X0306 4 2022-02-04 0 0001527599 SYNLOGIC, INC. SYBX 0001714563 Brennan Aoife C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 1 1 0 0 See Remarks Common Stock 2022-02-04 4 A 0 106920 0.00 A 284237 D Stock Option (right to buy) 1.95 2022-02-04 4 A 0 434160 0.00 A 2032-02-04 Common Stock 434160 434160 D The shares of restricted stock were granted on February 4, 2022, and will vest beginning on April 1, 2022 (the "Vesting Start Date") in four equal annual installments on each anniversary of the Vesting Start Date, subject to the Reporting Person continuing to provide services to the Issuer as Chief Executive Officer through each such vesting date. The option will vest and become exercisable in equal monthly installments for forty-eight months beginning on the grant date, which is February 4, 2022, subject to the Reporting Person continuing to provide services to the Issuer as Chief Executive Officer through each such vesting date. President and Chief Executive Officer /s/ Aoife Brennan 2022-02-08