EXHIBIT 31.3

CERTIFICATION OF PRINCIPAL EXECUTIVE OFFICER

PURSUANT TO 18 U.S.C. SECTION 1350,

AS ADOPTED PURSUANT TO SECTION 302 OF

THE SARBANES-OXLEY ACT OF 2002

I, Andrew Kidd, certify that:

1. I have reviewed this Amendment No. 1 to the Annual Report on Form 10-K/A of Aptinyx Inc.; and

2. Based on my knowledge, this report does not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements made, in light of the circumstances under which such statements were made, not misleading with respect to the period covered by this report.