SYBX

SEC source: 0001193125-26-352228 · ownership.xml · derivative · entry 2

New Enterprise Associates 14, L.P. · CIK 0001544328 · Director · 10% owner

NEA Partners 14, L.P. · CIK 0001551531 · Director · 10% owner

NEA 14 GP, LTD · CIK 0001551532 · Director · 10% owner

Florence Anthony A. Jr. · CIK 0001559827 · Director · 10% owner

SANDELL SCOTT D · CIK 0001237289 · Director · 10% owner

Makhzoumi Mohamad · CIK 0001630226 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 2,640,845

Underlying: Common Stock · 2,640,845 shares

Expires 2028-10-03

F2 · price: The two transactions reported in Table II above involved the amendment of an outstanding warrant to reduce the exercise price from $3.408 a share to $0.70 a share. The amendment is reported above as the cancellation of the old warrant and the acquisition of a new one.

F1 · derivative.exercise_date: The warrants were immediately exercisable; provided, however, that the warrants carry a limitation on exercise preventing exercise if such exercise results in New Enterprise Associates 14, L.P. ("NEA 14") beneficially owning in excess of 4.99% (or, at the election of NEA 14, 9.99%) of the number of shares of the Issuer's Common Stock, which percentage can be increased or decreased at the option of NEA 14 upon 61 days' prior notice.

F3 · ownership.direct: The securities are directly held by NEA 14 and are indirectly held by NEA Partners 14, L.P. ("NEA Partners 14"), the sole general partner of NEA 14, NEA 14 GP, LTD ("NEA 14 LTD"), the sole general partner of NEA Partners 14, and the members of the Executive Committee (the "Executive Committee") of NEA Management Company, LLC (NEA Partners 14, NEA 14 LTD and the members of the Executive Committee together, the "Indirect Reporting Persons"). The members of the Executive Committee are Anthony A. Florence, Jr., Mohamad H. Makhzoumi, and Scott D. Sandell. The Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the securities held by NEA 14 in which the Indirect Reporting Persons have no pecuniary interest.

SEC source: 0001193125-26-352228 · ownership.xml · derivative · entry 1

New Enterprise Associates 14, L.P. · CIK 0001544328 · Director · 10% owner

NEA Partners 14, L.P. · CIK 0001551531 · Director · 10% owner

NEA 14 GP, LTD · CIK 0001551532 · Director · 10% owner

Florence Anthony A. Jr. · CIK 0001559827 · Director · 10% owner

SANDELL SCOTT D · CIK 0001237289 · Director · 10% owner

Makhzoumi Mohamad · CIK 0001630226 · Director · 10% owner

Joint disclosure: these amounts are not allocated separately to each reporting owner.

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 2,640,845 shares

Expires 2028-10-03

F2 · price: The two transactions reported in Table II above involved the amendment of an outstanding warrant to reduce the exercise price from $3.408 a share to $0.70 a share. The amendment is reported above as the cancellation of the old warrant and the acquisition of a new one.

F1 · derivative.exercise_date: The warrants were immediately exercisable; provided, however, that the warrants carry a limitation on exercise preventing exercise if such exercise results in New Enterprise Associates 14, L.P. ("NEA 14") beneficially owning in excess of 4.99% (or, at the election of NEA 14, 9.99%) of the number of shares of the Issuer's Common Stock, which percentage can be increased or decreased at the option of NEA 14 upon 61 days' prior notice.

F3 · ownership.direct: The securities are directly held by NEA 14 and are indirectly held by NEA Partners 14, L.P. ("NEA Partners 14"), the sole general partner of NEA 14, NEA 14 GP, LTD ("NEA 14 LTD"), the sole general partner of NEA Partners 14, and the members of the Executive Committee (the "Executive Committee") of NEA Management Company, LLC (NEA Partners 14, NEA 14 LTD and the members of the Executive Committee together, the "Indirect Reporting Persons"). The members of the Executive Committee are Anthony A. Florence, Jr., Mohamad H. Makhzoumi, and Scott D. Sandell. The Indirect Reporting Persons disclaim beneficial ownership within the meaning of Section 16 of the Securities Exchange Act of 1934, as amended, or otherwise of such portion of the securities held by NEA 14 in which the Indirect Reporting Persons have no pecuniary interest.

SEC source: 0001193125-25-260649 · ownership.xml · nonDerivative · entry 1

Dooley Mary Beth · CIK 0002015112 · See Remarks below

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 12,744

F1 · shares: 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.

SEC source: 0000950170-25-060267 · ownership.xml · nonDerivative · entry 1

Shea Richard P · CIK 0001294354 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 15,506

F1 · shares: Per the Amended and Restated Non-Employee Director Compensation Program, amended on April 26, 2025, and the 2015 Equity Incentive Award Plan, the Board of Directors of Synlogic, Inc. awarded each Non-Employee Director 15,000 shares of restricted stock. The shares were granted on April 26, 2025 and will fully vest on December 15, 2025, subject to the Reporting Person continuing to provide services to the Company as a Non-Employee Director, through such vesting date.

SEC source: 0000950170-25-060253 · ownership.xml · nonDerivative · entry 1

Flynn James P · CIK 0001955965 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 15,000

F1 · shares: Per the Amended and Restated Non-Employee Director Compensation Program, amended on April 26, 2025, and the 2015 Equity Incentive Award Plan, the Board of Directors of Synlogic, Inc. awarded each Non-Employee Director 15,000 shares of restricted stock. The shares were granted on April 26, 2025 and will fully vest on December 15, 2025, subject to the Reporting Person continuing to provide services to the Company as a Non-Employee Director, through such vesting date.

SEC source: 0000950170-25-050478 · ownership.xml · nonDerivative · entry 1

Dooley Mary Beth · CIK 0002015112 · See Remarks below

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 12,901

F1 · shares: Represents the number of shares sold by the reporting person on April 2, 2025 to cover the tax liability in connection with the vesting of three restricted stock awards, vesting on April 1, 2025, that were granted in 2021, 2022 and 2023.

SEC source: 0000950170-25-013831 · ownership.xml · nonDerivative · entry 1

Dooley Mary Beth · CIK 0002015112 · See Remarks below

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 13,045

F1 · shares: Represents the number of shares sold by the reporting person on February 3, 2025 to cover the tax liability in connection with the vesting of a restricted stock award, vesting on January 31, 2025, that was granted on January 2, 2024.

SEC source: 0000950170-24-119194 · ownership.xml · nonDerivative · entry 1

Dooley Mary Beth · CIK 0002015112 · Head of Finance

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 15,152

F1 · shares: Represents the number of shares sold by the reporting person on October 29, 2024 to cover the tax liability in connection with the vesting of a restricted stock award, vesting on October 28, 2024, that was granted on October 28, 2022.

SEC source: 0000950170-24-041790 · ownership.xml · nonDerivative · entry 1

Dooley Mary Beth · CIK 0002015112 · Head of Finance

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 15,231

F1 · shares: Represents the number of shares sold by the reporting person on April 2, 2024 to cover the tax liability in connection with the vesting of four restricted stock awards, vesting on April 1, 2024, that were granted in 2020, 2021, 2022 and 2023.

SEC source: 0000950170-24-041787 · ownership.xml · nonDerivative · entry 1

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 33,859

F1 · shares: Represents the number of shares sold by the reporting person on April 2, 2024 to cover the tax liability in connection with the vesting of three restricted stock awards, vesting on April 1, 2024, that were granted in 2020, 2021 and 2022.

SEC source: 0000950170-24-034866 · ownership.xml · derivative · entry 1

Flynn James P · CIK 0001955965 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 4,000

Underlying: Common Stock · 4,000 shares

Expires 2034-03-19

F1 · derivative.exercise_date: The option vests and becomes exercisable in substantially equal installments on each of the first three anniversaries of the Transaction Date, subject to the Reporting Person continuing to provide services to the Issuer through such vesting date.

SEC source: 0000950170-24-001821 · ownership.xml · derivative · entry 1

Barrett Peter · CIK 0001291895 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 24,923

Underlying: Common Stock · 24,923 shares

Expires 2034-01-02

F1 · derivative.exercise_date: 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 committee cash retainers of $81,500 in the aggregate. Such options vest in four equal quarterly installments on the last day of each calendar quarter during 2024 provided the Reporting Person continues to provide services to the Issuer.

F2 · ownership.direct: 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.

SEC source: 0000950170-24-001826 · ownership.xml · derivative · entry 1

Hurter Patricia N. · CIK 0001767191 · Director

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 14,678

Underlying: Common Stock · 14,678 shares

Expires 2034-01-02

F1 · derivative.exercise_date: 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 committee cash retainers of $48,000 in the aggregate. Such options vest in quarterly installments on the last day of each calendar quarter during 2024 provided the Reporting Person coninues to provide services to the Issuer.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 20

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 8,666

Underlying: Common Stock · 8,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F7 · derivative.exercise_date: These performance-based stock options, granted on March 16, 2023, vest when the achievement of certain clinical and regulatory development milestones are met.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 19

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 42,999

Underlying: Common Stock · 42,999 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F6 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 18

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 28,943

Underlying: Common Stock · 28,943 shares

Expires 2032-02-04

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F5 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on February 4, 2022 through February 4, 2026.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 17

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 18,999

Underlying: Common Stock · 18,999 shares

Expires 2031-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F4 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2021 through April 1, 2025.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 16

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 12,352

Underlying: Common Stock · 12,352 shares

Expires 2030-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F3 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2020 through April 1, 2024.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 15

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 12,332

Underlying: Common Stock · 12,332 shares

Expires 2029-03-05

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 14

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 9,999

Underlying: Common Stock · 9,999 shares

Expires 2028-10-31

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 13

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 3,600

Underlying: Common Stock · 3,600 shares

Expires 2028-06-05

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 12

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 3,733

Underlying: Common Stock · 3,733 shares

Expires 2028-03-14

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 11

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 5,591

Underlying: Common Stock · 5,591 shares

Expires 2027-05-15

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 10

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 8,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F7 · derivative.exercise_date: These performance-based stock options, granted on March 16, 2023, vest when the achievement of certain clinical and regulatory development milestones are met.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 9

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 42,999 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F6 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 8

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 28,943 shares

Expires 2032-02-04

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F5 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on February 4, 2022 through February 4, 2026.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 7

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 18,999 shares

Expires 2031-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F4 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2021 through April 1, 2025.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 6

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 12,352 shares

Expires 2030-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F3 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2020 through April 1, 2024.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 5

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 12,332 shares

Expires 2029-03-05

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 4

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 9,999 shares

Expires 2028-10-31

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 3

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 3,600 shares

Expires 2028-06-05

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 2

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 3,733 shares

Expires 2028-03-14

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063927 · ownership.xml · derivative · entry 1

Brennan Aoife · CIK 0001714563 · Director · President and CEO

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 5,591 shares

Expires 2027-05-15

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 6

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 6,666

Underlying: Common Stock · 6,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F4 · derivative.exercise_date: These performance-based stock options, granted on March 16, 2023, vest when the achievement of certain clinical and regulatory development milestones are met.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 5

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 13,332

Underlying: Common Stock · 13,332 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F3 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 4

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 15,332

Underlying: Common Stock · 15,332 shares

Expires 2032-03-03

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: These stock options vested 25% on the first anniversary of the March 3, 2022 grant date, and vest in 36 substantially-equal monthly installments thereafter, subject to the reporting person's continued employment through the applicable vesting date.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 3

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 6,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F4 · derivative.exercise_date: These performance-based stock options, granted on March 16, 2023, vest when the achievement of certain clinical and regulatory development milestones are met.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 2

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 13,332 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F3 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063926 · ownership.xml · derivative · entry 1

JENSEN MICHAEL VANGSTED · CIK 0001914184 · Chief Financial Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 15,332 shares

Expires 2032-03-03

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: These stock options vested 25% on the first anniversary of the March 3, 2022 grant date, and vest in 36 substantially-equal monthly installments thereafter, subject to the reporting person's continued employment through the applicable vesting date.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 16

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 16,666

Underlying: Common Stock · 16,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F8 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 15

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 11,031

Underlying: Common Stock · 11,031 shares

Expires 2032-02-04

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F7 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on February 4, 2022 through February 4, 2026.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 14

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 4,666

Underlying: Common Stock · 4,666 shares

Expires 2031-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F6 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2021 through April 1, 2025.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 13

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 4,666

Underlying: Common Stock · 4,666 shares

Expires 2030-07-14

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F5 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on July 1, 2020 through July 1, 2024.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 12

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 4,666

Underlying: Common Stock · 4,666 shares

Expires 2030-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F4 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2020 through April 1, 2024.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 11

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 6,666

Underlying: Common Stock · 6,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F3 · derivative.exercise_date: These performance-based stock options, granted on March 16, 2023, vest when the achievement of certain clinical and regulatory development milestones are met.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 10

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 666

Underlying: Common Stock · 666 shares

Expires 2029-03-05

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 9

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 3,666

Underlying: Common Stock · 3,666 shares

Expires 2029-02-28

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F2 · derivative.exercise_date: The shares subject to this option are fully vested as of the date hereof.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 8

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 16,666 shares

Expires 2033-03-16

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F8 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2023 through April 1, 2027.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 7

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 11,031 shares

Expires 2032-02-04

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F7 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on February 4, 2022 through February 4, 2026.

SEC source: 0000950170-23-063925 · ownership.xml · derivative · entry 6

Awad Antoine · CIK 0001820122 · Chief Operating Officer

10b5-1 filing: No plan indicated

Ownership: Direct

Disclosed balance after: 0

Underlying: Common Stock · 4,666 shares

Expires 2031-03-10

F1 · derivative.exercise_price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F1 · price: In accordance with the terms of the Synlogic, Inc. 2015 Equity Incentive Award Plan and the Company's 2017 Stock Incentive Plan (together the "Plans"), the Board of Directors of Synlogic, Inc. approved a stock option repricing pursuant to which option awards granted under the Plans were amended to reduce the exercise price to $1.85 per share, the closing stock price of the Company's Common Stock on November 10, 2023. Except for the modified exercise price, all other terms and conditions of each of the option awards will continue as set forth in the Plan and the applicable award agreements.

F6 · derivative.exercise_date: The shares subject to this option vest in approximately equal monthly installments beginning on April 1, 2021 through April 1, 2025.