Exhibit 5.1

                                Bingham Dana LLP
                               150 Federal Street
                                Boston, MA 02110


December 20, 2001

Essential Therapeutics, Inc.
1365 Main Street
Waltham, MA  02451

Re:  Registration Statement on Form S-3 under the Securities Act of 1933, as
     amended

Ladies and Gentlemen:

     We have acted as counsel to Essential Therapeutics, Inc., a Delaware
corporation (the "Company"), in connection with the registration under the
Securities Act of 1933, as amended (the "Act"), of 25,188,020 shares (the
"Shares") of the Company's Common Stock, $0.001 par value per share, to be
offered by certain stockholders of the Company pursuant to a Registration
Statement on Form S-3 initially filed by the Company with the Securities and
Exchange Commission on November 21, 2001.

     The Shares (i) have been issued in exchange for shares of The Althexis
Company, Inc. common stock pursuant to the Agreement and Plan of Merger and
Reorganization, dated as of July 27, 2001, by and among the Company, Althexis
and California MP Acquisition, Inc. (the "Merger Shares"), or (ii) are to be
issued upon conversion of shares of the Company's Series B convertible
redeemable preferred stock, $0.001 par value per share, pursuant to the terms of
the preferred stock (the "Conversion Shares").

     As counsel to the Company, we have reviewed the corporate proceedings taken
by the Company with respect to the authorization of the issuance of the Shares.
We have also examined and relied upon originals or copies, certified or
otherwise authenticated to our satisfaction, of such corporate records,
documents, agreements or other instruments of the Company as we have deemed
appropriate. As to all matters of fact (including factual conclusions and
characterizations and descriptions of purpose, intention or other state of
mind), we have entirely relied upon certificates of officers of the Company, and
have assumed, without independent inquiry, the accuracy of those certificates.


Essential Therapeutics, Inc.
December 20, 2001
Page 2


     We have assumed the genuineness of all signatures, the conformity to the
originals of all documents reviewed by us as copies, the authenticity and
completeness of all original documents reviewed by us in original or copy form
and the legal competence of each individual executing a document. We have also
assumed that the registration requirements of the Act and all applicable
requirements of state laws regulating the sale of securities will have been duly
satisfied. We have also assumed that the Company has received the specified
consideration for the Shares.

     This opinion is limited solely to the Delaware General Corporation Law, as
applied by courts located in Delaware, the applicable provisions of the Delaware
Constitution and the reported judicial decisions interpreting those laws.

     Subject to the foregoing, it is our opinion that (i) the Merger Shares have
been duly authorized, and are validly issued, fully paid and nonassessable, and
(ii) the Conversion Shares have been duly authorized and, upon issuance of the
Conversion Shares in accordance with the terms of the Company's Series B
convertible redeemable preferred stock, will be validly issued, fully paid and
non-assessable.

     We hereby consent to the filing of this opinion as an exhibit to the
Registration Statement and to the reference to this firm under the heading
"Legal Matters" in the Prospectus included in the Registration Statement.

Very truly yours,



/s/ Bingham Dana LLP
Bingham Dana LLP