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                                                                   EXHIBIT 10.18


                      SYNTHETIC COMPOUND PURCHASE AGREEMENT


         This Synthetic Compound Purchase Agreement ("Agreement"), is effective
as of June 25, 1997 ("Effective Date"), by and between Microcide
Pharmaceuticals, Inc. ("Microcide"), a Delaware corporation, with its principal
place of business located at 850 Maude Avenue, Mountain View, California, 94043,
U.S.A. and Daiichi Pharmaceutical Co., Ltd. ("Daiichi"), a Japanese corporation,
with its offices located at 16-13, Kitakasai 1-chome, Edogawa-Ku, Tokyo 134,
Japan.

         WHEREAS, Daiichi desires to obtain certain synthetic compounds
("Compounds") from Microcide for use in its drug discovery screening programs;
and

         WHEREAS, Microcide desires to provide such Compounds to Daiichi.

         NOW, THEREFORE, in consideration of the recitals and the covenants and
conditions set forth in this Agreement, the parties agree as follows.

1.       Delivery of Compounds. Microcide will provide to Daiichi [*] Compounds
in 96-well microtitre plate format (100 microliters at a concentration of 10
milligrams per milliliter in 100% DMSO) at a mutually acceptable date which is
not expected to be later than June 30, 1997. Microcide will also provide
structure and source files (SD files), and a description of plate well
locations. Microcide will subsequently provide, in shipments of [*] Compounds
each, the following supplies of synthetic compounds in dry powder format:

        [*] Compounds - 10-15 mg each
        [*] Compounds - 5 mg each

The last shipment of the supplies of synthetic compounds in dry powder format is
expected to be made prior to December 31, 1997. Microcide will use its best
efforts to provide SD files and description of plate well locations and to carry
out the weighing and labeling of the Compounds hereunder.

2.       Purchase Price and Costs. In consideration for the delivery of the
Compounds, Daiichi will pay to Microcide [*] within 30 days of receiving the [*]
Compounds in microtiter plates and a further [*] within 30 days of receiving
each shipment of [*] Compounds in dry powder format. These payments would be net
of payments for withholding taxes, if any, and fulfillment of any withholding
tax obligations would be the sole responsibility of Daiichi. Daiichi will
reimburse Microcide for its labor and material costs incurred in weighing out
the compounds, labeling the containers and packaging for shipment, as well as
for the actual shipping costs related to the delivery of the compounds,
including any customs duties that might arise. Microcide shall keep true and
accurate written records of such costs and shall invoice Daiichi for the entire
amount of such costs after the delivery of the last supplies of synthetic
compounds in dry powder format. Daiichi shall pay Microcide within 30 days after
receiving the invoice. Any payments to Microcide under this agreement shall be
made to the designated bank account of Microcide by bank wire transfer.

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*Confidential treatment requested pursuant to a request for confidential
 treatment filed with the Securities and Exchange Commission. Omitted portions
 have been filed separately with the Commission.
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3.       No Warranties; Limitation of Liability

         3.1 No Warranties. Daiichi acknowledges that the Compounds are being
provided "as-is", without warranty of any kind, including but not limited to no
warranty of merchantability or fitness for a particular program, and no warranty
of non-infringement with respect to the patent or other intellectual property
rights of third parties.

         3.2 Limitation of Liability. In no event shall either party be liable
to the other party for any lost profits or revenues or any special consequential
or incidental damages under any theory of liability.

4.       Miscellaneous.

         4.1 Disclosure of Agreement. Recognizing that Microcide is subject to
certain disclosure obligations as a publicly traded company, Microcide will have
the right to issue a press release, in form and substance similar to Exhibit A,
upon the execution of this Agreement.

         4.2 Indemnification. Daiichi hereby agrees to indemnify, protect,
defend and hold Microcide harmless from all claims, suits or actions, damages,
judgments, costs, expenses, including attorney's fees which may be sustained by
reason of Daiichi's screening and use of the Compounds, except to the extent
that such liabilities are caused by negligence, recklessness or intentional
misconduct of Microcide.

         4.3 Governing Law. This Agreement shall be governed in all respects,
including validity, interpretation and effect, by the laws of the State of
California, with the venue for any action or dispute being the Northern District
of California.

         IN WITNESS WHEREOF, Microcide and Daiichi have caused this Agreement to
be signed by their duly authorized respective officers as of the date written
above.


                                    MICROCIDE PHARMACEUTICALS, INC.

                                    By:     /S/  James E. Rurka
                                            -------------------------------
                                            President & CEO
                                            June 13, 1997


                                    DAIICHI PHARMACEUTICAL CO., LTD.

                                    By:     /S/  Tadashi Horiuchi
                                            -------------------------------
                                            General Manager, Basic Technology
                                            Research Laboratory
                                            June 25, 1997


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                                    Exhibit A

                              Form of Press Release

MICROCIDE ANNOUNCES AGREEMENT TO PROVIDE SYNTHETIC COMPOUNDS TO DAIICHI

Mountain View, CA (DATE, 1997) -- Microcide Pharmaceuticals, Inc. (Nasdaq: MCDE)
today announced the signing of an agreement with Daiichi Pharmaceutical Co.,
Ltd. whereby Microcide will provide Daiichi with a subset of its synthetic
molecular diversity collection for use in Daiichi's drug discovery screening
programs in consideration for $1.5 million. Delivery of the compounds and
receipt of the associated payments are expected to occur during the remainder of
1997.

Since 1994, Microcide has been building a molecular diversity collection, for
use in its partnered and unpartnered drug discovery programs. This collection,
which strives for optimal structural diversity, includes extracts from natural
product sources as well as synthetic molecules acquired only after careful
structural analysis. Currently in excess of 140,000 samples, Microcide intends
to continue to systematically grow this collection in the future.

In November 1995, Microcide and Daiichi entered into a multi-year collaboration
to discover and develop bacterial efflux pump inhibitors to be used in
combination with Daiichi's quinolone antibiotics to target Gram-negative
bacteria, including pseudomonas.

Microcide is a biopharmaceutical company founded to discover, develop and
commercialize novel antibiotics for the treatment of serious bacterial
infections. The Company's discovery and development programs address the growing
problem of bacterial drug resistance through two principal themes: (i) Targeted
Antibiotics, which focuses on developing novel antibiotics and antibiotic
potentiators to directly address existing bacterial resistance problems, and
(ii) Targeted Genomics, which utilizes bacterial genetics to discover new
classes of antibiotics and other novel treatments for bacterial disease.
Microcide has also extended its functional genomics technology platform into a
program designed to discover improved systemic antifungal agents.

The statements in this press release that are related to Microcide's expanding
its sample collection, providing a portion of this library to Daiichi and the
receipt of payment therefrom are forward-looking statements based upon current
expectations. Such forward-looking statements involve risks and uncertainties
including without limitation, the risks that the compounds will be successfully
delivered to Daiichi in the time frames discussed and in return for the
compensation discussed, the continuation of Microcide's collaboration with
Daiichi, and the other risks and uncertainties set forth in Microcide's Form
10-K dated March 31, 1997. Actual results and timing of certain events could
differ materially from those indicated in the forward-looking statements as a
result of these and other factors.