<PAGE>

                                                                   EXHIBIT 10.13


                               NEURON DATA, INC.

                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                 June 1, 1999

<PAGE>

                               TABLE OF CONTENTS
                               -----------------

<TABLE>
<CAPTION>
                                                                                                       Page
<S>                                                                                                    <C>
1.   Purchase and Sale of Stock.....................................................................      1
      1.1   Sale and Issuance of Series AA Preferred Stock..........................................      1
      1.2   Closing.................................................................................      1
      1.3   Subsequent Sale of Series AA Preferred Stock............................................      2
2.   Representations and Warranties of the Company..................................................      2
      2.1   Organization, Good Standing and Qualification...........................................      2
      2.2   Capitalization and Voting Rights........................................................      2
      2.3   Subsidiaries............................................................................      3
      2.4   Authorization...........................................................................      3
      2.5   Valid Issuance of Preferred and Common Stock............................................      3
      2.6   Governmental Consents...................................................................      4
      2.7   Offering................................................................................      4
      2.8   Litigation..............................................................................      4
      2.9   Proprietary Rights......................................................................      4
     2.10   Compliance with Other Instruments.......................................................      4
     2.11   Agreements..............................................................................      5
     2.12   Related-Party Transactions..............................................................      5
     2.13   Permits.................................................................................      5
     2.14   Environmental and Safety Laws...........................................................      5
     2.15   Disclosure..............................................................................      5
     2.16   Investors' Rights.......................................................................      6
     2.17   Corporate Documents.....................................................................      6
     2.18   Title to Property and Assets............................................................      6
     2.19   Financial Statements....................................................................      6
     2.20   Changes.................................................................................      6
     2.21   Employee Benefit Plans..................................................................      7
     2.22   Tax Returns, Payments and Elections.....................................................      7
     2.23   Insurance...............................................................................      7
     2.24   Minute Books............................................................................      7
     2.25   Labor Agreements and Actions............................................................      8
     2.26   U.S. Real Property Holding Corporation..................................................      8
3.   Representations and Warranties of the Investors................................................      8
      3.1   Authorization...........................................................................      8
      3.2   Purchase Entirely for Own Account.......................................................      8
      3.3   Disclosure of Information...............................................................      8
      3.4   Investment Experience...................................................................      9
      3.5   Accredited Investor.....................................................................      9
      3.6   Restricted Securities...................................................................      9
      3.7   Further Limitations on Disposition......................................................      9
      3.8   Legends.................................................................................      9
      3.9   Further Representations by Foreign Investors............................................     10
</TABLE>

                                       i
<PAGE>

<TABLE>
<S>                                                                                                    <C>
4.   California Commissioner of Corporations........................................................     10
      4.1   Corporate Securities Law................................................................     10
5.   Conditions of Investor's Obligations at Closing................................................     10
      5.1   Representations and Warranties..........................................................     10
      5.2   Performance.............................................................................     10
      5.3   Compliance Certificate..................................................................     11
      5.4   Qualifications..........................................................................     11
      5.5   Proceedings and Documents...............................................................     11
      5.6   Opinion of Company Counsel..............................................................     11
      5.7   Amended and Restated Investors' Rights Agreement........................................     11
      5.8   Restated Articles.......................................................................     11
      5.9   Board and Shareholder Approval for Increase in 1996 Stock Option/Stock Issuance Plan....     11
     5.10   Conversion of All Outstanding Preferred Stock...........................................     11
6.   Conditions of the Company's Obligations at Closing.............................................     11
      6.1   Representations and Warranties..........................................................     12
      6.2   Amended and Restated Investors' Rights Agreement........................................     12
      6.3   Payment of Purchase Price...............................................................     12
      6.4   Qualifications..........................................................................     12
7.   Miscellaneous..................................................................................     12
      7.1   Survival of Warranties..................................................................     12
      7.2   Successors and Assigns..................................................................     12
      7.3   Governing Law...........................................................................     12
      7.4   Counterparts............................................................................     12
      7.5   Titles and Subtitles....................................................................     12
      7.6   Notices.................................................................................     12
      7.7   Finder's Fee............................................................................     13
      7.8   Expenses................................................................................     13
      7.9   Amendments and Waivers..................................................................     13
     7.10   Severability............................................................................     13
     7.11   Aggregation of Stock....................................................................     13
     7.12   Entire Agreement........................................................................     13
</TABLE>

                                       ii
<PAGE>

<TABLE>
<CAPTION>
SCHEDULE OF EXCEPTIONS
<S>                 <C>
SCHEDULE A          Schedule of Investors

EXHIBIT A           -  Sixth Amended and Restated Articles of Incorporation
EXHIBIT B           -  Second Amended and Restated Investors' Rights Agreement
EXHIBIT C           -  Opinion of Counsel for the Company
</TABLE>

                                      iii
<PAGE>

                  SERIES AA PREFERRED STOCK PURCHASE AGREEMENT
                  --------------------------------------------



          THIS SERIES AA PREFERRED STOCK PURCHASE AGREEMENT (the "Agreement") is
made as of the 1st day of June, 1999, by and among Neuron Data, Inc., a
California corporation (the "Company"), and the investors listed on Schedule A
                                                                    ----------
hereto (each an "Investor," and collectively the "Investors").

                                    RECITALS
                                    --------

          A.   The Company wishes to sell and issue Series AA Preferred Stock to
the Investors; and

          B.   The Company wishes to induce the Investors to purchase the Series
AA Preferred Stock; and

          C.   The Company and the Investors have entered into a Third Amended
and Restated Investors' Rights Agreement (the "Investors' Rights Agreement").

                                   AGREEMENT
                                   ---------

          NOW, THEREFORE, in consideration of the mutual premises set forth in
this Agreement and other good and valuable consideration, the sufficiency of
which is hereby acknowledged, the parties intending to be legally bound hereby,
agree as follows:

     1.   Purchase and Sale of Stock.
          --------------------------

          1.1  Sale and Issuance of Series AA Preferred Stock.
               ----------------------------------------------

               (a) The Company shall adopt and file with the Secretary of State
of California, on or before the Closing (as defined below), the Sixth Amended
and Restated Articles of Incorporation in the form attached hereto as Exhibit A
                                                                      ---------
(the "Restated Articles").

              (b)  Subject to the terms and conditions of this Agreement, each
Investor shall, severally, purchase at the Closing, and the Company shall sell
and issue to each Investor at the Closing, that number of shares of the
Company's Series AA Preferred Stock set forth opposite each Investor's name on
Schedule A1 hereto for the purchase price set forth thereon or cancellation of
-----------
indebtedness pursuant to certain bridge notes totaling approximately One Million
Five Hundred Thousand Dollars ($1,500,000) plus interest, previously issued by
the Company.

              (c)  Subject to the terms and conditions of this Agreement, each
Investor listed on Schedule A2 hereto shall, severally, purchase at the Closing,
                   -----------
and the Company shall sell and issue to such Investor that additional number of
shares of the Company's Series AA Preferred Stock set forth opposite each
Investor's name on Schedule A2 hereto for the purchase price set forth thereon.
                   -----------

          1.2  Closing. The purchase and sale of the Series AA Preferred Stock
               -------
(the "Closing") shall take place at the offices of Brobeck, Phleger & Harrison
LLP,
<PAGE>

Two Embarcadero Place, 2200 Geng Road, Palo Alto, California, at 10:00 A.M., on
June 1, 1999, or at such other time and place as the Company and the Investors
mutually agree upon orally or in writing (which time and place are designated as
the "Closing"). At the Closing, the Company shall deliver to each Investor a
certificate representing the Series AA Preferred Stock that such Investor is
purchasing against payment of the purchase price therefor by check, wire
transfer, cancellation of indebtedness or any combination thereof.

          1.3  Subsequent Sale of Series AA Preferred Stock. The Company may
               --------------------------------------------
sell up to the balance of the authorized number of shares of Series AA Preferred
Stock not sold at the Closing to such purchasers as it shall select, at a price
of $0.27 per share. Any such Investor shall become a party to this Agreement and
that certain Amended and Restated Investors' Rights Agreement dated as of even
date herewith, by and among the Company the Investors and certain Shareholders,
the form of which is attached hereto as Exhibit B (the "Investors' Rights
                                        ---------
Agreement") and shall have the rights and obligations hereunder and thereunder.

     2.   Representations and Warranties of the Company. Except as set forth on
          ---------------------------------------------
a Schedule of Exceptions (the "Schedule of Exceptions") furnished to each
Investor and counsel for the Investors, which exceptions shall be deemed to be
representations and warranties as if made hereunder, the Company hereby
represents and warrants that:

          2.1  Organization, Good Standing and Qualification. The Company is a
               ---------------------------------------------
corporation duly organized, validly existing and in good standing under the laws
of the State of California and has all requisite corporate power and authority
to carry on its business as now conducted and as proposed to be conducted. The
Company is duly qualified to transact business and is in good standing in each
jurisdiction in which the failure to so qualify would have a material adverse
effect on its business or properties.

          2.2  Capitalization and Voting Rights. Upon the consummation of the
               --------------------------------
transactions contemplated hereby and effective as of the Closing, the authorized
capital of the Company will consist of:

               (i)  Preferred Stock. Thirty-Four Million (34,000,000) shares of
                    ---------------
Preferred Stock (the "Preferred Stock"), Thirty-Four Million (34,000,000) of
which have been designated as Series AA Preferred Stock and up to all of which
will be sold pursuant to this Agreement. The rights, privileges and preferences
of the Series AA Preferred Stock will be as stated in the Company's Restated
Articles.

               (ii) Common Stock. Fifty-Four Million (54,000,000) shares of
                    ------------
common stock ("Common Stock"), of which 11,630,133 shares are issued and
outstanding.

               (iii)  Except for (A) the conversion privileges of the Series AA
Preferred Stock, (B) the rights provided in Section 2.4 of the Investors' Rights
Agreement, (C) that certain warrant to purchase up to 214,286 shares of Common
Stock issued to Solmex Systems Limited in exchange for the warrant to purchase
214,286 shares of Series B Preferred Stock, (D) that certain warrant to purchase
up to 2,009 shares of Common Stock issued to Indigo Partners, (E) that certain
warrant to purchase up to 10,000 shares of Common Stock issued to William
Grotzinger, (F) currently outstanding options to purchase 8,200 shares of Common
Stock granted to employees pursuant to the Company's 1986 Stock Option Plan (the

                                       2
<PAGE>

"1986 Option Plan"), (G) currently outstanding options to purchase 2,378,693
shares of Common Stock granted to employees pursuant to the Company's 1996 Stock
Option Plan (the "1996 Option Plan") and (H) currently outstanding options to
purchase 714,286 shares of Common Stock issued to certain investors in exchange
for the Series E Preferred Stock options granted to certain investors pursuant
to the Series D Preferred Stock Purchase and Series E Preferred Stock Option
Agreement, dated June 28, 1996, there are not outstanding any options, warrants,
rights (including conversion or preemptive rights) or agreements for the
purchase or acquisition from the Company of any shares of its capital stock.  In
addition to the aforementioned options, the Company has reserved for purchase
upon exercise of options to be granted in the future under the 1996 Option Plan,
an additional amount of shares of its Common Stock that would increase the total
number of shares authorized for issuance pursuant to the 1996 Option Plan to 25%
of the fully-diluted capitalization of the Company, on a Common Stock equivalent
basis.  The Company is not a party or subject to any agreement or understanding,
and, to the best of the Company's knowledge, there is no agreement or
understanding between any persons and/or entities, which affects or relates to
the voting or giving of written consents with respect to any security or by a
director of the Company.

          2.3  Subsidiaries. The Company does not presently own or control,
               ------------
directly or indirectly, any interest in any other corporation, association, or
other business entity.

          2.4  Authorization. All corporate action on the part of the Company,
               -------------
its officers, directors and shareholders has been taken or will be taken prior
to the Closing that is necessary for: (1) the authorization, execution and
delivery of this Agreement and the Investors' Rights Agreement, respectively;
(2) the performance of all obligations of the Company under this Agreement and
the Investors' Rights Agreement; and (3) the authorization, issuance (or
reservation for issuance), sale and delivery of the Series AA Preferred Stock
being sold hereunder and the Common Stock issuable upon conversion of the Series
AA Preferred Stock. This Agreement and the Investors' Rights Agreement each
constitute valid and legally binding obligations of the Company, enforceable in
accordance with their respective terms, except (i) as limited by applicable
bankruptcy, insolvency, reorganization, moratorium and other laws of general
application affecting enforcement of creditors' rights generally, (ii) as
limited by laws relating to the availability of specific performance, injunctive
relief or other equitable remedies and (iii) to the extent the indemnification
provisions contained in the Investors' Rights Agreement may be limited by
applicable federal or state securities laws.

          2.5  Valid Issuance of Preferred and Common Stock. The Series AA
               --------------------------------------------
Preferred Stock that is being purchased by each of the Investors hereunder, when
issued, sold and delivered in accordance with the terms of this Agreement for
the consideration expressed herein, will be duly and validly issued, fully paid
and nonassessable, and will be free of restrictions on transfer other than
restrictions on transfer under this Agreement and the Investors' Rights
Agreement and under applicable state and federal securities laws. The Common
Stock issuable upon conversion of the Series AA Preferred Stock purchased under
this Agreement has been duly and validly reserved for issuance and, upon
issuance in accordance with the terms of the Restated Articles, will be duly and
validly issued, fully paid, and nonassessable and will be free of restrictions
on transfer other than restrictions on transfer under this Agreement and the
Investors' Rights Agreement and under applicable state and federal securities
laws.

                                       3
<PAGE>

          2.6  Governmental Consents. No consent, approval, order or
               ---------------------
authorization of, or registration, qualification, designation, declaration or
filing with, any federal, state or local governmental authority on the part of
the Company is required in connection with the consummation of the transactions
contemplated by this Agreement, except for (i) the filing of the Restated
Articles with the Secretary of State of the State of California and (ii) the
filing pursuant to Section 25102(f) of the California Corporate Securities Law
of 1968, as amended, and the rules thereunder, which filing will be effected
within fifteen (15) days of the sale of the Series AA Preferred Stock.

          2.7  Offering. Subject in part to the truth and accuracy of each
               --------
Investor's representations set forth in Section 3 of this Agreement, the offer,
sale and issuance of the Series AA Preferred Stock as contemplated by this
Agreement are exempt from the registration requirements of the Securities Act of
1933, as amended (the "Act").

          2.8  Litigation. There is no action, suit, proceeding or investigation
               ----------
pending against the Company that questions the validity of this Agreement or the
Investors' Rights Agreement, or the right of the Company to enter into such
agreements, or to consummate the transactions contemplated hereby or thereby, or
that might result, either individually or in the aggregate, in any material
adverse changes in the assets, condition or affairs of the Company. To its
knowledge, the Company is not a party or subject to the provisions of any order,
writ, injunction, judgment or decree of any court or government agency or
instrumentality. There is no action, suit, proceeding or investigation by the
Company currently pending.

          2.9  Proprietary Rights. To its knowledge, the Company has sufficient
               ------------------
title and ownership of all patents, trademarks, service marks, trade names,
copyrights, trade secrets, information, proprietary rights, technology and
processes to conduct its business as now conducted (collectively, "Proprietary
Rights"). The Company is not aware that any of its employees is bound by or a
party to any options, licenses or agreements of any kind with respect to the
Proprietary Rights of any other person or entity. The Company has not received
any communications alleging that the Company has violated any of the Proprietary
Rights of any other person or entity. The Company is not aware that any of its
employees is obligated under any contract or other agreement or subject to any
judgment, decree or order of any court or administrative agency, that would
interfere with the use of such employee's commercially reasonable efforts to
promote the interests of the Company or that would conflict with the Company's
business.

          2.10  Compliance with Other Instruments. The Company is not in
                ---------------------------------
violation or default in any material respect of any provision of its Restated
Articles or Bylaws, or in any material respect of any instrument, judgment,
order, writ, decree or material contract to which it is a party or by which it
is bound, or, to its knowledge, of any provision of any federal or state
statute, rule or regulation applicable to the Company. The execution, delivery
and performance of this Agreement and the Investors' Rights Agreement, and the
consummation of the transactions contemplated hereby and thereby will not result
in any such violation or be in conflict with or constitute, either a default in
any material respect under any such provision, instrument, judgment, order,
writ, decree or contract or an event that results in the creation of any lien,
charge or encumbrance upon any assets of the Company or the suspension,
revocation, impairment, forfeiture or nonrenewal of any material permit,
license, authorization or approval applicable to the Company.

                                       4
<PAGE>

          2.11  Agreements.
                ----------

                (a)  Except for agreements explicitly contemplated hereby and by
the Investors' Rights Agreement, there are no agreements between the Company and
any of its officers, directors, affiliates or any affiliate thereof.

                (b)  There are no agreements, instruments, contracts, judgments,
orders, writs or decrees to which the Company is a party or by which it is bound
that involve the license of any patent, copyright, trade secret or other
proprietary right to or from the Company other than those in the Company's
normal course of business as a software licensor.

                (c)  The Company has not (i) declared or paid any dividends or
authorized or made any distribution upon or with respect to any class or series
of its capital stock, (ii) incurred any outstanding indebtedness for money
borrowed or any other liabilities individually in excess of $50,000 or, in the
case of indebtedness and/or liabilities individually less than $50,000, in
excess of $300,000 in the aggregate, or (iii) made any loans or advances to any
person, other than ordinary advances for travel and other customary employee
business expenses.

                (d)  For the purposes of subsections (b) and (c) above, all
indebtedness, liabilities, agreements, instruments and contracts involving the
same person or entity (including persons or entities the Company has reason to
believe are affiliated therewith) shall be aggregated for the purpose of meeting
the individual minimum dollar amounts of such subsections.

                (e)  There are no agreements limiting the freedom of the Company
to compete in any line of business or in any geographic area or with any person.

          2.12 Related-Party Transactions. No officer or director of the Company
               --------------------------
or shareholder holding more than 100,000 shares of the Company's capital stock
or member of his or her immediate family is indebted to the Company, nor is the
Company indebted (or committed to make loans or extend or guarantee credit) to
any of them. To the Company's knowledge, no member of the immediate family of
any officer or director of the Company or shareholder holding more than 100,000
shares of the Company's capital stock is directly or indirectly interested in
any contract with the Company (other than as holders of less than 1% of any
class of securities of a publicly-traded company).

          2.13  Permits. The Company has all permits and licenses necessary for
                -------
the conduct of its business as now being conducted by it, the lack of which
could materially and adversely affect the business, properties or financial
condition of the Company. The Company is not in default in any material respect
under any of such permits and licenses.

          2.14  Environmental and Safety Laws. To its knowledge, the Company is
                -----------------------------
not in violation in any material respect of any applicable statute, law or
regulation relating to the environment or occupational health and safety, and to
its knowledge, no material expenditures are or will be required in order to
comply with any such existing statute, law or regulation.

          2.15  Disclosure. The Company has fully provided each Investor with
                ----------
all material information that such Investor would require in deciding whether to
purchase the

                                       5
<PAGE>

Series AA Preferred Stock. Neither this Agreement, the Investors' Rights
Agreement nor any other statements or certificates made or delivered in
connection herewith or therewith contains any untrue statement of a material
fact or omits to state a material fact necessary to make the statements herein
or therein not misleading.

          2.16  Investors' Rights. Except as provided in the Investors' Rights
                -----------------
Agreement, the Company has not granted or agreed to grant any registration
rights, including piggyback rights, to any person or entity.

          2.17  Corporate Documents. Except for amendments necessary to satisfy
                -------------------
representations and warranties or conditions contained herein (the form of which
amendments has been approved by the Investors), the Restated Articles and Bylaws
of the Company are in the form previously provided to counsel for the Investors.

          2.18  Title to Property and Assets. The Company owns its property and
                ----------------------------
assets free and clear of all mortgages, liens, loans and encumbrances, except
such encumbrances and liens that arise in the ordinary course of business and do
not materially impair the Company's ownership or use of such property or assets.
With respect to the property and assets it leases, the Company is in compliance
with such leases in all material respects.

          2.19  Financial Statements. The Company has delivered to each Investor
                --------------------
certain Company financial information, including a final draft of the audited
financial statements for the year ended and as of March 31, 1998 and unaudited
financial statements for the twelve (12) months ended as of March 31, 1999 (the
"Financial Statements"). The Financial Statements have been prepared in
accordance with generally accepted accounting principles applied on a consistent
basis throughout the periods indicated and with each other, except that
unaudited Financial Statements may not contain all footnotes required by
generally accepted accounting principles. The Financial Statements fairly
present the financial condition and operating results of the Company as of the
dates, and for the periods, indicated therein, subject in the case of unaudited
Financial Statements to normal year-end audit adjustments.

          2.20  Changes. Since March 31, 1999, and except with respect to this
                -------
Agreement and the Investors' Rights Agreement and the transactions contemplated
hereby and thereby, there has not been:

                (a)  any change in the assets, liabilities, financial condition
or operating results of the Company from that reflected in the Financial
Statements, except changes in the ordinary course of business that have not
been, in the aggregate, materially adverse;

                (b)  any damage, destruction or loss, whether or not covered by
insurance, materially and adversely affecting the assets, properties, financial
condition, operating results or business of the Company;

                (c)  any express waiver by the Company of a valuable right or of
a material debt owed to it;

                (d)  any satisfaction or discharge of any lien, claim or
encumbrance or payment of any obligation by the Company, except in the ordinary
course of business and that is

                                       6
<PAGE>

not material to the assets, properties, financial condition, operating results
or business of the Company;

                (e)  any material change or amendment to a material contract or
arrangement by which the Company or any of its assets or properties is bound or
subject;

                (f)  any material change in any compensation arrangement or
agreement with any executive officer;

                (g)  any sale, assignment or transfer of any patents,
trademarks, copyrights, trade secrets or other intangible assets other than in
the ordinary course of business;

                (h)  receipt of notice that there has been a loss of, or
material order cancellation by, any major customer of the Company;

                (i)  any loans or guarantees made by the Company to or for the
benefit of its officers or directors, or any members of their immediate
families, other than travel advances and other advances made in the ordinary
course of its business; or

                (j)  any declaration, setting aside or payment or other
distribution in respect of any of the Company's capital stock, or any direct or
indirect redemption, purchase or other acquisition of any of such stock by the
Company (other than repurchases from employees or consultants of the Company in
connection with their termination of employment).

          2.21  Employee Benefit Plans. The Company does not have any Employee
                ----------------------
Benefit Plan as defined in the Employee Retirement Income Security Act of 1974.

          2.22  Tax Returns, Payments and Elections. The Company has filed all
                -----------------------------------
tax returns and reports as required by law. These returns and reports are true
and correct in all material respects. The Company has paid all taxes and other
assessments due. The provision for taxes of the Company as shown in the
Financial Statements is adequate for taxes due or accrued as of the date
thereof. The Company has not elected pursuant to the Internal Revenue Code of
1986, as amended (the "Code"), to be treated as a Subchapter S corporation or a
collapsible corporation pursuant to Section 1362(a) or Section 341(f) of the
Code, nor has it made any other elections pursuant to the Code (other than
elections that relate solely to methods of accounting, depreciation or
amortization) that would have a material effect on the Company, its financial
condition, its business as presently conducted or proposed to be conducted or
any of its properties or material assets.

          2.23  Insurance. The Company has valid fire and casualty insurance
                ---------
policies, with extended coverage, sufficient in amount (subject to reasonable
deductibles) to allow it to replace any of its properties that might be damaged
or destroyed.

          2.24  Minute Books. The minute books of the Company made available to
                ------------
the Investors contain a complete summary of all meetings of directors and
shareholders since the time of incorporation.

                                       7
<PAGE>

          2.25  Labor Agreements and Actions. The Company is not bound by or
                ----------------------------
subject to (and none of its assets or properties is bound by or subject to) any
written or oral, express or implied, contract, commitment or arrangement with
any labor union, and no labor union has requested or, to the Company's
knowledge, has sought to represent any of the employees, representatives or
agents of the Company. There is no strike or other labor dispute involving the
Company pending, or to the Company's knowledge, threatened, that could have a
material adverse effect on the assets, properties, financial condition,
operating results, or business of the Company (as such business is presently
conducted and as it is proposed to be conducted), nor is the Company aware of
any labor organization activity involving its employees. The Company is not
aware that any officer or key employee, or that any group of key employees,
intends to terminate their employment with the Company, nor does the Company
have a present intention to terminate the employment of any of the foregoing.
The employment of each officer and employee of the Company is terminable at the
will of the Company.

          2.26  U.S. Real Property Holding Corporation. The Company is not now
                --------------------------------------
and has never been a "United States Real Property Holding Corporation" as
defined in Section 897(c)(2) of the Internal Revenue Code of 1986, as amended
and Section 1.897-2(b) of the regulations promulgated by the Internal Revenue
Service.

     3.   Representations and Warranties of the Investors. Each Investor hereby
          -----------------------------------------------
represents and warrants that:

          3.1 Authorization. Such Investor has full power and authority to enter
              -------------
into each of this Agreement and the Investors' Rights Agreement, and each such
Agreement constitutes its valid and legally binding obligation, enforceable in
accordance with its terms.

          3.2  Purchase Entirely for Own Account. This Agreement is made with
               ---------------------------------
each Investor in reliance upon such Investor's representation to the Company,
which by such Investor's execution of this Agreement such Investor hereby
confirms, that the Series AA Preferred Stock to be received by such Investor and
the Common Stock issuable upon conversion, or exercise and conversion, thereof
(collectively, the "Securities") will be acquired for investment for such
Investor's own account, not as a nominee or agent, and not with a view to the
resale or distribution of any part thereof, and that such Investor has no
present intention of selling, granting any participation in, or otherwise
distributing the same. By executing this Agreement, such Investor further
represents that such Investor does not have any contract, undertaking, agreement
or arrangement with any person to sell, transfer or grant participations to such
person or to any third person, with respect to any of the Securities.

          3.3  Disclosure of Information. Such Investor has received all the
               -------------------------
information it considers necessary, desirable or appropriate for deciding
whether to purchase the Series AA Preferred Stock. Such Investor further
represents that it has asked all the questions that it desired to ask of the
Company, that it has received complete answers from the Company in response to
those questions, that such answers were to the satisfaction of the Investor for
the purpose of deciding whether to invest in the Company, and that as a result
of its due diligence regarding the terms and conditions of the offering of the
Series AA Preferred Stock and the business, properties, prospects and financial
condition of the Company it has an informed understanding of the Company for
investment purposes.

                                       8
<PAGE>

          3.4  Investment Experience. Such Investor is an investor in securities
               ---------------------
of companies in the development stage and acknowledges that it is able to fend
for itself, can bear the economic risk of its investment, and has such knowledge
and experience in financial or business matters that it is capable of evaluating
the merits and risks of the investment in the Series AA Preferred Stock. If
other than an individual, the Investor also represents it has not been organized
for the purpose of acquiring the Series AA Preferred Stock.

          3.5  Accredited Investor. Unless indicated to the contrary on the
               -------------------
signature page hereof, such Investor is an "accredited investor" within the
meaning of Securities and Exchange Commission ("SEC") Rule 501 of Regulation D,
as presently in effect.

          3.6  Restricted Securities. Such Investor understands that the
               ---------------------
Securities it is purchasing are characterized as "restricted securities" under
the federal securities laws inasmuch as they are being acquired from the Company
in a transaction not involving a public offering and that under such laws and
applicable regulations such securities may be resold without registration under
the Act, only in certain limited circumstances. In this connection, such
Investor represents that it is familiar with SEC Rule 144, as presently in
effect ("Rule 144"), and understands the resale limitations imposed thereby and
by the Act.

          3.7  Further Limitations on Disposition. Without in any way limiting
               ----------------------------------
the representations set forth above, such Investor further agrees not to make
any disposition of all or any portion of the Securities unless and until:

               (a)  There is then in effect a Registration Statement under the
Act covering such proposed disposition and such disposition is made in
accordance with such Registration Statement; or

               (b)  Such transfer is made pursuant to Rule 144; or

               (c)  (i) Such Investor shall have notified the Company of the
proposed disposition and shall have furnished the Company with a detailed
statement of the circumstances surrounding the proposed disposition, (ii) if
reasonably requested by the Company, such Investor shall have furnished the
Company with an opinion of counsel, reasonably satisfactory to the Company that
such disposition will not require registration of such shares under the Act, and
(iii) the transferee has agreed in writing for the benefit of the Company to be
bound by this Section 3, and the Investors' Rights Agreement.

               (d)  Notwithstanding the provisions of paragraphs (a), (b) and
(c) above, no such registration statement or opinion of counsel shall be
necessary for a transfer by an Investor that 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 or her
spouse or to the siblings, lineal descendants or ancestors of such partner or
his or her spouse, if the transferee agrees in writing to be subject to the
terms hereof and of the Investors' Rights Agreement, to the same extent as if he
or she were an original Investor hereunder and thereunder.

          3.8  Legends. It is understood that the certificates evidencing the
               -------
Securities may bear one or all of the following legends:

                                       9
<PAGE>

               (a)  "These securities have not been registered under the
Securities Act of 1933, as amended. They may not be sold, offered for sale,
pledged or hypothecated in the absence of a registration statement in effect
with respect to the securities under such Act or an opinion of counsel
satisfactory to the Company that such registration is not required or unless
sold pursuant to Rule 144 of such Act."

               (b)  Any legend required by the laws of the State of California,
including any legend required by the California Department of Corporations and
Sections 417 and 418 of the California Corporations Code.

          3.9  Further Representations by Foreign Investors. If an Investor is
               --------------------------------------------
not a United States person, such Investor hereby represents that he or she has
satisfied himself or herself as to the full observance of the laws of his or her
jurisdiction in connection with any invitation to subscribe for the Securities
or any use of this Agreement, including (i) the legal requirements within his
jurisdiction for the purchase of the Securities, (ii) any foreign exchange
restrictions applicable to such purchase, (iii) any governmental or other
consents that may need to be obtained, and (iv) the income tax and other tax
consequences, if any, that may be relevant to the purchase, holding, redemption,
sale, or transfer of the Securities. Such Investor's subscription and payment
for, and his or her continued beneficial ownership of the Securities, will not
violate any applicable securities or other laws of his or her jurisdiction.

     4.   California Commissioner of Corporations.
          ---------------------------------------

          4.1  Corporate Securities Law. THE SALE OF THE SECURITIES THAT ARE THE
               ------------------------
SUBJECT OF THIS AGREEMENT HAS NOT BEEN QUALIFIED WITH THE COMMISSIONER OF
CORPORATIONS OF THE STATE OF CALIFORNIA AND THE ISSUANCE OF SUCH SECURITIES OR
THE PAYMENT OR RECEIPT OF ANY PART OF THE CONSIDERATION FOR SUCH SECURITIES
PRIOR TO SUCH QUALIFICATION IS UNLAWFUL, UNLESS THE SALE OF SECURITIES IS EXEMPT
FROM QUALIFICATION BY SECTION 25100, 25102 OR 25105 OF THE CALIFORNIA
CORPORATIONS CODE. THE RIGHTS OF ALL PARTIES TO THIS AGREEMENT ARE EXPRESSLY
CONDITIONED UPON SUCH QUALIFICATION BEING OBTAINED, UNLESS THE SALE IS SO
EXEMPT.

     5.   Conditions of Investor's Obligations at Closing. The obligations of
          -----------------------------------------------
each Investor under subsection 1.1(b) of this Agreement are subject to the
fulfillment on or before the Closing of each of the following conditions, the
waiver of which shall not be effective against any Investor who does not consent
in writing thereto:

          5.1  Representations and Warranties. The representations and
               ------------------------------
warranties of the Company contained in Section 2 shall be true on and as of the
Closing with the same effect as though such representations and warranties had
been made on and as of the date of such Closing.

          5.2  Performance. The Company shall have performed and complied with
               -----------
all agreements, obligations and conditions contained in this Agreement that are
required to be performed or complied with by it on or before the Closing.

                                       10
<PAGE>

          5.3  Compliance Certificate. The President of the Company shall
               ----------------------
deliver to each Investor at the Closing a certificate stating that the
conditions specified in Sections 5.1 and 5.2 have been fulfilled and stating
that there shall have been no material adverse change in the business, affairs,
operations, properties, assets or condition of the Company since the date of the
latest Financial Statements.

          5.4  Qualifications. All authorizations, approvals, or permits, if
               --------------
any, of any governmental authority or regulatory body of the United States or of
any state that are required in connection with the lawful issuance and sale of
the Securities pursuant to this Agreement shall be duly obtained and effective
as of the Closing.

          5.5  Proceedings and Documents. All corporate and other proceedings in
               -------------------------
connection with the transactions contemplated at the Closing and all documents
incident thereto shall be reasonably satisfactory in form and substance to
Investors' special counsel, and they shall have received all such counterpart
original and certified or other copies of such documents as they may reasonably
request.

          5.6  Opinion of Company Counsel. Each Investor shall have received
               --------------------------
from Brobeck, Phleger & Harrison LLP, counsel for the Company, an opinion, dated
as of the Closing, in the form attached hereto as Exhibit C.
                                                  ---------

          5.7  Amended and Restated Investors' Rights Agreement. The Company and
               ------------------------------------------------
each Investor shall have entered into the Investors' Rights Agreement in the
form attached as Exhibit B.
                 ---------

          5.8  Restated Articles. The Company's Restated Articles shall have
               -----------------
been accepted for filing by the office of the California Secretary of State and
the Company shall have properly authorized enough shares to issue the Series AA
Preferred Stock, the options to purchase shares of the Company's Common Stock
issued to the holders of Series E Options, the options to purchase shares of the
Company's Common Stock issued to the holders of Series B Options and reserved
for issuance such shares of Common Stock sufficient to effect the conversion of
the Series A, B, C, D and F Preferred Stock.

          5.9  Board and Shareholder Approval for Increase in 1996 Stock
               ---------------------------------------------------------
Option/Stock Issuance Plan. The Company shall have received the required board
--------------------------
and shareholder approval necessary to increase the shares authorized under the
Company's 1996 Stock Option/Stock Issuance Plan from 2,633,993 to 25% of the
fully-diluted capitalization of the Company on a Common Stock equivalent basis.

          5.10  Conversion of All Outstanding Preferred Stock. The Company shall
                ---------------------------------------------
have converted all of its outstanding shares of Preferred Stock and options to
purchase shares of Preferred Stock into shares of the Company's Common Stock or
options to purchase shares of Common Stock at a conversion ratio of 1:1 for
Series A, B, D and F Preferred Stock and a conversion ratio of 1: 1.0448 for
Series C Preferred Stock.

     6.  Conditions of the Company's Obligations at Closing. The obligations of
         --------------------------------------------------
the Company to each Investor under this Agreement are subject to the fulfillment
on or before the Closing of each of the following conditions by that Investor:

                                       11
<PAGE>

          6.1  Representations and Warranties. The representations and
               ------------------------------
warranties of the Investor contained in Section 3 shall be true on and as of the
Closing with the same effect as though such representations and warranties had
been made on and as of the Closing.

          6.2  Amended and Restated Investors' Rights Agreement. The Company and
               ------------------------------------------------
each Investor shall have entered into the Investors' Rights Agreement in the
form attached as Exhibit B.
                 ---------

          6.3  Payment of Purchase Price. The Investor shall have delivered the
               -------------------------
purchase price specified in Section 1.2.

          6.4  Qualifications. All authorizations, approvals, or permits, if
               --------------
any, of any governmental authority or regulatory body of the United States or of
any state that are required in connection with the lawful issuance and sale of
the Securities pursuant to this Agreement shall be duly obtained and effective
as of the Closing.

     7.   Miscellaneous.
          -------------

          7.1  Survival of Warranties. The warranties, representations and
               ----------------------
covenants of the Company and Investors contained in or made pursuant to this
Agreement shall survive the execution and delivery of this Agreement and the
Closing and shall in no way be affected by any investigation of the subject
matter thereof made by or on behalf of the Investors or the Company.

          7.2  Successors and Assigns. Except as otherwise provided herein, the
               ----------------------
terms and conditions of this Agreement shall inure to the benefit of and be
binding upon the respective successors and assigns of the parties (including
transferees of any Securities). Nothing in this Agreement, express or implied,
is intended to confer upon any party other than the parties hereto or their
respective successors and assigns any rights, remedies, obligations, or
liabilities under or by reason of this Agreement, except as expressly provided
in this Agreement.

          7.3  Governing Law. This Agreement shall be governed by and construed
               -------------
under the laws of the State of California as applied to agreements among
California residents entered into and to be performed entirely within
California.

          7.4  Counterparts. This Agreement 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.

          7.5  Titles and Subtitles. The titles and subtitles used in this
               --------------------
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

          7.6  Notices. Unless otherwise provided, any notice required or
               -------
permitted under this Agreement shall be given in writing and shall be deemed
effectively given, or received, upon personal delivery to the party to be
notified or upon deposit with the United States Post Office, by registered or
certified mail, postage prepaid and addressed to the party to be notified at the
address indicated for such party on the signature page hereof, or at such other
address as such party may designate in writing, provided that such other address
is received at least ten (10) days prior to the giving of any notice required or
permitted under this Agreement.

                                       12
<PAGE>

          7.7  Finder's Fee. Each party represents that it neither is nor will
               ------------
be obligated for any finders' fee or commission in connection with this
transaction. Each Investor agrees to indemnify and to hold harmless the Company
from any liability for any commission or compensation in the nature of a
finders' fee (and the costs and expenses of defending against such liability or
asserted liability) for which such Investor or any of its officers, partners,
employees, or representatives is responsible.

          The Company agrees to indemnify and hold harmless each Investor from
any liability for any commission or compensation in the nature of a finders' fee
(and the costs and expenses of defending against such liability or asserted
liability) for which the Company or any of its officers, employees or
representatives is responsible.

          7.8  Expenses. If and only if the issuance and sale of the Series AA
               --------
Preferred Stock is consummated, the Company shall pay up to an aggregate of
$15,000 for the reasonable fees and expenses of one counsel to the Investors
that it incurs with respect to the negotiation, execution, delivery and
performance of this Agreement. If any action at law or in equity is necessary to
enforce or interpret the terms of this Agreement, the Investors' Rights
Agreement and Right of First Refusal Agreement or the Restated Articles, the
prevailing party shall be entitled to reasonable attorney's fees, costs and
necessary disbursements in addition to any other relief to which such party may
be entitled.

          7.9  Amendments and Waivers. Any term of this Agreement may be amended
               ----------------------
and the observance of any term of this Agreement may be waived (either generally
or in a particular instance and either retroactively or prospectively), only
with the written consent of the Company and the holders of a majority of the
Common Stock issued or issuable upon conversion of the Series AA Preferred Stock
purchased hereby. Any amendment or waiver effected in accordance with this
paragraph shall be binding upon each holder of any securities purchased under
this Agreement at the time outstanding (including securities into which such
securities are convertible), each future holder of all such securities, and the
Company.

          7.10  Severability. If one or more provisions of this Agreement are
                ------------
held to be unenforceable under applicable law, such provision shall be excluded
from this Agreement and the balance of the Agreement shall be interpreted as if
such provision were so excluded and shall be enforceable in accordance with its
terms.

          7.11  Aggregation of Stock. All shares of the Preferred Stock held or
                --------------------
acquired by affiliated entities or persons shall be aggregated together for the
purpose of determining the availability of any rights under this Agreement.

          7.12  Entire Agreement. This Agreement and the documents referred to
                ----------------
herein constitute the entire agreement among the parties and no party shall be
liable or bound to any other party in any manner by any warranties,
representations, or covenants except as specifically set forth herein or
therein.

                                       13
<PAGE>

          IN WITNESS WHEREOF, the parties have executed this Series AA Preferred
Stock Purchase Agreement as of the date first above written.


                                 NEURON DATA, INC.


                                 By:
                                    ----------------------------------------
                                     Thomas Kelly
                                     President and Chief Executive Officer

                                 Address:  1310 Villa Street
                                           Mountain View, California 94041



                                 INVESTOR:

                                 By:
                                    ----------------------------------------
                                 Name:  Steven A. Yount

                                 Address:  7762 Fenway Road
                                           New Albany, OH 43054

                                 Accredited Status: (Please Check)
                                 [_] Accredited Investor
                                 [_] Non-Accredited Investor


                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       14
<PAGE>

                                 TL VENTURES III L.P.

                                 By: TL VENTURES III MANAGEMENT
                                     L.P., its general partner

                                 By: TL VENTURES III LLC,
                                     its general partner


                                 By:
                                     ----------------------------------------
                                 Name:
                                 Title:    Managing Director



                                 TL VENTURES III OFFSHORE L.P.

                                 By: TL VENTURES III OFFSHORE
                                     PARTNERS L.P., its general partner

                                 By: TL VENTURES III OFFSHORE LTD.,
                                     its general partner


                                 By:
                                     ----------------------------------------
                                 Name:
                                 Title:    Vice President



                                 TL VENTURES III INTERFUND L.P.

                                 By: TL VENTURES LLC, its general partner


                                 By:
                                     ----------------------------------------
                                 Name:
                                 Title:    Managing Director


                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       15
<PAGE>

                                 MORGAN STANLEY VENTURE CAPITAL FUND II, L.P.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner


                                 By:
                                     ----------------------------------------

                                 MORGAN STANLEY VENTURE CAPITAL FUND II, C.V.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its Investment General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner


                                 By:
                                     ----------------------------------------

                                 MORGAN STANLEY VENTURE INVESTORS, L.P.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner



                                 By:
                                     ----------------------------------------
                                     Vice President

                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       16
<PAGE>

                                 ALTA EMBARCADERO PARTNERS, LLC



                                 By:
                                     ----------------------------------------
                                     Member

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111


                                 ALTA IV LIMITED PARTNERSHIP

                                 By: Alta IV Management Partners, L.P.


                                 By:
                                     ----------------------------------------
                                     General Partner

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111

                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       17
<PAGE>

                                 C.V. SOFINNOVA PARTNERS FIVE

                                 By: Sofinnova (International) Five N.V.
                                     General Partner


                                 By:
                                     ----------------------------------------
                                     Under Power of Attorney

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111



                                 C.V. SOFINNOVA VENTURES



                                 By:
                                     ----------------------------------------
                                 Address:  140 Geary Street, 10th Floor
                                           San Francisco, CA 94018

                                       18
<PAGE>

                                 MORGAN STANLEY VENTURE CAPITAL FUND II, L.P.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner


                                 By:
                                     ----------------------------------------

                                 MORGAN STANLEY VENTURE CAPITAL FUND II, C.V.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its Investment General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner


                                 By:
                                     ----------------------------------------

                                 MORGAN STANLEY VENTURE INVESTORS, L.P.

                                 By: Morgan Stanley Venture Partners II, L.P.
                                     its General Partner

                                 By: Morgan Stanley Venture Capital II, Inc.
                                     Managing General Partner



                                 By:
                                     ----------------------------------------
                                     Vice President

                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       19
<PAGE>

                                 ALTA CALIFORNIA PARTNERS, L.P.

                                 By: Alta California Management Partners, L.P.



                                 By:
                                     ----------------------------------------
                                     General Partner

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111


                                 ALTA EMBARCADERO PARTNERS, LLC



                                 By:
                                     ----------------------------------------
                                     Member

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111


                                 ALTA IV LIMITED PARTNERSHIP

                                 By: Alta IV Management Partners, L.P.


                                 By:
                                     ----------------------------------------
                                     General Partner

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111

                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       20
<PAGE>

                                 C.V. SOFINNOVA PARTNERS FIVE

                                 By: Sofinnova (International) Five N.V.
                                     General Partner


                                 By:
                                     ----------------------------------------
                                     Under Power of Attorney

                                 Address:  One Embarcadero Center
                                           Suite 4050
                                           San Francisco, CA  94111



                                 C.V. SOFINNOVA VENTURES



                                 By:
                                     ----------------------------------------
                                 Address:  140 Geary Street, 10th Floor
                                           San Francisco, CA 94018






                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT



                                       21
<PAGE>

                                 INVESTOR:

                                 Print Name:
                                            ----------------------------------

                                            ----------------------------------


                                 ---------------------------------------------
                                           Signature of Investor

                             SIGNATURE PAGE TO THE
                 SERIES AA PREFERRED STOCK PURCHASE AGREEMENT

                                       22
<PAGE>

                                  SCHEDULE A1

                             SCHEDULE OF INVESTORS

                          First Closing:  June 1, 1999

<TABLE>
<CAPTION>
                                 Number of Shares of
                                 Series AA Preferred    Cancellation of      Net Amount Paid      Total Investment
Investor                           Stock Purchase        Indebtedness            Company               Amount
-------------------------------------------------------------------------------------------------------------------
<S>                              <C>                    <C>                  <C>                   <C>
Alta California Partners LP           1,736,482         $  195,039.92         $  273,810.09        $  468,850.01
-------------------------------------------------------------------------------------------------------------------
Alta Embarcadero Partners LLC            39,672         $    4,455.94         $    6,255.50        $   10,711.44
-------------------------------------------------------------------------------------------------------------------
Alta IV Limited Partnership             874,873         $  116,926.70         $  119,289.00        $  236,215.70
-------------------------------------------------------------------------------------------------------------------
C.V. Sofinnova Partners Five            159,623         $   21,334.64         $   21,763.64        $   43,098.28
-------------------------------------------------------------------------------------------------------------------
C.V. Sofinnova Ventures                 584,621         $   82,847.60         $   75,000.12        $  157,847.72
-------------------------------------------------------------------------------------------------------------------
Morgan Stanley Venture Capital          725,785         $  102,956.17         $   93,005.85        $  195,962.02
 Fund II, CV
-------------------------------------------------------------------------------------------------------------------
Morgan Stanley Venture Capital        2,913,197         $  413,251.18         $  373,312.02        $  786,563.20
 Fund II, LP
-------------------------------------------------------------------------------------------------------------------
Morgan Stanley Venture Investors        756,082         $  107,253.84         $   96,888.17        $  204,142.01
 LP
-------------------------------------------------------------------------------------------------------------------
TL Venture III Interfund LP             103,122         $   16,185.22         $   11,657.76        $   27,842.98
-------------------------------------------------------------------------------------------------------------------
TL Ventures III LP                    3,158,204         $  495,686.50         $  357,028.67        $  852,715.17
-------------------------------------------------------------------------------------------------------------------
TL Ventures III Offshore LP             661,084         $  103,758.49         $   74,734.23        $  178,492.72
-------------------------------------------------------------------------------------------------------------------
Steve Yount                                 241         $        0.00         $       65.07        $       65.07
-------------------------------------------------------------------------------------------------------------------
   TOTALS                            11,712,986         $1,659,696.21         $1,502,810.12        $3,162,506.33
-------------------------------------------------------------------------------------------------------------------
</TABLE>

                                       23
<PAGE>

                                  SCHEDULE A2

                             SCHEDULE OF INVESTORS

                          First Closing:  June 1, 1999



<TABLE>
<CAPTION>
                                              Number of Shares of Series AA   Total Investment
                 Investor                       Preferred Stock Purchased          Amount
                 --------                     -----------------------------   ----------------
<S>                                           <C>                             <C>
Alta California Partners LP                              471,693                 $  127,357.20
Alta Embarcadero Partners LLC                             11,715                 $    3,162.99
Alta IV Limited Partnership                              312,315                 $   84,325.10
C.V. Sofinnova Partners Five                              57,248                 $   15,457.03
TL Ventures III Interfund LP                              97,372                 $   26,290.51
TL Ventures III LP                                     2,982,108                 $  805,169.23
TL Ventures III Offshore LP                              624,223                 $  168,540.26
                                                       ---------                 -------------
        Totals:                                        4,556,674                 $1,230,302.32
                                                       =========                 =============
</TABLE>

                                       24
<PAGE>

                                  SCHEDULE A3

                             SCHEDULE OF INVESTORS

                      Second Closing:  September 28, 1999


<TABLE>
<CAPTION>
                                                 Number of Shares of Series AA
                   Investor                        Preferred Stock Purchased     Total Investment Amount
                   --------                      -----------------------------   -----------------------
<S>                                              <C>                             <C>
Michael Benson                                               56,303                    $ 15,201.97
Jack Bradley                                                 40,000                    $ 10,800.00
Laurent Delamare                                             75,000                    $ 20,250.00
Steven Friedman                                              21,270                    $  5,743.03
Robert Goodrich                                              77,948                    $ 21,045.95
Albert Gouyet                                                55,555                    $ 14,999.85
Kevin Q. Gu                                                   2,604                    $    703.09
Ted C. Ho                                                    23,761                    $  6,415.49
Ralph Love                                                   25,782                    $  6,961.25
Emmanuel Mignot                                              38,872                    $ 10,495.47
David Mowbray                                                 2,000                    $    540.00
James Owen                                                   19,079                    $  5,151.32
Paul Pelt                                                    15,315                    $  4,134.98
Robert Tykulsker                                              5,633                    $  1,521.03
Michael Wilson                                               51,565                    $ 13,922.50
David Wiser                                                  51,565                    $ 13,922.50
Steve Yount                                                     500                    $    135.00
                                                            -------                    -----------
        Totals:                                             562,752                    $151,943.43
                                                            =======                    ===========
</TABLE>

                                       25
<PAGE>

                                   EXHIBIT A

                           SIXTH AMENDED AND RESTATED
                           ARTICLES OF INCORPORATION

                                   See Tab 4

                                       26
<PAGE>

                                   EXHIBIT B

                              AMENDED AND RESTATED
                          INVESTORS' RIGHTS AGREEMENT

                                   See Tab 5

                                       27
<PAGE>

                                   EXHIBIT C

                       OPINION OF COUNSEL FOR THE COMPANY

                                   See Tab 8

                                       28