Exhibit 3.5

CERTIFICATE OF AMENDMENT

TO THE

AMENDED AND RESTATED

CERTIFICATE OF INCORPORATION

OF

SYNLOGIC, INC.

Synlogic, Inc. (the “Corporation”), a corporation organized and existing under the laws of the State of Delaware, does hereby certify as follows:

FIRST: That the name of the Corporation is Synlogic, Inc.

SECOND: That the Board of Directors of the Corporation duly adopted resolutions approving the following amendment of the Amended and Restated Certificate of Incorporation, declaring said amendment to be advisable and providing for such consideration of such amendment at the Corporation’s special meeting of the stockholders.

THIRD: On September 21, 2023 the Corporation’s special meeting of the stockholders was duly called and held, upon notice in accordance with Section 222 of the General Corporation Law of the State of Delaware (“DGCL”), at which meeting the necessary number of shares as required by statute were voted in favor of the amendment.

FOURTH: ARTICLE IV of the Amended and Restated Certificate of Incorporation of the Corporation is hereby amended to add the following Section D to read in its entirety as follows:

“D. Immediately upon the filing of this Certificate of Amendment of Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware each one (1) share of Common Stock outstanding immediately prior to such filing shall be automatically reclassified into one-fifteenth (1/15) of one share of Common Stock. The aforementioned reclassification shall be referred to collectively as the “Reverse Split.”

The Reverse Split shall occur without any further action on the part of the Corporation or stockholders of the Corporation and whether or not certificates representing such stockholders’ shares prior to the Reverse Split are surrendered for cancellation. No fractional interest in a share of Common Stock shall be deliverable upon the Reverse Split. All shares of Common Stock (including fractions thereof) issuable upon the Reverse Split held by a holder prior to the Reverse Split shall be aggregated for purposes of determining whether the Reverse Split would result in the issuance of any fractional share. Any fractional share resulting from such aggregation upon the Reverse Split shall be rounded down to the nearest whole number. Each holder who would otherwise be entitled to a fraction of a share of Common Stock upon the Reverse Split (after aggregating all fractions of a share to which such stockholder would otherwise be entitled) shall, in lieu thereof, be entitled to receive a cash payment in an amount equal to the fraction to which the stockholder would otherwise be entitled multiplied by the closing price of the Corporation’s Common Stock as reported on The Nasdaq Capital Market on the trading day immediately preceding the filing of this Certificate of Amendment of Amended and Restated Certificate of Incorporation with the Secretary of State of the State of Delaware. The Corporation shall not be obliged to issue certificates evidencing the shares of Common Stock outstanding as a result of the Reverse Split unless and until the certificates evidencing the shares held by a holder prior to the Reverse Split are either delivered to the Corporation or its transfer agent, or the holder notifies the Corporation or its transfer agent that such certificates have been lost, stolen or destroyed and executes an agreement satisfactory to the Corporation to indemnify the Corporation from any loss incurred by it in connection with such certificates.”

FIFTH: That this Certificate of Amendment to the Amended and Restated Certificate of Incorporation herein certified has been duly adopted in accordance with the provisions of Section 242 of the DGCL.

SIXTH: That this Certificate of Amendment to the Amended and Restated Certificate of Incorporation shall be effective at 5:00 pm Eastern Time September 27, 2023.

IN WITNESS WHEREOF, this Certificate of Amendment to the Restated Certificate of Incorporation has been executed by a duly authorized officer of this Corporation on this 27^th day of September, 2023.

SYNLOGIC, INC.
By:	/s/ Aoife Brennan
	Aoife Brennan
	President and Chief Executive Officer