X0306 4 2015-02-03 0 0001615219 Flex Pharma, Inc. FLKS 0001291961 Westphal Christoph H C/O FLEX PHARMA, INC. 800 BOYLSTON STREET BOSTON MA 02199 1 1 0 0 President and CEO Common Stock 2015-02-03 4 C 0 1868067 0.00 A 1868067 I By Longwood Fund II. L.P. Common Stock 2015-02-03 4 C 0 516697 0.00 A 2384764 I By Longwood Fund II, L.P. Series A Preferred Stock 0.00 2015-02-03 4 C 0 8000000 0.00 D Common Stock 8000000 0 I By Longwood Fund II. L.P. Series B Preferred Stock 0.00 2015-02-03 4 C 0 2212756 0.00 D Common Stock 2212756 0 I By Longwood Fund II. L.P. The shares automatically converted on a 4.2825-for-1 basis into shares of the Issuer's Common Stock upon the closing of a Qualified Public Offering (as defined in the Amended and Restated Certificate of Incorporation). Longwood Fund II GP, LLC is the ultimate General Partner of Longwood Fund II, L.P. Christoph Westphal, M.D., Ph.D., Richard Aldrich and Michelle Dipp, M.D., Ph.D. (collectively, the "Managers") are managers of Longwood Fund II GP, LLC, and, as such, may be deemed to have shared voting and dispositive power with respect to the issuer's securities held by Longwood Fund II, L.P. (the "Longwood Shares"). Each of the Managers disclaim beneficial ownership of the Longwood Shares, except to the extent of their respective pecuniary interest therein, and the inclusion of these shares in this report shall not be deemed an admission of beneficial ownership of the shares for purposes of Section 16 or for any other purpose. N/A. The shares have no expiration date. /s/ John McCabe, Attorney-in-Fact 2015-02-05