Shares ACHILLION PHARMACEUTICALS, INC. Common Stock UNDERWRITING AGREEMENT

Exhibit 1.1

Shares

ACHILLION PHARMACEUTICALS, INC.

Common Stock

UNDERWRITING AGREEMENT

, 2006

▇▇▇▇▇ AND COMPANY, LLC

CIBC WORLD MARKETS CORP.

JMP SECURITIES LLC

As Representatives of the several Underwriters

c/o Cowen and Company, LLC

▇▇▇▇ ▇▇▇▇▇▇ ▇▇ ▇▇▇ ▇▇▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Dear Sirs:

1. INTRODUCTORY. Achillion Pharmaceuticals, Inc., a Delaware corporation (the “Company”), proposes to sell, pursuant to the terms of this Agreement, to the several underwriters named in Schedule A hereto (the “Underwriters,” or, each, an “Underwriter”), an aggregate of shares of Common Stock, $.001 par value (the “Common Stock”) of the Company. The aggregate of shares so proposed to be sold is hereinafter referred to as the “Firm Stock”. The Company also proposes to sell to the Underwriters, upon the terms and conditions set forth in Section 3 hereof, up to an additional shares of Common Stock (the “Optional Stock”). The Firm Stock and the Optional Stock are hereinafter collectively referred to as the “Stock”. ▇▇▇▇▇ and Company, LLC (“Cowen”), CIBC World Markets Corp. and JMP Securities LLC are acting as representatives of the several Underwriters and in such capacity are hereinafter referred to as the “Representatives.”

The Company hereby confirms its engagement of CIBC World Markets Corp. (“CIBC”) and CIBC hereby confirms its agreement with the Company to render services as a “qualified independent underwriter” within the meaning of Rule 2720 of the Conduct Rules of the National Association of Securities Dealers, Inc. (“NASD”) with respect to the offering of the Stock. CIBC, solely in its capacity as the “qualified independent underwriter” with respect to the offering of the Stock, and not otherwise, is referred to herein as the “QIU.”

2. REPRESENTATIONS AND WARRANTIES OF THE COMPANY. The Company represents and warrants to, and agrees with, the several Underwriters and the QIU that as of the Applicable Time (as defined below in Section 2(c)(i)) and as of the date hereof:

(a) A registration statement on Form S-1 (File No. 333-132921) (the “Initial Registration Statement”) in respect of the Stock has been filed with the Securities and Exchange Commission (the “Commission”); the Initial Registration Statement and any post-effective amendment thereto, each in the form heretofore delivered to you, and, excluding exhibits thereto, to you for each of the other Underwriters, have been declared effective by the Commission in such form; other than a registration statement, if any, increasing the size of the offering (a “Rule 462(b) Registration Statement”), filed pursuant to Rule 462(b) under the Securities Act of 1933, as amended (the “Securities Act”) and the rules and regulations (the “Rules and Regulations”) of the Commission thereunder, which became effective upon filing, no other document with respect to the Initial Registration Statement has heretofore been filed with the Commission; and no stop order suspending the effectiveness of the Initial Registration Statement, any post-effective amendment thereto or the Rule 462(b) Registration Statement, if any, has been issued and no proceeding for that purpose has been initiated or, to the best knowledge of the Company, threatened by the

Commission (any preliminary prospectus included in the Initial Registration Statement or filed with the Commission pursuant to Rule 424(a) of the Rules and Regulations, is hereinafter called a “Preliminary Prospectus”); the various parts of the Initial Registration Statement and the Rule 462(b) Registration Statement, if any, including all exhibits thereto and including the information contained in the form of final prospectus filed with the Commission pursuant to Rule 424(b) under the Securities Act and deemed by virtue of Rule 430A under the Securities Act to be part of the Initial Registration Statement at the time it was declared effective, each as amended at the time such part of the Initial Registration Statement became effective or such part of the Rule 462(b) Registration Statement, if any, became or hereafter becomes effective, are hereinafter collectively called the “Registration Statements”; and such final prospectus, in the form first filed pursuant to Rule 424(b) under the Securities Act, is hereinafter called the “Prospectus”. No document has been or will be prepared or distributed in reliance on Rule 434 under the Securities Act. No order preventing or suspending the use of any Preliminary Prospectus has been issued by the Commission.

(b) The Initial Registration Statement conforms (and the Rule 462(b) Registration Statement, if any, the Prospectus and any amendments or supplements to either of the Registration Statements or the Prospectus, when they become effective or are filed with the Commission, as the case may be, will conform) in all material respects to the requirements of the Securities Act and the Rules and Regulations and do not and will not, as of the applicable effective date (as to the Registration Statements and any amendment thereto) and as of the applicable filing date (as to the Prospectus and any amendment or supplement thereto) contain 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; provided, however, that the foregoing representations and warranties shall not apply to information contained in or omitted from the Registration Statements, any Issuer Free Writing Prospectus (as defined below) or the Prospectus or any such amendment or supplement thereto in reliance upon, and in conformity with, written information furnished to the Company through the Representatives by or on behalf of any Underwriter specifically for inclusion therein, which information the parties hereto agree is limited to the Underwriter’s Information (as defined in Section 17).

(c) As of the Applicable Time (as defined below), neither (x) the Issuer General Use Free Writing Prospectus(es) (as defined below) issued at or prior to the Applicable Time and the Statutory Prospectus (as defined below) as of the Applicable Time and the pricing information included on Schedule B hereto, all considered together (collectively, the “General Disclosure Package”), nor (y) any individual Issuer Limited Use Free Writing Prospectus (as defined below), when considered together with the General Disclosure Package, included or will include any untrue statement of a material fact or omitted or will omit 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.

As used in this subsection and elsewhere in this Agreement:

(i)

“Applicable Time” means (Eastern time) on or such other time as agreed by the Company and the Representatives.

(ii)

“Issuer Free Writing Prospectus” means any “issuer free writing prospectus,” as defined in Rule 433 of the Securities Act (“Rule 433”), relating to the Stock that (a) is required to be filed with the Commission by the Company, (b) is a “road show that is a written communication” within the meaning of Rule 433(d)(8)(i) whether or not required to be filed with the Commission, or (c) is exempt from filing pursuant to Rule 433(d)(5)(i) because it contains a description of the Stock or of the offering that does not reflect the final terms, in each case in the form filed or required to be filed with the Commission or, if not required to be filed, in the form required to be retained in the Company’s records pursuant to Rule 433(g).

(iii)

“Issuer General Use Free Writing Prospectus” means any Issuer Free Writing Prospectus that is intended for general distribution to prospective investors (other than a Bona Fide Electronic Road Show (as defined below)), as evidenced by its being specified in Schedule C hereto.

(iv)

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

(v)

“Statutory Prospectus” as of any time means the prospectus relating to the Stock that is included in the Initial Registration Statement immediately prior to that time.

(d) The Company has complied with the filing requirements under Rule 433(d) of the Securities Act with respect to each Issuer Free Writing Prospectus.

(e) The Company has made available a “bona fide electronic road show,” as defined in Rule 433, in compliance with Rule 433(d)(8)(ii) (the “Bona Fide Electronic Road Show”) such that no filing of any “road show” (as defined in Rule 433(h)) is required in connection with the offering of the Stock.

(f) 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 Stock or until any earlier date that the issuer notified or notifies the Representatives as described in Section 4(b), did not, does not and will not include any information that conflicted, conflicts or will conflict with the information contained in the Registration Statements or the Prospectus, and any preliminary or other prospectus deemed to be a part thereof that has not been superseded or modified, and no Issuer Free Writing Prospectus contained or contains any untrue statement of a material fact or omitted or omits 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 Company has filed and will file with the Commission all Issuer Free Writing Prospectuses in the time and manner required under Rules 163(b)(2) and 433(d) under the Securities Act.

(g) At the time of filing the Initial Registration Statement, the 462(b) Registration Statement, if any, and any post effective amendments thereto, and as of the date hereof (with such date being used as the determination date), the Company was not and is not an “ineligible issuer” (as defined in Rule 405 under the Securities Act, without taking into account any determination by the Commission pursuant to Rule 405 under the Securities Act that it is not necessary that the Company be considered an ineligible issuer), including, without limitation, for purposes of Rules 164 and 433 under the Securities Act with respect to the offering of the Stock as contemplated by the Registration Statements.

(h) The Company has been duly incorporated and is validly existing as a corporation in good standing under the laws of its jurisdiction of incorporation, is duly qualified to do business and is in good standing as a foreign corporation in each jurisdiction in which its ownership or lease of property or the conduct of its businesses requires such qualification, and has all power and authority necessary to own or hold its properties and to conduct the business in which it is engaged, except where the failure to so qualify or have such power or authority would not have, singularly or in the aggregate, a material adverse effect on the condition (financial or otherwise), results of operations, business or prospects of the Company (a “Material Adverse Effect”). The Company has no subsidiaries (as defined in Section 15) and does not own or control, directly or indirectly, any corporation, partnership, limited liability partnership, limited liability company, associations or other entities.

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

(j) The Stock to be issued and sold by the Company to the Underwriters hereunder has been duly and validly authorized and, when issued and delivered against payment therefor as provided herein, will be duly and validly issued, fully paid and nonassessable and free of any preemptive or similar rights and will conform to the description thereof contained in the General Disclosure Package and the Prospectus.

(k) The Company has an authorized capitalization as set forth in the General Disclosure Package and the Prospectus, and all of the issued shares of capital stock of the Company, have been duly and validly authorized and issued, are fully paid and non-assessable, have been issued in compliance with federal and state securities laws, and conform to the description thereof contained in the General Disclosure Package and the Prospectus. None of the outstanding shares of Common Stock was issued in violation of any preemptive rights, rights of first refusal or other similar rights to subscribe for or purchase securities of the Company. There are no authorized or outstanding options, warrants, preemptive rights, rights of first

refusal or other rights to purchase, or equity or debt securities convertible into or exchangeable or exercisable for, any capital stock of the Company other than those accurately described in the General Disclosure Package and the Prospectus. The description of the Company’s stock option, stock bonus and other stock plans or arrangements, and the options or other rights granted thereunder, as described in the General Disclosure Package and the Prospectus accurately and fairly present the information required to be shown with respect to such plans, arrangements, options and rights.

(l) The execution, delivery and performance of this Agreement by the Company and the consummation of the transactions contemplated hereby will not conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company is a party or by which the Company is bound or to which any of the property or assets of the Company is subject, nor will such actions result in any violation of the provisions of the charter or by-laws of the Company or any statute or any order, rule or regulation of any court or governmental agency or body having jurisdiction over the Company or any of its properties or assets.

(m) Except for the registration of the Stock under the Securities Act and such consents, approvals, authorizations, registrations or qualifications as may be required under the Exchange Act and applicable state securities laws, the National Association of Securities Dealers, Inc. and the Nasdaq National Market in connection with the purchase and distribution of the Stock by the Underwriters, no consent, approval, authorization or order of, or filing or registration with, any such court or governmental agency or body is required for the execution, delivery and performance of this Agreement by the Company and the consummation of the transactions contemplated hereby.

(n) PricewaterhouseCoopers LLP, who have expressed their opinions on the audited financial statements and related schedules included in the Registration Statements, the General Disclosure Package and the Prospectus is an independent registered public accounting firm as required by the Securities Act and the Rules and Regulations and by the rules of the Public Company Accounting Oversight Board (the “PCAOB”).

(o) The financial statements, together with the related notes and schedules, included in the General Disclosure Package, the Prospectus and in each Registration Statement fairly present the financial position and the results of operations and changes in financial position of the Company at the respective dates or for the respective periods therein specified. Such statements and related notes and schedules have been prepared in accordance with generally accepted accounting principles applied on a consistent basis except as may be set forth in the General Disclosure Package and the Prospectus. The financial statements, together with the related notes and schedules, included in the General Disclosure Package and the Prospectus comply in all material respects with the Securities Act and the Rules and Regulations thereunder. The summary and selected financial data included in the Registration Statements, the General Disclosure Package and the Prospectus present fairly the information shown therein and have been compiled on a basis consistent with that of the audited financial information included in the Registration Statements, the General Disclosure Package and the Prospectus. No other financial statements (historical or pro forma) or supporting schedules or exhibits are required by the Securities Act or the Rules and Regulations thereunder to be included in the General Disclosure Package and the Prospectus.

(p) The Company has not sustained, since the date of the latest audited financial statements included in the General Disclosure Package and the Prospectus, any material loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or decree, otherwise than as set forth or contemplated in the Prospectus; and, since such date, there has not been any change in the capital stock or long-term debt of the Company (other than (i) issuance of Common Stock, if any, pursuant to the exercise of outstanding options or warrants described in the prospectus and (ii) the issuance of Series C-2 Convertible Preferred Stock and $5,000,000 in promissory notes on May 12, 2006, as described in the Prospectus) or any material adverse change, or any development involving a prospective material adverse change, in or affecting the business, financial position, stockholders’ equity or results of operations of the Company, otherwise than as set forth or contemplated in the Prospectus.

(q) Except as set forth in the Prospectus, there is no legal or governmental proceeding pending to which the Company is a party or of which any property or assets of the Company is the subject which is required to be described in the Registration Statement, the General Disclosure Package or the Prospectus and is not described therein, or which, singularly or in the aggregate, if determined adversely to the Company, would reasonably be expected to have a Material Adverse Effect or would prevent or adversely affect the ability of the Company to perform its obligations under this Agreement; and to the best of the Company’s knowledge, no such proceedings are threatened or contemplated by governmental authorities or threatened by others.

(r) The Company is not (i) in violation of its charter or by-laws, (ii) in default in any respect, and no event has occurred which, with notice or lapse of time or both, would constitute such a default, in the due performance or observance of any term, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which it is a party or by which it is bound or to which any of its property or assets is subject or (iii) in violation in any respect of any law, ordinance, governmental rule, regulation or court decree to which it or its property or assets may be subject, except, with respect to clauses (ii) and (iii), any violations or defaults which, singularly or in the aggregate, would not have a Material Adverse Effect.

(s) The Company possesses all licenses, certificates, authorizations and permits issued by, and has made all declarations and filings with, the appropriate state, federal and foreign regulatory agencies or bodies which are necessary or desirable for the ownership of its properties and the conduct of its business as described in the General Disclosure Package and the Prospectus except where any failures to possess or make the same, singularly or in the aggregate, would not have a Material Adverse Effect, including without limitation all such certificates, authorizations, filings, submissions and permits required by the United States Food and Drug Administration (the “FDA”) or any other federal, state or foreign agencies or bodies engaged in the regulation of pharmaceuticals or biohazardous materials, and the Company has not received notification of any revocation or modification of any such license, authorization or permit, and has no reason to believe that any such license, certificate, authorization or permit will not be renewed and, to the best knowledge of the Company, no party granting any such license, authorization or permit is considering limiting, suspending or revoking the same in any material respect. The Company has not failed to submit to the FDA an Investigational New Drug Application for each new drug for which it is sponsoring a clinical trial, except where such failure would not, singly or in the aggregate, have a Material Adverse Effect; all such submissions were in material compliance with applicable laws when submitted and no material deficiencies have been asserted by the FDA with respect to any such submissions, except any deficiencies which would not, singly or in the aggregate, have a Material Adverse Effect.

(t) The tests and preclinical studies and clinical trials conducted by or on behalf of the Company that are described in the Registration Statements, the General Disclosure Package and the Prospectus were and, if still pending, are being conducted in all material respects in accordance with experimental protocols, procedures and controls pursuant to, where applicable, accepted professional and scientific standards for products or product candidates comparable to those being developed by the Company; the descriptions of the results of such studies, tests and trials contained in the Registration Statements, the General Disclosure Package and the Prospectus do not contain any misstatement of a material fact or omit to state a material fact necessary to make such statements not misleading. There have been no studies, tests or trials conducted by or on behalf of the Company not described in the Registration Statements, the General Disclosure Package and the Prospectus the results of which reasonably call into question the results of the studies, tests and trials described in the Registration Statements, the General Disclosure Package or the Prospectus; and the Company has not received any notices or correspondence from the FDA or any foreign, state or local governmental body exercising comparable authority or any Institutional Review Board or comparable authority requiring or requesting the termination, suspension or material modification of any studies, tests or preclinical or clinical trials conducted by or on behalf of the Company which termination, suspension or material modification would reasonably be expected to have a Material Adverse Effect on the Company.

(u) All statistical or market-related data included in the Registration Statements, the General Disclosure Package or the Prospectus are based on or derived from sources that the Company believes to be

reliable and accurate, and the Company has obtained the written consent to the use of such data from such sources to the extent required.

(v) The Company is not, nor, after giving effect to the offering of the Stock and the application of the proceeds thereof as described in the Prospectus, will become an “investment company” within the meaning of the Investment Company Act of 1940, as amended and the rules and regulations of the Commission thereunder.

(w) Neither the Company nor any of its officers, directors or affiliates has taken or will take, directly or indirectly, any action designed or intended to stabilize or manipulate the price of any security of the Company, or which caused or resulted in, or which might in the future reasonably be expected to cause or result in, stabilization or manipulation of the price of any security of the Company.

(x) Except as described in the Registration Statements, the General Disclosure Package and the Prospectus, (a) the Company owns, possesses or has adequate rights to use the Company Intellectual Property (as defined below), (b) the Company has not received any notice of any infringement of, or conflict with, any intellectual property (as defined below) of any third party, (c) the Company is not aware of any third party, including any academic or governmental organization, which possesses or could obtain rights to the Company Intellectual Property which, if exercised, could enable such party to develop products competitive with those of the Company, and (d) the Company is not obligated to pay a material royalty, grant a material license, or provide other material consideration to any third party in connection with the Company Intellectual Property. Except as described in the Registration Statements, the General Disclosure Package and the Prospectus or as would not have a Material Adverse Effect, (x) the Company is not aware of any facts or circumstances that constitute an infringement by the Company of any valid claim of a third-party patent, (y) the Company is not aware of any facts or circumstances that constitute an infringement by the Company of, or conflict with, any non-patented intellectual property right of any third party, and (z) the Company is not aware of any facts or circumstances that would render any Company Intellectual Property invalid or unenforceable. For purposes of this Agreement, “intellectual property” means patents, patent rights, patent applications, licenses, inventions, copyrights, know how (including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures), trademarks, service marks and trade names, and “Company Intellectual Property” means intellectual property that is necessary to carry on the business now operated and as planned to be operated by the Company as described in the Prospectus.

(y) The Company has duly and properly filed or caused to be filed with the United States Patent and Trademark Office (the “PTO”) and applicable foreign and international patent authorities all patent applications owned by the Company (the “Company Patent Applications”). To the knowledge of the Company, the Company has complied with the PTO’s duty of candor and disclosure for the Company Patent Applications and has made no material misrepresentation in the Company Patent Applications. To the knowledge of the Company, the Company has complied with the duty of candor and disclosure for the Company Patent Applications pending in countries outside the United States. The Company is not aware of any information material to a determination of patentability regarding the Company Patent Applications not called to the attention of the PTO or similar foreign authority. The Company is not aware of any information not called to the attention of the PTO or similar foreign authority which would preclude the grant of a patent for the Company Patent Applications. The Company has no knowledge of any information which would preclude the Company from having clear title to the Company Patent Applications.

(z) The Company has good and marketable title in fee simple to, or has valid rights to lease or otherwise use, all items of real or personal property which are material to the business of the Company, in each case free and clear of all liens, encumbrances, claims and defects that may result in a Material Adverse Effect.

(aa) No labor disturbance by the employees of the Company exists or, to the best of the Company’s knowledge, is imminent which might be expected to have a Material Adverse Effect. The Company is not aware that any key employee or significant group of employees of the Company plans to terminate employment with the Company.

(bb) No “prohibited transaction” (as defined in Section 406 of the Employee Retirement Income Security Act of 1974, as amended, including the regulations and published interpretations thereunder (“ERISA”), or Section 4975 of the Internal Revenue Code of 1986, as amended from time to time (the “Code”)) or “accumulated funding deficiency” (as defined in Section 302 of ERISA) or any of the events set forth in Section 4043(b) of ERISA (other than events with respect to which the 30-day notice requirement under Section 4043 of ERISA has been waived) has occurred with respect to any employee benefit plan which could have a Material Adverse Effect; each employee benefit plan is in compliance in all material respects with applicable law, including ERISA and the Code; the Company has not incurred and does not expect to incur liability under Title IV of ERISA with respect to the termination of, or withdrawal from, any “pension plan”; and each “pension plan” (as defined in ERISA) for which the Company would have any liability that is intended to be qualified under Section 401(a) of the Code is so qualified in all material respects and nothing has occurred, whether by action or by failure to act, which could cause the loss of such qualification.

(cc) The Company is in compliance with all foreign, federal, state and local rules, laws and regulations relating to the use, treatment, storage and disposal of hazardous or toxic substances or waste and protection of health and safety or the environment which are applicable to their businesses, except where the failure to comply would not, singularly or in the aggregate, have a Material Adverse Effect. There has been no storage, generation, transportation, handling, treatment, disposal, discharge, emission, or other release of any kind of toxic or other wastes or other hazardous substances by, due to, or caused by the Company (or, to the best of the Company’s knowledge, any other entity for whose acts or omissions the Company is or may be liable) upon any of the property now or previously owned or leased by the Company, or upon any other property, in violation of any statute or any ordinance, rule, regulation, order, judgment, decree or permit or which would, under any statute or any ordinance, rule (including rule of common law), regulation, order, judgment, decree or permit, give rise to any liability, except for any violation or liability which would not have, singularly or in the aggregate with all such violations and liabilities, a Material Adverse Effect; there has been no disposal, discharge, emission or other release of any kind onto such property or into the environment surrounding such property of any toxic or other wastes or other hazardous substances with respect to which the Company has knowledge, except for any such disposal, discharge, emission, or other release of any kind which would not have, singularly or in the aggregate with all such discharges and other releases, a Material Adverse Effect.

(dd) The Company (i) has filed with all necessary federal, state and foreign income and franchise tax returns, (ii) has paid all federal state, local and foreign taxes due and payable for which it is liable, and (iii) does not have any tax deficiency or claims outstanding or assessed or, to the best of the Company’s knowledge, proposed against it which could reasonably be expected to have a Material Adverse Effect.

(ee) The Company carries, or is covered by, insurance in such amounts and covering such risks as is adequate for the conduct of its business and the value of its properties and as is customary for companies engaged in similar businesses in similar industries.

(ff) The Company maintains a system of internal accounting controls sufficient to provide reasonable assurances that (i) transactions are executed in accordance with management’s general or specific authorization; (ii) transactions are recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain accountability for assets; (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 existing assets at reasonable intervals and appropriate action is taken with respect to any differences.

(gg) The minute books of the Company have been made available to the Underwriters and counsel for the Underwriters, and such books (i) contain a complete summary of all meetings and actions of the board of directors (including each board committee) and shareholders of the Company since the time of its respective incorporation through the date of the latest meeting and action, and (ii) accurately in all material respects reflect all transactions referred to in such minutes.

(hh) There is no franchise, lease, contract, agreement or document required by the Securities Act or by the Rules and Regulations to be described in the General Disclosure Package and the Prospectus or to be

filed as an exhibit to the Registration Statements which is not described or filed therein as required; and all descriptions of any such franchises, leases, contracts, agreements or documents contained in the Registration Statements are accurate and complete descriptions of such documents in all material respects. Other than as described in the General Disclosure Package and the Prospectus, (i) no such franchise, lease, contract or agreement has been suspended or terminated for convenience or default by the Company or any of the other parties thereto, (ii) the Company has not received notice of any such pending or threatened suspension or termination and (iii) to the best knowledge of the Company no party to any such franchise, lease, contract or agreement is contemplating suspending or terminating such franchise, lease, contract or agreement, except for such pending or threatened suspensions or terminations that would not reasonably be expected to, singularly or in the aggregate, have a Material Adverse Effect.

(ii) No relationship, direct or indirect, exists between or among the Company on the one hand, and the directors, officers, stockholders, customers or suppliers of the Company on the other hand, which is required to be described in the General Disclosure Package and the Prospectus and which is not so described.

(jj) No person or entity has the right to require registration of shares of Common Stock or other securities of the Company because of the filing or effectiveness of the Registration Statements or otherwise, except for persons and entities who have expressly waived such right or who have been given timely and proper notice and have failed to exercise such right within the time or times required under the terms and conditions of such right.

(kk) The Company does not own any “margin securities” as that term is defined in Regulation U of the Board of Governors of the Federal Reserve System (the “Federal Reserve Board”), and none of the proceeds of the sale of the Stock will be used, directly or indirectly, for the purpose of purchasing or carrying any margin security, for the purpose of reducing or retiring any indebtedness which was originally incurred to purchase or carry any margin security or for any other purpose which might cause any of the Securities to be considered a “purpose credit” within the meanings of Regulation T, U or X of the Federal Reserve Board.

(ll) The Company is not a party to any contract, agreement or understanding with any person that would give rise to a valid claim against the Company or the Underwriters for a brokerage commission, finder’s fee or like payment in connection with the offering and sale of the Stock.

(mm) No forward-looking statement (within the meaning of Section 27A of the Securities Act and Section 21E of the Exchange Act) contained in the General Disclosure Package or the Prospectus has been made or reaffirmed without a reasonable basis or has been disclosed other than in good faith.

(nn) The Stock has been approved for listing subject to notice of issuance on the Nasdaq Stock Market’s National Market (“Nasdaq”), and the Company is in compliance in all material respects with all corporate governance requirements set forth in the Nasdaq Marketplace Rules that are in effect and applicable to the Company as of the date hereof. A registration statement has been filed on Form 8-A pursuant to Section 12 of the Exchange Act, which registration statement complies in all material respects with the Exchange Act.

(oo) The Company is in compliance with all applicable provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act of 2002 and all rules and regulations promulgated thereunder or implementing the provisions thereof (the “▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act”) that are in effect and applicable to the Company as of the date hereof.

(pp) Neither the Company, nor, to the best of the Company’s knowledge, any employee or agent of the Company, has made any contribution or other payment to any official of, or candidate for, any federal, state or foreign office in violation of any law or of the character required to be disclosed in the General Disclosure Package and the Prospectus.

(qq) There are no transactions, arrangements or other relationships between the Company and any of its affiliates (as such term is defined in Rule 405 of the Securities Act) or any unconsolidated entity, including, but not limited to, any structure finance, special purpose or limited purpose entity that could reasonably be

expected to materially affect the Company’s liquidity or the availability of or requirements for its capital resources required to be described in the General Disclosure Package and the Prospectus which have not been described as required.

(rr) There are no outstanding loans, advances (except normal advances for business expense in the ordinary course of business) or guarantees or indebtedness by the Company to or for the benefit of any of the officers or directors of the Company, except as disclosed in the General Disclosure Package and the Prospectus.

Any certificate signed by or on behalf of the Company and delivered to the Representatives or to counsel for the Underwriters shall be deemed to be a representation and warranty by the Company to each Underwriter as to the matters covered thereby.

3. PURCHASE SALE AND DELIVERY OF OFFERED SECURITIES. On the basis of the representations, warranties and agreements herein contained, but subject to the terms and conditions herein set forth, the Company agrees to sell to each Underwriter, and each Underwriter agrees, severally and not jointly, to purchase from the Company that number of shares of Firm Stock (rounded up or down, as determined by ▇▇▇▇▇ in its discretion, in order to avoid fractions) obtained by multiplying shares of Firm Stock by a fraction the numerator of which is the number of shares of Firm Stock set forth opposite the name of such Underwriter in Schedule A hereto and the denominator of which is the total number of shares of Firm Stock.

The purchase price per share to be paid by the Underwriters to the Company for the Stock will be $ per share (the “Purchase Price”).

The Company will deliver the Firm Stock to the Representatives for the respective accounts of the several Underwriters (in the form of definitive certificates, issued in such names and in such denominations as the Representatives may direct by notice in writing to the Company given at or prior to 12:00 Noon, New York time, on the second full business day preceding the First Closing Date (as defined below) against payment of the aggregate Purchase Price therefor by wire transfer to an account at a bank acceptable to ▇▇▇▇▇, payable to the order of the Company, all at the offices of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., ▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇▇, ▇▇ ▇▇▇▇▇. Time shall be of the essence, and delivery at the time and place specified pursuant to this Agreement is a further condition of the obligations of each Underwriter hereunder. The time and date of the delivery and closing shall be at 10:00 A.M., New York time, on , 2006, in accordance with Rule 15c6-1 of the Exchange Act. The time and date of such payment and delivery are herein referred to as the “First Closing Date”. The First Closing Date and the location of delivery of, and the form of payment for, the Firm Stock may be varied by agreement between among the Company and ▇▇▇▇▇.

The Company shall make the certificates for the Stock available to the Representatives for examination on behalf of the Underwriters in New York, New York at least twenty-four hours prior to the First Closing Date.

For the purpose of covering any over-allotments in connection with the distribution and sale of the Firm Stock as contemplated by the Prospectus, the Underwriters may purchase all or less than all of the Optional Stock. The price per share to be paid for the Optional Stock shall be the Purchase Price. The Company agrees to sell to the Underwriters the number of shares of Optional Stock specified in the written notice by ▇▇▇▇▇ described below and the Underwriters agree, severally and not jointly, to purchase such shares of Optional Stock. The option granted hereby may be exercised as to all or any part of the Optional Stock at any time, and from time to time, not more than thirty (30) days subsequent to the date of this Agreement. No Optional Stock shall be sold and delivered unless the Firm Stock previously has been, or simultaneously is, sold and delivered. The right to purchase the Optional Stock or any portion thereof may be surrendered and terminated at any time upon notice by ▇▇▇▇▇ to the Company.

The option granted hereby may be exercised by written notice being given to the Company by ▇▇▇▇▇ setting forth the number of shares of the Optional Stock to be purchased by the Underwriters and the date and time for delivery of and payment for the Optional Stock. Each date and time for delivery of and payment for the Optional Stock (which may be the First Closing Date, but not earlier) is herein called the “Option Closing Date” and shall in no event be earlier than two (2) business days nor later than five (5) business days after written notice is given. (The Option Closing Date and the First Closing Date are herein called the “Closing Dates”.)

The Company will deliver the Optional Stock to the Underwriters (in the form of definitive certificates, issued in such names and in such denominations as the Representatives may direct by notice in writing to the Company given at or prior to 12:00 Noon, New York time, on the second full business day preceding the Option Closing Date against payment of the aggregate Purchase Price therefor in federal (same day) funds by certified or official bank check or checks or wire transfer to an account at a bank acceptable to ▇▇▇▇▇ payable to the order of the Company all at the offices of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., ▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇, ▇▇▇▇▇▇, ▇▇ ▇▇▇▇▇. Time shall be of the essence, and delivery at the time and place specified pursuant to this Agreement is a further condition of the obligations of each Underwriter hereunder. The Company shall make the certificates for the Optional Stock available to the Representatives for examination on behalf of the Underwriters in New York, New York not later than 10:00 A.M., New York Time, on the business day preceding the Option Closing Date. The Option Closing Date and the location of delivery of, and the form of payment for, the Optional Stock may be varied by agreement between the Company and ▇▇▇▇▇.

The several Underwriters propose to offer the Stock for sale upon the terms and conditions set forth in the Prospectus.

4. FURTHER AGREEMENTS OF THE COMPANY. The Company agrees with the several Underwriters and the QIU that:

(a) The Company will prepare the Rule 462(b) Registration Statement, if necessary, in a form approved by the Representatives and file such Rule 462(b) Registration Statement with the Commission on the date hereof; prepare the Prospectus in a form approved by the Representatives and file such Prospectus pursuant to Rule 424(b) under the Securities Act not later than the second business day following the execution and delivery of this Agreement; make no further amendment or any supplement to the Registration Statements or to the Prospectus prior to the Option Closing Date to which the Representatives shall reasonably object by notice to the Company after a reasonable period to review; advise the Representatives, promptly after it receives notice thereof, of the time when any amendment to either Registration Statement has been filed or becomes effective or any supplement to the General Disclosure Package, the Prospectus or any amended Prospectus has been filed and to furnish the Representatives with copies thereof; advise the Representatives, promptly after it receives notice thereof, of the issuance by the Commission of any stop order or of any order preventing or suspending the use of any Preliminary Prospectus, Issuer Free Writing Prospectus or the Prospectus, of the suspension of the qualification of the Stock for offering or sale in any jurisdiction, of the initiation or threatening of any proceeding for any such purpose, or of any request by the Commission for the amending or supplementing of the Registration Statements, the General Disclosure Package or the Prospectus or for additional information; and, in the event of the issuance of any stop order or of any order preventing or suspending the use of any Preliminary Prospectus or the Prospectus or suspending any such qualification, use promptly its best efforts to obtain its withdrawal.

(b) If at any time prior to the expiration of nine months after the effective date of the Initial Registration Statement when a prospectus relating to the Stock is required to be delivered any event occurs as a result of which the Prospectus as then amended or supplemented would include any untrue statement of a material fact, or omit to state any material fact necessary to make the statements therein, in light of the circumstances under which they were made, not misleading, or if it is necessary at any time to amend the Prospectus to comply with the Securities Act, the Company will promptly notify the Representatives thereof and upon their request will prepare an amended or supplemented Prospectus which will correct such statement or omission or effect such compliance. The Company will furnish without charge to each Underwriter and to any dealer in securities as many copies as the Representatives may from time to time reasonably request of such amended or supplemented Prospectus; and in case any Underwriter is required to deliver a prospectus relating to the Stock nine months or more after the effective date of the Initial Registration Statement, the Company upon the request of the Representatives and at the expense of such Underwriter will prepare promptly an amended or supplemented Prospectus as may be necessary to permit compliance with the requirements of Section 10(a)(3) of the Securities Act. 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 contained in the Registration Statement relating to the Stock or included or 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, prevailing at that subsequent time, not misleading, the Company will promptly notify the Representatives and will promptly amend or supplement, at its own expense, such Issuer Free Writing Prospectus to eliminate or correct such conflict, untrue statement or omission.

(c) To furnish promptly to each of the Representatives and to counsel for the Underwriters a signed copy of each of the Registration Statements as originally filed with the Commission, and each amendment thereto filed with the Commission, including all consents and exhibits filed therewith.

(d) To deliver promptly to the Representatives in New York City such number of the following documents as the Representatives shall reasonably request: (i) conformed copies of the Registration Statements as originally filed with the Commission and each amendment thereto (in each case excluding exhibits), (ii) each Preliminary Prospectus, (iii) each Issuer Free Writing Prospectus and (iv) the Prospectus (not later than 10:00 A.M., New York time, of the business day following the execution and delivery of this Agreement) and any amended or supplemented Prospectus (not later than 10:00 A.M., New York City time, on the business day following the date of such amendment or supplement).

(e) To make generally available to its shareholders as soon as practicable, but in any event not later than eighteen months after the effective date of the Registration Statement (as defined in Rule 158(c) under the Securities Act), an earnings statement of the Company and its subsidiaries (which need not be audited) complying with Section 11(a) of the Securities Act and the Rules and Regulations (including, at the option of the Company, Rule 158).

(f) The Company will promptly take from time to time such actions as the Representatives may reasonably request to qualify the Stock for offering and sale under the securities or Blue Sky laws of such jurisdictions as the Representatives may designate and to continue such qualifications in effect for so long as required for the distribution of the Stock; provided, that the Company shall not be obligated to qualify as a foreign corporation in any jurisdiction in which it is not so qualified or to file a general consent to service of process in any jurisdiction.

(g) During the period of five years from the date hereof, the Company will deliver to the Representatives and, upon request, to each of the other Underwriters, (i) as soon as they are available, copies of all reports or other communications furnished to shareholders and (i) as soon as they are available, copies of any reports and financial statements furnished or filed with the Commission pursuant to the Exchange Act or any national securities exchange or automatic quotation system on which the Stock is listed or quoted. The ▇▇▇▇▇ filing or furnishing of any such report, communication or financial statement with the Commission under Section 13(a), 13(c), 14 or 15(d) of the Exchange Act shall be deemed to satisfy the requirement to deliver such report, communication or financial statement to the Representatives or Underwriters.

(h) The Company will not directly or indirectly offer, sell, assign, transfer, pledge, contract to sell, or otherwise dispose of any shares of Common Stock or securities convertible into or exercisable or exchangeable for Common Stock for a period of 180 days from the date of the Prospectus without the prior written consent of ▇▇▇▇▇ other than the Company’s sale of the Stock hereunder and the issuance of shares pursuant to employee benefit plans, qualified stock option plans or other employee compensation plans existing on the date hereof or pursuant to currently outstanding options, warrants or rights, provided, however, that if (i) the Company issues an earnings release or material news or a material event relating to the Company occurs during the last 17 days of the lock-up period, or (ii) prior to the expiration of the lock-up period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the lock-up period, the restrictions imposed by this section shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event. The Company also agrees that during such period, the Company will not file any registration statement, preliminary prospectus or prospectus, or any amendment or supplement thereto, under the Securities Act for any such transaction or which registers, or offers for sale, Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock, except for a registration statement on Form S-8 relating to employee benefit plans. The Company will cause each officer, director and shareholder listed in Schedule D to furnish to the Representatives, prior to the First Closing Date, a letter, substantially in the form of Exhibit I hereto, pursuant to which each such person

shall agree not to directly or indirectly offer, sell, assign, transfer, pledge, contract to sell, or otherwise dispose of any shares of Common Stock or securities convertible into or exercisable or exchangeable for Common Stock for the period set forth therein, without the prior written consent of ▇▇▇▇▇.

(i) The Company will supply the Representatives with copies of all correspondence to and from, and all documents issued to and by, the Commission in connection with the registration of the Stock under the Securities Act.

(j) Prior to each of the Closing Dates the Company will furnish to the Representatives, as soon as they have been prepared, copies of any unaudited interim consolidated financial statements of the Company for any periods subsequent to the periods covered by the financial statements appearing in the Registration Statement and the Prospectus.

(k) Prior to each of the Closing Dates, the Company will not issue any press release or other communication directly or indirectly or hold any press conference with respect to the Company, its condition, financial or otherwise, or earnings, business affairs or business prospects (except for routine oral marketing communications in the ordinary course of business and consistent with the past practices of the Company and of which the Representatives are notified), without first providing written notification to the Representatives.

(l) In connection with the offering of the Stock, until ▇▇▇▇▇ shall have notified the Company of the completion of the resale of the Stock, the Company will not, and will cause its affiliated purchasers (as defined in Regulation M under the Exchange Act) not to, either alone or with one or more other persons, bid for or purchase, for any account in which it or any of its affiliated purchasers has a beneficial interest, any Stock, or attempt to induce any person to purchase any Stock; and not to, and to cause its affiliated purchasers not to, make bids or purchase for the purpose of creating actual, or apparent, active trading in or of raising the price of the Stock.

(m) The Company will not take any action prior to the Option Closing Date which would require the Prospectus to be amended or supplemented pursuant to Section 4(b).

(n) The Company shall at all times comply in all material respects with all applicable provisions of the ▇▇▇▇▇▇▇▇-▇▇▇▇▇ Act in effect from time to time.

(o) The Company will apply the net proceeds from the sale of the Stock as set forth in the Prospectus under the heading “Use of Proceeds”.

(p) The Company represents and agrees that, unless it obtains the prior consent of the Representatives, and each Underwriter represents and agrees that, unless it obtains the prior consent of the Company and the Representatives, it has not made and will not make any offer relating to the Stock that would constitute an “issuer free writing prospectus,” as defined in Rule 433, 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 Representatives or by the Company and the Representatives, as the case may be, is hereinafter referred to as a “Permitted Free Writing Prospectus.” The Company represents that it has treated or 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 Rule 433 applicable to any Permitted Free Writing Prospectus, including timely filing with the Commission where required, legending and record keeping.

5. PAYMENT OF EXPENSES. The Company agrees with the Underwriter and the QIU to pay (a) the costs incident to the authorization, issuance, sale, preparation and delivery of the Stock and any taxes payable in that connection; (b) the costs incident to the Registration of the Stock under the Securities Act; (c) the costs incident to the preparation, printing and distribution of the Registration Statement, Preliminary Prospectus, Prospectus, and Permitted Free Writing Prospectus any amendments and exhibits thereto and any costs associated with electronic delivery of any of the foregoing by the Underwriters to any investor (d) the costs of printing, reproducing and

distributing, the “Agreement Among Underwriters” between the Representatives and the Underwriters, the Master Selected Dealers’ Agreement, the Underwriters’ Questionnaire and this Agreement by mail, telex or other means of communications; (e) the fees and expenses (including related fees and expenses of counsel for the Underwriters) incurred in connection with filings made with the National Association of Securities Dealers; (f) any applicable listing or other fees; (g) the fees and expenses of qualifying the Stock under the securities laws of the several jurisdictions as provided in Section 4(f) and of preparing, printing and distributing Blue Sky Memoranda and Legal Investment Surveys (including related fees and expenses of counsel to the Underwriters); (h) all fees and expenses of the registrar and transfer agent of the Stock; (i) any costs and expenses associated with the reforming of any contracts for sale of the Stock made by the Underwriters caused by a breach of the representations contained in Section 2(c), (j) the fees and expenses (including related reasonable fees and disbursements of its counsel) of the QIU incurred by the QIU in its capacity as a “qualified independent underwriter” within the meaning of Rule 2720 of the NASD’s Conduct Rules with respect to the offering of the Stock and (k) all other costs and expenses incident to the performance of the obligations of the Company under this Agreement (including, without limitation, the fees and expenses of the Company’s counsel and the Company’s independent accountants); provided, that, except as otherwise provided in this Section 5 and in Section 9, the Underwriters shall pay their own costs and expenses, including the fees and expenses of their counsel, any transfer taxes on the Stock which they may sell and the expenses of advertising any offering of the Stock made by the Underwriters.

6. CONDITIONS OF UNDERWRITERS’ OBLIGATIONS. The respective obligations of the several Underwriters hereunder are subject to the accuracy, when made and on each of the Closing Dates, of the representations and warranties of the Company contained herein, to the accuracy of the statements of the Company made in any certificates pursuant to the provisions hereof, to the performance by the Company of their obligations hereunder, and to each of the following additional terms and conditions:

(a) No stop order suspending the effectiveness of either the Registration Statements shall have been issued and no proceedings for that purpose shall have been initiated or threatened by the Commission, and any request for additional information on the part of the Commission (to be included in the Registration Statements or the Prospectus or otherwise) shall have been complied with to the reasonable satisfaction of the Representatives. The Rule 462(b) Registration Statement, if any, and the Prospectus shall have been timely filed with the Commission in accordance with Section 4(a).

(b) None of the Underwriters shall have discovered and disclosed to the Company on or prior to the Closing Date that any Registration Statement or any amendment or supplement thereto contains an untrue statement of a fact which, in the opinion of counsel for the Underwriters, is material or omits to state any fact which, in the opinion of such counsel, is material and is required to be stated therein or is necessary to make the statements therein not misleading, or that the General Disclosure Package, any Issuer Free Writing Prospectus or the Prospectus or any amendment or supplement thereto contains an untrue statement of fact which, in the opinion of such counsel, is material or omits to state any fact which, in the opinion of such counsel, is material and is necessary in order to make the statements, in light of the circumstances in which they were made, not misleading.

(c) All corporate proceedings and other legal matters incident to the authorization, form and validity of each of this Agreement, the Stock, the Registration Statement and the Prospectus and all other legal matters relating to this Agreement and the transactions contemplated hereby shall be reasonably satisfactory in all material respects to counsel for the Underwriters, and the Company shall have furnished to such counsel all documents and information that they may reasonably request to enable them to pass upon such matters.

(d) ▇▇▇▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇ and ▇▇▇▇ LLP shall have furnished to the Representatives such counsel’s written opinion, as counsel to the Company, addressed to the Underwriters and dated the Closing Date, in form and substance reasonably satisfactory to the Representatives and their counsel.

(e) (i)

▇▇▇▇▇▇ ▇▇▇▇▇▇ ▇▇▇▇▇▇▇▇▇ ▇▇▇▇ and ▇▇▇▇ LLP shall have furnished to the Representatives such counsel’s written opinion, as intellectual property counsel to the Company, addressed to the Underwriters and dated the Closing Date, in form and substance reasonably satisfactory to the Representatives and their counsel.

(ii)

▇▇▇▇▇▇ ▇▇▇▇▇▇▇ LLP shall have furnished to the Representatives such counsel’s written opinion, as intellectual property counsel to the Company, addressed to the Underwriters and dated the Closing Date, in form and substance reasonably satisfactory to the Representatives and their counsel.

(f) The Company shall have furnished to the Representatives a certificate, dated the Closing Date, of its Vice President, Regulatory Affairs stating that:

(i)

The Company is not in breach or violation of, or in default under, the Federal Food, Drug and Cosmetic Act or the regulations promulgated thereunder or any comparable foreign law or regulation relating to the regulation of pharmaceutical products (the “Food & Drug Laws”) or rule or any decree, judgment or order applicable to the Company relating to Food & Drug Laws, except where such breach, violation or default would not, individually or in the aggregate, have a Material Adverse Effect.

(ii)

The Company has all licenses, certificates, authorizations, permits, consents and approvals (collectively “Consents”) and has made all necessary declarations and filings required under any Food & Drug Laws relating to the regulation of pharmaceutical products, including without limitation all such Consents required by the FDA, all of such Consents are valid and in full force and effect; except where such failure would not, individually or in the aggregate have a Material Adverse Effect; all such Consents are free and clear of any restrictions or conditions that are in addition to, or materially different from, those that may be applicable to similarly situated companies; and the Company is not in violation of, or in default under, nor has the Company received notification of any proceedings relating to revocation or modification of any such Consent or any Food & Drug Law or any decree, order or judgment applicable to the Company relating thereto and the Company has no reason to believe that any such Consent will not be renewed.

(iii)

The Company is in compliance with all applicable Food & Drug Laws governing its business; except where such failure would not, individually or in the aggregate have a Material Adverse Effect; all preclinical and clinical studies undertaken to support approval of products for commercialization have been conducted, to the knowledge of the undersigned, in compliance with all applicable federal, state or foreign laws, rules, orders or regulations, including current Good Laboratory and Good Clinical Practices in all material respects, no filing or submission to the FDA or any comparable foreign regulatory body that is intended to be the basis for any approval contains, to the knowledge of the undersigned, any material omission or material misstatement of fact or other false information.

(iv)

The Prospectus does not contain any untrue statement of a material fact related to FDA matters or omit to state a material fact relating to FDA matters necessary to make the statements therein, in light of the circumstances under which they were made, not misleading, and the General Disclosure Package and the Bona Fide Electronic Road Show, as of the Applicable Time, did not contain any untrue statement of a material fact related to FDA matters or omit to state any material fact related to FDA matters required to be stated therein or necessary in order to make the statements therein, in light of the circumstances under which they were made, not misleading.

(g) The Representatives shall have received from Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C. counsel for the Underwriters, such opinion or opinions, dated the Closing Date, with respect to such matters as the Underwriters may reasonably require, and the Company shall have furnished to such counsel such documents as they request for enabling them to pass upon such matters.

(h) At the time of the execution of this Agreement, the Representatives shall have received from PricewaterhouseCoopers LLP a letter, addressed to the Underwriters and dated such date, in form and substance satisfactory to the Representatives (i) confirming that they are an independent registered public

accounting firm with respect to the Company and its subsidiaries within the meaning of the Securities Act and the Rules and Regulations and the rules of the PCAOB and (ii) stating the conclusions and findings of such firm with respect to the financial statements and certain financial information contained or incorporated by reference in the General Disclosure Package and the Statutory Prospectus.

(i) On the Closing Date, the Representatives shall have received a letter (the “bring-down letter”) from PricewaterhouseCoopers LLP addressed to the Underwriters and dated the Closing Date confirming, as of the date of the bring-down letter (or, with respect to matters involving changes or developments since the respective dates as of which specified financial information is given in the Prospectus as of a date not more than three business days prior to the date of the bring-down letter), the conclusions and findings of such firm with respect to the financial information and other matters covered by its letter delivered to the Representatives concurrently with the execution of this Agreement pursuant to Section 6(h).

(j) The Company shall have furnished to the Representatives a certificate, dated the Closing Date, of its President and Chief Executive Officer and its Vice President, Finance and Administration stating that (i) such officers have carefully examined the Registration Statements, the General Disclosure Package and the Prospectus and, in their opinion, the Registration Statements as of their respective effective dates, the Prospectus, as of each such effective date, and the General Disclosure Package, as of the Applicable Time, did not include any untrue statement of a material fact and did not omit to state a material fact required to be stated therein or necessary to make the statements therein not misleading, (ii) since the effective date of the Initial Registration Statement no event has occurred which should have been set forth in a supplement or amendment to the Registration Statements, the General Disclosure Package or the Prospectus, (iii) to the best of their knowledge after reasonable investigation, as of the Closing Date, the representations and warranties of the Company in this Agreement are true and correct and the Company has complied with all agreements and satisfied all conditions on its part to be performed or satisfied hereunder at or prior to the Closing Date, and (iv) subsequent to the date of the most recent financial statements included in the Prospectus, there has been no material adverse change in the financial position or results of operation of the Company, or any change, or any development including a prospective change, in or affecting the condition (financial or otherwise), results of operations, business or prospects of the Company, except as set forth in the Prospectus.

(k) Since the date of the latest audited financial statements included in the General Disclosure Package (i) the Company shall not have sustained any loss or interference with its business from fire, explosion, flood or other calamity, whether or not covered by insurance, or from any labor dispute or court or governmental action, order or decree, otherwise than as set forth or contemplated in the General Disclosure Package and the Prospectus and (ii) there shall not have been any change in the capital stock or long-term debt of the Company or any change, or any development involving a prospective change, in or affecting the business, general affairs, management, financial position, stockholders’ equity or results of operations of the Company, otherwise than as set forth or contemplated in the General Disclosure Package and the Prospectus, the effect of which, in any such case described in clause (i) or (ii), is, in the judgment of the Representatives, so material and adverse as to make it impracticable or inadvisable to proceed with the sale or delivery of the Stock on the terms and in the manner contemplated in the Prospectus.

(l) No action shall have been taken and no statute, rule, regulation or order shall have been enacted, adopted or issued by any governmental agency or body which would, as of the Closing Date, prevent the issuance or sale of the Stock or materially and adversely affect or potentially materially and adversely affect the business or operations of the Company; and no injunction, restraining order or order of any other nature by any federal or state court of competent jurisdiction shall have been issued as of the Closing Date which would prevent the issuance or sale of the Stock or materially and adversely affect or potentially materially and adversely affect the business or operations of the Company.

(m) Subsequent to the execution and delivery of this Agreement there shall not have occurred any of the following: (i) trading in securities generally on the New York Stock Exchange, Nasdaq or the American Stock Exchange or in the over-the-counter market, or trading in any securities of the Company on any exchange or in the over-the-counter market, shall have been suspended or minimum or maximum prices or maximum range for prices shall have been established on any such exchange or such market by the Commission, by such exchange or by any other regulatory body or governmental authority having

jurisdiction, (ii) a banking moratorium shall have been declared by Federal or state authorities or a material disruption has occurred in commercial banking or securities settlement or clearance services in the United States, (iii) the United States shall have become engaged in hostilities, or the subject of an act of terrorism, or there shall have been an escalation in hostilities involving the United States, or there shall have been a declaration of a national emergency or war by the United States or (iv) there shall have occurred such a material adverse change in general economic, political or financial conditions (or the effect of international conditions on the financial markets in the United States shall be such) as to make it, in the judgment of the Representatives, impracticable or inadvisable to proceed with the sale or delivery of the Stock on the terms and in the manner contemplated in the General Disclosure Package and the Prospectus.

(n) Nasdaq shall have approved the Stock for listing, subject only to official notice of issuance and evidence of satisfactory distribution.

(o) Cowen shall have received the written agreements, substantially in the form of Exhibit I hereto, of the officers, directors and shareholders of the Company listed in Schedule D to this Agreement.

All opinions, letters, evidence and certificates mentioned above or elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Underwriters.

7. INDEMNIFICATION AND CONTRIBUTION.

(a) The Company shall indemnify and hold harmless each Underwriter, its officers, employees, representatives and agents and each person, if any, who controls any Underwriter within the meaning of the Securities Act (collectively the “Underwriter Indemnified Parties” and, each an “Underwriter Indemnified Party”) against any loss, claim, damage or liability, joint or several, or any action in respect thereof, to which that Underwriter Indemnified Party may become subject, under the Securities Act or otherwise, insofar as such loss, claim, damage, liability or action arises out of or is based upon (i) any untrue statement or alleged untrue statement of a material fact contained in the Preliminary Prospectus, either of the Registration Statements, any Issuer Free Writing Prospectus or the Prospectus or in any amendment or supplement thereto, (ii) the omission or alleged omission to state in any Preliminary Prospectus, either of the Registration Statements, any Issuer Free Writing Prospectus or the Prospectus or in any amendment or supplement thereto a material fact required to be stated therein or necessary to make the statements therein not misleading or (iii) any act or failure to act, or any alleged act or failure to act, by any Underwriter in connection with, or relating in any manner to, the Stock or the offering contemplated hereby, and which is included as part of or referred to in any loss, claim, damage, liability or action arising out of or based upon matters covered by clause (i) or (ii) above (provided, that the Company shall not be liable in the case of any matter covered by this clause (iii) to the extent that it is determined in a final judgment by a court of competent jurisdiction that such loss, claim, damage, liability or action resulted directly from any such act or failure to act undertaken or omitted to be taken by such Underwriter through its gross negligence or willful misconduct) and shall reimburse each Underwriter Indemnified Party promptly upon demand for any legal or other expenses reasonably incurred by that Underwriter Indemnified Party in connection with investigating or preparing to defend or defending against or appearing as a third party witness in connection with any such loss, claim, damage, liability or action as such expenses are incurred; provided, however, that the Company shall not be liable in any such case to the extent that any such loss, claim, damage, liability or action arises out of or is based upon (i) an untrue statement or alleged untrue statement in or omission or alleged omission from the Preliminary Prospectus, either of the Registration Statements, any Issuer Free Writing Prospectus or the Prospectus or any such amendment or supplement in reliance upon and in conformity with written information furnished to the Company through the Representatives by or on behalf of any Underwriter specifically for use therein, which information the parties hereto agree is limited to the Underwriter’s Information (as defined in Section 17).

The Company shall indemnify and hold harmless the QIU and its directors, officers, managers, members, employees, representatives and agents and each person, if any, who controls the QIU within the meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act (collectively the “QIU Indemnified Parties,” and each a “QIU Indemnified Party”) from and against any loss, claim, damage, expense or

liability whatsoever (or any action, investigation or proceeding in respect thereof), joint or several, to which that QIU Indemnified Party may become subject, arising out of, or based upon, the QIU’s acting as a “qualified independent underwriter” (within the meaning of Rule 2720 to the NASD’s Conduct Rules) in connection with the offering contemplated by this Agreement, and shall reimburse each QIU Indemnified Party promptly upon demand for any legal fees or other expenses reasonably incurred by that QIU Indemnified Party in connection with investigating, or preparing to defend, or defending against, or appearing as a third party witness in respect of, or otherwise incurred in connection with, any such loss, claim, damage, expense, liability, action, investigation or proceeding, as such fees and expenses are incurred, provided, however, that the Company shall not be liable for any losses, claims, damages, liabilities, expenses, actions, investigations or proceedings to the extent that it is judicially determined in a final judgment by a court of competent jurisdiction to have resulted directly from the gross negligence or willful misconduct of the QIU.

This indemnity agreement is not exclusive and will be in addition to any liability which the Company might otherwise have and shall not limit any rights or remedies which may otherwise be available at law or in equity to each Underwriter Indemnified Party or the QIU Indemnified Party.

(b) Each Underwriter, severally and not jointly, shall indemnify and hold harmless the Company its officers, employees, representatives and agents, each of its directors and each person, if any, who controls the Company within the meaning of the Securities Act (collectively the “Company Indemnified Parties” and each a “Company Indemnified Party”) against any loss, claim, damage or liability, joint or several, or any action in respect thereof, to which the Company Indemnified Parties may become subject, under the Securities Act or otherwise, insofar as such loss, claim, damage, liability or action arises out of or is based upon (i) any untrue statement or alleged untrue statement of a material fact contained in the Preliminary Prospectus, either of the Registration Statements, any Issuer Free Writing Prospectus or the Prospectus or in any amendment or supplement thereto or (ii) the omission or alleged omission to state therein a material fact required to be stated therein or necessary to make the statements therein not misleading, but in each case only to the extent that the 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 through the Representatives by or on behalf of that Underwriter specifically for use therein, and shall reimburse the Company Indemnified Parties for any legal or other expenses reasonably incurred by such parties in connection with investigating or preparing to defend or defending against or appearing as third party witness in connection with any such loss, claim, damage, liability or action as such expenses are incurred; provided, that the parties hereto hereby agree that such written information provided by the Underwriters consists solely of the Underwriter’s Information. This indemnity agreement is not exclusive and will be in addition to any liability which the Underwriters might otherwise have and shall not limit any rights or remedies which may otherwise be available at law or in equity to the Company Indemnified Parties.

(c) Promptly after receipt by an indemnified party under this Section 7 of notice of any claim or the commencement of any action, the indemnified party shall, if a claim in respect thereof is to be made against the indemnifying party under this Section 7, notify the indemnifying party in writing of the claim or the commencement of that action; provided, however, that the failure to notify the indemnifying party shall not relieve it from any liability which it may have under this Section 7 except to the extent it has been materially prejudiced by such failure; and, provided, further, that the failure to notify the indemnifying party shall not relieve it from any liability which it may have to an indemnified party otherwise than under this Section 7. If any such claim or action shall be brought against an indemnified party, and it shall notify the indemnifying party thereof, the indemnifying party shall be entitled to participate therein and, to the extent that it wishes, jointly with any other similarly notified indemnifying party, to assume the defense thereof with counsel reasonably satisfactory to the indemnified party. After notice from the indemnifying party to the indemnified party of its election to assume the defense of such claim or action, the indemnifying party shall not be liable to the indemnified party under this Section 7 for any legal or other expenses subsequently incurred by the indemnified party in connection with the defense thereof other than reasonable costs of investigation; provided, however, that any indemnified party shall have the right to employ separate counsel in any such action and to participate in the defense thereof but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the employment thereof has been specifically authorized by the indemnifying party in writing, (ii) such indemnified party shall have been advised by such counsel that there may be one or more legal defenses available to it which

are different from or additional to those available to the indemnifying party and in the reasonable judgment of such counsel it is advisable for such indemnified party to employ separate counsel, (iii) such indemnified party is a QIU Indemnified Party that has been advised by its counsel that there may be one or more legal defenses available to the QIU Indemnified Parties that are different from or additional to those available to the other indemnified parties, or (iv) the indemnifying party has failed to assume the defense of such action and employ counsel reasonably satisfactory to the indemnified party, in which case, if such indemnified party notifies the indemnifying party in writing that it elects to employ separate counsel at the expense of the indemnifying party, the indemnifying party shall not have the right to assume the defense of such action on behalf of such indemnified party, it being understood, however, that the indemnifying party shall not, in connection with any one such action or separate but substantially similar or related actions in the same jurisdiction arising out of the same general allegations or circumstances, be liable for the reasonable fees and expenses of more than one separate firm of attorneys plus any local counsel at any time for all such indemnified parties, which firm shall be designated in writing by Cowen, if the indemnified parties under this Section 7 consist of any Underwriter Indemnified Party, or by the Company if the indemnified parties under this Section 7 consist of any Company Indemnified Parties. Each indemnified party, as a condition of the indemnity agreements contained in Sections 7(a) and 7(b), shall use all reasonable efforts to cooperate with the indemnifying party in the defense of any such action or claim. Subject to the provisions of Section 7(d) below, no indemnifying party shall be liable for any settlement of any such action effected without its written consent (which consent shall not be unreasonably withheld), but if settled with its written consent or if there be a final judgment for the plaintiff in any such action, the indemnifying party agrees to indemnify and hold harmless any indemnified party from and against any loss or liability by reason of such settlement or judgment.

(d) If at any time an indemnified party shall have requested that an indemnifying party reimburse the indemnified party for fees and expenses of counsel, such indemnifying party agrees that it shall be liable for any settlement of the nature contemplated by this Section 7 effected without its written consent if (i) such settlement is entered into more than 45 days after receipt by such indemnifying party of the request for reimbursement, (ii) such indemnifying party shall have received notice of the terms of such settlement at least 30 days prior to such settlement being entered into and (iii) such indemnifying party shall not have reimbursed such indemnified party in accordance with such request prior to the date of such settlement.

(e) If the indemnification provided for in this Section 7 is unavailable or insufficient to hold harmless an indemnified party under Section 7(a) or 7(b), then each indemnifying party shall, in lieu of indemnifying such indemnified party, contribute to the amount paid or payable by such indemnified party as a result of such loss, claim, damage or liability, or action in respect thereof, (i) in such proportion as shall be 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 Stock or 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 with respect to the statements or omissions which resulted in such loss, claim, damage or liability, or action in respect thereof, 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 with respect to such offering shall be deemed to be in the same proportion as the total net proceeds from the offering of the Stock purchased under this Agreement (before deducting expenses) received by the Company bear to the total underwriting discounts and commissions received by the Underwriters with respect to the Stock purchased under this Agreement, in each case as set forth in the table on the cover page of the Prospectus. 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 on the one hand or the Underwriters on the other, the intent of the parties and their relative knowledge, access to information and opportunity to correct or prevent such untrue statement or omission; provided, that the parties hereto agree that the written information furnished to the Company through the Representatives by or on behalf of the Underwriters for use in any Preliminary Prospectus, either of the Registration Statements or the Prospectus consists solely of the Underwriter’s Information. The Company and the Underwriters agree that the QIU has not received and will not receive any additional benefits hereunder for serving as the QIU in connection with the offering of the Stock. The Company and the Underwriters agree that it would not be just and equitable if contributions pursuant to this Section 7(e) were to be 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 into account the equitable considerations referred to herein. The amount paid or payable by an indemnified party as a result of the loss, claim, damage or liability, or action in respect thereof, referred to above in this Section 7(e) shall be deemed to include, for purposes of this Section 7(e), any legal or other expenses reasonably incurred by such indemnified party in connection with investigating or defending any such action or claim. Notwithstanding the provisions of this Section 7(e), no Underwriter shall be required to contribute any amount in excess of the amount by which the total price at which the Stock underwritten by it and distributed to the public were offered to the public less the amount of any damages which such Underwriter has otherwise paid or become liable to pay by reason of any untrue or alleged untrue statement or omission or alleged omission or in connection with its participation as a QIU. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be entitled to contribution from any person who was not guilty of such fraudulent misrepresentation.

The Underwriters’ obligations to contribute as provided in this Section 7(e) are several in proportion to their respective underwriting obligations and not joint.

8. TERMINATION. The obligations of the Underwriters hereunder may be terminated by Cowen, in its absolute discretion by notice given to and received by the Company prior to delivery of and payment for the Firm Stock if, prior to that time, any of the events described in Sections 6(k), 6(l) or 6(m) have occurred or if the Underwriters shall decline to purchase the Stock for any reason permitted under this Agreement.

9. REIMBURSEMENT OF UNDERWRITERS’ EXPENSES. If (a) this Agreement shall have been terminated pursuant to Section 8 or 10, (b) the Company shall fail to tender the Stock for delivery to the Underwriters for any reason not permitted under this Agreement, or (c) the Underwriters shall decline to purchase the Stock for any reason permitted under this Agreement, the Company shall reimburse the Underwriters for the reasonable fees and expenses of their counsel and for such other out-of-pocket expenses as shall have been reasonably incurred by them in connection with this Agreement and the proposed purchase of the Stock, and upon demand the Company shall pay the full amount thereof to Cowen. If this Agreement is terminated pursuant to Section 10 by reason of the default of one or more Underwriters, the Company shall not be obligated to reimburse any defaulting Underwriter on account of those expenses.

10. SUBSTITUTION OF UNDERWRITERS. If any Underwriter or Underwriters shall default in its or their obligations to purchase shares of Stock hereunder and the aggregate number of shares which such defaulting Underwriter or Underwriters agreed but failed to purchase does not exceed ten percent (10%) of the total number of shares underwritten, the other Underwriters shall be obligated severally, in proportion to their respective commitments hereunder, to purchase the shares which such defaulting Underwriter or Underwriters agreed but failed to purchase. If any Underwriter or Underwriters shall so default and the aggregate number of shares with respect to which such default or defaults occur is more than ten percent (10%) of the total number of shares underwritten and arrangements satisfactory to the Representatives and the Company for the purchase of such shares by other persons are not made within forty-eight (48) hours after such default, this Agreement shall terminate.

If the remaining Underwriters or substituted Underwriters are required hereby or agree to take up all or part of the shares of Stock of a defaulting Underwriter or Underwriters as provided in this Section 10, (i) the Company shall have the right to postpone the Closing Dates for a period of not more than five (5) full business days in order that the Company may effect whatever changes may thereby be made necessary in the Registration Statement or the Prospectus, or in any other documents or arrangements, and the Company agrees promptly to file any amendments to the Registration Statement or supplements to the Prospectus which may thereby be made necessary, and (ii) the respective numbers of shares to be purchased by the remaining Underwriters or substituted Underwriters shall be taken as the basis of their underwriting obligation for all purposes of this Agreement. Nothing herein contained shall relieve any defaulting Underwriter of its liability to the Company or the other Underwriters for damages occasioned by its default hereunder. Any termination of this Agreement pursuant to this Section 10 shall be without liability on the part of any non-defaulting Underwriter or the Company, except expenses to be paid or reimbursed pursuant to Sections 5 and 9 and except the provisions of Section 7 shall not terminate and shall remain in effect.

11. SUCCESSORS; PERSONS ENTITLED TO BENEFIT OF AGREEMENT. This Agreement shall inure to the benefit of and be binding upon the several Underwriters, the Company and their respective successors. Nothing expressed or mentioned in this Agreement is intended or shall be construed to give any person other than the persons mentioned

in the preceding sentence any legal or equitable right, remedy or claim under or in respect of this Agreement, or any provisions herein contained, this Agreement and all conditions and provisions hereof being intended to be and being for the sole and exclusive benefit of such persons and for the benefit of no other person; except that the representations, warranties, covenants, agreements and indemnities of the Company contained in this Agreement shall also be for the benefit of the Underwriter Indemnified Parties and the QIU Indemnified Parties and the indemnities of the several Underwriters shall also be for the benefit of the Company Indemnified Parties. It is understood that the Underwriter’s responsibility to the Company is solely contractual in nature and the Underwriters do not owe the Company, or any other party, any fiduciary duty as a result of this Agreement.

12. ABSENCE OF FIDUCIARY RELATIONSHIP. The Company acknowledges and agrees that:

(a) each Underwriter’s responsibility to the Company is solely contractual in nature, the Representatives have been retained solely to act as underwriters in connection with the sale of the Stock and no fiduciary, advisory or agency relationship between the Company and the Representatives has been created in respect of any of the transactions contemplated by this Agreement, irrespective of whether any of the Representatives has advised or is advising the Company on other matters;

(b) the price of the Stock set forth in this Agreement was established by the Company following discussions and arms-length negotiations with the Representatives, 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) it has been advised that the Representatives and their affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that the Representatives have no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and

(d) it waives, to the fullest extent permitted by law, any claims it may have against the Representatives for breach of fiduciary duty or alleged breach of fiduciary duty and agrees that the Representatives 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.

13. SURVIVAL OF INDEMNITIES, REPRESENTATIONS, WARRANTIES, ETC. The respective indemnities, covenants, agreements, representations, warranties and other statements of the Company and the several Underwriters, as set forth in this Agreement or made by them respectively, pursuant to this Agreement, shall remain in full force and effect, regardless of any investigation made by or on behalf of any Underwriter, the Company or any person controlling any of them and shall survive delivery of and payment for the Stock.

14. NOTICES. All statements, requests, notices and agreements hereunder shall be in writing, and:

(a) if to the Underwriters, shall be delivered or sent by mail, telex or facsimile transmission to ▇▇▇▇▇ and Company, LLC, Attention: General Counsel (Fax: ▇▇▇-▇▇▇-▇▇▇▇); and

(b) if to the Company shall be delivered or sent by mail, telex or facsimile transmission to Achillion Pharmaceuticals, Inc., Attention: President (Fax: ▇▇▇-▇▇▇-▇▇▇▇).

Any such statements, requests, notices or agreements shall take effect at the time of receipt thereof.

Notwithstanding the foregoing, any notice to an Underwriter pursuant to Section 7 shall be delivered or sent by mail, telex or facsimile transmission to such Underwriter at its address set forth in its acceptance telex to the Representatives, which address will be supplied to any other party hereto by the Representatives upon request.

15. DEFINITION OF CERTAIN TERMS. For purposes of this Agreement, (a) “business day” means any day on which the New York Stock Exchange, Inc. is open for trading and (b) “subsidiary” has the meaning set forth in Rule 405 of the Rules and Regulations.

16. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the laws of the State of New York, including without limitation Section 5-1401 of the New York General Obligations.

17. UNDERWRITERS’ INFORMATION. The parties hereto acknowledge and agree that, for all purposes of this Agreement, the Underwriters’ Information consists solely of the following information in the Prospectus: (i) the last paragraph on the front cover page concerning the terms of the offering by the Underwriters; and (ii) the statements relating to the amount of selling concession and reallowance in the third paragraph under the heading “Underwriting.”

18 AUTHORITY OF THE REPRESENTATIVES. In connection with this Agreement, you will act for and on behalf of the several Underwriters, and any action taken under this Agreement by the Representatives, will be binding on all the Underwriters.

19. PARTIAL UNENFORCEABILITY. The invalidity or unenforceability of any Section, paragraph or provision of this Agreement shall not affect the validity or enforceability of any other Section, paragraph or provision hereof. If any Section, paragraph or provision of this Agreement is for any reason determined to be invalid or unenforceable, there shall be deemed to be made such minor changes (and only such minor changes) as are necessary to make it valid and enforceable.

20. GENERAL. This Agreement constitutes the entire agreement of the parties to this Agreement and supersedes all prior written or oral and all contemporaneous oral agreements, understandings and negotiations with respect to the subject matter hereof. In this Agreement, the masculine, feminine and neuter genders and the singular and the plural include one another. The section headings in this Agreement are for the convenience of the parties only and will not affect the construction or interpretation of this Agreement. This Agreement may be amended or modified, and the observance of any term of this Agreement may be waived, only by a writing signed by the Company and the Representatives.

21. COUNTERPARTS. This Agreement may be signed in any number of counterparts, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument.

If the foregoing is in accordance with your understanding of the agreement between the Company and the several Underwriters, kindly indicate your acceptance in the space provided for that purpose below.


Very truly yours,

ACHILLION PHARMACEUTICALS, INC.

By:
		Name:
		Title:

Accepted as of

the date first above written:

▇▇▇▇▇ AND COMPANY, LLC

CIBC WORLD MARKETS CORP.

JMP SECURITIES LLC

Acting on their own behalf

and as Representatives of several

Underwriters referred to in the

foregoing Agreement.



By:	▇▇▇▇▇ AND COMPANY, LLC

By:
	Name:	▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇, ▇▇.
	Title:	Head of Equity Capital Markets

SCHEDULE A


Name	Number of Firm Shares to be Purchased	Number of Optional Shares to be Purchased
▇▇▇▇▇ and Company, LLC
CIBC World Markets Corp.
JMP Securities LLC
Total

SCHEDULE B

Pricing Information

1. The number of shares of Stock to be sold is shares, including shares of Optional Stock.

2. The initial public offering price for the Stock is $ per share.

3. The underwriting discounts and commissions for the Stock is $ per share.

SCHEDULE C

Issuer General Free Writing Prospectuses

SCHEDULE D

Advent Health Care & Life Sciences II Limited Partnership and affiliated funds

Atlas Venture Fund V, L.P. and affiliated funds

Bear ▇▇▇▇▇▇▇ Health Innoventures, L.P. and affiliated funds

Connecticut Innovations, Incorporated and affiliated entities

Gilead Sciences, Inc.

▇▇▇▇▇▇▇▇ Ventures International Life Sciences Fund II LP and affiliated funds

SGC Partners I LLC and affiliated funds

▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇

▇▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇▇

▇▇▇▇▇ ▇. ▇▇▇▇▇▇▇▇

▇▇▇▇ ▇▇▇ ▇▇▇▇▇▇

▇▇▇▇ ▇. ▇▇▇▇▇▇▇, ▇▇., M.D.

▇▇▇▇▇▇ ▇▇▇▇, Ph.D.

▇▇▇▇▇ Fisherman, M.D.

▇▇▇▇-▇▇▇▇▇▇▇▇ ▇▇▇▇▇▇▇, M.D.

▇▇▇▇▇ ▇▇▇▇▇▇

▇▇▇▇▇▇▇ ▇▇▇▇

▇▇▇▇▇▇ ▇▇▇▇▇, Ph.D.

▇▇▇▇▇ ▇. ▇▇▇▇▇▇

▇▇▇▇▇▇▇▇▇▇▇ ▇. ▇▇▇▇▇

Exhibit I

[Form of Lock-Up Agreement]

, 2006

▇▇▇▇▇ AND COMPANY, LLC

CIBC WORLD MARKETS CORP.

JMP SECURITIES LLC

As representatives of the several Underwriters

c/o Cowen and Company, LLC

▇▇▇▇ ▇▇▇▇▇▇ ▇▇ ▇▇▇ ▇▇▇▇▇▇▇▇

▇▇▇ ▇▇▇▇, ▇▇▇ ▇▇▇▇ ▇▇▇▇▇

Re:	Achillion Pharmaceuticals, Inc. - Public Offering of Shares of Common Stock

Dear Sirs:

In order to induce ▇▇▇▇▇ and Company, LLC (“Cowen”), CIBC World Markets Corp. and JMP Securities LLC (together with Cowen, the “Representatives”), to enter into a certain underwriting agreement with Achillion Pharmaceuticals, Inc., a Delaware corporation (the “Company”), with respect to the public offering of shares of the Company’s Common Stock, par value $0.001 per share (“Common Stock”), the undersigned hereby agrees that for a period of 180 days following the date of the final prospectus filed by the Company with the Securities and Exchange Commission in connection with such public offering, the undersigned will not, without the prior written consent of Cowen, directly or indirectly, (i) offer, sell, assign, transfer, pledge, contract to sell, or otherwise dispose of, any shares of Common Stock (including, without limitation, Common Stock which may be deemed to be beneficially owned by the undersigned in accordance with the rules and regulations promulgated under the Securities Act of 1933, as the same may be amended or supplemented from time to time (such shares, the “Beneficially Owned Shares”)) or securities convertible into or exercisable or exchangeable in Common Stock, (ii) enter into any swap, hedge or similar agreement or arrangement that transfers in whole or in part, the economic risk of ownership of the Beneficially Owned Shares or securities convertible into or exercisable or exchangeable in Common Stock or (iii) engage in any short selling of the Common Stock.

Notwithstanding the foregoing, the undersigned may transfer shares (i) as a bona fide gift or gifts, (ii) to any trust for the direct or indirect benefit of the undersigned or the immediate family of the undersigned, (iii) by will or intestate succession, (iv) to any affiliate (as defined in Regulation C under the Securities Act of 1933, as amended) of the undersigned, (v) if the undersigned is a corporation or similar entity, to any wholly-owned subsidiaries of such corporation or similar entity, (vi) if the undersigned is a partnership, limited liability company or similar entity, to any partners or members of such partnership, limited liability company or similar entity or (vii) with the prior written consent of Cowen on behalf of the underwriters; provided, that (1) Cowen receives a signed lock-up agreement for the balance of the lock-up period from each donee, trustee, distributee, or transferee as the case may be, (2) any such transfer shall not involve a disposition for value and (3) such transfers are not required to be reported in any public report or filing with the Securities and Exchange Commission, or otherwise including, without limitation, the filing of a Schedule 13D, a Schedule 13G and/or a Form 4. For purposes of this Agreement, “immediate family” shall mean any relationship by blood, marriage or adoption, not more remote than first cousin.

If (i) the Company issues an earnings release or material news or a material event relating to the Company occurs during the last 17 days of the lock-up period, or (ii) prior to the expiration of the lock-up period, the Company announces that it will release earnings results during the 16-day period beginning on the last day of the lock-up period, the restrictions imposed by this Agreement shall continue to apply until the expiration of the 18-day period beginning on the issuance of the earnings release or the occurrence of the material news or material event.

In addition, the undersigned hereby waives, from the date hereof until the expiration of the 180-day period following the date of the Company’s final Prospectus, any and all rights, if any, to request or demand registration pursuant to the Securities Act of any shares of Common Stock that are registered in the name of the undersigned or that are Beneficially Owned Shares. In order to enable the aforesaid covenants to be enforced, the undersigned hereby consents to the placing of legends and/or stop-transfer orders with the transfer agent of the Common Stock with respect to any shares of Common Stock or Beneficially Owned Shares.

This agreement shall automatically terminate on September 30, 2006 in the event that the registration statement has not been declared effective by that date.



Company Name (if applicable)

Address:

Shares ACHILLION PHARMACEUTICALS, INC. Common Stock UNDERWRITING AGREEMENT

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