Sec Form 4 Filing - Lichter Jay @ Synthorx, Inc. - 2020-01-23

FORM 4 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 Lichter Jay 2. Issuer Name and Ticker or Trading Symbol Synthorx, Inc. [ THOR] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) C/O SYNTHORX, INC., 11099 N. TORREY PINES ROAD, SUITE 190 3. Date of Earliest Transaction (MM/DD/YY) 01/23/2020 (Street) LA JOLLA, CA92037 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) __ X __ Form filed by One Reporting Person _____ 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 Common Stock 01/23/2020 U 150,000 D $ 68 0 I By Avalon Ventures X, L.P. ( 1 ) Common Stock 01/23/2020 U 448,567 D $ 68 0 I By Avalon Ventures X GP, LLC ( 1 ) Common Stock 01/23/2020 U 1,682,086 D $ 68 0 I By Avalon X SPV I, L.P. ( 1 )

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 Stock Option (right to buy) $ 11 01/23/2020 D 30,000 ( 2 ) 12/05/2028 Common Stock 30,000 $ 57 0 D Stock Option (right to buy) $ 12.4 01/23/2020 D 15,335 ( 3 ) 06/06/2029 Common Stock 15,335 $ 55.6 0 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Lichter Jay C/O SYNTHORX, INC. 11099 N. TORREY PINES ROAD, SUITE 190 LA JOLLA, CA92037 X Signatures /s/ Christian V. Kuhlen, Attorney-in-Fact 01/24/2020 Signature of Reporting Person Date

Explanation of Responses:

( 1 )The Reporting Person is a managing member of Avalon Ventures X GP LLC and Avalon Ventures X SPV GP LLC, the general partners of Avalon Ventures X, L.P. and Avalon X SPV I, L.P., and shares voting and investment power with respect to the shares held by Avalon Ventures X, L.P. and Avalon X SPV I, L.P. The Reporting Person disclaims beneficial ownership of the shares held by Avalon Ventures X, L.P., Avalon Ventures X GP LLC and Avalon X SPV I, L.P., except to the extent of his actual pecuniary interest therein if any. ( 2 )This option, which provided for vesting of the shares in equal monthly installments over the 12 months following December 6, 2018, was cancelled in connection with the merger of the Issuer with Sanofi's wholly owned subsidiary in exchange for a cash payment of $1,710,000.00, representing the difference between the exercise price of the option and the market value of the underlying common stock of the Issuer on the effective date of the merger ($68). ( 3 )This option, which provided for vesting of the shares in equal monthly installments over the 12 months following June 7, 2019, such that the option would be fully vested on the date of the Issuer's next annual stockholder meeting, was cancelled in connection with the merger of the Issuer with Sanofi's wholly owned subsidiary in exchange for a cash payment of $852,626.00, representing the difference between the exercise price of the option and the market value of the underlying common stock of the Issuer on the effective date of the merger ($68).

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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