
<PAGE>
 
                                                                   Exhibit 10.49

                                 PROMISSORY NOTE

                                  DEFINED TERMS

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Execution Date:       January __, 1998           City and State of Signing:  
                                                 Richmond, Virginia
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Loan Amount:          $121,800,000.00            Interest Rate:
                                                 6.61% per annum
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Borrower:             Boston Properties Limited Partnership,
                      a Delaware limited partnership

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Borrower's Address:   500 E Street, S.W.
                      Washington, D.C.  20024

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Holder: METROPOLITAN LIFE INSURANCE COMPANY, A NEW YORK CORPORATION
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Holder's Address:     Metropolitan Life Insurance Company
                      200 Park Avenue      12th Floor
                      New York, New York 10166
                      Attention:  Senior Vice-President,

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Maturity Date:  February 1, 2008          Advance Date: The date funds are 
                                          disbursed to Borrower.

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Interest Only Period: The period          Principal and Interest Installment
from the Advance Date and ending          Date:  The first day of the second
on the last day of the month in which     calendar month following the Advance
the Advance Date occurs.                  Date.
            
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Monthly Installment: Equal monthly        Permitted Prepayment Period: During 
installments of principal and interest    the 120 day period prior to the
at the Interest Rate each in the          Maturity Date, Borrower may prepay the
amount of $830,793.84.                    Loan without a Prepayment Fee. In
                                          addition, commencing on the first day 
The Monthly Installment is based upon     of the 37th month following the 
an amortization period of 25 years.       Advance Date, Borrower may prepay the 
                                          Loan with a Prepayment Fee on 60 days 
                                          prior written notice to Holder which 
                                          notice can be revoked by Borrower 
                                          giving notice to Holder of such
                                          revocation at least thirty (30) days 
                                          prior to the scheduled Payment Date 
                                          (and in the event of any such
                                          revocation, no Prepayment Fee shall 
                                          be payable).
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Liable Parties:  Boston Properties Limited Partnership, a Delaware limited 
                 partnership

Addresses of Liable Parties:  500 E Street SW, Washington, DC 20024

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Late Charge:  An amount equal to four cents ($.04) for each dollar that is 
              overdue.

Default Rate: An annual rate equal to the Interest Rate plus four percent (4%).

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Note: This Promissory Note. Deed of Trust: Deed of Trust, Security Agreement,
and Fixture Filing dated as of the Execution Date granted by Borrower to the
Trustee named in the Deed of Trust for the benefit of Holder. Loan Documents:
This Note, the Deed of Trust and any other documents evidencing or securing the
indebtedness evidenced by this Note and/or the Deed of Trust and all renewals,
amendments, modifications, restatements and extensions of these documents.
Indemnity Agreement: Unsecured Indemnity Agreement dated as of the Execution
Date and executed by Borrower in favor of Holder. The Unsecured Indemnity
Agreement is not a Loan Document and shall survive repayment of the Loan or
other termination of the Loan Documents.
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     FOR VALUE RECEIVED, Borrower promises to pay to the order of Holder at
Holder's Address or such other place as Holder may from time to time designate,
the Loan Amount with interest payable in the manner described below, in money of
the United States of America that at the time of payment shall be legal tender
for payment of all obligations.

     Capitalized terms which are not defined in this Note shall have the
meanings set forth in the Deed of Trust.

         1. Payment of Principal and Interest. Principal and interest under this
            ---------------------------------
Note shall be payable as follows:

            (a) Interest on the funded portion of the Loan Amount shall accrue
from the Advance Date at the Interest Rate and shall be paid on the first day of
the first calendar month following the Advance Date;

            (b) Commencing on the Principal and Interest Installment Date and on
the first day of each calendar month thereafter, to and including the first day
of the calendar month immediately preceding the Maturity Date, Borrower shall
pay the Monthly Installment; and

            (c) On the Maturity Date, a final payment in the aggregate amount of
the unpaid principal sum evidenced by this Note, all accrued and unpaid
interest, and all other sums evidenced by this Note or secured by the Deed of
Trust and/or any other Loan Documents as well as any future advances under the
Deed of Trust that may be made to or on behalf of Borrower by Holder following
the Advance Date (collectively, the "Aggregate Indebtedness"), shall become
immediately payable in full.

     Borrower acknowledges and agrees that a substantial portion of the original
Loan Amount shall be outstanding and due on the Maturity Date.

     Interest shall be calculated on the basis of a thirty (30) day month and a
three hundred sixty (360) day year, except that (i) if the Advance Date occurs
on a date other than the first day of a calendar month, interest payable for the
period commencing on the Advance Date and ending on the last day of the month in
which the Advance Date occurs shall be calculated on the basis of the actual
number of days elapsed over a 365 day or 366 day year, as applicable, and (ii)
if the Maturity Date occurs on a date other than the last day of the month,
interest payable for the period commencing on the first day of the month in
which the Maturity Date occurs and ending on the Maturity Date shall be
calculated on the basis of the actual number of days elapsed over a 365 day or
366 day year, as applicable.

         2. Application of Payments. At the election of Holder, and to the
            -----------------------
extent permitted by law, all payments shall be applied in the order selected by
Holder to any expenses, prepayment fees, late charges, escrow deposits and other
sums due and payable under the Loan Documents, and to unpaid interest at the
Interest Rate or at the Default Rate, as applicable. The balance of any payments
shall be applied to reduce the then unpaid Loan Amount.

         3. Security. The covenants of the Deed of Trust are incorporated by
            --------
reference into this Note. This Note shall evidence, and the Deed of Trust shall
secure, the Aggregate Indebtedness.

         4. Late Charge. If any payment of interest, any payment of a Monthly
            -----------
Installment or any payment of a required escrow deposit is not paid within 7
days of the due date, Holder shall have the option to charge Borrower the Late
Charge. The Late Charge is for the purpose of defraying the expenses incurred in
connection with handling and processing delinquent payments and is payable in
addition to any other remedy Holder may have. Unpaid Late Charges shall become
part of the Aggregate Indebtedness and shall be added to 

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any subsequent payments due under the Loan Documents.

     5. Acceleration Upon Default. At the option of Holder, if Borrower fails to
        -------------------------
pay any sum specified in this Note when due after giving effect to any grace
periods, or if an Event of Default occurs, the Aggregate Indebtedness, and all
other sums evidenced and/or secured by the Loan Documents, including without
limitation any applicable prepayment fees (collectively, the "Accelerated Loan
Amount") shall become immediately due and payable upon notice by Holder to
Borrower.

     6. Interest Upon Default. The Accelerated Loan Amount shall bear interest
        ---------------------
at the Default Rate which shall never exceed the maximum rate of interest
permitted to be contracted for under the laws of the Commonwealth of Virginia.
The Default Rate shall commence upon the occurrence of an Event of Default,
after giving effect to any grace periods and shall continue until all defaults
are cured.

     7. Limitation on Interest. The agreements made by Borrower with respect to
        ----------------------
this Note and the other Loan Documents are expressly limited so that in no event
shall the amount of interest received, charged or contracted for by Holder
exceed the highest lawful amount of interest permissible under the laws
applicable to the Loan. If at any time performance of any provision of this Note
or the other Loan Documents results in the highest lawful rate of interest
permissible under applicable laws being exceeded, then the amount of interest
received, charged or contracted for by Holder shall automatically and without
further action by any party be deemed to have been reduced to the highest lawful
amount of interest then permissible under applicable laws. If Holder shall ever
receive, charge or contract for, as interest, an amount which is unlawful, at
Holder's election, the amount of unlawful interest shall be refunded to Borrower
(if actually paid) or applied to reduce the then unpaid Loan Amount. To the
fullest extent permitted by applicable laws, any amounts contracted for, charged
or received under the Loan Documents included for the purpose of determining
whether the Interest Rate would exceed the highest lawful rate shall be
calculated by allocating and spreading such interest to and over the full stated
term of this Note.

     8. Prepayment. Borrower shall not have the right to prepay all or any
        ----------
portion of the Loan Amount at any time during the term of this Note except as
expressly set forth in the Defined Terms. If Borrower provides notice of its
intention to prepay, the Accelerated Loan Amount shall become due and payable on
the date specified in the prepayment notice unless Borrower revokes such notice
of prepayment at least thirty (30) days prior to the scheduled Payment Date (in
which event no Prepayment Fee shall be payable).

     9. Prepayment Fee. (a) Any tender of payment by Borrower or any other
        --------------
person or entity of the Aggregate Indebtedness, other than as expressly provided
in the Loan Documents, shall constitute a prohibited prepayment. If a prepayment
of all or any part of the Aggregate Indebtedness is made following (i) an Event
of Default and an acceleration of the Maturity Date or (ii) in connection with a
purchase of the Property or a repayment of the Aggregate Indebtedness at any
time before, during or after, a judicial or non-judicial foreclosure or sale of
the Property, then to compensate Holder for the loss of the investment, Borrower
shall pay an amount equal to the Prepayment Fee (as hereinafter defined). Any
prepayment as a result of the application of money to the principal of the Loan
after a casualty or condemnation shall not require the payment of a Prepayment
Fee.

     (b) The "Prepayment Fee" shall be the greater of (A) the Prepayment Ratio
(as hereinafter defined) multiplied by the difference between (x) and (y), where
(x) is the present value of all remaining payments of principal and interest
including the outstanding principal due on the Maturity Date, discounted at the
rate which, when compounded monthly, is equivalent to the Treasury Rate
compounded semi-annually, and (y) is the amount of the principal then
outstanding, or (B) one percent (1%) of the amount of the principal being
prepaid.

     (c) The "Treasury Rate" shall be the annualized yield on securities issued
by the United States Treasury having a maturity equal to the remaining stated
term of the Note, as quoted in the Federal Reserve Statistical Release [H. 15
                                   ------------------------------------------
(519)] under the heading "U.S. Government Securities Treasury Constant
------
Maturities" for the date on which prepayment is being made. If this rate is not
available as of the date of prepayment, the 

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Treasury Rate shall be determined by interpolating between the yield on
securities of the next longer and next shorter maturity. If the Treasury Rate is
no longer published, Holder shall select a comparable rate. Holder will, upon
request, provide an estimate of the amount of the Prepayment Fee two weeks
before the date of the scheduled prepayment.

     (d) The "Prepayment Ratio" shall be a fraction, the numerator of which
shall be the amount of principal being prepaid, and the denominator of which
shall be the principal then outstanding.

     10. Waiver of Right to Prepay Note Without Prepayment Fee. Borrower
         -----------------------------------------------------
acknowledges that Holder has relied upon the anticipated investment return under
this Note in entering into transactions with, and in making commitments to,
third parties and that the tender of any prohibited prepayment, shall, to the
extent permitted by law, include the Prepayment Fee. Borrower agrees that the
Prepayment Fee represents the reasonable estimate of Holder and Borrower of a
fair average compensation for the loss that may be sustained by Holder as a
result of a prohibited prepayment of the Note and it shall be paid without
prejudice to the right of Holder to collect any other amounts provided to be
paid under the Loan Documents.

     11. Liability of Borrower. Upon the occurrence of an Event of Default,
         ---------------------
except as provided in this Section 11, Holder will look solely to the Property
and the security under the Loan Documents for the repayment of the Loan and will
not enforce a deficiency judgment against Borrower or the general partners of
Borrower. However, nothing contained in this section shall limit the rights of
Holder to proceed against Borrower and the general partners of Borrower (i) to
recover actual damages for fraud, intentional material misrepresentation or
intentional waste; (ii) to recover condemnation proceeds or insurance proceeds
or other similar funds which have been misapplied by Borrower or which, under
the terms of the Loan Documents, should have been paid to Holder; (iii) to
recover any tenant security deposits, tenant letter of credit or other deposits
or fees paid to Borrower that are part of the collateral for the Loan or prepaid
rents for a period of more than 30 days which have been misapplied by Borrower;
(iv) to recover Rents and Profits (as defined in the Deed of Trust) received by
Borrower after an Event of Default occurs and prior to the date Holder acquires
title to the Property which have not been applied to the Loan or in accordance
with the Loan Documents to operating and maintenance expenses of the Property;
(v) to recover actual damages, costs and expenses arising from, or in connection
with the provisions of the Deed of Trust pertaining to hazardous materials or
the Indemnity Agreement; (vi) to recover all amounts due and payable pursuant to
Section 11.06 and 11.07 of the Deed of Trust; and/or (vii) to recover actual
damages arising from Borrower's failure to comply with the provisions of the
Deed of Trust pertaining to ERISA.

     12. Waiver by Borrower. Except as otherwise required hereunder or under the
         ------------------
Deed of Trust, Borrower and others who may become liable for the payment of all
or any part of the Note, and each of them, waive diligence, demand, presentment
for payment, notice of nonpayment, protest, notice of dishonor and notice of
protest, notice of intent to accelerate and notice of acceleration and
specifically consent to and waive notice of any amendments, modifications,
renewals or extensions of this Note, including the granting of extension of time
for payment, whether made to or in favor of Borrower or any other person or
persons.

     13. Exercise of Rights. No single or partial exercise by Holder, or delay
         ------------------
or omission in the exercise by Holder, of any right or remedy under the Loan
Documents shall waive or limit the exercise of any such right or remedy. Holder
shall at all times have the right to proceed against any portion of or interest
in the Property in the manner that Holder may deem appropriate, without waiving
any other rights or remedies. The release of any party under this Note shall not
operate to release any other party which is liable under this Note and/or under
the other Loan Documents or under the Unsecured Indemnity Agreement.

     14. Fees and Expenses. [Deleted.]
         -----------------

     15. No Amendments. This Note may not be modified or amended except in a
         -------------
writing executed by Borrower and Holder. No waivers shall be effective unless
they are set forth in a writing signed by the party which is waiving a right.
This Note and the other Loan Documents are the final expression of the 

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lending relationship between Borrower and Holder.

     16. Governing Law. This Note is to be construed and enforced in accordance
         -------------
with the laws of the Commonwealth of Virginia.

     17. Construction. The words "Borrower" and "Holder" shall be deemed to
         ------------
include their respective heirs, representatives, successors and assigns, and
shall denote the singular and/or plural, and the masculine and/or feminine, and
natural and/or artificial persons, as appropriate. The provisions of this Note
shall remain in full force and effect notwithstanding any changes in the
shareholders, partners or members of Borrower. If more than one party is
Borrower, the obligations of each party shall be joint and several. The captions
in this Note are inserted only for convenience of reference and do not expand,
limit or define the scope or intent of any section of this Note.

     18. Notices. All notices, demands, requests and consents permitted or
         -------
required under this Note shall be given in the manner prescribed in the Deed of
Trust.

     19. Time of the Essence. Time shall be of the essence with respect to all
         -------------------
of Borrower's obligations under this Note.

     20. Severability. If any provision of this Note should be held
         ------------
unenforceable or void, then that provision shall be deemed separable from the
remaining provisions and shall not affect the validity of this Note, except that
if that provision relates to the payment of any monetary sum, then Holder may,
at its option, declare the Aggregate Indebtedness (together with the Prepayment
Fee) immediately due and payable.

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<PAGE>
 
     IN WITNESS WHEREOF, Borrower has executed this Note as of the Execution
Date.


                                   BOSTON PROPERTIES LIMITED PARTNERSHIP,
                                   a Delaware limited partnership


                                   By:   Boston Properties, Inc.,
                                         doing business in Virginia
                                         as Delaware Boston Properties, Inc.,
                                         its general partner

                                         By:
                                            ------------------------------------
                                             Name:  David G. Gaw
                                             Title: Senior Vice President


245596
Promissory Note - Deed of Trust

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