X0306 4 2019-03-05 0 0001527599 SYNLOGIC, INC. SYBX 0001714564 Shegog Todd C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 0 1 0 0 See Remarks Stock Option (right to buy) 8.59 2019-03-05 4 A 0 58500 0.00 A 2029-03-05 Common Stock 58500 58500 D The options vest and become exercisable in substantially equal monthly installments beginning on April 5, 2019 and continuing until March 5, 2023, subject to the Reporting Person continuing to provide services to the Issuer through each such vesting date. Chief Financial Officer, Treasurer and Secretary /s/ William J. Bussiere, Jr., Attorney-in-fact 2019-03-06