Document:

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                                                                    EXHIBIT 10.7

                              CONSULTING AGREEMENT

                                   (Schinazi)

         CONSULTING AGREEMENT dated as of June 12, 1998 by and between Novirio
Pharmaceuticals, Inc., a Massachusetts corporation with a mailing address c/o
MPM Asset Management, LLC, One Cambridge Center, 9th Floor, Cambridge, MA 02142
(the "Company"), and Raymond F. Schinazi, with a mailing address
at_______________ ("Consultant").

                                    RECITALS

         A. The Company has been formed to engage in the business of development
and commercialization of pharmaceuticals for the treatment of human viral
diseases (the "Business").

         B. The Company desires to engage Consultant to provide services to the
Company and Consultant desire to provide such services to the Company as set
forth in this Agreement.

         C. In connection therewith, Consultant and the Company mutually desire
to enter into this Agreement effective as of the date hereof, which will govern
all work performed for the Company.

         NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Company and Consultant hereby
agrees as follows:

         1. Term. Company agrees to engage Consultant, and Consultant agrees to
accept such engagement, to provide advisory, consulting and other services to
the Company on the terms and conditions hereinafter provided, commencing as of
the date hereof (the "Engagement Date") and terminating on June 12, 2002 (the
"Initial Term"), unless terminated sooner pursuant to Section 8 hereof. Prior to
the expiration of the Initial Term, the Consulting Agreement may be renewed by
mutual agreement of the Company and the Consultant for one or more successive
one-year periods (such successive periods, with the Initial Term, are referred
to as the "Term").

         2. Services. Consultant shall provide consulting, advisory and other
services in the Business including, without limitations, (a) performing the
functions described on Exhibit A hereto, (b) assisting the Company in the
preparation and filing of patent applications; (c) assisting with the
development and research of products and potential products for the Business;
and (d) such other responsibilities as the Company and the Consultant may agree
(the "Services").

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         3. Compensation and Expenses.

                  (a) Compensation. During the Term, the Company shall pay
Consultant the $25,000 per year, payable quarterly in arrears, commencing June
1, 1998.

                  (b) Business Expenses. During the Term, the Company shall
reimburse Consultant for all reasonable and necessary expenses incurred by
Consultant in the furtherance of or in connection with the business of the
Company, including, without limitation, travel, board, lodging, telephone and
postage, in accordance with the Company policy then in effect. In order to
obtain reimbursement, Consultant shall submit to the Company an itemized
statement of such expenses along with copies of bills and receipts.

         4. Non-Competition; Non-Solicitation. Except as otherwise provided in
this Section 4, at all times during the Term, and for a period of eighteen (18)
months thereafter, Consultant shall not:

                  (a) Serve as an executive officer of a company engaged in the
Business (other than positions currently held by Consultant);

                  (b) induce or attempt to induce any customer, dealer or
distributor of the Company to reduce such customer's, dealer's or distributor's
business with the Company; or

                  (c) solicit any of the Company's consultants or employees to
leave the employ of the Company or hire or cause to be hired any person who was
during or for six (6) months after the termination of Consultant's engagement by
the Company, a consultant or employee of the Company.

         The above restrictions shall not be deemed to prohibit Consultant from
(i) taking a position as a faculty member with any university, college, hospital
or other research, treatment or teaching based nonprofit institution, or (ii)
maintaining any position set forth on Exhibit B hereto, or from any activities
undertaken in such position.

         5. Covenants of Consultant. Consultant shall provide expertise in the
area of drug resistance, cross-resistance, ways to overcome resistance, the
design of combination trials and virological issues in general. He also agrees
to use his best efforts to facilitate the license by the Company from Pharmasset
of inventions, improvements, modifications, discoveries, creations, methods,
processes and developments in the Business which are made or conceived by
Consultant alone or with others during the Term.

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         6. Confidentiality. During the course of his engagement with the
Company, Consultant may have access to, learn of, or participate in the
development of the Company's confidential information or confidential
information entrusted to the Company by other persons, corporations, or firms.
The Company's confidential information includes matters not generally known
outside of the Company, such as know-how, trade secrets, experimentation,
research and developments relating to existing and future products and services
to be or being marketed or used by the Company (whether or not such products or
services are actually realized or pursued by the Company), and also any
information which gives the Company a competitive advantage including, without
limitation, data relating to the general business operations of the Company
(e.g., sales, costs, profits, organizations, customer lists, pricing methods,
etc.). Confidential information shall not include information that may be
demonstrated by Consultant to have been known by Consultant prior to the date
hereof or which is otherwise disclosed to the Consultant by a third party who is
not under any confidentiality obligation preventing such disclosure. Consultant
agrees to hold such information as strictly confidential and not disclose any
such confidential information to any person, corporation or firm (other than the
Company). Consultant further agrees not to make use of such confidential
information except on the Company's behalf whether or not such information is
produced by his own efforts. These restrictions shall apply to all such
information whether written, oral, magnetic, optical or in some other form.
Consultant understands and agrees that his confidentiality obligations under
this Section 6 shall continue both during his engagement and after termination
of his engagement until such confidential information becomes generally
available to the public through legitimate means. It is understood and agreed
that specific information which Consultant may receive, observe, perceive,
create, develop or learn while a consultant to the Company shall not be deemed
to be generally available to the public merely because such specific information
is embraced by more general information which is generally available to the
public.

         7. Return of Information. At the end of the Term or at any time upon
the request of the Company, Consultant agrees to deliver to the Company all
records, drawings, notebooks, documents, computer disks and tapes and other data
in any and all forms which pertain to the Company's confidential information
(whether prepared by Consultant or others), and also to return to the Company
any equipment, tools, computers or other devices owned by the Company and in his
possession, provided however that the Consultant shall have the right to retain
one copy of such materials for his personal records (but in any event not to be
used in a manner inconsistent with the terms of this Agreement). Consultant
agrees that the above documents, data and devices are the exclusive property of
the Company and shall not be copied or removed from the Company premises except
in the pursuit of the business of the Company.

                                      -3-
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         8. Representations and Covenants.

                  (a) Consultant will not disclose to the Company, or induce the
Company to use, any confidential information of other persons, corporations, or
firms including his present or former employers (if any).

                  (b) Set forth on Exhibit B hereto is a list of all educational
institutions, companies, governmental entities and individuals with whom
Consultant has current representative, consultant, employment, business
partnership or similar relationships or of which Consultant owns greater than 5%
of the outstanding voting securities, and a description of all agreements with
such parties. Consultant shall notify the Company in writing promptly whenever
there are changes to this list.

                  (c) Consultant is responsible for ensuring that the
relationships set forth on Exhibit B hereto will not result, with the passage of
time or the giving of notice, or both, in a default under the terms of this
Agreement.

                  (d) Consultant represents that he has not been debarred nor
received notice of any action, or threat with respect to its debarment under the
provisions of the Generic Drug Enforcement Act of 1992, 21 U.S.C. Section
335(a). Consultant agrees promptly to notify the Company upon receipt of any
such notice and further agrees, upon the Company's request, to provide a
separate written certification, on a form provided by the Company, to this
effect.

         9. Termination of Engagement. Notwithstanding the provisions of Section
1, Consultant's engagement hereunder shall terminate under the following
circumstances:

                  (a) Death or Disability. Consultant's engagement hereunder
shall immediately terminate upon his death or disability (as hereinafter
defined). For purposes of this Agreement, Consultant shall be deemed disabled if
in the opinion of the Board of Directors of the Company, determined in good
faith, Consultant is unable to substantially perform services hereunder due to
illness, injury, accident or condition of either a physical or psychological
nature for greater than ninety (90) days.

                  (b) Termination by the Company for Cause. The Company may
terminate Consultant's engagement for "cause" (as hereinafter defined) after
prior written notice to Consultant setting forth in reasonable detail the nature
of such cause. For the purposes hereof, "cause" shall be determined by the Board
of Directors of the Company acting in good faith and shall include (but not be
limited to):

                           (i)      the conviction of Consultant by a court of
                                    competent jurisdiction of any felony,
                                    misdemeanor or any criminal

                                      -4-
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                                    offense involving breach of trust,
                                    misappropriation or dishonesty against the
                                    Company or Novirio Pharmaceuticals Limited,
                                    a Cayman Islands corporation ("Novirio
                                    Limited"), or any subsidiary of Novirio
                                    Limited, or the entering of a plea by
                                    Consultant of nolo contendere thereto;

                           (ii)     the commission by Consultant of an act of
                                    fraud upon the Company, Novirlo Limited or
                                    any subsidiary of Novirio Limited;

                           (iii)    Consultant's willful violation of any United
                                    States federal, state or local or foreign
                                    government law, rule or regulation governing
                                    the operation of the Company, Novirio
                                    Limited or any subsidiary of Novirio
                                    Limited; or

                           (iv)     a material breach by Consultant of this
                                    Agreement, which breach continues for more
                                    than twenty (20) business days after written
                                    notice given to Consultant, such notice to
                                    set forth in reasonable detail the nature of
                                    such breach.

                  (c) Termination by Consultant. Consultant may terminate his
engagement for any reason whatsoever upon ninety (90) days' prior written notice
to the Company.

         10. Payments Upon Termination. Upon termination of Consultant,
Consultant shall be entitled to receive from the Company, unpaid through the
date of termination and (ii) reimbursement of expenses which have been incurred
through the date of such termination.

         11. Independent Contractor. Both the Company and the Consultant agree
that Consultant acts as an independent contractor in the performance of his
duties under this Agreement. Nothing in this Agreement shall be deemed to make
the Consultant an employee, partner or agent for the Company, Novirio Limited or
any subsidiary of Novirio Limited, nor shall either party have any authority to
bind the other in any respect. Accordingly, the Consultant shall be responsible
for payment of, and shall indemnify and hold the Company harmless against, all
taxes, including, without limitation, federal, state and local taxes and taxes
assessed by foreign countries arising out of the Consultant's activities in
accordance with this Agreement, including by way of illustration but not
limitation, federal and state income tax, Social security tax, a foreign
country's income tax, unemployment insurance taxes, Medicare taxes and any other
taxes, or business license fees as required.

                                      -5-
<PAGE>

         12. Notices. Any notices, requests, demands and other communications
provided for by this Agreement shall be sufficient if in writing and delivered
in person or sent by registered or certified mail, postage paid, to Consultant
at the last address Consultant has filed in writing with the Company, or, in the
case of the Company, to the attention of its President. All such communications
shall be deemed given upon receipt. Any party may by notice in writing to the
other parties change the address to which notices to it or him are to be
addressed hereunder.

         13. Miscellaneous.

                  (a) Entire Agreement: Amendments; Waivers. This Agreement
contains the entire understanding of the parties regarding its subject matter
and any amendment to this Agreement, and any waiver of any provision hereof,
shall be in writing and shall require the prior written approval of the
Consultant and the Board of Directors of Novirio Limited. Any waiver by the
Company of a breach of any provision of this Agreement shall not operate or be
construed as a waiver of any subsequent breach hereof.

                  (b) Survival. Except as otherwise provided in this Agreement,
the obligations of the Company and Consultant contained in Sections 4, 6, 7 and
11 and this Section 13 shall survive the termination of this Agreement.

                  (c) Governing Law; Consent to Jurisdiction. Consultant agrees
that any dispute in the meaning, effect or validity of this Agreement shall be
resolved in accordance with the laws of the Commonwealth of Massachusetts
without regard to the conflict of laws provisions thereof. The Consultant hereby
agrees to submit to the nonexclusive jurisdiction of the court in and of the
Commonwealth of Massachusetts and to the courts to which an appeal of the
decisions of such courts may be taken and consents that service of process with
respect to all courts in and of the Commonwealth of Massachusetts may be made by
registered mail to Consultant's address set forth on page one hereof.

                  (d) Enforcement. In view of the substantial harm which will
result from the breach by Consultant of any of the covenants contained in
Sections 4, 6 and 7, the parties agree that such covenants shall be enforced to
the fullest extent permitted by law. Accordingly, if, in any judicial
proceeding, a court shall determine that such covenants are unenforceable
because they cover too extensive a geographic area or survive for too long a
period of time, or for any other reason, then the parties intend that such
covenants shall be deemed to cover such maximum geographic area and maximum
period of time and shall otherwise be deemed to be limited in such manner as
will permit enforceability by such court. If any term or provision of this
Agreement or the application thereof to any circumstance shall, to any extent,
be invalid or

                                      -6-
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unenforceable, the remainder of this Agreement or the application to other
persons and circumstances shall not be affected thereby and each term and
provision hereof shall be enforced to the fullest extent permitted by law.

                  (e) Remedies. Consultant agrees that his breach of any of the
provisions of Sections 4, 6 and 7 above will cause irreparable damage to the
Company and that the recovery by the Company of money damages will not alone
constitute an adequate remedy for such breach. Accordingly, Consultant agrees
that such provisions may be specifically enforced against it or him, in addition
to any other rights or remedies available to the Company on account of any such
breach.

                  (f) Indemnification.

                           (i)      Consultant will indemnify and hold the
                                    Company harmless, and will defend the
                                    Company against any and all loss, liability,
                                    damage, claims, demands or suits and related
                                    costs and expenses to persons or property
                                    that arise, directly or indirectly, from
                                    acts or omissions of Consultant, or breach
                                    by the Consultant of any term or condition
                                    of this Agreement.

                           (ii)     The Company will indemnify and hold the
                                    Consultant harmless, and will defend the
                                    Consultant against any and all loss,
                                    liability, damage, claims, demands or suits
                                    and related costs and expenses to persons or
                                    property that arise, directly or indirectly,
                                    from breach by the Company of any term or
                                    condition of this Agreement, and from acts
                                    taken by the Consultant on behalf of the
                                    Company if he (i) acted in good faith, in
                                    accordance with this Agreement and in a
                                    manner he reasonably believed to be in or
                                    not opposed to the best interests of the
                                    Company, and (ii) with respect to any
                                    criminal action or proceeding, had no
                                    reasonable cause to believe his conduct was
                                    unlawful.

                  (g) Successors and Assigns. This Agreement shall be binding
upon Consultant, and inure to the benefit of, the parties hereto and their
respective heirs, successors, assigns and personal representatives; provided,
however, that it shall not be assignable by Consultant.

                  (h) Attorney's Fees. If any action at law or in equity is
necessary to enforce or interpret the terms of this Agreement, the prevailing
party shall be entitled to reasonable attorney's fees, costs and necessary
disbursements, in addition to any other relief to which the party may be
entitled.

                                      -7-
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                  (i) Public Disclosure.

                           (i)      Except as required by law, neither
                                    Consultant nor the Company shall disclose
                                    the terms of this Agreement, or the
                                    transactions contemplated by this Agreement
                                    without the written consent of the other
                                    party and Emory University.

                           (ii)     Except as required by law, the Company shall
                                    not without the prior consent of the
                                    Consultant issue any press release or other
                                    public statement directed through the media
                                    which discloses the name of the Consultant
                                    or the Consultant's relationship with the
                                    Company

                  (j) Disputes arising under this Agreement shall be resolved by
a panel of three arbitrator in an arbitration conducted in accordance with the
rules of the American Arbitration Association. The decision of a majority of the
three arbitrators shall be final and binding upon the parties. The Consultant
shall select one arbitrator, the Company shall select a second arbitrator and
the two so selected shall select and designate a third arbitrator.

         IN WITNESS WHEREOF, the parties hereto have executed this Agreement as
a sealed document on the date first above written.

                                     NOVIRIO PHARMACEUTICALS, INC.

                                     By: /s/ Joachim Rothe
                                        ________________________________________

                                     Name: Joachim Rothe
                                          ______________________________________

                                     Title: CFO
                                           _____________________________________

                                     /s/ Raymond Schinazi
                                     ___________________________________________
                                     Raymond F. Schinazi

                                      -8-
<PAGE>
                                    EXHIBIT A

                             DUTIES OF A CONSULTANT

DR. RAYMOND SCHINAZI is Professor of Pediatrics and Chemistry, and Director,
Laboratory of Biochemical Pharmacology at Emory University. He will provide
expertise in the area of drug resistance, cross-resistance, ways to overcome
resistance, the design of combination trials and virological issues in general.
His knowledge of chemistry, in addition to virology, will provide rapid
solutions to technical issues at the interface of these two disciplines. As a
founder of both Pharmasset and the Company, he will facilitate technology
transfers from Pharmasset to the Company.
<PAGE>
                                    EXHIBIT B

                              CURRENT AFFILIATIONS

-        NIH

-        Emory University

-        VA Medical Center

-        Georgia State University

-        Pharmasset Ltd.

-        Quad Pharma

-        Triangle Pharmaceuticals

-        General Medical Industries

-        Murex/Abbott

-        Innogenetics

-        IVAX

-        Andrx Pharmaceuticals

-        Buckway Pharmaceutical

-        Chong Keun Dango

-        Moravak

-        [Illegible]

-        International Press<PAGE>

                                                                    EXHIBIT 10.8

                      FOUNDER'S STOCK RESTRICTION AGREEMENT

         THIS STOCK RESTRICTION AGREEMENT ("Agreement") is made as of June __,
1998, between Novirio Pharmaceuticals Limited, a Cayman Islands corporation (the
"Company"), and Dr. Raymond F. Schinazi ("Consultant").

                                    RECITALS

         In connection with Consultant's services to Novirio Pharmaceuticals,
Inc., a Massachusetts corporation which is a wholly owned subsidiary of the
Company ("Novirio"), pursuant to the Consulting Agreement dated the date hereof
between the Consultant and Novirio (the "Consulting Agreement"), the Company
desires to issue to the Consultant, and the Consultant desires to purchase from
the Company, the Company's Ordinary Shares upon the terms set forth herein.

         NOW, THEREFORE, in consideration of the foregoing premises and the
mutual promises set forth in this Agreement, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties to this Agreement, intending to be legally bound, agree as follows:

                                   SECTION 1

                                   DEFINITIONS

         1.1 Definitions. In addition to the other terms defined in this
Agreement, the terms below shall have the following respective meanings:

                  (a) "Board" means the Board of Directors of the Company.

                  (b) "Majority Stockholders" means, at any time, holders of a
majority of the sum of (i) the outstanding Ordinary Shares and (ii) those shares
of Ordinary Shares into which any Series A Preferred Shares are convertible.

                  (c) "Ordinary Shares" means the Company's Ordinary Shares,
$.001 par value per share.

                  (d) "Person" means an individual, partnership, corporation,
limited liability company, association, trust, joint venture, unincorporated
organization and any government, governmental department or agency or political
subdivision thereof.

                  (e) "Restricted Shares" has the meaning specified in Section
3.1(a).

                  (f) "Sale of the Company" means a single transaction or series
of related transactions, other than a public offering of securities, pursuant to
which a Person or Persons other than existing stockholders of the Company (i)
acquires capital stock of the Company possessing the voting power to elect a
majority of the Board, (ii) consummates a merger, amalgamation or

<PAGE>
consolidation with the Company as a result of which the stockholders of the
Company who own Ordinary Shares or other voting securities prior to such
transaction(s) shall own, directly or indirectly, less than fifty percent (50%)
of the voting securities of the surviving entity or its parent, or (iii)
acquires all or substantially all of the Company's assets (determined on a
consolidated basis with its subsidiaries).

                  (g) "Shares" means the Ordinary Shares issued to the
Consultant pursuant to this Agreement.

                                   SECTION 2

                               PURCHASE OF SHARES

         2.1 Issuance. In consideration of the payment by the Consultant to the
Company of cash in the amount of $.001 per Share concurrently herewith, the
Company hereby issues to the Consultant, and the Consultant hereby accepts from
the Company, 1,125,000 Ordinary Shares (the "Shares") upon the terms and
conditions set forth in this Agreement.

         2.2 Investment Representations.

                  (a) The Consultant hereby represents and warrants that the
Consultant is acquiring the Shares for the Consultant's own account as an
investment only and not with a view toward the sale or distribution thereof in
violation of the United States Securities Act of 1933, as amended (the
"Securities Act"), or any rule or regulation under the Securities Act.

                  (b) The Consultant has had such opportunity as he has deemed
adequate to obtain from representatives of the Company such information as is
necessary to permit him to evaluate the merits and risks of his investment in
the Company.

                  (c) The Consultant has sufficient experience in business,
financial and investment matters to be able to evaluate the risks involved in
the purchase of the Shares and to make an informed investment decision with
respect to such purchase.

                  (d) The Consultant can afford a complete loss of the value of
the Shares and is able to bear the economic risk of holding such Shares for an
indefinite period.

                  (e) The Consultant understands that (i) the Shares have not
been registered under the Securities Act and are "restricted securities" within
the meaning of Rule 144 under the Securities Act, (ii) the Shares cannot be
sold, transferred or otherwise disposed of unless they are subsequently
registered under the Securities Act or an exemption from registration is then
available; (iii) in any event, the exemption from registration under Rule 144
will not be available for at least one (1) year and even then will not be
available unless a public market then exists for the Ordinary Shares, adequate
information concerning the Company is then available to the public, and other
terms and conditions of Rule 144 are complied with; and (iv) there is now no
registration statement on file with the United States Securities and Exchange
Commission with

                                      -2-
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respect to any stock of the Company and the Company has no obligation or current
intention to register the Shares under the Securities Act.

                                   SECTION 3

                                    VESTING

         3.1 Vesting Schedule. The Shares held by the Consultant shall be
subject to vesting as follows:

                  (a) 50% of the Shares (the "Restricted Shares") shall be
subject to vesting with one-fourth of the Restricted Shares to vest on each of
the first four anniversaries of the date hereof so long as the Consulting
Agreement is in effect.

                  (b) Notwithstanding the foregoing, in the event of the closing
of a Sale of the Company at a time when the Consulting Agreement is in effect,
all of the Restricted Shares shall be deemed to have been fully vested
immediately prior to such closing.

         3.2 Forfeiture Upon Failure to Vest. Any Restricted Shares that do not
vest as of the applicable date shall thereupon be deemed for all purposes to
have been forfeited as of such date, and the Consultant shall have no further
rights with respect thereto. In addition, upon Consultant's failure to vest in
any portion of the Restricted Shares, Consultant shall be deemed to have
divested of (i) 25% of the total number of Shares, if such failure to vest
occurs prior to the second anniversary of the date hereof, or (ii) 12.5% of the
total number of Shares, if such failure to vest occurs after the second
anniversary of the date hereof but prior to the fourth anniversary of the date
hereof. All forfeited and divested Shares shall be deemed to have been
transferred to and redeemed by the Company without the need for any payment to
the Consultant or any action by the Company or any other Person as of the date
of such forfeiture or divestment, and the Consultant shall, immediately upon the
request of the Company, deliver to the Company all stock certificates evidencing
such forfeited and/or divested Shares, duly endorsed for transfer to the Company
or its designee.

                                   SECTION 4

                                 MISCELLANEOUS

         4.1 Adjustments for Stock Splits, Stock Dividends, etc. If from time to
time during the term of this Agreement there is any stock split-up, stock
dividend, stock distribution or other reclassification of the Ordinary Shares of
the Company, any and all new, substituted or additional securities to which the
Consultant is entitled by reason of his ownership of the Shares shall be
immediately subject to the provisions of this Agreement in the same manner and
to the same extent as the Shares.

         4.2 Tax Issues. THE ISSUANCE OF THE SHARES TO THE CONSULTANT PURSUANT
TO THIS AGREEMENT INVOLVES COMPLEX AND SUBSTANTIAL TAX CONSIDERATIONS,
INCLUDING, WITHOUT LIMITATION, CONSIDERATION OF THE

                                      -3-
<PAGE>
ADVISABILITY OF THE CONSULTANT MAKING AN ELECTION UNDER SECTION 83(B) OF THE
UNITED STATES INTERNAL REVENUE CODE. THE CONSULTANT IS URGED TO CONSULT HIS OWN
TAX ADVISOR WITH RESPECT TO THE TRANSACTIONS DESCRIBED IN THIS AGREEMENT. THE
COMPANY MAKES NO WARRANTIES OR REPRESENTATIONS WHATSOEVER TO THE CONSULTANT
REGARDING THE TAX CONSEQUENCES OF THE CONSULTANT'S PURCHASE OF THE SHARES OR
THIS AGREEMENT.

         4.3 Independent Contractor. Consultant acknowledges that he or she is a
consultant to Novirio, and not an employee or agent of the Company or any of its
subsidiaries. Nothing in this Agreement shall render Consultant an employee or
agent of the Company or any of its subsidiaries, nor authorize or empower
Consultant to speak for, represent or obligate the Company or any of its
subsidiaries in any way.

         4.4 Transferees. Each and every transferee or assignee of any Shares
from the Consultant (other than pursuant to a Sale of the Company) shall be
bound by and subject to all the terms and conditions of this Agreement on the
same basis as the Consultant is bound. So long as this Agreement is in effect,
the Company shall require as a condition precedent to the transfer of any Shares
by the Consultant that the transferee agrees in writing to be bound by, and
subject to, the terms and conditions of this Agreement and to ensure that such
transferees' transferees shall be likewise bound.

         4.5 Legends. The Company and Consultant agree that, so long as this
Agreement is in effect, the certificate representing the Shares will be stamped
or otherwise imprinted with legends in the following form:

         THE SHARES EVIDENCED BY THIS CERTIFICATE ARE SUBJECT TO AGREEMENTS,
COVENANTS AND RESTRICTIONS PROVIDED IN A STOCK RESTRICTION AGREEMENT DATED JUNE
__, 1998, AS AMENDED FROM TIME TO TIME, BETWEEN NOVIRIO PHARMACEUTICALS LIMITED
AND THE HOLDER OF THIS CERTIFICATE.

         THE SHARES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
UNDER THE UNITED STATES SECURITIES ACT OF 1933, AS AMENDED, AND MAY NOT BE SOLD,
TRANSFERRED OR OTHERWISE DISPOSED OF IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
STATEMENT UNDER SUCH ACT OR AN OPINION OF COUNSEL SATISFACTORY TO THE
CORPORATION TO THE EFFECT THAT SUCH REGISTRATION IS NOT REQUIRED.

         4.6 Remedies.

                  (a) The rights and remedies provided by this Agreement are
cumulative and the use of any one right or remedy by any party shall not
preclude or waive its right to use any or all other remedies. Said rights and
remedies are given in addition to any other rights the parties may have at law
or in equity.

                                      -4-
<PAGE>
                  (b) Without limitation of the foregoing, the parties hereto
agree that irreparable harm would occur in the event that any of the agreements
and provisions of this Agreement were not performed fully by the parties hereto
in accordance with their specific terms or were otherwise breached, and that
money damages are an inadequate remedy for breach of the Agreement because of
the difficulty of ascertaining and quantifying the amount of damage that will be
suffered by the parties hereto in the event that this Agreement is not performed
in accordance with its term or is otherwise breached. It is accordingly hereby
agreed that the parties hereto shall be entitled to an injunction or injunctions
to restrain, enjoin and prevent breaches of this Agreement, such remedy being in
addition to and not in lieu of any other rights and remedies to which the other
parties are entitled to at law or in equity.

                  (c) Except where a time period is otherwise specified, no
delay on the part of any party in the exercise of any right, power, privilege or
remedy hereunder shall operate as a waiver thereof, nor shall any exercise or
partial exercise of any such right, power, privilege or remedy preclude any
further exercise thereof or the exercise of any right, power, privilege or
remedy.

         4.7 Waivers and Amendments. The rights and obligations of the Company
and the rights and obligations of the Consultant under this Agreement may be
waived (either generally or in a particular instance, either retroactively or
prospectively, and either for a specified period of time or indefinitely) or
amended only with the written consent of the President of the Company, the
Consultant and the Board.

         4.8 Governing Law. This Agreement shall be governed by and construed
under the laws of the Commonwealth of Massachusetts (without giving effect to
any conflicts or choice of law provisions thereof that would cause the
application of the domestic substantive laws of any other jurisdiction).

         4.9 Successors and Assigns. Except as otherwise expressly provided
herein, the provisions hereof shall inure to the benefit of, and be binding
upon, the successors, assigns, heirs, executors and administrators of the
parties hereto.

         4.10 Entire Agreement. This Agreement constitutes the full and entire
understanding and agreement between the parties with regard to the subjects
hereof and supersedes all prior agreements and understandings, whether oral or
written, with respect thereto. Without limiting the foregoing, the Consultant
agrees that the provisions of this Agreement fulfill all obligations that the
Company may have to issue to the Consultant stock, options or equity interests
in the Company or any of its subsidiaries.

         4.11 Notices. Any and all notices provided for in this Agreement shall
be addressed: (i) if to the Company, to the principal executive office of the
Company; and (ii) if to the Consultant, to the address of the Consultant as
reflected on the signature page of this Agreement. Notices shall be deemed
delivered upon the earlier to occur of (i) receipt by the party to whom such
notice is directed; (ii) if sent by facsimile machine, on the day (other than a
Saturday, Sunday or legal holiday in the jurisdiction to which such notice is
directed) such notice is sent if sent (as evidenced by the facsimile confirmed
receipt) prior to 5:00 p.m. Eastern Standard Time and, if sent after 5:00 p.m.
Eastern Standard Time, on the day (other than a Saturday, Sunday or legal
holiday in the jurisdiction to which such notice is directed) after which such
notice is sent; (iii) on the first business day (other than a Saturday, Sunday
or legal

                                      -5-
<PAGE>
holiday in the jurisdiction to which such notice is directed) following the day
the same is deposited with the commercial carrier if sent by commercial
overnight delivery service; or (iv) the fifth day (other than a Saturday, Sunday
or legal holiday in the jurisdiction to which such notice is directed) following
deposit thereof with the U.S. Postal Service as aforesaid. Each party, by notice
duly given in accordance herewith, may specify a different address for the
giving of any notice hereunder.

         4.12 Severability. In case any provision of this Agreement shall be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions of this Agreement shall not in any way be affected or
impaired thereby, and each provision of this Agreement shall be enforced to the
fullest extent permitted by law.

         4.13 No Third Party Beneficiaries. There are no third party
beneficiaries of this Agreement.

         4.14 Duration. This Agreement shall be valid and continue in full force
and effect until the earlier of (i) the vesting of all of the Restricted Shares
in accordance with Section 3 hereof and (ii) the consummation of a Sale of the
Company.

         4.15 Securities Act Exemption. The Company and the Consultant agree
that this Agreement constitutes "a written contract relating to the
compensation" of the Consultant within the meaning of Rule 701 under the
Securities Act.

         4.16 Titles and Subtitles. The titles of the sections and subsections
of this Agreement are for convenience of reference only and are not to be
considered in construing this Agreement.

         4.17 Gender. The use of any gender in this Agreement shall be deemed to
be or include the other genders, and the use of the singular in this Agreement
shall be deemed to be or include the plural (and vice versa), wherever
appropriate.

         4.18 Counterparts. This Agreement may be executed in any number of
counterparts, each of which shall be an original, but all of which together
constitute one agreement.

                       [SIGNATURES ARE ON FOLLOWING PAGE.]

                                      -6-

<PAGE>
         IN WITNESS WHEREOF, the Company and the Consultant have executed this
Agreement as of the day and year first written above.

NOVIRIO PHARMACEUTICALS LIMITED                CONSULTANT:

By: /s/ B. Lucidi                              Signature: /s/ Raymond Schinazi
   ______________________________                        _______________________
     Title: Director
                                               Name: Raymond F. Schinazi
                                                    ____________________________

                                      -7-

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