X0306 4 2021-03-10 0 0001527599 SYNLOGIC, INC. SYBX 0001786692 Riese Richard J. C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 0 1 0 0 Chief Medical Officer Common Stock 2021-03-10 4 A 0 17500 0.00 A 39000 D Stock Option (right to buy) 3.50 2021-03-10 4 A 0 70000 0.00 A 2031-03-10 Common Stock 70000 70000 D The shares of restricted stock were granted on March 10, 2021, and will vest beginning on April 1, 2021 (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 Medical Officer through each such vesting date. The option will vest and become exercisable in equal monthly installments for forty-eight months beginning on April 1, 2021, with the first installment vesting on May 1, 2021 subject to the Reporting Person continuing to provide services to the Issuer as Chief Medical Officer through each such vesting date. /s/ Richard Riese 2021-03-12