Daniel Radden

c/o Armistice Capital, LLC

510 Madison Avenue

7^th Floor

New York, NY 10022

Telephone Number: (212) 231-4930

(Name, Address and Telephone Number of Person Authorized to Receive

Notices and Communications)

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The name of the issuer is Tetraphase Pharmaceuticals, Inc., a Delaware corporation (the "Issuer").  The address of the Issuer's principal executive offices is 480 Arsenal Way, Watertown, Massachusetts 02472.  This Amendment No. 3 to Schedule 13D relates to the Issuer's Common Stock, $0.001 par value (collectively, the "Shares").

Armistice Capital is an investment adviser registered with the Securities and Exchange Commission (the “SEC”) that is principally engaged in the business of providing investment management services to private investment vehicles, including the Master Fund. The principal business address of Armistice Capital is 510 Madison Avenue, 7^th Floor, New York, New York 10022.

The Master Fund is principally engaged in the business of investing in securities. The principal business address of the Master Fund is c/o dms Corporate Services Ltd., 20 Genesis Close, P.O. Box 314, Grand Cayman KY1-1104, Cayman Islands. The board of directors of the Master Fund consists of Steven Boyd, Kevin A. Phillip and Gregory S. Bennett.

Steven Boyd is the managing member of Armistice Capital and a director of the Master Fund. Mr. Boyd’s business address is 510 Madison Avenue, 7^th Floor, New York, New York 10022.

None of the Reporting Persons have, during the last five years, been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

The funds for the purchase of the 1,460,019 Shares beneficially owned by the Reporting Persons came from the working capital of the Master Fund.  No borrowed funds were used to purchase the Shares, other than any borrowed funds used for working capital purposes (including certain leverage arrangements) in the ordinary course of business.

In connection with the announced proposed merger (the “Merger”) of the Issuer and La Jolla Pharmaceutical Company (“La Jolla”), on June 24, 2020, the Master Fund entered into a support agreement (the “Support Agreement”) with: (i) La Jolla; and (ii) TTP Merger Sub, Inc., a wholly-owned subsidiary of La Jolla (the “La Jolla Subsidiary”). Pursuant to the Support Agreement, the Master Fund agreed to, among other things, (i) vote against other proposals to acquire the Issuer, and (ii) subject to certain exceptions, to tender its Shares in connection with the La Jolla Subsidiary’s cash tender offer, on behalf of La Jolla, to acquire all of the Issuer’s Shares. The Support Agreement also sets forth terms relating to the treatment of warrants of the Issuer currently held by the Master Fund upon consummation of the Merger. The Support Agreement will terminate upon the first to occur of: (i) the termination of the Agreement and Plan of Merger, dated June 24, 2020, by and among the Issuer, La Jolla and the La Jolla Subsidiary (the “Merger Agreement”); (ii) the effective time of the Merger; (iii) any amendment to the Merger Agreement that reduces the amount, or changes the form, of consideration payable to the Master Fund in the transactions contemplated by the Merger and related agreements, imposes additional restrictions on the Master Fund or otherwise materially and adversely impacts the Master Fund; (iv) a Company Adverse Change in Recommendation (as such term is defined in the Merger Agreement); or (v) the mutual written consent of the Master Fund and La Jolla.

The foregoing was a summary of certain material terms of the Support Agreement. The foregoing description is not, and does not purport to be, complete and is qualified in its entirety by reference to the full text of the form of Support Agreement, which has been filed as Exhibit B hereto and is incorporated herein by reference.

Mr. Boyd and Keith Maher, a Managing Director at Armistice Capital, currently serve as members of the Issuer’s board of directors (the “Board”).

The Reporting Persons purchased the Shares for investment in the ordinary course of their investment activities based on the Reporting Persons’ belief that the Shares, when purchased, were undervalued and represented an attractive investment opportunity. The Reporting Persons intend to review their investment in the Issuer on a continuing basis. Depending on various factors including, without limitation, the Issuer’s financial position, the price levels of the Shares, conditions in the securities markets and general economic and industry conditions, the Reporting Persons may in the future take such actions with respect to their investment in the Issuer as they deem appropriate including, without limitation, engaging in communications with management and/or the Board, engaging in discussions with stockholders of the Issuer and others about the Issuer and the Reporting Persons’ investment, reshaping the Issuer's corporate strategy, revitalizing the Issuer’s promising Research and Development pipeline, restructuring the Issuer’s expense base, recommending business development transactions including mergers and acquisitions, proposing changes to management, operations and the structure of the Board (including the composition of the Board), purchasing additional Shares, selling some or all of their Shares, engaging in short selling of or any hedging or similar transaction with respect to the Shares, or changing their intention with respect to any and all matters referred to in subparagraphs (a) - (j) of Item 4 of Schedule 13D.

Except as otherwise set forth herein, the Reporting Persons do not have any present plans or proposals which would relate to, or result in, the matters set forth in subparagraphs (a) – (j) of Item 4 of Schedule 13D. However, subject to market conditions and in compliance with applicable securities laws, the Reporting Persons reserve the right, at a later date, to effect one or more of such changes or transactions in the number of Shares they may be deemed to beneficially own in open-market or privately negotiated transactions, on such terms and at such times as the Reporting Persons may deem advisable.

There have been no transactions in the Shares by the Reporting Persons during the past sixty days.

The information set forth in Item 4 above is incorporated by reference in its entirety in this Item 6.

The Master Fund currently holds 8,957,654 warrants of the Issuer, subject to blocker provisions that prevent the Master Fund from exercising the warrants if it would be more than a 4.99%, 9.99% or 19.99% (as applicable) beneficial owner of the Shares following any such exercise.

The Reporting Persons do not have any contract, arrangement, understanding or relationship with any person with respect to securities of the Issuer that is not described herein or in a prior Schedule 13D filed by the Reporting Persons in respect of the Issuer.