X0306 4 2019-01-09 1 0001615219 Flex Pharma, Inc. FLKS 0001762003 Boston Foundation, Inc. 75 ARLINGTON STREET BOSTON MA 02116 0 0 1 0 Common Stock, par value $0.0001 2019-01-09 4 S 0 337000 0.3675 D 1600000 D Price reported of $0.3675 is the weighted average price of the sales prices received for the stock sales during the day of 1/9/2019. George C. Wilson, Assistant Treasurer 2019-01-10