Document:

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                                                                   EXHIBIT 10.21

        THIS WARRANT AND THE SECURITIES ISSUABLE UPON THE EXERCISE HEREOF HAVE
        NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE
        "ACT"), OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR
        SALE, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED IN THE ABSENCE OF A
        REGISTRATION STATEMENT IN EFFECT WITH RESPECT TO THE SECURITIES UNDER
        SUCH ACT OR AN OPINION OF COUNSEL REASONABLY SATISFACTORY TO THE COMPANY
        THAT SUCH REGISTRATION IS NOT REQUIRED OR UNLESS SOLD PURSUANT TO AN
        EXEMPTION TO SUCH ACT.

                                                                      Void after
                                                              September 10, 2002

                        WARRANT TO PURCHASE 32,634 SHARES
                                 OF COMMON STOCK

                                       of

                                      IRORI

             INCORPORATED UNDER THE LAWS OF THE STATE OF CALIFORNIA

        THIS CERTIFIES THAT, for value received, Crosspoint Venture
Partners-1996, together with its successors and assigns (the "Holder") is
entitled to subscribe for and purchase, on the terms hereof, 32,634 shares of
Common Stock (the "Common Stock") of Irori, a California corporation (the
"Company"), subject to adjustment as provided herein.

        This Warrant is subject to the following terms and conditions:

        1. Compliance with Agreements. This Warrant is issued pursuant to a
letter agreement dated November 5, 1996 and an Agreement to Fix the Number of
Warrant Shares dated October 31, 1997, each between the Company and the Holder.

        2. Exercise of Warrant. The terms and conditions upon which this Warrant
may be exercised, and the Common Stock covered hereby (the "Warrant Stock") may
be purchased, are as follows:

               2.1 Term. Subject to the terms hereof, this Warrant may be
exercised at any time after the date hereof, or from time to time, in whole or
in part; provided, however, that in no event may this Warrant be exercised (the
"Exercise Date") later than 5:00 p.m. (Pacific Time) on the earlier of (a) the
close of business on September 10, 2002, (b) (i) the closing of the acquisition
of the Company by another entity by means of a transaction or series of related
transactions or (ii) the closing of the sale of all or substantially all of the
assets of the Company, unless the Company's shareholders of record prior to such
acquisition or sale shall hold at least

<PAGE>   2

fifty percent (50%) of the voting power of the acquiring or surviving entity
immediately after such acquisition or sale, or (c) the initial underwritten
public offering of the Company's common stock (the "Common Stock") (the
"Exercise Period"). At least ten (10) days prior to the occurrence of an event
specified in (a), (b) or (c) of this Section 2.1, the Company shall send to the
Holder notice of such event and that the Holder's rights under this Warrant
shall terminate upon the occurrence of such event; provided, that if the Company
sends such notice less than ten (10) days prior to the occurrence of such event,
the Holder's right to exercise this Warrant shall be extended for a period of
ten (10) days after the date of the notice, after which time the Holder's rights
under this Warrant shall terminate.

               2.2 Purchase Price. The per share purchase price for the shares
of Common Stock to be issued upon exercise of this Warrant shall be $0.20,
subject to adjustment as provided herein.

               2.3 Method of Exercise. The exercise of the purchase rights
evidenced by this Warrant shall be effected by (a) the surrender of the Warrant,
together with a duly executed copy of the form of a subscription attached
hereto, to the Company at its principal offices and (b) the delivery of the
purchase price by check or bank draft payable to the Company's order or by wire
transfer to the Company's account for the number of shares for which the
purchase rights hereunder are being exercised or any other form of consideration
approved by the Company's Board of Directors. Each exercise of this Warrant
shall be deemed to have been effected immediately prior to the close of business
on the day on which this Warrant shall have been surrendered to the Company as
provided herein or at such later date as may be specified in the executed form
of subscription, and at such time the person or persons in whose name or names
any certificate or certificates for shares of Common Stock shall be issuable
upon such exercise as provided herein shall be deemed to have become the holder
or holders of record thereof.

               2.4 Net Issuance.

                      2.4.1 Right to Convert. In addition to and without
limiting the rights of the Holder under the terms of this Warrant, the Holder
shall have the right to convert this Warrant or any portion thereof (the
"Conversion Right") into shares of Common Stock as provided in this Section 2.4
at any time or from time to time during the Exercise Period. Upon exercise of
the Conversion Right with respect to a particular number of shares subject to
the Warrant (the "Converted Warrant Shares"), the Company shall deliver to the
Holder (without payment by the Holder of any exercise price or any cash or other
consideration) that number of shares of fully paid and nonassessable Common
Stock computed using the following formula:

                             X = Y (Z - $0.20)
                                 -------------
                                        Z

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

                Y = the number of Converted Warrant Shares

                                       2
<PAGE>   3

                Z = the per share fair market value of the Common Stock on the
                    Conversion Date (as defined below)

The Conversion Right may only be exercised with respect to a whole number of
shares subject to the Warrant. No fractional shares shall be issuable upon
exercise of the Conversion Right, and if the number of shares to be issued
determined in accordance with the foregoing formula is other than a whole
number, the Company shall pay to the Holder an amount in cash equal to the fair
market value of the resulting fractional share on the Conversion Date (as
defined below). Shares issued pursuant to the Conversion Right shall be treated
as if they were issued upon the exercise of the Warrant.

                      2.4.2 Method of Exercise. The Conversion Right may be
exercised by the Holder by the surrender of the Warrant at the principal office
of the Company together with a written statement specifying that the Holder
thereby intends to exercise the Conversion Right and indicating the total number
of shares under the Warrant that the Holder is exercising through the Conversion
Right. Such conversion shall be effective upon receipt by the Company of the
Warrant together with the aforesaid written statement, or on such later date as
is specified therein (the "Conversion Date"). Certificates for the shares
issuable upon exercise of the Conversion Right and, if applicable, a new warrant
evidencing the balance of the shares remaining subject to the Warrant, shall be
issued as of the Conversion Date and shall be delivered to the Holder promptly
following the Conversion Date.

                      2.4.3 Determination of Fair Market Value. For purposes of
this Section 2.4, fair market value of a share of Common Stock on the Conversion
Date shall mean the fair market value as determined by the Board of Directors of
the Company.

        3. Limit on Rights of the Holder upon Exercise. The Holder acknowledges
and agrees that upon the exercise of this Warrant in full or in part, the
following provisions shall apply to the rights of the Holder as a holder of
Common Stock.

               3.1 Market Stand-Off Agreement. During the period of duration
(not to exceed 180 days) specified by the Company and an underwriter of Common
Stock or other securities of the Company, following the effective date of a
registration statement of the Company filed under the Act, the Holder shall not,
to the extent requested by the Company and such underwriter, directly or
indirectly sell, offer to sell, contract to sell (including, without limitation,
any short sale), grant any option to purchase or otherwise transfer or dispose
of (other than to transferees or donees who agree to be similarly bound) any
securities of the Company held by it at any time during such period except
Common Stock included in such registration; provided, however, that this Section
3.1 shall be applicable only to the first such registration statement of the
Company pursuant to which Common Stock (or other securities) of the Company are
to be sold on its behalf to the public in an underwritten offering, and (b) all
officers and directors of the Company and all other persons with registration
rights enter into similar agreements. In order to enforce the foregoing
covenant, the Company may impose stop-transfer instructions with respect to the
Common Stock of the Holder (and the shares or securities of every other person
subject to the foregoing restriction) until the end of such period.

                                       3
<PAGE>   4

        4. Adjustments to Conversion Price. The number and kind of shares of
Common Stock (or any shares of stock or other securities which may be) issuable
upon the exercise of this Warrant and the exercise price hereunder shall be
subject to adjustment from time to time upon the happening of certain events, as
follows:

               4.1 Dividends, Distributions, Stock Splits or Combinations. If
the Company shall at any time or from time to time after the date hereof make or
issue, or fix a record date for the determination of holders of Common Stock
entitled to receive, a dividend or other distribution payable in additional
shares of common or preferred stock (as the case may be), then and in each such
event the exercise price hereunder then in effect shall be decreased as of the
time of such issuance or, in the event such a record date shall have been fixed,
as of the close of business on such record date, by multiplying the exercise
price hereunder then in effect by a fraction: (a) the numerator of which shall
be the total number of shares of Common Stock (assuming the conversion of all
outstanding securities of the Company that are convertible into Common Stock and
the exercise of all options to purchase Common Stock or securities that are
convertible into Common Stock) issued and outstanding immediately prior to the
time of issuance or the close of business on such record date; and (b) the
denominator of which shall be the total number of shares of Common Stock
(assuming the conversion of all outstanding securities of the Company that are
convertible into Common Stock and the exercise of all options to purchase Common
Stock or securities that are convertible into Common Stock) issued and
outstanding immediately after the time of issuance or the close of business on
such record date. If the Company shall at any time subdivide the outstanding
shares of Common Stock, or if the Company shall at any time combine the
outstanding shares of Common Stock, then the exercise price hereunder
immediately shall be decreased proportionally (in the case of a subdivision) or
increased proportionally (in the case of a combination). Any such adjustment
shall become effective at the close of business on the date the subdivision or
combination becomes effective.

               4.2 Reclassification or Reorganization. If the Common Stock (or
any shares of stock or other securities which may be) issuable upon the exercise
of this Warrant shall be changed into the same or different number of shares of
any class or classes of stock, whether by capital reorganization,
reclassification or otherwise (other than a subdivision or combination of shares
or stock dividend provided for in Section 4.1 above, or a reorganization,
merger, consolidation or sale of assets provided for in Section 4.3 below), then
and in each such event the Holder shall be entitled to receive upon the exercise
of this Warrant the kind and amount of shares of stock and other securities and
property receivable upon such reorganization, reclassification or other change,
to which a holder of the number of shares of Common Stock (or any shares of
stock or other securities which may be) issuable upon the exercise of this
Warrant would have received if this Warrant had been exercised immediately prior
to such reorganization, reclassification or other change, all subject to further
adjustment as provided herein.

               4.3 Merger, Consolidation or Sale of Assets. If at any time or
from time to time there shall be a capital reorganization of the Common Stock
(other than a subdivision, combination, reclassification or exchange of shares
provided for elsewhere in this Section 4) or a merger or consolidation of the
Company with or into another corporation, or the sale of all or substantially
all of the Company's assets and properties to any other person or entity, then
as a

                                       4
<PAGE>   5

part of such reorganization, merger, consolidation or sale, provision shall be
made so that the Holder shall thereafter be entitled to receive upon the
exercise of this Warrant, the number of shares of stock or other securities or
property of the Company, or of the successor corporation resulting from such
reorganization, merger, consolidation or sale, to which a holder of the number
of shares of Common Stock (or any shares of stock or other securities which may
be) issuable upon the exercise of this Warrant would have received if this
Warrant had been exercised immediately prior to such reorganization, merger,
consolidation or sale.

               4.4 Notice of Adjustments and Record Dates. The Company shall
promptly notify the Holder in writing of each adjustment or readjustment of the
exercise price hereunder and the number of shares of Common Stock (or any shares
of stock or other securities which may be) issuable upon the exercise of this
Warrant. Such notice shall state the adjustment or readjustment and show in
reasonable detail the facts on which that adjustment or readjustment is based.
In the event of any taking by the Company of a record of the holders of Common
Stock for the purpose of determining the holders thereof who are entitled to
receive any dividend or other distribution, the Company shall notify the Holder
in writing of such record date at least twenty (20) days prior to the date
specified therein.

               4.5 No Impairment. The Company shall not avoid or seek to avoid
the observance or performance of any of the terms to be observed or performed
hereunder by the Company, but shall at all times in good faith assist in the
carrying out of all the provisions of this Warrant. Without limiting the
generality of the foregoing, the Company (a) shall at all times reserve and keep
available a number of its authorized shares of Common Stock, free from all
preemptive rights therein, which shall be sufficient to permit the exercise of
this Warrant and (b) shall take all such action as may be necessary or
appropriate in order that all shares of Common Stock as may be issued pursuant
to the exercise of this Warrant shall, upon issuance, be duly and validly
issued, fully paid and nonassessable and free from all taxes, liens and charges
with respect to the issue thereof.

        5. Replacement of Warrants. On receipt by the Company 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 of this Warrant, on delivery of an indemnity agreement reasonably
satisfactory in form and amount to the Company or, in the case of any such
mutilation, on surrender and cancellation of such Warrant, the Company at its
expense shall execute and deliver to the Holder, in lieu thereof, a new Warrant
of like tenor.

        6. Investment Intent. Unless a current registration statement under the
Securities Act of 1933, as amended, shall be in effect with respect to the
securities to be issued upon exercise of this Warrant, the Holder, by accepting
this Warrant, covenants and agrees that, at the time of exercise hereof, and at
the time of any proposed transfer of any securities acquired upon exercise
hereof, the Holder shall deliver to the Company a written statement that the
securities acquired by the Holder upon exercise hereof are for the own account
of the Holder for investment and are not acquired with a view to, or for sale in
connection with, any distribution thereof (or any portion thereof) and with no
present intention (at any such time) of offering or distributing such securities
(or any portion thereof).

                                       5
<PAGE>   6

        7. No Rights or Liability as a Shareholder. This Warrant does not
entitle the Holder hereof to any voting rights or other rights as a shareholder
of the Company. No provisions hereof, in the absence of affirmative action by
the Holder to purchase Common Stock, and no enumeration herein of the rights or
privileges of the Holder, shall give rise to any liability of the Holder as a
shareholder of the Company.

        8. Miscellaneous.

               8.1 Transfer of Warrant. This Warrant shall not be transferable
or assignable in any manner and no interest shall be pledged or otherwise
encumbered by Holder without the express written consent of the Company, and any
such attempted disposition of this Warrant or any portion hereof shall be of no
force or effect.

               8.2 Titles and Subtitles. The titles and subtitles used in this
Warrant are for convenience only and are not to be considered in construing or
interpreting this Warrant.

               8.3 Notices. Any notice required or permitted under this Warrant
shall be given in writing.

               8.4 Attorneys' Fees. If any action at law or in equity is
necessary to enforce or interpret the terms of this Warrant, the prevailing
party shall be entitled to reasonable attorneys' fees, costs and disbursements
in addition to any other relief to which such party may be entitled.

               8.5 Amendments and Waivers. Any term of this Warrant may be
amended and the observance of any term of this Warrant may be waived (either
generally or in a particular instance and either retroactively or
prospectively), with the written consent of the Company and the holders of
Warrants representing together the right to purchase at least fifty-one percent
(51%) of all of the Common Stock of the Company subject to purchase pursuant to
the original 32,634-share Warrants. Any amendment or waiver effected in
accordance with this Section 8.5 shall be binding upon the Holder of this
Warrant (and of any securities into which this Warrant is convertible), each
future holder of all such securities, and the Company.

               8.6 Severability. If one or more provisions of this Warrant are
held to be unenforceable under applicable law, such provision shall be excluded
from this Warrant and the balance of the Warrant shall be interpreted as if such
provision were so excluded and shall be enforceable in accordance with its
terms.

               8.7 Governing Law. This Warrant shall be governed by and
construed and enforced in accordance with the laws of the State of California,
without giving effect to its conflicts of laws principles.

                [REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]

                                       6
<PAGE>   7

               8.8 Counterparts. This Warrant may be executed in one or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

Date: May 20, 1998                      IRORI, a California corporation

                                        By: /s/ Jack Fitzpatrick
                                            -----------------------------------
                                            Jack Fitzpatrick
                                            Chief Financial Officer

ACKNOWLEDGED AND AGREED:

CROSSPOINT VENTURE PARTNERS-1996

By: /s/ Donald Milder
    ----------------------------
Name: Don Milder

Its: General Partner

<PAGE>   8

                                   SCHEDULE 1

                              FORM OF SUBSCRIPTION

                   (To be signed only on exercise of Warrant)

To: IRORI

        The undersigned, the holder of the Warrant attached hereto, hereby
irrevocably elects to exercise the purchase rights represented by such Warrant
for, and to purchase thereunder, * shares of Common Stock of IRORI, and herewith
makes payment of $_________ therefor, and requests that the certificates for
such shares be issued in the name of, and delivered to ________________________,
whose address is _________________________________________.

                                        ________________________________________
                                        (Signature must conform in all respects
                                        to name of the Holder as specified on
                                        the face of the Warrant)

                                        ________________________________________
                                                      (Print Name)

                                        ________________________________________
                                                       (Address)

Dated: ________________

--------------
        * Insert here the number of shares as to which the Warrant is being
exercised.<PAGE>   1
                                                                   EXHIBIT 10.22

                                PLEDGE AGREEMENT

        In consideration of the loan which Discovery Partners International,
Inc., a California corporation (the "Company") having its principal offices at
11149 North Torrey Pines Road, La Jolla, CA 92037, has on this day extended to
the undersigned Riccardo Pigliucci and as security for the payment of that
certain promissory note ("Note") in the principal sum of $172,000.00 payable to
the Company or order which the undersigned has on this day executed to evidence
such loan, the undersigned hereby grants the Company a security interest in, and
pledges with the Company, the following securities and other property:

        (i) 430,000 shares of the Company's Common Stock represented by share
certificate no. 54 (the "Shares");

        (ii) any and all new, additional or different securities subsequently
distributed with respect to the shares identified in (i) above which are to be
delivered to and deposited with the Company Secretary pursuant to the
requirements of Section 3 of this Agreement:

        (iii) any and all other property and money which is delivered to or
comes into possession of the Company pursuant to the terms and provisions of
this Agreement; and

        (iv) the proceeds of any sale, exchange or disposition of the property
and securities described in (i), (ii), or (iii) above.

        All securities, property and money so assigned, transferred to and
pledged with the Company shall be herein referred to as the "Collateral." The
Company shall hold the Collateral in accordance with the following terms and
provisions:

        1. Warranties. The undersigned hereby warrants that the undersigned is
the owner of the Collateral and has the right to pledge the Collateral and that
the Collateral is free from liens, adverse claims and other security interests
(other than the Company's repurchase rights against the Shares).

        2. Rights and Powers. The Company may, without obligation to do so,
exercise at any time and from time to time one or more of the following rights
and powers with respect to any or all of the collateral:

             a. accept in its discretion other property of the undersigned in
exchange for all or part of the Collateral and release Collateral to the
undersigned to the extent necessary to effect such exchange, and in such event
the money, property or securities received in the exchange shall be held by the
Company as substitute security for the Note and all other indebtedness secured
hereunder;

             b. perform such acts as are necessary to preserve and protect the
Collateral and the rights, powers and remedies granted with respect to such
Collateral by this Agreement; and

<PAGE>   2

             c. receive, endorse and give receipt for, or collect by legal
proceedings or otherwise, dividends or other distributions made or paid with
respect to the Collateral, provided and only if there exists at the time an
outstanding event of default under Section 8 of this Agreement.

             Expenses reasonably incurred in the exercise of such rights and
powers shall be payable by the undersigned and form part of the indebtedness
secured hereunder as provided in Section 10.

             So long as there exists no event of default under Section 8 of this
Agreement, the undersigned may exercise all shareholder voting rights and be
entitled to receive any cash distributions with respect to the Collateral.
Accordingly, until such time as an event of default occurs under this Agreement,
all shareholder meeting notices and other shareholder materials which the
Company receives with respect to the Collateral shall be delivered to the
undersigned at the address indicated below.

        3. Duty to Deliver. Any Shares and any new, additional or different
securities which may now or hereafter become distributable with respect to the
Collateral by reason of a stock dividend, stock split or reclassification of the
capital stock of the Company or by reason of a merger, consolidation or other
reorganization affecting the capital structure of the Company shall, upon
receipt by the undersigned, be promptly delivered to and deposited with the
Company Secretary as part of the Collateral hereunder. Such securities shall be
accompanied by one or more properly endorsed stock power assignments.

        4. Care of Collateral. The Company shall exercise reasonable care in the
custody and preservation of the Collateral, but shall have no obligation to
initiate any action with respect to, or otherwise inform the undersigned of, any
conversion, call, exchange right, preemption right, subscription right, purchase
offer or other right or privilege relating to or affecting the Collateral. The
Company shall have no duty to preserve the rights of the undersigned against
adverse claims or to protect the Collateral against the possibility of a decline
in market value. The Company shall not be obligated to take any action with
respect to the Collateral requested by the undersigned unless the request is
made in writing and the Company determines that the requested action will not
unreasonably jeopardize the value of the Collateral as security for the Note and
other indebtedness secured hereunder.

             The Company may at any time deliver all or part of the Collateral
to the undersigned, and the receipt thereof by the undersigned shall constitute
a complete and full acquittance for the Collateral so delivered. The Company
shall accordingly be discharged from any further liability or responsibility for
the delivered Collateral.

        5. Payment of Taxes and Other Charges. The undersigned shall pay, prior
to the delinquency date, all taxes, liens, assessments and other charges against
the Collateral, and in the event of the undersigned's failure to do so, the
Company may at its election pay any or all of such taxes and charges without
contesting the validity of legality thereof. The payments so made shall become
part of the indebtedness secured hereunder and shall be payable immediately by
the undersigned, without demand, and until paid shall bear interest at the same
rate as provided for in the Note.

                                       2
<PAGE>   3

        6. Transfer of Collateral. In connection with the transfer or assignment
of the Note (whether by negotiation, discount or otherwise), the Company may
transfer all or any part of the Collateral, and the transferee shall thereupon
succeed to all the rights, powers and remedies granted the Company hereunder
with respect to the Collateral so transferred. Upon such transfer, the Company
shall be fully discharged from all liability and responsibility for the
transferred Collateral.

        7. Release of Collateral. Provided all indebtedness secured hereunder
shall at the time have been paid in full, any Shares and other Collateral shall
be released from pledge and returned to the undersigned.

        8. Events of Default. The occurrence of one or more of the following
events shall constitute an event of default under this Agreement:

             a. failure of the undersigned to pay when due under the Note
(either at scheduled maturity or upon acceleration) any principal or accrued
interest;

             b. the occurrence of any event of default specified in the Note;

             c. the failure of the undersigned to perform any obligation imposed
upon the undersigned by reason of this Agreement; or

             d. the breach of any warranty of the undersigned contained in this
Agreement.

             Upon the occurrence of any such event of default, the Company may,
at its election, declare the Note and all other indebtedness secured hereunder
to become immediately due and payable and may exercise any or all of the rights
and remedies granted to a secured party under the provisions of the California
Uniform Commercial Code (as now or hereafter in effect), including (without
limitation) the power to dispose of the Collateral by public or private sale or
to accept the Collateral in full payment of the Note and all other indebtedness
secured hereunder. Any proceeds realized from the disposition of the Collateral
pursuant to the power of sale hereby granted to the Company shall first be
applied to the payment of expenses incurred by the Company in connection with
the disposition, and the balance shall be applied to the payment of the Note and
any other indebtedness secured hereunder in such order of application as the
Company shall deem appropriate. Any surplus proceeds shall be paid over to the
undersigned. In the event such proceeds prove insufficient to satisfy all
indebtedness secured hereunder, then the undersigned shall be personally liable
for the deficiency.

        9. Other Remedies. The rights, powers and remedies granted to the
Company pursuant to the provisions of this agreement shall be in addition to all
rights, powers and remedies granted to the Company under any statute or rule of
law. Any forbearance, failure or delay by the Company in exercising any right,
power or remedy under this Agreement shall not be deemed to be a waiver of such
right, power or remedy. Any single or partial exercise of any right, power or
remedy under this Agreement shall not preclude the further exercise thereof, and
every right, power and remedy of the Company under this Agreement shall continue
in full force and effect until such right, power or remedy is specifically
waived by an instrument executed by the Company.

                                       3
<PAGE>   4

        10. Costs and Expenses. All costs and expenses (including reasonable
attorneys' fees) incurred by the Company in the exercise or enforcement of any
right, power, or remedy granted it under this Agreement shall become part of the
indebtedness secured hereunder and shall be payable immediately by the
undersigned, without demand, and until paid shall bear interest at the maximum
rate permitted by law.

        11. Applicable Law. This Agreement shall be governed by and construed in
accordance with the internal laws of the State of California and shall be
binding upon the executors, administrators, heirs and assigns of the
undersigned.

        12. Severability. If any provision of this Agreement is held to be
invalid under applicable law, then such provision shall be ineffective only to
the extent of such invalidity, and neither the remainder of such provision nor
any other provisions of this Agreement shall be affected thereby.

        13. Amendment. This Agreement may not be amended except in a writing
signed by the undersigned and the Company.

        14. Entire Agreement. This Agreement constitutes the entire agreement of
the undersigned and the Company with regard to the subject matter hereof, and
supersedes all prior or contemporaneous discussions, negotiations,
understandings and agreements, whether written or oral.

        IN WITNESS WHEREOF, this Pledge Agreement has been executed by the
undersigned on this 30th day of November, 1998.

                                       /s/ Riccardo Pigliucci
                                       --------------------------------------
                                       Riccardo Pigliucci

                            Address:
                                       --------------------------------------

                                       --------------------------------------

                                       --------------------------------------
Agreed to and Accepted by:

Discovery Partners International, Inc.

By: /s/ Jack Fitzpatrick
    ---------------------------------
    Jack Fitzpatrick
    Chief Financial Officer

                                       4

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