<PAGE>

                           ELITRA PHARMACEUTICALS INC.


                   SERIES D PREFERRED STOCK PURCHASE AGREEMENT

<PAGE>

<TABLE>
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                                TABLE OF CONTENTS
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                                                                                                              PAGE

1.       AGREEMENT TO SELL AND PURCHASE...........................................................................1

         1.1      Authorization of Shares.........................................................................1

         1.2      Issuance of Shares..............................................................................1

2.       CLOSING, DELIVERY AND PAYMENT............................................................................1

         2.1      Closing.........................................................................................1

         2.2      Delivery........................................................................................2

3.       REPRESENTATIONS AND WARRANTIES OF THE COMPANY............................................................2

         3.1      Organization, Good Standing and Qualification...................................................2

         3.2      Capitalization..................................................................................2

         3.3      Authorization; Binding Obligations..............................................................3

         3.4      Financial Statements............................................................................3

         3.5      Compliance With Other Instruments...............................................................3

         3.6      Litigation......................................................................................4

         3.7      Compliance With Laws............................................................................4

         3.8      Offering Valid..................................................................................4

4.       REPRESENTATIONS AND WARRANTIES OF PURCHASER..............................................................4

         4.1      Requisite Power and Authority...................................................................4

         4.2      Investment Representations......................................................................4

         4.3      Transfer Restrictions...........................................................................6

5.       CONDITIONS TO CLOSING....................................................................................6

         5.1      Conditions to Purchaser's Obligations at the Closing............................................6

         5.2      Conditions to Obligations of the Company at the Closing.........................................7

6.       MISCELLANEOUS............................................................................................8

         6.1      Governing Law...................................................................................8

         6.2      Survival........................................................................................8

         6.3      Successors and Assigns..........................................................................8

         6.4      Entire Agreement................................................................................8

         6.5      Severability....................................................................................8

         6.6      Amendment and Waiver............................................................................8

         6.7      Delays or Omissions.............................................................................8


                                       i.
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<CAPTION>
                                TABLE OF CONTENTS
                                   (CONTINUED)
                                                                                                              PAGE

         6.8      Notices.........................................................................................9

         6.9      Expenses........................................................................................9

         6.10     Attorneys' Fees.................................................................................9

         6.11     Titles and Subtitles............................................................................9

         6.12     Counterparts....................................................................................9

         6.13     Broker's Fees...................................................................................9

         6.14     California Corporate Securities Law.............................................................9

         6.15     Publicity......................................................................................10


Restated Certificate of Incorporation                                                        Exhibit A

Schedule of Exceptions                                                                       Exhibit B

Investor Rights Agreement                                                                    Exhibit C

Co-Sale Agreement                                                                            Exhibit D

Opinion of Company Counsel                                                                   Exhibit E
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                                      ii.
<PAGE>

                           ELITRA PHARMACEUTICALS INC.

                   SERIES D PREFERRED STOCK PURCHASE AGREEMENT


         THIS SERIES D PREFERRED STOCK PURCHASE AGREEMENT (the "Agreement") is
entered into as of June 30th, 2000, by and between ELITRA PHARMACEUTICALS INC.,
a Delaware corporation having an address of 3510 Dunhill Street, San Diego, CA
92121 (the "Company"), and INCYTE GENOMICS, INC., a Delaware corporation having
its principal place of business at 3160 Porter Drive, Palo Alto, CA 94304
("Purchaser").

                                    RECITALS

         WHEREAS, the Company and Purchaser have entered into that certain
Microbial Information Agreement of even date herewith (the "Microbial
Information Agreement");

         WHEREAS, in connection with, and as partial consideration for the
transfer of certain assets of Purchaser to the Company pursuant to, the
Microbial Information Agreement, the Company desires to issue to Purchaser and
Purchaser desires to receive from the Company, one million five hundred
thirty-eight thousand four hundred sixty-two (1,538,462) shares of Series D
Preferred Stock of the Company (the "Shares") on the terms and subject to the
conditions set forth herein;

         NOW, THEREFORE, in consideration of the foregoing recitals and the
mutual promises hereinafter set forth, the parties hereto agree as follows:

         1.       AGREEMENT TO SELL AND PURCHASE.

                  1.1      AUTHORIZATION OF SHARES. On or prior to the Closing
(as defined in Section 2 below), the Company shall have authorized (i) the sale
and issuance to Purchaser of the Shares, and (ii) the issuance of such shares of
Common Stock, par value $.001, to be issued upon conversion of the Shares (the
"Conversion Shares"). The Shares and the Conversion Shares shall have the
rights, preferences, privileges and restrictions set forth in the Restated
Certificate of Incorporation of the Company, in the form attached hereto as
EXHIBIT A (the "Restated Certificate").

                  1.2      ISSUANCE OF SHARES. Subject to the terms and
conditions hereof, at the Closing (as hereinafter defined) the Company hereby
agrees to issue the Shares to Purchaser in partial consideration for the
transfer of certain assets of Purchaser to the Company pursuant to the terms of
the Microbial Information Agreement at the Closing.

         2.       CLOSING, DELIVERY AND PAYMENT.

                  2.1      CLOSING. The closing of the issuance of the Shares
under this Agreement (the "Closing") shall take place at 1:00 p.m. on the date
hereof, at the offices of Cooley Godward LLP, 4365 Executive Drive, Suite 1100,
San Diego, California 92121 or at such other time or place as the Company and
Purchaser may mutually agree (the "Closing Date") or at such time and date
thereafter as Purchaser and the Company may agree.


                                       1.
<PAGE>

                  2.2      DELIVERY. At the Closing, subject to the terms and
conditions hereof, the Company will deliver to Purchaser a certificate
representing the number of Shares to be issued at the Closing to Purchaser,
against payment of the purchase price therefor by delivery to the Company by the
Purchaser of certain assets of Purchaser pursuant to the Microbial Information
Agreement.

         3.       REPRESENTATIONS AND WARRANTIES OF THE COMPANY.

         Except as set forth on a Schedule of Exceptions, attached hereto as
EXHIBIT B, the Company hereby represents and warrants to Purchaser as of the
date of this Agreement as follows:

                  3.1      ORGANIZATION, GOOD STANDING AND QUALIFICATION. The
Company is a corporation duly organized, validly existing and in good standing
under the laws of the State of Delaware. The Company has all requisite corporate
power and authority to own and operate its properties and assets, to execute and
deliver this Agreement, the Second Amended and Restated Investor Rights
Agreement in substantially the form attached hereto as EXHIBIT C (the "Investor
Rights Agreement") and the Second Amended and Restated Right of First Offer and
Co-Sale Agreement in substantially the form attached hereto as EXHIBIT D (the
"Co-Sale Agreement" and collectively with the Investor Rights Agreement, the
"Related Agreements"), to issue and sell the Shares and to issue the Conversion
Shares and to carry out the provisions of this Agreement, the Related Agreements
and the Restated Certificate and to carry on its business as presently conducted
and as presently proposed to be conducted. The Company is duly qualified and is
authorized to do business and is in good standing as a foreign corporation in
all jurisdictions in which the nature of its activities and of its properties
(both owned and leased) makes such qualification necessary, except for those
jurisdictions in which the failure to do so would not have a material adverse
effect on the assets, financial condition or operations of the Company.

                  3.2      CAPITALIZATION. The authorized capital stock of the
Company immediately prior to the Closing will consist of forty-five million
(45,000,000) shares of Common Stock, par value $0.001, four million six hundred
five thousand nine hundred nine (4,605,909) shares of which are issued and
outstanding, and twenty-eight million seven hundred seventy-six thousand six
hundred forty-eight (28,776,648) shares of Preferred Stock, par value $0.001,
four million five hundred forty-five thousand four hundred fifty-six (4,545,456)
of which are designated Series A Preferred Stock, all of which are issued and
outstanding, twenty-one million six hundred fifty-one thousand sixty-three
(21,651,063) of which are designated Series B Preferred Stock, twenty-one
million three hundred thirty-three thousand three hundred thirty-four
(21,333,334) of which are issued and outstanding, one million forty-one thousand
six hundred sixty-seven (1,041,667) of which are designated Series C Preferred
Stock, all of which are issued and outstanding, and one million five hundred
thirty-eight thousand four hundred sixty-two (1,538,462) of which are designated
Series D Preferred Stock, none of which are issued and outstanding. The rights,
preferences, privileges and restrictions of the Series D Preferred Stock are as
stated in the Restated Certificate. The Conversion Shares have been duly and
validly reserved for issuance. Other than conversion rights of the Series A,
Series B, Series C and Series D Preferred Stock and such rights as may be
granted pursuant to this Agreement, the Related Agreements and the Microbial
Information Agreement, there are no outstanding options, warrants, rights
(including conversion or preemptive rights and rights of first refusal), proxy
or


                                       2.
<PAGE>

stockholder agreements, or agreements of any kind for the purchase or
acquisition from the Company of any of its securities, other than three million
six hundred eighty-eight thousand four hundred twenty-five (3,688,425) shares
reserved for issuance to employees and consultants of the Company under the 1998
Equity Incentive Plan. When issued in compliance with the provisions of this
Agreement and the Restated Certificate, the Shares and Conversion Shares will be
validly issued, fully paid and nonassessable.

                  3.3      AUTHORIZATION; BINDING OBLIGATIONS. All corporate
action on the part of the Company, its officers, directors and stockholders
necessary for the authorization of this Agreement and the Related Agreements,
the performance of all obligations of the Company hereunder at the Closing and
the authorization, sale, issuance and delivery of the Shares pursuant hereto and
the authorization, issuance and delivery of the Conversion Shares pursuant to
the Restated Certificate has been taken or will be taken prior to the Closing.
The Agreement and the Related Agreements, when executed and delivered, will be a
valid and binding obligation of the Company enforceable in accordance with its
terms, except (a) as limited by applicable bankruptcy, insolvency,
reorganization, moratorium or other laws of general application affecting
enforcement of creditors' rights and (b) general principles of equity that
restrict the availability of equitable remedies. The sale of the Shares and the
subsequent conversion of the Shares into Conversion Shares, if applicable, are
not and will not be subject to any preemptive rights or rights of first refusal
that have not been properly waived or complied with.

                  3.4      FINANCIAL STATEMENTS. The Company has delivered to
Purchaser (a) its audited balance sheet as at December 31, 1999 and audited
statement of income and cash flow for the twelve months ending December 31, 1999
and (b) its unaudited balance sheet as at March 31, 2000 (the "Statement Date")
and unaudited statement of income and cash flows for the three-month period
ended on the Statement Date (collectively, the "Financial Statements"). The
Financial Statements have been prepared in accordance with generally accepted
accounting principles applied on a consistent basis, except as disclosed
therein, and present fairly the financial condition and position of the Company
as of the Statement Date; provided, however, that the Financial Statements are
subject to normal recurring year-end audit adjustments and do not contain all
footnotes required under generally accepted accounting principles.

                  3.5      COMPLIANCE WITH OTHER INSTRUMENTS. The execution,
delivery, and performance of and compliance with this Agreement, and the
issuance and sale of the Shares pursuant hereto and the issuance of the
Conversion Shares pursuant to the Restated Certificate, will not, with or
without the passage of time or giving of notice, result in any such violation,
or be in conflict with or constitute a default under any such term or provision
which would materially and adversely affect the assets, financial condition or
operations of the Company, or result in the creation of any mortgage, pledge,
lien, encumbrance or charge upon any of the properties or assets of the Company
or the suspension, revocation, impairment, forfeiture or nonrenewal of any
permit license, authorization or approval applicable to the Company, its
business or operations or any of its assets or properties.

                  3.6      LITIGATION. There is no (a) claim, arbitration,
action, suit, proceeding or investigation at law or in equity or by or before
any federal or state governmental instrumentality or other agency pending, or to
the best of the Company's knowledge, currently threatened against the Company or
(b) judgment, decree, injunction or order of any court, governmental


                                       3.
<PAGE>

department, commission, agency, instrumentality or arbitrator against the
Company, in either case, which might result, either individually or in the
aggregate, in any material adverse change in the assets, financial condition or
operations of the Company, financially or otherwise. There is no action, suit,
proceeding or investigation by the Company currently pending or which the
Company intends to initiate.

                  3.7      COMPLIANCE WITH LAWS. No governmental orders,
permissions, consents, approvals or authorizations are required to be obtained
and no registrations or declarations are required to be filed in connection with
the execution and delivery of this Agreement or the Related Agreements and the
issuance of the Shares or the Conversion Shares, except such as has been duly
and validly obtained or filed, or with respect to any filings that must be made
after the Closing, will be filed in a timely manner.

                  3.8      OFFERING VALID. Assuming the accuracy of the
representations and warranties of Purchaser contained in Section 4.2 hereof, the
offer, sale and issuance of the Shares and the issuance of Conversion Shares
will be exempt from the registration requirements of the Securities Act of 1933,
as amended (the "Securities Act"), and will have been registered or qualified
(or are exempt from registration and qualification) under the registration,
permit or qualification requirements of all applicable state securities laws.
Neither the Company nor any agent on its behalf has solicited or will solicit
any offers to sell or has offered to sell or will offer to sell all or any part
of the Shares to any person or persons so as to bring the sale of such shares by
the Company within the registration provisions of the Securities Act or any
state securities laws.

         4.       REPRESENTATIONS AND WARRANTIES OF PURCHASER.

         Purchaser hereby represents and warrants to the Company as follows:

                  4.1      REQUISITE POWER AND AUTHORITY. Purchaser has all
necessary power and authority under all applicable provisions of law to execute
and deliver this Agreement and the Related Agreements and to carry out their
provisions. All actions on Purchaser's part required for the lawful execution
and delivery of this Agreement and the Related Agreements have been or will be
effectively taken prior to the Closing. Upon their execution and delivery, this
Agreement will be valid and binding obligations of Purchaser, enforceable in
accordance with their terms, except (a) as limited by applicable bankruptcy,
insolvency, reorganization, moratorium or other laws of general application
affecting enforcement of creditors' rights and (b) general principles of equity
that restrict the availability of equitable remedies.

                  4.2      INVESTMENT REPRESENTATIONS. Purchaser understands
that neither the Shares nor the Conversion Shares have been registered under the
Securities Act. Purchaser also understands that the Shares and the Conversion
Shares are being offered and sold pursuant to an exemption from registration
contained in the Securities Act based in part upon Purchaser's representations
contained in this Agreement. Purchaser hereby represents and warrants as
follows:

                           (a)      PURCHASER BEARS ECONOMIC RISK. Purchaser has
substantial experience in evaluating and investing in private placement
transactions of securities in


                                       4.
<PAGE>

companies similar to the Company so that it is capable of evaluating the merits
and risks of its investment in the Company and has the capacity to protect its
own interests. Purchaser must bear the economic risk of this investment
indefinitely unless the Shares (or the Conversion Shares) are registered
pursuant to the Securities Act, or an exemption from registration is available.
Purchaser understands that the Company has no present intention of registering
the Shares, the Conversion Shares or any shares of its Common Stock. Purchaser
also understands that there is no assurance that any exemption from registration
under the Securities Act will be available and that, even if available, such
exemption may not allow Purchaser to transfer all or any portion of the Shares
or the Conversion Shares under the circumstances, in the amounts or at the times
Purchaser might propose.

                           (b)      ACQUISITION FOR OWN ACCOUNT. Purchaser is
acquiring the Shares and any Conversion Shares issuable upon conversion thereof
for Purchaser's own account for investment only, and not with a view towards
their distribution.

                           (c)      PURCHASER CAN PROTECT ITS INTEREST.
Purchaser represents that by reason of its, or of its management's, business or
financial experience, Purchaser has the capacity to protect its own interests in
connection with the transactions contemplated in this Agreement, and the Related
Agreements. Further, Purchaser is aware of no publication of any advertisement
in connection with the transactions contemplated in the Agreement.

                           (d)      ACCREDITED INVESTOR. Purchaser represents
that it is an accredited investor within the meaning of Regulation D under the
Securities Act.

                           (e)      COMPANY INFORMATION. Purchaser believes such
Purchaser has received all the information such Purchaser considers necessary or
appropriate for deciding whether to purchase the Shares and has had an
opportunity to discuss the Company's business, management and financial affairs
with directors, officers and management of the Company and has had the
opportunity to review the Company's operations and facilities. Purchaser has
also had the opportunity to ask questions of and receive answers from, the
Company and its management regarding the terms and conditions of this
investment.

                           (f)      RULE 144. Purchaser acknowledges and agrees
that the Shares, and, if issued, the Conversion Shares must be held indefinitely
unless they are subsequently registered under the Securities Act or unless an
exemption from such registration is available. Purchaser has been advised or is
aware of the provisions of Rule 144 promulgated under the Securities Act as in
effect from time to time, which permits limited resale of shares purchased in a
private placement subject to the satisfaction of certain conditions, including,
among other things: the availability of certain current public information about
the Company, the resale occurring following the required holding period under
Rule 144 and the number of shares being sold during any three-month period not
exceeding specified limitations.

                           (g)      RESIDENCE. The office of Purchaser in which
its investment decision was made is located at the address or addresses of
Purchaser set forth in the first paragraph hereof.


                                       5.
<PAGE>

                  4.3      TRANSFER RESTRICTIONS. Each Purchaser acknowledges
and agrees that the Shares and, if issued, the Conversion Shares are subject to
restrictions on transfer as set forth in the Related Agreements and the Bylaws.

         5.       CONDITIONS TO CLOSING.

                  5.1      CONDITIONS TO PURCHASER'S OBLIGATIONS AT THE CLOSING.
Purchaser's obligation to purchase the Shares at the Closing are subject to the
satisfaction, at or prior to the Closing Date, of the following conditions:

                           (a)      REPRESENTATIONS AND WARRANTIES TRUE;
PERFORMANCE OF OBLIGATIONS. The representations and warranties made by the
Company in Section 3 hereof as modified by the Schedule of Exceptions shall be
true and correct in all material respects as of the Closing Date. The Company
shall have performed all obligations and conditions herein required to be
performed or observed by it on or prior to the Closing.

                           (b)      CONSENTS, PERMITS, AND WAIVERS. The Company
shall have obtained any and all consents, permits and waivers necessary or
appropriate for consummation of the transactions contemplated by the Agreement
(except for such as may be properly obtained subsequent to the Closing).

                           (c)      FILING OF RESTATED CERTIFICATE. The Restated
Certificate shall have been filed with the Secretary of State of the State of
Delaware.

                           (d)      RESERVATION OF CONVERSION SHARES. The
Conversion Shares issuable upon conversion of the Shares shall have been duly
authorized and reserved for issuance upon such conversion.

                           (e)      COMPLIANCE CERTIFICATE. The Company shall
have delivered to Purchaser a Compliance Certificate, executed by the President
of the Company, dated the Closing Date, to the effect that the conditions
specified in subsections (a), (b), (c) and (d) of this Section 5.1 have been
satisfied.

                           (f)      INVESTOR RIGHTS AGREEMENT. The Investor
Rights Agreement substantially in the form attached hereto as EXHIBIT C shall
have been executed and delivered by the Company.

                           (g)      CO-SALE AGREEMENT. The Co-Sale Agreement
substantially in the form attached hereto as EXHIBIT D shall have been executed
and delivered by the Company.

                           (h)      MICROBIAL INFORMATION AGREEMENT. The
Microbial Information Agreement shall have been executed and delivered by the
Company.

                           (i)      SOFTWARE LICENSE AGREEMENTS. Each of the
LifeTools Software License Agreement and the Microbial Dataflow Software License
Agreement between the Company and Purchaser of even date herewith (together, the
"Software License Agreements") shall have been executed and delivered by the
Company.


                                       6.
<PAGE>

                           (J)      LEGAL OPINION. Purchaser shall have received
from legal counsel to the Company an opinion to Purchaser, dated as of the
Closing Date, substantially in the form attached hereto as EXHIBIT E.

                           (K)      PROCEEDINGS AND DOCUMENTS. All corporate and
other proceedings in connection with the transactions contemplated at the
Closing hereby and all documents and instruments incident to such transactions
shall be reasonably satisfactory in substance and form to Purchaser and their
special counsel, and Purchaser and their special counsel shall have received all
such counterpart originals or certified or other copies of such documents as
they may reasonably request.

                  5.2      CONDITIONS TO OBLIGATIONS OF THE COMPANY AT THE
CLOSING. The Company's obligation to issue and sell the Shares at the Closing is
subject to the satisfaction, on or prior to the Closing, of the following
conditions:

                           (A)      REPRESENTATIONS AND WARRANTIES TRUE;
PERFORMANCE OF OBLIGATIONS. The representations and warranties made by the
Purchasers in Section 4 hereof shall be true and correct in all material
respects at the date of the Closing, with the same force and effect as if they
had been made on and as of said date. The Purchasers shall have performed and
complied with all agreements and conditions herein required to be performed or
complied with by the Purchasers on or before the Closing.

                           (B)      PAYMENT OF PURCHASE PRICE. Purchaser shall
have transferred certain assets to the Company as provided in the Microbial
Information Agreement as payment in full of the purchase price for the Shares at
the Closing.

                           (C)      MICROBIAL INFORMATION AGREEMENT. The
Microbial Information Agreement shall have been executed and delivered by
Purchaser.

                           (D)      SOFTWARE LICENSE AGREEMENTS. Each of the
Software License Agreements shall have been executed and delivered by Purchaser.

                           (E)      CONSENTS, PERMITS, AND WAIVERS. The Company
shall have obtained any and all consents, permits and waivers necessary or
appropriate for consummation of the transactions contemplated by the Agreement
(except for such as may be properly obtained subsequent to the Closing).

                           (F)      FILING OF RESTATED CERTIFICATE. The Restated
Certificate shall have been filed with the Secretary of State of the State of
Delaware.

                           (G)      INVESTOR RIGHTS AGREEMENT. The Investor
Rights Agreement substantially in the form attached hereto as EXHIBIT C shall
have been executed and delivered by the Purchaser.

                           (H)      CO-SALE AGREEMENT. The Co-Sale Agreement
substantially in the form attached hereto as EXHIBIT D shall have been executed
and delivered by the Purchaser.


                                       7.
<PAGE>

         6.       MISCELLANEOUS.

                  6.1      GOVERNING LAW. The corporate law of the State of
Delaware shall govern all issues concerning the relative rights of the Company
and its stockholders. All other questions concerning the construction, validity
and interpretation of this Agreement shall be governed in all respects by the
laws of the State of California as such laws are applied to agreements between
California residents entered into and performed entirely in California.

                  6.2      SURVIVAL. The representations, warranties, covenants
and agreements made herein shall survive any investigation made by Purchaser and
the closing of the transactions contemplated hereby. All statements as to
factual matters contained in any certificate or other instrument delivered by or
on behalf of the Company pursuant hereto in connection with the transactions
contemplated hereby shall be deemed to be representations and warranties by the
Company hereunder solely as of the date of such certificate or instrument.

                  6.3      SUCCESSORS AND ASSIGNS. Except as otherwise expressly
provided herein, the provisions hereof shall inure to the benefit of, and be
binding upon, the successors, assigns, heirs, executors and administrators of
the parties hereto and shall inure to the benefit of and be enforceable by each
person who shall be a holder of the Shares from time to time.

                  6.4      ENTIRE AGREEMENT. This Agreement, the Exhibits and
Schedules hereto, and the other documents delivered pursuant hereto constitute
the full and entire understanding and agreement between the parties with regard
to the subjects hereof and no party shall be liable or bound to any other in any
manner by any representations, warranties, covenants and agreements except as
specifically set forth herein and therein.

                  6.5      SEVERABILITY. In case any provision of the Agreement
shall be invalid, illegal or unenforceable, the validity, legality and
enforceability of the remaining provisions shall not in any way be affected or
impaired thereby.

                  6.6      AMENDMENT AND WAIVER.

                           (A)      This Agreement may be amended or modified
only upon the mutual written consent of the Company and Purchaser.

                           (B)      The obligations of the Company and Purchaser
under the Agreement may be waived only with the mutual written consent of the
Company and Purchaser.

                  6.7      DELAYS OR OMISSIONS. It is agreed that no delay or
omission to exercise any right, power or remedy accruing to any party, upon any
breach, default or noncompliance by another party under this Agreement or the
Restated Certificate, shall impair any such right, power or remedy, nor shall it
be construed to be a waiver of any such breach, default or noncompliance, or any
acquiescence therein, or of or in any similar breach, default or noncompliance
thereafter occurring. It is further agreed that any waiver, permit, consent or
approval of any kind or character on Purchaser's part of any breach, default or
noncompliance under this Agreement or under the Restated Certificate or any
waiver on such party's part of any provisions or conditions of the Agreement or
the Restated Certificate must be in writing and shall be effective only to the
extent specifically set forth in such writing. All remedies, either


                                       8.
<PAGE>

under this Agreement, the Restated Certificate, by law, or otherwise afforded to
any party, shall be cumulative and not alternative.

                  6.8      NOTICES. All notices required or permitted hereunder
shall be in writing and shall be deemed effectively given: (a) upon personal
delivery to the party to be notified; (b) when sent by confirmed telex or
facsimile if sent during normal business hours of the recipient, if not, then on
the next business day; (c) five (5) days after having been sent by registered or
certified mail, return receipt requested, postage prepaid; or (d) one (1) day
after deposit with a nationally recognized overnight courier, specifying next
day delivery, with written verification of receipt. All communications shall be
sent to the Company and to Purchaser at the address as set forth on the
signature page hereof or at such other address as the Company or Purchaser may
designate by ten (10) days advance written notice to the other party hereto.

                  6.9      EXPENSES. The Company shall pay all costs and
expenses that it incurs with respect to the negotiation, execution, delivery and
performance of the Agreement.

                  6.10     ATTORNEYS' FEES. In the event that any dispute among
the parties to this Agreement should result in litigation, the prevailing party
in such dispute shall be entitled to recover from the losing party all fees,
costs and expenses of enforcing any right of such prevailing party under or with
respect to this Agreement, including without limitation, such reasonable fees
and expenses of attorneys and accountants, which shall include, without
limitation, all fees, costs and expenses of appeals.

                  6.11     TITLES AND SUBTITLES. The titles of the sections and
subsections of the Agreement are for convenience of reference only and are not
to be considered in construing this Agreement.

                  6.12     COUNTERPARTS. This Agreement may be executed in any
number of counterparts, each of which shall be an original, but all of which
together shall constitute one instrument.

                  6.13     BROKER'S FEES. Each party hereto represents and
warrants that no agent, broker, investment banker, person or firm acting on
behalf of or under the authority of such party hereto is or will be entitled to
any broker's or finder's fee or any other commission directly or indirectly in
connection with the transactions contemplated herein. Each party hereto further
agrees to indemnify each other party for any claims, losses or expenses incurred
by such other party as a result of the representation in this Section 6.13 being
untrue.

                  6.14     CALIFORNIA CORPORATE SECURITIES LAW. The sale of the
securities which are the subject of this agreement has not been qualified with
the commissioner of corporations of the State of California and the issuance of
such securities or the payment or receipt of any part of the consideration
therefor prior to such qualification or in the absence of an exemption from such
qualification is unlawful. Prior to acceptance of such consideration by the
Company, the rights of all parties to this agreement are expressly conditioned
upon such qualification being obtained or an exemption from such qualification
being available.

                  6.15     PUBLICITY. No party to this Agreement shall originate
any publicity, news release or other public announcement, written or oral,
relating to this Agreement or the


                                       9.
<PAGE>

transactions contemplated hereby without the prior written consent of the other
parties hereto if such other parties are named in such publicity, news release
or public announcement; provided, however, that each party need only wait a
reasonable amount of time for such written consent.

              [THE REMAINDER OF THIS PAGE INTENTIONALLY LEFT BLANK]


                                      10.
<PAGE>

         IN WITNESS WHEREOF, the parties hereto have executed the SERIES D
PREFERRED STOCK PURCHASE AGREEMENT as of the date set forth in the first
paragraph hereof.

COMPANY:                                  PURCHASER:


ELITRA PHARMACEUTICALS INC.               INCYTE GENOMICS, INC.


/s/ Harry F. Hixson, Jr.                  /s/ Randy Scott
-----------------------------------       -----------------------------------
By:  Dr. Harry F. Hixson, Jr.             By:  Randy Scott
Title:  President                         Title:  President


                               SIGNATURE PAGE TO
                  SERIES D PREFERRED STOCK PURCHASE AGREEMENT