<PAGE>


                                                                   EXHIBIT 4.2


                               PURCHASE AGREEMENT


                  THIS AGREEMENT is made as of the 30th day of January, 2001, by
and between Triangle Pharmaceuticals, Inc. (the "Company"), a corporation
organized under the laws of the State of Delaware, with its principal offices at
4 University Place, 4611 University Drive, Durham, North Carolina 27707 and the
purchaser whose name and address is set forth on the signature page hereof (the
"Purchaser").

                  IN CONSIDERATION of the mutual covenants contained in this
Agreement, the Company and the Purchaser agree as follows:

                  SECTION 1. AUTHORIZATION OF SALE OF THE SHARES. Subject to the
terms and conditions of this Agreement, the Company has authorized the sale of
up to 7,700,000 shares (the "Shares") of common stock, par value $0.001 per
share (the "Common Stock"), of the Company.

                  SECTION 2. AGREEMENT TO SELL AND PURCHASE THE SHARES. At the
Closing (as defined in Section 3), the Company will sell to the Purchaser and
the Purchaser will buy from the Company, upon the terms and conditions
hereinafter set forth, the number of Shares (at the purchase price) shown below:

                                Price Per
       Number to Be              Share In                  Aggregate
        Purchased                Dollars                    Price
       ------------             ---------                  ---------



                  The Company proposes to enter into this same form of purchase
agreement with certain other investors (the "Other Purchasers") and expects to
complete sales of the Shares to them. The Purchaser and the Other Purchasers are
hereinafter sometimes collectively referred to as the "Purchasers," and this
Agreement and the agreements executed by the Other Purchasers are hereinafter
sometimes collectively referred to as the "Agreements." The term "Placement
Agent" shall mean Banc of America Securities LLC.

                  SECTION 3. DELIVERY OF THE SHARES AT THE CLOSING. The
completion of the purchase and sale of the Shares (the "Closing") shall occur
within three business days (or on such other later date as the Placement Agent
and the Company both agree) of the date of receipt by the Company of
confirmation by the Securities and Exchange Commission (the "Commission") of the
Commission's willingness to declare effective the registration statement to be
filed by the Company pursuant to Section 7.1 hereof (the "Registration
Statement") at a place and time (the "Closing Date") to be agreed upon by the
Company and the Placement Agent and of which the Purchasers will be notified by
facsimile transmission or otherwise.


<PAGE>

                  At the Closing, the Company shall deliver to the Purchaser one
or more stock certificates registered in the name of the Purchaser, or in such
nominee name(s) as designated by the Purchaser in writing, representing the
number of Shares set forth in Section 2 above. The name(s) in which the stock
certificates are to be registered are set forth in the Stock Certificate
Questionnaire attached hereto as part of Appendix I. The Company's obligation to
complete the purchase and sale of the Shares and deliver such stock
certificate(s) to the Purchaser at the Closing shall be subject to the following
conditions, any one or more of which may be waived by the Company: (a) receipt
by the Company of same-day funds in the full amount of the purchase price for
the Shares being purchased hereunder; (b) completion of the purchases and sales
under the Agreements with all of the Other Purchasers; and (c) the accuracy of
the representations and warranties made by the Purchasers and the fulfillment of
those undertakings of the Purchasers to be fulfilled prior to the Closing. The
Purchaser's obligation to accept delivery of such stock certificate(s) and to
pay for the Shares evidenced thereby shall be subject to the following
conditions: (a) the Commission has notified the Company of the Commission's
willingness to declare the Registration Statement effective on or prior to the
75th day after the date such Registration Statement was filed by the Company;
and (b) the accuracy in all material respects of the representations and
warranties made by the Company herein and the fulfillment in all material
respects of those undertakings of the Company to be fulfilled prior to Closing.
The Purchaser's obligations hereunder are expressly not conditioned on the
purchase by any or all of the Other Purchasers of the Shares that they have
agreed to purchase from the Company.

SECTION 4. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY. The Company
hereby represents and warrants to, and covenants with, the Purchaser as follows:

                  4.1 ORGANIZATION AND QUALIFICATION. The Company is a
corporation duly organized, validly existing and in good standing under the laws
of its jurisdiction of incorporation, and the Company is qualified to do
business as a foreign corporation in each jurisdiction in which qualification is
required, except where failure to so qualify would not have a Material Adverse
Effect (as defined herein). The Company has only one subsidiary, which is a
direct, wholly-owned subsidiary (the "Subsidiary") of the Company and which has
no material assets, other than those license agreements described in the
Company's 10-K for the year ended December 31, 1999 (Exhibit A). The Subsidiary
is duly organized, validly existing and in good standing under the laws of its
jurisdiction of incorporation and is qualified to do business as a foreign
corporation in each jurisdiction in which qualification is required, except
where failure to so qualify would not have a Material Adverse Effect.

                  4.2 AUTHORIZED CAPITAL STOCK. Except as disclosed in or
contemplated by the Confidential Private Placement Memorandum dated January 17,
2001 prepared by the Company, including all Exhibits (except Exhibit G),
supplements and amendments thereto (the "Private Placement Memorandum"), the
Company had authorized and outstanding capital stock as set forth under the
heading "Capitalization" in the Private Placement Memorandum as of the date set
forth therein; the issued and outstanding shares of the Company's Common Stock
have been duly authorized and validly issued, are fully paid and nonassessable,
have been issued in compliance with all federal and state securities laws, were
not issued in violation of or subject to any preemptive rights or other rights
to subscribe for or purchase securities, and conform in all




                                      -2-
<PAGE>

material respects to the description thereof contained in the Private Placement
Memorandum. Except as disclosed in or contemplated by the Private Placement
Memorandum (including the issuance of options under the Company's 1996 Stock
Incentive Plan and the issuance of shares of Common Stock pursuant to the
Company's Employee Stock Purchase Plan after September 30, 1998), the Company
does not have outstanding any options to purchase, or any preemptive rights or
other rights to subscribe for or to purchase, any securities or obligations
convertible into, or any contracts or commitments to issue or sell, shares of
its capital stock, any shares of capital stock of any subsidiary or any such
options, rights, convertible securities or obligations. The description of the
Company's stock, stock bonus and other stock plans or arrangements and the
options or other rights granted and exercised thereunder, set forth in the
Private Placement Memorandum accurately and fairly presents the information
required to be shown with respect to such plans, arrangements, options and
rights.

                  4.3 ISSUANCE, SALE AND DELIVERY OF THE SHARES. The Shares have
been duly authorized and, when issued, delivered and paid for in the manner set
forth in this Agreement, will be duly authorized, validly issued, fully paid and
nonassessable, and will conform in all material respects to the description
thereof set forth in the Private Placement Memorandum. No preemptive rights or
other rights to subscribe for or purchase exist with respect to the issuance and
sale of the Shares by the Company pursuant to this Agreement. No stockholder of
the Company has any right (which has not been waived or has not expired by
reason of lapse of time following notification of the Company's intent to file
the Registration Statement) to require the Company to register the sale of any
shares owned by such stockholder under the Securities Act of 1933, as amended
(the "Securities Act"), in the Registration Statement. No further approval or
authority of the stockholders or the Board of Directors of the Company will be
required for the issuance and sale of the Shares to be sold by the Company as
contemplated herein.

                  4.4 DUE EXECUTION, DELIVERY AND PERFORMANCE OF THE AGREEMENTS.
The Company has full legal right, corporate power and authority to enter into
the Agreements and perform the transactions contemplated hereby. The Agreements
have been duly authorized, executed and delivered by the Company. The making and
performance of the Agreements by the Company and the consummation of the
transactions herein contemplated will not violate any provision of the
organizational documents of the Company or its Subsidiary and will not result in
the creation of any lien, charge, security interest or encumbrance upon any
assets of the Company or its Subsidiary pursuant to the terms or provisions of,
or will not conflict with, result in the breach or violation of, or constitute,
either by itself or upon notice or the passage of time or both, a default under
any agreement, mortgage, deed of trust, lease, franchise, license, indenture,
permit or other instrument to which the Company or its Subsidiary is a party or
by which the Company or its Subsidiary or their respective properties may be
bound or affected and in each case which would have a material adverse effect on
the condition (financial or otherwise), properties, business, prospects or
results of operations of the Company and its Subsidiary taken as a whole (a
"Material Adverse Effect") or, to the Company's knowledge, any statute or any
authorization, judgment, decree, order, rule or regulation of any court or any
regulatory body, administrative agency or other governmental body applicable to
the Company or its Subsidiary or any of its respective properties. No consent,
approval, authorization or other order of any court, regulatory body,
administrative agency or other governmental body is required for the execution
and delivery of this Agreement or the consummation of the


                                      -3-
<PAGE>

transactions contemplated by this Agreement, except for compliance with the Blue
Sky laws and federal securities laws applicable to the offering of the Shares.
Upon their execution and delivery, and assuming the valid execution thereof by
the respective Purchasers, the Agreements will constitute valid and binding
obligations of the Company, enforceable in accordance with their respective
terms, except as enforceability may be limited by applicable bankruptcy,
insolvency, reorganization, moratorium or similar laws affecting creditors' and
contracting parties' rights generally and except as enforceability may be
subject to general principles of equity (regardless of whether such
enforceability is considered in a proceeding in equity or at law) and except as
the indemnification agreements of the Company in Section 7.3 hereof may be
legally unenforceable.

                  4.5 ACCOUNTANTS. PricewaterhouseCoopers LLP, who has expressed
its opinion with respect to the consolidated financial statements to be
incorporated by reference from the Company's Annual Report on Form 10-K for the
year ended December 31, 1999 into the Registration Statement and the Prospectus
which forms a part thereof, are independent accountants as required by the
Securities Act and the rules and regulations promulgated thereunder (the "Rules
and Regulations").

                  4.6 NO DEFAULTS. Except as disclosed in the Private Placement
Memorandum, and except as to defaults, violations and breaches which
individually or in the aggregate would not be material to the Company or its
Subsidiary taken as a whole, neither the Company nor its Subsidiary is in
violation or default of any provision of its certificate of incorporation or
bylaws, or other organizational documents, or in breach of or default with
respect to any provision of any agreement, judgment, decree, order, mortgage,
deed of trust, lease, franchise, license, indenture, permit or other instrument
to which it is a party or by which it or any of its properties are bound; and
there does not exist any state of fact which, with notice or lapse of time or
both, would constitute an event of default on the part of the Company or its
Subsidiary as defined in such documents, except such defaults which individually
or in the aggregate would not be material to the Company and its Subsidiary
taken as a whole.

                  4.7. CONTRACTS. The contracts described in the Private
Placement Memorandum that are material to the Company and its Subsidiary taken
as a whole, are in full force and effect on the date hereof; and neither the
Company nor its Subsidiary is, nor to the Company's knowledge is any other
party, in breach of or default under any of such contracts which would have a
Material Adverse Effect.

                  4.8 NO ACTIONS. Except as disclosed in the Private Placement
Memorandum, there are no legal or governmental actions, suits or proceedings
pending or, to the Company's knowledge, threatened to which the Company or its
Subsidiary is or may be a part or of which property owned or leased by the
Company or its Subsidiary is or may be the subject, or related to environmental
or discrimination matters, which actions, suits or proceedings, individually or
in the aggregate, might prevent or might reasonably be expected to materially
and adversely affect the transactions contemplated by this Agreement or result
in a material adverse change in the condition (financial or otherwise),
properties, business, prospects or results of operations of the Company and its
Subsidiary, taken as a whole (a "Material Adverse Change"); and no labor
disturbance by the employees of the Company or its Subsidiary exists, to the
Company's




                                      -4-
<PAGE>

knowledge, or is imminent which might reasonably be expected to have a Material
Adverse Effect. Except as disclosed in the Private Placement Memorandum, neither
the Company nor its Subsidiary is a party to or subject to the provisions of any
material injunction, judgment, decree or order of any court, regulatory body
administrative agency or other governmental body.

                  4.9 PROPERTIES. Each of the Company and its Subsidiary has
good and marketable title to all the properties and assets reflected as owned by
it in the consolidated financial statements included in the Private Placement
Memorandum, subject to no lien, mortgage, pledge, charge or encumbrance of any
kind except (i) those, if any, reflected in such consolidated financial
statements, or (ii) those which are not material in amount and do not adversely
affect the use made and promised to be made of such property by the Company or
its Subsidiary. Each of the Company and its Subsidiary holds its leased
properties under valid and binding leases, with such exceptions as are not
materially significant in relation to their respective businesses. Except as
disclosed in the Private Placement Memorandum, each of the Company and its
Subsidiary owns or leases all such properties as are necessary to its operations
as now conducted.

                  4.10 NO MATERIAL CHANGE. Since September 30, 2000 and except
as described in or specifically contemplated by the Private Placement
Memorandum, (i) the Company and its Subsidiary have not incurred any material
liabilities or obligations, indirect, or contingent, or entered into any
material verbal or written agreement or other transaction which is not in the
ordinary course of business or which could reasonably be expected to result in a
material reduction in the future earnings of the Company; (ii) the Company and
its Subsidiary have not sustained any material loss or interference with their
businesses or properties from fire, flood, windstorm, accident or other calamity
not covered by insurance; (iii) the Company and its Subsidiary have not paid or
declared any dividends or other distributions with respect to their capital
stock and none of the Company and its Subsidiary is in default in the payment of
principal or interest on any outstanding debt obligations; (iv) there has not
been any change in the capital stock of the Company or its Subsidiary other than
the sale of the Shares hereunder and shares or options issued pursuant to
employee equity incentive plans or purchase plans approved by the Company's
Board of Directors, or indebtedness material to the Company or its Subsidiary
(other than in the ordinary course of business); and (v) except for the
operating losses and negative cash flow the Company has continued to incur,
there has not been a Material Adverse Change.

                  4.11 INTELLECTUAL PROPERTY. Except as disclosed in or
specifically contemplated by the Private Placement Memorandum, (i) the Company
and its Subsidiary own or have obtained valid and enforceable licenses or
options for the inventions, patent applications, patents, trademarks (both
registered and unregistered), tradenames, copyrights and trade secrets necessary
for the conduct of the Company's and its Subsidiary's respective businesses as
currently conducted and as the Private Placement Memorandum indicates the
Company and its Subsidiary contemplate conducting (collectively, the
"Intellectual Property"); and (ii) to the Company's knowledge (for each of the
following subsections (a) through (e)): (a) there are no third parties who have
any ownership rights to any Intellectual Property that is owned by, or has been
licensed to, the Company or its Subsidiary for the product indications described
in the Private Placement Memorandum that would preclude the Company or its
Subsidiary from


                                      -5-
<PAGE>

conducting their respective businesses as currently conducted and as the Private
Placement Memorandum indicates the Company and its Subsidiary contemplate
conducting, except for the ownership rights of the owners of the Intellectual
Property licensed or optioned by the Company or its Subsidiary; (b) there are
currently no sales of any products that would constitute an infringement by
third parties of any Intellectual Property owned, licensed or optioned by the
Company or its Subsidiary; (c) there is no pending or threatened action, suit,
proceeding or claim by others challenging the rights of the Company or its
Subsidiary in or to any Intellectual Property owned, licensed or optioned by the
Company or its Subsidiary, other than non-material claims; (d) there is no
pending or threatened action, suit, proceeding or claim by others challenging
the validity or scope of any Intellectual Property owned, licensed or optioned
by the Company, other than non-material claims; and (e) there is no pending or
threatened action, suit, proceeding or claim by others that the Company
infringes or otherwise violates any patent, trademark, copyright, trade secret
or other proprietary right of others, other than non-material claims.

                  4.12 COMPLIANCE. None of the Company and its Subsidiary has
been advised, nor do they have any reason to believe, that they are not
conducting business in compliance with all applicable laws, rules and
regulations of the jurisdictions in which they are conducting their business,
including, without limitation, all applicable local, state and federal
environmental laws and regulations; except where failure to be so in compliance
would not have a Material Adverse Effect.

                  4.13 TAXES. Each of the Company and its Subsidiary has filed
all necessary federal, state and foreign income and franchise tax returns and
has paid or accrued all taxes shown as due thereon, and each of the Company and
its Subsidiary has no knowledge of a tax deficiency which has been or might be
asserted or threatened against it which could have a Material Adverse Effect.

                  4.14 TRANSFER TAXES. On the Closing Date, all stock transfer
or other taxes (other than income taxes) which are required to be paid in
connection with the sale and transfer of the Shares to be sold to the Purchaser
hereunder will be, or will have been, fully paid or provided for by the Company
and all laws imposing such taxes will be or will have been fully complied with.

                  4.15 INVESTMENT COMPANY. The Company is not an "investment
company" or an "affiliated person" of, or "promoter" or "principal underwriter"
for an investment company, within the meaning of the Investment Company Act of
1940, as amended.

                  4.16 OFFERING MATERIALS. The Company has not distributed and
will not distribute prior to the Closing Date any offering material in
connection with the offering and sale of the Shares other than the Private
Placement Memorandum or any amendment or supplement thereto. The Company has not
in the past nor will it hereafter take any action independent of the Placement
Agent to sell, offer for sale or solicit offers to buy any securities of the
Company which would bring the offer, issuance or sale of the Shares, as
contemplated by this Agreement, within the provisions of Section 5 of the
Securities Act, unless such offer, issuance or sale was or shall be within the
exemptions of Section 4 of the Securities Act.


                                      -6-
<PAGE>

                  4.17 INSURANCE. Each of the Company and its Subsidiary
maintains insurance of the types and in the amounts that the Company reasonably
believes is adequate for its business, including, but not limited to, insurance
covering all real and personal property owned or leased by the Company or its
Subsidiary against theft, damage, destruction, acts of vandalism and all other
risks customarily insured against by similarly situated companies, all of which
insurance is in full force and effect.

                  4.18 CONTRIBUTIONS. Neither the Company at any time since its
incorporation nor its Subsidiary at any time since it was acquired by the
Company has, directly or indirectly, (i) made any unlawful contribution to any
candidate for public office, or failed to disclose fully any contribution in
violation of law, or (ii) made any payment to any federal or state governmental
officer or official, or other person charged with similar public or quasi-public
duties, other than payments required or permitted by the laws of the United
States or any jurisdiction thereof.

                  4.19 ADDITIONAL INFORMATION. The information contained in the
following documents, which the Placement Agent has furnished to the Purchaser,
or will furnish prior to the Closing, is or will be true and correct in all
material respects as of their respective final dates:

                  (a) the Company's Annual Report on Form 10-K for the fiscal
         year ended December 31, 1999 (without exhibits);

                  (b) the Company's Proxy Statement for the 2000 Annual Meeting
         of Stockholders;

                  (c) the Company's Quarterly Reports on Form 10-Q for the
         fiscal quarters ended March 31, 2000, June 30, 2000 and September 30,
         2000 (each without exhibits);

                  (d) the Company's Current Report on Form 8-K filed with the
         Commission on November 3, 2000 (without exhibits);

                  (e) the Registration Statement;

                  (f) the Private Placement Memorandum, including all addenda
         and exhibits thereto (other than the Appendices); and

                  (g) all other documents, if any, filed by the Company with the
         Securities and Exchange Commission since September 30, 2000 pursuant to
         the reporting requirements of the Securities Exchange Act of 1934, as
         amended (the "Exchange Act").

                  4.20 LEGAL OPINION. Prior to the Closing, Brobeck, Phleger &
Harrison, LLP, counsel to the Company, will deliver its legal opinion to the
Placement Agent reasonably satisfactory to the Placement Agent and counsel to
the Placement Agent. Such opinion shall also state that each of the Purchasers
may rely thereon as though it were addressed directly to such Purchaser.


                                      -7-
<PAGE>

                  4.21 INTELLECTUAL PROPERTY OPINION. Prior to the Closing, King
& Spalding, patent counsel for the Company, will deliver its legal opinion to
the Placement Agent reasonably satisfactory to the Placement Agent and counsel
to the Placement Agent. Such opinion shall state that each of the Purchasers may
rely thereon as though it were addressed directly to such Purchaser.

                  4.22 NO INTEGRATION. Neither the Company nor any of its
affiliates nor any person acting on the Company's behalf has, directly or
indirectly, at any time within the past six (6) months made, nor will any such
party make within six (6) months of the Closing Date, any offer or sale of any
security or solicitation of any offer to buy any security under circumstances,
that in the opinion of the Company's counsel, concurred by the Placement Agent's
counsel, would eliminate the availability of the exemption from registration
under Regulation D under the Securities Act in connection with the offer and
sale of the Securities as contemplated hereby.

                  4.23 CERTIFICATE. At the Closing, the Company will deliver to
Purchaser a certificate executed by the Chairman of the Board or President and
the chief financial or accounting officer of the Company, dated the Closing
Date, in form and substance reasonably satisfactory to the Purchasers, to the
effect that the representations and warranties of the Company set forth in this
Section 4 are true and correct in all material respects as of the date of this
Agreement and as of the Closing Date, and the Company has complied with all the
agreements and satisfied all the conditions herein on its part to be performed
or satisfied on or prior to such Closing Date.

                  SECTION 5. REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE
PURCHASER. (a) The Purchaser represents and warrants to, and covenants with, the
Company that: (i) the Purchaser is knowledgeable, sophisticated and experienced
in making, and is qualified to make, decisions with respect to investments in
shares representing an investment decision like that involved in the purchase of
the Shares, including investments in securities issued by the Company, and has
requested, received, reviewed and considered all information it deems relevant
in making an informed decision to purchase the Shares; (ii) the Purchaser is
acquiring the number of Shares set forth in Section 2 above in the ordinary
course of its business and for its own account for investment only and with no
present intention of distributing any of such Shares or any arrangement or
understanding with any other persons regarding the distribution of such Shares;
(iii) the Purchaser will not, directly or indirectly, offer, sell, pledge,
transfer or otherwise dispose of (or solicit any offers to buy, purchase or
otherwise acquire or take a pledge of) any of the Shares except in compliance
with the Securities Act and the Rules and Regulations; (iv) the Purchaser has
completed or caused to be completed the Registration Statement Questionnaire
attached hereto as part of Appendix I, for use in preparation of the
Registration Statement, and the answers thereto are true and correct as of the
date hereof and will be true and correct as of the effective date of the
Registration Statement; (v) the Purchaser has, in connection with its decision
to purchase the number of Shares set forth in Section 2 above, relied solely
upon the Private Placement Memorandum and the documents included therein and the
representations and warranties of the Company contained herein; and (vi) the
Purchaser is either a "large institutional accredited investor" as defined in
Rule 501(a)(1), (2), (3), (7) or (8) (and within the meaning of the SEC
No-Action Letters: Black Box, Inc. (June 26, 1990) and Squadron, Elenoff,
Pleasant & Lehrer (February 28, 1992)) or is a "qualified institutional buyer"
as such term is defined in Rule 144A(a)(1) under the Securities Act.


                                      -8-
<PAGE>

                  (b) The Purchaser understands that the Shares are being
         offered and sold to it in reliance upon specific exemptions from the
         registration requirements of the Securities Act, the Rules and
         Regulations and state securities laws and that the Company is relying
         upon the truth and accuracy of, and the Purchaser's compliance with,
         the representations, warranties, agreements, acknowledgments and
         understandings of the Purchaser set forth herein in order to determine
         the availability of such exemptions and the eligibility of the
         Purchaser to acquire the Shares.

                  (c) The Purchaser understands that the information contained
         in the Private Placement Memorandum is strictly confidential and
         proprietary to the Company and has been prepared from the Company's
         publicly available documents and other information and is being
         submitted to the Purchaser solely for such Purchaser's confidential
         use. The Purchaser agrees to use the information contained in the
         Private Placement Memorandum for the sole purpose of evaluating a
         possible investment in the Shares and the Purchaser hereby acknowledges
         that except as required by applicable securities laws, it is prohibited
         from reproducing or distributing the Private Placement Memorandum, this
         Purchase Agreement, or any other offering materials, in whole or in
         part, or divulging or discussing any of their contents. Further, the
         Purchaser understands and expressly agrees that the existence and
         nature of all conversations and presentations, if any, regarding the
         Company and this offering, as well as any other information about the
         Company received by the Purchaser in connection with this Offering must
         be kept strictly confidential. The Purchaser understands that the
         federal securities laws impose restrictions on trading based on
         information regarding this offering. In addition, the Purchaser hereby
         acknowledges that unauthorized disclosure of information regarding this
         offering may cause the Company to violate Regulation FD.

                  (d) The Purchaser understands that its investment in the
         Shares involves a significant degree of risk and that the market price
         of the Common Stock has been volatile and that no representation is
         being made as to the future value of the Common Stock. The Purchaser
         has the knowledge and experience in financial and business matters as
         to be capable of evaluating the merits and risks of an investment in
         the Shares and has the ability to bear the economic risks of an
         investment in the Shares.

                  (e) The Purchaser understands that no United States federal or
         state agency or any other government or governmental agency has passed
         upon or made any recommendation or endorsement of the Shares.

                  (f) The Purchaser understands that until the Shares may be
         sold pursuant to Rule 144 under the Securities Act without any
         restriction as to the number of securities as of a particular date that
         can then be immediately sold, the Shares may bear a restrictive legend
         in substantially the following form (and a stop transfer order may be
         placed against transfer of the certificates for the Shares):


                                      -9-
<PAGE>

                  "THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
                  REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED. THE
                  SECURITIES MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED IN THE
                  ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT FOR THE
                  SECURITIES UNDER SAID ACT, OR AN OPINION OF COUNSEL, IN FORM,
                  SUBSTANCE AND SCOPE REASONABLY ACCEPTABLE TO THE COMPANY, THAT
                  REGISTRATION IS NOT REQUIRED UNDER SAID ACT OR UNLESS SOLD
                  PURSUANT TO RULE 144 UNDER SAID ACT."

                  (g) The Purchaser's principal executive offices are in the
         jurisdiction set forth immediately below the Purchaser's name on the
         signature pages hereto.

                  (h) The Purchaser hereby covenants with the Company not to
         make any sale of the Shares under the Registration Statement without
         effectively causing the prospectus delivery requirement under the
         Securities Act to be satisfied, and the Purchaser acknowledges and
         agrees that such Shares are not transferable on the books of the
         Company unless the certificate submitted to the transfer agent
         evidencing the Shares is accompanied by a separate Purchaser's
         Certificate of Subsequent Sale: (i) in the form of Appendix II hereto,
         (ii) executed by an officer of, or other authorized person designated
         by, the Purchaser, and (iii) to the effect that (A) the Shares have
         been sold in accordance with the Registration Statement, the Securities
         Act and any applicable state securities or blue sky laws and (B) the
         requirement of delivering a current prospectus has been satisfied. The
         Purchaser acknowledges that there may occasionally be times when the
         Company must suspend the use of the prospectus forming a part of the
         Registration Statement until such time as an amendment to the
         Registration Statement has been filed by the Company and declared
         effective by the Commission, or until such time as the Company has
         filed an appropriate report with the Commission pursuant to the
         Exchange Act. The Purchaser hereby covenants that it will not sell any
         Shares pursuant to said prospectus during the period commencing at the
         time at which the Company gives the Purchaser written notice of the
         suspension of the use of said prospectus and ending at the time the
         Company gives the Purchaser written notice that the Purchaser may
         thereafter effect sales pursuant to said prospectus. The Company hereby
         covenants that it will promptly notify the Purchaser of the
         commencement and ending of such period. The Purchaser further covenants
         to notify the Company promptly of the sale of all of its Shares.

                  (i) The Purchaser further represents and warrants to, and
         covenants with, the Company that (i) the Purchaser has full right,
         power, authority and capacity to enter into this Agreement and to
         consummate the transactions contemplated hereby and has taken all
         necessary action to authorize the execution, delivery and performance
         of this Agreement, and (ii) upon the execution and delivery of this
         Agreement, this Agreement shall constitute a legal, valid and binding
         obligation of the Purchaser, enforceable in accordance with its terms,
         except as enforceability may be limited by applicable bankruptcy,
         insolvency, reorganization, moratorium or similar laws affecting
         creditors' and contracting parties' rights generally and except as
         enforceability may be subject to general principles of equity
         (regardless of whether such enforceability is considered in a


                                      -10-
<PAGE>

         proceeding in equity or at law) and except as the indemnification
         agreements of the Purchaser in Section 7.3 hereof may be legally
         unenforceable.

                  (j) The Purchaser hereby represents that if the Purchaser is
         not a United States person (as such term is defined under Regulation S
         of the Securities Act), the Purchaser has satisfied itself as to the
         full observance of the laws of its jurisdiction in connection with any
         invitation to subscribe for the Shares or any use of this Agreement,
         including (i) the legal requirements within its jurisdiction for the
         purchase of the Shares, (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 Shares. The Purchaser further
         represents that its subscription and payment for, and its continued
         beneficial ownership of the Shares, will not violate any applicable
         securities or other laws of its jurisdiction.


                  SECTION 6. SURVIVAL OF REPRESENTATIONS, WARRANTIES AND
AGREEMENTS. Notwithstanding any investigation made by any party to this
Agreement or by the Placement Agent, all covenants, agreements, representations
and warranties made by the Company and the Purchaser herein and in the
certificates for the Shares delivered pursuant hereto shall survive the
execution of this Agreement, the delivery to the Purchaser of the Shares being
purchased and the payment therefor.

                  SECTION 7. REGISTRATION OF THE SHARES; COMPLIANCE WITH THE
SECURITIES ACT.

                  7.1      REGISTRATION PROCEDURES AND EXPENSES. The Company
                           shall:

                  (a)      as soon as practicable, prepare and file with the
                           Commission the Registration Statement on Form S-3
                           relating to the sale of the Shares by the Purchaser
                           from time to time on the Nasdaq National Market or
                           the facilities of any national securities exchange on
                           which the Common Stock is then traded or in
                           privately-negotiated transactions;

                  (b)      use its reasonable efforts, subject to receipt of
                           necessary information from the Purchasers, to cause
                           the Commission to notify the Company of the
                           Commission's willingness to declare the Registration
                           Statement effective within 75 days after the
                           Registration Statement is filed by the Company;

                  (c)      promptly prepare and file with the Commission such
                           amendments and supplements to the Registration
                           Statement and the prospectus used in connection
                           therewith as may be necessary to keep the
                           Registration Statement effective until the earlier of
                           (i) two years after the effective date of the
                           Registration Statement or (ii) the date on which the
                           Shares may be resold by the Purchasers without
                           registration by reason of Rule 144(k) under the
                           Securities Act or any other rule of similar effect;


                                      -11-
<PAGE>

                  (d)      furnish to the Purchaser with respect to the Shares
                           registered under the Registration Statement (and to
                           each underwriter, if any, of such Shares) such number
                           of copies of prospectuses and such other documents as
                           the Purchaser may reasonably request, in order to
                           facilitate the public sale or other disposition of
                           all or any of the Shares by the Purchaser; PROVIDED,
                           HOWEVER, that the obligation of the Company to
                           deliver copies of prospectuses to the Purchaser shall
                           be subject to the receipt by the Company of
                           reasonable assurances from the Purchaser that the
                           Purchaser will comply with the applicable provisions
                           of the Securities Act and of such other securities or
                           blue sky laws as may be applicable in connection with
                           any use of such prospectuses;

                  (e)      file documents required of the Company for normal
                           blue sky clearance in states specified in writing by
                           the Purchaser; PROVIDED, HOWEVER, that the Company
                           shall not be required to qualify to do business or
                           consent to service of process in any jurisdiction in
                           which it is not now so qualified or has not so
                           consented; and

                  (f)      bear all expenses in connection with the procedures
                           in paragraphs (a) through (e) of this Section 7.1 and
                           the registration of the Shares pursuant to the
                           Registration Statement, other than fees and expenses,
                           if any, of counsel or other advisers to the Purchaser
                           or the Other Purchasers or underwriting discounts,
                           brokerage fees and commissions incurred by the
                           Purchaser or the Other Purchasers, if any.

                  7.2 TRANSFER OF SHARES AFTER REGISTRATION. The Purchaser
agrees that it will not effect any disposition of the Shares or its right to
purchase the Shares that would constitute a sale within the meaning of the
Securities Act, except as contemplated in the Registration Statement referred to
in Section 7.1, and that it will promptly notify the Company of any changes in
the information set forth in the Registration Statement regarding the Purchaser
or its plan of distribution.

                  7.3  INDEMNIFICATION.  For the purpose of this Section 7.3:

                  (i)      the term "Purchaser/Affiliate" shall mean any
                           affiliates of the Purchaser and any person who
                           controls the Purchaser or any affiliate of the
                           Purchaser within the meaning of Section 15 of the
                           Securities Act or Section 20 of the Exchange Act; and

                  (ii)     the term "Registration Statement" shall include any
                           final prospectus, exhibit, supplement or amendment
                           included in or relating to, and any document
                           incorporated by reference in, the Registration
                           Statement referred to in Section 7.1.

                  (a) The Company agrees to indemnify and hold harmless each of
the Purchasers and each Purchaser/Affiliate, against any losses, claims,
damages, liabilities or


                                      -12-
<PAGE>

expenses, joint or several, to which such Purchasers or such
Purchaser/Affiliates may become subject, under the Securities Act, the Exchange
Act, or any other federal or state statutory law or regulation, or at common law
or otherwise (including in settlement of any litigation, if such settlement is
effected with the written consent of the Company), insofar as such losses,
claims, damages, liabilities or expenses (or actions in respect thereof as
contemplated below) arise out of or are based upon any untrue statement or
alleged untrue statement of any material fact contained in the Registration
Statement, including the prospectus, financial statements and schedules, and all
other documents filed as a part thereof, as amended at the time of effectiveness
of the Registration Statement, including any information deemed to be a part
thereof as of the time of effectiveness pursuant to paragraph (b) of Rule 430A,
or pursuant to Rule 434, of the Rules and Regulations, or the prospectus, in the
form first filed with the Commission pursuant to Rule 424(b) of the Regulations,
or filed as part of the Registration Statement at the time of effectiveness if
no Rule 424(b) filing is required (the "Prospectus"), or any amendment or
supplement thereto, or arise out of or are based upon the omission or alleged
omission to state in any of them a material fact required to be stated therein
or necessary to make the statements in the Registration Statement or any
amendment or supplement thereto not misleading or in the Prospectus or any
amendment or supplement thereto not misleading in the light of the circumstances
under which they were made, or arise out of or are based in whole or in part on
any inaccuracy in the representations and warranties of the Company contained in
this Agreement, or any failure of the Company to perform its obligations
hereunder or under law, and will reimburse each Purchaser and each such
Purchaser/Affiliate for any legal and other expenses as such expenses are
reasonably incurred by such Purchaser or such Purchaser/Affiliate in connection
with investigating, defending, settling, compromising or paying any such loss,
claim, damage, liability, expense or action; PROVIDED, HOWEVER, that the Company
will not be liable in any such case to the extent that any such loss, claim,
damage, liability or expense arises out of or is based upon (i) an untrue
statement or alleged untrue statement or omission or alleged omission made in
the Registration Statement, the Prospectus or any amendment or supplement
thereto in reliance upon and in conformity with written information furnished to
the Company by or on behalf of the Purchaser expressly for use therein, or (ii)
the failure of such Purchaser to comply with the covenants and agreements
contained in Sections 5(h) or 7.2 hereof respecting the sale of the Shares, or
(iii) the inaccuracy of any representations made by such Purchaser herein or
(iv) any statement or omission in any Prospectus that is corrected in any
subsequent Prospectus that was delivered to the Purchaser prior to the pertinent
sale or sales by the Purchaser.

                  (b) Each Purchaser will severally, but not jointly, indemnify
and hold harmless the Company, each of its directors, each of its officers who
signed the Registration Statement and each person, if any, who controls the
Company within the meaning of Section 15 of the Securities Act or Section 20 of
the Exchange Act, against any losses, claims, damages, liabilities or expenses
to which the Company, each of its directors, each of its officers who signed the
Registration Statement or controlling person may become subject, under the
Securities Act, the Exchange Act, or any other federal or state statutory law or
regulation, or at common law or otherwise (including in settlement of any
litigation, if such settlement is effected with the written consent of such
Purchaser) insofar as such losses, claims, damages, liabilities or expenses (or
actions in respect thereof as contemplated below) arise out of or are based upon
(i) any failure to comply with the covenants and agreements contained in
Sections 5(h) or 7.2 hereof respecting the sale of the Shares or (ii) the
inaccuracy of any representation made by such


                                      -13-
<PAGE>

Purchaser herein or (iii) any untrue or alleged untrue statement of any material
fact contained in the Registration Statement, the Prospectus, or any amendment
or supplement thereto, or arise out of or are based upon the omission or alleged
omission to state therein a material fact required to be stated therein or
necessary to make the statements in the Registration Statement or any amendment
or supplement thereto not misleading or in the Prospectus or any amendment or
supplement thereto not misleading in the light of the circumstances under which
they were made, in each case to the extent, but only to the extent, that such
untrue statement or alleged untrue statement or omission or alleged omission was
made in the Registration Statement, the Prospectus, or any amendment or
supplement thereto, in reliance upon and in conformity with written information
furnished to the Company by or on behalf of any Purchaser expressly for use
therein, and will reimburse the Company, each of its directors, each of its
officers who signed the Registration Statement or controlling person for any
legal and other expense reasonably incurred by the Company, each of its
directors, each of its officers who signed the Registration Statement or
controlling person in connection with investigating, defending, settling,
compromising or paying any such loss, claim, damage, liability, expense or
action.

                  (c) Promptly after receipt by an indemnified party under this
Section 7.3 of notice of the threat or commencement of any action, such
indemnified party will, if a claim in respect thereof is to be made against an
indemnifying party under this Section 7.3 promptly notify the indemnifying party
in writing thereof; but the omission so to notify the indemnifying party will
not relieve it from any liability which it may have to any indemnified party for
contribution or otherwise than under the indemnity agreement contained in this
Section 7.3 or to the extent it is not prejudiced as a result of such failure.
In case any such action is brought against any indemnified party and such
indemnified party seeks or intends to seek indemnity from an indemnifying party,
the indemnifying party will be entitled to participate in, and, to the extent
that it may wish, jointly with all other indemnifying parties similarly
notified, to assume the defense thereof with counsel reasonably satisfactory to
such indemnified party; PROVIDED, HOWEVER, if the defendants in any such action
include both the indemnified party, and the indemnifying party and the
indemnified party shall have reasonably concluded that there may be a conflict
of interest, based upon the advice of such indemnified party's counsel, between
the positions of the indemnifying party and the indemnified party in conducting
the defense of any such action or that there may be legal defenses available to
it and/or other indemnified parties which are different from or additional to
those available to the indemnifying party, the indemnified party or parties
shall have the right to select separate counsel to assume such legal defenses
and to otherwise participate in the defense of such action on behalf of such
indemnified party or parties. Upon receipt of notice from the indemnifying party
to such indemnified party of its election so to assume the defense of such
action and approval by the indemnified party of counsel, the indemnifying party
will not be liable to such indemnified party under this Section 7.3 for any
legal or other expenses subsequently incurred by such indemnified party in
connection with the defense thereof unless (i) the indemnified party shall have
employed such counsel in connection with the assumption of legal defenses in
accordance with the proviso to the preceding sentence (it being understood,
however, that the indemnifying party shall not be liable for the expenses of
more than one separate counsel, approved by such indemnifying party in the case
of paragraph (a), representing the indemnified parties who are parties to such
action, plus local counsel, if appropriate) or (ii) the indemnifying party shall
not have employed counsel reasonably satisfactory to the indemnified party to
represent the indemnified party within a


                                      -14-
<PAGE>

reasonable time after notice of commencement of action, in each of which cases
the reasonable fees and expenses of counsel shall be at the expense of the
indemnifying party.

                  (d) If the indemnification provided for in this Section 7.3 is
required by its terms but is for any reason held to be unavailable to or
otherwise insufficient to hold harmless an indemnified party under paragraphs
(a), (b) or (c) of this Section 7.3 in respect to any losses, claims, damages,
liabilities or expenses referred to herein, then each applicable indemnifying
party shall contribute to the amount paid or payable by such indemnified party
as a result of any losses, claims, damages, liabilities or expenses referred to
herein (i) in such proportion as is appropriate to reflect the relative benefits
received by the Company and the Purchaser from the placement of the Common Stock
contemplated by this Agreement or (ii) if the allocation provided by clause (i)
above is not permitted by applicable law, in such proportion as is appropriate
to reflect not only the relative benefits referred to in clause (i) above but
the relative fault of the Company and the Purchaser in connection with the
statements or omissions or inaccuracies in the representations and warranties in
this Agreement that resulted in such losses, claims, damages, liabilities or
expenses, as well as any other relevant equitable considerations. The relative
benefits received by the Company on the one hand and each Purchaser on the other
shall be deemed to be in the same proportion as the amount paid by such
Purchaser to the Company pursuant to this Agreement for the Shares purchased by
such Purchaser that were sold pursuant to the Registration Statement bears to
the difference (the "Difference") between the amount such Purchaser paid for the
Shares that were sold pursuant to the Registration Statement and the amount
received by such Purchaser from such sale. The relative fault of the Company on
the one hand and each Purchaser on the other shall be determined by reference
to, among other things, whether the untrue or alleged statement of a material
fact or the omission or alleged omission to state a material fact or the
inaccurate or the alleged inaccurate representation and/or warranty relates to
information supplied by the Company or by such Purchaser and the parties'
relative intent, knowledge, access to information and opportunity to correct or
prevent such statement or omission. The amount paid or payable by a party as a
result of the losses, claims, damages, liabilities and expenses referred to
above shall be deemed to include, subject to the limitations set forth in
paragraph (c) of this Section 7.3, any legal or other fees or expenses
reasonably incurred by such party in connection with investigating or defending
any action or claim. The provisions set forth in paragraph (c) of this Section
7.3 with respect to the notice of the threat or commencement of any threat or
action shall apply if a claim for contribution is to be made under this
paragraph (d); PROVIDED, HOWEVER, that no additional notice shall be required
with respect to any threat or action for which notice has been given under
paragraph (c) for purposes of indemnification. The Company and each Purchaser
agree that it would not be just and equitable if contribution pursuant to this
Section 7.3 were determined solely by pro rata allocation (even if the Purchaser
were treated as one entity for such purpose) or by any other method of
allocation which does not take account of the equitable considerations referred
to in this paragraph. Notwithstanding the provisions of this Section 7.3, no
Purchaser shall be required to contribute any amount in excess of the amount by
which the Difference exceeds the amount of any damages that such Purchaser has
otherwise been required to pay by reason of such untrue or alleged untrue
statement or omission or alleged omission. No person guilty of fraudulent
misrepresentation (within the meaning of Section 11(f) of the Securities Act)
shall be entitled to contribution from any person who was not guilty of such
fraudulent misrepresentation. The Purchasers' obligations to contribute pursuant
to this Section 7.3 are several and not joint.


                                      -15-
<PAGE>

                  7.4 TERMINATION OF CONDITIONS AND OBLIGATIONS. The conditions
precedent imposed by Section 5 or this Section 7 upon the transferability of the
Shares shall cease and terminate as to any particular number of the Shares upon
the passage of two years from the effective date of the Registration Statement
covering such Shares or at such time as an opinion of counsel satisfactory in
form and substance to the Company shall have been rendered to the effect that
such conditions are not necessary in order to comply with the Securities Act.

                  7.5 INFORMATION AVAILABLE. So long as the Registration
Statement is effective covering the resale of Shares owned by the Purchaser, the
Company will furnish to the Purchaser:

                  (a)      as soon as practicable (but in the case of the
                           Company's Annual Report to Stockholders, within 150
                           days after the end of each fiscal year of the
                           Company), one copy of (i) its Annual Report to
                           Stockholders (which Annual Report shall contain
                           financial statements audited in accordance with
                           generally accepted accounting principles in the
                           United States of America by a firm of certified
                           public accountants of recognized standing), (ii) if
                           not included in substance in the Annual Report to
                           Stockholders, upon the request of the Purchaser, its
                           Annual Report on Form 10-K, (iii) upon the request of
                           the Purchaser, each of its Quarterly Reports to its
                           stockholders and, if not included in substance in its
                           quarterly report to stockholders, its quarterly
                           report on Form 10-Q, (iv) a copy of the Registration
                           Statement (the foregoing, in each case, excluding
                           exhibits);

                  (b)      upon the request of the Purchaser, all exhibits
                           excluded by the parenthetical to subparagraph (a)(iv)
                           of this Section 7.5; and

                  (c)      upon the request of the Purchaser, a reasonable
                           number of copies of the prospectuses to supply to any
                           other party requiring such prospectuses;

and the Company, upon the reasonable request of the Purchaser, will meet with
the Purchaser or a representative thereof at the Company's headquarters to
discuss information relevant for disclosure in the Registration Statement
covering the Shares and will otherwise reasonably cooperate with any Purchaser
conducting an investigation for the purpose of reducing or eliminating such
Purchaser's exposure to liability under the Securities Act, including the
reasonable production of information at the Company's headquarters, subject to
appropriate confidentiality limitations.

                  SECTION 8. BROKER'S FEE. The Purchaser acknowledges that the
Company intends to pay to the Placement Agent a fee in respect of the sale of
the Shares to the Purchaser. Each of the parties hereto hereby represents that,
on the basis of any actions and agreements by it, there are no other brokers or
finders entitled to compensation in connection with the sale of the Shares to
the Purchaser.


                                      -16-
<PAGE>

                  SECTION 9. NOTICES. All notices, requests, consents and other
communications hereunder shall be in writing, shall be mailed by first-class
registered or certified airmail, confirmed facsimile or nationally recognized
overnight express courier postage prepaid, and shall be deemed given when so
mailed and shall be delivered as addressed as follows:

                  (a)      if to the Company, to:

                                    Triangle Pharmaceuticals, Inc.
                                    4 University Place
                                    4611 University Drive
                                    Durham, North Carolina  27707
                                    Attention:  Andrew Finkle, Esq.
                                    Facsimile:  (919) 402-1192

                           with a copy to:

                                    Brobeck, Phleger & Harrison LLP
                                    1633 Broadway
                                    47th Floor
                                    New York, New York  10019
                                    Attention:   Luci Staller Altman, Esq.
                                    Telephone:  (212) 237-2520
                                    Facsimile:   (212) 586-7878

                           or to such other person at such other place as the
                           Company shall designate to the Purchaser in writing;
                           and

                  (b)      if to the Purchaser, at its address as set forth at
                           the end of this Agreement, or at such other address
                           or addresses as may have been furnished to the
                           Company in writing.

                  SECTION 10. CHANGES. This Agreement may not be modified or
amended except pursuant to an instrument in writing signed by the Company and
the Purchaser.

                  SECTION 11. HEADINGS. The headings of the various sections of
this Agreement have been inserted for convenience of reference only and shall
not be deemed to be part of this Agreement.

                  SECTION 12. SEVERABILITY. In case any provision contained in
this Agreement should be invalid, illegal or unenforceable in any respect, the
validity, legality and enforceability of the remaining provisions contained
herein shall not in any way be affected or impaired thereby.

                  SECTION 13. GOVERNING LAW. This Agreement shall be governed by
and construed in accordance with the laws of the State of New York and the
federal law of the United States of America.


                                      -17-
<PAGE>

                  SECTION 14. COUNTERPARTS. This Agreement may be executed in
two or more counterparts, each of which shall constitute an original, but all of
which, when taken together, shall constitute but one instrument, and shall
become effective when one or more counterparts have been signed by each party
hereto and delivered to the other parties. Facsimile signatures shall be deemed
original signatures.

                  SECTION 15. ENTIRE AGREEMENT. This Agreement and the
instruments referenced herein contain the entire understanding of the parties
with respect to the matters covered herein and therein and, except as
specifically set forth herein or therein, neither the Company nor the Purchaser
makes any representation, warranty, covenant or undertaking with respect to such
matters.

                  SECTION 16. THIRD PARTY BENEFICIARIES. This Agreement is
intended for the benefit of the parties hereto and their respective permitted
successors and assigns, and is not for the benefit of, nor may any provision
hereof be enforced by, any other person.


                                      -18-
<PAGE>


                  IN WITNESS WHEREOF, the parties hereto have caused this
Agreement to be executed by their duly authorized representatives as of the day
and year first above written.


                                      TRIANGLE PHARMACEUTICALS, INC.



                                      By:
                                         ----------------------------------
                                            Name:
                                            Title:


Print or Type:
                                      Name of Purchaser
                                        (Individual or Institution):

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

                                      Name of Individual
                                        representing Purchaser
                                        (if an Institution):

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

                                      Title of Individual
                                        representing Purchaser
                                        (if an Institution):

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


Signature by:
                                      Individual Purchaser or Individual
                                        representing Purchaser:

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

                                      Address:
                                                     ---------------------------

                                      Telephone:
                                                     ---------------------------

                                      Facsimile:
                                                     ---------------------------


                                      -19-
<PAGE>

                     SUMMARY INSTRUCTION SHEET FOR PURCHASER

                   (to be read in conjunction with the entire
                        Purchase Agreement which follows)


A.       Complete the following items on BOTH Purchase Agreements:

         1.       Page 19 - Signature:

                  (i)      Name of Purchaser (Individual or Institution)

                  (ii)     Name of Individual representing Purchaser (if an
                           Institution)

                  (iii)    Title of Individual representing Purchaser (if an
                           Institution)

                  (iv)     Signature of Individual Purchaser or Individual
                           representing Purchaser

         2.       Appendix I - Stock Certificate Questionnaire:

                  Provide the information requested by the Stock Certificate
                  Questionnaire.

         3.       Return BOTH properly completed and signed Purchase Agreements
                  including the properly completed Appendix I to:

                           Banc of America Securities LLC
                           9 West 57th Street
                           New York, NY  10019
                           Attention:  Isaac Osaki, Esq.

B.       Instructions regarding the transfer of funds for the purchase of Shares
         will be sent by facsimile to the Purchaser by the Placement Agent at a
         later date.

C.       Upon the resale of the Shares by the Purchasers after the Registration
         Statement covering the Shares is effective, as described in the
         Purchase Agreement, the Purchaser:

                  (i)      must deliver a current prospectus of the Company to
                           the buyer (prospectuses must be obtained from the
                           Company at the Purchaser's request); and

                  (ii)     must send a letter in the form of Appendix II to the
                           Company so that the Shares may be properly
                           transferred.


<PAGE>

                                                                      Appendix I


TRIANGLE PHARMACEUTICALS, INC.
STOCK CERTIFICATE QUESTIONNAIRE



         Pursuant to Section 3 of the Agreement, please provide us with the
following information:

1.       The exact name that your Shares
         are to be registered in (this is
         the name that will appear on your
         stock certificate(s)). You may use
         a nominee name if appropriate:                  _______________________

2.       The relationship between the Purchaser
         of the Shares and the Registered Holder
         listed in response to item 1 above:             _______________________

3.       The mailing address of the Registered
         Holder listed in response to item 1 above:      _______________________

                                                         _______________________

                                                         _______________________

                                                         _______________________

4.       The Social Security Number or Tax
         Identification Number of the Registered
         Holder listed in response to item 1 above:      _______________________

<PAGE>

                                                                      Appendix I

                         TRIANGLE PHARMACEUTICALS, INC.
                      REGISTRATION STATEMENT QUESTIONNAIRE


                  In connection with the preparation of the Registration
Statement, please provide us with the following information:

                  1. Pursuant to the "Selling Shareholder" section of the
Registration Statement, please state your or your organization's name exactly as
it should appear in the Registration Statement:

                  2. Please provide the number of shares that you or your
organization will own immediately after Closing, including those Shares
purchased by you or your organization pursuant to this Purchase Agreement and
those shares purchased by you or your organization through other transactions:

                  3. Have you or your organization had any position, office or
other material relationship within the past three years with the Company or its
affiliates?


                           _____ Yes         _____ No

                  If yes, please indicate the nature of any such relationships
below:

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

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

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

                  4. Are you (i) an NASD Member (see definition), (ii) a
Controlling (see definition) shareholder of an NASD Member, (iii) a Person
Associated with a Member of the NASD (see definition), or (iv) an Underwriter or
a Related Person (see definition) with respect to the proposed offering; or (b)
do you own any shares or other securities of any NASD Member not purchased in
the open market; or (c) have you made any outstanding subordinated loans to any
NASD Member?

<PAGE>

         Answer:  / / Yes  / / No     If "yes," please describe below

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

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

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

         NASD MEMBER. The term "NASD member" means either any broker or dealer
admitted to membership in the National Association of Securities Dealers, Inc.
("NASD"). (NASD Manual, By-laws Article I, Definitions)

       CONTROL. The term "control" (including the terms "controlling,"
"controlled by" and "under common control with") means the possession, direct or
indirect, of the power, either individually or with others, to direct or cause
the direction of the management and policies of a person, whether through the
ownership of voting securities, by contract, or otherwise. (Rule 405 under the
Securities Act of 1933, as amended)

       PERSON ASSOCIATED WITH A MEMBER OF THE NASD. The term "person associated
with a member of the NASD" means every sole proprietor, partner, officer,
director, branch manager or executive representative of any NASD Member, or any
natural person occupying a similar status or performing similar functions, or
any natural person engaged in the investment banking or securities business who
is directly OR INDIRECTLY controlling or controlled by a NASD Member, whether or
not such person is registered or exempt from registration with the NASD pursuant
to its bylaws. (NASD Manual, By-laws Article I, Definitions)

       UNDERWRITER OR A RELATED PERSON. The term "underwriter or a related
person" means, with respect to a proposed offering, underwriters, underwriters'
counsel, financial consultants and advisors, finders, members of the selling or
distribution group, and any and all other persons associated with or related to
any of such persons. (NASD Interpretation)

                                       2

<PAGE>

                                                                     APPENDIX II

Attention:

                   PURCHASER'S CERTIFICATE OF SUBSEQUENT SALE

         The undersigned, [an officer of, or other person duly authorized by]

-------------------------------------------------------------
         [fill in official name of individual or institution]

hereby certifies that he/she [said institution] is the Purchaser
of the shares evidenced by the attached certificate, and as such,
sold such shares on________in accordance with
                    [date]

Registration Statement number _____________________________________
                                           [fill in the number of or otherwise

________________________________ and the requirement of delivering a
identify Registration Statement]

current prospectus by the Company has been complied with in connection with such
sale.

Print or Type:

          Name of Purchaser
            (Individual or
             Institution):       ______________________

          Name of Individual
            representing
            Purchaser (if an
            Institution)         ______________________

          Title of Individual
            representing
            Purchaser (if an
            Institution):        ______________________

<PAGE>

Signature by:

          Individual Purchaser
            or Individual repre-
            senting Purchaser:   ______________________



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