Document:

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                                                                     Exhibit 4.2

                          DISCOVERY THERAPEUTICS, INC.

                       RESTATED INVESTOR RIGHTS AGREEMENT

                                 March 31, 1995

                                Table Of Contents

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ARTICLE 1           DEFINITIONS ............................................................     1

         1.1    Certain Definitions ........................................................     1

ARTICLE 2           RESTRICTIONS ON TRANSFER ...............................................     2

         2.1    Restrictions on Transferability ............................................     2

         2.2    Restrictive Legend .........................................................     3

         2.3    Notice of Proposed Transfers ...............................................     3

ARTICLE 3           REGISTRATION RIGHTS ....................................................     4

         3.1    Demand Registration Rights .................................................     4

         3.2    Company Registration .......................................................     6

         3.3    Form S-3 Registration Rights ...............................................     6

         3.4    Expenses of Registration ...................................................     7

         3.5    Registration Procedures ....................................................     8

         3.6    Indemnification ............................................................     9

         3.7    Information by Holder ......................................................    11

         3.8    Rule 144 Reporting .........................................................    11

         3.9    Transfer of Registration Rights ............................................    11

         3.10   Termination of Registration Rights .........................................    12

         3.11   "Market Stand Off" Agreement ...............................................    12

         3.12   Inclusion of Stock Held by Founders and Common Stock held by Holders .......    12

         3.13   Limitations on Subsequent Registration Rights ..............................    13

ARTICLE 4           AFFIRMATIVE COVENANTS OF THE COMPANY ...................................    13

         4.1    Financial Information ......................................................    13

         4.2    Inspection .................................................................    13

         4.3    Assignment of Rights to Financial Information ..............................    13

         4.4    Attendance at Board Meetings ...............................................    14

         4.5    Compensation Committee .....................................................    14

         4.6    Sales of Series B Preferred ................................................    14

         4.7    Termination of Covenants ...................................................    14

ARTICLE 5           AFFIRMATIVE COVENANTS OF HOLDERS; RIGHT OF FIRST REFUSAL ...............    15
</TABLE>

                                       i.

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                                Table Of Contents
                                   (continued)

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         5.1      Confidential Information, etc. ......................................    15

         5.2      Right of First Refusal ..............................................    15

ARTICLE 6             MISCELLANEOUS ...................................................    16

         6.1      Governing Law .......................................................    16

         6.2      Successors and Assigns ..............................................    16

         6.3      Entire Agreement ....................................................    16

         6.4      Rights of Holders ...................................................    17

         6.5      Notices, etc. .......................................................    17

         6.6      Counterparts ........................................................    17

         6.7      Severability ........................................................    17

         6.8      Approval of Amendments and Waivers ..................................    17
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                                       ii.

<PAGE>

                          DISCOVERY THERAPEUTICS, INC.

                       RESTATED INVESTOR RIGHTS AGREEMENT

         This Restated Investor Rights Agreement (the "Agreement") is entered
into as of March 31, 1995 by and among DISCOVERY THERAPEUTICS, INC., a Delaware
corporation with its principal office located at 2028 Dabney Road, Suite E-17,
Richmond, Virginia 23230 (the "Company"), and DONALD A. MCAFEE, NOEL J. CUSACK,
JAMES V. PECK, GEVORK MINASKANIAN and SANDERLING (collectively, the "Founders"),
and the undersigned persons (the "Investors") who hereby amend and restate that
certain Investor Rights Agreement, dated as of April 22, 1994, by and among the
Company, the Founders and certain Investors (the "Prior Agreement").

                                    Recitals

         Whereas, the Company is issuing shares of its Series B Preferred Stock
("Series B Preferred") pursuant to that certain Series B Preferred Stock
Purchase Agreement dated as of the date hereof (the "Series B Agreement") and
shares of its Common Stock (the "Common Shares") to Alliance Technology
Ventures, L.P., ATV/MFJ Parallel Fund, L.P. and ATV/GP Parallel Fund, L.P.
pursuant to common stock investment letters dated as of the date hereof and
desires to grant to the parties thereto the rights herein set forth.

         Now, Therefore, in consideration of the mutual agreements, covenants
and conditions contained herein, the Company, the Founders and the Investors
hereby agree that all consents or conditions required to be obtained or
satisfied under the Prior Agreement in connection with the transactions
contemplated in the Series B Agreement are hereby given and that the Prior
Agreement is amended and restated to read in full as follows:

                                    ARTICLE 1

                                   DEFINITIONS

         1.1      Certain Definitions. As used in this Agreement, the following
terms shall have the following respective meanings:

         "Commission" shall mean the Securities and Exchange Commission or any
other federal agency at the time administering the Securities Act.

         "Form S-3" shall mean Form S-3 under the Securities Act as in effect on
the date of this Agreement, or any substantially similar, equivalent or
successor form under the Securities Act.

         "Founders' Shares" shall mean those shares of the Company's Common
Stock owned by the Founders and outstanding as of the date of this Agreement.

         "Holder" shall mean any Investor or any transferee of registration
rights under Section 3.9 hereof who then holds any outstanding shares of the
Company's Series A Preferred Stock or

                                       1.

<PAGE>

Series B Preferred Stock (collectively, the "Preferred") or any Common Shares
and any Founder or Investor deemed to be a Holder pursuant to Section 3.12, but
solely for the purposes set forth therein.

         The terms "register," "registered" and "registration" refer to a
registration effected by preparing and filing a registration statement in
compliance with the Securities Act, and the declaration or ordering of the
effectiveness of such registration statement.

         "Registrable Securities" means (i) shares of the Company's Common Stock
issued or issuable upon the conversion of shares of Preferred which have not
been sold to the public and (ii) shares of the Company's Common Stock issued in
respect of such shares of the Company's Common Stock, Preferred or Common Stock
issued or issuable upon the conversion of Preferred upon any stock split, stock
dividend, recapitalization, or similar event, which have not been sold to the
public, (iii) shares of the Company's Common Stock deemed to be Registrable
Securities pursuant to Section 3.12, but solely for the purposes set forth
therein, which have not been sold to the public and (iv) the Common Shares.

         "Registration Expenses" shall mean all expenses incurred by the Company
in complying with Sections 3.1, 3.2 and 3.3 hereof, including, without
limitation, all registration, qualification and filing fees, printing expenses,
escrow fees, fees and disbursements of counsel for the Company, blue sky fees
and expenses, 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).

         "Restricted Securities" shall mean the securities of the Company
required to bear the legend set forth in Section 2.2 hereof and all shares of
Common Stock outstanding on the date of this Agreement.

         "Securities Act" shall mean the Securities Act of 1933, as amended, or
any similar federal statute and the rules and regulations of the Commission
thereunder, all as the same shall be in effect at the time.

         "Selling Expense" shall mean all underwriting discounts and selling
commissions applicable to the sale.

                                    ARTICLE 2

                            RESTRICTIONS ON TRANSFER

         2.1      Restrictions on Transferability. The Preferred (and any Common
Stock into which the Preferred may be converted), the Common Shares and the
Founders' Shares shall not be transferable except upon the conditions specified
in this Agreement, which conditions are intended to insure compliance with the
provisions of the Securities Act, or upon such other terms as are in the opinion
of counsel to the Company satisfactory to comply with the provisions of the
Securities Act. Except for transfers made pursuant to Rule 144 of the Securities
Act ("Rule 144") or pursuant to an effective registration statement, each
Investor will cause any proposed transferee of Preferred (and any Common Stock
into which the Preferred may be converted) and

                                       2.

<PAGE>

any Common Shares held by such Investor, and each Founder will cause any
proposed transferee of Founders' Shares, to agree to take and hold such
securities subject to the provisions and upon the conditions specified in this
Agreement and it will be a condition precedent to the effectiveness of any such
transfer that the Company shall have secured a written agreement in form and
substance satisfactory to the Company to that effect, if so requested by the
Company.

         2.2      Restrictive Legend. Each certificate representing (i) the
Preferred, (ii) the Common Shares, (iii) the Founders' Shares and (iv) shares of
the Company's Common Stock issued upon conversion of the Preferred or issued in
respect of such Preferred, Common Shares, Founders' Shares or Common Stock upon
any stock split, stock dividend, recapitalization, merger, consolidation or
similar event shall (unless otherwise permitted by the provisions of Section 2.3
below) be stamped or otherwise imprinted with a legend substantially in the
following form (in addition to any legend required under applicable California
or other state securities laws):

         THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE BEEN ACQUIRED FOR
         INVESTMENT AND HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF
         1933. SUCH SHARES MAY NOT BE SOLD OR TRANSFERRED IN THE ABSENCE OF SUCH
         REGISTRATION OR AN EXEMPTION THEREFROM UNDER SAID ACT. COPIES OF THE
         AGREEMENT COVERING THE PURCHASE OF THESE SHARES 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.

         2.3      Notice of Proposed Transfers. The holder of each certificate
representing Restricted Securities, by acceptance thereof, agrees to comply in
all respects with the provisions of this Section 2.3. Prior to any proposed
transfer of any Restricted Securities, unless there is in effect a registration
statement under the Securities Act covering the proposed transfer, the holder
thereof shall give written notice to the Company of such holder's intention to
effect such transfer. Each such notice shall describe the manner and
circumstances of the proposed transfer in sufficient detail, and shall be
accompanied (except in transactions in compliance with Rule 144) by either (i) a
written opinion of legal counsel reasonably satisfactory to the Company
addressed to the Company and reasonably satisfactory in form and substance to
the Company's counsel, to the effect that the proposed transfer of the
Restricted Securities may be effected without registration under the Securities
Act, or (ii) a "no action letter" from the Commission, and a copy of the
investor's request (together with all supplements or amendments thereto), which
shall have been provided to the Company at or prior to the time of first
delivery to the Commission's staff, to the effect that the transfer of such
securities without registration will not result in a recommendation by such
staff that action be taken with respect thereto, whereupon the holder of such
Restricted Securities shall be entitled to transfer such Restricted Securities
in accordance with the terms of the notice delivered by the holder to the
Company. Each certificate evidencing the Restricted Securities transferred as
provided for above shall bear the appropriate restrictive legend set forth in
Section 2.2 above, except that such certificate shall not bear such restrictive
legend if, in the opinion of counsel for the Company or counsel for such holder,
which opinion and counsel shall be satisfactory to counsel for the Company, such
legend is not required in order to establish compliance with any provisions of
the Securities Act.

                                       3.

<PAGE>

         Notwithstanding the provisions above, no such opinion of counsel or "no
action letter" shall be necessary for a transfer by an Investor which is a
partnership to a partner of such partnership or a retired partner of such
partnership who retires after the date hereof, or to the estate of any such
partner or retired partner or the transfer by gift, will or intestate succession
of any partner to his spouse or to the siblings, lineal descendants or ancestors
of such partner or his spouse, if the transferee agrees in writing to be subject
to the terms hereof to the same extent as if he were an original Investor
hereunder.

                                    ARTICLE 3

                               REGISTRATION RIGHTS

         3.1      Demand Registration Rights.

                  (a)      If the Company shall receive a written request
(specifying that it is being made pursuant to this Section 3.1) from the Holders
of at least fifty percent (50%) of the outstanding Registrable Securities (the
"Initiating Holders") that the Company file a registration statement or similar
document under the Securities Act covering the registration of at least fifty
percent (50%) of the then outstanding Registrable Securities, or any lesser
percentage if the anticipated aggregate offering proceeds, net of Selling
Expenses, would be equal to or exceed $5,000,000, then the Company shall
promptly notify all other Holders of such request and shall use its best efforts
to cause all Registrable Securities that such Holders have requested, within 15
days after receipt of such written notice, to be registered under the Securities
Act in accordance with this Section 3.1.

         Notwithstanding the foregoing, (1) the Company shall not be obligated
to effect a registration pursuant to this Section 3.1, (i) during the period
starting with the date ninety (90) days prior to the Company's estimated date of
filing of, and ending on a date sixty (60) days following the effective date of,
a registration statement pertaining to an underwritten public offering of the
Company's securities, provided that the Company is actively employing in good
faith all reasonable efforts to cause such registration statement to become
effective and that the Company's estimate of the date of filing such
registration statement is made in good faith, or (ii) within the 12 month period
following the closing of the initial underwritten public offering of the
Company's Common Stock, or (iii) prior to the second anniversary of the closing
date of the sale of Series B Preferred pursuant to the Series B Agreement, and
(2) if the Company shall furnish to such Holders a certificate signed by the
President of the Company stating that in the good faith judgment of the Board of
Directors it would be seriously detrimental to the Company or its Holders for a
registration statement to be filed in the near future, then the Company's
obligation to use its best efforts to file a registration statement shall be
deferred for a period not to exceed one hundred eighty (180) days; provided,
however, that the Company shall not obtain such a deferral more than once in any
12-month period.

         The Company shall be obligated to effect not more than one registration
pursuant to this Section 3.1; provided, however, a demand registration request
shall not count as such until the registration statement to which it relates has
been declared effective by the Securities and Exchange Commission ("SEC"),
except that if, after it has been declared effective, such offering

                                       4.

<PAGE>

is interfered with by any stop order, injunction or other order or requirement
by the SEC or any other governmental authority, such registration shall be
deemed not to have been effected unless such stop order, injunction or other
order or requirement shall subsequently have been vacated or otherwise removed
or resulted from any action taken or information supplied by an Initiating
Holder, in which case a demand registration request shall only count as such
with respect to such Initiating Holder.

                  (b)      If the Initiating Holders intend to distribute the
Registrable Securities covered by their demand by means of an underwriting, they
shall so advise the Company as part of their demand made pursuant to this
Section 3.1, and the Company shall include such information in the notice
referred to in Section 3.1(a). In such event, the right of any Holder to
registration pursuant to this Section 3.1 shall be conditioned upon such
Holder's participation in such underwriting and the inclusion of such Holder's
Registrable Securities in the underwriting (unless otherwise mutually agreed by
a majority in interest of the Initiating Holders and such Holder) to the extent
provided herein.

         The Company shall, together with all Holders proposing to distribute
their securities through such underwriting, enter into an underwriting agreement
in customary form with the underwriter or underwriters selected by a majority in
interest of the Initiating Holders and reasonably satisfactory to the Company.
Notwithstanding any other provision of this Section 3.1, and subject to the
provisions of Section 3.2, if the underwriter shall advise the Company in
writing that marketing factors (including, without limitation, an adverse effect
on the per share offering price) require a limitation of the number of shares to
be underwritten, then the Company shall so advise all Holders of Registrable
Securities that would otherwise be registered and underwritten pursuant hereto,
and the number of shares of Registrable Securities that may be included in the
registration and underwriting shall be allocated pro rata among such Holders
thereof 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 foregoing 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, the
underwriter, and the Initiating Holders. The Registrable Securities so withdrawn
shall also be withdrawn from registration. 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 in this Section 3.1(b).

         If the underwriter has not limited the number of Registrable Securities
to be underwritten, the Company may include securities for its own account (or
for the account of other stockholders) in such registration if the underwriter
so agrees and if the number of Registrable Securities that would otherwise have
been included in such registration and underwriting will not thereby be limited.

                                       5.

<PAGE>

         3.2      Company Registration.

                  (a)      Notice to Holders. If, at any time or from time to
time, the Company shall determine to register any of its securities, either for
its own account or the account of others, other than a registration relating
solely to employee benefit plans on Form S-8 or similar forms which may be
promulgated in the future or a registration on Form S-4 or similar forms which
may be promulgated in the future relating solely to a Rule 145 (as defined
below) or similar transaction, the Company will (i) promptly give to each Holder
written notice thereof and (ii) include in such registration (and any related
qualification under Blue Sky laws or other compliance), and in any underwriting
involved therein, all Registrable Securities of such Holders as specified in a
written request or requests made within 15 days after receipt of such written
notice from the Company.

                  (b)      Underwriting. If the registration statement of which
the Company gives notice under Section 3.2(a) is for an underwritten offering,
the Company shall so advise the Holders of Registrable Securities. In such
event, the right of any such Holder to be included in a registration pursuant to
this Section 3.2 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. All Holders proposing to distribute
their Registrable Securities through such underwriting (together with the
Company and other holders distributing their securities through such
underwriting) shall enter into an underwriting agreement in customary form with
the underwriter or underwriters selected for such underwriting. Notwithstanding
any other provision of this Agreement, if the underwriter determines in good
faith that marketing factors require a limitation of the number of shares to be
underwritten, the number of shares that may be included in the underwriting
shall be allocated, first, to the Company; second, to the Holders on a pro rata
basis based on the total number of Registrable Securities held by the Holders;
and third, to any stockholder of the Company (other than a Holder) on a pro rata
basis. No such reduction shall reduce the securities being offered by the
Company for its own account to be included in the registration and underwriting,
except that in no event shall the amount of securities of the selling Holders
included in the registration be reduced below thirty percent (30%) of the total
amount of securities included in such registration, unless such offering is the
first underwritten public offering of the Company's securities and such
registration does not include shares of any other selling stockholders, in which
event any or all of the Registrable Securities of the Holders may be excluded in
accordance with the immediately preceding sentence. In no event will shares of
any other selling stockholder be included in such registration which would
reduce the number of shares which may be included by Holders without the written
consent of Holders of not less than a majority of the Registrable Securities
proposed to be sold in the offering. If any Holder disapproves of the terms of
any such underwriting, such Holder may elect to withdraw therefrom by written
notice to the Company and the underwriter. Any securities excluded or withdrawn
from such underwriting shall be withdrawn from such registration.

         3.3      Form S-3 Registration Rights. After the Company's initial
registered underwritten public offering, the Company shall use its best efforts
to qualify for registration on Form S-3, and to that end the Company shall use
its best efforts to comply with the reporting requirements of the Securities
Exchange Act of 1934, as amended (the "Securities Exchange Act"), within twelve
(12) months following the effective date of the first registration of any

                                       6.

<PAGE>

securities of the Company for an underwritten registered public offering. After
the Company has qualified for the use of Form S-3, and subject to the provisions
of Section 3.10, each Holder shall have the right to request registrations on
Form S-3 (such requests shall be in writing and shall state the number of shares
of Registrable Securities to be disposed of and the intended method of
disposition of such shares by each such Holder), subject only to the following
limitations:

                  (a)      The Company shall be obligated to effect only two (2)
such registrations on Form S-3 in any twelve month period;

                  (b)      The Company shall not be obligated to cause a
registration on Form S-3 to become effective prior to one hundred eighty (180)
days following the effective date of a Company initiated registration (other
than a registration effected solely to qualify an employee benefit plan on Form
S-8 or to effect a business combination pursuant to Rule 145 of the Securities
Act ("Rule 145"));

                  (c)      The Company shall not be required to effect a
registration pursuant to this Section 3.3 unless the Holder or Holders
requesting such a registration propose to dispose of shares of Registrable
Securities having an aggregate disposition price (net of Selling Expenses) of at
least $1,000,000;

                  (d)      The Company shall not be required to effect a
registration pursuant to this Section 3.3 if the Company shall furnish to the
requesting Holders a certificate signed by the President 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 or its Holders for the
registration statement to be filed at the date filing would be required, in
which case the Company shall have an additional period of not more than one
hundred eighty (180) days within which to file such registration statement;
provided however, that the Company shall not use this right more than once in
any twelve (12) month period; and

                  (e)      The Company shall not be required to maintain and
keep any such registration on Form S-3 effective for a period exceeding one
hundred and twenty (120) days from the effective date thereof.

         The Company shall give notice to all Holders of the receipt of a
request for registration pursuant to this Section 3.3 and shall use its best
efforts to cause all Registrable Securities that such Holders have requested,
within 15 days after receipt of such written notice, be registered in accordance
with this Section 3.3 to be registered under the Securities Act. Subject to the
foregoing, the Company will use its best efforts to effect promptly any
registration pursuant to this Section 3.3. The provisions of Section 3.1(b)
shall apply to any registration effected pursuant to this Section 3.3.

         3.4      Expenses of Registration. All Registration Expenses incurred
in connection with any registration, qualification or compliance pursuant to
Sections 3.1, 3.2 and 3.3 (exclusive of Selling Expenses but inclusive of the
reasonable fees and expenses of one special counsel to the selling Holders)
shall be borne by the Company. Notwithstanding anything to the contrary herein,
the Company shall not be required to pay for any expenses of any registration
proceeding under Section 3.1 if the registration request is subsequently
withdrawn at the request of the

                                       7.

<PAGE>

Holders of a majority of the Registrable Securities to have been registered,
unless such Holders agree to forfeit their right to a demand registration
pursuant to Section 3.1 (in which event such right shall be forfeited by all
Holders). In the absence of such an agreement to forfeit, the Holders of
Registrable Securities to have been registered shall bear all such expenses pro
rata on the basis of the Registrable Securities to have been registered.
Notwithstanding the foregoing, however, if at the time of the withdrawal, the
Holders have learned of a material adverse change in the condition, business, or
prospects of the Company from that known to the Holders at the time of their
request, of which the Company had knowledge at the time of the request, then the
Holders shall not be required to pay any of said expenses and shall retain their
rights pursuant to Section 3.1.

         3.5      Registration Procedures. In the case of each registration,
qualification or compliance effected by the Company pursuant to this Section 3,
the Company will keep each Holder advised in writing as to the initiation of
each registration, qualification and compliance and as to the completion
thereof. At its expense the Company will:

                  (a)      Keep such registration, qualification or compliance
effective for a period of 120 days or until the Holder or Holders have completed
the distribution described in the registration statement relating thereto,
whichever first occurs;

                  (b)      Prepare and file with the Commission such amendments
and supplements to such registration statement and the prospectus used in
connection with such registration statement as may be necessary to comply with
the provisions of the Securities Act with respect to the disposition of all
securities covered by such registration statement;

                  (c)      Furnish to the Holders such numbers of copies of a
prospectus, including a preliminary prospectus, in conformity with the
requirements of the Securities Act, and such other documents as they may
reasonably request in order to facilitate the disposition of Registrable
Securities owned by them;

                  (d)      Use its best efforts to register and qualify the
securities covered by such registration statement under such other securities or
Blue Sky laws of such jurisdictions as shall be reasonably requested by the
Holders, 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;

                  (e)      In the event of any underwritten public offering,
enter into and perform its obligations under an underwriting agreement, in usual
and customary form, with the managing underwriter of such offering. Each Holder
participating in such underwriting shall also enter into and perform its
obligations under such an agreement; and

                  (f)      Notify each Holder of Registrable Securities covered
by such registration statement at any time when a prospectus relating thereto is
required to be delivered under the Securities Act of the happening of any event
as a result of which the prospectus included in such registration statement, as
then in effect, includes an untrue statement of a material fact or omits to
state a material fact required to be stated therein or necessary to make the
statements therein not misleading in the light of the circumstances then
existing.

                                       8.

<PAGE>

         Notwithstanding any provision to the contrary in this Agreement, the
Company shall not be required in connection with any registration pursuant to
Sections 3.1, 3.2 or 3.3 to qualify shares in any state or jurisdiction which
requires the Company to qualify to do business or to file a general consent to
service of process.

         3.6      Indemnification.

                  (a)      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, qualification or compliance has been effected pursuant to this
Section 3, against all expenses, claims, losses, damages and 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, qualification or compliance, 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 the light of the circumstances in
which they were made, not misleading, or any violation by the Company of any
rule or regulation promulgated under the Securities Act applicable to the
Company and relating to action or inaction required of the Company in connection
with any such registration, qualification or compliance, and will reimburse each
such Holder, each of its officers and directors and partners, and each person
controlling such Holder, for any legal and any other expenses reasonably
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 and in
conformity with written information furnished to the Company by an instrument
duly executed by such Holder or underwriter and stated to be specifically for
use therein.

                  (b)      Each Holder will, if Registrable Securities held by
such Holder are included in the securities as to which such registration,
qualification or compliance is being effected, indemnify the Company, each of
its directors and officers, each person who controls the Company or such
underwriter within the meaning of Section 15 of the Securities Act, and each
other such 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, against all expenses, claims, losses, damages and 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 such registration statement, prospectus, offering circular or other
document, or any amendment or supplement thereto, incident to any such
registration, qualification or compliance 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 the light of the circumstances in
which they were made, not misleading, or any violation by the Company of any
rule or regulation promulgated under the Securities Act applicable to the
Company in connection with any such registration, qualification, or compliance,
and will reimburse the Company, such Holders, such directors, officers,
partners, persons, or control persons for any legal or any other expenses
reasonably

                                       9.

<PAGE>

incurred in connection with investigating, preparing or defending any such
claim, loss, damage, liability or action, in each case to the extent, but only
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 or any amendment or supplement
thereto in reliance upon and in conformity with written information furnished to
the Company by an instrument duly executed by such Holder and stated to be
specifically for use therein; provided, however, that the obligations of such
Holders hereunder shall be limited to an amount equal to the net proceeds to
each such Holder of Registrable Securities sold as contemplated herein.

                  (c)      Each party entitled to indemnification under this
Section 3.6 (the "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 be
unreasonably withheld), and the Indemnified Party may participate in such
defense at its own expense; provided, however, that an Indemnified Party
(together with all other indemnified parties which may be represented without
conflict by one counsel) shall have the right to retain one separate counsel,
with the fees and expenses to be paid by the Indemnifying Party, if
representation of such Indemnified Party by the counsel retained by the
Indemnifying Party would be inappropriate due to actual or potential conflicts
of interests between such Indemnified Party and any other party represented by
such counsel in such proceeding. The failure of any Indemnified Party to give
notice as provided herein shall not relieve the Indemnifying Party of its
obligations under this Section 3.6 unless such failure resulted in actual
detriment to the Indemnifying Party. No Indemnifying Party, in the defense of
any such claim or litigation, shall, except with the consent of each Indemnified
Party, 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 a release from all liability in respect of
such claim or litigation.

                  (d)      If the indemnification provided for in this Section
3.6 is held by a court of competent jurisdiction to be unavailable to an
Indemnified Party with respect to any loss, liability, claim, damage, or expense
referred to therein, then the Indemnifying Party, in lieu of indemnifying such
Indemnified Party hereunder, shall contribute to the amount paid or payable by
such Indemnified Party as a result of such loss, liability, claim, damage, or
expense in such proportion as is appropriate to reflect the relative fault of
the Indemnifying Party on the one hand and of the Indemnified Party on the other
in connection with the statements or omissions that resulted in such loss,
liability, claim, damage, or expense as well as any other relevant equitable
considerations. The relative fault of the Indemnifying Party and of the
Indemnified Party shall be determined by reference to, among other things,
whether the untrue or alleged untrue statement of a material fact or the
omission to state a material fact relates to information supplied by the
Indemnifying Party or by the Indemnified Party and the parties relative intent,
knowledge, access to information, and opportunity to correct or prevent such
statement or omission.

                                       10.

<PAGE>

                  (e)      The obligations of the Company and Holders under this
Section 3.6 shall survive the completion of any offering of Registrable
Securities in a registration statement under this Section 3.

         3.7      Information by Holder. The Holder or Holders of Registrable
Securities included in any registration shall furnish to the Company such
information regarding such Holder or Holders and the distribution proposed by
such Holder or Holders as the Company may request in writing and as shall be
required in connection with any registration, qualification or compliance
referred to in this Section 3.

         3.8      Rule 144 Reporting. With a view to making available the
benefits of certain rules and regulations of the Commission which may at any
time permit the sale of the Restricted Securities to the public without
registration, after such time as a public market exists for the Common Stock of
the Company, the Company agrees to:

                  (a)      Use its best efforts to make and keep public
information available, as those terms are understood and defined in Rule 144
under the Securities Act at all times after the effective date of the first
registration under the Securities Act filed by the Company for an offering of
its securities to the general public;

                  (b)      Use its best efforts to then file with the Commission
in a timely manner all reports and other documents required of the Company under
the Securities Exchange Act at any time after it has become subject to such
reporting requirements;

                  (c)      So long as an Holder owns any Restricted Securities,
to furnish to such Holder forthwith upon request a written statement by the
Company as to its compliance with the reporting requirements of said Rule 144
(at any time after 90 days after the effective date of the first registration
statement filed by the Company for an offering of its securities to the general
public) and of the Securities Act and the Securities Exchange Act (at any time
after it has become subject to such reporting requirements), a copy of the most
recent annual or quarterly report of the Company, and such other reports and
documents of the Company as an Holder may reasonably request in availing itself
of any rule or regulation of the Commission allowing an Holder to sell any such
securities without registration.

         3.9      Transfer of Registration Rights. The rights to cause the
Company to register securities granted under Sections 3.1, 3.2 and 3.3 may be
assigned or otherwise conveyed to a transferee or assignee of Registrable
Securities, who shall be considered a "Holder" for purposes of this Section 3,
provided that (a) such transfer is effected in accordance with applicable
federal and state securities laws, (b) the Company is given written notice by
such Holder at the time of or within a reasonable time after said transfer,
stating the name, address and a reasonably detailed description of the principal
business or occupation of said transferee or assignee and any such other
information as is reasonably requested by the Company in order to carry out the
intent of these provisions and identifying the securities with respect to which
such registration rights are being assigned, (c) the Company reasonably
determines that the proposed transferee or assignee is not a direct competitor
or future competitor of the Company and (d) such transferee or assignee (i) is a
Holder, (ii) is an affiliate of a Holder, including a wholly-owned subsidiary or
constituent partner (including limited partners and partners who retire from a
transferror

                                       11.

<PAGE>

partnership after the date hereof) of the transferring Holder, (iii) is a family
member of the transferring Holder, (iv) is a trust for the benefit of an
individual transferror or his family members, or (v) acquires at least 50,000
shares (as presently constituted) of the Registrable Securities held by the
transferring Holder. No such transfer or assignment shall be valid or effective
unless the proposed transferee or assignee expressly agrees to be subject to all
of the provisions of this Agreement relating to such rights, including without
limitation the provisions of Sections 3.6 and 3.11 of this Agreement.

         3.10     Termination of Registration Rights. The registration rights
granted pursuant to this Section 3 shall terminate (i) upon the fifth
anniversary of the effective date of the first registration statement filed by
the Company covering a firm commitment underwritten offering of its securities
to the general public, which offering has closed, or (ii) if earlier, as to any
individual Holder, at such time after the Company's initial registered public
offering as all Registrable Securities held by such Holder can be sold without
compliance with the registration requirements of the Securities Act pursuant to
Rule 144(k) promulgated thereunder and such Holder owns less than 1% of the
Company's outstanding capital stock.

         3.11     "Market Stand Off" Agreement. Each Holder and each Founder
hereby agrees that it shall not, to the extent requested by the Company and an
underwriter of Common Stock (or other securities) of the Company, sell or
otherwise transfer or dispose of (other than to those who agree to be similarly
bound) any Registrable Securities, Founders' Shares, or any other securities of
the Company for a period (the "Stand Off Period") of up to one hundred eighty
(180) days following the effective date of a registration statement of the
Company filed under the Securities Act; provided, however, that (i) such
agreement shall only be applicable to the first such registration statement of
the Company which covers shares (or securities) to be sold on its behalf to the
public in an underwritten offering; and (ii) the length of the Stand Off Period
shall not exceed the shortest period of time agreed to by any officer, director
or 5% holder of the Company.

         In order to enforce the foregoing covenant, the Company may impose
stop-transfer instructions with respect to the Registrable Securities of Holders
and Founders (and the shares or securities of every other person subject to the
foregoing restriction) until the end of the Stand Off Period.

         3.12     Inclusion of Stock Held by Founders and Common Stock held by
Holders. In connection with any registration effected pursuant to Section 3.2
hereof, each of the Founders and each of the Holders, with respect to shares of
Common Stock of the Company that are held by the Founders and the Holders and
are not "Registrable Securities" for purposes of this Agreement, shall be
entitled to participate in such registration, on the same terms and conditions
as Holders selling their Registrable Securities in such registration and, for
purposes of Section 3.2, (i) each such Founder and Holder shall be entitled to
all of the rights and shall be subject to all of the obligations applicable to a
Holder in connection with such registration, including without limitation the
provisions of Sections 3.6 and 3.11 of this Agreement, (ii) all such securities,
and any shares of Common Stock issued in respect thereof upon any stock split,
stock dividend, recapitalization or similar event, shall be deemed to be
"Registrable Securities," (iii) all references to "Holder" in this Agreement
shall be deemed to include such Founder and Holder

                                       12.

<PAGE>

for purposes of such registration and (iv) any Underwriter Cutback shall apply
pro rata to the shares so included by the Founders and Holders participating in
such registration.

         3.13     Limitations on Subsequent Registration Rights. From and after
the date of this Agreement, the Company shall not, without the prior written
consent of Holders holding more than fifty percent (50%) of the Registrable
Securities, enter into any agreement with any holder or prospective holder of
any securities of the Company which would allow such holder or prospective
holder to (i) require the Company to effect a registration or (ii) include any
securities in any registration filed under Sections 3.1, 3.2 or 3.3 hereof
unless, under the terms of such agreement, such holder or prospective holder may
include such securities in any such registration only to the extent that the
inclusion of such securities will not diminish the amount of Registrable
Securities which are included in such registration, and such agreement includes
the equivalent of Section 3.11 as a term.

                                    ARTICLE 4

                      AFFIRMATIVE COVENANTS OF THE COMPANY

         4.1      Financial Information. The Company will furnish the following
reports to each Holder for so long as such Holder is a holder of (or is entitled
to purchase under this Agreement) at least 100,000 shares of Preferred or Common
Stock issued upon conversion of the Preferred or a combination thereof (a
"Significant Holder"):

                  (a)      As soon as practicable after the end of each fiscal
year, audited consolidated balance sheets of the Company and its subsidiaries,
if any, as of the end of such fiscal year, and a consolidated statement of
operations and a consolidated statement of cash flow of the Company and its
subsidiaries, if any, for such year, prepared in accordance with generally
accepted accounting principles and setting forth in each case in comparative
form the figures for the previous fiscal year, all in reasonable detail and
certified by independent public accountants of recognized national standing
selected by the Company; and

                  (b)      As soon as practicable after the end of each fiscal
quarter and in any event within 45 days thereafter, an unaudited consolidated
balance sheet of the Company and its subsidiaries, if any, as of the end of each
such quarter, and a consolidated statement of operations and a consolidated
statement of cash flow of the Company and its subsidiaries for such period and
for the year to date, prepared in accordance with generally accepted accounting
principals, subject to changes resulting from year-end audit adjustments.

         4.2      Inspection. The Company shall permit each Holder, at such
Holder's expense, to visit and inspect the Company's properties, to examine its
books of account and records and to discuss the Company's affairs, finances and
accounts with its officers, all at such reasonable times as may be requested by
the Holder; provided, however, that the Company shall not be obligated pursuant
to this Section 4.2 to provide access to any information which it reasonably
considers to be a trade secret or similar confidential information.

         4.3      Assignment of Rights to Financial Information. The rights
granted pursuant to Section 4.1 may be assigned by Holders (or by any permitted
transferee of any such rights) only

                                       13.

<PAGE>

in connection with the transfer to a single transferee of not less than 100,000
shares of Preferred or Common Stock issued upon conversion thereof or a
combination thereof (including, for such purposes, transfers by affiliates of a
transferror) and only so long as (i) the Company is given notice of any such
assignment within thirty (30) days of the date the same is effected, which
notice shall disclose the name of such assignee and provide a reasonably
detailed description of such assignee's business or principal occupation and the
circumstances surrounding such assignment, (ii) the Company reasonably
determines that the assignee is not a direct competitor or potential competitor
of the Company and (iii) if the Company reasonably believes that it is necessary
to protect proprietary information, the Company may require that the assignee
execute a confidentiality agreement as a condition to receiving such
information.

         4.4      Attendance at Board Meetings. Each Significant Holder (or its
representative) shall have the right to attend all meetings of the Board of
Directors in a nonvoting observer capacity, to receive notice of such meetings
and to receive the information provided by the Company to the Board of
Directors; provided, however, that each person proposing to attend any meeting
of the Board of Directors and each person to have access to any of the
information provided by the Company to the Board of Directors shall agree to
hold in confidence and trust and to act in a fiduciary manner with respect to
all information so received during such meeting or otherwise; and, provided
further, that the Company reserves the right not to provide information and to
exclude such Significant Holder (or its representative) from any meeting or
portion thereof if delivery of such information or attendance at such meeting by
such Significant Holder (or its representative) would result in disclosure of
trade secrets to such Significant Holder (or its representative) or would
adversely affect the attorney-client privilege between the Company and its
counsel or if such Significant Holder (or its representative) is a direct
competitor of the Company.

         4.5      Compensation Committee. The Series A Preferred (voting as a
class) and the Series B Preferred (voting as a class) shall each have the right
to appoint one member, which member shall be satisfactory to the other series of
Preferred, to the compensation committee of the Board of Directors (the
"Compensation Committee"), which shall initially consist of two members which
shall be Robert G. McNeil and Michael A. Henos. The size and composition of the
Compensation Committee shall not be changed without the consent of the Series A
Preferred (voting as a class) and the Series B Preferred (voting as a class).
The rights granted to the Series A Preferred and the Series B Preferred pursuant
to this Section 4.5 shall terminate on the second anniversary of the initial
closing of the purchase and sale of Series B Preferred.

         4.6      Sales of Series B Preferred. The Company shall not sell any
shares of Series B Preferred after December 31, 1995, unless the Company has
received a letter of intent to purchase shares of Series B Preferred, dated as
of or prior to such date, in which case the Company may sell shares of Series B
Preferred pursuant to such letter of intent after such date.

         4.7      Termination of Covenants. The covenants and rights set forth
in Sections 4.1 and 4.4 shall terminate and be of no further force or effect
after the earlier of the date upon which the first registration statement filed
by the Company under the Securities Act in connection with the firm commitment
underwritten public offering of its securities becomes effective, which offering
has closed.

                                       14.

<PAGE>

                                    ARTICLE 5

            AFFIRMATIVE COVENANTS OF HOLDERS; RIGHT OF FIRST REFUSAL

         5.1      Confidential Information, etc. Each Holder agrees that all
information received by it pursuant to Section 4, and any other information
relating to the Company's technology, processes or formulas that is disclosed by
the Company to any Holder in writing and is marked "Confidential," shall be
considered confidential information. Each Holder further agrees that it shall
hold all confidential information relating to the Company in confidence and
shall not disclose any such confidential information to any third party other
than its counsel or accountants nor shall such Holder use such confidential
information for any purpose other than evaluation of such Holder's investment in
the Company; provided, however, that the foregoing obligation to hold in
confidence and not to disclose confidential information shall not apply to any
such information that (a) was known to the public prior to disclosure by the
Company, (b) becomes known to the public through no fault of such Holder, (c) is
disclosed to such Holder on a non-confidential basis by a third party having a
legal right to make such disclosure or (d) is independently developed by such
Holder.

         5.2      Right of First Refusal. The Company hereby grants to each
Purchaser (defined below) the right of first refusal to purchase its Pro Rata
Share (defined below) of all (or any part) of any New Securities (defined below)
that the Company may from time to time propose to sell and issue. Such
Purchaser's "Pro Rata Share," for purposes of this right of first refusal, is
the ratio of the number of shares of Common Stock (assuming conversion to Common
Stock of all shares of the Preferred) then held by such Purchaser to the total
number of shares of Common Stock then outstanding (assuming conversion to Common
Stock of all outstanding shares of the Company's Preferred Stock). This right of
first refusal shall be subject to the following provisions:

                  (a)      "Purchaser" shall mean, with respect to any issuance
of New Securities of the Company, each Founder who then holds any Common Stock
and each Holder who then holds any Preferred (or Common Stock issued upon
conversion thereof) or any Common Shares.

                  (b)      "New Securities" shall mean any Common Stock or
Preferred Stock of the Company, whether now authorized or not, and rights,
options or warrants to purchase said Common Stock or Preferred Stock, and
securities of any type whatsoever that are, or may become, convertible into or
exchangeable for said Common Stock or Preferred Stock; provided, however, that
"New Securities" does not include (i) securities issuable upon conversion of or
with respect to the Preferred or any future series of Preferred Stock of the
Company; (ii) securities offered to the public pursuant to a registration
statement filed under the Securities Act; (iii) securities issued pursuant to
the acquisition of another corporation or other business entity by the Company
by merger, purchase of all or substantially all of the assets or other
reorganization; (iv) up to 500,000 shares of the Company's Common Stock or other
securities (or related options) issued to directors, officers or employees of,
or consultants to, the Company pursuant to an agreement or an option or purchase
plan or another director, officer, employee or consultant stock incentive
program approved by the Board of Directors of the Company; (vi) shares of the
Company's Common Stock or Preferred Stock issued in connection with any stock
split, stock dividend, or recapitalization by the Company; (vii) securities
issued to persons or

                                       15.

<PAGE>

entities in connection with bank or equipment lease financing, technology
licensing or corporate partnering transactions and the like approved by the
Board of Directors of the Company; and (viii) shares of Preferred issued
pursuant to the Series B Agreement.

                  (c)      In the event that the Company proposes to undertake
an issuance of New Securities, it shall give each Purchaser written notice of
its intention, describing the type of New Securities, the price, and the general
terms upon which the Company proposes to issue the same. Each Purchaser shall
have ten (10) days from the date of delivery of any such notice to agree to
purchase his Pro Rata Share of such New Securities for the price and upon the
general terms specified in the notice by giving written notice to the Company
and stating therein the quantity of New Securities to be purchased.

                  (d)      In the event that Purchasers fail to exercise in full
the right of first refusal within said ten (10) day period, the Company shall
have sixty (60) business days thereafter to sell (or enter into an agreement
pursuant to which the sale of New Securities covered thereby shall be closed, if
at all, within sixty (60) business days from the date of said agreement) the New
Securities respecting which the Purchasers' rights were not exercised, at a
price and upon general terms no more favorable to the purchasers thereof than
specified in the Company's notice. In the event the Company has not sold the New
Securities within said sixty (60) business day period (or sold and issued new
Securities in accordance with the foregoing within sixty (60) business days from
the date of said agreement), the Company shall not thereafter issue or sell any
New Securities, without first offering such securities to the Purchasers in the
manner provided above.

                  (e)      The right of first refusal granted under this
Agreement shall expire upon the earlier of (i) the closing of the Company's
first underwritten public offering of Common Stock pursuant to a registration
statement declared effective under the Securities Act, or (ii) a merger,
acquisition or other change in control of the Company. As used herein, "change
of control" means the occurrence of an event that results in the existing
stockholders of the Company, just prior to the event, owning less than 50% of
the voting power of the Company, as measured just following the event.

                  (f)      This right of first refusal is nonassignable except
to any other Purchaser or to any parent, subsidiary or general or limited
partner of any Purchaser.

                                    ARTICLE 6

                                  MISCELLANEOUS

         6.1      Governing Law. This Agreement shall be governed by the laws of
the State of California as applicable to contracts entered into and performed
entirely within the State of California.

         6.2      Successors and Assigns. Except as otherwise 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.

                                       16.

<PAGE>

         6.3      Entire Agreement. This Agreement constitutes the full and
entire understanding and agreement between the parties with regard to the
subject matter hereof.

         6.4      Rights of Holders. Each Holder and Founder shall have the
absolute right to exercise or refrain from exercising any right or rights that
such Holder or Founder may have by reason of this Agreement or the ownership of
any Preferred or Common Stock, including without limitation the right to consent
to the waiver of any obligation of the Company under this Agreement to such
Holder or Founder and to enter into an agreement with the Company for the
purpose of modifying this Agreement or any agreement affecting any such
modification, and such Holder or Founder shall not incur any liability to any
other Founder, Holder or holders of Preferred with respect to exercising or
refraining from exercising any such right or rights.

         6.5      Notices, etc. All notices and other communications required or
permitted hereunder shall be in writing and shall be mailed by registered or
certified mail, postage prepaid, or facsimile or otherwise delivered by hand or
by messenger, addressed (a) if to a Holder or Founder, at such Holder's or
Founder's address set forth below or at such other address as such Holder or
Founder shall have furnished to the Company in writing, (b) if to any other
holder of Preferred, at such address as such holder shall have furnished the
Company in writing or (c) if to the Company, one copy shall be sent to its
address set forth above and addressed to the attention of the President and
another copy shall be sent to Cooley Godward Castro Huddleson & Tatum, 5 Palo
Alto Square, 4th Floor, Palo Alto, California 94306, Attention: Alan C.
Mendelson, Esq., or at such other addresses as the Company shall have furnished
to the Holders and the Founders. All notices and other communications mailed or
sent by facsimile pursuant to the provisions of this Section 6.5 shall be deemed
delivered when mailed or sent by facsimile, provided, if sent by facsimile,
confirmation of receipt is ascertained and a copy of the notice is concurrently
mailed to the addressee thereof by U.S. Mail.

         6.6      Counterparts. This Agreement may be executed in counterparts,
each of which shall be enforceable against the party actually executing such
counterpart, and which together shall constitute one instrument.

         6.7      Severability. In the event that any provision of this
Agreement becomes or is declared by a court of competent jurisdiction to be
illegal, unenforceable or void, this Agreement shall continue in full force and
effect without said provision; provided that no such severability shall be
effective if it materially changes the economic benefit of this Agreement to any
party.

         6.8      Approval of Amendments and Waivers. Any term of this agreement
may be amended or terminated and the observance of any term of this Agreement
may be waived (either generally or in a particular instance and either
retroactively or prospectively) with the written consent of the Company and
Holders (or their transferees) holding at least a majority of the then
outstanding shares of Registrable Securities, excluding from the determination
of such a majority (both in determining the total number of such shares
outstanding and the number of such shares consenting or not consenting) all
shares previously disposed of by Holders or their transferees pursuant to one or
more registration statements under the Securities Act or pursuant to Rule 144
thereunder; provided, however, that no such amendment or waiver shall adversely
affect the right of any Founder to participate in registrations under Section
3.2 of this Agreement as provided for in Section 3.12 without such Founder's
written consent; it being understood, however, that the

                                       17.

<PAGE>

amendment of this Agreement to increase the number of shares defined as
Registrable Securities or to add additional parties as Holders shall be deemed
not to adversely affect such right under Section 3.2. Any amendment, termination
or waiver effected in accordance with this section shall be binding upon each
Founder, each Holder, each of their transferees and the Company. Each Founder
and each Holder acknowledges that by the operation of this Section 6.8 the
Holders of a majority of the outstanding Registrable Securities may have the
right and power to diminish or eliminate all rights of such Holder under this
Agreement as provided for above.

                                       18.

<PAGE>

         The Foregoing Agreement is hereby executed as of the date first above
written.

The Company:

Discovery Therapeutics, Inc.

By /s/ Donald A. McAfee
   -----------------------------------------

Title    President

                                       19.

<PAGE>

The Founders:

               /s/ Donald McAfee
---------------------------------------
Donald McAfee

Address:  _____________________________
          _____________________________

               /s/ Noel Cusack
---------------------------------------
Noel Cusack

Address:  _____________________________
          _____________________________

               /s/ James Peck
---------------------------------------
James Peck

Address:  _____________________________
          _____________________________

Gevork Minaskanian

               /s/ Gevork Minaskanian
---------------------------------------

Address:
          _____________________________
          _____________________________

                                       20.

<PAGE>

The Investors:

Sanderling Venture Partners III

Sanderling III Biomedical

Sanderling III Limited

Sanderling Ventures Management

By  /s/ Fred Middleton
    --------------------------------------
           On behalf of and as General Partner
           of each of the above-entitled entities

Address:   c/o Marc Prisant
           2730 Sand Hill Road, Suite 200
           Menlo Park, CA 94025

Alliance Technology Ventures, L.P.

By /s/ Michael Henos
   ----------------------------------------------

Title  General Partner

ATV/MFJ Parallel Fund, L.P.

By /s/ Michael Henos
   ----------------------------------------------

Title General Partner

ATV/GP Parallel Fund, L.P.

By /s/ Michael Henos
   ----------------------------------------------

Title General Partner

Address: c/o Michael Henos
         3343 Peachtree Road
         East Tower, Suite 1140
         Atlanta, GA 30326

                                       22.

<PAGE>

Gc&H Investments

By /s/
   -------------------------------------------

Title Executive Partner

Address: c/o John Cardoza
         Cooley Godward Castro Huddleson & Tatum
         One Maritime Plaza
         20th Floor
         San Francisco, CA 94111-3580

                                       23.

<PAGE>

                          DISCOVERY THERAPEUTICS, INC.
                                  AMENDMENT TO

                       RESTATED INVESTOR RIGHTS AGREEMENT

         This Amendment (the "Amendment") to the Restated Investor Rights
Agreement, dated as of March 31, 1995 (the "Restated Investor Rights
Agreement"), between Discovery Therapeutics, Inc., a Delaware corporation (the
"Company"), and the undersigned parties thereto (the "Initial Investors"), is
made and entered into as of this 3rd day of November, 1995, by and among the
Company, the undersigned additional investor (the "Additional Investor") and
certain of the Initial Investors.

         Whereas, the Additional Investor has purchased shares of the Company's
Series B Preferred Stock (the "Shares") pursuant to that certain Series B
Preferred Stock Purchase Agreement, dated March 31, 1995, by and among the
Company and the purchasers listed on Exhibit A attached thereto, as amended by
that certain Amendment to Series B Preferred Stock Purchase Agreement of even
date herewith (the "Purchase Agreement"); and

         Whereas, the Company and certain of the Initial Investors which are
parties hereto wish to amend the Restated Investor Rights Agreement to add the
Additional Investor as a party thereto pursuant to this Amendment.

         Now Therefore, in consideration of the mutual agreements, covenants and
considerations contained herein, the undersigned hereby agree as follows:

         1.       The Restated Investor Rights Agreement is hereby amended to
include the Additional Investor as an Investor thereunder, with the Additional
Investor agreeing to be bound by all terms and conditions therein and being
entitled to all the benefits thereof.

         2.       The Initial Investors hereby waive the right of first refusal
granted to such parties under Section 5.2 of the Restated Investor Rights
Agreement (and the notice periods with respect thereto) with respect to, and
only with respect to, the issuance of the Shares to the Additional Investor
pursuant to the Purchase Agreement.

         3.       This Amendment may be executed in two or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

         4.       Except as hereby expressly amended, the Restated Investor
Rights Agreement shall remain in full force and effect pursuant to its terms.

         5.       Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to such terms in the Restated Investor Rights
Agreement.

                                       1.

<PAGE>

         In Witness Whereof, the undersigned have executed this Amendment as of
the day and year first set forth above.

Discovery Therapeutics, Inc.            Additional Purchaser:

                                        New York Life Insurance Company

By: /s/ Donald A. McAfee
    ------------------------------
    Donald A. McAfee, President         By:__________________________________

                                        Title:_______________________________

                                        Initial Investors:

                                        Sanderling Venture Partners III
                                        Sanderling III Biomedical
                                        Sanderling III Limited Partnership
                                        Sanderling Ventures Management

                                        By:__________________________________

                                        Title:_______________________________

                                        Alliance Technology Ventures, L.P.
                                        ATV/GP Parallel Fund, L.P.
                                        ATV/MFJ Parallel Fund, L.P.

                                        By:__________________________________

                                        Title:_______________________________

                Amendment to Restated Investor Rights Agreement

<PAGE>

                          Discovery Therapeutics, Inc.
                               Second Amendment to
                       Restated Investor Rights Agreement

         This Second Amendment (the "Second Amendment") to the Restated Investor
Rights Agreement dated as of March 31, 1995 (the "Rights Agreement"), between
Discovery Therapeutics, Inc., a Delaware corporation (the "Company"), and the
undersigned parties thereto, and New York Life Insurance Company (the "Initial
Investors"), is made and entered into as of this 21st day of June, 1999, by and
among the Company, the undersigned shareholders of Renalogics, Inc. a Georgia
Corporation (the "Additional Investors") and certain of the Initial Investors.

         Whereas, on March 31, 1995 the Company entered into a Restated Investor
Rights Agreement (the "Rights Agreement") with four (4) of its founders (the
"Founders") and certain named investors (the "Initial Investors") pursuant to
which the Company granted to the Founders and the Initial Investors a right of
first refusal to purchase a pro rata share of all New Securities (as defined in
the Rights Agreement) that the Company may from time to time propose to sell and
issue;

         Whereas, on November 3, 1995, the Company entered into an Amendment to
the Rights Agreement, which defined New York Life Insurance Company as an
Additional Investor under the Rights Agreement, subject to the registration,
information and other rights set forth therein;

         Whereas, the Rights Agreement defined New Securities and excluded from
said definition, among other things, up to 500,000 shares of the Company's
Common Stock or other securities (or related options) issued to directors,
officers or employees of, or consultants to, the Company pursuant to an
agreement or an option to purchase plan or another director, officer, employee
or consultant stock incentive program approved by the Board of Directors of the
Company;

         Whereas, the Company, the Founders, and the Investors, now wish to
amend the Rights Agreement a second time to increase the number of shares
reserved for issuance to directors, officers or employees of, or consultants to,
the Company from five hundred thousand (500,000) shares to one million
(1,000,000) shares;

         Whereas, the Company has entered into that certain Stock Purchase
Agreement among the Company, Renalogics, Inc., and the shareholders of
Renalogics, Inc. (the "Renalogics Agreement") pursuant to which the shareholders
of Renalogics shall swap 100% of the outstanding capital stock of Renalogics for
a maximum of two hundred fifty nine thousand one hundred sixty one (259,161)
shares of Common Stock and two hundred ninety six thousand six hundred seventy
eight (296,678) shares of Series B Preferred Stock of the Company;

         Whereas, the Company and certain of the Initial Investors, which are
parties hereto, wish to amend the Restated Investor Rights Agreement so that
those shareholders of Renalogics who receive shares of the Company's Series B
Preferred Stock under the Renalogics Agreement are defined as Investors under
the Rights Agreements;

                                       1.

<PAGE>

         Now Therefore, in consideration of the mutual agreements, covenants and
considerations contained herein, the undersigned hereby agree as follows:

         1.       Section 5.2(b) of the Rights Agreement shall be amended and
restated to read in its entirety as follows:

                  "New Securities" shall mean any Common Stock or Preferred
                  Stock of the Company, whether now authorized or not, and
                  rights, options, or warrants to purchase said Common Stock or
                  Preferred Stock, and securities of any type whatsoever that
                  are, or may become, convertible into or exchangeable for said
                  Common Stock or Preferred Stock; provided, however, that "New
                  Securities" does not include (i) securities issuable upon
                  conversion of or with respect to the Preferred or any future
                  series of Preferred Stock of the Company; (ii) securities
                  offered to the public pursuant to a registration statement
                  filed under the Securities Act; (iii) securities issued
                  pursuant to the acquisition of another corporation or other
                  business entity by the Company by merger, purchase of all or
                  substantially all of the assets or other reorganization; (iv)
                  up to one million (1,000,000) shares of the Company's Common
                  Stock or other securities (or related options) issued to
                  directors, officers or employees of, or consultants to, the
                  Company pursuant to an agreement or an option or purchase plan
                  or another director, officer, employee or consultant stock
                  incentive program approved by the Board of Directors of the
                  Company; (vi) shares of the Company's Common Stock or
                  Preferred Stock issued in connection with any stock split,
                  stock dividend, or recapitalization by the Company; (vii)
                  securities issued to persons or entities in connection with
                  bank or equipment lease financing, technology licensing or
                  corporate partnering transactions and the like approved by the
                  Board of Directors of the Company; and (viii) shares of
                  Preferred issued pursuant to the Series B Agreement.

         2.       Effective upon the Closing as defined in the Renalogics
Agreement, the Rights Agreement is hereby amended to include those shareholders
of Renalogics who receive shares of the Company's Series B Preferred Stock under
the Renalogics Agreement as Investors thereunder, with said Renalogics
shareholders agreeing to be bound by all terms and conditions therein and being
entitled to all the benefits thereof.

         3.       This Amendment may be executed in two or more counterparts,
each of which shall be deemed an original, but all of which together shall
constitute one and the same instrument.

         4.       Except as hereby expressly amended, the Rights Agreement shall
remain in full force and effect pursuant to its terms.

                                       2.

<PAGE>

         5.       Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to such terms in the Rights Agreement.

         THE REMAINDER OF THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK.

                                       3.

<PAGE>

         In Witness Whereof, the undersigned have executed this Amendment as of
the day and year first set forth above.

DISCOVERY THERAPEUTICS, INC.         INITIAL INVESTORS:

                                     New York Life Insurance Company

By: /s/ Donald A. McAfee
    ----------------------------
    Donald A. McAfee, President      By: /s/
                                         ------------------------------
                                     Title: Vice President
                                            ---------------------------
                                     Sanderling Venture Partners III
                                     Sanderling III Biomedical
                                     Sanderling III Limited Partnership
                                     Sanderling Ventures Management

                                     By: /s/ Robert McNeil
                                         ------------------------------
                                    Title: General Partner
                                           ----------------------------
                                     Alliance Technology Ventures, L.P.
                                     ATV/GP Parallel Fund, L.P.
                                     ATV/MFJ Parallel Fund, L.P.

                                     By: /s/ Stephen Fleming
                                         ------------------------------
                                     Title: General Partner
                                            ---------------------------

                                       4.

<PAGE>

                                    ADDITIONAL INVESTORS:

                                    /s/ Dennis Schafer
                                    -------------------------------------
                                    Dennis Schafer

                                    Address: 2800 Milan Court, Suite 225
                                             Birmingham, AL 35211

                                    Alliance Technology Ventures

                                    By: /s/  Stephen Fleming
                                       ----------------------------------
                                       Stephen Fleming

                                    Title:   General Partner

                                    Address: 3343 Peachtree Road, N.E.
                                             Suite 1140, East Tower
                                             Atlanta, GA 30326

                                    Atv/GP Parallel Fund

                                   By: /s/  Stephen Fleming
                                       ----------------------------------
                                       Stephen Fleming

                                    Address: 3343 Peachtree Road, N.E.
                                             Suite 1140, East Tower
                                             Atlanta, GA 30326

                                    Atv/MFJ Parallel Fund

                                     By: /s/  Stephen Fleming
                                         ----------------------------------
                                         Stephen Fleming

                                    Address: 3343 Peachtree Road, N.E.
                                             Suite 1140, East Tower
                                             Atlanta, GA 30326

                                       5.

<PAGE>
                                    Intelligent Systems Corporation

                                    By: /s/ Bonnie L. Herron
                                        -----------------------------------
                                        Bonnie L. Herron

                                    Address:  4355 Shackleford Road
                                              Norcross, GA 30093

                                    William M. Spencer, III

                                    By: /s/ William M. Spencer, III
                                        -----------------------------------
                                    Address:  3300 Cahaba Road, Suite 105
                                              Birmingham, AL 35223

                                    Portrush Group L.L.C.

                                    By: /s/ Roger C. Shuttle, Jr., M.D.
                                        -----------------------------------
                                        Roger C. Suttle, Jr., M.D.

                                    Title: Managing Director
                                           --------------------------------
                                    Address:  414 South Fourth Street
                                              Gadsden, AL 35902

                                    Suttle Bros. Investments, L.L.C.

                                    By: /s/ Roger C. Shuttle, Jr., M.D.
                                        -----------------------------------
                                        Roger C. Suttle, Jr., M.D.

                                    Title: Managing Director
                                           --------------------------------
                                    Address:  414 South Fourth Street
                                              Gadsden, AL 35902

                                       6.

<PAGE>

                          Discovery Therapeutics, Inc.

                               Third Amendment to

                       Restated Investor Rights Agreement

         This Third Amendment (the "Third Amendment") to the Restated Investor
Rights Agreement, dated as of March 31, 1995 (the "Rights Agreement"), between
Discovery Therapeutics, Inc., a Delaware corporation (the "Company"), and the
undersigned parties thereto, is made and entered into as of this 21/st/ day of
February, 2001, by and among the Company, the undersigned purchasers of Series D
Preferred Stock of the Company (the "Additional Investors"), and certain of the
Initial Investors (as defined herein).

         Whereas, on March 31, 1995, the Company entered into the Rights
Agreement with four of its founders (the "Founders") and certain named investors
(the "Initial Investors"), pursuant to which the Company granted to the Founders
and the Initial Investors a right of first refusal to purchase a pro rata share
of all New Securities (as defined in the Rights Agreement) that the Company may
from time to time propose to sell and issue;

         Whereas, on November 3, 1995, the Company entered into an Amendment to
the Rights Agreement which defined New York Life Insurance Company as an
Additional Investor under the Rights Agreement, subject to the registration,
information, and other rights set forth therein;

         Whereas, on June 21, 1999, the Company, certain shareholders of
Renalogics, Inc., and certain of the Initial Investors entered into a Second
Amendment to the Rights Agreement which increased the number of shares reserved
for issuance to directors, officers or employees of, or consultants to, the
Company and defined certain shareholders of Renalogics, Inc. as Investors;

         Whereas, the Company has entered into that certain Series D Preferred
Stock Purchase Agreement, dated as of February 21, 2001, by and among the
Company and the Additional Investors (the "Series D Purchase Agreement"),
pursuant to which the Additional Investors shall purchase shares of the
Company's Series D Preferred Stock (the "Shares"); and

         Whereas, the Company and certain of the Initial Investors which are
parties hereto wish to amend the Rights Agreement to add the Additional
Investors as parties thereto pursuant to this Agreement.

         Now Therefore, in consideration of the mutual agreements, covenants and
considerations contained herein, the undersigned hereby agree as follows:

         1.       The definition of "Holder" in Section 1.1 of the Rights
Agreement shall be amended and restated to read in its entirety as follows:

         "Holder" shall mean any Investor or any transferee of registration
         rights under Section 3.9 hereof who then holds any outstanding shares
         of the Company's Series A Preferred Stock, Series B Preferred Stock, or
         Series D Preferred Stock (collectively, the

<PAGE>

         "Preferred") or any Common Shares and any Founder or Investor deemed to
         be a Holder pursuant to Section 3.12, but solely for the purposes set
         forth therein.

         2.       Section 5.2(b) of the Rights Agreement shall be amended and
restated to read in its entirety as follows:

         "New Securities" shall mean any Common Stock or Preferred Stock of the
         Company, whether now authorized or not, and rights, options, or
         warrants to purchase said Common Stock or Preferred Stock, and
         securities of any type whatsoever that are, or may become, convertible
         into or exchangeable for said Common Stock or Preferred Stock;
         provided, however, that "New Securities" does not include (i)
         securities issuable upon conversion of or with respect to the Preferred
         or any future series of Preferred Stock of the Company; (ii) securities
         offered to the public pursuant to a registration statement filed under
         the Securities Act; (iii) securities issued pursuant to the acquisition
         of another corporation or other business entity by the Company by
         merger, purchase of all or substantially all of the assets or other
         reorganization; (iv) up to one million (1,000,000) shares of the
         Company's Common Stock or other securities (or related) options issued
         to directors, officers or employees of, or consultants to, the Company
         pursuant to an agreement or an option or purchase plan or another
         director, officer, employee or consultant stock incentive program
         approved by the Board of Directors of the Company; (vi) shares of the
         Company's Common Stock or Preferred Stock issued in connection with any
         stock split, stock dividend, or recapitalization by the Company; (vii)
         securities issued to persons or entities in connection with bank or
         equipment lease financing, technology licensing or corporate partnering
         transactions and the like approved by the Board of Directors of the
         Company; and (viii) shares of Preferred issued pursuant to the Series B
         Agreement or that certain Series D Preferred Stock Purchase Agreement,
         dated as of February 21, 2001, by and among the Company and the
         signatories thereto.

         3.       Section 6.5 of the Rights Agreement shall be amended to
substitute "LeClair Ryan, A Professional Corporation, 707 East Main Street,
11/th/ Floor, Richmond, Virginia 23219, Attention: Gary D. LeClair, Esq." for
"Cooley Godward Castro Huddleson & Tatum, 5 Palo Alto Square, 4/th/ Floor, Palo
Alto, California 94306, Attention: Alan C. Mendelson, Esq."

         4.       Effective upon the Closing (as defined in the Series D
Purchase Agreement), the Rights Agreement is hereby amended to include the
Additional Investors as Investors thereunder, with each Additional Investor
agreeing to be bound by all the terms and conditions therein and being entitled
to all the benefits thereof.

         5.       The Initial Investors hereby waive the right of first refusal
granted to such parties under Section 5.2 of the Rights Agreement (and the
notice periods with respect thereto) with respect to, and only with respect to,
the issuance of the Shares to the Additional Investors pursuant to the Series D
Purchase Agreement (and the issuance of any shares of capital stock upon
conversion thereof).

         6.       Notwithstanding anything to the contrary contained herein, if
the Company shall sell additional Shares pursuant to the Series D Purchase
Agreement, any purchaser of such

                                        2

<PAGE>

Shares may become a party to this Third Amendment by executing and delivering an
additional counterpart signature page to this Third Amendment and shall be
deemed an "Additional Investor" hereunder.

         7.       This Third Amendment may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         8.       Except as hereby expressly amended, the Rights Agreement shall
remain in full force and effect pursuant to its terms.

         9.       Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to such terms in the Rights Agreement.

         [The Remainder of This Page has Been Intentionally Left Blank.]

                                        3

<PAGE>

         In Witness Whereof, the undersigned have executed this Third Amendment
as of the day and year first set forth above.

DISCOVERY THERAPEUTICS, INC.                 INITIAL INVESTORS:

                                             New York Life BioVenture Partners
By: /s/ Peter G. Savas                       LLC
    -------------------------------
    Peter G. Savas, President

                                             By: /s/
                                                 ___________________________

                                             Title: ________________________

                                             Sanderling Venture Partners III
                                             Sanderling III Biomedical
                                             Sanderling III Limited Partnership
                                             Sanderling Ventures Management

                                             By: /s/ Robert G. McNeal
                                                 ___________________________

                                             Title: General Partner
                                                    ________________________

                                             Alliance Technology Ventures, L.P.
                                             ATV/GP Parallel Fund, L.P.
                                             ATV/MFJ Parallel Fund, L.P.

                                             By: /s/ Michael Henos
                                                 ___________________________

                                             Title: ________________________

                                        4

<PAGE>

                                             ADDITIONAL INVESTORS:

                                             [Name]

                                             By: /s/ David Nikodem Ph.D.
                                                 ___________________________

                                             Title: Senior Analyst
                                                    ________________________

                                        5

<PAGE>

                          Discovery Therapeutics, Inc.
                               Fourth Amendment to
                       Restated Investor Rights Agreement

         This Fourth Amendment (the "Fourth Amendment") to the Restated Investor
Rights Agreement, dated as of March 31, 1995 (the "Rights Agreement"), between
Discovery Therapeutics, Inc., a Delaware corporation (the "Company"), and the
parties thereto, is made and entered into as of this ____ day of _________,
2001, by and among the Company and the undersigned parties hereto (the
"Investors").

         Whereas, on March 31, 1995, the Company entered into the Rights
Agreement with four of its founders (the "Founders") and certain named investors
(the "Initial Investors"), pursuant to which the Company granted to the Founders
and the Initial Investors a right of first refusal to purchase a pro rata share
of all New Securities (as defined in the Rights Agreement) that the Company may
from time to time propose to sell and issue;

         Whereas, on November 3, 1995, the Company entered into an Amendment to
the Rights Agreement which defined New York Life Insurance Company as an
Additional Investor under the Rights Agreement, subject to the registration,
information, and other rights set forth therein;

         Whereas, on June 21, 1999, the Company, certain shareholders of
Renalogics, Inc., and certain of the Initial Investors entered into a Second
Amendment to the Rights Agreement which increased the number of shares reserved
for issuance to directors, officers or employees of, or consultants to, the
Company pursuant to an agreement or an option to purchase plan or another
director, officer, employee or consultant stock incentive program approved by
the Board of Directors of the Company and defined certain shareholders of
Renalogics, Inc. as Investors;

         Whereas, as of February 21, 2001, the Company, purchasers of Series D
Preferred Stock of the Company (the "Series D Holders"), and certain of the
Initial Investors entered into a Third Amendment to the Rights Agreement which
defined the Series D Holders as Holders under the Rights Agreement and excluded
from the definition of New Securities shares of Preferred Stock issued pursuant
to the Series D Preferred Stock Purchase Agreement, dated as of February 21,
2001, by and among the Company and the Series D Holders; and

         Whereas, the Company and the undersigned Investors wish to amend the
Rights Agreement to increase the number of shares reserved for issuance to
directors, officers or employees of, or consultants to, the Company pursuant to
an agreement or an option to purchase plan or another director, officer,
employee or consultant stock incentive program approved by the Board of
Directors of the Company from one million (1,000,000) shares to one million five
hundred thousand (1,500,000) shares.

         Now Therefore, in consideration of the mutual agreements, covenants and
considerations contained herein, the undersigned hereby agree as follows:

<PAGE>

         1.       Section 5.2(b) of the Rights Agreement shall be amended and
restated to read in its entirety as follows:

         "New Securities" shall mean any Common Stock or Preferred Stock of the
         Company, whether now authorized or not, and rights, options, or
         warrants to purchase said Common Stock or Preferred Stock, and
         securities of any type whatsoever that are, or may become, convertible
         into or exchangeable for said Common Stock or Preferred Stock;
         provided, however, that "New Securities" does not include (i)
         securities issuable upon conversion of or with respect to the Preferred
         or any future series of Preferred Stock of the Company; (ii) securities
         offered to the public pursuant to a registration statement filed under
         the Securities Act; (iii) securities issued pursuant to the acquisition
         of another corporation or other business entity by the Company by
         merger, purchase of all or substantially all of the assets or other
         reorganization; (iv) up to one million five hundred thousand
         (1,500,000) shares of the Company's Common Stock or other securities
         (or related) options issued to directors, officers or employees of, or
         consultants to, the Company pursuant to an agreement or an option or
         purchase plan or another director, officer, employee or consultant
         stock incentive program approved by the Board of Directors of the
         Company; (vi) shares of the Company's Common Stock or Preferred Stock
         issued in connection with any stock split, stock dividend, or
         recapitalization by the Company; (vii) securities issued to persons or
         entities in connection with bank or equipment lease financing,
         technology licensing or corporate partnering transactions and the like
         approved by the Board of Directors of the Company; and (viii) shares of
         Preferred issued pursuant to the Series B Agreement or that certain
         Series D Preferred Stock Purchase Agreement, dated as of February 21,
         2001, by and among the Company and the signatories thereto, as amended.

         2.       This Fourth Amendment may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         3.       Except as hereby expressly amended, the Rights Agreement shall
remain in full force and effect pursuant to its terms.

         4.       Capitalized terms used herein but not otherwise defined shall
have the meanings assigned to such terms in the Rights Agreement.

        [THE REMAINDER OF THIS PAGE HAS BEEN INTENTIONALLY LEFT BLANK.]

                                       2
<PAGE>

         In Witness Whereof, the undersigned have executed this Fourth Amendment
as of the day and year first set forth above.

Discovery Therapeutics, Inc.

By: /s/ Peter G. Savas
    -------------------------------
    Peter G. Savas, President

INVESTORS:

Alliance Technology Ventures, L.P.
ATV/GP Parallel Fund, L.P.
ATV/MFJ Parallel Fund, L.P.

By: /s/ Michael A. Henos
    -------------------------------
Name: Michael A. Henos
      -----------------------------
Title: General Partner
       ----------------------------

Orbitex Health and Biotechnology ("2V1I")
Orbitex Life Science and Biotechnology Fund ("2VlZ")

By: /s/ David Nikodem, Ph.D.
    -------------------------------
Name: David Nikodem, Ph.D.
      -----------------------------
Title: Senior Analyst
       ----------------------------

New York Life BioVenture Partners LLC

By: Perseus Soros BioPharmaceutical Fund
Its: Agent
     ------------------------------

     By: /s/
         --------------------------
     Name:
           ------------------------
     Title: Agent
            -----------------------

Palladin Opportunity Fund LLC

By: /s/ Robert Chendes
    -------------------------------
Name: Robert Chendes
      -----------------------------
Title: Managing Director
       ----------------------------

                     [SIGNATURES CONTINUE ON FOLLOWING PAGE]

                                        3

<PAGE>

Sanderling III Biomedical, L.P.
Sanderling III Limited Partnership
Sanderling Venture Partners III, L.P.
Sanderling IV Biomedical Co-Investment Fund, L.P.
Sanderling Venture Partners IV Co-Investment Fund, L.P.

By: ______________________________
Name: ____________________________
Title: ___________________________

Sanderling Ventures Management
     FBO Fred A. Middleton

By: ______________________________
Name: ____________________________
Title: ___________________________

Sanderling Management Company, LLC Retirement Trust
     FBO Robert G. McNeil

By: ______________________________
Name: ____________________________
Title: ___________________________

Sanderling Ventures Management

By: ______________________________
Name: ____________________________
Title: ___________________________

Sanderling Venture Partners V Co-Investment Fund, L.P.

By:   Middleton, McNeil & Mills Associates V, LLC
Its:  ____________________________

     By: ______________________________
     Name: ____________________________
     Title: ___________________________

                    [SIGNATURES CONTINUE ON FOLLOWING PAGE]

                                        4

<PAGE>

Singapore Bio-Innovations Pte Ltd.

By: /s/ Lily Chan
    ______________________________
Name: Lily Chan Ph.D.
      ____________________________
Title: General Manager
       ___________________________

Endpoint Late-Stage Fund, L.P.

By: /s/ F.D. Townsen
    ______________________________
Name: F.D. Townsen
      ____________________________
Title: General Partner
       ___________________________

Schwarz Pharma AG

By: /s/ Klaus Langer
    ______________________________
Name: Klaus Langer
      ____________________________
Title: Member of the Executive Board
       ___________________________

By: /s/ Klaus Hommerich
    ______________________________
Name: Klaus Hommerich
      ____________________________
Title: Corporate Counsel
       ___________________________

China Development Industrial Bank Inc.

By: /s/ Tai-Ying Liu
    ______________________________
Name: Tai-Ying Liu
      ____________________________
Title: Chairman & CEO
       ___________________________

MDS Life Sciences Technology Fund USA, L.P.

By:  MDS Capital USA (GP) Inc.
Its: General Partner

     By: /s/ Thomas E. Willet
         ______________________________
     Name: Thomas E. Willet
           ____________________________
     Title: Director
            ___________________________

                     [SIGNATURES CONTINUE ON FOLLOWING PAGE]

                                        5

<PAGE>

MDS life Sciences Technology Barbados Investment Trust

By:  /s/ Roland E. Jackson
    ------------------------------
Name:  Roland E. Jackson
      ----------------------------
Title:  Trustee
       ---------------------------
MDS Life Sciences Technology Fund Limited Partnership

By:  MDS Life Sciences Technology Fund (GP) Inc
Its: General Partner

     By:  /s/ Richard Lockie / /s/ Michael Gallagher
         -------------------------------------------
     Name:  Richard Lockie / Michael Gallagher
           -----------------------------------------
     Title:  Vice President & Vice President
            ----------------------------------------
MDS Life Sciences Technology Fund Canadian Unit Trust

By:  MDS Capital Corp
Its: Manager

     By:  /s/ Richard Lockie / /s/ Michael Gallagher
         -------------------------------------------
     Name:  Richard Lockie / Michael Gallagher
           -----------------------------------------
     Title:  Vice President & Vice President
            ----------------------------------------

One Objective Ltd.

By:  /s/ Chas A. Chow
    ------------------------------
Name:  Chas A. Chow
      ----------------------------
Title:  Manager
       ---------------------------
    /s/ Donald A. McAfee
----------------------------------
Donald A. McAfee

    /s/ Noel Cusack
----------------------------------
Noel J. Cusack

                     [SIGNATURES CONTINUE ON FOLLOWING PAGE]

                                        6

<PAGE>

    /s/ James Peck
----------------------------------
James V. Peck

    /s/ Gevork Minaskanian
----------------------------------
Gevork Minaskanian

                                        7<PAGE>

                                                                     Exhibit 4.3

         THIS WARRANT AND ANY SECURITIES ACQUIRED UPON THE EXERCISE OF THIS
WARRANT HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED
("THE SECURITIES ACT"), OR ANY STATE SECURITIES LAWS AND NEITHER THE SECURITIES
NOR ANY INTEREST THEREIN MAY BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR OTHERWISE
DISPOSED OF EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT UNDER SUCH
ACT OR SUCH LAWS OR AN EXEMPTION FROM REGISTRATION UNDER SUCH ACT AND SUCH LAWS.

                          ADERIS PHARMACEUTICALS, INC.

                          COMMON STOCK PURCHASE WARRANT

         This certifies that, for good and valuable consideration, Aderis
Pharmaceuticals, Inc., a Delaware corporation (the "Company"), grants to Midtown
Holdings, LLC, or registered assigns (the "Warrantholder"), the right to
subscribe for and purchase from the Company 225,000 validly issued, fully paid
and nonassessable shares (the "Warrant Shares") of the Company's Common Stock,
par value $0.001 per share (the "Common Stock"), at the purchase price per share
of $3.6364 (the "Exercise Price"), from time to time, prior to 5:00 PM Eastern
Standard Time on March 30, 2006 (the "Expiration Date"), all subject to the
terms, conditions and adjustments herein set forth.

Certificate No. CW-3

Number of Shares: 225,060

Name of Warrantholder: Midtown Holdings, LLC

<PAGE>

         1.       Duration and Exercise of Warrant; Limitation on Exercise;
Payment of Taxes.

                  1.1.     Duration and Exercise of Warrant. Subject to the
terms and conditions set forth herein, the Warrant may be exercised, in whole or
in part, by the Warrantholder by:

                           1.1.1.   the surrender of this Warrant to the
Company, with a duly executed Exercise Form specifying the number of Warrant
Shares to be purchased, during normal business hours on any Business Day prior
to the Expiration Date; and

                           1.1.2.   the delivery of payment to the Company, for
the account of the Company, by cash or by certified or bank cashier's check, of
the Exercise Price for the number of Warrant Shares specified in the Exercise
Form in lawful money of the United States of America. The Company agrees that
such Warrant Shares shall be deemed to be issued to the Warrantholder as the
record holder of such Warrant Shares as of the close of business on the date on
which this Warrant shall have been surrendered and payment made for the Warrant
Shares as aforesaid (or as provided in Section 1.2 below).

                  1.2.     Conversion Right.

                           1.2.1.   In lieu of the payment of the Exercise
Price, the Warrantholder shall have the right (but not the obligation), to
require the Company to convert this Warrant, in whole or in part, into shares of
Common Stock (the "Conversion Right") as provided for in this Section 1.2. Upon
exercise of the Conversion Right, the Company shall deliver to the Warrantholder
(without payment by the Warrantholder of any of the Exercise Price; provided,
however, that the Warrantholder shall be required to pay the par value for any
shares of Common Stock so delivered) that number of shares of Common Stock equal
to the quotient obtained by dividing (x) the value of the Warrant at the time
the Conversion Right is exercised (determined by subtracting the aggregate
Exercise Price in effect immediately prior to the exercise of the Conversion
Right from the aggregate Fair Market Value for the shares of Common Stock
issuable upon exercise of the Warrant immediately prior to the exercise of the
Conversion Right) by (y) the Fair Market Value of one share of Common Stock
immediately prior to the exercise of the Conversion Right.

                           1.2.2.   The Conversion Right may be exercised by the
Warrantholder on any Business Day prior to the Expiration Date by delivering the
Warrant Certificate, together with a duly executed Exercise Form (with the
conversion section completed) and the par value for any shares of Common Stock
deliverable pursuant to such conversion, to the Company, exercising the
Conversion Right and specifying the total number of shares of Common Stock the
Warrantholder will be issued pursuant to such conversion.

                           1.2.3.   Fair Market Value of a share of Common Stock
as of a particular date (the "Determination Date") shall mean:

                           1.2.3.1. If the Common Stock is listed on a national
securities exchange, then the Fair Market Value shall be the average of the last
ten "daily sales prices" of the Common Stock on the principal national
securities exchange on which the Common Stock is listed or admitted for trading
on the last ten Business Days prior to the Determination Date, or if

                                        3

<PAGE>

not listed or traded on any such exchange, then the Fair Market Value shall be
the average of the last ten "daily sales prices" of the Common Stock on the
National Market (the "National Market") of the National Association of
Securities Dealers Automated Quotations System ("Nasdaq") on the last ten
Business Days prior to the Determination Date. The "daily sales price" shall be
the closing price of the Common Stock at the end of each day; or

                           1.2.3.2. If the Common Stock is not so listed or
admitted to unlisted trading privileges or if no such sale is made on at least
nine of such days, then the Fair Market Value shall be the fair value as
reasonably determined in good faith by the Company's Board of Directors or a
duly appointed committee of the Board (which determination shall be reasonably
described in the written notice delivered to the Warrantholder together with the
Common Stock certificates).

                  1.3.     Limitations on Exercise. Notwithstanding anything to
the contrary herein, this Warrant may be exercised only upon the delivery to the
Company of any certificates, legal opinions, or other documents reasonably
requested by the Company to satisfy the Company that the proposed exercise of
this Warrant may be effected without registration under the Securities Act. The
Warrantholder shall not be entitled to exercise this Warrant, or any part
thereof, unless and until such certificates, legal opinions or other documents
are reasonably acceptable to the Company.

                  1.4.     Warrant Shares Certificate. A stock certificate or
certificates for the Warrant Shares specified in the Exercise Form shall be
delivered to the Warrantholder within ten Business Days after receipt of the
Exercise Form and receipt of payment of the purchase price if the Conversion
Right is not exercised. If this Warrant shall have been exercised only in part,
the Company shall, at the time of delivery of the stock certificate or
certificates, deliver to the Warrantholder a new Warrant evidencing the rights
to purchase the remaining Warrant Shares, which new Warrant shall in all other
respects be identical with this Warrant.

                  1.5.     Payment of Taxes. The issuance of certificates for
Warrant Shares shall be made without charge to the Warrantholder for any stock
transfer or other issuance tax in respect thereto; provided, however, that the
Warrantholder shall be required to pay any and all taxes which may be payable in
respect of any transfer involved in the issuance and delivery of any certificate
in a name other than that of the then Warrantholder as reflected upon the books
of the Company.

                  1.6.     Divisibility of Warrant; Transfer of Warrant.

                           1.6.1.   Subject to the provisions of this Section
1.6, this Warrant may be divided into warrants of one thousand shares or
multiples thereof, upon surrender at the principal office of the Company,
without charge to any Warrantholder. Upon such division, the Warrants may be
transferred of record as the then Warrantholder may specify without charge to
such Warrantholder (other than any applicable transfer taxes). In addition,
subject to the provisions of this Section 1.6, the Warrantholder shall also have
the right to transfer this Warrant in its entirety to any person or entity.

                                        4

<PAGE>

                           1.6.2.   Upon surrender of this Warrant to the
Company with a duly executed Assignment Form and funds sufficient to pay any
transfer tax, the Company shall, without charge, execute and deliver a new
Warrant or Warrants of like tenor in the name of the assignee named in such
Assignment Form, and this Warrant shall promptly be canceled. Each Warrantholder
agrees that prior to any proposed transfer (whether as the result of a division
or otherwise) of this Warrant, such Warrantholder shall give advance written
notice to the Company of such Warrantholder's intention to effect such transfer.
Each such notice shall describe the manner and circumstances of the proposed
transfer in reasonably sufficient detail, and, if reasonably requested by the
Company, shall be accompanied by a written opinion of legal counsel, which
opinion shall be addressed to the Company and be reasonably satisfactory in form
and substance to the Company's counsel, to the effect that the proposed transfer
of this Warrant may be effected without registration under the Securities Act.
In addition, the Warrantholder and the transferee shall execute any
documentation reasonably required by the Company to ensure compliance with the
Securities Act. The Warrantholder shall not be entitled to transfer this
Warrant, or any part thereof, if such legal opinion is not reasonably acceptable
to the Company or if such documentation is not provided. The term "Warrant" as
used in this Agreement shall be deemed to include any Warrants issued in
substitution or exchange for this Warrant.

                  1.7.     Fractional Shares. No fractional shares or script
representing fractional shares shall be issued upon the exercise of this
Warrant. With respect to any fraction of a share called for upon exercise
hereof, the Company shall pay to the Warrantholder an amount in cash equal to
such fraction multiplied by the current Fair Market Value of a share.

         2.       Restrictions on Transfer; Restrictive Legends.

         Except as otherwise permitted by this Section 2, each Warrant shall
(and each Warrant issued upon direct or indirect transfer or in substitution for
any Warrant pursuant to Section 1.6 or Section 4 shall) be stamped or otherwise
imprinted with a legend in substantially the following form:

                           THIS WARRANT AND ANY SECURITIES ACQUIRED UPON THE
                  EXERCISE OF THIS WARRANT HAVE NOT BEEN REGISTERED UNDER THE
                  SECURITIES ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES
                  LAWS AND NEITHER THE SECURITIES NOR ANY INTEREST THEREIN MAY
                  BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR OTHERWISE DISPOSED
                  OF EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION STATEMENT
                  UNDER SUCH ACT OR SUCH LAWS OR AN EXEMPTION FROM REGISTRATION
                  UNDER SUCH ACT AND SUCH LAWS.

Except as otherwise permitted by this Section 2, each stock certificate for
Warrant Shares issued upon the exercise of any Warrant and each stock
certificate issued upon the direct or indirect transfer of any such Warrant
Shares shall be stamped or otherwise imprinted with a legend in substantially
the following form:

                           THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE
                  NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
                  AMENDED, OR ANY STATE SECURITIES LAWS AND NEITHER THE
                  SECURITIES NOR ANY

                                        5

<PAGE>

         INTEREST THEREIN MAY BE OFFERED, SOLD, TRANSFERRED, PLEDGED OR
         OTHERWISE DISPOSED OF EXCEPT PURSUANT TO AN EFFECTIVE REGISTRATION
         STATEMENT UNDER SUCH ACT OR SUCH LAWS OR AN EXEMPTION FROM REGISTRATION
         UNDER SUCH ACT AND SUCH LAWS.

                  THE WARRANT SHARES ARE SUBJECT TO A RIGHT OF FIRST REFUSAL
         OPTION IN FAVOR OF THE COMPANY AND ITS OTHER STOCKHOLDERS, AS PROVIDED
         IN THE BYLAWS OF THE COMPANY.

                  INFORMATION REGARDING THE DESIGNATIONS, RELATIVE RIGHTS,
         PREFERENCES AND LIMITATIONS APPLICABLE TO EACH CLASS OR SERIES OF
         CAPITAL STOCK OF THE COMPANY, THE VARIATIONS THEREIN AND THE AUTHORITY
         OF THE BOARD OF DIRECTORS TO DETERMINE VARIATIONS FOR FUTURE CLASSES OR
         SERIES MAY BE OBTAINED AT NO COST BY WRITTEN REQUEST MADE BY THE HOLDER
         OF RECORD HEREOF TO THE SECRETARY OF THE COMPANY AT THE PRINCIPAL
         EXECUTIVE OFFICE OF THE COMPANY.

         Notwithstanding the foregoing, the Warrantholder may require the
Company to issue a Warrant or a stock certificate for Warrant Shares, in each
case without a legend, if either (i) such Warrant or such Warrant Shares, as the
case may be, have been registered for resale under the Securities Act or (ii)
the Warrantholder has delivered to the Company an opinion of legal counsel,
which opinion shall be addressed to the Company and be reasonably satisfactory
in form and substance to the Company's counsel, to the effect that such
registration is not required with respect to such Warrant or such Warrant
Shares, as the case may be.

         3.       Reservation and Registration of Shares, Etc. The Company
covenants and agrees as follows:

                  3.1.     all Warrant Shares which are issued upon the exercise
of this Warrant will, upon issuance, be validly issued, fully paid, and
nonassessable, not subject to any preemptive rights, and free from all taxes,
liens, security interests, charges, and other encumbrances with respect to the
issue thereof, other than taxes with respect to any transfer occurring
contemporaneously with such issue;

                  3.2.     during the period within which this Warrant may be
exercised, the Company will at all times have authorized and reserved, and keep
available free from preemptive rights, a sufficient number of shares of Common
Stock to provide for the exercise of the rights represented by this Warrant; and

                  3.3.     the Company will, from time to time, take all such
action as may be required to assure that the par value per share of the Warrant
Shares is at all times equal to or less than the then effective Exercise Price.

                                        6

<PAGE>

         4.       Loss or Destruction of Warrant.

         Subject to the terms and conditions hereof, upon receipt by the Company
of evidence reasonably satisfactory to it of the loss, theft, destruction or
mutilation of this Warrant (including, but not limited to, an affidavit of the
Warrantholder) and, in the case of loss, theft or destruction, of such bond or
indemnification as the Company may reasonably require, and, in the case of such
mutilation, upon surrender and cancellation of this Warrant, the Company will
execute and deliver a new Warrant of like tenor.

         5.       Ownership of Warrant.

         The Company may deem and treat the person in whose name this Warrant is
registered as the holder and owner hereof (notwithstanding any notations of
ownership or writing hereon made by anyone other than the Company) for all
purposes and shall not be affected by any notice to the contrary, until
presentation of this Warrant for registration of transfer.

         6.       Company Representations. The Company hereby represents and
warrants to the Warrantholder that:

                  6.1.     This Warrant has been duly authorized and executed by
the Company and is a valid and binding obligation of the Company enforceable in
accordance with its terms, subject to applicable bankruptcy, insolvency,
reorganization, moratorium or other laws of general application affecting the
enforcement of creditors' rights.

                  6.2.     The execution and delivery of this Warrant are not,
and the issuance of the Warrant Shares upon exercise of this Warrant in
accordance with the terms hereof will not be, inconsistent with the Company's
Certificate of Incorporation or Bylaws, do not and will not contravene any law,
governmental rule or regulation, judgment or order applicable to the Company,
and do not and will not conflict with or contravene any provision of, or
constitute a material default under, any material indenture, mortgage, contract
or other instrument of which the Company is a party or by which it is bound or
require the consent or approval of, the giving of notice to, the registration or
filing with or the taking of any action in respect of or by, any federal, state
or local government authority or agency (other than such consents, approvals,
notices, actions, filings, etc., as have already been obtained or made, as the
case may be).

         7.       Adjustment of Exercise Price and Number of Warrant Shares;
Record Date. The number of Warrant Shares issuable upon the exercise of this
Warrant and the Exercise Price shall be subject to adjustment from time to time
upon the occurrence of certain events, as follows:

                  7.1.     Adjustment for Dividends in Stock. In case at any
time or from time to time the holders of shares of the Common Stock shall have
received or, on or after the record date fixed for the determination of eligible
stockholders, shall have become entitled to receive, without payment therefor,
other or additional stock of the Company by way of dividend then, and in each
case, the Warrantholder shall, upon the exercise hereof, be entitled to receive,
in addition to the number of Warrant Shares receivable thereupon, and without
payment of any additional consideration therefor, the amount of such other or
additional stock of the Company which such Warrantholder would hold on the date
of such exercise had it been the holder of

                                        7

<PAGE>

record of shares of the Common Stock on the date hereof and had thereafter,
during the period from the date hereof to and including the date of such
exercise, retained such shares and/or all other additional stock receivable by
it as aforesaid during such period, giving effect to all adjustments called for
during such period by Sections 7.2 and 7.3.

                  7.2.     Reclassification, Reorganization or Merger. In case
of any reclassification, capital reorganization or other change of outstanding
shares of the Common Stock, or in the case of any consolidation or merger of the
Company with or into another corporation (other than a merger with a subsidiary
in which merger the Company is the continuing corporation and which does not
result in any reclassification, capital reorganization or other change of
outstanding shares of Common Stock or a change of more than 25% of the voting
power of the Common Stock) or in the case of any sale, lease or conveyance to
another corporation of the property of the Company as an entirety, the Company
shall, as a condition precedent to such transaction, cause effective provisions
to be made so that the Warrantholder shall have the right thereafter by
exercising this Warrant at any time prior to the expiration of the Warrant, to
purchase the kind and amount of shares of stock and other securities and
property receivable upon such reclassification, capital reorganization and other
change, consolidation, merger, sale or conveyance by a holder of the number of
shares of Common Stock that might have been purchased upon exercise of this
Warrant immediately prior to such reclassification, change, consolidation,
merger, sale or conveyance. Any such provision shall include provision for
adjustments that shall be as nearly equivalent as may be practicable to the
adjustments provided for in this Warrant. The foregoing provisions of this
Section 7.2 shall similarly apply to successive reclassifications, capital
reorganizations and changes of shares of Common Stock and to successive
consolidations, mergers, sales or conveyances. In the event that in connection
with any such capital reorganization or reclassification, consolidation, merger,
sale or conveyance, additional shares of Common Stock shall be issued in
exchange, conversion, substitution or payment, in whole or in part, for
securities of the Company other than Common Stock, any such issue shall be
treated as an issue of Common Stock covered by the provisions of Section 7.1.

                  7.3.     Stock Splits and Reverse Stock Splits. If the Company
shall subdivide its outstanding shares of Common Stock into a greater number of
shares, the Exercise Price in effect immediately prior to such subdivision shall
thereby be proportionately reduced and the number of Warrant Shares receivable
upon exercise of this Warrant shall thereby be proportionately increased; and,
conversely, if the outstanding number of shares of Common Stock shall be
combined into a smaller number of shares, the Exercise Price in effect
immediately prior to such combination shall thereby be proportionately increased
and the number of Warrant Shares receivable upon exercise of the Warrant shall
be proportionately decreased.

                  7.4.     Notices of Record Date, Etc. In the event of (a) any
taking by the Company of a record of the holders of any class of securities for
the purpose of determining the holders thereof who are entitled to receive any
dividend or other distribution (the "Distribution"), (b) any capital
reorganization or reclassification of the stated capital of the Company or any
consolidation or merger of the Company with any other corporation or
corporations (other than a wholly-owned subsidiary), or the sale or distribution
of all or substantially all of the Company's property and assets (the
"Reorganization Event"), or (c) any proposed filing of a registration statement
under the Act in connection with a primary public offering of the Company's
Common

                                        8

<PAGE>

Stock (the "Registration Event"), the Company will mail or cause to be mailed to
the Warrantholder a notice specifying (i) the date of any such Distribution
stating the amount and character of such Distribution, (ii) the date on which
any such Reorganization Event or Registration Event is expected to become
effective, and (iii) the time, if any, that is to be fixed as to when the
holders of record of the Company's securities shall be entitled to exchange
their shares of the Company's securities for securities or other property
deliverable upon such Reorganization Event. Such notice shall be mailed at least
thirty (30) days prior to the date therein specified.

                  7.5.     Notice of Adjustments. Notice of any adjustment in
this Warrant shall be given by the Company to the Warrantholder, and such
adjustment (whether or not such notice is given) shall be effective and binding
for all purposes.

         8.       Registration Rights. The Warrantholder shall have the same
registration rights with respect to Registrable Shares as the Holders (as
defined in the Investor Rights Agreement (as defined below)) of Registrable
Securities (as defined in the Investor Rights Agreement) under Article 3 of that
certain Restated Investor Rights Agreement dated as of March 31, 1995, among the
Company, the Founders and the Investors named therein, as such agreement was
amended as of November 3, 1995, as of June 21, 1999, as of February 21, 2001,
and as of August 15, 2001 (and as the same may be amended from time to time, the
"Investor Rights Agreement"); and all of the terms and provisions of such
Article 3 (a copy of which is attached as Exhibit C hereto), including without
limitation Section 3.11 therein, shall apply to the Warrantholder and its
Registrable Shares. The Warrantholder agrees that it may include its Registrable
Shares in any such registration only to the extent that the inclusion of such
Registrable Shares will not diminish the amount of Registrable Securities (as
defined in the Investor Rights Agreement) which are included in such
registration.

         9.       Amendments. Any provision of this Warrant (including
registration rights) may be amended and the observance thereof may be waived
(either generally or in a particular instance and either retroactively or
prospectively) only with the written consent of the Company and the
Warrantholders who hold a majority in interest of the Registrable Shares. Any
amendment or waiver effected in accordance with this Section 9 shall be binding
upon each Warrantholder and the Company.

         10.      Expiration of the Warrant. Except with respect to the
indemnification and contribution provisions set forth in Article 3 of the
Investor Rights Agreement and applicable pursuant to Section 8 hereof, the
obligations of the Company pursuant to this Warrant shall terminate on the
Expiration Date.

         11.      Definitions.

         As used herein, unless the context otherwise requires, the following
terms have the following respective meanings:

         Assignment Form: an Assignment Form in the form annexed hereto as
Exhibit B.

         Business Day: any day other than a Saturday, Sunday or a day on which
national banks are authorized by law to close in The City of New York, State of
New York.

                                        9

<PAGE>

         Common Stock: the meaning specified on the cover of this Warrant.

         Company: the meaning specified on the cover of this Warrant.

         Exercise Form: an Exercise Form in the form annexed hereto as Exhibit
         A.

         Exercise Price: the meaning specified on the cover of this Warrant.

         Expiration Date: the meaning specified on the cover of this Warrant.

         Fair Market Value: the meaning specified in Section 1.2.3.

         Investor Rights Agreement: the meaning specified in Section 8.

         Nasdaq: the meaning specified in Section 1.2.3.1.

         National Market: the meaning specified in Section 1.2.3.1.

         Registrable Shares: (i) the shares of the Company's Common Stock issued
or issuable upon exercise of the Warrants and (ii) any securities issued or
issuable with respect to any securities referred to in subdivision (i) by way of
stock split, stock dividend, recapitalization, or similar event, which have not
been sold to the public.

         SEC: the Securities and Exchange Commission or any other Federal agency
at the time administering the Securities Act or the Securities Exchange Act of
1934, as amended, whichever is the relevant statute for the particular purpose.

         Securities Act: the meaning specified on the cover of this Warrant, or
any similar Federal statute, and the rules and regulations of the SEC
thereunder, all as the same shall be in effect at the time. Reference to a
particular section of the Securities Act shall include a reference to the
comparable section, if any, of any such similar Federal statute.

         Warrantholder: the meaning specified on the cover of this Warrant.

         Warrant Shares: the meaning specified on the cover of this Warrant.

         12.      Miscellaneous.

                  12.1.    Entire Agreement. This Warrant constitutes the entire
agreement between the Company and the Warrantholder with respect to the
Warrants.

                  12.2.    Binding Effects; Benefits. This Warrant shall inure
to the benefit of and shall be binding upon the Company and the Warrantholder
and their respective heirs, legal representatives, successors and assigns.
Nothing in this Warrant, expressed or implied, is intended to or shall confer on
any person other than the Company and the Warrantholder, or their respective
heirs, legal representatives, successors or assigns, any rights, remedies,
obligations or liabilities under or by reason of this Warrant.

                  12.3.    Section and Other Headings. The section and other
headings contained in this Warrant are for reference purposes only and shall not
be deemed to be a part of this Warrant or to affect the meaning or
interpretation of this Warrant.

                  12.4.    Pronouns. All pronouns and any variations thereof
refer to the masculine, feminine or neuter, singular or plural, as the context
may require.

                                       10

<PAGE>

                  12.5.    Further Assurances. Each of the Company and the
Warrantholder shall do and perform all such further acts and things and execute
and deliver all such other certificates, instruments and documents as the
Company or the Warrantholder may, at any time and from time to time, reasonably
request in connection with the performance of any of the provisions of this
Warrant.

                  12.6.    Notices. All notices and other communications
required or permitted to be given under this Warrant shall be in writing and
shall be deemed to have been duly given if delivered personally or sent by
United States mail, postage prepaid, to the parties hereto at the following
addresses or to such other address as any party hereto shall hereafter specify
by notice to the other party hereto:

                           12.6.1.  if to the Company, addressed to:
                                    Aderis Pharmaceuticals, Inc.
                                    85 Main Street
                                    Hopkinton, Massachusetts 01748
                                    Attention: President

                           12.6.2.  if to the Warrantholder, addressed to:
                                    the address of such Warrantholder
                                    appearing on the books of the Company.

Except as otherwise provided herein, all such notices and communications shall
be deemed to have been received on the date of delivery thereof, if delivered
personally, or on the third Business Day after the mailing thereof.

                  12.7.    Separability. Any term or provision of this Warrant
which is invalid or unenforceable in any jurisdiction shall, as to such
jurisdiction, be ineffective to the extent of such invalidity or
unenforceability without rendering invalid or unenforceable the terms and
provisions of this Warrant or affecting the validity or enforceability of any of
the terms or provisions of this Warrant in any other jurisdiction.

                  12.8.    Governing Law. This Warrant shall be deemed to be a
contract made under the laws of the State of Delaware and for all purposes shall
be governed by and construed in accordance with the laws of such State
applicable to such agreements made and to be performed entirely within such
State.

                  12.9.    No Rights or Liabilities as Stockholder. Nothing
contained in this Warrant shall be determined as conferring upon the
Warrantholder any rights as a stockholder of the Company or as imposing any
liabilities on the Warrantholder to purchase any securities whether such
liabilities are asserted by the Company or by creditors or stockholders of the
Company or otherwise.

                                       11

<PAGE>

         IN WITNESS WHEREOF, the Company has caused this Warrant to be signed by
its duly authorized officer.

                           ADERIS PHARMACEUTICALS, INC.

                           By:     /s/ PETER G. SAVAS
                              ---------------------------------
                                   Name: Peter G. Savas
                                   Title: President

Dated: June 16, 2003

                                       12

<PAGE>

                                    EXHIBIT A

                                  EXERCISE FORM

                 (To be executed upon exercise of this Warrant)

                  The undersigned hereby irrevocably elects to exercise the
right, represented by this Warrant, to purchase __________ of the Warrant Shares
and herewith tenders (i) payment for such Warrant Shares to the order of
Aderis Pharmaceuticals, Inc. (the "Company") in the amount of $__________ or
(ii) Warrants to purchase __________ shares of Common Stock of the Company in
order to exercise the Conversion Right (as defined in Section 1.2 of this
Warrant) and payment of the par value for _________ of the Warrant Shares, in
either case, in accordance with the terms of this Warrant. The undersigned
requests that a certificate for such Warrant Shares be registered in the name of
_______________ and that such certificates be delivered to __________________
whose address is
________________________________________________________________. (If this is a
partial exercise of the Warrant, a new Warrant for the remaining number of
unexercised Warrants shall be issued by the Company.)

Dated:___________

                     Signature_____________________________

                              _____________________________
                                       (Print Name)

                              _____________________________
                                      (Street Address)

                              _____________________________
                                 (City) (State) (Zip Code)

Signed in the Presence of:

__________________________

<PAGE>

                                    EXHIBIT B

                                 ASSIGNMENT FORM

               (To be executed only upon transfer of this Warrant)

                  For value received, the undersigned registered holder of the
within Warrant hereby sells, assigns and transfers unto ______________________
the right represented by such Warrant to purchase ________________ shares of
Common Stock of Aderis Pharmaceuticals, Inc. (the "Company") to which such
Warrant relates and all other rights of the Warrantholder under the within
Warrant (including, without limitation, the registration rights provided in
Section 8 of the within Warrant), and appoints _______________________ Attorney
to make such transfer on the books of the Company maintained for such purpose,
with full power of substitution in the premises.

Dated:______________

                         Signature_____________________________

                                  _____________________________
                                         (Print Name)

                                  _____________________________
                                        (Street Address)

                                  _____________________________
                                    (City) (State) (Zip Code)

Signed in the presence of:

_____________________________

<PAGE>

                                    EXHIBIT C

         Article 3 of the Restated Investor Rights Agreement dated as of March
         31, 1995, among the Company, the Founders and the Investors named
         therein, as such agreement was amended as of November 3, 1995, as of
         June 21, 1999, as of February 21, 2001, and as of August 15, 2001

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