Document:

<PAGE>   1
                                                                    Exhibit 4.23

[CHASE LOGO]

                                                      Fixed Rate Promissory Note
                                                                (Multiple Loans)

New York, New York                   January 17, 2000

         For value received, the undersigned (the "Borrower") unconditionally
promises to pay to the order of THE CHASE MANHATTAN BANK (the "Bank"), at its
principal office located at 270 Park Avenue, New York, New York 10017, the
principal amount of each loan made by the Bank to the Borrower and outstanding
under this Note, on the maturity date(s) as evidenced in the Bank's records as
provided in the fifth paragraph hereof.

         The Borrower promises to pay interest on the unpaid balance of the
principal amount of each such loan for each day outstanding at a fixed rate per
annum equal to the rate as evidenced in the Bank's records as provided in the
fifth paragraph hereof; provided that principal and (to the extent permitted by
law) interest not paid when due (whether at stated maturity, by acceleration or
otherwise) shall bear interest for each day overdue at a variable rate per annum
equal to: (a) the higher of: (i) the Federal Funds Rate plus 1/2 of 1% or (ii)
the Prime Rate; plus (b) 2%. "Federal Funds Rate" means, for any day, the rate
per annum equal to the weighted average of the rates on overnight Federal funds
transactions as published by the Federal Reserve Bank of New York for such day
(or for any day that is not a banking day in New York City, for the immediately
preceding banking day). "Prime Rate" means, for any day, that rate of interest
from time to time announced by the Bank at its principal office as its prime
commercial lending rate, as in effect for such day in accordance with
announcements by the Bank of changes in such rate. Interest shall be calculated
on the basis of a year of 360 days and paid for the actual number of days
elapsed (including the first day but excluding the last day). Interest on each
loan shall be due and payable at the maturity thereof (and quarterly, if
requested by the Bank). In no case shall the interest on this Note exceed the
maximum amount which the Bank may charge or collect under applicable law.

         Each loan hereunder may be prepaid in whole but not in part, provided
that accrued and unpaid interest is paid on the date of such prepayment,
together with any compensation payable in accordance with the following. If
there is any payment (whether by voluntary prepayment, acceleration or
otherwise) of principal of a loan under this Note on a date other than the
scheduled maturity date thereof set forth in the first paragraph hereof, then
the Borrower will pay the Bank such amount as will be sufficient in the
reasonable opinion of the Bank to compensate it for any loss, cost or expense
which the Bank determines is attributable thereto within ten (10) days after
written notice from the Bank to Borrower of the amount of such loss, cost or
expense and a statement in reasonable detail of the basis for and calculation of
such amount. Without limiting the foregoing, such compensation shall include an
amount equal to the excess, if any, of: (a) the aggregate amount of interest
which otherwise would have accrued on the principal amount so paid for the
period from and including the date of payment to but excluding such maturity
date at the rate of interest provided herein over (b) the amount of interest the
Bank would pay (as determined by the Bank in good faith, such determination to
be conclusive) on a deposit placed with the Bank on the date of such payment in
an amount comparable to such principal amount and with a maturity comparable to
such period.

         All payments under this Note shall be made in lawful money of the
United States of America and in immediately available funds at the Bank's
principal office specified above. If any loan evidenced by this Note becomes due
and payable on a day which is not a banking day in New York City, the maturity
of such loan shall be extended to the next succeeding banking day, and interest
shall be payable for such extension on such loan at the rate of interest
specified in this Note.

         The date, amount, rate of interest and maturity date of each loan under
this Note as verbally agreed to between the Bank and Borrower at the time each
Loan is requested by Borrower hereunder and each payment of principal, loan(s)
to which such principal is applied (as designated by Borrower at the time such
payment is made) and the outstanding principal balance of loans shall be
recorded by the Bank on its books and prior to any transfer and delivery of this
Note, endorsed by the Bank on the schedule attached or any continuation of the
schedule. Any such endorsement shall be conclusive in the absence of manifest
error.

         If any of the following events of default shall occur: (a) the Borrower
fails to pay any liability to the Bank under this Note when due and payable in
the case of principal, within five (5) days after the same became due and
<PAGE>   2
payable in the case of interest and within ten (10) days after written notice
from the Bank to Borrower in all other cases; (b) the Borrower shall breach in
any material respect any representation, warranty or covenant in this Note or
other document executed and delivered by Borrower in connection with this Note
(this Note and any such document being a "Facility Document") or in any
certificate or financial or other statement delivered in connection with a
Facility Document; (c) the Borrower shall become insolvent (however evidenced)
or shall seek any relief under any bankruptcy or similar law of any jurisdiction
(or any person shall seek such relief against the Borrower and such involuntary
case or other proceeding shall remain undismissed and unstayed for a period of
90 days); (e) any Facility Document shall at any time cease to be in full force
and effect or its validity or enforceability shall be disputed or contested; or
(f) any lien or security interest securing this Note shall cease to create a
valid and perfected first priority lien or security interest in the property
purported to be subject thereto; THEN, if the Bank shall elect by notice to the
Borrower, the unpaid principal amount of this Note, together with interest and
any other amounts due hereunder shall become forthwith due and payable; provided
that in the case of an event of default under (d) above, such amounts shall
automatically become due and payable without any notice or other action by the
Bank.

         The Borrower waives presentment, notice of dishonor, protest and any
other formality with respect to this Note.

         The Borrower shall reimburse the Bank on demand for all reasonable
costs and expenses (including, without limitation, the reasonable fees and
charges of external legal counsel for the Bank) in connection with the
enforcement of this Note.

         This Note shall be binding on the Borrower and its successors and
assigns and shall inure to the benefit of the Bank and its successors and
assigns; provided that the Borrower may not delegate any obligations hereunder
without the prior written consent of the Bank. Without limiting any provision of
this Note, the obligations under this Note shall continue in full force and
effect and shall be binding on: (a) the estate of the Borrower if the Borrower
is an individual; and (b) any successor partnership and on previous partners and
their respective estates if the Borrower is a partnership, regardless of any
change in the partnership as a result of death, retirement or otherwise.

         THIS NOTE SHALL BE GOVERNED BY THE LAW OF THE STATE OF NEW YORK. THE
BORROWER CONSENTS TO THE NONEXCLUSIVE JURISDICTION AND VENUE OF THE STATE OR
FEDERAL COURTS LOCATED IN THE CITY OF NEW YORK. SERVICE OF PROCESS BY THE BANK
IN CONNECTION WITH ANY SUCH DISPUTE SHALL BE BINDING ON THE BORROWER IF SENT TO
THE BORROWER BY REGISTERED MAIL AT THE ADDRESS SPECIFIED BELOW. THE BORROWER
AND, BY ITS ACCEPTANCE OF THIS NOTE, LENDER WAIVE ANY RIGHT EACH MAY HAVE TO
JURY TRIAL.

Address: Two North Riverside Plaza      EOP OPERATING LIMITED PARTNERSHIP,
         Suite 2200                     a Delaware limited partnership
         Chicago, Illinois 60606
         Attention:  Treasurer          By: Equity Office Properties Trust,
                                            its managing general partner

                                            By: /s/ MAUREEN FEAR
                                               ---------------------------------
                                            Name: Maureen Fear
                                                 -------------------------------
                                            Title: Sr. Vice President, Treasurer
                                                  ------------------------------
<PAGE>   3

<TABLE>
<CAPTION>
                                                               Amount of
   Date                                                        Payment and         Principal
   and                 Amount                                  Loan Number         Balance
   Loan                of Loan             Maturity            to Which            Remaining              Notation
   Number              and Rate            Date                Applied             Unpaid                 Made By
---------------------  ------------------  ------------------  ------------------  ---------------------  --------------------
<S>                    <C>                 <C>                 <C>                 <C>                    <C>

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

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

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

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

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

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

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

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

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

---------------------  ------------------  ------------------  ------------------  ---------------------  --------------------
</TABLE><PAGE>   1
                                                                  EXHIBIT 4.21

                 FIRST AMENDMENT TO SECOND AMENDED AND RESTATED
                           REVOLVING CREDIT AGREEMENT

                  THIS FIRST AMENDMENT TO SECOND AMENDED AND RESTATED REVOLVING
CREDIT AGREEMENT (this "Amendment") is made as of June 18, 1999, by and among
EOP OPERATING LIMITED PARTNERSHIP (the "Borrower"), EQUITY OFFICE PROPERTIES
TRUST (the "Guarantor"), NATIONSBANK, N.A., as Administrative Agent for the
Banks (the "Administrative Agent"), MORGAN GUARANTY TRUST COMPANY OF NEW YORK,
THE CHASE MANHATTAN BANK, as Documentation Agent and as Managing Agent, J.P.
MORGAN SECURITIES INC., as Syndication Agent, THE BANK OF NOVA SCOTIA,
COMMERZBANK AKTIENGESELLSCHAFT, DRESDNER BANK AG, NEW YORK AND CAYMAN BRANCHES,
PNC BANK, NATIONAL ASSOCIATION, and UNION BANK OF SWITZERLAND, NEW YORK BRANCH,
as Managing Agents, CREDIT LYONNAIS, NEW YORK BRANCH, FLEET NATIONAL BANK, and
U.S. BANK NATIONAL ASSOCIATION, as Co-Agents, and the BANKS party hereto.

                              W I T N E S S E T H:

                  WHEREAS, the Borrower has executed and delivered to the Agents
(or their predecessors), the Managing Agents, certain of the Co-Agents and the
Banks that certain Second Amended and Restated Revolving Credit Agreement dated
as of May 29, 1998, by and among the Borrower, certain of the Banks, the
Managing Agents, the Co-Agents and the Agents (the "Credit Agreement");

                  WHEREAS, the Borrower has requested that the Banks agree to
modify the Credit Agreement in order to amend certain provisions therein, upon
the terms and conditions set forth herein, and the Administrative Agent has
recommended that such modification be approved by the Banks.

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

                  1. Definitions. All capitalized terms not otherwise defined
herein shall have the meanings ascribed to them in the Credit Agreement.

                  2. Amendments.

                  (a) The definition of "Applicable Margin" set forth in the
Credit Agreement is hereby amended by adding the following clause at the end of
the first sentence thereof:

                  "; provided, however, that, during the twelve (12) month
                  period following the closing of an Identified Merger or
                  Acquisition (as hereinafter defined), if the ratio of Total
                  Liabilities to Total Asset Value of the Borrower at any time
                  exceeds 0.50:1, then the Applicable Margin for Euro-Dollar
                  Loans made or outstanding during the period that such ratio
                  exceeds 0.50:1 shall be Applicable Margin set forth on the
                  table below plus 0.20%.

<PAGE>   2

                  (b) The definition of "Documentation Agent" set forth in the
Credit Agreement is hereby deleted and the following is substituted therefor:

                  "Documentation Agent" means The Chase Manhattan Bank, in its
                  capacity as Documentation Agent hereunder, and its permitted
                  successors in such capacity in accordance with the terms of
                  this Agreement.

                  (c) The definition of "Joint Venture Subsidiary" is hereby
amended by (1) inserting the word "substantially" between "is" and "controlled"
in clause (ii) of the first sentence thereof, and (2) inserting the following
clause at the end of the first sentence thereof: ", subject to customary
provisions set forth in the organizational documents of such Joint Venture
Subsidiary with respect to refinancings or rights of first refusal granted to
other members of such Joint Venture Subsidiary."

                  (d) The definition of "Unencumbered Asset Value" is hereby
amended by (1) inserting the words "the sum of" after the word "means" in the
first line thereof, (2) inserting the following words after "(i)" in the first
line thereof: "all Cash and Cash Equivalents of the Borrower, all Financing
Partnerships and Joint Venture Subsidiaries which are not subject to any pledge,
negative pledge, encumbrance, hypothecation or other restriction (provided that
in the case of Cash and Cash Equivalents of any Joint Venture Subsidiary, the
amount of Cash and Cash Equivalents attributable to such Joint Venture
Subsidiary shall be reduced to a percentage equal to the Borrower's percentage
ownership interest (whether direct or indirect) in such Joint Venture
Subsidiary), plus (ii)", (3) deleting "$1.50" from the fifth line thereof and
substituting therefor "$0.50", (4) renumbering clause (ii) in the tenth line
thereof as clause (iii) and revising all cross-references to such clause within
such definition, (5) deleting "twenty-five percent (25%)" from line 23 thereof
and substituting therefor "twenty percent (20%)", and (6) deleting "twenty-five
percent (25%)" from line 27 thereof and substituting therefor "fifteen percent
(15%)."

                  (e) Section 5.8(a) of the Credit Agreement is hereby deleted
in its entirety and substituted therefor is the following covenant:

                  (a) Total Liabilities to Total Asset Value. The Borrower shall
                  not permit the ratio of Total Liabilities to Total Asset Value
                  of Borrower to exceed 0.50:1 at any time except for the twelve
                  (12) month period described in the following sentence. During
                  the twelve (12) month period following the closing of the
                  Identified Merger or Acquisition, Borrower shall not permit
                  the ratio of Total Liabilities to Total Asset Value of the
                  Borrower to exceed 0.55:1. As used in this Agreement, the term
                  "Identified Merger or Acquisition" shall mean the first merger
                  or acquisition by Borrower or any Subsidiary which Borrower
                  has designated in writing to the Administrative Agent as the
                  Identified Merger or Acquisition at least thirty (30) days
                  prior to the closing of such merger or acquisition and for
                  which Borrower has, prior to the closing of such merger or
                  acquisition, provided the Administrative Agent with

<PAGE>   3

                  Borrower's projections for the twelve (12) month period
                  following such merger or acquisition, after giving effect to
                  such merger or acquisition, outlining in reasonable detail the
                  anticipated performance of Borrower during such twelve (12)
                  month period and anticipated compliance with the requirements
                  of Section 5.8 hereof during such twelve (12) month period.

                  (f) Section 5.8(j) of the Credit Agreement is hereby amended
by deleting "fifteen percent (15%)" from the sixth line thereof and substituting
therefor "twenty percent (20%)".

                  3. Confirmation of Guaranties. Guarantor hereby acknowledges
and agrees that the Amended and Restated Guaranty of Payment - No. 1 dated as of
May 29, 1998 and the Amended and Restated Guaranty of Payment - No. 2 dated as
of May 29, 1998, each entered into in connection with the Credit Agreement, and
the Guarantor's obligations under each such guaranty, continue in full force and
effect notwithstanding this Amendment.

                  4. Representations and Warranties. The Borrower hereby
represents and warrants to the Banks that no Default or Event of Default exists
under the Credit Agreement and that the representations and warranties of the
Borrower set forth in the Credit Agreement are true and correct on and as of the
date hereof, except to the extent that such representations and warranties
expressly speak only as of a prior date, in which case such representations and
warranties were true and correct on and as of such prior date.

                  5. Effective Date. This Amendment shall become effective upon
receipt by the Administrative Agent of counterparts hereof signed by each of the
parties hereto (or, in the case of any party as to which an executed counterpart
shall not have been received, receipt by the Administrative Agent in form
satisfactory to it of telegraphic, telex or other written confirmation from such
party of execution of a counterpart hereof by such party).

                  6. Entire Agreement. This Amendment constitutes the entire and
final agreement among the parties hereto with respect to the subject matter
hereof and there are no other agreements, understandings, undertakings,
representations or warranties among the parties hereto with respect to the
subject matter hereof except as set forth herein.

                  7. Governing Law. This Amendment shall be governed by, and
construed in accordance with, the law of the State of Illinois.

                  8. Counterparts. This Amendment may be executed in any number
of counterparts, all of which taken together shall constitute one and the same
agreement, and any of the parties hereto may execute this Amendment by signing
any such counterpart.

                  9. Headings, Etc. Section or other headings contained in this
Amendment are for reference purposes only and shall not in any way affect the
meaning or interpretation of this Amendment.

<PAGE>   4

                  10. No Further Modifications. Except as modified herein, all
of the terms and conditions of the Credit Agreement, as modified hereby shall
remain in full force and effect and, as modified hereby, the Borrower confirms
and ratifies all of the terms, covenants and conditions of the Credit Agreement
in all respects.

                            Signature Pages to Follow

<PAGE>   5

                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed by their respective authorized officers as of the
day and year first above written.

                                       EOP OPERATING LIMITED PARTNERSHIP, a
                                       Delaware limited partnership

                                       By: Equity Office Properties Trust, a
                                       Maryland real estate investment trust,
                                       its managing general partner

                                       By: /s/ RICHARD D. KINCAID
                                       Name:   Richard D. Kincaid
                                       Title:  Executive Vice President and
                                               Chief Financial Officer

WITH RESPECT TO
SECTION 3 HEREOF
ONLY:                                  EQUITY OFFICE PROPERTIES TRUST

                                       By: /s/ RICHARD D. KINCAID
                                       Name:   Richard D. Kincaid
                                       Title:  Executive Vice President and
                                               Chief Financial Officer

                                       THE BANK OF NOVA SCOTIA, as a Managing
                                       Agent and as a Bank

                                       By: /s/ R.H. BOESE
                                       Name:   R.H. Boese
                                       Title: Sr. Relationship Manager

                                       Commitment: $65,000,000

                                       COMMERZBANK AKTIENGESELLSCHAFT, as a
                                       Managing Agent and as a Bank

                                       By: /s/ DOUGLAS P. TRAYNOR
                                       Name:   Douglas P. Traynor
                                       Title:  Vice President

                                       By: /s/ DAVID BUETTNER
                                       Name:   David Buettner
                                       Title:  Assistant Treasurer

                                       Commitment: $65,000,000

                                       DRESDNER BANK AG, NEW YORK AND CAYMAN
                                       BRANCHES, as a Managing Agent and as Bank

                                       By: /s/ BEVERLY G. CASON
                                       Name:   Beverly G. Cason
                                       Title:  Vice President

                                       By: /s/ JOHN W. SWEENEY
                                       Name:   John W. Sweeney
                                       Title:  Vice President

                                       Commitment: $65,000,000

                                       PNC BANK, NATIONAL ASSOCIATION, as a
                                       Managing agent and as a bank

                                       By: /s/ MICHAEL E. SMITH
                                       Name:   Michael E. Smith
                                       Title:  Vice President

                                       Commitment: $65,000,000
<PAGE>   6

                                       NATIONSBANK, N.A., as Administrative
                                       Agent, as Swingline Lender and as a Bank

                                       By: /s/ PATRICK TROWBRIDGE
                                       Name:   Patrick Trowbridge
                                       Title:  Vice President

                                       Commitment: $138,000,000

                                       UBS AG, STAMFORD BRANCH,
                                       successor-in-interest to Union Bank of
                                       Switzerland, New York Branch, as a
                                       Managing Agent and as a Bank

                                       By: /s/ JEFFREY W. WALD
                                       Name:   Jeffrey W. Wald
                                       Title:  Executive Director

                                       By: /s/ DAVID GOLDMAN
                                       Name:   David Goldman
                                       Title:  Director

                                       Commitment: $65,000,000

                                       CREDIT LYONNAIS, NEW YORK BRANCE, as a
                                       Co-Agent and as a Bank

                                       By: /s/ JAMES R. FITZGERALD
                                       Name:   James R. Fitzgerald
                                       Title:  Senior Vice President

                                       Commitment: $54,000,000

                                       FLEET NATIONAL BANK, as a Co-Agent and as
                                       a Bank

                                       By: /s/ THOMAS J. PONTES
                                       Name:   Thomas J. Pontes
                                       Title:  Vice President

                                       Commitment: $54,000,000

                                       BANK ONE, ILLINOIS, N.A., as a Bank

                                       By: /s/ LYNN BRAUN
                                       Name:   Lynn Braun
                                       Title:  Vice President

                                       Commitment: $50,000,000

                                       U.S. BANK NATIONAL ASSOCIATION,
                                       as a Co-Agent and as a Bank

                                       By:
                                       Name:
                                       Title:

                                       Commitment: $54,000,000

                                       BAYERISCHE HYPO-UND VEREINSBANK AG,
                                       as successor by Merger to
                                       BAYERISCHE HYPOTHEKEN-UND WECHSEL-BANK
                                       AKTIENGESELLSCHAFT, as a Bank

                                       By: /s/ MEGGAN W. WALSH
                                       Name:   Meggan W. Walsh
                                       Title:  Managing Director

                                       By: /s/ DENNIS B. TRACEY
                                       Name:   Dennis B. Tracey
                                       Title:  Director

                                       Commitment: $50,000,000
<PAGE>   7

                                       THE CHASE MANHATTAN BANK, as
                                       Documentation Agent, as a Managing Agent
                                       and as a Bank

                                       By: /s/ MARC E. COSTANTINO
                                       Name:   Marc E. Costantino
                                       Title:  Vice President

                                       Commitment: $65,000,000

                                       BANKBOSTON, N.A., as a Bank

                                       By: /s/ DOUGLAS S. NOVITCH
                                       Name:   Douglas S. Novitch
                                       Title:  Authorized Officer

                                       Commitment: $31,000,000

                                       LASSALE NATIONAL BANK, as a Bank

                                       By: /s/ PETER MARGOLIN
                                       Name:   Peter Margolin
                                       Title:  A.V.P.

                                       Commitment: $30,000,000

                                       MELLON BANK, as a Bank

                                       By: /s/ MICHAEL FALLON
                                       Name:   Michael Fallon
                                       Title:  Vice President

                                       Commitment: $30,000,000

                                       UNION BANK OF CALIFORNIA, N.A., as a Bank

                                       By: /s/ DIANA GIACOMINI
                                       Name:   Diana Giacomini
                                       Title:  Vice President

                                       Commitment: $30,000,000

                                       THE INDUSTRIAL BANK OF JAPAN, LIMITED, as
                                       a Bank

                                       By: /s/ TAKESHI KUBO
                                       Name:   Takeshi Kubo
                                       Title:  Vice President

                                       Commitment: $20,000,000

<PAGE>   8
                                       J.P. MORGAN SECURITIES, INC., as
                                       Syndication Agent

                                       By: /s/ JENNY Y. LEE
                                       Name:   Jenny Y. Lee
                                       Title:  Vice President

                                       MORGAN GUARANTY TRUST COMPANY OF NEW
                                       YORK, as a Bank

                                       By: /s/ ROBERT BOTTAMEDI
                                       Name:   Robert Bottamedi
                                       Title:  Vice President

                                       Commitment: $69,000,000

Source: [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00005-of-00352.parquet"}, [{"source": "alea-institute/alea-institute/kl3m-data-edgar-agreements/train-00005-of-00352.parquet"}]]