<PAGE>

                                                                     EXHIBIT 4.3

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR INVESTMENT
AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED OR
STATE SECURITIES LAWS. THESE SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE
ABSENCE OF SUCH REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT OR STATE
SECURITIES LAWS.

No. 003     Right to Purchase Shares of Common Stock of Memory Pharmaceuticals
            Corp.

                          MEMORY PHARMACEUTICALS CORP.

                          Common Stock Purchase Warrant

         This is to certify that, FOR VALUE RECEIVED, Alexandria Real Estate
Equities, L.P. (the "Holder"), is entitled to purchase, subject to the
provisions of this Warrant, from Memory Pharmaceuticals Corp., a Delaware
corporation (the "Company"), 12,500 fully paid, validly issued and nonassessable
shares of Common Stock, par value $.001 per share, of the Company (the "Common
Stock") at an exercise price of $2.75 per share; provided, that such exercise
price shall be adjusted once on the closing date of the next round of
convertible preferred financing occurring after the date hereof to a per share
exercise price equal to the purchase price at which such preferred shares are
sold. The number of shares of Common Stock to be received upon the exercise of
this Warrant and the price to be paid for each share of Common Stock may be
adjusted from time to time as hereinafter set forth. The exercise price
adjustment described in the preceding sentence may be triggered only once. The
shares of Common Stock deliverable upon such exercise, and as adjusted from time
to time, are hereinafter sometimes referred to as "Warrant Shares" and the
exercise price of a share of Common Stock in effect at any time and as adjusted
from time to time is hereinafter sometimes referred to as the "Exercise Price".

         1.       EXERCISE OF WARRANT.

                  a.       Exercise for Cash. This Warrant may be exercised in
whole or in part at any time or from time to time after the date hereof and on
or before the tenth anniversary hereof (the "Exercise Period"). This Warrant may
be exercised by presentation and surrender hereof to the Company at its
principal office, or at the office of its stock transfer agent, if any, with the
Purchase Form annexed hereto duly executed and accompanied by payment of the
Exercise Price for the number of Warrant Shares specified in such form. The
Exercise Price may be paid by bank check, wire transfer or cancellation of
indebtedness. As soon as practicable after each such exercise of this Warrant,
but not later than seven (7) days from the date of such exercise, the Company
shall issue and deliver to the Holder a certificate for the Warrant Shares
issuable upon such exercise, registered in the name of the Holder. If this
Warrant should be exercised in part only, the Company shall, upon surrender of
this Warrant for cancellation, execute and deliver a new Warrant evidencing the
rights of the Holder thereof to purchase the balance of the Warrant Shares
purchasable thereunder. Upon receipt by the Company of this Warrant at its
office, or by the stock transfer agent of the Company at its office, in proper
form for exercise, the Holder shall be deemed to be the holder of record of the
shares of Common Stock issuable upon such exercise, notwithstanding that the
stock transfer books of the Company shall then be closed or that certificates
representing such shares of Common Stock shall not then be physically delivered
to the Holder.

<PAGE>

                  b.       Warrant Exchange. At any time during the Exercise
Period, the Holder may, at its option, exchange this Warrant, in whole or in
part (a "Warrant Exchange"), into the number of Warrant Shares determined in
accordance with this Section 1(b), by surrendering this Warrant at the principal
office of the Company or at the office of its stock transfer agent, accompanied
by a notice stating the Holder's intent to effect such exchange, the number of
Warrant Shares to be exchanged and the date on which the Holder requests that
such Warrant Exchange occur (the "Notice of Exchange"). The Warrant Exchange
shall take place on the date specified in the Notice of Exchange or, if later,
the date the Notice of Exchange is received by the Company (the "Exchange
Date"). Certificates for the shares issuable upon such Warrant Exchange and, if
applicable, a new warrant of like tenor evidencing the balance of the shares
remaining subject to this Warrant, shall be issued as of the Exchange Date and
delivered to the Holder within seven (7) days following the Exchange Date. In
connection with any Warrant Exchange, this Warrant shall represent the right to
subscribe for and acquire the number of Warrant Shares equal to (i) the number
of Warrant Shares specified by the Holder in its Notice of Exchange (the "Total
Number") less (ii) the number of Warrant Shares equal to the quotient obtained
by dividing (A) the product of the Total Number and the existing Exercise Price
by (B) the Fair Market Value, provided that any fractional shares determined by
this calculation shall be represented by the issuance of a new Warrant. "Fair
Market Value" shall be determined as follows: (1) if the Common Stock is listed
on a national securities exchange or admitted to unlisted trading privileges on
such exchange or listed for trading on the Nasdaq Stock Market, the Fair Market
Value shall be the average of the last reported sale prices of the Common Stock
on such exchange or system for the twenty (20) consecutive trading days
preceding the date for which the determination is being made; or (2) if the
Common Stock is not so listed or admitted to unlisted trading privileges, the
Fair Market Value shall be the average of the last reported bid and asked prices
reported by the National Quotation Bureau, Inc. for the twenty (20) consecutive
trading days preceding the date for which the determination is being made; or
(3) if the Common Stock is not so listed or admitted to unlisted trading
privileges and bid and asked prices are not so reported, the Fair Market Value
shall be an amount, not less than book value thereof as at the end of the most
recent fiscal quarter of the Company ending prior to the Exchange Date,
determined in good faith by the Board of Directors of the Company.

         2.       RESERVATION OF SHARES. The Company shall at all times reserve
for issuance and/or delivery upon exercise of this Warrant such number of shares
of its Common Stock as shall be required for issuance and delivery upon exercise
of this Warrant.

         3.       FRACTIONAL SHARES. No fractional shares of Common Stock shall
be issued upon the exercise of this Warrant. With respect to any fraction of a
share called for upon any exercise hereof, the Company shall pay to the Holder
an amount in cash equal to such fraction multiplied by the Fair Market Value of
a share of Common Stock.

         4.       ANTI-DILUTION PROVISIONS.

                  4.1      Mergers, Consolidations or Sale of Assets. If after
the date hereof there shall be a capital reorganization (other than a
combination or subdivision of Common Stock otherwise provided for herein), or
spin-off, or a merger or consolidation of the Company with or into another
corporation, or the sale of all or substantially all of the Company's properties
and assets to any other person, then, as a part of such transaction, lawful
provision shall be made so that the Holder shall thereafter be entitled to
receive upon exercise of this Warrant, during the period specified in this
Warrant and upon payment of the purchase price, the number of shares of stock or
other securities, cash or property of the Company or the successor corporation

<PAGE>

resulting from such transaction, to which a holder of the Common Stock
deliverable upon exercise of this Warrant would have been entitled under the
provisions of the agreement in such transaction if this Warrant had been
exercised immediately before such transaction. In any such case, appropriate
adjustment (as determined reasonably and in good faith by the Company's Board of
Directors) shall be made in the application of the provisions of this Warrant
with respect to the rights and interests of the Holder after such transaction to
the end that the provisions of this Warrant (including adjustment of the
purchase price then in effect and the number of shares of Common Stock issuable
upon exercise hereof) shall be applicable after that event, as near as
reasonably may be, in relation to any shares or other property deliverable after
that event upon exercise of this Warrant.

                  4.2      Splits and Subdivisions; Dividends. If the Company
should effect or fix a record date for the effectuation of a split or
subdivision of the outstanding shares of Common Stock or the determination of
the holders of Common Stock entitled to receive a dividend or other distribution
payable in additional shares of Common Stock or other securities or warrants,
options or other rights convertible into, or entitling the holder thereof to
receive directly or indirectly, additional shares of Common Stock (hereinafter
referred to as "Common Stock Equivalents") without payment of any consideration
by such holder for the additional shares of Common Stock or Common Stock
Equivalents (including the additional shares of Common Stock issuable upon
conversion or exercise thereof), then, as of such record date (or the date of
such distribution, split or subdivision if no record date is fixed), the per
share purchase price shall be appropriately decreased and the number of shares
of Common Stock issuable upon exercise hereof shall be appropriately increased
in proportion to such increase of outstanding shares.

                  4.3      Combination of Shares. If the number of shares of
Common Stock outstanding at any time after the date hereof is decreased by a
combination of the outstanding shares of Common Stock, the per share purchase
price shall be appropriately increased and the number of shares of Common Stock
issuable upon exercise hereof shall be appropriately decreased in proportion to
such decrease in outstanding shares.

                  4.4      Adjustments for Other Distributions. In the event the
Company shall declare a distribution payable in securities of the Company (other
than Common Stock Equivalents) or other persons, evidences of indebtedness
issued by the Company or other persons, assets (including cash dividends) or
options or rights not referred to in subsection 4.2, then, in each such case for
purposes of this subsection 4.4, upon exercise of this Warrant the holder hereof
shall be entitled to a proportionate share of any such distribution as though
such holder was the holder of the number of shares of Common Stock of the
Company into which this Warrant may be exercised as of the record date fixed for
the determination of the holders of Common Stock of the Company entitled to
receive such distribution.

                  4.5      Issuance of Additional Common Stock.

                           (a)      If, after the date hereof, the Company shall
                                    issue or sell

                                    (i)      Additional Shares (defined below)
                                    without consideration or for a consideration
                                    per share less than the higher of (A) the
                                    exercise price and (B) the Fair Market Value
                                    of a share of Common Stock in effect
                                    immediately prior to such issue or sale, or

                                    (ii)     Common Stock Equivalents
                                    exercisable for Additional Shares with a
                                    minimum exercise or exchange price less than
                                    the higher of (A) the exercise price and (B)
                                    the Fair Market Value of a share of Common
                                    Stock,

                                        3
<PAGE>

then, and in each such case, the exercise price shall be reduced, concurrently
with such issue or sale, to a price (calculated to the nearest .001 of a cent)
determined by multiplying such exercise price by a fraction:

                                    (i)      the numerator of which shall be (A)
                                    the number of shares of Common Stock
                                    outstanding immediately prior to such issue
                                    or sale plus (B) the number of shares of
                                    Common Stock that the aggregate
                                    consideration received by the Company upon
                                    such issuance or sale (or, in the case of
                                    Common Stock Equivalents exercisable for
                                    Additional Shares, receivable by the Company
                                    upon exercise or exchange) would purchase at
                                    such exercise price or fair market value, as
                                    the case may be, and

                                    (ii)     the denominator of which shall be
                                    the number of shares of Common Stock
                                    outstanding immediately after such issue or
                                    sale (or, in the case of Common Stock
                                    Equivalents exercisable for Additional
                                    Shares, assuming exercise or exchange
                                    thereof).

                           (b)      For the purposes of this Section 4.5, the
consideration for the issue or sale of Additional Shares shall, irrespective of
the accounting treatment of such consideration, (i) insofar as it consists of
cash, be computed at the net amount of cash received by the Company, and (ii)
insofar as it consists of property (including securities) other than cash, be
computed at the fair value thereof at the time of such issue or sale as
determined in good faith by the Board of Directors of the Company.

                           (c)      Notwithstanding anything contained herein to
the contrary, the consideration for any Common Stock Equivalents shall be the
total amount of consideration received by the Company for the issuance of such
Common Stock Equivalents plus the minimum amount of consideration payable to the
Company upon exercise, conversion or exchange of Common Stock Equivalents (the
"Net Consideration") determined as of the date of issuance of such Common Stock
Equivalents. Any obligation, agreement or understanding to issue Common Stock
Equivalents at any time in the future shall be deemed to be an issuance at the
time such obligation or agreement is made or arises. No adjustment of the
exercise price shall be made under this Section 4.5 upon the issuance of any
shares of Common Stock which are issued pursuant to the exercise, conversion or
exchange of any Common Stock Equivalents if any adjustment shall previously have
been made upon the issuance of any such Common Stock Equivalents.

                                    Should the Net Consideration for any such
Common Stock Equivalents be increased or decreased from time to time, then, upon
the effectiveness of such change, the exercise price will be that which would
have been obtained (i) had the adjustments made upon the issuance of such Common
Stock Equivalents been made upon the basis of the actual Net Consideration (as
so increased or decreased) of such Common Stock Equivalents, and (ii) had
adjustments to such exercise price since the date of issuance of such Common
Stock Equivalents been made to such exercise price as adjusted pursuant to (i)
above. Any adjustment of the exercise price with respect to this paragraph which
relates to Common Stock Equivalents shall be disregarded if, as, and when all of
such Common Stock Equivalents expire or are canceled without being exercised, so
that the exercise price effective immediately upon cancellation or expiration
shall be equal to the exercise price in effect at the time of the issuance of
the expired or canceled Common Stock Equivalents, with such additional
adjustments as would have been made to such exercise price had the expired or
canceled Common Stock Equivalents not been issued.

                                        4
<PAGE>

                           (d)      "Additional Shares" means all shares of
Common Stock, whether or not subsequently reacquired or retired by the Company
other than shares of Common Stock issued or to be issued to directors, officers,
employees and consultants of the Company or any subsidiary pursuant to any bona
fide qualified or non-qualified stock option plan or agreement, stock purchase
plan or agreement, stock restriction agreement, or employee stock ownership plan
(ESOP).

                           (e)      The number of shares of Common Stock that
the holder of this Warrant shall be entitled to receive upon each exercise
hereof after any adjustment pursuant to this Section 4.5 shall be determined by
multiplying (i) the number of shares of Common Stock that were issuable
immediately prior to such adjustment, by (ii) the fraction of which (A) the
numerator is the exercise price immediately prior to such adjustment and (B) the
denominator is the exercise price immediately following such adjustment.

                  4.6      Certificate as to Adjustments. In the case of each
adjustment or readjustment of the exercise price pursuant to this Section 4, the
Company at its expense will promptly compute such adjustment or readjustment in
accordance with the terms hereof and cause a certificate, signed by the
Company's Chief Financial Officer, setting forth such adjustment or readjustment
and showing in detail the facts upon which such adjustment or readjustment is
based to be delivered to the holder of this Warrant. The Company will furnish or
cause to be furnished to such Holder a certificate setting forth (a) such
adjustments and readjustments, (b) the exercise price at the time in effect and
how it was calculated and (c) the number of shares of Common Stock issuable upon
exercise hereof and the amount, if any, of other property at the time receivable
upon the exercise of the Warrant.

                  4.7      Notices of Record Date, etc.

                           In the event of: (a) any taking by the Company of a
record of the holders of any class of securities of the Company for the purpose
of determining the holders thereof who are entitled to receive any dividend
(other than a cash dividend payable out of earned surplus at the same rate as
that of the last such cash dividend theretofore paid) or other distribution, or
any right to subscribe for, purchase or otherwise acquire any shares of stock of
any class or any other securities or property, or to receive any other right;
(b) any capital reorganization of the Company, any reclassification or
recapitalization of the capital stock of the Company or any transfer of all or
substantially all of the assets of the Company to any other person or any
consolidation or merger involving the Company; or (c) any voluntary or
involuntary dissolution, liquidation or winding-up of the Company, the Company
will mail to the Holder of this Warrant at least twenty (20) days prior to the
earliest date specified below, a notice specifying: (i) the date on which any
such record is to be taken for the purpose of such dividend, distribution or
right, and the amount and character of such dividend, distribution or right; and
(ii) the date on which any such reorganization, reclassification, transfer,
consolidation, merger, dissolution, liquidation or winding-up is expected to
become effective and the record date for determining stockholders entitled to
vote thereon and the time, if any such time is to be fixed, as of which the
holders of record of Common Stock shall be entitled to exchange their shares of
Common Stock for the securities or other property deliverable upon such
reorganization, reclassification, recapitalization, consolidation, merger,
transfer, dissolution, liquidation or winding-up.

         5.       LOSS OF WARRANT. Upon receipt by the Company of evidence
satisfactory to it of the loss, theft, destruction or mutilation of this
Warrant, and (in the case of loss, theft or destruction) of reasonably
satisfactory indemnification, and upon surrender and cancellation of this
Warrant, if mutilated, the Company will execute and deliver a new warrant of
like tenor and date.

                                        5
<PAGE>

         6.       NO RIGHTS AS STOCKHOLDER. The Holder shall not, as holder of
this Warrant, be entitled to vote, if applicable, or to receive dividends or to
be deemed the holder of Common Stock that may at any time be issuable upon
exercise of this Warrant for any purpose whatsoever, nor shall anything
contained herein be construed to confer upon the Holder, as such, any of the
rights of a stockholder of the Company or, if applicable, any right to vote for
the election of directors or upon any matter submitted to stockholders at any
meeting thereof, or to give or withhold consent to any corporate action (whether
upon any recapitalization, issue or reclassification of stock, change of par
value or change of stock to no par value, consolidation, merger or conveyance or
otherwise), or to receive notice of meetings, or to receive dividends or
subscription rights, until such holder shall have exercised the Warrant and been
issued the Warrant Shares in accordance with the provisions hereof.

         7.       NON-TRANSFERABILITY. Except as set forth in Section 12,
neither this Warrant nor any Warrant Shares shall be registered under the
Securities Act of 1933, as amended, and applicable state securities laws.
Therefore, the Company shall require, as a condition of allowing the transfer or
exchange of this Warrant or such Warrant Shares, that the Holder of this Warrant
or such Warrant Shares, as the case may be, furnish to the Company an opinion of
counsel reasonably acceptable to the Company to the effect that such transfer or
exchange will be exempt from the registration and prospectus delivery
requirements under the Securities Act of 1933, as amended, and applicable state
securities laws. The certificates evidencing the Warrant Shares shall bear a
legend to the effect that the Warrant Shares evidenced by such certificate have
not been registered under the Securities Act of 1933, as amended, and applicable
state securities laws and are, therefore, subject to restrictions on transfer in
the absence of such registration or an exemption therefrom under said act or
state securities laws.

         8.       INVESTMENT REPRESENTATIONS AND WARRANTIES. The Holder hereby
represents and warrants to the Company that (a) it has knowledge and experience
in financial and business matters sufficient to enable it to evaluate the merits
and risks of an investment in the Company; (b) it has assets sufficient to
enable it to bear the economic risk of its investment in this Warrant and the
Warrant Shares and is an "accredited investor" as defined in Rule 501 under the
Securities Act of 1933, as amended; (c) it is acquiring this Warrant and, upon
exercise, will acquire the Warrant Shares, for its own account, and not with a
view to, or for sale in connection with, any distribution thereof; (d) it or its
representatives have received from the Company such information with respect to
the Company as it has deemed necessary and relevant in connection with this
Warrant and the Warrant Shares and it has had the opportunity, directly or
through such representatives, to ask questions of and receive answers from
persons acting on behalf of the Company necessary to verify the information so
obtained; and (e) it and its officers, directors, employees and agents have not
employed any broker or finder or incurred any liability for any brokerage or
finder's fees or commissions or similar payments in connection with this Warrant
and the Warrant Shares.

         9.       GOVERNING LAW. This Agreement and all amendments,
modifications, alterations, or supplements hereto shall be construed under and
governed by the laws of the State of New Jersey and the United States of
America, without regard to the principles of conflicts of law thereof.

         10.      MISCELLANEOUS. Except as provided in Sections 4 and 12 hereof,
this Warrant and any term hereof may be changed, waived, discharged or
terminated only by an instrument in writing signed by the party against which
enforcement of such change, waiver, discharge or termination is sought. The
headings in this Warrant are for purposes of reference only and shall not limit
or otherwise affect any of the terms hereof. The invalidity or unenforceability
of any provision hereof shall in no way affect the validity or enforceability of
any other provision.

                                        6
<PAGE>

         11.      EXPIRATION. The right to exercise this Warrant shall expire at
5:00 P.M. Eastern Standard Time on the tenth anniversary of the date hereof.

         12.      REGISTRATION RIGHTS.

                           (a)      If at any time the Company proposes to file
a registration statement under the Securities Act of 1933, as amended (the
"Act") with respect to an offering of equity securities by the Company for its
own account or for the account of any securityholders of any class of its equity
securities (other than (i) a registration statement on Form S-4 or S-8 (or any
substitute form that may be adopted by the Securities and Exchange Commission
(the "Commission")) or (ii) a registration statement filed in connection with an
exchange offer or offering of securities solely to the Company's existing
securityholders) or (iii) the initial public offering, then the Company shall
give written notice of such proposed filing to the Holder as soon as practicable
(but in no event less than 20 days before the anticipated filing date), and,
subject to the terms and conditions hereof, such notice shall offer such Holder
the opportunity to register such number of shares of Registrable Securities as
the Holder may request (which request shall specify the Registrable Securities
intended to be disposed of and the intended method of distribution thereof) (a
"Piggy-Back Registration").

                  The Company shall use best efforts to cause the managing
Underwriter or Underwriters of a proposed underwritten public offering to permit
the Registrable Securities requested by the Holder to be included in a
Piggy-Back Registration on the same terms and conditions as any similar
securities of the Company or any other securityholder included therein and to
permit the sale or other disposition of such Registrable Securities in
accordance with the intended method of distribution thereof. If the total amount
of securities, including the Registrable Securities, requested by the
securityholders to be included in such offering exceeds the amount of securities
sold other than by the Company that the underwriters determine in their sole
discretion is compatible with the success of the offering, then the Company
shall be required to include in the offering only that number of such
securities, including Registrable Securities, that the underwriters determine in
their sole discretion will not jeopardize the success of the offering (the
securities so included to be apportioned pro rata among the selling holders
according to the total amount of securities entitled to be included therein
owned by each selling holder or in such other proportions as shall mutually be
agreed to by such selling holders). The Holder shall have the right to withdraw
its request for inclusion of its Registrable Securities in any registration
statement pursuant to this Section 12 by giving written notice to the Company of
its request to withdraw. The Company may withdraw a Piggy-Back Registration at
any time prior to the time it becomes effective. No failure to effect a
registration under this Section 12 and to complete the sale of Registrable
Securities in connection therewith shall relieve the Company of any other
obligation under this Agreement (including, without limitation, the Company's
obligations under Sections 12(b) and 12(c)).

                           (b)      The Company shall keep effective and
maintain for 180 days following its effectiveness any registration,
qualification, approval or listing specified in this Section 12 for such period
as may be necessary for the Holder to dispose of Registrable Securities in
accordance with their intended method or methods of distribution, and from time
to time shall amend or supplement the prospectus used in connection therewith to
the extent necessary in order to comply with applicable law. All expenses,
disbursements and fees in connection with any action to be taken hereunder,
including, without limitation, all registration and filing fees, fees and
expenses of compliance with securities or blue sky laws, printing expenses and
fees and expenses of counsel for the Company and its independent certified
public accountants (all such expenses being herein called "Registration
Expenses") will be borne by the Company; provided that in no event shall
Registration Expenses include any underwriting discounts, sales commissions or
similar fees attributable to

                                        7
<PAGE>

the sale of Registrable Securities. The Company shall have no responsibility for
any expenses, disbursements and fees of the Holder or any counsel retained by
Holder in connection with any registration, qualification, approval or listing
specified in this Section 12, except to the extent the Company has agreed in
writing to incur the expenses, disbursements and fees of one (1) counsel
retained on behalf of the group of selling stockholders to which the Holder is a
participant.

                           (c)      The Company hereby indemnifies, to the
fullest extent permitted by law, the Holder or each person, if any, who controls
Holder within the meaning of Section 15 of the Act, and the directors, officers,
employees, agents and representatives of each of them, against all losses,
claims, damages, liabilities, costs and expenses (including, without limitation,
fees and expenses of counsel), as incurred, arising out of, relating to, or
caused by any untrue statement or alleged untrue statement of a material fact
contained in any registration statement, prospectus or preliminary prospectus
(or any amendment or supplement thereto) or any omission or alleged omission to
state therein a material fact required to be stated therein or necessary to make
the statements therein not misleading, except insofar as such losses, claims,
damages, liabilities or expenses are caused by any untrue statement contained
in, or omission from, information furnished in writing to the Company by Holder
expressly for use therein. In connection with any registration statement in
which Holder is participating, Holder will furnish to the Company in writing
such information as shall reasonably be requested by the Company for use in any
such registration statement or prospectus and will indemnify, to the extent
permitted by law, the Company, its directors and officers and each person, if
any, who controls the Company within the meaning of the Act against any losses,
claims, damages, liabilities and expenses resulting from any untrue statement or
alleged untrue statement of a material fact or any omission or alleged omission
of a material fact required to be stated in the registration statement or
prospectus or necessary to make the statements therein not misleading, but only
to the extent that such untrue statement of a material fact is contained in, or
such material fact is omitted from, information so furnished in writing by the
Holder expressly for use therein.

         (d)      For purposes of this Section 12, the Holder shall include any
transferee of the Holder if such transfer is made in accordance herewith.

         13.      SECURITIES MATTERS.

                  Whether or not the Company is subject to the reporting
requirements of the Securities Exchange Act of 1934, as amended (the "Exchange
Act"), and in order to make available the benefits of certain rules and
regulations of the Commission which may at any time permit the sale of the
shares of Common Stock issuable upon exercise of the Warrant to the public
without registration, the Company agrees to deliver to the Holder all such
reports, information and other documents as it would be required to file with
the Commission if it were subject to the requirements of Section 13 or 15(d) of
the Exchange Act within 15-days after the date it would have been required to
file such reports with the Commission. From and after the time the Company files
a registration statement with the Commission with respect to the Warrants or the
shares of Common Stock issuable thereunder, the Company shall file such
information with the Commission; provided, that the Company shall not be in
default of the provisions of this Section 13 for any failure to file reports
with the Commission solely by refusal by the Commission to accept the same for
filing.

         14.      NOTICES.

                  Except as otherwise provided in this Warrant, any requirement
for a notice, demand or request under this Warrant will be satisfied by a
writing (a) hand delivered with receipt; (b) mailed by United States registered
or certified mail or Express Mail, return receipt requested, postage prepaid; or
(c) sent by Federal

                                        8
<PAGE>

Express or any other nationally recognized overnight courier service, and
addressed as follows: if to the Holder, at 135 No. Los Robles Avenue, Suite 250,
Pasadena, California 91101, Attn: Senior Vice President, Legal Affairs; and if
to the Company, at 3960 Broadway, New York, New York 10032, Attn: Chief
Financial Officer. All notices that are sent in accordance with this Section 14
will be deemed received by the holder or the Company on the earliest of the
following applicable time periods: (i) the date the return receipt is executed;
or (ii) the date delivered as documented by the overnight courier service or the
hand delivery receipt. Either the Holder or the Company may designate a change
of address by written notice to the other party.

         This Warrant is executed as of the 8th day of March, 2000

Witness:                                MEMORY PHARMACEUTICALS CORP.

/s/ ROBERT COHEN                        By: /s/ JOANNE LEONARD
------------------------                    --------------------------------
ROBERT COHEN, ITS CEO                       JOANNE LEONARD, ITS SR.
                                            VP AND CFO

                                        9
<PAGE>

                              FORM OF SUBSCRIPTION
                   (To be signed only on exercise of Warrant)

TO: Memory Pharmaceuticals Corp.

                  The undersigned, the holder of the within Warrant, hereby
irrevocably elects to exercise this Warrant for, and to purchase
thereunder_____________ shares of Common Stock, $.001 par value per share, of
Memory Pharmaceuticals Corp. and herewith makes payment of $__________________
therefor, and requests that the certificates for such shares be issued in the
name of, and delivered to the undersigned at_______________.

Dated:                    ______________________________________________________
                          (Signature must conform to name of holder as specified
                          on the face of the Warrant)

                          __________________________________
                                      (Address)

                          __________________________________