<PAGE>   1
                                                      Exhibit 4i

                      SUBSCRIPTION AGREEMENT

     SUBSCRIPTION AGREEMENT (this "Agreement"), dated as of _________, 1998, by
and among DynaGen, Inc., a corporation organized under the laws of the State of
Delaware (the "Company"), with headquarters located at 840 Memorial Drive,
Cambridge, Massachusetts 02139 and the undersigned ("Purchaser").

     WHEREAS:

A.   The Company and Purchaser are executing and delivering this Agreement in
     reliance upon the exemption from securities registration afforded by
     Section 4(2) of the Securities Act of 1933, as amended (the "Securities
     Act").

B.   The Company desires to sell and issue to Purchaser and Purchaser desires to
     purchase, upon the terms and conditions stated in this Agreement, the
     number of shares of Series H Preferred Stock, $.01 par value per share (the
     "Preferred Stock"), of the Company convertible into shares of common stock,
     par value $.01 per share, of the Company (the "Common Stock") in accordance
     with the terms and conditions set forth therein. The Series H Preferred
     Stock Designation setting forth the rights, preferences, including the
     terms upon which the shares of Preferred Stock are convertible into shares
     of Common Stock, is attached hereto as Exhibit A. The shares of Common
     Stock issuable upon conversion of the Preferred Stock or otherwise pursuant
     to the Preferred Stock are referred to herein as the "Conversion Shares."
     The Preferred Stock and the Conversion Shares are collectively referred to
     herein as the "Securities."

     NOW, THEREFORE, the Company and the Purchaser hereby agree as follows:

     1.   PURCHASE AND SALE OF PREFERRED STOCK

          a.      Purchase of Preferred Stock. on the Closing Date (as defined
below), subject to the satisfaction (or waiver) of the conditions set forth in
Sections 6 and 7 below, the Company shall issue and sell to Purchaser and
Purchaser agrees to purchase from the Company, the number of shares of Preferred
Stock (the "Preferred Shares") set forth on the signature page. The purchase
price (the "Purchase Price Per Share") for each of the Preferred Shares.

          b.      Form of Payment. On the Closing Date (as hereinafter defined),
Purchaser shall pay the aggregate Purchase Price for the Preferred Shares by
wire transfer or check to Foley, Hoag & Eliot LLP as escrow agent (the "Escrow
Agent") and shall deliver by telecopier (with originals following by first class
mail) a fully executed copy of this Subscription Agreement to the Escrow Agent.
Payment and delivery instructions are attached as Exhibit B hereto. The Company
shall deliver one or more certificates (the "Certificates") representing 
<PAGE>   2
the Preferred Shares to the Escrow Agent and an executed copy of this Agreement
indicating the Company's acceptance of the Purchaser's subscription. Promptly
upon receipt of the Purchase Price, the executed and accepted Agreement and the
Certificates representing the Preferred Shares, the Escrow Agent shall (1)
deliver the Purchase Price together with copies of the executed and accepted
agreement to the Company in accordance with the instructions delivered to the
Escrow Agent by the Company and (2) deliver the Certificates together with the
accepted Agreement to the Purchaser by Federal Express or other overnight
courier at the address set forth on the signature page of this Agreement.

          c.      Closing Date. Subject to the satisfaction (or waiver) of the
conditions thereto set forth in Section 6 and Section 7 below, the date and time
of the issuance and sale of the shares of Preferred Shares Pursuant to this
Agreement shall take place from time to time as may be mutually agreed upon by
the Company and Purchaser. Each closing shall occur at the offices of Foley,
Hoag & Eliot LLP, One Post Office Square, Boston, MA 02109.

     2.   PURCHASER'S REPRESENTATIONS AND WARRANTIES

     Purchaser represents and warrants to the Company that:

          a.      Investment Purpose. Purchaser is purchasing the Preferred 
Stock for Purchaser's own account for investment only and not with a present
view towards the public sale or distribution thereof, except pursuant to sales
that are exempt from the registration requirements of the Securities Act and/or
sales registered under the Securities Act. Purchaser understands that Purchaser
must bear the economic risk of this investment indefinitely, unless the
Preferred Shares or the Conversion Shares are registered pursuant to the
Securities Act and any applicable state securities or blue sky laws or an
exemption from such registration is available, and that the Company has no
present intention of registering any such Securities other than as contemplated
by Section 5 of this Agreement.

          b.      Accredited Investor Status. Purchaser is an "accredited 
investor" as defined in Rule 501(a) promulgated under the Securities Act.

          c.      Reliance on Exemptions. Purchaser understands that the 
Preferred Shares and the Conversion Shares are being offered and sold to
Purchaser in reliance upon specific exemptions from the registration
requirements of United States federal and state securities laws and that the
Company is relying upon the truth and accuracy of, and Purchaser's compliance
with, the representations, warranties, agreements, acknowledgments and
understandings of Purchaser set forth herein in order to determine the
availability of such exemptions and the eligibility of Purchaser to acquire the
Preferred Shares and Conversion Shares.

          d.      Information. Purchaser and its counsel or representative, if 
any, have been furnished all materials relating to the business, finances and
operations of the Company and materials relating to the offer and sale of the
Preferred Shares which have been requested by Purchaser or its counsel or
representative. Purchaser and its counsel, if any, have been 


                                       2
<PAGE>   3
afforded the opportunity to ask questions of the Company and have received what
Purchaser believes to be complete and satisfactory answers to any such
inquiries. Neither such inquiries nor any other due diligence investigation
conducted by Purchaser or its counsel or any of its representatives shall
modify, amend or affect Purchaser's right to rely on the Company's
representations and warranties contained in Section 3 below. Purchaser has been
informed and understands that (i) this investment involves a HIGH DEGREE OF
RISK, (ii) the Company's independent auditing have included an explanatory
paragraph in their opinion on the Company's financial statements expressing
substantial doubt about the Company's ability to continue as a going concern and
(iii) the Company has been notified by the NASDAQ Stock Market that it does not
meet the applicable listing requirements and that its common stock is subject to
delisting.

          e.      Governmental Review. Purchaser understands that no United 
States federal or state agency or any other government or governmental agency
has passed upon or made any recommendation or endorsement of the Securities.

          f.      Transfer or Resale. Purchaser understands that (i) except as
provided in Section 5 of this Agreement, the Securities have not been and are
not being registered under the Securities Act or any state securities laws, and
may not be transferred unless (a) subsequently registered thereunder, or (b)
Purchaser shall have delivered to the Company an opinion of counsel (which
opinion shall be in form, substance and scope customary for opinions of counsel
in comparable transactions) to the effect that the Securities to be sold or
transferred may be sold or transferred pursuant to an exemption from such
registration, including without limitation Rule 144 promulgated under the
Securities Act (or a successor rule) ("Rule 144"), or (c) transferred without
consideration to an affiliate of Purchaser; (ii) any sale of such Securities
made in reliance on Rule 144 may be made only in accordance with the terms of
said Rule and further, if said Rule 144 is not applicable, any resale of such
Securities under circumstances in which the seller (or the person through whom
the sale is made) may be deemed to be an underwriter (as that term is defined in
the Securities Act) may require compliance with some other exemption under the
Securities Act or the rules and regulations of the Securities and Exchange
Commission (the "SEC") thereunder; and (iii) neither the Company nor any other
person is under any obligation to register such Securities under the Securities
Act or any state securities laws or to comply with the terms and conditions of
any exemption thereunder (in each case, other than pursuant to the Registration
Rights Agreement).

          g.      Legends. Purchaser understands that the Preferred Shares and, 
until such time as the Conversion Shares have been registered under the
Securities Act as contemplated by Section 5 of this Agreement or otherwise may
be sold by Purchaser pursuant to Rule 144 without any restriction as to the
public resale thereof, the certificates for the Conversion Shares, may bear a
restrictive legend in substantially the following form (and a stop-transfer
order may be placed against transfer of the certificates for such Securities):

     The securities represented by this certificate have not been registered
     under the Securities Act of 1933, as amended. The securities have been
     acquired for investment 



                                       3
<PAGE>   4
     and may not be sold, transferred or assigned in the absence of an effective
     registration statement for the securities under said Act, or an opinion of
     counsel, in form, substance and scope customary for opinions of counsel in
     comparable transactions, that registration is not required under said Act
     or unless the Company is provided with reasonable assurances that the
     securities were sold pursuant to Rule 144 under said Act.

     The legend set forth above shall be removed and the Company shall issue a
certificate without such legend upon conversion of the Preferred Stock to the
holder of any Security upon which it is stamped, if (a) the resale of such
Security is registered under the Securities Act, or (b) such holder provides the
Company with an opinion of counsel, in form, substance and scope customary for
opinions of counsel in comparable transactions, to the effect that a public sale
or transfer of such Security may be made without registration under the
Securities Act or (c) such holder provides the Company with reasonable
assurances that such Security has been sold pursuant to Rule 144 or can be sold
pursuant to Rule 144 without any restriction as to the number of Securities
acquired as of a particular date that can then be immediately sold. Purchaser
agrees to sell all Securities, including those represented by a certificate(s)
from which the legend has been removed, pursuant to an effective registration
statement and to deliver a prospectus in connection with such sale (if and to
the extent such delivery is required) or in compliance with an exemption from
the registration requirements of the Securities Act. In the event the above
legend is removed from any Security and thereafter the effectiveness of a
registration statement covering such Security is suspended or the Company
determines that a supplement or amendment thereto is required by applicable
securities laws, then upon reasonable advance notice to Purchaser the Company
may require that the above legend be placed on any such Security that cannot
then be sold pursuant to an effective registration statement or Rule 144 without
any restriction as to the number of Securities acquired as of a particular date
that can then be immediately sold, which legend shall be removed when such
Security has been sold pursuant to Rule 144 or may be sold pursuant to an
effective registration statement or Rule 144 without any restriction as to the
number of Securities acquired as of a particular date that can then be
immediately sold.

          h.      Authorization; Enforcement. This Agreement has been duly and
validly authorized, executed and delivered on behalf of Purchaser and are valid
and binding agreements of Purchaser enforceable in accordance with their
respective terms.

          i.      Location of Purchaser. Purchaser has advised the Company in 
writing with respect to the jurisdictions wherein the investment decision
regarding Purchaser's acquisition of the Preferred Stock has been made.

     3.   REPRESENTATIONS AND WARRANTIES OF THE COMPANY

     The Company represents and warrants to Purchaser that:

          a.      Organization and Qualification. The Company is a corporation 
duly organized and existing in good standing under the laws of the jurisdiction
in which it is incorporated, and has the requisite corporate power to own its
properties and to carry on its
 



                                       4
<PAGE>   5
business as now being conducted. The Company is duly qualified as a foreign
corporation to do business and is in good standing in every jurisdiction where
the failure so to qualify would have a Material Adverse Effect. "Material
Adverse Effect" means any material adverse effect on the operations, properties,
condition (financial or otherwise) or prospects of the Company and its
subsidiaries, taken as a whole on a consolidated basis or on the ability of the
Company to perform its obligations in connection with the transactions
contemplated hereby on a timely basis.

          b.      Authorization; Enforcement. The Company has the requisite 
corporate power and authority to enter into and perform this Agreement, to issue
and sell the Preferred Shares in accordance with the terms hereof, and to issue
the Conversion Shares upon conversion of the Preferred Shares in accordance with
their terms. The execution, delivery and performance of this Agreement by the
Company and the consummation by it of the transactions contemplated hereby and
thereby (including, without limitation, the issuance of the Preferred Shares and
the issuance and reservation for issuance of the Conversion Shares) have been
duly authorized by the Company's Board of Directors and no further consent or
authorization of the Company, its Board or Directors, or its stockholders is
required; this Agreement has been duly executed and delivered by the Company;
and this Agreement constitutes the valid and binding obligations of the Company
enforceable against the Company in accordance with its respective terms.

          c.      Issuance of Securities. The Preferred Stock is duly authorized
and, upon issuance in accordance with the terms of this Agreement, the Preferred
Shares will be validly issued, fully paid and non-assessable. The Conversion
Shares have been duly authorized by the Company's Board of Directors, and have
been reserved for issuance upon conversion of the Preferred Shares in accordance
with the terms thereof, will be validly issued, fully paid and non-assessable.

          d.      No Conflicts. The execution, delivery and performance of this
Agreement by the Company, the performance by the Company of its obligations
hereunder and thereunder, and the consummation by the Company of the
transactions contemplated hereby and thereby (including, without limitation, the
issuance and reservation for issuance, as applicable, of the Preferred Shares
and the Conversion Shares) will not (i) result in a violation of the Certificate
of Incorporation or By-laws or (ii) conflict with, or constitute a default (or
an event which with notice or lapse of time or both would become a default)
under, or give to others any rights of termination, amendment, acceleration or
cancellation of, any agreement, indenture or instrument to which the Company or
any of its subsidiaries is a party, or result in a violation of any law, rule,
regulation, order, judgment or decree (including U.S. federal and state
securities laws and regulations) applicable to the Company or any of its
subsidiaries or by which any property or asset of the Company or any of its
subsidiaries is bound or affected (except for such conflicts, defaults,
terminations, amendments, accelerations, cancellations and violations as would
not, individually or in the aggregate, have or reasonably be expected to result
in a Material Adverse Effect or for which consents have been obtained). Except
as described in the SEC Documents (as hereinafter defined) neither the Company
nor any of its subsidiaries is in violation of its Certificate of Incorporation
or other organizational


                                       5
<PAGE>   6
documents and neither the Company nor any of its subsidiaries is in default (and
no event has occurred which, with notice or lapse of time or both, would put the
Company or any of its Subsidiaries in default) under, nor has there occurred any
event giving others (with notice or lapse of time or both) any rights of
termination, amendment, acceleration or cancellation of, any agreement,
indenture or instrument to which the Company or any of its subsidiaries is a
party, except for defaults as would not, individually or in the aggregate, have
or reasonably be expected to result in a Material Adverse Effect or for which
consents have been obtained. The businesses of the Company and its subsidiaries
are not being conducted, and shall not be conducted so long as Purchaser owns
any of the Securities, in violation of any law, ordinance or regulation of any
governmental entity, except for possible violations the sanctions for which
either singly or in the aggregate would not have or reasonably be expected to
result in a Material Adverse Effect. Except as specifically contemplated by this
Agreement and except for the filing of a Form D with the Securities and Exchange
Commission, the filing of the registration statement contemplated by this
Agreement under the Securities Act, any filings required by applicable state
securities laws and the filing of an application with Nasdaq (as defined below)
to list or approve for quotation the Conversion Shares, the Company is not
required to obtain any consent, authorization or order of, or make any filing or
registration with, any court or governmental agency or any regulatory or self
regulatory agency in order for it to execute, deliver or perform any of its
obligations under this Agreement, or the Preferred Stock, in each case in
accordance with the terms hereof or thereof. The Company has been notified that
it is not in compliance with new listing requirements of the Nasdaq SmallCap
Market ("Nasdaq") and the Common Stock is subject to delisting by Nasdaq.

          e.      SEC Documents, Financial Statements. Since December 31, 1995, 
the Company has timely filed all reports, schedules, forms, statements and other
documents required to be filed by it with the SEC pursuant to the reporting
requirements of the Securities Exchange Act of 1934, as amended (the "Exchange
Act") (all of the foregoing, filed prior to the date hereof and after December
31, 1995, and all exhibits included therein and financial statements and
schedules thereto and documents (other than exhibits) incorporated by reference
therein together with any registration statements or other documents filed by
the Company pursuant to the Securities Act prior to the date hereof and all news
releases by the Company being hereinafter referred to herein as the "SEC
Documents"). The Company has made available to Purchaser true and complete
copies of the SEC Documents, except for such exhibits, schedules and
incorporated documents. As of their respective dates, the SEC Documents complied
in all material respects with the requirements of the Exchange Act or the
Securities Act, as the case may be, and the rules and regulations of the SEC
promulgated thereunder applicable to the SEC Documents, and none of the SEC
Documents, at the time they were filed with the SEC, contained any untrue
statement of a material fact or omitted to state a material fact required to be
stated therein or necessary in order to make the statements therein, in light of
the circumstances under which they were made, not misleading. as of their
respective dates, the financial statements of the Company included in the SEC
Documents complied in all material respects with applicable accounting
requirements and the published rules and regulations of the SEC with respect
thereto. Such financial statements have been prepared in accordance with U.S.
generally accepted accounting principles, consistently applied, during the
periods involved (except (i) as may be otherwise indicated in such financial


                                       6
<PAGE>   7
statements or the notes thereto, or (ii) in the case of unaudited interim
statements, to the extent they may include footnotes or may not be condensed or
summary statements) and fairly present in all material respects the consolidated
financial position of the Company and its consolidated subsidiaries as of the
dates thereof and the consolidated results of their operations and cash flows
for the periods then ended (subject, in the case of unaudited statements, to
normal year-end audit adjustments). Except as set forth in the financial
statements of the Company included in the SEC Documents, the Company has no
liabilities, contingent or otherwise, other than (i) liabilities incurred in the
ordinary course of business subsequent to the date of the most recent financial
statements included in the SEC Documents and (ii) obligations under contracts
and commitments incurred in the ordinary course of business and not required
under generally accepted accounting principles to be reflected in such financial
statements, which, individually or in the aggregate, are not material to the
financial condition or operating results of the Company.

          f.      Absence of Litigation. Except as disclosed in the SEC 
Documents or otherwise disclosed to Purchaser, there is no action, suit,
proceeding, inquiry or investigation before or by any court, public board,
government agency, self-regulatory organization or body pending or, to the
knowledge of the Company or any of its subsidiaries, threatened against or
affecting the Company, any of its subsidiaries, or any of their respective
directors or officers in their capacities as such, wherein an unfavorable
decision, ruling or finding would or could reasonably be expected to result in a
Material Adverse effect.

          g.      Disclosure. All information relating to or concerning the 
Company set forth in this Agreement or provided to Purchaser pursuant to Section
2(d) hereof and otherwise in connection with the transactions contemplated
hereby is true and correct in all material respects and the Company has not
omitted to state any material fact necessary in order to make the statements
made herein or therein, in light of the circumstances under which they were
made, not misleading. No event or circumstance has occurred or exists with
respect to the Company or its subsidiaries or their respective businesses,
properties, prospects, operations or financial conditions, which, under
applicable law, rule or regulation, requires public disclosure or announcement
by the Company but which has not been so publicly announced or disclosed
(assuming for this purpose that the Company's Exchange Act Reports are being
incorporated into an effective registration statement filed by the Company under
the Securities Act).

          h.      Current Public Information. The Company is currently eligible 
to register the resale of its Common Stock by a stockholder on a registration
statement on Form S-3 under the Securities Act. The Company has been notified
that it is not in compliance with new listing requirements of the Nasdaq
SmallCap Market ("Nasdaq") and the Common Stock is subject to delisting by
Nasdaq. If the Common Stock should be delisted, the Company may no longer be
eligible to register the sale of its Common Stock on Form S-3.

          i.      No General Solicitation. Neither the Company nor any person 
acting for the Company has conducted any "general solicitation," as such term is
defined in Regulation D, with respect to any of the Securities being offered
hereby.

                                       7
<PAGE>   8
          j.      No Integrated Offering. Neither the Company, nor any of its
affiliates, nor any person acting on its or their behalf, has directly or
indirectly made any offers or sales of any security or solicited any offers to
buy any security under circumstances that would require registration of the
Securities being offered hereby under the Securities Act.

     4.   COVENANTS

          a.      Best Efforts. The parties shall use their best efforts timely 
to satisfy each of the conditions described in Sections 6 and 7 of this
Agreement.

          b.      Blue Sky Laws. The Company shall take such action as the 
Company or Purchaser shall reasonably determine is necessary to qualify the
Securities for sale to Purchaser pursuant to this Agreement under applicable
securities or "blue sky" laws of the states of the United States or obtain
exemption therefrom, and shall provide evidence of any such action so taken to
Purchaser.

          c.      Reporting Status. So long as Purchaser beneficially owns any 
of the Securities, the Company shall timely file all reports required to be
filed with the SEC pursuant to the Exchange Act.

          d.      Use of Proceeds. The Company shall use the proceeds from the 
sale of the Preferred Stock for internal working capital purposes, mergers and
acquisitions, investments and general corporate purposes.

          e.      Financial Information. Upon the written request of Purchaser 
while holding any Preferred Shares, the Company shall send the following reports
to Purchaser: a copy of its Annual Report on Form 10-K, its Quarterly Reports on
Form 10-Q, any proxy statements, any Current Reports on Form 8-K and any press
releases issued by the Company or any of its subsidiaries.

          f.      Reservation of Shares. The Company shall reserve and shall at 
all times thereafter have authorized and reserved for the purpose of issuance a
sufficient number of shares of Common Stock to provide for the full conversion
of the shares of Preferred Shares issued in accordance herewith and issuance of
the Conversion Shares in connection therewith and as otherwise required by the
terms of the Preferred Stock.

          g.      Corporate Existence. So long as Purchaser beneficially owns 
the Preferred Shares, the Company shall maintain its corporate existence, except
in the event of a merger, consolidation or sale of all or substantially all of
the Company's assets, as long as the surviving or successor entity in such
transaction (i) assumes the Company's obligations hereunder and under the
agreements and instruments entered into in connection herewith regardless of
whether or not the Company would have had a sufficient number of shares of
Common Stock authorized and available for issuance in order to effect the
conversion of the Preferred Shares as of the date of such transaction and (ii)
is a publicly traded corporation 



                                       8
<PAGE>   9
whose common stock is listed for trading on the Nasdaq Stock Market, the New
York Stock Exchange or The American Stock Exchange.

     5.   REGISTRATION; TRANSFER AGENT INSTRUCTIONS

     (a)  Registration. On or before the later of (i) six (6) months after the
Company's registration statement relating to the registration of the Company of
shares of common stock issuable upon conversion of the Company's Series C and D
Convertible Preferred Stock shall have been declared effective or (ii) nine
months after the date hereof, the Company shall file with the Securities and
Exchange Commission a registration statement on Form S-3 (or such other form as
shall be available) to register the resale of the Conversion Shares. The Company
shall use its best efforts, subject to receipt of necessary information from the
Purchaser to cause the Registration Statement to become effective within 60 days
of filing.

     (b)  Transfer Agent Instructions. The Company shall instruct its transfer
agent to issue certificates, registered in the name of Purchaser or its nominee,
for the Conversion Shares in such amounts as specified from time to time by
Purchaser to the Company upon conversion of the Preferred Shares. Prior to
registration of the Conversion Shares under the Securities Act or resale of such
Securities under Rule 144, all such certificates shall bear the restrictive
legend specified in Section 2(g) of this Agreement. The Company warrants that no
instruction other than such instructions referred to in this Section 5, and stop
transfer instructions to give effect to Section 2(f) hereof in the case of the
Conversion Shares prior to registration of the Conversion Shares under the
Securities Act, will be given by the Company to its transfer agent and that the
Securities shall otherwise be freely transferable on the books and records of
the Company as and to the extent provided in this Agreement and the Preferred
Stock terms. Nothing in this Section shall affect in any way Purchaser's
obligations and agreement set forth in Section 2(f) hereof not to resell the
Securities except pursuant to an effective registration statement (and to
deliver a prospectus in connection with such a sale) or in compliance with an
exemption from the registration requirements of applicable securities law. If
Purchaser provides the Company with an opinion of counsel, which opinion of
counsel shall be in form, substance and scope customary for opinions of counsel
in comparable transactions, to the effect that the Securities to be sold or
transferred may be sold or transferred pursuant to an exemption from
registration, the Company shall permit the transfer, and, in the case of the
Conversion Shares, promptly instruct its transfer agent to issue one or more
certificates in such name and in such denominations as specified by a Purchaser.

     (c)  Rule 144. The Company will use its best efforts to make all filings 
and take all other actions so that Rule 144 promulgated under the Securities Act
of 1933, as amended, will be available for the resale of the Conversion Shares.

     6.   CONDITIONS TO THE COMPANY'S OBLIGATION TO SELL

     The obligation of the Company hereunder to issue and sell the Preferred
Shares to Purchaser at the closing is subject to the satisfaction, at or before
the Closing Date, of each of the following conditions thereto, provided that
these conditions are for the Company's sole benefit and may be waived by the
Company at any time in its sole discretion.

                                       9
<PAGE>   10
               (a)  Purchaser shall have executed the execution page to this
Agreement and delivered the same to the Company.

               (b)  Purchaser shall have delivered the Purchase Price for the
Preferred Shares.

               (c)  The representations and warranties of Purchaser shall be 
true and correct in all material respects.

               (d)  No statute, rule, regulation, executive order, decree, 
ruling or injunction shall have been enacted, entered, promulgated or endorsed
by any court or governmental authority of competent jurisdiction or any
self-regulatory organization having authority over the matters contemplated
hereby which prohibits the consummation of any of the transactions contemplated
by this Agreement.

     7.   CONDITIONS TO PURCHASER'S OBLIGATION TO PURCHASE

     The obligation of Purchaser hereunder to purchase the Preferred Shares on
the Closing Date is subject to the satisfaction of each of the following
conditions, provided that these conditions are for Purchaser's sole benefit and
may be waived by Purchaser at any time in Purchaser's sole discretion:

               (a)  The Company shall have executed the signature page to this
Agreement and delivered the same to Purchaser.

               (b)  The Company shall have delivered to Purchaser one or more
duly executed Certificates representing the Preferred Shares purchased hereby in
the principal amount being purchased by Purchaser in accordance with Section
1(b) above.

               (c)  The representations and warranties of the Company shall be
true and correct as of the Closing Date in all material respects and the Company
shall have performed, satisfied and complied in all material respects the
covenants, agreements and conditions required by this Agreement to be performed,
satisfied or complied with by the Company at or prior to the Closing Date.

               (d)  No statute, rule, regulation, executive order, decree, 
ruling or injunction shall have been enacted, entered, promulgated or endorsed
by any court or governmental authority of competent jurisdiction or any
self-regulatory organization having authority over the matters contemplated
hereby which prohibits the consummation of any of the transactions contemplated
by this Agreement.


     8.   GOVERNING LAW; MISCELLANEOUS

                                       10
<PAGE>   11
          a.      Governing Law; Jurisdiction. This Agreement shall be governed 
by and construed in accordance with the laws of the State of Delaware applicable
to contracts made and to be performed in the State of Delaware. The parties
consent to the jurisdiction of the United States District Courts for the
Southern District of New York in any suit or proceeding based on or arising
under this Agreement and agree that all claims in respect of such suit or
proceeding may be determined in such court. The parties irrevocably waive the
defense of an inconvenient forum to the maintenance of such suit or proceeding.
The parties further agree that service of process mailed by first class mail
shall be deemed in every respect effective service of process in any suit or
proceeding arising hereunder. Nothing herein shall affect Purchaser's right to
serve process in any other manner permitted by law. The parties agree that a
final non-appealable judgment in any such suit or proceeding shall be conclusive
and may be enforced in other jurisdictions by suit on such judgment or in any
other lawful manner.

          b.      Counterparts. This Agreement may be executed in two or more
counterparts, all of which shall be considered one and the same agreement and
shall become effective when counterparts have been signed by each party and
delivered to the other party.


          c.      Headings. The headings of this Agreement are for convenience 
of reference and shall not form part of, or affect the interpretation of, this
Agreement.

          d.      Severability. If any provision of this Agreement shall be 
invalid or unenforceable in any jurisdiction, such invalidity or
unenforceability shall not affect the validity or enforceability of the
remainder of this Agreement or the validity or enforceability of this Agreement
in any other jurisdiction.

          e.      Entire Agreement; Amendments. This Agreement and the 
instruments referenced herein contain the entire understanding of the parties
with respect to the matters covered herein and therein and, except as
specifically set forth herein or therein, neither the Company nor Purchaser make
any representation, warranty, covenant or undertaking with respect to such
matters. No provision of this Agreement may be waived other than by an
instrument in writing signed by the party to be charged with enforcement and no
provision of this Agreement may be amended other than by an instrument in
writing signed by the Company and Purchaser.

          f.      Notices. Any notices required or permitted to be given under 
the terms of this Agreement shall be sent by certified or registered mail
(return receipt requested) or delivered personally or by courier, overnight
delivery service or by confirmed telecopy, and shall be effective five days
after being placed in the mail, if mailed, or upon receipt or refusal of
receipt, if delivered personally or by courier, overnight delivery service or
confirmed telecopy, in each case addressed to a party. The addresses for such
communications shall be:

     If to the Company:



                                       11
<PAGE>   12
                    DynaGen, Inc.
                    840 Memorial Drive
                    Cambridge, Massachusetts 02139
                    Telecopy: (617) 354-3902
                    Attention: Dhananjay G. Wadekar

     with a copy to:

                    Foley, Hoag & Eliot LLP
                    One Post Office Square
                    Boston, Massachusetts  02109
                    Telecopy:  (617) 832-7000
                    Attention: David A. Broadwin, Esq.

     If to Purchaser, to :

                    to the address set forth on the signature page hereof.

     Each party shall provide notice to the other parties of any change in
address.

          g.      Successors and Assigns. This Agreement shall be binding upon 
and inure to the benefit of the parties and their successors and assigns.
Neither the Company nor Purchaser shall assign this Agreement or any rights or
obligations hereunder without the prior written consent of the other. This
provision shall not limit Purchaser's right to transfer the Securities pursuant
to the terms of the Preferred Stock and this Agreement or to assign Purchaser's
rights hereunder to any such transferee, nor shall this provision limit the
right of Purchaser to transfer or assign its rights under such agreements and
instruments to an affiliate (provided that Purchaser makes no more than two (2)
such transfers), provided that the representations and warranties set forth in
Section 2 are true and correct with respect to such affiliate or managed
account.

          h.      Third Party Beneficiaries. This Agreement is intended for the
benefit of the parties hereto and their respective permitted successors and
assigns, and is not for the benefit of, nor may any provision hereof be enforced
by, any other person.

          i.      Survival. The representations and warranties of the parties 
and the agreements and covenants set forth in Sections 2, 3, 4 and 5 shall
survive the closing hereunder and any conversion of the Preferred Stock,
notwithstanding any due diligence investigation conducted by or on behalf of
Purchaser.

          j.      Purchaser. Purchaser shall not make any press release or other
public statement concerning the transactions contemplated hereby without the
prior written consent of the Company.

                                       12
<PAGE>   13
          k.      Publicity. Purchaser shall not make any press release or other
public statement concerning the transactions contemplated hereby without the
prior written consent of the Company.

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



               [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]

                                       13
<PAGE>   14
IN WITNESS WHEREOF, the undersigned Purchaser and the Company have caused this
Agreement to be duly executed as of the date first above written.


         SUBSCRIPTION AMOUNT                PURCHASER

         Number of Shares                   By:
                          ---------            -------------------------------
         Total Purchase Price               Name:
                             ---------         -------------------------------
                                            Title:
                                                  ----------------------------


                                            ACCEPTED:

                                            DYNAGEN, INC.

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