Sec Form 3 Filing - Longitude Capital Partners II, LLC @ Aptinyx Inc. - 2018-06-20

FORM 3 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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1. Name and Address of Reporting Person Longitude Capital Partners II, LLC 2. Issuer Name and Ticker or Trading Symbol Aptinyx Inc. [ APTX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director X __ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) 2740 SAND HILL RD 2ND FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 06/20/2018 (Street) MENLO PARK, CA94025 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ Form filed by More than One Reporting Person (City) (State) (Zip)

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned 1.Title of Security (Instr. 3) 2. Transaction Date (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned ( e.g. , puts, calls, warrants, options, convertible securities) 1. Title of Derivative Security (Instr. 3) 2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 4. Transaction Code (Instr. 8) 5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5) 6. Date Exercisable and Expiration Date (MM/DD/YY) 7. Title and Amount of Underlying Securities (Instr. 3 and 4) 8. Price of Derivative Security (Instr. 5) 9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4) 10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4) 11. Nature of Indirect Beneficial Ownership (Instr. 4) Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares Series A-1 Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,047,450 I By: Longitude Venture Partners II, L.P. ( 2 ) Series A-2 Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 1,197,076 I By: Longitude Venture Partners II, L.P. ( 2 ) Series B Convertible Preferred Stock ( 1 ) ( 1 ) ( 1 ) Common Stock 795,553 I By: Longitude Venture Partners II, L.P. ( 2 )

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Longitude Capital Partners II, LLC 2740 SAND HILL RD 2ND FLOOR MENLO PARK, CA94025 X Tammenoms Bakker Juliet 2740 SAND HILL RD 2ND FLOOR MENLO PARK, CA94025 X Longitude Venture Partners II, L.P. 2740 SAND HILL RD 2ND FLOOR MENLO PARK, CA94025 X Signatures LONGITUDE CAPITAL PARTNERS II, LLC, a Delaware limited liability company, By: /s/ Patrick G. Enright, Managing Member 06/20/2018 Signature of Reporting Person Date LONGITUDE VENTURE PARTNERS II, L.P., By: Longitude Capital Partners II, LLC, a Delaware limited liability company, Its General Partner, By: /s/ Patrick G. Enright, Managing Member 06/20/2018 Signature of Reporting Person Date /s/ Juliet Tammenoms Bakker 06/20/2018 Signature of Reporting Person Date

Explanation of Responses:

( 1 )All series of convertible preferred stock will automatically convert into the number of shares of the Issuer's common stock on a 27.58621-for-1 basis immediately prior to the closing of the Issuer's initial public offering and have no expiration date. ( 2 )This report is filed jointly by Longitude Capital Partners II, LLC ("Longitude Capital II"), Longitude Venture Partners II, L.P. ("Longitude Venture II"), and Juliet Tammenoms Bakker ("Ms. Bakker"), all of whom share beneficial ownership of more than 10% of the capital stock of the Issuer. Longitude Capital II as general partner of Longitude Venture II maybe deemed to have shared voting, investment and dispositive power over the shares held by Longitude Venture II. Patrick G. Enright ("Mr. Enright") and Ms. Bakker are each managing members of Longitude Capital II and in their capacity as such, may be deemed to exercise shared voting and investment power over the shares held by Reporting Persons. Each of Longitude Capital II, Mr. Enright and Ms. Bakker disclaims beneficial ownership of such shares except to the extent of its, his or her pecuniary interest therein. Mr. Enright is filing a separate form 3 in his capacity as a director of the Issuer.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).

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