FORM 4 [X] 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 OF SECURITIES
                                                                                  
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Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940
                      

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/YYYY)

1/23/2020
(Street)

LA JOLLA, CA 92037
(City)        (State)        (Zip)
4. If Amendment, Date Original Filed (MM/DD/YYYY)

 
 6. Individual or Joint/Group Filing (Check Applicable Line)

_X _ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3) 		2. Trans. Date 2A. Deemed Execution Date, if any 3. Trans. 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 1/23/2020  U  150000 D$68.00 0 I By Avalon Ventures X, L.P. (1)
Common Stock 1/23/2020  U  448567 D$68.00 0 I By Avalon Ventures X GP, LLC (1)
Common Stock 1/23/2020  U  1682086 D$68.00 0 I By Avalon X SPV I, L.P. (1)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivate Security
(Instr. 3)		2. Conversion or Exercise Price of Derivative Security3. Trans. Date3A. Deemed Execution Date, if any4. Trans. Code
(Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date7. Title and Amount of Securities Underlying Derivative Security
(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)
CodeV(A)(D)Date ExercisableExpiration DateTitleAmount or Number of Shares
Stock Option (right to buy) $11.00 1/23/2020  D     30000   (2)12/5/2028 Common Stock 30000 $57.00 0 D  
Stock Option (right to buy) $12.40 1/23/2020  D     15335   (3)6/6/2029 Common Stock 15335 $55.60 0 D  
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).
Reporting Owners
Reporting Owner Name / Address
Relationships
Director10% OwnerOfficerOther
Lichter Jay
C/O SYNTHORX, INC.
11099 N. TORREY PINES ROAD, SUITE 190
LA JOLLA, CA 92037		X
Signatures
/s/ Christian V. Kuhlen, Attorney-in-Fact1/24/2020
**Signature of Reporting PersonDate
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