Document:

EXHIBIT 4.11

THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE NOT TRANSFERABLE WITHOUT THE
EXPRESS WRITTEN CONSENT OF KERYX BIOPHARMACEUTICALS, INC. (THE "COMPANY") AND
HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933 OR ANY APPLICABLE
STATE SECURITIES LAWS, AND MAY NOT BE SOLD, OFFERED FOR SALE, PLEDGED OR
HYPOTHECATED OR OTHERWISE TRANSFERRED IN THE ABSENCE OF A REGISTRATION STATEMENT
IN EFFECT WITH RESPECT TO THE SECURITIES UNDER SUCH ACT OR AN EXEMPTION
THEREFROM. ANY SUCH TRANSFER MAY ALSO BE SUBJECT TO APPLICABLE STATE SECURITIES
LAWS.

                         KERYX BIOPHARMACEUTICALS, INC.

                      Warrant for the Purchase of Shares of
                                  Common Stock

No. 1                                                         200,000 Shares

            FOR VALUE RECEIVED, KERYX BIOPHARMACEUTICALS, INC., a Delaware
corporation (the "Company"), hereby certifies that YISSUM RESEARCH DEVELOPMENT
COMPANY OF THE HEBREW UNIVERSITY OF JERUSALEM or its registered assigns (the
"Holder") is entitled to purchase from the Company, subject to the provisions of
this Warrant, at any time commencing upon the date (the "Vesting Date") of the
issuance by the United States Patent and Trademark Office ("USPTO") of the first
patent arising from the invention described in the utility patent application
entitled NEW HETEROCYCLIC COMPOUNDS, METHOD OF DEVELOPING NEW DRUG LEADS AND
COMBINATORIAL LIBRARIES USED IN SUCH METHOD, filed with the USPTO on January 3,
2002, and prior to 5:00 P.M., New York City time, on January 9, 2012 (the
"Termination Date"), Two Hundred Thousand (200,000) fully paid and
non-assessable shares of the Common Stock, $.001 par value, of the Company
("Common Stock") at an initial per share exercise price equal to $6.19, or an
initial aggregate exercise price of $1,382,000.00. The number of shares of
Common Stock to be received upon exercise of this Warrant and the price to be
paid for each share of Common Stock are subject to possible adjustment from time
to time as hereinafter set forth. The shares of Common Stock or other securities
or property deliverable upon such exercise as adjusted from time to time is
hereinafter sometimes referred to as the "Warrant Shares," the exercise price of
a share of Common Stock in effect at any time and as adjusted from time to time
is hereinafter sometimes referred to as the "Per Share Exercise Price" and the
aggregate purchase price payable for the Warrant Shares hereunder is hereinafter
sometimes referred to as the "Aggregate Exercise Price." The Aggregate Exercise
Price is not subject to adjustment. The Per Share Exercise Price is subject to
adjustment as hereinafter provided; in the event of any such adjustment, the
number of Warrant Shares shall be adjusted by dividing the Aggregate Exercise
Price by the Per Share Exercise Price in effect immediately after such
adjustment. This Warrant is one of a duly authorized issue of Warrants
constituting components of units being sold by the Company on the date hereof
(collectively, the "Warrants").

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      1. Exercise of Warrant.

      (a) This Warrant is not transferable and may not be assigned or otherwise
disposed of by the Holder until the Vesting Date.

      (b) This Warrant may be exercised in whole or in part, at any time by the
Holder commencing upon the Vesting Date and prior to the Termination Date:

      (i) by presentation and surrender of this Warrant (with the subscription
form at the end hereof duly executed) at the address set forth in Subsection
8(a) hereof, together with payment, by certified or official bank check payable
to the order of the Company, of the Aggregate Exercise Price or the
proportionate part thereof if exercised in part.

      (ii) by the surrender of this Warrant (with the cashless exercise form at
the end hereof duly executed) (a "Cashless Exercise") at the address set forth
in Section 8(a) hereof. Such presentation and surrender shall be deemed a waiver
of the Holder's obligation to pay the Aggregate Exercise Price, or the
proportionate part thereof if this Warrant is exercised in part. In the event of
a Cashless Exercise, the Holder shall exchange its Warrant for that number of
Warrant Shares subject to such Cashless Exercise multiplied by a fraction, the
numerator of which shall be the difference between (A) the last sale price of
the Common Stock on the trading day prior to such date or, in case no such
reported sales take place on such day, the average of the last reported bid and
asked prices of the Common Stock on such day, in either case on the principal
national securities exchange on which the Common Stock is admitted to trading or
listed, or if not listed or admitted to trading on any such exchange, the
representative closing sale price of the Common Stock as reported by the
National Association of Securities Dealers, Inc. Automated Quotations System
("NASDAQ"), or other similar organization if NASDAQ is no longer reporting such
information, or, if the Common Stock is not reported on NASDAQ, the high per
share sale price for the Common Stock in the over-the-counter market as reported
by the National Quotation Bureau or similar organization, or if not so
available, the fair market value of the Common Stock as determined in good faith
by the Board of Directors (the "Current Market Price") and (B) the Per Share
Exercise Price, and the denominator of which shall be the then Current Market
Price. For purposes of any computation under this Section 1(a), the then Current
Market Price shall be based on the trading day immediately prior to the Cashless
Exercise.

      (c) If this Warrant is exercised in part only, the Company shall, upon
presentation of this Warrant upon such exercise, execute and deliver (with the
certificate for the Warrant Shares purchased) a new Warrant evidencing the
rights of the Holder hereof to purchase the balance of the Warrant Shares
purchasable hereunder upon the same terms and conditions as herein set forth.
Upon proper exercise of this Warrant, the Company promptly shall deliver
certificates for the Warrant Shares to the Holder duly legended as authorized by
the subscription form. No fractional shares shall be issued upon exercise of
this Warrant. With respect to any fraction of a share called for upon exercise
hereof, the Company shall pay to the Holder an amount in cash equal to such
fraction multiplied by the Current Market Price of one (1) share of Common
Stock.

      2. Reservation of Warrant Shares; Fully Paid Shares; Taxes. The Company
hereby undertakes until expiration of this Warrant to reserve for issuance or
delivery upon exercise of this Warrant, such number of shares of the Common
Stock as shall be required for issuance and/or delivery upon exercise of this
Warrant in full, and agrees that all Warrant Shares so issued and/or delivered
will be validly issued, fully paid and non-assessable, and further agrees to pay
all taxes and charges that may be imposed upon such issuance and/or delivery.

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      3. Protection Against Dilution.

      (a) In case the Company shall hereafter (i) pay a dividend or make a
distribution on its capital stock in shares of Common Stock, (ii) subdivide its
outstanding shares of Common Stock into a greater number of shares, (iii)
combine its outstanding shares of Common Stock into a smaller number of shares
or (iv) issue by reclassification of its Common Stock any shares of capital
stock of the Company, the Per Share Exercise Price shall be adjusted to be equal
to a fraction, the numerator of which shall be the Aggregate Exercise Price and
the denominator of which shall be the number of shares of Common Stock or other
capital stock of the Company which the Holder would have owned immediately
following such action had this Warrant been exercised immediately prior thereto.
An adjustment made pursuant to this Subsection 3(a) shall become effective
immediately after the record date in the case of a dividend or distribution and
shall become effective immediately after the effective date in the case of a
subdivision, combination or reclassification.

      (b) In the event of any capital reorganization or reclassification, or any
consolidation or merger to which the Company is a party other than a merger or
consolidation in which the Company is the continuing corporation, or in case of
any sale or conveyance to another entity of the property of the Company as an
entirety or substantially as an entirety, or in the case of any statutory
exchange of securities with another corporation (including any exchange effected
in connection with a merger of a third corporation into the Company), the Holder
of this Warrant shall have the right thereafter to receive on the exercise of
this Warrant the kind and amount of securities, cash or other property which the
Holder would have owned or have been entitled to receive immediately after such
reorganization, reclassification, consolidation, merger, statutory exchange,
sale or conveyance had this Warrant been exercised immediately prior to the
effective date of such reorganization, reclassification, consolidation, merger,
statutory exchange, sale or conveyance and in any such case, if necessary,
appropriate adjustment shall be made in the application of the provisions set
forth in this Section 3 with respect to the rights and interests thereafter of
the Holder of this Warrant to the end that the provisions set forth in this
Section 3 shall thereafter correspondingly be made applicable, as nearly as may
reasonably be, in relation to any shares of stock or other securities or
property thereafter deliverable on the exercise of this Warrant. The above
provisions of this Subsection 3(b) shall similarly apply to successive
reorganizations, reclassifications, consolidations, mergers, statutory
exchanges, sales or conveyances. The issuer of any shares of stock or other
securities or property thereafter deliverable upon the exercise of this Warrant
shall be responsible for all of the agreements and obligations of the Company
hereunder. Notice of any such reorganization, reclassification, consolidation,
merger, statutory exchange, sale or conveyance and of said provisions so
proposed to be made, shall be mailed to the Holders of the Warrants not less
than 30 days prior to such event. A sale of all or substantially all of the
assets of the Company for a consideration consisting primarily of securities
shall be deemed a consolidation or merger for the foregoing purposes.

      (c) No adjustment in the Per Share Exercise Price shall be required unless
such adjustment would require an increase or decrease of at least $0.05 per
share of Common Stock; provided, however, that any adjustments that by reason of
this Subsection 3(c) are not required to be made shall be carried forward and
taken into account in any subsequent adjustment; provided, further, however,
that adjustments shall be required and made in accordance with the provisions of
this Section 3 (other than this Subsection 3(c)) not later than such time as may
be required in order to preserve the tax-free nature of a distribution to the
Holder of this Warrant or Common Stock issuable upon the exercise hereof. All
calculations under this Section 3 shall be made to the nearest cent or to the
nearest 1/100th of a share, as the case may be. Anything in this Section 3 to
the contrary notwithstanding, the Company shall be entitled to make such
reductions in the Per Share Exercise Price, in addition to those required by
this Section 3, as it in its discretion shall deem to be advisable in order that
any stock dividend, subdivision of shares or distribution of rights to purchase
stock or securities

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convertible or exchangeable for stock hereafter made by the
Company to its stockholders shall not be taxable.

      (d) Whenever the Per Share Exercise Price is adjusted as provided in this
Section 3 and upon any modification of the rights of a Holder of Warrants in
accordance with this Section 3, the Company shall promptly provide a certificate
of its Chief Accounting Officer setting forth the Per Share Exercise Price and
the number of Warrant Shares after such adjustment or the effect of such
modification, a brief statement of the facts requiring such adjustment or
modification and the manner of computing the same and cause copies of such
certificate to be mailed to the Holders of the Warrants.

      (e) If, as a result of an adjustment made pursuant to this Section 3, the
Holder of any Warrant thereafter surrendered for exercise shall become entitled
to receive shares of two or more classes of capital stock or shares of Common
Stock and other capital stock of the Company, the Board of Directors (whose
determination shall be conclusive and shall be described in a written notice to
the Holder of any Warrant promptly after such adjustment) shall determine the
allocation of the adjusted Per Share Exercise Price between or among shares or
such classes of capital stock or shares of Common Stock and other capital stock.

      4. Limited Transferability. In addition to the limitation on
transferability set forth in Section 1(a) hereof, this Warrant may not be sold,
transferred, assigned or hypothecated by the Holder except in compliance with
the provisions of the Act and the applicable state securities "blue sky" laws,
and is so transferable only upon the books of the Company which it shall cause
to be maintained for such purpose. The Company may treat the registered Holder
of this Warrant as he or it appears on the Company's books at any time as the
Holder for all purposes. The Company shall permit any Holder of a Warrant or his
duly authorized attorney, upon written request during ordinary business hours,
to inspect and copy or make extracts from its books showing the registered
holders of Warrants. All Warrants issued upon the transfer or assignment of this
Warrant will be dated the same date as this Warrant, and all rights of the
holder thereof shall be identical to those of the Holder.

      5. Loss, etc., of Warrant. Upon receipt of evidence satisfactory to the
Company of the loss, theft, destruction or mutilation of this Warrant, and of
indemnity reasonably satisfactory to the Company, if lost, stolen or destroyed,
and upon surrender and cancellation of this Warrant, if mutilated, the Company
shall execute and deliver to the Holder a new Warrant of like date, tenor and
denomination.

      6. Status of Holder. This Warrant does not confer upon the Holder any
right to vote or to consent to or receive notice as a stockholder of the
Company, as such, in respect of any matters whatsoever, or any other rights or
liabilities as a stockholder, prior to the exercise hereof.

      7. Notices. No notice or other communication under this Warrant shall be
effective unless, but any notice or other communication shall be effective and
shall be deemed to have been given, if the same is in writing and is mailed by
first-class mail, postage prepaid, addressed to:

If to the Holder: If to the Holder: 46 Jabotinsky Street, Jerusalem, Israel
Attn: Avi Barak; or

If to the Company: If to the Company: 7 Hartom Street, POB 23706, Jerusalem,
Israel 91236 Attn: General Counsel

      8. Headings. The headings of this Warrant have been inserted as a matter
of convenience and shall not affect the construction hereof.

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      9. Applicable Law. This Warrant shall be governed by and construed in
accordance with the laws of the Commonwealth of Massachusetts, without regard to
principles of conflicts of law. Notwithstanding anything to the contrary
contained herein, in no event may the effective rate of interest collected or
received by the Holder exceed that which may be charged, collected or received
by the Holder under applicable law. The parties agree to settle any disputes
through binding arbitration in the city of Boston.

            IN WITNESS WHEREOF, the Company has caused this Warrant to be signed
by its Chief Executive Officer and attested by its Secretary this 10th day of
January 2002.

                              KERYX BIOPHARMACEUTICALS, INC.

                              By: /s/ Benjamin Corn
                                  ---------------------------
                              Name: Benjamin Corn, M.D.
                              Title: Chief Executive Officer and President

ATTEST:

/s/ Bob Trachtenberg
--------------------
      Secretary

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<PAGE>

 (NOT PERMITTED UNTIL INITIAL VESTING DATE)

                                  SUBSCRIPTION

            The undersigned, ___________________, pursuant to the provisions of
the foregoing Warrant, hereby elects to exercise the within Warrant to the
extent of purchasing ____________________ shares of Common Stock thereunder and
hereby makes payment of $___________ by certified or official bank check in
payment of the exercise price therefor.

            The undersigned hereby represents and warrants to the Company that
the undersigned is acquiring the shares of the Company's Common Stock pursuant
to exercise of the within Warrant for investment purposes only. The undersigned
hereby further acknowledges that the undersigned understands that such shares
(a) have not been registered under the Securities Act of 1933, as amended, and
are being issued to the undersigned by the Company in reliance upon the
foregoing representation and warranty and (b) may not be resold except in
accordance with the requirements of the Act, including Rule 144 thereunder, if
applicable. The undersigned further consents to the placing of a legend on the
certificates for the shares being purchased to the foregoing effect.

Dated:_______________               Signature:____________________

                                    Address:______________________

                                   ASSIGNMENT

            FOR VALUE RECEIVED _______________ hereby sells, assigns and
transfers unto ____________________ the foregoing Warrant and all rights
evidenced thereby, and does irrevocably constitute and appoint
_____________________, attorney, to transfer said Warrant on the books of Keryx
Biopharmaceuticals, Inc.

Dated:_______________               Signature:____________________

                                    Address:______________________

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                                CASHLESS EXERCISE

            The undersigned ___________________, pursuant to the provisions of
the foregoing Warrant, hereby elects to exchange its Warrant for
___________________ shares of Common Stock, par value $.001 per share, of
SignalSite, Inc. pursuant to the Cashless Exercise provisions of the Warrant.

Dated:_______________               Signature:____________________

                                    Address:______________________

                               PARTIAL ASSIGNMENT

            FOR VALUE RECEIVED _______________ hereby assigns and transfers unto
____________________ the right to purchase _______ shares of the Common Stock,
no par value per share, of SignalSite, Inc. covered by the foregoing Warrant,
and a proportionate part of said Warrant and the rights evidenced thereby, and
does irrevocably constitute and appoint ____________________, attorney, to
transfer that part of said Warrant on the books of Keryx Biopharmaceuticals,
Inc.

Dated:_______________               Signature:____________________

                                    Address:______________________

                                       7EXHIBIT 10.1

                                    February 27, 2002

BY FACSIMILE TRANSMISSION

Morris Laster, M.D.
Reuven Sheri 11
Jerusalem, Israel 97289

Dear Dr. Laster:

As we discussed and agreed, your employment with Keryx Biopharmaceuticals, Inc.
(the "Company") will terminate, effective March 21, 2003 or at an earlier date
to be agreed upon by you and the Company (the "Termination Date"). As part of
the termination of your employment with the Company, effective December 23,
2002, you shall cease to hold the position of Executive Chairman of the Company
and all other positions you held as a director or officer of the Company and any
subsidiary or affiliate of the Company, but you shall remain employed by the
Company and shall receive the same rate of compensation and benefits as you are
currently receiving through the Termination Date (the "Transition Period"). In
exchange for such compensation and benefits, you agree that you shall assist
designated Company employees with transitional matters throughout the Transition
Period.

As we discussed, following the Termination Date, the Company will provide you
with the enhanced severance benefits described on Attachment A hereto if you
sign and return this letter agreement (the "Agreement") on or before March 6,
2003 and you execute, on the Termination Date, the Release Agreement attached as
Attachment B to this Agreement (the "Release Agreement").

By signing and returning the Agreement and the Release Agreement, you will be
agreeing to the terms and conditions set forth in the paragraphs therein,
including the release of claims. Therefore, you are advised to consult with an
attorney before signing this Agreement and the Release Agreement and you may
take up to seven (7) days to do so. If you choose not to timely sign and return
both this Agreement and the Release Agreement, you shall not receive any
enhanced severance benefits from the Company.

If you choose not to sign this Agreement by March 6, 2003 or the Release
Agreement on the Termination Date, you shall not receive the enhanced severance
benefits described in Attachment A. You will, however, receive payment for any
accrued wages, unused vacation time and any severance payments due pursuant to
the terms of the Severance Compensation Law - 1963 that accrued through the
Termination Date. Also, regardless of signing this Agreement or the Release
Agreement, you may elect to continue receiving group medical insurance pursuant
to the federal "COBRA" law, 29 U.S.C. Section 1161 et seq. All premium costs
shall be paid by you on a monthly basis for as long as, and to the extent that,
you remain eligible for COBRA continuation. You should consult the COBRA
materials to be provided by the Company for details regarding

<PAGE>

these benefits. All other benefits, including life insurance and long-term
disability, will cease upon the Termination Date in accordance with the plan
documents.

The following paragraphs and attachments set forth the terms and conditions that
will apply if you timely sign and return this Agreement by February 27, 2003 and
if you sign and return the Release Agreement on the Termination Date:

1.    Termination Date - The effective date of the termination or your
      employment with the Company is March 21, 2003.

2.    Description of Enhanced Severance Benefits - The enhanced severance
      benefits to be paid to you if you timely sign and return this Agreement
      and the Release Agreement are described in the "Description of Enhanced
      Severance Benefits" attached as Attachment A (the "enhanced severance
      benefits").

3.    Release - Subject to the fulfillment of the Enhanced Severance Benefits
      Agreement by the Company and the release declaration of the Company and in
      consideration of the payment of the enhanced severance benefits, which you
      acknowledge you would not otherwise be entitled to receive, you hereby
      fully, forever, irrevocably and unconditionally release, remise and
      discharge TriNet Employer Group, Inc. and the Company, including all of
      their respective officers, directors, stockholders, corporate affiliates,
      subsidiaries, and parent companies and their respective agents and
      employees, from any and all claims, charges, complaints, demands, actions,
      causes of action, suits, rights, debts, sums of money, costs, accounts,
      reckonings, covenants, contracts, agreements, promises, doings, omissions,
      damages, executions, obligations, liabilities, and expenses (including
      attorneys' fees and costs), of every kind and nature that you ever had or
      now have against TriNet Employer Group, Inc. and the Company, including
      all of their respective officers, directors, stockholders, corporate
      affiliates, subsidiaries and parent companies and their respective agents
      and employees, arising out of your employment with and/or separation from
      the Company including, but not limited to, all employment discrimination
      claims under Title VII of the Civil Rights Act of 1964, 42 U.S.C. Section
      2000e et seq., the Americans With Disabilities Act of 1990, 42 U.S.C.
      Section 12101 et seq., the Family and Medical Leave Act, 29 U.S.C. Section
      2601 et seq., the Worker Adjustment and Retraining Notification Act
      ("WARN"), 29 U.S.C. Section 2101 et seq. and the Rehabilitation Act of
      1973, 29 U.S.C. Section 701 et seq., all as amended, and all claims
      arising out of the Fair Credit Reporting Act, 15 U.S.C. Section 1681 et
      seq., the Employee Retirement Income Security Act of 1974 ("ERISA"), 29
      U.S.C. Section 1001 et seq., the Massachusetts Fair Employment Practices
      Act, M.G.L. c.151B, Section 1 et seq., the Massachusetts Civil Rights Act,
      M.G.L. c.12, Sections 11H and 11I, the Massachusetts Equal Rights Act,
      M.G.L. c.93, Section 102 and M.G.L. c.214, Section 1C, the Massachusetts
      Labor and Industries Act, M.G.L. c.149, Section 1 et seq., the
      Massachusetts Privacy Act, M.G.L. c.214, Section 1B, and the Massachusetts
      Maternity Leave Act, M.G.L. c.149, Section 105(d), and all relevant laws
      of the State of Israel, all as amended, all common law claims including,
      but not limited to, actions in tort, defamation and breach of contract
      (including all claims alleged under the terms of the Employment Agreement,
      as defined below), all claims to any non-vested ownership interest in the
      Company, contractual or otherwise, including, but not limited to, claims
      to

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      stock or stock options, and any claim or damage arising out of your
      employment with and/or separation from the Company (including a claim for
      retaliation) under any common law theory or any federal, state or local
      statute or ordinance not expressly referenced above; provided, however,
      that nothing in this Agreement shall prevent you from filing, cooperating
      with, or participating in a discrimination proceeding before a state or
      federal Fair Employment Practices Agency or court (except that you
      acknowledge that you may not recover any monetary benefit in such
      proceeding unless this Agreement is held invalid by such an agency or
      court).

4.    Non-Disclosure, Non-Competition and Inventions - You acknowledge your
      obligation to keep confidential all non-public information concerning the
      Company that you acquired during the course of your employment with the
      Company, as stated more fully in Sections 8.8 and 8.9 of the Amended
      Employment Agreement you executed on November 26, 2001 (the "Employment
      Agreement"), which Sections remain in full force and effect. You further
      acknowledge and reaffirm your obligations under Sections 8.10 and 9 of the
      Employment Agreement, including your obligation not to compete with the
      Company, which also remain in full force and effect.

5.    Non-Interference - Further you acknowledge and agree that during the
      period ending 12 months after the Termination Date (the "Non-Interference
      Period"), you shall not, directly or indirectly, without the prior written
      consent of the Company:

      (a)   interfere with, disrupt or attempt to disrupt any past, present or
            prospective relationship, contractual or otherwise, between the
            Company and any of its licensors, licensees, clients, customers,
            suppliers, employees or other related parties, or solicit or induce
            for hire any of the employees, agents, consultants or advisors of
            the Company or any such individual who in the past was employed or
            retained by the Company, within six (6) months of the termination of
            said individual's employment or retention by the Company.; and

      (b)   attempt to license, directly or indirectly, any of the technologies,
            projects or products currently under license by the Company from
            either Yissum Research and Development Company of the Hebrew
            University of Jerusalem ("Yissum") or the Children's Medical Center
            Corporation ("CMCC") (collectively, the "Licensed Projects") or
            become an officer, director, employee, consultant or shareholder in
            any entity that seeks to license, directly or indirectly, any of the
            Licensed Projects during the Non-Interference Period.

      (c)   The burden of proof for any breach, by you, of this section 5, shall
            be on the Company.

6.    Return of Company Property - You agree to return within seven (7) days of
      the Termination Date all Company property including, but not limited to,
      keys, files, office

                                      -3-
<PAGE>

      equipment, passwords, passcodes, computer software (and all copies
      thereof), and computer hardware, that is in your possession or control.
      You further agree to leave intact all electronic Company documents,
      including those that you developed during your employment.

7.    Execution of Release Agreement - You agree to execute on the Termination
      Date the Release Agreement in the form attached hereto as Attachment B.

8.    Termination of Employment Positions - You hereby terminate, effective
      December 23, 2002, to act in the position of Executive Chairman of the
      Company, as well as from any and all other positions as an officer or
      director of the Company and any and all of its subsidiaries or affiliates.

9.    Non-Disparagement - To the extent not in violation of the law, you
      understand and agree that as a condition for payment to you of the
      enhanced severance benefits herein described, you shall not make any
      false, disparaging or derogatory statements to any media outlet, industry
      group, financial institution or current or former employee, consultant,
      client or customer of the Company regarding the Company, its subsidiaries
      and their respective directors, officers, employees, agents or
      representatives or about the Company's business affairs, financial
      condition, products and technologies.

10.   Amendment - This Agreement, including the Release Agreement, shall be
      binding upon the parties and may not be modified in any manner, except by
      an instrument in writing of concurrent or subsequent date signed by duly
      authorized representatives of the parties hereto. This Agreement and the
      Release Agreement are binding upon and shall inure to the benefit of the
      parties and their respective agents, assigns, heirs, executors, successors
      and administrators.

11.   Waiver of Rights - No delay or omission by the Company in exercising any
      right under this Agreement or the Release Agreement shall operate as a
      waiver of that or any other right. A waiver or consent given by the
      Company on any one occasion shall be effective only in that instance and
      shall not be construed as a bar to or waiver of any right on any other
      occasion. Furthermore, in the event you breach any term of the Agreement,
      including the Release Agreement, the Company reserves its right to pursue
      any and all remedies and damages available to it concerning such breach.

12.   Validity - Should any provision of this Agreement or the Release Agreement
      be declared or be determined by any court of competent jurisdiction to be
      illegal or invalid, the validity of the remaining parts, terms or
      provisions shall not be affected thereby and said illegal or invalid part,
      term or provision shall be deemed not to be a part of this Agreement or
      the Release Agreement, as applicable.

13.   Confidentiality - To the extent permitted by law, you understand and agree
      that as a condition for payment to you of the enhanced severance benefits
      herein described, the terms and contents of this Agreement and the Release
      Agreement, and the contents of the negotiations and discussions resulting
      in this Agreement and the Release Agreement,

                                      -4-
<PAGE>

      shall be maintained as confidential by you and your agents and
      representatives and shall not be disclosed to any third party except to
      the extent required by federal or state law or as otherwise agreed to in
      writing by the Company. You understand and agree that the Company will
      have to file the Agreement and Release Agreement with appropriate federal
      agencies.

14.   Nature of Agreement - You understand and agree that this Agreement and the
      Release Agreement is a severance agreement and does not constitute an
      admission of liability or wrongdoing on the part of the Company.

15.   Acknowledgments - You acknowledge that you have been given at least seven
      (7) days to consider this Agreement and that the Company advised you to
      consult with an attorney of your own choosing prior to signing this
      Agreement.

16.   Voluntary Assent - You affirm that no other promises or agreements of any
      kind have been made to or with you by any person or entity whatsoever to
      cause you to sign this Agreement or the Release Agreement, and that you
      fully understand the meaning and intent of this Agreement and the Release
      Agreement. You state and represent that you have had an opportunity to
      fully discuss and review the terms of this Agreement, including
      Attachments A and B, with an attorney. You further state and represent
      that you have carefully read this Agreement, including Attachments A and
      B, understand the contents herein, freely and voluntarily assent to all of
      the terms and conditions hereof, and sign your name of your own free act.

17.   Applicable Law - This Agreement and the Release Agreement shall be
      interpreted and construed by the laws of the Commonwealth of
      Massachusetts, without regard to conflict of laws provisions. You hereby
      irrevocably submit to and acknowledge and recognize the jurisdiction of
      the courts of the Commonwealth of Massachusetts, or if appropriate, a
      federal court located in Massachusetts (which courts, for purposes of this
      Agreement and the Release Agreement, are the only courts of competent
      jurisdiction), over any suit, action or other proceeding arising out of,
      under or in connection with this Agreement, the Release Agreement or the
      subject matter hereof.

18.   Entire Agreement - This Agreement, including Attachments A and B, contains
      and constitutes the entire understanding and agreement between the parties
      hereto with respect to your enhanced severance benefits and the settlement
      of claims against the Company and cancels all previous oral and written
      negotiations, agreements, commitments, writings in connection therewith.
      Nothing in this paragraph, however,

                                      -5-
<PAGE>

19.   shall modify, cancel or supersede your obligations set forth in paragraph
      4.

      If you have any questions about the matters covered in this Agreement or
the Release Agreement, please call me. If you choose to execute this Agreement,
please return all pages of this Agreement, including Attachments A and B, to me
no later than February 27, 2003. You may retain the enclosed copy of the
Agreement for your records.

                                    Very truly yours,

                                    By:    /s/ Michael. S. Weiss
                                       ----------------------------------------
                                          Name: Michael S. Weiss
                                          Title:Chief Executive Officer

I hereby agree to the terms and conditions set forth above and in Attachments A
and B. I have been given at least seven (7) days to consider this Agreement and
the Release Agreement and I have chosen to execute this Agreement on the date
below. I intend that this Agreement and the Release Agreement will become a
binding agreement between the Company and me.

 /s/ Morris Laster                                    Date  2/27/03
-------------------------------------                     ---------------
Employee Name:  Morris Laster, M.D.

To be returned by March 6, 2003.

                                      -6-
<PAGE>

                                  ATTACHMENT A

                   DESCRIPTION OF ENHANCED SEVERANCE BENEFITS

In exchange for your timely execution of this Agreement and the Release
Agreement, including the release of claims found therein, the Company agrees to
provide you with the following enhanced severance benefits (collectively, the
"Enhanced Severance Benefits"):

For avoidance of any doubt and for clarification purpose, you shall be entitled
to receive the following benefits according to Israeli law, in addition to the
Enhanced Severance Benefits described herein in sections (a-e) these benefits
(1-4) will be paid to you unconditionally, regardless of the Release Agreement:

      1.    The Company shall pay all your salaries and benefits until March 21,
            2003 .

      2.    The Company shall furnish you a notice of release to the insurance
            company of Bituach Menahalim in your name, which includes severance
            pay as required by Israeli law.

      3.    The Company shall furnish you a notice of release of your Keren
            Hishtalmut.

      4.    Your last salary payment following the Termination Date shall
            include a payment for any and all accrued but unused vacation days.

(a)   Severance Pay - The Company agrees to provide you with severance pay in
      the amount of two hundred fifty thousand dollars ($250,000), less all
      applicable taxes and withholdings, which is equivalent to twelve (12)
      months of salary continuation at your current annualized base rate of (the
      "Severance Pay"). The Severance Pay shall be paid to you over a twelve
      (12) month period beginning on May 1, 2003, in accordance with the
      Company's normal payroll procedures (i.e. the Severance Pay shall be paid
      in such time and manner as the Company pays its employees their monthly
      salary, however, for the avoidance of doubt, payment of the Severance Pay
      shall in no way be considered the payment of salary and shall not be
      deemed to be evidence of an employer-employee relationship.

(b)   Accelerated Vesting - You currently have 25,000 unvested options.
      Notwithstanding anything to the contrary in the 1999 or 2000 Share Option
      Plan, effective upon the Termination Date, one hundred percent (100%) of
      the portion of your option to purchase shares of common stock of the
      Company that remains unvested as of the Termination Date shall become
      immediately vested and exercisable in full.

                                      -7-
<PAGE>

(c)   Extension of Exercise Period - Notwithstanding anything to the contrary in
      the 1999 or 2000 Share Option Plans, effective upon the Termination Date,
      the Company shall extend the period during which you may exercise your
      stock options, to the extent such options are fully vested on the
      Termination Date after giving effect to the acceleration provided for in
      paragraph (b) above, until March 21, 2005.

(d)   Consulting Arrangement - The Company agrees to negotiate with you a
      consulting arrangement for up to one (1) year from the Termination Date,
      under terms and conditions to be mutually agreed upon by the parties. A
      failure to reach such agreement shall not be deemed a breach of this
      severance agreement.

(e)   Bonus Payment - The Company agrees to provide you, or, to the extent
      legally permissible, a person or entity designated by you, with a one-time
      cash bonus of one hundred twenty-five thousand dollars ($125,000), less
      all applicable taxes and withholdings. Such one-time cash bonus shall be
      paid in one lump-sum payment after the Company doses the first patient in
      the KRX-101 U.S. Phase 3 Clinical Trial (hereinafter "the Milestone"),
      provided that you continue to participate, at the Company's reasonable
      request, in the Company's efforts to commence the Phase 3 Clinical Trial.
      Such participation shall include, but not be limited to, you responding in
      a timely manner to requests from the Company for advice and guidance with
      respect to the proposed clinical development program.

      These participatory conditions shall apply only prior to the Termination
      Date. As of the Termination Date, such conditions or any other conditions
      for the receipt of the mentioned bonus from the Company, shall be
      stipulated in the Consulting Agreement mentioned in paragraph (d), above.
      Alternatively, in the event that a Consulting Agreement is not reached
      between you and the Company, the mentioned bonus shall be provided to you
      by the Company upon reaching the Milestone, regardless of your
      participation in the Company's efforts subsequent to the Termination Date.

                                      -8-
<PAGE>

                                  ATTACHMENT B

                                RELEASE AGREEMENT

      Subject to the fulfillment of the Enhanced Severance Benefits Agreement by
the Company and in consideration of the mutual promises set forth herein and in
the letter agreement between the parties dated February 27, 2003 (the
"Agreement"), which you acknowledge you would not otherwise be entitled to
receive, you hereby fully, forever, irrevocably and unconditionally release,
remise and discharge TriNet Employer Group, Inc. and the Company, including all
of their respective officers, directors, stockholders, corporate affiliates,
subsidiaries, and parent companies and their respective agents and employees,
from any and all claims, charges, complaints, demands, actions, causes of
action, suits, rights, debts, sums of money, costs, accounts, reckonings,
covenants, contracts, agreements, promises, doings, omissions, damages,
executions, obligations, liabilities, and expenses (including attorneys' fees
and costs), of every kind and nature that you ever had or now have against
TriNet Employer Group, Inc. and the Company, including all of their respective
officers, directors, stockholders, corporate affiliates, subsidiaries and parent
companies and their respective agents and employees, arising out of your
employment with and/or separation from the Company including, but not limited
to, all employment discrimination claims under Title VII of the Civil Rights Act
of 1964, 42 U.S.C. Section 2000e et seq., the Americans With Disabilities Act of
1990, 42 U.S.C. Section 12101 et seq., the Family and Medical Leave Act, 29
U.S.C. Section 2601 et seq., the Worker Adjustment and Retraining Notification
Act ("WARN"), 29 U.S.C. Section 2101 et seq. and the Rehabilitation Act of 1973,
29 U.S.C. Section 701 et seq., all as amended, and all claims arising out of the
Fair Credit Reporting Act, 15 U.S.C. Section 1681 et seq., the Employee
Retirement Income Security Act of 1974 ("ERISA"), 29 U.S.C. Section 1001 et
seq., the Massachusetts Fair Employment Practices Act, M.G.L. c.151B, Section 1
et seq., the Massachusetts Civil Rights Act, M.G.L. c.12, Sections 11H and 11I,
the Massachusetts Equal Rights Act, M.G.L. c.93, Section 102 and M.G.L. c.214,
Section 1C, the Massachusetts Labor and Industries Act, M.G.L. c.149, Section 1
et seq., the Massachusetts Privacy Act, M.G.L. c.214, Section 1B, and the
Massachusetts Maternity Leave Act, M.G.L. c.149, Section 105(d), and all
relevant laws of the State of Israel, all as amended, all common law claims
including, but not limited to, actions in tort, defamation and breach of
contract (including all claims alleged under the terms of the Employment
Agreement, as defined in the Agreement), all claims to any non-vested ownership
interest in the Company, contractual or otherwise, including, but not limited
to, claims to stock or stock options, and any claim or damage arising out of
your employment with and/or separation from the Company (including a claim for
retaliation) under any common law theory or any federal, state or local statute
or ordinance not expressly referenced above; provided, however, that nothing in
this Release Agreement shall prevent you from filing, cooperating with, or
participating in a discrimination proceeding before a state or federal Fair
Employment Practices Agency or court (except that you acknowledge that you may
not recover any monetary benefit in such proceeding unless this Release
Agreement is held invalid by such an agency or court).

You acknowledge that you have been given a reasonable amount of time to consider
this Release Agreement, and that the Company advised you to consult with an
attorney of your choosing prior

                                      -9-
<PAGE>

to signing this Release Agreement. You understand that after signing the Release
Agreement it will become binding between the Company and you.

You acknowledge that you have been reimbursed by the Company for all business
expenses incurred by you in conjunction with your employment with the Company
and that no other reimbursements are owed to you. You further acknowledge that
you have been provided with all compensation and benefits due to you as of the
date of this Release Agreement, including, but not limited to, any and all
wages, expense reimbursements, bonuses and any accrued but unused vacation time,
and that you are not entitled to receive any additional consideration beyond
that provided for in Attachment A of the Agreement.

Subject to your declarations under this Agreement the Company, the Company
including all of its respective officers, directors, stockholders, corporate
affiliates, subsidiaries, and parent companies and their respective agents and
employees, irrevocably and unconditionally releases, remises and discharges you
from any and all claims, charges, complaints, demands, actions, causes of
action, suits, rights, debts, sums of money, costs, accounts, reckonings,
covenants, contracts, agreements, promises, doings, omissions, damages,
executions, obligations, liabilities, and expenses (including attorneys' fees
and costs), of every kind and nature arising out of your services for the
Company (apart from any ongoing obligations arising from the Severance Agreement
and your Amended Employment Agreement, dated November 26, 2001, including, but
not limited to, your obligations of confidentiality, non-competition,
non-solicitation and non-disparagement. This release is subject to the
assumption that in your service you met the standards for reasonable conduct and
acted in a manner reasonably believed by the Company to be in its best interest
The Company shall indemnify you for any such action arising out of your services
for the Company in accordance with the Indemnification Agreement signed between
you and the Company on October 16, 2000.

      IN WITNESS WHEREOF, all parties have set their hand and seal to this
Release Agreement as of the dates below.

      Morris Laster, M.D.

       /s/ Morris Laster                        Date: 3/21/03
      ----------------------------------

      Keryx Biopharmaceuticals, Inc.../s/ Michael S. Weiss    Date: 3/21/03
                                      -----------------------

                                      -10-

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