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                                                                     Exhibit 4.5

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED OR ANY STATE SECURITIES LAWS. NO SALE OR DISPOSITION MAY BE EFFECTED
WITHOUT (i) EFFECTIVE REGISTRATION STATEMENTS RELATED THERETO, (ii) AN OPINION
OF COUNSEL OR OTHER EVIDENCE, REASONABLY SATISFACTORY TO THE COMPANY, THAT SUCH
REGISTRATIONS ARE NOT REQUIRED, (iii) RECEIPT OF NO-ACTION LETTERS FROM THE
APPROPRIATE GOVERNMENTAL AUTHORITIES, OR (iv) OTHERWISE COMPLYING WITH THE
PROVISIONS OF SECTION 7 OF THIS WARRANT.

                               ACTIVBIOTICS, INC.

                        WARRANT TO PURCHASE        SHARES
                          OF SERIES C-2 PREFERRED STOCK

     THIS CERTIFIES THAT, for value received,
      and its assignees is entitled to subscribe for and purchase        shares
of the fully paid and nonassessable Series Preferred Stock (as adjusted pursuant
to Section 4 hereof, the "Shares") of ACTIVBIOTICS, INC., a Delaware corporation
(the "Company"), at the price of $4.517 per share (such price and such other
price as shall result, from time to time, from the adjustments specified in
Section 4 hereof is herein referred to as the "Warrant Price"), subject to the
provisions and upon the terms and conditions hereinafter set forth. As used
herein, (a) the term "Series Preferred" shall mean the Company's presently
authorized Series C-2 Preferred Stock, and any stock into or for which such
Series C-2 Preferred Stock may hereafter be converted or exchanged, and after
the automatic conversion of the Series C-2 Preferred Stock to Common Stock shall
mean the Company's Common Stock, (b) the term "Date of Grant" shall mean June
16, 2006, and (c) the term "Other Warrants" shall mean any other warrants issued
by the Company in connection with the transaction with respect to which this
Warrant was issued, and any warrant issued upon transfer or partial exercise of
or in lieu of this Warrant. The term "Warrant" as used herein shall be deemed to
include Other Warrants unless the context clearly requires otherwise.

     1. Term. The purchase right represented by this Warrant is exercisable, in
whole or in part, at any time and from time to time from the Date of Grant
through the later of (i) ten (10) years after the Date of Grant or (ii) five (5)
years after the closing of the Company's initial public offering of its Common
Stock ("IPO") effected pursuant to a Registration Statement on Form S-l (or its
successor) filed under the Securities Act of 1933, as amended (the "Act").

     2. Method of Exercise; Payment; Issuance of New Warrant. Subject to Section
1 hereof, the purchase right represented by this Warrant may be exercised by the
holder hereof, in whole or in part and from time to time, at the election of the
holder hereof, by (a) the surrender of this Warrant (with the notice of exercise
substantially in the form attached hereto as Exhibit A-l duly completed and
executed) at the principal office of the Company and by the payment to the
Company, by certified or bank check, or by wire transfer to an account
designated by the Company (a "Wire Transfer") of an amount equal to the then
applicable Warrant Price multiplied by the number of Shares then being
purchased; (b) if in connection with a registered public offering of the
Company's securities, the surrender of this Warrant (with the notice of exercise
form attached hereto as

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Exhibit A-2 duly completed and executed) at the principal office of the Company
together with notice of arrangements reasonably satisfactory to the Company for
payment to the Company either by certified or bank check or by Wire Transfer
from the proceeds of the sale of shares to be sold by the holder in such public
offering of an amount equal to the then applicable Warrant Price per share
multiplied by the number of Shares then being purchased; or (c) exercise of the
"net issuance" right provided for in Section 10.2 hereof. The person or persons
in whose name(s) any certificate(s) representing shares of Series Preferred
shall be issuable upon exercise of this Warrant shall be deemed to have become
the holder(s) of record of, and shall be treated for all purposes as the record
holder(s) of, the shares represented thereby (and such shares shall be deemed to
have been issued) immediately prior to the close of business on the date or
dates upon which this Warrant is exercised. In the event of any exercise of the
rights represented by this Warrant, certificates for the shares of stock so
purchased shall be delivered to the holder hereof as soon as possible and in any
event within thirty (30) days after such exercise and, unless this Warrant has
been fully exercised or expired, a new Warrant representing the portion of the
Shares, if any, with respect to which this Warrant shall not then have been
exercised shall also be issued to the holder hereof as soon as possible and in
any event within such thirty-day period; provided, however, at such time as the
Company is subject to the reporting requirements of the Securities Exchange Act
of 1934, as amended, if requested by the holder of this Warrant, the Company
shall cause its transfer agent to deliver the certificate representing Shares
issued upon exercise of this Warrant to a broker or other person (as directed by
the holder exercising this Warrant) within the time period required to settle
any trade made by the holder after exercise of this Warrant.

     3. Stock Fully Paid; Reservation of Shares. All Shares that may be issued
upon the exercise of the rights represented by this Warrant will, upon issuance
pursuant to the terms and conditions herein, be fully paid and nonassessable,
and free from all preemptive rights and taxes, liens and charges with respect to
the issue thereof. During the period within which the rights represented by this
Warrant may be exercised, the Company will at all times have authorized, and
reserved for the purpose of the issue upon exercise of the purchase rights
evidenced by this Warrant, a sufficient number of shares of its Series Preferred
to provide for the exercise of the rights represented by this Warrant and a
sufficient number of shares of its Common Stock to provide for the conversion of
the Series Preferred into Common Stock.

     4. Adjustment of Warrant Price and Number of Shares. The number and kind of
securities purchasable upon the exercise of this Warrant and the Warrant Price
shall be subject to adjustment from time to time upon the occurrence of certain
events, as follows:

          (a) Reclassification or Merger. In case of any reclassification or
change of securities of the class issuable upon exercise of this Warrant (other
than a change in par value, or from par value to no par value, or from no par
value to par value, or as a result of a subdivision or combination), or in case
of any merger of the Company with or into another corporation (other than a
merger with another corporation in which the Company is the acquiring and the
surviving corporation and which does not result in any reclassification or
change of outstanding securities issuable upon exercise of this Warrant), or in
case of any sale of all or substantially all of the assets of the Company, the
Company, or such successor or purchasing corporation, as the case may be, shall
duly execute and deliver to the holder of this Warrant a new Warrant (in form
and substance

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satisfactory to the holder of this Warrant), so that the holder of this Warrant
shall have the right to receive upon exercise of this Warrant, at a total
purchase price not to exceed that payable upon the exercise of the unexercised
portion of this Warrant, and in lieu of the shares of Series Preferred
theretofore issuable upon exercise of this Warrant, the kind and amount of
shares of stock, other securities, money and property receivable upon such
reclassification, change, merger or sale by a holder of the number of shares of
Series Preferred then purchasable under this Warrant. Any new Warrant shall
provide for adjustments that shall be as nearly equivalent as may be practicable
to the adjustments provided for in this Section 4. The provisions of this
Section 4(a) shall similarly apply to successive reclassifications, changes,
mergers and sales.

          (b) Subdivision or Combination of Shares. If the Company at any time
while this Warrant remains outstanding and unexpired shall subdivide or combine
its outstanding shares of Series Preferred, the Warrant Price shall be
proportionately decreased and the number of Shares issuable hereunder shall be
proportionately increased in the case of a subdivision and the Warrant Price
shall be proportionately increased and the number of Shares issuable hereunder
shall be proportionately decreased in the case of a combination.

          (c) Stock Dividends and Other Distributions. If the Company at any
time while this Warrant is outstanding and unexpired shall (i) pay a dividend
with respect to Series Preferred payable in Series Preferred, then the Warrant
Price shall be adjusted, from and after the date of determination of
shareholders entitled to receive such dividend or distribution, to that price
determined by multiplying the Warrant Price in effect immediately prior to such
date of determination by a fraction (A) the numerator of which shall be the
total number of shares of Series Preferred outstanding immediately prior to such
dividend or distribution, and (B) the denominator of which shall be the total
number of shares of Series Preferred outstanding immediately after such dividend
or distribution; or (ii) make any other distribution with respect to Series
Preferred (except any distribution specifically provided for in Sections 4(a)
and 4(b)), then, in each such case, provision shall be made by the Company such
that the holder of this Warrant shall receive upon exercise of this Warrant a
proportionate share of any such dividend or distribution as though it were the
holder of the Series Preferred (or Common Stock issuable upon conversion
thereof) as of the record date fixed for the determination of the shareholders
of the Company entitled to receive such dividend or distribution.

          (d) Adjustment of Number of Shares. Upon each adjustment in the
Warrant Price, the number of Shares of Series Preferred purchasable hereunder
shall be adjusted, to the nearest whole share, to the product obtained by
multiplying the number of Shares purchasable immediately prior to such
adjustment in the Warrant Price by a fraction, the numerator of which shall be
the Warrant Price immediately prior to such adjustment and the denominator of
which shall be the Warrant Price immediately thereafter.

          (e) Antidilution Rights. The other antidilution rights applicable to
the Shares of Series Preferred purchasable hereunder are set forth in the
Company's Certificate of Incorporation, as amended through the Date of Grant
(the "Charter"). Such antidilution rights shall not be restated, amended,
modified or waived in any manner that is adverse to the holder hereof and does
not similarly affect the holders of the Series Preferred without such holder's
prior written consent. The

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Company shall promptly provide the holder hereof with any restatement,
amendment, modification or waiver of the Charter promptly after the same has
been made.

     5. Notice of Adjustments. Whenever the Warrant Price or the number of
Shares purchasable hereunder shall be adjusted pursuant to Section 4 hereof, the
Company shall make a certificate signed by its chief financial officer setting
forth, in reasonable detail, the event requiring the adjustment, the amount of
the adjustment, the method by which such adjustment was calculated, and the
Warrant Price and the number of Shares purchasable hereunder after giving effect
to such adjustment, and shall cause copies of such certificate to be mailed
(without regard to Section 13 hereof, by first class mail, postage prepaid) to
the holder of this Warrant. In addition, whenever the conversion price or
conversion ratio of the Series Preferred shall be adjusted, the Company shall
make a certificate signed by its chief financial officer setting forth, in
reasonable detail, the event requiring the adjustment, the amount of the
adjustment, the method by which such adjustment was calculated, and the
conversion price or ratio of the Series Preferred after giving effect to such
adjustment, and shall cause copies of such certificate to be mailed (without
regard to Section 13 hereof, by first class mail, postage prepaid) to the holder
of this Warrant.

     6. Fractional Shares. No fractional shares of Series Preferred will be
issued in connection with any exercise hereunder, but in lieu of such fractional
shares the Company shall make a cash payment therefor based on the fair market
value of the Series Preferred on the date of exercise as reasonably determined
in good faith by the Company's Board of Directors.

     7. Compliance with Act; Disposition of Warrant or Shares of Series
Preferred.

          (a) Compliance with Act. The holder of this Warrant, by acceptance
hereof, agrees that this Warrant, and the shares of Series Preferred to be
issued upon exercise hereof and any Common Stock issued upon conversion thereof
are being acquired for investment and that such holder will not offer, sell or
otherwise dispose of this Warrant, or any shares of Series Preferred to be
issued upon exercise hereof or any Common Stock issued upon conversion thereof
except under circumstances which will not result in a violation of the Act or
any applicable state securities laws. Upon exercise of this Warrant, unless the
Shares being acquired are registered under the Act and any applicable state
securities laws or an exemption from such registration is available, the holder
hereof shall confirm in writing that the shares of Series Preferred so purchased
(and any shares of Common Stock issued upon conversion thereof) are being
acquired for investment and not with a view toward distribution or resale in
violation of the Act and shall confirm such other matters related thereto as may
be reasonably requested by the Company. This Warrant and all shares of Series
Preferred issued upon exercise of this Warrant and all shares of Common Stock
issued upon conversion thereof (unless registered under the Act and any
applicable state securities laws) shall be stamped or imprinted with a legend in
substantially the following form:

"THE SECURITIES EVIDENCED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES
ACT OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAWS. NO SALE OR DISPOSITION
MAY BE EFFECTED WITHOUT (i) EFFECTIVE REGISTRATION STATEMENTS RELATED THERETO,
(ii) AN OPINION OF COUNSEL OR OTHER EVIDENCE, REASONABLY SATISFACTORY TO THE
COMPANY, THAT SUCH REGISTRATIONS ARE NOT REQUIRED, (iii) RECEIPT OF NO-ACTION
LETTERS FROM

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THE APPROPRIATE GOVERNMENTAL AUTHORITIES, OR (iv) OTHERWISE COMPLYING WITH THE
PROVISIONS OF SECTION 7 OF THE WARRANT UNDER WHICH THESE SECURITIES WERE ISSUED,
DIRECTLY OR INDIRECTLY."

     Said legend shall be removed by the Company, upon the request of a holder,
at such time as the restrictions on the transfer of the applicable security
shall have terminated. In addition, in connection with the issuance of this
Warrant, the holder specifically represents to the Company by acceptance of this
Warrant as follows:

               (1) The holder is aware of the Company's business affairs and
financial condition, and has acquired information about the Company sufficient
to reach an informed and knowledgeable decision to acquire this Warrant. The
holder is acquiring this Warrant for its own account for investment purposes
only and not with a view to, or for the resale in connection with, any
"distribution" thereof in violation of the Act.

               (2) The holder understands that this Warrant has not been
registered under the Act in reliance upon a specific exemption therefrom, which
exemption depends upon, among other things, the bona fide nature of the holder's
investment intent as expressed herein.

               (3) The holder further understands that this Warrant must be held
indefinitely unless subsequently registered under the Act and qualified under
any applicable state securities laws, or unless exemptions from registration and
qualification are otherwise available. The holder is aware of the provisions of
Rule 144, promulgated under the Act.

               (4) The holder is an "accredited investor" as such term is
defined in Rule 501 of Regulation D promulgated under the Act.

          (b) Disposition of Warrant or Shares. With respect to any offer, sale
or other disposition of this Warrant or any shares of Series Preferred acquired
pursuant to the exercise of this Warrant prior to registration of such Warrant
or shares, the holder hereof agrees to give written notice to the Company prior
thereto, describing briefly the manner thereof, together with a written opinion
of such holder's counsel, or other evidence, if reasonably satisfactory to the
Company, to the effect that such offer, sale or other disposition may be
effected without registration or qualification (under the Act as then in effect
or any federal or state securities law then in effect) of this Warrant or such
shares of Series Preferred or Common Stock and indicating whether or not under
the Act certificates for this Warrant or such shares of Series Preferred to be
sold or otherwise disposed of require any restrictive legend as to applicable
restrictions on transferability in order to ensure compliance with such law.
Upon receiving such written notice and reasonably satisfactory opinion or other
evidence, the Company, as promptly as practicable but no later than fifteen (15)
days after receipt of the written notice, shall notify such holder that such
holder may sell or otherwise dispose of this Warrant or such shares of Series
Preferred or Common Stock, all in accordance with the terms of the notice
delivered to the Company. If a determination has been made pursuant to this
Section 7(b) that the opinion of counsel for the holder or other evidence is not
reasonably satisfactory to the Company, the Company shall so notify the holder
promptly with details thereof after such determination has been made.
Notwithstanding the foregoing, this Warrant or such shares of Series Preferred
or Common Stock may, as to such federal laws, be offered, sold or otherwise

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disposed of in accordance with Rule 144 or 144A under the Act, provided that the
Company shall have been furnished with such information as the Company may
reasonably request to provide a reasonable assurance that the provisions of Rule
144 or 144A have been satisfied. Each certificate representing this Warrant or
the shares of Series Preferred thus transferred (except a transfer pursuant to
Rule 144 or 144A) shall bear a legend as to the applicable restrictions on
transferability in order to ensure compliance with such laws, unless in the
aforesaid opinion of counsel for the holder, such legend is not required in
order to ensure compliance with such laws. The Company may issue stop transfer
instructions to its transfer agent in connection with such restrictions.

          (c) Applicability of Restrictions. Neither any restrictions of any
legend described in this Warrant nor the requirements of Section 7(b) above
shall apply to any transfer of, or grant of a security interest in, this Warrant
(or the Series Preferred or Common Stock obtainable upon exercise thereof) or
any part hereof (i) to a partner of the holder if the holder is a partnership or
to a member of the holder if the holder is a limited liability company, (ii) to
a partnership of which the holder is a partner or to a limited liability company
of which the holder is a member, or (iii) to any affiliate of the holder if the
holder is a corporation; provided, however, in any such transfer, if applicable,
the transferee shall on the Company's request agree in writing to be bound by
the terms of this Warrant as if an original holder hereof. Notwithstanding the
foregoing, any member of Horizon Technology Funding Company II LLC may, in a
single transaction or series of related transactions, transfer its interest in
this Warrant to a business development company (as such term is defined in
Section 2(a)(48) of the Investment Company Act of 1940, as amended) in which,
either prior to such transaction or transactions or as a result thereof, any one
or more members of Horizon Technology Funding Company II LLC has an equity
ownership interest (individually or together with other such members) of more
than 5%.

     8. Rights as Shareholders; Information. No holder of this Warrant, as such,
shall be entitled to vote or receive dividends or be deemed the holder of Series
Preferred or any other securities of the Company which may at any time be
issuable upon the exercise hereof for any purpose, nor shall anything contained
herein be construed to confer upon the holder of this Warrant, as such, any of
the rights of a shareholder of the Company or any right to vote for the election
of directors or upon any matter submitted to shareholders at any meeting
thereof, or to receive notice of meetings, or to receive dividends or
subscription rights or otherwise until this Warrant shall have been exercised
and the Shares purchasable upon the exercise hereof shall have become
deliverable, as provided herein. Notwithstanding the foregoing, the Company will
transmit to the holder of this Warrant such information, documents and reports
as are generally distributed to the holders of any class or series of the
securities of the Company concurrently with the distribution thereof to the
shareholders.

     9. Registration Rights. Simultaneously with the execution of this Warrant,
the holder of this Warrant will execute that certain Amendment No. 1 to the
Fourth Amended and Restated Stockholders' Agreement, dated as of the date
hereof, and thereby receive the same piggyback registration rights granted by
the Company to the other stockholders signatory thereto.

     10. Additional Rights.

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     10.1 Acquisition Transactions. The Company shall provide the holder of this
Warrant with at least twenty (20) days' written notice prior to closing thereof
of the terms and conditions of any of the following transactions (to the extent
the Company has notice thereof): (i) the sale, lease, exchange, conveyance or
other disposition of all or substantially all of the Company's property or
business, or (ii) its merger into or consolidation with any other corporation
(other than a wholly-owned subsidiary of the Company), or any transaction
(including a merger or other reorganization) or series of related transactions,
in which more than 50% of the voting power of the Company is disposed of
(collectively, a "Sale").

     10.2 Right to Convert Warrant into Stock: Net Issuance.

          (a) Right to Convert. In addition to and without limiting the rights
of the holder under the terms of this Warrant, the holder shall have the right
to convert this Warrant or any portion thereof (the "Conversion Right") into
shares of Series Preferred as provided in this Section 10.2 after an IPO or upon
a Sale. Upon exercise of the Conversion Right with respect to a particular
number of shares subject to this Warrant (the "Converted Warrant Shares"), the
Company shall deliver to the holder (without payment by the holder of any
exercise price or any cash or other consideration) that number of shares of
fully paid and nonassessable Series Preferred as is determined according to the
following formula:

     X=  B-A
         ---
          Y

     Where: X = the number of shares of Series Preferred that shall be issued to
                holder

            Y = the fair market value of one share of Series Preferred

            A = the aggregate Warrant Price of the specified number of Converted
                Warrant Shares immediately prior to the exercise of the
                Conversion Right (I.E., the number of Converted Warrant Shares
                MULTIPLIED BY the Warrant Price)

            B = the aggregate fair market value of the specified number of
                Converted Warrant Shares (I.E., the number of Converted Warrant
                Shares MULTIPLIED BY the fair market value of one Converted
                Warrant Share)

     No fractional shares shall be issuable upon exercise of the Conversion
Right, and, if the number of shares to be issued determined in accordance with
the foregoing formula is other than a whole number, the Company shall pay to the
holder an amount in cash equal to the fair market value of the resulting
fractional share on the Conversion Date (as hereinafter defined). For purposes
of Section 10 of this Warrant, shares issued pursuant to the Conversion Right
shall be treated as if they were issued upon the exercise of this Warrant.

          (b) Method of Exercise. The Conversion Right may be exercised by the
holder by the surrender of this Warrant at the principal office of the Company
together with a written statement (which may be in the form of Exhibit A-l or
Exhibit A-2 hereto) specifying that the holder

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thereby intends to exercise the Conversion Right and indicating the number of
shares subject to this Warrant which are being surrendered (referred to in
Section 10.2(a) hereof as the Converted Warrant Shares) in exercise of the
Conversion Right. Such conversion shall be effective upon receipt by the Company
of this Warrant together with the aforesaid written statement, or on such later
date as is specified therein (the "Conversion Date"), and, at the election of
the holder hereof, may be made contingent upon the closing of the sale of the
Company's Common Stock to the public in a public offering pursuant to a
Registration Statement under the Act (a "Public Offering"). Certificates for the
shares issuable upon exercise of the Conversion Right and, if applicable, a new
warrant evidencing the balance of the shares remaining subject to this Warrant,
shall be issued as of the Conversion Date and shall be delivered to the holder
within thirty (30) days following the Conversion Date.

          (c) Determination of Fair Market Value. For purposes of this Section
10.2, "fair market value" of a share of Series Preferred (or Common Stock if the
Series Preferred has been automatically converted into Common Stock) as of a
particular date (the "Determination Date") shall mean:

               (i) If the Conversion Right is exercised in connection with and
contingent upon a Public Offering, and if the Company's Registration Statement
relating to such Public Offering ("Registration Statement") has been declared
effective by the Securities and Exchange Commission, then the initial "Price to
Public" specified in the final prospectus with respect to such offering.

               (ii) If the Conversion Right is not exercised in connection with
and contingent upon a Public Offering, then as follows:

          (A) If traded on a securities exchange, the fair market value of the
Common Stock shall be deemed to be the average of the closing prices of the
Common Stock on such exchange over the five trading days immediately prior to
the Determination Date, and the fair market value of the Series Preferred shall
be deemed to be such fair market value of the Common Stock multiplied by the
number of shares of Common Stock into which each share of Series Preferred is
then convertible;

          (B) If traded on the Nasdaq Stock Market or other over-the-counter
system, the fair market value of the Common Stock shall be deemed to be the
average of the closing bid prices of the Common Stock over the five trading days
immediately prior to the Determination Date, and the fair market value of the
Series Preferred shall be deemed to be such fair market value of the Common
Stock multiplied by the number of shares of Common Stock into which each share
of Series Preferred is then convertible; and

          (C) If there is no public market for the Common Stock, then fair
market value shall be determined by the Board of Directors of the Company in
good faith.

In making a determination under clauses (A) or (B) above, if on the
Determination Date, five trading days had not passed since the IPO, then the
fair market value of the Common Stock shall be the average closing prices or
closing bid prices, as applicable, for the shorter period beginning on and

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including the date of the IPO and ending on the trading day prior to the
Determination Date (or if such period includes only one trading day the closing
price or closing bid price, as applicable, for such trading day). If closing
prices or closing bid prices are no longer reported by a securities exchange or
other trading system, the closing price or closing bid price shall be that which
is reported by such securities exchange or other trading system at 4:00 p.m. New
York City time on the applicable trading day.

     10.3 Exercise Prior to Expiration. To the extent this Warrant is not
previously exercised as to all of the Shares subject hereto, and if the fair
market value of one share of the Series Preferred is greater than the Warrant
Price then in effect, this Warrant shall be deemed automatically exercised
pursuant to Section 10.2 above (even if not surrendered) immediately before its
expiration. For purposes of such automatic exercise, the fair market value of
one share of the Series Preferred upon such expiration shall be determined
pursuant to Section 10.2(c). To the extent this Warrant or any portion thereof
is deemed automatically exercised pursuant to this Section 10.3, the Company
agrees to promptly notify the holder hereof of the number of Shares, if any, the
holder hereof is to receive by reason of such automatic exercise.

     11. Representations and Warranties. The Company represents and warrants to
the holder of this Warrant as follows:

          (a) This Warrant has been duly authorized and executed by the Company
and is a valid and binding obligation of the Company enforceable in accordance
with its terms, subject to laws of general application relating to bankruptcy,
insolvency and the relief of debtors and the rules of law or principles at
equity governing specific performance, injunctive relief and other equitable
remedies.

          (b) The Shares have been duly authorized and reserved for issuance by
the Company and, when issued in accordance with the terms hereof, will be
validly issued, fully paid and nonassessable and free from preemptive rights.

          (c) The rights, preferences, privileges and restrictions granted to or
imposed upon the Series Preferred and the holders thereof are as set forth in
the Charter, and on the Date of Grant, each share of the Series Preferred
represented by this Warrant is convertible into one share of Common Stock.

          (d) The shares of Common Stock issuable upon conversion of the Shares
have been duly authorized and reserved for issuance by the Company and, when
issued in accordance with the terms of the Charter will be validly issued, fully
paid and nonassessable.

          (e) The execution and delivery of this Warrant are not, and the
issuance of the Shares upon exercise of this Warrant in accordance with the
terms hereof will not be, inconsistent with the Company's Charter or by-laws, do
not and will not contravene any law, governmental rule or regulation, judgment
or order applicable to the Company, and do not and will not conflict with or
contravene any provision of, or constitute a default under, any indenture,
mortgage, contract or other instrument of which the Company is a party or by
which it is bound or require the consent or approval of, the giving of notice
to, the registration or filing with or the taking of any action in

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respect of or by, any Federal, state or local government authority or agency or
other person, except for the filing of notices pursuant to federal and state
securities laws, which filings will be effected by the time required thereby.

          (f) There are no actions, suits, audits, investigations or proceedings
pending or, to the knowledge of the Company, threatened against the Company in
any court or before any governmental commission, board or authority which, if
adversely determined, will have a material adverse effect on the ability of the
Company to perform its obligations under this Warrant.

          (g) The number of shares of Common Stock of the Company outstanding on
the date hereof, on a fully diluted basis (assuming the conversion of all
outstanding convertible securities and the exercise of all outstanding options
and warrants), does not exceed 20,500,000 shares.

     12. Modification and Waiver. This Warrant and any provision hereof may be
changed, waived, discharged or terminated only by an instrument in writing
signed by the party against which enforcement of the same is sought.

     13. Notices. Any notice, request, communication or other document required
or permitted to be given or delivered to the holder hereof or the Company shall
be delivered, or shall be sent by certified or registered mail, postage prepaid,
to each such holder at its address as shown on the books of the Company or to
the Company at the address indicated therefor on the signature page of this
Warrant.

     14. Binding Effect on Successors. This Warrant shall be binding upon any
corporation succeeding the Company by merger, consolidation or acquisition of
all or substantially all of the Company's assets, and all of the obligations of
the Company relating to the Series Preferred issuable upon the exercise or
conversion of this Warrant shall survive the exercise, conversion and
termination of this Warrant and all of the covenants and agreements of the
Company shall inure to the benefit of the successors and assigns of the holder
hereof.

     15. Lost Warrants or Stock Certificates. The Company covenants to the
holder hereof that, upon receipt of evidence reasonably satisfactory to the
Company of the loss, theft, destruction or mutilation of this Warrant or any
stock certificate and, in the case of any such loss, theft or destruction, upon
receipt of an indemnity reasonably satisfactory to the Company, or in the case
of any such mutilation upon surrender and cancellation of such Warrant or stock
certificate, the Company will make and deliver a new Warrant or stock
certificate, of like tenor, in lieu of the lost, stolen, destroyed or mutilated
Warrant or stock certificate.

     16. Descriptive Headings. The descriptive headings of the various Sections
of this Warrant are inserted for convenience only and do not constitute a part
of this Warrant. The language in this Warrant shall be construed as to its fair
meaning without regard to which party drafted this Warrant.

     17. Governing Law. This Warrant shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the laws of
the State of Delaware.

                                       10

<Page>

     18. Survival of Representations, Warranties and Agreements. All
representations and warranties of the Company and the holder hereof contained
herein shall survive the Date of Grant, the exercise or conversion of this
Warrant (or any part hereof) or the termination or expiration of rights
hereunder. All agreements of the Company and the holder hereof contained herein
shall survive indefinitely until, by their respective terms, they are no longer
operative.

     19. Remedies. In case any one or more of the covenants and agreements
contained in this Warrant shall have been breached, the holders hereof (in the
case of a breach by the Company), or the Company (in the case of a breach by a
holder), may proceed to protect and enforce their or its rights either by suit
in equity and/or by action at law, including, but not limited to, an action for
damages as a result of any such breach and/or an action for specific performance
of any such covenant or agreement contained in this Warrant.

     20. No Impairment of Rights. The Company will not, by amendment of its
Charter or through any other means, avoid or seek to avoid the observance or
performance of any of the terms of this Warrant, but will at all times in good
faith assist in the carrying out of all such terms and in the taking of all such
action as may be necessary or appropriate in order to protect the rights of the
holder of this Warrant against impairment.

     21. Severability. The invalidity or unenforceability of any provision of
this Warrant in any jurisdiction shall not affect the validity or enforceability
of such provision in any other jurisdiction, or affect any other provision of
this Warrant, which shall remain in full force and effect.

     22. Recovery of Litigation Costs. If any legal action or other proceeding
is brought for the enforcement of this Warrant, or because of an alleged
dispute, breach, default, or misrepresentation in connection with any of the
provisions of this Warrant, the successful or prevailing party or parties shall
be entitled to recover reasonable attorneys' fees and other costs incurred in
that action or proceeding, in addition to any other relief to which it or they
may be entitled.

     23. Entire Agreement; Modification. This Warrant constitutes the entire
agreement between the parties pertaining to the subject matter contained in it
and supersedes all prior and contemporaneous agreements, representations, and
undertakings of the parties, whether oral or written, with respect to such
subject matter.

                                       11

<Page>

     The Company has caused this Warrant to be duly executed and delivered as of
the Date of Grant specified above.

                                        ACTIVBIOTICS, INC.

                                        By:
                                            ------------------------------------
                                        Name:
                                        Title:
                                        Address:

                                       12

<Page>

                                   EXHIBIT A-l

                               NOTICE OF EXERCISE

To: ACTIVBIOTICS, INC. (the "Company")

     1. The undersigned hereby:

          |_|  elects to purchase _____________ shares of [Series Preferred
               Stock] [Common Stock] of the Company pursuant to the terms of the
               attached Warrant, and tenders herewith payment of the purchase
               price of such shares in full, or

          |_|  elects to exercise its net issuance rights pursuant to Section
               10.2 of the attached Warrant with respect to _______________
               Shares of [Series Preferred Stock] [Common Stock].

     2. Please issue a certificate or certificates representing ______________
shares in the name of the undersigned or in such other name or names as are
specified below:

                      -----------------------------------
                                     (Name)

                       -----------------------------------

                       -----------------------------------
                                    (Address)

     3. The undersigned represents that the aforesaid shares are being acquired
for the account of the undersigned for investment and not with a view to, or for
resale in connection with, the distribution thereof and that the undersigned has
no present intention of distributing or reselling such shares, all except as in
compliance with applicable securities laws.

                                                   -----------------------------
                                                   (Signature)

-------------------
(Date)

<Page>

                                   EXHIBIT A-2

                               NOTICE OF EXERCISE

To: ACTIVBIOTICS, INC. (the "Company")

     1. Contingent upon and effective immediately prior to the closing (the
"Closing") of the Company's public offering contemplated by the Registration
Statement on Form S __________, filed ___________, 200___, the undersigned
hereby:

     |_| elects to purchase __________ shares of [Series Preferred Stock]
[Common Stock] of the Company (or such lesser number of shares as may be sold on
behalf of the undersigned at the Closing) pursuant to the terms of the attached
Warrant, or

     |_| elects to exercise its net issuance rights pursuant to Section 10.2 of
the attached Warrant with respect to ___________ Shares of [Series Preferred
Stock] [Common Stock].

     2. Please deliver to the custodian for the selling shareholders a stock
certificate representing such ____________ shares.

     3. The undersigned has instructed the custodian for the selling
shareholders to deliver to the Company $______________ or, if less, the net
proceeds due the undersigned from the sale of shares in the aforesaid public
offering. If such net proceeds are less than the purchase price for such shares,
the undersigned agrees to deliver the difference to the Company prior to the
Closing.

                                                      --------------------------
                                                      (Signature)

-------------------
(Date)<Page>

                                                                    Exhibit 10.1

                                                                       METAPHORE
                                                                    CONFIDENTIAL

                         METAPHORE PHARMACEUTICALS, INC.

                             1998 STOCK OPTION PLAN

                (AS AMENDED AND RESTATED EFFECTIVE MAY 14, 2004,
EFFECTIVE WITH RESPECT TO ALL BENEFITS GRANTED UNDER THE PLAN AND THE PRIOR PLAN
                 INCLUDING THOSE BENEFITS GRANTED BEFORE 2003.)

<Page>

                         METAPHORE PHARMACEUTICALS, INC.

                             1998 STOCK OPTION PLAN

                 (as amended and restated effective May 14, 2004,
      effective with respect to all Benefits granted under the Plan and the
            Prior Plan including those Benefits granted before 2003.)

                                TABLE OF CONTENTS

                                                                            PAGE
                                                                            ----
1.   NAME AND PURPOSE                                                         1
        1.1   Name                                                            1
        1.2   Purpose                                                         1

2.   DEFINITIONS OF TERMS AND RULES OF CONSTRUCTION                           1
        2.1   General Definitions                                             1
              2.1.1  Affiliate                                                1
              2.1.2  Agreement                                                1
              2.1.3  Benefit                                                  1
              2.1.4  Board                                                    1
              2.1.5  Board Advisor                                            2
              2.1.6  Business Entity                                          2
              2.1.7  Cause                                                    2
              2.1.8  Change of Control                                        2
              2.1.9  Code                                                     3
              2.1.10 Company                                                  3
              2.1.11 Committee                                                3
              2.1.12 Common Stock                                             3
              2.1.13 Director                                                 3
              2.1.14 Effective Termination Event                              3
              2.1.15 Employee                                                 3
              2.1.16 Employer                                                 3
              2.1.17 Fair Market Value                                        3
              2.1.18 ISO                                                      4
              2.1.19 NQSO                                                     4
              2.1.20 Option                                                   4
              2.1.21 Parent                                                   4
              2.1.22 Participant                                              4
              2.1.23 Plan                                                     4
              2.1.24 Prior Plan                                               4
              2.1.25 Related Entity                                           5
              2.1.26 Reload Option                                            5
              2.1.27 SAR                                                      5
              2.1.28 Scientific Advisory Board Members                        5

                                        i

<Page>

                 2.1.29 Share                                                  5
                 2.1.30 Subsidiary                                             5
         2.2     Other Definitions                                             5
         2.3     Conflicts                                                     5

3.    COMMON STOCK                                                             6
         3.1     Number of Shares                                              6
         3.2     Reusage                                                       6
         3.3     Adjustments                                                   6

4.    ELIGIBILITY                                                              6
         4.1     Determined By Committee                                       6

5.    ADMINISTRATION                                                           6
         5.1     Committee                                                     6
         5.2     Authority                                                     7
         5.3     Delegation                                                    7
         5.4     Determination                                                 7

6.    AMENDMENT OF PLAN                                                        8
         6.1     Power of Board                                                8
         6.2     Limitation                                                    8

7.    TERM AND TERMINATION OF PLAN                                             8
         7.1     Term                                                          8
         7.2     Termination                                                   8

8.    MODIFICATION OF BENEFITS                                                 8
         8.1     General Right of Committee                                    8
         8.2     Restriction                                                   8

9.    CHANGE OF CONTROL                                                        9
         9.1     Committee Discretion to Protect Benefits                      9
         9.2     Automatic Accelerated Vesting of Benefits                     9

10.   AGREEMENTS                                                               9
         10.1    Grant Evidenced By Agreement                                  9
         10.2    Provisions of Agreement                                      10
         10.3    Transferability                                              10

11.   REPLACEMENT AND TANDEM AWARDS                                           10
         11.1    Replacement                                                  10
         11.2    Tandem Awards                                                10

12.   PAYMENT, DIVIDENDS, DEFERRAL AND WITHHOLDING                            10
         12.1    Payment                                                      10
         12.2    Dividend Equivalents                                         11
         12.3    Deferral                                                     11

                                       ii

<Page>

         12.4    Withholding                                                  11

13.   OPTIONS                                                                 11
         13.1    Types of Options                                             11
         13.2    Grant of ISOs and Option Price                               11
         13.3    Other Requirements for ISOs                                  12
         13.4    NQSOs                                                        12
         13.5    Determination by Committee                                   12

14.   SARS                                                                    12
         14.1    Grant and Payment                                            12
         14.2    Grant of Tandem Award                                        12
         13.3    ISO Tandem Award                                             12
         14.4    Payment of Awards                                            12

15.   MISCELLANEOUS PROVISIONS                                                12
         15.1    Underscored References                                       12
         15.2    Number and Gender                                            13
         15.3    Unfunded Status of Plan                                      13
         15.4    Termination of Employment                                    13
         15.5    Designation of Beneficiary                                   14
         15.6    Governing Law                                                15
         15.7    Purchase for Investment                                      15
         15.8    No Employment Contract                                       15
         15.9    No Effect on Other Benefits                                  15
         15.10   Restrictions                                                 15

                                       iii

<Page>

                         METAPHORE PHARMACEUTICALS, INC.

                             1998 STOCK OPTION PLAN

                (as amended and restated effective May 14, 2004,
effective with respect to all Benefits granted under the Plan and the Prior Plan
                 including those Benefits granted before 2003.)

1    NAME AND PURPOSE

     1.1  NAME.

          The name of this Plan is the "Metaphore Pharmaceuticals, Inc. 1998
Stock Option Plan."

     1.2  PURPOSE.

          The Company has established this Plan to attract, retain, motivate and
reward Employees and other individuals and to encourage ownership of the
Company's Common Stock by Employees and other individuals.

2    DEFINITIONS OF TERMS AND RULES OF CONSTRUCTION

     2.1  GENERAL DEFINITIONS.

          The following words and phrases, when used in the Plan, unless
otherwise specifically defined or unless the context clearly otherwise requires,
shall have the following respective meanings:

          2.1.1 AFFILIATE.

               A Parent or Subsidiary of the Company or any Business Entity
     which, directly or indirectly, is controlled by the Company.

          2.1.2 AGREEMENT.

               The document which evidences the grant of any Benefit under the
     Plan and which sets forth the Benefit and the terms, conditions and
     provisions of, and restrictions relating to, such Benefit.

          2.1.3 BENEFIT.

               Any benefit granted to a Participant under the Plan

          2.1.4 BOARD.

               The Board of Directors of the Company.

                                       1

<Page>

          2.1.5 BOARD ADVISOR.

               An advisor of the Board, so designated by the Board.

          2.1.6 BUSINESS ENTITY.

               Any corporation, partnership, limited liability partnership,
     limited liability company, trust, association, or other business or not for
     profit entity.

          2.1.7 CAUSE.

               Cause shall be determined by the Committee and shall include, but
     not be limited to, gross negligence, willful misconduct, flagrant or
     repeated violations of the Employer's policies, rules or ethics,
     intoxication, substance abuse, sexual or other unlawful harassment,
     disclosure of confidential or proprietary information, engaging in a
     business competitive with the Employer, or dishonest, illegal or immoral
     conduct.

          2.1.8 CHANGE OF CONTROL.

               Change of Control means any of the following:

               (a) The acquisition, with or without the approval of the Board,
     by any "person" or "group" (as that term is used in Section 13(d) and
     14(d)(2) of the Securities Exchange Act of 1934, as amended ("Exchange
     Act")), other than the Company or a Related Entity, of beneficial ownership
     (as defined in Rule 13d-3 under the Exchange Act) of outstanding voting
     securities of the Company carrying more than 20% of the combined voting
     power in the election of directors through a tender offer, exchange offer
     or otherwise provided, however, that the sale of voting securities by the
     Company that constitutes a financing round shall not constitute a Change of
     Control;

               (b) the liquidation or dissolution of the Company following a
     sale or other disposition of all or substantially all of its assets;

               (c) a merger or consolidation involving the Company as a result
     of which persons who were shareholders of the Company immediately prior
     to the effective date of the merger or consolidation shall have beneficial
     ownership of less than 50% of the combined voting power in the election of
     directors of the surviving corporation following the effective date of such
     merger or consolidation;

               (d) or any time during any two year period in which individuals
     who constituted the Board at the start of such period (or whose election
     was approved by at least two thirds of the then members of the Board who
     were members at the start of the two year period) do not constitute at
     least 50% of the Board for any reason.

     In addition, in the case of Participants employed by a Subsidiary or a
     division of the Company or a Subsidiary, the sale of a Subsidiary or the
     sale of all or substantially all of the assets of the Subsidiary or
     division shall constitute a Change of Control.

                                       2

<Page>

     2.1.9 CODE.

          The Internal Revenue Code of 1986, as amended. Any reference to the
Code includes the regulations promulgated pursuant to the Code.

     2.1.10 COMPANY.

          Metaphore Pharmaceuticals, Inc.

     2.1.11 COMMITTEE.

          The Committee described in Section 5.1.

     2.1.12 COMMON STOCK.

          The Company's common stock.

     2.1.13 DIRECTOR.

          A member of the Board or a member of the Board of Directors of an
Affiliate.

     2.1.14 EFFECTIVE TERMINATION EVENT.

          Any of the following events: a termination of Participant's employment
by the Employer without Cause; a material decrease in Participant's
compensation; a substantial decrease in the nature or scope of Participant's
duties, responsibilities, powers, authority, title, position or status; or a
material breach by the Employer of an employment, compensation or similar
agreement between the Participant and the Employer.

     2.1.15 EMPLOYEE.

          Any person employed by the Employer.

     2.1.16 EMPLOYER.

          The Company and all Affiliates.

     2.1.17 FAIR MARKET VALUE.

          The last sale price, regular way, or, in case no such sale takes place
on such date, the average of the closing bid and asked prices, regular way, of
the Shares, in either case as reported in the principal consolidated transaction
reporting system with respect to securities listed or admitted to trading on the
New York Stock Exchange, Inc. (the "NYSE") or, if the Shares are not listed or
admitted to trading on the NYSE, as reported in the principal consolidated
transaction reporting system with respect to securities listed on the principal
national securities exchange on which the Shares are listed or admitted to
trading or, if the Shares are not listed or admitted to trading on any

                                        3

<Page>

national securities exchange, the last quoted sale price on such date or, if not
so quoted, the average of the high bid and low asked prices in the
over-the-counter market on such date, as reported by the National Association of
Securities Dealers, Inc. Automated Quotations System or such other system then
in use, or, if on any such date the Shares are not quoted by any such
organization, the average of the closing bid and asked prices on such date as
furnished by a professional market maker making a market in the Shares selected
by the Committee. If the Shares are not publicly held or so listed or publicly
traded, the determination of the Fair Market Value per Share shall be made in
good faith by the Committee.

     2.1.18 ISO.

          An Incentive Stock Option as defined in Section 422 of the Code.

     2.1.19 NQSO.

          A non-qualified stock Option, which is an Option that does not qualify
as an ISO.

     2.1.20 OPTION.

          An option to purchase Shares granted under the Plan.

     2.1.21 PARENT.

          Any Business Entity (other than the Company or a Subsidiary) in an
unbroken chain of Business Entities ending with the Company, if, at the time of
the grant of an Option or other Benefit, each of the Business Entities (other
than the Company) owns equity possessing 50% or more of the total combined
voting power of all classes of equity in one of the other Business Entities in
such chain.

     2.1.22 PARTICIPANT.

          An individual who is granted a Benefit under the Plan. Benefits may be
granted only to Employees, Directors, Board Advisors, Scientific Advisory Board
Members or consultants of the Company or an Affiliate.

     2.1.23 PLAN.

          The Metaphore Pharmaceuticals, Inc. 1998 Stock Option Plan and all
amendments and supplements to it.

     2.1.24 PRIOR PLAN.

          The MetaPhore Pharmaceuticals, Inc. 1998 Stock Option Plan as amended
up to January 1, 1999. As of January 1, 1999, the Plan shall be an amendment and
restatement of the Prior Plan.

                                        4

<Page>

          2.1.25 RELATED ENTITY.

               The Parent, a Subsidiary or any employee benefit plan (including
     a trust forming a part of such a plan) maintained by the Parent, the
     Company or a Subsidiary.

          2.1.26 RELOAD OPTION.

               An Option to purchase the number of Shares used by a Participant
     to exercise an Option and to satisfy any withholding requirement incident
     to the exercise of such Option

          2.1.27 SAR.

               A stock appreciation right, which is the right to receive an
     amount equal to the appreciation, if any, in the Fair Market Value of a
     Share from the date of the grant of the right to the date of its payment

          2.1.28 SCIENTIFIC ADVISORY BOARD MEMBERS.

               An member of the scientific advisory board of the Company, so
     designated by the Board

          2.1.29 SHARE.

               A share of Common Stock

          2.1.30 SUBSIDIARY.

               Any Business Entity (other than the Company) in an unbroken chain
     of Business Entities beginning with the Company if, at the time of grant of
     an Option or other Benefit, each of the Business Entities, other than the
     last Business Entity in the unbroken chain, owns equity possessing 50% or
     more of the total combined voting power of all classes of equity in one of
     the other Business Entities in such chain.

     2.2  OTHER DEFINITIONS.

          In addition to the above definitions, certain words and phrases used
in the Plan and any Agreement may be defined in other portions of the Plan or in
such Agreement.

     2.3  CONFLICTS.

          In the case of any conflict in the terms of the Plan relating to a
Benefit, the provisions in the section of the Plan which specifically grants
such Benefit shall control those in a different section. In the case of any
conflict between the terms of the Plan relating to a Benefit and the terms of an
Agreement relating to a Benefit, the terms of the Plan shall control.

                                        5

<Page>

3.   COMMON STOCK

     3.1  NUMBER OF SHARES.

          The number of Shares which may be issued or sold or for which Options
or SARs may be granted under the Plan shall be 4,308,219 Shares. Such Shares may
be authorized but unissued Shares, Shares held in the treasury, or both The full
number of Shares available may be used for any type of Option or SAR

     3.2  REUSAGE.

          If an Option or SAR expires or is terminated, surrendered, or canceled
without having been fully exercised, the Shares covered by such Option or SAR,
as the case may be, shall again be available for use under the Plan. Any Shares
which are used as full or partial payment to the Company upon exercise of an
Option shall be available for purposes of the Plan

     3.3  ADJUSTMENTS.

          If there is any change in the Common Stock of the Company by reason of
any stock split, stock dividend, spin off, split up, spin out, recapitalization,
merger, consolidation, reorganization, combination or exchange of shares, or
otherwise, the number of SARs and number and class of shares available for
Options and the number of Shares subject to outstanding Options or SARs, and the
price thereof, as applicable, shall be appropriately adjusted by the Committee.

4.   ELIGIBILITY

     4.1  DETERMINED BY COMMITTEE.

          The Participants and the Benefits they receive under the Plan shall be
determined solely by the Committee. In making its determinations, the Committee
shall consider past, present and expected future contributions of Participants
and potential Participants to the Employer, including, without limitation, the
performance of, or the refraining from the performance of, services. Unless
specifically provided otherwise herein, all determinations of the Committee in
connection with the Plan or an Agreement shall be made in its sole discretion

5.   ADMINISTRATION

     5.1  COMMITTEE.

          The Plan shall be administered by the Committee. The Committee shall
consist of the Board, unless the Board appoints a Committee of three or more but
less than all of the Board. If the Committee does not include the entire Board,
it shall serve at the pleasure of the Board, which may from time to time appoint
members in substitution for members previously appointed and fill vacancies,
however caused, in the Committee. The Committee may select one of its members as
its Chairman and shall hold its meetings at such times and places as it may
determine. A majority of its members shall constitute a quorum. All
determinations of the Committee made at a meeting at which a quorum is present
shall be made by a majority of its

                                        6

<Page>

members present at the meeting. Any decision or determination reduced to writing
and signed by a majority of the members shall be fully as effective as if it had
been made by a majority vote at a meeting duly called and held.

     5.2  AUTHORITY.

          Subject to the terms of the Plan, the Committee shall have
discretionary authority to:

          (a) determine the individuals to whom Benefits are granted, the type
     and amounts of Benefits to be granted and the date of issuance and duration
     of all such grants;

          (b) determine the terms, conditions and provisions of, and
     restrictions relating to, each Benefit granted;

          (c) interpret and construe the Plan and all Agreements;

          (d) prescribe, amend and rescind rules and regulations relating to the
     Plan;

          (e) determine the content and form of all Agreements;

          (f) determine all questions relating to Benefits under the Plan;

          (g) maintain accounts, records and ledgers relating to Benefits;

          (h) maintain records concerning its decisions and proceedings;

          (i) employ agents, attorneys, accountants or other persons for such
     purposes as the Committee considers necessary or desirable;

          (j) take, at any time, any action required or permitted by Section 9
     irrespective of whether any Change of Control has occurred or is imminent;

          (k) determine limits on Options and SARs which may be granted to any
     Participant over a particular period of time; and

          (l) do and perform all acts which it may deem necessary or appropriate
     for the administration of the Plan and carry out the purposes of the Plan.

     5.3  DELEGATION.

          The Committee may delegate all or any part of its authority under the
Plan to any Employee, Employees or committee.

     5.4  DETERMINATION.

          All determinations of the Committee shall be final.

                                        7

<Page>

6.   AMENDMENT OF PLAN.

     6.1  POWER OF BOARD.

          Except as provided in Section 6.2 or 8.2, the Board shall have the
sole right and power to amend the Plan at any time and from time to time.

     6.2  LIMITATION.

          The Board may not amend the Plan, without approval of the shareholders
of the Company:

          (a) in a manner which would cause Options which are intended to
     qualify as ISOs to fail to qualify; or

          (b) in a manner which would violate applicable law.

7.   TERM AND TERMINATION OF PLAN

     7.1  TERM.

          The Plan shall commence as of January 1, 1999 and, subject to the
terms of the Plan, including those requiring approval by the shareholders of the
Company and those limiting the period over which ISOs or any other Benefits may
be granted, shall continue in full force and effect until terminated.

     7.2  TERMINATION.

          Subject to Section 8.2, the Plan may be terminated at any time by the
Board.

8.   MODIFICATION OF BENEFITS

     8.1  GENERAL RIGHT OF COMMITTEE.

          Subject to Section 8.2, any Benefit may be converted, modified,
forfeited or canceled, in whole or in part, by the Committee if and to the
extent permitted in the Plan or applicable Agreement. Except as may be provided
in an Agreement, the Committee may, in its sole discretion, in whole or in part,
waive any restrictions or conditions applicable to, or accelerate the vesting
of, any Benefit.

     8.2  RESTRICTION.

          Notwithstanding the provisions of Sections 6.1, 7.2 or 8.1, without
the consent of the Participant to whom a Benefit was granted, no amendment or
termination of the Plan or conversion, modification, forfeiture or cancellation
of a Benefit may adversely affect such Participant's right to such Benefit
granted prior to such amendment or termination of the Plan or conversion,
modification, forfeiture or cancellation of such Benefit.

                                        8

<Page>

9    CHANGE OF CONTROL

     9.1  COMMITTEE DISCRETION TO PROTECT BENEFITS.

          In order to maintain a Participant's rights in the event of a Change
of Control, the Committee, in its sole discretion, may, in any Agreement
evidencing a Benefit, or at any time prior to, or simultaneously with or after a
Change in Control, provide such protection as it may deem necessary. Without in
any way limiting the generality of the foregoing sentence or requiring any
specific protection, the Committee may:

          (a) provide for the acceleration of any time periods relating to the
     exercise or realization of such benefit so that such benefit may be
     exercised or realized on or before a date fixed by the Committee;

          (b) provide for the purchase of any Benefit for an amount of cash
     equal to the amount which could have been attained upon the exercise or
     realization of such Benefit had such Benefit been currently exercisable or
     payable;

          (c) make such adjustment to the Benefits then outstanding as the
     Committee deems appropriate to reflect such transaction or change; and/or

          (d) cause the Benefits then outstanding to be assumed, or new Benefits
     substituted therefor, by the surviving corporation in such change.

     9.2  AUTOMATIC ACCELERATED VESTING OF BENEFITS.

          Without the necessity of any action by the Committee, if within the
one (1) year period following a Change of Control, a Participant experiences an
Effective Termination Event, then effective upon the Company's receipt from
Participant of written notice of such Effective Termination Event, then all time
periods relating to the exercise or realization of the Participant's Benefit
shall be accelerated so that such Benefit may be exercised or realized in
accordance with the Participant's Agreement as if fully vested on the
termination date and as if the Participant was terminated without Cause.
Participant's written notice shall be sent to the Company's corporate offices
and shall set forth in reasonable detail (a) the facts and circumstances claimed
to provide a basis for Effective Termination Event, and (b) if the termination
date is other than the date of receipt of such notice, the actual termination
date.

10.  AGREEMENTS

     10.1 GRANT EVIDENCED BY AGREEMENT.

          The grant of any Benefit under the Plan may be evidenced by an
Agreement which shall describe the specific Benefit granted and the terms and
conditions of the Benefit. The granting of any Benefit shall be subject to, and
conditioned upon, the recipient's execution of any Agreement required by the
Committee. Except as otherwise provided in an Agreement, all capitalized terms
used in the Agreement shall have the same meaning as in the Plan, and the
Agreement shall be subject to all of the terms of the Plan.

                                        9

<Page>

     10.2 PROVISIONS OF AGREEMENT.

          Each Agreement shall contain such provisions that the Committee shall
determine to be necessary, desirable and appropriate for the Benefit granted
which may include, but not necessarily be limited to, the following with respect
to any Benefit: description of the type of Benefit; the Benefit's duration; its
transferability; if an Option, the exercise price, the exercise period and the
person or persons who may exercise the Option; the effect upon such Benefit of
the Participant's death, disability, changes of duties or termination of
employment; the Benefit's conditions; when, if, and how any Benefit may be
forfeited, converted into another Benefit, modified, exchanged for another
Benefit, or replaced; and the restrictions on any Shares purchased or granted
under the Plan.

     10.3 TRANSFERABILITY.

          Unless otherwise specified in an Agreement or permitted by the
Committee, each Benefit granted shall be not transferable other than by will or
the laws of descent and distribution and shall be exercisable during a
Participant's lifetime only by him.

11.  REPLACEMENT AND TANDEM AWARDS

     11.1 REPLACEMENT.

          The Committee may permit a Participant to elect to surrender a Benefit
in exchange for a new Benefit.

     11.2 TANDEM AWARDS.

          Awards may be granted by the Committee in tandem. However, no Benefit
may be granted in tandem with an ISO except SARs.

12.  PAYMENT, DIVIDENDS, DEFERRAL AND WITHHOLDING

     12.1 PAYMENT.

          Upon the exercise of an Option, the amount due the Company is to be
paid:

          (a) in cash;

          (b) by the surrender of all or part of a Benefit (including the Option
     being exercised);

          (c) by the tender to the Company of Shares owned by the Participant
     and registered in his name having a Fair Market Value equal to the amount
     due to the Company;

          (d) in other property, rights and credits deemed acceptable by the
     Committee, including the Participant's promissory note;

          (e) by a cashless exercise arrangement or an attestation arrangement;
     or

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          (f) by any combination of the payment methods specified in (a), (b),
     (c), (d), and (e) above

          Notwithstanding, the foregoing, any method of payment other than (a)
may be used only with the consent of the Committee or if and to the extent so
provided in an Agreement. The proceeds of the sale of Shares purchased pursuant
to an Option and any payment to the Company for other Benefits shall be added to
the general funds of the Company or to the Shares held in treasury, as the case
may be, and used for the corporate purposes of the Company as the Board shall
determine.

     12.2 DIVIDEND EQUIVALENTS.

          Grants of Benefits in Shares or Share equivalents may include dividend
equivalent payments or dividend credit rights.

     12.3 DEFERRAL.

          The right to receive any Benefit under the Plan may, at the request
of the Participant, be deferred for such period and upon such terms as the
Committee shall determine, which may include crediting of interest on deferrals
of cash and crediting of dividends on deferrals denominated in Shares.

     12.4 WITHHOLDING.

          The Company may, at the time any distribution is made under the Plan,
whether in cash or in Shares, or at the time any Option is exercised, withhold
from such distribution or Shares issuable upon the exercise of an Option, any
amount necessary to satisfy federal, state and local income and/or other tax
withholding requirements with respect to such distribution or exercise of such
Options. The Committee or the Company may require a participant to tender to the
Company cash and/or Shares in the amount necessary to comply with any such
withholding requirements.

13.  OPTIONS.

     13.1 TYPES OF OPTIONS.

          It is intended that both ISOs and NQSOs, which may be Reload Options,
may be granted by the Committee under the Plan.

     13.2 GRANT OF ISOS AND OPTION PRICE.

          Each ISO must be granted to an Employee and granted within ten years
from January 21, 1998, which is the date which is earlier of the date of
adoption of the Prior Plan by the Board or Company's shareholders. The purchase
price for Shares under any ISO shall be no less than the Fair Market Value of
the Shares at the time the Option is granted.

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     13.3 OTHER REQUIREMENTS FOR ISOS.

          The terms of each Option which is intended to qualify as an ISO shall
meet all requirements of Section 422 of the Code.

     13.4 NQSOs.

          The terms of each NQSO shall provide that such Option will not be
treated as an ISO. The purchase price for Shares under any NQSO shall be no less
than $.01 per Share.

     13.5 DETERMINATION BY COMMITTEE.

          Except as otherwise provided in Section 13.2 through Section 13.4,
the terms of all Options shall be determined by the Committee.

14.  SARS.

     14.1 GRANT AND PAYMENT.

          The Committee may grant SARs. Upon electing to receive payment of a
SAR, a Participant shall receive payment in cash, in Shares, or in any
combination of cash and Shares, as the Committee shall determine.

     14.2 GRANT OF TANDEM AWARD.

          The Committee may grant SARs in tandem with an Option, in which case:
the exercise of the Option shall cause a correlative reduction in SARs standing
to a Participant's credit which were granted in tandem with the Option; and the
payment of SARs shall cause a correlative reduction of the Shares under such
Option.

     14.3 ISO TANDEM AWARD.

          When SARs are granted in tandem with an ISO, the SARs shall have such
terms and conditions as shall be required for the ISO to qualify as an ISO.

     14.4 PAYMENT OF AWARD.

          SARs shall be paid by the Company to a Participant, to the extent
payment is elected by the Participant (and is otherwise due and payable), as
soon as practicable after the date on which such election is made.

15.  MISCELLANEOUS PROVISIONS

     15.1 UNDERSCORED REFERENCES.

          The underscored references contained in the Plan are included only for
convenience, and they shall not be construed as a part of the Plan or in any
respect affecting or modifying its provisions.

                                       12

<Page>

     15.2 NUMBER AND GENDER.

          The masculine and neuter, wherever used in the Plan, shall refer to
either the masculine, neuter or feminine; and, unless the context otherwise
requires, the singular shall include the plural and the plural the singular.

     15.3 UNFUNDED STATUS OF PLAN.

          The Plan is intended to constitute an "unfunded" plan for incentive
and deferred compensation. With respect to any payments or deliveries of Shares
not yet made to a Participant by the Company, nothing contained herein shall
give any rights that are greater than those of a general creditor of the
Company. The Committee may authorize the creation of trusts or other
arrangements to meet the obligations created under the Plan to deliver Shares or
payments hereunder consistent with the foregoing.

     15.4 TERMINATION OF EMPLOYMENT.

               (a) If the employment of a Participant by the Company terminates
     for any reason, except as otherwise provided in an Agreement, all
     unexercised, deferred, and unpaid Benefits may be exercisable or paid only
     in accordance with rules established by the Committee. These rules may
     provide, as the Committee may deem appropriate, for the expiration,
     forfeiture, continuation, or acceleration of the vesting of all or part of
     the Benefits.

               (b) For all awards of Benefits prior to January 1, 2002 and for
     all awards of Benefits on or after January 1, 2002 which do not
     specifically override this Section 15.4(b) in the Award, the following
     shall apply in the event of termination of employment:

                    (i) Termination for Cause After Option is Vested. If, on or
     after the date that the Option shall have first become exercisable, the
     Participant's employment shall be terminated by the Employer for. "Cause",
     as defined below, then the Participant's full interest in the Option shall
     terminate on the date of such termination of employment and all rights
     thereunder shall cease. Whether a Participant's employment is terminated
     for Cause shall be determined by the Committee. Cause shall include, but
     not be limited to gross negligence, willful misconduct, flagrant or
     repeated violations of the Employer's policies, rules or ethics,
     intoxication, substance abuse, sexual or other unlawful harassment,
     disclosure of confidential or proprietary information, engaging in a
     business competitive with the Employer, or dishonest, illegal or immoral
     conduct. The employment of a Director, Board Advisor or Scientific Advisory
     Board Member shall be deemed to be terminated when he ceases to be in such
     role. If a Participant is both a Director, Board Advisor or Scientific
     Advisory Board Member and an Employee, his employment shall not be deemed
     to have been terminated as long as he remains in any of those roles.

                    (ii) Other Termination After Option is Vested If, on or
     after the date that the Option shall first have become exercisable, the
     Participant's employment shall be terminated for disability (as such term
     is defined at Section 422(c)(6) of the

                                       13

<Page>

     Code), for death, by the Employer without Cause, or by the Participant,
     then the Participant or his personal representative and/or beneficiary, as
     the case may be, shall have the right (but not later than the Option
     Expiration Date) to exercise such Option to the extent that such Option or
     any installment thereof shall have accrued at the date of such termination
     of employment and shall not have been exercised (A) for one year following
     termination of employment, if the Participant becomes disabled or dies, and
     (B) for three months following termination of employment, in the other
     cases described in this Section 15.4(b)(ii). If the Participant's
     employment terminates for a reason described in this Section 15.4(b)(ii)
     other than death or disability, and, if the Participant dies or becomes
     disabled prior to three months following termination of employment, then
     the Participant or his personal representative and/or beneficiary, as the
     case may be, shall have the right (but not later than the Option Expiration
     Date), to exercise such Option to the extent that such Option or any
     installment thereof shall have accrued at the date of such termination of
     employment and shall not have been exercised for a period which, when added
     to the period which has elapsed following termination of employment until
     death or disability, equals one year Notwithstanding the foregoing, if the
     employment of a Director or a Scientific Advisory Board Member is
     terminated for a reason described in this Section 15.4(b)(ii), the Director
     or Scientific Advisory Board Member, or his personal representative and/or
     beneficiary, as the case may be, shall have the right to exercise any
     Option granted on or after July 23, 2004 to the extent that such Option or
     any installment thereof shall have accrued at the date of such termination
     of employment and shall not have been exercised, until the first
     anniversary of the date of such termination of employment. The employment
     of a Director, Board Advisor or Scientific Advisory Board Member shall be
     deemed to have been terminated by the Employer without Cause if the
     Participant ceases to serve in such role solely due to the failure to be
     reelected or reappointed and such failure is not a result of an act or
     omission which would constitute Cause.

                    (iii) Option Not Vested If the Participant's employment (or
     service as a Director, Board Advisor or Scientific Advisory Board Member)
     shall terminate before all or part of the Option shall have first become
     exercisable, then the Participant's interest in the Option to the extent
     not vested shall terminate and all rights to the extent not vested shall
     cease.

     15.5 DESIGNATION OF BENEFICIARY.

          A Participant may file with the Committee a written designation of a
beneficiary or beneficiaries (subject to such limitations as to the classes and
number of beneficiaries and contingent beneficiaries as the Committee may from
time to time prescribe) to exercise, in the event of the death of the
Participant, an Option, or to receive, in such event, any Benefits. The
Committee reserves the right to review and approve beneficiary designations. A
Participant may from time to time revoke or change any such designation of
beneficiary and any designation of beneficiary under the Plan shall be
controlling over any other disposition, testamentary or otherwise; provided,
however, that if the Committee shall be in doubt as to the right of any such
beneficiary to exercise any Option or to receive any Benefit, the Committee may
determine to recognize only an exercise by the legal representative of the
recipient, in which case the

                                       14

<Page>

Company, the Committee and the members thereof shall not be under any further
liability to anyone.

     15.6 GOVERNING LAW.

          This Plan shall be construed and administered in accordance with the
laws of the State of Missouri.

     15.7 PURCHASE FOR INVESTMENT.

          So long as the Common Stock of the Company is not publicly traded, the
Committee may require each person purchasing Shares pursuant to an Option or
other award under the Plan to represent to and agree with the Company in writing
that such person is acquiring the Shares for investment and without a view to
distribution or resale. The certificates for such Shares may include any legend
which the Committee deems appropriate to reflect any restrictions on transfer.
All certificates for Shares delivered under the Plan shall be subject to such
stock transfer orders and other restrictions as the Committee may deem advisable
under all applicable laws, rules and regulations, and the Committee may cause a
legend or legends to be put on any such certificates to make appropriate
references to such restrictions.

     15.8 NO EMPLOYMENT CONTRACT.

          Neither the adoption of the Plan nor any Benefit granted hereunder
shall confer upon any Employee any right to continued employment nor shall the
Plan or any Benefit interfere in any way with the right of the Employer to
terminate the employment of any of its Employees at any time.

     15.9 NO EFFECT ON OTHER BENEFITS.

          The receipt of Benefits under the Plan shall have no effect on any
benefits to which a Participant may be entitled from the Employer, under another
plan or otherwise, or preclude a Participant from receiving any such benefits.

     15.10 RESTRICTIONS.

          In addition to any restrictions imposed upon Shares acquired under the
Plan set forth in Section 15.7, such Shares shall be subject to any restrictions
contained in the Agreement or in any other agreement between the Participant and
the Employer.

                                       15

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