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                                                            Exhibit No. 10.67

                            STOCK PURCHASE AGREEMENT

                               FOR THE PURCHASE OF

                        COMMON SHARES OF METHYLGENE INC.

                                      FROM

                                 HYBRIDON, INC.

                                   THE SELLER

                                       BY

             PAUL CAPITAL PARTNERS VI, L.P. AND PCP ASSOCIATES, L.P.

                                 THE PURCHASERS

                                 MARCH 30, 2001


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                                TABLE OF CONTENTS

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ARTICLE I Purchase and Sale of Shares............................................................................       1
         1.1      CERTAIN DEFINITIONS............................................................................       1
         1.2      PURCHASE AND SALE OF SHARES....................................................................       3
         1.3      PURCHASE PRICE.................................................................................       3
         1.4      REALIZATIONS...................................................................................       3
         1.5      FINANCIAL STATEMENTS...........................................................................       3
         1.6      MATERIAL ADVERSE CHANGE........................................................................       4
         1.7      NONASSIGNABLE SHARES OR CONTRACTUAL RIGHTS.....................................................       4

ARTICLE II Representations and Warranties of the Seller..........................................................       4
         2.1      ORGANIZATION...................................................................................       4
         2.2      AUTHORIZATION..................................................................................       4
         2.3      VALIDITY.......................................................................................       4
         2.4      OWNERSHIP OF THE SHARES........................................................................       5
         2.5      CAPITALIZATION OF THE COMPANY..................................................................       5
         2.6      REALIZATIONS...................................................................................       6
         2.7      CERTAIN CONDUCT................................................................................       6
         2.8      COMPLETENESS OF DOCUMENTS......................................................................       6
         2.9      SHAREHOLDERS' AGREEMENT........................................................................       6
         2.10     LITIGATION.....................................................................................       6
         2.11     FINDERS........................................................................................       7
         2.12     FULL DISCLOSURE; ACCURACY OF INFORMATION.......................................................       7
         2.13     COMPLIANCE WITH SECURITIES LAWS................................................................       7

ARTICLE III Representations and Warranties of the Purchaser......................................................       8
         3.1      ORGANIZATION...................................................................................       8
         3.2      AUTHORIZATION..................................................................................       8
         3.3      VALIDITY.......................................................................................       8
         3.4      PURCHASE FOR INVESTMENT........................................................................       8
         3.5      ACCREDITED INVESTOR............................................................................       8
         3.6      RESTRICTED SECURITIES..........................................................................       8
         3.7      FINDERS........................................................................................       9

ARTICLE IV Covenants  9
         4.1      COOPERATION....................................................................................       9
         4.2      FILINGS BY SELLER..............................................................................       9
         4.3      TRANSFER TAXES, FEES AND EXPENSES..............................................................       9
         4.4      CONSENTS AND WAIVERS...........................................................................       9
         4.5      ACCESS.........................................................................................      10
         4.6      CERTAIN CONDUCT................................................................................      10
         4.7      CONFIDENTIALITY................................................................................      10
         4.8      OTHER NEGOTIATIONS.............................................................................      11

                                                                                                 STOCK PURCHASE AGREEMENT
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<TABLE>
<S>                                                                                                                    <C>
ARTICLE V Closing Matters........................................................................................      11
         5.1      THE CLOSING....................................................................................      11
         5.2      DELIVERY OF SHARES AND ASSIGNMENTS.............................................................      11
         5.3      DOCUMENTS AND CERTIFICATES.....................................................................      11

ARTICLE VI Conditions of Closing.................................................................................      12
         6.1      CONDITIONS APPLICABLE TO THE PURCHASER.........................................................      12
         6.2      CONDITIONS APPLICABLE TO THE SELLER............................................................      14

ARTICLE VII Termination..........................................................................................      15
         7.1      BY MUTUAL CONSENT..............................................................................      15
         7.2      BY PURCHASER...................................................................................      15
         7.3      BY SELLER......................................................................................      15
         7.4      BY EITHER PARTY................................................................................      15
         7.5      SURVIVAL UPON TERMINATION......................................................................      16
         7.6      EXPENSES.......................................................................................      16

ARTICLE VIII Indemnification.....................................................................................      16
         8.1      INDEMNIFICATION................................................................................      16
         8.2      INDEMNIFICATION BY PURCHASER...................................................................      16
         8.3      INDEMNIFICATION PROCEDURE......................................................................      17
         8.4      NO WAIVER; OTHER INDEMNIFICATION PROVISIONS....................................................      17

ARTICLE IX Miscellaneous.........................................................................................      17
         9.1      SURVIVAL OF REPRESENTATION AND WARRANTIES......................................................      17
         9.2      ADDITIONAL DOCUMENTS AND ACTS..................................................................      18
         9.3      SPECIFIC PERFORMANCE...........................................................................      18
         9.4      NOTICES........................................................................................      18
         9.5      ASSIGNMENT.....................................................................................      19
         9.6      WAIVER.........................................................................................      19
         9.7      ENTIRE AGREEMENT...............................................................................      19
         9.8      AMENDMENTS, SUPPLEMENTS, ETC...................................................................      19
         9.9      INTERPRETATION.................................................................................      20
         9.10     HEADINGS AND CAPTIONS..........................................................................      20
         9.11     COUNTERPARTS...................................................................................      20
         9.12     SUCCESSORS AND ASSIGNS.........................................................................      20
         9.13     ATTORNEYS' FEES................................................................................      20
         9.14     SEVERABILITY...................................................................................      20
         9.15     GOVERNING LAW..................................................................................      20

                                                                                                 STOCK PURCHASE AGREEMENT
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                            STOCK PURCHASE AGREEMENT

         This Stock Purchase Agreement is made and entered into as of March 30,
2001 (the "Agreement") by PAUL CAPITAL PARTNERS VI, L.P. and PCP ASSOCIATES,
L.P. (collectively, the "Purchaser" or the "Purchasers"), and HYBRIDON, INC.
(the "Seller").

                                   WITNESSETH

                  WHEREAS, the Seller is the owner of the Shares (as hereinafter
defined); and

                  WHEREAS, the Seller is a party to the Shareholders' Agreement
(as hereinafter defined) governing disposition of the Shares and granting
certain rights with respect to the Shares;

                  WHEREAS, the Purchasers desire to purchase from the Seller,
and the Seller desires to sell to the Purchasers, the Shares upon the terms and
subject to the conditions set forth in this Agreement;

                  WHEREAS, the purchase of the Shares is conditional upon the
Purchasers becoming parties to the Shareholders' Agreement as same is to be
amended as set forth hereinafter;

                  NOW, THEREFORE, in consideration of the premises and the
mutual agreements, covenants, representations, warranties and indemnities
contained in this Agreement, the Purchasers and the Seller hereby agree as
follows:

                                   ARTICLE I

                           PURCHASE AND SALE OF SHARES

         1.1 CERTAIN DEFINITIONS. For purposes of this Agreement, the following
terms shall have the meanings set forth below:

                  (a) "Ancillary Agreements" shall mean the Shareholders'
Agreement Amendment.

                  (b) "C$" shall mean Canadian dollars.

                  (c) "Closing" shall have the meaning assigned to it in Section
5.1 hereof.

                  (d) "Closing Date" shall have the meaning assigned to it in
Section 5.1 hereof.

                  (e) "Company" shall mean MethylGene Inc., a corporation
organized under the laws of Quebec.

                  (f) "Contractual Rights" shall mean all of the contractual
rights of the Seller relating to the Shares or the Company, including, without
limitation, all rights of first refusal,

                                                       STOCK PURCHASE AGREEMENT
                                       1.
<PAGE>   5

first offer and co-sale among shareholders or partners of the Company; and all
rights to receive financial and other information from the Company as is
currently held by the Company's shareholders.

                  (g) "Encumbrance" shall mean any Lien pertaining to the sale,
assignment, disposition, transfer or the voting rights of, on or pertaining to
the Shares (including, without limitation, any consents or approvals of
transfers, options, rights of first refusal and co-sale rights).

                  (h) "Lien", shall mean any lien, pledge, claim, security
interest, encumbrance, charge, restriction or limitation of any kind, whether
arising by agreement, operation of law or otherwise other than Permitted
Encumbrances.

                  (i) "Material Adverse Change" shall have the meaning set forth
in Section 1.6 hereof.

                  (j) "Permitted Encumbrances" shall mean those Encumbrances
arising under the Shareholders' Agreement to the extent they do not relate or
apply to the transactions contemplated by this Agreement.

                  (k) "Portfolio Company Certificates" shall mean certificates
provided by the Company to the Purchaser substantially in the form of Exhibit A
and Exhibit B attached hereto pursuant to which the Company represents and
warrants to the Purchasers as follows:

                  (i)     In Exhibit A, with respect to the Company, the
         representations and warranties of the Seller set forth in Section 2.5
         are true and correct as to the number of authorized and outstanding
         shares of capital stock and Share Equivalents of the Company and the
         number of securities held by the Seller;

                  (ii)    In Exhibit B, the Certificate of Transfer, that with
         respect to the Company, the transfer of the Shares to the Purchaser
         will upon Closing be made by the Company's transfer agent and the
         Purchasers shall become the holders of record of the Shares;

                  (l) "Realizations" shall mean all pre-tax and pre-withholding
payments, interest, dividends, and other distributions declared, paid or made to
and received by or on behalf of the Seller with respect to or in connection with
the ownership of, and any proceeds from the sale, assignment, transfer,
conversion, exchange, redemption, exercise, repayment, waiver, release,
compromise, settlement or satisfaction of, any Shares held by the Seller after
the Record Date and prior to the Closing.

                  (m) "Record Date" shall mean December 31, 2000.

                  (n) "Securities" shall have the meaning ascribed to that term
in the Securities Act of 1933, as amended.

                  (o) "Share Equivalents" shall have the meaning assigned to it
in Section 2.5;

                                                       STOCK PURCHASE AGREEMENT
                                       2.
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                  (p) "Shareholders' Agreement" shall mean, collectively (i)
that certain Shareholders' Agreement, dated as of January 4, 1996, among Fonds
de solidarite des travailleurs du Quebec (F.T.Q.) ("Fonds"), Fonds
d'Investissement en Biotechnologie BioCapital II, societe en commandite
("Biocapital"), Societe Innovatech du Grand Montreal ("Innovatech"), Seller and
the Company, as amended by that certain Amendment to Shareholders' Agreement,
dated as of February 27, 1998, Amendment to Shareholders' Agreement, dated as of
July 14, 2000, and Amendment to Shareholders' Agreement, dated as of August 31,
2000; and (ii) that certain Unanimous Shareholders' Agreement, dated as of
January 4, 1996, among Fonds, Biocapital, Innovatech, Seller and the Company, as
amended by that certain Amendment to Unanimous Shareholders' Agreement, dated as
of February 27, 1998.

                  (q) "Shares" shall mean 2,350,000 Common shares of the Company
to be acquired by the Purchasers at the Closing created by the conversion of the
Company's Class A shares and Class B shares into Common shares which is
contemplated by this Agreement. The number of such Shares will be appropriately
adjusted for any stock splits or dividends which are declared and paid after the
Record Date and prior to the Closing.

         1.2 PURCHASE AND SALE OF SHARES. Upon the terms and subject to the
conditions set forth in this Agreement, at the Closing the Seller shall sell,
assign, transfer and deliver to the Purchasers at the Closing and the Purchasers
shall purchase and acquire from the Seller at the Closing, all right, title and
interest in and to that number of the Shares as set forth opposite each such
Purchaser's name on Schedule 1.2 hereto, free and clear of all Liens (other than
the Encumbrances to the extent they do not apply to the transactions
contemplated by this Agreement).

         1.3 PURCHASE PRICE. The purchase price due and payable at Closing (the
"Payment") for the Shares to be sold pursuant to this Agreement shall be
C$6,697,500 (less the value of any Realizations after the Record Date and the
value of the Withholding, if any) and shall be paid to the Seller, by wire
transfer of federal funds or other immediately available funds, to the account
designated by the Seller.

         1.4 REALIZATIONS. Realizations shall be retained by the Seller and
shall reduce the Purchase Price as provided in Section 1.3. Within five (5)
business days after receipt by the Seller of any Realizations or any notice of
an entitlement to receive any Realizations but in no event later than the
Closing Date, the Seller shall notify the Purchaser of the receipt of such
Realizations or such notice, as the case may be, and the amount, nature and time
of receipt or anticipated receipt, as the case may be, of the Realizations
received or to be received by the Seller.

         1.5 FINANCIAL STATEMENTS. The Seller will cooperate with the Purchaser
in its efforts to have the Company make financial statements available to the
Purchaser.

         1.6 MATERIAL ADVERSE CHANGE. From the Record Date until the Closing
Date, in the event of a material adverse change in the Company, the value of the
Shares or the Contractual Rights ("Material Adverse Change"), the Purchaser, in
its sole discretion, upon written notice to the Seller, may terminate this
Agreement with respect to its obligations hereunder.

                                                       STOCK PURCHASE AGREEMENT
                                       3.
<PAGE>   7

         1.7 NONASSIGNABLE SHARES OR CONTRACTUAL RIGHTS. To the extent that the
assignment of the Shares or Contractual Rights shall require the consent of any
other party thereto, or shall be subject to any option in any other person by
virtue of a request for permission to sell, assign or transfer or by reason of
or pursuant to any sale, assignment or transfer to the Purchaser, this Agreement
shall not constitute a contract to assign the same to the extent that an
attempted assignment would (i) constitute a breach thereof, (ii) create rights
in others not desired by the Purchaser or (iii) create rights in third parties
against the Seller. The Seller shall cooperate with the Purchaser in any
reasonable arrangement not in violation of the Shareholders' Agreement requested
by the Purchaser designed to provide for the Purchaser the economic benefits,
rights, privileges and entitlements of the Shares, provided, that the Seller
shall not be required to pay any monetary compensation to any third party as a
part of such arrangements.

                                   ARTICLE II

                  REPRESENTATIONS AND WARRANTIES OF THE SELLER

     The Seller hereby represents and warrants to the Purchaser as follows:

         2.1 ORGANIZATION. The Seller is duly formed, validly existing and in
good standing under the laws of the jurisdiction in which it is organized.

         2.2 AUTHORIZATION. The Seller has all necessary power and authority to
enter into, execute and deliver this Agreement and the Ancillary Agreements and
to perform all of the obligations to be performed by it hereunder and
thereunder. Each of this Agreement and the Ancillary Agreements has been duly
authorized, executed and delivered by the Seller and constitutes its valid and
binding obligation, enforceable against the Seller in accordance with its terms.

         2.3 VALIDITY. Neither the execution and delivery of this Agreement or
the Ancillary Agreements nor the performance or consummation of the transactions
contemplated hereby or thereby will conflict with, result in a breach or
violation of, constitute a default under, or accelerate the performance provided
by the terms of: (i) any law, any rule or regulation of any government or any
agency of any government, or any judgment, order, writ, decree, permit or
license of any court or other agency of any government to which the Seller may
be subject; (ii) the articles or the by-laws of this Company; or (iii) subject
to obtaining appropriate waivers of rights of first refusal and co-sale rights,
the Shareholders' Agreement or any other contract, agreement, commitment or
instrument to which the Seller is a party or by which it or any of its assets is
bound or committed. Neither the execution and delivery of this Agreement or the
Ancillary Agreements nor the performance or consummation of the transactions
contemplated hereby or thereby will constitute an event which, with the lapse of
time or action by a third party, could result in the default under any of the
foregoing or result in the creation of any Lien upon the Shares. Other than the
registrations, filings, consents and approvals that have been made or obtained
and the filings required to be made by Seller pursuant for Section 4.2 below,
and the execution and delivery of this Agreement and the Ancillary Agreements
and the performance and consummation of the transactions contemplated hereby and
thereby will not require any registration, filing, consent or approval under any
such law, rule, regulation, judgment, order,

                                                       STOCK PURCHASE AGREEMENT
                                       4.
<PAGE>   8

writ, decree, permit or license, or consent or approval of, any third party,
including , without limitation, any governmental or regulatory authority or any
party to any of the Shareholders' Agreement or other contract, agreement,
commitment or instrument.

         2.4 OWNERSHIP OF THE SHARES. Except as set forth on Schedule 2.4, the
Seller owns, or immediately prior to the Closing will own, all right, title and
interest (legal and beneficial) in and to the Shares identified as being owned
by the Seller free and clear of all Liens. All of the Encumbrances potentially
applicable to the transaction contemplated by this Agreement will have been duly
waived or satisfied on or before the Closing Date, or, in the case of any rights
of first refusal, first offer, or co-sale will have been duly waived or all
applicable notice periods will have expired without such rights having been
exercised on or before the Closing Date, by all interested parties. Upon
delivery of the Shares identified as being owned by the Seller to the Purchaser
and payment therefor in accordance with this Agreement, the Purchaser will
acquire such Shares free and clear of all Liens. The Shares have been validly
subscribed and issued and are outstanding as fully paid and non-assessable.

         2.5 CAPITALIZATION OF THE COMPANY. To the best of the Seller's
knowledge, after due inquiry; (i) set forth on Schedule 2.5 attached hereto is a
complete and accurate list of all of the Company's Securities for each class and
series of Securities issued by the Company, the aggregate number of such
Security authorized and the aggregate number of each such Security outstanding,
all of which are fully paid and nonassessable and (ii) except as set forth on
Schedule 2.5, there are no (A) equity securities of any class or series of the
Company, or (B) any security exchangeable into or exercisable for such equity
securities, issued, reserved for issuance or outstanding, and there are no
options, warrants, equity securities, calls, rights, commitments or agreements
of any character to which the Company is a party or by which the Company is
bound obligating the Company to issue, deliver or sell, or cause to be issued,
delivered or sold additional shares of capital stock of the Company
(collectively, "Share Equivalents").

         2.6 REALIZATIONS. The Seller has not, since the Record Date, received,
or been notified that it is entitled to receive, any Realizations. The Seller
has no obligations pursuant to any letter of credit, guarantee, pledge,
hypothecation, borrowing or other similar arrangement in connection with the
acquisition of any of the Shares or any transaction with the Company.

         2.7 CERTAIN CONDUCT. Since the Record Date, the Seller has not, except
with the prior acknowledgment and approval by the Purchaser, (i) sold, assigned,
transferred, delivered or otherwise disposed of any of the Shares, (ii)
converted, exchanged or redeemed any of the Shares, (iii) forgiven, released,
compromised or demanded payment of any indebtedness owed to it by the Company
other than upon full payment thereof, (iv) amended, canceled or terminated the
Shareholders' Agreement or entered into any new Shareholders' Agreement, (v)
waived, amended, cancelled, terminated, exercised or failed to exercise any of
the material Contractual Rights, (vi) created or permitted to exist any Lien on
any of the Shares other than the Encumbrances, or (vii) agreed to do any of the
foregoing.

         2.8 COMPLETENESS OF DOCUMENTS. The Seller or the Company has furnished
the Purchaser with, or has made available to the Purchaser, accurate and
complete copies of all instruments, agreements and other documents representing,
relating to or constituting the Shares or any part thereof and all material
correspondence and other written communications sent or

                                                       STOCK PURCHASE AGREEMENT
                                       5.
<PAGE>   9

received by or on behalf of the Seller in its capacity as a shareholder of the
Company or by virtue of its representation on the Board of Directors of the
Company (including any written internal compilations, analyses or reports
derived therefrom), which would reasonably be expected to influence the
Purchaser's decision to complete the transactions contemplated by this
Agreement.

         2.9 SHAREHOLDERS' AGREEMENT. Attached hereto as Schedule 2.9 are
accurate and complete copies of the Shareholders' Agreement, including all
amendments and interventions thereto up to and including the date hereof.
Neither the Seller, nor to the best knowledge of the Seller, any other party is
in breach or violation of, or in default under, the Shareholders' Agreement. The
documents attached hereto as Schedule 2.9 constitute the only agreements among
the shareholders of the Company regarding the subject matter thereof or the
Shares.

         2.10 LITIGATION. There is no (i) action, suit, claim, proceeding or
investigation pending or threatened against the Seller, at law or in equity, or
before or by any federal, provincial state, municipal or other governmental
department, commission, board, bureau, agency court, or instrumentality,
domestic or foreign, (ii) arbitration proceeding relating to the Seller pending,
or (iii) governmental inquiry pending or threatened against the Seller, which,
if adversely determined, would question the validity of, or prevent the
consummation of, the transactions contemplated by this Agreement. There is no
action or suit by the Seller pending or threatened against others relating to
the Shares.

         2.11 FINDERS. The Seller has not directly or indirectly dealt with
anyone acting in the capacity of a finder or broker or incurred any obligation
for any finder's or broker's fee or commission in connection with the
transactions contemplated by this Agreement. The Seller agrees to indemnify and
hold harmless the Purchaser from any liability for any commission or
compensation in the nature of a finders' fee (and the costs and expenses of
defending against such liability or asserted liability) for which the Seller is
responsible.

         2.12 FULL DISCLOSURE; ACCURACY OF INFORMATION. The Seller has fully
provided the Purchaser with all the information that the Purchaser has requested
for deciding whether to purchase the Shares and all agreements to which the
Seller is a party and all information relating to the Shares and the Company
that the Seller possesses or has received in its capacity as a shareholder of
the Company or by virtue of its representation on the Board of Directors of the
Company (including any written internal compilations, analyses or reports
derived therefrom), which would reasonably be expected to influence the
Purchaser's decision to complete the transactions contemplated by this
Agreement. Neither this Agreement nor the Schedules or Exhibits thereto or any
certificate to be delivered at the Closing by the Seller to the Purchaser in
connection with this Agreement or any of the transactions contemplated hereby
contains an untrue statement of a material fact or omits to state a material
fact necessary to make the statements made, in the light of the circumstances
under which they are made, not misleading, or contains a material statement
which is misleading. Except as set forth in this Agreement, the Schedules and
Exhibits attached hereto and any certificate to be delivered at the Closing,
there is no fact that the Seller has not disclosed to the Purchaser in writing
and of which it has become aware in its capacity as a shareholder of the Company
or by virtue of its representation on the Board of Directors of the Company
(including any written internal compilations, analyses or reports derived
therefrom) and that has had or would reasonably be expected to have a material
adverse effect upon the financial condition, operating results, assets, customer
or supplier
                                                        STOCK PURCHASE AGREEMENT
                                       6.
<PAGE>   10

relations, employee relations or business prospects of the Company or on the
value of the Shares or the Contractual Rights. The statements contained in any
certificate to be delivered at the Closing by the Seller to the Purchaser in
connection with this Agreement or any of the transactions contemplated hereby
shall be deemed to constitute representations and warranties under this
Agreement to the same extent as if set forth in this Agreement in full.

         2.13 COMPLIANCE WITH SECURITIES LAWS. Neither the Seller nor anyone
acting on Seller's behalf has offered to sell the Shares by means of any general
solicitation or any advertising.

                                  ARTICLE III

                 REPRESENTATIONS AND WARRANTIES OF THE PURCHASER

     The Purchaser hereby represents and warrants to the Seller as follows:

         3.1 ORGANIZATION. The Purchaser is duly formed, validly existing and in
good standing under the laws of the jurisdiction in which it is organized.

         3.2 AUTHORIZATION. The Purchaser has all necessary power and authority
to enter into, execute and deliver this Agreement and the Ancillary Agreements
and to perform all of the obligations to be performed by it hereunder and
thereunder. Each of this Agreement and the Ancillary Agreements has been duly
authorized, executed and delivered by the Purchaser and constitutes its valid
and binding obligation, enforceable against the Purchaser in accordance with its
terms.

         3.3 VALIDITY. Neither the execution and delivery of this Agreement or
the Ancillary Agreements nor the performance or consummation of the transactions
contemplated hereby or thereby will conflict with, result in a breach or
violation of, constitute a default under, or accelerate the performance provided
by the terms of: (i) any law, any rule or regulation of any government or any
agency of any government, or any judgment, order, writ, decree, permit or
license of any court or other agency of any government to which the Purchaser
may be subject; (ii) any contract, agreement, commitment or instrument to which
the Purchaser is a party or by which the Purchaser or any of its assets are
bound or committed; or (iii) the Purchaser's constituent charter documents or
other governing instruments.

         3.4 PURCHASE FOR INVESTMENT. The Shares to be purchased by the
Purchaser pursuant to this Agreement are being purchased for the Purchaser's own
account, for investment and not with a view to the distribution or resale
thereof, except in compliance with the Securities Act of 1933, as amended (the
"Act") and applicable Canadian legislation.

         3.5 ACCREDITED INVESTOR. The Purchaser is an Accredited Investor within
the meaning of Rule 501 of Regulation D of the Act.

         3.6 RESTRICTED SECURITIES. The Purchaser understands that the Shares it
is purchasing are characterized as "restricted securities" under U.S. federal
securities laws inasmuch as they are being acquired in a transaction not
involving a public offering and that under such laws and
                                                        STOCK PURCHASE AGREEMENT
                                       7.
<PAGE>   11

applicable regulations such Shares may be resold without registration under the
Act only in certain limited circumstances. In the absence of an effective
registration statement covering the Shares or an available exemption from
registration under the Act, the Shares must be held indefinitely. In this
connection, the Purchaser represents that it is familiar with SEC Rule 144, as
presently in effect, and understands the resale limitations imposed thereby and
by the Act.

         3.7 FINDERS. The Purchaser has not directly or indirectly dealt with
anyone acting in the capacity of a finder or broker and has not incurred any
obligations for any finders' or broker's fee or commission in connection with
the transactions contemplated by this Agreement.

                                   ARTICLE IV

                                    COVENANTS

         4.1 COOPERATION. The parties hereto shall cooperate fully with each
other in furnishing any information or performing any action reasonably
requested by each to the other party, which information or action is necessary
to the prompt and successful consummation of the transactions contemplated by
this Agreement. Subject to its further rights under this Agreement, each party
hereto shall cause the Closing to occur by the Closing Date or as soon
thereafter as practicable.

         4.2 FILINGS BY SELLER. The Seller shall, at its own expense, make in a
timely manner, all appropriate filings required to be made with the Quebec
Securities Commission or any other Canadian regulatory agency in connection with
the sale of the Shares pursuant to this Agreement, including the filing required
to be made pursuant to Section 51 of the Quebec Securities Act.

         4.3 TRANSFER TAXES, FEES AND EXPENSES. Each party shall bear
responsibility for its own expenses associated with the sale, purchase and
transfer of the Shares. Any expenses incurred in connection with the transfer of
the Shares and requested to be paid by the Company shall be paid by the Seller.

         4.4 CONSENTS AND WAIVERS. The Seller shall use its best efforts to
obtain the Portfolio Company Certificates, and, to the extent necessary,
appropriate or desirable, consents in writing to the transactions contemplated
by this Agreement and/or such amendments, assignments, waivers or modifications
of such documents or instruments as may be required so that the transactions
contemplated by this Agreement may be consummated and shall not result in any
default or breach of any of the articles or bylaws of the Company, the
Shareholders' Agreement or other contract, agreement, commitment or instrument
to which the Seller is a party or by which the Seller or any of the Seller's
assets are bound or committed, including waivers of all rights of first refusal,
first offer or co-sale rights potentially applicable to the sale, assignment or
transfer of the Shares and consents to, or approvals of, the sale, assignment
and transfer to the Purchaser of all of the Contractual Rights.

         4.5 ACCESS. The Seller shall permit the Purchaser and its partners,
advisors, attorneys, accountants and other representatives full access after
reasonable notice during normal business hours to the Shares, the Shareholders'
Agreement and all other instruments, agreements and
                                                        STOCK PURCHASE AGREEMENT
                                       8.
<PAGE>   12

documents representing or constituting the Shares or any part thereof or
relating to the capital stock of the Company that are in the Seller's possession
on the date hereof.

         4.6 CERTAIN CONDUCT. Without the prior written consent of the
Purchaser, prior to the Closing Date the Seller shall not (i) sell, assign,
transfer, deliver or otherwise dispose of the Shares, (ii) forgive, release,
compromise or demand payment of any indebtedness owed to it by the Company other
than upon full payment thereof, (iii) amend, cancel or terminate the
Shareholders' Agreement, (iv) waive, amend, cancel, terminate, exercise or fail
to exercise any of the Contractual Rights, (v) create or permit to exist any
Lien on the Shares or (vi) agree to do any of the foregoing.

         4.7 CONFIDENTIALITY. All information furnished by the Purchaser to the
Seller or by the Seller to the Purchaser in connection with this Agreement and
the transactions contemplated hereby, as well as the terms, conditions and
provisions of this Agreement and the Ancillary Agreements, including the amount
and form of the Payment, shall be kept strictly confidential by the Seller and
the Purchaser and shall be used by the Seller and the Purchaser only in
connection with this Agreement and the transactions contemplated hereby, except
to the extent that such information (i) is already known by the party to whom
the information is disclosed or in the public domain at the time the information
is disclosed, other than by reason of breach of this provision, (ii) thereafter
becomes lawfully obtainable from other sources other than by breach of the
confidentiality obligations of such party, (iii) is required to be disclosed in
any document to be filed with any federal, state, provincial, municipal or other
governmental department, commission, board, court, bureau, agency or
instrumentality, domestic or foreign or (iv) is required under securities laws
or regulations applicable to the Seller or Purchaser (including notice of the
transactions contemplated hereby given pursuant to rules and regulations of the
Securities and Exchange Commission and applicable Canadian securities
legislation); provided, however, in the cases of subsections (iii) and (iv) of
this sentence, any party required to make any such disclosure shall only do so,
to the extent feasible, after notice to, and consultation with the other parties
hereto. No party hereto shall issue any press release or make any public
announcement relating to the subject matter of this Agreement without the prior
written approval, not to be unreasonably withheld, of the other parties hereto
except as may be required by law (and then, to the extent feasible, only after
notice to, and consultation with the other party). Notwithstanding the
foregoing, the Seller and the Purchaser may disclose such information to their
partners, directors, officers, employees, investors, advisors, trustees and
representatives on a need-to-know basis in connection with the transactions
contemplated hereby (disclosure by Purchaser of asset price information to its
investors shall qualify under the need-to-know-basis), provided that such
persons shall be informed of the confidential nature of such information and
shall be contractually obligated to keep such information confidential pursuant
to the terms of this Section 4.7.

         4.8 OTHER NEGOTIATIONS. The Seller shall not, and shall not authorize
or permit any of its agents or other representatives to, directly or indirectly,
initiate, facilitate, solicit, encourage or participate in discussions with,
provide information to, or approve or enter into a transaction, agreement or
contract with, any corporation, partnership, person or other entity or group
concerning any sale, assignment, transfer or other disposition of any of the
Shares (all such transactions being referred to herein as "Disposition
Transactions"). The Seller shall promptly communicate to the Purchaser the terms
of any proposal which it may receive in respect of a
                                                        STOCK PURCHASE AGREEMENT
                                       9.
<PAGE>   13

Disposition Transaction and any request by or indication of interest on the part
of any third party with respect to initiation of any Disposition Transaction or
discussions with respect thereto.

                                   ARTICLE V

                                 CLOSING MATTERS

         5.1 THE CLOSING. Subject to satisfaction or waiver of all conditions
precedent set forth in Article VI, the closing with respect to the transfer of
the Shares (the "Closing") shall be held at the offices of Brobeck, Phleger &
Harrison LLP, San Francisco, CA 94105, at 3:00 pm on April 30, 2001, or on such
other date as the Purchaser and the Seller may agree (the "Closing Date"). If
any condition in Article VI is not satisfied in any respect (or is not duly
waived) at the Closing, the party or parties whose obligations are subject to
such condition may extend the date of the Closing (during which extension each
of the other parties shall use all reasonable efforts to cause all such
conditions to be satisfied in all respects). If all conditions are determined to
be satisfied (or are duly waived) at the Closing (whether or not delayed), the
Closing shall be consummated.

         5.2 DELIVERY OF SHARES AND ASSIGNMENTS. At the Closing, the Seller
shall deliver, to the extent not previously delivered, or cause to be delivered
to the Purchaser (i) all of the instruments and other documents that represent
or constitute the Shares to be transferred at the Closing, together with all
transfer forms duly signed necessary to register the transfer of the Shares to
the Purchaser in the books of the Company, (ii) such releases, approvals,
consents, waivers and other supporting documents as may in the reasonable
opinion of the Purchaser be necessary to permit the Purchaser to acquire the
Shares free and clear of all Liens (other than the Encumbrances to the extent
they do not apply to the transactions contemplated by this Agreement), and (iii)
the Shareholders' Agreement Amendment, and (iv) the other documents and
agreements referenced in Section 6.1.

         5.3 DOCUMENTS AND CERTIFICATES. The Purchaser and the Seller shall use
all reasonable efforts, on or prior to the Closing, to execute and deliver all
such instruments, documents or certificates as may be necessary, appropriate or
desirable, on the advice of counsel, for the consummation at the Closing of the
transactions contemplated by this Agreement.

                                   ARTICLE VI

                              CONDITIONS OF CLOSING

         6.1 CONDITIONS APPLICABLE TO THE PURCHASER. The obligations of the
Purchaser under this Agreement to consummate the transactions contemplated by
this Agreement at the Closing are, at its option, subject to the following
conditions:

                  (a) PERFORMANCE OF THIS AGREEMENT. All the terms, covenants
and conditions of this Agreement to be complied with and performed by the Seller
at or before the Closing shall have been fully complied with and performed in
all material respects.
                                                        STOCK PURCHASE AGREEMENT
                                      10.
<PAGE>   14

                  (b) ACCURACY OF REPRESENTATIONS AND WARRANTIES. The
representations and warranties of the Seller set forth in this Agreement shall
be true and correct in all material respects both on the date of this Agreement
and as of the Closing Date (with the same force and effect as if such
representations and warranties were made anew at and as of the Closing Date,
except (i) to the extent that such representations and warranties are by their
express provisions made as of the date of this Agreement or another specified
date and (ii) for the effect of any activities or transactions which may have
taken place after the date of this Agreement which are contemplated by this
Agreement).

                  (c) LITIGATION. No action, suit, litigation, proceeding or
investigation shall (i) have been formally instituted and be pending with regard
to the transactions contemplated by this Agreement or (ii) be threatened with
regard to the transactions contemplated by this Agreement. On the Closing Date,
there shall not be in force any injunction, order or decree restricting or
enjoining consummation of the transactions contemplated by this Agreement.

                  (d) REQUIRED CONSENTS, WAIVERS AND NOTICES. The Seller shall
have obtained all required consents in writing to the transactions contemplated
by this Agreement and such amendments, assignments, waivers or modifications of
such documents or instruments as may be required so that the transactions
contemplated by this Agreement may be consummated and shall not result in any
default or breach of the Shareholders' Agreement or any other agreement,
contract, commitment or instrument to which the Seller are parties or by which
the Seller or any of their assets are bound or committed, including waivers of
all rights of first refusal, first offer or co-sale rights potentially
applicable to the sale, assignment or transfer of the Shares and consents to, or
approvals of, the sale, assignment and transfer to the Purchaser of all of the
Contractual Rights. The Seller shall have timely given notice to all parties
that may be required in order to effect the transfer of the Shares and all
rights relating thereto. All such consents, waivers and approvals referred to in
this Section 6.1(d) shall be in a form and substance which is satisfactory to
the Purchaser, in its sole discretion.

                  (e) CERTIFICATE CONCERNING THIS AGREEMENT. The Seller shall
furnish to the Purchaser a certificate dated the Closing Date, signed by it to
the effect that the conditions set forth in subsections (a) through (d) of this
Section 6.1 have been satisfied.

                  (f) MATERIAL ADVERSE CHANGE, INACCURACY OR BREACH. No fact or
circumstance shall have come to the attention of the Purchaser which in the
judgment of the Purchaser constitutes or would constitute a Material Adverse
Change, or constitute a material breach of any covenant of the Seller hereunder
or constitute or reflect any material inaccuracy in or breach of any
representation and warranty made or to be made by the Seller in connection with
this Agreement.

                  (g) PROCEEDINGS. All proceedings to be taken by the Seller in
connection with the transactions contemplated by this Agreement and all
documents incident thereto shall be reasonably satisfactory in form and
substance to the Purchaser, and the Purchaser shall have received copies of all
such documents and other evidence as it may reasonably request to establish the
consummation of such transactions and the taking of all proceedings in
connection therewith.
                                                        STOCK PURCHASE AGREEMENT
                                      11.
<PAGE>   15

                  (h) PORTFOLIO COMPANY CERTIFICATES. The Purchaser shall have
received the Portfolio Company Certificates from the Company.

                  (i) LEGAL OPINION. The Purchaser shall have received from
Holland & Knight a legal opinion, addressed to the Purchaser and dated the
Closing Date, substantially in the form of Exhibit 6.1(i) hereto.

                  (j) TAX CLEARANCE CERTIFICATES. The Seller shall have received
tax clearance certificates from each of the Canada Customs and Revenue Agency
and the Minister of Revenue for Quebec with respect to the sale of the Shares,
in each case fixing a certificate limit or an estimated or actual amount of
proceeds of disposition which, in the aggregate, shall not be less than
C$6,697,500 (the "Certificate Limit"), and the Purchaser shall have received
copies of each such certificate (the "Clearance Certificates").

                  The Purchaser may waive the preceding condition if the Seller
has not received and delivered the Clearance Certificates at the Closing in
which case the Purchaser will withhold thirty seven percent (37%) of the Payment
(the "Withholding"). If the Seller delivers to the Purchaser the Clearance
Certificates before the last business day that is not more than twenty seven
(27) days after the last day of the month in which the Closing occurred (the
"Remittance Date"), the Purchaser shall remit to the Seller forthwith upon the
delivery of such Clearance Certificates the amount of the Withholding. If the
Clearance Certificates are not delivered to the Purchaser on or before the
Remittance Date, the Purchaser shall remit the amount of the Withholding to the
Receiver General of Canada and the Minister of Revenue for Quebec in accordance
with the Income Tax Act (Canada) and the Taxation Act (Quebec). The Seller shall
have no recourse against the Purchaser for having withheld and remitted any
amount in compliance with this paragraph and the Income Tax Act (Canada) and the
Taxation Act (Quebec).

                  (k) SHAREHOLDERS' AGREEMENT. The Seller, the Company and all
other parties to the Shareholders' Agreement shall have entered into an
amendment to the Shareholders' Agreement in a form and substance satisfactory to
the Purchaser in its sole discretion (the "Shareholders' Agreement Amendment").

                  (l) AMENDMENT TO ARTICLES OF INCORPORATION. The Articles of
Incorporation of the Company shall have been amended to convert the Company's
Class A shares and Class B shares into Common shares of the Company in a form
and substance satisfactory to the Purchaser in its sole discretion.

                  (m) NOTE HOLDER RELEASE. The Purchaser shall have received
evidence, in a form and substance satisfactory to the Purchaser in its sole
discretion, that the holders of the Seller's 8% notes due 2002 and the holders
of the Seller's $6,000,000 notes due 2003, have released their security interest
in the Shares.

         6.2 CONDITIONS APPLICABLE TO THE SELLER. The obligations of the Seller
under this Agreement to consummate the transactions contemplated by this
Agreement at the Closing are, at their option, subject to the following
conditions:
                                                        STOCK PURCHASE AGREEMENT
                                      12.
<PAGE>   16

                  (a) PERFORMANCE OF THIS AGREEMENT. All terms, covenants and
conditions of this Agreement to be complied with and performed by the Purchaser
at or before the Closing shall have been fully complied with and performed in
all material respects.

                  (b) ACCURACY OF REPRESENTATIONS AND WARRANTIES. The
representations and warranties of the Purchaser set forth in this Agreement
shall have been true and correct in all material respects both on the date of
this Agreement and as of the Closing Date (with the same force and effect as if
such representations and warranties were made anew at and as of the Closing
Date, except (i) to the extent that such representations and warranties are by
their express provisions made as of the date of this Agreement or another
specified date and (ii) for the effect of any activities or transactions which
may have taken place after the date of this Agreement which are contemplated by
this Agreement).

                  (c) LITIGATION. No action, suit, litigation, arbitration,
proceeding or investigation shall (i) have been formally instituted and be
pending with regard to the transactions contemplated by this Agreement or (ii)
be threatened by any governmental authority of the United States or any State
thereof with regard to the transactions contemplated by this Agreement. On the
Closing Date, there shall not be in force any injunction, order or decree
restraining or enjoining consummation of the transactions contemplated by this
Agreement.

                  (d) REQUIRED CONSENTS AND WAIVERS. The Seller shall have
obtained all required consents in writing to the transactions contemplated by
this Agreement and such amendments, assignments, waivers or modifications of
such documents or instruments as may be required so that the transactions
contemplated by the Agreement may be consummated and shall not result in any
default or breach of the Shareholders' Agreement, or any other agreement,
contract, commitment or instrument to which the Seller is a party or by which
the Seller or any of its assets are bound or committed, including waivers of all
rights of first refusal and rights of co-sale potentially applicable to the
sale, assignment or transfer of the Shares and consents to, or approvals of, the
sale, assignment and transfer to the Purchaser of all of the Contractual Rights.

                  (e) SHAREHOLDERS' AGREEMENT. The Purchaser, the Company and
all other parties to the Shareholders' Agreement shall have entered into the
Shareholders' Agreement Amendment.

                  (f) PROCEEDINGS. All proceedings to be taken by the Purchaser
in connection with the transactions contemplated by this Agreement and all
documents incident thereto shall be reasonably satisfactory in form and
substance to the Seller, and the Seller shall have received copies of all such
documents and other evidence as the Seller may reasonably request to establish
the consummation of such transactions and the taking of all proceedings in
connection therewith.

                                  ARTICLE VII

                                   TERMINATION

         7.1 BY MUTUAL CONSENT. This Agreement may be terminated and the
transactions contemplated by this Agreement abandoned before the Closing
pursuant to the mutual written consent of the Purchaser and the Seller at any
time prior to the Closing for any reason.
                                                        STOCK PURCHASE AGREEMENT
                                      13.
<PAGE>   17

         7.2 BY PURCHASER. This Agreement may be terminated at any time by the
Purchasers (i) in accordance with Section 1.6; or (ii) if any event occurs or
condition exists which would render impossible the satisfaction of one or more
conditions to the obligations of the Purchasers to consummate the transactions
contemplated by this Agreement as set forth in Section 6.1; provided, however,
that the right to terminate this Agreement under this Section 7.2 shall not be
available if Purchaser's failure to fulfill any obligation under this Agreement
shall have been the cause of, or shall have resulted in, the failure to satisfy
such conditions.

         7.3 BY SELLER. This Agreement may be terminated at any time by the
Seller if any event occurs or condition exists which would render impossible the
satisfaction of one or more conditions to the obligations of the Seller to
consummate the transactions contemplated by this Agreement as set forth in
Section 6.2; provided, however, that the right to terminate this Agreement under
this Section 7.3 shall not be available if Seller's failure to fulfill any
obligation under this Agreement shall have been the cause of, or shall have
resulted in, the failure to satisfy such conditions.

         7.4 BY EITHER PARTY. This Agreement may be terminated by either the
Purchasers or the Seller if the Closing shall not have occurred by April 30,
2001, which date may be extended by mutual agreement of the parties pursuant to
Section 5.1; provided, however, that the right to terminate this Agreement under
this Section 7.4 shall not be available to any party whose failure to fulfill
any obligation under this Agreement shall have been the cause of, or shall have
resulted in, the failure of the Closing to occur on or prior to such date.

         7.5 SURVIVAL UPON TERMINATION. If this Agreement is terminated, the
agreements of the Seller and the Purchaser contained in Sections 4.7, 7.5, 7.6
and 9.1 and Article VIII shall survive such termination.

         7.6 EXPENSES. In the event of termination of this Agreement under
Section 7.1, each party hereto will pay all of its own fees and expenses and
there will be no further liability hereunder on the part of any party hereto,
except for liability for a willful breach by a party of its covenants or
representations and warranties hereunder.

                                  ARTICLE VIII

                                 INDEMNIFICATION

         8.1 INDEMNIFICATION. The Seller hereby agrees to defend, indemnify and
hold harmless the Purchaser from and against any damage, liability, loss, cost
or expense (including reasonable attorneys' fees) occasioned or caused by,
resulting from or arising out of (i) any failure by the Seller to perform any of
its covenants or obligations as set forth in this Agreement or in any
certificate or instrument delivered pursuant to this Agreement; (ii) any
inaccuracy in or breach of any of the representations or warranties of the
Seller set forth in this Agreement; and (iii) any and all actions, suits,
litigations, arbitrations, proceedings, investigations or claims arising out of
any of the foregoing or out of facts relating to the foregoing that have
occurred on or prior to the Closing Date even though such proceeding or claim
may not be filed or come to light until after the Closing Date (the "Purchaser's
Damages").
                                                        STOCK PURCHASE AGREEMENT
                                      14.
<PAGE>   18

                  The maximum aggregate amount for which the Seller shall be
liable for under the indemnification obligations set forth in this Section 8.1
is an amount equal to the Payment. In no event whether in contract or tort
(including breach of warranty, negligence and strict liability in tort), shall
either party be liable to the other party for indirect or consequential damages,
even if such party has been advised of the possibility of such damages in
advance.

         8.2 INDEMNIFICATION BY PURCHASER. The Purchaser hereby agrees to
defend, indemnify and hold harmless the Seller from and against any damage,
liability, loss, cost or expense (including reasonable attorneys' fees)
occasioned or caused by, resulting from or arising out of (i) any failure by the
Purchaser to perform any of its covenants or obligations as set forth in this
Agreement or in any certificate or instrument delivered pursuant to this
Agreement; (ii) any inaccuracy in or breach of any of the representations or
warranties of the Purchaser set forth in this Agreement; and (iii) any and all
actions, suits, litigations, arbitrations, proceedings, investigations or claims
arising out of any of the foregoing or out of facts relating to the foregoing
that have occurred on or prior to the Closing Date even though such proceeding
or claim may not be filed or come to light until after the Closing Date (the
"Seller's Damages").

                  The maximum aggregate amount for which the Purchaser shall be
liable for under the indemnification obligations set forth in this Section 8.2
is an amount equal to the Payment. In no event whether in contract or tort
(including breach of warranty, negligence and strict liability in tort), shall
either party be liable to the other party for indirect or consequential damages,
even if such party has been advised of the possibility of such damages in
advance.

         8.3 INDEMNIFICATION PROCEDURE. As used in this Section 8.3, the term
"Indemnified Party" shall mean either the Seller or the Purchaser, as the case
may be, that is asserting a claim for indemnity under this Article VIII and the
term "Indemnifying Party" shall mean the party against whom the Indemnified
Party is seeking indemnification. The Indemnified Party agrees to give the
Indemnifying Party prompt notice of any event, or any written claim by a third
party, of which it obtains knowledge, which could give rise to any damage,
liability, loss, cost or expense as to which it may request indemnification
under this Agreement, and, in the case of such third party claims or assertions,
the Indemnified Party, at the expense of the Indemnifying Party, will cooperate
with the Indemnifying Party in determining the validity of any such claim or
assertion. In connection with any such third party claim if the Indemnifying
Party shall have acknowledged in writing its obligation to indemnify in respect
of such claim which might give rise to a claim for indemnity hereunder, the
Indemnifying Party may select counsel to direct the defense of such third party
claim, which counsel shall be reasonably satisfactory to the indemnified party.
The Indemnifying Party shall arrange for such counsel to inform the Indemnified
Party on a regular basis of the status of such case. The Indemnified Party may,
at its election and expense, participate in the defense of such third party
claim. The Indemnifying Party shall not settle any such claim without the
consent of the Indemnified Party if any relief, other than the payment of money
damages, would be granted by such settlement or if the Indemnified Party would
be liable to the third party for the amount of such settlement.

         8.4 NO WAIVER; OTHER INDEMNIFICATION PROVISIONS. In no event will the
any party hereto be deemed to waive any breach by the other parties of any
representation, warranty, covenant or agreement by reason of such party's
completing the Closing with knowledge thereof. Except as provided in Section
8.1, the indemnification provisions of this Article VIII are in
                                                        STOCK PURCHASE AGREEMENT
                                      15.
<PAGE>   19

addition to, and not in derogation of, any statutory or common law remedy any
party may have for breach of representation, warranty, or covenant.

                                   ARTICLE IX

                                  MISCELLANEOUS

         9.1 SURVIVAL OF REPRESENTATION AND WARRANTIES. All representations and
warranties of the parties to this Agreement shall survive for twenty-four (24)
months following the execution and delivery of this Agreement except that
Seller's representations and warranties pursuant to Sections 2.4 shall survive
in perpetuity; provided, however, that the representations and warranties of the
parties to this Agreement shall not survive the termination of this Agreement
pursuant to Sections 7.1, 7.2 or 7.3, and, upon such termination, there shall be
no liability on the part of either party hereto except (i) as set forth in
Section 7.5, and (ii) that nothing herein shall relieve either party from
liability for any willful and intentional breach of this Agreement. Any
investigation or other examination that may have been made or may be made at any
time by or on behalf of the party to whom representations and warranties are
made shall not limit, diminish or in any way affect the representations and
warranties in this Agreement, and the parties may rely on the representations
and warranties in this Agreement irrespective of any information obtained by
them by any investigation, examination or otherwise.

         9.2 ADDITIONAL DOCUMENTS AND ACTS. After the Closing, each of the
parties hereto shall execute and deliver such additional documents, certificates
and instruments, and perform such additional acts, as may be reasonably
requested and necessary or appropriate to carry out all of the provisions of
this Agreement and to consummate all of the transactions contemplated by this
Agreement.

         9.3 SPECIFIC PERFORMANCE. Each of the parties hereto acknowledges that
the other party will have no adequate remedy at law if it fails to perform any
of its obligations under this Agreement. In such event, each of the parties
agrees that the other party shall have the right, in addition to any other
rights it may have (whether at law or in equity), to specific performance of
this Agreement.

         9.4 NOTICES. All notices, consents, waivers and other communications
hereunder shall be in writing and shall be deemed to have been duly given when
delivered in person, sent by facsimile transmission or posted by registered or
certified mail, return receipt requested, with postage prepaid, addressed as
follows:

                  if to any Purchaser:

                                    c/o Paul Capital Partners
                                    50 California Street, Suite 3000
                                    San Francisco, CA  94111
                                    Attention:  Jeffrey Moelis

                  with a copy (not constituting notice) to:
                                                        STOCK PURCHASE AGREEMENT
                                      16.
<PAGE>   20

                                    Brobeck, Phleger & Harrison LLP
                                    One Market
                                    Spear Street Tower
                                    San Francisco, CA 94105
                                    Attention: Ronald B. Moskovitz, Esq.

                  if to the Seller:

                                    Hybridon, Inc.
                                    345 Vassar Street
                                    Cambridge, MA 02139
                                    Attention:  Robert Andersen

                  with a copy (not constituting notice) to:

                                    Holland & Knight LLP
                                    One Beacon Street
                                    Boston, MA 02108
                                    Attention:  James Pollock, Esq.

                  or to such other address or addresses as the Purchasers or the
Seller may from time to time designate by notice as provided herein, except that
notices of changes of address shall be effective only upon receipt.

         9.5 ASSIGNMENT. Neither party hereto may assign or delegate this
Agreement or any rights or obligations hereunder to any person without the prior
written consent of the other.

         9.6 WAIVER. Either party hereto may, by express written notice to the
other, (i) extend the time for the performance of any of the obligations or
other actions of the other party under this Agreement; (ii) waive any
inaccuracies in the representations or warranties of the other party contained
in this Agreement or in any document delivered pursuant to this Agreement; (iii)
waive compliance with any of the conditions or covenants of the other party
contained in this Agreement; or (iv) waive or modify performance of any of the
obligations of the other party under this Agreement. Except as provided in the
preceding sentence, no action taken pursuant to this Agreement, including,
without limitation, any investigation by or on behalf of any party, shall be
deemed to constitute a waiver by the party taking such action of compliance by
the other party with any of the representations, warranties, covenants,
conditions, agreements or indemnities contained in this Agreement. The waiver by
any party of a breach of any provision of this Agreement shall not operate or be
construed as a waiver of any subsequent breach.

         9.7 ENTIRE AGREEMENT. This Agreement and the Ancillary Agreements,
together with the Schedules and Exhibits to this Agreement (which are
incorporated herein by reference) and certificates to be delivered at Closing
pursuant to this Agreement, supersedes any other agreement, whether written or
oral, that may have been made or entered into by the parties hereto relating to
the matters contemplated hereby, and constitutes the entire agreement of the
parties hereto with respect to the subject matter hereof.
                                                        STOCK PURCHASE AGREEMENT
                                      17.
<PAGE>   21

         9.8 AMENDMENTS, SUPPLEMENTS, ETC. This Agreement may be amended or
supplemented only by additional written agreements, articles or certificates
signed by the Purchaser and the Seller, as may be determined by the parties
hereto to be necessary, appropriate or desirable to further the purposes of this
Agreement, to clarify the intention of the parties, or to add to or to modify
the covenants, terms or conditions hereof.

         9.9 INTERPRETATION. When a reference is made in this Agreement to
Articles, Sections, Schedules, Exhibits or certificates such reference shall be
to an Article, Section, Schedule, Exhibit or certificate to this Agreement
unless otherwise indicated. The words "include," "includes" and "including" when
used herein shall be deemed in each case to be followed by the words "without
limitation." Neither party hereto shall be or be deemed to be the drafter of
this Agreement for the purposes of construing this Agreement against one party
or the other.

         9.10 HEADINGS AND CAPTIONS. The headings and captions in this Agreement
are for convenience and reference purposes only and shall not be considered a
part of or affect the construction or interpretation of any provision of this
Agreement.

         9.11 COUNTERPARTS. This Agreement may be executed in two or more
counterparts, each of which shall be an original, but all of which together
shall constitute one and the same instrument.

         9.12 SUCCESSORS AND ASSIGNS. This Agreement shall be binding upon,
inure to the benefit of and may be enforced by, each of the parties hereto and
their respective permitted successors and assigns.

         9.13 ATTORNEYS' FEES. In the event of any legal action or proceeding
respecting this Agreement, the prevailing party shall be entitled to recover its
costs and expenses (including, without limitation, reasonable attorneys' fees)
incurred in such action or proceeding.

         9.14 SEVERABILITY. If any provision of this Agreement is held to be
invalid or unenforceable, the remaining provision shall nevertheless be given
full force and effect.

         9.15 GOVERNING LAW. This Agreement shall be governed by and construed,
interpreted and enforced in accordance with the laws of the State of California,
without giving effect to the principles of conflicts of law thereof.

                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]
                                                        STOCK PURCHASE AGREEMENT
                                      18.
<PAGE>   22

                  IN WITNESS WHEREOF, the Purchasers and the Seller have caused
this Stock Purchase Agreement to be duly executed and delivered as of the date
first above written.

<TABLE>
<CAPTION>
SELLER:                                                      PURCHASERS:
HYBRIDON, INC.                                               PAUL CAPITAL PARTNERS VI HOLDINGS
<S>                                                          <C>
                                                             By:    PAUL CAPITAL MANAGEMENT, LLC
By:                                                                 Its General Partner
   ---------------------------------------------
Name:  Robert Andersen
Its:  Vice President and Chief Financial Officer

                                                             By:
                                                                ---------------------------------------
                                                                    Jeffrey Moelis, Manager Member
                                                                    50 California Street
                                                                    Suite 3000
                                                                    San Francisco, CA  94111

                                                             PCP ASSOCIATES, L.P.
                                                             By:    PAUL CAPITAL MANAGEMENT, LLC
                                                                    Its General Partner
                                                             By:
                                                                ---------------------------------------
                                                                    Jeffrey Moelis, Manager Member
                                                                    50 California Street
                                                                    Suite 3000
                                                                    San Francisco, CA  94111
</TABLE>

                                SIGNATURE PAGE TO
                          STOCK PURCHASE AGREEMENT FOR
                       PURCHASE OF METHYLGENE INC. SHARES
                               FROM HYBRIDON, INC.
                                                        STOCK PURCHASE AGREEMENT
                                      19.

<PAGE>   23


                                    EXHIBIT A
                          CERTIFICATE OF CAPITALIZATION

The undersigned hereby certifies to the Purchaser, its affiliated entities and
its investors that he or she is the duly elected President, Chief Financial
Officer or Secretary of MethylGene Inc., a corporation formed under the laws of
Quebec (the "Company"), and that as such he or she is authorized to execute this
certificate for and on behalf of the Company, and further certifies for and on
behalf of the Company that set forth on Annex A attached hereto is a complete
and accurate list of the authorized and outstanding shares of capital stock of
the Company, including all shares and securities which are issuable upon the
exercise, exchange or conversion of any rights, options or warrants to purchase
shares of the capital stock of the Company, issued by the Company as of the date
first written below, and the number of shares of such stock and/or securities
and rights, options or warrants to purchase such shares or securities of the
Company held by Hybridon, Inc. Further, there has been no issuance of common
stock equivalents issued since the date of the capitalization table set forth on
Annex A.

                  IN WITNESS HEREOF, this Certificate of Capitalization is
hereby executed as of             , 2001.
                     -------------


METHLYGENE Inc.



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


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

--------------------------------
(Title)



                                     Annex A
<PAGE>   24
                                    EXHIBIT B

                             CERTIFICATE OF TRANSFER


                  The undersigned hereby certifies to the Purchaser (the
"Transferee") that he or she is the duly elected President, Chief Financial
Officer or Secretary of MethylGene Inc., a corporation formed under the laws of
Quebec (the "Company"), and that as such he or she is authorized to execute this
certificate for and on behalf of the Company, and further certifies for and on
behalf of the Company that the proposed transfer of 2,350,000 Common shares of
the Company (the "Shares") owned by Hybridon, Inc. (the "Transferor"), will upon
delivery of the share certificates duly endorsed or accompanied with a transfer
form duly signed for transfer of the Shares for the Transferee be duly recorded
in the corporate records of the Company and that the Transferee will be the
holder of record of the Shares and as such will have all attendant rights
pertaining to the shares granted under the articles of the Company.


         IN WITNESS HEREOF, this Certificate of Transfer is hereby executed as
of         , 2001.
   --------

                                         METHYLGENE INC.


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


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

                                         --------------------------------
                                         (Title)

                                  Attachment A
<PAGE>   25
                                  SCHEDULE 1.2
                                PURCHASER DETAILS



           Purchaser Name              Number of Common Shares being Purchased
           --------------              ---------------------------------------
   Paul Capital Partners VI, L.P.                     2,009,964
        PCP Associates, L.P.                           340,036
<PAGE>   26
                                  SCHEDULE 2.4

THE METHYLGENE INC. SHARES OWNED BY SELLER ARE THE SUBJECT OF A SECURITY
INTEREST FOR THE BENEFIT OF THE HOLDERS OF SELLER'S 8% NOTES DUE 2002 AND
SELLER'S $6,000,000 NOTES DUE 2003. SUCH HOLDERS HAVE SIGNED AN INSTRUMENT
WAIVING THEIR RIGHTS WITH RESPECT TO DISPOSITIONS OF THE METHYLGENE INC. AND
RELEASING THEIR SECURITY INTEREST THEREIN FOR THE PURPOSE OF PERMITTING SUCH
SHARES TO BE SOLD BY SELLER TO PURCHASER.
<PAGE>   27
                                  SCHEDULE 2.5
                             COMPANY CAPITALIZATION
<PAGE>   28
                                  SCHEDULE 2.9
                             SHAREHOLDERS' AGREEMENT









                                       1
<PAGE>   29
                                 EXHIBIT 6.1(i)
                       FORM OF OPINION OF SELLER'S COUNSEL


April __, 2001

PAUL CAPITAL PARTNERS VI, L.P. and
PCP ASSOCIATES, L.P.
c/o Paul Capital Partners
50 California Street, Suite 3000
San Francisco, CA  94111

Attention:  Jeffrey Moelis

        Re:       Hybridon, Inc. Sale of Stock of Methylgene, Inc.
                  Under Stock Purchase Agreement
                  dated as of March 30, 2001

Ladies and Gentlemen:

         We have acted as special counsel for Hybridon, Inc., a Delaware
corporation (the "COMPANY"), in connection with the preparation, execution and
delivery of, and sale of stock under, the Stock Purchase Agreement, dated as of
March __, 2001, between you and the Company (the "AGREEMENT"). This letter is
delivered to you pursuant to Section 6.1(i) of the Agreement. Capitalized terms
not defined in this letter have the meanings ascribed to them in the Agreement.

         For purposes of our opinions, we have reviewed such documents and made
such other investigation as we have deemed appropriate. As to matters of fact,
we have relied on the representations and warranties made by the parties in the
Agreement and on certificates of public officials and officers of the Company.
We have made no independent investigation of the accuracy or completeness of
such matters of fact.


                                       1
<PAGE>   30
         In rendering the following opinions, we have relied, without
independent investigation, upon the following assumptions:

                  (a) Each party to the Agreement (other than the Company) is
duly organized and is validly existing and in good standing in its jurisdiction
of organization;

                  (b) Each party to the Agreement (other than the Company) has
full power and authority to execute, deliver and perform its obligations under
the Agreement, and the Agreement has been duly authorized by all necessary
action on its part and has been duly executed and duly delivered by it;

                  (c) The Agreement constitutes the valid and binding obligation
of each party to the Agreement (other than the Company), enforceable against
such party in accordance with its terms;

                  (d) Each natural person executing the Agreement or any
document referred to herein is legally competent to do so;

                  (e) Each party to the Agreement (other than the Company) has
complied with all legal requirements pertaining to its status as such status
relates to its rights to enforce the Agreement against the Company (including,
but not limited to, qualifying to do business, if required, in the Commonwealth
of Massachusetts;

                  (f) Each document submitted to us for review is accurate and
complete, each such document that is an original is authentic, each such
document that is a copy conforms to an authentic original, and all signatures on
each such document are genuine;

                  (g) There has not been any mutual mistake of fact or
misunderstanding, fraud, duress or undue influence;

                  (h) The Agreement will be enforced in circumstances and in a
manner in which it is commercially reasonable to do so and the conduct of the
parties complies with any requirement of good faith and fair dealing;

                  (i) There are no agreements or understandings among the
parties, written or oral, and there is no usage of trade or course of prior
dealing among the parties that would, in either case, define, supplement or
qualify the terms of the Agreement; and


                                       2
<PAGE>   31
                  (j) Each person who has taken any action relevant to any of
our opinions in the capacity of director or officer was duly elected to that
director or officer position and held that position when such action was taken.

         For purposes of this opinion letter, the terms "to our knowledge", "we
are not aware" or similar terms means the conscious awareness of facts or other
information, at the time of delivery of this opinion letter, by the lawyers in
our firm who have had involvement in the negotiation and preparation of the
Agreement. Except to the extent expressly set forth herein, we have not
undertaken any independent investigation to determine the existence or absence
of any facts or other information, and no inference as to our knowledge or the
existence or absence of any such facts or other information should be drawn from
the fact of our representation of the Company as special counsel.

         Notwithstanding our opinions expressed herein, we express no opinion
with respect to any of the following provisions in the Agreement:

                  (a)      Choice-of-law provisions;

                  (b) Covenants not to compete, including covenants not to
interfere with business or employee relations, covenants not to solicit
customers, and covenants not to solicit or hire employees;

                  (c) Indemnification of a party for its own gross negligence,
willful misconduct, recklessness or other wrongful conduct;

                  (d) Provisions mandating contribution towards judgments or
settlements among various parties;

                  (e) Waivers of (i) legal or equitable defenses, (ii) rights to
damages, (iii) rights to counter claim or set off, (iv) statutes of limitations,
(v) rights to notice, (vi) the benefits of statutory, regulatory, or
constitutional rights, unless and to the extent the statute, regulation, or
constitution explicitly allows waiver, and (vii) other benefits to the extent
they cannot be waived under applicable law;

                  (f) Provisions providing for forfeitures or the recovery of
amounts deemed to constitute penalties or for liquidated damages;

                  (g) Provisions that provide a time limitation after which a
remedy may not be enforced;

                  (h) Agreements to submit to the jurisdiction of any particular
court or other governmental authority; provisions restricting access to courts;
waiver of service of process requirements which would otherwise be applicable;
and provisions otherwise purporting to affect the jurisdiction and venue of
courts;


                                       3
<PAGE>   32
                  (i) Provisions that attempt to change or waive rules of
evidence or fix the method or quantum of proof to be applied in litigation or
similar proceedings;

                  (j) Any Federal, state or local law relating to taxation,
zoning, land use, the environment, antitrust, banking, securities or ERISA; and

                  (k) Provisions regarding arbitration.

         Based on and subject to the foregoing and subject to the exceptions,
qualifications and limitations hereinafter set forth, we express the following
opinions.

                  1. The Company is a corporation duly organized, validly
existing and in good standing under the laws of the State of Delaware, and the
Company has the requisite corporate power and authority to own its properties
and to conduct its business as, to our knowledge, it is presently conducted.

The Company has the requisite corporate power and authority to execute, deliver
     and perform the Agreement. The Agreement has been duly and validly
     authorized by the Company, has been duly executed and delivered by an
     authorized officer of the Company and constitutes a legal, valid and
     binding obligation of the Company, enforceable by you against the Company
     in accordance with its terms.

Neither the execution or delivery by the Company of the Agreement nor the
     consummation by the Company at the Closing of the transactions contemplated
     thereby will (i) violate any provision of the Articles of Incorporation or
     Bylaws of the Company, (ii) violate or be in conflict with any federal or
     Massachusetts laws which to our knowledge are applicable to the Company,
     (iii) to our knowledge, violate or contravene any judgment, decree,
     injunction or order of any federal or Massachusetts court, or any
     arbitrator or governmental agency or authority, having jurisdiction over
     the Company or its properties or by which the Company may be bound or (iv)
     constitute a material breach of, or result in a material default under, any
     term or provision of any material contracts of which we have knowledge.

                  2. No consents, approvals or authorizations of or filings with
any governmental authority of the Commonwealth of Massachusetts, State of
Delaware or the United States are required or necessary on the part of the
Company in connection with the execution, delivery and performance at the
Closing by the Company of the Agreement, except for (i) such consents,
approvals, authorizations or filings which have been obtained, waived or made
prior to the date hereof, and (ii) the consents, approvals, authorizations and
filings listed in Section 2.1 of the Disclosure Schedule to the Purchase
Agreement.


                                       4
<PAGE>   33
                  3. We are not aware that there is any action, proceeding or
governmental investigation pending, or threatened in writing, against the
Company which questions the validity or enforceability of the Agreement or the
right of the Company to enter into the Agreement.

The offer and sale of the Shares pursuant to the Agreement are exempt from the
  registration requirements of the Securities Act of 1933, as amended, and from
  the registration requirements of the applicable securities laws of the
  Commonwealth of Massachusetts.


         Our opinions are subject to bankruptcy, insolvency, fraudulent
conveyance, reorganization, moratorium and other laws affecting the rights and
remedies of creditors generally and to general principles of equity, regardless
of whether considered in a proceeding in equity or at law.

         Our opinions are also subject to the effect of rules of law that:

                  (a) limit or affect the enforcement of provisions of a
contract that purport to waive, or to require waiver of, the obligations of good
faith, fair dealing, diligence and reasonableness;

                  (b) provide that forum selection clauses in contracts are not
necessarily binding on the court(s) in the forum selected;

                  (c) limit the availability of a remedy under certain
circumstances where another remedy has been elected;

                  (d) provide a time limitation after which a remedy may not be
enforced;

                  (e) limit the right of a creditor to use force or cause a
breach of the peace in enforcing rights;

                  (f) relate to the sale or disposition of collateral or the
requirements of a commercially reasonable sale;

                  (g) limit the enforceability of provisions releasing,
exculpating or exempting a party from, or requiring indemnification of a party
for, liability for its own action or inaction, to the extent the action or
inaction involves gross negligence, recklessness, willful misconduct, unlawful
conduct, violation of law or public policy or litigation against another party
determined adversely to such party;

                  (h) may, if less than all of a contract is unenforceable,
limit the enforceability of the remainder of the contract to circumstances in
which the unenforceable portion is not an essential part of the agreed exchange;


                                       5
<PAGE>   34
                  (i) govern and afford judicial discretion regarding the
determination of damages and entitlement to attorneys' fees and other costs;

                  (j) permit a party that has materially failed to render or
offer performance required by the contract to cure that failure unless (i)
permitting a cure would unreasonably hinder the aggrieved party from making
substitute arrangements for performance, or (ii) it was important in the
circumstances to the aggrieved party that performance occur by the date stated
in the contract; and

                  (k) in the absence of a waiver or consent, discharge a
guarantor to the extent that (i) action by a creditor impairs the value of
collateral securing guaranteed debt to the detriment of the guarantor, or (ii)
guaranteed debt is materially modified.

         This opinion letter is based as to matters of law solely on (i) the
General Corporation Law of the State of Delaware, and (ii) such internal law of
the Commonwealth of Massachusetts (but not including any statutes, ordinances,
administrative decisions, rules or regulations of any political subdivision of
the Commonwealth of Massachusetts), and such Federal law that, in each case in
our experience, is normally applicable to a transaction of the type contemplated
by the Agreement and to the parties thereto.

         Our advice on each legal issue addressed herein represents our opinion
concerning how that issue would be resolved were it to be considered by the
highest court of the jurisdiction upon whose law our opinion on that issue is
based. The manner in which any particular issue would be treated in any actual
court case would depend in part on facts and circumstances peculiar to the case,
and our opinions are not a guaranty of an outcome of any legal dispute which may
arise with regard to the Agreement.

         This letter speaks as of the date hereof. We disclaim any obligation to
provide you with any subsequent opinion or advice by reason of any future
changes or events which may affect or alter any opinion rendered herein.

         This letter is being delivered to you in connection with the Agreement
and may not be relied upon by you for any other purpose. This letter may not be
relied upon by, furnished to, referred to, quoted, in whole or part, by, or
filed with, any other Person without our prior written consent.

                                            Very truly yours,

                                            HOLLAND & KNIGHT LLP


                                        6