Document:

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                                                                     EXHIBIT 4.4

THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED UNDER
THE SECURITIES ACT OF 1933 OR ANY OTHER SECURITIES LAWS. THESE SECURITIES HAVE
BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A VIEW TO DISTRIBUTION OR RESALE. SUCH
SECURITIES MAY NOT BE OFFERED FOR SALE, SOLD, DELIVERED AFTER SALE, TRANSFERRED,
PLEDGED OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT
COVERING SUCH SECURITIES UNDER THE SECURITIES ACT OF 1933 AND ANY OTHER
APPLICABLE SECURITIES LAWS, UNLESS THE HOLDER SHALL HAVE OBTAINED AN OPINION OF
COUNSEL REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT
REQUIRED.

                          MEMORY PHARMACEUTICALS CORP.

                   WARRANT TO PURCHASE SHARES OF COMMON STOCK

         THIS CERTIFIES that, for value received, Hoffmann-La Roche Inc., its
successors and permitted assigns (the "HOLDER"), is entitled, upon the terms and
subject to the conditions hereinafter set forth, to subscribe for and purchase
from Memory Pharmaceuticals Corp., a Delaware corporation with principal offices
at 100 Philips Parkway, Montvale, New Jersey 07645 (the "COMPANY"), Three
Hundred Forty-Seven Thousand Two Hundred Twenty-Two (347,222) fully paid and
nonassessable shares of the common stock, par value $.001 per share, of the
Company (the "COMMON STOCK" or the "SHARES"), at a price per share equal to
$4.32 (the "EXERCISE PRICE"), subject to the provisions and upon the terms and
conditions hereinafter set forth.

         1.       Method of Exercise; Payment.

                  (a)      Cash Exercise. The purchase rights represented by
this Warrant may be exercised by the Holder, in whole or in part, from time to
time on or after the date hereof and until 5:00 p.m. EST on September 11, 2008
by: (i) the surrender of this Warrant (with the notice of exercise form (the
"NOTICE OF EXERCISE") attached hereto as Exhibit A duly executed) at the
principal office of the Company; and (ii) by the payment to the Company of an
amount equal to the Exercise Price multiplied by the number of Shares being
purchased, which amount may be paid, at the election of the Holder, by wire
transfer or certified check payable to the order of the Company. The person or
persons in whose name(s) any certificate(s) representing Shares shall be
issuable upon exercise of this Warrant shall be deemed to have become the
holder(s) of record of, and shall be treated for all purposes as the record
holder(s) of, the Shares represented thereby (and such Shares shall be deemed to
have been issued) immediately prior to the close of business on the date or
dates upon which this Warrant is exercised.

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                  (b)      Net Issue Exercise. In lieu of exercising this
Warrant pursuant to Section 1(a) hereof, the Holder may elect, in whole or in
part, from time to time, on or after the date hereof and until 5:00 p.m. EST on
September 11, 2008 to receive a number of Shares equal to the value (as
determined below) of this Warrant (or the portion thereof being canceled) by
surrender of this Warrant at the principal office of the Company, together with
the Notice of Exercise in which Alternative No. 1(b) is initialed by the Holder.
In such event, the Company shall issue to the Holder a number of Shares computed
using the following formula:

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

Where    X = the number of Shares to be issued to the Holder.

         Y = the number of Shares subject to this warrant.

         A = the fair market value of one share of Common Stock.

         B = the Exercise Price (as adjusted to the date of such calculation).

                  (c)      Fair Market Value. For purposes of this Section 1,
the fair market value of the Common Stock shall mean:

         (i)      if the Company's Common Stock is traded on a national
securities exchange, the average of the closing price each day over the ten (10)
trading day period prior to the surrender of this Warrant for exercise in
accordance with the terms hereof;

         (ii)     if the Company's Common Stock is actively traded over-the
counter, the average of the closing bid and asked prices quoted on the NASDAQ
system (or similar system) each day over the ten (10) trading day period prior
to the surrender of this Warrant for exercise in accordance with the terms
hereof; or

         (iii)    if this Warrant is being exercised in conjunction with a
public offering of the Company's equity securities, the per share price to the
public pursuant to such public offering; or

         (iv)     if at any time the Company's Common Stock is not listed on any
national securities exchange or quoted in the NASDAQ System or the
over-the-counter market, then as determined by the board of directors of the
Company in good faith.

                  (d)      Stock Certificates. In the event of any exercise of
the rights represented by this Warrant (whether pursuant to Section 1(a) or
1(b)), certificates for the Shares so purchased shall be delivered to the Holder
and, unless this Warrant has been fully exercised, a new Warrant representing
the Shares with respect to which this Warrant shall not have been exercised
shall also be issued to the Holder within such time.

                                      -2-
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         2.       Stock Fully Paid; Reservation of Shares. All of the Shares
issuable upon the exercise of the rights represented by this Warrant will, upon
issuance and receipt of the Exercise Price therefor, be fully paid and
nonassessable, and free from all preemptive rights, rights of first refusal or
first offer, taxes, liens and charges with respect to the issuance thereof.
During such time as this Warrant remains outstanding, the Company shall at all
times have authorized and reserved for issuance sufficient shares of its Common
Stock to provide for the exercise of the rights represented by this Warrant.

         3.       Adjustment of Exercise Price and Number of Shares. The number
and kind of Shares purchasable upon the exercise of this Warrant and the
Exercise Price therefor shall be subject to adjustment from time to time upon
the occurrence of certain events, as follows:

                  (a)      Stock Splits, Dividends and Combinations. In the
event that the Company shall at any time subdivide the outstanding shares of
Common Stock, or shall issue a stock dividend on its outstanding shares of
Common Stock, the number of Shares issuable upon exercise of this Warrant
immediately prior to such subdivision or to the issuance of such stock dividend
shall be proportionately increased, and the Exercise Price shall be
proportionately decreased, and in the event that the Company shall at any time
combine the outstanding shares of Common Stock, the number of Shares issuable
upon exercise of this Warrant immediately prior to such combination shall be
proportionately decreased, and the Exercise Price shall be proportionately
increased, effective at the close of business on the date of such subdivision,
stock dividend or combination, as the case may be.

                  (b)      Recapitalizations. If at any time or from time to
time there shall be a recapitalization of the Common Stock (other than a
subdivision, combination or merger or sale of assets transaction provided for
elsewhere in this Section 3), provision shall be made so that the Holder of this
Warrant will thereafter be entitled to receive upon exercise of this Warrant the
number of shares of stock or other securities or property of the Company to
which a holder of Common Stock would have been entitled on such
recapitalization. In any such case, appropriate adjustment shall be made in the
application of the provisions of this Section 3 with respect to the rights of
the Holder of this Warrant after the recapitalization to the end that the
provisions of this Section 3 (including adjustment of the Exercise Price then in
effect and the number of shares issuable upon exercise of this Warrant) shall be
applicable after that event in as nearly an equivalent manner as may be
practicable.

                  (c)      Merger. If at any time there shall occur (a) the
acquisition of the Company by another entity by means of any transaction or
series of related transactions (including, without limitation, any stock
acquisition, reorganization, merger or consolidation but excluding any sale of
stock for capital raising purposes) other than a transaction or series of
transactions in which the holders of the voting securities of the Company
outstanding immediately prior to such transaction continue to retain (either by
such voting securities remaining outstanding or by such voting securities being
converted into voting securities of the surviving entity), more than fifty
percent (50%) of the total voting power represented by the voting securities of
the Company or such surviving entity outstanding immediately after such
transaction or series of transactions; or (b) a sale of all or substantially all
of the assets of the Company (each, a "MERGER EVENT"), then as a part of such

                                      -3-
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Merger Event and as a condition thereto, lawful provision shall be made so that
the Holder shall thereafter be entitled to receive, upon exercise of this
Warrant, the number of shares of stock or other securities of the successor
corporation resulting from such Merger Event, equivalent in value to that which
would have been issuable if the Holder had exercised this Warrant immediately
prior to the Merger Event. In any such case, appropriate adjustment (as
determined 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
interest of the Holder after the Merger Event to the end that the provisions of
this Warrant (including adjustments of the Exercise Price and number of Shares
purchasable) shall be applicable to the greatest extent possible.

                  (d)      Notices. Upon any adjustment of the Exercise Price
and any increase or decrease in the number of Shares purchasable upon the
exercise of this Warrant in accordance with Section 3 hereof, then, and in each
such case, the Company, as soon as practicable, shall give written notice
thereof to the Holder at the address of such Holder as shown on the books of the
Company which notice shall state the Exercise Price as adjusted and, if
applicable, the increased or decreased number of Shares purchasable upon the
exercise of this Warrant, setting forth in reasonable detail the method of
calculation of each. Any written notice by the Company required or permitted
hereunder shall be given by hand delivery or first class mail, postage prepaid,
addressed to the Holder at the address shown on the books of the Company for the
Holder.

         4.       Fractional Shares. No fractional shares of Common Stock will
be issued in connection with any exercise hereunder, but in lieu of such
fractional shares the Company shall make a cash payment therefor upon the basis
of the Exercise Price then in effect.

         5.       Representations and Warranties by the Company.

                  (a)      Due Authority. The execution and delivery by the
Company of this Warrant and the performance of all obligations of the Company
hereunder, including the issuance to the Holder of the right to acquire Shares,
have been duly authorized by all necessary corporate action on the part of the
Company. The issuance of this Warrant does not contravene any law or
governmental rule, regulation or order applicable to the Company, and does not
and will not contravene any provision of, or constitute a default under, any
indenture, mortgage, contract or other instrument to which the Company is a
party or by which it is bound. This Warrant constitutes a legal, valid and
binding agreement of the Company, enforceable in accordance with its respective
terms.

                  (b)      Consents and Approvals. No consent or approval of,
giving of notice to, registration with, or taking of any other action in respect
of any state, federal or other governmental authority or agency is required with
respect to the execution, delivery and performance by the Company of its
obligations under this Warrant, other than (i) the filing of notices pursuant to
Regulation D under the Securities Act of 1933, as amended (the "ACT"), and any
filing required by applicable state securities law, which filings shall be made
by the time required thereby, and (ii) in connection with the Hart-Scott-Rodino
Antitrust Improvements Act of 1976, as amended.

         6.       Representations and Warranties by the Holder. The Holder
represents and warrants to the Company as follows:

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                  (a)      This Warrant and the shares of Common Stock issuable
hereunder (the "SECURITIES") are being acquired for the Holder's own account,
for investment and not with a view to, or for resale in connection with, any
distribution or public offering thereof within the meaning of the Act, and the
Holder has no present intention of selling or engaging in any public
distribution thereof pursuant to a registration or exemption.

                  (b)      The Holder understands that the Securities have not
been registered under the Act by reason of their issuance in a transaction
exempt from the registration and prospectus delivery requirements of the Act
pursuant to Section 4(2) thereof, and that they must be held by the Holder
indefinitely, and that the Holder must therefore bear the economic risk of such
investment indefinitely, unless a subsequent disposition thereof is registered
under the Act or is exempted from such registration.

                  (c)      The Holder has such knowledge and experience in
financial and business matters that it is capable of evaluating the merits and
risks of the purchase of the Securities and of protecting its interests in
connection therewith.

                  (d)      The Holder is able to bear the economic risk of the
purchase of the Shares pursuant to the terms of this Warrant.

         7.       Rights of Stockholders. Nothing contained herein shall confer
upon the Holder any of the rights of a stockholder of the Company or 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, issuance of stock,
reclassification of stock, change of par value, consolidation, merger,
conveyance, or otherwise) or to receive notice of meetings, or to receive
dividends or subscription rights or otherwise until the Warrant shall have been
exercised and the Shares purchasable upon the exercise hereof shall have been
issued.

         8.       Miscellaneous.

                  (a)      This Warrant shall be governed by, and construed in
accordance with, the laws of the State of New Jersey, without regard to
principles of conflict of laws.

                  (b)      The headings in this Warrant are for purposes of
reference only, and shall not limit or otherwise affect any of the terms hereof.

                  (c)      The terms of this Warrant shall be binding upon and
shall inure to the benefit of any successors in interest of the Company or the
Holder.

                  (d)      This Warrant and the other documents delivered
pursuant hereto constitute the full and entire understanding and agreement
between the parties with regard to the subjects hereof and thereof.

                  (e)      The Company shall not, by amendment of its
certificate of incorporation or through any other means, directly or indirectly,
avoid or seek to avoid the observance or

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performance of any of the terms of this Warrant and shall at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
action as may be necessary or appropriate in order to protect the rights of the
holder of this Warrant against impairment.

                  (f)      Upon receipt of evidence reasonably satisfactory to
the Company of the loss, theft, destruction or mutilation of this Warrant and,
in the case of any such loss, theft or destruction, upon delivery of an
indemnity agreement reasonably satisfactory in form and amount to the Company
or, in the case of any such mutilation, upon surrender and cancellation of such
Warrant, the Company, at its expense, will execute and deliver to the holder of
record, in lieu thereof, a new Warrant of like date and tenor.

                  (g)      This Warrant and any provision hereof may be amended,
waived or terminated only by an instrument in writing signed by the Company and
the Holder.

                  (h)      This Warrant may be executed in counterparts, each of
which when so executed shall be deemed an original, but both of which when taken
together shall constitute one and the same instrument.

                  (i)      The Company acknowledges and agrees that the holder
of this Warrant is entitled to certain "incidental" registration rights with
respect to the Shares issuable upon exercise of this Warrant. The terms of such
registration rights are contained in Section 4 of that certain Fourth Amended
and Restated Investor Rights Agreement of even date herewith, by and among the
Company and the other parties thereto.

                            [SIGNATURE PAGE FOLLOWS]

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         IN WITNESS WHEREOF, each of the Company and the Holder has caused this
Warrant to be signed by its duly authorized officer.

         Issued this 11 day of September, 2003.

                                    MEMORY PHARMACEUTICALS CORP.

                                    By: /s/ Tony Scullion
                                        -----------------------------------
                                        Name: Tony Scullion
                                        Title: CEO

                                    HOFFMANN-LA ROCHE INC.

                                    By: /s/ Frederick C. Kentz III
                                        -----------------------------------
                                        Name: Frederick C. Kentz III
                                        Title: Vice President & Secretary

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                                    EXHIBIT A
                               NOTICE OF EXERCISE

TO:      Memory Pharmaceuticals Corp.
         Attention: President

Alternatives: Choose either 1(a) or 1(b).

         1(a). The undersigned hereby elects to purchase _______________ (leave
blank if you choose alternative No. 1(b) below) shares of Common Stock pursuant
to the terms of this Warrant, and tenders herewith payment of the purchase price
of such shares in full.

         1(b). In lieu of exercising the attached Warrant for cash or check, the
undersigned hereby elects to effect the net issuance provision of Section 1(b)
of this Warrant and receive ____________ (leave blank if you choose Alternative
No. 1(a) above) shares of Common Stock pursuant to the terms of this Warrant.
(Initial here if the undersigned elects this alternative).______________.

         2. Please issue a certificate or certificates representing said shares
of Common Stock in the name of the undersigned or in such other name as is
specified below:

                   ___________________________________________
                                     (Name)

                   ___________________________________________

                   ___________________________________________
                                    (Address)

         3. The undersigned hereby represents and warrants that the aforesaid
shares of Common Stock are being acquired for the account of the undersigned for
investment and not with a view to, or for resale, in connection with the
distribution thereof, and that the undersigned has no present intention of
distributing or reselling such shares except pursuant to a registration or
exemption, and all representations and warranties of the undersigned set forth
in Section 6 of the attached Warrant are true and correct as of the date hereof.

                                           By: _________________________________

                                           Name: _______________________________
                                                          (please print)

                                           Title: ______________________________

                                           Date: _______________________________<PAGE>

                                                                     EXHIBIT 4.5

              FOURTH AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT

                  FOURTH AMENDED AND RESTATED INVESTOR RIGHTS AGREEMENT made as
of September 11, 2003 by and among (i) Memory Pharmaceuticals Corp., a Delaware
corporation (the "Company"), (ii) Hoffmann-La Roche Inc. (the "Series Roche
Purchaser"), (iii) the Purchasers listed on Exhibit A (the "Series D
Purchasers") of that certain Preferred Stock Purchase Agreement dated as of
March 4, 2002 (the "Series D Purchase Agreement"), (iv) the Purchasers listed on
Exhibit A (the "Series C Purchasers") of that certain Preferred Stock Purchase
Agreement dated as of June 21, 2000 (the "Series C Purchase Agreement"), (v) the
Purchasers listed on Exhibit A (the "Series B Purchasers") of that certain
Preferred Stock Purchase Agreement dated as of December 22, 1998 (the "Series B
Purchase Agreement") and (vi) the Purchasers listed on Exhibit A of that certain
Preferred Stock Purchase Agreement dated April 24, 1998 (the "Series A
Purchasers" and together with the Series B Purchasers, the Series C Purchasers,
the Series D Purchasers, and the Series Roche Purchaser, the "Purchasers"). The
Purchasers may be referred to herein individually as an "Investor," and
collectively as the "Investors".

                  WHEREAS, the Company and the Series A Purchasers entered into
an Investor Rights Agreement, dated as of April 24, 1998 (the "Original
Agreement");

                  WHEREAS, the Company and the Series A Purchasers and the
Series B Purchasers entered into an Amended Investor Rights Agreement, dated as
of December 22, 1998 (the "First Amended Agreement"), which First Amended
Agreement amended and restated the Original Agreement;

                  WHEREAS, the Company and the Series A Purchasers, the Series B
Purchasers and the Series C Purchasers entered into a Second Amended Investor
Rights Agreement, dated as of June 21, 2000 (the "Second Amended Agreement"),
which Second Amended Agreement amended and restated the First Amended Agreement;

                  WHEREAS, the Company and the Series A Purchasers, the Series B
Purchasers, the Series C Purchasers and the Series D Purchasers entered into a
Third Amended Investor Rights Agreement dated as of March 4, 2002 (the "Third
Amended Agreement"), which Third Amended Agreement amended and restated the
Second Amended Agreement;

                  WHEREAS, the Company proposes to issue and sell (i) an
aggregate of 2,777,778 shares of Series Roche Convertible Preferred Stock, par
value $.001 per share (the "Series Roche Stock"), and (ii) a warrant exercisable
for 347,222 shares of Common Stock ("the "Warrant"), to the Series Roche
Purchaser pursuant to that certain Securities Purchase Agreement dated as of
August 19, 2003 by and between the Company and the Series Roche Purchaser (the
"Series Roche Purchase Agreement");

                  WHEREAS, as a condition to entering into the Series Roche
Purchase Agreement, the Series Roche Purchaser has requested that the Company
extend to it registration rights and certain other rights and covenants as set
forth herein;

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                  WHEREAS, the Company and the Series A Purchasers, the Series B
Purchasers, the Series C Purchasers and the Series D Purchasers desire to amend
and restate the Third Amended Agreement and to add the Series Roche Purchaser as
a party thereto to extend to the Series Roche Purchaser certain registration
rights and certain other rights and covenants as set forth herein;

                  WHEREAS, the Board of Directors of the Company has determined
that it is in the best interests of the Company that the Company enter into this
Agreement; and

                  WHEREAS Walter Gilbert, Ph.D., Eric R. Kandel, M.D, Axel
Unterbeck, Ph.D., Oxford Bioscience Partners II, L.P., Oxford Bioscience
Partners (Bermuda) II Limited Partnership and HealthCare Ventures V L.P. are all
founders and holders of common stock, par value $.001 per share, of the Company.

                  NOW, THEREFORE, in consideration of the covenants and
agreements set forth herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby mutually acknowledged, the parties
hereto covenant and agree as follows:

                               GENERAL PROVISIONS

                  1.1      SHARES SUBJECT TO THIS AGREEMENT. The Investors
expressly agree that the terms and restrictions of this Agreement shall apply to
all shares of capital stock which any of them now owns or hereafter acquires by
any means, including without limitation by purchase, assignment or operation of
law, or as a result of any stock dividend, stock split, reorganization,
reclassification, whether voluntary or involuntary, or other similar
transaction, and to any shares of capital stock of any successor in interest of
the Company, whether by sale, merger, consolidation or other similar
transaction, or by purchase, assignment or operation of law (the "Shares").

                  1.2      NO PARTNERSHIP RELATIONSHIP. Notwithstanding, but not
in limitation of, any other provision of this Agreement, the parties understand
and agree that the creation, management and operation of the Company shall not
create or imply a general partnership between or among the Investors and shall
not make any Investor the agent or partner of any other Investor for any
purpose.

                  1.3      CERTAIN DEFINITIONS. As used in this Agreement, the
following terms shall have the following respective meanings:

                  "Affiliate" has the meaning ascribed to that term in Rule
12b-2 under the Exchange Act, or any successor rule.

                  "Commission" shall mean the U.S. Securities and Exchange
Commission and any successor agency of the Federal government administering the
Securities Act and the Exchange Act.

                  "Common Stock" shall mean (i) the common stock, $.001 par
value per share, of

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the Company, (ii) any other capital stock of the Company, however designated,
authorized on or after the date hereof, which shall neither be limited to a
fixed sum or percentage of par value in respect of the rights of the holders
thereof to participate in dividends nor entitled to a preference in the
distribution of assets upon the voluntary or involuntary liquidation,
dissolution or winding up of the Company; and (iii) any other securities into
which or for which any of the securities described in (i) or (ii) may be
converted or exchanged pursuant to a plan of recapitalization, reorganization,
merger, consolidation, sale of assets or other similar transaction.

                  "Exchange Act" shall mean the U.S. Securities Exchange Act of
1934, as amended, and any similar or successor Federal statute, and the rules
and regulations of the Commission thereunder, all as the same shall be in effect
from time to time.

                  "Federal" shall mean with respect to any executive,
legislative or judicial branch of government or other agency or organ of
government, a branch or other agency or organ of the government of the United
States.

                  "Initial Public Offering" shall mean the first underwritten
public offering of Common Stock of the Company, offered on a firm commitment
basis pursuant to a registration statement filed with the Commission under the
Securities Act on Form S-1 or its then equivalent, in which (i) the initial
public offering price per share is not less than $4.00 if the closing of such
offering occurs within six (6) months of the date on which shares of Series D
Stock were first issued ("Series D First Issuance"), $5.45 if such closing
occurs after six (6) months from and within eighteen (18) months of the Series D
First Issuance, $7.90 if such closing occurs after eighteen (18) months from and
within thirty (30) months of the Series D First Issuance, and $11.40 if such
closing occurs after thirty (30) months from the Series D First Issuance (in
each case such dollar amount being subject to equitable adjustment in the event
of any stock dividend, stock split, combination, reorganization,
recapitalization or similar event involving a change in the Common Stock) and
(ii) the aggregate net proceeds to the Company equals or exceeds $50,000,000.

                  "Person" means an individual, corporation, partnership, joint
venture, trust or unincorporated organization, or a government or any agency or
political subdivision thereof.

                  "Preferred Stock" means the Series A Stock, the Series B
Stock, the Series C Stock, the Series D Stock and the Series Roche Stock.

                  The terms "register", "registered" and "registration" shall
refer to a registration effected by preparing and filing a registration
statement in compliance with the Securities Act and applicable rules and
regulations thereunder, and the declaration or ordering of the effectiveness of
such registration statement, or, as the context may require, under the Exchange
Act or applicable state securities laws.

                  "Registrable Securities" shall mean (i) shares of Preferred
Stock; (ii) shares of Common Stock or other securities issued or issuable
pursuant to the conversion of the Preferred Stock or pursuant to the exercise of
the Warrant; and (iii) any shares of Common Stock or other securities issued or
issuable with respect to the Preferred Stock or the Warrant by reason of any

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stock split, stock dividend, recapitalization, reorganization, merger,
consolidation, sale of assets or similar event, excluding in any event
securities which have been (a) registered under the Securities Act pursuant to
an effective registration statement filed thereunder and disposed of in
accordance with the registration statement covering them or (b) publicly sold
pursuant to Rule 144 under the Securities Act. Wherever reference is made in
this Agreement to a request or consent of holders of a certain percentage of
Registrable Securities, the determination of such percentage shall be calculated
on the basis of shares of Common Stock issued or issuable upon conversion of the
Preferred Stock and upon exercise of the Warrant even if such exercise has not
been effected.

                  "Registration Expenses" shall mean the expenses so described
in Section 4.7.

                  "Second Amended and Restated Certificate of Incorporation"
shall mean the Second Amended and Restated Certificate of Incorporation of the
Company as filed with the Secretary of State of the State of Delaware on
September 8, 2003, as amended from time to time thereafter in accordance with
its terms, the By-laws of the Company, and the laws of the State of Delaware.

                  "Securities Act" shall mean the U.S. Securities Act of 1933,
as amended, and any similar or successor Federal statute, and the rules and
regulations of the Commission thereunder, all as the same shall be in effect
from time to time.

                  "Series A Stock" shall mean the Series A Convertible Preferred
Stock, par value $.001 per share of the Company.

                  "Series B Stock" shall mean the Series B Convertible Preferred
Stock, par value $.001 per share of the Company.

                  "Series C Stock" shall mean the Series C Convertible Preferred
Stock, par value $.001 per share of the Company.

                  "Series D Stock" shall mean the Series D Convertible Preferred
Stock, par value $.001 per share of the Company.

                  "Series Roche Stock" shall mean the Series Roche Convertible
Preferred Stock, par value $.001 per share of the Company as described in the
recitals to this Agreement.

                  "Selling Expenses" shall mean the expenses so described in
Section 4.7.

                   "Subsidiary" or "Subsidiaries" shall mean any corporation,
partnership, trust or other entity of which the Company and/or any of its other
Subsidiaries directly or indirectly owns at the time a majority of the
outstanding shares of any class of equity security of such corporation,
partnership, trust or other entity.

                  2.       PERCENTAGE MAINTENANCE RIGHTS

                                       4

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                  2.1      NOTICE OF NEW ISSUANCE. Except with respect to
"Exempt Issuances" as defined in Section 2.3, in the event that the Company
issues any (i) shares of Common Stock, (ii) warrants, options or other rights to
purchase Common Stock (collectively, "Rights"), or (iii) any debentures or other
securities convertible into or exchangeable for shares of Common Stock
(collectively, "Convertible Securities"), the Company will deliver to the
Purchasers a notice (the "Offer Notice") upon the completion of such issuance
(the "New Issuance"), stating the price and other terms and conditions thereof.

                  2.2      RIGHT TO PURCHASE SHARES, RIGHTS OR CONVERTIBLE
SECURITIES.

                  (a)      In the event of a New Issuance (other than an Exempt
Issuance), the holders of Series A Stock, the holders of Series B Stock, the
holders of Series C Stock, the holders of Series D Stock and the holders of
Series Roche Stock (the "Series A, B, C, D and R Holders") shall have the right
to purchase such number of shares of Common Stock, Rights or Convertible
Securities at the price and on the terms upon which the New Issuance was made,
such price to be paid in full in cash or by check at the time of issuance of
such securities to the Series A, B, C, D and R Holders so that, after giving
effect to the issuance to the Series A, B, C, D and R Holders and the
conversion, exercise and exchange into or for (whether directly or indirectly)
shares of Common Stock of all such Rights and Convertible Securities, each
holder of Series A Stock, each holder of Series B Stock, each holder of Series C
Stock, each holder of Series D Stock and each holder of Series Roche Stock who
exercises such right will continue to maintain its same proportionate ownership
of Common Stock as of the date immediately preceding the New Issuance, treating
each Series A, B, C, D and R Holder, for the purpose of such computation, as the
holder of the number of shares of Common Stock which would be issuable to it
upon conversion, exercise and exchange of all Rights and Convertible Securities
held by it on the date immediately preceding the New Issuance and assuming the
like conversion, exercise and exchange of all such securities held by other
persons. The rights set forth in this Article 2 shall be exercised by the Series
A, B, C, D and R Holders, if at all, by written notice to the Company delivered
not later than thirty (30) days after the receipt by the Series A, B, C, D and R
Holders of the Offer Notice in accordance with the terms and conditions stated
therein, and such right shall expire at the end of the thirtieth day after the
day of the receipt by the Series A, B, C, D and R Holders of the Offer Notice.

                  (b)      If any Series A, B, C, D or R Holder fails to
exercise its right hereunder to purchase its proportionate ownership interest
("Equity Percentage") of a New Issuance (or fails to pay the purchase price in
respect of such New Issuance in full in cash at the proposed time of closing),
the Company shall so notify the other Series A, B, C, D and R Holders in a
written notice (the "Excess Securities Notice"). The Excess Securities Notice
shall be given by the Company promptly after it learns of the intention of any
Series A, B, C, D or R Holder not to purchase all of its Equity Percentage of
the New Issuance or the failure of any Series A, B, C, D or R Holder to pay such
purchase price, but in no event later than ten (10) days after the expiration of
the 30-day period. The Series A, B, C, D and R Holders who or which have agreed
to purchase their Equity Percentage of the New Issuance shall have the right to
purchase the portion not purchased by such holder of Series A Stock, Series B
Stock, Series C Stock, Series D Stock or Series Roche Stock (the "Excess
Securities"), on a pro rata basis, by giving notice within ten (10) days after
receipt of the Excess Securities Notice from the Company. The twenty

                                       5

<PAGE>

(20) day period during which (i) the Company must give the Excess Securities
Notice to the other Series A, B, C, D and R Holders, and (ii) each of the other
Series A, B, C, D and R Holders must give the Company notice of its intention to
purchase all or any portion of its pro rata share of the its Excess Securities,
is hereinafter referred to as the "Excess Securities Period."

                  2.3      EXEMPT ISSUANCES. The term "Exempt Issuances"
referred to in Section 2.1 which will not give the Series A, B, C, D and R
Holders the rights described in Section 2.2 are issuances of Excluded Shares as
such term is defined in Section B(2)(d)(i)(D) of Article Fifth of the Second
Amended and Restated Certificate of Incorporation, as such definition may be
amended from time to time.

                  2.4      TERMINATION. The respective rights and obligations of
the parties under this Article 2 shall terminate upon the closing of the
Company's Initial Public Offering.

                  3.       KANDEL STOCK PLAN ISSUANCES

         3.1      ANTI-DILUTION PROTECTION FOR DR. ERIC KANDEL. The Investors
acknowledge and agree that if, during the term of the consulting agreement (the
"Kandel Agreement") between the Company and Dr. Eric R. Kandel ("Kandel") and
until immediately prior to the closing of the Company's Initial Public Offering
(the "IPO"), the Company issues additional shares of Common Stock, or shares of
capital stock or debt convertible into or exchangeable for shares of Common
Stock (excluding shares issued in the IPO), the Company will become obligated to
grant to Kandel an option to purchase, at an exercise price per share equal to
the price per share of the issued securities giving rise to the option grant, an
aggregate number of additional shares of Common Stock such that, after giving
effect to such issuance by the Company and such grant to Kandel, Kandel and
members of Kandel's immediate family shall continue to beneficially own, in the
aggregate, the same percentage of the Company's issued and outstanding Common
Stock that they owned immediately prior to such issuance. The Investors further
acknowledge and agree that the Company shall in no event grant to Kandel options
to purchase additional shares of Common Stock if, after giving effect to such
grant, Kandel and members of Kandel's immediate family would beneficially own,
in the aggregate, more than five percent (5%) of the Company's issued and
outstanding Common Stock. Notwithstanding the foregoing, if the Company
hereafter issues shares of its Common Stock or preferred stock (or securities
convertible into Common Stock or preferred stock) (other than "Excluded Shares",
as defined in the Amended and Restated Certificate of Incorporation of the
Company) ("New Securities") for a purchase price (or exercise or conversion
price, as applicable) per share less than the Effective Price (as defined
below), then the options to purchase additional shares of Common Stock that
Kandel would otherwise receive pursuant to the foregoing shall be reduced by
multiplying the five percent (5%) amount referred to above by an Adjustment
Factor calculated as follows:

         (A)      The "Adjustment Factor" shall be determined by:

                           (i)      dividing an amount equal to the sum of:

                                    (a)      the number of shares of Common
Stock outstanding on a fully-diluted basis immediately prior to such issuance,
and

                                       6

<PAGE>

                                    (b)      the consideration, if any, received
by the Company from such issuance divided by the Effective Price, by

                           (ii)     by the total number of shares of Common
Stock outstanding on a fully-diluted basis immediately after such issuance.

The Investors further acknowledge and agree that, subject to the preceding
sentence and compliance with applicable law, contemporaneously with and subject
to the closing of the Company's IPO, the Company will be obligated to grant to
Kandel an option to purchase an aggregate number of additional shares of Common
Stock equal to the product of (A) the number of options to purchase Common Stock
outstanding immediately prior to the closing of the Company's IPO (excluding
options to purchase Common Stock issued to Kandel or to members of Kandel's
immediate family), multiplied by (B) the percentage of the Company's issued and
outstanding Common Stock owned by Kandel and members of Kandel's immediate
family immediately prior to the closing of the Company's IPO. For purposes of
the Kandel Agreement, (i) in determining Kandel's percentage holdings of any
class of the Company's equity securities, there shall be included in the
numerator all shares of stock of such class that Kandel holds, directly or
indirectly, and all shares of stock of such class issuable to Kandel, directly
or indirectly, upon the exercise of stock options, rights or other equity or
equity-based securities (other than shares issuable only upon the occurrence of
an event of dilution), but shall include in the denominator only shares of such
class actually issued and outstanding, plus all shares of such class issuable to
Kandel, directly or indirectly, upon the exercise of stock options, rights or
other equity or equity-based securities (other than shares issuable only upon
the occurrence of an event of dilution) and (ii) in determining the amount of
securities Kandel holds, directly or indirectly, or that are issuable to Kandel,
directly or indirectly, there will be included, without limitation, (A) any
securities issued or issuable by the Company to members of Kandel's immediate
family and (B) any securities issued or issuable by the Company to Kandel, or
securities allocated or allocable to Kandel under Columbia University's
inventorship policies, as royalties under a license by the Company of technology
of which Kandel is an inventor (the "University Shares"), unless Kandel has
instructed the University not to deliver or transfer University Shares to Kandel
personally but instead to hold such shares until the University decides to
liquidate them and then to contribute the cash proceeds to Kandel's laboratory.

         3.2      DETERMINATION OF CONSIDERATION RECEIVED. In the case of the
issuance of New Securities in whole or in part for cash, the consideration
received by the Company shall be deemed to be the amount of cash paid therefor,
plus the value of any property other than cash received by the Company as
provided in the next sentence. In the case of the issuance of New Securities for
consideration in whole or in part in property or consideration other than cash,
the value of such property or consideration other than cash shall be deemed to
be the fair market value thereof as determined in good faith by the Board of
Directors of the Company.

         3.3      EFFECTIVE PRICE. As used herein, the "Effective Price" shall
initially be $2.50. The Effective Price shall be equitably adjusted from time to
time to account for any stock split, stock dividend, combination,
reorganization, recapitalization or similar event involving a change in the
Common Stock.

                                       7

<PAGE>

                  4.       TRANSFER OF REGISTRABLE SECURITIES;
                           REGISTRATION

                  4.1      RESTRICTIVE LEGEND. Each certificate representing
Registrable Securities shall, except as otherwise provided in this Section 4.1
or in Section 4.2, be stamped or otherwise imprinted with a legend substantially
in the following form (in addition to any legend required under applicable state
securities laws):

                  "The securities represented by this certificate have not been
                  registered under the Securities Act of 1933 or any other
                  securities laws. These securities have been acquired for
                  investment and not with a view to distribution or resale. Such
                  securities may not be offered for sale, sold, delivered after
                  sale, transferred, pledged or hypothecated in the absence of
                  an effective registration statement covering such securities
                  under the Securities Act of 1933 and any other applicable
                  securities laws, unless the holder shall have obtained an
                  opinion of counsel reasonably satisfactory to the corporation
                  that such registration is not required."

                  Upon request of a holder of such a certificate, the Company
shall remove the foregoing legend from the certificate or issue to such holder a
new certificate therefor free of any transfer legend, if there is an effective
registration statement covering the securities represented by such certificate
or, with such request, the Company shall have received either the opinion
referred to in Section 4.2(a)(i) or the "no-action" letter referred to in
Section 4.2(a)(ii).

                  4.2      NOTICE OF PROPOSED TRANSFER.

                  (a)      Prior to any proposed sale, pledge, hypothecation or
other transfer of any Registrable Securities (other than under the circumstances
described in Section 4.3, 4.4 or 4.5), the holder thereof shall give written
notice to the Company of its intention to effect such sale, pledge,
hypothecation or other transfer. Each such notice shall describe the manner of
the proposed sale, pledge, hypothecation or other transfer and, if requested by
the Company shall be accompanied by either (i) an opinion of counsel reasonably
satisfactory to the Company to the effect that the proposed sale, pledge,
hypothecation or other transfer may be effected without registration under the
Securities Act or (ii) a "no action" letter from the Commission to the effect
that the distribution of such securities without registration will not result in
a recommendation by the staff of the Commission that action be taken with
respect thereto, whereupon the holder of such stock shall be entitled to
transfer such stock in accordance with the terms of its notice; provided,
however, that no such opinion of counsel or "no action" letter shall be required
for a distribution to one or more partners or members of the transferor (in the
case of a transferor that is a partnership or limited liability company), to a
stockholder (in the case of a transferor that is a corporation) or to a trust
grantor (in the case of a transferor that is a trust) in each case in respect of
the beneficial interest of such partner, stockholder or trust. Each certificate
for Registrable Securities transferred as above provided shall bear the
appropriate restrictive legend set forth in Section 4.1, except that such
certificate shall not bear such legend if (i) such transfer is in accordance
with the provisions of Rule 144 (or any other rule permitting public sale
without registration under the Securities Act) or (ii) the opinion of counsel or
"no-action" letter referred

                                       8

<PAGE>

to above is to the further effect that the transferee and any subsequent
transferee (other than an Affiliate of the Company) would be entitled to
transfer such securities in a public sale without registration under the
Securities Act or that such legend is not required to establish compliance with
any provisions of the Securities Act. Notwithstanding any other provision
hereof, the restrictions provided for in this Section 4.2 shall not apply to
securities which are not required to bear the legend prescribed by Section 4.1
in accordance with the provisions of that Section. If the Company does not
accept an opinion of counsel required hereby signed by the original holder's
counsel (it being agreed that an opinion of Dewey Ballantine LLP, Gibbons, Del
Deo, Dolan, Griffinger & Vecchione, P.C., Wollmuth Maher & Deutsch LLP or Sidley
Austin Brown & Wood LLP shall be considered satisfactory), the Company will pay
the reasonable fees and disbursements of other counsel in connection with all
opinions rendered by them pursuant to this Section 4.2.

                  (b)      No such opinion of counsel or "no action" letter from
the Commission, as set forth in Section 4.2(a) above, shall be required in the
event of a sale, pledge, hypothecation or other transfer of any Registrable
Securities to (i) any Affiliate of an Investor, including, without limitation,
any venture capital limited partnership now existing or hereafter formed which
controls, is controlled by or is under common control with such Investor; and
(ii) any successors or assigns of any of the foregoing persons, provided that
the transferee agrees in writing to be subject to this Agreement to the same
extent as if such transferee were originally a signatory.

                  4.3      REQUIRED REGISTRATION.

                  (a)      At any time after the Initial Public Offering, one or
more of the holders of Registrable Securities constituting at least 25% of the
total shares of Registrable Securities then outstanding may request the Company
to register for sale under the Securities Act all or any portion of the shares
of Registrable Securities held by such requesting holder or holders for sale in
the manner specified in such notice; provided, however, that the proposed
offering price of the Registrable Securities held by such holder or holders must
be at least $5,000,000.

                  (b)      Following receipt of any notice under this Section
4.3, the Company shall immediately notify all holders of Registrable Securities
from whom notice has not been received and such holders shall then be entitled
within thirty (30) days after receipt of such notice from the Company to request
the Company to include in the requested registration all or any portion of their
shares of Registrable Securities. The Company shall use its best efforts to
register under the Securities Act, for public sale in accordance with the method
of disposition specified in the notice from requesting holders described in
paragraph (a) above, within 180 days of its receipt of such notice, the number
of shares of Registrable Securities specified in such notice (and in all notices
received by the Company from other holders within thirty (30) days after the
receipt of such notice by such holders). The Company shall be obligated to
register the Registrable Securities pursuant to this Section 4.3 on three (3)
occasions only, provided, however, that such obligation shall be deemed
satisfied only when a registration statement covering all shares of Registrable
Securities specified in notices received as aforesaid (except to the extent
reduced (but not by more than 10%) by the managing underwriter, if any, pursuant
to Section 4.3(d)), for sale in accordance with the method of disposition
specified by the requesting holders, shall have become effective and, if such
method of disposition is a firm commitment underwritten public

                                       9

<PAGE>

offering, all such shares shall have been sold pursuant thereto. Notwithstanding
anything to the contrary contained herein, no request may be made under this
Section 4.3 after the effective date of a registration statement filed by the
Company covering a firm commitment underwritten public offering and prior to the
later to occur of the completion of the period of distribution for such offering
or 90 days after the effective date of such registration statement.

                  (c)      If the holders requesting such registration intend to
distribute the Registrable Securities covered by their request by means of an
underwriting, they shall so advise the Company as a part of their request made
pursuant to this Section 4.3 and the Company shall include such information in
the written notice referred to in paragraph (b) above. The right of any holder
to registration pursuant to this Section 4.3 shall be conditioned upon such
holder's agreeing to participate in such underwriting and to permit inclusion of
such holder's Registrable Securities in the underwriting. If such method of
disposition is an underwritten public offering, the holders of at least a
majority in interest of the shares of Registrable Securities to be sold in such
offering may designate the managing underwriter of such offering, which managing
underwriter shall be reasonably acceptable to the Company. A holder may elect to
include in such underwriting all or a part of the Registrable Securities it
holds.

                  (d)      A registration statement filed pursuant to this
Section 4.3 may, subject to the following provisions, include (i) shares of
Common Stock for sale by the Company for its own account, (ii) shares of Common
Stock held by officers or directors of the Company, and (iii) shares of Common
Stock held by persons who by virtue of agreements with the Company in compliance
with the provisions of Section 4.12 hereof are entitled to include such shares
in such registration (the "Other Shareholders"), in each case for sale in
accordance with the method of disposition specified by the requesting holders;
provided, however, that if the number of shares so included pursuant to clauses
(i), (ii) and (iii) above exceeds the number of Registrable Securities presented
by the holders requesting registration thereof, then such registration shall be
deemed to be a registration in accordance with Section 4.4. If such registration
shall be underwritten, the Company, such officers and directors and Other
Shareholders proposing to distribute their shares through such underwriting
shall enter into an underwriting agreement in customary form with the
representative of the underwriter or underwriters selected for such underwriting
on terms no less favorable to such officers, directors or Other Shareholders
than the terms afforded the holders of Registrable Securities. If and to the
extent that the managing underwriter determines that marketing factors require a
limitation on the number of shares to be included in such registration, then the
shares of Common Stock held by officers or directors (other than Registrable
Securities) of the Company or by Other Shareholders (other than Registrable
Securities) and shares of Common Stock to be sold by the Company for its own
account shall be excluded from such registration to the extent so required by
such managing underwriter, and unless the holders of such shares and the Company
have otherwise agreed in writing, such exclusion shall be applied first to the
shares held by the directors and officers and the Other Shareholders to the
extent required by the managing underwriter, then to the shares of Common Stock
of the Company to be included for its own account to the extent required by the
managing underwriter. If the managing underwriter determines that marketing
factors require a limitation of the number of Registrable Securities to be
registered under this Section 4.3, then Registrable Securities shall be excluded
in such manner that the securities to be sold shall be

                                       10

<PAGE>

allocated among the selling holders pro rata based on their ownership of
Registrable Securities. In any event all securities to be sold other than
Registrable Securities will be excluded prior to any exclusion of Registrable
Securities. No Registrable Securities or any other security excluded from the
underwriting by reason of the underwriter's marketing limitation shall be
included in such registration. If any holder of Registrable Securities, officer,
director and Other Shareholder who has requested inclusion in such registration
as provided above, disapproves of the terms of the underwriting, such holder of
securities may elect to withdraw therefrom by written notice to the Company and
the managing underwriter. The securities so withdrawn shall also be withdrawn
from registration. Except for registration statements on Form S-4, S-8 or any
comparable form or successor thereto, the Company will not file with the
Commission any other registration statement with respect to its Common Stock,
whether for its own account or that of other stockholders, from the date of
receipt of a notice from requesting holders pursuant to this Section 4.3 until
the completion of the period of distribution of the registration contemplated
thereby or 120 days after the effective date of such registration, whichever is
later.

                  4.4      INCIDENTAL REGISTRATION. If the Company at any time
(other than pursuant to Section 4.3 or Section 4.5) proposes to register any of
its securities under the Securities Act for sale to the public, whether for its
own account or for the account of other security holders or both (except with
respect to registration statements on Forms S-4, S-8 or any successor to such
forms or another form not available for registering the Registrable Securities
for sale to the public), each such time it will promptly give written notice to
all holders of the Registrable Securities of its intention so to do. Upon the
written request of any such holder, received by the Company within thirty (30)
days after the giving of any such notice by the Company, to register any or all
of its Registrable Securities, the Company will use its best efforts to cause
the Registrable Securities as to which registration shall have been so requested
to be included in the securities to be covered by the registration statement
proposed to be filed by the Company, all to the extent requisite to permit the
sale or other disposition by the holder (in accordance with its written request)
of such Registrable Securities so registered. If the registration of which the
Company gives notice is for a registered public offering involving an
underwriting, the Company shall so advise the holders of Registrable Securities
as a part of the written notice given pursuant to this Section 4.4. In such
event the right of any holder of Registrable Securities to registration pursuant
to this Section 4.4 shall be conditioned upon such holder's participation in
such underwriting to the extent provided herein. All holders of Registrable
Securities proposing to distribute their securities through such underwriting
shall (together with the Company and the Other Shareholders distributing their
securities through such underwriting) enter into an underwriting agreement in
customary form with the underwriter or underwriters selected for underwriting by
the Company. Notwithstanding any other provision of this Section 4.4, if the
underwriter determines that marketing factors require a limitation on the number
of shares to be underwritten, the Company shall so advise all holders of
securities requesting registration of any limitations on the number of shares to
be underwritten, and the number of shares of securities that are entitled to be
included in the registration and underwriting shall be allocated (i) first to
the Company with respect to shares of Common Stock being sold for its own
account; and (ii) then, to holders of Registrable Securities requesting
registration in proportion, as nearly as practicable, to the respective amounts
of securities owned by them. Notwithstanding the foregoing provisions, the
Company may withdraw any registration statement referred to in this

                                       11
<PAGE>

Section 4.4 without thereby incurring any liability to the holders of
Registrable Securities. If any holder of Registrable Securities disapproves of
the terms of any such underwriting, it may elect to withdraw therefrom by
written notice to the Company and the underwriter. Any Registrable Securities or
other securities excluded or withdrawn from such underwriting shall be withdrawn
from such registration.

                  4.5      REGISTRATION ON FORM S-3.

                  (a)      In addition to the rights provided in Sections 4.3
and 4.4, subject to a limit of one (1) registration hereunder in any six (6)
month period, if at any time (i) any holder or holders of the Registrable
Securities request that the Company file a registration statement on Form S-3 or
any comparable or successor form thereto for a public offering of all or any
portion of the shares of Registrable Securities held by such requesting holder
or holders, the reasonably anticipated aggregate price to the public of which
would exceed $500,000, and (ii) the Company is a registrant entitled to use Form
S-3 or any comparable or successor form thereto to register such shares, then
the Company shall use its best efforts to register under the Securities Act on
Form S-3 or any comparable or successor form thereto, for public sale in
accordance with the method of disposition specified in such notice, the number
of shares of Registrable Securities specified in such notice. Whenever the
Company is required by this Section 4.5 to use its best efforts to effect the
registration of Registrable Securities, each of the procedures and requirements
of Section 4.3, including but not limited to the requirement that the Company
notify all holders of Registrable Securities from whom notice has not been
received and provide them with the opportunity to participate in the offering,
shall apply to such registration, provided, however, that except as provided
above, there shall be no limitation on the number of registrations on Form S-3
which may be requested and obtained under this Section 4.5.

                  (b)      The Company shall use its best efforts to qualify for
registration on Form S-3 or any comparable or successor form or forms; and to
that end the Company shall register (whether or not required by law to do so)
the Common Stock under the Exchange Act in accordance with the provisions of
that Act following the effective date of the first registration of any
securities of the Company on Form S-1 or any comparable or successor form.

                  4.6      REGISTRATION PROCEDURES. If and whenever the Company
is required by the provisions of Section 4.3, 4.4 or 4.5 to use its best efforts
to effect the registration of any Registrable Securities under the Securities
Act, the Company will, as expeditiously as possible:

                  (a)      prepare and file with the Commission a registration
statement (which, in the case of an underwritten public offering pursuant to
Section 4.3, shall be on Form S-1 or other form of general applicability
satisfactory to the managing underwriter selected as therein provided) with
respect to such securities including executing an undertaking to file
post-effective amendments and use its best efforts to cause such registration
statement to become and remain effective for the period of the distribution
contemplated thereby;

                  (b)      prepare and file with the Commission such amendments
and supplements to such registration statement and the prospectus used in
connection therewith as may be necessary to keep such registration statement
effective for the period specified herein and

                                       12
<PAGE>

comply with the provisions of the Securities Act with respect to the disposition
of all Registrable Securities covered by such registration statement in
accordance with the sellers' intended method of disposition set forth in such
registration statement for such period;

                  (c)      furnish to each seller of Registrable Securities and
to each underwriter such number of copies of the registration statement and each
such amendment and supplement thereto (in each case including all exhibits) and
the prospectus included therein (including each preliminary prospectus) as such
persons reasonably may request in order to facilitate the public sale or other
disposition of the Registrable Securities covered by such registration
statement;

                  (d)      use its best efforts to register or qualify the
Registrable Securities covered by such registration statement under the
securities or "blue sky" laws of such jurisdictions as the sellers of
Registrable Securities or, in the case of an underwritten public offering, the
managing underwriter reasonably shall request, provided, however, that the
Company shall not for any such purpose be required to qualify generally to
transact business as a foreign corporation in any jurisdiction where it is not
so qualified or to consent to general service of process in any such
jurisdiction, unless the Company is already subject to service in such
jurisdiction;

                  (e) use its best efforts to list the Registrable Securities
covered by such registration statement with any securities exchange on which the
Common Stock of the Company is then listed;

                  (f)      comply with all applicable rules and regulations
under the Securities Act and Exchange Act;

                  (g)      immediately notify each seller of Registrable
Securities and each underwriter under such registration statement, at any time
when a prospectus relating thereto is required to be delivered under the
Securities Act, of the happening of any event of which the Company has knowledge
as a result of which the prospectus contained in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in light of the circumstances then existing,
and promptly prepare and furnish to such seller a reasonable number of copies of
a prospectus supplemented or amended so that, as thereafter delivered to the
purchasers of such Registrable Securities, such prospectus shall not include an
untrue statement of a material fact or omit to state a material fact required to
be stated therein or necessary to make the statements therein not misleading in
light of the circumstances then existing;

                  (h)      if the offering is underwritten and at the request of
any seller of Registrable Securities, use its best efforts to furnish on the
date that Registrable Securities are delivered to the underwriters for sale
pursuant to such registration: (i) an opinion dated such date of counsel
representing the Company for the purposes of such registration, addressed to the
underwriters to such effects as reasonably may be requested by counsel for the
underwriters, and (ii) a letter dated such date from the independent public
accountants retained by the Company, addressed to the underwriters stating that
they are independent public accountants within the meaning of the Securities Act
and that, in the opinion of such accountants, the financial

                                       13
<PAGE>

statements of the Company included in the registration statement or the
prospectus, or any amendment or supplement thereof, comply as to form in all
material respects with the applicable accounting requirements of the Securities
Act, and such letter shall additionally cover such other financial matters
(including information as to the period ending no more than five (5) business
days prior to the date of such letter) with respect to such registration as such
underwriters reasonably may request;

                  (i)      make available for inspection by each seller of
Registrable Securities, any underwriter participating in any distribution
pursuant to such registration statement, and any attorney, accountant or other
agent retained by such seller or underwriter, reasonable access to all financial
and other records, pertinent corporate documents and properties of the Company,
as such parties may reasonably request, and cause the Company's officers,
directors and employees to supply all information reasonably requested by any
such seller, underwriter, attorney, accountant or agent in connection with such
registration statement;

                  (j)      cooperate with the selling holders of Registrable
Securities and the managing underwriter, if any, to facilitate the timely
preparation and delivery of certificates representing Registrable Securities to
be sold, such certificates to be in such denominations and registered in such
names as such holders or the managing underwriter may request at least two
business days prior to any sale of Registrable Securities;

                  (k)      permit any holder of Registrable Securities which
holder, in the sole and exclusive judgment, exercised in good faith, of such
holder, might be deemed to be a controlling person of the Company, to
participate in good faith in the preparation of such registration or comparable
statement and to require the insertion therein of material, furnished to the
Company in writing, which in the reasonable judgment of such holder and its
counsel should be included; and

                  (l)      in the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in usual
and customary form, with the managing underwriter of such offering.

                  For purposes of this Agreement, the period of distribution of
Registrable Securities in a firm commitment underwritten public offering shall
be deemed to extend until each underwriter has completed the distribution of all
securities purchased by it, and the period of distribution of Registrable
Securities in any other registration shall be deemed to extend until the earlier
of the sale of all Registrable Securities covered thereby or 180 days after the
effective date thereof, provided, however, in the case of any registration of
Registrable Securities on Form S-3 or a comparable or successor form which are
intended to be offered on a continuous or delayed basis, such 180 day-period
shall be extended, if necessary, to keep the registration statement effective
until all such Registrable Securities are sold, provided that Rule 415, or any
successor rule under the Securities Act, permits an offering on a continuous or
delayed basis, and provided further that applicable rules under the Securities
Act governing the obligation to file a posteffective amendment, permit, in lieu
of filing a post-effective amendment which (y) includes any prospectus required
by Section 10(a)(3) of the Securities Act or (z) reflects facts or events
representing a material or fundamental change in the information set forth in
the registration

                                       14
<PAGE>

statement, the incorporation by reference of information required to be included
in (y) and (z) above contained in periodic reports filed pursuant to Section 13
or 15(d) of the Exchange Act in the registration statement.

                  In connection with each registration hereunder, the sellers of
Registrable Securities will furnish to the Company in writing such information
requested by the Company with respect to themselves and the proposed
distribution by them as shall be reasonably necessary in order to assure
compliance with Federal and applicable state securities laws.

                  4.7      EXPENSES.

                  (a)      All expenses incurred by the Company in complying
with Sections 4.3, 4.4 and 4.5, including, without limitation, all registration
and filing fees, printing expenses, fees and disbursements of counsel and
independent public accountants for the Company, fees and expenses (including
counsel fees) incurred in connection with complying with state securities or
"blue sky" laws, fees of the National Association of Securities Dealers, Inc.,
transfer taxes, fees of transfer agents and registrars, costs of any insurance
which might be obtained by the Company with respect to the offering by the
Company, and fees and disbursements of one counsel selected by the holders of at
least two-thirds (2/3) of the Registrable Securities being sold, but excluding
any Selling Expenses, are called "Registration Expenses". All underwriting
discounts and selling commissions applicable to the sale of Registrable
Securities are called "Selling Expenses".

                  (b)      The Company will pay all Registration Expenses in
connection with each registration statement under Section 4.3, 4.4 or 4.5;
provided, that, in the event of a registration pursuant to Section 4.3 hereof
which is withdrawn at the request of the Investors other than (i) as a result of
the Company's failure to perform its obligations hereunder, (ii) as a result of
a cutback by the underwriter of such registration in the amount of Registrable
Securities which may be included in such registration by more than 10% or (iii)
as a result of information concerning a materially adverse change in the
Company's business or financial condition that is made known to the Investors
after the date on which such registration was requested, the Investors shall pay
the Registration Expenses with respect to such registration. In the event that a
registration pursuant to Section 4.3 hereof is withdrawn pursuant to clauses
(i), (ii) or (iii) of this Section 4.7(b), the Investors shall, immediately
following such withdrawal, be entitled to that number of registration requests
pursuant to Section 4.3 hereof to which they would have been entitled not taking
into account the withdrawn request. All Selling Expenses in connection with each
registration statement under Section 4.3, 4.4 or 4.5 shall be borne by the
participating sellers in proportion to the number of shares registered by each,
or by such participating sellers other than the Company (except to the extent
the Company shall be a seller) as they may agree.

                  4.8      INDEMNIFICATION AND CONTRIBUTION.

                  (a)      In the event of a registration of any of the
Registrable Securities under the Securities Act pursuant to Section 4.3, 4.4 or
4.5, the Company will indemnify and hold harmless each holder of Registrable
Securities, its officers, directors and partners, each underwriter of such
Registrable Securities thereunder and each other person, if any, who controls
such holder or underwriter within the meaning of the Securities Act (each, an
"Indemnitee"), against any losses,

                                       15
<PAGE>

claims, damages or liabilities, joint or several, to which such Indemnitee may
become subject under the Securities Act or otherwise, insofar as such losses,
claims, damages or liabilities (or actions in respect thereof) arise out of or
are based upon (i) any untrue statement or alleged untrue statement of any
material fact contained in any prospectus, offering circular or other document
incident to such registration (including any related notification, registration
statement under which such Registrable Securities were registered under the
Securities Act pursuant to Section 4.3, 4.4 or 4.5, any preliminary prospectus
or final prospectus contained therein, or any amendment or supplement thereof),
(ii) any blue sky application or other document executed by the Company
specifically for that purpose or based upon written information furnished by the
Company filed in any state or other jurisdiction in order to qualify any or all
of the Registrable Securities under the securities laws thereof (any such
application, document or information herein called a "Blue Sky Application"),
(iii) any omission or alleged omission to state in any such registration
statement, prospectus, amendment or supplement or in any Blue Sky Applications
executed or filed by the Company, a material fact required to be stated therein
or necessary to make the statements therein not misleading, (iv) any violation
by the Company or its agents of the Securities Act or any rule or regulation
promulgated under the Securities Act applicable to the Company or its agents and
relating to action or inaction required of the Company in connection with such
registration, or (v) any failure to register or qualify the Registrable
Securities in any state where the Company or its agents has affirmatively
undertaken or agreed in writing that the Company (the undertaking of any
underwriter chosen by the Company being attributed to the Company) will
undertake such registration or qualification (provided that in such instance the
Company shall not be so liable if it has used its best efforts to so register or
qualify the Registrable Securities) and will reimburse each Indemnitee for any
legal or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability or action,
promptly after being so incurred, provided, however, that the Company will not
be liable to an Indemnitee if and to the extent that any such loss, claim,
damage or liability arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission so made in conformity
with written information furnished by such Indemnitee, in writing specifically
stated to be for use in such registration statement or prospectus.

                  (b)      In the event of a registration of any of the
Registrable Securities under the Securities Act pursuant to Section 4.3, 4.4 or
4.5, each seller of such Registrable Securities thereunder, severally and not
jointly, will indemnify and hold harmless the Company, each person, if any, who
controls the Company within the meaning of the Securities Act, each officer of
the Company who signs the registration statement, each director of the Company,
each other seller of Registrable Securities, each underwriter and each person
who controls any underwriter within the meaning of the Securities Act, against
all losses, claims, damages or liabilities, joint or several, to which the
Company or such officer, director, other seller, underwriter or controlling
person may become subject under the Securities Act or otherwise, insofar as such
losses, claims, damages or liabilities (or actions in respect thereof) arise out
of or are based upon any untrue statement or alleged untrue statement of any
material fact contained in any prospectus offering circular or other document
incident to such registration (including any related notification, registration
statement under which such Registrable Securities were registered under the
Securities Act pursuant to Section 4.3, 4.4 or 4.5, any preliminary prospectus
or final prospectus

                                       16
<PAGE>

contained therein, or any amendment or supplement thereof), or any Blue Sky
Application or arise out of or are based upon the omission or alleged omission
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading, and will reimburse the Company and
each such officer, director, other seller, underwriter and controlling person
for any legal or other expenses reasonably incurred by them in connection with
investigating or defending any such loss, claim, damage, liability or action,
promptly after being so incurred, provided, however, that such seller will be
liable hereunder in any such case if and only to the extent that any such loss,
claim, damage or liability arises out of or is based upon an untrue statement or
alleged untrue statement or omission or alleged omission made in reliance upon
and in conformity with information pertaining to such seller, as such, furnished
in writing to the Company by such seller specifically for use in such
registration statement or prospectus; and provided further, however, that the
liability of each seller hereunder shall be limited to the proportion of any
such loss, claim, damage, liability or expense which is equal to the proportion
that the public offering price of the securities sold by such seller under such
registration statement bears to the total public offering price of all
securities sold thereunder, but not in any event to exceed the proceeds received
by such seller from the sale of Registrable Securities covered by such
registration statement. Not in limitation of the foregoing, it is understood and
agreed that the indemnification obligations of any seller hereunder pursuant to
any underwriting agreement entered into in connection herewith shall be limited
to the obligations contained in this subparagraph (b).

                  (c)      Promptly after receipt by an indemnified party
hereunder of notice of the commencement of any action, such indemnified party
shall, if a claim in respect thereof is to be made against the indemnifying
party hereunder, notify the indemnifying party in writing thereof, but the
omission so to notify the indemnifying party shall not relieve it from any
liability which it may have to such indemnified party other than under this
Section 4.8 and shall only relieve it from any liability which it may have to
such indemnified party under this Section 4.8 if and to the extent the
indemnifying party is prejudiced by such omission. In case any such action shall
be brought against any indemnified party and it shall notify the indemnifying
party of the commencement thereof, the indemnifying party shall be entitled to
participate in and, to the extent it shall wish, to assume and undertake the
defense thereof with counsel satisfactory to such indemnified party, and, after
notice from the indemnifying party to such indemnified party of its election so
to assume and undertake the defense thereof, the indemnifying party shall not be
liable to such indemnified party under this Section 4.8 for any legal expenses
subsequently incurred by such indemnified party in connection with the defense
thereof other than reasonable costs of investigation and of liaison with counsel
so selected, provided, however, that, if the defendants in any such action
include both the indemnified party and the indemnifying party and the
indemnified party shall have reasonably concluded that there may be reasonable
defenses available to it which are different from or additional to those
available to the indemnifying party or that the interests of the indemnified
party reasonably may be deemed to conflict with the interests of the
indemnifying party, the indemnified party shall have the right to select a
separate counsel and to assume such legal defenses and otherwise to participate
in the defense of such action, with the expenses and fees of such separate
counsel and other expenses related to such participation to be reimbursed by the
indemnifying party as incurred. No indemnifying party, in the defense of any
such claim or action, shall, except with the consent of each indemnified party,

                                       17
<PAGE>

consent to entry of any judgment or enter into any settlement which does not
include as an unconditional term thereof the giving by the claimant or plaintiff
to such indemnified party of a release from all liability in respect to such
claim or action. Each indemnified party shall furnish such information regarding
itself or the claim in question as an indemnifying party may reasonably request
in writing and as shall be reasonably required in connection with defense of
such claim and litigation resulting therefrom.

                  (d)      In order to provide for just and equitable
contribution to joint liability under the Securities Act in any case in which
either (i) any holder of Registrable Securities exercising rights under this
Agreement, or any controlling person of any such holder, makes a claim for
indemnification pursuant to this Section 4.8 but it is judicially determined (by
the entry of a final judgment or decree by a court of competent jurisdiction and
the expiration of time to appeal or the denial of the last right of appeal) that
such indemnification may not be enforced in such case notwithstanding the fact
that this Section 4.8 provides for indemnification in such case, or (ii)
contribution under the Securities Act may be required on the part of any such
selling holder or any such controlling person in circumstances for which
indemnification is provided under this Section 4.8; then, and in each such case,
the Company and such holder will contribute to the aggregate losses, claims,
damages or liabilities to which they may be subject (after contribution from
others) in such proportion so that such holder is responsible for the portion
represented by the percentage that the public offering price of its Registrable
Securities offered by the registration statement bears to the public offering
price of all securities offered by such registration statement, and the Company
is responsible for the remaining portion; provided, however, that, in any such
case, (A) no such holder of Registrable Securities will be required to
contribute any amount in excess of the proceeds received from the sale of all
such Registrable Securities offered by it pursuant to such registration
statement; and (B) no person or entity guilty of fraudulent misrepresentation
(within the meaning of Section 11(f) of the Securities Act) will be entitled to
contribution from any person or entity who was not guilty of such fraudulent
misrepresentation.

                  (e)      The indemnities and obligations provided in this
Section 4.8 shall survive the transfer of any Registrable Securities by such
holder.

                  4.9      CHANGES IN COMMON STOCK. If, and as often as, there
is any change in the Common Stock by way of a stock split, stock dividend,
combination or reclassification, or through a merger, consolidation,
reorganization or recapitalization, or by any other means, appropriate
adjustment shall be made in the provisions hereof so that the rights and
privileges granted hereby shall continue with respect to the Common Stock as so
changed.

                  4.10     RULE 144 AND 144A REPORTING. With a view to making
available the benefits of certain rules and regulations of the Commission which
may at any time permit the sale of the Registrable Securities to the public
without registration, except as provided in paragraph (c) below, at all times
after any registration statement covering a public offering of securities of the
Company under the Securities Act shall have become effective, the Company agrees
to:

                  (a)      use its best efforts to comply with all of the
reporting requirements of the

                                       18
<PAGE>

Exchange Act (whether or not it shall be required to do so) and shall comply
with all other public information reporting requirements of the Commission as a
condition to the availability of an exemption from the Securities Act for the
sale of any of the Registrable Securities by any holder of Registrable
Securities (including any such exemption pursuant to Rule 144 or Rule 144A
thereof, as amended form time to time, or any successor rule thereto or
otherwise);

                  (b)      cooperate with each holder of Registrable Securities
in supplying such information as may be necessary for such holder of Registrable
Securities to complete and file any information reporting forms presently or
hereafter required by the Commission as a condition to the availability of an
exemption from the Securities Act (under Rule 144 or Rule 144A thereunder or
otherwise) for the sale of any of the Registrable Securities by any holder of
Registrable Securities; and

                  (c)      furnish to each holder of Registrable Securities
forthwith upon request a written statement by the Company as to its compliance
with the reporting requirements of such Rule 144 or Rule 144A (or any successor
rule) and, at any time after it has become subject to such reporting
requirements, of the Securities Act and the Exchange Act, a copy of the most
recent annual or quarterly report of the Company, and such other reports and
documents so filed by the Company as such holder may reasonably request in
availing itself of any rule or regulation of the Commission allowing such holder
to sell any Registrable Securities without registration.

                  4.11     "MARKET STAND-OFF' AGREEMENT. Each of the Investors
agrees, severally and not jointly, if requested by the Company and an
underwriter of Common Stock (or other securities) of the Company, not to sell or
otherwise transfer or dispose of any Common Stock (or other securities) of the
Company held by such Purchaser during a period not to exceed (i) one hundred and
eighty (180) days following the effective date of the first registration
statement of the Company filed under the Securities Act and (ii) ninety (90)
days following the effective date of any subsequent registration statement filed
by the Company under the Securities Act, and to enter into an agreement to such
effect; provided that (y) all persons including Shares in such offering and (z)
all of the Company's officers, directors and holders of at least 5% of the
outstanding Common Stock (or securities convertible into at least 5% of the
Common Stock) also enter into agreements to such effect.

                  The Company may impose stop-transfer instructions with respect
to the shares (or securities) subject to the foregoing restriction until the end
of said period.

                  4.12     LIMITATION ON SUBSEQUENT REGISTRATION RIGHTS. The
Company shall not, without the approval of the Board of Directors, including a
majority of the Preferred Stock Directors (as defined in the Second Amended and
Restated Certificate of Incorporation of the Company), which majority shall
include the Series D Director (as defined in the Second Amended and Restated
Certificate of Incorporation of the Company), grant to any third party any
registration rights more favorable than, or in any way conflicting with, any of
those contained herein, so long as any of the registration rights under this
Agreement remains in effect, provided, in any event, (i) any grant of demand or
required registration rights shall provide that the Purchasers have incidental
or "piggyback" registration rights with respect thereto in accordance

                                       19
<PAGE>

with the provisions of Section 4.4 hereof, and (ii) such rights shall not become
effective prior to the rights of the holders of Registrable Securities
hereunder.

                  4.13     ASSIGNMENT OF REGISTRATION RIGHTS. The rights to
cause the Company to register Registrable Securities pursuant to this Section 4
may be assigned (but only with all related obligations) by a holder of
Registrable Securities to a transferee or assignee of such securities who is not
engaged in a business activity competitive with the Company (as reasonably
determined by the Company's Board of Directors) and who, after such assignment
or transfer, holds at least 100,000 shares of Registrable Securities (subject to
appropriate adjustment for stock splits, stock dividends, combinations and
similar recapitalization events), provided the Company is, within a reasonable
time after such transfer, furnished with written notice of the name and address
of such transferee or assignee and the securities with respect to which such
registration rights are being assigned; and provided, further, that such
assignment shall be effective only if (i) immediately following such transfer
the further disposition of such securities by the transferee or assignee is
restricted under the Act and (ii) the transferee or assignee shall acknowledge
in writing that the transferred or assigned Registrable Securities shall remain
subject to this Agreement. For the purposes of determining the number of shares
of Registrable Securities held by a transferee or assignee, the holdings of
transferees and assignees of a partnership who are partners or retired partners
of such partnership (including spouses and ancestors, lineal descendants and
siblings of such partners or spouses who acquire Registrable Securities by gift,
will or intestate succession) shall be aggregated together and with the
partnership; provided that all assignees and transferees who would not qualify
individually for assignment of registration rights shall have a single
attorney-in-fact for the purpose of exercising any rights, receiving notices or
taking any action under this Section 4.

                  5.       BOARD OF DIRECTORS

                  5.1      ELECTION OF DIRECTORS. Each Investor shall take or
cause to be taken such actions as may be required from time to time to establish
and maintain the number of persons comprising the Board of Directors of the
Company at nine (9), or such other number as the Board of Directors, including a
majority of the Preferred Stock Directors, in their discretion, may determine
from time to time, and to elect as directors (i) the five (5) Preferred Stock
Directors, which shall initially include (A) Jonathan Fleming who shall serve as
Chairman of the Board of Directors, (B) Dr. Anthony B. Evnin, (C) Dr. Alix
Marduel, (D) an individual designated by OrbiMed Advisors LLC or its Affiliates,
who initially shall be Dr. Michael E. Sheffery, and (E) an individual designated
by Biomedicine, L.P. or its Affiliates, who initially shall be Michael E.
Meyers, (ii) an individual designated by the holders of the Common Stock, (iii)
Dr. Axel Unterbeck, so long as he is then employed as the Company's President or
Chief Scientific Officer, (iv) Tony Scullion, so long as he is then employed as
the Company's Chief Executive Officer, and (v) an individual with experience in
the pharmaceutical industry who is not an officer or employee of the Company and
who shall be reasonably acceptable to a majority of the other members of the
Board of Directors, including a majority of the Preferred Stock Directors (which
majority shall include the Series D Director). Mr. Fleming, Dr. Evnin, Dr.
Marduel and Dr. Sheffery shall serve as the Series A-B-C Directors (as defined
in the Amended and Restated Certificate of Incorporation); and Mr. Meyers shall
serve as the Series D Director. Without limiting the generality of the
foregoing, at each annual meeting of the stockholders, and at each

                                       20
<PAGE>

special meeting of the stockholders called for the purpose of electing directors
of the Company, and at any time at which the stockholders have the right to, or
shall, elect directors of the Company, then, and in each event, the Investors
shall vote all Shares owned by them (or shall consent in writing in lieu of a
meeting of stockholders, as the case may be) to set the number of, and to elect
persons as, directors of the Company in accordance with the preceding sentence.
In addition, the Audit Committee of the Board of Directors of the Company shall
be initially comprised of Dr. Evnin, Dr. Gilbert and Dr. Sheffery, and the
Compensation Committee of the Board of Directors of the Company shall be
initially comprised Mr. Fleming, Dr. Marduel and Mr. Meyers.

                  5.2      REMOVAL OF DIRECTORS; FILLING OF VACANCIES. Each
Investor shall take all action necessary to remove forthwith any director when
such removal is requested for any reason, with or without cause, by the Investor
that designated such director for election. In the case of the death,
resignation or removal as herein provided of a director, each Investor shall
vote all Shares owned by him, her or it to elect another person designated by
the same Investor that designated the deceased, resigning or removed director
if, at the time such vacancy occurs, such Investor shall have the right to have
a person designated by him elected as a director pursuant to Section 5.1. Each
Investor agrees to use his best efforts to prevent any action from being taken
by the Board of Directors during the pendency of any vacancy due to the death,
resignation or removal of a director unless the party entitled to have a person
designated by him to fill such vacancy shall have failed for a period often (10)
days after written notice of such vacancy to designate a replacement.

                  5.3      TERMINATION. The provisions set forth in this Article
5 shall be of no further force and effect upon the closing of the Company's
Initial Public Offering.

                  6.       AFFIRMATIVE COVENANTS OF THE COMPANY

                  The Company covenants and agrees that, from the date of the
Closing under the Series D Purchase Agreement and thereafter so long as any
Purchaser owns Registrable Securities, it will perform and observe the following
covenants and provisions, and will cause each Subsidiary, if and when such
Subsidiary exists, to perform and observe the following covenants and provisions
as applicable to such Subsidiary.

                  6.1      FINANCIAL STATEMENTS; OTHER REPORTS. The Company and
each Subsidiary will maintain proper books of account and records in accordance
with generally accepted accounting principles applied on a consistent basis, and
will deliver to each Purchaser owning at least one hundred thousand (100,000)
shares of the Company's capital stock on a fully diluted basis, treating all
preferred stock on an as converted basis but excluding any unexercised options,
warrants or purchase rights (each, a "Rights Holder"):

                  (a)      as soon as available and in any event within
forty-five (45) days after the end of each of the first three quarters of each
fiscal year of the Company, a consolidated balance sheet of the Company and its
Subsidiaries as of the end of such quarter and the related statements of income
and stockholders' equity and of cash flows of the Company for the period
commencing at the end of the previous fiscal year and ending with the end of
such quarter,

                                       21
<PAGE>

setting forth in each case in comparative form the corresponding figures for the
corresponding period of the preceding fiscal year and the budget for such
current year, all in reasonable detail and prepared in accordance with generally
accepted accounting principles consistently applied, and duly certified (subject
to year-end audit adjustments) by the chief financial officer of the Company;

                  (b)      as soon as available and in any event within thirty
(30) days after the end of each quarter of each fiscal year of the Company, a
certificate executed by the President, Vice President or Chief Financial Officer
of the Company stating that the Company is, and has been during such quarterly
accounting period, in compliance with the terms and conditions set forth in this
Agreement;

                  (c)      as soon as available and in any event within one
hundred twenty (120) days after the end of each fiscal year of the Company, a
copy of the annual audit report for such year for the Company, including therein
a consolidated balance sheet of the Company and its Subsidiaries as of the end
of such fiscal year and statements of income and stockholders' equity and of
cash flows of the Company for such fiscal year, setting forth in each case in
comparative form the corresponding figures for the preceding fiscal year, all
duly certified by independent public accountants of recognized standing
acceptable to the Rights Holders;

                  (d)      promptly upon receipt thereof, any written report
submitted to the Company by independent public accountants in connection with an
annual or interim audit of the books of the Company and its Subsidiaries made by
such accountants;

                  (e)      promptly after sending, making available, or filing
the same, such reports and financial statements as the Company shall send or
make available to the stockholders of the Company;

                  (f)      promptly after the commencement thereof, notice of
all actions, suits and proceedings before any court or governmental department,
commission, board, bureau, agency or instrumentality, domestic or foreign,
affecting the Company or its Subsidiaries, any technology or patent rights which
it has or they have, or any other assets of the Company or its Subsidiaries or
any key employee or officer (in their capacity as such);

                  (g)      promptly after the occurrence thereof and in any
event within five (5) business days after it becomes aware of each occurrence,
notice of any material adverse change in the business, assets, properties,
management, operations or financial condition of the Company or its
Subsidiaries;

                  (h)      promptly upon becoming available: (i) copies of all
financial statements, minutes, reports, press releases, notices, proxy
statements and other documents sent by the Company to its Stockholders or
released to the public and copies of all regular and periodic reports, if any,
filed by the Company with the Commission or any securities exchange or
self-regulatory organization; and (ii) any other financial or other information
available to management of the Company that any of the Purchasers shall have
reasonably requested on a timely basis; and

                                       22
<PAGE>

                  (i)      at least 15 days prior to the beginning of each
fiscal year of the Company, an operating plan with monthly and quarterly
breakdowns (the "Budget") for each fiscal year, which the Company shall be
required to prepare and submit to the Board. The Budget shall be deemed accepted
as the Budget for such fiscal year only when it has been approved by the Board.
The Budget shall be reviewed by the Company periodically and all changes
therein, and all material deviations therefrom, shall be reviewed by the Board
on at least a quarterly basis.

                  Neither the foregoing provisions of this Section nor any other
provision of this Agreement shall be in limitation of any rights which a
Purchaser may have with respect to the books and records of the Company and its
Subsidiaries, or to inspect their properties or discuss their affairs, finances
and accounts, under the laws of the jurisdictions in which they are
incorporated.

                  6.2      INSPECTION AND OTHER INFORMATION. Each Rights Holder
and such agents, advisors and counsel as such Rights Holder may designate, may,
at its expense, visit and inspect any of the properties of the Company and each
Subsidiary, examine the books of account of the Company and each Subsidiary,
take extracts therefrom and discuss the affairs, finances and accounts of the
Company and each Subsidiary with its officers and employees and public
accountants (and by this provision the Company and each Subsidiary hereby
authorizes said accountants to discuss with such Rights Holder and such persons
its finances and accounts), at reasonable times and with reasonable prior notice
during normal business hours. All such visits and inspections shall be conducted
in a manner which will not unreasonably interfere with the normal business
operations of the Company and each Subsidiary. The Company and each Subsidiary
will furnish to each such Rights Holder such other information as it from time
to time may reasonably request.

                  6.3      INDEPENDENT ACCOUNTANTS. The Company will retain KPMG
or such other independent public accountants of recognized national standing
approved by the Company's Board of Directors who shall certify the Company's
consolidated financial statements at the end of each fiscal year. In the event
the services of the independent public accountants, so selected, or any firm of
independent public accountants hereafter employed by the Company are terminated,
the Company will promptly thereafter notify the Rights Holders and will request
the firm of independent public accountants whose services are terminated to
deliver to the Rights Holders a letter of such firm setting forth the reasons
for the termination of their services. In the event of such termination, the
Company will promptly thereafter engage another such firm of independent public
accountants. In its notice to the Rights Holders, the Company shall state
whether the change of accountants was recommended or approved by the Board of
Directors or any committee thereof.

                  6.4      MAINTENANCE OF INSURANCE. The Company and each
Subsidiary will maintain insurance with financially sound and reputable
insurance companies or associations in such amounts and covering such risks as
is usually carried by companies engaged in similar businesses and owning similar
properties in the same general areas in which the Company operates, including,
without limitation, directors' and officers' liability insurance.

                                       23
<PAGE>

                  6.5      MAINTENANCE OF KEY-PERSON LIFE INSURANCE. The Company
will continue to maintain in full force and effect without interruption term
life insurance on the life of Dr. Axel Unterbeck, with a financially sound and
reputable insurance company or association and in the amount of at least
$1,000,000, which proceeds shall be payable to the order of the Company. The
Company will not cause or permit any assignment of the proceeds of either policy
or change in beneficiary, and will not borrow against either policy. The Company
will add the Purchasers as notice parties to each such policy, and will request
that the issuer of each such policy provide each Purchaser with twenty (20)
days' notice before such policy is terminated (for failure to pay premiums or
otherwise) or assigned, or before any change is made in the designation of the
beneficiary thereof.

                  6.6      EMPLOYEE NONDISCLOSURE AND NONCOMPETITION AGREEMENTS.
The Company shall use its best efforts to obtain, and shall cause its
subsidiaries (if any) to use their best efforts to obtain, a Confidentiality and
Noncompetition Agreement in substantially the form of Exhibit C attached to the
Series D Purchase Agreement from all key employees and from any other employees
who will have access to confidential information of the Company or any of its
subsidiaries, upon their employment by the Company or any of its subsidiaries.

                  6.7      PRESERVATION OF CORPORATE EXISTENCE. The Company and
each Subsidiary will preserve and maintain its corporate existence, rights,
franchises and privileges in the jurisdiction of its incorporation, and qualify
and remain qualified, as a foreign corporation in each jurisdiction in which
such qualification is necessary or desirable in view of its business and
operations or the ownership of its properties. The Company and each Subsidiary
shall preserve and maintain all licenses and other rights to use patents,
processes, licenses, trademarks, trade names, inventions, Intellectual Property
Rights or copyrights owned or possessed by it and necessary to the conduct of
its business.

                  6.8      COMPLIANCE WITH LAWS. The Company will comply, and
cause each of its Subsidiaries to comply, with all applicable laws, rules,
regulations and orders of any governmental authority, noncompliance with which
could materially adversely affect its business or condition, financial or
otherwise.

                  6.9      COMPENSATION. The Company and each Subsidiary shall
pay to its management compensation which is not in excess of compensation
customarily paid to management in companies of similar size, of similar
maturity, and in similar businesses and all management compensation and all
policies relating thereto, shall be approved in advance by a majority of the
Company's Board of Directors.

                  6.10     NEW DEVELOPMENTS. The Company and each Subsidiary
will cause all technological developments, patentable or unpatentable
inventions, discoveries or improvements by their officers, employees or
consultants to be documented in accordance with appropriate professional
standards, cause all officers, employees and consultants to execute appropriate
patent and copyright assignment agreements to the Company and such Subsidiary,
as the case may be, and, where possible and appropriate, cause all officers,
employees and consultants to file

                                       24
<PAGE>

and execute United States and foreign patent or copyright applications relating
to and protecting such developments on behalf of the Company or such Subsidiary.

                  6.11     MEETINGS OF DIRECTORS AND COMMITTEES; EXPENSES OF
DIRECTORS. The Company shall hold meetings of the Company's Board of Directors
not less frequently than six times during any calendar year. The Company shall
promptly reimburse in full each director of the Company for all of his or her
reasonable out-of-pocket expenses incurred in attending each meeting of the
Board of Directors of the Company or any committee thereof or in connection with
any special project. No action shall be taken at any such meeting if at least
three Preferred Stock Directors are not present at such meeting.

                  6.12     PROMPT PAYMENT OF TAXES, ETC. The Company and each
Subsidiary will promptly pay and discharge, or cause to be paid and discharged,
when due and payable, all lawful taxes, assessments and governmental charges or
levies imposed upon the income, profits, property or business of the Company or
any Subsidiary; provided, however, that any such tax, assessment, charge or levy
need not be paid if the validity thereof shall currently be contested in good
faith by appropriate proceedings and if the Company or such Subsidiary shall
have set aside on its books adequate reserves with respect thereto, and
provided, further, that the Company and each Subsidiary will pay all such taxes,
assessments, charges or levies forthwith upon the commencement of proceedings to
foreclose any Lien which may have attached as security therefor. The Company and
each Subsidiary will promptly pay or cause to be paid when due, or in
conformance with customary trade terms, all other Indebtedness incident to
operations of the Company and each Subsidiary.

                  6.13     MAINTENANCE OF PROPERTIES AND LEASES. The Company
will keep its properties and those of its Subsidiaries in good repair, working
order and condition, reasonable wear and tear excepted, and from time to time
make all needful and proper repairs, renewals, replacements, additions and
improvements thereto; and the Company and its Subsidiaries will at all times
comply with each provision of all leases to which any of them is a party or
under which any of them occupies property if the breach of such provision might
have a material adverse effect on the condition, financial or otherwise, or
operations of the Company or such Subsidiary.

                  6.14     COMPLIANCE WITH AGREEMENTS. The Company and all of
its Subsidiaries shall duly comply with all of the provisions of the contracts,
obligations, agreements, plans, arrangements and commitments to which any of
them is a party or by which any of them is bound.

                  6.15     AVAILABILITY OF COMMON STOCK. The Company will, from
time to time, in accordance with the laws of the State of Delaware, use its best
efforts to obtain from its shareholders approval of an increase in the
authorized amount of Common Stock if at any time the number of shares of Common
Stock remaining unissued and available for issuance shall be insufficient to
permit conversion of all then outstanding shares of Preferred Stock.

                  6.16     STOCK DISPOSITIONS. The Company and each employee or
officer of the Company who hereafter acquires shares of the Company's capital
stock from the Company, or any option or right to acquire shares of the
Company's capital stock from the Company, shall

                                       25
<PAGE>

enter into (if they have not already done so) an agreement in such form as
approved by the Board of Directors, pursuant to which the Company shall have the
right to repurchase such shares of the Company's capital stock from such
employee or officer upon the cessation of his or her employment with the
Company.

                  6.17     TERMINATION OF AFFIRMATIVE COVENANTS. The covenants
set forth in this Article 6 shall be of no further force or effect upon the
closing of the Company's Initial Public Offering.

                  7.       NEGATIVE COVENANTS

                  Without limiting any other covenants or provisions hereof, the
Company covenants and agrees that it will comply with and observe the following
negative covenants and provisions, and will cause each Subsidiary to comply with
and observe such of the following negative covenants and provisions as are
applicable to such Subsidiary, if and when such Subsidiary exists, and will not,
without first having obtained either (y) the approval of the Board of Directors,
including a majority of the Preferred Stock Directors (which majority shall
include the Series D Director), or (z) the affirmative vote or written consent
of the holders of at least 66 2/3% of the outstanding shares of Preferred Stock,
do any of the actions set forth in the following negative covenants and
provisions, provided, however, that if any of the actions set forth below
adversely affects the Series A Stock, the Series B Stock, the Series C Stock,
the Series D Stock or the Series Roche Stock only, such action must be approved
by the affirmative vote or written consent of holders of at least 66 2/3% of the
outstanding shares of such series voting separately from any other series or
class of shares.

                  7.1      BUSINESS. The Company will not engage in any business
other than the business of research, development and production of
pharmaceutical products that improve memory or enhance cognition or any other
activities directly related to the foregoing.

                  7.2      MERGER AND SALE OF ASSETS; LIQUIDATION AND
DISSOLUTION. The Company will not merge or consolidate with any other Person or
sell, assign, lease or otherwise dispose of all or substantially all of its
assets, in one transaction or in a series of transactions, nor dissolve or
liquidate the Company.

                  7.3      AMENDMENTS TO CHARTER AND BY-LAWS. The Company will
not amend its Certificate of Incorporation or By-laws.

                  7.4      DISTRIBUTIONS; SECTION 305. Neither the Company nor
any Subsidiary will purchase, redeem, retire, or otherwise acquire for value any
shares of its capital stock (or rights, options or warrants to purchase such
shares) now or hereafter outstanding, return any capital to its stockholders
(such transactions being hereinafter referred to as "Distributions"), and
neither the Company nor any Subsidiary shall declare or pay any dividends or
make any distribution of assets to its stockholders as such, except for (i)
dividends on the Common Stock paid out of earnings; and (ii) repurchases of
shares of Common Stock held by employees, consultants, directors, or officers of
the Company that are subject to stock repurchase agreements under which the
Company has the right to repurchase such shares in the event of termination of

                                       26
<PAGE>

employment.

                  7.5      DEALINGS WITH AFFILIATES. Except for existing
agreements described in Schedule 2.21 to the Series D Purchase Agreement,
neither the Company nor any Subsidiary will enter into any transaction or
agreement other than indemnification and employment transactions in the ordinary
course of the Company's business with any employee, officer or director or any
member of their families, or any corporation or other entity in which any one or
more of such persons holds, directly or indirectly, five percent (5%) or more of
any class of capital stock, or with any other Affiliate of the Company, except
agreements and transactions on terms no less favorable to the Company or any
Subsidiary than it would obtain in a transaction between unrelated parties, and
then only if such agreements or transactions are approved by the disinterested
members of the Board of Directors.

                  7.6      TRANSFERS OF TECHNOLOGY. Neither the Company nor any
Subsidiary will transfer any ownership or interest in, or material rights
relating to, any of its Intellectual Property Rights to any Person, except
pursuant to licensing agreements and other transfers made in the ordinary course
of business and approved by the Board of Directors.

                  7.7      RESTRICTIVE AGREEMENTS PROHIBITED. Neither the
Company nor any of its Subsidiaries shall become a party to any agreement which
by its terms restricts the Company's performance of its obligations pursuant to
the terms of this Agreement, the Series Roche Purchase Agreement, the Series D
Purchase Agreement, the Series C Purchase Agreement, the Series B Purchase
Agreement, that certain Purchase Agreement dated April 24, 1998 relating to the
sale by the Company of the Series A Stock, or the provisions relating to the
Series A Stock, Series B Stock, Series C Stock, Series D Stock or Series Roche
Stock included in the Second Amended and Restated Certificate of Incorporation,
including, but not limited to, registration rights and the payment of dividends
on, the redemption, voting or conversion of the Series A Stock, the Series B
Stock, the Series C Stock, the Series D Stock or the Series Roche Stock,
provided, however, that nothing in this Section 7.7 shall prohibit any amendment
of or waiver of any provision of this Agreement or any of the foregoing
agreements or the Second Amended and Restated Certificate of Incorporation, if
such amendment or waiver is in accordance with the applicable provisions of this
Agreement and other applicable law.

                  7.8      MERGERS, SALE OF ASSETS, ETC. OF SUBSIDIARIES. The
Company shall not permit any Subsidiary to consolidate or merge into or with or
sell or transfer all or substantially all its assets, except that any Subsidiary
may (i) consolidate or merge into or with or sell or transfer assets to any
other Subsidiary, or (ii) merge into or sell or transfer assets to the Company.

                  7.9      MAINTENANCE OF OWNERSHIP OF SUBSIDIARIES. The Company
shall not sell or otherwise transfer any shares of capital stock of any
Subsidiary, except to the Company or another Subsidiary, or permit any
Subsidiary to issue, sell or otherwise transfer any shares of its capital stock
or the capital stock of any Subsidiary, except to the Company or another
Subsidiary.

                  7.10     SECURITIES OF OTHER PERSONS. Except for short-term
investments in

                                       27
<PAGE>

highly rated instruments, money market funds, bank certificates of deposit or
similar low risk securities, neither the Company nor any Subsidiary shall
purchase any stock or other securities of any Person, unless such Person is
wholly-owned.

                  7.11     U.S. REAL PROPERTY HOLDING CORPORATION. The Company
will not be a "United States real property holding corporation", as defined in
Section 897(c)(2) of the Code and Section 1.897-2(b) of the Regulations
promulgated by the Internal Revenue Service and upon written request, will
provide to any holder of Registrable Securities a statement to the effect
informing such holder whether such interest constitutes a U.S. real property
interest.

                  7.12     STOCK AND OPTION AGREEMENTS. The Company will not
issue Common Stock or stock options to its officers, directors, employees or
others who render services to the Company except (A) pursuant to the 1998
Employee, Director and Consultant Stock Option Plan in an aggregate amount not
exceeding 9,500,000 shares of Common Stock or such greater number of shares of
Common Stock as approved by the Board of Directors, including a majority of the
Preferred Stock Directors, or (B) pursuant to any other stock option plan
approved by the Board of Directors, including a majority of the Preferred Stock
Directors; provided, however, that the negative covenants of this Section 7.12
shall not apply to options granted to Eric R. Kandel, M.D. pursuant to a
Consulting Agreement dated as of April 1, 1998, as heretofore amended, by and
between the Company and Dr. Eric R. Kandel, provided further, that such options
issued to Eric R. Kandel have an exercise price approved by the Board of
Directors, including a majority of the Preferred Stock Directors. The Company
will not amend or modify the 1998 Employee, Director and Consultant Stock Option
Plan, or otherwise enact a new stock option plan without the approval of the
Board of Directors, including a majority of the Preferred Stock Directors. For
purposes of this Section 7.12, in each case where reference to a majority of the
Preferred Stock Directors is made, such majority shall include the Series D
Director.

                  7.13     TERMINATION OF NEGATIVE COVENANTS. The covenants set
forth in this Article 7 shall be of no further force or effect upon the closing
of the Initial Public Offering.

                  8.       MISCELLANEOUS

                  8.1      NOTICES. All notices, requests, consents and other
communications hereunder shall be in writing, shall be addressed to the
receiving party's address set forth below or to such other address as a party
may designate by notice hereunder, and shall be either (i) delivered by hand,
(ii) made by telecopy or facsimile transmission, (iii) sent by a nationally
recognized (or substantially equivalent international) overnight courier, or
(iv) sent by registered or certified mail, return receipt requested, postage
prepaid; provided, however, that certified mail shall not be used to effectuate
any such notice, request, consent or other communication to addresses outside
the United States.

                  If to the Company:     Memory Pharmaceuticals Corp.

                  With a copy to:        Sills Cummis Radin Tischman Epstein
                                         & Gross, A Professional Corporation
                                         One Riverfront Plaza

                                       28
<PAGE>

                                         Newark, New Jersey 07102-5400
                                         Attn: Ira Rosenberg, Esq.
                                         (973) 643-7000 (Telephone)
                                         (973) 643-6500 (Fax)

                 If to the Purchasers:   To the addresses set forth on Exhibit A

                                         With a copy to:
                                         Sidley Austin Brown & Wood LLP
                                         875 Third Avenue
                                         New York, New York 10022
                                         Attn: Alan L. Jakimo, Esq.
                                         (212) 906-2724 (Telephone)
                                         (212) 906-2021 (Fax)

                  All notices, requests, consents and other communications
hereunder shall be deemed to have been given either (i) if by hand, at the time
of the delivery thereof to the receiving party at the address of such party set
forth above, (ii) if made by telecopy or facsimile transmission, at the time
that receipt thereof has been acknowledged by electronic confirmation or
otherwise, (iii) if sent by overnight courier, on the next business day
following the day such notice is delivered to the courier service, or (iv) if
sent by registered or certified mail, on the fifth business day following the
day such mailing is made.

                  8.2      ENTIRE AGREEMENT. This Agreement embodies the entire
agreement and understanding between the parties hereto with respect to the
subject matter hereof and supersedes all prior oral or written agreements and
understandings relating to the subject matter hereof. No statement,
representation, warranty, covenant or agreement of any kind not expressly set
forth in this Agreement shall affect, or be used to interpret, change or
restrict, the express terms and provisions of this Agreement.

                  8.3      MODIFICATIONS AND AMENDMENTS. This Agreement may not
be amended or modified, and no provision hereof may be waived, without the
written consent of the Company and the holders of at least two-thirds (2/3) of
the outstanding shares of Preferred Stock. Any waiver or consent hereunder shall
be effective only in the specific instance and for the purpose for which it was
given, and shall not constitute a continuing waiver or consent.

                  8.4      ASSIGNMENT. The rights and obligations under this
Agreement may not be assigned by the Company without the prior written consent
of at least a majority of the holders of Registrable Securities, unless
specifically permitted by the terms hereof.

                  8.5      BENEFIT. All statements, representations, warranties,
covenants and agreements in this Agreement shall be binding on the parties
hereto and shall inure to the benefit of the respective successors and permitted
assigns of each party hereto. Nothing in this Agreement shall be construed to
create any rights or obligations except among the parties hereto, and no person
or entity shall be regarded as a third-party beneficiary of this Agreement,
except for Dr. Walter Gilbert, Dr. Axel Unterbeck, and the Company's Chief
Executive Officer

                                       29
<PAGE>

as contemplated by Section 5.1 hereof.

                  8.6      GOVERNING LAW. This Agreement and the rights and
obligations of the parties hereunder shall be construed in accordance with and
governed by the law of the State of Delaware, without giving effect to the
conflict of law principles thereof.

                  8.7      JURISDICTION AND SERVICE OF PROCESS. Any legal action
or proceeding with respect to this Agreement shall be brought in the courts of
the State of New Jersey or of the United States of America for the District of
New Jersey. By execution and delivery of this Agreement, each of the parties
hereto accepts for itself and in respect of its property, generally and
unconditionally, the jurisdiction of the aforesaid courts. Each of the parties
hereto irrevocably consents to the service of process of any of the
aforementioned courts in any such action or proceeding by the mailing of copies
thereof by certified mail, postage prepaid, to the party at its address set
forth in Section 8.1 hereof.

                  8.8      SEVERABILITY. In the event that any court of
competent jurisdiction shall determine that any provision, or any portion
thereof, contained in this Agreement shall be unenforceable in any respect, then
such provision shall be deemed limited to the extent that such court deems it
enforceable, and as so limited shall remain in full force and effect. In the
event that such court shall deem any such provision, or portion thereof, wholly
unenforceable, the remaining provisions of this Agreement shall nevertheless
remain in full force and effect.

                  8.9      INTERPRETATION. The parties hereto acknowledge and
agree that: (i) each party and its counsel reviewed and negotiated the terms and
provisions of this Agreement and have contributed to its revision; (ii) the rule
of construction to the effect that any ambiguities are resolved against the
drafting party shall not be employed in the interpretation of this Agreement;
and (iii) the terms and provisions of this Agreement shall be construed fairly
as to all parties hereto and not in favor of or against any party, regardless of
which party was generally responsible for the preparation of this Agreement.

                  8.10     HEADINGS AND CAPTIONS. The headings and captions of
the various subdivisions of this Agreement are for convenience of reference only
and shall in no way modify or affect the meaning or construction of any of the
terms or provisions hereof.

                  8.11     ENFORCEMENT. Each of the parties hereto acknowledges
and agrees that the rights acquired by each party hereunder are unique and that
irreparable damage would occur in the event that any of the provisions of this
Agreement to be performed by the other parties were not performed in accordance
with their specific terms or were otherwise breached. Accordingly, in addition
to any other remedy to which the parties hereto are entitled at law or in
equity, each party hereto shall be entitled to an injunction or injunctions to
prevent breaches of this Agreement by any other party and to enforce
specifically the terms and provisions hereof in any federal or state court to
which the parties have agreed hereunder to submit to jurisdiction.

                  8.12     NO WAIVER OF RIGHTS, POWERS AND REMEDIES. No failure
or delay by a party hereto in exercising any right, power or remedy under this
Agreement, and no course of dealing among the parties hereto, shall operate as a
waiver of any such right, power or remedy of

                                       30
<PAGE>

the party. No single or partial exercise of any right, power or remedy under
this Agreement by a party hereto, nor any abandonment or discontinuance of steps
to enforce any such right, power or remedy, shall preclude such party from any
other or further exercise thereof or the exercise of any other right, power or
remedy hereunder. The election of any remedy by a party hereto shall not
constitute a waiver of the right of such party to pursue other available
remedies. No notice to or demand on a party not expressly required under this
Agreement shall entitle the party receiving such notice or demand to any other
or further notice or demand in similar or other circumstances or constitute a
waiver of the rights of the party giving such notice or demand to any other or
further action in any circumstances without such notice or demand.

                  8.13     TERMINATION OR AMENDMENT OF PRIOR AGREEMENTS. The
parties hereto agree that the Third Amended Agreement shall hereby be terminated
and of no force and effect, and shall be superseded in its entirety by this
Agreement. The parties hereto also acknowledge and agree that the provisions set
forth in Article 5 and Article 6 of the Preferred Stock Purchase Agreement dated
April 24, 1998 by and among the Company and the Series A Purchasers have been
deleted in their entirety, and are void and of no further force and effect.

                  8.14     COUNTERPARTS. This Agreement may be executed in one
or more counterparts, and by different parties hereto on separate counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

                                       31
<PAGE>

                  IN WITNESS WHEREOF, the parties hereto have executed this
Agreement or caused this Agreement to be executed by their duly authorized
representatives as of the date first written above.

                                         MEMORY PHARMACEUTICALS CORP.

                                         By /s/ Tony Scullion
                                            -------------------------------
                                            Name:  Tony Scullion
                                            Title: Chief Executive Officer

                                         SERIES A PURCHASERS:

                                         OXFORD BIOSCIENCE
                                         PARTNERS II L.P.
                                         By: OBP Management II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title: General Partner

                                         OXFORD BIOSCIENCE
                                         PARTNERS (BERMUDA) II LIMITED
                                         PARTNERSHIP
                                         By: OBP Management II (Bermuda)
                                         Limited Partnership

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title:

                                         OXFORD BIOSCIENCE
                                         PARTNERS (ADJUNCT) II, L.P.
                                         By: OBP Management II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title: General Partner

                                       32
<PAGE>

                                         OXFORD BIOSCIENCE
                                         PARTNERS (GS-ADJUNCT) II, L.P.
                                         By: OBP Management II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title: General Partner

                                         HEALTHCARE VENTURES V L.P.

                                         By /s/ Harold Werner
                                            -------------------------------
                                            Name:  Harold Werner
                                            Title:

                                         RHO MANAGEMENT TRUST II

                                         By: Rho Capital Partners, Inc.,
                                             Investment Advisors

                                         By /s/ Mark Leschly
                                            -------------------------------
                                            Name:  Mark Leschly
                                            Title: Managing Partner

                                         HUDSON TRUST

                                         By_____________________________
                                           Name:
                                           Title:

                                         SERIES B PURCHASERS:

                                         VENROCK ASSOCIATES

                                         By /s/ Anthony B. Evnin
                                            -------------------------------
                                            Name:  Anthony B. Evnin
                                            Title: General Partner

                                         VENROCK ASSOCIATES II, L.P.

                                         By /s/ Anthony B. Evnin
                                            -------------------------------
                                            Name:  Anthony B. Evnin
                                            Title: General Partner

                                       33
<PAGE>

                                         ALTA CALIFORNIA PARTNERS II, L.P.

                                         By: Alto California Management
                                             Partners II LLC, its General
                                             Manager

                                         By: /s/ Alix Marduel
                                            -------------------------------
                                            Name:  Alix Marduel
                                            Title: Member

                                         ALTA EMBARCADERO PARTNERS II LLC

                                         By /s/ Hilary Strain
                                            -------------------------------
                                            Name:  Hilary Strain
                                            Title: Under Power of Attorney

                                         GIMV

                                         By /s/ P. Van Beneden
                                            -------------------------------
                                            Name:  P. Van Beneden
                                            Title: Vice-President

                                         By /s/ Dirk Boogmans
                                            -------------------------------
                                            Name:  Dirk Boogmans
                                            Title: CEO

                                         GLSLP INVESTMENT I LTD.

                                         By /s/ Christopher W. Cochrane
                                            -------------------------------
                                            Name:  Christopher W. Cochrane
                                            Title: Director

                                         S.R. ONE LIMITED

                                         By /s/ Philip L. Smith
                                            -------------------------------
                                            Name:  Philip L. Smith
                                            Title: Vice President

                                         ALEXANDRIA REAL ESTATE
                                         EQUITIES, L.P.

                                         By /s/ Joel S. Marcus
                                            -------------------------------
                                            Name:  Joel S. Marcus
                                            Title: CEO

                                       34
<PAGE>

                                         SERIES C PURCHASERS:

                                         PHARMA/w HEALTH

                                         By /s/ Michael Sheffery
                                            -------------------------------
                                            Name:  Michael Sheffery
                                            Title: General Partner,
                                                   OrbiMed Advisors LLC

                                         FINSBURY WORLDWIDE
                                         PHARMACEUTICAL TRUST

                                         By /s/ Michael Sheffery
                                            -------------------------------
                                            Name:  Michael Sheffery
                                            Title: General Partner,
                                                   OrbiMed Advisors LLC

                                         EATON VANCE WORLDWIDE
                                         HEALTH SCIENCES PORTFOLIO

                                         By /s/ Michael Sheffery
                                            -------------------------------
                                            Name:  Michael Sheffery
                                            Title: General Partner,
                                                   OrbiMed Advisors LLC

                                         OXFORD BIOSCIENCE PARTNERS
                                         II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title:

                                         OXFORD BIOSCIENCE PARTNERS
                                         (GS-ADJUNCT) II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title:

                                         OXFORD BIOSCIENCE PARTNERS
                                         (BERMUDA) II L.P.

                                         By /s/ Jonathan J. Fleming
                                            -------------------------------
                                            Name:  Jonathan J. Fleming
                                            Title:

                                       35
<PAGE>

                                         OXFORD BIOSCIENCE PARTNERS
                                         (ADJUNCT) II L.P.

                                         By /s/ Jonathan J. Fleming
                                           ------------------------------
                                           Name:
                                           Title:

                                         ARTAL SERVICES N.V.

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

                                         VENROCK ASSOCIATES II, L.P.

                                         By /s/ Anthony B. Evnin
                                           ------------------------------
                                           Name:  Anthony B. Evnin
                                           Title: General Partner

                                         VENROCK ASSOCIATES

                                         By /s/ Anthony B. Evnin
                                           ------------------------------
                                           Name:  Anthony B. Evnin
                                           Title: General Partner

                            .            VENROCK ENTREPRENEUERS
                                         FUND, L.P.

                                         By: Venrock Management
                                           LLC, its General Partner

                                         By /s/ Anthony B. Evnin
                                           ------------------------------
                                           Name:  Anthony B. Evnin
                                           Title: General Partner

                                         ALTA CALIFORNIA PARTNERS II
                                         L.P.

                                         By /s/ Alix Marduel
                                           ------------------------------
                                           Name:  Alix Marduel
                                           Title: Member

                                       36
<PAGE>

                                         ALTA EMBARCADERO PARTNERS
                                         II LLC

                                         By
                                           ------------------------------

                                           Name:
                                           Title:

                                         MEDICA II INVESTMENT
                                         (ISRAEL), LP

                                         By
                                           ------------------------------

                                           Name:
                                           Title:

                                         MEDICA II INVESTMENT
                                         (INTERNATIONAL), LP

                                         By
                                           ------------------------------

                                           Name:
                                           Title:

                                         HEALTHCARE VENTURES V L.P.

                                         By
                                           ------------------------------

                                           Name:
                                           Title:

                                         GLSLP INVESTMENT I LTD.

                                         By /s/ Christopher W. Cochrane
                                           ------------------------------
                                           Name:  Christopher W. Cochrane
                                           Title: Director

                                         S.R. ONE LIMITED

                                         By /s/ Philip L. Smith
                                           ------------------------------
                                           Name:  Philip L. Smith, Ph.D.
                                           Title: Vice President

                                       37
<PAGE>

                                         RHO MANAGEMENT TRUST II

                                         By /s/ Rho Capital Partners,
                                           Inc., Investment Advisors

                                         By /s/ Mark Leschly
                                           ------------------------------
                                           Name:  Mark Leschly
                                           Title: Managing Partner

                                         GIMV

                                         By /s/ P. Van Beneden
                                           ------------------------------
                                           Name:  P. Van Beneden
                                           Title: Vice-President

                                           /s/ Dirk Boogmans
                                           ------------------------------
                                           Name: Dirk Boogmans
                                           Title: CEO

                                         ALEXANDRIA REAL ESTATE
                                         EQUITIES, L.P., a Delaware Limited
                                         liability company

                                         By: ARE-QRS Corp., a Maryland
                                             Corporation, general partner

                                         By /s/ Joel S. Marcus
                                           ------------------------------
                                           Joel S. Marcus, CEO

                                         MEMORIES PLUS, LLC

                                         By /s/ Robert DiVincent
                                           ------------------------------
                                           Name:  Robert DiVincent
                                           Title: Pres.

                                         M&G EQUITIES

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

                                         KENNETH J. NOVACK

                                         By /s/
                                           ------------------------------
                                           Name:
                                           Title:

                                         HUDSON TRUST

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

                                       38
<PAGE>

                                         LARRY ABRAMS

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

                                         SERIES D PURCHASERS:

                                         ARTAL SERVICES N.V.

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

                                         HARE & CO., FAO FINSBURY WORLDWIDE
                                         PHARMACEUTICAL TRUST PLC

                                         By: /s/ Michael Sheffery
                                           ------------------------------
                                            Name:  Michael Sheffery
                                            Title: General Partner,
                                                   Orbimed Advisors, LLC

                                         EATON VANCE WORLDWIDE HEALTH
                                         SCIENCES PORTFOLIO

                                         By: /s/ Michael Sheffery
                                           ------------------------------
                                            Name:  Michael Sheffery
                                            Title: General Partner,
                                                   Orbimed Advisors, LLC

                                         GIMV

                                         By: /s/ P. Van Beneden
                                           ------------------------------
                                            Name:  P. Van Beneden
                                            Title: Vice-President

                                         By: /s/ Dirk Boogmans
                                           ------------------------------
                                            Name:  Dirk Boogmans
                                            Title: CEO

                                         ADVIESBEHEER GIMV LIFE SCIENCES

                                         By: /s/ P. Van Beneden
                                           ------------------------------
                                            Name:   P. Van Beneden
                                            Title:  Vice-President

                                         By: /s/ Dirk Boogmans
                                           ------------------------------
                                            Name:  Dirk Boogmans
                                            Title: CEO
                                       39
<PAGE>

                                         GLS LP INVESTMENT I LTD.

                                         By: /s/ Christopher W. Cochrane
                                            -------------------------------
                                            Name:  Christopher W. Cochrane
                                            Title: Director

                                         BIOVEDA FUND PTE LTD
                                         By: BioVeda Capital Pte Ltd, its
                                             Investment Manager

                                         By: /s/ Damien Lim
                                             ------------------------------
                                             Name:  Damien Lim
                                             Title: General Partner

                                         HEALTHCARE VENTURES V L.P.

                                         By:_____________________________
                                            Name:
                                            Title:

                                         MEDICA II INVESTMENTS
                                         (P.F.)(ISRAEL) L.P.

                                         By:_____________________________
                                            Name:
                                            Title:

                                         MEDICA II INVESTMENTS (ISRAEL) L.P.

                                         By:_____________________________
                                            Name:
                                            Title:

                                         MEDIA II INVESTMENTS
                                         (INTERNATIONAL) L.P.

                                         By:_____________________________
                                            Name:
                                            Title:

                                       40
<PAGE>

                                         OXFORD BIOSCIENCE PARTNERS II L.P.
                                         By: OBP Management II L.P.

                                         By: /s/ Jonathan J. Fleming
                                             -----------------------------
                                             Name:
                                             Title:

                                         OXFORD BIOSCIENCE PARTNERS
                                         (BERMUDA) II L.P.
                                         By: OBP Management II (Bermuda)
                                         Limited Partnership

                                         By: /s/ Jonathan J. Fleming
                                             -----------------------------
                                             Name:
                                             Title:

                                         OXFORD BIOSCIENCE PARTNERS
                                         (ADJUNCT) II L.P.
                                         By: OBP Management II L.P.

                                         By: /s/ Jonathan J. Fleming
                                             -----------------------------
                                             Name:
                                             Title:

                                         OXFORD BIOSCIENCE PARTNERS
                                         (GS-ADJUNCT) II L.P.
                                         By: OBP Management II L.P.

                                         By: /s/ Jonathan J. Fleming
                                             -----------------------------
                                             Name:
                                             Title:

                                         OXFORD BIOSCIENCE PARTNERS II
                                         (ANNEX) L.P.

                                         By: OBP Management II L.P.

                                         By: /s/ Jonathan J. Fleming
                                             ------------------------------
                                             Name:
                                             Title:

                                       41
<PAGE>

                                         THE YASUDA ENTERPRISE
                                         DEVELOPMENT I LIMITED
                                         PARTNERSHIP

                                         By: /s/ Minoru Oka
                                             ----------------------------
                                             Name:  Minoru Oka
                                             Title: President and Representative
                                                    Director

                                         GRAY GHOST, LLC

                                         By: /s/ Philip Goelet
                                             ----------------------------
                                            Name:  Philip Goelet
                                            Title: Manager

                                         VENROCK ASSOCIATES

                                         By: /s/ Anthony B. Evnin
                                             -----------------------------
                                             Name:  Anthony B. Evnin
                                             Title: General Partner

                                         VENROCK ASSOCIATES II, L.P.

                                         By: /s/ Anthony B. Evnin
                                             ------------------------------
                                            Name:  Anthony B. Evnin
                                            Title: General Partner

                                         S.R. ONE, LIMITED

                                         By: /s/ Philip L. Smith
                                             ----------------------------
                                             Name:  Philip L. Smith, Ph.D.
                                             Title: Vice President

                                       42
<PAGE>

                                         MITSUBISHI CORPORATION

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

                                         MITSUBISHI INTERNATIONAL
                                         CORPORATION

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

                                         CZ VENTURE OPERATIONS, INC.

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

                                         /s/ Larry Abrams
                                         --------------------------------
                                         Larry Abrams

                                         /s/ Kenneth A. Sorensen, Ph.D.
                                         --------------------------------
                                         Kenneth A. Sorensen, Ph.D.

                                         /s/ Hans-Jurgen Hess, Ph.D.
                                         --------------------------------
                                         Hans-Jurgen Hess, Ph.D.

                                         MCHUGH, DIVINCENT, ALLESSI, INC.

                                         By: /s/ Julian Alessi
                                            -----------------------------
                                            Name:  Julian Alessi
                                            Title: Pres.

                                       43
<PAGE>

                                 SG COWEN VENTURES II, LP
                                 By: Societe Generale Investment
                                     Corporation, Its General Partner

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

                                 /s/ Alexander Scriabine, M.D.
                                 --------------------------------
                                 Alexander Scriabine, M.D.

                                 RHO MANAGEMENT TRUST II
                                 By: RHO Capital Partners, Inc.,
                                 Investment Advisor

                                 By: /s/ Mark Leschly
                                     -----------------------------
                                 Name:  Mark Leschly
                                 Title: Managing Partner

                                 YAMANOUCHI VENTURE CAPITAL, LLC

                                 By: /s/ Yoshitaka Yoneyama
                                     -----------------------------
                                     Name:  Yoshitaka Yoneyama
                                     Title: President and Chief
                                            Executive Officer

                                 ALTA CALIFORNIA PARTNERS II, L.P.
                                 By: Alta California Management Partners
                                 II, LLC, its General Partner

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

                                       44
<PAGE>

                                         ALTA EMBARCADERO PARTNERS II,
                                         LLC

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

                                         BIOMEDICINE L.P.
                                         By: International BM Biomedicine
                                         Holdings
                                             (Cayman) Ltd., Its General Partner

                                         By: /s/ Philip Sutcliffe
                                            -----------------------------
                                            Name:  Philip Sutcliffe
                                            Title: Director

                                         By: /s/ Julie Arnall
                                            -----------------------------
                                            Name:  Julie Arnall
                                            Title: Director

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

                                         NEW ENGLAND PARTNERS CAPITAL, L.P.
                                         By: NEP Capital, LLC, Its General
                                             Partner

                                         By: /s/ John Rousseau
                                            -----------------------------
                                            Name: John Rousseau
                                            Its:  President

                                         By:
                                            -----------------------------
                                            Name:
                                            Its:

                                       45
<PAGE>

                                         /s/ Steven Ostrofsky
                                         --------------------
                                         Steven Ostrofsky

                                         MIDDLEGATE VENTURES, LLC

                                         By: /s/ Albert Sutton
                                            ---------------------
                                            Name: Albert Sutton
                                            Title: Managing Partner

                                         /s/ David I. Wolsk
                                         --------------------
                                             DAVID I. WOLSK

                                         /s/ Kenneth J. Novack
                                         ---------------------
                                             Kenneth J. Novack

                                         /s/ David R. Novack
                                         ----------------------
                                             David R. Novack

                                         /s/ Helen Novack
                                         -----------------------
                                             Helen Novack

                                         /s/ Hyman Novack
                                         ------------------------
                                             Hyman Novack

                                         /s/ Natalie C. Scriabine
                                         -------------------------
                                             Natalie C. Scriabine

                                         /s/ Christine B. Scriabine
                                         ---------------------------
                                             Christine B. Scriabine

                                         /s/ Peter Smith
                                         --------------------------
                                             Peter Smith

                                       46
<PAGE>

                                         /s/Judith Smith
                                         -----------------------------
                                            Judith Smith

                                         /s/ Stephen White
                                         ------------------------------
                                             Stephen White

                                         /s/ Mariam White
                                         ------------------------------
                                             Mariam White

                                         SERIES ROCHE PURCHASER:

                                         HOFFMANN-LA ROCHE INC.

                                         By: /s/ Frederick C. Kentz III
                                             ----------------------------
                                             Name: Frederick C. Kentz III
                                             Title Vice President & Secretary

                                       47
<PAGE>

                                                                       EXHIBIT A

                                   Purchasers

                                       48

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