EXHIBIT 10.28

EMPLOYMENT AGREEMENT OF MICHAEL R. STAPLETON

This employment agreement (the "Agreement") is made and entered into as of the day of May 1, 2001 by and between Pharmacopeia, Inc., (hereinafter
the "Company"), and Dr. Micheal R. Stapleton (hereinafter "Dr. Stapleton").

RECITALS

WHEREAS, Dr. Stapleton has been employed by the company in the United Kingdom;

WHEREAS,
the Company desires to employ Dr. Stapleton in the United States to render services in the capacity of Executive Vice President and Chief Operating Officer on the
terms set forth in this Agreement;

WHEREAS,
Dr. Stapleton desires to render services in the capacity of Executive Vice President and Chief Operating Officer on the terms set forth in this Agreement;

NOW,
THEREFORE, in consideration of their mutual promises and intending to be legally bound, the parties agree as follows:

1.Employment.



2.Compensation.



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3.Relocation.



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4.Termination.Dr. Stapleton's employment as Executive Vice President and Chief Operating Officer is
at-will and may be terminated at any time for any reason. In the event of termination of his employment, the Company shall have no liability to Dr. Stapleton as Executive Vice
President and Chief Operating Officer for compensation or benefits except as specified in this Section 4 or as required by the Company's benefits policy.



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5.Vacation and Holiday.Dr. Stapleton shall be entitled vacation each year, in accordance with
the Company's standard vacation policy, and to those holidays observed by the Company. As an essential employee of the Company, Dr. Stapleton shall schedule his vacation and holiday observances
so as not to interfere with the performance of his duties as Executive Vice President and Chief Operating Officer.

6.Health Insurance; Life Insurance; Other Fringe Benefits.Dr. Stapleton shall be entitled to
the benefit of such group medical, accident and long-term disability insurance as the Company shall make available from time to time to its executive employees.

7.Professional Expenses.Dr. Stapleton will be reimbursed in accordance with the Company's
policy and procedure for the reasonable costs of property documented professional and business related travel
expenses required in the course of his employment. The Company will also pay for appropriate professional dues and memberships, which must be approved in advance by the Board.

8.Taxes.Dr. Stapleton will be responsible for the payment of any tax liability incurred as a
result of this Agreement. The Company may withhold tax on any payments or benefits provided to him as required by law or regulation.

9.Confidential Information.Except as reasonably necessary to perform his duties as Executive Vice
President and Chief Operating Officer, Dr. Stapleton agrees not to reveal to any other person or entity or use for his own benefit any confidential information of or about the Company or its
operations, both during and after his employment under this Agreement, including without limitation marketing plans, financial information, key personnel, employees' capabilities, salaries and
benefits, customer lists, pricing and cost structures, operation methods and any other information not available to the public, without the Company's prior written consent. Dr. Stapleton also
agrees to execute the Company's U.S. Invention and Non-Disclosure Agreement which is attached hereto and made a part hereof.

10.Non-Competition.Dr. Stapleton shall not, during the course of his employment
with the Company or for a period of twenty-four months thereafter, directly or indirectly:



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11.Arbitration.Any and all disputes between the parties (except actions to enforce the provisions of
Section 10 of this Agreement), arising under or relating to this Agreement or any other dispute arising between the parties, including claims arising under any employment discrimination laws,
shall be adjudicated and resolved exclusively through binding arbitration before the American Arbitration Association pursuant to the American Arbitration Association's
then-in-effect National Rules for the Resolution of Employment Disputes (hereafter "Rules"). The initiation and conduct of any arbitration hereunder shall be in accordance with
the Rules and each side shall bear its own costs and counsel fee in such arbitration. Any arbitration hereunder shall be conducted in Princeton, New Jersey, San Diego, California, or at such other
location as mutually agreed by the Parties. Any arbitration award shall be final and binding on the Parties. The arbitrator shall have no authority to depart from, modify, or add
to the written terms of this Agreement. The arbitration provisions of this Section shall be interpreted according to, and governed by, the Federal Arbitration Act, 9 U.S.C. § 1 et seq., and any
action pursuant to such Act to enforce any rights hereunder shall be brought exclusively in the United States District Court for the
Southern District of California. The parties consent to the jurisdiction of (and the laying of venue in) such court.

12.Waiver.The waiver by the Company of any breach of any provision of this Agreement shall not
operate or be construed as a waiver of any subsequent breach by Dr. Stapleton of any provision of the Agreement.

13.Severability.In the event that any section, paragraph or term of this Agreement shall be
determined to be invalid or unenforceable by any competent authority or tribunal for any reason, the remainder of this Agreement shall be unaffected thereby and shall remain in full force and effect,
and any such section, paragraph, or term shall be deemed modified to the extent to make it enforceable.

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14.Successors and Assigns.This Agreement shall bind and inure to the benefit of the successors and
assigns of the Company, and the heirs, executors or personal representatives of Dr. Stapleton. This Agreement may not be assigned by Dr. Stapleton. This Agreement may be assigned to any
successor in interest to the Company and Dr. Stapleton hereby consents to such assignment.

15.Entire Agreement; Amendments.This Agreement, including the recitals (which are a part hereof),
together with the applicable bylaws and policies of the Company, constitutes the entire Agreement between the parties hereto and there are no other understandings, agreements or representations,
expressed or implied. This Agreement supercedes any and all prior or contemporaneous agreements, oral or written, concerning Dr. Stapleton's employment and compensation. This Agreement may be
amended only in writing signed by Dr. Stapleton and the Chief Executive Officer or Vice President of Human Resources.

16.Governing Law.This Agreement shall be governed by and construed in accordance with the laws of the
State of New Jersey.

Dated
this 1 day of May, 2001.

| |  | PHARMACOPEIA, INC.                         
| |  | -------------------------------------------
| |  | BY:                                        
| |  | /s/MICHAEL R. STAPLETONMichael R. Stapleton

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