This Amendment No. 1 (“Amendment No. 1”) amends and supplements Items 4 and 9 in the
Solicitation/Recommendation Statement on Schedule 14D-9 filed by Tetraphase Pharmaceuticals, Inc. (the “Company”) with the U.S. Securities and Exchange Commission on June 12, 2020 (as amended
and supplemented from time to time, the “Schedule 14D-9”). The Schedule 14D-9 relates to the tender offer by Toronto Transaction Corp. (“Purchaser”),
a wholly owned subsidiary of Melinta Therapeutics, Inc. (“Parent”), to acquire the Company for an aggregate of $39.0 million in cash (representing consideration of $1.79 per share of Tetraphase common stock), plus contingent value
rights (“CVRs”) representing the right to receive cash consideration based on the achievement of certain net sales milestones, in an aggregate amount of up to $16.0 million, upon the terms and subject to the conditions set forth in
the Offer to Purchase of Parent and Purchaser dated June 12, 2020, and in the related Letter of Transmittal, as each may be amended or supplemented from time to time.
Except as otherwise set forth below, the information set forth in the Schedule 14D-9 remains unchanged and is incorporated herein by reference as relevant to
items in this Amendment No. 1. Capitalized terms used but not otherwise defined herein have the meanings ascribed to such terms in the Schedule 14D-9.
Item 4. The Solicitation or Recommendation.
Item 4 of the Schedule 14D-9 is hereby amended and supplemented by inserting the disclosure set forth below at the
end of the subsection entitled “Background of the Offer” as follows:
On June 19, 2020, Tetraphase received an unsolicited proposal from La
Jolla Pharmaceutical Company (“La Jolla”) to acquire Tetraphase for $43.0 million in cash, plus an additional $16.0 million in cash potentially payable under contingent value rights to be issued in the transaction (the
“La Jolla Proposal”), including drafts of a merger agreement, guarantee, form of contingent value rights agreement and support agreement. Under the La Jolla Proposal, the upfront cash consideration would be paid as follows: (i) $2.00
per share of Tetraphase common stock (including common stock underlying restricted stock units, performance-based stock units and pre-funded warrants), (ii) $2.68 per share of Tetraphase common stock
underlying the common stock warrants issued by Tetraphase in November 2019, and (iii) $2.69 per share of Tetraphase common stock underlying the common stock warrants issued by Tetraphase in January 2020.
On June 20, 2020, the Tetraphase Board met telephonically with members of management, representatives from WilmerHale and representatives from Janney to
discuss and evaluate the La Jolla Proposal. WilmerHale reviewed with the Tetraphase Board its fiduciary duties in considering the La Jolla Proposal and representatives of Janney reviewed financial aspects of the La Jolla Proposal, including the
treatment of the Company’s outstanding warrants. At this meeting, the Tetraphase Board determined in good faith, after consultation with its independent financial advisors and outside legal counsel, that the unsolicited La Jolla Proposal could
reasonably be expected to lead to a Superior Offer as defined in the Melinta merger agreement and that the failure to (1) furnish, pursuant to an Acceptable Confidentiality Agreement, information (including
non-public information) to La Jolla and (2) engage in or otherwise participate in discussions or negotiations with La Jolla in respect of the La Jolla Proposal could reasonably be expected to be
inconsistent with the fiduciary duties of the Tetraphase Board to Tetraphase’s stockholders under applicable legal requirements. Accordingly, in accordance with the Melinta merger agreement, the Tetraphase Board determined to consider the La
Jolla Proposal, to enter into discussions and/or negotiations with respect to the La Jolla Proposal and, subject to an Acceptable Confidentiality Agreement, to furnish non-public information to La Jolla.
Later that day, Tetraphase provided notice to Melinta of the La Jolla Proposal and the Tetraphase Board’s determination in accordance with the Melinta
merger agreement. Also on that day and into the following day, Tetraphase’s financial advisors, Janney Montgomery Scott LLC, and its legal advisors, WilmerHale, engaged in discussions with Mr. Tang and La Jolla’s legal advisors,
respectively, regarding various aspects of the draft merger agreement from La Jolla. On June 21, 2020, La Jolla’s legal advisors sent a revised draft of the proposed merger agreement in respect of the La Jolla Proposal.
On June 21, 2020, the Tetraphase Board met telephonically with members of management, representatives from WilmerHale and representatives from Janney to
discuss and evaluate the La Jolla Proposal. After reviewing with