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                                                                  EXHIBIT 10.64



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                  LIMITED LIABILITY COMPANY OPERATING AGREEMENT

                                       OF

                        CHIROCHEM DISCOVERY SERVICES LLC,

                     A CALIFORNIA LIMITED LIABILITY COMPANY

                                DECEMBER 1, 1998


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


NEITHER THE UNITED STATES SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE
REGULATORY AUTHORITY HAS APPROVED OR DISAPPROVED THIS LIMITED LIABILITY COMPANY
OPERATING AGREEMENT OR THE LIMITED LIABILITY COMPANY MEMBERSHIP INTERESTS
("INTERESTS") PROVIDED FOR HEREIN. ANY REPRESENTATION TO THE CONTRARY IS
UNLAWFUL.

THE INTERESTS HAVE NOT BEEN REGISTERED UNDER THE UNITED STATES SECURITIES ACT OF
1933, AS AMENDED, INCLUDING THE RULES AND REGULATIONS THEREUNDER (THE
"SECURITIES ACT"), AND THE COMPANY IS UNDER NO OBLIGATION TO REGISTER THE
INTERESTS UNDER THE SECURITIES ACT IN THE FUTURE.

AN INTEREST MAY NOT BE SOLD, PLEDGED, HYPOTHECATED OR OTHERWISE TRANSFERRED IN
THE ABSENCE OF AN EFFECTIVE REGISTRATION UNDER THE SECURITIES ACT OR AN OPINION
OF COUNSEL SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.
ADDITIONAL RESTRICTIONS ON THE TRANSFER OF INTERESTS ARE CONTAINED IN ARTICLE XI
OF THIS AGREEMENT. BASED UPON THE FOREGOING, EACH ACQUIRER OF AN INTEREST MUST
BE PREPARED TO BEAR THE ECONOMIC RISK OF INVESTMENT THEREIN FOR AN INDEFINITE
PERIOD OF TIME.





*** Certain confidential portions of this Exhibit were omitted by means of
blackout of the text (the "Mark"). This Exhibit has been filed separately with
the Secretary of the Commission without the Mark pursuant to the Company's
Application Requesting Confidential Treatment under Rule 24b-2 under the Act.

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                                TABLE OF CONTENTS


<TABLE>
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ARTICLE I FORMATION OF LIMITED LIABILITY COMPANY...............................1
        1.1    Formation.......................................................1
        1.2    Name and Principal Place of Business............................1
        1.3    Office for Records and Agent for Service of Process.............1
        1.4    Agreement.......................................................1
        1.5    Purposes........................................................1
        1.6    Definitions.....................................................2
        1.7    Term............................................................2

ARTICLE II MEMBERSHIP; UNITS...................................................3
        2.1    Members.........................................................3
        2.2    Representations and Warranties..................................3
        2.3    Units...........................................................4
        2.4    Substitute Members..............................................4
        2.5    Resignation or Withdrawal of a Member...........................4
        2.6    Dissociation of a Member........................................5
        2.7    Rights of Dissociated Member....................................5
        2.8    No Contracts....................................................5
        2.9    Other Ventures and Activities...................................5
        2.10   Member Expenses.................................................6
        2.11   Member Compensation.............................................6
        2.12   Tax Matters.....................................................6

ARTICLE III CONTRIBUTIONS TO CAPITAL...........................................7
        3.1    Capital Commitments.............................................7
        3.2    Capital Contributions...........................................7
        3.3    Issuance of Units...............................................7
        3.4    Additional Contributions and Loans..............................7
        3.5    Interest........................................................8
        3.6    Failure To Make Capital Contribution............................8

ARTICLE IV ACTION BY MEMBERS...................................................9
        4.1    Meetings of Members.............................................9
        4.2    Voting Standard.................................................9
</TABLE>



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                                TABLE OF CONTENTS
                                   (CONTINUED)


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ARTICLE V MANAGEMENT; RESTRICTIONS; EXPENSES..................................9 
        5.1    Management by Board of Managers................................9 
        5.2    Number; Vacancies..............................................10
        5.3    Meetings of Managers...........................................10
        5.4    Voting Procedures..............................................11
        5.5    Action Without Meeting.........................................12
        5.6    Normal Functions of Board of Managers..........................12
        5.7    Conflict of Interest Matters...................................13
        5.8    Loss of Vote...................................................13
        5.9    Manager Compensation and Expenses..............................14

ARTICLE VI NOTICES............................................................14
        6.1    Notices........................................................14
        6.2    Waiver of Notice...............................................14

ARTICLE VII OFFICERS..........................................................15
        7.1    Chair..........................................................15
        7.2    Other Officers.................................................15
        7.3    Contracts......................................................15

ARTICLE VIII ACCOUNTING AND RECORDS...........................................16
        8.1    Financial Statements and Records...............................16
        8.2    Inspection of Books............................................16
        8.3    Annual and Monthly Reports.....................................16
        8.4    Tax Returns....................................................16

ARTICLE IX ALLOCATIONS........................................................17
        9.1    Allocation of Net Income or Net Loss...........................17
        9.2    Partnership Status.............................................17

ARTICLE X DISTRIBUTIONS.......................................................17
        10.1   Allocation of Distributions among Holders of Units.............17
        10.2   Discretionary Distributions....................................17
        10.3   No Other Withdrawals...........................................17
</TABLE>



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                                TABLE OF CONTENTS


<TABLE>
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ARTICLE XI TRANSFERS..........................................................18
        11.1   Transfer of Units..............................................18
        11.2   Transfer Void..................................................18
        11.3   Transfer of Control of Member..................................18
        11.4   Transfer of Control of Affiliates..............................18
        11.5   Acquisition of ***.............................................19

ARTICLE XII BUY-SELL PROVISION................................................19
        12.1   Application....................................................19
        12.2   Procedures.....................................................19

ARTICLE XIII INDEMNIFICATION AND LIMITATION OF LIABILITY......................20
        13.1   Indemnification................................................20
        13.2   Limitation of Liability........................................22

ARTICLE XIV TERMINATION.......................................................22
        14.1   Termination....................................................22
        14.2   Continuance of the Company.....................................22
        14.3   Authority to Wind Up...........................................23
        14.4   Winding Up and Certificate of Cancellation.....................23
        14.5   Distribution of Assets.........................................23
        14.6   Effect of Termination..........................................24

ARTICLE XV DEFINITIONS........................................................24
        15.1   Definitions....................................................24

ARTICLE XVI DISPUTE RESOLUTION................................................28
        16.1   Board of Managers Deadlock.....................................28
        16.2   Arbitration....................................................29
</TABLE>



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                                TABLE OF CONTENTS
                                  (Continued)

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ARTICLE XVII MISCELLANEOUS....................................................29
        17.1   Amendment......................................................29
        17.2   Withholding Taxes..............................................29
        17.3   Publicity......................................................30
        17.4   Further Assurances.............................................30
        17.5   Construction...................................................30
        17.6   Time...........................................................30
        17.7   Headings.......................................................31
        17.8   Severability...................................................31
        17.9   Variation of Terms.............................................32
        17.10  Governing Law..................................................32
        17.11  Binding Effect.................................................32
        17.12  Entire Agreement...............................................32
        17.13  Counterparts...................................................32
</TABLE>



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                        CHIROCHEM DISCOVERY SERVICES LLC

                            LIMITED LIABILITY COMPANY
                               OPERATING AGREEMENT


        THIS LIMITED LIABILITY COMPANY OPERATING AGREEMENT, dated December 1,
1998, is by and between the persons listed on the signature page hereto as
members of ChiroChem Discovery Services LLC, a California limited liability
company (the "Company").

                                    ARTICLE I
                     FORMATION OF LIMITED LIABILITY COMPANY

        1.1 Formation. The Members have formed the Company pursuant to the
Beverly-Killea Limited Liability Company Act (as amended, the "Act") by causing
articles of organization ("Articles") for the Company to be filed with the
California Secretary of State and entering into this Agreement. By this
Agreement the Members intend to establish rules and regulations governing
ownership and control of the Company.

        1.2 Name and Principal Place of Business. Unless and until changed in
accordance with this Agreement and the Act, the name of the Company will be
"ChiroChem Discovery Services LLC". The principal place of business of the
Company shall be at 9050 Camino Santa Fe, San Diego, California or such other
place as the Board of Managers may hereafter designate.

        1.3 Office for Records and Agent for Service of Process. The Company
shall maintain an office at which shall be maintained the records required by
Section 17058 of the Act and an agent for service of process as required by
Section 17057 of the Act. The office at which shall be maintained the records
required by Section 17058 of the Act shall be the principal office of CombiChem,
9050 Camino Santa Fe, San Diego, California 92121, and the name and address of
the agent for service of process shall be Karin Eastham c/o CombiChem, 9050
Camino Santa Fe, San Diego, California 92121, or such other person and place as
the Board of Managers may hereafter designate.

        1.4 Agreement. For and in consideration of the mutual covenants herein
contained and for other good and valuable consideration, the receipt and
sufficiency of which is hereby acknowledged, the Members executing this
Agreement hereby agree to the terms and conditions of this Agreement, as it may
from time to time be amended.

        1.5 Purposes. The purposes of the Company are:


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               (a) to use chiral templates made available to it pursuant to the
CT License, and the technology licensed to it pursuant to the Combi License, to
design, synthesize and market chemical libraries consisting of Chiral Compounds
to third parties;

               (b) to use chiral templates made available to it pursuant to the
CT License, and the technology licensed to it pursuant to the Combi License, to
design, synthesize and market customized chemical libraries consisting of Chiral
Compounds in response to third party purchase orders and specifications;

               (c) to use chiral templates made available to it pursuant to the
CT License, and the technology licensed to it pursuant to the Combi License, to
synthesize and market individual quantities of a Chiral Compound selected from
chemical libraries sold pursuant to paragraphs (a) or (b) to a maximum quantity
of ten (10) grams per lot; and

               (d) to engage in all other lawful activities helpful, necessary
or appropriate to maximize the ability of the Company to accomplish the
foregoing purposes.

        1.6 Definitions. Terms not otherwise defined in this Agreement shall
have the meanings set forth in Article XV.

        1.7 Term. The term of the Company shall commence on the Effective Date
and, unless the term of the Company is otherwise terminated pursuant to the
provisions of this Agreement, shall continue until the third calendar
anniversary of the Effective Date (the "Initial Term"). Such term may be
extended for additional periods of three (3) years by future amendment of this
Agreement signed by all Members prior to the expiration of the then current
term.



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                                   ARTICLE II
                                MEMBERSHIP; UNITS

        2.1 Members. The initial Members of the Company are each of the two
Persons whose names are set forth on the initial signature page of this
Agreement, each of which is admitted as a Member upon execution and delivery of
this Agreement. Additional signature pages may hereafter be added by the Board
of Managers as appropriate to reflect the admission of Substitute Members in
accordance with the provisions of this Agreement but not otherwise.

        2.2 Representations and Warranties. Each Member hereby represents and
warrants to the Company and the other Member as follows:

               (a) Authorization. The Member is duly organized, validly
existing, and in good standing under the law of its jurisdiction of
organization; it has full power and authority to execute and enter into this
Agreement and to perform its obligations hereunder; and all actions necessary
for the due authorization, execution, delivery and performance by that Member of
this Agreement have been duly taken. This Agreement has been duly executed and
delivered by the Member and constitutes the legal obligation of the Member
enforceable in accordance with its terms.

               (b) Compliance with Other Instruments. The Member's
authorization, execution, delivery, and performance of this Agreement do not
conflict with or violate any law applicable to the Member or any other agreement
or arrangement to which such Member is a party or by which such Member or such
Member's assets is bound.

               (c) Purchase Entirely for Own Account. The Member is acquiring
such Member's interest in the Company for the Member's own account, not as a
nominee or agent, for investment purposes only and not with a view to or for the
resale, distribution, subdivision or fractionalization thereof. The Member has
no contract, present intention, understanding, undertaking, agreement or
arrangement of any kind with any Person to sell, transfer or pledge to any
Person such Member's interest or any part thereof, nor does such Member have any
plans to enter into any such agreement.

               (d) Investment Experience. The Member has such knowledge and
experience in financial and business matters to be capable of evaluating the
merits and risks of its investment in the Company, is able to bear the economic
risks of an investment in the Company, and is able, without materially impairing
its financial condition, to hold the Units (as hereinafter defined) for an
indefinite period of time and to suffer a complete loss of such investment.



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               (e) Disclosure of Information. The Member is aware of the
Company's business affairs and financial condition and has acquired all of the
information about the Company it has requested from the Company and considers
necessary to reach an informed and knowledgeable decision to acquire an interest
in the Company.

               (f) Federal and State Securities Laws. The Member acknowledges
that the Units have not been registered under the Securities Act of 1933, as
amended (the "Securities Act") or any state securities laws, inasmuch as they
are being acquired in a transaction not involving a public offering, and under
such laws, may not be resold or transferred by the Member without appropriate
registration or the availability of an exemption from such requirements. In this
connection, the Member represents that he is familiar with Rule 144 promulgated
under the Securities Act, as presently in effect, and understands the resale
limitations imposed thereby and by the Securities Act. The Member is an
"accredited investor" within the meaning of Regulation D promulgated under the
Securities Act of 1933, as amended.

               (g) Brokers and Finders. The Member has not retained any
investment banker, broker or finder in connection with his, her or its
investment in the Company.

        2.3 Units. Ownership of the Company shall be divided into and
represented by one class of units of the Company (the "Units"). Each Unit shall
be entitled to one vote and to equal participation in the profits, losses,
capital and distributions of the Company, unless additional or different classes
of Units are established by the Board of Managers and approved by the Members.

        2.4 Substitute Members. A Substitute Member shall have all the rights
and powers and will be subject to all the restrictions and liabilities of the
Member who Transferred the Units.

        2.5 Resignation or Withdrawal of a Member. Except as specifically
provided below, and subject to the provisions on Transfer contained in Article
XI, no Member may resign, retire or withdraw from membership in the Company or
withdraw such Member's interest in the capital of the Company prior to the
dissolution and winding up of the Company.



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        2.6 Dissociation of a Member. The Bankruptcy or Dissolution of a Member
(i) will cause such Member to be dissociated from the Company (a "Dissociated
Member"), (ii) will terminate the continued membership of such Member in the
Company, and (iii) will constitute a Dissolution Event and cause a dissolution
and winding up of the Company pursuant to Article XIV hereof except as expressly
provided therein to the contrary.

        2.7 Rights of Dissociated Member. In the event any Member becomes a
"Dissociated Member", the Dissociated Member (or such Member's legal
representative) shall be entitled to participate in the winding up of the
Company to the same extent as any other Member.

        2.8 No Contracts. Each Member hereby covenants not to use any actual or
apparent authority or power to bind the Company to any contract or commitment,
or to otherwise incur any liability to which the Company will be subject,
without the express authorization of the Board of Managers. Each Member hereby
agrees to indemnify and hold the Company and the other Member(s) harmless for
any loss, liability, expense, damage or injury suffered or sustained by the
Company and/or the other Members in consequence of such Member's exercise of
such actual or apparent authority or power to bind the Company in violation of
the restrictions set forth herein. Upon any material breach of a Member's
obligations under this Section, the Company shall have a right of offset against
all distributions under this Agreement payable to such Member (and all amounts
thereafter payable to such Member or any Affiliate of such Member under any
other contract binding on the Company) for amounts owed to the Company pursuant
to the indemnification described in the preceding sentence.

        2.9 Other Ventures and Activities.

               (a) The Members: (i) acknowledge that the Members and their
respective Affiliates are or may be involved in other research and development,
manufacturing, sales or business activities; and (ii) agree that each Member and
its Affiliates may engage for their own accounts and for the accounts of others
in any such ventures and activities, provided, however, that such ventures
and/or activities shall not violate the limitations on activities found in
Section 2.2 (Retained Rights) of the CT License or the CombiChem License (as
applicable). Except as otherwise required by fiduciary duties, (i) neither the
Company nor any Member shall have any right by virtue of this Agreement or the
existence of the Company in and to such ventures or activities or to the income
or profits derived therefrom, and (ii) the Members, their Affiliates, and other
related Persons shall have no duty or obligation to make any reports to the
Members or the Company with respect to any such ventures or activities.



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               (b) Each Member acknowledges that the other Member(s) may be
prohibited from taking action for the benefit of the Company: (i) due to
confidential information acquired or obligations incurred in connection with an
outside activity permitted to such Member or its Affiliates under this Section
2.9; or (ii) in connection with activities undertaken prior to the Effective
Date. No Person shall be liable to the Company or any Member for any failure to
act for the benefit of the Company in consequence of a prohibition described in
the preceding sentence.

        2.10 Member Expenses. No Member shall be reimbursed for expenses
incurred on behalf of, or otherwise in connection with, the Company except to
the extent so provided in any Chiro Ancillary Agreement, Combi Ancillary
Agreement or this Section. All expenses reasonably incurred by a Member in
connection with the preparation, negotiation, execution and delivery of this
Agreement and the aforesaid Ancillary Agreements and otherwise in connection
with the formation of the Company shall be reimbursed by the Company upon
presentation of evidence of such expenses reasonably satisfactory to the Board
of Managers.

        2.11 Member Compensation. Except as provided in a Chiro Ancillary
Agreement or a Combi Ancillary Agreement, no Member shall be entitled to
compensation for services provided by such Member to, or for the benefit of, the
Company.

        2.12 Tax Matters.

               (a) CombiSub is hereby designated the "tax matters partner" of
the Company within the meaning of Section 6231(a)(7) of the Code. Except to the
extent specifically provided in the Code or the Treasury Regulations (or the
laws of other relevant taxing jurisdictions), the tax matters partner shall have
exclusive authority to act for or on behalf of the Company with regard to tax
matters, including the authority to make (or decline to make) any available tax
elections.

               (b) Except to the extent otherwise required by applicable law
(disregarding for this purpose any requirement that can be avoided through the
filing of an election or similar administrative procedure), the tax matters
partner shall cause the Company to take the position that the Company is a
"partnership" for federal, state and local income tax purposes and shall cause
to be filed with the appropriate tax authorities any elections or other
documents necessary to give due legal effect to such position. A Member shall
not file (and each Member hereby represents that it has not filed) any income
tax election or other document that is inconsistent with the Company's position
regarding its classification as a "partnership" for applicable federal, state
and local income tax purposes.

               (c) No Member shall file a notice with the United States Internal
Revenue Service under Section 6222(b) of the Code in connection with such
Member's



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intention to treat an item on such Member's federal income tax return in a
manner which is inconsistent with the treatment of such item on the Company's
federal income tax return unless such Member has, not less than 30 days prior to
the filing of such notice, provided all Members with a copy of the notice and
thereafter in a timely manner provides such other information related thereto as
any such Member shall reasonably request.

               (d) Any Member entering into a settlement agreement with the
United States Department of the Treasury which concerns a Company item shall
notify all Members of such settlement agreement and its terms within 60 days
after the date thereof.

                                   ARTICLE III
                            CONTRIBUTIONS TO CAPITAL

        3.1 Capital Commitments. The required contributions to the capital of
the Company by each Member shall be those amounts of cash and/or property set
forth opposite such Member's name in the Annual Budgets (each such amount being
a "Capital Commitment"). Each Member's Capital Commitments represent, in the
aggregate, the maximum amount of cash and/or property that such Member has
agreed to contribute to the Company in accordance with the terms hereof, and no
Member shall be obligated to contribute cash and/or property to the Company in
any amount in excess of such Member's aggregated Capital Commitments. The
initial Members currently agree that the aggregate of all Capital Commitments
for the Initial Term shall not exceed *** for each Member without further
written agreement of the Members.

        3.2 Capital Contributions. Except to the extent provided to the contrary
in any Annual Budget, all Capital Contributions shall be in cash. The obligation
of a Member to satisfy each of its Capital Commitments shall be without
interest. The Members shall make Capital Contributions equal to 100 percent of
their respective Capital Commitments in the amounts and on the dates for Capital
Contributions set forth in the Annual Budgets.

        3.3 Issuance of Units. Each Member shall be promptly issued one Unit for
every One U.S. Dollar ($1.00) of Capital Contribution made by the Member.

        3.4 Additional Contributions and Loans. Except as set forth in Section
3.6, and except if the Members mutually agree to fund the activities of the
Company through loans rather than Capital Contributions, no Member shall be
permitted or required to make any additional contribution to the capital of the
Company without the consent of the Board of Managers and the Members. No Member
shall lend, or be required to lend, any money to the Company or guaranty any
Company indebtedness unless all Members agree



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to participate in such loan or guaranty in proportion to the number of Units
held by each. The Annual Budgets for 1998 and 1999 will anticipate a requirement
of *** in third-party lease financing, which shall be guaranteed by the Members
to the extent required by the lender. Any additional loans or guarantees by
Members shall be approved in writing by the Members.

        3.5 Interest. Except for interest paid to Members for loans approved in
accordance with Section 3.4 above, no Member shall be entitled to any interest
with respect to such Member's contributions to or share of the capital of the
Company or its share of unallocated Net Income.

        3.6 Failure To Make Capital Contribution. In the event a Member fails to
make a Capital Contribution when due hereunder to satisfy a Capital Commitment,
the other Member (the "Aggrieved Member") may give the noncontributing Member
notice of such failure. If such failure continues for thirty (30) days after
such notice has been given, the Aggrieved Member may elect to take any of the
alternative actions described herein if it has made all of the Capital
Contributions theretofore due from it to the Company. Such an election shall
remain available to the Aggrieved Member until such time as the noncontributing
Member's Capital Commitment has been, or deemed to be, fully satisfied.

               (a) The Aggrieved Member may initiate the procedures described in
Article XII; or

               (b) The Aggrieved Member may contribute to the Company the cash
or property then due to the Company from the noncontributing Member, and the
amount of such cash (or the value of such property) shall be deemed to be a loan
from the Aggrieved Member to the noncontributing Member (a "Default Loan") and a
Capital Contribution by the noncontributing Member to the Company, in which
event the noncontributing Member's unsatisfied Capital Commitment shall be
deemed satisfied and the Company shall issue in the name of the noncontributing
Member that number of Units issuable on account of such a Capital Contribution
and deliver such Units (the "Pledged Units") to the Aggrieved Member to hold as
collateral for payment of the Default Loan. To secure payment of a Default Loan
and all accrued interest thereon for which it may hereafter become liable, each
Member hereby pledges to the other Member and grants to the other Member a
security interest in any Pledged Units. Any Default Loan shall bear interest at
the lesser of the maximum rate permitted by applicable law (if there is such a
maximum) or the prime rate of interest from time to time quoted by Bank of
America plus six percent (6%) and shall be due and payable in full (including
all accrued interest) within ninety (90) days after the Aggrieved Member
contributes the cash or property then due to the Company from the
noncontributing Member. If not



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                                      -8-
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sooner repaid, a Default Loan shall be repaid from any cash distributions
otherwise to be made by the Company to the noncontributing Member under this
Agreement and any payment otherwise to be made by the Company to the
noncontributing Member or Affiliate under any other contract binding on the
Company. Upon repayment of the Default Loan in full (other than disposal of the
Pledged Units), the Aggrieved Member shall deliver the Pledged Units to the
noncontributing Member and release its security interest therein. If a Default
Loan is not repaid in full when due and payable, the Aggrieved Member may, at
its sole election, dispose of the Pledged Units in accordance with the
California Uniform Commercial Code, as amended from time to time, as payment in
full of the Default Loan. Any unpaid Default Loan (including all accrued
interest) may also be offset against any amount to be paid to the
noncontributing Member by the Aggrieved Member in purchase of the
noncontributing Member's Units pursuant to Article XII.

                                   ARTICLE IV
                                ACTION BY MEMBERS

        4.1 Meetings of Members. Meetings of Members may be held for any purpose
at the request of any Member. Members may participate in a meeting of the
Members by means of conference telephone or similar communications equipment by
means of which all persons participating in the meeting can hear each other, and
such participation in a meeting shall constitute presence in person at the
meeting.

        4.2 Voting Standard. At any duly noticed meeting at which a quorum is
present, the vote of the Member(s) holding a Supermajority of the Units
represented at the meeting shall decide any question brought before the meeting,
except to the extent that the express provisions of law or this Agreement
require a different vote.

                                    ARTICLE V
                       MANAGEMENT; RESTRICTIONS; EXPENSES

        5.1 Management by Board of Managers. Except for situations in which the
approval of the Members is required by statute or this Agreement, in accordance
with Section 17151 of the Act, the Company shall be managed and controlled by
the Managers acting as a "Board of Managers." The Board of Managers may exercise
all powers of the Company and do all such lawful acts and things that are not by
statute, the Articles or this Agreement, directed or required to be exercised or
done by the Members themselves. It is intended that the powers and authority of
the Board of Managers shall be substantially the same as the powers and
authority of a board of directors of a corporation formed under the laws of the
State of California. Notwithstanding the foregoing, the Board of Managers may
not do or permit to be done any of the following without the approval of the
Members:



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               (a) Any act or thing that the Act or this Agreement requires to
be approved, consented to or authorized by the Members;

               (b) Voluntarily cause the dissolution of the Company;

               (c) Compromise the liability of any Member for improper
distributions; or

               (d) Sell all or a substantial part of the Company's assets, other
than in the ordinary course of business.

        5.2 Number; Vacancies. The Board of Managers shall be comprised of six
(6) Managers, three of whom shall be appointed by ChiroSub (the "Chiro
Managers") and three of whom may be appointed by CombiSub (the "Combi
Managers"). A Chiro Manager may be removed from office by ChiroSub, and a Combi
Manager may be removed from office by CombiSub, at any time for any reason. In
the event that any Manager dies, resigns or is removed as a Manager, a
substitute manager may be appointed by the Member that appointed the former
Manager whose vacancy is being filled. On the Effective Date, the Chiro Managers
shall be Christine Soden, Alan Shaw and Ray McCague and the Combi Managers shall
be Peter Myers, Karin Eastham and Lee McCracken.

        5.3 Meetings of Managers. The Board of Managers may hold meetings, both
regular and special, either within or without the State of California. Regular
meetings of the Board of Managers shall be held at least once a month and may be
held at times and places determined by the Board of Managers. Special meetings
of the Board of Managers may be called by any Manager on 48 hours notice to each
Manager by any reasonable means, including but not limited to telephone or
facsimile transmission. Subject to Sections 5.7 and 5.8, at all meetings of the
Board of Managers, a majority of the Managers consisting of at least two Chiro
Managers and at least two Combi Managers shall constitute a quorum for the
transaction of business. If a quorum is not present at a meeting of the Board of
Managers, the Managers present may adjourn the meeting from time to time,
without notice other than announcement at the meeting, until a quorum shall be
present. Managers may participate in a meeting of the Board of Managers by means
of conference telephone or similar communications equipment by means of which
all persons participating in the meeting can hear each other, and such
participation in a meeting shall constitute presence in person at the meeting,
except that, for at least one meeting held each calendar quarter (which shall be
designated by the Chair as such in advance of the meeting), the Managers must
attend in person in order to participate. Meetings will alternate between the
offices of the Members or shall be held in New York, New York unless otherwise
agreed. The Member hosting any meeting shall appoint a secretary to the meeting
to record the minutes of the meeting, which will be circulated to the Managers
promptly following the meeting for review and comment and then kept in a minute
book for the Company available to all Managers and Members.



                                      -10-
<PAGE>   16

        5.4 Voting Procedures. Subject to Sections 5.7 and 5.8, the Chiro
Managers shall have, in the aggregate, one (1) vote and the Combi Managers shall
have, in the aggregate, one (1) vote, on each matter coming before the Board of
Managers at a meeting. Each such vote shall be cast by a majority of the Chiro
Managers or the Combi Managers, as the case may be, in attendance at the
meeting. Subject to Sections 5.7 and 5.8, any proposed action of the Board of
Managers shall require approval by both votes cast at a duly called meeting of
the Board of Managers at which a quorum is present to be effective.



                                      -11-
<PAGE>   17

        5.5 Action Without Meeting. Subject to Sections 5.7 and 5.8, any action
required or permitted to be taken at any meeting of the Board of Managers may be
taken without a meeting if all Managers consent thereto in writing, by single or
counterpart writings, and the writing or writings are filed with the minutes of
proceedings of the Board of Managers.

        5.6 Normal Functions of Board of Managers. Without limiting the
generality of Section 5.1, and subject to the other provisions of this
Agreement, the Board of Managers shall perform the functions described herein.

               (a) Prior to the end of each Fiscal Year, the Board of Managers
shall consider and approve an "Annual Budget" for next Fiscal Year consisting of
at least                               ***
                                       ***
                                       ***
                                       ***                       ; provided, 
however that the Annual Budgets for the Fiscal Years ending December 31, 1998
and December 31, 1999 shall be adopted at the first meeting of the Board of
Managers. The Capital Commitment of each Member in an Annual Budget shall be
equal, in aggregate amount and in dates and amounts of required Capital
Contributions, to that of every other Member.

               (b) The Board of Managers shall oversee the business activities
of the Company and at all times endeavor to operate the Company in a manner
consistent with the Annual Budget. Any Company expenditure(s) in any year that
will be more than (i) *** in excess of the line item budget for that expenditure
in the Annual Budget or (ii) *** of the aggregate expense budget in the Annual
Budget shall require prior approval of the Board of Managers before it may be
made.

               (c) The Board of Managers shall oversee, generally or
specifically, the design, production and marketing of chemical libraries of
Chiral Compounds to third parties and shall, from time to time, select those
Chiral Compounds to be individually synthesized and marketed.

               (d) The Board of Managers shall determine the best interest of
the Company in all dealings and proposed dealing with third parties and shall
approve, generally or specifically, the terms of any contract, agreement, deed,
lease, promissory note, or other instrument or document to be executed and
delivered by the Company.



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                                      -12-
<PAGE>   18

               (e) The Board of Managers shall take such steps as are reasonably
necessary and prudent to protect the proprietary rights of the Company in the
data, trade secrets, technical information, know-how, inventions, discoveries
and other proprietary or confidential information of the Company. Such steps may
include (i) filing for patents, trademarks and copyrights when and as
appropriate and (ii) opposing patent, copyright and trademark applications filed
by third parties which may have an adverse impact upon the Company's proprietary
rights. Any such patents, trademarks or copyrights which are issued during the
term of the Company shall be in the name of the Company and shall be the
property of the Company.

        5.7 Conflict of Interest Matters. If a Member or an Affiliate of a
Member is or will be a party to a contract or an arbitration proceeding under
Section 16.2 in which the Company also is, or is proposed to be, a party, those
Managers designated by that Member shall not participate in the consideration of
or vote upon any proposed action by the Company concerning said contract or
arbitration proceeding. Notwithstanding Sections 5.3, 5.4 and 5.5, in such an
event the quorum for a meeting of the Board of Managers to consider such a
proposal shall be any three (3), and the proposal shall be considered approved
by the Board of Managers upon the single vote approving the proposal cast by the
participating Managers at such a meeting or upon a written consent to the
proposal signed by all Managers who were eligible to participate in
consideration of the proposal. Without limiting the generality of the foregoing,

               (a) the Chiro Managers shall not consider or vote upon any
proposal by which the Company would rescind, waive, modify, enforce or exercise
any remedy under or with respect to the CT License, the ChiroTech, Inc. Services
Agreement, the CT Limited Services Agreement or those portions of the
Cooperation Agreement by which ChiroSub or CT Limited are bound;

               (b) the Chiro Managers shall not consider or vote upon any
proposal for the Company to initiate or respond to any arbitration proceeding
against ChiroSub pursuant to Section 16.2 or concerning the conduct of the
Company in such a proceeding;

               (c) the Combi Managers shall not consider or vote upon any
proposal by which the Company would rescind, waive, modify, enforce or exercise
any remedy under or with respect to the CombiChem License, the CombiChem
Services Agreement, or those portions of the Cooperation Agreement by which
CombiSub or CombiChem are bound; and

               (d) the Combi Managers shall not consider or vote upon any
proposal for the Company to initiate or respond to any arbitration proceeding
against CombiSub pursuant to Section 16.2 or concerning the conduct of the
Company in such a proceeding.

        5.8 Loss of Vote. In the event one Member acquires additional Units
pursuant to Section 3.6(b) on account of the failure of another Member to make
Capital 



                                      -13-
<PAGE>   19

Contributions sufficient to satisfy its Capital Commitments and, as a result,
said Member owns not less than a Supermajority of all then-issued and
outstanding Units, the voting right of the Managers designated by the
noncontributing Member shall be suspended until such time (if ever) as said
Member owns less than a Supermajority of all then-issued and outstanding Units.
Notwithstanding Section 5.3, 5.4 and 5.5, during any such suspension the quorum
for a meeting of the Board of Managers shall be any three (3), and the Board of
Managers will act upon the single vote then eligible to be cast or upon a
written consent signed by all Managers who were eligible to participate in the
casting of that vote.

        5.9 Manager Compensation and Expenses. The Board of Managers shall
receive no compensation from the Company for their services as Managers, but
each Manager shall be reimbursed for his or her reasonable out-of-pocket
expenses incurred in attending meetings of the Board of Managers and performing
related duties of the office under reasonable reimbursement procedures.

                                   ARTICLE VI
                                     NOTICES

        6.1 Notices. Whenever notice or demand is required to be given to any
Member by the Act, the Articles or this Agreement, it shall be given in writing,
by mail, addressed to such Member at such Member's address as it appears on the
records of the Company with postage thereon prepaid, and shall be deemed given
three days after it is deposited in the United States mail. Notice to Members
may also be given by facsimile and shall be deemed given upon the sending
thereof with electronic confirmation of receipt.

        6.2 Waiver of Notice. A Member may waive notice, provided that the
waiver is in writing signed by the Member whether before or after the notice is
required to be given.



                                      -14-
<PAGE>   20

                                   ARTICLE VII
                                    OFFICERS

        7.1 Chair. The initial Chair of the Board of Managers shall be Alan
Shaw, and he shall serve in such capacity until the end of Fiscal Year 1999.
Then CombiSub shall designate one Manager from among the CombiSub Managers to
serve as Chair of the Board of Managers for a term of one (1) year concurrent
with the next Fiscal Year. Thereafter the Chair shall be a Chiro Manager
designated by ChiroSub, then a Combi Manager designated by CombiSub, and so
forth for successive one year terms. In the event a Chair ceases to be a Manager
during his or her term of office as the Chair, the Member which appointed the
former Chair shall designate another Manager to serve as the Chair for the
balance of the former Chair's term. The Chair shall preside at all meetings of
the Board of Managers.

        7.2 Other Officers. The Board of Managers may create such other offices
and elect such other officers as it deems appropriate. Any number of offices may
be held by the same person. The duties of such officers shall be established
from time to time by the Board of Managers.

        7.3 Contracts. After the Effective Date, the Board of Managers shall
expressly designate one or more Managers or officers to execute and deliver, on
behalf of the Company, any contract, agreement, deed, lease or other document or
instrument approved generally or specifically by it, and any such document or
instrument executed and delivered by such an authorized Person or Persons shall
be deemed to have been duly executed and delivered by the Company. No Member's
signature shall be required in connection with execution and delivery on such
documents and instruments by the Company, and third parties to such documents
and instruments shall be entitled to rely upon the Board of Manager's general or
specific approval and delegation of authority to the signatory or signatories on
behalf of the Company without otherwise ascertaining whether the requirements of
this Agreement have been satisfied.



                                      -15-
<PAGE>   21

                                  ARTICLE VIII
                             ACCOUNTING AND RECORDS

        8.1 Financial Statements and Records. The Company shall prepare its
financial statements and tax returns using such methods of accounting as the
Board of Managers deems necessary or appropriate. The Company shall maintain
proper and complete books of account and records of the business of the Company,
under the supervision of the Board of Managers, at the Company's principal
office or at such other place or places as may be designated by the Board of
Managers. The Board of Managers shall give notice to each Member of any change
in the location of the books and records. The Company has initially contracted
with CombiChem for preparation of such statements, books and records pursuant to
the CombiChem Services Agreement.

        8.2 Inspection of Books. The Company's books and records shall be open
to inspection, audit and copying by any Member, or such Member's designated
representative, upon reasonable notice at any time during business hours for any
purpose reasonably related to the Member's interest in the Company. Any
information so obtained shall be kept confidential by the Member except as
required by law.

        8.3 Annual and Monthly Reports. Financial statements of the Company
shall be prepared as of the end of each Fiscal Year and audited by a firm of
independent certified public accountants selected by the Board of Managers,
provided, however, that the Board of Managers may waive the audit requirement at
any time and for any reason. A copy of the annual financial statements shall be
transmitted to the Members within 45 days after the end of each Fiscal Year. In
addition, the Company shall cause unaudited monthly financial statements,
including a comparison of actual results to the projections found in the Annual
Budget applicable for the reporting period, to be prepared and distributed to
the Members within 30 days after the end of each month beginning with December
1998.

        8.4 Tax Returns. Within 90 days after the end of each Fiscal Year, the
Board of Managers shall file a federal income tax information return and
transmit to each Member a schedule showing such Member's distributive share of
the Company's income, deductions and credits, and all other information
necessary for such Member to timely file its own federal income tax return for
the Fiscal Year. The Board of Managers similarly shall file, and provide
information to the Members regarding, all appropriate state and local income tax
returns.

                                   ARTICLE IX
                                   ALLOCATIONS



                                      -16-
<PAGE>   22

        9.1 Allocation of Net Income or Net Loss. For each Accounting Period ,
Net Income or Net Loss of the Company, or items thereof, shall be allocated to
the Members in proportion to the number of Units held by each.

        9.2 Partnership Status. The Members agree that the Company shall be
treated as a partnership for all U.S. federal income tax purposes.

                                    ARTICLE X
                                  DISTRIBUTIONS

        10.1 Allocation of Distributions among Holders of Units. All
distributions by the Company to holders of Units shall be made in proportion to
the holders' ownership of such Units at the time of the distribution.

        10.2 Discretionary Distributions. The Board of Managers may cause the
Company to make distributions to the holders of Units in accordance with Section
10.1 in such amounts and at such times as they shall from time to time determine
to be in the best interests of the Company and its Members; provided, however,
that distribution of an amount equal to any estimated distribution amount set
forth in the Annual Budget for a Fiscal Year shall be presumptively valid if the
Company realized excess cash flow in at least that amount from operations during
that Fiscal Year. If any assets are distributed in kind, then they shall be
distributed on the basis of the fair market value thereof as determined by the
Members, and shall be deemed to have been sold at such fair market value for
purposes of the allocations under Article IX.

        10.3 No Other Withdrawals. Except as otherwise expressly provided for in
this Agreement, no withdrawals or distributions shall be required or permitted.



                                      -17-
<PAGE>   23

                                   ARTICLE XI
                                    TRANSFERS

        11.1 Transfer of Units. A Member may Transfer one or more Units to
another Member. A Member may also Transfer one or more Units to a Substitute
Member, in whole or in part, and the Substitute Member will be admitted to the
Company as a member, only if: (i) the Substitute Member shall have agreed in
writing to assume all of the obligations of the Member with respect to the Units
being so Transferred (including the obligations imposed hereunder as a condition
to any transfer); (ii) the Board of Managers shall have concluded (which
conclusion may be based upon an opinion of counsel satisfactory to it) that the
Transfer will not result in a termination of the Company for federal or state
income tax purposes, result in (or materially increase the risk of) the Company
being taxable as a corporation for federal income tax purposes, or result in a
violation of any law, rule or regulation by the Member, the Substitute Member,
the Company or the other Member(s); and (iii) all other Member(s) shall have
consented to the Transfer, such consent not to be unreasonably withheld.

        11.2 Transfer Void. Any purported Transfer of Units in contravention of
this Article XI shall be void and of no effect to, on or against the Company,
any Member, any creditor of the Company or any claimant against the Company.

        11.3 Transfer of Control of Member. Any Transfer of legal or beneficial
ownership or control of a Member, whether by sale or issuance of the Member's
equity securities, voting trust agreement, irrevocable proxy or otherwise, shall
be deemed an attempted Transfer of the Units owned by that Member for purposes
of this Article XI in contravention of Section 11.1.

        11.4 Transfer of Control of Affiliates.

               (a) If there is any Transfer of legal or beneficial ownership or
control of *** , whether by sale or issuance of equity securities, voting trust
agreement, irrevocable proxy or otherwise, and *** continues to be an
    *** after such Transfer, *** may, in its sole discretion, institute the
buy-sell provisions described in Article XII.

               (b) If there is any Transfer of legal or beneficial ownership or
control of *** , whether by sale or issuance of equity securities, voting trust
agreement, irrevocable proxy or otherwise, and *** continues to be an



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                                      -18-
<PAGE>   24

*** after such Transfer, *** may, in its sole discretion, institute the buy-sell
provisions described in Article XII.

               (c) As used herein, a *** is a Person for whom at least *** of
its consolidated revenues during its most recently completed fiscal year were
earned from the sale of goods or services that *** (i) in the case of *** , with
those *** by any *** that accounted for at least *** of the consolidated
revenues of *** during the same period, and (ii) in the case of *** , with those
*** by any *** that accounted for at least *** of the consolidated revenues of
*** during the same period.

        11.5 Acquisition of        ***      .

               (a) If *** or its Affiliates acquire legal or beneficial
ownership or control of a *** , whether by purchase of equity securities, a
voting trust agreement, irrevocable proxy or otherwise, *** may, in its sole
discretion, institute the buy-sell provisions described in Article XII.

               (b) If *** or its Affiliates acquire legal or beneficial
ownership or control of a *** , whether by purchase of equity securities, a
voting trust agreement, irrevocable proxy or otherwise, *** may, in its sole
discretion, institute the buy-sell provisions described in Article XII.

                                   ARTICLE XII
                               BUY-SELL PROVISION

        12.1 Application. The procedures described in this Article XII are
available only so long as there are only two Members admitted to the Company.
Either Member may initiate the procedures, by giving the other Member notice
pursuant to Section 12.2(a), during the ninety (90) days following (i)
dissolution of the Company pursuant to Section 14.1 or (ii) declaration of a
Board Deadlock pursuant to Section 16.1. In addition, an Aggrieved Member under
Section 3.6(a) may initiate the procedures, by giving the other Member notice
pursuant to Section 12.2(a), as provided therein.

        12.2 Procedures

               (a) The Member initiating these procedures shall give the other
Member a notice (the "Price Notice") of its election to do so, together with a
statement of a 



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                                      -19-
<PAGE>   25

hypothetical sale price for all the Company's assets, free and clear of the
Company's secured and unsecured liabilities, and a calculation of the net
proceeds per Unit (the "Per Unit Price") that each Member would receive if the
Company sells all of its assets for cash in the amount of the hypothetical sale
price, satisfies all of its liabilities, and distributes the net proceeds to the
Members in accordance with this Agreement on the date the Price Notice is given.

               (b) The other Member shall have thirty (30) days after the Price
Notice is given in which to elect to purchase the Units of the initiating
Member, or to sell its Units to the initiating Member, for a price per Unit
equal to the Per Unit Price. Such an election shall be made by notice given to
the initiating Member, in the absence of which the other Member shall be deemed
to have elected to sell its Units to the initiating Member. The price shall be
payable in cash at closing, which will occur on the tenth (10th) business day
after the other Member has elected (or is deemed to have elected) to sell its
Units to the initiating Member or purchase the Units of the initiating Member.
At the closing, each Member shall execute and deliver such documents and take
such other actions as may be necessary or customary to lawfully effect the sale
and transfer of Units from one Member or the other.

                                  ARTICLE XIII
                   INDEMNIFICATION AND LIMITATION OF LIABILITY

        13.1 Indemnification.

               (a)To the extent permitted by the Act and by law, the Managers,
the Members as such, and the directors, officers, employees and agents of any of
the foregoing (herein collectively referred to as "Indemnitees") shall, in
accordance with this Section, be indemnified and held harmless by the Company
from and against any and all loss, claims, damages, liabilities joint and
several, expenses, judgments, fines, settlements and other amounts arising from
any and all claims (including reasonable legal expenses and reasonable
attorneys' fees), demands, actions, suits or proceedings (civil, criminal,
administrative or investigative) in which the Indemnitee may be involved, as a
party or otherwise, by reason of management of, or involvement in, the affairs
of the Company, or rendering of advice or consultation with respect thereto, or
which relate to the Company, its properties, business or affairs, if (i) such
Indemnitee acted in good faith and in a manner such Indemnitee reasonably
believed to be in, or not opposed to, the best interests of the Company, and
(ii) with respect to any criminal proceeding, such Indemnitee had no reasonable
cause to believe the conduct of such Indemnitee was unlawful. The termination of
a proceeding by judgment, order, settlement, conviction or upon a plea of nolo
contendere, or its equivalent, shall not, of itself, create a presumption that
the Indemnitee did not act in good faith and in a manner which the Indemnitee
reasonably believed to be in, or not opposed to, the best interests of the
Company or that the Indemnitee had reasonable cause to believe that the
Indemnitee's conduct was unlawful (unless there has been a final adjudication in
the proceeding that the Indemnitee 



                                      -20-
<PAGE>   26

did not act in good faith and in a manner which the Indemnitee reasonably
believed to be in or not opposed to the best interests of the Company; or that
the Indemnitee did have reasonable cause to believe that the Indemnitee's
conduct was unlawful).

               (b) The Company may also indemnify any Person who was or is a
party or is threatened to be made a party to any threatened, pending, or
completed action by or in the right of the Company to procure a judgment in its
favor by reason of the fact that such Person is or was an officer, employee or
agent of the Company, against expenses reasonably incurred by such Person in
connection with the defense or settlement of such action, if such Person acted
in good faith and in a manner such Person reasonably believed to be in, or not
opposed to, the best interests of the Company, except that indemnification shall
be made in respect of any claim, issue or matter as to which such Person shall
have been adjudged to be liable for misconduct in the performance of the
Person's duty to the Company only to the extent that the court in which such
action or suit was brought, or another court of appropriate jurisdiction,
determines upon application that, despite the adjudication of liability, but in
view of all circumstances of the case, such Person is fairly and reasonably
entitled to indemnity for such expenses which such court shall deem proper. To
the extent that the Person has been successful on the merits or otherwise in
defense of any proceedings referred to herein, or in defense of any claim, issue
or matter therein, the Person shall be indemnified by the Company against
expenses actually and reasonably incurred by the Person in connection therewith.
Notwithstanding the foregoing, no Person shall be entitled to indemnification
hereunder for any conduct arising from the gross negligence or willful
misconduct or reckless disregard in the performance of the Person's duties under
this Agreement.

               (c) Expenses (including attorneys' fees) incurred in defending
any proceeding under Sections 13.1 (a) or (b) shall be paid by the Company in
advance of the final disposition of such proceeding upon receipt of an
undertaking by or on behalf of the Indemnitee or Person to repay such amount if
it shall ultimately be determined that the Indemnitee or Person is not entitled
to be indemnified by the Company as authorized hereunder.

               (d) The indemnification provided by this Section 13.1 shall not
be deemed to be exclusive of any other rights to which any Person may be
entitled under any agreement, or as a matter of law, or otherwise, both as to
action in a Person's official capacity and to action in another capacity.

               (e) The Board of Managers shall have power to purchase and
maintain insurance on behalf of the Company, the Managers, Members, officers,
employees or agents of the Company and any other Indemnitees at the expense of
the Company, against any liability asserted against or incurred by them in any
such capacity whether or not the Company would have the power to indemnify such
Persons against such liability under the provisions of this Agreement.



                                      -21-
<PAGE>   27

        13.2 Limitation of Liability. Notwithstanding anything to the contrary
herein contained, the debts, obligations and liabilities of the Company shall be
solely the debts, obligations and liabilities of the Company; and no Manager or
Member shall be obligated personally for any such debt, obligation or liability
of the Company solely by reason of being a Manager or Member of the Company.

                                   ARTICLE XIV
                                   TERMINATION

        14.1 Termination. The Company shall be dissolved, its assets disposed
of, and its affairs wound up upon the first to occur of the following:

               (a) the expiration of its stated term;

               (b) the affirmative vote of Member(s) holding not less than a
Supermajority of the Units;

               (c) the entry of a decree of judicial dissolution under the Act;
or

               (d) 90 days following the occurrence of a Dissolution Event.

        14.2 Continuance of the Company. Notwithstanding Section 14.1(d), upon
the occurrence of a Dissolution Event, if there are at least two remaining
Members, all remaining Members may avoid dissolution of the Company by electing,
within 90 days after a Dissolution Event, to continue the business of the
Company on the same terms as this Agreement. Expenses incurred in the
continuance of the Company shall be deemed expenses of the Company



                                      -22-
<PAGE>   28

        14.3 Authority to Wind Up. The Board of Managers shall have all
necessary power and authority required to marshal the assets of the Company, to
pay its creditors and liabilities, to distribute assets and otherwise wind up
the business and affairs of the Company. The Board of Managers shall continue to
conduct the business and affairs of the Company for such period as may be
necessary to allow an exercise of purchase rights under Article XII ( and
consummation of any purchase and sale resulting from the exercise of such
rights) and shall thereafter continue to conduct the business and affairs of the
Company only insofar as such continued operation remains consistent, in the
judgment of the Board of Managers, with an orderly winding up of the Company.

        14.4 Winding Up and Certificate of Cancellation.The winding up of the
Company shall be completed when all debts, liabilities and obligations of the
Company have been paid and discharged or reasonably adequate provision therefor
has been made, and all of the remaining property and assets of the Company have
been distributed to the Members. Upon the completion of winding up of the
Company, a Certificate of Cancellation shall be filed with the Office of the
Secretary of State of California.

        14.5 Distribution of Assets. Upon dissolution and winding up of the
Company, the affairs of the Company shall be wound up and the Company liquidated
by the Board of Managers. Pursuant to such liquidation, the assets of the
Company in the form of intellectual property owned by the Company (other than
rights under the CT License and the Combi License which shall terminate upon the
winding up of the Company except as provided in Section 6.2 of each such license
agreements) shall be distributed in kind, and the other assets of the Company
shall be sold unless the Members shall consent to a distribution in kind of such
other assets. If the Members do not consent to a distribution in kind but the
Board of Managers determines that an immediate sale would be financially
inadvisable, they may defer sale of the Company assets for a reasonable time. If
any assets are distributed in kind, then they shall be distributed on the basis
of the fair market value thereof as determined by appraisal, and shall be deemed
to have been sold at such fair market value for purposes of the allocations
under Article IX. Unless the Members otherwise agree, if any assets are to be
distributed in kind, they shall be distributed to the Members, as
tenants-in-common, in undivided interests in proportion to distributions to
which the Members are entitled under this Section 14.5. The assets of the
Company, whether cash or in kind, shall be distributed as follows in accordance
with the Act:

               (a) to creditors of the Company in the order of priority provided
by law; and

               (b) the Members in proportion to the number of Units held by
each.



                                      -23-
<PAGE>   29

        14.6 Effect of Termination. The Company shall terminate and cease to
exist when all of its assets have been sold and/or distributed and all of its
affairs have been wound up.

                                   ARTICLE XV
                                   DEFINITIONS

        15.1 Definitions. The following terms shall have the meanings set forth
herein for purposes of this Agreement:

               (a) "Accounting Period" shall mean, for each Fiscal Year, the
period beginning January 1 and ending December 31, provided however, that the
first Accounting Period shall commence on the date of formation of the Company,
the last Accounting Period shall end on the date of the final winding up of the
affairs of the Company, and a new Accounting Period shall commence on any date
on which the Company terminates for tax purposes.

               (b) "Act" shall have the meaning set forth in Section 1.1.

               (c) "Affiliate" shall mean, with respect to a specified Person,
(other than a natural person), a Person that directly, or indirectly through one
or more intermediaries, controls or is controlled by, or is under common control
with, the specified Person.

               (d) "Agreement" shall mean this Limited Liability Company
Operating Agreement as the same may be amended from time to time.

               (e) "Annual Budget" shall mean the budget of income and expenses
for the Company for each Fiscal Year, and related financial information,
approved by the Board of Managers pursuant to Section 5.6 (a).

               (f) "Articles" shall have the meaning set forth in Section 1.1.

               (g) "Bankruptcy" shall mean, with respect to any Person, that a
petition shall have been filed by or against such Person as a "debtor" and the
adjudication of such Person as a bankrupt under the provisions of the bankruptcy
laws of the United States of America shall have commenced, or that such Person
shall have made an assignment for the benefit of its creditors generally or a
receiver shall have been appointed for substantially all of the property and
assets of such Person.

               (h) "Board of Managers" shall have the meaning set forth in
Section 5.1.

               (i) "Capital Commitment" shall mean, for each Member, the amount
of money and/or property required to be contributed by that Member to the
capital of the Company pursuant to Article III.



                                      -24-
<PAGE>   30

               (j) "Capital Contribution" shall mean, for each Member, that
amount of money and/or property actually contributed by that Member to the
capital of the Company pursuant to Article III .

               (k) "Carrying Value" means, with respect to any asset, the
asset's adjusted basis for federal income tax purposes, except as follows:

                      (1) The initial Carrying Value of any asset contributed by
a Member to the Company shall be the agreed-upon fair market value of the asset
upon contribution, as determined by the contributing Member and the Company. The
initial Carrying Value of any asset contributed to the Company as a Capital
Contribution shall be set forth in the Annual Budget calling for that Capital
Contribution.

                      (2) In the discretion of the Board of Managers, the
Carrying Values of all assets may be adjusted to equal their respective fair
market values, as determined by the Board of Managers, and the resulting
unrecognized gain or loss allocated to each Member as though such assets had
been sold for their respective fair market values as of the following times: (A)
the acquisition of any additional Units in the Company by any new or existing
Member in exchange for more than a de minimis Capital Contribution; and (B) the
distribution by the Company to a Member of more than a de minimis amount of
assets, unless all Members receive simultaneous distributions of either
undivided interests in the distributed property or identical assets in
proportion to their ownership of Units in the Company.

                      (3) The Carrying Values of all assets shall be adjusted to
equal their respective fair market values, as determined by the Board of
Managers, and the resulting unrecognized gain or loss allocated to each Member
as though such assets had been sold for their respective fair market values as
of the following times: (A) the date the Company is liquidated within the
meaning of Treasury Regulation Section 1.704-1 (b)(2)(ii)(g); and (B) the
termination of the Company pursuant to the provisions of this Agreement.

                      (4) The Carrying Values of assets shall be increased or
decreased to the extent required under Treasury Regulation Section
1.704-1(b)(2)(iv)(m) in the event that the adjusted tax basis of assets is
adjusted pursuant to Code Sections 732, 734 or 743.

                      (5) The Carrying Value of an asset that is distributed
(whether in liquidation of the Company or otherwise) to one or more Members
shall be adjusted to equal its fair market value, as determined by the Board of
Managers, and the resulting unrecognized gain or loss allocated to each Member
as though such asset had been sold for such fair market value.



                                      -25-
<PAGE>   31

                      (6) The Carrying Value of an asset shall be adjusted by
the depreciation, amortization or other cost recovery deductions, if any, taken
into account by the Company with respect to such asset in computing Net Profit
or Net Loss.

               (l) "Chiral Compound" shall mean a chemical compound manufactured
by or on behalf of the Company pursuant to rights granted in the License
Agreements.

               (m) "Chiro Ancillary Agreements" shall mean the Cooperation
Agreement, the CT License, the Chirotech Services Agreement and the CT Limited
Services Agreement.

               (n) "ChiroSub" shall mean Chirotech Limited, a company organized
and existing under the laws of England and Wales.

               (o) "Chirotech, Inc." shall mean Chirotech, Inc., a Delaware
corporation.

               (p) "Chirotech Services Agreement" shall mean that certain
Services Agreement of even date herewith between Chirotech, Inc. and the
Company.

               (q) "Code" shall mean the Internal Revenue Code of 1986, as
amended.

               (r) "Combi Ancillary Agreements" shall mean the Cooperation
Agreement, the CombiChem License and the CombiChem Services Agreement.

               (s) "CombiChem" shall mean CombiChem, Inc., a Delaware
corporation.

               (t) "CombiChem License" shall mean that certain License Agreement
of even date herewith between CombiChem and the Company.

               (u) "CombiChem Services Agreement" shall mean that certain
Services Agreement of even date herewith between CombiChem and the Company.

               (v) "CombiSub" shall mean CombiChem JVR, Inc., a Delaware
corporation.

               (w) "Cooperation Agreement" shall mean that certain Cooperation
Agreement of even date herewith between CT Limited, Chirosub, CombiChem,
CombiSub and the Company.

               (x) "CT License" shall mean that certain License Agreement of
even date herewith between CT Limited and the Company.

               (y) "CT Limited" shall mean Chirotech Technology Limited, a
company organized and existing under the laws of England and Wales.



                                      -26-
<PAGE>   32

               (z) "CT Limited Services Agreement" shall mean that certain
Services Agreement of even date herewith between CT Limited and the Company.

               (aa) "Dissociated Member" shall have the meaning set forth in
Section 2.6.

               (bb) "Dissolution" of a Member that is not a natural person shall
mean that such Member has terminated its existence, whether partnership,
corporate or limited liability company, wound up its affairs and dissolved;
provided, however, that a change in the membership of any Member that is a
general partnership shall not constitute "Dissolution" hereunder, whether or not
the Member is deemed technically dissolved for partnership law purposes, so long
as the business of the Member is continued.

               (cc) "Dissolution Event" shall mean the Bankruptcy or Dissolution
of a Member, the occurrence of which terminates the Member's continued
membership in the Company and results in the dissolution and winding up of the
Company under the Act unless the remaining Members (if more than one)
unanimously agree otherwise pursuant to Section 14.2.

               (dd) "Effective Date" shall mean the later of (i) the date on
which the Articles are filed in the office of the Secretary of State of
California, or (ii) the date on which this Agreement is executed and delivered
by the initial Members, the Chiro Ancillary Agreements are executed and
delivered by the parties thereto, and the Combi Ancillary Agreements are
executed and delivered by the parties thereto.

               (ee) "Fiscal Year" shall mean the period from January 1 to
December 31 of each year, or as otherwise required by law.

               (ff) "Initial Term" shall have the meaning set forth in Section
1.7.

               (gg) " *** " shall have the meaning set forth in Section 11.4.

               (hh) "Manager" shall mean a natural person appointed to the Board
of Managers under Article V and who has not resigned or been removed as a
manager pursuant to this Agreement.

               (ii) "Members" shall mean the initial Members of the Company and
all Substitute Members, but does not include Dissociated Members.

               (jj) "Net Income or Net Loss" shall mean the net book income or
loss of the Company for any relevant period. The net book income or loss of the
Company shall be computed in accordance with federal income tax principles (i)
under the method of 



----------

        *** Portions of this page have been omitted pursuant to a request for
Confidential Treatment and filed separately with the Commission.


                                      -27-
<PAGE>   33

accounting elected by the Company for federal income tax purposes, (ii) as
applied without regard to any recharacterization of transactions or relationship
that might otherwise be required under such tax principles and (iii) as
otherwise adjusted by:

                      (1) including as income or deductions, as appropriate, any
tax-exempt income and related expenses that are neither properly included in the
computation of taxable income nor capitalized for federal income tax purposes;

                      (2) including as a deduction when paid or incurred
(depending on the Company's method of accounting) any amounts utilized to
organize the Company or to promote the sale of (or to sell) an interest in the
Company, except that amounts for which an election is properly made by the
Company under Section 709(b) of the Code shall be accounted for as provided
therein; and

                      (3) calculating the gain or loss on disposition of assets
and the depreciation, amortization or other cost-recovery deductions, if any,
with respect to assets by reference to their Carrying Values rather than their
adjusted tax basis.

               (kk) "Person" shall mean a natural person, partnership (whether
general or limited), limited liability company, trust, estate, association,
corporation, custodian, nominee, or any other individual or entity in its own or
representative capacity, whether domestic or foreign.

               (ll) "Substitute Member" shall mean only an Affiliate of an
initial Member.

               (mm) "Supermajority" shall mean, when referring to Units, greater
than seventy-five percent (75%) of all outstanding Units.

               (nn) "Transfer" shall mean any transfer, sale, exchange,
encumbrance, pledge, mortgage, assignment or other disposition, whether
voluntary or involuntary.

               (oo) "Treasury Regulation" shall mean any regulation issued by
the United States Department of the Treasury pursuant or relating to the Code.

                                   ARTICLE XVI
                               DISPUTE RESOLUTION

        16.1 Board of Managers Deadlock. In the event the Board of Managers
fails to approve an Annual Budget for a Fiscal Year pursuant to Section 5.6 (a)
before the commencement of that Fiscal Year, the Annual Budget for the preceding
Fiscal Year shall be deemed approved for the Fiscal Year until such time as the
Board of Managers approves a new one for that Fiscal Year. In the event of any
other deadlock in voting at a meeting of the Board of Managers regarding any
material decision relating to the Company, any Manager may declare the existence
of a deadlocked vote, in which event 



                                      -28-
<PAGE>   34

the proposal or other subject matter of the deadlocked vote shall be referred by
the Company to the chief executive officer of CombiChem and the chairman of CT
Limited, who shall confer in good faith in an effort to eliminate the deadlock
and otherwise consider the matter for a period of thirty (30) days following
referral. If the deadlock is not so broken by that date, either Member may
declare that a Board Deadlock exists, and exercise the rights provided in
Section 12.1, at any time during the next ninety (90) days.

        16.2 Arbitration. Except as hereinabove provided, any controversy
between the Members and any claim by one Member against the Company or another
Member arising out of or relating to this Agreement, or the breach thereof,
shall be settled by arbitration in San Francisco, California in accordance with
the then-applicable commercial arbitration rules of the American Arbitration
Association. Judgment upon the award rendered may be entered into any court
having jurisdiction thereof. The losing party shall bear the costs and expenses
of such arbitration.

                                  ARTICLE XVII
                                  MISCELLANEOUS

        17.1 Amendment. Except as provided herein, this Agreement may be amended
only with the written consent of a majority of the Board of Managers and of
Member(s) holding a Supermajority of Units.

        17.2 Withholding Taxes.

               (a)The Company shall at all times be entitled to make payments
with respect to any Member in amounts required to discharge any obligation of
the Company to withhold or make payments to any governmental authority with
respect to any federal, state, local or other jurisdictional tax liability of
such Member arising as a result of such Member's interest in the Company. To the
extent each such payment satisfies an obligation of the Company to withhold with
respect to any distribution to a Member on which the Company did not withhold or
with respect to any Member's allocable share of the income of the Company, each
such payment shall be deemed to be a loan by the Company to such Member (which
loan shall be deemed to be immediately due and payable) and shall not be deemed
a distribution to such Member. The amount of such payments made with respect to
such Member, plus interest on each such amount from the date of each such
payment until such amount is repaid to the Company accruing at an interest rate
per annum equal to the Bank of America prime rate from time to time in effect,
shall be repaid to the Company by (i) deduction from any cash distributions made
to such Member pursuant to this Agreement; (ii) deduction from any non-cash
distributions made to such Member, or (iii) earlier payment by such Member to
the Company, in each case as determined by the Board of Managers in its sole
discretion. The Board of Managers may, in its discretion, defer making
distributions to any Member owing amounts to the Company pursuant to this
Section until such amounts are paid to 



                                      -29-
<PAGE>   35

the Company and shall in addition exercise any other rights of a creditor with
respect to such amounts.

               (b) Each Member agrees to indemnify and hold harmless the
Company, the Managers and the Members, from and against any liability for taxes,
interest or penalties that may be asserted by reason of the failure to deduct
and withhold tax on amounts distributable or allocable to said Member. Any
amount payable as indemnity hereunder by a Member shall be paid promptly to the
Company upon request for such payment from the Board of Managers, and if not so
paid, the Board of Managers and the Company shall be entitled to claim against
and deduct all such amounts from the allocated portion of Net Profits of, or
from any distribution due to, the affected Member.

        17.3 Publicity. The Company will consult each of the Members and with
Chiroscience Group plc ("Chiroscience"), currently the holder of 70% of the
outstanding equity of CT Limited, prior to any public announcement relating to
the Company and transactions and/or activities contemplated by this Agreement,
the Chiro Ancillary Agreements or the Combi Ancillary Agreements and the terms
hereof and thereof; provided, however, that if the percentage of the equity
ownership of CT Limited held by Chiroscience becomes less than 50%, the Company
will no longer be required to consult with Chiroscience prior to any such public
announcement. The Members and Chiroscience, if applicable, will mutually and
reasonably approve the timing, content and dissemination of any public
announcement, except to the extent that any such party is not reasonably able to
consult in a timely manner with or obtain the approval of the other parties when
disclosures are required by applicable law; and, provided further, that either
party may disclose the transactions contemplated by this Agreement, the Chiro
Ancillary Agreements or the Combi Ancillary Agreements and the terms hereof and
thereof in connection with any bona fide corporate finance transaction
(including ongoing credit facilities), the merger or consolidation of a party or
any other transaction effecting a significant change in the ownership or control
of a Member or an Affiliate or all or substantially all of a Member's or an
Affiliate's business, assets or stock, or other similar corporate transaction or
purpose not related to pricing strategies or marketing plans.

        17.4 Further Assurances. The parties agree to execute and deliver any
further instruments or documents and perform any additional acts that are or may
become necessary to effectuate and carry on the Company created by this
Agreement.

        17.5 Construction. Every covenant, term and provision of this Agreement
shall be construed simply according to its fair meaning and not strictly for or
against any Member.

        17.6 Time. In computing any period of time pursuant to this Agreement,
the day of the act, event or default from which the designated period of time
begins to run shall not be included, but the time shall begin to run on the next
succeeding day. The last day 



                                      -30-
<PAGE>   36

of the period so computed shall be included, unless it is not a business day, in
which event the period shall run until the end of the next business day.

        17.7 Headings. Section and other headings contained in this Agreement
are for reference purposes only and are not intended to describe, interpret,
define, or limit the scope, extent, or intent of this Agreement or any provision
hereof.

        17.8 Severability. Except as otherwise provided in the succeeding
sentence, every provision of this Agreement is intended to be severable, and, if
any term or provision of this Agreement is illegal or invalid for any reason
whatsoever, such illegality or invalidity shall not affect the validity or
legality of the remainder of this Agreement. The preceding sentence of this
Section shall be of no force or effect if the consequence of enforcing the
remainder of this Agreement without such illegal or invalid term or provision
would be to cause Member to lose the material benefit of its economic bargain.



                                      -31-
<PAGE>   37

        17.9 Variation of Terms. All terms and any variations thereof shall be
deemed to refer to masculine, feminine, or neuter, singular or plural, as the
identity of the Person or Persons may require.

        17.10 Governing Law. The laws of the State of California shall govern
the validity of this Agreement, the construction of its terms, and the
interpretation of the rights and duties arising hereunder.

        17.11 Binding Effect. Subject to the restrictions on Transfer set forth
in Article XI, this Agreement shall be binding on and inures to the benefit of
the Members and their respective transferees, successors, assigns and legal
representatives.

        17.12 Entire Agreement. This Agreement constitutes the entire agreement
among the parties with respect to the subject matter herein.

        17.13 Counterparts.This Agreement may be executed in one or more
counterparts with the same force and effect as if each of the signatories had
executed the same instrument.



                                      -32-
<PAGE>   38

        IN WITNESS WHEREOF, all of the Members of ChiroChem Discovery Services
LLC, a California limited liability company, have executed this Limited
Liability Company Operating Agreement as of the day and year first above
written.

                                    MEMBERS:

                                    CHIROTECH LIMITED, a company organized and
                                    existing under the laws of England and Wales

                                    By:   /s/  Christine H. Soden
                                         ---------------------------------------
                                    Name:  Christine H. Soden
                                          --------------------------------------
                                    Title:   Director
                                          --------------------------------------

                                    Address:      Cambridge Science Park
                                                  Milton Road
                                                  Cambridge CB4 4WE
                                                  England


                                    COMBICHEM JVR, INC., a Delaware corporation

                                    By:  /s/  Vicente Anido, Jr.
                                         ---------------------------------------
                                    Name:   Vicente Anido, Jr.
                                          --------------------------------------
                                    Title:  President & CEO
                                          --------------------------------------

                                    Address:      9050 Camino Santa Fe
                                                  San Diego, CA  92121




                        [SIGNATURE PAGE TO LLC AGREEMENT]