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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