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                                                                     EXHIBIT 4.1

                    CONVERTIBLE DEBENTURE PURCHASE AGREEMENT

                                      Among

                              NEOTHERAPEUTICS, INC.

                                       and

                         THE INVESTORS SIGNATORY HERETO




                            Dated as of April 6, 2000







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         CONVERTIBLE DEBENTURE PURCHASE AGREEMENT (this "Agreement"), dated as
of April 6, 2000, among NeoTherapeutics, Inc., a Delaware corporation (the
"Company"), and the investors signatory hereto on the date hereof (each such
investor is a "Purchaser" and all such investors are, collectively, the
"Purchasers").

         WHEREAS, subject to the terms and conditions set forth in this
Agreement, the Company desires to issue and sell to the Purchasers and the
Purchasers, severally and not jointly, desire to purchase from the Company an
aggregate principal amount of $10,000,000 of the Company's 5% Convertible
Debentures, due April 6, 2005, which shall be in the form of Exhibit A (the
"Debentures"), and which are convertible into shares of the Company's common
stock, $.001 par value per share (the "Common Stock"), and certain other
securities of the Company as more fully described in this Agreement.

         NOW, THEREFORE, IN CONSIDERATION of the mutual covenants contained in
this Agreement, and for other good and valuable consideration the receipt and
adequacy are hereby acknowledged, the Company and the Purchasers agree as
follows:

                                    ARTICLE I
                                PURCHASE AND SALE

         1.1      The Closing.

                  (a) The Closing. (i) Subject to the terms and conditions set
forth in this Agreement, the Company shall issue and sell to the Purchasers and
the Purchasers shall, severally and not jointly, purchase from the Company the
Debentures for an aggregate purchase price of $10,000,000. The closing of the
purchase and sale of the Debentures (the "Closing") shall take place at the
offices of Robinson Silverman Pearce Aronsohn & Berman LLP ("Robinson
Silverman"), 1290 Avenue of the Americas, New York, New York 10104, immediately
following the execution hereof or such later date as the parties shall agree.
The date of the Closing is hereinafter referred to as the "Closing Date."




         (ii) At the Closing, the parties shall deliver or shall cause to be
delivered the following: (A) the Company shall deliver to each Purchaser (1) the
Debentures in the aggregate principal amount of the purchase price indicated
below such Purchaser's name on the signature page to this Agreement, registered
in the name of such Purchaser, (2) a Common Stock purchase warrant, in the form
of Exhibit D, registered in the name of such Purchaser, pursuant to which such
Purchaser shall have the right at any time and from time to time thereafter
through the fifth anniversary of the Closing Date to acquire shares of Common
Stock upon the terms set forth therein (collectively, the "Class A Warrants"),
(3) a Common Stock purchase warrant, in the form of Exhibit E, registered in the
name of such Purchaser, pursuant to which such Purchaser shall have the right to
acquire shares of Common Stock upon the terms set forth therein (collectively,
the "Class B Warrants" and together with the Class A Warrants, the "Warrants"),
(4) the legal opinion of Latham & Watkins, outside counsel to the Company,
substantially in the form of Exhibit C, and (5) all other documents, instruments
and writings required to be delivered at or prior to the Closing by the Company
pursuant to this Agreement, including an executed Registration Rights Agreement,
dated the date hereof,


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among the Company and the Purchasers, in the form of Exhibit B (the
"Registration Rights Agreement"), the Transfer Agent Instructions, in the form
of Exhibit F, delivered to and acknowledged by the Company's transfer agent (the
"Transfer Agent Instructions") and the Letter Agreement, dated the date hereof,
among the Purchasers and the Company in the form of Exhibit G (the "Letter
Agreement"); and (B) each Purchaser shall deliver to the Company (1) the
purchase price indicated below such Purchaser's name on the signature page to
this Agreement in United States dollars in immediately available funds by wire
transfer to an account designated for such purpose prior to the Closing Date in
writing by the Company, and (2) all documents, instruments and writings required
to have been delivered at or prior to the Closing Date by such Purchaser
pursuant to this Agreement, including an executed Registration Rights Agreement
and Letter Agreement.

                  1.2 Certain Defined Terms. For purposes of this Agreement,
"Conversion Price," "Original Issue Date" and "Trading Day" shall have the
meanings set forth in the Debentures; "Business Day" shall mean any day except
Saturday, Sunday and any day which shall be a federal legal holiday or a day on
which banking institutions in the State of New York and the State of California
generally are authorized or required by law or other governmental action to
close. A "Person" means an individual or corporation, partnership, trust,
incorporated or unincorporated association, joint venture, limited liability
company, joint stock company, government (or an agency or subdivision thereof)
or other entity of any kind.


                                   ARTICLE II
                         REPRESENTATIONS AND WARRANTIES

         2.1 Representations and Warranties of the Company. The Company hereby
makes the following representations and warranties to the Purchasers:

                  (a) Organization and Qualification. The Company is a
corporation duly incorporated, validly existing and in good standing under the
laws of the State of Delaware with the requisite corporate power and authority
to own and use its properties and assets and to carry on its business as
currently conducted. The Company has no subsidiaries other than as set forth in
Schedule 2.1(a) (collectively the "Subsidiaries"). Each of the Subsidiaries is
an entity, duly organized, validly existing and in good standing under the laws
of the jurisdiction of its incorporation or organization (as applicable), with
the requisite corporate power and authority to own and use its properties and
assets and to carry on its business as currently conducted. Each of the Company
and the Subsidiaries is duly qualified to do business and is in good standing as
a foreign corporation or other entity in each jurisdiction in which the nature
of the business conducted or property owned by it makes such qualification
necessary, except where the failure to be so qualified or in good standing, as
the case may be, could not, individually or in the aggregate, (x) adversely
affect the legality, validity or enforceability of the Securities (as defined
below) or any of this Agreement, the Registration Rights Agreement, the Letter
Agreement, the Transfer Agent Instructions, the Debentures or the Warrants
(collectively, the "Transaction Documents"), (y) have or result in a material
adverse effect on the results of operations, assets, prospects, or condition
(financial or otherwise) of the Company and the Subsidiaries, taken as a whole,
or (z) adversely impair the Company's ability to perform fully on a timely basis
its obligations under any of the Transaction Documents (any of (x), (y) or (z),
a "Material Adverse Effect").
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                  (b) Authorization; Enforcement. The Company has the requisite
corporate power and authority to enter into and to consummate the transactions
contemplated by each of the Transaction Documents and otherwise to carry out its
obligations thereunder. The execution and delivery of each of the Transaction
Documents by the Company and the consummation by it of the transactions
contemplated thereby have been duly authorized by all necessary corporate action
on the part of the Company and no further action is required by the Company.
Each of the Transaction Documents has been duly executed by the Company and,
when delivered (or filed, as the case may be) in accordance with the terms
hereof, will constitute the valid and binding obligation of the Company
enforceable against the Company in accordance with its terms. Neither the
Company nor any Subsidiary is in violation of any of the provisions of its
respective certificate of incorporation, by-laws or other charter or
organizational documents.

                  (c) Capitalization. The number of authorized, issued and
outstanding capital stock of the Company is set forth in Schedule 2.1(c). Except
as disclosed in Schedule 2.1(c), the Company owns all of the capital stock of
each Subsidiary. No securities of the Company or any Subsidiary are entitled to
preemptive or similar rights, nor is any holder of securities of the Company or
any Subsidiary entitled to preemptive or similar rights arising out of any
agreement or understanding with the Company or any Subsidiary by virtue of any
of the Transaction Documents. Except as disclosed in Schedule 2.1(c), there are
no outstanding options, warrants, script rights to subscribe to, calls or
commitments of any character whatsoever relating to, or securities, except as a
result of the purchase and sale of the Securities or rights or obligations
convertible into or exchangeable for, or giving any Person any right to
subscribe for or acquire, any shares of Common Stock, or contracts, commitments,
understandings, or arrangements by which the Company or any Subsidiary is or may
become bound to issue additional shares of Common Stock, or securities or rights
convertible or exchangeable into shares of Common Stock. To the knowledge of the
Company, except as specifically disclosed in the SEC Reports (as defined below)
or Schedule 2.1(c), no Person or group of related Persons beneficially owns (as
determined pursuant to Rule 13d-3 promulgated under the Securities Exchange Act
of 1934, as amended (the "Exchange Act")), or has the right to acquire by
agreement with or by obligation binding upon the Company, beneficial ownership
of in excess of 5% of the Common Stock.

                  (d) Issuance of the Securities. The Securities are duly
authorized and, when issued and paid for in accordance with the terms hereof,
will be duly and validly issued, fully paid and nonassessable, free and clear of
all liens, encumbrances and rights of first refusal of any kind (collectively,
"Liens"). The Company has reserved a number of duly authorized number of shares
of Common Stock for issuance hereunder upon conversion of the Debentures and
exercise of the Warrants that is not less than the sum of (i) 200% of the number
of shares of Common Stock which would be issuable upon conversion in full of the
Debentures, assuming such conversion occurred at the Conversion Price (as
defined in the Debenture) in effect on the Original Issue Date, the Debentures
remain outstanding for five years and all interest is paid in shares of Common
Stock and (ii) the maximum number of shares of Common Stock issuable upon
exercise in full of the Warrants and, in the case of the Class A Warrants,
assuming the maximum amount of Warrant Shares (as defined in the Warrants) has
vested thereunder (such number of shares of Common Stock as contemplated in
clauses (i)-(ii), the "Initial Minimum"). The shares of Common Stock issuable
upon conversion of the Debentures and upon exercise of the Warrants are referred
to herein as the "Underlying Shares." The Debentures, the Warrants and the
Underlying Shares are collectively referred to herein as, the "Securities."

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                  (e) No Conflicts. The execution, delivery and performance of
the Transaction Documents by the Company and the consummation by the Company of
the transactions contemplated thereby do not and will not (i) conflict with or
violate any provision of the Company's or any Subsidiary's certificate of
incorporation, bylaws or other charter documents (each as amended through the
date hereof), or (ii) subject to obtaining the Required Approvals (as defined
below), conflict with, or constitute a default (or an event which with notice or
lapse of time or both would become a default) under, or give to others any
rights of termination, amendment, acceleration or cancellation (with or without
notice, lapse of time or both) of, any agreement, credit facility, debt or other
instrument (evidencing a Company or Subsidiary debt or otherwise) or other
understanding to which the Company or any Subsidiary is a party or by which any
property or asset of the Company or any Subsidiary is bound or affected, or
(iii) result in a violation of any law, rule, regulation, order, judgment,
injunction, decree or other restriction of any court or governmental authority
to which the Company or a Subsidiary is subject (including federal and state
securities laws and regulations), or by which any property or asset of the
Company or a Subsidiary is bound or affected; except in the case of each of
clauses (ii) and (iii), as could not, individually or in the aggregate, have or
result in a Material Adverse Effect. The business of the Company is not being
conducted in violation of any law, ordinance or regulation of any governmental
authority, except for violations which, individually or in the aggregate, could
not have or result in a Material Adverse Effect.

                  (f) Filings, Consents and Approvals. Neither the Company nor
any Subsidiary is required to obtain any consent, waiver, authorization or order
of, give any notice to, or make any filing or registration with, any court or
other federal, state, local or other governmental authority or other Person in
connection with the execution, delivery and performance by the Company of the
Transaction Documents, other than (i) the filings required pursuant to Section
3.10, (ii) the filing with the Securities and Exchange Commission (the
"Commission") of one or more registration statements meeting the requirements
set forth in the Registration Rights Agreement and covering the resale of the
Underlying Shares by the Purchasers (collectively, the "Underlying Shares
Registration Statement"), (iii) the application(s) to the Nasdaq National Market
("NASDAQ") for the listing of the Underlying Shares with the NASDAQ (and with
any other national securities exchange of market in which the Common Stock is
then listed) in the time and manner required thereby , (vi) applicable Blue Sky
filings, and (v) in all other cases where the failure to obtain such consent,
waiver, authorization or order, or to give such notice or make such filing or
registration could not have or result in, individually or in the aggregate, a
Material Adverse Effect (the items described in clauses (i)-(vi) are
collectively, the "Required Approvals").

                  (g) Litigation; Proceedings. Except as specified in the SEC
Reports or Schedule 2.1(g), there is no action, suit, notice of violation,
proceeding or investigation pending or, to the knowledge of the Company,
threatened against or affecting the Company or any of its Subsidiaries or any of
their respective properties before or by any court, governmental or
administrative agency or regulatory authority (federal, state, county, local or
foreign) which (i) adversely affects or challenges the legality, validity or
enforceability of any of the Transaction Documents or the Securities or (ii)
could, individually or in the aggregate, have or result in a Material Adverse
Effect.

                  (h) No Default or Violation. Neither the Company nor any
Subsidiary (i) is in default under or in violation of (and no event has occurred
which has not been waived which, with notice or lapse of time or both, would
result in a default by the Company or any Subsidiary under),

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nor has the Company or any Subsidiary received notice of a claim that it is in
default under or that it is in violation of, any indenture, loan or credit
agreement or any other agreement or instrument to which it is a party or by
which it or any of its properties is bound (whether or not such default or
violation has been waived), (ii) is in violation of any order of any court,
arbitrator or governmental body, or (iii) is in violation of any statute, rule
or regulation of any governmental authority, except as could not individually or
in the aggregate, have or result in a Material Adverse Effect.

                  (i) Private Offering. Assuming the accuracy of the
representations and warranties of the Purchasers set forth in Sections
2.2(b)-(g), the offer, issuance and sale of the Securities to the Purchasers as
contemplated hereby are exempt from the registration requirements of the
Securities Act of 1933, as amended (the "Securities Act"). Neither the Company
nor any Person acting on its behalf has taken or is, to the knowledge of the
Company, contemplating taking any action which could subject the offering,
issuance or sale of the Securities to the registration requirements of the
Securities Act including soliciting any offer to buy or sell the Securities by
means of any form of general solicitation or advertising.

                  (j) SEC Reports; Financial Statements. The Company has filed
all reports required to be filed by it under the Securities Act of 1933, as
amended (the "Securities Act"), and the Exchange Act for the two years preceding
the date hereof (or such shorter period as the Company was required by law to
file such material) (the foregoing materials being collectively referred to
herein as the "SEC Reports" and, together with the Schedules to this Agreement
the "Disclosure Materials") on a timely basis or has received a valid extension
of such time of filing and has filed any such SEC Reports prior to the
expiration of any such extension. As of their respective dates, the SEC Reports
complied in all material respects with the requirements of the Securities Act
and the Exchange Act and the rules and regulations of the Commission promulgated
thereunder, and none of the SEC Reports, when filed, contained any untrue
statement of a material fact or omitted to state a material fact required to be
stated therein or necessary in order to make the statements therein, in light of
the circumstances under which they were made, not misleading. All material
agreements to which the Company is a party or to which the property or assets of
the Company are subject have been filed as exhibits to the SEC Reports. The
financial statements of the Company included in the SEC Reports comply in all
material respects with applicable accounting requirements and the rules and
regulations of the Commission with respect thereto as in effect at the time of
filing. Such financial statements have been prepared in accordance with
generally accepted accounting principles applied on a consistent basis during
the periods involved ("GAAP"), except as may be otherwise specified in such
financial statements or the notes thereto, and fairly present in all material
respects the financial position of the Company and its consolidated subsidiaries
as of and for the dates thereof and the results of operations and cash flows for
the periods then ended, subject, in the case of unaudited statements, to normal,
immaterial, year-end audit adjustments. Since September 30, 1999, except as
specifically disclosed in the SEC Reports, (a) there has been no event,
occurrence or development that has or that could result in a Material Adverse
Effect, (b) the Company has not incurred any liabilities (contingent or
otherwise) other than (x) liabilities incurred in the ordinary course of
business consistent with past practice and (y) liabilities not required to be
reflected in the Company's financial statements pursuant to GAAP or required to
be disclosed in filings made with the Commission, (c) the Company has not
altered its method of accounting or the identity of its auditors and (d) the
Company has not declared or made any payment or distribution of cash or other
property to its stockholders or officers or directors (other than in compliance
with existing Company stock or stock option plans and existing agreements and
terms of employment) with respect to its

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capital stock, or purchased, redeemed (or made any agreements to purchase or
redeem) any shares of its capital stock.

                  (k) Investment Company. The Company is not, and is not an
Affiliate (as defined in Rule 405 under the Securities Act) of, an "investment
company" within the meaning of the Investment Company Act of 1940, as amended.

                  (l) Certain Fees. Except as are payable to Brighton Capital,
Ltd. by the Company, no fees or commissions will be payable by the Company to
any broker, financial advisor or consultant, finder, placement agent, investment
banker, bank or other person, with respect to the transactions contemplated by
this Agreement. The Purchasers shall have no obligation with respect to any fees
or with respect to any claims made by or on behalf of other Persons for fees of
a type contemplated in this Section that may be due in connection with the
transactions contemplated by this Agreement. The Company shall indemnify and
hold harmless the Purchasers, their employees, officers, directors, agents, and
partners, and its respective Affiliates, from and against all claims, losses,
damages, costs (including the costs of preparation and attorney's fees) and
expenses suffered in respect of any such claimed or existing fees, as such fees
and expenses are incurred.

                  (m) Form S-3 Eligibility. The Company is eligible to register
its Common Stock for resale under Form S-3 promulgated under the Securities Act.

                  (n) Seniority. Other than as set forth in Schedule 2.1(n), no
indebtedness of the Company is senior to the Debentures in right of payment,
whether with respect to interest or upon liquidation or dissolution, or
otherwise.

                  (o) Listing and Maintenance Requirements. The Company has not,
in the two years preceding the date hereof received notice (written or oral)
from the NASDAQ or any other stock exchange, market or trading facility on which
the Common Stock is or has been listed (or on which it has been quoted) to the
effect that the Company is not in compliance with the listing or maintenance
requirements of such exchange, market or trading facility. The Company is, and
has no reason to believe that it will not in the foreseeable future continue to
be, in compliance with all such listing and maintenance requirements.

                  (p) Patents and Trademarks. The Company and its Subsidiaries
have, or have rights to use, all patents, patent applications, trademarks,
trademark applications, service marks, trade names, copyrights, licenses and
rights (collectively, the "Intellectual Property Rights") which are necessary or
material for use in connection with their respective business as described in
the SEC Reports and as contemplated to be conducted, and which the failure to so
have would have a Material Adverse Effect. Neither the Company nor any
Subsidiary has received a written notice that the Intellectual Property Rights
used by the Company or its Subsidiaries violates or infringes upon the rights of
any Person, to the best knowledge of the Company. All such Intellectual Property
Rights are enforceable and there is no existing infringement by another Person
of any of the Intellectual Property Rights.

                  (q) Regulatory Permits. The Company and its Subsidiaries
possess all certificates, authorizations and permits issued by the appropriate
federal, state or foreign regulatory authorities necessary to conduct their
respective businesses as described in the SEC Reports, except


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where the failure to possess such permits could not, individually or in the
aggregate, have or result in a Material Adverse Effect ("Material Permits"), and
neither the Company nor any such Subsidiary has received any notice of
proceedings relating to the revocation or modification of any Material Permit.

                  (r) Title. Except as set forth in Schedule 2.1(r), the Company
and the Subsidiaries have good and marketable title in fee simple to all real
property and personal property owned by them which is material to the business
of the Company and its Subsidiaries, in each case free and clear of all Liens,
except for Liens as do not materially affect the value of such property and do
not materially interfere with the use made and proposed to be made of such
property by the Company and its Subsidiaries. Any real property and facilities
held under lease by the Company and its Subsidiaries are held by them under
valid, subsisting and enforceable leases with such exceptions as are not
material and do not materially interfere with the use made and proposed to be
made of such property and buildings by the Company and its Subsidiaries.

                  (s) Disclosure. The Company confirms that it has not provided
the Purchasers or their agents or counsel with any information that constitutes
or might constitute material non-public information. The Company understands and
confirms that the Purchasers shall be relying on the foregoing representations
in effecting transactions in securities of the Company. All disclosure provided
to the Purchasers regarding the Company, its business and the transactions
contemplated hereby, including the Schedules to this Agreement, furnished by or
on behalf of the Company are true and correct and do not contain any untrue
statement of a material fact or omit to state any material fact required to be
stated therein or necessary in order to make the statements therein, in light of
the circumstances under which they were made, not misleading.

         2.2 Representations and Warranties of the Purchasers. Each Purchaser
hereby for itself and for no other Purchaser, represents and warrants to the
Company as follows:

                  (a) Organization; Authority. Such Purchaser is an entity duly
organized, validly existing and in good standing under the laws of the
jurisdiction of its organization with the requisite corporate or partnership
power and authority to enter into and to consummate the transactions
contemplated by the Transaction Documents and otherwise to carry out its
obligations thereunder. The purchase by such Purchaser of the Securities
hereunder has been duly authorized by all necessary action on the part of such
Purchaser. Each of this Agreement, the Letter Agreement and the Registration
Rights Agreement has been duly executed by such Purchaser, and when delivered by
such Purchaser in accordance with the terms hereof, will constitute the valid
and legally binding obligation of such Purchaser, enforceable against it in
accordance with its terms.

                  (b) Investment Intent. Such Purchaser is acquiring the
Securities as principal for its own account for investment purposes only and not
with a view to or for distributing or reselling the Securities or any part
thereof. Such Purchaser has no present intention of selling or granting any
participation in, or otherwise distributing the Securities. Such Purchaser is
not party to any agreement or arrangement with any person to distribute any of
the Securities.

                  (c) Purchaser Status. At the time such Purchaser was offered
the Securities, it was, and at the date hereof it is, a "Qualified Institutional
Buyer" as defined in Rule 144A under the

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<PAGE>   9
Securities Act. Such Purchaser has not been formed solely for the purpose of
acquiring the Securities

                  (d) Experience of such Purchaser. Such Purchaser, either alone
or together with its representatives, has such knowledge, sophistication and
experience in business and financial matters so as to be capable of evaluating
the merits and risks of the prospective investment in the Securities, and has so
evaluated the merits and risks of such investment.

                  (e) Ability of such Purchaser to Bear Risk of Investment. Such
Purchaser is able to bear the economic risk of an investment in the Securities
and, at the present time, is able to afford a complete loss of such investment.

                  (f) Access to Information. Such Purchaser acknowledges that it
has reviewed the Disclosure Materials and has been afforded (i) the opportunity
to ask such questions as it has deemed necessary of, and to receive answers
from, representatives of the Company concerning the terms and conditions of the
offering of the Securities and the merits and risks of investing in the
Securities; (ii) access to information about the Company and the Company's
financial condition, results of operations, business, properties, management and
prospects sufficient to enable it to evaluate its investment; and (iii) the
opportunity to obtain such additional information which the Company possesses or
can acquire without unreasonable effort or expense that is necessary to make an
informed investment decision with respect to the investment. Neither such
inquiries nor any other investigation conducted by or on behalf of any Purchaser
or its representatives or counsel shall modify, amend or affect a Purchaser's
right to rely on the truth, accuracy and completeness of the Disclosure
Materials and the Company's representations and warranties contained in the
Transaction Documents.

                  (g) General Solicitation. Such Purchaser is not purchasing the
Securities as a result of or subsequent to any advertisement, article, notice or
other communication regarding the Securities published in any newspaper,
magazine or similar media or broadcast over television or radio or presented at
any seminar or any other general solicitation or general advertisement.

                  (h) Reliance. Such Purchaser understands and acknowledges that
(i) the Securities are being offered and sold to it without registration under
the Securities Act in a private placement that is exempt from the registration
provisions of the Securities Act and (ii) the availability of such exemption,
depends in part on, and the Company will rely upon the accuracy and truthfulness
of, the foregoing representations and such Purchaser hereby consents to such
reliance.

                  The Company acknowledges and agrees that no Purchaser makes or
has made any representations or warranties with respect to the transactions
contemplated hereby other than those specifically set forth in this Section 2.2.

                                   ARTICLE III
                         OTHER AGREEMENTS OF THE PARTIES

         3.1 Transfer Restrictions. (a) Securities may only be disposed of
pursuant to an effective registration statement under the Securities Act, to the
Company or pursuant to an available exemption from or in a transaction not
subject to the registration requirements of the Securities Act,

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and in compliance with any applicable federal and state securities laws. In
connection with any transfer of Securities other than pursuant to an effective
registration statement or to the Company, except as otherwise set forth herein,
the Company may require the transferor thereof to provide to the Company an
opinion of counsel selected by the transferor, the form and substance of which
opinion shall be reasonably satisfactory to the Company, to the effect that such
transfer does not require registration under the Securities Act. Notwithstanding
the foregoing, the Company, without requiring a legal opinion as described in
the immediately preceding sentence, hereby consents to and agrees to register on
the books of the Company and with any transfer agent for the securities of the
Company any transfer of Securities by a Purchaser to an Affiliate of such
Purchaser or to one or more funds or managed accounts under common management
with such Purchaser, and any transfer among any such Affiliates or one or more
funds or managed accounts, provided (i) that the transferee certifies to the
Company that it is an "accredited investor" within the meaning of Rule 501(a)
under the Securities Act, (ii) that it is acquiring the Securities solely for
investment purposes (subject to the qualifications hereof), and (iii) that any
such transferee shall agree in writing to be bound by the terms of this
Agreement and shall have the rights of the Purchaser under this Agreement and
the Registration Rights Agreement.

                  (b) The Purchasers agree to the imprinting, so long as is
required by this Section 3.1(b), of the following legend on the Securities:

                  NEITHER THESE SECURITIES NOR THE SECURITIES INTO WHICH THESE
         SECURITIES ARE [CONVERTIBLE] [EXERCISABLE] HAVE BEEN REGISTERED WITH
         THE SECURITIES AND EXCHANGE COMMISSION OR THE SECURITIES COMMISSION OF
         ANY STATE IN RELIANCE UPON AN EXEMPTION FROM REGISTRATION UNDER THE
         SECURITIES ACT OF 1933, AS AMENDED (THE "SECURITIES ACT"), AND,
         ACCORDINGLY, MAY NOT BE OFFERED OR SOLD EXCEPT PURSUANT TO AN EFFECTIVE
         REGISTRATION STATEMENT UNDER THE SECURITIES ACT OR PURSUANT TO AN
         AVAILABLE EXEMPTION FROM, OR IN A TRANSACTION NOT SUBJECT TO, THE
         REGISTRATION REQUIREMENTS OF THE SECURITIES ACT AND IN ACCORDANCE WITH
         APPLICABLE STATE SECURITIES LAWS.

                  Underlying Shares shall not contain the legend set forth above
nor any other legend at any time while an Underlying Shares Registration
Statement covering such Underlying Shares is effective under the Securities Act
or, in the event there is not an effective Registration Statement, covering such
Underlying Shares at such time if such legend is not required under applicable
requirements of the Securities Act (including judicial interpretations and
pronouncements issued by the staff of the Commission). The Company shall cause
its counsel to issue the legal opinion included in the Transfer Agent
Instructions to the Company's transfer agent on the day that such Underlying
Shares Registration Statement is declared effective by the Commission (the
"Effective Date"). The Company agrees that with respect to any Underlying Shares
that are issued with a legend in accordance with this Section 3.1(b), it will,
within three (3) Trading Days after request therefor by a Purchaser and the
surrender by such Purchaser of the certificate representing the applicable
Underlying Shares, provide such Purchaser with a certificate or certificates
representing such Underlying Shares, free from such legend at such time as such
legend would not have been required under this Section 3.1(b) had such issuance
occurred on the date of such request. The Company may not make any notation on
its records or give instructions to any transfer agent of the Company which


                                      -9-
<PAGE>   11
enlarge the restrictions of transfer set forth in this Section. Each Purchaser
will comply with the prospectus delivery requirements of the Securities Act as
applicable to it in connection with sales of Registrable Securities (as defined
in the Registration Rights Agreement) pursuant to an Underlying Shares
Registration Statement.

         3.2 Acknowledgment of Dilution. The Company acknowledges that the
issuance of the Underlying Shares upon (i) conversion of the Debentures in
accordance with the terms of the Debentures, and (ii) exercise of the Warrants
in accordance with their terms, will result in dilution of the outstanding
shares of Common Stock, which dilution may be substantial under certain market
conditions. The Company further acknowledges that its obligation to issue
Underlying Shares upon (x) conversion of the Debentures in accordance with the
terms of the Debentures, and (y) exercise of the Warrants in accordance with
their terms, is unconditional and absolute, subject to the limitations set forth
herein in the Debentures or pursuant to the Warrants, regardless of the effect
of any such dilution.

         3.3 Furnishing of Information. As long as the Purchasers own
Securities, the Company covenants to file timely (or obtain extensions in
respect thereof and file within the applicable grace period) all reports
required to be filed by the Company after the date hereof pursuant to the
Exchange Act. So long as the Purchasers own Securities, if the Company is not
required to file reports pursuant to such laws, it will prepare and furnish to
the Purchasers and make publicly available in accordance with Rule 144(c)
promulgated under the Securities Act such information as is required for the
Purchasers to sell the Securities under Rule 144 promulgated under the
Securities Act. The Company further covenants that it will take such further
action as any holder of Securities may reasonably request, all to the extent
required from time to time to enable such Person to sell Underlying Shares
without registration under the Securities Act within the limitation of the
exemptions provided by Rule 144 promulgated under the Securities Act, including
the legal opinion referenced above in this Section. Upon the request of any such
Person, the Company shall deliver to such Person a written certification of a
duly authorized officer as to whether it has complied with such requirements.

         3.4 Integration. The Company shall not, and shall use its best efforts
to ensure that, no Affiliate shall, sell, offer for sale or solicit offers to
buy or otherwise negotiate in respect of any security (as defined in Section 2
of the Securities Act) that would be integrated with the offer or sale of the
Securities in a manner that would require the registration under the Securities
Act of the sale of the Securities to the Purchasers or that would be integrated
with the offer or sale of the Securities for purposes of the rules and
regulations of the Nasdaq Stock Market.

         3.5 Increase in Authorized Shares. If on any date the Company would be,
if a notice of conversion or exercise (as the case may be) were to be delivered
on such date, precluded from issuing (a) 200% of the number of Underlying Shares
as would then be issuable upon a conversion in full of the Debentures, and (b)
the number of Underlying Shares issuable upon exercise in full of the Warrants
(the "Current Required Minimum"), in either case, due to the unavailability of a
sufficient number of authorized but unissued or reserved shares of Common Stock,
then the Board of Directors of the Company shall promptly (and in any case,
within 60 Business Days from such date) prepare and mail to the stockholders of
the Company proxy materials requesting authorization to amend the Company's
certificate of incorporation to increase the number of shares of Common Stock
which the Company is authorized to issue to at least such number of shares as is
reasonably

                                      -10-
<PAGE>   12
adequate to enable the Company to comply with its issuance, conversion, exercise
and reservation of shares obligations as set forth in this Agreement, the
Debentures and the Warrants (the sum of (x) the number of shares of Common Stock
then outstanding plus all shares of Common Stock issuable upon exercise of all
outstanding options, warrants and convertible instruments, and (y) the Current
Required Minimum, shall be a reasonable number). In connection therewith, the
Board of Directors shall (a) adopt proper resolutions authorizing such increase,
(b) recommend to and otherwise use its best efforts to promptly and duly obtain
stockholder approval to carry out such resolutions (and hold a special meeting
of the stockholders no later than the earlier to occur of the 60th day after
delivery of the proxy materials relating to such meeting and the 90th day after
request by a holder of Securities to issue the number of Underlying Shares in
accordance with the terms hereof) and (c) within five Business Days of obtaining
such stockholder authorization, file an appropriate amendment to the Company's
certificate of incorporation to evidence such increase.

         3.6 Reservation and Listing of Underlying Shares. (a) The Company shall
(i) in the time and manner required by the NASDAQ and such other national
securities exchange or, market or trading or quotation facility on which the
Common Stock is then listed for trading, prepare and file with the NASDAQ (and
such other national securities exchange or market or trading or quotation
facility on which the Common Stock is then listed for trading) an additional
shares listing application covering a number of shares of Common Stock which is
not less than the Initial Minimum, (ii) take all steps necessary to cause such
shares of Common Stock to be approved for listing in the NASDAQ (as well as on
any such other national securities exchange or market or trading or quotation
facility on which the Common Stock is then listed) as soon as possible
thereafter, and (iii) provide to the Purchasers evidence of such listing, and
the Company shall maintain the listing of its Common Stock thereon. If the
number of Underlying Shares issuable upon conversion in full of the then
outstanding Debentures and upon exercise of the then unexercised portion of the
Warrants exceeds 85% of the number of Underlying Shares previously listed on
account thereof with NASDAQ (and any such other required exchanges), then the
Company shall take the necessary actions to list immediately a number of
Underlying Shares as equals no less than the then Current Required Minimum with
respect thereto.

                  (b) The Company shall maintain a reserve of shares of Common
Stock for issuance upon conversion of the Debentures in full and upon exercise
in full of the Warrants in accordance with this Agreement, the Debentures and
the Warrants, respectively, in such amount as may be required to fulfill its
obligations in full under the Transaction Documents, which reserve shall equal
no less than the then Current Required Minimum.

         3.7 Conversion and Exercise Procedures. The Transfer Agent
Instructions, Conversion Notice (as defined in the Debentures) and Notice of
Exercise under the Warrants set forth the totality of the procedures with
respect to the conversion of the Debentures and exercise of the Warrants,
including the form of legal opinion, if necessary, that shall be rendered to the
Company's transfer agent and such other information and instructions as may be
reasonably necessary to enable the Purchasers to convert their Debentures and
exercise their Warrants as contemplated in the Debentures and the Warrants (as
applicable).

         3.8 Notice of Breaches. Each of the Company and the Purchasers shall
give prompt written notice to the other of any breach by it of any
representation, warranty or other agreement contained in any Transaction
Document, as well as any events or occurrences arising after the date

                                      -11-
<PAGE>   13
hereof which would reasonably be likely to cause any representation or warranty
or other agreement of such party, as the case may be, contained therein to be
incorrect or breached as of the Closing Date. However, no disclosure by a party
pursuant to this Section shall be deemed to cure any breach of any
representation, warranty or other agreement contained in any Transaction
Document.

         3.9 Right of First Refusal; Subsequent Registrations. (a) The Company
shall not, directly or indirectly, without the prior written consent of the
Purchasers (which shall not be unreasonably withheld), offer, sell, grant any
option to purchase, or otherwise dispose of (or announce any offer, sale, grant
or any option to purchase or other disposition) any of its or its Affiliates'
equity or equity-equivalent securities in a transaction intended to be exempt or
not subject to registration under the Securities Act (a "Subsequent Placement")
until the 310th day after the Closing Date (the "Threshold Date"), except (i)
the granting of options or warrants to employees, officers, directors,
consultants and other service providers , and the issuance of shares upon
exercise of options granted, under any stock option plan heretofore or
hereinafter duly adopted by the Company, (ii) shares of Common Stock issuable
upon exercise of currently outstanding options and warrants and upon conversion
of any currently outstanding convertible securities of the Company and , in each
case to the extent disclosed in Schedule 2.1(c) but not with respect to any
amendment or modification thereof, and convertible securities issued in
compliance with this Section 3.9(a), (iii) shares of Common Stock issuable upon
conversion of the Debentures and exercise of the Warrants in accordance with the
terms thereof, (iv) shares of Common Stock issuable in connection with a
Strategic Transaction (as defined below), (v) an underwritten public offering of
the Common Stock resulting in net proceeds to the Company in excess of
$10,000,000, (vi) warrants issuable to Brighton Capital, Ltd. in connection with
this transaction and the issuance of shares upon exercise thereof, (vii)
warrants to be issued by the Company to Kingsbridge Capital Limited to purchase
25,000 shares of Common Stock and the issuance of shares upon exercise thereof,
(viii) the granting of warrants to purchase up to 10,000 shares of Common Stock
in connection with equipment leasing or other debt financing transactions and
(ix) a single issuance of shares of Common Stock, at a discount of up to 10% of
the market price of the Common Stock at the time of such issuance and, in
connection therewith, the issuance of warrants to purchase Common Stock at a
price no less than 10% of the market price of the Common Stock at the time of
such issuance and the issuance of shares of Common Stock or warrants to purchase
Common Stock as payment of any placement fee, unless (A) the Company delivers to
each Purchaser a written notice (the "Subsequent Placement Notice") of its
intention to effect such Subsequent Placement, which Subsequent Placement Notice
shall describe in reasonable detail the proposed terms of such Subsequent
Placement, the amount of proceeds intended to be raised thereunder, the Person
with whom such Subsequent Placement shall be effected, and attached to which
shall be a term sheet or similar document relating thereto and (B) such
Purchaser shall not have notified the Company by 5:30 p.m. (New York City time)
on the second (2nd) Trading Day after its receipt of the Subsequent Placement
Notice of its willingness to cause such Purchaser to provide (or to cause its
sole designee to provide), subject to completion of mutually acceptable
documentation, financing to the Company on the same terms set forth in the
Subsequent Placement Notice. If the Purchasers shall fail to notify the Company
of their intention to enter into such negotiations within such time period, the
Company may effect the Subsequent Placement substantially upon the terms and to
the Persons (or Affiliates of such Persons) set forth in the Subsequent
Placement Notice; provided, that the Company shall provide the Purchasers with a
second Subsequent Placement Notice, and the Purchasers shall again have the
right of first refusal set forth above in this Section (a), if the Subsequent
Placement subject to the initial Subsequent Placement Notice shall not have been
consummated for any reason substantially on the terms set

                                      -12-
<PAGE>   14
forth in such Subsequent Placement Notice within thirty (30) Trading Days after
the date of the initial Subsequent Placement Notice with the Person (or an
Affiliate of such Person) identified in the Subsequent Placement Notice. The
rights of the Purchasers under this Section shall apply to each Subsequent
Placement contemplated by the Company or such Subsidiary, regardless of any
prior waivers or non-participation. If the Purchasers shall indicate a
willingness to provide financing in excess of the amount set forth in the
Subsequent Placement Notice, then each Purchaser shall be entitled to provide
financing pursuant to such Subsequent Placement Notice up to an amount equal to
such Purchaser's pro rata portion of the principal amount of Debentures
purchased by such Purchaser under this Agreement, but the Company shall not be
required to accept financing from the Purchasers in an amount less than or in
excess of the amount set forth in the Subsequent Placement Notice. For purposes
of this Section 3.9, a "Strategic Transaction" shall mean a transaction or
relationship in which the Company issues shares of Common Stock to an entity
which is, itself or through its subsidiaries, an operating company in a business
related to the business of the Company and in which the Company receives
material benefits in addition to the investment of funds, but shall not include
a transaction in which the Company is issuing securities primarily for the
purpose of raising capital or to an entity whose primary business is investing
in securities (such entity, a "Strategic Partner").

                  (b) Except for (x) Underlying Shares, (y) other "Registrable
Securities" (as such term is defined in the Registration Rights Agreement) to be
registered, and securities of the Company as set forth in Schedule 6(b) of the
Registration's Rights Agreement to be registered, in the Underlying Shares
Registration Statement in accordance with the Registration Rights Agreement, and
(z) Common Stock permitted to be issued pursuant to paragraph (a)(i) - (ix) of
Section 3.9 (a), the Company shall not, for a period of not less than 90 Trading
Days after the Effective Date, without the prior written consent of the
Purchasers (i) issue or sell any of its or any of its Affiliates' equity or
equity-equivalent securities pursuant to Regulation S promulgated under the
Securities Act, or (ii) file a registration statement for the issuance or resale
of any securities of the Company. Any days that a Purchaser, by action of the
Company or the Commission, is not permitted or unable to utilize the prospectus
or otherwise to sell Underlying Shares under the Underlying Shares Registration
Statement shall be added to such 90 Trading Day period for the purposes of this
Section.

                  (c) The rights of first refusal and limitations on
registration set forth in Sections 3.9(a) and (b) are intended to supercede and
replace any and all similar rights or limitations currently held by the
Purchasers and all such rights and limitations are hereby terminated.

         3.10 Certain Securities Laws Disclosures; Publicity. The Company shall:
(i) on the Closing Date, issue a press release acceptable to the Purchasers
disclosing the transactions contemplated hereby, (ii) file with the Commission a
Report on Form 8-K or Form 10-Q (as applicable) disclosing the transactions
contemplated hereby within ten (10) Business Days after the Closing Date, and
(iii) timely file with the Commission a Form D promulgated under the Securities
Act as required under Regulation D promulgated under the Securities Act and
provide a copy thereof to the Purchasers promptly after the filing thereof. The
Company shall, no less than two (2) Business Days prior to the filing of any
disclosure required by clauses (ii) and (iii) above, provide a copy thereof to
the Purchasers. The Company and the Purchasers shall consult with each other in
issuing any press releases or otherwise making public statements or filings and
other communications with the Commission or any regulatory agency or stock
market or trading facility

                                      -13-
<PAGE>   15
with respect to the transactions contemplated hereby and neither party shall
issue any such press release or otherwise make any such public statement,
filings or other communications pertaining to the transactions contemplated
hereby without the prior written consent of the other, which consent shall not
be unreasonably withheld or delayed, except that no prior consent shall be
required if such disclosure is required by law or such consent can not
reasonably be expected to be received prior to the time required to complete
such filing or make such statement in accordance with such applicable law, in
which such case the disclosing party shall provide the other party with prior
notice of such public statement, filing or other communication. Notwithstanding
the foregoing, the Company shall not publicly disclose the name of a Purchaser,
or include the name of a Purchaser in any filing with the Commission, or any
regulatory agency, trading facility or stock market without the prior written
consent of such Purchaser, except to the extent such disclosure is required by
law, in which case the Company shall provide such Purchaser with prior notice of
such disclosure.

         3.11 Transfer of Intellectual Property Rights. Except in connection
with the sale of all or substantially all of the assets of the Company, prior to
the 180th day after the Effective Date the Company shall not sell or otherwise
dispose of any Intellectual Property Rights or allow any of the Intellectual
Property Rights to become subject to any Liens, or fail to renew such
Intellectual Property Rights (if renewable and it would otherwise lapse if not
renewed), without the prior written consent of the Purchasers. Notwithstanding
the foregoing, the Company may license the right to promote and use its
Intellectual Property Rights to Strategic Partners in the ordinary course of its
business without the prior consent of the Purchasers.

         3.12 Use of Proceeds. The Company shall use the net proceeds from the
sale of Securities hereunder for working capital purposes and not to redeem any
Company equity or equity-equivalent securities, except as may be expressly
permitted by the Transaction Documents. Pending application of the proceeds of
this placement in the manner permitted hereby, the Company will invest such
proceeds in interest bearing accounts and/or short-term, investment grade
interest bearing securities.

         3.13 Reimbursement. If any Purchaser, other than by reason of its gross
negligence or willful misconduct, becomes involved in any capacity in any
action, proceeding or investigation brought by or against any Person, including
stockholders of the Company, in connection with or as a result of the
consummation of the transactions contemplated by Transaction Documents, the
Company will reimburse such Purchaser for its reasonable legal and other
expenses (including the cost of any investigation and preparation and travel in
connection therewith) incurred in connection therewith, as such expenses are
incurred. In addition, other than with respect to any matter in which any of the
Purchasers is a named party, the Company will pay such Purchaser the charges, as
reasonably determined by such Purchaser, for the time of any officers or
employees of such Purchaser devoted to appearing and preparing to appear as
witnesses, assisting in preparation for hearings, trials or pretrial matters, or
otherwise with respect to inquiries, hearings, trials, and other proceedings
relating to the subject matter of this Agreement. The reimbursement obligations
of the Company under this paragraph shall be in addition to any liability which
the Company may otherwise have, shall extend upon the same terms and conditions
to any Affiliates of the Purchasers who are actually named in such action,
proceeding or investigation, and partners, directors, agents, employees and
controlling persons (if any), as the case may be, of the Purchasers and any such
Affiliate, and shall be binding upon and inure to the benefit of any successors,
assigns, heirs and personal representatives of the Company, the Purchasers and
any such Affiliate and any such Person. The Company also agrees that neither the
Purchasers nor any such Affiliates, partners, directors,

                                      -14-
<PAGE>   16
agents, employees or controlling persons shall have any liability to the Company
or any Person asserting claims on behalf of or in right of the Company in
connection with or as a result of the consummation of the Transaction Documents
except to the extent that any losses, claims, damages, liabilities or expenses
incurred by the Company result from the gross negligence or willful misconduct
of the applicable Purchaser or entity in connection with the transactions
contemplated by this Agreement.

         3.14 Shareholders Rights Plan. In the event that a shareholders rights
plan is adopted by the Company, no claim will be made or enforced by the Company
or any other Person that any Purchaser is an "Acquiring Person" under any such
plan or in any way could be deemed to trigger the provisions of such plan by
virtue of receiving Underlying Shares under the Transaction Documents.

         3.15 Voting. During the period in which it owns Securities, each
Purchaser agrees to vote each voting security of the Company held by such
Purchaser as directed by the Company's management in all matters on which the
holder of such security is entitled to vote.


                                   ARTICLE IV
                                  MISCELLANEOUS

                  4.1 Fees and Expenses. At the Closing the Company shall
reimburse the Purchasers for their legal fees and expenses incurred in
connection with the preparation and negotiation of the Transaction Documents by
paying to Robinson Silverman $25,000 for the preparation and negotiation of the
Transaction Documents. The $25,000 may be deducted from the proceeds of the
Purchase Price payable to the Company and paid directly by the Purchasers to
Robinson Silverman. Other than the amounts contemplated in the immediately
preceding sentence, and except as otherwise set forth in the Registration Rights
Agreement, each party shall pay the fees and expenses of its advisers, counsel,
accountants and other experts, if any, and all other expenses incurred by such
party incident to the negotiation, preparation, execution, delivery and
performance of this Agreement. The Company shall pay all stamp and other taxes
and duties levied in connection with the issuance of the Securities.

                  4.2 Entire Agreement; Amendments. The Transaction Documents,
together with the Exhibits and Schedules thereto contain the entire
understanding of the parties with respect to the subject matter hereof and
supersede all prior agreements and understandings, oral or written, with respect
to such matters, which the parties acknowledge have been merged into such
documents, exhibits and schedules.

                  4.3 Notices. Any and all notices or other communications or
deliveries required or permitted to be provided hereunder shall be in writing
and shall be deemed given and effective on the earliest of (i) the date of
transmission, if such notice or communication is delivered via facsimile at the
facsimile telephone number specified in this Section prior to 8:00 p.m. (New
York City time) on a Business Day, (ii) the Business Day after the date of
transmission, if such notice or communication is delivered via facsimile at the
facsimile telephone number specified in this Agreement later than 8:00 p.m. (New
York City time) on any date and earlier than 11:59 p.m. (New York City time) on
such date, (iii) the Business Day following the date of mailing, if sent by

                                      -15-
<PAGE>   17
nationally recognized overnight courier service, or (iv) if sent other than by
the methods set forth in (i)-(iii) of this Section 4.3, upon actual receipt by
the party to whom such notice is required to be given. The address for such
notices and communications shall be as follows:

         If to the Company:              NeoTherapeutics, Inc.
                                         157 Technology Drive
                                         Irvine, CA 92618
                                         Facsimile No.: (949) 788-6706
                                         Attn: Chief Financial Officer

         With copies to:                 Latham & Watkins
                                         650 Town Center Drive, Suite 2000
                                         Costa Mesa, CA 92661-1925
                                         Facsimile No.: (714) 755-8290
                                         Attn: Alan W. Pettis, Esq.



                                      -16-
<PAGE>   18

         If to a Purchaser:              To the address
                                         set forth under such
                                         Purchaser's name on the
                                         signature pages hereto.

or such other address as may be designated in writing hereafter, in the same
manner, by such Person.

                  4.4 Amendments; Waivers. No provision of this Agreement may be
waived or amended except in a written instrument signed, in the case of an
amendment, by both the Company and the Purchasers or, in the case of a waiver,
by the party against whom enforcement of any such waiver is sought. No waiver of
any default with respect to any provision, condition or requirement of this
Agreement shall be deemed to be a continuing waiver in the future or a waiver of
any other provision, condition or requirement hereof, nor shall any delay or
omission of either party to exercise any right hereunder in any manner impair
the exercise of any such right accruing to it thereafter.


                  4.5 Headings. The headings herein are for convenience only, do
not constitute a part of this Agreement and shall not be deemed to limit or
affect any of the provisions hereof.

                  4.6 Successors and Assigns. This Agreement shall be binding
upon and inure to the benefit of the parties and their successors and permitted
assigns. The Company may not assign this Agreement or any rights or obligations
hereunder without the prior written consent of the Purchasers. Except as set
forth in Section 3.1(a), the Purchasers may not assign this Agreement or any of
the rights or obligations hereunder without the consent of the Company.

                  4.7 No Third-Party Beneficiaries. This Agreement is intended
for the benefit of the parties hereto and their respective successors and
permitted assigns and is not for the benefit of, nor may any provision hereof be
enforced by, any other Person.

                  4.8 Governing Law. The corporate laws of the State of Delaware
shall govern all issues concerning the relative rights of the Company and its
stockholders. All other questions concerning the construction, validity,
enforcement and interpretation of the Transaction Documents shall be governed by
and construed and enforced in accordance with the internal laws of the State of
New York, without regard to the principles of conflicts of law thereof. Each
party hereby irrevocably submits to the exclusive jurisdiction of the state and
federal courts sitting in the City of New York, borough of Manhattan, for the
adjudication of any dispute hereunder or in connection herewith or with any
transaction contemplated hereby or discussed herein (including with respect to
the enforcement of the any of the Transaction Documents), and hereby irrevocably
waives, and agrees not to assert in any suit, action or proceeding, any claim
that it is not personally subject to the jurisdiction of any such court, that
such suit, action or proceeding is improper. Each party hereby irrevocably
waives personal service of process and consents to process being served in any
such suit, action or proceeding by mailing a copy thereof to such party at the
address in effect for notices to it under this Agreement and agrees that such
service shall constitute good and sufficient service of process and notice
thereof. Nothing contained herein shall be deemed to limit in any way any right
to serve process in any manner permitted by law.

                  4.9 Survival. The representations, warranties, agreements and
covenants contained herein shall survive the Closing, the delivery, exercise and
conversion (as the case may be) of the Warrants and the Debentures.

                                      -17-
<PAGE>   19

                  4.10 Execution. This Agreement may be executed in two or more
counterparts, all of which when taken together shall be considered one and the
same agreement and shall become effective when counterparts have been signed by
each party and delivered to the other party, it being understood that both
parties need not sign the same counterpart. In the event that any signature is
delivered by facsimile transmission, such signature shall create a valid and
binding obligation of the party executing (or on whose behalf such signature is
executed) the same with the same force and effect as if such facsimile signature
page were an original thereof.

                  4.11 Severability. In case any one or more of the provisions
of this Agreement shall be invalid or unenforceable in any respect, the validity
and enforceability of the remaining terms and provisions of this Agreement shall
not in any way be affecting or impaired thereby and the parties will attempt to
agree upon a valid and enforceable provision which shall be a reasonable
substitute therefor, and upon so agreeing, shall incorporate such substitute
provision in this Agreement.

                  4.12 Remedies. In addition to being entitled to exercise all
rights provided herein or granted by law, including recovery of damages, the
Purchasers will be entitled to specific performance of the obligations of the
Company under the Transaction Documents. Each of the Company and the Purchasers
agree that monetary damages may not be adequate compensation for any loss
incurred by reason of any breach of its obligations described in the foregoing
sentence and hereby agrees to waive in any action for specific performance of
any such obligation the defense that a remedy at law would be adequate.

                  4.13 Independent Nature of Purchasers' Obligations and Rights.
The obligations of each Purchaser under any Transaction Document is several and
not joint with the obligations of any other Purchaser, and no Purchaser shall be
responsible in any way for the performance of the obligations of any other
Purchaser under any Transaction Document. Nothing contained herein or in any
Transaction Document, and no action taken by any Purchaser pursuant thereto,
shall be deemed to constitute the Purchasers as a partnership, an association, a
joint venture or any other kind of entity, or create a presumption that the
Purchasers are in any way acting in concert with respect to such obligations or
the transactions contemplated by the Transaction Document. Each Purchaser shall
be entitled to independently protect and enforce its rights, including without
limitation the rights arising out of this Agreement or out of the Transaction
Documents, and it shall not be necessary for any other Purchaser to be joined as
an additional party in any proceeding for such purpose.


                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                             SIGNATURE PAGES FOLLOW]



                                      -18-
<PAGE>   20

                  IN WITNESS WHEREOF, the parties hereto have caused this
Convertible Debenture Purchase Agreement to be duly executed by their respective
authorized signatories as of the date first indicated above.

                                       NEOTHERAPEUTICS, INC.



                                       By:      /s/Samuel Gulko
                                         ----------------------------
                                       Name:       Samuel Gulko
                                       Title:      Chief Financial Officer


                   [REMAINDER OF PAGE INTENTIONALLY LEFT BLANK
                      SIGNATURE PAGE FOR PURCHASER FOLLOWS]



<PAGE>   21
                 MONTROSE INVESTMENTS LTD.


                 By:    /s/Harlan B. Korenvaes
                      ----------------------------
                 Name:     Harlan B. Korenvaes
                 Title:    Authorized Signatory

                 Debentures Purchase Price:$5,000,000


                 Address for Notice:

                 Montrose Investments Ltd.
                 300 Crescent Court, Suite 700
                 Dallas, TX 75201
                 Facsimile: (214) 758-1221
                 Attn: Will Rose and Kim Rozman

                 With copies to:
                 Robinson Silverman Pearce Aronsohn & Berman LLP
                 1290 Avenue of the Americas
                 New York, NY  10104
                 Facsimile No.:  (212) 541-4630 and (212) 541-1432
                 Attn: Kenneth L. Henderson, Esq. and Eric L. Cohen, Esq.



<PAGE>   22



                 STRONG RIVER INVESTMENTS, INC.


                 By:  /s/ Kenneth L. Henderson
                      -------------------------
                 Name:    Kenneth L. Henderson
                 Title:   Attorney-in-fact

                  Debentures Purchase Price:         $5,000,000


                  Address for Notice:

                  Strong River Investments, Inc.
                  c/o Gonzalez-Ruiz 7 Aleman (BVI) Limited
                  Wickhams Cay I, Vanterpool Plaza
                  P.O. Box 873
                  Road Town, Tortolla, BVI

                  With copies to:
                  Robinson Silverman Pearce Aronsohn & Berman LLP
                  1290 Avenue of the Americas
                  New York, NY  10104
                  Facsimile No.:  (212) 541-4630 and (212) 541-1432
                  Attn: Kenneth L. Henderson, Esq. and Eric L. Cohen, Esq.