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Exhibit 10.91

SPARTA PHARMACEUTICALS, INC.

                       NONQUALIFIED STOCK OPTION AGREEMENT


         AGREEMENT made as of the 17th day of June, 1997, between Sparta
Pharmaceuticals, Inc. (the "Company"), a Delaware corporation having a principal
place of business 111 Rock Road, Horsham, Pennsylvania, and Sir John Vane, an
individual having his residence at White Angles, 7 Beech Dell, Keston Park, Kent
BR2 6EP, England (sometimes referred to below as the "Director" and as the
"Optionee").

         WHEREAS, the Company desires to grant to the Director an Option to
purchase shares of its common stock, $.001 par value (the "Shares") under and
for the purposes of the 1991 Stock Plan of the Company (the "Plan");

         WHEREAS, the Company and the Director understand and agree that any
terms used and not defined herein have the same meanings as in the Plan;

         WHEREAS, the Company and the Director each intend and understand that
the Option granted herein is not an Incentive Stock Option.

         NOW, THEREFORE, in consideration of the mutual covenants hereinafter
set forth and for other good and valuable consideration, the parties hereto
agree as follows:

         1.       GRANT OF OPTION

         The Company hereby irrevocably grants to the Director, as of the date
first set forth above (the "Effective Date"), the right and option to purchase
all or any part of an aggregate of Ten Thousand (10,000) Shares on the terms and
conditions and subject to all the limitations set forth herein and in the Plan,
which is incorporated herein by reference. The number of Shares is subject to
adjustment, as provided in the Plan, in the event of a stock split, reverse
stock split or other events affecting the holders of Shares after the date
hereof. Determinations made in connection with this Option pursuant to the Plan
shall be governed by the Plan as it exists on this date. The Director
acknowledges receipt of a copy of the Plan.

         This Option is in addition to any other options heretofore or hereafter
granted to the Director by the Company, but a duplicate original of this
instrument shall not effect the grant of another option.



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         2.       PURCHASE PRICE

         The purchase price of the Shares covered by the Option shall be at a
price per Share of Eighty One and One Quarter Cents ($.8125) (subject to
adjustment, as provided in the Plan, in the event of a stock split, a further
reverse stock split or other events affecting the holders of Shares). Payment
may be by cash or certified check.

         3.       EXERCISE OF OPTION

         If Director's service to the Company has continued on the following
dates, the Director may exercise the Option for the number of Shares (subject to
adjustment as provided in the Plan) set opposite the applicable date:

         Prior to the first anniversary                      as to no Shares
           of the Effective Date

         On or after the first anniversary                   up to 10,000 Shares
           of the Effective Date

The foregoing rights are cumulative and subject to the other terms and
conditions of this Agreement and the Plan, including, without limitation, the
term of the Option and the provisions affecting the Director's ability to
exercise the Option after termination of the employment.


         4.       TERM OF OPTION

         The Option shall terminate ten (10) years from the date of this
Agreement, but shall be subject to earlier termination as provided herein or in
the Plan.

         a.       Termination of Service (Other than for Death or Disability)

         If the Director's service to the Company ceases (for any reason other
than death or Disability), the Option may be exercised within three (3) months
after the date the Director's employment ceases, or within the originally
prescribed term of the Option, whichever is earlier, but may not be exercised
thereafter.

         Notwithstanding the foregoing, in the event of the Director's death
within three (3) months after the termination of such service, the Optionee's
Survivors may exercise the Option within one (1) year after the date of the
Director's death, but in no event after the date of expiration of the term of
the Option.




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         b.       Termination of Service as a Result of Disability or Death

         In the event the Director's service to the Company terminates by reason
of Disability, as determined in accordance with the Plan, or death, the Option
shall be exercisable only within one (1) year after the date of such Disability
or death, as the case may be, or if earlier, the term originally prescribed by
the Option.

         c.       Change of Status

         The term, "service to the Company" as used in this Agreement shall
include service as a member of the Board of Directors of the Company or as a
consultant to the Company, or any of its Affiliates, and a change of status from
consultant to Director or Director to consultant shall not be treated as a
termination of "service to the Company" hereunder.

         5.       METHOD OF EXERCISING OPTION

         Subject to the terms and conditions of this Agreement, including,
without limitation, Section 10 hereof, the Option may be exercised by written
notice to the Company, at the principal executive office of the Company. Such
notice shall state the election to exercise the Option and the number of Shares
in respect of which it is being exercised, shall be signed by the person or
persons so exercising the Option, and shall be in substantially the form
attached hereto as Exhibit A. Such notice shall be accompanied by payment of the
full purchase price for such Shares in United States dollars, and the Company
shall deliver a certificate or certificates representing such Shares as soon as
practicable after the notice shall be received, provided, however, that the
Company may delay issuance of such Shares until completion of any action or
obtaining of any consent, which the Company deems necessary under any applicable
law (including, without limitation, state securities or "blue sky" laws). The
certificate or certificates for the Shares as to which the Option shall have
been so exercised shall be registered in the name of the person or persons so
exercising the Option (or, if the Option shall be exercised by Director and if
Director shall so request in the notice exercising the Option, shall be
registered in the name of the Director and another person jointly, with right of
survivorship) and shall be delivered as provided above to or upon the written
order of the person or persons exercising the Option. In the event the Option
shall be exercised, pursuant to Section 4 hereof, by any person or persons other
than the Director, such notice shall be accompanied by appropriate proof of the
right of such person or persons to exercise the Option. All Shares that shall be
purchased upon the exercise of the Option as provided herein shall be fully paid
and non-assessable.

         6.       PARTIAL EXERCISE

         Exercise of this Option to the extent above stated may be made in part
at any time and from time to time within the above limits, except that no
fractional Share shall be issued pursuant to this Option.

         7.       NON-ASSIGNABILITY



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         The Option shall not be transferable by the Director otherwise than by
will or by the laws of descent and distribution and shall be exercisable, during
the Director's lifetime, only by the Director. Except as provided in the
preceding sentence, the Option shall not be assigned, pledged or hypothecated in
any way (whether by operation of law or otherwise) and shall not be subject to
execution, attachment or similar process. Any attempted transfer, assignment,
pledge, hypothecation or other disposition of the Option or of any rights
granted hereunder contrary to the provisions of this Section 7, or the levy of
any attachment or similar process upon the Option or such rights, shall be null
and void.

         8.       NO RIGHTS AS STOCKHOLDER UNTIL EXERCISE

         The Director shall have no rights as a stockholder with respect to
Shares subject to this Agreement until a stock certificate therefor has been
issued to the Director and is fully paid for. Except as is expressly provided in
the Plan with respect to certain changes in the capitalization of the Company,
no adjustment shall be made for dividends or similar rights for which the record
date is prior to the date such stock certificate is issued.

         9.       CAPITAL CHANGES AND BUSINESS SUCCESSIONS

         The Plan contains provisions covering the treatment of Options in a
number of contingencies such as stock splits and mergers and sales of the
Company. Provisions in the Plan for adjustment with respect to stock subject to
Options and the related provisions with respect to successors to the business of
the Company are hereby made applicable hereunder and are incorporated herein by
reference.

         10.      TAXES AND WITHHOLDING

         The Director acknowledges that any income or other taxes due from him
or her with respect to this Option or the Shares issuable pursuant to this
Option shall be the Director's responsibility.

         In the event of the exercise of this Option, the Company may withhold
from the Director's fees, if any, or other remuneration, or as a condition of
the exercise hereof, may require the Director to pay, additional federal, state,
and local income tax withholding and if applicable at such time, Director
contributions to employment taxes, in respect of the amount that is considered
compensation includable in such person's gross income.

         11.      PURCHASE FOR INVESTMENT

         Unless the offering and sale of the Shares to be issued upon the
particular exercise of the Option shall have been effectively registered under
the Securities Act of 1933, as now in force or hereafter amended (the "Act"),
the Company shall be under no obligation to issue the Shares covered by such
exercise unless and until the following conditions have been fulfilled:

         (a)      The person(s) who exercise the Option shall warrant to the
                  Company, at the


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                  time of such exercise, that such person(s) are acquiring such
                  Shares for their own respective accounts, for investment, and
                  not with a view to, or for sale in connection with, the
                  distribution of any such Shares, in which event the person(s)
                  acquiring such Shares shall be bound by the provisions of the
                  following legend which shall be endorsed upon the
                  certificate(s) evidencing the Shares issued pursuant to such
                  exercise:

                           "The shares represented by this certificate have been
                           taken for investment and they may not be sold or
                           otherwise transferred by any person, including a
                           pledgee, unless (1) either (a) a registration
                           statement with respect to such shares shall be
                           effective under the Securities Act of 1933, as
                           amended, or (b) the Company shall have received an
                           opinion of counsel satisfactory to it that an
                           exemption from registration under such Act is then
                           available, and (2) there shall have been compliance
                           with all applicable state securities laws."

         (b)      If the Company so requires, the Company shall have received an
                  opinion of its counsel that the Shares may be issued upon such
                  particular exercise in compliance with the Act without
                  registration thereunder. Without limiting the generality of
                  the foregoing, the Company may delay issuance of the Shares
                  until completion of any action or obtaining of any consent
                  which the Company deems necessary under any applicable law
                  (including without limitation state securities or "blue sky"
                  laws).

         12.      NO OBLIGATION TO RETAIN

         Neither the Company nor any subsidiary is by the Plan or this Agreement
obligated to continue the Director as an Director to the Company or any
subsidiary or in any other capacity.

         13.      OPTION IS NOT AN INCENTIVE STOCK OPTION

      The parties each intend and understand that the Option is not an incentive
stock option. Director should consult with Director's own tax advisors regarding
the tax effects of the Option.

         14.      CONSULTATION WITH TAX ADVISOR

         Director should consult with Director's own tax advisors regarding the
tax effects of the Option and the consequences of the nonqualified status of the
Option.

         15.      NOTICES

         Any notices required or permitted by the terms of this Agreement or the
Plan shall be given when delivered in person or by overnight courier with a
receipt obtained therefor, or by registered or certified mail, return receipt
requested, addressed as follows:


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                                 To the Company:

                                 Sparta Pharmaceuticals, Inc.
                                 111 Rock Road
                                 Horsham, PA   19044-2310
                                 Attn: President


                                 To the Director:

                                 Sir John Vane
                                 White Angles
                                 7 Beech Dell
                                 Keston Park
                                 Kent BR2 6EP
                                 England

or to such other address or addresses of which notice in the same manner has
previously been given. Any such notice shall be deemed to have been given when
received in accordance with the foregoing provisions.

         16.      GOVERNING LAW

         This Agreement shall be construed and enforced in accordance with the
law of the State of Delaware.

         17.      BENEFIT OF AGREEMENT

         Subject to the provisions of the Plan and the other provisions hereof,
this Agreement shall be for the benefit of and shall be binding upon the heirs,
executors, administrators, successors and assigns of the parties hereto.

         18.      ENTIRE AGREEMENT

         This Agreement, together with the Plan, embodies the entire agreement
and understanding between the parties hereto with respect to the subject matter
hereof and supersedes all prior oral or written agreements and understandings
relating to the subject matter hereof. No statement, representation, warranty,
covenant or agreement not expressly set forth in this Agreement shall affect or
be used to interpret, change or restrict, the express terms and provisions of
this Agreement, provided, however, in any event, this Agreement shall be subject
to and governed by the Plan.

         19.      MODIFICATIONS AND AMENDMENTS

         The terms and provisions of this Agreement may be modified or amended
only by written agreement executed by all parties hereto.


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         20.      WAIVERS AND CONSENTS

         The terms and provisions of this Agreement may be waived, or consent
for the departure therefrom granted, only by written document executed by the
party entitled to the benefits of such terms or provisions. No such waiver or
consent shall be deemed to be or shall constitute a waiver or consent with
respect to any other terms or provisions of this Agreement, whether or not
similar. Each such waiver or consent shall be effective only in the specific
instance and for the purpose for which it was given, and shall not constitute a
continuing waiver or consent.

         21.      HEADINGS AND CAPTIONS

         The headings and captions of the various subdivisions of this Agreement
are for convenience of reference only and shall in no way modify, or affect the
meaning or construction of, any of the terms or provisions hereof.

         22.      SURVIVAL

         The expiration or other termination of the Option granted to the
Director shall neither affect nor alter the Director's obligations under
Sections 10 and 11 hereof.



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         IN WITNESS WHEREOF, the Company has caused this Nonqualified Stock
Option Agreement to be executed by a duly authorized officer, and the Director
has hereunto set his or her hand, all as of the day and year first above
written.


                                      SPARTA PHARMACEUTICALS, INC.


                                      By       /s/ William M. Sullivan
                                         -------------------------------
                                               William M. Sullivan
                                               Chairman of the Board




                                                /s/ John Vane
                                      ----------------------------------
                                               Sir John Vane







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                                                                       EXHIBIT A


                 NOTICE OF EXERCISE OF NONQUALIFIED STOCK OPTION


To:  Sparta Pharmaceuticals, Inc.


Ladies and Gentlemen:

         I hereby exercise my Nonqualified Option to purchase ________ shares
(the "Shares") of the common stock, $.001 par value, of Sparta Pharmaceuticals,
Inc. (the "Company"), at the exercise price of $____ per share, pursuant to and
subject to the terms of that certain Nonqualified Stock Option Agreement between
the undersigned and the Company dated as of June 17, 1997.

         I am aware that the Shares have not been registered under the
Securities Act of 1933, as amended (the "1933 Act") or any state securities
laws. I understand that the reliance by the Company on exemptions under the 1933
Act is predicated in part upon the truth and accuracy of the statements by me in
this Notice of Exercise.

         I hereby represent and warrant that (1) I have been furnished with all
information which I deem necessary to evaluate the merits and risks of the
purchase of the Shares; (2) I have had the opportunity to ask questions
concerning the Shares and the Company and all questions posed have been answered
to my satisfaction; (3) I have been given the opportunity to obtain any
additional information I deem necessary to verify the accuracy of any
information obtained concerning the Shares and the Company; and (4) I have such
knowledge and experience in financial and business matters that I am able to
evaluate the merits and risks of purchasing the Shares and to make an informed
investment decision relating thereto.

         I hereby represent and warrant that I am purchasing the Shares for my
own personal account for investment and not with a view to the sale or
distribution of all or any part of the Shares.

         I understand that because the Shares have not been registered under the
1933 Act, I must continue to bear the economic risk of the investment for an
indefinite time and the Shares cannot be sold unless the Shares are subsequently
registered under applicable federal and state securities laws or an exemption
from such registration requirements is available.

         I agree that I will in no event sell or distribute or otherwise dispose
of all or any part of the Shares unless (1) there is an effective registration
statement under the 1933 Act and applicable state securities laws covering any


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such transaction involving the Shares or (2) the Company receives an opinion of
my legal counsel (concurred in by legal counsel for the Company) stating that
such transaction is exempt from registration or the Company otherwise satisfies
itself that such transaction is exempt from registration.

         I consent to the placing of a legend on my certificate for the Shares
stating that the Shares have not been registered and setting forth the
restriction on transfer contemplated hereby and to the placing of a stop
transfer order on the books of the Company and with any transfer agents against
the Shares until the Shares may be legally resold or distributed without
restriction.

         I understand that at the present time Rule 144 of the Securities and
Exchange Commission (the "SEC") may not be relied on for the resale or
distribution of the Shares by me. I understand that the Company has no
obligation to me to register the Shares with the SEC and has not represented to
me that it will register the Shares.

         I am aware that it is my responsibility to have consulted with
competent tax and legal advisors about the relevant national, state and local
income tax and securities laws affecting the exercise of the Option and the
purchase and subsequent sale of the Shares.

         My check payable to the order of the Company in the amount of $ is
enclosed in payment of 100% of the option exercise price for the Shares.

         I acknowledge that the Company is authorized to withhold from my wages,
if any, or other remuneration, or may require me, as a condition of the exercise
of the Option, to pay, additional federal, state and local income tax
withholding and if applicable, Director contributions to employment taxes in
respect of the amount that is considered compensation includable in my gross
income.

         Please issue the stock certificate for the Shares (check one):

         ____  to me

         ____  to me and   _________ as joint tenants with right of survivorship

         and mail the certificate to me at the following address:

         ____________________________________________________

         ____________________________________________________



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         My mailing address, if different from the address listed above, for
shareholder communications is:



         ____________________________________________________

         ____________________________________________________


                                            Very truly yours,



                                            ---------------------------
                                            Director (signature)


                                            ---------------------------
                                            Print Name


                                            ---------------------------
                                            Date


                                            ---------------------------
                                            Social Security Number