X0306 5 2017-12-31 0 0 0 0001527599 SYNLOGIC, INC. SYBX 0001667657 Gutierrez-Ramos Jose-Carlos C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 1 1 0 0 See Remarks Common Stock 2017-10-02 5 G 0 10000 0.00 D 352619 D This Report relates to a gift of 10,000 shares of common stock made by the Reporting Person on October 2, 2017. The gifted shares were fully vested as of the date of the gift in accordance with the vesting schedule described in footnote 2. Pursuant to the terms of a restricted stock agreement by and between the Issuer and the Reporting Person, one-fourth of the total number of shares originally granted pursuant to the restricted stock agreement vested on May 14, 2016, with the remainder vesting in equal monthly installments until May 14, 2019, provided that at the relevant vesting dates the Reporting Person continues service to the Issuer and has not been terminated as defined in, and as determined under, the Issuer's 2017 Stock Incentive Plan. President and Chief Executive Officer /s/ William J. Bussiere, Jr., Attorney-in-fact 2018-02-13