UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 13, 2017

SYNLOGIC, INC.

(Exact name of registrant as specified in its charter)

(617) 401-9947

Registrant’s telephone number, including area code

Not applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (17 CFR §230.405) or Rule 12b-2 of the Securities Exchange Act of 1934 (17 CFR §240.12b-2).

Emerging Growth Company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☒

On October 13, 2017, Synlogic, Inc. (the “Company”) entered into a Sales Agreement (the “Agreement”) with Cowen and Company, LLC (“Cowen”) with respect to an at-the-market offering program under which the Company may offer and sell, from time to time at its sole discretion, shares of its common stock, par value $0.001 per share (the “Common Stock”), having an aggregate offering price of up to $50,000,000 (the “Placement Shares”) through Cowen as its sales agent. The issuance and sale, if any, of the Placement Shares by the Company under the Agreement is subject to the effectiveness of the Company’s registration statement on Form S-3, filed with the Securities and Exchange Commission on October 13, 2017. The Company makes no assurances as to if or when the registration statement will become effective or, if it does become effective, as to the continued effectiveness of the registration statement.

After the registration statement becomes effective, Cowen may sell the Placement Shares by any method permitted by law deemed to be an “at the market” offering as defined in Rule 415 of the Securities Act of 1933, as amended, including, without limitation, sales made through The NASDAQ Capital Market or on any other existing trading market for the Common Stock. Cowen will use commercially reasonable efforts to sell the Placement Shares from time to time, based upon instructions from the Company (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company will pay Cowen a commission equal to three percent (3.0%) of the gross sales proceeds of any Placement Shares sold through Cowen under the Agreement, and also has provided Cowen with customary indemnification and contribution rights.

The Company is not obligated to make any sales of Common Stock under the Agreement. The offering of Placement Shares pursuant to the Agreement will terminate upon the earlier of (i) the sale of all Placement Shares subject to the Agreement or (ii) termination of the Agreement in accordance with its terms.

The foregoing description of the Agreement is not complete and is qualified in its entirety by reference to the full text of the Agreement, a copy of which is filed herewith as Exhibit 10.1 to this Current Report on Form 8-K and is incorporated herein by reference.

This Current Report on Form 8-K shall not constitute an offer to sell or the solicitation of an offer to buy the securities discussed herein, nor shall there be any offer, solicitation, or sale of the securities in any state in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state.

(d) Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: October 16, 2017