AGREEMENT

                       for the purchase of Common Stock of

                                   SUGEN, INC.

                                       by

                         ASTA MEDICA AKTIENGESELLSCHAFT


<PAGE>
                                Table Of Contents

                                                                            Page

1.       Purchase and Sale of Common Stock.....................................1

         1.1      Issue of Common Stock........................................1

2.       Closing Date; Delivery................................................1

         2.1      First Closing................................................1

         2.2      Payment and Delivery.........................................1

         2.3      Second Closing...............................................2

         2.4      Delivery.....................................................2

3.       Representations, Warranties and Covenants of the Company..............2

         3.1      Organization.................................................2

         3.2      Authority....................................................2

         3.3      Issuance of the Shares.......................................2

         3.4      Registration Rights Covenant.................................2

4.       Representations, Warranties and Covenants of Purchaser................5

         4.1      Legal Power..................................................6

         4.2      Due Execution................................................6

         4.3      Investment Representations and Covenants.....................6

         4.4      Standstill Covenant..........................................7

         4.5      Lockup Covenant..............................................7

5.       Conditions to First Closing...........................................8

         5.1      Conditions to Obligations of Purchaser.......................8

         5.2      Conditions to Obligations of the Company.....................8

6.       Conditions to Second Closing..........................................8

         6.1      Conditions to Obligations of Purchaser.......................8

         6.2      Conditions to Obligations of the Company.....................9

7.       Miscellaneous.........................................................9

         7.1      Governing Law................................................9

         7.2      Successors and Assigns.......................................9

         7.3      Entire Agreement............................................10

         7.4      Separability................................................10

         7.5      Amendment and Waiver........................................10

                                       i.
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         7.6      Notices.....................................................10

         7.7      Fees and Expenses...........................................10

         7.8      Titles and Subtitles........................................10

         7.9      Counterparts................................................10

         7.10     Consent to Jurisdiction and Venue...........................10

                                      ii.
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                         COMMON STOCK PURCHASE AGREEMENT


         This Common Stock Purchase Agreement (the "Agreement) is made as of the
31st day of December,  1998, by and between SUGEN, Inc., a Delaware  corporation
(the  "Company"),  and Asta  Medica  Aktiengesellschaft,  a  German  corporation
("Purchaser"). In connection with that First Amendment, dated as of December 31,
1998 (the "First Amendment"),  to that certain Collaboration Agreement, dated as
of  December  5,  1995,   by  and  between  the  Company  and   Purchaser   (the
"Collaboration  Agreement"),  and  in  consideration  of  the  mutual  promises,
representations,  warranties  and conditions  set forth in this  Agreement,  the
Company and Purchaser agree as follows:

1.       Purchase and Sale of Common Stock.

         1.1      Issue of Common Stock.

                  (a) The Company has  authorized the issuance and sale of up to
the aggregate number of shares of its common stock,  $.01 par value (the "Common
Stock"), set forth in Sections 2.1 and 2.3 hereof (the "Shares").

                  (b)  In  reliance   upon   Purchaser's   representations   and
warranties contained in Section 4 hereof and subject to the terms and conditions
set forth  herein,  the Company  agrees to sell to Purchaser  the Shares,  to be
issued and sold at a price per share equal to two hundred  percent (200%) of the
Fair Market Value  thereof.  For purposes of this  Agreement,  Fair Market Value
shall  equal the  average  closing  sales  price of a share of  Common  Stock as
reported  for the  Nasdaq  National  Market for the twenty  (20)  business  days
preceding the day on which the Shares are issued.

                  (c) In reliance upon the representations and warranties of the
Company  contained  in Section 3 hereof and subject to the terms and  conditions
set forth  herein,  Purchaser  hereby  agrees to purchase  the Shares at the per
share purchase price set forth above.

2.       Closing Date; Delivery.

         2.1 First Closing.  The closing of the sale and purchase of that number
of Shares (the "Initial  Shares") under this  Agreement  (the "First  Closing"),
having a value of  $375,000  based on a price  per  share  equal to two  hundred
percent (200%) of the Fair Market Value thereof, shall be held on or about 10:00
a.m.  (Pacific  Standard Time) on or about December 31, 1998 (the "First Closing
Date"),  at the offices of Cooley  Godward LLP,  Five Palo Alto Square,  3000 El
Camino  Real,  Palo  Alto,  California,  or at such  other time and place as the
Company and Purchaser may agree.  At the First  Closing,  the Company will issue
and sell,  and  Purchaser  will  purchase,  the Initial  Shares for an aggregate
purchase price of $375,000.

         2.2 Payment and Delivery.  At the First  Closing,  subject to the terms
and  conditions   hereof,   the  Company  will  deliver  to  Purchaser  a  stock
certificate,  registered  in the name of  Purchaser,  representing  the  Initial
Shares to be purchased by Purchaser from the Company, dated

                                       1.
<PAGE>
as of the First Closing Date,  against payment of the purchase price therefor by
wire  transfer,  unless  other  means of payment  shall have been agreed upon by
Purchaser and the Company.

         2.3 Second Closing. The closing of the sale and purchase of that number
of Shares (the "Additional Shares") under this Agreement (the "Second Closing"),
having a value of  $375,000  based on a price  per  share  equal to two  hundred
percent (200%) of the Fair Market Value  thereof,  shall take place on March 31,
1999 (the "Second Closing Date") at the offices of Cooley Godward LLP, Five Palo
Alto Square, 3000 El Camino Real, Palo Alto,  California,  or at such other time
and place as the Company and Purchaser  may agree.  At the Second  Closing,  the
Company will issue and sell, and Purchaser will purchase,  the Additional Shares
for an  aggregate  purchase  price  of  $375,000;  provided,  however,  that the
Company's  sole remedy for failure by ASTA  Medica to  purchase  the  Additional
Shares at the Second  Closing shall be  forfeiture  of ASTA  Medica's  rights in
accordance with Section 4 of the First Amendment.

         2.4  Delivery.  At  the  Second  Closing,  subject  to  the  terms  and
conditions  hereof,  the Company will deliver to Purchaser a stock  certificate,
registered in the name of Purchaser,  representing  the Additional  Shares to be
purchased by Purchaser  from the Company,  dated as of the Second  Closing Date,
against  payment of the purchase price  therefor by wire transfer,  unless other
means of payment shall have been agreed upon by Purchaser and the Company

3.       Representations, Warranties and Covenants of the Company

         The Company hereby represents and warrants to Purchaser as follows:

         3.1  Organization.  The Company is a  corporation,  duly  incorporated,
validly  existing and in good standing under the laws of the jurisdiction of its
incorporation.

         3.2  Authority.  The Company has all  requisite  power and authority to
enter into this  Agreement,  and to  consummate  the  transactions  contemplated
hereby. The execution and delivery of this Agreement and the consummation of the
transactions  contemplated  hereby have been duly  authorized  by all  necessary
corporate action on the part of the Company,  and upon execution and delivery by
the Company,  this Agreement will  constitute a valid and binding  obligation of
the  Company,  enforceable  against  the Company in  accordance  with its terms,
subject to applicable  bankruptcy,  insolvency,  reorganization,  moratorium and
similar  laws  relating to or affecting  creditor's  rights from time to time in
effect, and subject to general equity principles.

         3.3  Issuance of the Shares.  The Shares,  when issued  pursuant to the
terms of this Agreement,  will be duly and validly authorized and issued,  fully
paid and nonassessable.

         3.4 Registration Rights Covenant.

                  (a)  At  any  time  during  the  180-day  period   immediately
following  the   termination  of  the  Screening   Period  (as  defined  in  the
Collaboration  Agreement,  as amended by the First  Amendment),  Purchaser shall
have the right to cause the Company to file a registration  statement  under the
Securities Act of 1933, as amended (the "Securities Act"), for a public offering
of no less than 250,000 shares of Common Stock  beneficially owned by Purchaser,

                                       2.
<PAGE>
provided  that such  shares  include all of the Shares,  by  delivering  written
notice thereof to the Company  specifying the number of Shares to be included in
such  registration  and  the  intended  method  of  distribution   thereof  (the
"Registration  Request").  Upon receipt of the Registration Request, the Company
shall, as expeditiously as possible, use its best efforts to promptly effect the
registration under the Securities Act, and all applicable state securities laws,
to the extent necessary to permit the sale or other  disposition by Purchaser of
the Shares to be so registered in accordance with such notice.

                  (b) The demand  registration  rights granted in Section 3.4(a)
are subject to the following limitations: (i) the Company shall not be obligated
to effect  more than one  registration  pursuant  to  Section  3.4(a),  (ii) the
Company  shall not be obligated to effect such  registration  for a period of 60
days following the closing of an  underwritten  public offering of the Company's
equity  securities  that is in  registration  at the time of the  receipt of the
Registration Request (provided that the period within which Purchaser may demand
registration  hereunder  will be  extended  by the  number  of days by which the
registration  requested by Purchaser is delayed pursuant to this sentence);  and
(iii) if the Company  shall  furnish to  Purchaser a  certificate  signed by the
Chairman of the Board of Directors of the Company stating that in the good faith
judgment  of the  Board of  Directors  of the  Company,  it  would be  seriously
detrimental  to the Company and its  stockholders  for such  registration  to be
effected at such time, then the Company shall have the right to defer the filing
of the  registration for a period of not more than 180 days after receipt of the
Registration Request (provided that the period within which Purchaser may demand
registration  hereunder  will be  extended  by the  number  of days by which the
registration requested by Purchaser is delayed pursuant to this sentence).

                  (c) If and when the Company is required by the  provisions  of
Section  3.4(a)  to  include  all of the  Shares  in a  registration  under  the
Securities  Act,  Purchaser  will  furnish in  writing  such  information  as is
reasonably requested by the Company for inclusion in the registration  statement
relating to such offering and such other  information and  documentation  as the
Company shall  reasonably  request,  and the Company will, as  expeditiously  as
possible:

                           (i) Prepare and file with the Securities and Exchange
Commission ("SEC") a registration  statement with respect to such securities and
use its best efforts to cause such  registration to become and remain  effective
for such period as may be necessary to permit the  successful  marketing of such
securities but not exceeding 120 days  (excluding any period during which a stop
order is in effect).

                           (ii)  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 and to keep such registration statement effective for that period
of time specified in paragraph (i) of this section.

                           (iii)   Furnish   to   Purchaser   such   number   of
prospectuses and preliminary prospectuses in conformity with the requirements of
the  Securities  Act, and such other  documents as such Purchaser may reasonably
request in order to  facilitate  the  public  sale or other  disposition  of the
Shares registered hereunder.

                                       3.
<PAGE>
                           (iv) Use its best  efforts to register or qualify the
Shares covered by such  registration  statement  under such other  securities or
blue sky laws of such jurisdictions as Purchaser shall reasonably request and do
any and all other acts and things  which may be necessary or desirable to enable
Purchaser  to  consummate   the  public  sale  or  other   disposition  in  such
jurisdictions  of the Shares covered by such  registration  statement,  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 states or jurisdictions.

                  (d) In the event of a registration  of any of the Shares under
the Securities Act pursuant to Section 3.4(a) in connection with an underwritten
public offering,  the Company will enter into and perform its obligations  under
an  underwriting  agreement,  in usual and  customary  form,  with the  managing
underwriters of such offering,  including without limitation providing usual and
customary  indemnification.  In the event  Purchaser  proposes to sell Shares in
accordance with this Section pursuant to an underwritten  offering,  the Company
shall have the right to approve the  managing  underwriters  for such  offering;
provided,  however,  that  such  approval  shall not be  unreasonably  withheld.
Purchaser will also provide usual and customary  indemnification  to the Company
and its affiliates with respect to claims,  losses and damages arising out of or
based on any untrue  statement (or alleged untrue  statement) of a material fact
contained in any registration  statement,  prospectus 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;
provided,  however,  that in no event  shall any  indemnity  under this  Section
3.4(d) exceed the gross proceeds from the offering received by Purchaser.

                  (e) At any time or from time to time following  termination of
the Screening Period (as defined in the Collaboration  Agreement,  as amended by
the First  Amendment),  if the Company  shall  determine  to register any of its
securities  either for its own  account or the  account of a security  holder or
holders  exercising  their  respective  demand  registration  rights (other than
pursuant to Section 3.4(a) hereof), other than a registration relating solely to
employee  benefit  plans,  or a  registration  relating  solely  to a  Rule  145
transaction,  or a registration  on any  registration  form that does not permit
secondary sales, then the Company will:

                           (i)  promptly  give to  Purchaser  a  written  notice
thereof; and

                           (ii)  use  its  best   efforts  to  include  in  such
registration  (and  any  related  qualification  under  blue  sky  laws or other
compliance),   except  as  set  forth  in  Section  3.4(f)  below,  and  in  any
underwriting  involved therein, all the Shares specified in a written request or
requests made by Purchaser  and received by the Company  within twenty (20) days
after the  written  notice  from the  Company  described  in clause (i) above is
mailed or delivered by the Company.

                  (f) If the  registration  of which the Company gives notice to
Purchaser is for a registered  public offering  involving an  underwriting,  the
Company shall so advise Purchaser as a part of the written notice given pursuant
to Section  3.4(e)(i).  In such event,  the right of Purchaser  to  registration
pursuant to Section 3.4(e) shall be conditioned upon  Purchaser's  participation
in such underwriting and the inclusion of Purchaser's Shares in the underwriting
to the extent

                                       4.
<PAGE>
provided  herein.  Purchaser  shall  (together  with the  Company  and the other
holders of securities  of the Company with  registration  rights to  participate
therein  distributing their securities through such underwriting)  enter into an
underwriting  agreement  in  customary  form  with  the  representative  of  the
underwriter or underwriters selected by the Company.

         Notwithstanding  any other  provision of Sections 3.4(e) or (f), if the
representative of the underwriters advises the Company in writing that marketing
factors  require a limitation  on the number of shares to be  underwritten,  the
representative  may (subject to the  limitations  set forth  below)  exclude all
Shares from,  or limit the number of Shares to be included in, the  registration
and  underwriting.  The Company  shall so advise  Purchaser and other holders of
securities requesting  registration,  and the number of shares that are entitled
to be included in the registration and underwriting  shall be allocated first to
the Company for  securities  being sold for its own account and  thereafter  the
number of shares that are entitled to be included in the  registration  shall be
allocated among Purchaser and other holders requesting  inclusion of shares on a
pro rata basis,  subject to any prior agreements among the Company and its other
stockholders,  but only to the extent  that such other  agreements  provide  for
additional  limitations on the number of shares such other  stockholders  or the
Company will be entitled to include in the registration, which agreements are in
effect as of the date hereof. If Purchaser or any other person does not agree to
the terms of any such underwriting, Purchaser and any other such person shall be
excluded  therefrom by written notice from the Company or the  underwriter.  Any
Shares or other securities  excluded or withdrawn from such  underwriting  shall
also be withdrawn from such registration.

                  (g) As used  herein,  "Registration  Expenses"  shall mean all
expenses incurred by the Company in complying with this Section 3.4,  including,
without  limitation,  all registration,  qualification and filing fees; printing
expenses;  fees and  disbursements  of counsel for the Company (and the fees and
disbursements  of  counsel  for the  Company in its  capacity  as counsel to the
Purchaser hereunder;  if Company counsel does not make itself available for this
purpose,  the Company  will pay the  reasonable  fees and  disbursements  of one
counsel  for the  Purchaser  as  selected  by  Purchaser)  and of the  Company's
independent accounting firm; blue sky fees and expenses;  underwriting discounts
and commissions and the expense of any special audits incident to or required by
any such  registration  (but excluding the compensation of regular  employees of
the Company which shall be paid in any event by the Company). Purchaser will pay
all Registration  Expenses in connection with a registration pursuant to Section
3.4(a) hereof;  provided,  however,  that in the event of a registration  of the
Shares pursuant to Section 3.4(a) either as a result of a material breach of the
Collaboration  Agreement  by the Company or the  inability  to replace a Project
pursuant  to  Section  2.6  of  the  Collaboration  Agreement,  or if  Purchaser
withdraws its demand for registration after having learned of a material adverse
change in the condition,  business,  or prospects of the Company from that known
to Purchaser at the time of its demand (in which case Purchaser shall retain its
rights pursuant to Section 3.4(a)), all Registration  Expenses shall be borne by
the Company.  All  Registration  Expenses in  connection  with any  registration
pursuant  to Section  3.4(e)  hereof  shall be borne by the  Company;  provided,
however,  that any incremental expenses incurred by the Company solely by reason
of Purchaser's  exercise of registration rights pursuant to Section 3.4(e) shall
be borne by the Purchaser.

                                       5.
<PAGE>
                  (h) The rights conferred upon Purchaser under this Section 3.4
may be assigned by Purchaser to any permitted transferee of the Shares, provided
that each such transfer  complies with Section 4.5 and provided,  further,  that
only Purchaser  shall be authorized to give notice to the Company of any request
for registration  under this Section 3.4(a) and only Purchaser shall be entitled
to receive notice pursuant to Section 3.4(a) hereof.

4.       Representations, Warranties and Covenants of Purchaser.

         Purchaser hereby represents, warrants and covenants with the Company as
follows:

         4.1 Legal Power.  Purchaser  has the requisite  corporate  power and is
authorized to enter into this Agreement, to purchase the Shares hereunder and to
carry out and perform its obligations under the terms of this Agreement.

         4.2 Due Execution. This Agreement has been duly authorized executed and
delivered by Purchaser, and upon due execution and delivery by the Company, this
Agreement will be a valid and binding agreement of Purchaser.

         4.3 Investment Representations and Covenants.

         Purchaser is acquiring  the Shares for its own account,  not as nominee
or agent,  for  investment  and not with a view to or for  resale in  connection
with,  any  distribution  or public  offering  thereof within the meaning of the
Securities Act.  Purchaser  understands that the Shares have not been registered
under the  Securities  Act, but are instead  being offered and sold to Purchaser
pursuant to an exemption from registration contained in the Securities Act based
in part upon the following representations and warranties:

                  (a) Purchaser is capable of evaluating the merits and risks of
its investment in the Company and has the capacity to protect its own interests.
Purchaser must bear the economic risk of this  investment  unless the Shares are
registered  pursuant to the Securities Act, or an exemption from registration is
available.  Purchaser  understands that the Company has no present  intention of
registering the Shares.  Purchaser also  understands  that there is no assurance
that any exemption from registration  under the Securities Act will be available
and that,  even if available,  such  exemption  may not allow such  Purchaser to
transfer  all or any  portion  of the  Shares  under the  circumstances,  in the
amounts or at the times Purchaser might propose.

                  (b) Purchaser is acquiring the Shares for such Purchaser's own
account for investment only, and not with a view towards their distribution.

                  (c)  Purchaser  represents  that by reason  of its,  or of its
management's,  business or financial  experience,  Purchaser has the capacity to
protect its own interests in connection  with the  transactions  contemplated in
this Agreement.

                  (d) Purchaser has had an  opportunity to discuss the Company's
business,   management  and  financial  affairs  with  directors,  officers  and
management  of the Company and has had the  opportunity  to review the Company's
operations and facilities. Purchaser has also

                                       6.
<PAGE>
had the  opportunity  to ask questions of and receive  answers from, the Company
and its management regarding the terms and conditions of this investment.

                  (e) Purchaser  acknowledges and agrees that the Shares must be
held indefinitely  unless they are subsequently  registered under the Securities
Act or an exemption  from such  registration  is  available.  Purchaser has been
advised  or is  aware  of the  provisions  of Rule  144  promulgated  under  the
Securities  Act, which permits  limited resale of shares  purchased in a private
placement subject to the satisfaction of certain  conditions,  including,  among
other things:  the availability of certain current public  information about the
Company,  the  resale  occurring  not less  than  two  years  after a party  has
purchased  and paid for the  security  to be sold,  the sale  being  through  an
unsolicited  "broker's  transaction" or in  transactions  directly with a market
maker (as said term is defined  under the  Securities  Exchange Act of 1934,  as
amended  (the  "Exchange  Act")) and the number of shares  being sold during any
three-month  period  not  exceeding  specified  limitations.   Each  certificate
representing  Shares  shall be  stamped  or  otherwise  imprinted  with a legend
substantially similar to the following:

         THE SECURITIES  REPRESENTED  HEREBY HAVE NOT BEEN REGISTERED  UNDER THE
         SECURITIES  ACT OF 1933 (THE  "ACT")  AND MAY NOT BE  OFFERED,  SOLD OR
         OTHERWISE  TRANSFERRED,  ASSIGNED,  PLEDGED OR HYPOTHECATED  UNLESS AND
         UNTIL THEY ARE  REGISTERED  UNDER THE ACT OR UNLESS (A) THE COMPANY HAS
         RECEIVED  AN OPINION OF COUNSEL  SATISFACTORY  TO THE  COMPANY  AND ITS
         COUNSEL THAT SUCH REGISTRATION IS NOT REQUIRED OR (B) SUCH SALE IS MADE
         PURSUANT TO RULE 144 UNDER THE ACT.

         4.4 Standstill  Covenant.  Purchaser agrees that neither  Purchaser nor
any of its  affiliates  will in any manner,  directly or indirectly  (i) effect,
seek,  offer or propose to effect any acquisition of any securities or assets of
the  Company,  any  tender or  exchange  offer,  merger,  business  combination,
recapitalization or other extraordinary transaction involving the Company or any
solicitation  of  proxies  or  consents  to vote any  voting  securities  of the
Company,  (ii) form,  join or in any way participate in a "group" (as defined in
the Exchange Act) with respect to any voting  securities  of the Company,  (iii)
solicit or participate in any  solicitation of proxies  relating to the election
of  directors of the Company,  or (iv) enter into any  agreement  with any other
person with  respect to the  foregoing,  or assist any other person to do any of
the foregoing; provided that (A) Purchaser may purchase additional securities in
an  amount  sufficient  to  allow  Purchaser  to own  up to  4.9%  of  the  then
outstanding  shares of Common Stock of the Company  (excluding any shares issued
directly to Purchaser or its  Affiliates  by the  Company);  (B) the transfer of
Shares in accordance  with Section 4.5 and the voting  thereof by the transferee
shall not be deemed a prohibited group formation or proxy solicitation;  and (C)
this sentence  shall not prohibit the  acquisition  or disposition of shares for
investment  purposes  only in the open  market  in the  ordinary  course  by any
pension  fund  or  trust  for the  benefit  of  employees  of  Purchaser  or its
affiliates.

         4.5 Lockup Covenant.  Purchaser agrees that during the Screening Period
(as defined in the Collaboration  Agreement, as amended by the First Amendment),
Purchaser will not,  without the prior written  approval of the Company,  offer,
sell or otherwise dispose of, directly or

                                       7.
<PAGE>
indirectly,  any capital stock of the Company which  Purchaser may own directly,
indirectly or beneficially; provided that (i) Purchaser may transfer some or all
of the  Shares to a  corporation,  partnership  or other  legal  entity of which
Purchaser has actual control,  but only if such transferee  agrees in writing to
hold such  Shares  subject to all of the  provisions  of this  Agreement  and to
transfer such Shares to Purchaser if such transferee  ceases to be controlled by
Purchaser (all such Shares so  transferred  shall be deemed to be shares held by
Purchaser for all purposes hereunder),  (ii) the restrictions  contained in this
sentence shall  terminate  automatically  upon the  acquisition by any person or
group (as defined in the Exchange Act), other than Purchaser and its affiliates,
of more than 21% of the outstanding voting securities of the Company,  and (iii)
this sentence  shall not prohibit the  acquisition  or disposition of shares for
investment  purposes  only in the open  market  in the  ordinary  course  by any
pension  fund  or  trust  for the  benefit  of  employees  of  Purchaser  or its
affiliates.

5.       Conditions to First Closing.

         5.1 Conditions to Obligations of Purchaser.  Purchaser's  obligation to
purchase the Initial Shares at the First Closing is subject to the  fulfillment,
at or prior to the First Closing, of all of the following conditions:

                  (a)  Representations  and  Warranties  True;   Performance  of
Obligations. The representations and warranties made by the Company in Section 3
hereof shall be true and correct in all material  respects on the First  Closing
Date with the same  force and  effect as if they had been made on and as of said
date. The Company shall have  performed all  obligations  and conditions  herein
required to be performed by it on or prior to the First Closing Date.

                  (b)  Proceedings  and  Documents.   All  corporate  and  other
proceedings  in  connection  with the  transactions  contemplated  at the  First
Closing hereby and all documents and instruments  incident to such  transactions
shall be reasonably satisfactory in substance and form to Purchaser.

         5.2 Conditions to Obligations of the Company.  The Company's obligation
to issue and sell the  Initial  Shares at the First  Closing  is  subject to the
fulfillment, to the Company's satisfaction, on or prior to the First Closing, of
the following conditions:

                  (a)  Representations  and Warranties True. The representations
and  warranties  made by Purchaser in Section 4 hereof shall be true and correct
at the First  Closing  Date with the same  force and  effect as if they had been
made on and as of the date of the First Closing Date.

                  (b) Performance of Obligations. Purchaser shall have performed
and complied with all agreements and conditions  herein required to be performed
or complied  with by them on or before the First  Closing  Date,  and  Purchaser
shall have  delivered  payment to the  Company  in  respect of its  purchase  of
Initial Shares.

                  (c)  Qualifications,  Legal  Investment.  All  authorizations,
approvals,  or permits, if any, of any governmental authority or regulatory body
of the United  States or of any state that are required in  connection  with the
lawful sale and issuance of the Initial Shares at the

                                       8.
<PAGE>
First Closing pursuant to this Agreement shall have been duly obtained and shall
be effective on and as of the First  Closing  Date. No stop order or other order
enjoining  the  sale  of the  Initial  Shares  shall  have  been  issued  and no
proceedings  for such  purpose  shall be  pending  or, to the  knowledge  of the
Company,  threatened by the SEC or any  commissioner  of corporations or similar
officer of any state having  jurisdiction over this transaction.  At the time of
the First  Closing,  the sale and issuance of the Initial Shares to be purchased
and  sold at the  First  Closing  shall  be  legally  permitted  by all laws and
regulations to which Purchaser and the Company are subject.

6.       Conditions to Second Closing.

         6.1 Conditions to Obligations of Purchaser.  Purchaser's  obligation to
purchase  the  Additional  Shares  at  the  Second  Closing  is  subject  to the
fulfillment,  at or  prior  to the  Second  Closing,  of  all  of the  following
conditions:

                  (a)  Representations  and  Warranties  True;   Performance  of
Obligations. The representations and warranties made by the Company in Section 3
hereof shall be true and correct in all material  respects on the Second Closing
Date with the same  force and  effect as if they had been made on and as of said
date. The Company shall have  performed all  obligations  and conditions  herein
required to be performed by it on or prior to the Second Closing Date.

                  (b)  Proceedings  and  Documents.   All  corporate  and  other
proceedings  in  connection  with the  transactions  contemplated  at the Second
Closing hereby and all documents and instruments  incident to such  transactions
shall be reasonably satisfactory in substance and form to Purchaser.

         6.2 Conditions to Obligations of the Company.  The Company's obligation
to issue and sell the Additional  Shares at the Second Closing is subject to the
fulfillment,  to the Company's satisfaction,  on or prior to the Second Closing,
of the following conditions:

                  (a)  Representations  and Warranties True. The representations
and  warranties  made by Purchaser in Section 4 hereof shall be true and correct
at the  Second  Closing  Date with the same force and effect as if they had been
made on and as of the date of the Second Closing Date.

                  (b) Performance of Obligations. Purchaser shall have performed
and complied with all agreements and conditions  herein required to be performed
or complied  with by them on or before the Second  Closing  Date,  and Purchaser
shall have  delivered  payment to the  Company  in  respect of its  purchase  of
Additional Shares.

                  (c)  Qualifications,  Legal  Investment.  All  authorizations,
approvals,  or permits, if any, of any governmental authority or regulatory body
of the United  States or of any state that are required in  connection  with the
lawful sale and issuance of the Additional Shares at the Second Closing pursuant
to this Agreement shall have been duly obtained and shall be effective on and as
of the Second  Closing Date. No stop order or other order  enjoining the sale of
the Additional Shares shall have been issued and no proceedings for such purpose
shall be pending or, to the  knowledge of the Company,  threatened by the SEC or
any commissioner of

                                       9.
<PAGE>
corporations  or similar  officer  of any state  having  jurisdiction  over this
transaction.  At the time of the Second  Closing,  the sale and  issuance of the
Additional  Shares  to be  purchased  and sold at the  Second  Closing  shall be
legally permitted by all laws and regulations to which Purchaser and the Company
are subject.

7.       Miscellaneous.

         7.1 Governing  Law. This  Agreement  shall be governed by and construed
under  the laws of the  State of  California  as  applied  to  agreements  among
California  residents,  made and to be  performed  entirely  within the State of
California, without regard to principles of conflict of laws.

         7.2  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.

         7.3 Entire Agreement.  This Agreement and the Exhibits hereto,  and the
other  documents  delivered  pursuant  hereto,  constitute  the full and  entire
understanding and agreement among the parties with regard to the subjects hereof
and no party  shall be liable or bound to any other  party in any  manner by any
representations, warranties, covenants, or agreements except as specifically set
forth  herein or therein.  Nothing in this  Agreement,  express or  implied,  is
intended  to confer  upon any  party,  other than the  parties  hereto and their
respective  successors  and  assigns,  any  rights,  remedies,  obligations,  or
liabilities under or by reason of this Agreement,  except as expressly  provided
herein.

         7.4  Separability.  In case any  provision of this  Agreement  shall be
invalid,  illegal,  or  unenforceable,  it shall to the extent  practicable,  be
modified so as to make it valid,  legal and  enforceable and to retain as nearly
as  practicable  the intent of the  parties,  and the  validity,  legality,  and
enforceability  of the remaining  provisions shall not in any way be affected or
impaired thereby.

         7.5 Amendment and Waiver. Except as otherwise provided herein, any term
of this  Agreement  may be  amended,  and  the  observance  of any  term of 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),  with the  written  consent of the  Company  and  Purchaser.  Any
amendment or waiver  effected in  accordance  with this section shall be binding
upon any  holder of any  security  purchased  under  this  Agreement  (including
securities into which such securities have been  converted),  each future holder
of all such securities, and the Company.

         7.6 Notices. All notices and other communications required or permitted
hereunder  shall be in  writing  and  shall be  deemed  effectively  given  upon
personal  delivery,  on the first  business day  following  mailing by overnight
courier,  or on the fifth day following mailing by registered or certified mail,
return  receipt  requested,  postage  prepaid,  addressed  to  the  Company  and
Purchaser at the addresses included herein.

         7.7 Fees and Expenses.  The Company and Purchaser  shall bear their own
expenses  and legal fees with  respect to this  Agreement  and the  transactions
contemplated hereby.

                                      10.
<PAGE>
         7.8  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.

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

         7.10  Consent  to  Jurisdiction  and  Venue.  Any claim or  controversy
arising  out of or  related to this  Agreement  or any  breach  hereof  shall be
submitted to a court of applicable  jurisdiction  in the State of California and
each party hereby consents to the jurisdiction and venue of such court.

                                      11.
<PAGE>
         In Witness Whereof,  the parties hereto have executed this Common Stock
Purchase Agreement as of the date set forth in the first paragraph hereof.

                                    SUGEN, Inc.



                                    By: /s/ Stephen Evans-Freke
                                            Name:    Stephen Evans-Freke
                                            Title:   Chief Executive Officer and
                                                     Chairman of the Board



                                    Asta Medica Aktiengesellschaft


                                    By:_________________________________________
                                            Name:_______________________________
                                            Title:______________________________

                                      12.