Document:

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                                                                   EXHIBIT 10.25

                              [MEDIMMUNE LOGO HERE]

                                    AMENDMENT

         This Amendment, effective on the last date of signature below, modifies
and amends the Collaboration and License Agreement dated effective April 19,
2001 (the "Agreement"), by and between Genaera Corporation ("GENAERA") and
MedImmune, Inc. ("MEDIMMUNE").

                                   WITNESSETH

         WHEREAS, MEDIMMUNE and GENAERA desire to amend the Agreement in order
to modify the research plan proposed thereunder;

         NOW THEREFORE, in consideration of the promises and of the mutual
covenants and agreements herein set forth, the parties hereto agree as follows:

         1.        Appendix D of the Agreement is hereby amended by deleting it
                   in its entirety and replacing it with the Revised Joint R&D
                   Program ("Exhibit I") attached hereto and incorporated by
                   reference.

         2.        The Revised Joint R&D Program will be re-assessed in April
                   2002 and revised accordingly. Priority will given to the
                   Primary Goals, with emphasis on Primary Goal I (in vivo
                   bioassays). Secondary Goals will be addressed if Primary
                   Goals are complete and resources allow.

         This Amendment and the Agreement set forth the entire agreement and
understanding between the parties as to the subject matter thereof and
supersedes all prior agreements and understandings in this respect. There shall
be no amendments or modifications to this Amendment or the Agreement, except by
a written document which is signed by both parties.

         IN WITNESS WHEREOF, the parties have each caused this Amendment to be
signed and delivered by its duly authorized officer or representative as
indicated below.

MEDIMMUNE                                            GENAERA

By:  /s/ Peter Kiener, Ph.D.                         By: /s/ Roy C. Levitt, M.D.
    --------------------------------                     -----------------------
Name:    Peter Kiener, Ph.D.                         Name:
Title:   Vice President, Research                    Title:

Date:    1/14/02                                     Date:    1/08/02
     -------------                                        -------------

                                       1<PAGE>

                                                                   EXHIBIT 10.27

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED. IT MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE
ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT AS TO THE WARRANT UNDER SUCH ACT
OR AN OPINION OF COUNSEL SATISFACTORY TO GENAERA CORPORATION THAT SUCH
REGISTRATION IS NOT REQUIRED.

                              GENAERA CORPORATION
              WARRANT FOR THE PURCHASE OF SHARES OF COMMON STOCK

No. W-22    50,000 Shares

THIS CERTIFIES that, for value received, Genaera Corporation, a Delaware
corporation (the "Company"), upon the surrender of this Warrant to the Company
at the address specified herein, at any time during the Exercise Period (as
defined below) will upon receipt of the Exercise Price (as defined below), sell
and deliver to Ladenburg Thalmann & Co. Inc. (the "Holder") up to the number of
duly authorized, validly issued and fully paid and nonassessable shares of
common stock of the Company, par value $0.002 per share, set forth above. The
term "Common Stock" shall mean the aforementioned common stock of the Company
together with any other equity securities that may be issued by the Company in
connection therewith or in substitution therefor, as provided herein, that is
not limited as to final sum or percentage in respect of the rights of the
holders thereof to participate in dividends or in distribution of assets upon
the voluntary or involuntary liquidation, dissolution or winding up of the
Company. The "Exercise Period" shall begin on December 12, 2001 and shall end on
December 12, 2006. During the Exercise Period, the Holder may purchase such
number of shares of Common Stock at a purchase price per share equal to three
dollars and seventy nine cents ($3.79) as appropriately adjusted pursuant to
Section H hereof (the "Exercise Price") such that the Holder may purchase (1) up
to twenty-five percent of the Warrant Shares (as defined) on or after March 12,
2002 and an additional twenty-five percent of the Warrant Shares on or after
each of June 12, 2002, September 12, 2002 and December 12, 2002, or, (2) up to
one hundred percent of the Warrant Shares upon a closing of a Financing with
aggregate gross proceeds of not less than $15,000,000. "Financing" shall be
given the meaning as is set forth in the letter agreement between the Company
and the Holder dated December 12, 2001 (the "Letter Agreement"). The Letter
Agreement provides for the issuance of warrants to purchase up to 250,000 shares
of Common Stock to the Holder upon the terms and conditions set forth therein of
which this certificate represents 50,000 shares.

The number of shares of Common Stock to be received upon the exercise of this
Warrant and the price to be paid for a share of Common Stock are subject to
adjustment from time to time as hereinafter set forth. The shares of Common
Stock deliverable upon such exercise, as adjusted from time to time, are
hereinafter sometimes referred to as "Warrant Shares."

                                      -1-
<PAGE>

         Section A. Exercise of Warrant. This Warrant may be exercised in whole
         ---------  -------------------
or in part, at any time or from time to time, during the Exercise Period by
presentation and surrender hereof to the Company at its principal office at 5110
Campus Drive, Plymouth Meeting, Pennsylvania 19462 (or at such other address as
the Company or its agent may hereafter designate in writing to the Holder), or
at the office of its warrant agent, with the Notice of Exercise Form contained
herein duly executed and accompanied by wire transfer of immediately available
funds, cash or a certified or official bank check drawn to the order of "Genaera
Corporation" in the amount of the Exercise Price multiplied by the number of
Warrant Shares specified in such form. In the alternative the Holder may, at its
option, elect to pay some or all of the Exercise Price payable upon an exercise
of this Warrant by canceling all or a portion of this Warrant. If the Registered
Holder wishes to exercise this Warrant by this method, the number of Warrant
Shares purchasable (which shall in no event exceed the total number of Warrant
Shares purchasable under this Warrant as set forth above), subject to adjustment
under Section H of this Warrant) shall be determined as follows:

X= Y[(A-B)/A]; where
-------------------
X= the number of Warrant Shares to be issued to the Holder.

Y= the number of Warrant Shares with respect to which this Warrant is being
   exercised.

A= the Fair Market Value of one share of Common Stock.

B= the Exercise Price of one share of Common Stock.

The Fair Market Value per share of Common Stock shall be determined as
follows:

             (a) If the Common Stock is listed on a national securities
         exchange, the Nasdaq National Market or another nationally recognized
         trading system (including, without limitation, the OTC Bulletin Board
         and, if the average daily trading volume for the preceding 10 days has
         been at least 100,000 shares, the Pink Sheets) as of the date of
         exercise, the Fair Market Value per share of Common Stock shall be
         deemed to be the average of the high and low reported sale prices per
         share of Common Stock thereon on the trading day immediately preceding
         the date of exercise (provided that if no such price is reported on
         such day, the Fair Market Value per share of Common Stock shall be
         determined pursuant to clause (b)).

             (b) If the Common Stock is not listed on a national securities
         exchange, the Nasdaq National Market or another nationally recognized
         trading system as of the date of exercise, the Fair Market Value per
         share of Common Stock shall be deemed to be the amount most recently
         determined by the Board of Directors to represent the fair market value
         per share of the Common Stock (including without limitation a
         determination for purposes of granting Common Stock options or issuing
         Common Stock under an employee benefit plan of the Company); and, upon
         request of the Holder, the Board of Directors (or a representative
         thereof) shall promptly notify the Holder of the Fair Market Value per
         share of Common Stock. Notwithstanding the foregoing, if the Board of

                                      -2-
<PAGE>

         Directors has not made such a determination within the three-month
         period prior to the date of exercise, then (A) the Board of Directors
         shall make a determination of the Fair Market Value per share of the
         Common Stock within 15 days of a request by the Holder that it do so,
         and (B) the exercise of this Warrant pursuant to this subsection (b)
         shall be delayed until such determination is made.

If this Warrant should be exercised in part only, the Company shall, upon
surrender of this Warrant, promptly execute and deliver a new Warrant evidencing
the rights of the Holder thereof to purchase the balance of the Warrant Shares
purchasable hereunder. Upon receipt by the Company during the Exercise Period of
this Warrant and such Notice of Exercise Form, in proper form for exercise,
together with proper payment of the Exercise Price, at such office, or by the
warrant agent of the Company at its office, the Holder shall be deemed to be the
holder of record of the number of Warrant Shares specified in such form;
provided, however, that if the date of such receipt by the Company or its agent
is a date on which the stock transfer books of the Company are closed, such
person shall be deemed to have become the record holder of such shares on, and
such certificate shall be dated, the next succeeding business day on which the
stock transfer books of the Company are open. The Company shall pay any and all
documentary, stamp or similar issue or transfer taxes payable in respect of the
issue or delivery of such Warrant Shares. Any new or substitute Warrant issued
under this Section A or any other provision of this Warrant shall be dated the
date of this Warrant. Upon exercise of this Warrant, the Company or its warrant
agent shall promptly cause to be issued and shall promptly deliver upon written
order of the Holder of this Warrant, and in such name or names as such Holder
may designate, a certificate or certificates for the Warrant Shares.

Section B. Warrant Register. This Warrant will be registered in a register (the
---------  ----------------
"Warrant Register") to be maintained by the Company or its agent at its
principal office in the name of the recordholder to whom it has been
distributed. The Company may deem and treat the registered holder of this
Warrant as the absolute owner thereof (notwithstanding any notation of ownership
or other writing hereon made by anyone), for the purpose of any exercise thereof
or any distribution to the holder thereof and for all other purposes, and the
Company shall not be affected by any notice to the contrary.

Section C. Reservation of Shares. The Company hereby agrees that at all times
---------  ---------------------
there shall be reserved for issuance and delivery upon exercise of this Warrant
all shares of its Common Stock or other shares of capital stock of the Company
from time to time issuable upon exercise of this Warrant. All such shares shall
be duly authorized and, when issued upon such exercise in accordance with the
terms of this Warrant, shall be validly issued, fully paid and nonassessable,
free and clear of all liens, security interests, charges and other encumbrances
or restrictions on sale and free and clear of all preemptive rights.

Section D. Transfer of Warrant. This Warrant may not be transferred by the
---------  -------------------
Holder, except in its entirety to a wholly-owned subsidiary of the Holder, to a
party that acquires all or substantially all of the assets of the Holder or to
an Affiliate (as defined). Subject to the foregoing, this Warrant shall inure
to the benefit of the successors to the Holder (the "Transferees"). This
Warrant and all rights hereunder, in whole or in part, is registrable at the
office or agency of the Company referred to above by the Holder hereof in person
or by his duly

                                      -3-
<PAGE>

authorized attorney, upon surrender of this Warrant properly endorsed.
"Affiliate" shall mean, with respect to any Person (as defined below), any other
Person controlling, controlled by or under direct or indirect common control
with such Person (for the purposes of this definition "control," when used with
respect to any specified Person, shall mean the power to direct the management
and policies of such person, directly or indirectly, whether through ownership
of voting securities, by contract or otherwise; and the terms "controlling" and
"controlled" shall have meanings correlative to the foregoing). "Person" shall
mean any person, individual, corporation, limited liability company,
partnership, trust or other non-governmental entity or any governmental agency,
court, authority or other body (whether foreign, federal, state, local or
otherwise).

Section E. Registration of Warrant Shares. If at any time or from time to time
---------  ------------------------------
the Company shall determine to register its Common Stock, either for its own
account or for the account of any holder of the Company's Common Stock, the
Company will promptly give written notice thereof to the Holder, and include in
such registration and in any underwriting involved therein, all the Warrant
Shares specified in a written request made within 20 days after the date of such
written notice from the Company, by the Holder. If the registration of which the
Company gives notice is for a registered public offering involving an
underwriting, the Company shall so advise the Holder as a part of the written
notice set forth above. In the event that the Holder elects to participate in
any such registration, the right of the Holder to registration shall be
conditioned as follows:

         1. If the registration gives notice of an underwriting and the managing
underwriter determines that marketing factors require a limitation of the number
of shares to be underwritten, the managing underwriter may limit the number of
Warrant Shares to be included in such registration.

         2. The Holder shall furnish to the Company such information regarding
the Holder, the Warrant Shares and the distribution proposed by the Holder as
the Company may request in writing and shall be required in connection with any
registration pursuant to this Warrant. The Holder further agrees to notify the
Company promptly (i) of the sale of any Warrant Shares and (ii) in writing of
any material changes in the information set forth in the registration statement
relating to the Holder or its proposed distribution, or of any supplemental
information required to be included in the registration statement relating to
the Holder or its proposed distribution.

         3. All selling expenses relating to Warrant Shares registered on behalf
of the Holder shall be borne by the Holder. Selling expenses shall mean all
underwriting discounts, selling commissions and stock transfer taxes applicable
to the Warrant Shares registered by the Holder and all fees and disbursements of
counsel for the Holder other than the fees and disbursements for one special
counsel to the Holder or Holders.

         4. The rights of the Holder granted pursuant to this Section E shall
terminate, with respect to each Warrant Share, on the date that such Warrant
Share may immediately be sold under Rule 144 of the Securities Act of 1933, as
amended.

         5. The rights granted to the Holder under this Section E may be
assigned to a Transferee by the Holder provided that (i) such transfer is
accorded in accordance with applicable securities laws and the terms of this
Warrant, (ii) such Transferee acquires all 50,000 Warrant Shares from

                                      -4-
<PAGE>

the Holder, (iii) written notice is promptly given to the Company stating the
name and address of the Transferee and identifying the securities with respect
to which the rights are being transferred, and (iv) such Transferee agrees to
be bound by the provisions of this Section E.

         6. (i) With respect to a registration pursuant to this Section E, the
Company will indemnify the Holder, each of its officers, directors, partners and
each person controlling such Holder (each, a "Holder Indemnitee") against all
expenses, claims, losses, damages or liabilities arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any registration statement, prospectus, circular or other document, or any
amendment or supplement thereto, incident to any such registration, or based on
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading, or any violation by the
Company of any securities law applicable to any such registration, and the
Company will reimburse the Holder, each of its directors, officers, partners and
each person controlling such Holder for any legal and other expenses reasonably
incurred in connection with investigating, preparing or defending any such
claim, loss, damage, liability or action; provided, however, that the Company
shall not be liable in any case to the extent that any such loss, claim, damage
or liability arises out of or is based upon any untrue statement (or alleged
untrue statement) or omission (or alleged omission) made in such registration
statement, prospectus, circular or other document, or any amendment or
supplement thereto, in reliance upon and in conformity with information
furnished by any Holder Indemnitee to the Company for use in the preparation
thereof. (ii) With respect to a registration pursuant to this Section E, the
Holder will indemnify the Company, each of its officers, directors, each person
controlling the Company and each other holder of the Company's securities
covered by such registration statement, each of such other holder's officers,
directors, partners and each person controlling such other holder against all
expenses, claims, losses, damages or liabilities arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any registration statement, prospectus, circular or other document, or any
amendment or supplement thereto, incident to any such registration, or based on
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading, or any violation by the
Holder of any securities law applicable to any such registration, and the Holder
will reimburse the Company, such other holders, such directors, officers,
partners or control persons for any legal and other expenses reasonably incurred
in connection with investigating, preparing or defending any such claim, loss,
damage, liability or action but only to the extent that such untrue statement
(or alleged untrue statement) or omission (or alleged omission) is made in such
registration statement, prospectus, circular or document in reliance upon and in
conformity with information furnished to the Company by a written instrument
duly executed by the Holder and stated to be specifically for use therein.

Section F. Lost, Mutilated or Missing Warrant. Upon receipt by the Company of
---------  ----------------------------------
evidence reasonably satisfactory to it of the loss, theft, destruction or
mutilation of this Warrant, and (in the case of loss, theft or destruction) of
reasonably satisfactory indemnification, and upon surrender and cancellation of
this Warrant, if mutilated, the Company, at its expense, shall execute and
deliver a new Warrant of like tenor and date.

                                      -5-
<PAGE>

Section G. Rights of the Holder. Subject to applicable law, the Holder shall
---------  --------------------
not, by virtue hereof, be entitled to any rights or subject to any obligation or
liability of a shareholder in the Company, either at law or equity, and the
rights of the Holder are limited to those expressed in this Warrant.

Section H. Adjustments. The Exercise Price and the number of shares purchasable
---------  -----------
hereunder are subject to adjustment from time to time as follows:

     1. Stock Dividend, Split or Subdivision of Shares. If the number of shares
        ----------------------------------------------
     of Common Stock outstanding at any time after the date hereof is increased
     by a stock dividend payable to all holders of Common Stock in shares of
     Common Stock or by a subdivision or split-up of shares of Common Stock,
     then, following the record date fixed for the determination of holders of
     Common Stock entitled to receive such stock dividend, subdivision or
     split-up, the Exercise Price shall be appropriately decreased and the
     number of shares of Common Stock issuable on exercise of each Warrant shall
     be increased in proportion to such increase in outstanding shares.

     2. Combination of Shares. If, at any time after the date hereof, the number
        ---------------------
     of shares of Common Stock outstanding is decreased by a combination or
     consolidation of the outstanding shares of Common Stock, by
     reclassification, reverse stock split or otherwise, then, following the
     record date for such combination, the Exercise Price shall be appropriately
     increased and the number of shares of Common Stock issuable on exercise of
     each Warrant shall be decreased in proportion to such decrease in
     outstanding shares.

     3. Calculations. All calculations under this Section shall be made to the
        ------------
     nearest one-tenth of a cent ($.001), or to the nearest one-tenth of a
     share, as the case may be.

     4. Merger and Consolidation. If at any time there is a capital
        ------------------------
     reorganization or reclassification of shares of Common Stock, or a merger
     or consolidation of the Company with or into another corporation where the
     Company is not the surviving corporation, or the sale of all or
     substantially all of the Company's properties and assets to anyother
     person, then as part of such reorganization, merger, consolidation
     or sale, lawful provision shall be made so that the Holder shall thereafter
     be entitled to receive upon exercise of its rights to purchase Common
     Stock, the number of shares of Common Stock, cash, property or shares of
     the successor corporation resulting from such merger or consolidation, to
     which a holder of Common Stock, deliverable upon exercise of the rights to
     purchase Common Stock hereunder, would have been entitled in such capital
     reorganization, merger or consolidation or sale if the right to purchase
     such Common Stock hereunder had been exercised immediately prior to such
     capital reorganization, merger, consolidation or sale. In any such event,
     appropriate adjustment shall be made in the application of the provisions
     of this Warrant with respect to the rights and interests of the Holder
     after such capital reorganization, merger, consolidation or sale so that
     the provisions of this Warrant (including Exercise Price and the number of
     shares of Common Stock purchasable pursuant to the terms and conditions of
     this Warrant) shall be applicable after that event as near as reasonably
     may be, in relation to any shares deliverable upon the exercise of the
     Holder's rights to purchase Common Stock pursuant to this Warrant.

                                      -6-
<PAGE>

     5. Certificate as to Adjustments. Upon the occurrence of each adjustment or
        -----------------------------
     readjustment pursuant to this Section H, the Company, at its own expense,
     shall promptly compute such adjustment or readjustment in accordance with
     the terms hereof and furnish to each Holder a certificate setting forth
     such adjustment or readjustment and showing in detail the facts upon which
     such adjustment or readjustment is based. The Company shall, upon the
     written request, at any time, of any such Holder, furnish or cause to be
     furnished to such Holder a like certificate setting forth: (a) such
     adjustments and readjustments; (b) the Exercise Price at the time in
     effect; and (c) the number of shares and the amount, if any of other
     property that at the time would be received upon the exercise of the
     Warrant.

Section I.  Fractional Shares. No fractional shares of the Company's Common
---------   -----------------
Stock will be issued in connection with any purchase hereunder but in lieu of
such fractional shares the Company shall make a cash refund therefor equal in
amount to the product of the applicable fraction multiplied by the Exercise
Price paidby the Holder for one Warrant Share upon such exercise.

Section J.  Notices of Certain Events. In the event:
---------   -------------------------

     1. the Company authorizes the issuance to all holders of its Common Stock
     of rights or warrants to subscribe for or purchase shares of its Common
     Stock or of any other subscription rights or warrants; or

     2. the Company authorizes the distribution to all holders of its Common
     Stock of evidences of its indebtedness or assets (other than cash dividends
     or distributions except extraordinary cash dividends or distributions); or

     3. of any capital reorganization or reclassification of the Common Stock
     (other than a subdivision or combination of the outstanding Common Stock
     and other than a change in par value of the Common Stock) or of any
     consolidation or merger to which the Company is a party or of the
     conveyance or transfer of all or substantially all of the properties and
     assets of the Company; or

     4. of the voluntary or involuntary dissolution, liquidation or winding-up
     of the Company; or

     5. any other actions would require an adjustment under Section G hereof;

then the Company will cause to be mailed to the Holder, at least 5 days before
the applicable record or effective date hereinafter specified, a notice stating
(A) the date as of which the holders of Common Stock of record entitled to
receive any such rights, warrants or distributions are to be determined, or (B)
the date on which any such consolidation, merger, conveyance, transfer,
dissolution, liquidation or winding-up is expected to become effective, and the
date as of which it is expected that holders of Common Stock of record will be
entitled to exchange their shares of Common Stock for securities or other
property, if any, deliverable upon such reorganization, reclassification,
consolidation, merger, conveyance, transfer, dissolution, liquidation or
winding-up.

Section K. Listing on Securities Exchanges. The Company will list on
---------  -------------------------------
the Nasdaq National Market System and each national securities exchange on which
any Common Stock may at any time be listed all shares of Common Stock from time
to time issuable upon the exercise of this

                                      -7-
<PAGE>

Warrant, subject to official notice of issuance upon the exercise of this
Warrant, and will maintain such listing so long as any other shares of its
Common Stock are so listed; and the Company shall so list on the Nasdaq National
Market System and each national securities exchange, and shall maintain such
listing of, any other shares of capital stock of the Company issuable upon the
exercise of this Warrant if and so long as any shares of capital stock of the
same class are listed on the Nasdaq National Market System and such national
securities exchange by the Company. Any such listing will be at the Company's
expense.

Section L. Successors. All the provisions of this Warrant by or for the benefit
---------  ----------
of the Company shall bind and inure to the benefit of its respective successors
and assigns.

Section M. Headings. The headings of sections of this Warrant have been inserted
---------  --------
for convenience of reference only, are not to be considered a part
hereof and shall in no way modify or restrict any of the terms or provisions
hereof.

Section N. Amendments. The terms and provisions of this Warrant may not be
---------  ----------
modified or amended, or any provisions hereof waived, temporarily
or permanently, except by written consent of the Company and the Holder
hereof.

Section O. Notices. Unless otherwise provided in this Warrant, all notices,
---------  -------
requests, consents and other communications hereunder shall be in writing, shall
be sent by U.S. Mail or a nationally recognized overnight express courier
postage prepaid, and shall be deemed given one day after being so sent, or if
delivered by hand shall be deemed given on the date of such delivery to such
party, or if sent to such party (in the case of a Holder) at its address in the
Warrant Register that will be maintained by the Company or its agent in
accordance with Section B hereof or (in the case of the Company) at its address
set forth above, Attention: Chief Financial Officer, or to such other address as
is designated by written notice, similarly given to each other party hereto.

Section P. Governing Law. This Warrant shall be deemed to be a contract made
---------  -------------
under the laws of the Commonwealth of Pennsylvania and for all purposes shall be
construed in accordance with the laws of said Commonwealth as applied to
contracts made and to be performed in Pennsylvania between Pennsylvania
residents.

IN WITNESS WHEREOF, the Company has duly caused this Warrant to be signed and
attested by its duly authorized officer and to be dated as of December 12, 2001.

                               GENAERA CORPORATION

                               By: /s/ Roy Clifford Levitt, M.D.
                                   -----------------------------
                               Name:  Roy Clifford Levitt, M.D.
                               Title: President and Chief Executive Officer

                                      -8-
<PAGE>

                              NOTICE OF EXERCISE

                                                          Date: _________, 20__

The undersigned hereby elects to exercise this Warrant to purchase ____ shares
of Common Stock and hereby makes payment of $____________ in payment of the
exercise price thereof.

                                LADENBURG THALMANN & CO. INC.

                                By: ________________________________
                                Name:
                                Title:

                                      -9-
<PAGE>

THIS WARRANT HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
AMENDED. IT MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR HYPOTHECATED IN THE
ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT AS TO THE WARRANT UNDER SUCH ACT
OR AN OPINION OF COUNSEL SATISFACTORY TO GENAERA CORPORATION THAT SUCH
REGISTRATION IS NOT REQUIRED.

                              GENAERA CORPORATION

              WARRANT FOR THE PURCHASE OF SHARES OF COMMON STOCK

No. W-23    200,000 Shares

THIS CERTIFIES that, for value received, Genaera Corporation, a Delaware
corporation (the "Company"), upon the surrender of this Warrant to the Company
at the address specified herein, at any time during the Exercise Period (as
defined below) will upon receipt of the Exercise Price (as defined below), sell
and deliver to Ladenburg Thalmann & Co. Inc. (the "Holder") up to the number of
duly authorized, validly issued and fully paid and nonassessable shares of
common stock of the Company, par value $0.002 per share, set forth above. The
term "Common Stock" shall mean the aforementioned common stock of the Company
together with any other equity securities that may be issued by the Company in
connection therewith or in substitution therefor, as provided herein, that is
not limited as to final sum or percentage in respect of the rights of the
holders thereof to participate in dividends or in distribution of assets upon
the voluntary or involuntary liquidation, dissolution or winding up of the
Company. The "Exercise Period" shall begin on December 12, 2001 and shall end on
the December 12, 2006. During the Exercise Period, the Holder may purchase such
number of shares of Common Stock at a purchase price per share equal to three
dollars and seventy nine cents ($3.79) as appropriately adjusted pursuant to
Section H hereof (the "Exercise Price") such that the Holder may purchase (1) up
to 50,000 shares of Common Stock on or after the closing of a Financing (as
defined in the letter agreement between the Company and the Holder dated
December 12, 2001 (the "Letter Agreement") with aggregate gross proceeds to the
Company of at least $28,000,000 and for which the Holder is compensated in
accordance with Section (a) of the Letter Agreement, or (2) up to 100,000 shares
of Common Stock on or after the closing of a Financing with gross proceeds to
the Company of at least $36,000,000 and for which the Holder is compensated in
accordance with Section (a) of the Letter Agreement, or (3) up to 150,000 shares
of Common Stock on or after the closing of a Financing with aggregate gross
proceeds to the Company of at least $45,000,000 and for which the Holder is
compensated in accordance with Section (a) of the Letter Agreement, or (4) up to
200,000 shares of Common Stock on or after the closing of a Financing with
aggregate gross proceeds to the Company of at least $50,000,000 and for which
the Holder is compensated in accordance with Section (a) of the Letter
Agreement. In the event that more than one Financing is consummated prior to the
termination of the Letter Agreement, upon the closing of any subsequent
Financing the Holder may exercise this Warrant for such

                                     - 1 -
<PAGE>

additional number of shares of Common Stock as is equal to the difference
between the number of shares for which this Warrant would have been exercisable
based on a Financing with gross proceeds to the Company equal to the aggregate
gross proceeds of all prior and the subsequent Financing and the number of
shares for which this Warrant was exercisable based on the gross proceeds to
the Company based on all prior Financings. The Letter Agreement provides for
the issuance of warrants to purchase up to 250,000 shares of Common Stock to
the Holder upon the terms and conditions set forth therein of which this
certificate represents up to 200,000 shares.

The number of shares of Common Stock to be received upon the exercise of this
Warrant and the price to be paid for a share of Common Stock are subject to
adjustment from time to time as hereinafter set forth. The shares of Common
Stock deliverable upon such exercise, as adjusted from time to time, are
hereinafter sometimes referred to as "Warrant Shares."

         Section A. Exercise of Warrant. This Warrant may be exercised in whole
         ---------  -------------------
or in part, at any time or from time to time, during the Exercise Period by
presentation and surrender hereof to the Company at its principal office at 5110
Campus Drive, Plymouth Meeting, Pennsylvania 19462 (or at such other address as
the Company or its agent may hereafter designate in writing to the Holder), or
at the office of its warrant agent, with the Notice of Exercise Form contained
herein duly executed and accompanied by wire transfer of immediately available
funds, cash or a certified or official bank check drawn to the order of "Genaera
Corporation" in the amount of the Exercise Price multiplied by the number of
Warrant Shares specified in such form. In the alternative, the Holder may, at
its option, elect to pay some or all of the Exercise Price payable upon an
exercise of this Warrant by canceling all or a portion of this Warrant. If the
Registered Holder wishes to exercise this Warrant by this method, the number of
Warrant Shares purchasable (which shall in no event exceed the total number of
Warrant Shares purchasable under this Warrant as set forth above), subject to
adjustment under Section H of this Warrant) shall be determined as follows:

X= Y[(A-B)/A]; where
X= the number of Warrant Shares to be issued to the Holder.
Y= the number of Warrant Shares with respect to which this Warrant is being
   exercised.
A= the Fair Market Value of one share of Common Stock.
B= the Exercise Price of one share of Common Stock.

                                     - 2 -
<PAGE>

The Fair Market Value per share of Common Stock shall be determined as
follows:

                  (a) If the Common Stock is listed on a national securities
         exchange, the Nasdaq National Market or another nationally recognized
         trading system (including, without limitation, the OTC Bulletin Board
         and, if the average daily trading volume for the preceding 10 days has
         been at least 100,000 shares, the Pink Sheets) as of the date of
         exercise, the Fair Market Value per share of Common Stock shall be
         deemed to be the average of the high and low reported sale prices per
         share of Common Stock thereon on the trading day immediately preceding
         the date of exercise (provided that if no such price is reported on
         such day, the Fair Market Value per share of Common Stock shall be
         determined pursuant to clause (b)).

                   (b) If the Common Stock is not listed on a national
         securities exchange, the Nasdaq National Market or another nationally
         recognized trading system as of the date of exercise, the Fair Market
         Value per share of Common Stock shall be deemed to be the amount most
         recently determined by the Board of Directors to represent the fair
         market value per share of the Common Stock (including without
         limitation a determination for purposes of granting Common Stock
         options or issuing Common Stock under an employee benefit plan of the
         Company); and, upon request of the Holder, the Board of Directors (or a
         representative thereof) shall promptly notify the Holder of the Fair
         Market Value per share of Common Stock. Notwithstanding the foregoing,
         if the Board of Directors has not made such a determination within the
         three-month period prior to the date of exercise, then (A) the Board of
         Directors shall make a determination of the Fair Market Value per share
         of the Common Stock within 15 days of a request by the Holder that it
         do so, and (B) the exercise of this Warrant pursuant to this subsection
         (b) shall be delayed until such determination is made.

If this Warrant should be exercised in part only, the Company shall, upon
surrender of this Warrant, promptly execute and deliver a new Warrant evidencing
the rights of the Holder thereof to purchase the balance of the Warrant Shares
purchasable hereunder. Upon receipt by the Company during the Exercise Period of
this Warrant and such Notice of Exercise Form, in proper form for exercise,
together with proper payment of the Exercise Price, at such office, or by the
warrant agent of the Company at its office, the Holder shall be deemed to be the
holder of record of the number of Warrant Shares specified in such form;
provided, however, that if the date of such receipt by the Company or its agent
is a date on which the stock transfer books of the Company are closed, such
person shall be deemed to have become the record holder of such shares on, and
such certificate shall be dated, the next succeeding business day on which the
stock transfer books of the Company are open. The Company shall pay any and all
documentary, stamp or similar issue or transfer taxes payable in respect of the
issue or delivery of such Warrant Shares. Any new or substitute Warrant issued
under this Section A or any other provision of this Warrant shall be dated the
date of this Warrant. Upon exercise of this Warrant, the Company or its warrant
agent shall promptly cause to be issued and shall promptly deliver upon written
order of the Holder of this Warrant, and in such name or names as such Holder
may designate, a certificate or certificates for the Warrant Shares.

                                      - 3 -
<PAGE>

Section B. Warrant Register. This Warrant will be registered in a register (the
---------  ----------------
"Warrant Register") to be maintained by the Company or its agent at its
principal office in the name of the recordholder to whom it has been
distributed. The Company may deem and treat the registered holder of this
Warrant as the absolute owner thereof (notwithstanding any notation of ownership
or other writing hereon made by anyone), for the purpose of any exercise thereof
or any distribution to the holder thereof and for all other purposes, and the
Company shall not be affected by any notice to the contrary.

Section C. Reservation of Shares. The Company hereby agrees that at all times
---------  ---------------------
there shall be reserved for issuance and delivery upon exercise of this Warrant
all shares of its Common Stock or other shares of capital stock of the Company
from time to time issuable upon exercise of this Warrant. All such shares shall
be duly authorized and, when issued upon such exercise in accordance with the
terms of this Warrant, shall be validly issued, fully paid and nonassessable,
free and clear of all liens, security interests, charges and other encumbrances
or restrictions on sale and free and clear of all preemptive rights.

Section D. Transfer of Warrant. This Warrant may not be transferred by the
---------  -------------------
Holder, except in its entirety to a wholly-owned subsidiary of the Holder, to
a party that acquires all or substantially all of the assets of the Holder or to
an Affiliate (as defined). Subject to the foregoing, this Warrant shall inure to
the benefit of the successors to the Holder (the "Transferees"). This Warrant
and all rights hereunder, in whole or in part, is registrable at the office or
agency of the Company referred to above by the Holder hereof in person or by his
duly authorized attorney, upon surrender of this Warrant properly endorsed.
"Affiliate" shall mean, with respect to any Person (as defined below), any other
Person controlling, controlled by or under direct or indirect common control
with such Person (for the purposes of this definition "control," when used
with respect to any specified Person, shall mean the power to direct the
management and policies of such person, directly or indirectly, whether through
ownership of voting securities, by contract or otherwise; and the terms
"controlling" and "controlled" shall have meanings correlative to the
foregoing). "Person" shall mean any person, individual, corporation, limited
liability company, partnership, trust or other non-governmental entity or any
governmental agency, court, authority or other body (whether foreign, federal,
state, local or otherwise).

Section E. Registration of Warrant Shares. If at any time or from time to time
---------  ------------------------------
the Company shall determine to register its Common Stock, either for its own
account or for the account of any holder of the Company's Common Stock, the
Company will promptly give written notice thereof to the Holder, and include in
such registration and in any underwriting involved therein, all the Warrant
Shares specified in a written request made within 20 days after the date of such
written notice from the Company, by the Holder. If the registration of which the
Company gives notice is for a registered public offering involving an
underwriting, the Company shall so advise the Holder as a part of the written
notice set forth above. In the event that the Holder elects to participate in
any such registration, the right of the Holder to registration shall be
conditioned as follows:

         1.    If the registration gives notice of an underwriting and the
managing underwriter determines that marketing factors require a limitation of
the number of shares to be underwritten, the managing underwriter may limit the
number of Warrant Shares to be included in such

                                     - 4 -
<PAGE>

registration.

         2.    The Holder shall furnish to the Company such information
regarding the Holder, the Warrant Shares and the distribution proposed by the
Holder as the Company may request in writing and shall be required in connection
with any registration pursuant to this Warrant. The Holder further agrees to
notify the Company promptly (i) of the sale of any Warrant Shares and (ii) in
writing of any material changes in the information set forth in the registration
statement relating to the Holder or its proposed distribution, or of any
supplemental information required to be included in the registration statement
relating to the Holder or its proposed distribution.

         3.    All selling expenses relating to Warrant Shares registered on
behalf of the Holder shall be borne by the Holder. Selling expenses shall mean
all underwriting discounts, selling commissions and stock transfer taxes
applicable to the Warrant Shares registered by the Holder and all fees and
disbursements of counsel for the Holder other than the fees and disbursements
for one special counsel to the Holder or Holders.

         4. The rights of the Holder granted pursuant to this Section E shall
terminate, with respect to each Warrant Share, on the date that such
Warrant Share may immediately be sold under Rule 144 of the Securities Act of
1933, as amended.

         5. The rights granted to the Holder under this Section E may be
assigned to a Transferee by the Holder provided that (i) such transfer is
accorded in accordance with applicable securities laws and the terms of this
Warrant, (ii) such Transferee acquires at least 50,000 Warrant Shares from the
Holder, (iii) written notice is promptly given to the Company stating the name
and address of the Transferee and identifying the securities with respect to
which the rights are being transferred, and (iv) such Transferee agrees to be
bound by the provisions of this Section E.

         6. (i) With respect to a registration pursuant to this Section E, the
Company will indemnify the Holder, each of its officers, directors, partners and
each person controlling such Holder (each, a "Holder Indemnitee") against all
expenses, claims, losses, damages or liabilities arising out of or based on any
untrue statement (or alleged untrue statement) of a material fact contained in
any registration statement, prospectus, circular or other document, or any
amendment or supplement thereto, incident to any such registration, or based on
any omission (or alleged omission) to state therein a material fact required to
be stated therein or necessary to make the statements therein, in light of the
circumstances in which they were made, not misleading, or any violation by the
Company of any securities law applicable to any such registration, and the
Company will reimburse the Holder, each of its directors, officers, partners and
each person controlling such Holder for any legal and other expenses reasonably
incurred in connection with investigating, preparing or defending any such
claim, loss, damage, liability or action; provided, however, that the Company
shall not be liable in any case to the extent that any such loss, claim, damage
or liability arises out of or is based upon any untrue statement (or alleged
untrue statement) or omission (or alleged omission) made in such registration
statement, prospectus, circular or other document, or any amendment or
supplement thereto, in reliance upon and in conformity with information
furnished by any Holder Indemnitee to the Company for use in the preparation
thereof. (ii) With respect to a registration pursuant to this Section E, the
Holder will indemnify the Company, each of its officers, directors, each person
controlling the Company and each other holder of the Company's securities
covered by such registration statement, each of such other holder's officers,
directors, partners and each person controlling

                                     - 5 -
<PAGE>

such other holder against all expenses, claims, losses, damages or liabilities
arising out of or based on any untrue statement (or alleged untrue statement) of
a material fact contained in any registration statement, prospectus, circular or
other document, or any amendment or supplement thereto, incident to any such
registration, or based on any omission (or alleged omission) to state therein a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances in which they were made, not misleading,
or any violation by the Holder of any securities law applicable to any such
registration, and the Holder will reimburse the Company, such other holders,
such directors, officers, partners or control persons for any legal and other
expenses reasonably incurred in connection with investigating, preparing or
defending any such claim, loss, damage, liability or action but only to the
extent that such untrue statement (or alleged untrue statement) or omission (or
alleged omission) is made in such registration statement, prospectus, circular
or document in reliance upon and in conformity with information furnished to
the Company by a written instrument duly executed by the Holder and stated to
be specifically for use therein.

Section F. Lost, Mutilated or Missing Warrant. Upon receipt by the Company
---------  ----------------------------------
of evidence reasonably satisfactory to it of the loss, theft, destruction
or mutilation of this Warrant, and (in the case of loss, theft or destruction)
of reasonably satisfactory indemnification, and upon surrender and cancellation
of this Warrant, if mutilated, the Company, at its expense, shall execute and
deliver a new Warrant of like tenor and date.

Section G. Rights of the Holder. Subject to applicable law, the Holder shall
---------  --------------------
not, by virtue hereof, be entitled to any rights or subject to any obligation
or liability of a shareholder in the Company, either at law or equity, and the
rights of the Holder are limited to those expressed in this Warrant.

Section H. Adjustments. The Exercise Price and the number of shares purchasable
---------  -----------
hereunder are subject to adjustment from time to time as follows:

     1. Stock Dividend, Split or Subdivision of Shares. If the number of shares
        ----------------------------------------------
     of Common Stock outstanding at any time after the date hereof is increased
     by a stock dividend payable to all holders of Common Stock in shares of
     Common Stock or by a subdivision or split-up of shares of Common Stock,
     then, following the record date fixed for the determination of holders of
     Common Stock entitled to receive such stock dividend, subdivision or
     split-up, the Exercise Price shall be appropriately decreased and the
     number of shares of Common Stock issuable on exercise of each Warrant shall
     be increased in proportion to such increase in outstanding shares.

     2. Combination of Shares. If, at any time after the date hereof, the number
        ---------------------
     of shares of Common Stock outstanding is decreased by a combination or
     consolidation of the outstanding shares of Common Stock, by
     reclassification, reverse stock split or otherwise, then, following the
     record date for such combination, the Exercise Price shall be appropriately
     increased and the number of shares of Common Stock issuable on exercise of
     each Warrant shall be decreased in proportion to such decrease in
     outstanding shares.

     3. Calculations. All calculations under this Section shall be made to the
        ------------
     nearest one-tenth of a cent ($.001), or to the nearest one-tenth of a
     share, as the case may be.

                                     - 6 -
<PAGE>

     4. Merger and Consolidation. If at any time there is a capital
        ------------------------
     reorganization or reclassification of shares of Common Stock, or a
     merger or consolidation of the Company with or into another corporation
     where the Company is not the surviving corporation, or the sale of all
     or substantially all of the Company's properties and assets  to any
     other person, then as part of such reorganization, merger,
     consolidation or sale, lawful provision shall be made so that the Holder
     shall thereafter be entitled to receive upon exercise of its rights to
     purchase Common Stock, the number of shares of Common Stock, cash, property
     or shares of the successor corporation resulting from such merger or
     consolidation, to which a holder of Common Stock, deliverable upon exercise
     of the rights to purchase Common Stock hereunder, would have been entitled
     in such capital reorganization, merger or consolidation or sale if the
     right to purchase such Common Stock hereunder had been exercised
     immediately prior to such capital reorganization, merger, consolidation or
     sale. In any such event, appropriate adjustment shall be made in the
     application of the provisions of this Warrant with respect to the rights
     and interests of the Holder after such capital reorganization, merger,
     consolidation or sale so that the provisions of this Warrant (including
     Exercise Price and the number of shares of Common Stock purchasable
     pursuant to the terms and conditions of this Warrant) shall be applicable
     after that event as near as reasonably may be, in relation to any shares
     deliverable upon the exercise of the Holder's rights to purchase Common
     Stock pursuant to this Warrant.

     5. Certificate as to Adjustments. Upon the occurrence of each adjustment or
        -----------------------------
     readjustment pursuant to this Section G, the Company, at its own expense,
     shall promptly compute such adjustment or  readjustment in accordance
     with the terms hereof and furnish to each Holder a certificate setting
     forth such adjustment or readjustment and showing in detail the facts upon
     which such adjustment or readjustment is based. The Company shall, upon the
     written request, at any time, of any such Holder, furnish or cause to be
     furnished to such Holder a like certificate setting forth: (a) such
     adjustments and readjustments; (b) the Exercise Price at the time in
     effect; and (c) the number of shares and the amount, if any of other
     property that at the time would be received upon the exercise of the
     Warrant.

Section I.  Fractional Shares. No fractional shares of the Company's Common
---------   -----------------
Stock will be issued in connection with any purchase hereunder but in lieu of
such fractional shares the Company shall make a cash refund therefor equal in
amount to the product of the applicable fraction multiplied by the Exercise
Price paid by the Holder for one Warrant Share upon such exercise.

Section J. Notices of Certain Events. In the event:
---------  -------------------------
     1. the Company authorizes the issuance to all holders of its Common Stock
     of rights or warrants to subscribe for or purchase shares of its Common
     Stock or of any other subscription rights or warrants; or

     2. the Company authorizes the distribution to all holders of its Common
     Stock of evidences of its indebtedness or assets (other than cash dividends
     or distributions except extraordinary cash dividends or distributions); or

     3. of any capital reorganization or reclassification of the Common Stock
     (other than a subdivision or combination of the outstanding Common Stock
     and other than a change in par

                                     - 7 -
<PAGE>

     value of the Common Stock) or of any consolidation or merger to which the
     Company is a party or of the conveyance or transfer of all or substantially
     all of the properties and assets of the Company; or

    4. of the voluntary or involuntary dissolution, liquidation or winding-up of
    the Company; or

    5. any other actions would require an adjustment under Section G hereof;

then the Company will cause to be mailed to the Holder, at least 5 days before
the applicable record or effective date hereinafter specified, a notice stating
(A) the date as of which the holders of Common Stock of record entitled to
receive any such rights, warrants or distributions are to be determined, or (B)
the date on which any such consolidation, merger, conveyance, transfer,
dissolution, liquidation or winding-up is expected to become effective, and the
date as of which it is expected that holders of Common Stock of record will be
entitled to exchange their shares of Common Stock for securities or other
property, if any, deliverable upon such reorganization, reclassification,
consolidation, merger, conveyance, transfer, dissolution, liquidation or
winding-up.

Section K. Listing on Securities Exchanges. The Company will list on
---------  -------------------------------
the Nasdaq National Market System and each national securities exchange on which
any Common Stock may at any time be listed all shares of Common Stock from time
to time issuable upon the exercise of this Warrant, subject to official notice
of issuance upon the exercise of this Warrant, and will maintain such listing so
long as any other shares of its Common Stock are so listed; and the Company
shall so list on the Nasdaq National Market System and each national securities
exchange, and shall maintain such listing of, any other shares of capital stock
of the Company issuable upon the exercise of this Warrant if and so long as any
shares of capital stock of the same class are listed on the Nasdaq National
Market System and such national securities exchange by the Company. Any such
listing will be at the Company's expense.

Section L. Successors. All the provisions of this Warrant by or for the benefit
---------  ----------
of the Company shall bind and inure to the benefit of its respective successors
and assigns.

Section M. Headings. The headings of sections of this Warrant have been inserted
---------  --------
for convenience of reference only, are not to be considered a part hereof and
shall in no way modify or restrict any of the terms or provisions hereof.

Section N. Amendments. The terms and provisions of this Warrant may not be
---------  ----------
modified or amended, or any provisions hereof waived, temporarily or
permanently, except by written consent of the Company and the Holder hereof.

Section O. Notices. Unless otherwise provided in this Warrant, all notices,
---------  -------
requests, consents and other communications hereunder shall be in writing, shall
be sent by U.S. Mail or a nationally recognized overnight express courier
postage prepaid, and shall be deemed given one day after being so sent, or if
delivered by hand shall be deemed given on the date of such delivery to such
party, or if sent to such party (in the case of a Holder) at its address in the
Warrant Register that will be maintained by the Company or its agent in
accordance with Section B hereof or (in the case of the Company) at its address
set forth above, Attention: Chief Financial Officer, or to such other address as
is designated by written notice, similarly given to each other party hereto.

                                     - 8 -
<PAGE>

Section P. Governing Law. This Warrant shall be deemed to be a contract made
---------  -------------
under the laws of the Commonwealth of Pennsylvania and for all purposes shall be
construed in accordance with the laws of said Commonwealth as applied to
contracts made and to be performed in Pennsylvania between Pennsylvania
residents.

IN WITNESS WHEREOF, the Company has duly caused this Warrant to be signed and
attested by its duly authorized officer and to be dated as of December 12, 2001.

                               GENAERA CORPORATION

                               By: /s/ Roy Clifford Levitt, M.D.
                                   -----------------------------
                               Name:  Roy Clifford Levitt, M.D.
                               Title: President and Chief Executive Officer

                                     - 9 -
<PAGE>

                               NOTICE OF EXERCISE

                                                             Date: ______, 20__

The undersigned hereby elects to exercise this Warrant to purchase ____ shares
of Common Stock and hereby makes payment of $____________ in payment of the
exercise price thereof.

                                                 LADENBURG THALMANN & CO. INC.

                                                 By:__________________________
                                                 Name:
                                                 Title:

                                    - 10 -

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