6,153,846 Shares XENOPORT, INC. Common Stock (par value $0.001 per share) UNDERWRITING AGREEMENT

Exhibit 1.1

EXECUTION VERSION

6,153,846 Shares

XENOPORT, INC.

Common Stock

(par value $0.001 per share)

UNDERWRITING AGREEMENT

July 25, 2012

CREDIT SUISSE SECURITIES (USA) LLC,

As Representative of the Several Underwriters,

Eleven Madison Avenue,

New York, N.Y. 10010-3629

Dear Sirs:

1. Introductory. XenoPort, Inc., a Delaware corporation (“Company”), agrees with the several Underwriters named in Schedule A hereto (“Underwriters”) to issue and sell to the several Underwriters 6,153,846 shares (“Firm Securities”) of its common stock, par value $0.001 per share (“Common Stock”), and also proposes to issue and sell to the Underwriters, at the option of the Underwriters, an aggregate of not more than 923,076 additional shares (“Optional Securities”) of its Common Stock as set forth below. The Firm Securities and the Optional Securities are herein collectively called the “Offered Securities”.

2. Representations and Warranties of the Company. The Company represents and warrants to, and agrees with, the several Underwriters that:

(a) Filing and Effectiveness of Registration Statement; Certain Defined Terms. The Company has filed with the Commission a registration statement on Form S-3 (No. 333-167972), including a related prospectus or prospectuses, covering the registration of the Offered Securities under the Act, which has become effective. “Registration Statement” at any particular time means such registration statement in the form then filed with the Commission, including any amendment thereto, any document incorporated by reference therein and all 430B Information and all 430C Information with respect to such registration statement, that in any case has not been superseded or modified. “Registration Statement” without reference to a time means the Registration Statement as of the Effective Time. For purposes of this definition, 430B Information shall be considered to be included in the Registration Statement as of the time specified in Rule 430B.

For purposes of this Agreement:

“430B Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430B(e) or retroactively deemed to be a part of the Registration Statement pursuant to Rule 430B(f).

“430C Information” means information included in a prospectus then deemed to be a part of the Registration Statement pursuant to Rule 430C.

“Act” means the Securities Act of 1933, as amended.

“Applicable Time” means 6:00 p.m (Eastern time) on the date of this Agreement.

“Closing Date” has the meaning defined in Section 3 hereof.

“Commission” means the Securities and Exchange Commission.

“Effective Time” of the Registration Statement relating to the Offered Securities means the time of the first contract of sale for the Offered Securities.

“Exchange Act” means the Securities Exchange Act of 1934, as amended.

“Final Prospectus” means the Statutory Prospectus that discloses the public offering price, other 430B Information and other final terms of the Offered Securities and otherwise satisfies Section 10(a) of the Act.

“General Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is intended for general distribution to prospective investors, as evidenced by its being so specified in Schedule B to this Agreement.

“Issuer Free Writing Prospectus” means any “issuer free writing prospectus,” as defined in Rule 433, relating to the Offered Securities in the form filed or required to be filed with the Commission or, if not required to be filed, in the form retained in the Company’s records pursuant to Rule 433(g).

“Limited Use Issuer Free Writing Prospectus” means any Issuer Free Writing Prospectus that is not a General Use Issuer Free Writing Prospectus.

“Rules and Regulations” means the rules and regulations of the Commission.

“Securities Laws” means, collectively, the Sarbanes-Oxley Act of 2002 (“Sarbanes-Oxley”), the Act, the Exchange Act, the Rules and Regulations, the auditing principles, rules, standards and practices applicable to auditors of “issuers” (as defined in Sarbanes-Oxley) promulgated or approved by the Public Company Accounting Oversight Board and, as applicable, the rules of the New York Stock Exchange and the NASDAQ Stock Market (“Exchange Rules”).

“Statutory Prospectus” with reference to any particular time means the prospectus relating to the Offered Securities that is included in the Registration Statement immediately prior to that time, including any document incorporated by reference therein and all 430B Information and all 430C Information with respect to the Registration Statement, that in any case has not been superseded or modified. For purposes of the

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foregoing definition, 430B Information shall be considered to be included in the Statutory Prospectus only as of the actual time that form of prospectus (including a prospectus supplement) is filed with the Commission pursuant to Rule 424(b) and not retroactively.

Unless otherwise specified, a reference to a “rule” is to the indicated rule under the Act.

(b) Compliance with Securities Act Requirements. (i) (A) At the time the Registration Statement initially became effective, (B) at the time of each amendment thereto for the purposes of complying with Section 10(a)(3) of the Act (whether by post-effective amendment, incorporated report or form of prospectus), (C) at the Effective Time relating to the Offered Securities and (D) on the Closing Date, the Registration Statement conformed and will conform in all material respects to the requirements of the Act and the Rules and Regulations and did not and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein not misleading and (ii) (A) on its date, (B) at the time of filing the Final Prospectus pursuant to Rule 424(b) and (C) on the Closing Date, the Final Prospectus will conform in all material respects to the requirements of the Act and the Rules and Regulations, and will not include any untrue statement of a material fact or omit to state any material fact required to be stated therein or necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements in or omissions from any such document based upon written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information is that described as such in Section 8(b) hereof.

(c) Shelf Registration Statement. The date of this Agreement is not more than three years subsequent to the initial effective time of the Registration Statement. If, immediately prior to the third anniversary of the initial effective time of the Registration Statement, any of the Offered Securities remain unsold by the Underwriters, the Company will (i) prior to that third anniversary file, if it has not already done so, a new shelf registration statement relating to the Offered Securities, in a form satisfactory to the Representative, (ii) use its reasonable best efforts to cause such registration statement to be declared effective within 180 days after that third anniversary, and (iii) take all other action necessary or appropriate to permit the public offering and sale of the Offered Securities to continue as contemplated in the expired registration statement relating to the Offered Securities. References herein to the Registration Statement shall include such new shelf registration statement.

(d) Ineligible Issuer Status. (i) At the earliest time after the filing of the Registration Statement that the Company or another offering participant made a bona fide offer (within the meaning of Rule 164(h)(2)) of the Offered Securities and (ii) as of the date of this Agreement, the Company was not and is not an “ineligible issuer,” as defined in Rule 405, including (x) the Company or any other subsidiary in the preceding three years not having been convicted of a felony or misdemeanor or having been made the subject of a judicial or administrative decree or order as described in Rule 405 and (y) the

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Company in the preceding three years not having been the subject of a bankruptcy petition or insolvency or similar proceeding, not having had a registration statement be the subject of a proceeding under Section 8 of the Act and not being the subject of a proceeding under Section 8A of the Act in connection with the offering of the Securities, all as described in Rule 405.

(e) General Disclosure Package. As of the Applicable Time, neither (i) the General Use Issuer Free Writing Prospectus(es) issued at or prior to the Applicable Time and the preliminary prospectus supplement, dated July 25, 2012, including the base prospectus, dated July 13, 2010, (which is the most recent Statutory Prospectus distributed to investors generally), and the other information, if any, stated in Schedule B to this Agreement to be included in the General Disclosure Package, all considered together (collectively, the “General Disclosure Package”), nor (ii) any individual Limited Use Issuer Free Writing Prospectus, when considered together with the General Disclosure Package, included any untrue statement of a material fact or omitted to state any material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. The preceding sentence does not apply to statements made in or omissions from any Statutory Prospectus or any Issuer Free Writing Prospectus in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in Section 8(b) hereof.

(f) Issuer Free Writing Prospectuses. Each Issuer Free Writing Prospectus, as of its issue date and at all subsequent times through the completion of the public offer and sale of the Offered Securities or until any earlier date that the Company notified or notifies the Representative as described in the next sentence, did not, does not and will not include any information that conflicted, conflicts or will conflict with the information then contained in the Registration Statement. If at any time following issuance of an Issuer Free Writing Prospectus there occurred or occurs an event or development as a result of which such Issuer Free Writing Prospectus conflicted or would conflict with the information then contained in the Registration Statement or as a result of which such Issuer Free Writing Prospectus, if republished immediately following such event or development, would include an untrue statement of a material fact or omitted or would omit to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading, (i) the Company has promptly notified or will promptly notify the Representative and (ii) the Company has promptly amended or will promptly amend or supplement such Issuer Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission.

(g) Documents Incorporated by Reference. Each document filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Registration Statement, General Disclosure Package or Final Prospectus complied or will comply when so filed in all material respects with the requirements of the Exchange Act and the applicable Rules and Regulations thereunder.

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(h) Good Standing of the Company. The Company has been duly incorporated and is existing and in good standing under the laws of the State of Delaware, with power and authority (corporate and other) to own its properties and conduct its business as described in the General Disclosure Package; and the Company is duly qualified to do business as a foreign corporation in good standing in all other jurisdictions in which its ownership or lease of property or the conduct of its business requires such qualification, except to the extent that the failure to be so qualified or be in good standing would not have a material adverse effect on the Company.

(i) Subsidiaries. The Company has no subsidiaries.

(j) Offered Securities. The Offered Securities and all other outstanding shares of capital stock of the Company have been duly authorized; the authorized equity capitalization of the Company is as set forth in the General Disclosure Package; all outstanding shares of capital stock of the Company are, and, when the Offered Securities have been delivered and paid for in accordance with this Agreement on each Closing Date, such Offered Securities will have been, validly issued, fully paid and nonassessable, will conform in all material respects to the information in the General Disclosure Package and to the description of such Offered Securities contained in the Final Prospectus; the stockholders of the Company have no preemptive rights with respect to the issuance by the Company of the Common Stock and none of the outstanding shares of capital stock of the Company have been issued by the Company in violation of any preemptive or similar rights of any security holder.

(k) No Finder’s Fee. Except as disclosed in the General Disclosure Package, there are no contracts, agreements or understandings between the Company and any person that would give rise to a valid claim against the Company or any Underwriter for a brokerage commission, finder’s fee or other like payment in connection with this offering.

(l) Registration Rights. Except as disclosed in the General Disclosure Package, and except as set forth in those Purchase Agreements, each dated December 30, 2008, between the Company and the investors named therein, there are no contracts, agreements or understandings between the Company and any person granting such person the right to require the Company to file a registration statement under the Act with respect to any securities of the Company owned or to be owned by such person or to require the Company to include such securities in the securities registered pursuant to a Registration Statement or in any securities being registered pursuant to any other registration statement filed by the Company under the Act.

(m) Listing. If required, the Company has notified the NASDAQ Global Select Market of the intended listing of the Offered Securities on the NASDAQ Global Select Market.

(n) Absence of Further Requirements. No consent, approval, authorization, or order of, or filing or registration with, any person (including any governmental agency or body or any court) is required to be obtained or made by the Company for the

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consummation of the transactions contemplated by this Agreement in connection with the offering, issuance and sale of the Offered Securities by the Company, except such as have been obtained, or made and such as may be required under state securities laws.

(o) Title to Property. The Company has good and marketable title to all personal property owned by it that is material to the business of the Company, free from liens, charges, encumbrances and defects except as described in the General Disclosure Package or such as do not materially affect the value of such property and do not interfere with the use made and proposed to be made of such property by the Company; and any real property and buildings held under lease by the Company is held under valid, subsisting and enforceable leases with such exceptions as are not material and do not interfere with the use made and proposed to be made of such property and buildings by the Company, except as described in the General Disclosure Package. The Company does not own any real property.

(p) Absence of Defaults and Conflicts Resulting from Transaction. The execution, delivery and performance of this Agreement by the Company, and the issuance and sale of the Offered Securities, will not contravene any provision of (i) applicable law, (ii) the certificate of incorporation or bylaws of the Company, (iii) any agreement or other instrument binding upon the Company, or (iv) any judgment, order or decree of any governmental body, agency or court having jurisdiction over the Company except, in the case of clause (iii) above, for any such contravention that would not have a material adverse effect on the Company

(q) Absence of Existing Defaults and Conflicts. The Company is not in violation of its certificate of incorporation or bylaws or in default (or with the giving of notice or lapse of time would be in default) under any existing obligation, agreement, covenant or condition contained in any indenture, loan agreement, mortgage, lease or other agreement or instrument to which the Company is a party or by which the Company is bound or to which any of its properties is subject, except such defaults that would not have a material adverse effect on the Company.

(r) Authorization of Agreement. This Agreement has been duly authorized, executed and delivered by the Company.

(s) Possession of Licenses and Permits. The Company has all necessary consents, authorizations, approvals, orders, certificates and permits of and from, and has made all required declarations and filings with, all federal, state, local and other governmental authorities, all self-regulatory organizations and all courts and other tribunals, to own, lease, license and use its properties and assets and to conduct its business in the manner described in the General Disclosure Package, including, without limitation, all necessary U.S. Food and Drug Administration (“FDA”) and applicable foreign regulatory agency approvals, except as disclosed in the General Disclosure Package, and except to the extent that the failure to obtain such consents, authorizations, approvals, orders, certificates, permits, or to make such declarations or filings would not have a material adverse effect on the Company. The Company has not received any

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notice of proceedings relating to the revocation or modification of any such consent, authorization, approval, order, certificate or permit which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, would have a material adverse effect on the Company, except as described in the General Disclosure Package.

(t) Absence of Labor Dispute. No material labor dispute with the employees of the Company exists, except as described in the General Disclosure Package, or, to the knowledge of the Company, is imminent; and the Company is not aware of any existing, threatened or imminent labor disturbance by the employees of any of its principal suppliers, manufacturers or contractors that would reasonably be expected to have a material adverse effect on the Company.

(u) Intellectual Property.

(i) The Company is the owner or co-owner, as applicable, of all patents and patent applications owned or co-owned by the Company (the “Owned Patents”), and holds all right, title and interest in and to such Owned Patents free and clear of all liens, encumbrances, defects or other restrictions, except as would not, singly or in the aggregate, have a material adverse effect on the Company; and the Company is not aware of any valid or bona fide basis for a finding that any of the Owned Patents in their entirety is unpatentable, invalid or unenforceable; and the Company reasonably believes that the Owned Patents are patentable, valid and enforceable, except as would not, singly or in the aggregate, have a material adverse effect on the Company.

(ii) In connection with the Owned Patents, all known relevant prior art references were disclosed or will be disclosed to the U.S. Patent and Trademark Office (the “USPTO”) to the extent required by and in accordance with 37 C.F.R. Section 1.56; all information submitted to the USPTO in such patent applications, and in connection with the prosecution of such applications, was accurate in all material respects; and neither the Company nor, to the Company’s knowledge, any other person made any material misrepresentations or concealed any material information from the USPTO in such applications, or in connection with the prosecution of such applications, in violation of 37 C.F.R. Section 1.56.

(iii) Except as set forth in the General Disclosure Package, the Company owns or possesses rights to use, or can acquire on reasonable terms ownership of or rights to use, all patents, patent applications, patent rights, licenses, inventions, copyrights, know-how (including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures), trademarks, service marks, trade names and other intellectual property (collectively, “Intellectual Property”) necessary for the conduct of the Company’s business substantially as now conducted, and for the manufacture, use or sale of its presently proposed products, as described in the General Disclosure Package. The Company has not received any notice of infringement

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of or conflict with asserted rights of others with respect to any of the foregoing that, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, would have a material adverse effect on the Company.

(iv) To the Company’s knowledge, after due inquiry, other than as described in the General Disclosure Package, and except as would not have a material adverse effect on the Company, there are no valid and enforceable rights of third parties to any Intellectual Property that are or would be infringed by the business currently conducted by the Company or in the manufacture, use, sale, offer for sale or import of its presently proposed products, as described in the General Disclosure Package.

(v) The Company is not subject to any judgment, order, writ, injunction or decree of any court or any federal, state, local, foreign or other governmental department, commission, board, bureau, agency or instrumentality, domestic or foreign, or any arbitrator. Except as would not have a material adverse effect on the Company, the Company is not a party to any contract, which restricts or impairs its use of any Intellectual Property.

(vi) To the Company’s knowledge, after due inquiry, and except as would not have a material adverse effect on the Company, there are no ongoing infringements by others of any Intellectual Property owned by the Company in connection with the business currently conducted by the Company or its presently proposed products, as described in the General Disclosure Package.

(vii) Other than as disclosed in the General Disclosure Package and except as would not have a material adverse effect on the Company, to the Company’s knowledge, after due inquiry, there is no U.S. patent or published U.S. patent application which contains valid and enforceable claims that dominate or that would dominate any Intellectual Property described in the General Disclosure Package as being owned by the Company or that interferes with the issued or pending claims of any such Intellectual Property.

(v) Environmental Laws. The Company (i) is in compliance with any and all applicable foreign, federal, state and local laws and regulations relating to the protection of human health and safety, the environment or hazardous or toxic substances or wastes, pollutants or contaminants (“Environmental Laws”), (ii) has received all permits, licenses or other approvals required under applicable Environmental Laws to conduct its business and (iii) is in compliance with all terms and conditions of any such permit, license or approval, except where such noncompliance with Environmental Laws, failure to receive required permits, licenses or other approvals or failure to comply with the terms and conditions of such permits, licenses or approvals would not, singly or in the aggregate, have a material adverse effect on the Company. There are no costs or liabilities associated with Environmental Laws (including, without limitation, any capital or operating expenditures required for clean-up, closure of properties or compliance with Environmental Laws or any permit, license or approval, any related constraints on operating activities and any potential liabilities to third parties) that would, singly or in the aggregate, have a material adverse effect on the Company.

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(w) Accurate Disclosure. The statements in the General Disclosure Package and the Final Prospectus under the headings “Material U.S. Federal Income and Estate Tax Consequences to Non.-U.S. Holders” and “Description of Capital Stock,” insofar as such statements summarize legal matters, agreements, documents or proceedings discussed therein, are in all material respects accurate and fair summaries of such legal matters, agreements, documents or proceedings and present the information required to be shown.

(x) Absence of Manipulation. The Company has not taken, directly or indirectly, any action that is designed to or that has constituted or that would reasonably be expected to cause or result in the stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Offered Securities; provided, however, that no representation is made with regard to any actions of the Underwriters.

(y) Statistical and Market-Related Data. Any third-party statistical and market-related data included or incorporated by reference in a Registration Statement, a Statutory Prospectus or the General Disclosure Package are based on or derived from sources that the Company believes to be reliable and accurate.

(z) Internal Controls and Compliance with the Sarbanes-Oxley Act.

(i) The Company has established and maintains disclosure controls and procedures (as defined in Rule 13a-15 under the Exchange Act). Such disclosure controls and procedures are designed to ensure that information required to be disclosed by the Company is recorded, processed, summarized and reported, within the time periods specified in the Commission’s rules and forms, and that such information is accumulated and communicated to the Company’s principal executive officer and its principal financial officer. Such disclosure controls and procedures are sufficient to provide reasonable assurance that the Company’s principal executive officer and principal financial officer are alerted to material information required to be included in the Company’s periodic reports required under the Exchange Act so as to allow timely decisions regarding required disclosure.

(ii) The Company maintains a system of internal control over financial reporting (as defined in Rule 13a-15 under the Exchange Act) sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are recorded as necessary to permit preparation of financial statements in accordance with U.S. generally accepted accounting principles and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

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(iii) There are no outstanding loans made by the Company to any executive officer (as defined in Rule 3b-7 under the Exchange Act) or director of the Company which are prohibited by Section 402 of the Sarbanes-Oxley Act of 2002, as amended. The Company has not since January 19, 2005 taken any action prohibited by Section 402 of the Sarbanes-Oxley Act of 2002, as amended.

(aa) Legal and Governmental Proceedings.

(i) There are no legal or governmental proceedings pending or, to the Company’s knowledge, threatened to which the Company is a party or to which any of the properties of the Company is subject (i) other than proceedings accurately described in all material respects in the General Disclosure Package and proceedings that would not have a material adverse effect on the Company or on the power or ability of the Company to perform its obligations under this Agreement or to consummate the transactions contemplated by the General Disclosure Package or (ii) that are required to be described in the Registration Statement or the Final Prospectus and are not so described; and there are no statutes, regulations, contracts or other documents that are required to be described in the Registration Statement or the Final Prospectus or to be filed as exhibits to the Registration Statement that are not described or filed as required.

(ii) The Company is not subject to any judgment, order, writ, injunction or decree of any court or any federal, state, local, foreign or other governmental department, commission, board, bureau, agency or instrumentality, domestic or foreign, or any arbitrator.

(bb) No Material Adverse Change in Business. There has not occurred any material adverse change, or any development involving a prospective material adverse change, in the condition, financial or otherwise, or in the earnings, business or operations of the Company, from that set forth or contemplated in the General Disclosure Package. Subsequent to the respective dates as of which information is given in each of the Registration Statement, the General Disclosure Package and the Final Prospectus, (i) the Company has not incurred any material liability or obligation, direct or contingent, nor entered into any material transaction not in the ordinary course of business; (ii) the Company has not purchased any of its outstanding capital stock other than ordinary and customary repurchases of restricted stock from employees upon termination of service pursuant to the terms of the Company’s equity incentive plans, nor declared, paid or otherwise made any dividend or distribution of any kind on its capital stock other than ordinary and customary dividends; and (iii) there has not been any material change in the capital stock, short-term debt or long-term debt of the Company, except in each case as described in each of the Registration Statement, the General Disclosure Package and the Final Prospectus.

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(cc) Investment Company Act. The Company is not and, after giving effect to the offering and sale of the Offered Securities and the application of the proceeds thereof as described in the General Disclosure Package, will not be an “investment company” as defined in the Investment Company Act of 1940, as amended.

(dd) Tax Matters. The Company has filed all federal, state, local and foreign tax returns required to be filed through the date of this Agreement or has requested extensions thereof (except where the failure to file would not, individually or in the aggregate, have a material adverse effect) and has paid all taxes required to be paid thereon (except for cases in which the failure to pay would not have a material adverse effect, or, except as currently being contested in good faith and for which reserves required by U.S. GAAP have been created in the financial statements of the Company), and no tax deficiency has been determined adversely to the Company which has had (nor does the Company have any notice or knowledge of any tax deficiency which could reasonably be expected to be determined adversely to the Company and which could reasonably be expected to have) a material adverse effect.

(ee) No Unlawful Payments. Neither the Company nor, to the Company’s knowledge, any director, officer, employee, agent, or representative of the Company, has taken or, with respect to the Company, will take any action in furtherance of an offer, payment, promise to pay, or authorization or approval of the payment or giving of money, property, gifts or anything else of value, directly or indirectly, to any “government official” (including any officer or employee of a government or government-owned or controlled entity or of a public international organization, or any person acting in an official capacity for or on behalf of any of the foregoing, or any political party or party official or candidate for political office) to influence official action or secure an improper advantage; and the Company has conducted its business in compliance with applicable anti-corruption laws and has instituted and maintained and will continue to maintain policies and procedures designed to promote and achieve compliance with such laws and with the representation and warranty contained herein.

(ff) Compliance with Anti-Money-Laundering Laws. The operations of the Company are and have been conducted at all times in material compliance with all applicable financial recordkeeping and reporting requirements, including those of the Bank Secrecy Act, as amended by Title III of the Uniting and Strengthening America by Providing Appropriate Tools Required to Intercept and Obstruct Terrorism Act of 2001 (USA PATRIOT Act), and the applicable anti-money laundering statutes of jurisdictions where the Company conducts business, the rules and regulations thereunder and any related or similar rules, regulations or guidelines, issued, administered or enforced by any governmental agency (collectively, the “Anti-Money Laundering Laws”), and no action, suit or proceeding by or before any court or governmental agency, authority or body or any arbitrator involving the Company with respect to the Anti-Money Laundering Laws is pending or, to the best knowledge of the Company, threatened.

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(gg) Compliance with OFAC. (i) The Company represents that neither the Company nor, to the knowledge of the Company, any director, officer, employee, agent, affiliate or representative of the Company, is an individual or entity (“Person”) that is, or is owned or controlled by a Person that is:

(A) the subject of any sanctions administered or enforced by the U.S. Department of Treasury’s Office of Foreign Assets Control (“OFAC”), the United Nations Security Council (“UNSC”), the European Union (“EU”), Her Majesty’s Treasury (“HMT”), or other relevant sanctions authority (collectively, “Sanctions”), nor

(B) located, organized or resident in a country or territory that is the subject of Sanctions (including, without limitation, Burma/Myanmar, Cuba, Iran, Libya, North Korea, Sudan and Syria).

(ii) The Company represents and covenants that it will not, directly or indirectly, use the proceeds of the offering, or lend, contribute or otherwise make available such proceeds to any joint venture partner or other Person:

(A) to fund or facilitate any activities or business of or with any Person or in any country or territory that, at the time of such funding or facilitation, is the subject of Sanctions; or

(B) in any other manner that will result in a violation of Sanctions by any Person (including any Person participating in the offering, whether as underwriter, advisor, investor or otherwise).

(iii) The Company represents and covenants that, for the past 5 years, it has not knowingly engaged in, is not now knowingly engaged in, and will not knowingly engage in, any dealings or transactions with any Person, or in any country or territory, that at the time of the dealing or transaction is or was to the Company’s knowledge the subject of Sanctions.

(hh) Insurance. The Company is insured by insurers of recognized financial responsibility against such losses and risks and in such amounts as are prudent and customary in the businesses in which it is engaged; and the Company currently expects that it will be able to renew its existing insurance coverage as and when such coverage expires or to obtain similar coverage from similar insurers as may be necessary to continue its business at a cost that would not have a material adverse effect on the Company, except as described in the General Disclosure Package.

(ii) Issuances of Common Stock. Except as described in the General Disclosure Package, the Company has not sold, issued or distributed any shares of Common Stock during the six-month period preceding the date hereof, including any sales pursuant to Rule 144A under, or Regulation D or S of, the Act, other than shares issued pursuant to employee benefit plans, qualified stock option plans or other employee compensation plans or arrangements, or pursuant to outstanding options, restricted stock units, rights or warrants.

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(jj) Other Regulatory Matters.

(i) No investigational new drug (“IND”) application filed by or on behalf of the Company with the FDA has been terminated by the FDA, and neither the FDA nor any applicable foreign regulatory agency has commenced, or, to the knowledge of the Company, threatened to initiate, any action to place a clinical hold order on, or otherwise delay or suspend, proposed or ongoing clinical investigations conducted or proposed to be conducted by or on behalf of the Company.

(ii) To the best of the Company’s knowledge, all the operations of the Company and all the manufacturing facilities and operations of the Company’s suppliers of products and product candidates and the components thereof manufactured in or imported into the United States are in compliance with applicable FDA regulations, including current Good Manufacturing Practices, and meet sanitation standards set by the Federal Food, Drug and Cosmetic Act of 1938, as amended, and all the operations of the Company and all the manufacturing facilities and operations of the Company’s suppliers of products and product candidates manufactured outside, or exported from, the United States are in compliance with applicable foreign regulatory requirements and standards, except to the extent that the failure to be in compliance with such regulations and standards would not have a material adverse effect on the Company.

(iii) Except as described in the General Disclosure Package, the clinical trials and the human and animal studies that are described in the General Disclosure Package were and, if still pending, are being, conducted (to the knowledge of the Company with respect to such studies conducted by or on behalf of third parties) in accordance in all material respects with standard medical and scientific research procedures and all applicable rules, regulations and policies of the FDA, including the current Good Clinical Practices and Good Laboratory Practices, and all applicable foreign regulatory requirements and standards.

(iv) The Company has operated its business and currently is in compliance in all material respects with all applicable rules, regulations and policies of the FDA and any applicable foreign regulatory organization.

3. Purchase, Sale and Delivery of Offered Securities. On the basis of the representations, warranties and agreements and subject to the terms and conditions set forth herein, the Company agrees to sell to the several Underwriters, and each of the Underwriters agrees, severally and not jointly, to purchase from the Company, at a purchase price of $6.12625 per share, the respective number of shares of Firm Securities set forth opposite the names of the Underwriters in Schedule A hereto.

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The Company will deliver the Firm Securities to or as instructed by the Representative for the accounts of the several Underwriters in a form reasonably acceptable to the Representative against payment of the purchase price by the Underwriters in Federal (same day) funds by wire transfer to an account at a bank acceptable to the Representative drawn to the order of the Company at the office of Davis Polk & Wardwell, LLP, 1600 El Camino Real, Menlo Park, California 94025, at 10:00 a.m., New York time, on July 30, 2012, or at such other time not later than seven full business days thereafter as the Representative and the Company determine, such time being herein referred to as the “First Closing Date”. For purposes of Rule 15c6-1 under the Securities Exchange Act of 1934, the First Closing Date (if later than the otherwise applicable settlement date) shall be the settlement date for payment of funds and delivery of securities for all the Offered Securities sold pursuant to the offering. The Firm Securities so to be delivered or evidence of their issuance will be made available for checking at the above office of Davis Polk & Wardwell LLP at least 24 hours prior to the First Closing Date.

In addition, upon written notice from the Representative given to the Company from time to time not more than 30 days subsequent to the date of the Final Prospectus, the Underwriters may purchase all or less than all of the Optional Securities at the purchase price per Security to be paid for the Firm Securities. The Company agrees to sell to the Underwriters the number of shares of Optional Securities specified in such notice and the Underwriters agree, severally and not jointly, to purchase such Optional Securities. Such Optional Securities shall be purchased for the account of each Underwriter in the same proportion as the number of shares of Firm Securities set forth opposite such Underwriter’s name bears to the total number of shares of Firm Securities (subject to adjustment by the Representative to eliminate fractions) and may be purchased by the Underwriters only for the purpose of covering over-allotments made in connection with the sale of the Firm Securities. No Optional Securities shall be sold or delivered unless the Firm Securities previously have been, or simultaneously are, sold and delivered. The right to purchase the Optional Securities or any portion thereof may be exercised from time to time and to the extent not previously exercised may be surrendered and terminated at any time upon notice by the Representative to the Company.

Each time for the delivery of and payment for the Optional Securities, being herein referred to as an “Optional Closing Date”, which may be the First Closing Date (the First Closing Date and each Optional Closing Date, if any, being sometimes referred to as a “Closing Date”), shall be determined by the Representative but shall be not later than five full business days after written notice of election to purchase Optional Securities is given. The Company will deliver the Optional Securities being purchased on each Optional Closing Date to or as instructed by the Representative for the accounts of the several Underwriters in a form reasonably acceptable to the Representative against payment of the purchase price therefor in Federal (same day) funds by wire transfer to an account at a bank acceptable to the Representative drawn to the order of the Company, at the above office of Davis Polk & Wardwell LLP. The Optional Securities being purchased on each Optional Closing Date or evidence of their issuance will be made available for checking at the above office of Davis Polk & Wardwell LLP at a reasonable time in advance of such Optional Closing Date.

4. Offering by Underwriters. It is understood that the several Underwriters propose to offer the Offered Securities for sale to the public as set forth in the Final Prospectus.

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5. Certain Agreements of the Company. The Company agrees with the several Underwriters that:

(a) Filing of Prospectuses. The Company has filed or will file each Statutory Prospectus (including the Final Prospectus) pursuant to and in accordance with Rule 424(b)(2) (or, if applicable and consented to by the Representative, subparagraph (5)) not later than the second business day following the earlier of the date it is first used or the execution and delivery of this Agreement. The Company has complied and will comply with Rule 433.

(b) Filing of Amendments; Response to Commission Requests. The Company will promptly advise the Representative of any proposal to amend or supplement the Registration Statement or any Statutory Prospectus at any time and will offer the Representative a reasonable opportunity to comment on any such amendment or supplement; and the Company will also advise the Representative promptly of (i) the filing of any such amendment or supplement, (ii) any request by the Commission or its staff for any amendment to the Registration Statement, for any supplement to any Statutory Prospectus or for any additional information, (iii) the institution by the Commission of any stop order proceedings in respect of the Registration Statement or the threatening of any proceeding for that purpose, and (iv) the receipt by the Company of any notification with respect to the suspension of the qualification of the Offered Securities in any jurisdiction or the institution or threatening of any proceedings for such purpose. The Company will use its reasonable best efforts to prevent the issuance of any such stop order or the suspension of any such qualification and, if issued, to obtain as soon as possible the withdrawal thereof.

(c) Continued Compliance with Securities Laws. If, at any time when a prospectus relating to the Offered Securities is (or but for the exemption in Rule 172 would be) required to be delivered under the Act by any Underwriter or dealer, any event occurs as a result of which the Final Prospectus as then amended or supplemented would include an untrue statement of a material fact or omit to state any material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, or if, in the opinion of counsel for the Underwriters, it is necessary at any time to amend the Registration Statement or supplement the Final Prospectus to comply with the Act, the Company will promptly notify the Representative of such event and will promptly prepare and file with the Commission and furnish, at its own expense, to the Underwriters and the dealers and any other dealers upon request of the Representative, an amendment or supplement which will correct such statement or omission or an amendment which will effect such compliance. Neither the Representative’s consent to, nor the Underwriters’ delivery of, any such amendment or supplement shall constitute a waiver of any of the conditions set forth in Section 7 hereof.

(d) Rule 158. As soon as practicable, but not later than 16 months, after the date of this Agreement, the Company will make generally available to its securityholders an earnings statement (which need not be audited) covering a period of at least 12 months beginning after the date of this Agreement and satisfying the provisions of Section 11(a) of the Act and Rule 158.

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(e) Furnishing of Prospectuses. The Company will furnish to the Representative copies of the Registration Statement, including all exhibits, any Statutory Prospectus, the Final Prospectus and all amendments and supplements to such documents, in each case as soon as available and in such quantities as the Representative reasonably requests. The Company will pay the expenses of printing and distributing to the Underwriters all such documents.

(f) Blue Sky Qualifications. The Company will arrange for the qualification of the Offered Securities for sale under the laws of such jurisdictions as the Representative designates and will continue such qualifications in effect so long as required for the distribution; provided, that, in connection therewith, the Company will not be required to file a general consent to service of process or to qualify as a foreign corporation or as a dealer in securities in any jurisdiction in which it is not so qualified, or subject itself to taxation for doing business in any jurisdiction in which it is not otherwise so subject.

(g) Reporting Requirements. During the period of three years hereafter, the Company will furnish, upon request, to the Representative and to each of the other Underwriters, as soon as practicable after the end of each fiscal year, a copy of its annual report to stockholders for such year; and the Company will furnish to the Representative (i) as soon as available, a copy of each report and any definitive proxy statement of the Company filed with the Commission under the Exchange Act or mailed to stockholders, and (ii) from time to time, such other information concerning the Company as the Representative may reasonably request; provided, that, if the Representative shall request nonpublic confidential information, the Company shall only be required to provide the Representative with such information if the Representative shall enter into a customary confidentiality agreement with the Company with respect thereto. However, so long as the Company is subject to the reporting requirements of either Section 13 or Section 15(d) of the Exchange Act and is timely filing reports with the Commission on its Electronic Data Gathering, Analysis and Retrieval system (“EDGAR”), it is not required to furnish such reports or statements to the Representative or the Underwriters.

(h) Payment of Expenses. The Company will pay all expenses incident to the performance of its obligations under this Agreement, including but not limited to any filing fees and other expenses (including reasonable fees and disbursements of counsel to the Underwriters) incurred in connection with qualification of the Offered Securities for sale under the laws of such jurisdictions as the Representative designates and the preparation and printing of memoranda relating thereto, costs and expenses related to the review by the Financial Industry Regulatory Authority of the Offered Securities (including reasonable filing fees and the reasonable fees and expenses of counsel for the Underwriters relating to such review), costs and expenses relating to investor presentations or any “road show” in connection with the offering and sale of the Offered Securities including, without limitation, any travel expenses of the Company’s officers and employees and any other expenses of the Company including, with the Company’s

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prior consent, the chartering of airplanes, fees and expenses incident to listing the Offered Securities on the NASDAQ Global Select Market and other national and foreign exchanges, fees and expenses in connection with the registration of the Offered Securities under the Exchange Act, and expenses incurred in distributing preliminary prospectuses and the Final Prospectus (including any amendments and supplements thereto) to the Underwriters and for expenses incurred for preparing, printing and distributing any Issuer Free Writing Prospectuses to investors or prospective investors.

(i) Use of Proceeds. The Company will use the net proceeds received in connection with this offering in the manner described in the “Use of Proceeds” section of the General Disclosure Package and, except as disclosed in the General Disclosure Package, the Company does not intend to use any of the proceeds from the sale of the Offered Securities hereunder to repay any outstanding debt owed to any affiliate of any Underwriter.

(j) Absence of Manipulation. The Company will not take, directly or indirectly, any action designed to or that would constitute or that might reasonably be expected to cause or result in, stabilization or manipulation of the price of any securities of the Company to facilitate the sale or resale of the Offered Securities; provided, however, that no representation is made with regard to any actions of the Underwriters.

(k) Restriction on Sale of Securities. For the period specified below (the “Lock-Up Period”), the Company will not, directly or indirectly, take any of the following actions with respect to shares of its Common Stock or any securities convertible into or exchangeable or exercisable for Common Stock (“Lock-Up Securities”): (i) offer, sell, issue, contract to sell, pledge or otherwise dispose of Lock-Up Securities, (ii) offer, sell, issue, contract to sell, contract to purchase or grant any option, right or warrant to purchase Lock-Up Securities, (iii) enter into any swap, hedge or any other agreement that transfers, in whole or in part, the economic consequences of ownership of Lock-Up Securities, (iv) establish or increase a put equivalent position or liquidate or decrease a call equivalent position in Lock-Up Securities within the meaning of Section 16 of the Exchange Act or (v) file with the Commission a registration statement under the Act relating to Lock-Up Securities, or publicly disclose the intention to take any such action, without the prior written consent of the Representative, except (A) the issuance by the Company of the Lock-Up Securities to be sold hereunder, (B) the issuance by the Company of Lock-Up Securities upon the exercise of an option or warrant, the vesting or settlement of any restricted stock units or other equity compensation awards or the conversion of a security outstanding on the date hereof; (C) the grant of options, restricted stock units or other equity compensation awards, or the issuance of Lock-Up Securities by the Company to employees, officers, directors, advisors or consultants of the Company in each case either (x) pursuant to equity incentive, stock option, inducement award and employee stock purchase plans described in the Final Prospectus or (y) as an inducement grant within the meaning of NASDAQ Rule 5635(c)(4) consistent with past practice, and the issuance by the Company of any Lock-Up Securities upon the exercise, vesting or settlement of such equity compensation awards; or (D) the filing of any registration statement (x) on Form S-8 in respect of any

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equity compensation plans or arrangements maintained by the Company or (y) that the Company is contractually obligated to file pursuant to the terms of those certain Purchase Agreements, each dated December 30, 2008, between the Company and the investors named therein. The initial Lock-Up Period will commence on the date hereof and continue for 90 days after the date hereof or such earlier date that the Representative consents to in writing.

6. Free Writing Prospectuses. The Company represents and agrees that, unless it obtains the prior consent of the Representative, and each Underwriter represents and agrees that, unless it obtains the prior consent of the Company and the Representative, it has not made and will not make any offer relating to the Offered Securities that would constitute an Issuer Free Writing Prospectus, or that would otherwise constitute a “free writing prospectus,” as defined in Rule 405, required to be filed with the Commission. Any such free writing prospectus consented to by the Company and the Representative is hereinafter referred to as a “Permitted Free Writing Prospectus.” The Company represents that it has treated and agrees that it will treat each Permitted Free Writing Prospectus as an “issuer free writing prospectus,” as defined in Rule 433, and has complied and will comply with the requirements of Rules 164 and 433 applicable to any Permitted Free Writing Prospectus, including timely Commission filing where required, legending and record keeping

7. Conditions of the Obligations of the Underwriters. The obligations of the several Underwriters to purchase and pay for the Firm Securities on the First Closing Date and the Optional Securities to be purchased on each Optional Closing Date will be subject to the accuracy of the representations and warranties of the Company herein (as though made on such Closing Date), to the accuracy of the statements of Company officers made pursuant to the provisions hereof, to the performance by the Company of its obligations hereunder and to the following additional conditions precedent:

(a) Accountants’ Comfort Letter. The Representative shall have received letters, dated, respectively, the date hereof and each Closing Date, in form and substance satisfactory to the Underwriters, of Ernst & Young LLP confirming that they are a registered public accounting firm and independent public accountants within the meaning of the Securities Laws (except that, in any letter dated a Closing Date, the specified date referred to therein shall be a date no more than three days prior to such Closing Date).

(b) Filing of Prospectus. The Final Prospectus shall have been filed with the Commission in accordance with the Rules and Regulations and Section 5(a) hereof. No stop order suspending the effectiveness of the Registration Statement or of any part thereof shall have been issued and no proceedings for that purpose shall have been instituted or, to the knowledge of the Company or any Underwriter, shall be contemplated by the Commission.

(c) No Material Adverse Change. Subsequent to the execution and delivery of this Agreement, there shall not have occurred (i) any change, or any development or event involving a prospective change, in the condition (financial or otherwise), results of operations, business, properties or prospects of the Company which, in the judgment of

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the Representative, is material and adverse and makes it impractical or inadvisable to market the Offered Securities; or (ii) any downgrading in the rating of any debt securities of the Company by any “nationally recognized statistical rating organization” (as defined for purposes of Rule 436(g)), or any public announcement that any such organization has under surveillance or review its rating of any debt securities of the Company (other than an announcement with positive implications of a possible upgrading, and no implication of a possible downgrading, of such rating).

(d) Lock-Up Agreements. The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between the Representative and each executive officer and director of the Company relating to sales and certain other dispositions of shares of Common Stock or certain other securities, delivered to the Representative on or before the date hereof, shall be in full force and effect on the Closing Date.

(e) Opinions of Counsel for Company. The Representative shall have received on the Closing Date (i) an opinion of Cooley LLP, outside counsel for the Company, together with a negative assurance letter, each dated the Closing Date, in the form agreed upon as of the date hereof and (ii) an opinion of Gianna M. Bosko, General Counsel of the Company, dated the Closing Date, in the form agreed upon as of the date hereof.

(f) Opinion of Intellectual Property Counsel. The Representative shall have received on the Closing Date an opinion of D. Byron Miller, internal patent counsel for the Company, dated the Closing date, in the form agreed upon as of the date hereof.

(g) Opinion of Counsel for Underwriters. The Representative shall have received on the Closing date, an opinion of Davis Polk & Wardwell LLP, counsel for the Underwriters, with respect to such matters as the Representative may require, together with a negative assurance letter, each dated the Closing Date, and the Company shall have furnished to such counsel such documents as they request for the purpose of enabling them to pass upon such matters.

(h) Officer’s Certificate. The Representative shall have received a certificate, dated such Closing Date, of an executive officer of the Company and a principal financial or accounting officer of the Company in which such officers shall state that: the representations and warranties of the Company in this Agreement are true and correct; the Company has complied, in all material respects, with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to such Closing Date; no stop order suspending the effectiveness of the Registration Statement has been issued and no proceedings for that purpose have been instituted or, to the best of their knowledge, are contemplated by the Commission; and, subsequent to the date of the most recent financial statements in the General Disclosure Package, there has been no material adverse change, nor any development or event involving a prospective material adverse change, in the condition (financial or otherwise), results of operations, business, properties or prospects of the Company except as set forth in the General Disclosure Package or as described in such certificate.

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The Company will furnish the Representative with such conformed copies of such opinions, certificates, letters and documents as the Representative reasonably requests. The Representative may in its sole discretion waive on behalf of the Underwriters compliance with any conditions to the obligations of the Underwriters hereunder, whether in respect of an Optional Closing Date or otherwise.

8. Indemnification and Contribution.

(a) Indemnification of Underwriters. The Company will indemnify and hold harmless each Underwriter, its partners, members, directors, officers, employees, agents, affiliates and each person, if any, who controls such Underwriter within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, an “Indemnified Party”), against any and all losses, claims, damages or liabilities, joint or several, to which such Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time, any Statutory Prospectus as of any time, the Final Prospectus or any Issuer Free Writing Prospectus, or arise out of or are based upon the omission or alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, and will reimburse each Indemnified Party for any legal or other expenses reasonably incurred by such Indemnified Party in connection with investigating or defending against any loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Indemnified Party is a party thereto), whether threatened or commenced, and in connection with the enforcement of this provision with respect to any of the above as such expenses are incurred; provided, however, that the Company will not be liable in any such case to the extent that any such loss, claim, damage or liability arises out of or is based upon an untrue statement or alleged untrue statement in or omission or alleged omission from any of such documents in reliance upon and in conformity with written information furnished to the Company by any Underwriter through the Representative specifically for use therein, it being understood and agreed that the only such information furnished by any Underwriter consists of the information described as such in subsection (b) below.

(b) Indemnification of Company. Each Underwriter will severally and not jointly indemnify and hold harmless the Company, each of its directors and each of its officers who signs a Registration Statement and each person, if any, who controls the Company within the meaning of Section 15 of the Act or Section 20 of the Exchange Act (each, an “Underwriter Indemnified Party”), against any losses, claims, damages or liabilities to which such Underwriter Indemnified Party may become subject, under the Act, the Exchange Act, other Federal or state statutory law or regulation or otherwise, insofar as such losses, claims, damages or liabilities (or actions in respect thereof) arise out of or are based upon any untrue statement or alleged untrue statement of any material fact contained in any part of the Registration Statement at any time, any Statutory Prospectus as of any time, the Final Prospectus, or any Issuer Free Writing Prospectus, or

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arise out of or are based upon the omission or the alleged omission of a material fact required to be stated therein or necessary to make the statements therein not misleading, in each case to the extent, but only to the extent, that such untrue statement or alleged untrue statement or omission or alleged omission was made in reliance upon and in conformity with written information furnished to the Company by such Underwriter through the Representative specifically for use therein, and will reimburse any legal or other expenses reasonably incurred by such Underwriter Indemnified Party in connection with investigating or defending against any such loss, claim, damage, liability, action, litigation, investigation or proceeding whatsoever (whether or not such Underwriter Indemnified Party is a party thereto), whether threatened or commenced, based upon any such untrue statement or omission, or any such alleged untrue statement or omission as such expenses are incurred, it being understood and agreed that the only such information furnished by any Underwriter consists of the following information in the Final Prospectus furnished on behalf of each Underwriter: the concession figure appearing in the fifth paragraph and the information contained in the twelfth paragraph under the caption “Underwriting.”

(c) Actions against Parties; Notification. Promptly after receipt by an indemnified party under this Section of notice of the commencement of any action, such indemnified party will, if a claim in respect thereof is to be made against the indemnifying party under subsection (a) or (b) above, notify the indemnifying party of the commencement thereof; but the failure to notify the indemnifying party shall not relieve it from any liability that it may have under subsection (a) or (b) above except to the extent that it has been materially prejudiced (through the forfeiture of substantive rights or defenses) by such failure; and provided further that the failure to notify the indemnifying party shall not relieve it from any liability that it may have to an indemnified party otherwise than under subsection (a) or (b) above. In case any such action is brought against any indemnified party and it notifies the indemnifying party of the commencement thereof, the indemnifying party will be entitled to participate therein and, to the extent that it may wish, jointly with any other indemnifying party similarly notified, to assume the defense thereof, with counsel satisfactory to such indemnified party (who shall not, except with the consent of the indemnified party, be counsel to the indemnifying party), and after notice from the indemnifying party to such indemnified party of its election so to assume the defense thereof, the indemnifying party will not be liable to such indemnified party under this Section for any legal or other expenses subsequently incurred by such indemnified party in connection with the defense thereof other than reasonable costs of investigation. No indemnifying party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened action in respect of which any indemnified party is or could have been a party and indemnity could have been sought hereunder by such indemnified party unless such settlement (i) includes an unconditional release of such indemnified party from all liability on any claims that are the subject matter of such action and (ii) does not include a statement as to, or an admission of, fault, culpability or a failure to act by or on behalf of an indemnified party.

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(d) Contribution. If the indemnification provided for in this Section is unavailable or insufficient to hold harmless an indemnified party under subsection (a) or (b) above, then each indemnifying party shall contribute to the amount paid or payable by such indemnified party as a result of the losses, claims, damages or liabilities referred to in subsection (a) or (b) above (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Underwriters on the other from the offering of the Offered Securities or (ii) if the allocation provided by clause (i) above is not permitted by applicable law, in such proportion as is appropriate to reflect not only the relative benefits referred to in clause (i) above but also the relative fault of the Company on the one hand and the Underwriters on the other in connection with the statements or omissions which resulted in such losses, claims, damages or liabilities as well as any other relevant equitable considerations. The relative benefits received by the Company on the one hand and the Underwriters on the other shall be deemed to be in the same proportion as the total net proceeds from the offering (before deducting expenses) received by the Company bear to the total underwriting discounts and commissions received by the Underwriters. The relative fault shall be determined by reference to, among other things, whether the untrue or alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or the Underwriters and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such untrue statement or omission. The amount paid by an indemnified party as a result of the losses, claims, damages or liabilities referred to in the first sentence of this subsection (d) shall be deemed to include any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any action or claim which is the subject of this subsection (d). Notwithstanding the provisions of this subsection (d), no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Securities underwritten by it and distributed to the public were offered to the public exceeds the amount of any damages which such Underwriter has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The Underwriters’ obligations in this subsection (d) to contribute are several in proportion to their respective underwriting obligations and not joint. The Company and the Underwriters agree that it would not be just and equitable if contribution pursuant to this Section 8(d) were determined by pro rata allocation (even if the Underwriters were treated as one entity for such purpose) or by any other method of allocation which does not take account of the equitable considerations referred to in this Section 8(d).

9. Default of Underwriters. If any Underwriter or Underwriters default in their obligations to purchase Offered Securities hereunder on either the First or any Optional Closing Date and the aggregate number of shares of Offered Securities that such defaulting Underwriter or Underwriters agreed but failed to purchase does not exceed 10% of the total number of shares of Offered Securities that the Underwriters are obligated to purchase on such Closing Date, the Representative may make arrangements satisfactory to the Company for the purchase of such Offered Securities by other persons, including any of the Underwriters, but if no such

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arrangements are made by such Closing Date, the non-defaulting Underwriters shall be obligated severally, in proportion to their respective commitments hereunder, to purchase the Offered Securities that such defaulting Underwriters agreed but failed to purchase on such Closing Date. If any Underwriter or Underwriters so default and the aggregate number of shares of Offered Securities with respect to which such default or defaults occur exceeds 10% of the total number of shares of Offered Securities that the Underwriters are obligated to purchase on such Closing Date and arrangements satisfactory to the Representative and the Company for the purchase of such Offered Securities by other persons are not made within 36 hours after such default, this Agreement will terminate without liability on the part of any non-defaulting Underwriter or the Company, except as provided in Section 10 (provided that if such default occurs with respect to Optional Securities after the First Closing Date, this Agreement will not terminate as to the Firm Securities or any Optional Securities purchased prior to such termination). As used in this Agreement, the term “Underwriter” includes any person substituted for an Underwriter under this Section. Nothing herein will relieve a defaulting Underwriter from liability for its default.

10. Survival of Certain Representations and Obligations. The respective indemnities, agreements, representations, warranties and other statements of the Company or its officers and of the several Underwriters set forth in or made pursuant to this Agreement will remain in full force and effect, regardless of any investigation, or statement as to the results thereof, made by or on behalf of any Underwriter, the Company or any of their respective representatives, officers or directors or any controlling person, and will survive delivery of and payment for the Offered Securities. If the purchase of the Offered Securities by the Underwriters is not consummated for any reason other than solely because of the termination of this Agreement pursuant to Section 9 hereof, the Company will reimburse the Underwriters for all out-of-pocket expenses (including fees and disbursements of counsel) reasonably incurred by them in connection with the offering of the Offered Securities, and the respective obligations of the Company and the Underwriters pursuant to Section 8 hereof shall remain in effect; provided, however that, if such failure to consummate shall take place after the First Closing Date with respect to any Optional Securities, such reimbursement will be limited to the reasonable out-of-pocket expenses incurred after the First Closing Date solely with respect to such Optional Securities. In addition, if any Offered Securities have been purchased hereunder, the representations and warranties in Section 2 and all obligations under Section 5 shall also remain in effect.

11. Notices. All communications hereunder will be in writing and, if sent to the Underwriters, will be mailed, delivered or telegraphed and confirmed to the Representative c/o Credit Suisse Securities (USA) LLC, Eleven Madison Avenue, New York, N.Y. 10010-3629, Attention: LCD-IBD, or, if sent to the Company, will be mailed, delivered or telegraphed and confirmed to XenoPort, Inc., 3410 Central Expressway, Santa Clara, CA 95051, Fax No. (408)  ###-###-####, Attention: Chief Executive Officer, with a copy (which shall not constitute notice hereunder) to Cooley LLP, 3175 Hanover Street, Palo Alto, California ###-###-####, Fax No. (650)  ###-###-####, Attention: Chad Mills; provided, however, that any notice to an Underwriter pursuant to Section 8 will be mailed, delivered or telegraphed and confirmed to such Underwriter.

12. Successors. This Agreement will inure to the benefit of and be binding upon the parties hereto and their respective successors and the officers and directors and controlling persons referred to in Section 8, and no other person will have any right or obligation hereunder.

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13. Representation of Underwriters. The Representative will act for the several Underwriters in connection with this financing, and any action under this Agreement taken by the Representative will be binding upon all the Underwriters.

14. Counterparts. This Agreement may be executed in any number of counterparts, each of which shall be deemed to be an original, but all such counterparts shall together constitute one and the same Agreement.

15. Absence of Fiduciary Relationship. The Company acknowledges and agrees that:

(a) No Other Relationship. The Representative has been retained solely to act as an underwriter in connection with the sale of Offered Securities and that no fiduciary, advisory or agency relationship between the Company and the Representative has been created in respect of any of the transactions contemplated by this Agreement or the Final Prospectus, irrespective of whether the Representative has advised or is advising the Company on other matters;

(b) Arms’ Length Negotiations. The price of the Offered Securities set forth in this Agreement was established by the Company following discussions and arms-length negotiations with the Representative and the Company is capable of evaluating and understanding and understands and accepts the terms, risks and conditions of the transactions contemplated by this Agreement;

(c) Absence of Obligation to Disclose. The Company has been advised that the Representative and its affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that the Representative has no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and

(d) Waiver. The Company waives, to the fullest extent permitted by law, any claims it may have against the Representative for breach of fiduciary duty or alleged breach of fiduciary duty in connection with the sale of Offered Securities, and agrees that the Representative shall have no liability (whether direct or indirect) to the Company in respect of such a fiduciary duty claim or to any person asserting a fiduciary duty claim on behalf of or in right of the Company, including stockholders, employees or creditors of the Company.

16. Applicable Law. This Agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

The Company hereby submits to the non-exclusive jurisdiction of the Federal and state courts in the Borough of Manhattan in The City of New York in any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby. The Company irrevocably and unconditionally waives any objection to the laying of venue of any suit or proceeding arising out of or relating to this Agreement or the transactions contemplated hereby in Federal and state courts in the Borough of Manhattan in The City of New York and irrevocably and unconditionally waives and agrees not to plead or claim in any such court that any such suit or proceeding in any such court has been brought in an inconvenient forum.

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17. Integration. This Agreement constitutes the entire agreement of the parties to this Agreement and supersedes and replaces all prior written or oral and all contemporaneous oral agreements, understandings and negotiations with respect to the subject matter hereof.

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If the foregoing is in accordance with the Representative’s understanding of our agreement, kindly sign and return to the Company one of the counterparts hereof, whereupon it will become a binding agreement between the Company and the several Underwriters in accordance with its terms.

SCHEDULE A

SCHEDULE B

“General Use Issuer Free Writing Prospectus” includes each of the following documents:

None.

The following information is also included in the General Disclosure Package:

EXHIBIT A

Form of Lock-Up Letter

XenoPort, Inc.

3410 Central Expressway

Santa Clara, CA 95051

Credit Suisse Securities (USA) LLC

as Representative of the Underwriters

Eleven Madison Avenue

New York, NY 10010-3629

Dear Sirs:

As an inducement to the Underwriters to execute the Underwriting Agreement, pursuant to which an offering (the “Public Offering”) will be made that is intended to result in an orderly market for shares of common stock, par value $0.001 per share (the “Common Stock”), of XenoPort, Inc., and any successor (by merger or otherwise) thereto, (the “Company”), the undersigned hereby agrees that during the period specified in the following paragraph (the “Lock-Up Period”), the undersigned will not offer, sell, contract to sell, pledge or otherwise dispose of, directly or indirectly, any shares of Common Stock or securities convertible into or exchangeable or exercisable for any shares of Common Stock, enter into a transaction which would have the same effect, or enter into any swap, hedge or other arrangement that transfers, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such aforementioned transaction is to be settled by delivery of the Common Stock or such other securities, in cash or otherwise, or publicly disclose the intention to make any such offer, sale, pledge or disposition, or to enter into any such transaction, swap, hedge or other arrangement, without, in each case, the prior written consent of Credit Suisse Securities (USA) LLC (“Credit Suisse”). In addition, the undersigned agrees that, without the prior written consent of Credit Suisse, it will not, during the Lock-Up Period, make any demand for or exercise any right with respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for the Common Stock.

The Lock-Up Period will commence on the date of this Lock-Up Agreement and continue and include the date 90 days after the public offering date set forth on the final prospectus used to sell the Common Stock (the “Public Offering Date”) pursuant to the Underwriting Agreement, to which Credit Suisse is or is expected to become a party.

Any shares of Common Stock received upon exercise of options granted to the undersigned will also be subject to this Lock-Up Agreement. Deemed dispositions of any restricted stock unit awards granted by the Company to the undersigned upon the vesting or settlement of such awards in accordance with their terms shall not be subject to this Lock-Up Agreement, provided that Common Stock acquired upon the vesting or settlement of such restricted stock unit awards shall be subject to the restrictions imposed by this Lock-Up Agreement.

Notwithstanding the foregoing, the undersigned may (1) effect transactions relating to shares of Common Stock or other securities acquired by the undersigned in open market transactions, provided that that no filing under Section 16(a) of the Securities and Exchange Act of 1934, as amended (the “Exchange Act”) shall be required or shall be made voluntarily in connection with subsequent sales of any shares of Common Stock or other securities acquired in such open market transactions (other than a filing made after the expiration of the Lock-Up Period); (2) transfer shares of Common Stock or securities convertible into or exchangeable or exercisable for Common Stock by gift or gifts, will or intestacy to a member or members of his or her immediate family, to a trust formed for the benefit of any such person, or to a partnership, the partners of which are exclusively the undersigned and/or a member or members of his or her immediate family and/or a charity, provided that (i) the transferee execute a copy of this Lock-Up Agreement, (ii) no filing by any party (donor, donee, transferor or transferee) under Section 16(a) of the Exchange

Act shall be required or shall be made voluntarily in connection with such transfer (other than a filing on Form 5 made after the expiration of the Lock-Up Period), and (iii) no such transfer may include a disposition for value; (3) enter into a trading plan meeting the requirements of Rule 10b5-1 under the Exchange Act during the Lock-Up Period if sales under such plan do not occur until after the expiration of the Lock-Up Period; (4) exercise outstanding options or warrants to purchase Common Stock in accordance with their terms; (5) transfer shares of Common Stock to the Company to satisfy tax withholding obligations pursuant to Company equity compensation plans or arrangements; and (6) transfer shares of Common Stock or securities convertible into or exchangeable or exercisable for Common Stock pursuant to a sale or an offer to purchase 100% of the outstanding Common Stock, whether pursuant to a merger, tender offer or otherwise, to a third party or group of third parties. For purposes of this paragraph, “immediate family” means the spouse, domestic partner, lineal descendants, father, mother, brother or sister of the transferor.

In furtherance of the foregoing, the Company and its transfer agent and registrar are hereby authorized to decline to make any transfer of shares of Common Stock if such transfer would constitute a violation or breach of this Lock-Up Agreement.

This Lock-Up Agreement shall be binding on the undersigned and the successors, heirs, personal representatives and assigns of the undersigned. This Lock-Up Agreement shall lapse and become null and void if (a) the Public Offering Date shall not have occurred on or before September 30, 2012, (b) the Company notifies Credit Suisse in writing that it does not intend to proceed with the Public Offering or (c) if the Underwriting Agreement (other than the provisions thereof which survive termination) shall terminate or be terminated for any reason prior to payment for and delivery of the Common Stock to be sold thereunder. This agreement shall be governed by, and construed in accordance with, the laws of the State of New York.

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