Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No. )

Your Vote Counts! APTINYX INC. 2022 Annual Meeting Vote by May 25, 2022 11:59 PM ET You invested in APTINYX INC. and it’s time to vote! You have the right to vote on proposals being presented at the Annual Meeting. This is an important notice regarding the availability of proxy material for the shareholder meeting to be held on May 26, 2022. Vote Virtually at the Meeting* May 26, 2022 10:00 AM Eastern Time, 9:00 AM Central Time Virtually at: www.virtualshareholdermeeting.com/APTX2022 *Please check the meeting materials for any special requirements for meeting attendance. Smartphone users Point your camera here and vote without entering a control number V1.1 For complete information and to vote, visit www.ProxyVote.com Control # D78433-P66090 Get informed before you vote View the Notice and Proxy Statement and Form 10-K online OR you can receive a free paper or email copy of the material(s) by requesting prior to May 12, 2022. If you would like to request a copy of the material(s) for this and/or future shareholder meetings, you may (1) visit www.ProxyVote.com, (2) call 1-800-579-1639 or (3) send an email to sendmaterial@proxyvote.com. If sending an email, please include your control number (indicated below) in the subject line. Unless requested, you will not otherwise receive a paper or email copy. APTINYX INC. 909 DAVIS STREET, SUITE 600 EVANSTON, IL 60201

THIS IS NOT A VOTABLE BALLOT This is an overview of the proposals being presented at the upcoming shareholder meeting. Please follow the instructions on the reverse side to vote these important matters. Vote at www.ProxyVote.com Prefer to receive an email instead? While voting on www.ProxyVote.com, be sure to click “Sign up for E-delivery”. Voting Items Board Recommends D78434-P66090 01) Gilmore O’Neill 02) Norbert G. Riedel 03) Rachel E. Sherman 1. Election of Class I Directors Nominees: To be elected for a three-year term expiring in 2025. 2. To ratify the appointment of Deloitte & Touche LLP as Aptinyx Inc.’s Independent Registered Public Accounting firm for the fiscal year ending December 31, 2022. NOTE: In their discretion, the proxies are authorized to vote upon any other matters that are properly brought by or at the direction of the Board of Directors before the Annual Meeting and at any adjournments or postponements thereof. For For

o	Preliminary Proxy Statement
o	Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))
o	Definitive Proxy Statement
x	Definitive Additional Materials
o	Soliciting Material under §240.14a-12

Payment of Filing Fee (Check the appropriate box):
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