Document:

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                                                                   Exhibit 10.20

                                 UROGEN CORP.

                        COMMON STOCK PURCHASE AGREEMENT

     THIS COMMON STOCK PURCHASE AGREEMENT (the "Agreement") is made as of
February 22, 2000 by and among UroGen Corp., a Delaware corporation (the
"Company"), with its principal office at 10835 Altman Row, Suite 150, San Diego,
California 92121 and the investors whose names appear on the Schedule of
Investors attached hereto as Exhibit A (the "Investors").
                             ---------

                                   ARTICLE I

                           Purchase of Common Stock

     1.1  Common Stock.  Subject to the terms and conditions hereof, the Company
          ------------
will issue and sell to each Investor, and each Investor will each purchase from
the Company, severally, the number of shares (the "Shares") of the Company's
Common Stock (the "Common Stock") set forth opposite such Investor's name on the
Schedule of Investors, at a purchase price of $8.50 per Share. The maximum
aggregate number of Shares issuable hereunder is 2,000,000 Shares.

     1.2  Purchase Price.  The purchase price payable by each Investor for
          --------------
the Shares to be purchased hereunder (the "Purchase Price") shall be equal to
the number of Shares to be purchased by that Investor multiplied by $8.50, as
set forth opposite such Investor's name on the Schedule of Purchasers.

     1.3  Obligations of Investors.  The obligations of the Investors hereunder
          ------------------------
are several and not joint.

                                  ARTICLE II

                             Closing and Delivery

     2.1  Place and Date of Closing.  The initial closing of the transactions
          -------------------------
provided for herein (the "Closing") will be held at the offices of Wilson
Sonsini Goodrich & Rosati, 650 Page Mill Road, Palo Alto, California 94304 at
9:00 a.m. on February 23, 2000 (the "Closing Date") or at such other time and
place as the parties shall mutually agree.

     2.2  Subsequent Closings.  The Company may, at its option, schedule
          -------------------
additional closings (the "Additional Closings") after the first Closing has been
completed on such date or dates as the Company may determine, but not later than
February 29, 2000. The date of each Additional Closing is hereinafter referred
to as an "Additional Closing Date." The first Closing and each Additional
Closing are sometimes referred to herein individually as a "Closing," and the
first Closing Date and each Additional Closing Date are sometimes referred to
herein individually as a "Closing Date." At each Additional Closing, the Company
shall prepare a
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revised Schedule of Investors to include any additional Investors, and each such
additional Investor shall execute a signature page to this Agreement.

     2.3  Delivery.  At the Closing, the Company will deliver to each Investor
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a certificate representing the number of Shares set forth opposite such
Investor's name on the Schedule of Investors. Each Investor shall deliver to the
Company the Purchase Price set forth opposite such Investor's name on the
Schedule of Investors by check or by wire transfer.

                                  ARTICLE III

                 Representations and Warranties of the Company

          The Company hereby represents and warrants to each Investor as
follows:

     3.1  Organization and Standing.  The Company is a corporation duly
          -------------------------
organized and validly existing under, and by virtue of, the laws of the State of
Delaware and is in good standing under such laws. The Company has the requisite
corporate power to own and operate its properties and assets, and to carry on
its business as presently conducted and as proposed to be conducted.

     3.2  Corporate Power.  The Company will have at the Closing all requisite
          ---------------
legal and corporate power to execute and deliver this Agreement, to issue the
Common Stock and to carry out and perform its obligations under the terms of
this Agreement.

     3.3  Authorization.  All corporate action on the part of the Company,
          -------------
its officers, directors and stockholders that is necessary for the
authorization, execution and delivery of this Agreement by the Company, for the
performance of the Company's obligations hereunder, and for the authorization,
issuance and delivery of the Common Stock, has been taken or will be taken prior
to the Closing. This Agreement, when executed and delivered, shall constitute
the legal and binding obligations of the Company, enforceable against the
Company in accordance with their respective terms, subject to judicial
principles respecting election of remedies or limiting the availability of
specific performance, injunctive relief, and other equitable remedies, and
bankruptcy, insolvency, reorganization, moratorium or other similar laws now or
hereafter in effect generally relating to or affecting creditors' rights.

     3.4  Capitalization.
          --------------

          (a)  As of February 22, 2000, the authorized capital stock of the
Company consisted of 40,000,000 shares of Common Stock, of which 18,958,927
shares were issued and outstanding; and 5,000,000 shares of preferred stock
("Preferred Stock"), of which 40,000 shares have been designated Series A
Preferred Stock, of which 5,830 shares were issued and outstanding; 10,000
shares have been designated Series B Preferred Stock, of which 2,998 shares were
issued and outstanding; and 17,000 shares have been designated Series C
Preferred Stock, of which no shares were issued or outstanding. The Series A
Preferred Stock converts to Common Stock on a 1,000-to-1 basis. The Series B and
C Preferred Stock convert to Common

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Stock based upon the fair market value of the Common Stock at the date of
conversion. All issued and outstanding shares of Common Stock and Preferred
Stock have been duly authorized and validly issued, and are fully paid and non-
assessable. The Company has agreed to repay certain indebtedness to Baxter
Healthcare Corporation, under a Credit Agreement dated July 8, 1998, in shares
of Series B Preferred Stock. As of February 22, 2000, the amount of such
indebtedness was $1,876,003, which will convert into 1,876 shares of Series B
Preferred Stock. In addition, Baxter is obligated to purchase shares of Series C
Preferred Stock upon the Company's achievement of certain milestones.

          (b)  As of February 22, 2000, the Company had reserved 5,656,832
shares of Common Stock for issuance to employees, officers, directors and
consultants of the Company, as may be determined by the Company's Board of
Directors from time to time under the Company's 1995 Stock Plan, as amended, and
1999 Stock Plan (the "Option Plans"). As of February 22, 2000, options to
purchase 3,076,842 shares of Common Stock were outstanding. As of February 22,
2000, there were no outstanding rights, options, warrants, preemptive rights,
conversion rights, rights of first refusal or similar rights or agreements, oral
or written, for the purchase or acquisition from the Company of any shares of
its capital stock or any other securities, except for outstanding options under
the Option Plans and the following warrants: (i) in July 1998, in connection
with the issuance of convertible debt, the Company issued warrants, expiring in
July 2005, to purchase 452,500 shares of Common Stock at $0.74 per share; (ii)
in April 1999, in connection with the issuance of additional convertible debt,
the Company issued warrants, expiring in April 2006, to purchase 1,247,500
shares of Common Stock at $0.30 per share; (iii) in October 1999, in connection
with a capital lease line, the Company issued warrants, expiring in October
2006, to purchase 250,000 shares of Common Stock at $0.30 per share; (iv) in
January 2000, in connection with the issuance of Common Stock, the Company
issued warrants to purchase 2,133,899 shares of Common Stock. The warrants
expire five years from date of issuance and are exercisable at $0.75 per share;
(vi) in connection with a guaranty provided by Baxter, the Company has proposed
to issue warrants to Baxter, expiring in January 2005, to purchase 100,000
shares of Common Stock at $2.00 per share.

          (c)  Validity of Securities; Reservation of Shares.  The Shares, when
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issued, sold and delivered in accordance with the terms of this Agreement, will
be duly authorized, validly issued, fully paid and nonassessable and will be
free and clear of any liens or encumbrances; provided, however, that the Shares
                                             --------  -------
may be subject to restrictions on transfer to the extent provided herein or
under state and/or federal securities laws. Based in part upon the
representations of the Investors in this Agreement, the offer, sale and issuance
of the Shares will be in compliance with all applicable federal and state
securities laws.

     3.5  Governmental Consent, etc.  No consent, approval or authorization
          --------------------------
of or designation, declaration or filing with any state or federal governmental
authority on the part of the Company is required in connection with the valid
execution and delivery of this Agreement or the offer, sale or issuance of the
Shares, or the consummation of any other transaction contemplated hereby
(excluding Article VI hereof), except the qualification (or the taking of such
action as may be necessary to secure an exemption from qualification, if
available), under the California Corporate Securities Law and other applicable
blue sky laws, of the offer and sale of

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the Shares, which qualification, if required, will be accomplished in a timely
manner prior to or promptly upon completion of the Closing.

     3.6  SEC Documents; Parent Financial Statements.  The Company has
          ------------------------------------------
furnished or made available to the Investors true and complete copies of all
reports or registration statements filed by it with the U.S. Securities and
Exchange Commission (the "SEC") under the Securities Act of 1933 (the
"Securities Act") or the Securities Exchange Act of 1934 (the "Exchange Act")
since January 1, 1999, all in the form so filed (all of the foregoing being
collectively referred to as the "SEC Documents"), which are all the documents
(other than preliminary materials) that the Company was required to file with
the SEC since such date. As of their respective filing dates, the SEC Documents
complied in all material respects with the requirements of the Securities Act or
the Exchange Act, as the case may be, and none of the SEC Documents contained
any untrue statement of a material fact or omitted to state a material fact
required to be stated therein or necessary to make the statements made therein,
in light of the circumstances in which they were made, not misleading, except to
the extent corrected by a document subsequently filed with the SEC. The
financial statements of the Company, including the notes thereto, included in
the SEC Documents (the "Financial Statements") comply as to form in all material
respects with applicable accounting requirements and with the published rules
and regulations of the SEC with respect thereto, have been prepared in
accordance with generally accepted accounting principles consistently applied
(except as may be indicated in the notes thereto or, in the case of unaudited
statements, as permitted by Form 10-Q of the SEC) and present fairly the
consolidated financial position of the Company at the dates thereof and the
consolidated results of its operations and cash flows for the periods then ended
(subject, in the case of unaudited statements, to normal recurring adjustments).
There has been no change in the Company's accounting policies except as
described in the notes to the Financial Statements.

     3.7  No Material Adverse Change.  Since the date of the balance sheet
          --------------------------
included in the Company's most recently filed report on Form 10-QSB or Form
10-KSB, the Company has conducted its business in the ordinary course and there
has not occurred: (a) any material adverse change in the financial condition,
liabilities, assets or business of the Company; (b) any amendment or change in
the Certificate of Incorporation or Bylaws of the Company; or (c) any damage to,
destruction or loss of any assets of the Company (whether or not covered by
insurance) that materially and adversely affects the financial condition or
business of the Company.

     3.8  Litigation.  There is no action, suit, proceeding, claim, arbitration
          ----------
or investigation pending, or as to which the Company has received any notice of
assertion against the Company, which in any manner challenges or seeks to
prevent, enjoin, alter or materially delay any of the transactions contemplated
by this Agreement.

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                                  ARTICLE IV

                Representations and Warranties of the Investors

     Each Investor represents and warrants to the Company, as of the Closing
Date, as follows:

     4.1  Authorization.  All action on the part of the Investor for the
          -------------
authorization, execution, delivery and performance by the Investor of this
Agreement has been taken, and this Agreement constitutes a valid and binding
obligation of the Investor, enforceable in accordance with its terms, except as
may be limited by applicable bankruptcy, insolvency, reorganization, or similar
laws relating to or affecting the enforcement of creditors' rights.

     4.2  Experience/Risk.  The Investor is experienced in evaluating and
          ---------------
investing in new companies such as the Company. The Investor is a sophisticated
investor with such knowledge and experience in financial and business matters so
as to be capable of evaluating the merits and risks of a prospective investment
in the Securities and of bearing the economic risks of such investment.

     4.3  Investment.  The Investor is acquiring the Shares for investment
          ----------
for its own account and not with a view to, or for resale in connection with,
any distribution. The Investor understands that the Shares to be acquired have
not been registered under the Securities Act by reason of a specific exemption
from the registration provisions of the Securities Act that depends upon, among
other things, the bona fide nature of the investment intent as expressed herein.

     4.4  Restricted Securities.  The Investor acknowledges that the Shares
          ---------------------
must be held indefinitely unless subsequently registered under the Securities
Act or unless an exemption from such registration is available. The Investor is
aware of the provisions of Rule 144 promulgated under the Securities Act, which
permits limited resale of securities purchased in a private placement subject to
the satisfaction of certain conditions, including, in case the Investor has held
the Shares for less than two years or is an affiliate of the Company, among
other things: the availability of certain current public information about the
Company, the resale occurring not less than one year after a party has purchased
and paid for the Shares to be sold, the sale being through a "broker's
transaction" or in transactions directly with a "market maker," and the number
of Shares being sold during any three-month period not exceeding specified
limitations.

     4.5  Limited Public Market.  The Investor understands that only an
          ---------------------
extremely limited public market now exists for the Common Stock, and that a
public market for the Common Stock may not develop or be sustained sufficiently
to permit the resale of the Shares.

     4.6  Access to Data.  The Investor has had an opportunity to discuss
          --------------
the Company's business, management and financial affairs with the Company's
management. The Investor understands that such discussions, as well as the
written information issued by the Company, were intended to describe the aspects
of the Company's business and prospects which it believes to be material but
were not necessarily a thorough or exhaustive description.

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     4.7  Accredited Investor Status.  The Investor currently does and will
          --------------------------
as of the Closing Date qualify as an "accredited investor" within the meaning of
Regulation D (17 C.F.R. (S) 230.501) of the rules and regulations promulgated
under the Securities Act.

     4.8  Government Consents.  No consent, approval or authorization of or
          -------------------
designation, declaration or filing with any state, federal or foreign
governmental authority on the part of the Investor is required in connection
with the valid execution and delivery of this Agreement by the Investor and the
consummation by the Investor of the transactions contemplated hereby.

     4.9  Legends.  Each certificate representing the Shares shall be endorsed
          -------
with the following legend (in addition to any legend required under applicable
state securities laws):

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
     INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933.
     SUCH SECURITIES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH
     REGISTRATION, UNLESS SUCH SALE OR TRANSFER IS EXEMPT FROM THE REGISTRATION
     AND PROSPECTUS DELIVERY REQUIREMENT OF SAID ACT. COPIES OF THE AGREEMENT
     COVERING THE ACQUISITION OF THESE SECURITIES AND RESTRICTING THEIR TRANSFER
     MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER OF RECORD
     OF THIS CERTIFICATE TO THE SECRETARY OF THE CORPORATION AT THE PRINCIPAL
     EXECUTIVE OFFICES OF THE CORPORATION.

The Company need not record, and may instruct its transfer agent not to record,
a transfer of Shares, unless the conditions specified in the foregoing legend
are satisfied.

                                   ARTICLE V

                 Transfer Restrictions; Rights as Stockholder

     5.1  Restrictions on Transfer.  Each Investor acknowledges that the Shares
          ------------------------
may not be transferred or assigned in whole or in part without (i) the prior
written consent of the Company and (ii) compliance with applicable federal and
state securities laws; provided, however, that the Securities may be transferred
                       --------  -------
without the prior written consent of the Company in the following transactions:

          (a)  A transfer of Shares in whole by a holder who is a natural person
during such holder's lifetime or on death by will or intestacy to such holder's
immediate family or to any custodian or trustee for the account of such holder
or such holder's immediate family. As used herein, "immediate family" shall mean
spouse, lineal descendant, father, mother, brother, or sister of the holder.

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          (b)  A transfer of Shares in whole to the Company or to any
stockholder of the Company.

          (c)  A transfer of Shares in whole or in part to a person who, at the
time of such transfer, is, or is an affiliate of, an officer or director of the
Company.

          (d)  A transfer of Shares in whole but not in part pursuant to and in
accordance with the terms of any merger, consolidation, reclassification of
shares or capital reorganization of a corporate stockholder or pursuant to a
sale of all or substantially all of the stock or assets of a corporate
stockholder.

          (e)  A transfer of Shares in accordance with Rule 144 under the
Securities Act.

          (f)  A transfer of Shares by a holder which is a limited or general
partnership to any of its partners or former partners.

          (g)  A transfer of Shares which is registered under the Securities
Act.

                                  ARTICLE VI

                              Registration Rights

     6.1  Registrable Securities.  The Shares shall be deemed "Registrable
          ----------------------
Securities," and the holders of such shares (the "Holders") shall be entitled to
registration rights with respect thereto as set forth in this Article VI.

     6.2  Registration.  The Company shall use commercially reasonable efforts
          ------------
to cause the Registrable Securities held by each Holder to be registered under
the Securities Act so as to permit the resale thereof, and in connection
therewith shall use all commercially reasonable efforts to prepare and file with
the Securities and Exchange Commission (the "SEC") on or before 90 days after
the date hereof, and shall use commercially reasonable efforts to cause to
become effective as soon as practicable thereafter, a registration statement
under the Securities Act covering the Registrable Securities; provided, however,
                                                              --------  -------
that each Holder shall provide all such information and materials to the Company
and take all such action as may be required in order to permit the Company to
comply with all applicable requirements of the SEC and to obtain any desired
acceleration of the effective date of such registration statement. Such
provision of information and materials is a condition precedent to the
obligations of the Company to such Holder pursuant to this Article VI. The
Company shall not be required to effect more than one (1) registration under
this Article VI.

     6.3  Company Obligations.  The Company shall (i)  keep the registration
          -------------------
statement filed in accordance with Section 6.2 hereof effective until the
earlier of (A) two years after the registration statement has been declared
effective by the SEC or (B) such time as no Holders shall own any Shares; (ii)
forthwith prepare and file with the SEC such amendments and supplements to such
registration statement and the prospectus used in connection therewith as may be
necessary to comply with the provisions of the Securities Act with respect to
the sale or

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other disposition of all securities proposed to be registered in such
registration statement; (iii) furnish to each Holder such number of copies of
any prospectus (including any preliminary prospectus and any amended or
supplemented prospectus) in conformity with the requirements of the Securities
Act, and such other documents, as each Holder may reasonably request in order to
effect the offering and sale of the shares of the Registrable Securities to be
offered and sold, but only while the Company shall be required under the
provisions hereof to cause the registration statement to remain current; (iv)
provide a CUSIP number, transfer agent and registrar for all Registrable
Securities; and (v) use its commercially reasonable efforts to register or
qualify the shares of the Registrable Securities covered by such registration
statement under the securities or blue sky laws of such jurisdictions as each
Holder shall reasonably request (provided that the Company shall not be required
in connection therewith or as a condition thereto to qualify to do business or
to file a general consent to service of process in any such jurisdiction where
it has not been qualified). The Company agrees to pay to each Holder an amount
equal to $0.001 per Share held by such Holder for each day that the Company has
failed to have filed a registration statement as required by Section 6.2 hereof
beyond 90 days after the date hereof.

     6.4  Underwriting.  If the distribution of the Registrable Securities
          ------------
covered by a registration pursuant to this Article VI is to be effected by means
of a firm commitment underwriting, the right of any Holder to include
Registrable Securities in such registration shall be conditioned upon such
Holder's participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting to the extent provided herein.

          (a)  The Company (together with all Holders proposing to distribute
their securities through such underwriting) shall enter into an underwriting
agreement in customary form with a managing underwriter of nationally recognized
standing selected for such underwriting by the Company but subject to the
approval of a majority in interest of the Holders, which approval shall not
unreasonably be withheld. Notwithstanding any other provision of this Article
VI, if the managing underwriter determines that marketing factors require a
limitation of the number of shares to be underwritten, then the underwriters may
limit the number of shares of Registrable Securities that may be included in the
registration and underwriting, provided that no shares other than Registrable
Securities are included in such registration and underwriting. The shares so
limited shall be allocated among Holders in proportion, as nearly as
practicable, to the respective amounts of Registrable Securities held by such
Holders at the time of filing the registration statement. No Registrable
Securities excluded from the underwriting by reason of the managing
underwriter's marketing limitation shall be included in such registration. If
any Holder disapproves of the terms of the underwriting, such Holder may elect
to withdraw therefrom by written notice to the Company and the managing
underwriter. The Registrable Securities so withdrawn from such underwriting
shall also be withdrawn from registration; provided, however, that if by the
                                           --------  -------
withdrawal of such Registrable Securities a greater number of Registrable
Securities held by other Holders may be included in such registration (up to the
maximum of any limitation imposed by the underwriters), then the Company shall
offer to all Holders who have included Registrable Securities in the
registration the right to include additional Registrable Securities in the same
proportion used in determining the underwriter limitation as set forth above.

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          (b)  If the managing underwriter has not limited the number of
Registrable Securities to be underwritten in any registration requested pursuant
to Section 6.2, the Company may include securities for its own account or for
the account of others in such registration if the managing underwriter so agrees
and if the number of Registrable Securities held by Holders which would
otherwise have been included in such registration and underwriting will not
thereby be limited. The inclusion of such shares shall be on the same terms as
for the Registrable Securities, subject to the following sentence. In the event
that the managing underwriter excludes some of the securities to be registered
pursuant to Section 6.2, the securities to be sold for the account of the
Company and any other holders shall be excluded in their entirety prior to the
exclusion of any Registrable Securities.

     6.5  Selling Procedures.  Any sale of Registrable Securities pursuant to
          ------------------
the registration statement filed in accordance with Section 6.2 hereof shall be
subject to the following conditions and procedures:

          (a)  Updating the Prospectus.  If the distribution of the Registrable
               -----------------------
Securities covered by a registration pursuant to this Article VI is not to be
effected by means of a firm commitment underwriting, and if the Company informs
the selling Holders that the registration statement or final prospectus then on
file with the SEC is not current or otherwise does not comply with the
Securities Act, the Company shall use commercially reasonable efforts to provide
to the selling Holders a current prospectus that complies with the Securities
Act on or before the date of the intended sale of the Registrable Securities;
provided, however, that no more than once during any one hundred eighty-day
--------  -------
period (the "Information Delay Period"), the Company shall have the right to
delay the preparation of a current prospectus that complies with the Securities
Act for up to forty-five (45) days, if the Board of Directors of the Company,
acting in good faith, determines that there exists material nonpublic
information about the Company which the Board does not wish to disclose in a
registration statement (due to the fact that such disclosure may not be in the
best interests of the Company's stockholders), which information would otherwise
be required by the Securities Act to be disclosed in the registration statement
to be filed pursuant to Section 6.2 above;

          (b)  General.  Notwithstanding the foregoing, the Company shall notify
               -------
each Holder (A) of any request by the SEC or any other federal or state
governmental authority during the period of effectiveness of the registration
statement for amendments or supplements to the registration statement or related
prospectus or for additional information relating to the registration statement,
(B) of the issuance by the SEC or any other federal or state governmental
authority of any stop order suspending the effectiveness of the registration
statement or the initiation of any proceedings for that purpose, (C) of the
receipt by the Company of any notification with respect to the suspension of the
qualification or exemption from qualification of any of the Registrable
Securities for sale in any jurisdiction or the initiation or threatening of any
proceeding for such purpose, or (D) of the happening of any event which makes
any statement made in the registration statement or related prospectus or any
document incorporated or deemed to be incorporated therein by reference untrue
in any material respect or which requires the making of any changes in the
registration statement or prospectus so that, in the case of the registration
statement, it will not contain an untrue statement of a material fact or omit to
state a

                                      -9-
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material fact required to be stated therein or necessary to make the statements
therein not misleading, and that in the case of the prospectus, it will not
contain an untrue statement of a material fact or omit to state a material fact
necessary in order to make the statements therein, in the light of the
circumstances under which they were made, not misleading. In such event, the
Company may suspend use of the prospectus on written notice to each Holder, in
which case each Holder shall not dispose of Registrable Securities covered by
the registration statement or prospectus until copies of a supplemented or
amended prospectus are distributed to the Holders or until the Holders are
advised in writing by the Company that the use of the applicable prospectus may
be resumed. The Company shall use its commercially reasonable efforts to ensure
that the use of the prospectus may be resumed as soon as practicable. The
Company shall use its commercially reasonable efforts to obtain the withdrawal
of any order suspending the effectiveness of the registration statement, or the
lifting of any suspension of the qualification (or exemption from qualification)
of any of the securities for sale in any jurisdiction. The Company shall, upon
the occurrence of any event contemplated by clause (D), forthwith prepare a
supplement or post-effective amendment to the registration statement or a
supplement to the related prospectus or any document incorporated therein by
reference or file any other required document so that, as thereafter delivered
to the purchasers of the Registrable Securities being sold thereunder, such
prospectus will not contain an untrue statement of a material fact or omit to
state a material fact necessary to make the statements therein, in light of the
circumstances under which they were made, not misleading.

     6.6  Expenses.  The Company shall reimburse, in an amount not to exceed
          --------
$25,000, the out-of-pocket expenses of the Holders incurred, other than
underwriting or selling discounts and commissions, in connection with the
registration of Registrable Securities pursuant to this Article VI including,
without limitation, all SEC, National Association of Securities Dealers, Inc.
and blue sky registration and filing fees, printing expenses, transfer agents'
and registrars' fees, and the reasonable fees and disbursements of the Company's
outside counsel and the Company's independent accountants.

     6.7  Indemnification.
          ---------------

          (a)  In connection with any registration pursuant to this Article VI,
the Company will indemnify each Holder, each of its officers and directors and
partners, and each person controlling such Holder within the meaning of Section
15 of the Securities Act, with respect to which registration has been effected
pursuant to this Agreement, against all expenses, claims, losses, damages or
liabilities (or actions in respect thereof), including any of the foregoing
incurred in settlement of any litigation, commenced or threatened, arising out
of or based on any untrue statement (or alleged untrue statement) of a material
fact contained in any registration statement, prospectus, offering circular or
other document, or any amendment or supplement thereto, incident to any such
registration, or based on any omission (or alleged omission) to state therein a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances in which they were made, not misleading,
or any violation by the Company of the Securities Act, the Exchange Act, state
securities laws or any rule or regulation promulgated under such laws applicable
to the Company in connection with any such registration, and the Company will
reimburse each such Holder, each of its officers and

                                     -10-
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directors, and each person controlling such Holder, for any legal and any other
expenses reasonably incurred, as such expenses are incurred, in connection with
investigating, preparing or defending any such claim, loss, damage, liability or
action, provided that the Company will not be liable in any such case to the
extent that any such claim, loss, damage, liability or expense arises out of or
is based on any untrue statement or omission or alleged untrue statement or
omission, made in reliance upon information furnished to the Company by such
Holder or controlling person, provided, however, that the foregoing indemnity
agreement is subject to the condition that, insofar as it relates to any such
untrue statement, alleged untrue statement, omission or alleged omission made in
a preliminary prospectus on file with the Commission at the time the
registration statement becomes effective or the amended prospectus is filed with
the Commission pursuant to Rule 424(b) (the "Final Prospectus"), such indemnity
agreement shall not inure to the benefit of any Holder, if a copy of the Final
Prospectus was not furnished to the person asserting the loss, liability, claim
or damage at or prior to the time such action is required by the Securities Act,
and if the Final Prospectus would have cured the defect giving rise to the loss,
liability, claim or damage .

          (b)  Each Holder will indemnify the Company, each of its directors and
officers, other holders of the Company's securities covered by such registration
statement, each person who controls the Company within the meaning of Section 15
of the Securities Act, and each other such Holder, each of its officers and
directors and each person controlling such other Holder within the meaning of
Section 15 of the Securities Act, against all claims, losses, damages and
liabilities (or actions in respect thereof) arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any such registration statement, prospectus, offering circular or other
document, or any omission (or alleged omission) to state therein a material fact
required to be stated therein or necessary to make the statements therein not
misleading, or any violation by the Holder of the Securities Act, the Exchange
Act, state securities laws or any rule or regulation promulgated under such laws
applicable to the Holder, and will reimburse the Company, such other Holders,
such directors, officers, persons, underwriters or control persons for any legal
or any other expenses reasonably incurred, as such expenses are incurred, in
connection with investigating or defending any such claim, loss, damage,
liability or action, to the extent that such untrue statement (or alleged untrue
statement) or omission (or alleged omission) is made in such registration
statement, prospectus, offering circular or other document in reliance
information furnished to the Company by such Holder.

          (c)  Each party entitled to indemnification under this Section 6.7 (an
"Indemnified Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
has actual knowledge of any claim as to which indemnity may be sought, and shall
permit the Indemnifying Party to assume the defense of any such claim or any
litigation resulting therefrom, provided that counsel for the Indemnifying
Party, who shall conduct the defense of such claim or litigation, shall be
approved by the Indemnified Party (whose approval shall not unreasonably be
withheld), and the Indemnified Party may participate in such defense at such
party's expense, and provided further that the failure of any Indemnified Party
to give notice as provided herein shall not relieve the Indemnifying Party of
its obligations under this Agreement unless the failure to give such notice is
materially prejudicial to an Indemnifying Party's ability to defend such action,
and provided

                                     -11-
<PAGE>

further that the Indemnifying Party shall not assume the defense for matters as
to which there is a conflict of interest or there are separate and different
defenses; provided, that the Indemnifying Party shall remain liable for
reasonable legal expenses of one counsel for the Indemnified Party. No
Indemnifying Party, in the defense of any such claim or litigation, shall,
except with the consent of each Indemnified Party (whose consent shall not be
unreasonably withheld), consent to entry of any judgment or enter into any
settlement which does not include as an unconditional term thereof the giving by
the claimant or plaintiff to such Indemnified Party of a release from all
liability in respect to such claim or litigation.

          (d)  Notwithstanding the foregoing, to the extent that provisions
relating to indemnification and contribution contained in an underwriting
agreement entered into in connection with an underwritten public offering
pursuant to Section 6.4 are in conflict with the foregoing provisions, the
provisions in such underwriting agreement shall control.

                                  ARTICLE VII

                     Additional Covenants of the Investors

     7.1  Voting.  Until such time as an Investor holds securities of the
          ------
Company representing less than 5% of the total outstanding voting stock of the
Company, such Investor shall: (i) take such all action necessary or appropriate
such that all voting stock owned by such Investor and its affiliates are voted
(in person or by proxy) (A) for the nominees to the Company's Board of Directors
nominated and recommended to the Company's stockholders by the Company
management, and (B) on all other matters to be voted on by the Company's
stockholders, in such manner as is recommended by the Company's management to
the stockholders; and (ii) be present, in person or by proxy, at all duly held
meetings of the stockholders of the Company so that all voting stock held by
such Investor may be counted for purposes of determining the presence of a
quorum at such meetings.

     7.2  Voting Trusts.  Except as consented to by the Company in writing, no
          -------------
Investor shall deposit any voting stock of the Company owned by it in a voting
trust or subject any such stock to any similar arrangement or agreement with
respect to the voting of such stock.

     7.3  Solicitation of Proxies.  Without the Company's prior written consent,
          -----------------------
no Investor shall solicit proxies with respect to any voting stock of the
Company, nor become a "participant" in any "election contest" as such terms are
used in Rule 14a-11 of Regulation 14A under the Exchange Act relating to the
election of directors of the Company.

     7.4  Acts in Concert with Others.  Except as permitted in writing by the
          ---------------------------
Company, no Investor shall join any group or otherwise act in concert with any
third person for the purpose of acquiring, holding or disposing of voting stock
of the Company.

                                     -12-
<PAGE>

                                 ARTICLE VIII

                                 Miscellaneous

     8.1  Waivers and Amendments.  With the written consent of the holders of a
          ----------------------
majority of the Shares, the obligations of the Company and the rights of the
holders of Shares under this Agreement may be waived (either generally or in a
particular instance, either retroactively or prospectively and either for a
specified period of time or indefinitely), and with the same consent the
Company, when authorized by resolution of its board of directors, may enter into
a supplementary agreement for the purpose of adding any provisions to or
changing in any manner or eliminating any of the provisions of this Agreement;
provided, however, that (i) all persons affected by such waiver or supplemental
--------  -------
agreement are treated in the same manner, unless the record or beneficial
holders of all Shares consent to such amendment or supplemental agreement, and
(ii) no such waiver or supplemental agreement shall reduce the above percentage
of holders of Shares which is required to consent to any waiver or supplemental
agreement, without the consent of the record or beneficial holders of all
Shares. Upon the effectuation of each such waiver, consent, agreement, amendment
or modification the Company shall promptly give written notice thereof to the
record holders of Shares who have not previously consented thereto in writing.
Neither this Agreement nor any provisions hereof may be changed, waived,
discharged or terminated orally, but only by a signed statement in writing.

     8.2  Governing Law.  This Agreement shall be governed in all respects by
          -------------
the laws of the State of California as such laws are applied to agreements
between California residents entered into and to be performed entirely within
California.

     8.3  Survival.  The representations, warranties, covenants and agreements
          --------
made herein shall survive the execution and delivery of this Agreement and the
sale of the Shares.

     8.4  Successors and Assigns.  Except as otherwise expressly provided
          ----------------------
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the
parties hereto.

     8.5  Entire Agreement.  This Agreement and the other documents delivered
          ----------------
pursuant hereto constitute the full and entire understanding and agreement
between the parties with regard to the subjects hereof and thereof.

     8.6  Severability.  In case any provision of this Agreement shall be
          ------------
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not in any way be affected or impaired thereby.

     8.7  California Corporate Securities Law.  THE SALE OF THE SECURITIES WHICH
          -----------------------------------
ARE THE SUBJECT OF THIS AGREEMENT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER
OF CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF THE SECURITIES OR
THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION THEREFOR PRIOR TO SUCH
QUALIFICATION IS UNLAWFUL UNLESS THE SALE OF SECURITIES IS EXEMPT FROM THE
QUALIFICATION BY

                                     -13-
<PAGE>

SECTION 25100, 25102, OR 25105 OF THE CALIFORNIA CORPORATIONS CODE. THE RIGHTS
OF ALL PARTIES TO THIS AGREEMENT ARE EXPRESSLY CONDITIONED UPON SUCH
QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS SO EXEMPT.

     8.8  Titles and Subtitles.  The titles of the paragraphs and subparagraphs
          --------------------
of this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

     8.9  Delays or Omissions.  It is agreed that no delay or omission to
          -------------------
exercise any right, power or remedy accruing to the Investor, upon any breach or
default of the Company under this Agreement, shall impair any such right, power
or remedy, nor shall it be construed to be a waiver of any such breach or
default, or any acquiescence therein, or of or in any similar breach or default
thereafter occurring; nor shall any waiver of any single breach or default be
deemed a waiver of any other breach or default theretofore or thereafter
occurring. It is further agreed that any waiver, permit, consent or approval of
any kind or character by the Investor of any breach or default under this
Agreement, or any waiver by the Investor of any provisions or conditions of this
Agreement must be in writing and shall be effective only to the extent
specifically set forth in writing and that all remedies, either under this
Agreement, or by law or otherwise afforded to the Investor, shall be cumulative
and not alternative.

     8.10 Notices.  Any notice or report required in this Agreement or permitted
          -------
to be given shall be given by depositing the same in the United States mail,
postage prepaid and addressed to the parties as follows: (i) if to the Company,
to the attention of the President at the Company's principal address set forth
on the first page hereof, with a copy to Herbert P. Fockler, Wilson Sonsini
Goodrich & Rosati, 650 Page Mill Road, Palo Alto, California 94304, and (ii) if
to an Investor, to such Investor at such Investor's address as set forth on the
Schedule of Investors.

     8.11 Counterparts.  This Agreement may be executed in any number of
          ------------
counterparts, each of which shall be an original, but all of which together
shall constitute one instrument.

                     [This space intentionally left blank]

                                     -14-
<PAGE>

     IN WITNESS WHEREOF, the parties have caused this Common Stock Purchase
Agreement to be duly executed and delivered as of the date first written above.

     THE COMPANY:                  UROGEN CORP.

                                   By: /s/ ROBERT E. SOBOL, M.D.
                                      -----------------------------------------
                                      Robert E. Sobol, M.D.
                                      President and Chief Executive Officer

     THE INVESTORS:                INVESTOR

                                   By:
                                      -----------------------------------------
                                      Name: ((FirstName)) ((LastName))
                                           ------------------------------------
                                      Title:
                                           ------------------------------------

              [Signature Page to Common Stock Purchase Agreement]
<PAGE>

                                   EXHIBIT A

                             SCHEDULE OF INVESTORS

Name and Address of Investor            Aggregate              Number of Shares
                                        Purchase Price         of Common Stock

((FirstName)) ((LastName))
((Address1))                           ((investment))
((City)), ((State)) ((PostalCode))

TOTAL                                   $

                                     -A1-<PAGE>

                                                                   Exhibit 10.16

                                               [LOGO OF GEO SPECIALTY CHEMICALS]

July 16, 1998

Mr. Michael B. Linscott
25 Schuler Lane
Easton, Pennsylvania 18042

Dear Mike:

It is my pleasure to offer you the position of Vice President/General Manager,
Performance Chemicals for GEO Specialty Chemicals effective August 1, 1998. The
starting base salary will be $130,000 per annum. GEO Specialty Chemicals will
grant you a starting bonus of $10,000 upon your start of work in Charlotte.
Additionally, we will guarantee you a bonus payment for performance against
mutually agreed upon goals of $25,000 which will be payable in 1999 at the time
our regular Management Incentive Bonuses (MIP's) are awarded.

You also will receive all of the standard GEO Specialty Chemicals employee
benefits including pension plan, matching 401(k), medical and dental insurance,
disability, life insurance and participation in GEO's MIP at the Tier I level of
30% maximum. We will begin your vacation participation at the level of three
weeks instead of the normal two weeks.

The position is located in Charlotte, North Carolina and we would expect you to
relocate to the Charlotte area as soon as possible. I would suggest that you
plan to utilize your initial visits to Charlotte as regular business trips. To
assist you with your move, you will participate in GEO's moving policy at the
regular employee level as indicated in our internal policy. Additionally, we
will gross up your taxable moving expenses to cover the tax consequences of your
move. This will also include a miscellaneous expenses amount of $5,000 which is
also grossed up for tax purposes. During your temporary living status while your
home is being sold and the move taking place, we will provide you full use of a
leased vehicle which we currently have in our fleet.

Our 401(k) vesting provisions are set by an IRS approved plan that we are not
allowed to, by law, make special exceptions to for individuals.

This offer is contingent upon your satisfactorily passing a standard physical
and drug test, verification of degree and a reference check. Upon commencement
of employment you will be expected to sign a one year noncompete and a five-year
confidentiality agreement.

<PAGE>

Mike, we are excited that you have decided to join the GEO Specialty Chemicals
team and will support you in any way possible to assist you in achieving the
goals of turning the Performance Chemicals Business around and significantly
improving its profitability. I am sure we will work well together and personally
look forward to your participation as a member of the GEO Management Team. We
can have fun in an entrepreneurial team environment that challenges all of us to
achieve more then we could possibly do as individuals. Attached is a copy of
GEO's values which represent the spirit and environment in which we work.

Please sign the two originals of this letter to indicate your acceptance of the
position under the terms outlined above. Keep one of your files and return the
other to me.

Best regards,

/s/ Joseph A. Boelter                           /s/ Michael B. Linscott
---------------------                           -----------------------
Joseph A. Boelter                               Michael B. Linscott,
Chief Operating Officer                         Agreed and Accepted

JAB/mb

Enclosure: GEO Values

cc: G. P. Ahearn w/o att.
    W. P. Eckman w/o att.
    J. M. Payne w/o att.

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