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                                                                   Exhibit 10.42

                          REGISTRATION RIGHTS AGREEMENT

This Registration Rights Agreement (the "AGREEMENT") is made and entered into as
of this __ day of August, 2005 by and among CombinatoRx, Incorporated, a
Delaware corporation (the "COMPANY") and BioMedical Sciences Investment Fund Pte
Ltd (the "INVESTOR").

                                   AGREEMENT:

     WHEREAS, the parties desire to enter into this Agreement in connection with
the issuance and sale of shares of the Series A Preference Stock, $0.001 par
value per share (the "PREFERRED STOCK") and certain secured Notes (the "NOTES")
of CombinatoRx (Singapore) Pte Ltd (the "SUBSIDIARY") to the Investor pursuant
to a Subscription and Shareholders Agreement by and among the Subsidiary, the
Investor and the Company dated as of even date herewith (the "SSA");

     WHEREAS, the SSA provides for the possible conversion of the Preferred
Stock and the Notes into Common Stock of the Company.

     WHEREAS, the Investor desires to be granted the rights created herein.

     NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto agree as follows:

     1.  DEFINITIONS.

         1.1   CERTAIN DEFINED TERMS. As used in this Agreement, the following
terms shall have the following respective meanings:

     "BUSINESS DAY" means a day other than a Saturday, Sunday or other day on
which commercial banks are authorized or required to close under the laws of the
United States or the State of New York.

     "COMMON STOCK" means the Company's common stock, $0.001 par value per
share.

     "ELIGIBLE FILING DATE" shall have the meaning set forth in Section 2.1.

     "EXCHANGE ACT" shall mean the United States Securities Exchange Act of
1934, as amended, or any successor federal statute, and the rules and
regulations of the SEC issued under such act, as they each may, from time to
time, be in effect.

     "FORM S-3" means such form under the Securities Act as in effect on the
date hereof or any registration statement under the Securities Act subsequently
adopted by the SEC which permits inclusion or incorporation of substantial
information by reference to other documents filed by the Company with the SEC.

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     "PERSON" or "PERSON" means any individual, corporation, partnership,
limited liability company, joint venture, association, joint-stock company,
trust, unincorporated organization or government or other agency or political
subdivision thereof.

     "PROSPECTUS" shall have the meaning set forth in Section 2.1(b).

     "REGISTRABLE SECURITIES" means any Common Stock acquired by the Investor
pursuant to the terms of the SSA.

     "REGISTRATION STATEMENT" shall have the meaning set forth in Section
2.1(a).

     "REGISTRATION PERIOD" shall have the meaning set forth in Section 2.1(a).

     "SEC" shall mean the United States Securities and Exchange Commission or
any other federal agency at the time administering the Securities Act.

     "Securities Act" means the United States Securities Act of 1933, as
amended, or any successor federal statute, and the rules and regulations of the
SEC issued under such act, as they each may, from time to time, be in effect.

     "SUSPENSION" shall have the meaning set forth in Section 3.3.

     "SUSPENSION NOTICE" shall have the meaning set forth in Section 3.3.

         1.2   CONSTRUCTION. Unless the context otherwise requires

             (1) a term has the meaning assigned to it;

             (2) "or" is not exclusive;

             (3) words in the singular include the plural, and words in the
plural include the singular; and

             (4) "herein," "hereof" and other words of similar import refer to
this Agreement as a whole and not to any particular Article, Section or other
subdivision.

     2.  REGISTRATION RIGHTS.

         2.1   The Company shall, as promptly as possible upon receipt by the
Investor of Registrable Securities and after twelve (12) months after the
effective date of the first registration statement filed by the Company for an
underwritten public offering of securities of the Company (the "ELIGIBLE FILING
DATE"):

               (A) prepare and file with the SEC (which filing shall in no event
         occur more than ten (10) days after the Eligible Filing Date) a
         registration statement on Form S-3 (the "REGISTRATION STATEMENT"), to
         enable the resale of the Registrable Securities by the Investor from
         time to time and use all commercially reasonable

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         efforts to cause such Registration Statement to be declared effective
         as promptly as possible after filing, but in any event, within ninety
         (90) days following the such filing or, in the event of a review of the
         Registration Statement by the SEC, within one hundred twenty (120) days
         following such filing (such date as is applicable the "Required
         Registration Date"), and to remain continuously effective until the
         earlier of (1) the second anniversary of the effective date of the
         Registration Statement (subject to Section 3.6 hereof), (2) the date on
         which all Registrable Securities have been sold thereunder or (3) the
         date on which the Registrable Securities can be sold by nonaffiliates
         of the Company pursuant to Rule 144(k) promulgated under the Securities
         Act (the "REGISTRATION PERIOD"). In the event the Registration
         Statement cannot be kept effective for such period, the Company shall
         use commercially reasonable efforts to prepare and file with the SEC
         and have declared effective as promptly as possible another
         registration statement on the same terms as the initial Registration
         Statement and such registration statement shall be considered the
         Registration Statement for the purposes hereof. In the event that the
         Company does not meet the requirements for the use of Form S-3, the
         Company shall use such other form as is available for such a
         registration, and shall convert such other form to Form S-3, or file a
         replacement registration statement on Form S-3, as promptly as
         practicable after the first date on which it meets such requirements;

               (B) prepare and file with the SEC such amendments (including
         post-effective amendments) and supplements to the Registration
         Statement and the prospectus included in the Registration Statement
         (the "PROSPECTUS", as amended or supplemented by any prospectus
         supplement and by all other amendments thereto and all material
         incorporated by reference in such Prospectus) used in connection
         therewith as may be necessary to keep the Registration Statement
         effective and to comply with the provisions of the Securities Act with
         respect to the disposition of all securities covered by such
         Registration Statement at all times until the end of the Registration
         Period;

               (C) furnish to the Investor with respect to the Registrable
         Securities registered under the Registration Statement such reasonable
         number of copies of such Registration Statement and any Prospectus in
         conformity with the requirements of the Securities Act, each amendment
         and supplement thereto and any documents incorporated by reference
         therein and such other documents as the Investor may reasonably
         request, in order to facilitate the public sale or other disposition of
         all or any of the Registrable Securities (and the Company hereby
         consents to the Investor's use of the Prospectus in such sale or other
         disposition);

               (D) use its commercially reasonable efforts to register or
         qualify the Registrable Securities under such other securities or blue
         sky laws is such jurisdictions as are specified in writing by the
         Investor; use its commercially reasonable efforts to keep each such
         registration or qualification (or exemption therefrom) effective during
         the Registration Period and take any other action that may be
         reasonably necessary to enable the Investor to consummate the
         disposition in such jurisdiction of the Registrable Securities;
         provided, however, that the

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         Company shall not be required to qualify to do business or consent to
         service of process in any jurisdiction in which it is not now so
         qualified or has not so consented;

               (E) take all such action as is required of it to cause the
         Registrable Securities to be listed on the national securities exchange
         or automated quotation system on which the Common Stock is then traded;

               (F) promptly notify the Investor in writing (i) when the
         Registration Statement, a Prospectus or any supplement or amendment to
         either of them has been filed and, with respect to the Registration
         Statement or any post-effective amendment thereto, when the same has
         been declared effective and (ii) of the issuance by any state
         securities or other regulatory authority of any order suspending the
         qualification or exemption from qualification of any of the Registrable
         Securities under state securities or "blue sky" laws or the initiation
         of any proceedings for that purpose;

               (G) promptly notify the Investor in writing of the existence of
         any fact or the happening of any event, during the Registration Period
         (but not as to the substance of any such fact or event), that makes any
         statement of a material fact made in the Registration Statement, the
         Prospectus, any amendment or supplement thereto, or any document
         incorporated by reference therein untrue, or that requires the making
         of any additions to or changes in the Registration Statement or the
         Prospectus in order to make the statements therein not misleading
         (PROVIDED, HOWEVER, that no notice by the Company shall be required
         pursuant to this subsection (g) in the event that the Company either
         contemporaneously files a prospectus supplement to update the
         Prospectus or a Form 8-K or other appropriate Exchange Act report that
         is incorporated by reference into the Registration Statement, which, in
         either case, contains the requisite information with respect to such
         material event that results in such Registration Statement no longer
         containing any such untrue or misleading statements), provided,
         however, that the Company shall be under no obligation to file such
         prospectus supplement, Form 8-K or other appropriate Exchange Act
         report that is incorporated by reference into the Registration
         Statement to update the Prospectus if in the good faith judgment of the
         Company's Board of Directors it would be seriously detrimental to the
         Company and its stockholders for such supplement, Form 8-K or other
         report to be filed. After any notice provided to Investor pursuant to
         this subsection (g) during the Registration Period, the Company may
         require the Investor to discontinue disposition of any Registrable
         Securities until advised in writing by the Company that the use of the
         Prospectus may be resumed, and if applicable, the Investor is provided
         with a supplemented or amended Prospectus as contemplated by this
         subsection (g);

               (H) furnish to the Investor upon written request, from the date
         of this Agreement until the end of the Registration Period, one copy of
         its periodic reports filed with the SEC pursuant to the Exchange Act
         and the rules and regulations promulgated thereunder

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               (I) cooperate with the Investor to facilitate the timely
         preparation and delivery of certificates (which shall not bear any
         restrictive legends unless required under applicable law) representing
         securities sold under any Registration Statement, and enable such
         securities to be in such denominations and registered in such names as
         the Investor may request and keep available and make available to the
         Company's transfer agent prior to the effectiveness of such
         registration statement a supply of such certificates

               (J) provide a transfer agent and registrar for all Registrable
         Securities registered hereunder and provide a CUSIP number for the
         Registrable Securities included in any Registration Statement not later
         than the effective date of such Registration Statement

               (K) cooperate with the Investor and its counsel in connection
         with any filings required to be made with the National Association of
         Securities Dealers, Inc.;

               (L) promptly file all documents required to be filed with the SEC
         pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act;

               (M) following the effectiveness of such Registration Statement,
         notify the Investor promptly of any request by the SEC for the amending
         or supplementing of such Registration Statement or Prospectus or for
         additional information

               (N) prepare and file with the SEC promptly any amendments or
         supplements to such Registration Statement or Prospectus which, in the
         reasonable opinion of counsel for the Company, is required in
         connection with the distribution of the Registrable Securities

               (O) advise the Investor, promptly after the Company shall receive
         notice or obtain knowledge thereof, of the issuance of any stop order
         by the SEC suspending the effectiveness of such Registration Statement
         or the initiation or threatening of any proceeding for such purpose and
         promptly use its commercially reasonable efforts to prevent the
         issuance of any stop order or to obtain its withdrawal at the earliest
         possible moment if such stop order should be issued; and

               (P) bear all expenses in connection with the procedures described
         in paragraphs (a) through (o) of this Section 2.1 and the registration
         of the Registrable Securities pursuant to the Registration Statement
         other than fees and expenses, if any, of legal counsel or other
         advisers to the Investor or underwriting discounts, brokerage fees and
         commissions incurred by the Investor, if any.

         2.2   It shall be a condition precedent to the obligations of the
Company to take any action pursuant to this Section 2 with respect to
Registrable Securities held by the Investor that:

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               (A) the Investor shall timely furnish to the Company a completed
         Registration Statement questionnaire on or before the Eligible Filing
         Date and such other written information regarding itself, the
         Registrable Securities and the intended method of disposition of the
         Registrable Securities as shall reasonably be required to effect the
         registration of the Registrable Securities and as shall be reasonably
         be requested by the Company in advance or from time to time; and

               (B) the Investor is unable otherwise to sell in a single
         transaction the Registrable Securities eligible to be sold pursuant to
         the limitations set forth in the SSA without registration of such
         Registrable Securities. For purposes of this Section 2.2, the sale of
         Registrable Securities without registration shall mean that the
         Registrable Securities may be sold by the Investor pursuant to
         Regulation S or Rule 144 under the Securities Act or any other
         applicable provisions of the Securities Act pursuant to which the
         subsequent sale by the purchaser of such securities would not be
         subject to registration. In the event of a disagreement as to the
         salability of the Registrable Securities without registration as
         described in this Section 2.2(b), or as to the salability of the
         Registrable Securities by nonaffiliates of the Company pursuant to Rule
         144(k) promulgated under the Securities Act as described in Section
         2.1(a), the Company shall be entitled to rely on the opinion of Ropes &
         Gray LLP or any other recognized United States securities law counsel,
         provided, however, that if, in the opinion of Skadden, Arps, Slate,
         Meagher & Flom or other recognized United States securities law counsel
         to the Investor such Registrable Securities are not so salable without
         registration, the Parties shall resolve such dispute on the basis of a
         legal opinion of a mutually acceptable recognized United States
         securities law counsel.

         2.3 LIMITATION ON SUBSEQUENT REGISTRATION RIGHTS. The Company
acknowledges and agrees that the Company will not grant or allow any other
Persons any registration rights with respect to any securities of the Company
which (i) impair the rights of the Investor to exercise its rights under this
Agreement, or (ii) conflict with or violate the provisions of this Agreement.

         2.4 In addition to any other remedies available to the Investor under
this Agreement or at law or equity, if no Registration Statement has been
declared effective by the Required Registration Date or such Registration
Statement is not available with respect to all Registrable Securities at any
time on or after the Required Registration Date and during the Registration
Period (except during a Suspension permitted by Section 3.2 or 3.3) the Company
shall cause to be wire transferred to an account specified by the Investor on
the last Business Day of each month an amount, in immediately available United
States funds, equal to:

                                     1/20% x ND x MV

                           Where:

                               ND =  the number of business days in such month
                                     that the Registration Statement has not
                                     been declared effective by the Required
                                     Registration Date or such Registration
                                     Statement is

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                                     not available (each such day a
                                     "Shortfall Day") with respect to
                                     Registrable Securities that may not
                                     otherwise be sold by the Investor
                                     immediately pursuant to Rule 144 without
                                     compliance with the registration
                                     requirements of the Securities Act after
                                     giving effect to any limitations on the
                                     Investor's ability to sell Registrable
                                     Securities imposed by the SSA ("Non-Rule
                                     144 Stock"); and

                               MV =  the average closing price of a single
                                     share of Common Stock on the Shortfall Days
                                     in such month multiplied by the average
                                     number of shares of Non-Rule 144 Stock
                                     issued and outstanding on each of the days
                                     included in "ND" above.

     3.  TRANSFER OF REGISTRABLE SECURITIES AFTER REGISTRATION; SUSPENSION.

         3.1   The Investor agrees that it will not offer to sell or make any
sale, assignment, pledge, hypothecation or other transfer with respect to the
Registrable Securities that would constitute a sale within the meaning of the
Securities Act except pursuant to an effective registration statement under the
Securities Act or pursuant to an available exemption therefrom.

         3.2   In addition to any suspension rights under Section 3.3 below, if
(i) an event has occurred and is continuing as a result of which any such
Registration Statement or Prospectus would, in the Company's reasonable
judgment, contain an untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary to make the statements
therein not misleading or (ii) if the Company notifies the Investor that any
filing of any Registration Statement pursuant to this Agreement, any filing of
any amendment thereto, any furnishing of any supplement to a Prospectus included
in a Registration Statement pursuant to Section 2.1(g) hereof, any other filing
with the SEC, the effectiveness of any Registration Statement or other filing
with the SEC, or any similar action would, in the good faith judgment of outside
counsel to the Company, require the disclosure of material non-public
information which the Company has a bona fide business purpose for preserving as
confidential and which the Company would not otherwise be required to disclose,
then the Company may, on not more than two (2) non-consecutive occasions for not
more than thirty (30) days on each such occasion, (x) refrain from filing any
Registration Statement pursuant to this Agreement, filing any amendment thereto,
furnishing any supplement to a Prospectus included in a Registration Statement
pursuant to Section 2.1(g) hereof, making any other filing with the SEC
otherwise required by this Agreement, causing the effectiveness of any
Registration Statement or other filing with the SEC, or taking any similar
action and (y) suspend use of the Prospectus, on written notice to the Investor
(which notice will not disclose the content of any material non-public
information and will indicate the date of the beginning and end of the intended
period of suspension, if known), in which case the Investor shall discontinue
disposition of Registrable Securities covered by the Registration Statement or
Prospectus until copies of a supplemented or amended Prospectus are distributed
to the Investor or until the Investor are advised in writing by the Company that
sales of Registrable Securities under the applicable Prospectus may be resumed
and have received copies of any additional or supplemental filings that are
incorporated or deemed incorporated by reference in any such Prospectus. The
suspension and notice thereof

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described in clause (y) of this Section 3.2 shall be held in strictest
confidence and shall not be disclosed by the Investor.

         3.3   Subject to Section 3.4 below, in the event of: (1) any request by
the SEC or any other federal or state governmental authority during the period
of effectiveness of the Registration Statement for amendments or supplements to
a Registration Statement or related prospectus or for additional information,
(2) the issuance by the SEC or any other federal or state governmental authority
of any stop order suspending the effectiveness of a Registration Statement or
the initiation of any proceedings for that purpose, (3) the receipt by the
Company of any notification suspending the qualification or exemption from
qualification of any of the Registrable Securities for sale in any jurisdiction
or the initiation of any proceeding for such purpose, or (4) any event or
circumstance which necessitates the making of any changes in the Registration
Statement or Prospectus, or any document incorporated or deemed to be
incorporated therein by reference, so that, in the case of the Registration
Statement, it will not contain any untrue statement of a material fact or any
omission to state a material fact required to be stated therein or necessary to
make the statements therein not misleading, and that in the case of the
Prospectus, it will not contain any untrue statement of a material fact or any
omission to state a material fact required to be stated therein or necessary to
make the statements therein, in the light of the circumstances under which they
were made, not misleading, then the Company shall deliver a certificate in
writing to the Investor (the "SUSPENSION NOTICE") to the effect of the foregoing
(which notice will not disclose the content of any material non-public
information and will indicate the date of the beginning and end of the intended
period of suspension, if known), and, upon receipt of such Suspension Notice,
the Investor will discontinue disposition of Registrable Securities covered by
to the Registration Statement or Prospectus (a "SUSPENSION") until the
Investor's receipt of copies of a supplemented or amended Prospectus prepared
and filed by the Company, or until the Investor are advised in writing by the
Company that the current Prospectus may be used, and have received copies of any
additional or supplemental filings that are incorporated or deemed incorporated
by reference in any such prospectus. In the event of any Suspension, the Company
will use its commercially reasonable efforts to cause the use of the Prospectus
so suspended to be resumed as soon as possible after delivery of a Suspension
Notice to the Investor.

         3.4   Provided that a suspension is not then in effect, the Investor
may sell Registrable Securities under the Registration Statement, provided that
the selling Investor arranges for delivery of a current Prospectus to the
transferee of such Registrable Securities to the extent such delivery is
required by applicable law.

         3.5   In the event of a sale of Registrable Securities by the Investor,
the Investor must also deliver to the Company's transfer agent, with a copy to
the Company, a certificate of subsequent sale reasonably satisfactory to the
Company, so that ownership of the Registrable Securities may be properly
transferred. The Company will cooperate to facilitate the timely preparation and
delivery of certificates (unless otherwise required by applicable law)
representing Registrable Securities sold.

         3.6   For the purpose of determining the Registration Period pursuant
to Section 2.1, the occurrence of any Suspension pursuant to Section 3.3 or the
non-effectiveness of the Registration Statement during any period during which
such effectiveness is required pursuant to

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the terms of Section 2.1(a) shall cause the second anniversary of the effective
date of the Registration Statement to be deemed extended by a number of days
equivalent to the duration of any Suspension or the number of days of such
non-effectiveness.

     4.  INDEMNIFICATION.

         For the purpose of this Section 4, the term "REGISTRATION STATEMENT"
shall include any preliminary or final Prospectus, exhibit, supplement or
amendment included in or relating to the Registration Statement referred to in
Section 2, together with any document incorporated by reference into any of the
same.

         4.1   INDEMNIFICATION BY THE COMPANY. The Company agrees to indemnify
and hold harmless each of the Investor, and each of its employees, advisors,
agents, representatives, partners, officers and directors, and each person, if
any, who controls the Investor within the meaning of the Securities Act or the
Exchange Act (all such persons together, the "Investor Indemnitees"), to the
fullest extent permitted by law, against any and all losses, claims, damages,
liabilities or expenses, joint or several, to which the Investor or such
controlling person may become subject, under the Securities Act, the Exchange
Act or any other federal or state statutory law or regulation, or at common law
or otherwise (including in settlement of any litigation, if such settlement is
effected with the written consent of the Company, which consent shall not be
unreasonably withheld) (including, without limitation, attorneys' fees and
disbursements), insofar as such losses, claims, damages, liabilities or expenses
(or actions in respect thereof as contemplated below) arise out of, are based
upon, relate to or result from any untrue statement or alleged untrue statement
of any material fact contained in the Registration Statement, the Prospectus, or
any amendment or supplement thereto, or arise out of, are based upon, relate to
or result from the omission or alleged omission to state in any of them a
material fact required to be stated therein or necessary to make the statements
in any of them, in light of the circumstances under which they were made, not
misleading, and will reimburse the Investor Indemnitees for any reasonable legal
and other expenses as such reasonable expenses are incurred by the Investor
Indemnitees in connection with investigating, defending (or preparing to
defend), settling, compromising or paying any such loss, claim, damage,
liability, expense or action; PROVIDED, HOWEVER, that the Company will not be
liable in any such case to the extent that any such loss, claim, damage,
liability, expense or action arises out of, is based upon, relates to or results
from (1) an untrue statement or alleged untrue statement or omission or alleged
omission made in the Registration Statement, the Prospectus or any amendment to
or supplement of the Registration Statement or Prospectus made in reliance upon
and in conformity with information furnished to the Company by or on behalf of
the Investor expressly for use in the Registration Statement or the Prospectus,
(2) the failure of the Investor to comply with the covenants and agreements
contained in this Agreement respecting sale of the Registrable Securities, or
(3) any untrue statement or omission of a material fact required to make such
statement not misleading in any Prospectus that is corrected in any subsequent
Prospectus that was delivered to the Investor before the pertinent sale or sales
by the Investor.

         4.2   INDEMNIFICATION BY THE INVESTOR. The Investor will indemnify and
hold harmless the Company, each of its directors, each of its officers who
signed the Registration Statement and each person, if any, who controls the
Company within the meaning of the

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Securities Act, against any losses, claims, damages, liabilities or expenses to
which the Company, its directors, its officers who signed the Registration
Statement and any controlling persons may become subject, under the Securities
Act, the Exchange Act, or any other federal or state statutory law or
regulation, or at common law or otherwise (including in settlement of any
litigation, if such settlement is effected with the written consent of the
Investor, which consent shall not be unreasonably withheld) insofar as such
losses, claims, damages, liabilities or expenses (or actions in respect thereof
as contemplated below) arise out of, are based upon, relate to or result from
any untrue statement or alleged untrue statement of any material fact contained
in the Registration Statement, the Prospectus, or any amendment or supplement to
the Registration Statement or Prospectus, or arise out of, are based upon,
relate to or result from the omission or alleged omission to state therein a
material fact required to be stated therein or necessary to make the statements
therein not misleading, in each case to the extent, but only to the extent, that
such untrue statement or alleged untrue statement or omission or alleged
omission was made in the Registration Statement, the Prospectus, or any
amendment or supplement thereto, solely in reliance upon and in conformity with
written information furnished to the Company by or on behalf of the Investor
expressly for use therein, and the Investor will reimburse the Company, each of
its directors, each of its officers who signed the Registration Statement, and
any controlling persons for any reasonable legal and other expense incurred by
the Company, its directors, its officers who signed the Registration Statement,
and any controlling persons, in connection with investigating, defending (or
preparing to defend), settling, compromising or paying any such loss, claim,
damage, liability, expense or action; PROVIDED, HOWEVER, that the Investor shall
not be liable for any such untrue statement or alleged untrue statement or
omission or alleged omission with respect to which the Investor has delivered to
the Company in writing a correction before the occurrence of the event from
which such loss was incurred. Notwithstanding the provisions of this Section
4.2, the Investor shall not be liable for any indemnification obligation under
this Agreement in excess of the aggregate amount of net proceeds received by the
Investor from the sale of the Registrable Securities pursuant to the
Registration Statement.

         4.3   INDEMNIFICATION PROCEDURE. Promptly after receipt by an
indemnified party under this Section 4 of notice of the threat or commencement
of any action, such indemnified party will, if a claim in respect thereof is to
be made against an indemnifying party under this Section 4, promptly notify the
indemnifying party in writing of the claim; but the omission so to notify the
indemnifying party will not relieve it from any liability which it may have to
any indemnified party for contribution or otherwise under the indemnity
agreement contained in this Section 4 or otherwise, to the extent it is not
prejudiced as a result of such failure. The reasonable fees and expenses of
counsel for the indemnified party shall be at the expense of the indemnifying
party.

     5.  RULE 144 INFORMATION.

         5.1   Until the expiration of the Registration Period, the Company
shall (i) make and keep public information available, as those terms are defined
in Rule 144 under the Securities Act, at all times after the effective date that
the Company becomes subject to the reporting requirements of the Securities Act
or the Exchange Act; (ii) file in a timely manner all reports required to be
filed by it under the Securities Act and the Exchange Act and the rules and
regulations promulgated thereunder; (iii) furnish to Investor, so long as
Investor owns any

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Registrable Securities, upon request by Investor, (a) a written statement by the
Company that it has complied with the reporting requirements of Rule 144 and of
the Securities Act and the Exchange Act, (b) a copy of the most recent annual or
quarterly report of the Company and (c) such other publicly available reports
and documents of the Company and other publicly available information in the
possession of or reasonably obtainable by the Company as a Holder may reasonably
request in availing itself of any rule or regulation of the SEC allowing a
Holder to sell any such securities without registration; and (iv) take such
further action to the extent required to enable the Investor to sell the
Registrable Securities pursuant to Rule 144 under the Securities Act (as such
rule may be amended from time to time).

     6.  REPRESENTATIONS AND WARRANTIES

         6.1   CERTAIN REPRESENTATIONS AND WARRANTIES OF THE INVESTOR.  The
Investor represents and warrants to the Company as of the date hereof as
follows:

               (A)  BINDING AGREEMENT. The Investor has the capacity to execute
         and deliver this Agreement and to consummate the transactions
         contemplated hereby. The Investor has duly and validly executed and
         delivered this Agreement and this Agreement constitutes a legal, valid
         and binding obligation of the Investor, enforceable against the
         Investor in accordance with its terms, except as such enforceability
         may be limited by applicable bankruptcy, insolvency, reorganization or
         other similar laws affecting creditors' rights generally and by general
         equitable principles (regardless of whether enforceability is
         considered in a proceeding in equity or at law).

               (B)  NO CONFLICT. Neither the execution and delivery of this
         Agreement by the Investor, nor the performance by the Investor of its
         obligations hereunder will, (i) require any consent, approval,
         authorization or permit of, registration, declaration or filing (except
         for such filings as may be required under the federal securities laws
         and the rules and regulations thereunder, any "blue sky" or other state
         securities laws or as would not reasonably be expected to prevent or
         materially delay or otherwise impair the Investor's ability to perform
         its obligations hereunder) with, or notification to, any governmental
         entity, (ii) result in a violation of, or default under, or conflict
         with any provision of its certificate of incorporation, bylaws,
         partnership agreement, limited liability company agreement or similar
         organizational documents, (iii) result in a violation or breach of, or
         constitute (with or without due notice or lapse of time or both) a
         default (or give rise to any right of termination, cancellation, or
         acceleration) under any contract, trust, agreement, instrument,
         commitment, arrangement or understanding applicable to the Investor or
         its Registrable Securities, or result in the creation of a security
         interest, lien, charge, encumbrance, equity or claim with respect to
         any of the Investor's Registrable Securities, except, in the case of
         clause (iii), as would not prevent or materially delay or otherwise
         materially impair the Investor's ability to perform its obligations
         hereunder, (iv) require any consent, authorization or approval of any
         person other than a governmental entity, except, in the case of clause
         (iv), as would not reasonably be expected to prevent, materially delay
         or otherwise materially impair the Investor's ability to perform its
         obligations

Registration Rights Agreement skadden Aug 10(3)                      - 11 -

<Page>

         hereunder or (v) violate or conflict with any order, writ, injunction,
         decree, rule, regulation or law applicable to the Investor or its
         Registrable Securities.

         6.2   CERTAIN REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  The
Company represents and warrants to the Investor as of the date hereof as
follows:

               (A)  BINDING AGREEMENT. The Company is a corporation duly
         incorporated, validly existing and in good standing under the laws of
         the State of Delaware and has full corporate power and authority to
         execute and deliver this Agreement and to consummate the transactions
         contemplated hereby. The execution and delivery of this Agreement by
         the Company and the consummation of the transactions contemplated
         hereby have been duly and validly authorized by the Board of Directors
         of the Company, and no other corporate proceedings on the part of the
         Company are necessary to authorize the execution, delivery and
         performance of this Agreement by the Company and the consummation of
         the transactions contemplated hereby. The Company has duly and validly
         executed this Agreement and this Agreement constitutes a legal, valid
         and binding obligation of the Company, enforceable against the Company
         in accordance with its terms, except as such enforceability may be
         limited by applicable bankruptcy, insolvency, reorganization or other
         similar laws affecting creditors' rights generally and by general
         equitable principles (regardless of whether enforceability is
         considered in a proceeding in equity or at law).

               (B)  NO CONFLICT. Neither the execution and delivery by the
         Company of this Agreement, nor the performance by the Company of its
         obligations hereunder will, (i) require any consent, approval,
         authorization or permit of, registration, declaration or filing (except
         for such filings as may be required under the federal securities laws
         and the rules and regulations thereunder, any "blue sky" or other state
         securities laws or as would not reasonably be expected to prevent or
         materially delay or otherwise impair the Company's ability to perform
         its obligations hereunder) with, or notification to, any governmental
         entity, (ii) result in a violation of, or default under, or conflict
         with any provision of its Certificate of Incorporation or Bylaws, (iii)
         result in a violation or breach of, or constitute (with or without due
         notice or lapse of time or both) a default (or give rise to any right
         of termination, cancellation, or acceleration) under any contract,
         trust, agreement, instrument, commitment, arrangement or understanding
         applicable to the Company, except, in the case of clause (iii), as
         would not prevent or materially delay or otherwise materially impair
         the Company's ability to perform its obligations hereunder, (iv)
         require any consent, authorization or approval of any person other than
         a governmental entity, except, in the case of clause (iv), as would not
         reasonably be expected to prevent, materially delay or otherwise
         materially impair the Company's ability to perform its obligations
         hereunder or (v) violate or conflict with any order, writ, injunction,
         decree, rule, regulation or law applicable to the Company.

Registration Rights Agreement skadden Aug 10(3)                      - 12 -

<Page>

     7.  MISCELLANEOUS.

         7.1   SUCCESSORS. This Agreement shall inure to the benefit of and be
binding upon the parties hereto and their respective heirs, successors, assigns,
administrators, executors and other legal representatives. To the extent any
assignee of any of the Investor's rights under the SSA is also an owner of
Registrable Securities, such assignee shall have the same rights and
responsibilities hereunder with respect to such Registrable Securities as the
Investor has hereunder with respect to the Registrable Securities and any
reference to "the Investor" in this Agreement shall also be deemed to include
any such assignee.

         7.2   GOVERNING LAW.  This Agreement shall be governed by and construed
under the laws of the State of New York without regard to the principles of
conflicts of law.

         7.3   COUNTERPARTS.  This Agreement may be executed in any number of
counterparts, each of which shall be an original but all of which together shall
constitute one instrument.

         7.4   TITLES AND SUBTITLES.  The titles and subtitles used in this
Agreement are used for convenience only and are not to be considered in
construing or interpreting this Agreement.

         7.5   NOTICES. All notices, requests, consents, and other
communications under this Agreement shall be in writing and shall be deemed
delivered three business days after being sent via a reputable international
courier service guaranteeing three business day delivery, in each case to the
intended recipient as set forth below:

               (A) If to the Company, at 650 Albany Street, Boston, MA 02118,
         Attention: Chief Financial Officer, or at such other address as may
         have been furnished in writing by the Company to the other parties
         hereto, with a copy to Ropes & Gray LLP, One International Place,
         Boston, MA 02110, Attention: Geoffrey Davis, Esq.; or

               (B) If to the Investor, at 20 Biopolis Way, #09-01 Centros,
         Singapore 138668, Attention: Chief Executive Officer, Chu Swee Yeok, or
         at such other address as may have been furnished in writing by the
         Investor, with copies to each of Skadden, Arps, Slate, Meagher & Flom
         LLP, 30/F Tower Two, Lippo Centre, 89 Queensway, Central, Hong Kong,
         Attention: Alec P. Tracy and Allen & Gledhill, One Marina Boulevard
         #28-00, Singapore 018989, Attention: Tan Su May.

     Any party may give any notice, request, consent or other communication
under this Agreement using any other means (including, without limitation,
personal delivery, messenger service, telecopy, first class mail or electronic
mail), but no such notice, request, consent or other communication shall be
deemed to have been duly given unless and until it is actually received by the
party for whom it is intended. Any party may change the address to which
notices, requests, consents or other communications hereunder are to be
delivered by giving the other parties notice in the manner set forth in this
Section 7.5.

Registration Rights Agreement skadden Aug 10(3)                      - 13 -

<Page>

         7.6   ATTORNEY'S FEES. In the event that any suit or action is
instituted to enforce any provision in this Agreement, the prevailing party in
such dispute shall be entitled to recover from the losing party all reasonable
fees, costs and expenses of enforcing any right of such prevailing party under
or with respect to this Agreement, including without limitation, such reasonable
fees and expenses of attorneys and accountants, which shall include, without
limitation, all fees, costs and expenses of appeals.

         7.7   AMENDMENTS OR WAIVER. Any provision of this Agreement may be
amended or the observance thereof may be waived (either generally or
specifically and either retroactively or prospectively), only by an instrument
in writing executed by the Company and the Investor.

         7.8  SEVERABILITY. In the event that one or more of the provisions of
this Agreement are held to be unenforceable under applicable law, such provision
shall be excluded from this Agreement and the balance of the Agreement shall be
interpreted as if such provision were so excluded and shall be enforceable in
accordance with its terms.

         7.9   ENTIRE AGREEMENT. This Agreement constitutes the full and entire
understanding and agreement between the parties regarding the subject matters
hereof.

         7.10  SPECIFIC PERFORMANCE. The parties hereto hereby declare that it
is impossible to measure in money the damages which will accrue to a party
hereto or to their heirs, personal representatives, or assigns by reason of a
failure to perform any of the obligations under this Agreement and agree that
the terms of this Agreement shall be specifically enforceable. If any party
hereto or his heirs, personal representatives, or assigns institutes any action
or proceeding to specifically enforce the provisions hereof, any person against
whom such action or proceeding is brought hereby waives the claim or defense
therein that such party or such personal representative has an adequate remedy
at law, and such person shall not offer in any such action or proceeding the
claim or defense that such remedy at law exists. The remedies provided for
herein are cumulative and are not exclusive of any remedies that may be
available to any party hereunder at law or in equity or otherwise.

         7.11  WAIVER. No waivers of any breach of this Agreement extended by
any party hereto to any other party shall be construed as a waiver of any rights
or remedies of any other party hereto or with respect to any subsequent breach.
No failure or delay on the part of any party hereto in exercising any right,
power or remedy hereunder shall operate as a waiver thereof, nor shall any
single or partial exercise of any such right, power or remedy preclude any other
or further exercise thereof or the exercise of any other right, power or remedy.

Registration Rights Agreement skadden Aug 10(3)                      - 14 -

<Page>

IN WITNESS WHEREOF, the parties hereto have executed this Registration Rights
Agreement as of the date first above written.

THE COMPANY:                                  THE INVESTOR:

Registration Rights Agreement skadden Aug 10(3)                      - 15 -<Page>

                                                                   Exhibit 10.43

================================================================================

                                SWAP-UP AGREEMENT

                                      AMONG

                         COMBINATORX (SINGAPORE) PTE LTD

                   BIOMEDICAL SCIENCES INVESTMENT FUND PTE LTD

                                       AND

                            COMBINATORX INCORPORATED

                              DATED AUGUST __, 2005

================================================================================

<Page>

                                TABLE OF CONTENTS

<Table>
<Caption>
CONTENTS                                                                   PAGE
<S>                                                                          <C>
1.   DEFINITIONS..............................................................1

2.   SWAP-UP PUT AND CALL OPTIONS.............................................5

3.   PAYMENT OF NOTES.........................................................6

4.   DEFAULT..................................................................8

5.   SWAP UP CLOSING..........................................................9

6.   STOCK RESTRICTIONS AND REGISTRATION RIGHTS..............................10

7.   REPURCHASE..............................................................12

8.   PREFERENCE SHARES COMPLETION............................................12

9.   MISCELLANEOUS PROVISIONS................................................13
</Table>

                               SWAP UP AGREEMENT

This Swap-Up Agreement (the "AGREEMENT") is entered into as of August [ ], 2005
(the "EFFECTIVE DATE") by and among CombinatoRx (Singapore) Pte. Ltd., a
Singapore private limited company (the "COMPANY"), BioMedical Sciences
Investment Fund Pte Ltd, a Singapore private limited company (the "INVESTOR"),
and CombinatoRx, Incorporated, a Delaware corporation (the "PARENT"). The
Company, the Parent and the Investor are referred to collectively herein as the
"PARTIES."

                                   AGREEMENT:

WHEREAS, the Parent, the Investor and the Company have entered into a
Subscription and Shareholders Agreement (the "SSA") on even date relating to the
Investor's investment in the Company by way of subscribing for certain
Preference Shares and certain secured Notes of the Company, as defined in and
set out in the SSA and on the terms and conditions of the SSA; and

WHEREAS, as a condition to the Investor's investment in the Company, the Parties
have agreed to enter into this Agreement to provide for the possible purchase by
the Parent or repurchase by the Company of the Preference Shares, the possible
prepayment of the Notes, and the possible swap-up of the Preference Shares and
the Notes into stock of the Parent, all by way of the exercise of put and call
options by the Investor and/or the Parent and the allotment of shares in the
capital of the Parent;

NOW THEREFORE, in consideration of the mutual covenants and other consideration
provided herein and in the SSA, the sufficiency of which each Party expressly
acknowledges, the Parties agree as follows:

1.     DEFINITIONS

                                        2
<Page>

1.1    CERTAIN DEFINED TERMS. As used in this Agreement, the following terms
       shall have the following respective meanings:

       "APPLICABLE INTEREST RATE" shall mean the PER ANNUM rate of interest
       (based on a year of twelve 30 day months) of 5.0%, compounded and
       accumulated and payable on the Maturity Date unless the Notes are prepaid
       pursuant to Section 3.2. Notwithstanding the foregoing, the Applicable
       Interest Rate shall not exceed the highest rate permitted by applicable
       law to be charged on commercial loans;

       "APPLICABLE PERCENTAGE" shall mean:

              (i)    if an IPO occurs on or before December 31, 2006, 140%;

              (ii)   if an IPO occurs after December 31, 2006,

              (A)    in regard to the conversion of any Note issued prior to the
       IPO or of any Preference Share, the greater of (i) 100% or (ii) 140%
       minus the product, expressed in percentage points, yielded by multiplying
       40% by Z, where Z is the result of dividing the number of days after
       December 31, 2006 prior to the date of such IPO by 730, and

              (B)    in regard to the conversion of any Note issued after the
       IPO, 140%;

       and where the date of an IPO means the effective date of the registration
       statement filed in connection with such IPO.

       "CAPITALIZED DEFAULT INTEREST" shall mean all accrued and unpaid interest
       on such Notes from the date of issuance to the relevant Default Date,
       such interest accruing at the Default Interest Rate;

       "CAPITALIZED INTEREST" shall mean, for any given date, and with respect
       to all or any portion of the Outstanding Principal Balance of such Note,
       all accrued and unpaid interest capitalized on all or such portion of the
       Outstanding Principal Balance of such Note, as the case may be, as of
       such date, such interest accruing at the Applicable Interest Rate;

       "COMPANY" shall mean CombinatoRx (Singapore) Pte Ltd, a Singapore private
       limited company;

       "DEFAULT DATE" shall have the meaning set forth in the SSA;

       "DEFAULT INTEREST RATE" shall mean, with respect to the Notes, the PER
       ANNUM rate of interest (based on a year of twelve 30 day months) of ten
       percent (10%), which shall accrue from the date of issuance for each Note
       until payment is made in full and shall be compounded annually.
       Notwithstanding the foregoing, the Default Interest Rate shall not exceed
       the highest rate permitted by applicable law to be charged on commercial
       loans;

       "DOLLARS" shall mean United States dollars;

       "EVENT OF DEFAULT" shall have the meaning set forth in the SSA;

                                        3
<Page>

       "INITIAL CLOSING DATE" shall have the meaning set forth in the SSA;

       "INITIAL CONVERSION DATE" shall mean the date falling on the first
       anniversary of the Initial Closing Date;

       "INVESTOR" shall mean BioMedical Sciences Investment Fund Pte Ltd, a
       Singapore private limited company;

       "INVESTOR NOTE PREPAYMENT PUT OPTION" shall have the meaning set forth in
       Section 3.2.1;

       "INVESTOR NOTE REPAYMENT PUT OPTION" shall have the meaning set forth in
       Section 3.1.2;

       "INVESTOR NOTES DEFAULT OPTION" shall have the meaning set forth in
       Section 4.2.2;

       "INVESTOR PREFERENCE SHARE DEFAULT OPTION" shall have the meaning set
       forth in Section 4.2.1;

       "INVESTOR SWAP UP PUT OPTION" shall have the meaning set forth in Section
       2.1.

       "IPO" shall mean an underwritten initial public offering of the Parent
       Common Stock pursuant to an effective registration statement filed with
       the SEC under the Securities Act or any other transaction by which the
       Parent Common Stock becomes registered on a United States national
       securities exchange or authorized for quotation on an automated quotation
       system sponsored by a United States registered securities association;

       "ISSUE PRICE" shall have the meaning set forth in the SSA;

       "ISSUE PRICE PER PREFERENCE SHARE" shall have the meaning set forth in
       the SSA;

       "MANDATORY SHARES SWAP UP PERIOD" means, in the event that the Parent has
       completed an IPO, any period of twenty (20) consecutive trading days
       during which the average of the daily volume-weighted average price per
       share of Parent Common Stock on its principle exchange on each such
       trading day is at or above 125% of the Preference Shares Option Price;

       "MANDATORY NOTE SWAP UP PERIOD" means, in the case of any Note, in the
       event that the Parent has completed an IPO, any period of twenty (20)
       consecutive trading days during which the average of the daily
       volume-weighted average price per share of Parent Common Stock on its
       principle exchange on each such trading day is at or above 125% of the
       Notes Option Price relevant to such Note;

       "MATURITY DATE" shall mean December 31, 2009;

       "NOTE CONDITIONS" shall have the meaning set forth in the SSA;

       "NOTES" shall have the meaning set forth in the SSA;

                                        4
<Page>

       "NOTES DEFAULT AMOUNT" shall equal the sum of the Outstanding Principal
       Balance and Capitalized Default Interest on each of the Notes outstanding
       as of the Default Date;

       "NOTES OPTION PRICE" shall mean (i) in the case of any Note issued at
       least twenty one (21) trading days after an IPO, the Applicable
       Percentage of the average of the daily volume-weighted average price per
       share of Parent Common Stock on its principle exchange over the twenty
       (20) trading days immediately prior to the date of the issuance of such
       Note; or (ii) in the case of any Note issued on or prior to the twentieth
       (20th) trading date after an IPO, the Applicable Percentage of the
       average of the daily volume-weighted average price per share of Parent
       Common Stock on its principle exchange over the first twenty (20) trading
       days after the IPO PROVIDED, that, in either case, such Notes Option
       Price shall be adjusted as may be required to reflect any stock split or
       consolidation or similar event with respect to the Parent Common Stock;

       "OUTSTANDING PRINCIPAL BALANCE" shall mean, with respect to each
       outstanding Note, the unpaid principal amount (excluding interest) of
       such Note outstanding at any time;

       "PARENT" shall mean CombinatoRx, Incorporated, a Delaware corporation;

       "PARENT COMMON STOCK" shall mean the common stock, $0.001 par value per
       share, of the Parent;

       "PARENT NOTE CONVERSION CALL OPTION" has the meaning defined in Section
       3.3.

       "PARENT PREFERRED STOCK" shall mean, with respect to any payment or
       conversion under this Agreement, the latest series or class of Preferred
       Stock of the Parent issued in a financing round by the Parent prior to
       such payment or conversion;

       "PARENT PREFERRED STOCK PRICE PER SHARE" shall mean, with respect to any
       specific class or series of Parent Preferred Stock issued in any
       financing round, the lowest price per share paid for such class or series
       in such financing round;

       "PARENT SEC REPORTS" shall mean, as of any date, all forms, reports and
       documents filed by the Parent with the SEC on or prior to such date.

       "PARENT SHARE REPURCHASE OPTION" shall have the meaning set forth in
       Section 7.1;

       "PARENT SWAP UP CALL OPTION" shall have the meaning set forth in Section
       2.2;

       "PARENT WARRANTIES" shall have the meaning set forth in Section 6.1;

       "PERSON" means any individual, partnership, corporation, unincorporated
       organization, limited liability company, trust or joint venture, or a
       governmental agency or political subdivision thereof;

       "PREFERENCE SHARES" shall mean the Preference Shares, as such term is
       defined in the SSA;

                                        5
<Page>

       "PREFERENCE SHARES CLOSING" shall mean the closing of the transfer by the
       Investor to the Parent of the Preference Shares pursuant to the Parent
       Share Repurchase Option;

       "PREFERENCE SHARES DEFAULT AMOUNT" shall mean (i) the product of the
       number of Preference Shares outstanding on the Default Date and the Issue
       Price Per Preference Share, plus (ii) 10% interest PER ANNUM on such
       Preference Shares, compounded annually and accumulated from the Initial
       Closing Date to the Default Date;

       "PREFERENCE SHARES OPTION PRICE" shall mean, in the case in which the
       Initial Closing Date was at least twenty-one (21) trading days after the
       IPO, the Applicable Percentage of the average of the daily
       volume-weighted average price per share of Parent Common Stock on its
       principle exchange over the twenty (20) trading days immediately prior to
       the date of the issuance of the Preferred Stock and, in the case in which
       the Initial Closing Date was on or prior to the twentieth (20th) trading
       day after the IPO, the Applicable Percentage of the average of the daily
       volume-weighted average price per share of Parent Common Stock on its
       principle exchange over the first twenty (20) trading days after the IPO;
       PROVIDED, that, in either case, such Preference Shares Option Price shall
       be adjusted as may be required to reflect any stock split or
       consolidation or similar event with respect to the Parent Common Stock;

       "PRE-ORGANIC CHANGE CONVERSION SHARES" shall mean the shares of Parent
       Preferred or Common Stock that Investor would have received immediately
       prior to the Organic Change upon the exercise at that time of Investor's
       conversion rights with respect to the Preference Shares and the Notes,
       assuming, for the purpose of determining the number of such Pre-Organic
       Change Conversion Shares that all of Investor's conversion rights with
       respect to both the Preference Shares and the Notes are exercisable at
       such time;

       "PREPAYMENT AMOUNT" shall have the meaning set forth in Section 3.2;

       "PREPAYMENT NOTICE" shall have the meaning set forth in Section 3.2;

       "SEC" means the United States Securities and Exchange Commission;

       "SECURITIES ACT" means the United States Securities Act of 1933, as
       amended;

       "SHARES" shall have the meaning set forth in the SSA; "STOCK RESTRICTIONS
       AND REGISTRATION RIGHTS AGREEMENT" shall mean the Stock Restrictions and
       Registration Rights Agreement dated of even date herewith between the
       Investor and the Parent;

       "SWAP UP CLOSING" means the closing of the allotment of shares in the
       Parent to the Investor pursuant to the exercise of the Investor Swap Up
       Put Option, the Investor Note Prepayment Put Option, the Investor Note
       Repayment Put Option, the Investor Preference Share Default Option, the
       Investor Notes Default Option, the Parent Swap Up Call Option or the
       Parent Note Conversion Call Option; and

                                        6
<Page>

       "SWAP UP OUTSTANDING PRINCIPAL BALANCE" means, with respect to any Note,
       the Outstanding Principal Balance of such Note after deducting such
       portion of such Outstanding Principal Balance that the Investor, in its
       sole discretion, has validly elected, pursuant to the Note Conditions and
       Section 3.1.2, to be pre-paid in cash.

1.2    OTHER DEFINED TERMS.

1.2.1  Certain other words and phrases are defined or described elsewhere in
       this Agreement.

1.2.2  Capitalized words and phrases used in this Agreement but not defined in
       this Agreement shall have the meanings given to such words and phrases in
       the SSA.

1.2.3  Wherever used in this Agreement (i) the words "INCLUDE" or "INCLUDING"
       shall be construed as incorporating, also, "BUT NOT LIMITED TO" or
       "WITHOUT LIMITATION", (ii) the word "DAY" means a calendar day unless
       otherwise specified, (iii) the word "LAW" (or "LAWS") means any federal
       or state statute, ordinance, resolution, regulation, code, rule, order,
       decree, judgment, writ, injunction, mandate or other legally binding
       requirements of a government entity, (iv) the word "NOTICE" shall mean
       notice in writing (whether or not specifically stated) and shall include
       notices, consents, approvals and any other written communication
       contemplated under this Agreement, (v) the word "OR" shall mean either or
       both, (vi) the words "BUSINESS DAY" shall mean any day other than
       Saturday, Sunday or a day on which commercial banks located in either New
       York or Singapore are required or authorized by law to close, (vii) the
       words "PRINCIPAL EXCHANGE" shall mean the United States national
       securities exchange or automated quotation system on which shares of
       Parent Common Stock are principally traded following an IPO and (viii)
       the words "TRADING DAY" shall mean any day on which the principal
       exchange is open for business.

1.2.4  Unless the context otherwise requires, words in the singular number
       include the plural and vice versa.

2.     SWAP-UP PUT AND CALL OPTIONS

2.1    SHARE PURCHASE. Subject to the limitations set forth in Section 6.3, the
       Parent hereby irrevocably grants to the Investor the option (the
       "INVESTOR SWAP UP PUT OPTION") to require the Parent to purchase all or
       part of the Investor's Preference Shares on the terms set forth in this
       Section 2.1. The Investor Swap Up Put Option may be exercised by the
       Investor from time to time at any time after the Initial Conversion Date
       as follows:

       2.1.1  NO IPO. In the event that the Parent has not completed an IPO
              prior to the Initial Conversion Date, the Investor shall have the
              option to require the Parent to acquire, as the Investor may elect
              and as soon as reasonably practicable after such election, all or
              part of the Investor's Preference Shares by exchanging such
              Preference Shares for a number of shares of Parent Preferred Stock
              determined by dividing the aggregate amount paid by the Investor
              for such Preference Shares by the Parent Preferred Stock Price Per
              Share.

       2.1.2  IPO. At any time after the Parent has completed an IPO, the
              Investor shall have the option to require the Parent to acquire,
              as the Investor may elect and as soon as

                                        7
<Page>

              reasonably practicable after such election, all or part of the
              Investor's Preference Shares by exchanging such Preference Shares
              for a number of shares of Parent Common Stock equal to the result
              obtained by dividing the aggregate amount paid for such Preference
              Shares by the Preference Shares Option Price.

2.2    MANDATORY SHARE SWAP UP. Subject to the limitations set forth in Section
       6.3, the Investor hereby irrevocably grants to the Parent the option (the
       "PARENT SWAP UP CALL OPTION"), exercisable on the first trading day
       immediately after any Mandatory Shares Swap Up Period, to require the
       Investor to sell to the Parent all (but not less than all) of the
       Investor's then-outstanding Preference Shares in exchange for a number of
       shares of Parent Common Stock equal to (i) the aggregate price paid for
       such Preference Shares divided by (ii) the Preference Shares Option
       Price, provided, however, that Parent may not exercise the Parent Swap Up
       Call Option at any time when it is in possession of material undisclosed
       non-public information, except Parent may exercise the Parent Swap Up
       Call Option in connection with such disclosure. In the event that Section
       6.3 limits the number of Preference Shares to be sold under this Section
       2.2, the Investor shall sell to the Parent all such shares permitted to
       be sold consistent with Section 6.3.

3.     PAYMENT OF NOTES

3.1    REPAYMENT.

       3.1.1  The Parties acknowledge that under the Note Conditions, unless the
              Notes are prepaid pursuant to Section 3.2 of this Agreement and
              Condition 7.3 of the Note Conditions, the Investor is entitled to
              receive from the Company on the Maturity Date, the Outstanding
              Principal Balance of each Note on the Maturity Date in cash,
              together with Capitalized Interest for each such Note.

       3.1.2  Subject to the limitations set forth in Section 6.3, the Parent
              hereby irrevocably grants to the Investor, the option (the
              "INVESTOR NOTE REPAYMENT PUT OPTION"), exercisable in the
              Investor's sole discretion, to require the Parent to repay any
              portion of any such Outstanding Principal Balance that the
              Investor does not elect to have the Company repay in cash by
              issuing to the Investor stock of the Parent as follows:

              (A)    if the Parent has not completed an IPO on or prior to the
                     Maturity Date, by the issuance to the Investor of the
                     number of shares of Parent Preferred Stock equal to (i) the
                     aggregate Swap Up Outstanding Principal Balance of such
                     Notes divided by (ii) the applicable Parent Preferred Stock
                     Price Per Share; or

              (B)    if the Parent has completed an IPO on or prior to the
                     Maturity Date, by issuance to the Investor of a number of
                     shares of Parent Common Stock obtained by dividing the
                     aggregate Swap Up Outstanding Principal Balance of such
                     Notes by the Notes Option Price;

       3.1.3  NOTICE OF REPAYMENT. Six months prior to the Maturity Date, the
              Investor shall communicate to the Company its projected intent
              regarding its elected method of

                                        8
<Page>

              repayment with respect to the Notes, such expression to be a
              non-binding, good faith estimate of the repayment method. The
              Parties shall then maintain communications during the following
              120 days, during which the Investor agrees to notify the Company
              of any material changes to its projected intent. No later than 60
              days prior to the Maturity Date, the Investor shall provide
              written notice to the Company and the Parent of its elected method
              of repayment with respect to each Note. If the Investor elects to
              convert any portion of any Outstanding Principal Balance on any
              Note into Parent Common Stock pursuant to the terms of this
              Agreement, then the Parent shall issue such Parent Common Stock on
              the next business day following the Maturity Date in the name of
              Investor or its designee in exchange for cancellation and delivery
              of the applicable Note.

3.2    PREPAYMENT. The Parties acknowledge that pursuant to the Note Conditions,
       the Company may prepay (and shall prepay at the direction of Parent) part
       or all of the Notes by delivering to the Investor irrevocable written
       notice (the "PREPAYMENT NOTICE") of the Company's intention to prepay any
       Note, which Prepayment Notice shall be delivered by the Company no later
       than 40 days, and no earlier than 180 days, prior to the date of such
       prepayment and which Prepayment Notice shall specify.

          -   the Note(s) to be prepaid,

          -   the portion of the Outstanding Principal Balance of such Notes to
              be prepaid (the "OUTSTANDING PRINCIPAL BALANCE TO BE PREPAID"),

          -   the resulting "PREPAYMENT AMOUNT," which shall equal, with respect
              to any Outstanding Principal Balance To Be Prepaid, the sum of (i)
              such Outstanding Principal Balance To Be Prepaid multiplied by
              1.25 and (ii) the Capitalized Interest with respect to such
              Outstanding Principal Balance To Be Prepaid); and

          -   the date on which prepayment shall take place (such date, the
              "PREPAYMENT DATE").

       The Company shall pay the Investor the Prepayment Amount in cash (or such
       other consideration as the Parties may, in their sole respective
       discretion, agree), unless the Investor elects to exercise the Investor
       Note Prepayment Put Option (as defined and provided below) in respect of
       any or all of the Outstanding Principal Balance To Be Prepaid, in which
       case the Prepayment Amount shall be determined as provided above but
       after first giving effect to the reduction in the Outstanding Principal
       Balance To Be Prepaid resulting from the Investor's exercise of such
       option.

       3.2.1  The Parent hereby irrevocably grants to the Investor, an option
              (the "INVESTOR NOTE PREPAYMENT PUT OPTION"), subject to the terms
              of Section 3.2.2 and the limitations set forth in Section 6.3 of
              this Agreement, to convert all or any portion of any Outstanding
              Principal Balance To Be Prepaid into Parent Preferred Stock or
              Parent Common Stock.

                                        9
<Page>

       3.2.2  Upon receipt of a Prepayment Notice, the Investor shall be
              entitled, on any day at least twenty (20) days before the
              Prepayment Date, to exercise the Investor Note Prepayment Put
              Option by notifying the Company of the amount of the Outstanding
              Principal Balance To Be Prepaid to be converted into Parent
              capital stock by exercise of such Option (the "PREPAYMENT SWAP UP
              AMOUNT"). On exercise of the Investor Note Prepayment Put Option:

              (A)    if the Parent has not completed an IPO on or prior to the
                     date of such Prepayment Notice, Parent shall issue to the
                     Investor the number of shares of Parent Preferred Stock
                     equal to (i) the Prepayment Swap Up Amount divided by (ii)
                     the applicable Parent Preferred Stock Price Per Share; or

              (B)    if the Parent has completed an IPO on or prior to the date
                     of such Prepayment Notice, Parent shall issue to the
                     Investor the number of shares of Parent Common Stock equal
                     to (i) the Prepayment Swap Up Amount divided by (ii) the
                     applicable Notes Option Price.

3.3    MANDATORY CONVERSION. The Investor hereby irrevocably grants to the
       Parent an option (the "PARENT NOTE CONVERSION CALL OPTION") to acquire
       (subject to the limitations set forth in Section 6.3) some or all of the
       Notes in exchange for a number of shares of Parent Common Stock equal to
       the aggregate Outstanding Principal Balance of such Notes divided by the
       applicable Notes Option Price, exercisable on the first trading day
       immediately following any Mandatory Note Swap Up Period, provided,
       however, that Parent may not exercise the Parent Note Conversion Call
       Option at any time when it is in possession of material undisclosed
       non-public information, except Parent may exercise the Parent Note
       Conversion Call Option in connection with such disclosure.

3.4    OTHER PAYMENT TERMS. All other terms and conditions governing the payment
       of the Notes shall be as set forth in the Note Conditions.

4.     DEFAULT

4.1    EVENTS OF DEFAULT. Upon an Event of Default of the Parent or the Company
       pursuant to Section 15.2.1 of the SSA, in addition to the provisions set
       out in Section 15 of the SSA, the provisions of Section 4.2 shall apply.

4.2    INVESTOR'S RIGHTS AND REMEDIES.

       4.2.1  The Parent hereby grants to the Investor the option (the "INVESTOR
              PREFERENCE SHARE DEFAULT OPTION"), which Investor Preference Share
              Default Option shall be exercisable, by delivery of written notice
              of such election to Parent on or before the 30th day after a
              Default Date, to require the Parent to purchase, at the Investor's
              election and subject to the limitations set forth in Section 6.3,
              all or part of the Preference Shares held by the Investor as at
              the relevant Default Date and to allot and issue to the Investor
              such number of shares in the issued and outstanding capital of the
              Parent as follows:

                                       10
<Page>

              (A)    in the event that the Parent has not completed an IPO prior
                     to the Default Date, by the allotment to the Investor of a
                     number of shares of Parent Preferred Stock obtained by
                     dividing the relevant portion of the Preference Shares
                     Default Amount by the Parent Preferred Stock Price Per
                     Share; or

              (B)    in the event that the Parent has completed an IPO prior to
                     the Default Date, by the allotment to the Investor of a
                     number of shares of Parent Common Stock equal to the
                     relevant amount of the Preference Shares Default Amount
                     divided by:

                     (i)    in the case in which the Initial Closing Date was at
                            least twenty-one (21) trading days after an IPO, the
                            average of the daily volume-weighted average price
                            per share of Parent Common Stock on its principal
                            exchange over the twenty (20) trading days
                            immediately prior to the Initial Closing Date (which
                            price shall be adjusted as may be required to
                            reflect any stock split or consolidation or similar
                            event with respect to the Parent Common Stock); or

                     (ii)   in the case in which the Initial Closing Date was on
                            or prior to the twentieth (20th) trading day after
                            an IPO, the average of the daily volume-weighted
                            average price per share of Parent Common Stock on
                            its principal exchange over the first twenty (20)
                            trading days after the IPO (which price shall be
                            adjusted as may be required to reflect any stock
                            split or consolidation or similar event with respect
                            to the Parent Common Stock).

       4.2.2  The Parties acknowledge that in the event of an Event of Default
              of the Parent or the Company pursuant to Section 15.2.1 of the
              SSA, then, as provided in Condition 8.1 of the Note Conditions,
              the Notes Default Amount shall, at the option of the Investor,
              become immediately due and payable in full in cash, subject to the
              next sentence. The Parties further agree that, in lieu of
              receiving payment of the Notes Default Amount wholly in cash and
              subject to the limitations set forth in Section 6.3, the Parent
              hereby grants to the Investor the option (the "INVESTOR NOTES
              DEFAULT OPTION"), exercisable in the Investor's sole discretion,
              to receive payment of any portion of the Notes Default Amount (the
              "DEFAULT SWAP UP OUTSTANDING PRINCIPAL BALANCE") in the manner set
              out as follows:

              (A)    if no IPO has occurred prior to the Default Date, by the
                     allotment to the Investor of a number of shares of Parent
                     Preferred Stock obtained by dividing the Default Swap Up
                     Outstanding Principal Balance by the Parent Preferred Stock
                     Price Per Share; or

              (B)    if an IPO has occurred prior to the Default Date, by the
                     allotment to the Investors of a number of shares of Parent
                     Common Stock obtained by dividing the Default Swap Up
                     Outstanding Principal Balance by:

                                       11
<Page>

                     (i)    in the case of any Note issued at least twenty-one
                            (21) trading days after any IPO, the average of the
                            daily volume-weighted average price per share of
                            Parent Common Stock on its principal exchange over
                            the twenty (20) trading days immediately prior to
                            the date of the issuance of such Note (which price
                            shall be adjusted as may be required to reflect any
                            stock split or consolidation or similar event with
                            respect to the Parent Common Stock); or

                     (ii)   in the case of any Note not issued at least
                            twenty-one (21) trading days after any IPO, the
                            average of the daily volume-weighted average price
                            per share of Parent Common Stock on its principal
                            exchange over the first twenty (20) trading days
                            after the first IPO (which price shall be adjusted
                            as may be required to reflect any stock split or
                            consolidation or similar event with respect to the
                            Parent Common Stock).

5.     SWAP UP CLOSING

       5.1    Any Swap Up Closing pursuant to the Investor Swap Up Put Option,
the Parent Swap Up Call Option, the Investor Note Prepayment Put Option, the
Parent Note Conversion Call Option, the Investor Preference Share Default Option
or the Investor Notes Default Option (as the case may be) shall take place at
the offices of the Company on such date as the Parent and the Investor shall
agree (which date shall in all cases be no more than ten days after the date of
issue of the relevant notice of exercise) or at such other place and at such
other time as the Parent and the Investor may agree in writing.

       5.2    OBLIGATIONS OF THE PARENT

              At each Swap Up Closing, the Investor shall acquire from the
       Parent, and the Parent shall issue to the Investor, the relevant class
       and number of shares in the Parent and in connection therewith, deliver
       the following to the Investor: share certificates, dated the date of such
       Swap Up Closing (which share certificates shall comply in all material
       respects with the applicable law of the jurisdiction in which the Parent
       is incorporated and the applicable requirements of the Parent's
       certificate of incorporation and bylaws, each as in effect as of the date
       of such Swap Up Closing), in such denominations and in such name or names
       as the Investor may designate by written notice to the Company at least
       two days prior to the date of such Swap Up Closing, representing such
       shares in the Parent.

       5.3    OBLIGATIONS OF THE INVESTOR

              At each Swap Up Closing, the Investor shall deliver to Parent a
       copy of the duly executed share transfer form and original share
       certificate(s) with respect to the relevant number of Preference Shares
       in the capital of the Company, specifying the Parent as the transferee of
       the relevant Preference Shares.

       5.4    BREACH

                                       12
<Page>

              If, on the date of the relevant Swap Up Closing, the Parent fails
       to satisfy its obligations under Section 5.2 or the Investor fails to
       satisfy its obligations under Section 5.3, then the non-defaulting party
       shall be entitled (in addition to and without prejudice to all other
       rights and remedies available to it) to:

              5.4.1  require specific performance by the defaulting party of
       such party's obligations pursuant to the terms of this Agreement;

              5.4.2  effect such Swap Up Closing so far as is practicable
       (having regard to the defaults which have occurred); or

              5.4.3  fix a new date for such Swap Up Closing (which shall in no
       case be more than five days after the date first scheduled for such Swap
       Up Closing), in which case the provisions of this Article 5 shall also
       apply to any such new date or dates fixed for such Swap Up Closing.

6.     STOCK RESTRICTIONS AND REGISTRATION RIGHTS

6.1    WARRANTIES. The Parent shall make the representations, warranties and
       undertakings contained in Sections 6.2, 6.12 and 6.13 of the SSA on and
       as of the date of any Swap Up Closing.

6.2    STOCK RESTRICTION AND REGISTRATION RIGHTS AGREEMENT. Any Parent Preferred
       Stock or Parent Common Stock issued to the Investor by the Parent
       pursuant to this Agreement shall be subject to the provisions of the
       Stock Restriction and Registration Rights Agreement.

6.3    PARENT STOCK LIMITATIONS. In each case in which Parent Preferred Stock or
       Parent Common Stock is to be issued to the Investor pursuant to this
       Agreement, the Parent will not issue, and the Investor will not be
       obligated to accept, any shares of Parent Preferred Stock or Parent
       Common Stock to the extent that, immediately following such issuance, the
       Investor would be, on an as-converted basis, the beneficial owner of more
       than nineteen and nine-tenths percent (19.9%) of the issued and
       outstanding shares of Parent Common Stock.

6.4    SALE OF PARENT STOCK. Save as expressly set out in this Section 6.4, in
       no case shall the Investor sell more than 25% of the shares of Parent
       Common Stock then acquired by the Investor pursuant to the terms of this
       Agreement in any single calendar quarter; PROVIDED THAT, after the first
       anniversary of the date on which any such share was acquired, such
       restriction shall not apply to such share (which shall also mean that
       such share shall not be included in any computation of the number of
       shares of Parent Common Stock sold by the Investor), and such share shall
       cease to be included in calculating the number of shares of Parent Common
       Stock then acquired by the Investor pursuant to the terms of this
       Agreement.

7.     REPURCHASE

       7.1    Subject to Section 7.2, the Investor hereby irrevocably grants to
the Parent the option (the "PARENT SHARE REPURCHASE OPTION"), exercisable at any
time from the date of this

                                       13
<Page>

Agreement, to purchase for cash all (but not less than all) of the Investor's
then-outstanding Shares (the "REPURCHASE") at a price (the "REPURCHASE
CONSIDERATION") equal to 125% of the aggregate Purchase Price Per Share of such
Shares, plus the amount of all dividends accrued but unpaid as of the date of
the Repurchase, by providing written notice (the "REPURCHASE NOTICE") to the
Investor. The Repurchase Notice, which shall be irrevocable, shall specify the
Repurchase Consideration and the date on which the Repurchase shall take place,
and shall be delivered by the Parent to the Investor at least thirty (30) days
and not more than one hundred twenty (120) days before such date.

       7.2    Upon receipt of a Repurchase Notice, the Investor shall be
entitled, during the thirty (30) business days after the date of the Investor's
receipt of the Repurchase Notice, to exercise the Investor Swap Up Put Option,
notwithstanding any other restriction on the exercisability of such option. If
the Investor so elects to exercise the Investor Swap Up Put Option, then the
Parties shall not proceed with the Repurchase.

8.     PREFERENCE SHARES COMPLETION

       8.1    The Preference Shares Closing shall take place at the offices of
the Company within ten days from date of issue of the Repurchase Notice (or at
such other place as the Parties may agree in writing).

       8.2    OBLIGATIONS OF THE PARENT

              At the Preference Shares Closing, the Parent shall pay the
       Repurchase Consideration by way of a banker's draft or cashier's order
       drawn on a licensed bank in Singapore made out in favour of the Investor
       or as it may direct or by bank transfer to such bank account in Singapore
       as the Investor shall notify the Parent in writing not later than two
       business days prior to the date of the Preference Shares Closing:

       8.3    OBLIGATIONS OF THE INVESTOR

              At the Preference Shares Closing, the Investor shall deliver to
       Parent a copy of the duly executed share transfer form and original share
       certificate(s) with respect to the relevant number of Shares in the
       capital of the Company, specifying the Parent as the transferee of the
       relevant Shares.

       8.4    BREACH

              If on the date scheduled for the Preference Shares Closing, the
       Investor fails to satisfy its obligation under Section 8.3 or the Parent
       fails to satisfy its obligations under Section 8.2, then the
       non-defaulting party shall be entitled (in addition to and without
       prejudice to all other rights and remedies available to it) to:

              8.4.1  require specific performance by the defaulting party of
       such party's obligations pursuant to the terms of this Agreement;

              8.4.2  effect the Preference Shares Closing so far as practicable
       (having regard to the defaults which have occurred); or

                                       14
<Page>

              8.4.3  fix a new date for the Preference Shares Closing (not being
       more than five days after the original date scheduled for the Preference
       Shares Closing), in which case the provisions of this Section 8 shall
       also apply to any such new date or dates fixed for the Preference Shares
       Closing.

9.     REORGANIZATION, RECLASSIFICATION, CONSOLIDATION, MERGER OR SALE

       9.1    Any recapitalization, reorganization, reclassification,
consolidation, merger, sale of all or substantially all of the Parent's assets
to another Person or other transaction that is effected in such a way that
holders of Parent Common Stock or Parent Preferred Stock ("PARENT STOCK") are
entitled to receive (either directly or upon subsequent liquidation) stock,
securities, cash or other assets with respect to or in exchange for Parent Stock
or any successor security is referred to herein as an "ORGANIC CHANGE."

       9.2    Prior to the consummation of any Organic Change, the Parent shall
take all such steps as are necessary to insure that the Investor shall, on and
from the consummation of such Organic Change, have the right to acquire and
receive in lieu of or in addition to (as the terms of the Organic Change may
provide) the Pre-Organic Change Conversion Shares such shares of stock,
securities, cash or other assets as would have been issued or payable to the
Investor for, with respect to or in exchange for such Pre-Organic Change
Conversion Shares in connection with such Organic Change.

       9.3    Nothing in this Section 9 shall change the terms and conditions of
or accelerate any right the Investor may have to convert any Preference Shares
or any Notes under this Agreement, provided however, that:

              9.3.1  to the extent that as a result of the operation of the
       foregoing provisions the Investor becomes eligible to receive cash on the
       eventual conversion of any Note, the Investor's right to receive such
       cash amount shall be accelerated to a right to receive such cash amount
       at the same time and on the same terms and conditions as would have
       applied had such Note been converted into Pre-Organic Change Conversion
       Shares immediately prior to the Organic Transaction;

              9.3.2  if the Investor elects to receive such cash with respect to
       any Note, a proportional reduction shall be made in the Outstanding
       Principal Balance of the Note payable on the Maturity Date or an Event of
       Default (proportional to the proportion which the cash amount payable per
       Pre-Organic Change Conversion Share in the Organic Transaction bears to
       the total consideration payable per Pre-Organic Change Conversion Share
       in the Organic Transaction); and

              9.3.3  if an Organic Transaction is consummated, then the Initial
       Conversion Date for the purposes of Section 2.1 of this Agreement shall
       be deemed to be the business day immediately preceding the day on which
       such consummation occurs.

                                       15
<Page>

10.    MISCELLANEOUS PROVISIONS

10.1   GOVERNING LAW. This Agreement shall be governed in all respects by and
       construed in accordance with the laws of the State of New York in the
       United States without giving effect to any choice of law or conflict
       provision or rule (whether of the State of New York or any other
       jurisdiction) that would cause the laws of any jurisdiction other than
       the State of New York to be applied. Each of the Parties to this
       Agreement (i) consents to submit itself to the personal jurisdiction of
       the federal courts of the United States located in the City of New York,
       Borough of Manhattan, State of New York or any court of the State of New
       York located in such district in the event any dispute arises out of this
       Agreement or any of the transactions contemplated by this Agreement, (ii)
       agrees that it will not attempt to deny or defeat such personal
       jurisdiction or venue by motion or other request for leave from any such
       court and (iii) agrees that it will not bring any action relating to this
       Agreement or any of the transactions contemplated by this Agreement in
       any court other than such courts sitting in the State of New York. The
       remedies provided for herein are cumulative and are not exclusive of any
       remedies that may be available to any part hereto at law or in equity or
       otherwise.

10.2   ASSIGNMENT; THIRD-PARTY BENEFICIARIES. This Agreement shall not be
       assigned by any of the parties hereto without the prior written consent
       of the other parties hereto. Nothing in this Agreement, expressed or
       implied, is intended to or shall confer on any person other than the
       parties hereto or their respective successors and permitted assigns, any
       rights, remedies, obligations or liabilities under or by reason of this
       Agreement.

10.3   SURVIVAL. The representations, warranties, covenants and agreements made
       herein shall survive any investigation made by any party hereto and the
       closing of the transactions contemplated hereby (including the relevant
       Swap Up Closings).

10.4   ENTIRE AGREEMENT. This Agreement and the SSA constitute the entire
       understanding and agreement between the Parties with regard to the
       subject matter hereof and thereof and supersede all prior and
       contemporaneous agreements, whether written or oral.

10.5   NOTICES. All notices, requests, consents and other communications under
       this Agreement shall be in writing and shall be deemed effectively given:
       (a) upon personal delivery; (b) when sent by confirmed facsimile if sent
       during normal business hours of the recipient, if not, then on the next
       business day; (c) five days after having been sent by registered or
       certified mail, return receipt requested, postage prepaid; or (d) one day
       after deposit with a nationally recognized overnight courier, special
       next day delivery, with verification of receipt, at the address(es) set
       forth or specified below, or at such other address or addresses as may
       have been furnished in writing by the Company to the Investor, or by the
       Investor to the Company, as applicable:

                                       16
<Page>

If to the Company, at:
CombinatoRx, Incorporated
650 Albany Street
Boston, Massachusetts 02118
Attn: Chief Financial Officer

With a copy (which shall
not constitute notice) to:
Ropes & Gray LLP
One International Place
Boston, Massachusetts 02110
Attn: Geoffrey Davis

If to the Investor, at:
BioMedical Sciences Investment Fund Pte Ltd
20 Biopolis Way
#09-01 Centros
Singapore 138668
Attn: Ms Chu Swee Yeok
      Chief Executive Officer

With a copy (which shall
not constitute notice) to:
Skadden, Arps, Slate, Meagher & Flom LLP
30/F Tower Two
Lippo Centre, 89 Queensway
Central, Hong Kong
Attn: Alec Tracy

10.6   AMENDMENTS. Any term of this Agreement may be amended only with the
       written consent of the Company, the Parent and the Investor.

10.7   DELAYS OR OMISSIONS; WAIVERS. No delay or omission to exercise any right,
       power or remedy accruing to the Company, the Parent or to the Investor,
       upon any breach or default of any party hereto under this Agreement,
       shall impair any such right, power or remedy of the Company, the Parent
       or the Investor, nor shall it be construed to be a waiver of any such
       breach or default, or an acquiescence therein, or of any similar breach
       of default thereafter occurring; nor shall any waiver of any other breach
       or default theretofore or thereafter occurring. No waiver of any of the
       provisions contained in this Agreement shall be valid unless made in
       writing and executed by the Company (if it is the waiving party), the
       Parent (if it is the waiving party) or by the Investor (if it is the
       waiving party).

10.8   TITLES AND SUBTITLES. The titles of the paragraphs and subparagraphs of
       this Agreement are for convenience of reference only and are not to be
       considered in construing this Agreement.

                                       17
<Page>

10.9   COUNTERPARTS. This Agreement may be executed in any number of
       counterparts (including by facsimile), each of which shall be an
       original, but all of which together shall constitute one instrument.

10.10  SEVERABILITY. Should any provision of this Agreement be determined to be
       illegal or unenforceable, such determination shall not affect the
       remaining provisions of this Agreement.

10.11  EXPENSES. Each party shall pay its own costs and expenses in connection
       with this Agreement and the closing of the transactions contemplated
       hereby save that the legal fees and disbursements incurred by the
       Investor in connection with this Agreement shall be borne by the Company.

10.12  CONSTRUCTION. This Agreement is the result of negotiations among, and has
       been reviewed by, the Company and the Investor and their respective
       counsel. Accordingly, this Agreement shall be deemed to be the product of
       all Parties hereto, and no ambiguity shall be construed in favor of or
       against any Party.

10.13  MARKET STAND-OFF AGREEMENT. Investor agrees that, during the period
       specified by the Parent and an underwriter of a public offering of Parent
       Common Stock or other equity securities of the Parent following the
       effective date of a registration statement of the Parent filed under the
       Securities Act (the "Time Period"), it shall not, to the extent requested
       by the Parent and such underwriter, directly or indirectly sell, offer to
       sell, contract to sell, grant any option to purchase or otherwise
       transfer or dispose of (other than to donees who agree to be similarly
       bound) any securities of the Parent held by it at any time during such
       period except Parent Common Stock included in such registration;
       PROVIDED, HOWEVER, that:

              (A)    such restriction shall be applicable only to the first such
                     registration statement of the Parent filed with the SEC
                     which covers Common Stock (or other equity securities) to
                     be sold on its behalf to the public in an underwritten
                     offering;

              (B)    the Time Period shall not exceed 180 days;

              (C)    such restriction shall be effective against Investors only
                     if all officers and directors of the Parent and
                     substantially all other holders of at least 3% of the
                     shares of Common Stock outstanding immediately prior to
                     such registration enter into similar agreements.

       In order to enforce the foregoing covenant, the Parent may impose stop
       transfer instructions with respect to any Parent Common Stock issuable to
       Investor on conversion of any Note or Preference Share until the end of
       the Time Period.

                            [SIGNATURE PAGES FOLLOW]

                                       18
<Page>

IN WITNESS WHEREOF, the Parties have executed this Agreement to be effective as
of the date first above written.

THE COMPANY:                                  THE INVESTOR:

THE PARENT:

                                       19

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