<PAGE>

THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 AS
AMENDED, OR ANY STATE SECURITIES LAWS. THEY MAY NOT BE SOLD, OFFERED FOR SALE,
PLEDGED, OR HYPOTHECATED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT
RELATED THERETO OR AN OPINION OF COUNSEL (WHICH MAY BE COMPANY COUNSEL)
REASONABLY SATISFACTORY TO THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED
UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR ANY APPLICABLE STATE SECURITIES
LAWS.

                                WARRANT AGREEMENT

              TO PURCHASE SHARES OF THE SERIES B PREFERRED STOCK OF

                           ELITRA PHARMACEUTICALS INC.

              DATED AS OF NOVEMBER 12, 1999 (THE "EFFECTIVE DATE")


         WHEREAS, ELITRA PHARMACEUTICALS INC., a Delaware corporation (the
"COMPANY") has entered into a Master Lease Agreement dated as of May 7, 1999,
Equipment Schedule No. VL-1 and VL-2 dated as of May 7, 1999, and related
Summary Equipment Schedules (collectively, the "LEASES") with COMDISCO, INC., a
Delaware corporation (the "WARRANTHOLDER"); and

         WHEREAS, the Company desires to grant to Warrantholder, in
consideration for such Leases, the right to purchase shares of its Series B
Preferred Stock;

         NOW, THEREFORE, in consideration of the Warrantholder executing and
delivering such Leases and in consideration of mutual covenants and agreements
contained herein, the Company and Warrantholder agree as follows:

1.       GRANT OF THE RIGHT TO PURCHASE PREFERRED STOCK.

         The Company hereby grants to the Warrantholder, and the Warrantholder
is entitled, upon the terms and subject to the conditions hereinafter set forth,
to subscribe to and purchase, from the Company, 50,000 fully paid and
non-assessable shares of the Company's Series B Preferred Stock ("PREFERRED
STOCK") at a purchase price of $0.75 per share (the "EXERCISE PRICE"). The
number and purchase price of such shares are subject to adjustment as provided
in Section 8 hereof.

         Notwithstanding the term of this Warrant Agreement as set forth above,
the right to purchase Preferred Stock as granted shall expire, if not previously
exercised, immediately upon the closing of either of the following events:

                  (i)      the issuance and sale of shares of Common Stock of
         the Company in the Company's first public offering of securities for
         its own account pursuant to an effective registration statement under
         the Securities Act of 1933, as amended (the "INITIAL PUBLIC


                                       1.
<PAGE>

         OFFERING"), provided that the underwriters so request that the
         Warrantholder exercise at that time.

                  (ii)     upon the closing of a merger or consolidation of the
         Company with or into another corporation when the Company is not the
         surviving corporation, or the sale of all or substantially all of the
         Company's properties and assets to any other person (the "MERGER")
         provided that the Acquirer request so in writing.

         The Company shall notify the Warrantholder if the Initial Public
Offering or Merger is proposed within a reasonable period of time prior to the
filing of a registration statement and if the Company fails to deliver such
written notice within a reasonable period of time, anything to the contrary in
this Warrant Agreement notwithstanding, the rights to purchase will not expire
until ten (10) business days after the Company delivers such notice to the
Warrantholder. Such notice shall also contain such details of the proposed
Initial Public Offering or Merger as are reasonable in the circumstances and
notice that this Warrant Agreement is expected to expire upon closing thereof.
If such closing does not take place, the Company shall promptly notify the
Warrantholder that such proposed transaction has been terminated. Anything to
the contrary in this Warrant Agreement notwithstanding, the Warrantholder may
rescind any exercise of its purchase rights promptly after such notice of
termination of the proposed transaction if the exercise of warrants occurred
after the Company notified the Warrantholder that the Initial Public Offering or
Merger was proposed or if the exercise were otherwise precipitated by such
proposed Initial Public Offering or Merger. In the event of such rescission, the
Warrants will continue to be exercisable on the same terms and conditions.

2.       TERM OF THE WARRANT AGREEMENT.

         Except as otherwise provided for herein, including in Section 1(i)
hereof, the term of this Warrant Agreement and the right to purchase Preferred
Stock as granted herein shall commence on the Effective Date and shall be
exercisable for a period of (i) five (5) years from the Effective Date or (ii)
three (3) years from the effective date of the Company's Initial Public
Offering, whichever is shorter.

3.       EXERCISE OF THE PURCHASE RIGHTS.

         The purchase rights set forth in this Warrant Agreement are exercisable
by the Warrantholder, in whole or in part, at any time, or from time to time,
prior to the expiration of the term set forth in Section 2 above, by tendering
to the Company at its principal office a notice of exercise in the form attached
hereto as Exhibit I (the "NOTICE OF EXERCISE"), duly completed and executed.
Promptly upon receipt of the Notice of Exercise and the payment of the purchase
price in accordance with the terms set forth below, and in no event later than
twenty-one (21) days thereafter, the Company shall issue to the Warrantholder a
certificate for the number of shares of Preferred Stock purchased and shall
execute the acknowledgement of exercise in the form attached hereto as Exhibit
II (the "ACKNOWLEDGMENT OF EXERCISE") indicating the number of shares which
remain subject to future purchases, if any.

         The Exercise Price may be paid at the Warrantholder's election either
(i) by cash or check, or (ii) by surrender of Warrants ("Net Issuance") as
determined below. If the


                                       2.
<PAGE>

Warrantholder elects the Net Issuance method, the Company will issue Preferred
Stock in accordance with the following formula:

                             X = Y(A-B)
                                 ------
                                   A

         Where:     X =  the number of shares of Preferred Stock to be issued to
                         the Warrantholder.

                    Y =  the number of shares of Preferred Stock requested to be
                         exercised under this Warrant Agreement.

                    A =  the fair market value of one (1) share of Preferred
                         Stock.

                    B =  the Exercise Price.

         For purposes of the above calculation, current fair market value of
Preferred Stock shall mean with respect to each share of Preferred Stock:

                  (i)      if the exercise is in connection with an initial
         public offering of the Company's Common Stock, and if the Company's
         Registration Statement relating to such public offering has been
         declared effective by the SEC, then the fair market value per share
         shall be the product of (x) the initial "Price to Public" specified in
         the final prospectus with respect to the offering and (y) the number of
         shares of Common Stock into which each share of Preferred Stock is
         convertible at the time of such exercise;

                  (ii)     if this Warrant is exercised after, and not in
         connection with the Company's Initial Public Offering, and:

                           (a)      if traded on a securities exchange, the fair
                  market value shall be deemed to be the product of (x) the
                  average of the closing prices over a five (5) day period
                  ending three days before the day the current fair market value
                  of the securities is being determined and (y) the number of
                  shares of Common Stock into which each share of Preferred
                  Stock is convertible at the time of such exercise; or

                           (b)      if actively traded over-the-counter, the
                  fair market value shall be deemed to be the product of (x) the
                  average of the closing bid and asked prices quoted on the
                  NASDAQ system (or similar system) over the five (5) day period
                  ending three days before the day the current fair market value
                  of the securities is being determined and (y) the number of
                  shares of Common Stock into which each share of Preferred
                  Stock is convertible at the time of such exercise;

                  (iii)    if at any time the Common Stock is not listed on any
         securities exchange or quoted in the NASDAQ System or the
         over-the-counter market, the current fair market value of Preferred
         Stock shall be the product of (x) the highest price per share which the
         Company could obtain from a willing buyer (not a current employee or
         director) for shares of Common Stock sold by the Company, from
         authorized but unissued shares, as determined in good faith by


                                       3.
<PAGE>

         its Board of Directors and (y) the number of shares of Common Stock
         into which each share of Preferred Stock is convertible at the time of
         such exercise, unless the Company shall become subject to a Merger,
         acquisition or other consolidation pursuant to which the Company is not
         the surviving party, in which case the fair market value of Preferred
         Stock shall be deemed to be the value received by the holders of the
         Company's Preferred Stock on a common equivalent basis pursuant to such
         merger or acquisition.

         Upon partial exercise by either cash or Net Issuance, the Company shall
promptly issue an amended Warrant Agreement representing the remaining number of
shares purchasable hereunder. All other terms and conditions of such amended
Warrant Agreement shall be identical to those contained herein, including, but
not limited to the Effective Date hereof.

4.       RESERVATION OF SHARES.

         (a)      AUTHORIZATION AND RESERVATION OF SHARES. During the term of
this Warrant Agreement, the Company will at all times have authorized and
reserved a sufficient number of shares of its Preferred Stock to provide for the
exercise of the rights to purchase Preferred Stock as provided for herein.

5.       NO FRACTIONAL SHARES OR SCRIP.

         No fractional shares or scrip representing fractional shares shall be
issued upon the exercise of the Warrant, but in lieu of such fractional shares
the Company shall make a cash payment therefor upon the basis of the Exercise
Price then in effect.

6.       NO RIGHTS AS SHAREHOLDER.

         This Warrant Agreement does not entitle the Warrantholder to any voting
rights or other rights as a shareholder of the Company prior to the exercise of
the Warrant.

7.       WARRANTHOLDER REGISTRY.

         The Company shall maintain a registry showing the name and address of
the registered holder of this Warrant Agreement.

8.       ADJUSTMENT RIGHTS.

         The purchase price per share and the number of shares of Preferred
Stock purchasable hereunder are subject to adjustment, as follows:

         (a)      MERGER AND SALE OF ASSETS. If at any time there shall be a
capital reorganization of the shares of the Company's stock (other than a
combination, reclassification, exchange or subdivision of shares otherwise
provided for herein), or a merger or consolidation of the Company with or into
another corporation whether or not the Company is the surviving corporation, or
the sale of all or substantially all of the Company's properties and assets to
any other person (hereinafter referred to as a "MERGER EVENT"), then, as a part
of such Merger Event, lawful provision shall be made so that the Warrantholder
shall thereafter be entitled to receive, upon exercise of the Warrant, the
number of shares of preferred stock or other securities of the


                                       4.
<PAGE>

successor corporation resulting from such Merger Event, equivalent in value to
that which would have been issuable if Warrantholder had exercised this Warrant
immediately prior to the Merger Event. In any such case, appropriate adjustment
(as determined in good faith by the Company's Board of Directors) shall be made
in the application of the provisions of this Warrant Agreement with respect to
the rights and interest of the Warrantholder after the Merger Event to the end
that the provisions of this Warrant Agreement (including adjustments of the
Exercise Price and number of shares of Preferred Stock purchasable) shall be
applicable to the greatest extent possible.

         (b)      RECLASSIFICATION OF SHARES. If the Company at any time shall,
by combination, reclassification, exchange or subdivision of securities or
otherwise, change any of the securities as to which purchase rights under this
Warrant Agreement exist into the same or a different number of securities of any
other class or classes, this Warrant Agreement shall thereafter represent the
right to acquire such number and kind of securities as would have been issuable
as the result of such change with respect to the securities which were subject
to the purchase rights under this Warrant Agreement immediately prior to such
combination, reclassification, exchange, subdivision or other change.

         (c)      SUBDIVISION OR COMBINATION OF SHARES. If the Company at any
time shall combine or subdivide its Preferred Stock, the Exercise Price shall be
proportionately decreased in the case of a subdivision, or proportionately
increased in the case of a combination.

         (d)      STOCK DIVIDENDS. If the Company at any time shall pay a
dividend payable in, or make any other distribution (except any distribution
specifically provided for in the foregoing subsections (a) or (b)) of the
Company's stock, then the Exercise Price shall be adjusted, from and after the
record date of such dividend or distribution, to that price determined by
multiplying the Exercise Price in effect immediately prior to such record date
by a fraction (i) the numerator of which shall be the total number of all shares
of the Company's stock outstanding immediately prior to such dividend or
distribution, and (ii) the denominator of which shall be the total number of all
shares of the Company's stock outstanding immediately after such dividend or
distribution. The Warrantholder shall thereafter be entitled to purchase, at the
Exercise Price resulting from such adjustment, the number of shares of Preferred
Stock (calculated to the nearest whole share) obtained by multiplying the
Exercise Price in effect immediately prior to such adjustment by the number of
shares of Preferred Stock issuable upon the exercise hereof immediately prior to
such adjustment and dividing the product thereof by the Exercise Price resulting
from such adjustment.

         (e)      RIGHT TO PURCHASE ADDITIONAL STOCK. If the Warrantholder's
total cost of equipment leased pursuant to the Leases exceeds $250,000,
Warrantholder shall have the right to purchase from the Company, at the Exercise
Price (adjusted as set forth herein), an additional number of shares, which
number shall be determined by (i) multiplying the amount by which the
Warrantholder's total equipment cost exceeds 250,000 by 5%, and (ii) dividing
the product thereof by the Exercise Price per share referenced above.

         (f)      ANTIDILUTION RIGHTS. Additional antidilution rights applicable
to the Preferred Stock purchasable hereunder are as set forth in the Company's
Certificate of Incorporation, as amended through the Effective Date, a true and
complete copy of which is attached hereto as


                                       5.
<PAGE>

Exhibit IV (the "CHARTER"). The Company shall promptly provide the Warrantholder
with any restatement, amendment, modification or waiver of the Charter. The
Company shall provide Warrantholder with prior written notice of any dilutive
issuance of its stock or other equity security to occur after the Effective Date
of this Warrant, which notice shall include (a) the price at which such stock or
security is to be sold, (b) the number of shares to be issued, and (c) such
other information as necessary for Warrantholder to determine if a dilutive
event has occurred.

         (g)      NOTICE OF ADJUSTMENTS. If: (i) the Company shall declare any
dividend or distribution upon its stock, whether in cash, property, stock or
other securities; (ii) the Company shall offer for subscription prorata to the
holders of any class of its Preferred or other convertible stock any additional
shares of stock of any class or other rights; (iii) there shall be any Merger
Event; (iv) there shall be an Initial Public Offering; or (v) there shall be any
voluntary dissolution, liquidation or winding up of the Company; then, in
connection with each such event, the Company shall send to the Warrantholder:
(A) at least twenty (20) days' prior written notice of the date on which the
books of the Company shall close or a record shall be taken for such dividend,
distribution, subscription rights (specifying the date on which the holders of
Preferred Stock shall be entitled thereto) or for determining rights to vote in
respect of such Merger Event, dissolution, liquidation or winding up; (B) in the
case of any such Merger Event, dissolution, liquidation or winding up, at least
twenty (20) days' prior written notice of the date when the same shall take
place (and specifying the date on which the holders of Preferred Stock shall be
entitled to exchange their Preferred Stock for securities or other property
deliverable upon such Merger Event dissolution, liquidation or winding up); and
(C) in the case of an Initial Public Offering, the Company shall give the
Warrantholder at least twenty (20) days written notice prior to the effective
date thereof.

         Each such written notice shall set forth, in reasonable detail, (i) the
event requiring the adjustment, (ii) the amount of the adjustment, (iii) the
method by which such adjustment was calculated, (iv) the Exercise Price, and (v)
the number of shares subject to purchase hereunder after giving effect to such
adjustment, and shall be given by first class mail, postage prepaid, addressed
to the Warrantholder, at the address as shown on the books of the Company.

         (h)      TIMELY NOTICE. Failure to timely provide such notice required
by subsection (g) above shall entitle Warrantholder to retain the benefit of the
applicable notice period notwithstanding anything to the contrary contained in
any insufficient notice received by Warrantholder. The notice period shall begin
on the date Warrantholder actually receives a written notice containing all the
information specified above.

9.       REPRESENTATIONS, WARRANTIES AND COVENANTS OF THE COMPANY.

         (a)      RESERVATION OF PREFERRED STOCK. The Preferred Stock issuable
upon exercise of the Warrantholder's rights has been duly and validly reserved
and, when issued in accordance with the provisions of this Warrant Agreement,
will be validly issued, fully paid and non-assessable, and will be free of any
taxes, liens, charges or encumbrances of any nature whatsoever; PROVIDED,
HOWEVER, that the Preferred Stock issuable pursuant to this Warrant Agreement
may be subject to restrictions on transfer under state and/or Federal securities
laws. The Company has made available to the Warrantholder true, correct and
complete copies of its Charter and Bylaws, as amended. The issuance of
certificates for shares of Preferred Stock upon


                                       6.
<PAGE>

exercise of the Warrant Agreement shall be made without charge to the
Warrantholder for any issuance tax in respect thereof, or other cost incurred by
the Company in connection with such exercise and the related issuance of shares
of Preferred Stock. The Company shall not be required to pay any tax which may
be payable in respect of any transfer involved and the issuance and delivery of
any certificate in a name other than that of the Warrantholder.

         (b)      DUE AUTHORITY. The execution and delivery by the Company of
this Warrant Agreement and the performance of all obligations of the Company
hereunder, including the issuance to Warrantholder of the right to acquire the
shares of Preferred Stock, have been duly authorized by all necessary corporate
action on the part of the Company, and the Leases and this Warrant Agreement are
not inconsistent with the Company's Charter or Bylaws, do not contravene any law
or governmental rule, regulation or order applicable to it, do not and will not
contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument to which it is a party or by which it is
bound, and the Leases and this Warrant Agreement constitute legal, valid and
binding agreements of the Company, enforceable in accordance with their
respective terms.

         (c)      CONSENTS AND APPROVALS. No consent or approval of, giving of
notice to, registration with, or taking of any other action in respect of any
state, Federal or other governmental authority or agency is required with
respect to the execution, delivery and performance by the Company of its
obligations under this Warrant Agreement, except for the filing of notices
pursuant to Regulation D under the 1933 Act and any filing required by
applicable state securities law, which filings will be effective by the time
required thereby.

         (d)      ISSUED SECURITIES. All issued and outstanding shares of Common
Stock, Preferred Stock or any other securities of the Company have been duly
authorized and validly issued and are fully paid and nonassessable. All
outstanding shares of Common Stock, Preferred Stock and any other securities
were issued in full compliance with all Federal and state securities laws. In
addition:

                  (i)      The authorized capital of the Company consists of (A)
         10,000,000 shares of Common Stock, of which 3,541,699 shares are issued
         and outstanding, (B) 4,545,456 shares of Series A Preferred Stock, of
         which 4,545,456 shares are issued and outstanding and are convertible
         into 4,545,456 shares of Common Stock at $0.66 per share, (C)
         21,651,063 shares of Series B Preferred Stock, of which 21,333,334
         shares are issued and outstanding and are convertible into 21,333,334
         shares of Common Stock at $0.75 per share and (D) warrants to purchase
         67,606 shares of Series B Preferred Stock.

                  (ii)     The Company has reserved 2,988,425 shares of Common
         Stock for issuance under its 1998 Equity Incentive Plan, under which
         1,214,688 options are outstanding at an average price of $0.07 per
         share. There are no other options, warrants, conversion privileges or
         other rights, other than those mentioned in 9(d)(i), presently
         outstanding to purchase or otherwise acquire any authorized but
         unissued shares of the Company's capital stock or other securities of
         the Company.


                                       7.
<PAGE>

                  (iii)    In accordance with the Company's Certificate of
         Incorporation, no shareholder of the Company has preemptive rights to
         purchase new issuances of the Company's capital stock.

         (e)      INSURANCE. The Company has in full force and effect insurance
policies, with extended coverage, insuring the Company and its property and
business against such losses and risks, and in such amounts, as are customary
for corporations engaged in a similar business and similarly situated and as
otherwise may be required pursuant to the terms of any other contract or
agreement.

         (f)      OTHER COMMITMENTS TO REGISTER SECURITIES. Except as set forth
in this warrant Agreement and Investor Rights Agreement dated as of June 18,
1998, the Company is not, pursuant to the terms of any other agreement currently
in existence, under any obligation to register under the 1933 Act any of its
presently outstanding securities or any of its securities which may hereafter be
issued.

         (g)      EXEMPT TRANSACTION. Subject to the accuracy of the
Warrantholder's representations in Section 10 hereof, the issuance of the
Preferred Stock upon exercise of this Warrant will constitute a transaction
exempt from (i) the registration requirements of Section 5 of the 1933 Act, in
reliance upon Section 4(2) thereof, and (ii) the qualification requirements of
the applicable state securities laws.

         (h)      COMPLIANCE WITH RULE 144. Following the Initial Public
Offering, at the written request of the Warrantholder, who proposes to sell
Preferred Stock issuable upon the exercise of the Warrant in compliance with
Rule 144 promulgated by the Securities and Exchange Commission, the Company
shall furnish to the Warrantholder, within ten days after receipt of such
request, a written statement confirming the Company's compliance with the filing
requirements of the Securities and Exchange Commission as set forth in such
Rule, as such Rule may be amended from time to time.

10.      REPRESENTATIONS AND COVENANTS OF THE WARRANTHOLDER.

         This Warrant Agreement has been entered into by the Company in reliance
upon the following representations and covenants of the Warrantholder:

         (a)      INVESTMENT PURPOSE. The right to acquire Preferred Stock or
the Preferred Stock issuable upon exercise of the Warrantholder's rights
contained herein will be acquired for investment and not with a view to the sale
or distribution of any part thereof, and the Warrantholder has no present
intention of selling or engaging in any public distribution of the same except
pursuant to a registration or exemption.

         (b)      PRIVATE ISSUE. The Warrantholder understands (i) that the
Preferred Stock issuable upon exercise of this Warrant and the Common Stock
issuable upon conversion of the Preferred Stock is not registered under the 1933
Act or qualified under applicable state securities laws on the ground that the
issuance contemplated by this Warrant Agreement will be exempt from the
registration and qualifications requirements thereof, and (ii) that the
Company's reliance on such exemption is predicated on the representations set
forth in this Section 10.


                                       8.
<PAGE>

         (c)      DISPOSITION OF WARRANTHOLDER'S RIGHTS. In no event will the
Warrantholder make a disposition of any of its rights to acquire Preferred Stock
or Preferred Stock issuable upon exercise of such rights unless and until (i) it
shall have notified the Company of the proposed disposition, and (ii) if
requested by the Company, it shall have furnished the Company with an opinion of
counsel (which counsel may either be inside or outside counsel to the
Warrantholder) satisfactory to the Company and its counsel to the effect that
(A) appropriate action necessary for compliance with the 1933 Act has been
taken, or (B) an exemption from the registration requirements of the 1933 Act is
available. Notwithstanding the foregoing, the restrictions imposed upon the
transferability of any of its rights to acquire Preferred Stock or Preferred
Stock issuable on the exercise of such rights do not apply to transfers from the
beneficial owner of any of the aforementioned securities to its nominee or from
such nominee to its beneficial owner, and shall terminate as to any particular
share of Preferred Stock when (1) such security shall have been effectively
registered under the 1933 Act and sold by the holder thereof in accordance with
such registration or (2) such security shall have been sold without registration
in compliance with Rule 144 under the 1933 Act, or (3) a letter shall have been
issued to the Warrantholder at its request by the staff of the Securities and
Exchange Commission or a ruling shall have been issued to the Warrantholder at
its request by such Commission stating that no action shall be recommended by
such staff or taken by such Commission, as the case may be, if such security is
transferred without registration under the 1933 Act in accordance with the
conditions set forth in such letter or ruling and such letter or ruling
specifies that no subsequent restrictions on transfer are required. Whenever the
restrictions imposed hereunder shall terminate, as hereinabove provided, the
Warrantholder or holder of a share of Preferred Stock then outstanding as to
which such restrictions have terminated shall be entitled to receive from the
Company, without expense to such holder, one or more new certificates for the
Warrant or for such shares of Preferred Stock not bearing any restrictive
legend.

         (d)      FINANCIAL RISK. The Warrantholder has such knowledge and
experience in financial and business matters as to be capable of evaluating the
merits and risks of its investment, and has the ability to bear the economic
risks of its investment.

         (e)      RISK OF NO REGISTRATION. The Warrantholder understands that if
the Company does not register with the Securities and Exchange Commission
pursuant to Section 12 of the 1934 Act (the "1934 ACT"), or file reports
pursuant to Section 15(d), of the 1934 Act, or if a registration statement
covering the securities under the 1933 Act is not in effect when it desires to
sell (i) the rights to purchase Preferred Stock pursuant to this Warrant
Agreement, or (ii) the Preferred Stock issuable upon exercise of the right to
purchase, it may be required to hold such securities for an indefinite period.
The Warrantholder also understands that any sale of its rights of the
Warrantholder to purchase Preferred Stock or Preferred Stock which might be made
by it in reliance upon Rule 144 under the 1933 Act may be made only in
accordance with the terms and conditions of that Rule. The Warrantholder is
aware that the conditions for resale set forth in Rule 144 have not been
satisfied and that the Company presently has no plans to satisfy these
conditions until immediately following the Company's Initial Public Offering.

         (f)      ACCREDITED INVESTOR. Warrantholder is an "accredited investor"
within the meaning of the Securities and Exchange Rule 501 of Regulation D, as
presently in effect.


                                       9.
<PAGE>

         (g)      LEGEND. The Warrantholder understands and agrees that all
certificates evidencing the shares to be issued to the Warrantholder may bear
the following legend:

                  THESE SECURITIES HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
                  ACT OF 1933, AS AMENDED ("THE ACT"). THEY MAY NOT BE SOLD,
                  OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE ABSENCE OF
                  ANY EFFECTIVE REGISTRATION STATEMENT AS TO THE SECURITIES
                  UNDER THE ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE
                  COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED.

11.      RIGHT OF FIRST OFFER.

         The Company covenants to use its best efforts to amend the Investor
Rights Agreement dated June 18, 1998 (the "RIGHTS AGREEMENT") to the extent
necessary such that the Warrantholder will be considered an "Investor" and the
Preferred Stock will be considered "Shares" only for the purposes of Section
4.1, 4.2, 4.3, 4.4 and 4.6 of the Rights Agreement; PROVIDED, HOWEVER, that the
Warrantholder shall receive no other rights under the Rights Agreement.

12.      TRANSFERS.

         Subject to the terms and conditions contained in Section 10 hereof,
this Warrant Agreement and all rights hereunder are transferable in whole or in
part by the Warrantholder and any successor transferee, PROVIDED, HOWEVER, in no
event shall the number of transfers of the rights and interests in all of the
Warrants exceed three (3) transfers. The transfer shall be recorded on the books
of the Company upon receipt by the Company of a notice of transfer in the form
attached hereto as Exhibit III (the "TRANSFER NOTICE"), at its principal offices
and the payment to the Company of all transfer taxes and other governmental
charges imposed on such transfer.

13.      MISCELLANEOUS.

         (a)      EFFECTIVE DATE. The provisions of this Warrant Agreement shall
be construed and shall be given effect in all respects as if it had been
executed and delivered by the Company on the date hereof. This Warrant Agreement
shall be binding upon any successors or assigns of the Company.

         (b)      ATTORNEY'S FEES. In any litigation, arbitration or court
proceeding between the Company and the Warrantholder relating hereto, the
prevailing party shall be entitled to attorneys' fees and expenses and all costs
of proceedings incurred in enforcing this Warrant Agreement.

         (c)      GOVERNING LAW. This Warrant Agreement shall be governed by and
construed for all purposes under and in accordance with the laws of the State of
Illinois.


                                      10.
<PAGE>

         (d)      COUNTERPARTS. This Warrant Agreement may be executed in two or
more counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

         (e)      NOTICES. Any notice required or permitted hereunder shall be
given in writing and shall be deemed effectively given upon personal delivery,
facsimile transmission (provided that the original is sent by personal delivery
or mail as hereinafter set forth) or seven (7) days after deposit in the United
States mail, by registered or certified mail, addressed (i) to the Warrantholder
at 6111 North River Road, Rosemont, Illinois 60018, Attention: Venture Lease
Administration, cc: Legal Department, Attention: General Counsel, (and/or, if by
facsimile, (847) 518-5465 and (847) 518-5088) and (ii) to the Company at 3510
Dunhill Street, Suite A, San Diego, CA 92121, Attention: Chief Financial Officer
(and/or if by facsimile, (619) 410-3090) or at such other address as any such
party may subsequently designate by written notice to the other party.

         (f)      REMEDIES. In the event of any default hereunder, the
non-defaulting party may proceed to protect and enforce its rights either by
suit in equity and/or by action at law, including but not limited to an action
for damages as a result of any such default, and/or an action for specific
performance for any default where Warrantholder will not have an adequate remedy
at law and where damages will not be readily ascertainable. The Company
expressly agrees that it shall not oppose an application by the Warrantholder or
any other person entitled to the benefit of this Agreement requiring specific
performance of any or all provisions hereof or enjoining the Company from
continuing to commit any such breach of this Agreement.

         (g)      NO IMPAIRMENT OF RIGHTS. The Company will not, by amendment of
its Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
actions as may be necessary or appropriate in order to protect the rights of the
Warrantholder against impairment.

         (h)      SURVIVAL. The representations, warranties, covenants and
conditions of the respective parties contained herein or made pursuant to this
Warrant Agreement shall survive the execution and delivery of this Warrant
Agreement.

         (i)      SEVERABILITY. In the event any one or more of the provisions
of this Warrant Agreement shall for any reason be held invalid, illegal or
unenforceable, the remaining provisions of this Warrant Agreement shall be
unimpaired, and the invalid, illegal or unenforceable provision shall be
replaced by a mutually acceptable valid, legal and enforceable provision, which
comes closest to the intention of the parties underlying the invalid, illegal or
unenforceable provision.

         (j)      AMENDMENTS. Any provision of this Warrant Agreement may be
amended by a written instrument signed by the Company and by the Warrantholder.

         (k)      ADDITIONAL DOCUMENTS. The Company, upon execution of this
Warrant Agreement, shall provide the Warrantholder with certified resolutions
with respect to the representations, warranties and covenants set forth in
subparagraphs (a) through (d), (f) and (g)


                                      11.
<PAGE>

of Section 9 above. The Company shall also supply such other documents as the
Warrantholder may from time to time reasonably request.

         IN WITNESS WHEREOF, the parties hereto have caused this Warrant
Agreement to be executed by its officers thereunto duly authorized as of the
Effective Date.

                                         COMPANY:  ELITRA PHARMACEUTICALS INC.

                                         By: /s/ Alana B. Wheeler
                                            ------------------------------------

                                         Title: CFO
                                               ---------------------------------


                                         WARRANTHOLDER:  COMDISCO, INC.

                                         By: /s/ Illegible Signature
                                            ------------------------------------

                                         Title: VP
                                               ---------------------------------


                                      12.
<PAGE>

                                    EXHIBIT I

                               NOTICE OF EXERCISE

To: ___________________________

(1)      The undersigned Warrantholder hereby elects to purchase ___________
         shares of the Series B Preferred Stock of _______________, pursuant to
         the terms of the Warrant Agreement dated the ______ day of
         _________________, 2000 (the "WARRANT AGREEMENT") between
         _______________________________ and the Warrantholder, and tenders
         herewith payment of the purchase price for such shares in full,
         together with all applicable transfer taxes, if any.

(2)      In exercising its rights to purchase the Series B Preferred Stock of
         _________________, the undersigned hereby confirms and acknowledges the
         investment representations and warranties made in Section 10 of the
         Warrant Agreement.

(3)      Please issue a certificate or certificates representing said shares of
         Series B Preferred Stock in the name of the undersigned or in such
         other name as is specified below.


_____________________________________
(Name)


_____________________________________
(Address)


WARRANTHOLDER:  COMDISCO, INC.
By:__________________________________

Title:_______________________________

Date:________________________________


                                      13.
<PAGE>

                                   EXHIBIT II

                           ACKNOWLEDGMENT OF EXERCISE


         The undersigned _____________________ hereby acknowledge receipt of the
"Notice of Exercise" from COMDISCO, INC., to purchase _______________ shares of
the Series B Preferred Stock of _____________________, pursuant to the terms of
the Warrant Agreement, and further acknowledges that ____________shares remain
subject to purchase under the terms of the Warrant Agreement.

                                                     COMPANY:



                                                     By:________________________

                                                     Title:_____________________

                                                     Date:______________________


                                      14.
<PAGE>

                                   EXHIBIT III

                                 TRANSFER NOTICE


(TO TRANSFER OR ASSIGN THE FOREGOING WARRANT AGREEMENT EXECUTE THIS FORM AND
SUPPLY REQUIRED INFORMATION. DO NOT USE THIS FORM TO PURCHASE SHARES.)

         FOR VALUE RECEIVED, the foregoing Warrant Agreement and all rights
evidenced thereby are hereby transferred and assigned to

____________________________________________________
(Please Print)

whose address is ___________________________________

____________________________________________________


                  Dated:____________________________

                  Holder's Signature:_______________

                  Holder's Address:_________________


Signature Guaranteed:_______________________________

NOTE:    The signature to this Transfer Notice must correspond with the name as
         it appears on the face of the Warrant Agreement, without alteration or
         enlargement or any change whatever. Officers of corporations and those
         acting in a fiduciary or other representative capacity should file
         proper evidence of authority to assign the foregoing Warrant Agreement.


                                      15.