[Form 4] SYNLOGIC, INC. Insider Trading Activity

Rhea-AI Filing Summary

Synlogic (SYBX) insider transaction: Principal Executive and Financial Officer Mary Beth Dooley reported a sale of common stock. On October 29, 2025, she sold 157 shares at $1.81 per share.

The filing states the shares were sold to cover tax liabilities arising from a restricted stock award that vested on October 28, 2025 from a 2022 grant. Following the sale, she beneficially owned 12,744 shares directly. This appears to be routine tax withholding related to equity vesting rather than an open‑market discretionary sale.

SEC Form 4

FORM 4

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
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Dooley Mary Beth

(Last) (First) (Middle)

C/O SYNLOGIC, INC.

PO BOX 30

(Street)

WINCHESTER MA 01890

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
SYNLOGIC, INC. [ SYBX ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director		10% Owner
X	Officer (give title below)		Other (specify below)
	See Remarks below

3. Date of Earliest Transaction (Month/Day/Year)
10/29/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

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. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	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	10/29/2025		S		157(1)	D	$1.81	12,744	D

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 (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	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 (Month/Day/Year)		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: 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

Explanation of Responses:

1. Represents the number of shares sold by the reporting person on October 29, 2025 to cover the tax liability in connection with the vesting of a restricted stock award, vesting on October 28, 2025, that was granted in 2022.

Remarks:

Principal Executive Officer and Principal Financial Officer

	/s/ Mary Beth Dooley	10/31/2025
	** Signature of Reporting Person	Date
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).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What insider activity did SYBX report?

A Form 4 reports that Mary Beth Dooley sold 157 shares of Synlogic common stock at $1.81 on October 29, 2025.

Why were the SYBX shares sold?

The filing explains the sale was to cover tax liability from a restricted stock award that vested on October 28, 2025.

How many SYBX shares does the insider hold after the sale?

Following the transaction, the insider beneficially owned 12,744 shares directly.

What is the insider’s role at Synlogic (SYBX)?

Mary Beth Dooley is the company’s Principal Executive Officer and Principal Financial Officer.

Was this sale under a Rule 10b5-1 trading plan?

The form includes the standard 10b5-1 checkbox disclosure; the excerpt does not indicate it was checked.