X0306 4 2018-06-13 0 0001527599 SYNLOGIC, INC. SYBX 0001202793 POWELL MICHAEL C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 1 0 0 0 Stock Option (right to buy) 9.36 2018-06-13 4 A 0 10000 0.00 A 2028-06-13 Common Stock 10000 10000 D The option vests and becomes exercisable in full on the earlier of (A) the first anniversary of the date of grant or (B) immediately prior to the next annual meeting of the Corporation's stockholders after the date of grant, subject in each case to the reporting person's continued service as a director of the Corporation. /s/ William J. Bussiere, Jr., Attorney-in-fact 2018-06-14