X0306 4 2022-06-09 0 0001527599 SYNLOGIC, INC. SYBX 0001845596 Kelly-Croswell Lisa C/O SYNLOGIC, INC. 301 BINNEY STREET, SUITE 402 CAMBRIDGE MA 02142 1 0 0 0 Stock Option (right to buy) 1.17 2022-06-09 4 A 0 27000 0.00 A 2032-06-09 Common Stock 27000 27000 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 to the non-employee director's continued service as a director of the Corporation. /s/ Lisa Kelly-Croswell 2022-06-13