Document:

Rules of the KLA-Tencor Corporation 2004 Equity Incentive Plan

 Exhibit 10.50 
 Rules of the KLA-Tencor Corporation 
 2004 Equity Incentive Plan 
 For the Grant of Restricted Stock Units 
 To Participants in France 
  

	1.	Introduction 

 The Board of Directors (the
“Board”) of KLA-Tencor Corporation (the “Company”) has established the KLA-Tencor Corporation 2004 Equity Incentive Plan, As Amended and Restated (the “U.S. Plan”) for the benefit of certain eligible individuals,
including employees of the Company and its Subsidiaries, including its Subsidiary(ies) in France (each a “French Subsidiary”), of which the Company holds directly or indirectly at least 10% of the share capital. 
 Section 4 of the U.S. Plan authorizes the Board or any Committees appointed by it to administer the U.S. Plan (the “Administrator”) to do
all things necessary or desirable in connection with the administration of the U.S. Plan. Specifically, Section 4(b)(viii) of the U.S. Plan authorizes the Administrator to establish sub-plans to the extent deemed necessary or desirable for the
purpose of qualifying for preferred tax treatment under foreign tax laws. The Administrator has determined that it is desirable to establish a sub-plan for the purpose of permitting restricted stock units granted to employees of a French Subsidiary
to qualify for favorable tax and social security treatment in France. The Administrator, therefore, intends with this document to establish a sub-plan of the U.S. Plan for the purpose of granting restricted stock units which qualify for the
favorable tax and social security treatment in France applicable to shares granted for no consideration under Sections L. 225-197-1 to L. 225-197-5 of the French Commercial Code, as amended, to qualifying employees of a French Subsidiary who are
residents in France for French tax purposes and/or subject to the French social security regime (the “French Participants”). 
 The
terms of the U.S. Plan applicable to restricted stock units, as set out in Appendix 1 hereto, shall, subject to the modifications in these Rules of the KLA-Tencor Corporation 2004 Equity Incentive Plan for the Grant of Restricted Stock Units To
Participants in France (the “French Plan”), constitute the terms applicable to the grant of French-qualified Restricted Stock Units to French Participants. 
 Under the French Plan, qualifying French Participants selected at the Administrator’s discretion will be granted Restricted Stock Units only as defined in Section 2 hereunder. 
  

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	2.	Definitions 

 Capitalized terms not otherwise
defined herein shall have the same meanings as set forth in the U.S. Plan. The terms set out below will have the following meaning: 
 (a) The term “Closed Period” shall mean a closed period as set forth in Section L.225-197-1 of the French Commercial Code, as amended, which is as follows: 
  

	 	(i)	ten (10) quotation days preceding and following the disclosure to the public of the consolidated financial statements or the annual statements of the Company; or

  

	 	(ii)	any period during which the corporate management of the Company (i.e. those involved in the governance of the Company, such as the Board, a Committee, supervisory
directorate, etc.) possess confidential information which could, if disclosed to the public, significantly impact the trading price of the Common Stock, until ten (10) quotation days after the day such information is disclosed to the public.

 If, after adoption of the French Plan, the French Commercial Code is amended to modify the definition and/or applicability
of the Closed Periods to French-qualified Restricted Stock Units, such amendments shall become applicable to any French-qualified Restricted Stock Units granted under this French Plan, to the extent permitted or required under French law.

 (b) The term “Disability” shall mean disability as determined in categories 2 and 3 under Section L. 341-4 of the French
Social Security Code, as amended, and subject to the fulfillment of related conditions. 
 (c) The term “Grant Date” shall
be the date on which the Administrator both (i) designates the French Participants, and (ii) specifies the main terms and conditions of the French-qualified Restricted Stock Units, such as the number of Shares subject to the
French-qualified Restricted Stock Units. 
 (d) The term “Vesting Date” shall mean the date on which the Shares of the
Company underlying the French-qualified Restricted Stock Units become non-forfeitable and are issued to the French Participants, provided, however, that the Administrator may provide in the applicable Award Agreement that the Shares will be issued
only at a date occurring after the Vesting Date. 
  

	3.	Eligibility 

 (a) Subject to
Section 3(c) below, any individual who, on the Grant Date of the French-qualified Restricted Stock Unit and to the extent required under French law, is employed under the terms and conditions of an employment contract (“contrat de
travail”) by a French Subsidiary or who is a corporate officer of a French Subsidiary (subject to Section 3(b) below) shall be eligible to receive, at the discretion of the Administrator, French-qualified Restricted Stock Units under
this French Plan, provided he or she also satisfies the eligibility conditions of Section 5 of the U.S. Plan. 
  

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 (b) French-qualified Restricted Stock Units may not be issued to a corporate officer of a French
Subsidiary, other than the managing corporate officers (Président du Conseil d’Administration, Directeur Général, Directeur Général Délégué, Membre du Directoire, Gérant de
Sociétés par actions), unless the corporate officer is employed under the terms and conditions of an employment contract (“contrat de travail”) by a French Subsidiary, as defined by French law. 
 (c) French-qualified Restricted Stock Units may not be issued under the French Plan to French Participants owning more than ten percent
(10%) of the Company’s share capital or to individuals other than employees and corporate executives of a French Subsidiary, as set forth in this Section 3. 
  

	4.	Non-Transferability 

 Notwithstanding any
provision in the U.S. Plan and except in the case of death, French-qualified Restricted Stock Units may not be transferred to any third party. The Shares underlying the French-qualified Restricted Stock Units may not be issued to any third party and
shall be issued only to the French Participant during his or her lifetime, subject to Section 10 below. 
  

	5.	Disqualification of French-qualified Restricted Stock Units 

 In the event changes are made to the terms and conditions of the French-qualified Restricted Stock Units due to any requirements under Applicable Laws, or by decision of the Company’s stockholders, the Board or
the Administrator, the Restricted Stock Units may no longer qualify as French-qualified Restricted Stock Units. The Company does not undertake nor is it required to maintain the French-qualified status of the Restricted Stock Units, and by accepting
any Award under this French Plan, the French Participants understand, acknowledge and agree that it will be their responsibility to bear any additional taxes or social security contributions that may be payable as a result of the disqualification of
the French-qualified Restricted Stock Units. 
 If the Restricted Stock Units no longer qualify as French-qualified Restricted Stock Units,
the Administrator may, in its sole discretion, determine to lift, shorten or terminate certain restrictions applicable to the vesting of the Restricted Stock Units or the sale of the Shares underlying the Restricted Stock Units, which have been
imposed under this French Plan or in the applicable Award Agreement delivered to the French Participant, in order to achieve the favorable tax and social security treatment applicable to French-qualified Restricted Stock Units. 
  

	6.	Employment Rights 

 The adoption of this
French Plan shall not confer upon the French Participants, or any employees of the French Subsidiary, any employment rights and shall not be construed as a part of any employment contracts that the French Subsidiary has with its employees.

  

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	7.	Amendments 

 Subject to the terms of the U.S.
Plan, the Administrator reserves the right to amend or terminate this French Plan at any time in accordance with applicable French law. 
  

	8.	Conditions of French-Qualified Restricted Stock Units 

 (a) Vesting of French-qualified Restricted Stock Units 
 The first Vesting Date of the
Restricted Stock Units (or, if later, the date on which the Shares underlying the French-qualified Restricted Stock Units are issued to a French Participant) shall not occur prior to the second anniversary of the Grant Date, or such other period as
is required for the vesting period applicable to French-qualified Restricted Stock Units under Section L. 225-197-1 of the French Commercial Code, the relevant sections of the French Tax Code or of the French Social Security Code, as amended.

 (b) Holding of Shares 
 The sale or transfer of Shares issued pursuant to the French-qualified Restricted Stock Units may not occur prior to the relevant anniversary of the respective Vesting Date specified by the Administrator and in no
case prior to the expiration of a two-year period as calculated from the respective Vesting Date (or, if later, the date on which the Shares underlying the French-qualified Restricted Stock Units are issued to a French Participant), or such other
period as is required to comply with the minimum holding period applicable to French-qualified Restricted Stock Units under Section L. 225-197-1 of the French Commercial Code, or the relevant Sections of the French Tax Code or the French Social
Security Code, as amended, to benefit from the favorable tax and social security regime, even if the French Participant is no longer an employee or corporate officer of a French Subsidiary. 
 In addition, the Shares may not be sold or transferred during a Closed Period, so long as and to the extent those Closed Periods are
applicable to Shares underlying French-qualified Restricted Stock Units. 
 (c) Corporate Officer Restriction 
 To the extent applicable to French-qualified Restricted Stock Units granted by the Company, a specific holding period shall be imposed and
described in the applicable Award Agreement for the Shares subject to the French-qualified Restricted Stock Units held by any French Participant who qualifies as a managing director under French law (“mandataires sociaux”), as
defined in Section 3(b) above. 
  

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 (d) French Participant’s Account 
 The Shares underlying the French-qualified Restricted Stock Units shall be recorded in an account in the name of the French Participant
and must be held with the Company or a broker or in such manner as the Company may determine in order to ensure compliance with Applicable Laws, including any required holding periods applicable to French-qualified Restricted Stock Units.

 (e) Dividends - Dividend Equivalents 
 (f) To the extent required under French law applicable to French-qualified Restricted Stock Units, the French Participant shall not receive any dividends or receive or accrue any dividend equivalents during the
vesting period. 
  

	9.	Adjustments and Change in Control 

 Adjustments of the French-qualified Restricted Stock Units issued hereunder shall be made to preclude the dilution or enlargement of benefits under the French-qualified Restricted Stock Units in the event of a transaction by the Company as
listed under Section L. 225-181 of the French Commercial Code, as amended, and in case of a repurchase of Shares by the Company at a price higher than the stock quotation price in the open market, and according to the provisions of Section L. 228-99
of the French Commercial Code, as amended, as well as according to specific decrees. Nevertheless, the Administrator, at its discretion, may determine to make adjustments in the case of a transaction for which adjustments are not authorized under
French law, in which case the Restricted Stock Units may no longer qualify as French-qualified Restricted Stock Units. 
 In the event of an
adjustment upon a Change in Control as set forth in Section 18 of the U.S. Plan, adjustments to the terms and conditions of the French-qualified Restricted Stock Units or underlying Shares may be made only in accordance with the U.S. Plan and
pursuant to applicable French legal and tax rules. Nevertheless, the Administrator, at its discretion, may determine to make adjustments in the case of a transaction for which adjustments are not authorized under French law, in which case the
Restricted Stock Units may no longer qualify as French-qualified Restricted Stock Units. 
  

	10.	Death and Disability 

 In the event of the
death of a French Participant, the French-qualified Restricted Stock Units held by the French Participant at the time of death shall become immediately transferable to the French Participant’s heirs. The Company shall issue the underlying
Shares to the French Participant’s heirs, at their request, provided the heirs contact the Company within six (6) months following the death of the French Participant (or such other period as may be required by French law). If the French
Participant’s heirs do not request the issuance of the Shares underlying the French-qualified Restricted Stock Units within six (6) months following the French Participant’s death (or such other period as may be required by French
law), the French-qualified Restricted Stock Units will be forfeited. 
  

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 If a French Participant’s employment with the Company or any of its Subsidiaries terminates or if
he/she ceases to be employed by the Company or a Subsidiary, in either case by reason of his or her death or Disability (as defined in this French Plan), the French Participant’s heirs or the French Participant, as applicable, shall not be
subject to the restrictions on the transfer of Shares set forth in Section 8(b) of this French Plan. 
  

	11.	Interpretation 

 It is intended that
Restricted Stock Units granted under this French Plan shall qualify for the favorable tax and social security treatment applicable to Restricted Stock Units granted for no consideration under Sections L. 225-197-1 to L. 225-197-5 of the French
Commercial Code, as amended, and in accordance with the relevant provisions set forth by French tax and social security laws, but the Company does not undertake to maintain this status. The terms of this French Plan shall be interpreted accordingly
and in accordance with the relevant provisions set forth by French tax and social security laws and relevant guidelines published by French tax and social security administrations and subject to the fulfillment of legal, tax and reporting
obligations. 
 In the event of any conflict between the provisions of this French Plan and the U.S. Plan, the provisions of this French Plan
shall control for any grants of Restricted Stock Units made thereunder to French Participants. 
  

	12.	Adoption 

 The French Plan, in its entirety,
was adopted by the Administrator on November 13, 2008. 
  

 6Placement Agency Agreement dated January 29, 2009

 Exhibit 10.1 
 4,678,000 Shares 
 PHARMASSET, INC. 
 COMMON STOCK (PAR VALUE $0.001 PER SHARE) 
 PLACEMENT AGENCY AGREEMENT 

 January 29, 2009 
 Leerink Swann LLC 
 One Federal Street, 37th Floor 
 Boston, MA 02110 
 Ladies and Gentlemen: 
 This Agreement confirms our understanding that Pharmasset, Inc., a Delaware
corporation (the “Company”), hereby appoints Leerink Swann LLC as its exclusive placement agent (the “Placement Agent”) in connection with the proposed sale to certain investors (the “Direct
Offering”) of 4,678,000 shares of its Common Stock par value $0.001 per share (the “Shares”). On the basis of the representations and warranties contained herein, but subject to the terms and conditions set forth herein,
the Placement Agent agrees to use its best commercially practicable efforts to solicit and receive offers to purchase the Shares. Until the Closing Date (as defined below), the Company shall not, without the prior written consent of the Placement
Agent, solicit or accept offers to purchase Shares otherwise than through the Placement Agent. Notwithstanding anything to the contrary contained in this Agreement, the Placement Agent shall have no obligation to purchase any of the Shares, or any
liability to the Company if any prospective purchaser fails to consummate a purchase of any of the Shares. In soliciting the purchases of Shares, the Placement Agent shall act solely as the Company’s agent and not as principal. The shares of
Common Stock, par value $0.001 per share, of the Company are hereinafter referred to as the “Common Stock.” 
 Subject to
the provisions of this Agreement, offers for the purchase of Shares may be solicited by the Placement Agent as agent for the Company at such time and in such amounts as the Placement Agent deems advisable. The Company shall have the sole right to
accept offers to purchase the Shares and may reject any such offer, in whole or in part. The purchase of the Shares by investors in the Direct Offering shall be evidenced by the execution of a definitive subscription agreement (the “Purchase
Agreement”) between the Company and each purchaser (each, a “Purchaser” and, collectively, the “Purchasers”) of the Shares. 
 The Company has filed with the Securities and Exchange Commission (the “Commission”) a registration statement, including a prospectus, (the file number of which is set forth in Schedule I hereto) on
Form S-3, relating to the securities (the “Shelf Securities”), including the Shares, to be issued from time to time by the Company. The registration statement as amended to the date of this Agreement, including the information (if
any) deemed to be part of the registration statement at the time of effectiveness pursuant to Rule 430A or Rule 430B under the Securities Act of 1933, as amended (the “Securities Act”), is hereinafter referred to as the
“Registration Statement”, and the related prospectus covering the Shelf Securities dated June 26, 2008 in the form first used to confirm sales of the Shares (or in the form first made available to the Placement Agent by the
Company to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “Basic Prospectus.” The Basic Prospectus, 

 
as supplemented by the prospectus supplement specifically relating to the Shares in the form first used to confirm sales of the Shares (or in the form first
made available to the Placement Agent by the Company to meet requests of purchasers pursuant to Rule 173 under the Securities Act) is hereinafter referred to as the “Prospectus,” and the term “preliminary
prospectus” means any preliminary form of the Prospectus. For purposes of this Agreement, “free writing prospectus” has the meaning set forth in Rule 405 under the Securities Act, “Time of Sale Prospectus”
means the Basic Prospectus together with the free writing prospectuses, if any, each identified in Schedule I hereto, and “broadly available road show” means a “bona fide electronic road show” as defined in Rule 433(h)(5)
under the Securities Act that has been made available without restriction to any person. As used herein, the terms “Registration Statement,” “Basic Prospectus,” “preliminary prospectus,” “Time of Sale
Prospectus” and “Prospectus” shall include the documents, if any, incorporated by reference therein. The terms “supplement,” “amendment,” and “amend” as used herein with respect to
the Registration Statement, the Basic Prospectus, the Time of Sale Prospectus, any preliminary prospectus or free writing prospectus shall include all documents subsequently filed by the Company with the Commission pursuant to the Securities
Exchange Act of 1934, as amended (the “Exchange Act”), that are deemed to be incorporated by reference therein. 
 Concurrently with the execution and delivery of this Agreement, the Company, the Placement Agent and JPMorgan Chase Bank, N.A., as escrow agent (the “Escrow Agent”), shall enter into an escrow agreement (the “Escrow
Agreement”), pursuant to which an escrow account (the “Escrow Account”) will be established for the benefit of the Company and the Purchasers. Prior to the completion of the purchase and sale of the Shares pursuant to this
Agreement and the Purchase Agreements (the “Closing”), each such Purchaser shall deposit into the Escrow Account or, with the prior consent of the Company and the Placement Agent, make alternative arrangements for the payment
directly to the Company of, an amount equal to the product of (x) the number of Shares such Purchaser has agreed to purchase and (y) the purchase price per Share as set forth in the Purchase Agreements (as defined below) (the
“Purchase Amount”). The aggregate of such Purchase Amounts deposited with the Escrow Agent is herein referred to as the “Escrow Funds.” On the Closing Date, upon satisfaction or waiver of all of the conditions to
Closing, (i) the Escrow Agent will disburse the Escrow Funds to the Company and the Placement Agent as provided in the Escrow Agreement and Section 2 below, (ii) the Company shall cause the Shares to be delivered to the Purchasers who
have deposited their Purchase Amounts with the Escrow Agent, and (iii) the Company and any Purchaser who has made, with the consent of the Company and the Placement Agent, alternative arrangements for the payment directly to the Company of the
applicable Purchase Price, shall consummate the transactions contemplated hereby in accordance with such alternative arrangements. 
 Subject
to the terms and conditions hereof, delivery of the Shares shall be made by the Company to the Purchasers, and payment of the purchase price shall be made by the Purchasers through the Escrow Agent, at the office of Wilmer Cutler Pickering Hale and
Dorr LLP, 60 State Street, Boston, Massachusetts 02109 (or at such other place as agreed upon by the Placement Agent and the Company), at 10:00 a.m., New York City time, on or before February 4, 2009 or at such time on such other date as
may be agreed 

 
upon in writing by the Company and the Placement Agent but in no event prior to the date on which the Escrow Agent shall have received all of the Escrow
Funds to be paid to the Company through the Escrow Agent (such date of delivery and payment is hereinafter referred to as the “Closing Date”); provided that the Company, the Placement Agent and a Purchaser may agree as to an
alternative arrangement for the payment directly to the Company of the applicable purchase price for the Shares to be purchased by such Purchaser. The Shares shall be delivered, through the facilities of The Depository Trust Company, to such
persons, and shall be registered in such name or names and shall be in such denominations, as the Placement Agent may request by written notice to the Company prior to the Closing Date. The cost of original issue tax stamps and other transfer taxes,
if any, in connection with the issuance and delivery of the Shares by the Company to the respective Purchasers shall be borne by the Company. 
 1. Representations and Warranties. The Company represents and warrants to and agrees with the Placement Agent that: 
 (a) The
Registration Statement has become effective, no stop order suspending the effectiveness of the Registration Statement is in effect, and no proceedings for such purpose are pending before or, to the Company’s knowledge, threatened by the
Commission. 
 (b) (i) Each document, if any, filed or to be filed pursuant to the Exchange Act and incorporated by reference in the Time of
Sale Prospectus or the Prospectus complied or will comply when so filed in all material respects with the Exchange Act and the applicable rules and regulations of the Commission thereunder, (ii) each part of the Registration Statement, when
such part became effective, did not contain, and each such part, as amended or supplemented, if applicable, will not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make
the statements therein not misleading, (iii) the Registration Statement as of the date hereof does not contain any untrue statement of a material fact or omit to state a material fact required to be stated therein or necessary to make the
statements therein not misleading, (iv) the Registration Statement and the Prospectus comply, and as amended or supplemented, if applicable, will comply in all material respects with the Securities Act and the applicable rules and regulations
of the Commission thereunder, (v) the Time of Sale Prospectus does not, and at the time of each sale of the Shares in connection with the Direct Offering when the Prospectus is not yet available to prospective purchasers and at the Closing Date
(as defined in Section 2(a)), the Time of Sale Prospectus, as then amended or supplemented by the Company, if applicable, will not, contain any untrue statement of a material fact or omit to state a material fact necessary to make the
statements therein, in the light of the circumstances under which they were made, not misleading, (vi) each broadly available road show, if any, when considered together with the Time of Sale Prospectus, does not contain any untrue statement of
a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading and (vii) the Prospectus does not contain and, as amended or supplemented,
if applicable, will not contain any untrue statement of a material fact or omit to state a material fact necessary to make the statements therein, in the light of the circumstances under which they were made, not misleading, except that the
representations and warranties set forth in this paragraph do not apply to statements or omissions in the Registration Statement, the Time of Sale Prospectus or the Prospectus based upon information relating to the Placement Agent furnished to the
Company in writing by the Placement Agent expressly for use therein. 

 (c) The Company is not an “ineligible issuer” in connection with the Direct Offering pursuant
to Rules 164, 405 and 433 under the Securities Act. Any free writing prospectus that the Company is required to file pursuant to Rule 433(d) under the Securities Act has been, or will be, filed with the Commission in accordance with the requirements
of the Securities Act and the applicable rules and regulations of the Commission thereunder. Each free writing prospectus that the Company has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act or that was prepared by or
behalf of or used or referred to by the Company complies or will comply in all material respects with the requirements of the Securities Act and the applicable rules and regulations of the Commission thereunder. Except for the free writing
prospectuses, if any, identified in Schedule I hereto forming part of the Time of Sale Prospectus, and electronic road shows, if any, each furnished to the Placement Agent before first use, the Company has not prepared, used or referred to, and will
not, without the prior consent of the Placement Agent, prepare, use or refer to, any free writing prospectus. 
 (d) The Company has been
duly incorporated and is validly existing as a corporation in good standing under the laws of the jurisdiction of its incorporation and has corporate power and authority to own or lease, as the case may be, and operate its properties and to conduct
its business as described in the Time of Sale Prospectus and the Prospectus and to enter into and perform its obligations under this Agreement. The Company is duly qualified as a foreign corporation to transact business and is in good standing in
each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except for such jurisdictions where the failure to so qualify or to be in good standing would not,
individually or in the aggregate, result in a material adverse effect, on the condition, financial or otherwise, or on the earnings, business, properties, operations or prospects, whether or not arising from transactions in the ordinary course of
business of the Company (a “Material Adverse Effect”). 
 (e) The Company has no subsidiaries. 
 (f) Except for the Current Report on Form 8-K filed by the Company with the Commission on January 22, 2009 (the “January Report”),
the Company has filed in a timely manner all reports required to be filed pursuant to Sections 13(a), 13(e), 14 and 15(d) of the Exchange Act (except to the extent that Section 15(d) requires reports to be filed pursuant to Sections 13(d) and
13(g) of the Exchange Act, which shall be governed by the next clause of this sentence); the Company has filed in a timely manner all reports required to be filed pursuant to Sections 13(d) and 13(g) of the Exchange Act; and the failure to file the
January Report in a timely manner under the Exchange Act does not and will not impair the ability of the Company to use the Registration Statement. 

 (g) The Company has not distributed and will not distribute, prior to the later of the Closing Date (as
defined below) and the completion of the Placement Agent’s placement of the Shares, any offering material in connection with the placement of the Shares other than the Prospectus, any Issuer Free Writing Prospectus reviewed and consented to by
the Placement Agent or included in Schedule I hereto or the Registration Statement. 
 (h) This Agreement has been duly authorized, executed
and delivered by the Company. 
 (i) The authorized, issued and outstanding capital stock of the Company is as set forth in each of the Time
of Sale Prospectus and the Prospectus. The Common Stock (including the Shares) conforms in all material respects to the description thereof contained in each of the Time of Sale Prospectus and the Prospectus. All of the issued and outstanding shares
of Common Stock have been duly authorized and validly issued, are fully paid and nonassessable and have been issued in compliance with federal and state securities laws. None of the outstanding shares of Common Stock were 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 Company 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 described in the Time of Sale Prospectus and the Prospectus or options granted under the Company’s
2007 Equity Incentive Plan. The description of the Company’s stock option, stock bonus and other stock plans or arrangements, and the options or other rights granted thereunder, set forth in each of the Time of Sale Prospectus and the
Prospectus accurately and fairly presents in all material respects the information required to be shown with respect to such plans, arrangements, options and rights. 
 (j) The Company has filed in a timely manner a Notification Form: Listing of Additional Shares relating to the Shares with The NASDAQ Stock Market, LLC (“NASDAQ”). The Common Stock is registered under
Section 12(b) of the Exchange Act and is listed on the NASDAQ Global Market. 
 (k) The Shares to be placed by the Placement Agent on
behalf of the Company have been duly authorized for issuance and sale pursuant to any applicable Purchase Agreement and, when issued and delivered by the Company to prospective Purchasers, against payment of the applicable Purchase Price therefor,
pursuant to any applicable Purchase Agreement on the Closing Date, will be validly issued, fully paid and nonassessable. 
 (l) The Company
is not (i) in violation or in default (or, with the giving of notice or lapse of time, would be in default) (“Default”) under its certificate of incorporation or by-laws, (ii) in Default under any indenture, mortgage, loan
or credit agreement, deed of trust, note, contract, franchise, lease or other agreement, obligation, condition, covenant or instrument to which the Company is a party or by which it may be bound, or to which any of the property or assets of the
Company is subject (each, an “Existing Instrument”), or (iii) in violation of any statute, law, rule, regulation, judgment, order or decree of any court, regulatory body, 

 
administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its properties, as applicable, except
with respect to clause (ii) and (iii) only, for such Defaults as would not, individually or in the aggregate, have a Material Adverse Effect. The Company’s execution, delivery and performance of this Agreement and the Escrow Agreement
and consummation of the transactions contemplated hereby, thereby, by the Time of Sale Prospectus and by the Prospectus (i) have been duly authorized by all necessary corporate action and will not result in any Default under the certificate of
incorporation or by-laws of the Company, (ii) will not conflict with or constitute a breach of, or Default under, or result in the creation or imposition of any lien, charge or encumbrance upon any property or assets of the Company pursuant to,
or require the consent of any other party to, any Existing Instrument, and (iii) will not result in any violation of any statute, law, rule, regulation, judgment, order or decree applicable to the Company of any court, regulatory body,
administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its or their properties. No consent, approval, authorization or other order of, or registration or filing with, any court or other
governmental or regulatory authority or agency is required for the Company’s execution, delivery and performance of this Agreement and the Escrow Agreement and consummation of the transactions contemplated hereby, thereby, by the Time of Sale
Prospectus and by the Prospectus, except such as have been obtained or made by the Company and are in full force and effect under the Securities Act, applicable state securities or blue sky laws, with NASDAQ and from the Financial Industry
Regulatory Authority, Inc. (“FINRA”). 
 (m) Except as otherwise disclosed in the Time of Sale Prospectus and the
Prospectus, subsequent to the respective dates as of which information is given in the Time of Sale Prospectus: (i) there has been no material adverse change, or any development that could reasonably be expected to result in a material adverse
change, in the condition, financial or otherwise, or in the earnings, business, properties, operations or prospects, whether or not arising from transactions in the ordinary course of business of the Company; (ii) the Company has not incurred
any material liability or obligation, indirect, direct or contingent, nor entered into any material transaction or agreement; and (iii) there has been no dividend or distribution of any kind declared, paid or made by the Company on any class of
capital stock or repurchase or redemption by the Company of any class of capital stock. 
 (n) There are no legal or governmental actions,
suits or proceedings pending or, to the best of the Company’s knowledge, threatened (i) against or affecting the Company, (ii) which has as the subject thereof any officer or director of, or property owned or leased by, the Company or
(iii) relating to environmental or discrimination matters which would, individually or in the aggregate, have a Material Adverse Effect or adversely affect the consummation of the transactions contemplated by this Agreement. 
 (o) The Company is not, and after giving effect to the transactions contemplated hereby, by the Time of Sale Prospectus and by the Prospectus will not
be, required to be registered as an “investment company” within the meaning of the Investment Company Act of 1940, as amended (the “Investment Company Act”). 

 (p) Except as otherwise disclosed in the Time of Sale Prospectus and the Prospectus, (i) the Company
is not in violation of any federal, state, local or foreign law, regulation, order, permit or other requirement relating to pollution or protection of human health or the environment (including, without limitation, ambient air, surface water,
groundwater, land surface or subsurface strata) or wildlife, including without limitation, laws and regulations relating to emissions, discharges, releases or threatened releases of chemicals, pollutants, contaminants, wastes, toxic substances,
hazardous substances, petroleum and petroleum products (collectively, “Materials of Environmental Concern”), or otherwise relating to the manufacture, processing, distribution, use, treatment, storage, disposal, transport or
handling of Materials of Environment Concern (collectively, “Environmental Laws”), which violation includes, but is not limited to, noncompliance with any permits or other governmental authorizations required for the operation of
the business of the Company under applicable Environmental Laws, or noncompliance with the terms and conditions thereof, nor has the Company received any written communication, whether from a governmental authority, citizens group, employee or
otherwise, that alleges that the Company is in violation of any Environmental Laws, except as would not, individually or in the aggregate, have a Material Adverse Effect; (ii) there is no claim, action or cause of action filed with a court or
governmental authority, no investigation with respect to which the Company has received written notice, and no written notice by any person or entity alleging potential liability for investigatory costs, cleanup costs, governmental responses costs,
natural resources damages, property damages, personal injuries, attorneys’ fees or penalties arising out of, based on or resulting from the presence, or release into the environment, of any Material of Environmental Concern at any location
owned, leased or operated by the Company, now or in the past (collectively, “Environmental Claims”), pending or, to the Company’s knowledge, threatened against the Company or any person or entity whose liability for any
Environmental Claim the Company has retained or assumed either contractually or by operation of law, except as would not, individually or in the aggregate, have a Material Adverse Effect; (iii) to the Company’s knowledge, there are no past
or present actions, activities, conditions, events or incidents, including, without limitation, the release, emission, discharge, presence or disposal of any Material of Environmental Concern, that reasonably could result in a violation of any
Environmental Laws, require expenditures to be incurred pursuant to Environmental Laws, or form the basis of a potential Environmental Claim against the Company or against any person or entity whose liability for any Environmental Claim the Company
has retained or assumed either contractually or by operation of law, except as would not, individually or in the aggregate, have a Material Adverse Effect; and (iv) the Company is not subject to any pending or, to the Company’s knowledge,
threatened proceeding under Environmental Law to which a governmental authority is a party and which is reasonably likely to result in monetary sanctions of $100,000 or more. 
 (q) None of the following events has occurred or exists: (i) a failure to fulfill the obligations, if any, under the minimum funding standards of
Section 302 of the United States Employee Retirement Income Security Act of 1974, as amended (“ERISA”), and the regulations and published interpretations thereunder with respect to a Plan, determined without regard to any
waiver of such obligations or extension of any amortization period; (ii) an audit or investigation by the Internal Revenue Service, the U.S. Department of Labor, the Pension Benefit Guaranty Corporation or any other federal or state
governmental agency or any foreign 

 
regulatory agency with respect to the employment or compensation of employees by any member of the Company that could have a Material Adverse Effect;
(iii) any breach of any contractual obligation, or any violation of law or applicable qualification standards, with respect to the employment or compensation of employees by any member of the Company that could have a Material Adverse Effect.
None of the following events has occurred or is reasonably likely to occur: (i) a material increase in the aggregate amount of contributions required to be made to all Plans in the current fiscal year of the Company compared to the amount of
such contributions made in the Company’s most recently completed fiscal year; (ii) a material increase in the Company’s “accumulated post-retirement benefit obligations” (within the meaning of Statement of Financial
Accounting Standards 106) compared to the amount of such obligations in the Company’s most recently completed fiscal year; (iii) any event or condition giving rise to a liability under Title IV of ERISA that could have a Material Adverse
Effect; or (iv) the filing of a claim by one or more employees or former employees of the Company related to their employment that could have a Material Adverse Effect. For purposes of this paragraph, the term “Plan” means a
plan (within the meaning of Section 3(3) of ERISA) subject to Title IV of ERISA with respect to which any member of the Company may have any liability. 
 (r) There are no persons with registration or other similar rights to have any equity or debt securities registered for sale under the Registration Statement or included in the offering contemplated by this Agreement,
except for such rights as have been duly waived. 
 (s) Neither the Company nor, to the knowledge of the Company, any director, officer, or
employee of the Company is aware of or has taken any action, directly or indirectly, that would result in a violation by such persons of the Foreign Corrupt Practices Act of 1977, as amended, and the rules and regulations thereunder (the
“FCPA”), including, without limitation, making use of the mails or any means or instrumentality of interstate commerce corruptly in furtherance of an offer, payment, promise to pay or authorization of the payment of any money, or
other property, gift, promise to give, or authorization of the giving of anything of value to any “foreign official” (as such term is defined in the FCPA) or any foreign political party or official thereof or any candidate for foreign
political office, in contravention of the FCPA, and the Company has conducted its business in compliance with the FCPA. 
 (t) To the
Company’s knowledge, the statistical and market-related data included or incorporated by reference in the Registration Statement, the Time of Sale Prospectus or the Prospectus is based on or derived from sources that are materially reliable and
accurate. 
 (u) The preclinical and clinical studies and tests conducted by or on behalf of the Company that are described in the
Registration Statement, the Time of Sale Prospectus or the Prospectus or the results of which are referred to in the Registration Statement, the Time of Sale Prospectus or the Prospectus, were and, if still pending, are being conducted in all
material respects in accordance with experimental protocols, procedures and controls generally used by qualified experts in the preclinical and clinical study (as applicable) of new drugs or diagnostics as applied to products comparable to those
being developed by the Company. The descriptions of the results of the preclinical and clinical studies and tests contained in the Registration Statement, the Time of Sale Prospectus or the Prospectus are accurate and complete in all material
respects. 

 (v) The Company has (i) orally, to the Placement Agent or to counsel to the Placement Agent, fairly
summarized in all material respects the substance of all of its material communications with representatives of the FDA; and (ii) no knowledge of any pending communication from the FDA that would cause the Company to revise its strategy for
seeking marketing approval from the FDA for any of the Company’s products under development as described in the Registration Statement, the Time of Sale Prospectus or the Prospectus. 
 (w) There are no transfer taxes or other similar fees or charges under federal law or the laws of any state, or any political subdivision thereof,
required to be paid in connection with the execution and delivery of this Agreement or the issuance by the Company or sale by the Company of the Shares. 
 (x) Grant Thornton LLP (“Grant Thornton”), who have expressed their opinion with respect to the financial statements (which term as used in this Agreement includes the related notes thereto) and
supporting schedules, if any, filed with the Commission as a part of the Registration Statement and included in the Time of Sale Prospectus and the Prospectus, are independent public accountants with respect to the Company as required by the
Securities Act and the Securities Exchange Act of 1934, as amended (the “Exchange Act”) and the applicable rules and regulations thereunder. 
 (y) The financial statements filed with the Commission as a part of the Registration Statement and included in the Time of Sale Prospectus and the Prospectus present fairly in all material respects the financial
condition of the Company as of and at the dates indicated and the results of its operations and cash flows for the periods specified on the basis stated therein. Such financial statements comply as to form with the applicable accounting requirements
of the Securities Act and have been prepared in conformity with generally accepted accounting principles applied on a consistent basis throughout the periods involved, except as may be expressly stated in the related notes thereto. No other
financial statements or supporting schedules are required to be included in the Registration Statement. 
 (z) No labor dispute with the
employees of the Company exists or, to the Company’s knowledge, is threatened or imminent, and the Company is not aware of any existing or imminent labor dispute with the employees of any of its principal suppliers that could have a Material
Adverse Effect. 
 (aa) Except as described in the Time of Sale Prospectus and the Prospectus, the Company owns, possesses, licenses or has
other rights to use, on reasonable terms, all patents, patent applications, trade and service marks, trade and service mark registrations, trade names, copyrights, licenses, inventions, trade secrets, technology, know-how and other intellectual
property (collectively, the “Intellectual Property”) that are necessary for the conduct of the Company’s business as now conducted or, in connection with its major product candidates, as proposed in each of the Time of Sale
Prospectus and the Prospectus to be conducted. Except as set forth 

 
in the Time of Sale Prospectus and the Prospectus, (i) to the Company’s knowledge, there is no material infringement by third parties of any such
Intellectual Property owned by or exclusively licensed to the Company; (ii) there is no pending or, to the Company’s knowledge, threatened action, suit, proceeding or claim by others challenging the Company’s rights in or to any
Intellectual Property that would have a Material Adverse Effect; (iii) there is no pending or, to the Company’s knowledge, threatened action, suit, proceeding or claim by others challenging the validity or scope of any Intellectual
Property that would have a Material Adverse Effect; (iv) to the Company’s knowledge there is no pending or, threatened action, suit, proceeding or claim by others that the Company’s business as now conducted infringes or otherwise
violates any patent, trademark, copyright, trade secret or other proprietary rights of others; (v) to the Company’s knowledge the Company has complied in all material respects with the terms of each agreement pursuant to which material
Intellectual Property has been licensed to the Company, and all such agreements are in full force and effect; and (vi) to the Company’s knowledge, the product candidates described in the Time of Sale Prospectus and the Prospectus, if any,
as under development by the Company fall within the scope of the claims of one or more patents or patent applications owned by, or exclusively licensed to, the Company, and nothing has come to the Company’s attention that causes it to believe
that such patents are not valid or enforceable. 
 (bb) The Company possesses such valid and current licenses, certificates, authorizations
or permits issued by the appropriate state, federal or foreign regulatory agencies or bodies necessary to conduct its business which, singly or in the aggregate, if not obtained, would have a Material Adverse Effect, and the Company has not received
any notice of proceedings relating to the revocation or modification of, or non-compliance with, any such license, certificate, authorization or permit which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding,
could have a Material Adverse Effect. 
 (cc) Except as set forth in the Time of Sale Prospectus and the Prospectus, the Company has good and
marketable title to all the properties and assets reflected as owned in the financial statements referred to in Section 1(y) above, in each case free and clear of any security interests, mortgages, liens, encumbrances, equities, claims and
other defects, except such as do not materially and adversely affect the value of such property and do not materially interfere with the use made or proposed to be made of such property by the Company. The real property, improvements, equipment and
personal property held under lease by the Company are held under valid and enforceable leases, with such exceptions as are not material and do not materially interfere with the use made or proposed to be made of such real property, improvements,
equipment or personal property by the Company. 
 (dd) The Company has filed all necessary federal, state, local and foreign income and
franchise tax returns in a timely manner and has paid all taxes required to be paid by it and, if due and payable, any similar assessment or related fine or penalty levied against it, except for any taxes, assessments, fines or penalties as may be
being contested in good faith and by appropriate proceedings. The Company has made appropriate provisions in the applicable financial statements referred to in Section 1(y) above in respect of all federal, state, local and foreign income and
franchise taxes for all current or prior periods as to which the tax liability of the Company has not been finally determined. 

 (ee) Except as described in the Time of Sale Prospectus and the Prospectus, the Company is insured with
policies in such amounts and with such deductibles and covering such risks as are generally deemed adequate and customary for its business. All policies of insurance insuring the Company or its businesses, assets, employees, officers and directors
are in full force and effect; and there are no claims by the Company under any such policy or instrument as to which any insurance company is denying liability or defending under a reservation of rights clause. 
 (ff) The Company has not taken and will not take, directly or indirectly, any action designed to or that might be reasonably expected to cause or result
in stabilization or manipulation of the price of any security of the Company to facilitate the sale or resale of the Shares. 
 (gg) The
Company maintains a system of internal accounting controls sufficient to provide reasonable assurance that (i) transactions are executed in accordance with management’s general or specific authorizations; (ii) transactions are
recorded as necessary to permit preparation of financial statements in conformity with generally accepted accounting principles and to maintain asset accountability; (iii) access to assets is permitted only in accordance with management’s
general or specific authorization; and (iv) the recorded accountability for assets is compared with the existing assets at reasonable intervals and appropriate action is taken with respect to any differences. 
 (hh) The books, records and accounts of the Company accurately and fairly reflect in all material respects, in reasonable detail, the transactions in,
and dispositions of, the assets of, and the results of operations of, the Company. The Company has established and maintains “disclosure controls and procedures” (as such term is defined in Rule 13a-15 under the Exchange Act), which
(i) are designed to ensure that information required to be disclosed by the Company in the reports that it files or submits under the Exchange Act is recorded, processed, summarized and reported within the time periods specified in the
Commission’s rules and forms, (ii) are designed to ensure that information required to be disclosed by the Company in the reports that it files or submits under the Exchange Act is accumulated and communicated to the Company’s
management, including its principal executive officer and principal financial officer, as appropriate, to allow timely decisions regarding required disclosure and (iii) are sufficient to provide reasonable assurances with respect to the
performance of the functions for which they were established. The auditors have not brought to the Company’s attention any material weakness in the Company’s internal control over financial reporting (whether or not remediated). Based on
the most recent evaluation of the Company’s controls and procedures, the Company is not aware of (a) any significant deficiency in the design or operation of its internal controls which could adversely affect the Company’s ability to
record, process, summarize and report financial data or, (b) any material weaknesses in its internal controls or (c) any fraud, whether or not material, that involves management or other employees who have a significant role in the
Company’s internal controls. To the Company’s knowledge, there has been no change in the Company’s internal control over financial reporting that has materially affected, or is reasonably likely to materially affect, the
Company’s internal control over financial reporting. 

 (ii) Except as otherwise disclosed in the Time of Sale Prospectus and the Prospectus, there is no broker,
finder or other party that is entitled to receive from the Company any brokerage or finder’s fee or other fee or commission as a result of any transactions contemplated by this Agreement. 
 (jj) There are no outstanding loans, advances (except normal advances for business expenses 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 Time of Sale Prospectus and the Prospectus. 
 (kk) There is and has been no material failure on the part of the Company and, to the knowledge of the Company, any of the Company’s directors or
officers, in their capacities as such, to comply with any provision of the Sarbanes-Oxley Act of 2002 and the rules and regulations promulgated in connection therewith (the “Sarbanes Oxley Act”) that are applicable to the Company.

 (ll) Except as disclosed in the Time of Sale Prospectus and the Prospectus, the Company (i) does not have any material lending
relationship with any bank or lending affiliate of the Placement Agent and (ii) does not intend to use any of the proceeds from the sale of the Shares hereunder to repay any outstanding debt owed to any affiliate of the Placement Agent.

 2. Fees. (a) For this assignment the Placement Agent will charge the Company a placement fee (the “Placement
Fee”) of four percent (4%) of the aggregate price at which the Shares are sold by the Company. The Placement Fee shall be payable in immediately available funds on the Closing Date. At the Closing, the Company shall direct the Escrow Agent
to wire to an account or accounts designated by the Placement Agent the Placement Fee out of the Escrow Funds. 
 (b) The right of the
Placement Agent to receive the fees set forth in this Section 2 shall survive the termination of this Agreement in accordance with Section 7 hereof. 
 3. Conditions to the Placement Agent’s Obligations. The obligations of the Placement Agent are subject to the following conditions: 
 (a) Subsequent to the execution and delivery of this Agreement and prior to the Closing Date: 
 (i) there shall not have occurred any downgrading, nor shall any notice have been given of any intended or potential downgrading or of any
review for a possible change that does not indicate the direction of the possible change, in the rating accorded any of the securities of the Company by any “nationally recognized statistical rating organization,” as such term is defined
for purposes of Rule 436(g)(2) under the Securities Act; and 

 (ii) there shall not have occurred any change, or any development involving a prospective
change, in the condition, financial or otherwise, or in the earnings, business or operations of the Company from that set forth in the Time of Sale Prospectus as of the date of this Agreement that, in the Placement Agent’s judgment, is material
and adverse and that makes it, in the Placement Agent’s judgment, impracticable to market the Shares on the terms and in the manner contemplated in the Time of Sale Prospectus. 
 (b) The Placement Agent shall have received on the Closing Date a certificate, dated the Closing Date and signed by an executive officer of the Company,
to the effect set forth in Section 3(a)(i) above and to the effect that the representations and warranties of the Company contained in this Agreement are true and correct as of the Closing Date and that the Company has complied with all of the
agreements and satisfied all of the conditions on its part to be performed or satisfied hereunder on or before the Closing Date. 
 The
officer signing and delivering such certificate may rely upon the best of his or her knowledge as to proceedings threatened. 
 (c) The
Placement Agent shall have received on the Closing Date an opinion of Pepper Hamilton LLP, counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit B, the favorable opinion of in-house counsel for the
Company, dated as of such Closing Date, substantially in the form attached as Exhibit C, and the favorable opinion of Duane Morris LLP, patent counsel for the Company, dated as of such Closing Date, substantially in the form attached as Exhibit D.

 (d) The Placement Agent shall have received on the Closing Date an opinion of Wilmer Cutler Pickering Hale and Dorr LLP, counsel for the
Placement Agent, dated the Closing Date, in form and substance satisfactory to, and addressed to, the Placement Agent, with respect to such matters as the Placement Agent may reasonably require, and the Company shall have furnished to such counsel
such documents as they reasonably request for the purpose of enabling them to pass upon such matters. 
 (e) The Placement Agent shall have
received, on each of the date of the Purchase Agreement and the Closing Date, a letter dated the date of the Purchase Agreement or the Closing Date, as the case may be, in form and substance satisfactory to the Placement Agent, from Grant Thornton
LLP, independent public accountants, containing statements and information of the type ordinarily included in accountants’ “comfort letters” to the Placement Agent with respect to the financial statements and certain financial
information contained in the Registration Statement, the Time of Sale Prospectus and the Prospectus; provided that the letter delivered on the Closing Date shall use a “cut-off date” not earlier than three days prior to the Purchase
Agreement. 

 (f) The “lock-up” agreements, each substantially in the form of Exhibit A hereto, between the
Placement Agent and certain officers and directors of the Company relating to sales and certain other dispositions of shares of Common Stock or certain other securities, delivered to the Placement Agent or its counsel on or before the date hereof,
shall be in full force and effect on the Closing Date. 
 (g) On the Closing Date, the Placement Agent shall have received a certificate,
executed by the Chief Financial Officer of the Company and dated the date hereof, substantially in the form attached as Exhibit E. 
 (h) The
Company shall have entered into (i) Purchase Agreements with each of the Purchasers and (ii) the Escrow Agreement with the Placement Agent and the Escrow Agent, and such agreements shall be in full force and effect. 
 4. Covenants of the Company. The Company covenants with the Placement Agent as follows: 
 (a) To furnish to the Placement Agent, without charge, a signed copy of the Registration Statement (including exhibits thereto and documents incorporated
by reference therein) and to deliver to the Placement Agent during the period mentioned in Section 4(e) or 4(f) below, as many copies of the Time of Sale Prospectus, the Prospectus, any documents incorporated by reference therein and any
supplements and amendments thereto or to the Registration Statement as the Placement Agent may reasonably request. 
 (b) Before amending or
supplementing the Registration Statement, the Time of Sale Prospectus or the Prospectus, to furnish to the Placement Agent a copy of each such proposed amendment or supplement and not to file any such proposed amendment or supplement to which the
Placement Agent reasonably objects. 
 (c) To furnish to the Placement Agent a copy of each proposed free writing prospectus to be prepared
by or on behalf of, used by, or referred to by the Company and not to use or refer to any proposed free writing prospectus to which the Placement Agent reasonably objects. 
 (d) Not to take any action that would result in the Placement Agent or the Company being required to file with the Commission pursuant to Rule 433(d)
under the Securities Act a free writing prospectus prepared by or on behalf of the Placement Agent that the Placement Agent otherwise would not have been required to file thereunder. 
 (e) If the Time of Sale Prospectus is being used to solicit offers to buy the Shares at a time when the Prospectus is not yet available to prospective
purchasers and any event shall occur or condition exist as a result of which it is necessary to amend or supplement the Time of Sale Prospectus in order to make the statements therein, in the light of the circumstances, not misleading, or if any
event shall occur or condition exist as a result of which the Time of Sale Prospectus conflicts with the information contained in the Registration Statement then on file, or if, in the opinion of counsel for the Placement Agent, it is necessary to
amend or 

 
supplement the Time of Sale Prospectus to comply with applicable law, forthwith to prepare, file with the Commission and furnish, at its own expense, to the
Placement Agent and to any dealer upon request, either amendments or supplements to the Time of Sale Prospectus so that the statements in the Time of Sale Prospectus as so amended or supplemented will not, in the light of the circumstances when the
Time of Sale Prospectus is delivered to a prospective purchaser, be misleading or so that the Time of Sale Prospectus, as amended or supplemented, will no longer conflict with the Registration Statement, or so that the Time of Sale Prospectus, as
amended or supplemented, will comply with applicable law. 
 (f) If, during such period after the first date of the placement of the Shares
as in the opinion of counsel for the Placement Agent the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) of the Securities Act) is required by law to be delivered in connection with sales by the Placement Agent or a dealer, any
event shall occur or condition exist as a result of which it is necessary to amend or supplement the Prospectus in order to make the statements therein, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to
in Rule 173(a) of the Securities Act) is delivered to a purchaser, not misleading, or if, in the opinion of counsel for the Placement Agent, it is necessary to amend or supplement the Prospectus to comply with applicable law, forthwith to prepare,
file with the Commission and furnish, at its own expense, to the Placement Agent and other dealers (whose names and addresses the Placement Agent will furnish to the Company) upon request, either amendments or supplements to the Prospectus so that
the statements in the Prospectus as so amended or supplemented will not, in the light of the circumstances when the Prospectus (or in lieu thereof the notice referred to in Rule 173(a) of the Securities Act) is delivered to a Purchaser, be
misleading or so that the Prospectus, as amended or supplemented, will comply with applicable law. 
 (g) To endeavor to qualify the Shares
for offer and sale under the securities or Blue Sky laws of such jurisdictions as the Placement Agent shall reasonably request. 
 (h) To
make generally available to the Company’s security holders and to the Placement Agent as soon as practicable an earning statement covering a period of at least twelve months beginning with the first fiscal quarter of the Company occurring after
the date of this Agreement which shall satisfy the provisions of Section 11(a) of the Securities Act and the rules and regulations of the Commission thereunder. 
 (i) Whether or not the transactions contemplated in this Agreement are consummated or this Agreement is terminated, to pay or cause to be paid, subject to the limitation contained in the engagement letter dated
January 21, 2009 between the Company and the Placement Agent (the “Engagement Letter”), all expenses incident to the performance of its obligations under this Agreement, including: (i) the fees, disbursements and expenses
of the Company’s counsel and the Company’s accountants in connection with the registration and delivery of the Shares under the Securities Act and all other fees or expenses in connection with the preparation and filing of the Registration
Statement, any preliminary prospectus, the Time of Sale Prospectus, the Prospectus, any free writing prospectus prepared by or on behalf of, used by, or referred to by the Company and amendments and supplements to any of the 

 
foregoing, including the filing fees payable to the Commission relating to the Shares (within the time required by Rule 456 (b)(1), if applicable), all
printing costs associated therewith, and the mailing and delivering of copies thereof to the Placement Agent and dealers, in the quantities hereinabove specified, (ii) all costs and expenses related to the transfer and delivery of the Shares to
the Purchasers, including any transfer or other taxes payable thereon, (iii) the cost of printing or producing any Blue Sky or Legal Investment memorandum in connection with the offer and sale of the Shares under state securities laws and all
expenses in connection with the qualification of the Shares for offer and sale under state securities laws as provided in Section 4(g) hereof, including filing fees and the reasonable fees and disbursements of counsel for the Placement Agent in
connection with such qualification and in connection with the Blue Sky or Legal Investment memorandum, (iv) the reasonable fees and disbursements of counsel to the Placement Agent incurred in connection the transactions contemplated hereby,
(v) all costs and expenses incident to listing the Shares on NASDAQ, (vi) the cost of printing certificates representing the Shares, (vii) the costs and charges of any transfer agent, registrar or depositary, and the fees and expenses
of the Escrow Agent under the Escrow Agreement, (viii) the costs and expenses of the Company relating to investor presentations on any “road show” undertaken in connection with the marketing of the offering of the Shares, including,
without limitation, expenses associated with the preparation or dissemination of any electronic road show, expenses associated with the production of road show slides and graphics, fees and expenses of any consultants engaged in connection with the
road show presentations with the prior approval of the Company, travel and lodging expenses of the representatives and officers of the Company and any such consultants, and the cost of any aircraft chartered in connection with the road show,
(ix) the document production charges and expenses associated with printing this Agreement and (x) all other costs and expenses incident to the performance of the obligations of the Company hereunder for which provision is not otherwise
made in this Section. At the Closing, the Company shall direct the Escrow Agent to wire to an account or accounts designated by the Placement Agent out of the Escrow Funds all expenses of the Placement Agent for which the Company is obligated to pay
or reimburse the Placement Agent pursuant to this Agreement and the Engagement Letter. In addition, whether or not the transaction contemplated by this Agreement are consummated or this Agreement is terminated, the Company shall reimburse the
Placement Agent upon request for its reasonable fees and expenses (including the fees, disbursements and other charges of legal counsel to the Placement Agent) in accordance with the Engagement Letter. 
 (j) If the third anniversary of the initial effective date of the Registration Statement occurs before all the Shares have been placed by the Placement
Agent, prior to the third anniversary to file a new shelf registration statement and to take any other action necessary to permit the placement of the Shares to continue without interruption; references herein to the Registration Statement shall
include the new registration statement declared effective by the Commission; 
 (k) To prepare a final term sheet relating to the offering of
the Shares, containing only information that describes the final terms of the offering in a form consented to by the Placement Agent, and to file such final term sheet within the period required by Rule 433(d)(5)(ii) under the Securities Act
following the date the final terms have been established for the offering of the Shares. 

 The Company also covenants with the Placement Agent that, without the prior written consent of the
Placement Agent, it will not, during the period commencing on the date hereof and ending 60 days after the date of the final prospectus supplement relating to the Direct Offering, (1) offer, pledge, sell, contract to sell, sell any option or
contract to purchase, purchase any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or
exercisable or exchangeable for Common Stock or (2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction
described in clause (1) or (2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise or (3) file any registration statement with the Commission (other than on Form S-8 in respect of shares
of Common Stock issuable under the Company’s 2007 Equity Incentive Plan) relating to the offering of any shares of Common Stock or any securities convertible into or exercisable or exchangeable for Common Stock. The foregoing sentence shall not
apply to (a) the Shares to be sold in the Direct Offering, (b) the Company’s issuance of shares of Common Stock or options to purchase shares of Common Stock, or shares of Common Stock upon exercise of options, pursuant to the
Company’s 1998 Stock Plan or 2007 Equity Incentive Plan or (c) the Company’s issuance of shares of Common Stock upon exercise of warrants to purchase Common Stock outstanding on the date hereof. Notwithstanding the foregoing, if
(1) during the last 17 days of the lock-up restricted period the Company issues an earnings release or material news or a material event relating to the Company occurs; or (2) prior to the expiration of the lock-up restricted period, the
Company announces that it will release earnings results during the 16-day period beginning on the last day of the lock-up restricted 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. The Company shall promptly notify the Placement Agent of any earnings release, news or event that may give rise to an extension of the
initial lock-up restricted period. 
 5. Covenants of the Placement Agent. The Placement Agent covenants with the Company not to take
any action that would result in the Company being required to file with the Commission under Rule 433(d) a free writing prospectus prepared by or on behalf of the Placement Agent that otherwise would not be required to be filed by the Company
thereunder, but for the action of the Placement Agent 
 6. Indemnity and Contribution. (a) The Company agrees to indemnify and
hold harmless the Placement Agent, the partners, members, directors, officers, employees and agents of the Placement Agent, each person, if any, who controls the Placement Agent within the meaning of either Section 15 of the Securities Act or
Section 20 of the Exchange Act and each affiliate of the Placement Agent within the meaning of Rule 405 under the Securities Act from and against any and all losses, claims, damages and liabilities (including, without limitation, any legal
or other expenses reasonably incurred in connection with defending or investigating any 

 
such action or claim) (i) relating to, arising out of or in connection with the Direct Offering or (ii) caused by any untrue statement or alleged
untrue statement of a material fact contained in the Registration Statement or any amendment thereof, any preliminary prospectus, the Time of Sale Prospectus, any issuer free writing prospectus as defined in Rule 433(h) under the Securities Act, any
Company information that the Company has filed, or is required to file, pursuant to Rule 433(d) under the Securities Act, or the Prospectus or any amendment or supplement thereto, or caused by any omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements therein not misleading, except insofar as such losses, claims, damages or liabilities are caused by any such untrue statement or omission or alleged untrue statement or
omission based upon information relating to the Placement Agent furnished to the Company in writing by the Placement Agent expressly for use therein. With respect to clause (i) above, the Company will not, however, be responsible for
(x) any losses, claims, damages or liabilities (or expenses relating thereto) of the Placement Agent that are finally judicially determined to have resulted from the bad faith or gross negligence of the Placement Agent or (y) any losses,
claims, damages or liabilities (or expenses relating thereto) of any partner, member, director, officer, employee and agent of the Placement Agent that are finally judicially determined to have resulted from the bad faith or gross negligence of such
partner, member, director, officer, employee or agent of the Placement Agent. The Company also agrees that the Placement Agent shall not have any liability (whether direct or indirect, in contract or tort or otherwise) to the Company for or in
connection with the Direct Offering, except for any such liability for losses, claims, damages or liabilities with respect to clause (i) above incurred by the Company that are finally judicially determined to have resulted from the bad faith or
gross negligence of the Placement Agent. 
 (b) The Placement Agent agrees to indemnify and hold harmless the Company, its directors, its
officers who sign the Registration Statement and each person, if any, who controls the Company within the meaning of either Section 15 of the Securities Act or Section 20 of the Exchange Act to the same extent as the foregoing indemnity
from the Company to the Placement Agent contained in clause (ii), but only with reference to information relating to the Placement Agent furnished to the Company in writing by the Placement Agent expressly for use in the Registration Statement, any
preliminary prospectus, the Time of Sale Prospectus, any issuer free writing prospectus or the Prospectus or any amendment or supplement thereto. 
 (c) In case any proceeding (including any governmental investigation) shall be instituted involving any person in respect of which indemnity may be sought pursuant to Section 6(a) or 6(b), such person (the “indemnified
party”) shall promptly notify the person against whom such indemnity may be sought (the “indemnifying party”) in writing and the indemnifying party, upon request of the indemnified party, shall retain counsel reasonably
satisfactory to the indemnified party to represent the indemnified party and any others the indemnifying party may designate in such proceeding and shall pay the fees and disbursements of such counsel related to such proceeding. In any such
proceeding, any indemnified party shall have the right to retain its own counsel, but the fees and expenses of such counsel shall be at the expense of such indemnified party unless (i) the indemnifying party and the indemnified party shall have
mutually agreed to the retention of such counsel or (ii) the named parties to any such proceeding (including any 

 
impleaded parties) include both the indemnifying party and the indemnified party and representation of both parties by the same counsel would be
inappropriate due to actual or potential differing interests between them. It is understood that the indemnifying party shall not, in respect of the legal expenses of any indemnified party in connection with any proceeding or related proceedings in
the same jurisdiction, be liable for the fees and expenses of more than one separate firm (in addition to any local counsel) for all such indemnified parties and that all such fees and expenses shall be reimbursed as they are incurred. Such firm
shall be designated in writing by the Placement Agent, in the case of parties indemnified pursuant to Section 6(a), and by the Company, in the case of parties indemnified pursuant to Section 6(b). The indemnifying party shall not be liable
for any settlement of any proceeding effected without its written consent, but if settled with such consent or if there be a final judgment for the plaintiff, the indemnifying party agrees to indemnify the indemnified party from and against any loss
or liability by reason of such settlement or judgment. Notwithstanding the foregoing sentence, if at any time an indemnified party shall have requested an indemnifying party to reimburse the indemnified party for fees and expenses of counsel as
contemplated by the second and third sentences of this paragraph, the indemnifying party agrees that it shall be liable for any settlement of any proceeding effected without its written consent if (i) such settlement is entered into more than
30 days after receipt by such indemnifying party of the aforesaid request and (ii) such indemnifying party shall not have reimbursed the indemnified party in accordance with such request prior to the date of such settlement. No indemnifying
party shall, without the prior written consent of the indemnified party, effect any settlement of any pending or threatened proceeding in respect of which any indemnified party is or could have been a party and indemnity could have been sought
hereunder by such indemnified party, unless such settlement includes an unconditional release of such indemnified party from all liability on claims that are the subject matter of such proceeding. 
 (d) To the extent the indemnification provided for in Section 6(a) or 6(b) is unavailable to an indemnified party or insufficient in respect of any
losses, claims, damages or liabilities referred to therein, then each indemnifying party under such paragraph, in lieu of indemnifying such indemnified party thereunder, shall contribute to the amount paid or payable by such indemnified party as a
result of such losses, claims, damages or liabilities (i) in such proportion as is appropriate to reflect the relative benefits received by the Company on the one hand and the Placement Agent on the other hand from the Direct Offering or
(ii) if the allocation provided by clause 6(d)(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 6(d)(i) above but also the relative fault
of the Company on the one hand and of the Placement Agent on the other hand in connection with the statements or omissions that resulted in such losses, claims, damages or liabilities, as well as any other relevant equitable considerations. The
relative benefits received by the Company on the one hand and the Placement Agent on the other hand in connection with the Direct Offering shall be deemed to be in the same respective proportions as the net proceeds from the Direct Offering (before
deducting expenses) received by the Company and the total Placement Fee received by the Placement Agent bear to the aggregate public offering price of the Shares set forth in the Prospectus. The relative fault of the Company on the one hand and the
Placement Agent on the other hand shall be determined by reference to, among other things, whether the untrue or 

 
alleged untrue statement of a material fact or the omission or alleged omission to state a material fact relates to information supplied by the Company or by
the Placement Agent and the parties’ relative intent, knowledge, access to information and opportunity to correct or prevent such statement or omission. 
 (e) The Company and the Placement Agent agree that it would not be just or equitable if contribution pursuant to this Section 6 were determined by pro rata allocation or by any other method of allocation
that does not take account of the equitable considerations referred to in Section 6(d). The amount paid or payable by an indemnified party as a result of the losses, claims, damages and liabilities referred to in Section 6(d) shall be
deemed to include, subject to the limitations set forth above, 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 6, the Placement Agent shall not be required to contribute any amount in excess of the amount by which the total price at which the Shares placed by it were offered to the public exceeds the amount of any damages that the Placement
Agent has otherwise been required to pay by reason of such untrue or alleged untrue statement or omission or alleged omission. No person guilty of fraudulent misrepresentation (within the meaning of Section 11(f) of the Securities Act) shall be
entitled to contribution from any person who was not guilty of such fraudulent misrepresentation. The remedies provided for in this Section 6 are not exclusive and shall not limit any rights or remedies which may otherwise be available to any
indemnified party at law or in equity. 
 (f) The indemnity and contribution provisions contained in this Section 6 and the
representations, warranties and other statements of the Company contained in this Agreement shall remain operative and in full force and effect regardless of (i) any termination of this Agreement, (ii) any investigation made by or on
behalf of the Placement Agent, any person controlling the Placement Agent or any affiliate of the Placement Agent or by or on behalf of the Company, its officers or directors or any person controlling the Company and (iii) acceptance of and
payment for any of the Shares. 
 7. Termination. The Placement Agent may terminate this Agreement by notice given to the Company, if
after the execution and delivery of this Agreement and prior to the Closing Date (i) trading generally shall have been suspended or materially limited on, or by, as the case may be, any of the New York Stock Exchange, the American Stock
Exchange, the NASDAQ Global Market, the Chicago Board of Options Exchange, the Chicago Mercantile Exchange or the Chicago Board of Trade, (ii) trading of any securities of the Company shall have been suspended on any exchange or in any
over-the-counter market, (iii) a material disruption in securities settlement, payment or clearance services in the United States shall have occurred, (iv) any moratorium on commercial banking activities shall have been declared by Federal
or New York State authorities or (v) there shall have occurred any outbreak or escalation of hostilities, or any change in financial markets or any calamity or crisis that, in the Placement Agent’s judgment, is material and adverse and
which, singly or together with any other event specified in this clause (v), makes it, in the Placement Agent’s judgment, impracticable or inadvisable to proceed with the offer, sale or delivery of the Shares on the terms and in the manner
contemplated in the Time of Sale Prospectus or the Prospectus. In accordance with the Engagement Letter, if the sale and 

 
issuance of the Shares by the Company hereunder are not consummated for any reason, the Company will reimburse the Placement Agent for up to $100,000 of
out-of-pocket expenses (including fees and disbursements of counsel) reasonably incurred in connection with the offering of the Shares, and the respective obligations of the Company and the Placement Agent under Section 6 hereof shall remain in
effect. 
 8. Entire Agreement. This Agreement and the Engagement Letter, together with any contemporaneous written agreements and any
prior written agreements (to the extent not superseded by this Agreement) that relate to the Direct Offering, represents the entire agreement between the Company and the Placement Agent with respect to the preparation of any preliminary prospectus,
the Time of Sale Prospectus, the Prospectus, the conduct of the Direct Offering, and the purchase and sale of the Shares. 
 9.
Counterparts. This Agreement may be signed in two or more counterparts and by facsimile or electronic format, each of which shall be an original, with the same effect as if the signatures thereto and hereto were upon the same instrument.

 10. Applicable Law. This Agreement shall be governed by and construed in accordance with the internal laws of the State of New
York. 
 11. Headings. The headings of the sections of this Agreement have been inserted for convenience of reference only and shall
not be deemed a part of this Agreement. 
 12. Absence of Fiduciary Relationship. The Company acknowledges and agrees that:

 (a) No Other Relationship. The Placement Agent has been retained solely to act as placement agent in connection with
the sale of Shares and that no fiduciary, advisory or agency relationship between the Company and the Placement Agent has been created in respect of any of the transactions contemplated by this Agreement, any Purchase Agreement or the Prospectus,
irrespective of whether the Placement Agent has advised or is advising the Company on other matters; 
 (b)
Arm’s-Length Negotiations. The price of the Shares set forth in this Agreement was established by the Company following discussions and arm’s-length negotiations with the Placement Agent and the Company is capable of evaluating and
understanding and understands and accepts the terms, risks and conditions of the transactions contemplated by this Agreement; 
 (c) Absence of Obligation to Disclose. The Company has been advised that the Placement Agent and its affiliates are engaged in a broad range of transactions which may involve interests that differ from those of the Company and that
the Placement Agent has no obligation to disclose such interests and transactions to the Company by virtue of any fiduciary, advisory or agency relationship; and 

 (d) Waiver. The Company waives, to the fullest extent permitted by law, any claims
it may have against the Placement Agent for breach of fiduciary duty or alleged breach of fiduciary duty and agrees that the Placement Agent 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. Notices. All communications hereunder shall be in writing and effective only upon receipt and if to the Placement Agent shall be delivered, mailed or sent to the Placement Agent at the address set forth in
Schedule I hereto; and if to the Company shall be delivered, mailed or sent to the address set forth in Schedule I hereto. 
 [Remainder of
page intentionally left blank. Signature pages follow.] 

			
	 Very truly yours,
  
 Pharmasset, Inc.

		
	By:	 	 /s/ Kurt Leutzinger

	Name:	 	Kurt Leutzinger
	Title:	 	CFO

 [Signature Page to Placement Agency Agreement] 

 Accepted as of the date hereof 
  

			
	Leerink Swann LLC
		
	By:	 	 /s/ Donald D. Notman, Jr.

	Name:	 	Donald D. Notman, Jr.
	Title:	 	Managing Director

 [Signature Page to Placement Agency Agreement] 

 SCHEDULE I 
  

			
	Registration Statement File No.:	  	333-151749
		
	Time of Sale Prospectus	  	 1.      Prospectus dated June 26, 2008 relating to the Shares
  
 2.      Preliminary draft of
Subscription Agreement provided to prospective purchasers on January 29, 2009.
  
 3.      Term sheet dated January 29, 2009 relating to the Shares

		
	Title of Shares to be placed:	  	Common Stock, par value $0.001 per share
		
	Number of Shares:	  	4,678,000
		
	Public Offering Price	  	$9.73 per share
		
	Closing Date:	  	February 4, 2009
		
	Closing Location:	  	 Wilmer Cutler Pickering Hale and Dorr LLP
 60 State
Street
 Boston, Massachusetts 02109

		
	Address for Notices to Placement Agent:	  	 Leerink Swann LLC
 One Federal Street, 37th Floor
 Boston, Massachusetts 02110
 Attention: Donald Notman

		
	Address for Notices to the Company:	  	 303-A College Road East
 Princeton, New Jersey
08540
 Attention: Paul Lubetkin

 EXHIBIT A 
 FORM OF LOCK-UP LETTER 
 January     , 2009 
 Leerink Swann LLC 
 One Federal Street 
 Boston, Massachusetts 02110 
 Ladies and Gentlemen: 
 The undersigned understands that Leerink Swann LLC (the “Placement Agent”) proposes to enter into a Placement Agency Agreement (the
“Placement Agreement”) with Pharmasset, Inc., a Delaware corporation (the “Company”), providing for a registered direct offering (the “Direct Offering”) of shares of the common stock, $0.001 par
value per share, of the Company (the “Common Stock”), warrants to purchase shares of Common Stock or a combination thereof. 
 To induce the Placement Agent to continue its efforts in connection with the Direct Offering, the undersigned hereby agrees that, without the prior written consent of the Placement Agent, it will not, during the period commencing on the
date hereof and ending 60 days after the date of the final prospectus supplement relating to the Direct Offering (the “Prospectus”), (1) offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase
any option or contract to sell, grant any option, right or warrant to purchase, lend, or otherwise transfer or dispose of, directly or indirectly, any shares of Common Stock or any securities convertible into or exercisable or exchangeable for
Common Stock or (2) enter into any swap or other arrangement that transfers to another, in whole or in part, any of the economic consequences of ownership of the Common Stock, whether any such transaction described in clause (1) or
(2) above is to be settled by delivery of Common Stock or such other securities, in cash or otherwise. The foregoing sentence shall not apply to (a) transactions relating to shares of Common Stock or other securities acquired in open
market transactions after the completion of the Direct Offering, provided that no filing under Section 16(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), shall be required or shall be
voluntarily made in connection with subsequent sales of Common Stock or other securities acquired in such open market transactions, (b) transfers of shares of Common Stock or any security convertible into Common Stock as a bona fide gift,
(c) transfers of shares of Common Stock or any security convertible into Common Stock either during the undersigned’s lifetime or upon death by will or intestate succession to the immediate family of the undersigned or to a trust the
beneficiaries of which are exclusively the undersigned and/or a member or members of his immediate family, or (d) pursuant to any trading plan established pursuant to Rule 10b5-1 of the Exchange Act for the transfer of shares of Common Stock
that has been entered into by the undersigned prior to the date of this Agreement; provided that in the case of any transfer or distribution pursuant to clause (b) or (c), (i) each donee or distributee shall sign and deliver a
lock-up letter substantially in the form of this letter and (ii) no filing under Section 16(a) of the Exchange Act, reporting a reduction in beneficial ownership of 

 
shares of Common Stock, shall be required or shall be voluntarily made during the restricted period referred to in the foregoing sentence. In addition, the
undersigned agrees that, without the prior written consent of the Placement Agent, it will not, during the period commencing on the date hereof and ending 60 days after the date of the Prospectus, make any demand for or exercise any right with
respect to, the registration of any shares of Common Stock or any security convertible into or exercisable or exchangeable for Common Stock. The undersigned also agrees and consents to the entry of stop transfer instructions with the Company’s
transfer agent and registrar against the transfer of the undersigned’s shares of Common Stock except in compliance with the foregoing restrictions. For the purposes of this paragraph, “immediate family” shall mean spouse, domestic
partner, lineal descendant (including adopted children), father, mother, brother or sister of the transferor. 
 If: 
 (1) during the last 17 days of the restricted period the Company issues an earnings release or material news or a material event relating to the Company
occurs; or 
 (2) prior to the expiration of the restricted period, the Company announces that it will release earnings results during the
16-day period beginning on the last day of the restricted 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. 
 The
undersigned shall not engage in any transaction that may be restricted by this agreement during the 34-day period beginning on the last day of the initial restricted period unless the undersigned requests and receives prior written confirmation from
the Company or the Placement Agent that the restrictions imposed by this agreement have expired. 
 The undersigned understands that the
Company and the Placement Agent are relying upon this agreement in proceeding toward consummation of the Direct Offering. The undersigned further understands that this agreement is irrevocable and shall be binding upon the undersigned’s heirs,
legal representatives, successors and assigns. 
 Whether or not the Direct Offering actually occurs depends on a number of factors,
including market conditions. Any Direct Offering will only be made pursuant to a Placement Agreement, the terms of which are subject to negotiation between the Company and the Placement Agent. 
  

	
	Very truly yours,
	
	  

	
	  

	(Name)
	
	  

	(Address)

 EXHIBIT B 
 Form of Opinion of Counsel for the Company 
 Opinion of Pepper Hamilton LLP, counsel for the Company,
to be delivered pursuant to Section 3(c) of the Placement Agreement. 
 References to the Prospectus in this Exhibit B include any
supplements thereto at the Closing Date. 
 (i) The Company is a corporation validly existing and in good standing under the law of the State
of Delaware with corporate power and authority under such law to conduct its business as described in the Prospectus. 
 (ii) The Company
(a) has the corporate power to execute, deliver and perform the Placement Agreement, the Escrow Agreement and the Subscription Agreements and (b) has taken all corporate action necessary to authorize the execution, delivery and performance
of the Placement Agreement, the Escrow Agreement and the Subscription Agreements. 
 (iii) Each of the Placement Agreement, the Escrow
Agreement and the Subscription Agreements has been duly executed and delivered by the Company. 
 (iv) The Shares have been duly authorized
by the Company and, when issued and delivered as provided in the Placement Agreement and the Subscription Agreements, the Shares will be validly issued, fully paid and nonassessable, and the issuance of such Shares will not be subject to preemptive
rights pursuant to the General Corporation Law of the State of Delaware, the certificate of incorporation or by-laws of the Company or similar contractual rights granted by the Company pursuant to any contract or agreement listed in Schedule C to
such opinion. 
 (v) The statements in each of the Time of Sale Prospectus and the Prospectus under the caption “Description of Capital
Stock,” insofar as such statements purport to summarize certain provisions of the Common Stock or documents referred to therein, constitute a fair and accurate summary of those provisions and fairly summarize in all material respects the
documents referred to therein. The statements in the Prospectus Supplement under the caption “Certain U.S. Federal Income Tax Considerations for Non-U.S. Holders,” insofar as such statements constitute summaries of legal matters referred
to therein fairly summarize in all material respects such legal matters. 
 (vi) No authorization, approval or other action by, and no notice
to or filing with, any United States federal or New York governmental authority or regulatory body, is required for the due execution, delivery or performance of the Placement Agreement, the Escrow Agreement, the Subscription Agreements by the
Company and the issuance by the Company of the Shares, except as have been obtained and are in full force and effect under the Securities Act, or as may be required under the state securities or blue sky laws of any jurisdiction in the United States
(as to which we express no opinion) in connection with the sale of the Shares. 

 (vii) The execution and delivery by the Company of the Placement Agreement, the Escrow Agreement and the
Subscription Agreements do not, and the performance by the Company of its obligations thereunder (other than performance by the Company of its obligations under the indemnification section of the Placement Agreement, as to which no opinion is
expressed herein) will not (a) result in a violation of the Company’s certificate of incorporation or by-laws; (b) result in a violation of Applicable Law, or, to our knowledge, based solely upon a docket search conducted in the
Superior Court of Mercer County, New Jersey and the United States District Court for the District of New Jersey as of January 14, 2009, any order, writ, judgment, injunction, decree, determination or award binding on the Company or its assets, or
(c) result in a breach of, a default under or the acceleration of (or entitle any party to accelerate) the maturity of any obligation of the Company under, or result in or require the creation of any lien upon or security interest in any
property of the Company pursuant to the terms of, any agreement or document listed in Schedule A to such opinion. 
 (viii) The Company is
not and, upon the Closing of the Transaction, will not be, required to register as an investment company under the Investment Company Act of 1940, as amended. 
 (ix) The statements referenced on Schedule B to this opinion, insofar as such statements constitute summaries of applicable provisions of the Federal Food, Drug, and Cosmetic Act, as amended, and the regulations
promulgated thereunder, fairly summarize in all material respects the provisions purported to be summarized under such captions in the Prospectus. 
 In addition, such counsel shall state that they have reviewed and participated in discussions concerning the preparation of the Registration Statement, the Time of Sale Prospectus and the Prospectus with certain officers or employees of the
Company, with its auditors, and with the Placement Agent and its representatives. The limitations inherent in the independent verification of factual matters and in the role of outside counsel are such, however, that such counsel cannot and does not
assume any responsibility for the accuracy, completeness or fairness of the statements made in the Registration Statement, the Time of Sale Prospectus or the Prospectus, except as set forth in paragraph vii of such opinion addressed to you, dated
the date hereof. 
 Such counsel shall also state that on February 4, 2009, a member of the staff of the Commission informed such
counsel orally that no stop order suspending the effectiveness of the Registration Statement has been issued under the Securities Act. To the knowledge of such counsel, no proceedings for that purpose have been initiated or are pending or threatened
by the Commission. 
 Such counsel also advises you that, subject to the limitations set forth in the preceding paragraph, on the basis of
the information such counsel gained in the course of performing the services referred to above, each of the Registration Statement and the Prospectus (other than the financial statements and other financial data included therein or omitted
therefrom, as to which such counsel expresses no opinion) appears on its face to be appropriately responsive in all material respects to the requirements of the Securities Act and the 

 
applicable rules and regulations of the Commission thereunder, and no facts came to such counsel’s attention which gave such counsel reason believe that
(i) the Registration Statement (other than the financial statements and other financial data derived therefrom contained therein or omitted therefrom, as to which such counsel has not been requested to comment), at the time it became effective,
contained an untrue statement of a material fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein not misleading; (ii) the Time of Sale Prospectus (other than the financial
statements and other financial data contained therein or omitted therefrom, as to which such counsel has not been requested to comment), at the applicable time or on the date of such opinion, contained or contains an untrue statement of a material
fact or omitted to state a material fact required to be stated therein or necessary in order to make the statements therein, in the light of circumstances under which they were made, not misleading, or (iii) the Prospectus (other than the
financial statements and other financial data contained therein or omitted therefrom, as to which such counsel has not been requested to comment), as of its date or the date of such opinion, contained or contains an untrue statement of a material
fact or omitted or omits to state a material fact necessary in order to make the statements therein, in the light of the circumstances under which they were made, not misleading. 
 In rendering such opinion, such counsel may rely (A) as to matters involving the application of laws of any jurisdiction other than the General
Corporation Law of the State of Delaware, the New York Corporation Law or the federal law of the United States, to the extent they deem proper and specified in such opinion, upon the opinion (which shall be dated the Closing Date shall be reasonably
satisfactory in form and substance to the Placement Agent, shall expressly state that the Placement Agent may rely on such opinion as if it were addressed to them and shall be furnished to the Placement Agent) of other counsel of good standing whom
they believe to be reliable and who are reasonably satisfactory to counsel for the Placement Agent; and (B) as to matters of fact, to the extent they deem proper, on certificates of responsible officers of the Company and public officials.

 Schedule B to Opinion of Counsel for the Company 
 We have reviewed certain information incorporated by reference into the Registration Statement from the Company’s Annual Report on Form 10-K for the fiscal year
ended September 30, 2008 under the following captions: 
  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – We are subject to significant regulatory
requirements, which could delay, prevent or limit our ability to market our product candidates, including clevudine, Racivir, R7128, PSI-7851 and DFC;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – Our product candidates must undergo rigorous
clinical trials, the results of which are uncertain and could substantially delay or prevent us from bringing drugs to market;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – Delays in clinical trials could result in
increased costs to us and delay our ability to obtain regulatory approval and commercialize our product candidates;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – Failure to recruit and enroll patients/subjects
for clinical trials may cause the development of our product candidates to be delayed;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – Our product candidates may have undesirable
side effects when used alone or in combination with other products that prevent their regulatory approval or limit their use if approved;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – Even if we obtain regulatory approvals, our
marketed drugs will be subject to ongoing regulatory review. If we fail to comply with continuing U.S. and foreign regulations, we could lose our marketing approvals and our business would be seriously harmed;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Drug Discovery, Development and Commercialization – We and our collaborators will be subject to
stringent federal, state and foreign regulation of sales and marketing of any approved drug candidate and a failure to comply with these regulations could result in substantial penalties;” 

  

	 	•	 	 “Risks Related to Our Business – Risks Related to Our Dependence on Third Parties – We and our collaborators depend on third parties to conduct our
clinical trials, which may result in costs and delays that prevent us from obtaining regulatory approval or successfully commercializing our product candidates;” 

	 	•	 	 “Risks Related to Our Business – Risks Related to Our Dependence on Third Parties – If parties on whom we rely to manufacture our product candidates
do not manufacture the active pharmaceutical ingredients or finished products of satisfactory quality, in a timely manner, in sufficient quantities or at an acceptable cost, clinical development and commercialization of our product candidates could
be delayed;” and 

  

	 	•	 	 “Business – Government Regulation – Pharmaceutical Regulation in the United States.” 

 (collectively, the “FDA Regulatory Sections”) in the Company’s prospectus supplement dated January 29, 2009 (the “Prospectus”), forming a
part of the Company’s Registration Statement on Form S-3, (Registration No. 333-151749). 

 EXHIBIT C 
 Form of Opinion of In-house Counsel for the Company 
 Opinion of in-house counsel for the Company to
be delivered pursuant to Section 3(c) of the Placement Agreement. 
 References to the Prospectus in this Exhibit C include any
supplements thereto at the Closing Date. 
 (i) The Company’s authorized equity capitalization is as set forth in the Registration
Statement, the Time of Sale Prospectus and the Prospectus. The authorized, issued and outstanding capital stock of the Company (including the Common Stock) conform to the descriptions thereof set forth in the Registration Statement, the Time of Sale
Prospectus and the Prospectus. All of the outstanding shares of Common Stock have been duly authorized and validly issued, are fully paid and nonassessable. 
 (ii) To the best knowledge of such counsel, there are no legal or governmental actions, suits or proceedings pending or threatened which are required to be disclosed in the Registration Statement, other than those
disclosed therein or in the Time of Sale Prospectus. 
 (iii) Except as disclosed in the Time of Sale Prospectus and the Prospectus, to the
best knowledge of such counsel, there are no persons with registration or other similar rights to have any equity or debt securities registered for sale under the Registration Statement or included in the offering contemplated by the Placement
Agency Agreement, except for such rights as have been duly waived. 
 (iv) The Company is duly qualified as a foreign corporation to transact
business and is in good standing in each jurisdiction in which such qualification is required, whether by reason of the ownership or leasing of property or the conduct of business, except for such jurisdictions where the failure to so qualify or to
be in good standing would not, individually or in the aggregate, have a Material Adverse Effect. 
 (v) The statements in each of the Time of
Sale Prospectus and the Prospectus under the headings “Description of Capital Stock” and “Certain Relationships and Related Party Transactions,” in the Company’s annual report on Form 10-K for the year ended
September 30, 2008 filed with the SEC on December 18, 2008 under the headings “Business” and “Risk Factors,” and in Items 14 and 15 of the Registration Statement, insofar as such statements summarize legal matters,
agreements, documents or proceedings discussed therein, constitute a fair and accurate summary of those legal matters, agreements, documents or proceedings. 
 (vi) To the best knowledge of such counsel, the Company (A) is not in violation of any statute, law, rule, judgment, regulation, order or decree applicable to the Company of any court, regulatory body,
administrative agency, governmental body, arbitrator or other authority having jurisdiction over the Company or any of its properties or (B) is not in Default in the performance or observance of any obligation, agreement, covenant or condition
contained in any material Existing Instrument, except with respect to this clause (B) only, for such Defaults as would not, individually or in the aggregate, have a Material Adverse Effect. 

 (vii) The Company possesses such valid and current licenses, certificates, authorizations or permits
issued by the appropriate state, federal or foreign regulatory agencies or bodies necessary to conduct their respective businesses, and the Company has not received any notice of proceedings relating to the revocation or modification of, or
non-compliance with, any such license, certificate, authorization or permit which, singly or in the aggregate, if the subject of an unfavorable decision, ruling or finding, could have a Material Adverse Effect. 
 (viii) To the best knowledge of such counsel, the Company is not in violation of its charter or by-laws. 
 (ix) Except as disclosed in the Time of Sale Prospectus and the Prospectus, to the best of such counsel’s knowledge, the Company has not received
any notice of infringement of, and to the best of such counsel’s knowledge, there is no infringement of Intellectual Property Rights of others, which infringement would, singly or in the aggregate, have a Material Adverse Effect. The Company is
not a party to or bound by any options, licenses or agreements with respect to the Intellectual Property Rights of any other person or entity that are required to be set forth in the Prospectus and are not described in all material respects. To the
best of such counsel’s knowledge, none of the technology employed by the Company has been obtained or is being used by the Company in violation of any contractual obligation binding on the Company or any of its officers, directors or employees
or otherwise in violation of the rights of any persons. 

 EXHIBIT D 
 Form of Opinion of Patent Counsel for the Company 
 Opinion of Duane Morris LLP, patent counsel for
the Company, to be delivered pursuant to Section 3(c) of the Placement Agreement. 
 (i) We have no knowledge that the statements
relating to Covered Intellectual Property included in or incorporated by reference into the Time of Sale Prospectus and the Prospectus under the headings “Risk Factors – Risks Related to Our Intellectual Property” and “Business
– Intellectual Property” in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2008 contain any statement which, at the time and in light of the circumstances under which it is made, is false or
misleading with respect to any material fact or omits to state any material fact necessary to make the statements therein, at the time and in light of the circumstances under which they are made, not misleading. 
 (ii) To our knowledge, the Company owns all material Intellectual Property of which we are aware that is currently employed by the Company in connection
with the business now operated by it, or that is necessary for the manufacture, use or sale of its presently proposed products as described in the Time of Sale Prospectus and the Prospectus, or otherwise possesses sufficient right(s) with respect to
such Intellectual Property to permit such use. 
 (iii) To our knowledge, the Company has not received any communication or notice alleging
any act of infringement of any third party patents by the Company. 
 (iv) To our knowledge, the claims of all issued and unexpired patents
included in the Covered Intellectual Property are valid and enforceable under the U.S. patent laws. 
 (v) To our knowledge, no interference,
reexamination, or other judicial or administrative proceeding pertaining to the validity, enforceability or scope of the Covered Intellectual Property has been threatened or declared. 

 EXHIBIT E 
 Form of Chief Financial Officer’s Certificate 
 February 4, 2009 
 I, Kurt Leutzinger, do hereby certify that I am the Chief Financial Officer of Pharmasset, Inc., a Delaware company (the “Company”) and, in my
capacity as Chief Financial Officer, do hereby certify that: 
  

	 	1.	I am providing this certificate in connection with the offering (the “Offering”) by the Company of an aggregate of 4,678,000 shares of its common stock (the “Common
Stock”) as described in that certain Registration Statement on Form S-3 (No. 333-151749), including the prospectus filed with the Securities and Exchange Commission (the “SEC”) on June 26, 2008 and the prospectus supplement filed
with the SEC on January 30, 2009 pursuant to Rule 424(b)(5) of the Securities Act (the “Registration Statement”). 

  

	 	2.	I am familiar with the accounting, operations and records systems of the Company. 

  

	 	3.	The materials attached as Exhibit A hereto relating to the financial data of the Company as of dates and periods subsequent to September 30, 2008 are what they purport
to be and, to the best of my knowledge, are correct. As of December 31, 2008, the Company’s cash and cash equivalent balance was $51.8 million. 

  

	 	4.	I have supervised the compilation of and reviewed the circled information contained on the attached Exhibit B, which is included and/or incorporated by reference into the
Registration Statement. I have performed the following procedures with respect to the circled information identified on Exhibit B, which were applied as indicated below and, to my knowledge, such information is accurate in all material
respects: 

 A. Compared the amount to, or recalculated such amount from, the Company’s audited
consolidated financial statements or related notes to the audited consolidated financial statements and found it to be in agreement. 
 B. Compared the amount to, or recalculated such amount from, the Company’s unaudited consolidated financial statements or related notes to the unaudited consolidated financial statements and found it to be in agreement. 
 C. Compared the amount to, or recalculated such amount from, the Company’s general ledger or other accounting books and records for
periods indicated and found it to be in agreement. 

 D. Compared the amount to, or recalculated such amount from, a schedule or report
prepared by the Company from the Company’s accounting records and found it to be in agreement. 
 This certificate is being furnished to Leerink Swann
LLC as Placement Agent for the Offering, solely to assist in conducting their investigation of the Company in connection with the Offering. This certificate shall not be used, quoted or otherwise referred to without the prior written consent of the
Company.

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