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 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 * Barrett Peter 2. Issuer Name and Ticker or Trading Symbol SYNLOGIC, INC. [ SYBX ] 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 SYNLOGIC, INC., 301 BINNEY STREET, SUITE 402
3. Date of Earliest Transaction (MM/DD/YYYY)
1/4/2021
(Street)
CAMBRIDGE, MA 02142
(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

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 Security 3. Trans. Date 3A. Deemed Execution Date, if any 4. 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 Date 7. 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)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (right to buy)  $2.20  1/4/2021    A     57498       (1) 1/4/2031  Common Stock  57498  $0.00  57498  D (2)  

Explanation of Responses:
(1)  The options were issued to the Reporting Person pursuant to the Issuer's Amended and Restated Non-Employee Director Compensation Program and 2015 Equity Incentive Award Plan in lieu of the non-employee director board and audit committee cash retainers of $85,500 in the aggregate. Such options vest in four equal quarterly installments on the last day of each calendar quarter during 2021 provided the Reporting Person continues to provide services to the Issuer.
(2)  The reporting person is a member of Atlas Venture Associates IX, LLC ("AVA IX LLC") and is obligated to transfer the economic benefit, if any, received upon the sale of the shares issuable upon exercise of the equity grants to Atlas Venture Advisors, L.P. As such, the Reporting Person disclaims beneficial ownership of the securities reported herein for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, except to the extent of his pecuniary interest therein, if any.

Reporting Owners
Reporting Owner Name / Address
Relationships
Director 10% Owner Officer Other
Barrett Peter
C/O SYNLOGIC, INC.
301 BINNEY STREET, SUITE 402
CAMBRIDGE, MA 02142
X



Signatures
/s/ Frank Castellucci, Attorney-in-Fact 1/5/2021
**Signature of Reporting Person Date