Document:

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                                                                    Exhibit 10.5

                                March 18, 2002

CONFIDENTIAL

Mr. John Dunphy
24 Marion Lane
Scotch Plains, New Jersey 07076

Dear Mr. Dunphy:

On behalf of Novirio Pharmaceuticals, Inc. ("Novirio"), I am pleased to offer
you the position of Chief Financial Officer. In this position, you will report
directly to Novirio's Chief Executive Officer. The terms of employment set forth
below are intended to reflect our prior discussions.

     Commencement:         Employment will commence on or before March 1, 2002.
                           The initial term of this agreement will be for a
                           period of two years, renewable thereafter for
                           successive one year periods upon the mutual agreement
                           of the parties unless either party elects not to
                           renew and provides notice thereof to the other party
                           at least 30 days prior to the end of the initial two
                           year period or any subsequent one year period.

     Salary:               Your monthly salary will be $21,666.67 (equivalent to
                           $260,000 annually), payable semi-monthly in arrears
                           subject to applicable withholding. In no event will
                           your salary be reduced. Novirio annually reviews the
                           performance of and compensation (both cash and
                           equity) payable to its employees. You may expect to
                           be included in performance and compensation reviews
                           which occur subsequent to the commencement of your
                           employment.

     Bonus:                In connection with your acceptance of this position,
                           Novirio will pay to you the amount of $150,000. Such
                           bonus amount will be payable in three installments
                           commencing on the first and continuing thereafter on
                           each of the second and third anniversary of your
                           employment commencement provided that your employment
                           with Novirio has not been terminated for Cause (as
                           hereinafter defined) prior to such respective payment
                           date. In the event that your employment with Novirio
                           is: (i) terminated by you for Good Reason (as
                           hereinafter defined); (ii) is terminated by Novirio
                           without Cause (as hereinafter defined); or (iii)
                           Novirio elects not to renew the term of this
                           arrangement after the initial term, payment of the
                           bonus will be accelerated to the date of your
                           termination.
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Mr. John Dunphy
March 18, 2002
Page 2

                           It is currently anticipated that a bonus program for
                           officers of Novirio will be instituted upon
                           consummation of a Successful Initial Public Offering.
                           You may expect to participate in such bonus program
                           at a level commensurate with your position. The bonus
                           program will be intended to provide benefits similar
                           to those described in the draft report on Total
                           Compensation prepared by PricewaterhouseCoopers, a
                           copy of which has been previously provided to you.
                           For purposes hereof, a Successful Initial Public
                           Offering will be deemed to have occurred if the
                           transaction is complete on or before June 30, 2003,
                           the offering price per share exceeds $10.00 (or such
                           other equivalent amount if a stock split (forward or
                           reverse) is effected prior to the occurrence of an
                           initial public offering), the shares are traded on
                           the NASDAQ NMS and net proceeds to the Company from
                           the sale of the Ordinary Shares exceeds $80 million.

Equity:                    On the date your employment commences, you will be
                           granted an option to purchase up to 300,000 ordinary
                           shares ("Ordinary Shares") of Novirio's parent
                           company, Novirio Pharmaceuticals Limited ("Novirio
                           Limited"), at $3.00 per share. The option, which is
                           intended to be an incentive stock option and is
                           conditioned on your continued employment with Novirio
                           and other customary terms set forth in Novirio
                           Limited's 1998 Equity Incentive Plan, will to the
                           extent of 200,000 Ordinary Shares (the "Employment
                           Shares") become exercisable ratably in four annual
                           installments beginning on the first anniversary of
                           your employment commencement date. The remaining
                           option to purchase 100,000 Ordinary Shares (the
                           "Performance Shares") will vest on the earlier of:
                           (i) the first and second anniversary of the date of
                           consummation of a Successful Initial Public Offering
                           (in which case the options will vest ratably on each
                           anniversary date) or (ii) the fifth anniversary of
                           your employment commencement. To the extent, the
                           Board of Directors approves, in place of incentive
                           stock options, the substitution of immediately
                           exercisable stock options (which will have vesting
                           and transferability restrictions on the underlying
                           shares similar to those originally provided in the
                           incentive stock option award), you will be entitled
                           to receive such stock options in substitution for the
                           incentive stock options described above.
                           Notwithstanding the foregoing, in the event of a
                           change in control of Novirio Limited (other than by
                           means of an initial public offering of the equity
                           securities of Novirio Limited), the options (or to
                           the extent applicable, the Ordinary Shares) you
                           possess will become vested in full and fully
                           exercisable immediately prior to the consummation of
                           the Change in Control transaction. For purposes
                           hereof, a "Change in Control" is deemed to mean: (a)
                           any merger, amalgamation or consolidation which
                           results in the voting securities of Novirio Limited
                           outstanding immediately prior thereto representing
                           immediately thereafter (either by remaining
                           outstanding or by being converted into voting
                           securities of the surviving or acquiring entity) less
                           than 50% of the combined voting power of the voting
                           securities of Novirio Limited or such surviving or
                           acquiring entity outstanding immediately after such
                           merger or consolidation; (b) any sale of all or
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Mr. John Dunphy
March 18, 2002
Page 3

                           substantially all of the assets of the Novirio
                           Limited, (c) any sale of 50% or more of the
                           outstanding voting stock of Novirio Limited to any
                           person; or (c) the complete liquidation of Novirio
                           Limited. For this purpose, a "person" means any
                           individual, entity or group within the meaning of
                           Section 13 (d) (3) or 14 (d) (2) of the Securities
                           Exchange Act of 1934, as amended.

     Benefits:             You will be eligible to participate in all benefits
                           Novirio provides generally to its employees and to
                           the extent such programs become available, programs
                           provided by Novirio for the benefit of its officers
                           including incentive cash and equity compensation
                           programs. Currently, the benefit programs available
                           to Novirio employees and officers include major
                           medical, dental, disability and life insurance and a
                           401(k) plan.

     Relocation:           In connection with your relocation to the Cambridge,
                           Massachusetts area, Novirio will reimburse you for
                           reasonable moving and relocation expenses (not to
                           exceed $20,000), real estate commissions and
                           conveyancing fees in connection with the sale of your
                           principal residence (not to exceed 6%), actual
                           expenses of two househunting trips to Cambridge for
                           you and your wife and amounts required to gross up
                           the aggregate of all of the foregoing to offset any
                           related additional income tax liabilities.

     Disclosure of
          Inventions:      This offer is conditioned on your agreement, that as
                           an employee of Novirio, you will make full and prompt
                           disclosure to Novirio of all inventions,
                           improvements, modifications, discoveries, creations,
                           methods, processes and developments which are
                           created, made, or reduced to practice by you alone,
                           under your direction or with others in connection
                           with or relating to Novirio's then present or planned
                           business or research and development activities
                           during the term of your employment, whether or not
                           such developments are patentable or protected as
                           confidential information. Such disclosures will be
                           obligated during the period of your employment with
                           Novirio, whether or not such developments are made or
                           conceived during normal working hours or on or off
                           the premises of Novirio (all of which are hereinafter
                           collectively termed "Developments").

     Assignment of
          Inventions:      By your acceptance of this offer of employment, you
                           agree to assign and do hereby assign to Novirio all
                           your title, interests and rights, including, without
                           limitation, intellectual property rights, in and to
                           any and all inventions and Developments created
                           during the period of your employment with Novirio,
                           and you agree to assign to Novirio any and all
                           patents and patent applications arising from such
                           Developments, and to execute and deliver such
                           assignments, patents and patent applications and
                           other documents (including, without limitation, power
                           of attorney) as
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Mr. John Dunphy
March 18, 2002
Page 3

                           Novirio may direct. Additionally, you agree to
                           cooperate fully with Novirio both during and after
                           the term of your employment, to enable Novirio to
                           secure and maintain rights in said Developments
                           assigned to Novirio in any and all countries provided
                           that such cooperation will be at Novirio's expense
                           and if occurring after the term of employment will be
                           at such times as you are reasonably available and not
                           inconsistent with any obligations you may have with
                           respect to subsequent employment.

     No Conflict:          By your acceptance of this offer of employment, you
                           hereby represent that you are not bound by the terms
                           of any agreement with any previous employer to
                           refrain from competing, directly or indirectly, with
                           the business of such previous employer or any other
                           party. You further represent that your acceptance of
                           this offer of employment and employment by Novirio
                           does not and will not breach any agreement to keep in
                           confidence proprietary information, knowledge or data
                           acquired by you in confidence or in trust prior to
                           your employment with Novirio.

     Severance:            Either you or Novirio may terminate your employment
                           at any time on not less than 45 days prior written
                           notice. In the event that you voluntarily resign for
                           other than "Good Reason" (as hereinafter defined), or
                           Novirio terminates your employment for "Cause" (as
                           hereinafter defined), you will be entitled to receive
                           all accrued salary, bonus and other benefits and will
                           be allowed, in accordance with the terms of the 1998
                           Equity Incentive Plan, to exercise any vested options
                           to purchase Ordinary Shares. In such event, Novirio
                           will have no further obligation to you except for any
                           amounts to which you are entitled under applicable
                           law. The same provisions will apply in the event your
                           employment is terminated by reason of death or
                           disability, except that you or your estate will also
                           receive any amounts to which you or it may be
                           entitled under applicable life insurance and
                           disability plans maintained by Novirio.

                           In the event that your employment is terminated by
                           you for Good Reason, or by Novirio without Cause or
                           Novirio elects not to renew the term of employment,
                           in each case other than in connection with a Change
                           in Control of Novirio Limited, (i) you will receive a
                           lump sum payment equal to the salary and bonus which
                           would have been payable to you over the longer of (a)
                           the next succeeding year, or (b) the number of months
                           then remaining in the current term of the agreement,
                           with bonus to be determined based on targeted amounts
                           and prorated for any partial years, and (ii) you will
                           become vested in the greater of (A) 25% of the
                           unvested options to purchase Employment Shares and
                           any other options to purchase Ordinary Shares which
                           have been awarded to you subsequent to the
                           commencement of your employment which vest solely
                           based on the passage of time and continued employment
                           (the "Continuity Shares") or (B) the number of
                           unvested options to purchase Employment and
                           Continuity Shares which would have become vested over
                           the longer of (a) the next succeeding year, or (b)
                           the number of months then remaining in the current
                           term of the agreement. If a Successful Initial Public
                           Offering has been consummated on or prior to the date
                           of termination for
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Mr. John Dunphy
March 18, 2002
Page 4

                           the reasons set forth in this paragraph, you will
                           become fully vested in any then unvested Performance
                           Shares.

                           In the event that: (i) your employment is terminated
                           for any reason other than Cause or (ii) you
                           voluntarily resign at any time on, after or in
                           connection with a Change of Control of Novirio
                           Limited, you will receive (1) accelerated vesting of
                           any then unvested options to purchase Employment or
                           Continuity Shares (as described in the provision
                           herein captioned "Equity") and (2) payment equal to
                           salary and bonus which would have been payable to you
                           over the longer of (a) the next succeeding year, or
                           (b) the number of months then remaining in the
                           current term of the agreement, with bonus to be
                           determined based on targeted amounts and prorated for
                           any partial years. Further, to the extent that it is
                           approved for Novirio's Chief Executive Officer or any
                           other officer or employee of Novirio or Novirio
                           Limited, you will, in addition to receipt of the lump
                           sum payment, be entitled to receive payment for: (i)
                           for any excise taxes to which the lump sum payment
                           may be subject under Section 4999 of the Internal
                           Revenue Code of 1986, as amended, and (ii) related
                           taxes applicable to such additional payment.

                           For purposes hereof, "Good Reason" will be deemed to
                           mean (1) any change, without your prior written
                           consent, in your title, or any material diminution
                           of your authority, responsibilities or duties, (2) a
                           reduction, without your prior written consent, in
                           your annual compensation, including the opportunity
                           to participate in bonus programs at rates
                           proportionate to the immediately preceding prior
                           year, (3) a relocation of your primary place of
                           employment to a location more than 40 miles further
                           from your primary residence than the current location
                           of Novirio's offices in Cambridge, Massachusetts, or
                           (4) any other material breach of the terms of this
                           employment arrangement which is not promptly cured
                           after your delivery of written notice of such breach
                           to Novirio or Novirio Limited as the case may be.

                           For purposes hereof, "Cause" will be deemed to mean
                           (1) your willful and repeated failure to
                           substantially perform your duties as the Chief
                           Financial Officer of Novirio, (2) your commission of
                           or willful participation in an act of material fraud,
                           embezzlement or dishonesty against Novirio or its
                           affiliates, (3) your conviction of a felony or crime
                           involving moral turpitude or dishonesty, or (4) your
                           intentional, material violation of any agreement with
                           Novirio or its affiliates or any statutory duty owed
                           by you to Novirio or its affiliates which is not
                           corrected within 30 days after receipt of written
                           notice thereof.

In the position of Chief Financial Officer, you will have access to valuable,
confidential and proprietary information. Accordingly, as a condition to your
commencing employment, you will be required to enter into a confidentiality and
non-disclosure agreement in standard form regarding the nondisclosure and nonuse
of such valuable, confidential and proprietary information.
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Mr. John Dunphy
March 18, 2002
Page 6

If you agree with the above terms, please sign both copies of this letter
indicating your acceptance and return one copy to me at your earliest
convenience. Please retain the other copy for your records. This offer of
employment will expire on _____________, 2002.

We look forward to you joining us at Novirio!

Very truly yours,

Jean-Pierre Sommadossi, Ph.D.
Chief Executive Officer

ACCEPTED as of this 18th day of March, 2002

/s/ John Dunphy
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John Dunphy<PAGE>
                                                                    EXHIBIT 10.6

April 24, 2000

Jean-Pierre Sommadossi, Ph.D.
Chief Executive Officer and Chairman of the Board of Directors
Novirio Pharmaceuticals Limited
c/o Walker Secretaries
Box 265
Grand Cayman, Cayman Islands

Dear Jean-Pierre:

This Letter Agreement entered into as of the date hereof is intended to set
forth the terms of appointment, representation, and compensation of James J.
Egan of 2-6 Park Road, Grafton, Auckland, New Zealand ("Egan") for his
activities on behalf of Novirio Pharmaceuticals Limited, a company organized and
existing under the laws of the Cayman Islands (together with its subsidiaries,
successors and assigns, "Novirio"):

   1. Definitions. For purposes hereof, the following terms shall have the
meanings set forth below:

   "Confidentiality Agreement" means the Confidentiality and Non-disclosure
Agreement dated as of May 10, 2000 between Novirio and Egan.

   "Novirio HBV Drug Candidate" means any of the nucleoside compounds commonly
referred to by Novirio as L-dT and val-L-dC.

   "Significant Asian Company" means an internationally recognized company
actively engaged in the business of developing, commercializing, marketing and
selling pharmaceutical products in North East Asia.

   "Successful Business Transaction" means any contractual or other form of
legally binding commercial arrangement relating to the development,
commercialization and sale of a Novirio HBV Drug Candidate in the Territory,
which (i) is entered into between Novirio and a Significant Asian Company on or
prior to January 31, 2001 for L-dT and on or prior to the later of June 30, 2001
or 30 days after the date clinical data from val-L-dC Phase I/II clinical trial
becomes available for val-L-dC; and (ii) contemplates: (x) the Significant Asian
Company bearing or reimbursing Novirio for all costs (which costs are estimated
to approximate US$50 million in the aggregate) of development and global
registration of the licensed Novirio HBV Drug Candidate; and (y) the payment by
the Significant Asian Company to Novirio of royalties in an amount equal to or
exceeding twenty percent (20%) of the net wholesale prices charged by the
Significant Asian
<PAGE>
Company or its designee to an unrelated third party less reasonable returns,
allowances and rebates, in the Territory.

   "Territory" means Japan, such other territory or territories as Novirio may
in its sole discretion agree, or both in the sole discretion of Novirio.

   2. Services to be Performed. The obligations of Egan shall specifically
include the expeditious identification, pursuit, negotiation and conclusion of
one or more Successful Business Transactions.

   3. Representations, Warranties and Covenants: In the exercise of his duties
on behalf of Novirio, Egan acknowledges and warrants that:

      (a) Egan's negotiations on behalf of Novirio will be undertaken at all
times with full candor;

      (b) Egan will disclose to Novirio the content, strategy and goals of each
negotiation;

      (c) Egan owes a first loyalty fiduciary responsibility to Novirio before
all others with respect to the representation and pursuit of opportunities for
commercial collaborations in the Territory with respect to hepatitis B virus
therapeutic agents;

      (d) Egan represents that he is not subject to any agreement, restriction,
right or interest in any way limiting the scope of this Letter Agreement or his
engagement by Novirio. Egan covenants that he will not during the term hereof
enter into or grant to anyone any agreements, restrictions, rights or interests
that limit in any way the scope of this Letter Agreement or his engagement by
Novirio. Egan will not disclose to Novirio, or induce Novirio to use, any
confidential information of other persons, corporations, or firms including his
present or former employers;

      (e) Set forth on Exhibit A hereto is a list of all companies,
institutions, entities and individuals with whom Egan has current
representative, consultant, employment, business partnership or similar
relationships or of which Egan owns greater than 5% of outstanding voting
securities, and a description of all agreements with such parties. Egan will
notify Novirio in writing promptly whenever there is any change to this list;

      (f) Egan will disclose any and all actual or potential conflicts of
interest to Novirio upon becoming aware of the actuality or reasonable
possibility of such conflicts of interest; and

      (g) Egan will exert his commercially reasonable efforts and the highest
standards of personal ethics and performance, which efforts shall include but
not be limited to participating in all direct negotiations with any third party
over possible commercial terms for the licensing, development and
commercialization of the Novirio HBV Drug Candidates in the Territory and
developing and communicating to Novirio a complete strategy for negotiation,
conclusion and administration of a Successful Business
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Transaction. In this regard the parties acknowledge that Egan has other
performance obligations and that reasonable accommodation will be made regarding
the performance by Egan of his obligations owed to Novirio.

   4. Compensation.

   a. Product-by-Product Calculation. The compensation payable to Egan shall be
calculated on a compound by compound basis and the proceeds attributable to one
Successful Business Transaction will not be aggregated with the proceeds
attributable to any additional Successful Business Transaction relating to a
different Novirio HBV Drug Candidate.

   b. Cash Payments. Within 45 days after the consummation of a Successful
Business Transaction, Novirio shall pay to Egan an amount equal to US$1 million.

   c. Equity Compensation. As of the date of consummation of a Successful
Business Transaction, Novirio shall award to Egan an option to purchase 80,000
Ordinary Shares. Such options will be non-qualified stock option and will (i)
have a per share exercise price equal to the fair market value of the Ordinary
Shares as of the date of the award; and (ii) be subject to the terms and
conditions contained in the Novirio 1998 Equity Incentive Plan and a
Non-Qualified Stock Option Agreement pursuant to which the options will be
awarded. The fair market value of the Ordinary Shares on the date of award shall
be determined in the sole discretion of the Novirio Board of Directors acting in
good faith. The options shall be vested in full on the date of grant and
exercisable immediately subject to the terms of the Non-Qualified Stock Option
Agreement.

   d. Incentive Cash Compensation. Within 45 days after the consummation of a
Successful Business Transaction, Novirio will pay to Egan an amount equal to
US$40,000 for each percent that the rate of royalty payable to Novirio by the
Significant Asian Company exceeds 20%, subject to maximum of $400,000.
Additionally, in the event that a Significant Asian Company which is a party to
a Successful Business Transaction enters at the time of consummation of a
Successful Business Transaction or within three months thereafter, into a
binding agreement to make an investment in the equity securities of Novirio,
Novirio agrees to pay to Egan, subject to applicable laws relating the payment
of compensation to a broker or finder, an amount equal to 2% of the amount being
paid by the Significant Asian Company which exceeds either: (i) the price per
share paid by a third party in connection with most recent purchase and sale of
Novirio securities resulting in net proceeds to Novirio in an aggregate amount
of $10 million if such financing transaction has closed within three months of
the intended investment by the Significant Asian Company, or (ii) the fair
market value of the securities of Novirio as determined in the sole opinion of
the Novirio Board of Directors acting in good faith if the Significant Asian
Company's investment will occur more than three months after the consummation of
the financing transaction with the unrelated third party.
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   e. Conditional Payment of Compensation. The parties hereto agree that all
compensation payable to Egan is conditioned upon the consummation of one or more
Successful Business Transactions. Egan acknowledges and agrees that no
compensation will be due from Novirio if a Successful Business Transaction is
not consummated.

   5. Cooperation. Novirio undertakes to do or to cause its employees, agents
and representatives under its reasonable control, to do all commercially
practicable things reasonably necessary and desirable for the aggressive pursuit
of a Successful Business Transaction. Such actions shall include, but not be
limited to giving expeditious, complete disclosure of relevant scientific,
commercial, regulatory and other information relating to the Novirio HBV Drug
Candidates, subject to the terms of Section 6 of this Letter Agreement. The
expeditious and professional performance of all pre-clinical and clinical trials
is a condition precedent to the full performance of this Agreement by Egan.

   6. Confidentiality. Egan shall remain subject to the terms and conditions of
the Confidentiality Agreement. Notwithstanding the foregoing, Egan agrees to
hold in confidence and use only for the purposes of performance of this
Agreement all information disclosed by or on behalf Novirio to Egan. All
disclosures by or on behalf of Novirio to Egan shall be presumed confidential.
Egan acknowledges that Novirio shall not be obliged to disclose any information
to any third parties that Novirio in its reasonable judgment considers to be
confidential or proprietary, unless the disclosures are subject to
confidentiality and nonuse obligations reasonably acceptable to Novirio.

   7. Non-Solicitation. At all times during the period Egan is assisting Novirio
in the pursuit of a Successful Business Transaction, and for a period of
eighteen (18) months thereafter, Egan shall not:

   (a) induce or attempt to induce any Significant Asian Company or any actual
or potential customer, supplier, dealer, distributor, of Novirio to reduce such
Significant Asian Company's, or any actual or potential customer's, supplier's,
dealer's or distributor's business or potential business with Novirio; or

   (b) solicit any of Novirio's consultants or employees to leave the employ of
Novirio or hire or cause to be hired any person who was during or for six (6)
months after the termination of the Egan's services to Novirio, a consultant or
employee of Novirio.

   8. Expenses. Novirio agrees to reimburse Egan in accordance with the general
policies and procedures established by Novirio from time to time for all
reasonable expenses necessary to aggressively pursue a Successful Business
Transaction, including but not limited to telephone, travel, lodging, meals,
document preparation, research, data base fees, entertainment and other expenses
incurred in the pursuit of a Successful Business Transaction. In this regard,
Novirio shall have the right to review and to pre-approve any individual or
recurring charge exceeding $1,000. Such pre-approvals shall not apply to
reasonable travel, lodging, meals and entertainment expenses where the trip, the
lodging, the anticipated entertainment and other expense items have been
notified to
<PAGE>
Novirio in advance but cannot due to the circumstances of incurring such
expenses be pre-approved.

   9. Exclusivity. Egan acknowledges and agrees that Novirio is free without any
obligation or liability to Egan, to engage other consultants or employees or
take other reasonable actions to pursue a transaction for the license or
collaborative development of the Novirio HBV Drug Candidates: (i) in all areas
other than Japan at all times; and (ii) (x) if a Successful Business Transaction
for L-dT has not been consummated, in all Territories including Japan after
January 31, 2001 and (y) if a Successful Business Transaction for val-L-dC has
not been consummated, after the later of June 30, 2001 or 30 days after the
later of the date clinical data from a val-L-dC clinical trial becomes
available.

   10. Delegation of Duties.   It is understood that Egan shall not delegate nor
assign any aspect of the performance of this Agreement without the express,
prior, written consent of Novirio.

   11. Independent Contractor. Both Novirio and Egan agree that Egan acts as an
independent contractor in the performance of his services under this Letter
Agreement. Nothing in this Letter Agreement will be deemed to make Egan an
employee, partner or agent for Novirio, nor will either party have any authority
to bind the other in any respect. Accordingly, Egan shall be responsible for
payment of, and shall indemnify and hold Novirio harmless against, all taxes,
including, without limitation, federal, state and local taxes and taxes assessed
by foreign countries arising out of Egan's activities in accordance with this
Letter 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.

   12. Notices. Any notices, requests, demands and other communications provided
for by this Agreement shall be sufficient if in writing addressed to Egan or if
to Novirio, to its Chief Executive Officer, and shall be deemed duly given if
delivered personally or sent by registered or certified mail, postage paid,
return receipt requested, and deposited in the U.S. Mail. Any such notice shall
be deemed to be given on the date of personal delivery or as of the third day
after the date mailed. Either party may, by notice in writing to the other
party, change the address to which notices to it or him are to be addressed
hereunder.

   13. Miscellaneous.

   (a) Entire Agreement; Amendments; Waivers. This Letter Agreement contains the
entire understanding of the parties regarding its subject matter and any
amendment to this Letter Agreement, and any waiver of any provision hereof,
shall be in writing and shall require the prior written approval of the Chief
Executive Officer of Novirio and Egan. Any waiver by any party hereto of a
breach of any provision of this Letter Agreement shall not operate or be
construed as a waiver of any subsequent breach hereof.
<PAGE>
   (b) Survival. Except as otherwise provided in this Letter Agreement, the
obligations of Novirio and Egan contained in Sections 3, 6, 7 and 9 of this
Letter Agreement and this Section 13 shall survive the termination of this
Letter Agreement.

   (c) Governing Law; Consent to Jurisdiction. Egan agrees that any dispute in
the meaning, effect or validity of this Letter Agreement shall be resolved in
accordance with the laws of the Commonwealth of Massachusetts without regard to
the conflict of laws provisions thereof. Egan hereby agrees to submit to the
nonexclusive jurisdiction of the courts 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.

   (d) Enforcement. In view of the substantial harm that will result from the
breach by Egan of any of the covenants contained in Sections 3, 6, 7 and 10 of
this Letter Agreement, 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 unenforceable, the remainder of this Letter 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. The Consultant agrees that his breach of any of the provisions
of Sections 3, 6 and 7 of this Letter Agreement will cause irreparable damage to
Novirio and that the recovery by Novirio of money damages will not alone
constitute an adequate remedy for such breach. Accordingly, Egan agrees that
such provisions may be specifically enforced against him, in addition to any
other rights or remedies available to Novirio on account of any such breach.

   (f) Indemnification.

      (i) Egan will indemnify and hold Novirio harmless, and will defend Novirio
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 Egan, or breach of any term or condition
of this Letter Agreement.

      (ii) Novirio will indemnify and hold Egan harmless, and will defend Egan
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 Novirio of any term or condition of this Letter
Agreement, and from acts taken by Egan in pursuit of a Successful Business
Transaction and if he (a) acted in good faith, in accordance with this Letter
Agreement and in a manner he reasonably believed to be in or not opposed to
<PAGE>
the best interests of Novirio, and (b) with respect to any criminal action or
proceeding, had no reasonable cause to believe his conduct was unlawful.

   (g) 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.

   (h) Public Disclosure. Novirio shall have the right to disclose the terms of
this Agreement and the transactions contemplated by this Agreement as well as to
disclose Egan's name and likeness in any regulatory filings and publicity
materials prepared by it and in presentations to current or prospective clients,
investor and other third parties. Without obtaining the prior written consent of
Novirio, Egan shall not use Novirio's name in any publications or publicity or
other materials prepared by or on behalf of Egan.

   Please acknowledge your agreement and acceptance of the terms contained above
by executing a duplicate copy of this Letter Agreement in the space provided
below.

                                    Very truly yours,

                                    /s/ James Egan

                                    James J. Egan

Acknowledged, agreed and accepted
as of April 24, 2000

NOVIRIO PHARMACEUTICALS LIMITED

By:  /s/ Jean-Pierre Sommadossi
     ______________________________
      Jean-Pierre Sommadossi, Ph.D.
      CEO and Chairman of the Board

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