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                                                                    EXHIBIT 10.5

                            FIRST AMENDMENT TO LEASE

         This First Amendment to Lease ("FIRST AMENDMENT") is made as of
February 4, 2000, by and among ARE - 100 PHILIPS PARKWAY, LLC, a Delaware
limited liability company ("LANDLORD"), and MEMORY PHARMACEUTICALS CORP., a
Delaware corporation ("TENANT")

                                    RECITALS

         A. Landlord is the landlord and Tenant is the tenant under a Lease
dated as of June 4, 1999 as amended by letter agreement dated June 16, 1999,
between Landlord and Tenant (collectively the "LEASE"), under which Tenant
leases approximately 32,000 rentable square feet of space in the building
commonly known as 100 Philips Parkway, Montvale, New Jersey. Capitalized terms
used herein without definition shall have the meanings defined for such terms in
the Lease.

         B. Landlord and Tenant desire to amend the Lease to modify the
description of Landlord Work, the amount and allocation between Phase I and
Phase II of the TI Allowance provided by Landlord, to delay the Rent
Commencement Date by one month and to address other matters which have arisen
since the execution of the Lease.

                                    AGREEMENT

         Now, therefore, the parties hereto agree that the Lease is hereby
amended as follows:

1.       APPROVALS.

         (a)      Landlord hereby approves The Hillier Group as Tenant's
architect (the "ARCHITECT"). Subject to receipt of and Landlord's reasonable
satisfaction with a payment and performance bond from a surety with a Best's
Rating of A+ or higher, or equivalent, with respect to the work to be done by
McHugh, DiVicent & Alessi, Inc. ("MDA"). Landlord will approve MDA as Tenant's
general contractor ("CONTRACTOR"). Tenant shall deliver or cause MDA to deliver
such payment and performance bond before the commencement of any work by or on
behalf of Tenant in the Premises. All other engineering consultants, architects,
designers and subcontractors responsible for construction of Tenant's Work shall
be selected by Tenant, and approved by Landlord in Landlord's reasonable
discretion as provided in the Work Letter.

         (b)      Landlord hereby approves the design layout described in the
drawings dated as of January 10, 2000, prepared by the Architect (the "LAYOUT").
Upon submission of Design Drawings complying with the requirements of Section
2.2 of the Work Letter, Landlord shall not disapprove any matter shown in such
Design Drawings which are consistent with the Layout.

2.       MECHANICAL ROOM. Subject to receipt and review of proposed plans and
specifications for any portion of Tenant's HVAC system proposed to be located in
the common area mechanical room located on the ground floor of the Project (the
"COMMON AREA MECHANICAL ROOM") and provided that such proposed use of the Common
Area Mechanical Room does not materially interfere with the maintenance and
operation of the Project, in Landlord's sole discretion, Tenant may locate
certain mechanical portions of its HVAC system in such Common Area Mechanical
Room; provided

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however that no existing machinery, equipment or duct work shall be relocated,
ingress and egress to such Common Area Mechanical Room and access to the
existing machinery, equipment and duct work shall not be blocked or in any way
impaired, and not more than 70% of the ground floor of the Common Area
Mechanical Room nor 50% of the combined ground floor and mezzanine floor of the
Common Area Mechanical Room shall be used by Tenant. Landlord agrees that Tenant
shall not be required to pay any additional rent as a result of any such use of
the Common Area Mechanical Room for such HVAC equipment. Tenant's access to the
Common Area Mechanical Room may be restricted in Landlord's reasonable
discretion. Upon no less than one business day's prior notice from Tenant to
Landlord, which notice may be made by telephone, facsimile or electronic mail,
Tenant may have reasonable access to the Common Area Mechanical Room as may be
required for the installation, maintenance and repair of such system.

3.       TI ALLOWANCE. Section 4(a) of the Lease is hereby amended by deleting
the phrase "up to a maximum increase of $180 per square foot of Rentable Area of
the Premises," replacing the figure $4,700,000 with the figure $4,950,000,
deleting the phrase "and not to exceed a TI Allowance of $3,500,000 for Phase I
of the Premises" from the first sentence thereof and deleting the last row of
the chart set forth therein and adding the following rows to such chart:

<TABLE>
<CAPTION>
    TI Allowance            Increase in Base Rent         Initial Base Rent
    ------------            ---------------------         -----------------
<S>                         <C>                           <C>
      $205.00                       $1.40                     $37.30/RSF
Each $10 thereafter                 $1.40
</TABLE>

The entire $4,950,000 TI Allowance may be drawn down by Tenant in connection
with Phase I and the entire $75,000 Administrative Rent described in Section 5.1
of the Work Letter shall be paid in connection with Tenant's Work for Phase I.
Any portion of the TI Allowance not used by Tenant in connection with Phase I
may be drawn down by Tenant in connection with Phase II and there shall be no
Administrative Rent charged by Landlord in connection with Tenant's Work for
Phase II.

4.       RENT COMMENCEMENT DATES. The second paragraph of Section 2 of the Lease
is hereby amended and restated as follows:

                  The "RENT COMMENCEMENT DATE" shall be earliest of: (i) the
         date Tenant's Work for Phase I is Substantially Complete, and (ii) June
         1, 2000. On the Rent Commencement Date, Tenant shall pay Base Rent for
         the entire Premises. Such Rent shall be calculated for Phase I of the
         Premises on the basis of the actual TI Allowance provided by Landlord
         to Tenant for Phase I as set forth in Section 4(a) below, and shall be
         calculated at $10.00 per rentable square foot for any portion of the
         Premises not included in Phase I. On the earlier of (i) December
         1, 2001, or (ii) the date Tenant's Work for Phase II is complete, the
         Rent for the balance of the Premises shall be adjusted to the amount
         set forth in Section 4(a) below on the basis of the actual TI Allowance
         provided by Landlord to Tenant for Phase II; provided, however that in
         no event shall such Rent be less than $13.00 per rentable square foot
         per annum. Upon request of Landlord, Tenant shall execute and deliver a
         written acknowledgment of the Rent Commencement Date and the expiration
         date of the Term when such are established and shall attach the
         acknowledgment to this Lease as part

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         of Exhibit D; provided, however. Tenant's failure to execute and
         deliver such acknowledgment shall not affect Landlord's rights
         hereunder.

In addition, each reference in the Work Letter to the date "May 1, 2000" is
hereby changed to "June 1, 2000."

5.       LANDLORD'S WORK. Landlord and Tenant acknowledge and agree that:

                  (i)      All of Landlord's Work required for the commencement
                           and completion of Tenant's Work has been completed;

                  (ii)     Landlord has heretofore agreed to provide to Tenant
                           electric service of up to 2,000 amperes demand as
                           shown to be required by Tenant pursuant to a stamped,
                           sealed electrical load letter (or other document
                           reasonably satisfactory to Landlord) certified to
                           Landlord from Tenant's electrical engineer. Landlord
                           hereby agrees that such service shall be in existence
                           at the Project on or before May 1, 2000, subject to
                           Force Majeure Delay. For each day that such service
                           does not exist at the Project as required hereunder
                           for any reason other than Force Majeure Delay, the
                           Rent Commencement Date shall be delayed beyond June
                           1, 2000 the same number of days;

                  (iii)    Subject to receipt and approval of proposed plans and
                           specifications therefor, Landlord hereby grants
                           Tenant the right to erect, use and maintain, conduits
                           and wire from the Premises through the common areas
                           of the Project to the Project electrical room;

                  (iv)     In addition to the TI Allowance, Landlord shall
                           provide to Tenant an allowance of $10,000 for the
                           purpose solely of installing conduit and wire (and/or
                           reusing existing conduit and wire) from the Project
                           electrical room to the Premises central
                           mechanical/electrical room. Said allowance shall be
                           paid against invoices showing the completion of such
                           work;

                  (v)      Tenant's Work has not been delayed by reason of the
                           performance of Landlord's Work; and

                  (vi)     Tenant hereby accepts the Premises for the purpose of
                           construction of Tenant's Work.

Landlord and Tenant further agree that Landlord may delay certain exterior
improvements as described on Schedule A-1, attached hereto and incorporated
herein by this reference, until such work may be completed without undue
conflict with the work of completing Tenant's Work or with adverse winter
weather conditions; provided that such delayed exterior work shall be completed
no later than the later of June 1, 2000, or issuance of Tenant's occupancy
permit, subject in each case to Force Majeure Delays.

6.       EXHIBIT F. Attached hereto is Exhibit F to the Lease, which Exhibit F
may be amended in the future to include additional items agreed to by Landlord.

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7.       MISCELLANEOUS.

         (a)      This Amendment is the entire agreement between the parties
with respect to the subject matter hereof and supersedes all prior and
contemporaneous oral and written agreements and discussions with respect to the
matters addressed herein. This Amendment may be amended only by an agreement in
writing, signed by the parties hereto.

         (b)      This Amendment is binding upon and shall inure to the benefit
of the parties hereto, their respective agents, employees, representatives,
officers, directors, divisions, subsidiaries, affiliates, assigns, heirs,
successors in interest and shareholders.

         (c)      This Amendment may be executed in any number of counterparts,
each of which shall be deemed an original, but all of which when taken together
shall constitute one and the same instrument. The signature page of any
counterpart may be detached therefrom without impairing the legal effect of the
signature(s) thereon provided such signature page is attached to any other
counterpart identical thereto except having additional signature pages executed
by other parties to this Amendment attached thereto.

         (d)      Except as amended and/or modified by this Amendment, the Lease
is hereby ratified and confirmed and all other terms of the Lease shall remain
in full force and effect, unaltered and unchanged by this Amendment. In the
event of any conflict between the provisions of this Amendment and the
provisions of the Lease, the provisions of this Amendment shall prevail. Whether
or not specifically amended by this Amendment, all of the terms and provisions
of the Lease are hereby amended to the extent necessary to give effect to the
purpose and intent of this Amendment.

         (e)      As a condition to the effectiveness of this Amendment, Tenant
shall issue to Landlord Warrants and other consideration pursuant to a separate
letter agreement.

         IN WITNESS WHEREOF, this First Amendment to Lease has been duly
executed and delivered by Landlord and Tenant as of the date first above
written.

                                   TENANT:

                                   MEMORY PHARMACEUTICALS CORP.,
                                   a Delaware corporation

                                   By:  /s/ Joanne Leonard
                                        --------------------------------
                                   Its: CFO

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                                   LANDLORD:

                                   ARE - 100 PHILLIPS PARKWAY, LLC,
                                   a Delaware limited liability company

                                   By: ALEXANDRIA REAL ESTATE EQUITIES, L.P., a
                                       Delaware limited partnership, managing
                                       member

                                       By: ARE-QRS CORP., a Maryland
                                           corporation, general partner

                                           By:  /s/ Lynn Anne Shapiro
                                                --------------------------------
                                           Its: LYNN ANNE SHAPIRO
                                                GENERAL COUNSEL

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                           SCHEDULE A-1 TO WORK LETTER

The following exterior improvements are required by the Borough of Montvale, New
Jersey pursuant to its adoption of the Resolution to Approve Landlord's Site
Plan Amendment Application on December 7, 1999, and may be delayed by Landlord,
in its sole discretion, until the later of June 1, 2000, or issuance of Tenant's
occupancy permit, subject in each case to Force Majeure Delays:

1.  Restripe and widen impervious coverage of parking and drive areas where
    required.

2.  Plant five (5) eight foot tall white pines, or equivalent species in
    required locations.

3.  Add railroad tie islands and plant materials at the median of the south
    parking area where required.

4.  Substitute wood guardrails in lieu of wood bollards at areas required.

5.  Add three (3) stop signs and one (1) do not enter sign where required.

6.  Demolish existing railroad tie planter in north parking lot. Reinstall new
    railroad ties and re-pave areas where needed.

7.  Construct dumpster enclosure with two (2) twelve foot (12') wide gates.

8.  Demolish existing concrete sidewalks and curbs and install two (2) dropped
    curbs at driveway main entrance and add concrete sidewalk where required.

9.  Electric work for six (6) site light bollards, six (6) glare shields for
    site lighting, and fire alarm light.

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                                    EXHIBIT F

Rack Washer

Autoclaves

Glass Washer

Generator

Bottle Washer/Filler

Walk-in Refrigerator

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