EXHIBIT 4.5

THE SECURITIES REPRESENTED BY THIS CERTIFICATE ARE NOT TRANSFERABLE WITHOUT THE
EXPRESS WRITTEN CONSENT OF LARAKO 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. 5                                                              93,750 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
approval of the first Investigational New Drug Application by the United States
Food and Drug Administration for the technologies granted to the Company by the
Children's Medical Center Corporation ("CMCC") pursuant to a license agreement
entered into by and among the Company and CMCC on November 18 1999, and prior to
5:00 P.M., New York City time, on the date that is ten (10) years after the
Vesting Date (the "Termination Date"), Ninety-Three Thousand Seven Hundred and
Fifty (93,750) 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 $.0067, or an initial aggregate exercise price of $628.13. 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").


                                       1
<PAGE>

      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.


                                       2
<PAGE>

      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


                                       3
<PAGE>

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.


                                       4
<PAGE>

      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 12th day of
December 2001.

                              KERYX BIOPHARMACEUTICALS, INC.


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

ATTEST:

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


                                       5
<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:______________________


                                       6
<PAGE>

                                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:______________________


                                       7