Exhibit 4d

                            STOCK PURCHASE AGREEMENT


         THIS STOCK PURCHASE  AGREEMENT,  dated as of the date of acceptance set
forth  below,  is  entered  into  by  and  between  DYNAGEN,  INC.,  a  Delaware
corporation,   with   headquarters   located  at  99  Erie  Street,   Cambridge,
Massachusetts 02139 (the "Company"), and the undersigned (the "Buyer").

                              W I T N E S S E T H:

         WHEREAS,  the Company and the Buyer are executing and  delivering  this
Agreement in reliance upon  exemptions  from  securities  registration  afforded
under  Regulation  D  ("Regulation  D")  as  promulgated  by the  United  States
Securities and Exchange Commission (the "SEC") under the Securities Act of 1933,
as amended (the "1933 Act") and/or Section 4(2) of the 1933 Act; and

         WHEREAS,  the Buyer wishes to  purchase,  upon the terms and subject to
the conditions of this Agreement, Series C Convertible Preferred Stock, $.01 par
value  per  share  and  Series D  Convertible  Preferred  Stock  $.01 par  value
(collectively the "Preferred  Stock"),  of the Company which will be convertible
into shares of Common Stock,  $.01 par value per share (the "Common Stock"),  of
the Company upon the terms and subject to the conditions of such Preferred Stock
(the  Common  Stock  and  Preferred  Stock  sometimes   referred  to  herein  as
"Securities"),  and a Warrant to purchase  250,000  shares of Common  Stock (the
"Warrant") and subject to acceptance of this Agreement by the Company;

         NOW  THEREFORE,  in  consideration  of  the  premises  and  the  mutual
covenants  contained  herein  and other  good and  valuable  consideration,  the
receipt and sufficiency of which are hereby  acknowledged,  the parties agree as
follows:

         1.       AGREEMENT TO PURCHASE; PURCHASE PRICE.

         A. PURCHASE. The undersigned hereby agrees to purchase from the Company
Series  C  Preferred  Stock  of the  Company,  in the  amount  set  forth on the
signature page of this Agreement,  and having the terms and conditions set forth
in the  Certificate  of  Designations  attached  hereto as ANNEX I. The purchase
price for the Series C Preferred  Stock  shall be as set forth on the  signature
page hereto and shall be payable in United States Dollars.

         B. FORM OF  PAYMENT.  The Buyer  shall pay the  purchase  price for the
Preferred Stock by delivering  immediately available good funds in United States
Dollars to the escrow agent (the "Escrow Agent")  identified in the Joint Escrow
Instructions  attached hereto as ANNEX II (the "Joint Escrow  Instructions")  as
set forth below.  Promptly following payment by the Buyer to the Escrow Agent of
the  purchase  price  of the  Preferred  Stock,  the  Company  shall  deliver  a
Certificate for the Preferred  Stock duly executed on behalf of the Company,  to
the Escrow  Agent.  By signing this  Agreement,  the Buyer and the Company,  and
subject to acceptance  by the Escrow Agent,  each agrees to all of the terms and
conditions of, and becomes a party to, the Joint Escrow









Instructions,  all of the  provisions of which are  incorporated  herein by this
reference as if set forth in full.

         C. METHOD OF PAYMENT. Payment into escrow of the purchase price for the
Preferred Stock shall be made by wire transfer of funds to:

                  Bank of New York
                  350 Fifth Avenue
                  New York, New York 10001

                  ABA# 021000018
                  For credit to the account of Krieger & Prager, Esqs.
                  Account No. 105

Not later  than 1:00  p.m.,  New York  time,  on the date  which is two (2) NASD
trading days after the Company shall have accepted this Agreement and returned a
signed counterpart of this Agreement to the Escrow Agent by facsimile, the Buyer
shall  deposit  with the  Escrow  Agent  the  aggregate  purchase  price for the
Preferred  Stock, in immediately  available  funds.  Time is of the essence with
respect to such  payment,  and failure by the Buyer to make such  payment  shall
allow the Company to cancel this Agreement.

         2. BUYER  REPRESENTATIONS,  WARRANTIES,  ETC.;  ACCESS TO  INFORMATION;
INDEPENDENT INVESTIGATION.

         The Buyer  represents  and warrants to, and  covenants and agrees with,
the Company as follows:

         a.  Without  limiting  its right to resell the Common  Stock  under the
Registration  Rights Agreement,  the Buyer is purchasing the Preferred Stock and
will be acquiring  the shares of Common Stock  issuable  upon  conversion of the
Preferred  Stock for its own  account  for  investment  only and not with a view
towards the resale,  public sale or distribution  thereof and not with a view to
or for sale in connection with any distribution thereof;

         b. The Buyer is (i) an "accredited investor" as that term is defined in
Rule 501 of the General  Rules and  Regulations  under the 1933 Act by reason of
Rule 501(a)(3),  (ii) experienced in making investments of the kind described in
this Agreement and the related documents,  (iii) able, by reason of the business
and  financial  experience  of its  officers  (if an  entity)  and  professional
advisors (who are not  affiliated  with or compensated in any way by the Company
or any of its  affiliates  or selling  agents),  to protect its own interests in
connection with the  transactions  described in this Agreement,  and the related
documents,  and (iv) able to afford the  entire  loss of its  investment  in the
Preferred Stock:

         c. All  subsequent  offers  and  sales of the  Preferred  Stock and the
shares of Common Stock  issuable upon  conversion of, or issued as dividends on,
the Preferred  Stock by the Buyer shall be made pursuant to  registration of the
Shares under the 1933 Act or with respect to the Preferred  Stock pursuant to an
exemption from registration;


                                      -2-





         d. The Buyer  understands that the Preferred Stock is being offered and
sold, and the Shares are being offered, to it in reliance on 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, the and the
Buyer's   compliance   with,  the   representations,   warranties,   agreements,
acknowledgments  and  understandings  of the Buyer set forth  herein in order to
determine the  availability  of such exemptions and the eligibility of the Buyer
to acquire the Preferred Stock and to receive an offer of the Shares;

         e. The Buyer and its  advisors,  if any, have been  furnished  with all
materials  relating to the business,  finances and operations of the Company and
materials relating to the offer and sale of the Preferred Stock and the offer of
the Shares which have been requested by the Buyer, including ANNEX V hereto. The
Buyer and its  advisors,  if any,  have been  afforded  the  opportunity  to ask
questions of the Company and have received complete and satisfactory  answers to
any such inquiries.  Without limiting the generality of the foregoing, the Buyer
has also had the  opportunity  to obtain and to review the  Company's (1) Annual
Report on Form 10-K for the  fiscal  year ended June 30,  1996;  (2)  Transition
Report on Form 10-K for the  six-month  period from July 1, 1996 to December 31,
1996,  as amended;  (3) Quarterly  Reports on Form 10-Q for the fiscal  quarters
ended  September 30, 1996,  March 31, 1997 and June 30, 1997;  (4) The Company's
Proxy Statement for its Annual Meeting of Stockholders held on January 30, 1997;
(5) The  Company's  Current  Reports  on Form 8-K  filed  on  August  23,  1996,
September 23, 1996, January 15, 1997,  February 3, 1997, March 24, 1997 and July
3, 1997, as amended, and (6) The Company's Form S-3 Registration Statement filed
with the Securities and Exchange  Commission on August 11, 1997 (the  "Company's
SEC Documents").

         f. The Buyer understands that its investment in the Securities involves
a high degree of risk;

         g. The Buyer  understands that no United States federal or state agency
or any  other  government  or  governmental  agency  has  passed  on or made any
recommendation or endorsement of the Securities;

         h. This  Agreement has been duly and validly  authorized,  executed and
delivered  on behalf of the Buyer and is a valid and  binding  agreement  of the
Buyer enforceable in accordance with its terms,  subject as to enforceability to
general principles of equity and to bankruptcy, insolvency, moratorium and other
similar laws affecting the enforcement of creditors' rights generally.

         i.  Notwithstanding  the  provisions  hereof,  in no event (except with
respect to an Event of  Mandatory  Conversion)  shall the holder be  entitled to
convert any preferred  Stock in excess of that number of shares upon  conversion
of which the sum of (1) the number of shares of Common Stock  beneficially owned
by the Buyer and its affiliates  (other than shares of common Stock which may be
deemed  beneficially  owned through the ownership of the unconverted  portion of
the Preferred Stock), and (2) the number of shares of Common Stock issuable upon
the conversion of the Preferred Stock with respect to which the determination of
this proviso is being made,  would result in  beneficial  ownership by the Buyer
and its affiliates of more than 4.9% of the outstanding  shares of Common Stock.
For purposes of the proviso to the immediately  preceding 


                                      -3-









sentence,  beneficial  ownership  shall be determined in accordance with Section
13(d) of the Securities Exchange Act of 1934, as amended,  and Regulation 13 D-G
thereunder, except as otherwise provided in clause (1) of such proviso.

         3.       COMPANY REPRESENTATIONS, ETC.

         Except as disclosed in Annex V, delivered in writing to the Buyer,  the
Company represents and warrants to the Buyer that:

         A.  CONCERNING THE SHARES.  The Common Shares have been duly authorized
and, when issued upon  conversion  of, or as dividends on, the Preferred  Stock,
will be duly and  validly  issued,  fully paid and  non-assessable  and will not
subject the holder thereof to personal liability by reason of being such holder.
There are no preemptive rights except that the holders of the Company's Series A
Preferred  Stock have the right to acquire a portion of the Common  Shares which
rights have been waived or otherwise provided for.

         B.  REPORTING  COMPANY  STATUS.  The  Company  is  a  corporation  duly
organized,  validly existing and in good standing under the laws of the State of
Delaware and is duly qualified as a foreign  corporation in all jurisdictions in
which the  failure to so qualify  would  have a material  adverse  effect on the
Company and its  subsidiaries  taken as a whole.  The Company has registered its
Common Stock pursuant to Section 12 of the  Securities  Exchange Act of 1934, as
amended (the "Exchange  Act"),  and the Common Stock is listed and traded on the
NASDAQ/Small Cap Market.  The Company has timely filed all material  required to
be filed  pursuant to all reporting  obligations  under either  Section 13(a) or
15(d)  of  the  Exchange  Act  for a  period  of at  least  twelve  (12)  months
immediately preceding the offer or sale of the Preferred Stock, and has received
no notice,  either oral or written, with respect to the continued eligibility of
the Common Stock for such listing.

         C.  AUTHORIZED  SHARES.  The  Company  has  sufficient  authorized  and
unissued  Shares as may be reasonably  necessary to effect the conversion of the
Preferred  Stock.  The Common Shares have been duly  authorized and, when issued
upon  conversion  of, or as interest on, the Preferred  Stock,  will be duly and
validly issued,  fully paid and  non-assessable  and will not subject the holder
thereof to personal liability by reason of being such holder.

         D. STOCK PURCHASE  AGREEMENT;  REGISTRATION RIGHTS AGREEMENT AND STOCK.
This  Agreement  and the  Registration  Rights  Agreement,  the form of which is
attached hereto as ANNEX IV (the  "Registration  Rights  Agreement"),  have been
duly and  validly  authorized  by the  Company,  this  Agreement  has been  duly
executed  and  delivered  by  the  Company  and  this   Agreement  is,  and  the
Registration Rights Agreement,  when executed and delivered by the Company, will
be, valid and binding  agreements of the Company  enforceable in accordance with
their respective terms,  subject as to  enforceability to general  principles of
equity, the indemnification provisions of the Registration Rights Agreement, and
to  bankruptcy,  insolvency,  moratorium,  and other similar laws  affecting the
enforcement of creditors' rights generally; and the Preferred Stock will be duly
and validly issued,  fully paid and  non-assessable  when delivered on behalf of
the Company upon payment therefor in accordance with this Agreement,  subject to


                                      -4-







general principles of equity and to bankruptcy, insolvency, moratorium, or other
similar laws affecting the enforcement of creditors' rights generally.

         E. NON-CONTRAVENTION.  The execution and delivery of this Agreement and
the  Registration  Rights  Agreement  by  the  Company,   the  issuance  of  the
Securities,  and the  consummation  by the  Company  of the  other  transactions
contemplated by this  Agreement,  the  Registration  Rights  Agreement,  and the
Preferred  Stock do not and will not conflict  with or result in a breach by the
Company of any of the terms or provisions of, or constitute a default under, the
(i) certificate of incorporation or by-laws of the Company,  (ii) any indenture,
mortgage,  deed of trust, or other material agreement or instrument to which the
Company is a party or by which it or any of its  properties or assets are bound,
(iii)  any  material  existing  applicable  law,  rule,  or  regulation  or  any
applicable decree,  judgment,  or (iv) order of any court, United States federal
or state regulatory body,  administrative  agency,  or other  governmental  body
having jurisdiction over the Company or any of its properties or assets,  except
such conflict,  breach or default which would not have a material adverse effect
on the transactions contemplated herein.

         F.  APPROVALS.  No  authorization,  approval  or  consent of any court,
governmental body,  regulatory agency,  self-regulatory  organization,  or stock
exchange or market or the Stockholders of the Company is required to be obtained
by the  Company  for the  issuance  and sale of the  Securities  to the Buyer as
contemplated  by this  Agreement,  except  such  authorizations,  approvals  and
consents that have been obtained.

         G.  SEC  FILINGS.  None of the SEC  Filings  with  the  Securities  and
Exchange Commission at the time they were filed,  contained any untrue statement
of a material  fact or omitted to any state  material fact required to be stated
therein  or  necessary  to make the  statements  made  therein,  in light of the
circumstances under which they were made, not misleading. Except as set forth on
ANNEX V hereto,  the Company has timely filed all requisite  forms,  reports and
exhibits thereto with the Securities and Exchange Commission.

         H. ABSENCE OF CERTAIN CHANGES. Since January 1, 1997, there has been no
material  adverse  change and no material  adverse  development in the business,
properties,  operations,  financial  condition,  or results of operations of the
Company, except as disclosed in ANNEX V or in the Company's SEC Documents.

         I. FULL  DISCLOSURE.  There is no fact known to the Company (other than
general economic conditions known to the public generally), and other than facts
disclosed in the Company's SEC Documents, that has not been disclosed in writing
to the Buyer that (i) could  reasonably  be expected to have a material  adverse
effect on the condition  (financial or otherwise),  earnings,  business affairs,
properties  or assets of the  Company or (ii) could  reasonably  be  expected to
materially  and  adversely  affect  the  ability of the  Company to perform  its
obligations pursuant to this Agreement.

         J. ABSENCE OF LITIGATION. Except as set forth in ANNEX V hereto, and in
the Company's SEC Documents,  which the Buyer has reviewed,  there is no action,
suit, proceeding,  inquiry or investigation before or by any court, public board
or body pending or, to the knowledge of the Company or any of its  subsidiaries,
threatened against or affecting the Company 


                                      -5-







or any of its subsidiaries,  wherein an unfavorable decision,  ruling or finding
would have a material  adverse  effect on the  properties,  business,  condition
(financial or otherwise),  results of operations or prospects of the Company and
its  subsidiaries  taken as a whole  or the  transactions  contemplated  by this
Agreement or any of the documents  contemplated  hereby or which would adversely
affect the  validity or  enforceability  of, or the  authority or ability of the
Company to perform its  obligations  under,  this Agreement or any of such other
documents.

         K. ABSENCE OF EVENTS OR DEFAULT.  Except as set forth in ANNEX V hereto
and Section 3(e), no Event of Default, as defined in the respective agreement to
which the Company is a party,  and no event which,  with the giving of notice or
the passage of time or both,  would  become an Event of Default (as so defined),
has occurred and is  continuing,  which would have a material  adverse effect on
the Company's financial condition or results of operations.

         L. NO DEFAULT.  To its knowledge,  the Company is not in default in the
performance  or observance of any material  obligation,  agreement,  covenant or
condition contained in any indenture,  mortgage, deed of trust or other material
instrument or agreement to which it is a party or by which it or its property is
bound, and neither the execution of, nor the delivery by the Company of, nor the
performance  by the Company of its  obligations  under,  this  Agreement  or the
Preferred Stock, other than the conversion provision thereof, will conflict with
or result in the breach or  violation of any of the terms or  provisions  of, or
constitute  a default or result in the  creation  or  imposition  of any lien or
charge on any  assets or  properties  of the  Company  under,  (i) any  material
indenture,  mortgage deed of trust or other material agreement applicable to the
Company or  instrument  to which the Company is a party or by which it is bound,
(ii)  any  statute  applicable  to  the  Company  or  its  property,  (iii)  the
Certificate  of  Incorporation  or  By-Laws  of the  Company,  (iv) any  decree,
judgment,  order, rule or regulation of any court or governmental agency or body
having  jurisdiction  over the Company or its  properties,  or (v) the Company's
listing agreement for its Common Stock.

         M. PRIOR  ISSUES.  During the twelve  (12)  months  preceding  the date
hereof, the Company has not issued any securities other than (i) as reflected in
the Company's SEC Documents,  of which 44,700 shares of Series A Preferred Stock
and 7,500  shares of Series B  Preferred  Stock,  remain  unconverted,  and (ii)
options and warrants to purchase  shares of Common Stock which have been granted
to directors, employees, consultants and advisers of the Company, as further set
forth on Annex 3(m).

         4.       CERTAIN COVENANTS AND ACKNOWLEDGMENTS.

         A. TRANSFER  RESTRICTIONS.  The Buyer  acknowledges  that (1) Preferred
Stock has not been and is not being  registered under the provisions of the 1933
Act and, except as provided in the  Registration  Rights  Agreement,  the Shares
have not been and are not being  registered  under  the 1933 Act,  and may no be
transferred unless (A) subsequently registered thereunder or (B) the Buyer shall
have delivered to the Company an opinion of counsel,  reasonably satisfactory in
form,  scope and substance to the Company,  to the effect that the Securities to
be sold or transferred may be sold or transferred  pursuant to an exemption from
such  registration;  (2) any sale of the Securities made in reliance on Rule 144
promulgated  under the 1933 Act may be made only in accordance with the terms of
said  Rule and  further,  if said  Rule is not  applicable,  any  resale of



                                      -6-







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 used
in the 1933 Act, may require compliance with some other exemption under the 1933
Act or the rules and  regulations  of the SEC  thereunder;  and (3)  neither the
Company nor any other person is under any  obligation to register the Securities
(other than pursuant to the Registration Rights Agreement) under the 1933 Act or
to comply with the terms and conditions of any exemption thereunder.

         B.  RESTRICTIVE  LEGEND.  The Buyer  acknowledges  and agrees  that the
Preferred  Stock,  and, until such time as the Common Stock has been  registered
under the 1933 Act as contemplated by the Registration Rights Agreement and sold
in  accordance  with such  Registration  Statement,  the shares of Common  Stock
issued  to the  Buyer  upon  conversion  of the  Preferred  Stock  shall  bear a
restrictive  legend in  substantially  the following  form (and a  stop-transfer
order may be placed against  transfer of the Preferred  Stock and such shares of
Common Stock):

         THESE SECURITIES (THE  "SECURITIES")  HAVE NOT BEE REGISTERED UNDER THE
         SECURITIES  ACT OF 1933,  AS AMENDED  (THE  "SECURITIES  ACT"),  OR THE
         SECURITIES LAWS OF ANY STATE AND MAY NOT BE SOLD OR OFFERED FOR SALE IN
         THE ABSENCE OF AN EFFECTIVE  REGISTRATION  STATEMENT FOR THE SECURITIES
         OR  AN  OPINION  OF  COUNSEL  OR  OTHER  EVIDENCE   ACCEPTABLE  TO  THE
         CORPORATION THAT SUCH REGISTRATION IS NOT REQUIRED.

         C.  REGISTRATION  RIGHTS  AGREEMENT.  The parties hereto agree to enter
into the  Registration  Rights  Agreement,  in  substantially  the form attached
hereto as ANNEX IV, on or before the Closing Date (as defined in Section 7).

         D.  FILINGS.  The Company  undertakes  and agrees to make all necessary
filings in connection  with the sale of the  Preferred  Stock to the Buyer under
any United States laws and regulations,  or by any domestic  securities exchange
or trading  market,  and to provide a copy thereof to the Buyer  promptly  after
such filing.

         E. REPORTING STATUS. So long as the Buyer  beneficially owns any of the
Preferred  Stock,  the Company shall file all reports  required to be filed with
the SEC  pursuant to Section 13 or 15(d) of the  Exchange  Act,  and the Company
shall no terminate  its status as an issuer  required to file reports  under the
Exchange Act even if the Exchange  Act or the rules and  regulations  thereunder
would permit such termination.

         F. USE OF PROCEEDS.  The Company will use the proceeds from the sale of
the Preferred  Stock  (excluding  amounts paid by the Company for legal fees and
finder's fees in connection  with the sale of the Preferred  stock) for internal
working  capital  purposes,  and shall not,  directly  or  indirectly,  use such
proceeds for any loan to or  investment  in any other  corporation,  partnership
enterprise or other person.


                                      -7-






         G. CERTAIN  AGREEMENTS.  (i) Except as provided  herein with respect to
Acquisition  Financing  or in  4(g)(ii)(d)  hereof,  and the sale of up to 5,300
additional  shares of Series A Preferred Stock, the Company covenants and agrees
that it will not, without the prior written consent of the Buyer, enter into any
subsequent or further  offer or sale of Common Stock or  securities  convertible
into Common  Stock with any third party until the  expiration  of thirteen  (13)
months after the effective date of the  Registration  Statement (the  "Effective
Date").

                  (II)     SPECIAL PROVISION RELATING TO ACQUISITION FINANCING.

                           (a)  Following the issuance of the Series C Preferred
Stock to the Buyer,  and until the  expiration of the thirteen (13) month period
following  the  Expiration  Date,  the Company  shall provide the Buyer with the
following  rights to  participate in any private  placement  financing of equity
securities (or securities  convertible into Equity Securities of the Company) by
the Company (exempt from the registration  requirements of the Securities Act of
1993) where at least 90% of the  proceeds of such  financing  are intended to be
used by the Company to acquire the capital  stock or assets of another  business
enterprise  (including,  within the context of such Acquisition  Financing,  the
working  capital   requirements  of  the  acquired   entity)  (an   "Acquisition
Financing"). This right of first refusal is granted to the Buyer subject to, and
subordinate to, the prior rights of first refusal of the holders of the Series A
Preferred Stock with respect to private  placement of securities by the Company,
and is granted to Buyer  after the holders of Series A  Preferred  Stock  either
waive or decline to exercise their rights of first refusal, or if such rights of
first  refusal  of the  holders  of  Series  A  Preferred  Stock  are  otherwise
terminated.  If the Company  obtains  Acquisition  Financing  from a third party
during the  thirteen-month  period  following  the first  issuance  of shares of
Series D Preferred Stock, then the Buyer's  obligations under Section 4(i) below
to purchase  additional  tranches of Series D Preferred Stock shall be suspended
until the earlier of (x) such time that the Company provides written notice that
all equity securities  issued by the Company in such Acquisition  Financing have
been converted to Common Stock, or (y) the conclusion of the thirteen (13) month
period.

                           (b)  Notice  to  Participate.  Subject  to the  prior
exercise or waiver of the rights of the holders of the Series A Preferred Stock,
the Company shall, prior to any issuance by the Company of any of its securities
to be issued in an Acquisition  Financing,  offer to the Buyer by written notice
the right,  for a period of five (5)  business  days,  to  purchase  all of such
securities for cash at an amount equal to the price or other  consideration  for
which such securities proposed to be issued. The Company's written notice to the
Buyer shall  describe  the  securities  proposed to be issued by the Company and
specify the number,  price and payment  terms.  Except as may be necessary  with
respect to potential designees, the Buyer agrees to keep the terms and existence
of such securities issuance confidential. The Buyer, or its designee, may accept
the  company's  offer as to the full  number  of  securities  offered  to it, by
written notice thereof given by it to the Company prior to the expiration of the
aforesaid  five (5) day period,  in which event the Company shall  promptly sell
and such Buyer shall buy,  upon the terms  specified,  the number of  securities
agreed to be purchased by such Buyer, or its designee.  The rights  contained in
this Section are not transferable by the Buyer except as provided herein.



                                      -8-






                           (c)  Options  of Buyer.  Following  the  exercise  or
waiver of the rights of first refusal of the Series A Preferred Stock, the Buyer
shall  have the  following  rights:  (i) to  participate,  or have its  designee
participate,   or  decline  to  participate  in  the  Acquisition  Financing  by
delivering  notice (or fail to deliver notice) during the five-day period;  (ii)
continue to exercise its rights to purchase  shares of Series D Preferred  Stock
as provided in Section 4i; or (iii)  accelerate its right to purchase  shares of
Series D  Preferred  Stock up to an  aggregate  of  48,000  shares  of  Series D
Preferred Stock.

                           (d)  Exceptions  to Right to  Participate.  The first
refusal  rights  of the  Buyer  pursuant  to this  Section  shall  not  apply to
securities issued by the Company (i) upon conversion of any of the shares of any
series of Preferred  Stock or the exercise of Warrants to purchase Common Stock,
(ii) as a stock  dividend  or upon any  subdivision  of shares of Common  Stock,
provided  that  the  securities  issued  pursuant  to  such  stock  dividend  or
subdivision are limited to additional shares of Common Stock,  (iii) pursuant to
subscriptions,  warrants, options, convertible securities, or other rights which
are  outstanding on the date of this Agreement,  (iv) as non-cash  consideration
for the  acquisition  (whether by merger or  otherwise) by the Company or any of
its subsidiaries of all or substantially all of the stock or assets of any other
entity, (v) pursuant to exercise or warrants or options to purchase Common Stock
granted to  directors,  officers,  employees,  investment  bankers,  advisers or
consultants of the Company in connection with their service to the Company, (vi)
pursuant  to any  other  transaction  by the  Company  in  connection  with  the
financing of the acquisition of Superior  Pharmaceutical,  (vii) pursuant to the
licensing of technology  by the Company or from the Company,  or pursuant to any
corporate  partnership,  strategic alliance or joint venture entered into by the
Company,  and  (viii)  upon the  exercise  of any right  which was not itself in
violation of the terms of this Section.

                           (e)  Offering of  Securities  to Third  Parties.  The
Company shall be free at any time prior to sixty (60) days after the  expiration
of its  notice to offer to the  Buyer,  to offer and sell to any third  party or
parties the number of such  securities not agreed by the Buyer, or its designee,
to be purchased by it, at a price and on payment terms no less  favorable to the
Company than those specified in such notice of offer to the Buyer.  However,  if
such third  party sale or sales are not  consummated  within such sixty (60) day
period,  the  Company  shall  not sell  such  securities  as shall not have been
purchased  within such period  without again  complying  with this Section 5. No
Registration  Statement with respect to any Acquisition Financing with any third
party shall be made effective  until 45 days after the Effective Date as defined
above.

         H.  WARRANTS.  The Company agrees to issue to the Buyer at the Closing,
transferable  divisible  warrants (the  "Warrants") for 250,000 shares of Common
Stock.  Such Warrants  shall bear an exercise price per share of Common Stock as
follows: 125% of the Market Price, as defined in the Certificate of Designation,
on the Closing Date, and shall be exercisable immediately upon issuance, and for
a period  of three (3)  years  after  issuance,  in the form  annexed  hereto as
Exhibit  VI,  together  with   piggy-back   registration   rights,   and  demand
registration rights.

         I. SERIES D PREFERRED STOCK. The Buyer  irrevocably  agrees to purchase
up to  $4,800,000,  and the Company  irrevocably  agrees to sell the Buyer up to
$2,400,000  of Series D Preferred  Stock (the  "Series D Preferred  Stock") in a
series of tranches,  commencing thirty (30) 


                                      -9-







days after the Effective Date of the Registration  Statement contemplated by the
Registration  Rights  Agreement  attached  hereto  as ANNEX  IV (the  "Effective
Date").  Buyer's  obligation  to purchase  the Series D Preferred  Stock on each
Additional  Closing  Date (which shall occur not less than thirty (30 ) calendar
days  apart),  shall  be  contingent  upon  the  satisfaction  of the  following
conditions:

                   (a) The  Company  shall  give the Buyer  five (5) days  prior
written notice;

                  (b) The Series D Preferred  Stock issued in each tranche shall
be not less than $200,000 nor in excess of $400,000 principal amount;

                  (c)      On each Additional Closing Date;

                           (i) the Registration  Statement  required to be filed
under the Registration Rights Agreement, is effective;

                           (ii) The representations and warranties  contained in
Section 3 shall be true and
correct in all material respects;

                           (iii)  The  average  daily  trading  volume  for  the
previous thirty (30) trading days
must exceed $100,000;

                           (iv) The  average  daily  share  price of the  common
stock for the ten trading days
prior thereto, must exceed 60% of the price per share on the Closing Date of the
Series C Preferred  Stock, or on the immediately  preceding  Additional  Closing
Date as applicable; and

                  (d) In the event that (x) the Company  does not  exercise  its
option  to  require  the  Buyer to  purchase  at least  $2,400,000  of  Series D
Preferred  Stock,  or (y) the Buyer does not  purchase  at least  $2,400,000  of
Series D Preferred  Stock  because (A) the Buyer in its  discretion,  refuses to
purchase such amount  because of the failure to satisfy the conditions set forth
in  Paragraph  4i(c)(iii)  or  Paragraph  4i(c)(iv)  hereof,  or (B) the Buyer's
obligation to purchase is suspended under Paragraph 4g(i)(a),  the Company will,
not later than thirteen (13) months after the Effective  Date issue to the Buyer
an additional  300,000  Warrants upon the terms and conditions of Paragraph 4(h)
hereof.

                  (e) Notwithstanding anything to the contrary contained herein,
in the event the Buyer does not  purchase a tranche,  or at least  $200,000 of a
tranche,  of  Series D  Preferred  Stock  because  the  conditions  preceded  in
Paragraph  4(i)(c)(iii)  or (c)(iv)  have not been met, the Company may offer to
sell a tranche not  exceeding  $400,000  of such  Series D Preferred  Stock to a
third party, free of any other restrictions, provided however, that such refusal
by  Buyer  shall  not be  deemed  a waiver  of the  right  by Buyer to  purchase
subsequent tranches, or its entitlement to the Warrants in Paragraph 4(i)(d).

 

                                      -10-







        J. AVAILABLE SHARES. The Company shall have at all times authorized and
reserved  for  issuance,  free from  preemptive  rights,  shares of Common Stock
sufficient to yield the number of Common Stock  issuable at conversion as may be
required to satisfy the conversion rights of the Buyer pursuant to the terms and
conditions of the Preferred Stock.

         5.       TRANSFER AGENT INSTRUCTIONS.

         a.  Promptly  following  the  delivery  by the  Buyer of the  aggregate
purchase price for the Preferred  Stock in accordance  with Section 1(c) hereof,
the Company will  irrevocably  instruct its transfer agent to issue Common Stock
from time to time upon  conversion  of the  Preferred  Stock in such  amounts as
specified  from time to time by the Company to the transfer  agent,  bearing the
restrictive  legend  specified  in  Section  4(b) of  this  Agreement  prior  to
registration  of the Shares  under the 1933 Act,  registered  in the name of the
Buyer or its nominee and in such  denominations  to be specified by the Buyer in
connection with each  conversion of the Preferred  Stock.  The Company  warrants
that no instruction other than such instructions  referred to in this Section 5.
The Registration Rights Agreement, and stop transfer instructions to give effect
to Section  4(a) hereof prior to  registration  and sale of the Shares under the
1933 Act will be given by the Company to the transfer  agent and that the Shares
shall  otherwise be freely  transferable on the books and records of the Company
as to the extent provided in the Agreement,  the Registration  Rights Agreement,
and applicable law.  Nothing in this Section shall affect in any way the Buyer's
obligations  and agreement to comply with all  applicable  securities  laws upon
resale of the  Securities.  If the Buyer provides the Company with an opinion of
counsel reasonably  satisfactory to the Company that registration of a resale by
the Buyer of any of the  Securities in accordance  with clause (1)(B) of Section
4(a) of this  Agreement  is not required  under the 1933 Act, the Company  shall
(except as provided in clause (2) of Section 4(a) of this Agreement)  permit the
transfer of the Securities and, in the case of the Shares, promptly instruct the
Company's  transfer agent to issue one or more  certificates for Common Stock in
such name and in such denominations as specified by the Buyer.

         b. The Company  will permit the Buyer to exercise  its right to convert
the  Preferred  Stock and exercise the Warrants by  telecopying  an executed and
completed  Notice of  Conversion  or  Notice  of  Exercise  to the  Company  and
delivering  within  three  business  days  thereafter,  the  original  Notice of
Conversion or Notice of Exercise and the  certificate  for the  Preferred  Stock
representing the Shares or the Warrant to the Company by express  courier.  Each
date on which a Notice of  Conversion or Notice of Exercise is telecopied to and
received by the Company in accordance with the provisions hereof shall be deemed
a Conversion Date. The company will  immediately  confirm receipt of such notice
by telecopy  and  transmit the  certificates  representing  the Shares of Common
Stock  issuable  upon  conversion  of any  Preferred  Stock  (together  with the
Preferred  Stock  representing  the  Shares not so  converted)  to the Buyer via
express courier,  within three business days after receipt by the company of the
original  Notice of  Conversion  and the  certificate  for the  Preferred  Stock
representing the Shares to be converted (the "Delivery Date").

         c. The Company  understands  that a delay in the issuance of the Shares
of Common Stock beyond the  Delivery  Date could result in economic  loss to the
Buyer.  As  compensation  to the Buyer for such loss,  the Company agrees to pay
late  payments,  [not  exceeding  $200,000 per 


                                      -11-






tranche], to the Buyer for late issuance of Shares upon Conversion in accordance
with the following  schedule  (where "No.  Business Days Late" is defined as the
number of business days beyond three (3) business days from Delivery Date:

                                Late Payment for Each $10,000 of Preferred Stock
   No. Business Days Late                Principal Amount Being Converted

             1                                 $100
             2                                 $200
             3                                 $300
             4                                 $400
             5                                 $500
             6                                 $600
             7                                 $700
             8                                 $800
             9                                 $900
             10                                $1,000
             10                                $1,000 +$200 for each
                                               Business Day Late beyond
                                               10 days

The Company shall pay any payments  incurred  under this Section in  immediately
available  funds upon  demand.  Nothing  herein  shall limit a Buyer's  right to
pursue  actual  damages for the  Company's  failure to issue and deliver  Common
Stock to the Buyer. Furthermore,  in addition to any other remedies which may be
available  to the Buyer,  in the event that the Company  fails for any reason to
effect  delivery of such shares of Common Stock within five  business days after
the Delivery Date,  the Buyer will be entitled to revoke the relevant  Notice of
Conversion  by  delivering a notice to such effect to the Company  whereupon the
Company  and the Buyer  shall each be  restored  to their  respective  positions
immediately  prior to delivery of such Notice of Conversion  (and in such event,
the late payments described above shall not be due and payable).

         6.       DELIVERY INSTRUCTIONS.

         The Series C Preferred  Stock shall be  delivered by the Company to the
Escrow Agent pursuant to Section 1(b) hereof on a delivery against payment basis
at the closing.

         7.       CLOSING DATE

         The date and time of the  issuance  and sale of the Series C  Preferred
Stock (the "Closing Date") and the date and time of the issuance and sale of the
Additional  Preferred Stock (an "Additional  Closing Date") shall occur no later
than  12:00  Noon,  New York  time on the  second  NYSE  trading  day  after the
fulfillment or waiver of all Closing conditions pursuant to Sections 8 and 9, or
such other mutually  agreed to time. The closing shall occur on such date at the
offices of the Escrow Agent.  Notwithstanding anything to the contrary contained
herein,  the Escrow Agent will be authorized  to release the funds  representing
the Purchase Price for the Preferred Stock or 



                                      -12-








Additional  Preferred  Stock (as the case may be), and to release the  Preferred
Stock or Additional  Preferred Stock (as the case may be) only upon satisfaction
of the conditions set forth in Section 8 hereof.

         8.       CONDITIONS TO THE COMPANY'S OBLIGATION TO SELL

         The  Buyer  understands  that  the  Company's  obligation  to sell  the
Preferred  Stock on the  Closing  Date and any  Series D  Preferred  Stock on an
Additional Closing Date pursuant to this Agreement is conditioned upon:

         A. The receipt and acceptance by the Company of Buyer's  agreement,  as
evidenced by its execution of this Agreement, to purchase at least Seven Hundred
Fifty Thousand  ($750,000.00) Dollars in liquidation value of Series C Preferred
Stock (or such  lesser  amount as the  Company,  in its sole  discretion,  shall
determine);

         B.  Delivery by the Buyer to the Escrow  Agent of good funds as payment
in full of an amount  equal to the  purchase  price for the  Series C  Preferred
Stock or  Series D  Preferred  Stock  (as the  case may be) in  accordance  with
Section 1(c) hereof;

         C. The accuracy on the Closing Date or Additional  Closing Date (as the
case may be) of the  representations  and  warranties of the Buyer  contained in
this Agreement as if made on such date,  and the  performance by the Buyer on or
before such date of all  covenants and  agreements  of the Buyer  required to be
performed on or before such date;

         D. There shall not be in effect any law, rule or regulation prohibiting
or restricting the transactions contemplated hereby, or requiring any consent or
approval which shall not have been obtained.

         9.       CONDITIONS TO THE BUYER'S OBLIGATION TO PURCHASE.

         The Company  understands  that the Buyer's  obligation  to purchase the
Preferred  Stock on the  Closing  Date and any  Series D  Preferred  Stock on an
Additional Closing Date is conditioned upon:

         A. Acceptance by Buyer of an Agreement for the sale of Preferred Stock,
as indicated by execution of this Agreement, and Buyer's and Company's execution
of the Registration Rights Agreement;

         B. Delivery by the Company to the Escrow Agent of the Preferred  Stock,
the  Warrants,  and  the  Series  D  Preferred  Stock  (as the  case  may be) in
accordance with this Agreement;

         C.  The  accuracy  in all  material  respects  on the  Closing  Date or
Additional  Closing  Date  (as  the  case  may  be) of the  representations  and
warranties of the Company  contained in this  Agreement as if made on such date,
and the  performance  by the Company on or before such date (as the case may be)
of all  covenants and  agreements of the Company  required to be performed on or
before such date; and


                                      -13-






         D. On the Closing  Date or  Additional  Closing  Date the Buyer  having
received an opinion of counsel for the Company,  dated such date, in form, scope
and substance  reasonably  satisfactory to the Buyer, to the effect set forth in
ANNEX III attached hereto.

         10.      GOVERNING LAW:  MISCELLANEOUS.

         This Agreement  shall be governed by and interpreted in accordance with
laws of the State of Delaware.  Each of the parties consents to the jurisdiction
of the federal courts whose districts encompass any part of the City of New York
or the state  courts of the State of New York sitting in the City of New York in
connection with any dispute  arising under this Agreement and hereby waives,  to
the maximum  extent  permitted by law, any  objection,  including  any objection
based on forum non  convenients,  to the bringing of any such proceeding in such
jurisdictions.  A facsimile transmission of this signed Agreement shall be legal
and binding on all parties  hereto.  This Agreement may be signed in one or more
counterparts,  each of which shall be deemed an  original.  The headings of this
Agreement are for convenience of reference and shall not form part of, or affect
the interpretation of, this Agreement.  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.  This Agreement may be amended only by an instrument
in writing  signed by the party to be charged with  enforcement.  This Agreement
supersedes all prior agreements and understandings among the parties hereto with
respect to the subject matter hereof.

         11. NOTICES.  Any notice required or permitted hereunder shall be given
in writing (unless otherwise  specified herein) and shall be deemed  effectively
given upon, (a) personal delivery,  or (b) if advance copy is given by fax, upon
(i) seven  business days after  deposit in the United  states Postal  Service by
regular or certified mail, or (ii) three business days mailing by  international
express courier,  with postage and fees prepaid,  addressed to each of the other
parties  thereunto  entitled  at  the  following  addresses,  or at  such  other
addresses as a party may designate by ten days advance written notice to each of
the other parties hereto.

         COMPANY:            DynaGen, Inc.
                             99 Erie Street
                             Cambridge, Massachusetts 02139
                             Telecopier No. (617) 354-3902

                             with a copy to:

                             John M. Hession, Esq.
                             Testa, Hurwitz & Thibeault, LLP
                             High Street Tower
                             125 High Street
                             Boston, Massachusetts 02110
                             Telecopier No. (617) 248-7100



                                      -14-








      PURCHASER:             At the address set forth on the signature page
                             of this Agreement.

ESCROW AGENT:                Krieger & Prager, Esqs.
                             319 Fifth Avenue
                             New York, New York 10016

         12.   SURVIVAL   OF   REPRESENTATIONS   AND   WARRANTIES.   Purchaser's
representations  and warranties  shall survive the execution and delivery hereof
of this Agreement and the delivery of the preferred Stock.


                  [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK]



                                      -15-










                  IN WITNESS  WHEREOF,  this Agreement has been duly executed by
the Buyer or one of its officers  thereunto  duly  authorized as of the date set
forth below.

NUMBER OF SHARES OF PREFERRED STOCK TO BE PURCHASED:

AGGREGATE PURCHASE PRICE OF SUCH PREFERRED STOCK:    $750,000

                             SIGNATURES FOR ENTITIES

         IN WITNESS  WHEREOF,  the  undersigned  represents  that the  foregoing
statements  are true and  correct  and that it has caused  this  Stock  Purchase
Agreement to be duly executed on its behalf this 21st day of August, 1997




_________________________________           ENDEAVOUR CAPITAL FUND S. A.

Address                                     Printed Name of Subscriber

                                            By:      [illegible]
___________________________________            _______________________________
                                               (Signature of Authorized Person)
Telecopier No. ____________________

                                               _________________________________
                                                     Printed Name and Title
British Virgin Islands
_____________________________
Jurisdiction of Incorporation
or Organization.

        This Agreement has been accepted as of the date set forth below.

DYNAGEN, INC.

By:      /s/ Indu A. Muni
   _______________________________
         Indu A. Muni
Title:   President

Date:    August 21, 1997

                                      -16-