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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION
Washington,

WASHINGTON, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the

Securities Exchange Act of 1934 (Amendment

(Amendment No.      )

SYNLOGIC, INC.

(Name of Registrant as Specified In Its Charter)

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MIRNA THERAPEUTICS, INC.
2150 Woodward Street, Suite 100
Austin, Texas 78744

				May 16, 2018

To Our Stockholders:

You are cordially invited to attend the Stockholders2018 annual meeting of Mirna Therapeutics,stockholders of Synlogic, Inc.:

        The Annual Meeting of Stockholders, or the Annual Meeting, of Mirna Therapeutics, Inc., a Delaware corporation, or the Company, will to be held at 9:00 a.m. Eastern time on Wednesday, June 29, 201613, 2018 at 8:00 a.m. local time301 Binney Street, Suite 402, Cambridge, MA 02142.

Details regarding the meeting, the business to be conducted at the officesmeeting, and information about Synlogic that you should consider when you vote your shares are described in this proxy statement.

At the annual meeting, two persons will be elected to our Board of Latham & Watkins LLP, 885 Third Avenue, New York, New York for the following purposes:

1.

To elect three Class I directorsDirectors. In addition, we will ask stockholders to hold office until the 2019 Annual Meeting of Stockholders or until their successors are elected;



2.

To ratify the selection by the audit committee of our board of directors, of Ernst & YoungKPMG LLP as theour independent registered public accounting firm of the Company for itsour fiscal year ending December 31, 2016; and



3.

To transact such2018. The Board of Directors recommends the approval of each of the two proposals. Such other business will be transacted as may properly come before the Annual Meetingannual meeting.

We hope you will be able to attend the annual meeting. Whether you plan to attend the annual meeting or any adjournmentnot, it is important that you cast your vote either in person or postponement thereof.

        The foregoing items of business are more fully described inby proxy. You may vote over the Internet as well as by telephone or by mail. When you have finished reading the proxy statement, accompanyingyou are urged to vote in accordance with the instructions set forth in this Notice. Only stockholders who ownedproxy statement. We encourage you to vote by proxy so that your shares will be represented and voted at the Company'smeeting, whether or not you can attend.

Thank you for your continued support of Synlogic. We look forward to seeing you at the annual meeting.

Sincerely,

Jose-Carlos Gutiérrez-Ramos

CEO

May 16, 2018

NOTICE OF 2018 ANNUAL MEETING OF STOCKHOLDERS

TIME: 9:00 a.m. Eastern time

DATE: Wednesday, June 13, 2018

PLACE: Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge, MA 02142

PURPOSES:

1. To elect two Class III directors to serve three-year terms expiring in 2021;

2. To ratify the appointment of KPMG LLP as the Company’s independent registered public accounting firm for the fiscal year ending December 31, 2018; and

3. To transact such other business that is properly presented at the annual meeting and any adjournments or postponements thereof.

WHO MAY VOTE:

You may vote if you were the record owner of Synlogic, Inc. common stock at the close of business on May 2, 2016 may voteApril 24, 2018. A list of stockholders of record will be available at the Annual Meeting or any adjournments that take place.annual meeting and, during the 10 days prior to the annual meeting, at our principal executive offices located at 301 Binney Street, Suite 402, Cambridge, MA 02142.

        We have elected to provide our proxy materials to our stockholders over the internet as permitted by the rules of the U.S. Securities and Exchange Commission. As a result, we are mailing most of our stockholders a paper copy of the Notice of Internet Availability of Proxy Materials, or the Notice, but not a paper copy of our proxy statement. This process allows us to provide our proxy materials to our stockholders in a timelier and more readily accessible manner, while reducing the environmental impact and lowering the costs of printing and distributing our proxy materials. The Notice contains instructions on how to access those documents over the internet. The Notice also contains instructions on how to request a paper copy of our proxy materials, including this proxy statement and a form of proxy card or voting instruction card. All stockholders who have previously requested a paper copy of our proxy materials will continue to receive a paper copy of the proxy materials by mail.

        You are cordially invited to attend the Annual Meeting in person. annual meeting.Whether or not you plan to attend the annual meeting or not, we urge you to vote and submit your proxy by the Internet, telephone or mail in order to ensure the presence of a quorum.You may change or revoke your proxy at any time before it is voted at the meeting.

BY ORDER OF THE BOARD OF DIRECTORS

Maiken Keson-Brookes

Secretary

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i

SYNLOGIC, INC.

301 Binney Street, Suite 402

Cambridge, MA 02142

PROXY STATEMENT FOR THE 2018 ANNUAL MEETING OF STOCKHOLDERS

TO BE HELD ON JUNE 13, 2018

This proxy statement, along with the accompanying notice of 2018 annual meeting of stockholders, contains information about the 2018 annual meeting of stockholders of Synlogic, Inc., including any adjournments or postponements of the annual meeting. We are holding the annual meeting at 9:00 a.m., Eastern time, on Wednesday, June 13, 2018, at our corporate offices located at 301 Binney Street, Suite 402, Cambridge, MA 02142.

In this proxy statement, we refer to Synlogic, Inc. as “Synlogic”, “the Company”, “we”, and “us.”

This proxy statement relates to the solicitation of proxies by our Board of Directors for use at the annual meeting.

On or about May 16, 2018, we intend to begin sending this proxy statement, the attached Notice of Annual Meeting of Stockholders and the enclosed proxy card to all stockholders entitled to vote at the annual meeting.

Although not part of this proxy statement, we are also sending, along with this proxy statement, our Annual Report on Form10-K for the fiscal year ended December 31, 2017, which includes our financial statements for the fiscal year ended December 31, 2017.

EXPLANATORY NOTE

On August 28, 2017, Synlogic, Inc., formerly known as Mirna Therapeutics, Inc. (NASDAQ: MIRN) (“Mirna”), completed its business combination with Synlogic, Inc. (“Private Synlogic”) in accordance with the terms of the Agreement and Plan of Merger and Reorganization, dated as of May 15, 2017, by and among Mirna, Meerkat Merger Sub, Inc. (“Merger Sub”), and Private Synlogic (the “Merger Agreement”), pursuant to which Merger Sub merged with and into Private Synlogic, with Private Synlogic surviving as a wholly owned subsidiary of Mirna (the “Merger”). On August 28, 2017, immediately after completion of the Merger, Mirna changed its name to “Synlogic, Inc.” (“Public Synlogic”) (NASDAQ: SYBX).

In this proxy statement, unless the context specifically indicates otherwise, “the Company”, “we”, “us”, “our”, and “Synlogic” refer to Public Synlogic and its subsidiaries following the Merger, effective on August 28, 2017, and to Private Synlogic and its subsidiaries prior to the Merger. References to“Pre-Merger Mirna” means Mirna prior to the Merger effective on August 28, 2017.

IMPORTANT NOTICE REGARDING THE AVAILABILITY OF PROXY MATERIALS FOR THE

SHAREHOLDER MEETING TO BE HELD ON JUNE 13, 2018

This proxy statement and our 2017 annual report to stockholders are available for viewing, printing and downloading atwww.astproxyproposal.com/ast/21687/. To view these materials please have your12-digit control number(s) available that appears on your proxy card. On this website, you can also elect to receive future distributions of our proxy statements and annual reports to stockholders by electronic delivery.

Additionally, you can find a copy of our Annual Report on Form10-K, which includes our financial statements, for the fiscal year ended December 31, 2017 on the website of the Securities and Exchange Commission, or the SEC, atwww.sec.gov, or in the “Financials” section of the “Investors & Media” section of our website atwww.synlogictx.com.You may also obtain a printed copy of our Annual Report on Form10-K, including our financial statements, free of charge, from us by sending a written request to: Investor Relations, Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge, MA 02142. Exhibits will be provided upon written request and payment of an appropriate processing fee.

IMPORTANT INFORMATION ABOUT THE ANNUAL MEETING AND VOTING

Why is the Company Soliciting My Proxy?

The Board of Directors of Synlogic is soliciting your proxy to vote at the 2018 annual meeting of stockholders to be held at 301 Binney Street, Suite 402, Cambridge MA 02142, on Wednesday, June 13, 2018, at 9:00 a.m. Eastern time and any adjournments of the meeting, which we refer to as soonthe annual meeting. The proxy statement along with the accompanying Notice of Annual Meeting of Stockholders summarizes the purposes of the meeting and the information you need to know to vote at the Annual Meeting.

We have made available to you on the Internet or have sent you this proxy statement, the Notice of Annual Meeting of Stockholders, the proxy card and a copy of our Annual Report on Form10-K for the fiscal year ended December 31, 2017because you owned shares of Synlogic, Inc. common stock on the record date. The Company intends to commence distribution of the proxy materials to stockholders on or about May 16, 2018.

Who Can Vote?

Only stockholders who owned our common stock at the close of business on April 24, 2018 are entitled to vote at the annual meeting. On this record date, there were 25,450,808 shares of our common stock outstanding and entitled to vote. Our common stock is our only class of voting stock.

You do not need to attend the annual meeting to vote your shares. Shares represented by valid proxies, received in time for the annual meeting and not revoked prior to the annual meeting, will be voted at the annual meeting. For instructions on how to change or revoke your proxy, see “May I Change or Revoke My Proxy?” below.

How Many Votes Do I Have?

Each share of ourcommon stock that you own entitles you to one vote.

How Do I Vote?

Whether you plan to attend the annual meeting or not, we urge you to vote by proxy. All shares represented by valid proxies that we receive through this solicitation, and that are not revoked, will be voted in accordance with your instructions on the proxy card or as possible.instructed via Internet or telephone. You may vote overspecify whether your shares should be voted for or withheld for each nominee for director, and whether your shares should be voted for, against or abstain with respect to the internetother proposal. If you properly submit a proxy without giving specific voting instructions, your shares will be voted in accordance with the Board’s recommendations as noted below. Voting by proxy will not affect your right to attend the annual meeting. If your shares are registered directly in your name through our stock transfer agent, American Stock Transfer & Trust Company, LLC, or you have stock certificates registered in your name, you may vote:

Telephone and datedInternet voting facilities for stockholders of record will be available 24 hours a day and will close at 11:59 p.m. Eastern time on June 12, 2018.

If your shares are held in “street name” (held in the name of a bank, broker or other holder of record), you will receive instructions from the holder of record. You must follow the instructions of the holder of record in order for your shares to be voted. Telephone and Internet voting also will be offered to stockholders owning shares through certain banks and brokers. If your shares are not registered in your own name and you plan to vote your shares in person at the annual meeting, you should contact your broker or agent to obtain a legal proxy or broker’s proxy card or voting instruction cardand bring it to the annual meeting in order to vote.

How Does the envelope provided. Please note that any stockholder attendingBoard of Directors Recommend That I Vote on the Annual Meeting may vote in person, even if the stockholder has already returned a proxy card or voting instruction card.Proposals?

        Our boardThe Board of directorsDirectors recommends that you vote "as follows:

If any other matter is presented at the annual meeting, your proxy provides that your shares will be voted by the proxy holder listed in the proxy in accordance with his or her best judgment. At the time this proxy statement was first made available, we knew of no matters that needed to be acted on at the annual meeting, other than those discussed in this proxy statement.

May I Change or Revoke My Proxy?

If you give us your proxy, you may change or revoke it at any time before the annual meeting. You may change or revoke your proxy in any one of the following ways:

Your most current vote, whether by telephone, Internet or proxy card is the one that will be counted.

What if I Receive More Than One Notice or Proxy Card?

You may receive more than one Notice or proxy card if you hold shares of our common stock in more than one account, which may be in registered form or held in street name. Please vote in the manner described above under “How Do I Vote?” for each account to ensure that all of your shares are voted.

Will My Shares be Voted if I Do Not Vote?

If your shares are registered in your name or if you have stock certificates, they will not be counted if you do not vote as described above under “How Do I Vote?” If your shares are held in street name and you do not provide voting instructions to the bank, broker or other nominee that holds your shares as described above, the bank, broker or other nominee that holds your shares has the authority to vote your unvoted shares only with respect to Proposal No. 2 of2. Therefore, we encourage you to provide voting instructions to your bank, broker or other nominee. This ensures your shares will be voted at the proxy statement.annual meeting and in the manner you desire. A “brokernon-vote” will occur if your broker cannot vote your shares on a particular matter because it has not received instructions from you and does not have discretionary voting authority on that matter or because your broker chooses not to vote on a matter for which it does have discretionary voting authority.

What Vote is Required to Approve Each Proposal and How are Votes Counted?

What Constitutes a Quorum for the internetAnnual Meeting?

The presence, in person or upon your request, have delivered paperby proxy, materials to you, becauseof the boardholders of directorsa majority of Mirna Therapeutics, Inc., or the Company, is soliciting your proxyvoting power of all outstanding shares of our common stockentitled to vote at the Annual Meetingannual meeting is necessary to constitute a quorum at the annual meeting. Votes of Stockholders,stockholders of record who are present at the annual meeting in person or by proxy, abstentions, and brokernon-votes are counted for purposes of determining whether a quorum exists.

Attending the Annual Meeting or any adjournments that take place.

The Annual Meetingannual meeting will be held onat 9:00 a.m. Eastern timeon Wednesday, June 29, 2016 at 8:00 a.m. local time at13, 2018at 301 Binney Street, Suite 402, Cambridge, MA 02142. When you arrive, signs will direct you to the offices of Latham & Watkins LLP, 885 Third Avenue, New York, New York. As a stockholder, you are invited to attend the Annual Meeting and are requested to vote on the proposals described in this proxy statement. However, youappropriate meeting rooms. You do not need to attend the Annual Meetingannual meeting in order to vote.

What is included inHouseholding of Annual Disclosure Documents

SEC rules concerning the proxy materials?

        The proxy materials include:

•

This proxy statement, which includes information regarding the proposalsdelivery of annual disclosure documents allow us or your broker to be voted on at the Annual Meeting, the voting process, corporate governance, the compensation of our directors and certain executive officers, and other required information;



•

Our Annual Report on Form 10-K for the fiscal year ended December 31, 2015; and



•

The proxy cardsend a single Notice or, if applicable, a voting instruction card for the Annual Meeting.

        The proxy materials are being mailed or made available to stockholders on or about April 27, 2016.

Why did I receive a Notice of Internet Availability of Proxy Materials, or the Notice, in the mail instead of a completesingle set of paper proxy materials?

        We have elected to provide our proxy materials to our stockholders over the internet as permitted by the rules of the U.S. Securities and Exchange Commission (the "SEC"). As a result, we are mailing mostany household at which two or more of our stockholders a paper copyreside, if we or your broker believe that the stockholders are members of the Notice, but not a paper copysame family. This practice, referred to as “householding,” benefits both you and us. It reduces the volume of the proxy materials. This process allows usduplicate information received at your household and helps to providereduce our proxy materialsexpenses. The rule applies to our stockholdersNotices, annual reports, proxy statements and information statements. Once you receive notice from your broker or from us that communications to your address will be “householded,” the practice will continue until you are otherwise notified or until you revoke your consent to the practice. Stockholders who participate in a timelier and more readily accessible manner, while reducing the environmental impact and lowering the costs of printing and distributing our proxy materials. The Notice contains instructions on how to access the proxy materials over the Internet, and how to request a paper copy of the proxy materials. All stockholders who have

SECURITY OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT

        No. The Notice will, however, provide instructions on how to vote by telephone, by internet, by requesting and returning a paper proxy card or voting instruction card, or by submitting a ballot in person at the Annual Meeting.

How many votes do I have?

        On each matter to be voted upon, you have one vote for each share of the Company's common stock you own as of the Record Date.

What if I return a proxy card but do not make specific choices?

        If you return a signed and dated proxy card without marking any voting selections, your shares will be voted "FOR" the election of each nominee for director (Proposal No. 1) and "FOR" the ratification of the selection of Ernst & Young LLP as the independent registered public accounting firm of the Company for the fiscal year ending December 31, 2016 (Proposal No. 2). If any other matter is properly presented at the Annual Meeting, your proxyholder (one of the individuals named on your proxy card) will vote your shares in his or her discretion.

MANAGEMENT AND CORPORATE GOVERNANCE

The Board of Directors

Our bylaws provide that our business is to ratifybe managed by or under the selectiondirection of our independent registered public accounting firm, is a "routine" matter. Broker non-votes will not be counted toward the vote total for any proposal at the Annual Meeting.

How many votes are needed to approve each proposal?

•

Proposal No. 1—To elect three Class I directors to hold office until the 2019 Annual MeetingBoard of Stockholders or until their successors are elected. The two nominees receiving the most "FOR" votes (from the votesDirectors. Our Board of shares present in person or represented by proxy and entitled to vote on the election of directors) will be elected. Broker non-votes will not be counted towards the vote total for this proposal.



•

Proposal No. 2—To ratify the selection, by the audit committee of our board of directors, of Ernst & Young LLP as the independent registered public accounting firm of the Company for the fiscal year ending December 31, 2016. "FOR" votes from the holders of a majority of the shares cast (excluding abstentions and broker non-votes) are required to approve this proposal. Because Proposal No. 2 is considered a "routine" matter, broker non-votes are not expected in connection with this proposal.

How can I find out the results of the voting at the Annual Meeting?

        We will disclose final voting results in a Current Report on Form 8-K filed with the SEC within four business days after the Annual Meeting. If final voting results are unavailable at that time, then we intend to file a Current Report on Form 8-K to disclose preliminary voting results and file an amended Current Report on Form 8-K within four business days after the date the final voting results are available.

When are stockholder proposals due for next year's annual meeting?

        To be considered for inclusion in the proxy materials for the 2017 Annual Meeting of Stockholders, your proposal must be submitted in writing by December 27, 2016 to the Company's Corporate Secretary at Mirna Therapeutics, Inc., 2150 Woodward Street, Suite 100, Austin, Texas 78744. However, if the meeting is more than 30 days from June 29, 2017, then the deadline will be a reasonable time before we begin to print and mail our proxy materials for that meeting.

        If you wish to submit a proposal before the stockholders or nominate a director at the 2017 Annual Meeting of Stockholders, but you are not requesting that your proposal or nomination be included in the proxy materials for that meeting, then you must follow the procedures set forth in our bylaws and, among other things, notify the Company's Corporate Secretary in writing between March 1, 2017 and March 31, 2017. However, if the date of the 2017 Annual Meeting of Stockholders is more than 30 days before or more than 60 days after June 29, 2017, then you must give notice not later than the 90^th day prior to that meeting or, if later, the 10^th day following the day on which public disclosure of that annual meeting date is first made. You are also advised to review our bylaws, which contain additional requirements regarding advance notice of stockholder proposals and director nominations.

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PROPOSAL NO. 1
ELECTION OF DIRECTORS

        Our board of directorsDirectors is divided into three classes. Eachclasses for purposes of election. One class consists, as nearly as possible,is elected at each annual meeting of one-third of the total number of directors, and each class hasstockholders to serve for a three-year term. ExceptOur Board of Directors currently consists of seven members, classified into three classes as otherwise provided by law, vacancies onfollows: (1) Chau Khuong and Nick Leschlyconstitute a class with a term ending at the board2018 annual meeting; (2) Jose-Carlos Gutiérrez-Ramos and Richard P. Shea constitute a class with a term ending at the 2019 annual meeting; and (3) Peter Barrett, Edward Mathers and Michael Powell constitute a class with a term ending at the 2020 annual meeting.

On March 14, 2018, our Board of directors may be filled only by individuals elected by a majorityDirectors accepted the recommendation of the remaining directors. A director elected byNominating and Governance Committee and voted to nominate Chau Khuong and Nick Leschly for election at the board of directors to fillannual meeting for a vacancy in a particular class, including a vacancy created by an increase in the number of directors, shall serve for the remainder of the full term of that classthree years to serve until the 2021 annual meeting of stockholders, and until such director's successor istheir respective successors have been elected and qualified or until such director'sdirector’s earlier death, resignation or removal.

        Our boardSet forth below are the names of directors currently consists of eightthe persons nominated as directors and no vacancies, divided intodirectors whose terms do not expire this year, their ages, their offices in the three following classes:

•

The Class ICompany, if any, their principal occupations or employment for at least the past five years, the length of their tenure as directors are Elaine V. Jones, Ph.D., Matthew Winkler, Ph.D. and Peter S. Greenleaf, whose current terms will expirethe names of other public companies in which such persons hold or have held directorships during the past five years. Additionally, information about the specific experience, qualifications, attributes or skills that led to our Board of Directors’ conclusion at the Annual Meeting;



•

The Class II directors are Lawrence M. Alleva and Michael Powell, Ph.D., whose current terms will expire at the 2017 Annual Meetingtime of Stockholders; and



•

The Class III directors are Paul Lammers, M.D., M.Sc., Edward Mathers and Clay B. Siegall, Ph.D., whose current terms will expire at the 2018 Annual Meetingfiling of Stockholders.

        Dr. Winkler, Mr. Greenleaf and Dr. Perry Nisen, M.D., Ph.D. have been nominated tothis proxy statement that each person listed below should serve as Class I directors and have agreed to stand for election. If the nominees for Class I are elected at the Annual Meeting, then each nominee will serve for a three-year term expiring at the 2019 Annual Meeting of Stockholders, or until his or her successordirector is elected and qualified, or until his or her earlier death, resignation or removal.

        Our directors are elected by a plurality of the votes cast. If a choice is specified on the proxy card by a stockholder, the shares will be voted as specified. If a choice is not specified on the proxy card, and authority to do so is not withheld, the shares will be voted "FOR" the election of the three nominees for Class I above. If any of the nominees becomes unavailable for election as a result of an unexpected occurrence, shares that would have been voted for the nominee will instead be voted for the election of a substitute nominee proposed by the Company's management or the board of directors. Each person nominated for election has agreed to serve if elected. Our management has no reason to believe that any nominee will be unable to serve.set forth below:

 The following is a brief biography and discussion of the specific attributes, qualifications, experience and skills of each nominee for director and each director whose term will continue after the Annual Meeting. Our board of directors and management encourage each nominee for director and each continuing director to attend the Annual Meeting.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE
"FOR" EACH OF THE THREE CLASS I NOMINEES FOR DIRECTOR.

Development at Avidia Inc., a biopharmaceutical company, and Discovery Medicine. Before that,Peptimmune Inc., a biotechnology company, where he led significant efforts focused on the discovery of novel protein therapeutics and peptides for autoimmune disease, including multiple sclerosis and diabetes. Dr. Nisen was DivisionalGutiérrez-Ramos began his career in the drug industry at Millennium Pharmaceuticals (now a subsidiary of Takeda), a biopharmaceutical company, serving as Vice President of Cancer ResearchInflammation Drug Discovery. In that capacity, Dr. Gutiérrez-Ramos was responsible for advancingpre-clinical candidates in inflammation and Oncology Developmentimmunology into human clinical trials and advancing compounds (small molecules and antibodies) from discovery through clinical development. Dr. Gutiérrez-Ramos began his career in academia as part of the faculty at Abbott Laboratories.the Genetics department of Harvard Medical School. Dr. Nisen holdsGutiérrez-Ramos was also a B.S.member of the Basel Institute for Immunology in Basel, Switzerland, and a fellow at theMax-Plank Institute in Freiburg, Germany. Dr. Gutiérrez-Ramosreceived an M.S. in Biochemistry and Molecular Biology and a Ph.D. in Immunology from Stanford University and M.D. and Ph.D. degrees fromUniversidad Autónoma de Madrid. Dr. Gutiérrez-Ramos serves on the Albert Einstein Collegeboard of Medicine.directors of Momenta Pharmaceuticals, Inc., a publicly-traded biotechnology company. The board has concluded that Dr. Nisen has been chosenGutiérrez-Ramos possesses specific attributes that qualify him to joinserve as a member of our Board because of his medicalDirectors, including the perspective and scientificexperience he brings as our Chief Executive Officer, which brings operational expertise experience in the healthcare industry and broad management experience.to our Board of Directors.

        Matthew Winkler, Ph.D.Richard P. Shea    Dr. Matthew Winkler was our founder and, age 66, has served as a member of our Board of Directors since the Merger closed on August 28, 2017. Mr. Shea has served as the Chief Financial Officer of Syndax Pharmaceuticals, Inc. since February 2017. Mr. Shea previously served as a member of the Syndax Pharmaceuticals board of directors from January 2014 to February 2017. From July 2007 through December 2016, Mr. Shea served as Senior Vice President and Chief Financial Officer of Momenta Pharmaceuticals Inc., a publicly-traded biotechnology company, and was its Vice President and Chief Financial Officer since December 2007,October 2003. Prior to joining Momenta, Mr. Shea served as Chief Operating Officer and Chief Financial Officer of Variagenics Inc., a publicly-traded pharmacogenomics company, that was merged with Hyseq Pharmaceuticals Inc., and as Vice President, Finance of Genetics Institute, Inc., a publicly-traded biotechnology company, which was acquired by Wyeth Pharmaceuticals, Inc., which was then acquired by Pfizer, Inc. Mr. Shea received an A.B. from Princeton University and an M.B.A. from the Public Management Program at Boston University. The board has concluded Mr. Shea possesses specific attributes that qualify him to serve as a member of our Board of Directors, including his experience with the healthcare and pharmaceutical industries and his broad life sciences industry knowledge.

Peter Barrett, Ph.D., age 65, has served as Chairman until October 2012. During 2008of our Board of Directors since the Merger closed on August 28, 2017, and prior to 2009, Dr. Winklerthat time served as our Executive Chairman. Since January 2013, Dr. Winkler has been the Chairman of the boardPrivate Synlogic Board of Directors since March 2014. Dr. Barrett joined Atlas Venture L.P., an early-stage venture capital fund, in 2002, and currently serves as a Partner. From 1998 to 2002, Dr. Barrett was Executive Vice President and Chief Business Officer of Celera Genomics Group (now Celera Corporation, a subsidiary of Quest Diagnostics), a biotechnology company whichhe co-founded. From 1979 to 1998, Dr. Barrett held senior management positions at Perkin-Elmer Corporation, most recently serving as Vice President, Corporate Planning and Business Development. Dr. Barrett currently serves on the boards of directors of Asuragen, Inc. ("Asuragen"), a molecular diagnostic and pharmacogenomics service company, where he also served as the Chief Executive Officer from 2006 to December 2012. Prior to Asuragen, Dr. Winkler was the founder and Chief Executive Officer of Ambion,PerkinElmer, Inc., aZafgen, Inc. and several privately held company that developedcompanies. Dr. Barrett is a Senior Fellow at Harvard Business School and sold research reagents for RNA analysis. Until March 2016, Dr. Winkler served onis the faculty chair of the key advisory board of Second Genome,the Blavatnik Fellowship Program. Dr. Barrett is a biotherapeutics company.member of the research council at Boston Children’s Hospital. Dr. Winkler receivedBarrett holds a B.S. in GeneticsChemistry from Lowell Technological Institute (now the University of Massachusetts, Lowell) and a Ph.D. in ZoologyAnalytical Chemistry from the University of California at Berkeley.Northeastern University. He also completed Harvard Business School’s Management Development Program. The board has concluded that Dr. Winkler was an Assistant and Associate Professor of Zoology at the University of Texas from 1983 to 1991. Dr. Winkler has been chosenBarrett possesses specific attributes that qualify him to serve on ouras a member and chairman of the board, including his extensive leadership, executive, managerial and business experience with life sciences companies, including experience in the formation, development and business strategy of directors due to his management experiencemultiplestart-up companies in the life sciences and pharmaceutical industries.sector.

        Peter S. Greenleaf.Edward Mathers, age 58, has served as a member of our Board of Directors since October 2012. Mr. GreenleafMathers previously served on the Private Synlogic Board of Directors since July 2014. Since 2008, Mr. Mathers has been the Chief Executive Officer and a Director of Sucampo Pharmaceuticals, Inc. since March 2014 and was appointed chairman of the board in January

companies: ObsEva SA, Ra Pharmaceuticals, Inc. and Rhythm Pharmaceuticals, Inc. Mr. Mathers also serves on the Governing Board of the Emerging Companies Section. He is also a member of the board of directors of the Pharmaceutical Researchseveral privately held companies. From 2002 to 2008, Mr. Mathers served as Executive Vice President, Corporate Development and Manufacturers of America (PhRMA).Venture at MedImmune, Inc., a biopharmaceutical company, and led its venture capital subsidiary, MedImmune Ventures, Inc. Before joining MedImmune in 2002, Mr. Greenleaf's previous Board appointments include the University of Maryland Baltimore Foundation,Mathers was Vice President, Marketing and Corporate Licensing and Acquisitions at Inhale Therapeutic Systems, a biotechnology company. Previously, Mr. Mathers spent 15 years at Glaxo Wellcome, Inc.; Rib-X Pharmaceuticals; LigoCyte Pharmaceuticals; (GlaxoSmithKline), a pharmaceutical company, where he held various sales and Corridor Pharmaceuticals. Hemarketing positions. Mr. Mathers received a Master of Business Administration degreeB.S. in Chemistry from St. Joseph's University and a Bachelor of Science degree from Western ConnecticutNorth Carolina State University. The board has concluded that Mr. Greenleaf has been chosenMathers possesses specific attributes that qualify him to serve on our board of directors due to his leadership experience and extensive commercialization, strategic planning, and drug development experience in the biopharmaceutical industry.

THE BOARD OF DIRECTORS RECOMMENDS A VOTE
FOR THE ELECTION OF EACH OF THE ABOVE NAMED NOMINEES

Directors Continuing in Office Until the 2017 Annual Meeting of Stockholders

        Lawrence M. Alleva.    Mr. Lawrence M. Alleva joined our board in July 2014. Prior to his retirement in June 2010, Mr. Alleva worked with PricewaterhouseCoopers LLP, or PwC, for 39 years, 28 of which as a partnermember our Board of Directors, including his experience with the firm. Mr. Alleva served clients primarily in the technology sector, including numeroushealthcare and pharmaceutical industries and biotechnology companies. Additionally, he served PwC in a variety of office, regional and national practice leadership roles, most recently as the U.S. Ethics and Compliance Leader (Assurance) for PwC from 2006 until his retirement. Mr. Alleva is a Certified Public Accountant (inactive). Mr. Alleva received a Bachelor of Science degree from Ithaca College (magna cum laude) and attended Columbia University's Executive MBA program. Mr. Alleva also serves as a director for public companies Tesaro Inc. and Bright Horizons Family Solutions, and previously served on the board of GlobalLogic Inc. Mr. Alleva has been chosen to serve on our board of directors due to his financial and accounting experience as a director and a public accounting partner serving multiple healthcare, pharmaceutical and biopharmaceutical companies.broad management experience.

Michael Powell, Ph.D., age 63, has served as a member of our Board of Directors since October 2012. Dr. Michael Powell haspreviously served as Chairman of our boardBoard of directors sinceDirectors from October 2012.2012 until the Merger closed on August 28, 2017. Since 1997, Dr. Powell has been a General Partner of Sofinnova Ventures, a venture capital firm. Previously, Dr. Powell has held positions at Genentech, Inc., a biotechnology company, Cytel Inc., a research and development company, and Syntex Research Group, a pharmaceutical company. Dr. Powell is currently a directorserves on the board of Dauntless Pharmaceuticals, a biopharmaceutical company, Alvine Pharmaceuticals, a biopharmaceutical company, Ascenta Therapeutics, a biopharmaceutical company, Checkmate Pharmaceuticals, a biopharmaceutical company, Dauntless 1, a biopharmaceutical company, and Ocera Therapeutics, a publicly traded biopharmaceutical company.directors of numerous privately-held companies. Dr. Powell is an Adjunct

University of Maryland and a Ph.D. in Genetics from George Washington University. Dr. Siegall has been chosen to serve on our board of directors due to his experience as a director and executive of multiple healthcare and biopharmaceutical companies.

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PROPOSAL NO. 2
RATIFICATION OF SELECTION OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

        The audit committee of our board of directors has selected Ernst & Young LLP, or EY, as our independent registered public accounting firm for the year ending December 31, 2016, and is seeking ratification of such selection by our stockholders at the Annual Meeting. EY has audited our financial statements for the fiscal years ended December 31, 2015 and 2014. Representatives of EY are expected to be present at the Annual Meeting. They will have an opportunity to make a statement if they so desire and will be available to respond to appropriate questions

        Neither our bylaws nor other governing documents or law require stockholder ratification of the selection of EY as our independent registered public accounting firm. However, the audit committee is submitting the selection of EY to our stockholders for ratification as a matter of good corporate practice. If our stockholders fail to ratify the selection, the audit committee will reconsider whether or not to retain EY. Even if the selection is ratified, the audit committee in its discretion may select a different independent registered public accounting firm at any time during the year if they determine that such a change would be in the best interests of the Company and our stockholders.

Principal Accountant Fees and Services

        For the fiscal years ended December 31, 2015 and 2014, EY billed the approximate fees set forth below. All fees included below were approved by the audit committee.

Pre-Approval Policies and Procedures

        The audit committee has adopted a policy for the pre-approval of all audit and non-audit services to be performed for the Company by the independent registered public accounting firm. This policy is set forth in the charter of the audit committee and available at http://investor.mirnarx.com/corporate-governance.cfm. The audit committee approved all of the audit, audit-related, tax and other services provided by EY since our initial public offering in September 2015Molecular Biology Department and the estimated costsSpecial Olympics of those services. Actual amounts billed, to the extent in excess of the estimated amounts, are periodically reviewed and approved by the audit committee.Massachusetts. The audit committee has considered the role of EY in providing audit and audit-related services to the Company andboard has concluded that such services are compatible with EY's roleMr. Leschly possesses specific attributes that qualify him to serve as a member of our Board of Directors, including his experience in the Company's independent registered public accounting firm.venture capital industry and drug research and development.

THE BOARD OF DIRECTORS RECOMMENDS A VOTEFOR RATIFICATION OF OUR INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM.

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REPORT OF THE AUDIT COMMITTEE OF THE BOARD OF DIRECTORS

The material in this report is not "soliciting material," is not deemed "filed" with the SEC, and is not to be incorporated by reference into any filingCommittees of the Company under the Securities ActBoard of 1933, as amended, or the Securities Exchange Act of 1934, as amended.Directors and Meetings

        The primary purpose of the audit committee is to oversee our financial reporting processes on behalf of our board of directors. The audit committee's functions are more fully described in its charter, which is available on our website at http://investor.mirnarx.com/corporate-governance.cfm.

        In fulfilling its oversight responsibilities, the audit committee reviewed and discussed with management the Company's audited financial statements forMeeting Attendance.During the fiscal year ended December 31, 2015. The audit committee has discussed with EY,2017 and before the Company's independent registered public accounting firm, the matters required to be discussed by Auditing Standard No. 16, "Communications with Audit Committees," issued by the Public Company Accounting OversightMerger, which was effective as of August 28, 2017, Private Synlogic’s Board or PCAOB. In addition, the audit committee has discussed with EY their independence, and received from EY the written disclosuresof Directors held seven meetings, and the letter required by Ethics and Independence Rule 3526various committees of the PCAOB. Finally, the audit committee discussed with EY, with and without management present, the scope and resultsBoard met a total of EY's auditsix times. All directors attended at least 75% of the financial statements fortotal number of meetings of the Board and of committees of the Board on which he served during fiscal 2017. Private Synlogic did not hold an annual meeting in 2017.

During the fiscal year ended December 31, 2015.

        Based on these reviews2017 and discussions,before the audit committee has recommended to our board of directors that such audited financial statements be included in our Annual Report on Form 10-K for the year ended December 31, 2015 for filing with the SEC.

Merger,Pre-Merger

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CORPORATE GOVERNANCE

Board Composition

Director Independence

        Our board of directors currently consists of eight members. Our board of directors has determined that all of our directors, other than Dr. Paul Lammers, qualify as "independent" directors in accordance with the NASDAQ listing requirements. Dr. Lammers is not considered independent because he is an employee of Mirna. The NASDAQ independence definition includes a series of objective tests, such as that the director is not, and has not been for at least three years, one of our employees and that neither the director nor any of his family members has engaged in various types of business dealings with us. In addition, as required by NASDAQ rules, our board of directors has made a subjective determination as to each independent director that no relationships exist, which, in the opinion of our board of directors, would interfere with the exercise of independent judgment in carrying out the responsibilities of a director. In making these determinations, our board of directors reviewed and discussed information provided by the directors and us with regard to each director's business and personal activities and relationships as they may relate to us and our management. There are no family relationships among any of our directors or executive officers.

Classified Mirna’s Board of Directors

        In accordance with our amended and restated certificate of incorporation, our board of directors is divided into three classes with staggered, three-year terms as set forth below. At each annual meeting of stockholders, the successors to directors whose terms then expire will be elected to serve from the time of election and qualification until the third annual meeting following election.

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The Class I directors are Dr. Jones, Dr. Winkler and Mr. Greenleaf, and their terms will expire at the Annual Meeting;



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The Class II directors are Mr. Alleva and Dr. Powell, and their terms will expire at the 2017 Annual Meeting of Stockholders; and



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The Class III directors are Dr. Lammers, Mr. Mathers and Dr. Siegall, and their terms will expire at 2018 Annual Meeting of Stockholders.

        The authorized number of directors may be changed only by resolution of the board of directors. Any additional directorships resulting from an increase in the number of directors will be distributed among the three classes so that, as nearly as possible, each class will consist of one-third of the directors. The division of our board of directors into three classes with staggered three-year terms may delay or prevent a change of our management or a change in control of our company.

Leadership Structure of the Board

        Our board of directors has separated the positions of Chairman of the board and Chief Executive Officer. Separating these positions allows our Chief Executive Officer to focus on our day-to-day business, while allowing the Chairman of the board to lead the board in its fundamental role of providing advice to and independent oversight of management. The board recognizes the time, effort and energy that the Chief Executive Officer is required to devote to his position in the current business environment, as well as the commitment required to serve as Chairman of the board, particularly as the board's oversight responsibilities continue to grow. While our bylaws and corporate governance guidelines do not require that our Chairman and Chief Executive Officer positions be separate, the board believes that having separate positions and having an independent outside director serve as Chairman is the appropriate leadership structure for us and demonstrates our commitment to good

Compensation Committee’s role and responsibilities are set forth in the Compensation Committee’s written charter and includes reviewing, approving and making recommendations regarding our compensation policies, practices and procedures to ensure that legal and fiduciary responsibilities of the Board of Directors are carried out and that such policies, practices and procedures contribute to our success. Our compensation committeeCompensation Committee also administers our 2015 Equity Incentive Award Plan and 2017 Stock Incentive Plan. The Compensation Committee reviews and recommends policies relating to compensation and benefits of our officers and employees. The compensation committeeCompensation Committee reviews and recommends corporate goals and objectives relevant to compensation of our Chief Executive Officer and other executive officers, evaluates the performance of these officers in light of those goals and objectives and recommends to our boardthe Board of directorsDirectors the compensation of these officers based on such evaluations. The compensation committeeCompensation Committee also recommends to our boardthe Board of directorsDirectors the issuance of stock options and other awards under our stock plans. The compensation committee will review and evaluate, at least annually, the performanceBoard has delegated authority to our Chief Executive Officer to grant options to new hire employees as well as certain other employees in connection with their promotion who (i) are not then subject or who are reasonably expected to become subject to Section 16 of the compensation committee and its members, including compliance by the compensation committee with its charter. The current members of our compensation committee are Dr. Powell, who serves as the chairperson of the committee, Dr. Siegall and Mr. Mathers. Each of the members of our compensation committee is independent under the applicable rules and regulations of NASDAQ, is a "non-employee director" as defined in Rule 16b-3 promulgated under the Exchange Act, and is an "outside director" as that term is defined inor (iii) persons then or who are reasonably expected to be “covered employees” for purposes of Section 162(m) of the U.S. Internal Revenue Code of 1986, as amended, or Section 162(m).amended. The compensation committee operates under a written charter that satisfiespurpose of this delegation of authority is to enhance the applicable standardsflexibility of option administration within the Company and to facilitate the timely grant of options within specified limits approved by the Board of Directors. All members of the SECCompensation Committee qualify as independent under the definition promulgated by the Nasdaq Stock Market.

The Compensation Committee has the authority to directly retain the services of independent consultants and NASDAQ. A copyother experts to assist in fulfilling its responsibilities. The Compensation Committee has engaged the services of the compensation committee charter is available to security holders on the Company's website at http://investor.mirnarx.com/corporate-governance.cfm.

        Our compensation committee has retained Radford, Inc. ("Radford") a nationally recognizedbusiness unit of Aon plc (“Radford”), a national executive compensation consulting firm, to serve as its independent compensation consultantreview and to conduct market research and analysis on our various executive positions, to assistprovide recommendations concerning all of the committee in developing appropriate incentive plans for our executives on an annual basis, to providecomponents of the committee with advice and ongoing recommendations regarding materialCompany’s executive compensation decisions,program. Radford performs services solely on behalf of the Compensation Committee and has no relationship with the Company or management except as it may relate to review

Generally, our Nominating and Governance Committee considers candidates recommended by stockholders as well as from other sources such as other directors or officers, third party search firms or other appropriate sources. Once identified, the board of directors,Nominating and Governance Committee will evaluate a candidate’s qualifications in approving such candidates, will take into account many factors, including the following:

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accordance with our Corporate Governance Guidelines. Threshold criteria include: personal and professional integrity;



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integrity, ethics and values;



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experience in corporate management, such as serving as an officer or former officer of a publicly held company;



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strong finance experience; experience inrelevant to the industries in which we compete;



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Company’s industry; experience as a board member or executive officer of another publicly held company;



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diversity of expertise and experience in substantive matters pertaining to ourthe Company’s business relative to other board members;



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conflicts diversity of interest;background and



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perspective, including with respect to age, gender, race, place of residence and specialized business or career experience relevant to the success of the Company; practical and mature business judgment.

A copy of the Nominating and Governance Committee’s written charter, including its appendices, is publicly available on the Company’s website atwww.synlogictx.com.

Board Leadership Structure and Role in Risk Oversight

Leadership Structure of the Board

Our Board of Directors has separated the positions of Chairman of the Board of Directors and Chief Executive Officer. Separating these positions allows our Chief Executive Officer to focus onour day-to-day business, while allowing the Chairman of our Board of Directors to lead the board in its fundamental role of providing advice to and independent oversight of management. Our Board of Directors recognizes the time, effort and energy that the Chief Executive Officer is required to devote to such position in the current business environment, as well as the commitment required to serve as Chairman of our Board of Directors, particularly as the Board of Directors’ oversight responsibilities continue to grow. While our bylaws and corporate governance guidelines do not require that the Chairman and Chief Executive Officer positions be separate, our Board of Directors believes that having separate positions and having an independent outside director serve as Chairman is the appropriate leadership structure for us and demonstrates our commitment to good corporate governance. However, our Board of Directors will continue to periodically review our leadership structure and may make such changes in the future as it deems appropriate.

Role of Board in Risk Oversight Process

Risk assessment and oversight are an integral part of our governance and management processes. Our Board of Directors encourages management to promote a culture that incorporates risk management into our corporate strategyand day-to-day business operations. Management discusses strategic and operational risks at regular management meetings and conducts specific strategic planning and review sessions during the year that include a focused discussion and analysis of the risks facing us. Throughout the year, senior management reviews these risks with our Board of Directors at regular board meetings as part of management presentations that focus on particular business functions, operations or strategies, and presents the steps taken by management to mitigate or eliminate such risks.

Our Board of Directors does not have a standing risk management committee, but rather administers this oversight function directly through the Board of Directors as a whole, as well as through various standing committees of the Board of Directors that address risks inherent in their respective areas of oversight. In particular, our Board of Directors is responsible for monitoring and assessing strategic risk exposure and the Audit Committee is responsible for overseeing our major financial risk exposures and the steps management has taken to monitor and control these exposures. The Audit Committee also monitors compliance with legal and regulatory requirements and considers and approves or disapproves any related-persons transactions. Our Nominating and Governance Committee monitors the effectiveness of our corporate governance guidelines. The Compensation Committee assesses and monitors whether any of our compensation policies and programs has the potential to encourage excessive risk-taking.

Stockholder Communications to the Board

Generally, stockholders who have questions or concerns should contact our Investor Relations department at (617) 639-9122. However, any stockholders who wish to address questions regarding our business directly with

the Board of Directors, or any individual director, should direct his or her questions in writing to the Chairman of the Board at Synlogic, Inc., 301 Binney Street, Suite 402, Cambridge MA 02142. Communications will be distributed to the Board, or to any individual director or directors as appropriate, depending on the facts and circumstances outlined in the communications. Items that are unrelated to the duties and responsibilities of the Board may be excluded, such as:

In addition, any material that is unduly hostile, threatening, or illegal in nature may be excluded, provided that any communication that is filtered out will be made available to any outside director upon request.

Executive Officers

The following table sets forth certain information regarding our executive officers who are not also directors. We have employment agreements with each of our executive officers.

Todd Shegog, age 53, joined Private Synlogic in September 2016 as Chief Financial Officer and is responsible for the oversight and direction of our financial strategy and management as well as facilities and information systems. From April 2014 to August 2016, Mr. Shegog served as senior vice president and chief financial officer at Forum Pharmaceuticals Inc., a pharmaceutical company, where he was responsible for finance, operations and information systems in support of the pursuit of innovative therapies for schizophrenia and Alzheimer’s disease. From 1998 to March 2014, Mr. Shegog worked in a variety of roles at Millennium Pharmaceuticals, including as Senior Vice President and Chief Financial Officer from 2008 to 2014, where he was responsible for management of Millennium’s financial resources, corporate planning, financial reporting and compliance. During his tenure at Millennium Pharmaceuticals, Mr. Shegog held key leadership roles supporting the early evolution of Millennium and its transformation from a genomics company to a fully-integrated drug developer, the approval and launch of its flagship oncology product, VELCADE^®, and the $8.8 billion acquisition of Millennium Pharmaceuticals by Takeda Pharmaceutical Co Ltd. Mr. Shegog began his career in healthcare at Genetics Institute, Inc. (now Pfizer), a biotechnology research and development company, in a variety of financial positions supporting its research and development organizations and was a member of the commercial operations team that supported the launch of BeneFIX^®. Mr. Shegog holds an M.B.A. from the Tepper School of Management at Carnegie Mellon University and a bachelor’s degree in electrical engineering from Lafayette College.

Andrew Gengos, age 53, joined us in October 2017 as Chief Operating Officer and Head of Corporate Development. Mr. Gengos most recently served as President, Chief Executive Officer and as a director of ImmunoCellular Therapeutics, a publicly-traded immune-oncology company pursuing treatments for glioblastoma from December 2012 to December 2016. Previously, Mr. Gengos was the President and Chief Executive Officer of Neuraltus Pharmaceuticals from February 2010 to August 2012. Prior to his service with Neuraltus, Mr. Gengos served for more than seven years with Amgen where, as Vice President, Strategy and Corporate Development, he managed Amgen’s worldwidein-and-outbound business development activities, including a broad slate of acquisitions, licensing, spin-outs, divestitures, corporate venture capital investments, which included board of directors evaluatesdirector positions and alliance management. In addition, he led the execution of strategic

projects and supported the long-range planning process for the company. Before joining Amgen, Mr. Gengos was Vice President, Chief Financial Officer, and Chief Business Officer of Dynavax Technologies, where he led the company’s business functions, including finance and accounting, fundraising, budgeting and planning, and business development. Earlier in his career, Mr. Gengos served as Vice President of Strategy at the Chiron Corporation and as Senior Engagement Manager at McKinsey & Company. Mr. Gengos holds an M.B.A. from the UCLA Anderson School of Management and a B.S. in chemical engineering from the Massachusetts Institute of Technology.

Aoife M. Brennan, MB, BCh, BAO, MMSc, age 43, joined Private Synlogic in September 2016 as Chief Medical Officer and is responsible for the oversight and direction of our clinical development strategy and operations. From May 2011 to August 2016, Dr. Brennan was Vice President and Head of the Rare Disease Innovation Unit at Biogen, a biotechnology company, where she was responsible for research and development of the Biogen rare disease portfolio, which involved programs rangingfrom pre-clinical to commercial, including the approval of ALPROLIX^TM, ELOCTATE^TM and SPINRAZA^TM. From 2008 to 2011, Dr. Brennan was director of clinical development at Tolerx, Inc.,a start-up biotechnology company focusing on immunotherapy for Type 1 diabetes. Dr. Brennan holds a medical degree from Trinity College in Dublin, Ireland and completed post-graduate training in internal medicine, endocrinology and metabolism. Dr. Brennan also completed post-doctoral training in clinical research and metabolism at the Beth Israel Deaconess Medical Center in Boston and is a graduate of the Harvard Medical School Scholars in Clinical Science Program.

Paul Miller, Ph.D., age 58, joined Private Synlogic in September 2014 as Chief Scientific Officer and is accountable for all aspects of discovery research and platform expansion. From 2011 to September 2014, Dr. Miller was Vice President of Infection Biology at AstraZeneca, a biopharmaceutical company, where he was responsible for the early discovery portfolio and strategy while also leading several external collaborations. Prior to AstraZeneca, Dr. Miller led various aspects of antibacterials research at Pfizer, a biopharmaceutical company, beginning in 1997 and became Chief Scientific Officer for antibacterial research from 2008 to 2011, leading discovery teams that produced eight drug development candidates, provided critical research support for several successful marketed antibiotics including Zithromax and Zyvox, and also successfully advanced a novel oxazolidinone (sutezolid) for tuberculosis into Phase 2 studies. A microbial geneticist by training, Dr. Miller began his professional career at the Warner-Lambert Company, a pharmaceutical company that merged with Pfizer in 2000, where he integrated modern molecular-genetic approaches into a traditional antibacterial drug discovery program and established novel target discovery projects. Dr. Miller’s work at Warner-Lambert led to new insights into the mechanisms by which bacteria sense and respond to antibiotics and other environmental agents. Dr. Miller received a Ph.D. in microbiology and immunology from the Albany Medical College and conducted post-doctoral studies at NIH. Dr. Miller has also served as a member of the Institute of Medicine’s Forum on Microbial Threats and as a grant reviewer to the Bill & Melinda Gates Foundation and the European Union’s Innovative Medicines Initiative.

EXECUTIVE OFFICER AND DIRECTOR COMPENSATION

Summary Compensation Table

The following table presents information regarding the total compensation paid or accrued during the last two fiscal years for (1) our Chief Executive Officer, (2) our two next most highly compensated executive officers who earned more than $100,000 during the fiscal year ended December 31, 2017 and were serving as executive officers as of such date and (3) the Company’s former Chief Executive Officer (collectively the “Named Executive Officers”).

Base Salary

In 2017, the Compensation Committee and the Board of Directors of Private Synlogic approved an annual increase in base salaries for all employees, including the named executive officers resulting in an annual base salary of $450,000 for Dr. Gutiérrez-Ramos and $349,036 for Dr. Brennan. Mr. Gengos joined the Company in October 2017 with an annual base salary of $398,000 which was prorated based on service for 2017. In March 2018, the Compensation Committee and the Board approved base salary increases for the Company’s management team effective January 1, 2018, resulting in an annual base salary of $486,000 for Dr. Gutiérrez-Ramos, $401,980 for Mr. Gengos and $397,901 for Dr. Brennan.

Annual Bonuses

The Company employment agreements with its executive officers provide for the opportunity to earn a cash bonus based upon achievement of both corporate and individual goals determined by the Board of Directors in its discretion based on a target percentage of annual base salary. In March 2018, the Board of Directors awarded Dr. Gutiérrez-Ramos a cash bonus of $176,000, which represented 39.1% of his annual base salary, in recognition of his services provided in the year ended December 31, 2017 and in accordance with the terms of his employment agreement and bonus assessment. In March 2018, the Compensation Committee awarded Mr. Gengos a cash bonus of $34,268, prorated for the number of months in the year he was employed by the Company, which represented 34.4% of his prorated annual base salary in recognition of his services provided in the year ended December 31, 2017 and in accordance with the terms of his employment agreement and bonus assessment. In addition, Mr. Gengos also received a signing bonus of $100,000 in connection with his commencement of employment. With respect to his signing bonus, Mr. Gengos will be required to reimburse the Company if he voluntarily resigns within 12 months following the commencement of his employment or is terminated for cause. In March 2018, the Compensation Committee awarded Dr. Brennan a cash bonus of $111,412, which represented 31.9% of her annual base salary in recognition of her services provided in the year ended December 31, 2017 and in accordance with the terms of her employment agreement and bonus assessment. In March 2017, the Compensation Committee of Private Synlogic awarded Dr. Gutiérrez-Ramos a cash bonus of $116,802, prorated for the number of months in the year he was employed by Private Synlogic, which represented 28.4% of his annual base salary, in recognition of his services provided to Private Synlogic in the year ended December 31, 2016 and in accordance with the terms of his employment agreement and bonus assessment. In March 2017, the Compensation Committee of Private Synlogic awarded Dr. Brennan a cash bonus of $31,395, which represented 27.3% of her annual base salary, in recognition of her services provided to Private Synlogic in the year ended December 31, 2016, prorated for the number of months in the year she was employed by Private Synlogic and in accordance with the terms of her employment agreement and bonus assessment. In addition, Dr. Brennan also received a signing bonus of $85,000 plus a gross up for taxes to be paid on such compensation in connection with her commencement of employment.

2018 Stock Awards

In 2018 in connection with the Compensation Committee and the Board’s assessment of 2017 performance the Company granted the following options to its named executive officers: Dr. Gutiérrez-Ramos was granted an option to purchase 120,540 shares of common stock, Mr. Gengos was granted an option to purchase 10,000 shares of common stock and Dr. Brennan was granted an option to purchase 56,000 shares of common stock. Each option has an exercise price of $9.95 per share and is subject to vesting at a rate of one forty-eighth (1/48th) of the total number of shares subject thereto per month over four years.

Outstanding Equity Awards at Fiscal Year End

The following table presents the outstanding equity awards held by each of the named executive officers as of December 31, 2017. All equity awards set forth in the table below were granted under the 2017 Stock Incentive Plan except for the option granted to Andrew Gengos which was granted under the 2015 Equity Incentive Award Plan.

effective time of the Merger, the Company assumed all outstanding options to purchase shares of common stock of Private Synlogic, which were exchanged for options to purchase shares of the Company’s common stock, in each case appropriately adjusted based on the Exchange Ratio and all shares of Private Synlogic restricted stock were exchanged for shares of Company common stock in accordance with the Exchange Ratio and continue to vest on the same schedule as the original restricted stock awards.

Employment Agreements and Potential Payments Upon Termination of Employment or Change in Control

The Company has entered into employment agreements with each of its named executive officers as described below, as well as standard confidential information and/or inventions assignment agreements under which each of the named executive officers has agreed not to disclose confidential information. These employment agreements provide for “at will” employment.

Jose-Carlos Gutiérrez-Ramos, Ph.D.

Private Synlogic entered into an employment agreement with Dr. Gutiérrez-Ramos in 2015 that was subsequently amended on May 8, 2017 to increase Dr. Gutiérrez-Ramos’ base salary to $450,000 and to make him eligible to earn an annual cash incentive bonus of up to 40% of his base salary based on the achievement of corporate and/or individual performance goals, as determined by our Board of Directors. Dr. Gutiérrez-Ramos is also eligible to participate in the employee benefit plans available to employees, subject to the terms of those plans. In March 2018, Dr. Gutiérrez-Ramos received an increase in annual base salary to $486,000.

Dr. Gutiérrez-Ramos’ employment agreement also provides that, in the event that his employment is terminated for any reason other than for “cause,” death or “disability,” or by Dr. Gutiérrez-Ramos for “good reason” (each as defined in his employment agreement), subject to the execution and effectiveness of a separation agreement and release, he will be entitled to receive (i) continuing severance pay at a rate equal to 100% of his base salary, as then in effect (less applicable withholding), for a period of 12 months from the date of such termination, to be paid periodically in accordance with normal Company payroll practices; (ii) the right to continued health care benefits under COBRA, paid by the Company at a cost similar for active and similarly situated employees who receive the same type of coverage until the earlier of (a) 12 months after termination, or (b) the date on which Dr. Gutiérrez-Ramos becomes eligible for healthcare insurance with a subsequent employer, and (iii) alump-sum payment equal to the prorated portion of the target bonus for the fiscal year in which Dr. Gutiérrez-Ramos is terminated.

Dr. Gutiérrez-Ramos’ employment agreement provides that, in the event his employment is terminated on account of death, “disability,” resignation for “good reason” or without “cause,” in any case, within the12-month period immediately following or the 30 day period immediately prior to a change in control, then Dr. Gutiérrez-Ramos’ outstanding unvested restricted stock and/or options shall become fully vested.

In addition, Dr. Gutiérrez-Ramos has entered into anon-solicitation andnon-competition agreement that applies during the term of Dr. Gutiérrez-Ramos’ employment and for 12 months thereafter.

Andrew Gengos

We entered into an employment agreement with Mr. Gengos in September 2017 that initially provided for a base salary of $398,000, subject to review and adjustment. The agreement also provides that he is eligible to earn an annual cash incentive bonus of up to 35% of his base salary based on the achievement of corporate and/or individual performance goals, as determined by the Board of Directors. Mr. Gengos is also eligible to participate in the employee benefit plans available to employees, subject to the terms of those plans. In addition, Mr. Gengos’ employment agreement also provided him with a signing bonus of $100,000, in connection with commencement of employment and that he will be required to reimburse the Company those amounts if he voluntary resigns within 12 months following the commencement of his employment or is terminated for cause. In March 2018, Mr. Gengos received an increase in annual base salary to $401,980.

Mr. Gengos’ employment agreement provides that, in the event that Mr. Gengos’ employment is terminated for any reason other than for “cause,” death or “disability,” or by Mr. Gengos for “good reason” (each as defined in his employment agreement), subject to the execution and effectiveness of a separation agreement and release, he will be entitled to receive (i) continuing severance pay at a rate equal to 100% of his base salary, as then in effect (less applicable withholding), for a period of six months from the date of such termination, to be paid periodically in accordance with normal Company payroll practices; (ii) the right to continue health care benefits under COBRA, paid by the Company at a cost similar for active and similarly situated employees who receive the same type of coverage until the earlier of (a) six months from termination, or (b) the date on which Mr. Gengos becomes eligible for healthcare insurance with a subsequent employer, and (iii) alump-sum payment equal to the prorated portion of the target bonus for the fiscal year in which Mr. Gengos is terminated.

Mr. Gengos’ employment agreement provides that, in the event Mr. Gengos’ employment is terminated on account of death, “disability,” resignation for “good reason” or without “cause,” in any case, within the12-month period immediately following or the30-day period immediately prior to a “change in control,” then Mr. Gengos’ outstanding unvested restricted stock and/or options shall become fully vested.

In addition, Mr. Gengos has entered into anon-solicitation andnon-competition agreement that applies during the term of Mr. Gengos’ employment and for 12 months thereafter.

Aoife M. Brennan, MB, BCh, BAO, MMSc

Private Synlogic entered into an employment agreement with Dr. Brennan in September 2016 that initially provided for a base salary of $345,000, subject to review and adjustment. Dr. Brennan’s base salary was increased to $349,036 for 2017 and $397,901 for 2018. Pursuant to her May 8, 2017 amended employment agreement, Dr. Brennan is eligible to earn an annual cash incentive bonus of up to 30% of her base salary based on the achievement of corporate and/or individual performance goals, as determined by the Board of Directors. Dr. Brennan is also eligible to participate in the employee benefit plans available to employees, subject to the terms of those plans. In addition, Dr. Brennan’s amended employment agreement also provided her with a signing bonus of $85,000, plus a gross up for taxes to be paid on such compensation in connection with her commencement of employment and that she will be required to reimburse the Company those amounts if she voluntary resigns within 12 months following the commencement of her employment or is terminated for cause.

Dr. Brennan’s employment agreement provides that, in the event that Dr. Brennan’s employment is terminated for any reason other than for “cause,” death or “disability,” or by Dr. Brennan for “good reason” (each as defined in her employment agreement), subject to the execution and effectiveness of a separation agreement and release, she will be entitled to receive (i) continuing severance pay at a rate equal to 100% of her base salary, as then in effect (less applicable withholding), for a period of six months from the date of such termination, to be paid periodically in accordance with normal Company payroll practices; (ii) the right to continue health care benefits under COBRA, paid by the Company at a cost similar for active and similarly situated employees who receive the same type of coverage until the earlier of (a) six months from termination, or (b) the date on which Dr. Brennan becomes eligible for healthcare insurance with a subsequent employer, and (iii) alump-sum payment equal to the prorated portion of the target bonus for the fiscal year in which Dr. Brennan is terminated.

Dr. Brennan’s employment agreement provides that, in the event Dr. Brennan’s employment is terminated on account of death, “disability,” resignation for “good reason” or without “cause,” in any case, within the12-month period immediately following or the30-day period immediately prior to a “change in control,” then Dr. Brennan’s outstanding unvested restricted stock and/or options shall become fully vested.

In addition, Dr. Brennan has entered into anon-solicitation andnon-competition agreement that applies during the term of Dr. Brennan’s employment and for 12 months thereafter.

The following definitions apply to Dr. Gutiérrez-Ramos’, Mr. Gengos’ and Dr. Brennan’s employment agreements:

“Cause” is defined as the executive’s (i) conviction of a felony, plea of guilty or “no contest” to a felony, or confession of guilt to a felony; (ii) act or omission which constitutes willful misconduct or negligence that results in loss, damage or injury to the Company or its prospects, including, but not limited to (A) disloyalty, dishonesty or a breach of fiduciary duty to the Company or Stockholders, (B) theft, fraud, embezzlement or other illegal conduct, or (C) deliberate disregard of a rule or policy of Synlogic; (iii) failure, refusal or unwillingness to perform, to the reasonable satisfaction of the Board of Directors determined in good faith, any duty or responsibility assigned to the executive, which failure of performance continues for a period of more than two weeks after written notice thereof has been provided by the Board of Directors, setting forth in reasonable detail the nature of such failure of performance; or (iv) the material breach by the executive of any of the provisions of the employment agreement or its related agreements.

“Good reason” is defined as a resignation that occurs within 30 days following: (i) a change in the principal location at which the executive provides services to the Company beyond 50 miles from Cambridge, Massachusetts; (ii) a reduction in the executive’s compensation or a material reduction in the executive’s benefits, except such a reduction in connection with a general reduction in compensation or other benefits of all senior executives of the Company;(iii) a material breach of the executive’s employment agreement by the Company that has not been cured within 10 days after written notice thereof by the executive; or (iv) a failure by the Company to obtain the assumption of the employment agreement by any successor of the Company.

“Disability” is defined as the executive’s inability, due to physical or mental illness or disease, to perform the functions then performed by the executive for 180 consecutive days, accompanied by the likelihood, in the opinion of a physician chosen by the Company and reasonably acceptable to the executive, that the executive will be unable to perform such functions within the reasonably foreseeable future.

“Change in control” is defined as (i) the sale of the Company by merger in which the stockholders of the Company in their capacity as such no longer own a majority of the outstanding equity securities of the Company (or its successor); (ii) any sale of all or substantially all of the assets or capital stock of the Company (other than in aspin-off or similar transaction) or (iii) any other acquisition of the business of the Company, as determined by the Board of directors in its sole discretion. For the avoidance of doubt, in no event shall a bona fide equity or debt financing, including a financing in which greater than 50% of the Company’s outstanding equity securities are acquired by a third-party, or a reorganization required to affect an initial public offering, be deemed a “change in control.”

Other Benefits

Executive officers are eligible to participate in all of the Company’s employee benefit plans, including life insurance, medical, dental and vision, a 401(k)-retirement plan and a flex spending account plan. We also providepaid-time-off benefits to all similarly-situated employees.

Terms and Conditions of Paul Lammers’ Separation Agreement

On August 28, 2017, immediately prior to the effective time of the Merger, Dr. Lammers ceased serving as the Company’s President and Chief Executive Officer. In connection with his resignation, Dr. Lammers entered into a Separation Agreement with the Company pursuant to which he received (i) a severance payment equal to $933,975, which represents eighteen months of Dr. Lammers’ base salary in effect as of immediately prior to the separation date and one and one half times his target annual bonus, (ii) payment of his COBRA premiums equal to $43,831 for up to eighteen months following the separation date, and (iii) 100% vesting acceleration on his outstanding equity awards as of the separation date.

SYNLOGIC DIRECTOR COMPENSATION

Director Compensation Policy

The following is a description of the standard compensation arrangements under which our directors are compensated for their service as directors, including as members of the various committees of our board.

The Company generally providesits non-employee directors with cash and equity compensation for their service on the Board. The Board is responsible for considering and approving the compensation paid to theCompany’s non-employee directors, upon recommendation from the Compensation Committee. The Compensation Committee reviews the compensation paid to theCompany’s non-employee directors with input and market data provided by the Compensation Committee’s outside compensation consultant. In October 2015, in connection withPre-Merger Mirna’s initial public offering, the Board approveda non-employee director compensation policy that set forth the terms of the cash and equity compensation to be paid to theCompany’s non-employee directors beginning in October 2015. In December 2017, the Board amended and restated the director compensation policy to account for the changes in the Company as a result of the Merger. Directors who are also our employees, such as Dr. Gutiérrez-Ramos, will not receive additional compensation for their services as directors.

In 2017, no director ofPre-Merger Mirna was paid equity compensation prior to the Merger. On August 28, 2017, in connection with the consummation of the Merger pursuant to the director compensation policy in effect prior to the Merger, the Board made yearly equity grants as follows: Initial Awards (as defined below) of 2,857 options to Dr. Barrett and Messrs. Khuong, Leschly and Shea as they became directors of the Company for the first time in connection with the Merger and Annual Awards (as defined below) of 1,428 options to Mr. Mathers and Dr. Powell who continued as directors of the Company following the Merger. Following the Merger, the Board hired Radford to review and provide recommendations concerning all of the components of the Company’s executive compensation program. Based on Radford’s review and recommendations, the Board revised the director compensation policy. In connection with the amendment and restatement of thenon-employee director compensation policy in December 2017, on December 29, 2017, the Board issued pro rata grants of (a) 18,572 options to Mr. Mathers and Dr. Powell and (b) 17,143 options to Dr. Barrett and Messrs. Khuong, Leschly and Shea to true them up to the amounts reflected in the amended and restated director compensation policy. The vesting of the equity awards remained the same prior to and following the Merger and is discussed in more detail below.

Pursuant to our director compensation policy, until December 13, 2017, eachnon-employee director was paid an annual cash retainer of $35,000 for their services and anynon-employee director serving as Chairman of the Board was paid an additional annual cash retainer of $25,000 for such service. Committee members received additional annual cash retainers as follows:

Under the amended and restatednon-employee director compensation policy, upon a director’s initial appointment or election to our Board of Directors, suchnon-employee director will receive an option (the “Initial Award”) to purchase 20,000 shares of our common stock (subject to adjustment as provided in the applicable equity plan). In addition, eachnon-employee director who has been serving as a director for at least three months prior to any annual stockholder meeting following the date of this offering and will continue to serve as a director immediately following such annual stockholder meeting will be automatically granted, on the date of such annual stockholder meeting, an option (the “Annual Award”) to purchase 10,000 shares of our common stock (subject to adjustment as provided in the applicable equity plan). The Initial Award will vest in substantially equal installments on each of the first three anniversaries of the applicable grant date, subject to continued service through each applicable vesting date, and the Annual Award will vest in full on the earlier of the first anniversary of the applicable grant date or immediately prior to the next annual stockholder meeting after the applicable grant date, subject to continued service through such vesting date. In addition, pursuant to the terms of the Director Compensation Program, all equity awards outstanding and held by anon-employee director will vest in full immediately prior to the occurrence of a change in control.

We reimburse ournon-employee directors for all reasonable and customary business expenses incurred providing services to us in accordance with Company policy.

Director Compensation for the Year Ended December 31, 2017

The following table sets forth information for the year ended December 31, 2017 regarding the compensation awarded to, earned by or paid to ournon-employee directors:

EQUITY COMPENSATION PLAN INFORMATION

The following table provides certain aggregate information with respect to all of the Company’s equity compensation plans in effect as of December 31, 2017.

In addition, the Board of Directors or any committee to which the Board of Directors delegates authority may, with the consent of the affected plan participants,re-price or otherwise amend outstanding awards consistent with the terms of the 2017 Plan.

Upon a merger, consolidation or sale of all or substantially all of our assets, the Board of Directors or any committee to which the Board of Directors delegates authority, or the board of directors of any corporation assuming our obligations, may, in its sole discretion, take any one or more of the following actions pursuant to the 2017 Plan, as to some or all outstanding awards, to the extent not otherwise agreed under any individual agreement:

REPORT OF AUDIT COMMITTEE

The Audit Committee of the Board of Directors, which consists entirely of directors who meet the independence and experience requirements of Nasdaq, has furnished the following report:

The Audit Committee assists the Board of Directors in these various areas.

Code of Business Conductoverseeing and Ethics

        We have adopted a code of business conduct and ethics that applies to allmonitoring the integrity of our employees, officersfinancial reporting process, compliance with legal and directors, including those officers responsible for financial reporting. The coderegulatory requirements and the quality of business conductinternal and ethicsexternal audit processes. This committee’s role and responsibilities are set forth in our charter adopted by the Board of Directors, which is available on our website at http://investor.mirnarx.com/corporate-governance.cfm. We will disclosewww.synlogictx.com.This committee reviews and reassesses our charter annually and recommends any substantive amendmentschanges to the code of business conduct and ethics, or any waiver of its provisions, on our website. The reference to our website does not constitute incorporation by reference of the information contained at or available through our website.

Limitation on Liability and Indemnification Matters

        Our amended and restated certificate of incorporation contains provisions that limit the liability of our directors for monetary damages to the fullest extent permitted by Delaware law. Consequently, our directors will not be personally liable to us or our stockholders for monetary damages for any breach of fiduciary duties as directors, except liability for:

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any breach of the director's duty of loyalty to us or our stockholders;



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any act or omission not in good faith or that involves intentional misconduct or a knowing violation of law;



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unlawful payments of dividends or unlawful stock repurchases or redemptions as provided in Section 174 of the Delaware General Corporation Law; or



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any transaction from which the director derived an improper personal benefit.

        Our amended and restated certificate of incorporation and amended and restated bylaws provide that we are required to indemnify our directors and officers, in each case to the fullest extent permitted by Delaware law. Our amended and restated bylaws also provide that we are obligated to advance expenses incurred by a director or officer in advance of the final disposition of any action or proceeding, and permit us to secure insurance on behalf of any officer, director, employee or other agent for any liability arising out of his or her actions in that capacity regardless of whether we would otherwise be permitted to indemnify him or her under Delaware law.

        We have entered and expect to continue to enter into agreements to indemnify our directors, executive officers and other employees as determined by our board of directors. With specified exceptions, these agreements provide for indemnification for related expenses including, among other things, attorneys' fees, judgments, fines and settlement amounts incurred by any of these individuals in any action or proceeding brought against them by reason of the fact that they are or were our agents. We believe that these provisions in our amended and restated certificate of incorporation and amended and restated bylaws and indemnification agreements are necessary to attract and retain qualified directors and officers. We also maintain directors' and officers' liability insurance. This description of the limitation of liability and indemnification provisions of our amended and restated certificate of incorporation, of our amended and restated bylaws and of our indemnification agreements is qualified in its entirety by reference to these documents.

        The limitation of liability and indemnification provisions in our amended and restated certificate of incorporation and amended and restated bylaws may discourage stockholders from bringing a lawsuit against our directors and officers for breach of their fiduciary duty. They may also reduce the likelihood of derivative litigation against our directors and officers, even though an action, if successful,

SECTION 16(a) BENEFICIAL OWNERSHIP REPORTING COMPLIANCE

Our records reflect that all reports which were required to be filed pursuant to Section 16(a) of the boardSecurities Exchange Act of directors or compensation committee of any entity1934, as amended, were filed on a timely basis, except that has one or more executive officers on our board of directors or compensation committee.report, covering one transaction, was filed late by Andrew Gengos.

INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

(Notice Item 2)

The Audit Committee has appointed KPMG LLP, as our independent registered public accounting firm to a facility or location that would increase his or her one-way commute distance by more than 50 miles from his or her primary work location as of immediately prior to such change, (ii) the NEO provides written notice outlining such conditions, acts or omissions to us within 30 days immediately following such material change or reduction, (iii) such material change or reduction is not remedied by us within 30 days followingaudit our receipt of such written notice and (iv) the NEO's resignation is effective not later than 30 days after the expiration of such 30 day cure period.

        For purposes of the change in control severance agreements, "change in control" generally means (i) the transfer or exchange in a single transaction or series of related transactions by our stockholders of more than 50% of our voting stock to a person or group; (ii) a change in the composition of our board of directors over a two-year period such that 50% or more of the members of the board of directors were elected through one or more contested elections; (iii) a merger, consolidation, reorganization or business combination in which we are involved, directly or indirectly, other than a merger, consolidation, reorganization or business combination which results in our outstanding voting securities immediately before the transaction continuing to represent a majority of the voting power of the acquiring company's outstanding voting securities and after which no person or group beneficially owns 50% or more of the outstanding voting securities of the surviving entity immediately after the transaction; or (iv) the sale, exchange, or transfer of all or substantially all of our assets.

Terms and Conditions of Annual Bonuses

        For 2015, all of the NEOs were eligible for cash performance-based bonuses pursuant to the achievement of certain performance objectives. The performance targets are approved annually by our board of directors. When determining the 2015 performance bonus programfinancial statements for the NEOs, the board