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                                                                    EXHIBIT 10.5

                               SERVICES AGREEMENT

                             CHEMNAVIGATOR.COM, INC.

        THIS SERVICES AGREEMENT is entered into as of May __, 1999, by and
between CHEMNAVIGATOR.COM, INC. a Delaware corporation ("CNC"), and ROBERT
HOFFMAN ("Consultant").

        1.    CNC wishes to obtain the services of Consultant for certain
              purposes and Consultant wishes to provide such services, all
              subject to the terms and conditions of this Agreement.

        NOW, THEREFORE, in consideration of the mutual promises hereinafter set
forth, and intending to be legally bound hereby, CNC and Consultant hereby agree
as follows:

        1.    Services to be Provided. During the term of this Agreement,
              Consultant shall perform for CNC the services described on EXHIBIT
              A attached hereto and made a part hereof (the "Services").

        2.    Term. The initial term of this Agreement shall begin and terminate
              as set forth in EXHIBIT A.

        3.    Compensation; No Benefits.

              (a) As compensation for Consultant's performance of the services
to be performed by Consultant under this Agreement, CNC shall pay Consultant the
amounts specified in EXHIBIT A attached hereto, in accordance with the schedule
set forth in EXHIBIT A. Consultant shall be responsible for all expenses
incurred in connection with the performance of the Services, including travel,
hotel and meal expenses, UNLESS the travel, hotel and meal expenses are approved
in advance by CNC and the expenses are incurred in accordance with CNC's
reimbursement policies.

              (b) Consultant is not an employee of CNC and will not be entitled
to participate in or receive any benefit or right as an CNC employee under any
CNC employee benefit and welfare plans, including, without limitation, employee
insurance, pension, savings and security plans as a result of Consultant
entering into this Agreement.

        4.    Ownership of Results.

              (a) All findings, conclusions and data and all inventions,
discoveries, trade secrets, techniques, processes and know-how, whether or not
patentable, that are made by Consultant, either alone or with others, in the
performance of the Services or which result, to any extent, from use of CNC's
premises or property (collectively, "Inventions") shall become the exclusive
property of CNC. Consultant hereby assigns, transfers and conveys all of his/her
right, title and interest in and to any and all Inventions to CNC.

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              (b) Upon the request and at the expense of CNC, Consultant will
execute and deliver any and all instruments and documents and take such other
acts as may be necessary or desirable to document such transfer or to enable CNC
to apply for, prosecute and enforce patents, trademark registrations or
copyrights in any jurisdiction with respect to any Inventions or to obtain any
extension, validation, re-issue, continuance or renewal of any such intellectual
property right. Without limiting the foregoing, Consultant shall assign, grant
and convey unto CNC all of his/her right, title and interest, now existing or
that may exist in the future, in and to any copyrights in any findings, reports,
data compilations and other information and material resulting from the
performance of the Services. Consultant shall not submit applications for
copyright registration in any country for any information or materials created
by Consultant pursuant to this Agreement.

              (c) The provisions of this paragraph 4 shall survive the
expiration or sooner termination of the term of this Agreement.

        5.    Confidentiality. Consultant will not, either during or after the
term of this Agreement disclose to any third person or use any confidential or
proprietary information of CNC or its corporate collaborators for any purpose
other than the performance of the Services, without the prior written
authorization of CNC. This obligation shall not apply to information that is in
the public domain through no fault of Consultant. For purposes of this paragraph
5, "confidential or proprietary information" includes, without limitation, the
structure and activity of chemical compositions, biomaterials, micro-organisms,
cells, cell lines and the progeny and derivatives thereof, patent applications,
marketing methods and plans, pricing information, manufacturing information and
other unpublished information related to the business or the financial condition
of CNC and its affiliates and corporate collaborators. The provisions of this
paragraph 5 shall survive the expiration or sooner termination of the terms of
this Agreement.

        6.    Termination. Notwithstanding the provisions of paragraph 2, either
Party may terminate this Agreement for any reason whatsoever, upon thirty (30)
days written notice to the other Party. In such event, CNC shall be responsible
for any portion of the compensation owed to Consultant under paragraph 3 for any
Services rendered prior to the effective date of such termination.

        7.    Return of CNC Property. Consultant will return to CNC any property
of CNC in his/her possession, at any time when so requested by CNC and in any
event upon termination of this Agreement. Consultant will not remove any CNC
property from CNC premises without written authorization from CNC.

        8.    No Conflicting Agreements. Consultant represents that Consultant
is not a party to any existing agreements that would prevent Consultant from
entering into and performing this Agreement. Consultant will not enter into any
other agreement that is in conflict with his/her obligations under this
Agreement. Consultant shall not seek funding to support the Services from any
third party (including the U.S. Government), without the prior written consent
of CNC.

        9.    Independent Contractor. Consultant is an independent contractor
under this Agreement. Neither Party shall have the power to bind the other Party
to any agreement, contract, obligation or liability.

        10.   Entire Agreement, Amendment and Assignment. This Agreement is the
sole agreement between Consultant and CNC with respect to the Services to be
performed hereunder and it supersedes all prior agreements and understandings
with respect thereto, whether oral or


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written. No modification to any provision of this Agreement shall be binding
unless in writing and signed by both Consultant and a duly authorized
representative of CNC. All of the terms and provisions of this Agreement shall
be binding upon and inure to the benefit of and be enforceable by the respective
heirs, executors, administrators, legal representatives, successors and assigns
of the Parties hereto, except that the duties and responsibilities of Consultant
hereunder are of personal nature and shall not be assignable or delegable in
whole or in part by Consultant.

        11.   Governing Law. This Agreement shall be governed by and interpreted
in accordance with laws of the State of California, without giving effect to any
conflict of law provisions.

        12.   Notices. All notices and other communications required or
permitted hereunder or necessary or convenient in connection herewith shall be
in writing and shall be deemed to have been given when hand delivered, sent by
facsimile or mailed by registered or certified mail, as follows (provided that
notice of change of address shall be deemed given only when received):

              If to CNC, to:

        ChemNavigaotr.com, Inc.
        6166 Nancy Ridge Drive
        San Diego, CA  92121
        Attention:  Scott Hutton
        Facsimile No.: (858) 625-2377
        With a copy to: Corporate Secretary

              If to Consultant, to:

        Robert Hoffman
        c/o Arena Pharmaceuticals, Inc.
        6166 Nancy Ridge Drive
        San Diego, CA 92131
        Facsimile No.: (619) 453-7210

or to such other names or addresses as CNC or Consultant, as the case may be,
shall designate by notice to each other person entitled to receive notices in
the manner specified in this paragraph.

        13.   Counterparts. This Agreement shall become binding when any one or
more counterparts hereof, individually or taken together, shall bear the
signatures of Consultant and CNC. This Agreement may be executed in two or more
counterparts, each of which shall be deemed to be an original as against any
party whose signature appears thereon, but all of which together shall
constitute but one and the same instrument.

        14.   Severability. If any provision of this Agreement or application
thereof to anyone or under any circumstances is adjudicated to be invalid or
unenforceable in any jurisdiction, such invalidity or unenforceability shall not
affect any other provision or application of this Agreement which can be given
effect without the invalid or unenforceable provision or


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application and shall not invalidate or render unenforceable such provision or
application in any other jurisdiction.

        IN WITNESS WHEREOF, the undersigned, intending to be legally bound, have
duly executed, or caused to be duly executed, this Agreement as of the date
first above written.

CHEMNAVIGATOR.COM, INC.



By: /s/ Jack Lief                          By: /s/ Robert Hoffman
    ----------------------------               ----------------------------
    Jack Lief                                  Robert Hoffman
    President
    ChemNavigator.Com, Inc.
    6166 Nancy Ridge Drive
    San Diego, CA 92121

Date: May 26, 1999                         Date: May 26, 1999
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                                    EXHIBIT A

               DESCRIPTION OF CONSULTING SERVICES AND COMPENSATION

SCOPE OF SERVICES:

Consultant shall provide Company with accounting services support. Consultant
shall only be required to provide a maximum of 200 hours per year for Services.

COMPENSATION

Consultant shall be issued One Hundred Thousand (100,000) shares of Company
Common Stock, par value $.0001 ("Founders Shares").

TERM:

48 months

SCHEDULE OF PAYMENTS:

The Founders Shares shall be issued to Consultant by the Company as follows:

        Consultant shall make payment to the Company for the Founders Shares
        ($10.00), in full, within thirty (30) days of this Agreement.

        Founders Shares shall vest as follows:

               May 26, 2000:                25,000
               May 26, 2001:                25,000
               May 26, 2002:                25,000
               May 26, 2003:                25,000

        Accelerated vesting of all unvested shares shall occur at any of the
following events:

                    1)   on the completion of an acquisition or asset transfer
                         of the Company (other than through the issuance by the
                         Company of preferred stock), whereby at least 50.1% of
                         the assets of the Company are acquired or transferred
                         ("completion" being evidenced by the signing of a
                         definitive agreement between the Company and the
                         acquiring or transferee party); or

                    2)   on the closing of a firm commitment underwritten public
                         offering pursuant to an effective registration
                         statement on Form S-1 or any equivalent or successor
                         form under the Securities Act, covering the

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                         offer and sale of Common Stock for the account of the
                         Company to the public at a price per share (prior to
                         underwriter commissions and offering expenses) of not
                         less than $10.00 per share (appropriately adjusted for
                         any recapitalizations, stock splits, stock
                         combinations, stock dividends and the like) which
                         results in aggregate net cash proceeds to the Company
                         in excess of Fifteen Million Dollars ($15,000,000).

        Company reserves the right to re-purchase from Consultant any un-vested
        Founders Shares (at $.0001 per un-vested share) in the event that
        Consultant discontinues employment with Arena Pharmaceuticals, Inc.


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CONSULTANT
INITIALS

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