean and include an individual, a partnership, a
corporation, a trust, a joint venture, an unincorporated organization and a
government or any department or agency thereof and an "Affiliate" of any Person
shall mean any Person directly or indirectly controlling, controlled by or under
direct or indirect common control with, such other Person. A Person shall be
deemed to control a corporation if such Person possesses, directly or
indirectly, the power to direct or cause the direction of the management and
policies of such corporation, whether through the ownership of voting
securities, by contract or otherwise. Notwithstanding the foregoing, nothing set
forth in this Section 6.3.3 shall limit the Warrantholder's rights pursuant to
Section 6.3.1 in the event the Warrantholder does not make an election pursuant
to this Section 6.3.3.

     6.4. ADJUSTMENTS TO EXERCISE PRICE FOR CERTAIN DILUTING ISSUANCES OCCURRING
AFTER A MANDATORY CONVERSION EVENT.

          6.4.1. Special Definitions. The following definitions shall apply:

               (A) "Option" shall mean rights, options or warrants to subscribe
          for, purchase or otherwise acquire Common Stock or Convertible
          Securities.

                                       6
<PAGE>
               (B) "Mandatory Conversion Date" shall mean the date on which the
          Mandatory Conversion Event occurs.

               (C) "Convertible Securities" shall mean any evidence of
          indebtedness, shares or other securities directly or indirectly
          convertible into or exchangeable for Common Stock, but excluding
          Options.

               (D) "Additional Shares of Common Stock" shall mean all shares of
          Common Stock issued (or pursuant to Section 6.4.3 deemed to be issued)
          by the Company after the Mandatory Conversion Date, other than:

                    (I) shares of Common Stock issued or issuable upon
               conversion or exchange of any Convertible Securities or exercise
               of any Options outstanding on the Mandatory Conversion Date;

                    (II) shares of Common Stock issued or issuable as a dividend
               or distribution on Common Stock;

                    (III) shares of Common Stock issued or issuable by reason of
               a dividend, stock split, split-up or other distribution on shares
               of Common Stock that is covered by Subsection 6.1 or 6.2 above;
               and

                    (IV) shares of Common Stock (or Options with respect
               thereto), issued or issuable for compensatory purposes to
               employees or directors of, or consultants to, the Company or any
               of its subsidiaries pursuant to a plan, agreement or arrangement
               approved by the Board of Directors of the Company ("Employee
               Options").

          6.4.2. No Adjustment of Exercise Price. No adjustment in the Exercise
Price shall be made as the result of the issuance of Additional Shares of Common
Stock if: (a) the consideration per share (determined pursuant to Subsection
6.4.5 for such Additional Share of Common Stock issued or deemed to be issued by
the Company is equal to or greater than the Exercise Price in effect immediately
prior to the issuance or deemed issuance of such Additional Shares of Common
Stock, or (b) prior to such issuance or deemed issuance, the Company receives
written notice from the holders of Purchaser Warrants (as defined in Section
8.7) representing at least 66.67% of the number of shares of Common Stock then
subject to outstanding Purchaser Warrants agreeing that no such adjustment shall
be made as the result of the issuance or deemed issuance of Additional Shares of
Common Stock.

          6.4.3. Deemed Issue of Additional Shares of Common Stock. If the
Company at any time or from time to time after the Mandatory Conversion Date
shall issue any Options (excluding Employee Options) or Convertible Securities
or shall fix a record date for the determination of holders of any class of
securities entitled to receive any such Options or Convertible Securities, then
the maximum number of shares of Common Stock (as set forth in the instrument
relating thereto without regard to any provision contained therein for a
subsequent adjustment of such number) issuable upon the exercise of such Options
or, in the case of Convertible Securities and Options therefor, the conversion
or exchange of such Convertible Securities, shall be deemed to be Additional
Shares of Common Stock issued as of the time of such issue or, in case such a
record date shall have been fixed, as of the close of business on such record
date, provided that Additional Shares of Common Stock shall not be deemed to
have been issued unless the consideration per share (determined pursuant to
Subsection 6.4.5 hereof) of such Additional Shares of Common Stock would be less
than the applicable Exercise Price in effect on the date of and immediately
prior to such issue, or such record date, as the case may be, and provided
further that in any such case in which Additional Shares of Common Stock are
deemed to be issued:

               (A) No further adjustment in the Exercise Price shall be made
          upon the subsequent issue of Convertible Securities or shares of
          Common Stock upon the exercise of such Options or conversion or
          exchange of such Convertible Securities;

               (B) If such Options or Convertible Securities by their terms
          provide, with the

                                       7
<PAGE>
          passage of time or otherwise, for any increase or decrease in the
          consideration payable to the Company, then upon the exercise,
          conversion or exchange thereof, the Exercise Price computed upon the
          original issue thereof (or upon the occurrence of a record date with
          respect thereto), and any subsequent adjustments based thereon, shall,
          upon any such increase or decrease becoming effective, be recomputed
          to reflect such increase or decrease insofar as it affects such
          Options or the rights of conversion or exchange under such Convertible
          Securities;

               (C) Upon the expiration or termination of any such unexercised
          Option or unconverted Convertible Security, the Exercise Price shall
          not be readjusted, but the Additional Shares of Common Stock deemed
          issued as the result of the original issue of such Option or
          Convertible Security shall not be deemed issued for the purposes of
          any subsequent adjustment of the Exercise Price;

               (D) In the event of any change in the number of shares of Common
          Stock issuable upon the exercise, conversion or exchange of any such
          Option or Convertible Security, including, but not limited to, a
          change resulting from the anti-dilution provisions thereof, the
          Exercise Price then in effect shall forthwith be readjusted to such
          Exercise Price as would have obtained had the adjustment which was
          made upon the issuance of such Option or Convertible Security not
          exercised, converted or exchanged prior to such change been made upon
          the basis of such change but no further adjustments shall be made for
          the actual issuance of Common Stock upon exercise of any such Option
          or Convertible Security; and

               (E) No readjustment pursuant to clause (B) or (D) above shall
          have the effect of increasing the Exercise Price to an amount which
          exceeds the lower of (i) the Exercise Price on the original adjustment
          date, or (ii) the Exercise Price that would have resulted from any
          issuances of Additional Shares of Common Stock between the original
          adjustment date and such readjustment date.

     In the event that, after the Mandatory Conversion Date, the price at which
Options or Convertible Securities may be exercised or converted is decreased, or
the number of shares into which Options or Convertible Securities may be
exercised or converted is increased, (whether such Options or Convertible
Securities were outstanding on the Mandatory Conversion Date or were issued
after the Mandatory Conversion Date), then such Options or Convertible
Securities, as so modified, shall be deemed to have been issued after the
Mandatory Conversion Date and the provisions of this Subsection 6.4.3 shall
apply.

          6.4.4. Adjustment of Exercise Price Upon Issuance of Additional Shares
of Common Stock. In the event the Company shall at any time after the Mandatory
Conversion Date issue Additional Shares of Common Stock (including Additional
Shares of Common Stock deemed to be issued pursuant to Subsection 6.4.3, without
consideration or for a consideration per share less than the applicable Exercise
Price in effect immediately prior to such issue, then and in such event, such
Exercise Price shall be reduced, concurrently with such issue, to a price
(calculated to the nearest cent) determined by multiplying such Exercise Price
by a fraction, (A) the numerator of which shall be (1) the number of shares of
Common Stock outstanding immediately prior to such issue plus (2) the number of
shares of Common Stock which the aggregate consideration received or to be
received by the Company for the total number of Additional Shares of Common
Stock so issued would purchase at such Exercise Price; and (B) the denominator
of which shall be the number of shares of Common Stock outstanding immediately
prior to such issue plus the number of such Additional Shares of Common Stock so
issued, provided that, (i) for the purpose of this Subsection 6.4.4, all shares
of Common Stock issuable upon conversion or exchange of Convertible Securities
outstanding immediately prior to such issue shall be deemed to be outstanding,
and (ii) the number of shares of Common Stock deemed issuable upon conversion or
exchange of such outstanding Convertible Securities shall not give effect to any
adjustments to the conversion or exchange price or conversion or exchange rate
of such Convertible Securities resulting from the issuance of Additional Shares
of Common Stock that is the subject of this calculation.

          6.4.5 Determination of Consideration. For purposes of this Subsection
6.4, the consideration received by the Company for the issue of any Additional
Shares of Common Stock shall be computed as follows:

                                       8
<PAGE>
               (A) Cash and Property: Such consideration shall:

                    (I) insofar as it consists of cash, be computed at the
               aggregate of cash received by the Company, excluding amounts paid
               or payable for accrued interest;

                    (II) insofar as it consists of property other than cash, be
               computed at the fair market value thereof at the time of such
               issue, as determined in good faith by the Board of Directors; and

                    (III) in the event Additional Shares of Common Stock are
               issued together with other shares or securities or other assets
               of the Company for consideration which covers both, be the
               proportion of such consideration so received, computed as
               provided in clauses (I) and (II) above, as determined in good
               faith by the Board of Directors.

               (B) Options and Convertible Securities. The consideration per
          share received by the Company for Additional Shares of Common Stock
          deemed to have been issued pursuant to Subsection 6.4, relating to
          Options and Convertible Securities, shall be determined by dividing

                    (x) the total amount, if any, received or receivable by the
               Company as consideration for the issue of such Options or
               Convertible Securities, plus the minimum aggregate amount of
               additional consideration (as set forth in the instruments
               relating thereto, without regard to any provision contained
               therein for a subsequent adjustment of such consideration)
               payable to the Company upon the exercise of such Options or the
               conversion or exchange of such Convertible Securities, or in the
               case of Options for Convertible Securities, the exercise of such
               Options for Convertible Securities and the conversion or exchange
               of such Convertible Securities, by

                    (y) the maximum number of shares of Common Stock (as set
               forth in the instruments relating thereto, without regard to any
               provision contained therein for a subsequent adjustment of such
               number) issuable upon the exercise of such Options or the
               conversion or exchange of such Convertible Securities.

     6.5. NOTICE OF ADJUSTMENT. When any adjustment is required to be made in
the Exercise Price, the Company shall promptly notify the Warrantholder of such
event, of the calculation by which such adjustment is to be made and of the
resulting Exercise Price.

     6.6. DUTY TO MAKE FAIR ADJUSTMENTS IN CERTAIN CASES. If any event occurs as
to which in the opinion of the Board of Directors the other provisions of this
Section 6 are not strictly applicable or if strictly applicable would not fairly
protect the purchase and exercise rights of this Warrant in accordance with the
essential intent and principles of such provisions, then the Board of Directors
shall make an adjustment in the application of such provisions, in accordance
with such essential intent and principles, so as to protect such purchase rights
as aforesaid.

     7. RESERVATION OF WARRANT SHARES. The Company shall at all times reserve
and keep available out of its authorized but unissued capital stock a sufficient
number of (i) prior to the occurrence of the Mandatory Conversion Event, (a)
shares of its Series B Stock to provide for the exercise of the rights
represented by this Warrant and (b) shares of Common Stock to provide for the
conversion of the Series B Stock issuable upon exercise of this Warrant, and
(ii) after the occurrence of the Mandatory Conversion Event, shares of its
Common Stock to provide for the exercise of rights represented by this Warrant,
in each case as such number may change from time to time. Also, the Company
shall, at its own expense, take all such actions and obtain all such permits and
orders as may be necessary to enable the Company lawfully to issue the Warrant
Shares upon the exercise or conversion of this Warrant.

     8. MISCELLANEOUS.

                                       9
<PAGE>
     8.1. ENTIRE AGREEMENT. This Warrant constitutes the full and entire
understanding and agreements between the parties hereto with respect to the
subjects hereof and thereof.

     8.2. SUCCESSORS AND ASSIGNS. The terms and conditions of this Warrant shall
inure to the benefit of and be binding upon the respective successors and
assigns of the parties hereto, except as expressly provided otherwise herein.

     8.3. GOVERNING LAW. This Warrant shall be governed by and construed under
the laws of the Commonwealth of Massachusetts.

     8.4. NOTICES, ETC. All notices and other communications required or
permitted hereunder shall be in writing and shall be deemed effectively given
upon personal delivery or upon the seventh day following mailing by registered
air mail, postage prepaid, addressed (a) if to the Warrantholder, at
________________________, or at such other address as shall have furnished to
the Company in writing, (b) if to the Company, a copy should be sent to 625
Putnam Street, Cambridge, MA 02139, Attention: President, or at such other
address as the Company shall have furnished in writing to the Warrantholder,
with a copy to Mintz, Levin Cohn, Ferris, Glovsky and Popeo, P.C., One Financial
Center, MA 02111, Attention: Jonathan L. Kravetz, or (c) if to any other
Warrantholder, at such address as such holder shall have furnished to the
Company in writing, or, until such Warrantholder so furnishes an address to the
Company, then to and at the address of the last holder of such Warrant who so
furnished an address to the Company.

     8.5. DELAYS OR OMISSIONS. No delay or omission to exercise any right, power
or remedy accruing to any holder of any securities issued or sold or to be
issued or sold hereunder, upon any breach or default of the Company under this
Warrant, shall impair any such right, power or remedy of such holder nor shall
it be construed to be a waiver of any such breach or default, or an acquiescence
therein, or in any similar breach or default thereafter occurring, nor shall any
waiver of any single breach or default be deemed a waiver of any other breach or
default theretofore or thereafter occurring. Any waiver, permit, consent or
approval of any kind or character on the part of any holder of any breach or
default under this Warrant, or any waiver on the part of any holder of any
provisions or conditions of this Warrant must be in writing and shall be
effective only to the extent specifically set forth in such writing. All
remedies, either under this Warrant or by law or otherwise afforded to any
holder, shall be cumulative and not alternative.

     8.6. SURVIVAL. The representations, warranties, covenants and agreements
made herein shall survive the execution and delivery of this Warrant, except as
expressly provided otherwise herein or therein.

     8.7. WAIVERS AND AMENDMENTS. This Warrant is one of a series of Warrants
issued by the Company pursuant to the terms of that certain Series B Convertible
Preferred Stock Purchase Agreement, dated as of the Issuance Date (the "Series B
Purchase Agreement"), to the Purchasers (as defined in the Series B Purchase
Agreement), all of which are of like tenor, except as to the number of Warrant
Shares of Common Stock subject thereto (collectively, the "Purchaser Warrants").
Any term of this Warrant may be amended or waived upon the written consent of
the Company and the holders of Purchaser Warrants representing at least 66.67%
of the number of Warrant Shares then subject to outstanding Purchaser Warrants;
provided that any such amendment or waiver must apply to all Purchaser Warrants
then outstanding; and provided further that the number of Warrant Shares subject
to this Warrant and the Exercise Price of this Warrant may not be amended, and
the right to exercise this Warrant may not be waived, without the written
consent of the holder of this Warrant (it being agreed that an amendment to or
waiver under any of the provisions of Section 6 of this Warrant shall not be
considered an amendment of the number of Warrant Shares or the Exercise Price).
The Company promptly shall give written notice thereof to the record holders of
the Warrants and the Warrant Shares. This Warrant or any provision hereof may
not be changed, waived, discharged or terminated orally, but only by a statement
in writing signed by the party against which enforcement of the change, waiver,
discharge or termination is sought, except to the extent provided in this
Section 8.7.

     8.8. SEVERABILITY. If one or more provisions of this Warrant are held to be
invalid, illegal or unenforceable under applicable law, such provision shall be
modified in such manner as to be valid, legal and enforceable, but so as to most
nearly retain the intent of the parties and if such modification is not
possible, such provision shall be severed from this Warrant as if such provision
were not included. in either case, and the balance

                                       10
<PAGE>
of this Warrant shall not in any way be affected or impaired thereby and shall
be enforceable in accordance with its terms.

     8.9. REGISTERED HOLDER. The Company may deem and treat the registered
Warrantholder(s) hereof as the absolute owner(s) of this Warrant
(notwithstanding any notation of ownership or other writing hereon made by
anyone), for the purpose of any exercise or conversion hereof, of any
distribution to the Warrantholder(s) hereof, and for all other purposes, and the
Company shall not be affected by any notice to the contrary. Other than as set
forth herein, this Warrant does not entitle any Warrantholder hereof to any
rights of a stockholder of the Company.

     8.10. TITLES AND SUBTITLES. The titles of the sections and subsections of
this Warrant are for convenience and are not to be considered in construing this
Warrant.

                                       11
<PAGE>
     IN WITNESS WHEREOF, Company has caused this Warrant to be signed by its
duly authorized officer and issued as of the date set forth below.

Dated: September ___, 2001

                                        ALTUS BIOLOGICS INC.

                                        By:
                                            ------------------------------------
                                            Peter Lanciano
                                            President

                                       12
<PAGE>
                               NOTICE OF EXERCISE

                 (To be Executed by the Registered Warrantholder
                        in order to Exercise the Warrant)

     The undersigned hereby irrevocably elects to exercise the right to purchase
______________________________ ( _____________ ) Warrant Shares, covered by
Warrant No. W-___, according to the conditions thereof and herewith makes
payment of the Exercise Price of such Warrant Shares in full.

     I. Such payment is hereby tendered in the form of $____________________ by
wire transfer or certified or bank check.

     II. The undersigned elects to receive the net value of the Warrant Shares
pursuant to Section 1.2 of the Warrant.

                                        Printed Name of Warrantholder:

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

                                        Signature:

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

                                        Title (if signing on
                                        behalf of a Warrantholder):

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

                                        Date:

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

                                        Address:

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

                                       13
<PAGE>
                               FORM OF ASSIGNMENT

     For Value Received, the undersigned registered owner of this Warrant issued
by Altus Biologics Inc. hereby sells, assigns and transfers unto the Assignee
named below all of the rights of the undersigned under the within Warrant No.
W-_______________________________, with respect to the number of Warrant Shares
set forth below:

<TABLE>
<CAPTION>
Name of Assignee           Address           Number of Warrant Shares
----------------   -----------------------   ------------------------
<S>                <C>                       <C>

</TABLE>

and does hereby irrevocably constitute and appoint ____________________________
attorney to make such transfer on the books of Altus Biologics Inc., maintained
for such purpose, with full power of substitution in the premises.

Dated:
       ------------------------------   ----------------------------------------
                                        Signature of registered owner

Witness:
         ----------------------------

                                       14
<PAGE>
                           SCHEDULE OF WARRANT HOLDERS

Nomura International plc
U.S. Venture Partners VIII, L.P.
USVP VIII Affiliates Fund, L.P.
USVP Entrepreneur Partners VIII-A, L.P.
USVP Entrepreneur Partners VIII-B, L.P.
P/S BI Biomedicinsk Venture III
SG Cowen Ventures I, L.P.
Clariden Bank
Paul J. Leach
ML Investments LLC
CMEA Ventures Life Sciences 2000, L.P.
CMEA Ventures Life Sciences 2000, Civil Law Partnership
China Development Industrial Bank Incorporated
Palladin Opportunity Fund LLC
CDIB Biotech USA Investment, Company
USVP Venture Partners VIII, L.P.
USVP VIII Affiliates Fund, L.P.
U.S. Venture Partners VIII-A, L.P.
USVP Entrepreneur Partners VIII-B, L.P.
Boatung Venture Capital Corporation
Wantung Venture Capital Corporation
Chung-Shan Venture Capital Corporation
Chung-Shan II Venture Capital Corporation

                                       15

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