BIOAMBER INC. FIRST AMENDMENT TO THE AMENDED AND RESTATEDSHAREHOLDERS AGREEMENT

Exhibit 4.3

BIOAMBER INC.

FIRST AMENDMENT

TO THE AMENDED AND RESTATED SHAREHOLDERS’ AGREEMENT

THIS FIRST AMENDMENT TO THE AMENDED AND RESTATED SHAREHOLDERS’ AGREEMENT (this “Amendment”), entered into as of November 4, 2011, by and among BIOAMBER INC., a Delaware corporation (the “Corporation”), and the undersigned Security Holders (as defined in the Shareholders Agreement defined below).

R E C I T A L S

WHEREAS the Corporation and certain parties identified on the signature pages thereto are parties to that certain Amended and Restated Shareholders Agreement dated as of April 15, 2011 (the “Shareholders Agreement”);

WHEREAS, pursuant to its Section 12.5, the Shareholders Agreement may be amended or otherwise modified by an instrument in writing executed by (i) the Corporation, (ii) the Shareholders holding a majority of the then outstanding Shares of the Corporation, and (iii) the Investors representing an Investor Super-Majority, as such terms are defined in the Shareholders Agreement (the “Requisite Consent”);

WHEREAS, upon execution of this Amendment, the Requisite Consent shall have been received, and this Amendment shall be binding upon the Corporation and all Security Holders who are parties to the Shareholders Agreement;

WHEREAS the Security Holders who are parties to this Amendment believe that it is in their best interests to amend the terms and conditions of the Shareholders Agreement as set out in this Amendment; and

WHEREAS the Corporation has agreed to be a party to this Amendment in order to acknowledge the amendment to certain rights conferred upon the Security Holders in the Shareholders Agreement.

NOW, THEREFORE, in consideration of the premises and mutual covenants set forth herein, it is mutually agreed by and among the parties as follows:

A G R E E M E N T

“Subsidiary” – means any partnership, limited liability company, corporation, company or other entity, wherever or however incorporated, under the control of the Corporation. As of the date hereof, (i) BioAmber Canada Inc., a Canadian

corporation, (ii) BioAmber S.A.S., a Société par Actions Simplifiée, (iii) BioAmber USA Inc., a Delaware corporation, (iv) Sinoven Biopolymers, Inc., a Delaware corporation, (v) Sinoven Biopolymers Trading (Shanghai), LLC, a Chinese limited liability company, (vi) Bluewater Biochemicals Inc., a Canadian Corporation and (vii) BioAmber International SÀRL, a Luxembourg Societe a Responsabilite Limitee are the only Subsidiaries of the Corporation.

Notwithstanding anything else set forth herein, a majority of the Directors who are nominated pursuant to paragraphs (a), (b), (c) and (d) above shall have the authority to replace any of the Directors appointed pursuant to paragraph (e) above.

The Corporation agrees that the Board at all times shall maintain an audit committee (the “Audit Committee”) comprised of three (3) Directors:

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The Audit Committee’s authority and duties shall be as set forth in the Board’s enabling resolutions adopted in connection with the establishment of such committee, and shall include selection of the Corporation’s independent accountants and approval of the Corporation’s accounting and internal reporting policies. Actions of the Audit Committee shall require the approval of a majority of the members of the Audit Committee.

In addition to its other rights under this Agreement, Naxos shall be entitled to designate two (2) non-voting observers, who are initially expected to be Mr. Robert Frost and Ms Carole Piwnica (each, a “Naxos Observer”) and Mitsui CVP shall be entitled to designate one (1) non-voting observer (the “Mitsui Observer”). The Board may allow for one (1) additional non-voting observer, acting as representative of an Investor other than Naxos and Mitsui CVP or of other group(s) of Shareholders (the “Other Observer”, and collectively with the Naxos Observers and the Mitsui Observer, the “Observers”).

(a) The retention of any investment bank or similar advisor in connection with any proposed sale of any equity interests in the Corporation or its Subsidiaries or any of their assets, (b) the entry into a letter of intent (whether binding or non-binding) with respect to the same, or (c) the filing a registration (Form S-1) with the Securities and Exchange Commission with respect to a possible initial public offering of the Corporation’s shares of common stock.

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The Corporation and the Board shall at all times cause to be maintained a Business Advisory Board (the “Business Advisory Board”), which shall be comprised of such individuals as may be jointly designated from time to time by the Board and the Corporation’s senior management. For so long as Naxos is entitled to appoint a Director to the Board, Naxos shall be entitled to appoint the chairman of the Business Advisory Board, which individual need not be a Director or Observer. The Business Advisory Board’s duties shall be as set forth in the enabling charter approved by the Board, and essentially consist in advising the Corporation’s senior management concerning the operations of the Corporation. The Business Advisory Board shall meet at least four (4) times annually, or more frequently as circumstances dictate. Any meeting of the Business Advisory Board may be held by telephone, videoconference or any other means of telecommunication.

Subject to Section 5.2,

(a) if at any time after the date of this Agreement and prior to completion of an IPO, the Corporation issues (i) any Shares at a price per Share of less than $369.14 (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events), or (ii) any Convertible Securities which, if exercised, would result in the issuance of Shares at a price per Share of less than $369.14 (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events) (each a “Dilutive Issuance”), each of the Investors having purchased Shares in one or more of (a) Corporation’s private placements closed on April 15, 2011, (b) Corporation’s private placements closed on the date hereof and (c) the secondary sale transaction completed pursuant to the Stock Purchase Agreement dated as of May 9, 2011 entered into between the Corporation, Boivin Desbiens Senécal, g.p., acting as Escrow Agent pursuant to such Agreement, the sellers set forth on Schedule A thereto and the purchasers set forth on Schedule B thereto (collectively, the “Private Placements”) will be entitled to receive, upon closing of any such Dilutive Issuance, for no additional consideration, a number of Shares equal to the result of the following formula:

(369.14 x A / B ) – A

Where: “A” is the aggregate number of Shares purchased by the Investor in the Private Placements (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events

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as at the date of the moment immediately preceding the Dilutive Issuance); and “B” is the issue price per Share of the Dilutive Issuance. and

(b) if at any time after the date of this Agreement and prior to completion of an IPO, the Corporation issues (i) any Shares at a price per Share of $369.14 or more but less that $997.00 (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events), or (ii) any Convertible Securities which, if exercised, would result in the issuance of Shares at a price per Share of $369.14 or more but less than $997.00 (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events) (each a “Less Dilutive Issuance”), each of the Investors having purchased Shares in the Corporation private placement closed on the date hereof (the “November Placement”) will be entitled to receive, upon closing of any such Less Dilutive Issuance, for no additional consideration, a number of Shares equal to the result of the following formula:

(997.00 x A / B ) – A

Where: “A” is the number of Shares purchased by the Investor in the November Placement (subject to proportionate adjustment in the event of any stock splits, combinations, reclassifications or similar events as at the date of the moment immediately preceding the Less Dilutive Issuance); and “B” is the issue price per Share of the Less Dilutive Issuance.

“THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE SUBJECT TO AN AMENDED AND RESTATED SHAREHOLDERS’ AGREEMENT DATED AS OF APRIL 15, 2011 (AS AMENDED BY THAT CERTAIN FIRST AMENDMENT, DATED AS OF NOVEMBER 4, 2011, THE “SHAREHOLDERS’ AGREEMENT”) BY AND AMONG BIOAMBER INC. (THE “CORPORATION”) AND CERTAIN OF THE CORPORATION’S SHAREHOLDERS. THE TERMS OF SUCH SHAREHOLDERS’ AGREEMENT INCLUDE, AMONG OTHER THINGS, A VOTING AGREEMENT AMONG CERTAIN OF THE CORPORATION’S SHAREHOLDERS AND CONTRACTUAL PREEMPTIVE RIGHTS, IN FAVOR OF THE HOLDER HEREOF AND THE OTHER HOLDERS OF SHARES (AS SUCH TERM IS DEFINED THEREIN), ON CERTAIN ISSUANCES BY THE CORPORATION. A COPY OF SUCH SHAREHOLDERS’ AGREEMENT WILL BE FURNISHED WITHOUT CHARGE BY THE CORPORATION TO THE HOLDER HEREOF UPON WRITTEN REQUEST.”

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(signatures on next pages)

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IN WITNESS WHEREOF the parties have signed this Amendment at the place and as of the date first mentioned above.

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