EXHIBIT 4.d

NEITHER THIS WARRANT NOR THE SHARES OF COMMON STOCK ISSUABLE UPON EXERCISE OF
THIS WARRANT HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AND NEITHER
THIS WARRANT NOR SUCH SHARES MAY BE SOLD, ENCUMBERED OR OTHERWISE TRANSFERRED
EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH ACT OR AN
EXEMPTION FROM SUCH REGISTRATION REQUIREMENT, AND, IF AN EXEMPTION SHALL BE
APPLICABLE, THE HOLDER SHALL HAVE DELIVERED AN OPINION OF COUNSEL ACCEPTABLE TO
THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

Void after 5:00 p.m. Eastern Standard Time, on August 18, 2001.


                        WARRANT TO PURCHASE COMMON STOCK

                                       OF

                                  DYNAGEN, INC.


FOR VALUE RECEIVED, DYNAGEN, INC., a Massachusetts corporation (the "Company"),
hereby certifies that Porter Capital Corporation, or its permitted assigns, is
entitled to purchase from the Company, at any time or from time to time
commencing on August 18, 1998 and prior to 5:00 P.M., Eastern Standard Time, on
August 18, 2001, a total of Thirty-Seven Thousand Five Hundred (37,500) fully
paid and nonassessable shares of the common stock, par value $.01 per share, of
the Company for an aggregate purchase price of $0.40 per share. (Hereinafter,
(i) said common stock, together with any other equity securities which may be
issued by the Company with respect thereto or in substitution therefor, is
referred to as the "Common Stock," (ii) the shares of the Common Stock
purchasable hereunder are referred to as the "Warrant Shares," (iii) the
aggregate purchase price payable hereunder for the Warrant Shares is referred to
as the "Aggregate Warrant Price," (iv) the price payable hereunder for each of
the Warrant Shares is referred to as the "Exercise Price," (v) this Warrant, and
all warrants hereafter issued in exchange or substitution for this Warrant are
referred to as the "Warrant" and (vi) the holder of this Warrant is referred to
as the "Holder".) The Exercise Price is subject to adjustment as hereinafter
provided.

         1.       Exercise of Warrant.

         (a) Exercise. This Warrant may be exercised, in whole at any time or in
part from time to time, commencing on August 18, 1998 and prior to 5:00 P.M.,
Eastern Standard Time on August 18, 2001, by the Holder of this Warrant by the
surrender of this Warrant (with the subscription form at the end hereof duly
executed) at the address set forth in Subsection 9(a) hereof, together with
proper payment of the Aggregate Warrant Price, or the proportionate part thereof
if this Warrant is exercised in part. Payment for Warrant Shares shall be made
by certified or official bank check payable to the order of the Company. If this
Warrant is exercised in part, the Holder is entitled to receive a new Warrant
covering the number of Warrant Shares in



<PAGE>


respect of which this Warrant has not been exercised and setting forth the
proportionate part of the Aggregate Warrant Price applicable to such Warrant
Shares. Upon such surrender of this Warrant, the Company will (a) issue a
certificate or certificates in the name of the Holder for the largest number of
whole shares of the Common Stock to which the Holder shall be entitled if this
Warrant is exercised in whole and (b) deliver the proportionate part thereof if
this Warrant is exercised in part, pursuant to the provisions of the Warrant. In
lieu of any fractional share of the Common Stock which would otherwise be
issuable in respect to the exercise of the Warrant, the Company at its option
(a) may pay in cash an amount equal to the product of (i) the daily mean average
of the Closing Price of a share of Common Stock on the ten consecutive trading
days before the Conversion Date and (ii) such fraction of a share or (b) may
issue an additional share of Common Stock.

         Upon exercise of the Warrant, the Company shall issue and deliver to
the Holder certificates for the Common Stock issuable upon such exercise within
ten business days after such exercise and the person exercising shall be deemed
to be the holder of record of the Common Stock issuable upon such exercise.

         No warrant granted herein shall be exercisable after 5:00 p.m. Eastern
Standard Time on the third anniversary of the date of issuance.

         (b) Net Issuance. Notwithstanding anything to the contrary contained in
Subsection 1(a) hereof, in the case of any exercise on or prior to August 18,
2001 the Holder may elect to exercise this Warrant in whole or in part by
receiving shares of Common Stock equal to the net issuance value (as determined
below) of this Warrant, or any part hereof, upon surrender of this Warrant at
the principal office of the Company together with notice of such election (with
the form at the end hereof duly executed), in which event the Company shall
issue to the Holder a number of shares of Common Stock computed using the
following formula:

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

        Where:   X =  the number of shares of Common Stock to be issued to the
                      Holder

                 Y =  the number of shares of Common Stock as to which this 
                      Warrant is to be exercised

                 A = the current fair market value of one share of Common Stock
                     calculated as of the last trading day immediately
                     preceding the exercise of this warrant

                 B = the Exercise Price




                                        2

<PAGE>



         (c) Certain Adjustments

         The Exercise Price and the number of Warrant Shares shall be equitable
adjusted from time to time to account for stock splits, stock dividends,
combinations, recapitalizations, reclassifications and similar events.

         As used herein, current fair market value of the Common Stock as of a
specified date shall mean with respect to each share of Common Stock the average
of the closing bid prices of the Common Stock on the principal securities market
on which the Common Stock may at the time be traded over a period of five
business days consisting of the day as of which the current fair market value of
a share of Common Stock is being determined (or if such day is not a business
day, the business day next preceding such day) and the four consecutive business
days prior to such day. If on the date for which current fair market value is to
be determined the Common Stock is not eligible for trading on any securities
market, the current fair market value of Common Stock shall be the highest price
per share which the Company could then obtain from a willing buyer (not a
current employee or director) for shares of Common Stock sold by the Company,
from authorized but unissued shares, as determined in good faith by the Board of
Directors of the Company, which determination shall be conclusive, unless prior
to such date the Company has become subject to a merger, acquisition or other
consolidation pursuant to which the Company is not the surviving party, in which
case the current fair market value of the Common Stock shall be deemed to be the
value received by the holders of the Company's Common Stock for each share
thereof pursuant to the Company's acquisition.

         2. Reservation of Warrant Shares. The Company agrees that, prior to the
expiration of this Warrant, the Company will at all times have authorized and
reserved, and will keep available, solely for issuance or delivery upon the
exercise of this Warrant, the number of shares of the Common Stock as from time
to time shall be receivable upon the exercise of this Warrant.

         3. Fully Paid Stock: Taxes. The Company agrees that the shares of the
Common Stock represented by each and every certificate for Warrant Shares
delivered on the exercise of this Warrant shall, at the time of such delivery,
be validly issued and outstanding, fully paid and nonassessable, and not subject
to preemptive rights, and the Company will take all such actions as may be
necessary to assure that the par value or stated value, if any, per share of the
Common Stock is at all times equal to or less than the then Exercise Price. The
Company further covenants and agrees that it will pay, when due and payable, any
and all Federal and state stamp, original issue or similar taxes that may be
payable in respect of the issue of any Warrant Share or certificate therefor.

         4.       Transfer.

                  (a) Securities Laws. Neither this Warrant nor the Warrant
Shares issuable upon the exercise hereof have been registered under the
Securities Act of 1933, as amended (the "Securities Act"), or under any state
securities laws and unless so registered may not be

                                        3

<PAGE>



transferred, sold, pledged, hypothecated or otherwise disposed of unless an
exemption from such registration is available. In the event Holder desires to
transfer this Warrant or any of the Warrant Shares issued, the Holder must give
the Company prior written notice of such proposed transfer including the name
and address of the proposed transferee. Such transfer may be made only either
(i) upon publication by the Securities and Exchange Commission (the
"Commission") of a ruling, interpretation, opinion or "no action letter" based
upon facts presented to said Commission, or (ii) upon receipt by the Company of
an opinion of counsel to the Company in either case to the effect that the
proposed transfer will not violate the provisions of the Securities Act, the
Securities Exchange Act of 1934, as amended (the "Exchange Act"), or the rules
and regulations promulgated under either such act, or in the case of clause (ii)
above, to the effect that the Warrant or Warrant Shares to be sold or
transferred has been registered under the Securities Act and that there is in
effect a registration statement in which is included a prospectus meeting the
requirements of Subsection 10 (a) of the Securities Act, which is being or will
be delivered to the purchaser or transferee at or prior to the time of delivery
of the certificates evidencing the Warrant or Warrant Stock to be sold or
transferred. The Company agrees that, at any time beginning after the date that
is six months from the date of this Warrant's issuance, upon the written request
of the Holder and if and to the extent that the Warrant or the Warrant Shares
are not then transferable pursuant to one or more of the foregoing conditions,
the Company will use commercially reasonable efforts at the Company's expense to
include the Warrant Shares on any registration statement it files under the
Securities Act to register any shares of Common Stock.

                  (b) Conditions to Transfer. Prior to any such proposed
transfer, and as a condition thereto, if such transfer is not made pursuant to
an effective registration statement under the Securities Act, the Holder will,
if requested by the Company, deliver to the Company (i) an investment covenant
signed by the proposed transferee, (ii) an agreement by such transferee to the
impression of the restrictive investment legend set forth herein on the
certificate or certificates representing the securities acquired by such
transferee, (iii) an agreement by such transferee that the Company may place a
"stop transfer order" with its transfer agent or registrar, and (iv) an
agreement by the transferee to indemnify the Company to the same extent as set
forth in the next succeeding paragraph.

                  (c) Indemnity. The Holder acknowledges that the Holder
understands the meaning and legal consequences of this Section 4, and the Holder
hereby agrees to indemnify and hold harmless the Company, its representatives
and each officer and director thereof from and against any and all loss, damage
or liability (including all attorneys' fees and costs incurred in enforcing this
indemnity provision) due to or arising out of (a) the material inaccuracy of any
representation or the material breach of any warranty of the Holder contained
in, or any other material breach of, this warrant, (b) any transfer of the
Warrant or any of the Warrant Shares in violation of the Securities Act, the
Exchange Act or the rules and regulations promulgated under either of such acts,
(c) any transfer of the Warrant or any of the Warrant Shares not in accordance
with this Warrant or (d) any materially untrue statement or omission to state
any material fact in connection with the investment representations or with
respect to the facts and representations

                                        4

<PAGE>



supplied by the Holder to counsel to the Company upon which its opinion as to a
proposed transfer shall have been based.

                  (d) Transfer. Except as restricted hereby, this Warrant and
the Warrant Shares issued may be transferred by the Holder in whole or in part
at any time or from time to time. Upon surrender of this Warrant to the Company,
with assignment documentation duly executed and funds sufficient to pay any
transfer tax, and upon compliance with the foregoing provisions, the Company
shall, without charge, execute and deliver a new Warrant in the name of the
assignee named in such instrument of assignment, and this Warrant shall promptly
be canceled. Any assignment, transfer, pledge, hypothecation or other
disposition of this Warrant attempted contrary to the provisions of this
Warrant, or any levy of execution, attachment or other process attempted upon
the Warrant, shall be null and void and without effect.

                  (e) Legend and Stop Transfer Orders. Unless the Warrant Shares
have been registered under the Securities Act, upon exercise of any part of the
Warrant and the issuance of any of the Warrant Shares, the Company shall
instruct its transfer agent to enter stop transfer orders with respect to such
shares, and all certificates representing Warrant Shares shall bear on the face
thereof substantially the following legend, insofar as is consistent with
Massachusetts law:

         "The shares of common stock represented by this certificate have not
         been registered under the Securities Act of 1933, as amended, and may
         not be sold, offered for sale, assigned, transferred or otherwise
         disposed of unless registered pursuant to the provisions of that Act or
         an opinion of counsel to the Company is obtained stating that such
         disposition is in compliance with an available exemption from such
         registration."

         5. Loss, etc. of Warrant. Upon receipt of evidence satisfactory to the
Company of the loss, theft, destruction or mutilation of this Warrant, and of an
unsecured indemnity from the Holder reasonably satisfactory to the Company, if
lost, stolen or destroyed, and upon surrender and cancellation of the Warrant,
if mutilated, the Company shall execute and deliver to the Holder a new Warrant
of like date, tenor and denomination.

         6. Warrant Holder Not Shareholder. Except as otherwise provided herein,
this Warrant does not confer upon the Holder any right to vote or to consent to
or receive notice as a shareholder of the Company, as such, in respect of any
matters whatsoever, or any other rights or liabilities as a shareholder, prior
to the exercise hereof.

         7. Communication. No notice or other communication under this Warrant
shall be effective unless the same is in writing and is mailed by certified
mail, return receipt requested, addressed to:


                                        5

<PAGE>



                  (a) the Company at 840 Memorial Drive, Cambridge, MA 02139, or
such other address as the Company has designated in writing to the Holder, with
a copy to David A. Broadwin, Esq., Foley, Hoag & Eliot, One Post Office Square,
Boston, Massachusetts 021 10, or

                  (b) the Holder at 109 Danbury Road, Ridgefield, CT 06877, or
such other address as the Holder has designated in writing to the Company, with
a copy to Richard C. Agins, Esq., Agins, Siegel & Reiner, LLP, 342 Madison
Avenue, New York, NY 10173.

         Any notice given hereunder shall be effective upon the earlier of (i)
receipt, or (ii) a date three days from the date of posting.

         8. Headings. The headings of this Warrant have been inserted as a
matter of convenience and shall not affect the construction hereof.

         9. Reorganization, etc. If the Company is a party to a reorganization
or merger with one or more other corporations, whether or not the Company is the
surviving corporation, or if the Company consolidates with or into one or more
other corporations, or if the Company is liquidated or sells or otherwise
disposes of substantially all of its assets to another corporation (each
hereinafter referred to as a "Transaction"), in any such event while this
Warrant remains outstanding, then after the effective date of such Transaction,
the unexercised portion of this Warrant shall remain outstanding, and lawful and
adequate provision shall be made whereby the Holder shall thereafter have the
right to purchase and receive, upon the basis and upon the terms and conditions
herein specified and in lieu of the shares of Common Stock of the Company
immediately theretofore purchasable and receivable upon exercise of this
Warrant, such shares of stock, securities or assets as may be issued or payable
with respect to or in exchange for a number of outstanding shares of such Common
Stock equal to the number of shares of Common Stock immediately theretofore
purchasable and receivable upon the exercise of this Warrant had such
Transaction not taken place, and in any such case appropriate provision shall be
made with respect to the rights and interests of the Holder to the end that the
provisions hereof (including, without limitation, provisions for adjustments to
the Warrant Purchase Price and of the number of shares purchasable upon the
exercise of this Warrant) shall thereafter be applicable, as nearly as may be
practicable, in relation to any shares of stock, securities or assets thereafter
deliverable upon the exercise hereof.

         10. Applicable Law. This Warrant shall be governed by and construed in
accordance with the law of The Commonwealth of Massachusetts without giving
effect to the principles of conflicts of law thereof.



                                        6

<PAGE>



         IN WITNESS WHEREOF, DYNAGEN, INC. has caused this Warrant to be signed
by its Executive Vice President Officer and its corporate seal to be hereunto
affixed and attested by its Secretary this 18th day of August 1998.

ATTEST:                                      DYNAGEN, INC.


_______________________                      By: _____________________________
                                                 Dhananjay G. Wadekar
                                                 Executive Vice President



                                        7

<PAGE>



                                  SUBSCRIPTION

         The undersigned, _______________________________________, pursuant to
the provisions of the foregoing Warrant, hereby agrees to subscribe for the
purchase of ________ shares of the Common Stock of DYNAGEN, INC. covered by said
Warrant, and makes payment therefor in full at the price per share provided by
said Warrant.

Dated:____________________________          Signature:_________________________

Address:___________________________

        ___________________________


                                   ASSIGNMENT

         FOR VALUE RECEIVED ___________________________ hereby sells, assigns
and transfers unto ______________________________ the foregoing Warrant and all
rights evidenced thereby, and does irrevocably constitute and appoint
_____________________, attorney, to transfer said Warrant on the books of
DYNAGEN, INC..

Dated:____________________________          Signature:_________________________

Address:___________________________

        ___________________________


                               PARTIAL ASSIGNMENT

FOR VALUE RECEIVED _________________________ hereby sells, assigns and transfers
unto ___________________________ the right to purchase _________ shares of the
Common Stock of DYNAGEN, INC. by the foregoing Warrant, and a proportionate part
of said Warrant and the rights evidenced hereby, and does irrevocably constitute
and appoint ___________________________________, attorney, to transfer that part
of said Warrant on the books of DYNAGEN, INC.

Dated:____________________________          Signature:_________________________

Address:___________________________

        ___________________________



                                        8

<PAGE>


                              NET ISSUANCE ELECTION

         The undersigned, _______________________________, pursuant to the
provisions of the foregoing Warrant, hereby tenders the right to purchase _____
shares of the Common Stock of DYNAGEN, INC., and a proportionate part of said
Warrant and the rights evidenced thereby, in exchange for a number of shares of
said Common Stock to be computed in accordance with the provisions of Section
1(b) of said Warrant.

Dated:____________________________          Signature:_________________________

Address:___________________________

        ___________________________



                                        9