
<PAGE>
 
                                                                   Exhibit 99.13

                      PRUDENTIAL REALTY SECURITIES, INC.
                                8 CAMPUS DRIVE
                         PARSIPPANY, NEW JERSEY 07054


                                                  As of November 12, 1998


THREE EMBARCADERO CENTER VENTURE
C/O BOSTON PROPERTIES, INC.
8 ARLINGTON STREET
BOSTON, MASSACHUSETTS 02116-3495
ATTN: GENERAL COUNCIL

Ladies and Gentlemen:

     The undersigned, PRUDENTIAL REALTY SECURITIES, INC. (herein called the
"COMPANY"), hereby agrees with you as follows:

     1.   AUTHORIZATION OF ISSUE OF NOTES.  The Company will authorize the issue
of up to eight (8) of its senior promissory notes in the aggregate principal
amount of $76,897,000, to be dated the date of issue thereof, to mature in the
case of each Note so issued, subject to the terms and provisions of the next
sentence below, not more than 15 years after the date of original issuance
thereof as set forth in each such Note (the "MATURITY DATE") and listed on
Schedule 1 attached hereto, to bear interest on the unpaid balance thereof from
----------                                                                     
the date thereof until the Rate Reset Date or, if such Note does not have a Rate
Reset Date, the Maturity Date for each such Note at the rate per annum equal to
the Initial Treasury plus the Margin, and from the Rate Reset Date (if any) of
any such Note until the principal thereof shall have become due and payable at
the rate per annum equal to the Reset Treasury plus the Margin, and to have such
other particular terms, as shall be specified herein and therein, and to be
substantially in the form of Exhibit A attached hereto. Notwithstanding the
                             ---------                                     
foregoing, each Note shall either mature or have a Rate Reset Date within ten
(10) years after the date of original issuance of such Note.  The term "Notes"
as used herein shall include each such senior promissory note delivered pursuant
to any provision of this Agreement and each such senior promissory note
delivered in substitution or exchange for any other Note pursuant to any such
provision.

     2.   PURCHASE AND SALE OF NOTES.  The Company hereby agrees to sell to you
and, subject to the terms and conditions herein set forth, you agree to purchase
from the Company, Notes in the aggregate principal amount of $76,897,000 at 100%
of such 

                                       1
<PAGE>
 
aggregate principal amount. The Company will deliver to you, at the offices of
O'Melveny & Myers LLP at 275 Battery Street, Suite 2600, San Francisco,
California, (or such other location to be determined by mutual agreement between
the Company and you) one or more Notes registered in your name, evidencing the
aggregate principal amount of Notes to be purchased by you and in the
denomination or denominations specified in the Purchaser Schedule attached
hereto, against payment of the purchase price thereof by transfer of immediately
available funds for credit to the Company's account #890-0305-525 at The Bank of
New York, New York, New York, ABA No. 021-000-018 on the date of closing, which
shall be November 12, 1998 or any other date on or before November 13, 1998 upon
which the Company and you may mutually agree (herein called the "CLOSING" or the
"DATE OF CLOSING").

     3.   CONDITIONS OF CLOSING.  Your obligation to purchase and pay for the
Notes to be purchased by you hereunder is subject to the satisfaction, on or
before the date of closing, of the following conditions:

     3A.  EXECUTION AND DELIVERY OF DOCUMENTS.  The Company shall have
delivered, or cause to be delivered, to you duly executed, original or certified
copies of the following documents, each to be dated the date of closing unless
otherwise indicated:

          (i)       the Note(s), originally executed and in substantially the
     form of Exhibit A attached hereto.
             ---------                 

          (ii)      a favorable opinion of Deborah Shulevitz, Esq., counsel to
     the Company (or such other counsel designated by the Company and acceptable
     to you) satisfactory to you and substantially in the form of Exhibit B
                                                                  ---------
     attached hereto and as to such other matters as you may reasonably request.

          (iii)     the Certificate of Incorporation of the Company certified as
     of a date within 10 Business Days of closing by the Secretary of State of
     Delaware.

          (iv)      the Bylaws of the Company certified by the Secretary of the
     Company.

          (v)       an incumbency certificate signed by the Secretary or an
     Assistant Secretary of the Company certifying as to the names, titles and
     true signatures of the officers of the Company authorized to sign this
     Agreement and the Notes and the other documents to be delivered hereunder.

          (vi)      a certificate of the Secretary or Assistant Secretary of the
     Company (A) attaching resolutions of the Board of Directors of the Company
     evidencing approval of the transactions contemplated by this Agreement and
     the issuance of the Notes and the execution, delivery and performance
     thereof, and authorizing certain officers to execute and deliver the same,
     and certifying that such resolutions 

                                       2
<PAGE>
 
     were duly and validly adopted at a meeting duly noticed and held and such
     resolutions have not since been amended, revoked or rescinded, (B)
     certifying that no dissolution or liquidation proceedings as to the Company
     have been commenced or are contemplated, and (C) identifying and attaching
     any proposed or effected amendments to or changes in the Certificate of
     Incorporation of the Company since the date of the certified copies thereof
     provided pursuant to clause (iii) above or, if none, so certifying.
                          ------------                                  

          (vii)     (A) the representations and warranties contained in
     paragraph 8 shall be true on and as of the date of closing, except to the
     -----------
     extent of changes caused by the transactions herein contemplated; (B) there
     shall exist on the date of closing no Event of Default or Default and no
     Event of Default or Default will occur by reason of or immediately
     following the sale of the Notes hereunder; (C) no condition, event or act
     that has had or would have a Material Adverse Effect has occurred since
     December 31, 1997, and (D) you shall have received an Officer's Certificate
     certifying as to all of the foregoing.

          (viii)    a corporate good standing certificate as to the Company from
     the State of New Jersey.

          (xi)      additional documents or certificates with respect to such
     legal matters or corporate or other proceedings related to the transactions
     contemplated hereby as may be reasonably requested by you.

     3B.  PURCHASE PERMITTED BY APPLICABLE LAWS.  The purchase of and payment
for the Notes to be purchased by you on the date of closing on the terms and
conditions herein provided (including the use of the proceeds of such Notes by
the Company) shall not violate any applicable law or governmental regulation
(including, without limitation, Section 5 of the Securities Act or Regulation T,
U or X of the Board of Governors of the Federal Reserve System) and shall not
subject you to any tax, penalty, liability or other onerous condition under or
pursuant to any applicable law or governmental regulation, and you shall have
received such certificates or other evidence as you may request to establish
compliance with this condition.

     3C.  PROCEEDINGS.  All corporate and other proceedings taken or to be taken
in connection with the transactions contemplated hereby and all documents
incident thereto shall be satisfactory in substance and form to you, and you
shall have received all such counterpart originals or certified or other copies
of such documents as you may reasonably request.

     3D.  RATING.  The Company shall have obtained a rating of the Notes, as of
a date not more than 30 days prior to the closing hereof, of A or better from
S&P and the equivalent rating from Fitch and shall provide written evidence of
the same.

                                       3
<PAGE>
 
     3E.  PHASE ONE TRANSACTIONS.  Phase One of the transactions shall have been
completed or shall be consummated concurrently with the consummation of the
transactions described herein.

     3F.  EQUITY REDEMPTION AND PRUDENTIAL GUARANTIED LOANS.  You shall have
obtained the Prudential Guarantied Loan and Equity Redemption Loan or the
closing of such loans shall occur concurrently with the closing of the
transactions contemplated herein; and the lenders of the Prudential Guarantied
Loan and Equity Redemption Loan shall have made available to you in full the
proceeds of the Prudential Guarantied Loan and Equity Redemption Loan.

     4.   PREPAYMENTS.  The Notes are not prepayable during the first year of
the term thereof.  The Notes shall be subject to prepayment, in whole or in part
at any time after the first anniversary date of this Agreement, at the option of
the Company, at 100% of the principal amount so prepaid plus accrued interest
thereon to the prepayment date and the Yield-Maintenance Amount, if any, under
the applicable Note with respect to the principal amount so prepaid; provided,
however, that any prepayment, whether in whole or in part, made on a Rate Reset
Date shall be payable without any Yield-Maintenance Amount.  If the Company
elects to prepay any of the Notes at any time while any BP Party holds any
Notes, the Company shall first offer to prepay all Notes then held by such BP
Party(ies) before offering to prepay any Notes held by any other Person.  Within
three (3) business days after delivery to it of any such offer of prepayment,
each such BP Party shall provide the Company written notice of its election to
either have such BP Party's Notes prepaid first or to have the Notes held by
other Persons prepaid prior to the Notes held by such BP Party; provided that,
                                                                -------- ---- 
notwithstanding the election of any such BP Party to have Notes held by other
Persons paid first, the Company may prepay any portion of such BP Party's Notes
once the Company has prepaid in full all Notes held by such other Persons.  The
failure of any BP Party to provide such notice to the Company within such three
(3) business day period shall be deemed an election to prepay such BP Party's
Notes first.

     5.   AFFIRMATIVE COVENANTS.

     5A.  FINANCIAL STATEMENTS.  The Company covenants that it will deliver to
each Significant Holder in duplicate:

          (i) as soon as practicable and in any event within 60 days after the
     end of each quarterly period (other than the last quarterly period) in each
     fiscal year, statements of income, cash flows and shareholders' equity of
     the Company for the period from the beginning of the current year to the
     end of such quarterly period, and a balance sheet of the Company as at the
     end of such quarterly period, setting forth in comparative form statements
     of income and cash flows for the corresponding period in the preceding
     year, all in reasonable detail and certified by an authorized financial
     officer of the Company, subject to changes resulting from year-end
     adjustments;

                                       4
<PAGE>
 
          (ii)  as soon as practicable and in any event within 120 days after
     the end of each fiscal year, statements of income, cash flows and
     shareholders' equity of the Company for such year, and a balance sheet of
     the Company as at the end of such year, all prepared in accordance with
     GAAP, setting forth in each case in comparative form corresponding
     consolidated figures from the preceding annual audit, all in reasonable
     detail and satisfactory in form to the Required Holder(s)' and reported on
     by a Big Five Accounting Firm selected by the Company whose report shall be
     without limitation as to the scope of the audit and reasonably satisfactory
     in substance to the Required Holder(s) and shall be certified by such Big
     Five Accounting Firm to its knowledge with its unqualified opinion;

          (iii) promptly upon transmission thereof, copies of all such financial
     statements, proxy statements, notices and reports as it shall send to its
     stockholders;

          (iv)  promptly upon receipt thereof, a copy of each other report or
     management letter submitted to the Company by its independent public
     accountants in connection with any annual, interim or special audit made by
     them of the books of the Company;

           (v)  such other financial data and other information as the Company
     regularly provides to its other lenders, other holders of Debt or other
     creditors; and

          (vi)  with reasonable promptness, such other information and documents
     as such Significant Holder may reasonably request.

Together with each delivery of financial statements required by clauses (i) and
                                                                -----------    
(ii) above, the Company will deliver to each Significant Holder an Officer's
----                                                                        
Certificate demonstrating (with computations in reasonable detail) compliance by
the Company and its Subsidiaries with the provisions of paragraph 6A and stating
                                                        ------------            
that there exists no Event of Default or Default, or, if any Event of Default or
Default exists, specifying the nature and period of existence thereof and what
action the Company proposes to take with respect thereto.  Together with each
delivery of financial statements required by clause (ii) above, the Company will
                                             -----------                        
deliver to each Significant Holder a certificate of such accountants stating
that, in making the audit necessary for their report on such financial
statements, they have obtained no knowledge of any Event of Default or Default,
or, if they have obtained knowledge of any Event of Default or Default,
specifying the nature and period of existence thereof.  Such accountants,
however, shall not be liable to anyone by reason of their failure to obtain
knowledge of any Event of Default or Default which would not be disclosed in the
course of an audit conducted in accordance with generally accepted auditing
standards.

     The Company also covenants that promptly after any Responsible Officer
obtains knowledge of an Event of Default or Default, it will deliver to each
Significant Holder an Officer's Certificate specifying the nature and period of
existence thereof and what action the Company has taken, is taking or proposes
to take with respect thereto.

                                       5
<PAGE>
 
     5B.  INSPECTION OF BOOKS AND RECORDS.  The Company covenants that it will
permit any Person designated by any Significant Holder in writing, at such
Significant Holder's expense, to visit the Company's place of business to
examine the corporate books and financial records of the Company and make copies
thereof or extracts therefrom and to discuss the affairs, finances and accounts
of the Company with the principal officers thereof and its independent public
accountants, all at such reasonable times and as often as such Significant
Holder may reasonably request; provided, however that disclosure of any
                               --------                                
confidential or material non-public information of the Company requested by such
Person may be reasonably conditioned on such Person's execution and delivery of
a confidentiality agreement in form and substance acceptable to Company.

     5C.  COVENANT TO SECURE NOTE EQUALLY.  The Company covenants that if it
shall create or assume any Lien upon any of its property or assets, whether now
owned or hereafter acquired, other than Liens permitted by the provisions of
paragraph 6C(1) (unless prior written consent to the creation or assumption
---------------                                                            
thereof shall have been obtained pursuant to paragraph 11C), it will make or
                                             -------------                  
cause to be made effective provision whereby the Notes will be secured by such
Lien equally and ratably with any and all other Debt thereby secured so long as
any such other Debt shall be so secured; provided that the creation and
                                         --------                      
maintenance of such equal and ratable Lien shall not in any way limit or modify
the right of the holders of the Notes to enforce the provisions of paragraph
                                                                   ---------
6C(1).
----- 

     5D.  COMPLIANCE WITH LAWS.  The Company covenants that it and all of its
properties and facilities will comply at all times in all material respects with
all federal, state, local and regional statutes, laws, ordinances and judicial
or administrative orders, judgments, rulings and regulations, including those
relating to protection of the environment except, in any such case, where
failure to comply would not result in a Material Adverse Effect on the business,
condition (financial or otherwise) or operations of the Company.

     5E.  PAYMENT OF TAXES.  The Company covenants that it will file or cause to
be filed all federal, state and other income tax returns which, to the knowledge
of the officers of the Company, are required to be filed, and will pay all taxes
as shown on such returns and on all assessments received by it to the extent
that such taxes become due, except such taxes as are subject to a Good Faith
Contest.

     5F.  ENFORCEMENT OF MORTGAGE PROVISIONS.  The Company covenants that it
shall require any Commercial Mortgage Loans originated or acquired by it to
contain covenants to the effect that (1) the mortgagor shall obtain and maintain
at all times appropriate insurance coverage with respect to the mortgaged
property and (2) the mortgagor shall promptly pay and discharge any indebtedness
or lawful claims against the mortgaged property which if unpaid would constitute
a Lien on such property.  The Company further covenants and agrees that it will
use commercially reasonable efforts to enforce such covenants.

     6.   NEGATIVE COVENANTS.  So long as any Note or amount owing under this
Agreement shall remain unpaid, the Company covenants that:

                                       6
<PAGE>
 
     6A(1). DEBT SERVICE COVERAGE RATIO.  The Company will not, at any time,
permit the Debt Service Coverage Ratio to be less than 1.4 to 1.

     6A(2). DEBT TO TOTAL ASSETS RATIO.  The Company will not permit the ratio
of (i) Debt to (ii) the sum of Total Assets plus the cumulative depreciation of
any real property assets of the Company to exceed .70 to 1.

     6B.  RESTRICTED PAYMENTS.  The Company covenants that it will not make, pay
or declare, or commit to make, pay or declare, any Restricted Payment unless,
after giving effect thereto, (i) the aggregate amount of all Restricted Payments
made during the twelve month period commencing on the date hereof and expiring
on the one (1) year anniversary of the date hereof, and including all previously
made Restricted Payments, does not exceed 100% of the lesser of (A) Net Income
and (B) Net Income (determined without giving effect to any current income taxes
or any change in deferred taxes), in each case, for all such fiscal quarters
during such time period on a cumulative basis, and (ii) the aggregate amount of
all Restricted Payments made during any fiscal quarter after the expiration of
such twelve (12) month period, and including all previously made Restricted
Payments, does not exceed 105% of the lesser of (C) Net Income and (D) Net
Income (determined without giving effect to any current income taxes or any
change in deferred taxes), in each case, for all such fiscal quarters on a
cumulative basis, and (iii) no Default or Event of Default exists or would exist
after giving effect to such Restricted Payment.

     6C.  LIENS, DEBT, AND OTHER RESTRICTIONS.  The Company will not:

     6C(1). LIENS.  Create, assume or suffer to exist any Lien upon any of its
properties or assets, whether now owned or hereafter acquired, or any income,
participation, royalty or profits therefrom (whether or not provision is made
for the equal and ratable securing of the Notes in accordance with the
provisions of paragraph 5C), except for the Liens specified in clauses (i)
              ------------   ------                            -----------
through (xi) below (collectively, "PERMITTED LIENS");
        ----                                         

          (i)   Liens for taxes, assessments or other governmental levies or
     charges not yet due or which are subject to a Good Faith Contest;

          (ii)  statutory Liens of landlords and Liens of carriers, contractors,
     warehousemen, mechanics and materialmen incurred in the ordinary course of
     business for sums not yet due or which are subject to a Good Faith Contest;

          (iii) Liens (other than any Lien imposed by the Employee Retirement
     Income Security Act of 1974, as amended ("ERISA")) incurred, or deposits
     made, in the ordinary course of business (A) in connection with workers'
     compensation, unemployment insurance, old age benefit and other types of
     social security, (B) to secure (or to obtain letters of credit that secure)
     the performance of tenders, statutory obligations, surety and appeal bonds,
     bids, leases, performance bonds, purchase, construction, government or
     sales contracts and other similar obligations or (C) otherwise to satisfy
     statutory or legal obligations; provided, that in each such case 
                                     --------

                                       7
<PAGE>
 
     such Liens (1) were not incurred or made in connection with the incurrence
     or maintenance of Indebtedness, the borrowing of money, the obtaining of
     advances or credit, and (2) do not in the aggregate materially detract from
     the value of the property or assets so encumbered or materially impair the
     use thereof in the operation of its business;

          (iv)   Liens existing (A) prior to the time of acquisition upon any
     property acquired by the Company through purchase, merger or consolidation
     or otherwise, whether or not expressly assumed by the Company, or (B)
     placed on property at the time of acquisition by the Company or to secure
     all or a portion of (or to secure Debt incurred to pay all or a portion of)
     the purchase price thereof; provided that such Lien shall not have been
                                 --------                                   
     created, incurred or assumed in contemplation of such purchase, merger,
     consolidation or other event;

          (v)    Liens now or hereafter required by this Agreement;

          (vi)   Liens in existence on the date hereof as set forth on Schedule
                                                                       --------
     6C(1) hereto;
     -----        

          (vii)  leases, subleases, licenses and sublicenses granted to third
     parties not interfering in any material respect with the business of the
     Company;

          (viii) minor survey exceptions or minor encumbrances, easements or
     reservations, or rights of others for rights-of-way, utilities and other
     similar purposes, or zoning or other restrictions as to use of real
     property, that are necessary for the conduct of the operations of the
     Company or that customarily exist on properties of corporations engaged in
     similar businesses and are similarly situated and that do not in any event
     materially impair their use in the operations of the Company;

          (ix)   any attachment or judgment Lien, unless the judgment it secures
     shall not, within 60 days after the entry thereof, have been discharged or
     execution thereof stayed pending appeal, or shall not have been discharged
     within 60 days after the expiration of any such stay; provided the
                                                           --------    
     aggregate amount of such attachment or judgment Liens shall not secure
     obligations in excess of $10,000,000 at any time;

          (x)    Liens other than those described in clauses (i) through (ix)
                                                     -----------         ----
     above that secure Debt permitted by clauses (i) and (ii) of paragraph
                                         -----------     ----    ---------
     6C(2); provided that no Default or Event of Default shall exist and be
            --------                                                       
     continuing or shall result therefrom; or

          (xi)   any Lien renewing, extending or refunding any Lien permitted by
     clause (x) above.
     ----------       

     6C(2). DEBT.  Create, incur, assume or in any other way become liable in
respect of any Debt, except
                     ------

                                       8
<PAGE>
 
          (i)   the Notes;

          (ii)  Funded Debt of the Company described in Schedule 6C(2) and
                                                        --------------    
     outstanding as of the date hereof; and

          (iii) additional Funded Debt of the Company in an amount, which when
     added to all other Funded Debt of the Company then outstanding (but
     excluding the Funded Debt evidenced by the Notes and the Other EC Notes),
     does not exceed $1,000,000,000 at any one time outstanding.

     6C(3). LOANS, ADVANCES, INVESTMENTS AND CONTINGENT LIABILITIES.  Make or
permit to remain outstanding any loan or advance to, or extend credit other than
credit extended in the normal course of business to any Person who is not an
Affiliate of the Company to, or Guarantee, directly or indirectly, in connection
with the obligations, stock or dividends of, or own, purchase or acquire any
stock, obligations or securities of, or any other interest in, or make any
capital contribution to, any Person, or commit to do any of the foregoing, (all
of the foregoing collectively being "INVESTMENTS"), except for the Investments
                                                    ------                    
set forth in clauses (i) through (ix) below (collectively, "PERMITTED
             -----------         ----                                
INVESTMENTS"):

          (i)   obligations backed by the full faith and credit of the United
     States Government (whether issued by the United States Government or an
     agency thereof), and obligations guaranteed by the United States
     Government, in each case which mature within one year from the date
     acquired;

          (ii)  demand and time deposits with, Eurodollar deposits with or
     certificates of deposit issued by any commercial bank or trust company (1)
     organized under the laws of the United States or any of its states or
     having branch offices therein, (2) having equity capital in excess of
     $100,000,000 and (3) which issues either (x) senior debt securities rated A
     or better by S&P, A or better by Moody's or (y) commercial paper rated A-2
     or better by S&P or Prime-2 or better by Moody's (or, in either case, an
     equivalent rating from another nationally recognized credit rating agency)
     ("RATED BANKS"), in each case payable in the United States in United States
     dollars and in each case which mature within one year from the date
     acquired;

          (iii) marketable commercial paper and loan participations rated A-1 or
     better by S&P or P-1 or better by Moody's (or, in either case, an
     equivalent rating from another nationally recognized credit rating agency)
     and maturing not more than 270 days from the date acquired;

          (iv)  bonds, debentures, notes or similar debt instruments issued by a
     state or municipality given a "AA" rating or better by S&P or an equivalent
     rating by another nationally recognized credit rating agency and maturing
     not more than one year from the date acquired;

                                       9
<PAGE>
 
          (v)    the loans, investments and advances existing as of the date
     hereof and listed on Schedule 6C(3) hereto;
                          --------------        

          (vi)   repurchase agreements and similar commercial undertakings for
     terms of less than one year with any Rated Bank, provided that such
                                                      --------          
     repurchase agreements or undertakings are secured and collateralized by
     obligations backed by the full faith and credit of the United States
     Government in aggregate face amount equal to or greater than the
     obligations so secured;

          (vii)  money market mutual funds that (A) are denominated in U.S.
     Dollars, (B) have average asset maturities not in excess of 365 days, (C)
     have total invested assets in excess of $1,000,000,000 and (D) invest
     exclusively in Permitted Investments other than those described in Clause
                                                                        ------
     (ix) below, or are rated at least BBB- by S&P;
     ----                                          

          (viii) bonds, debentures, notes or similar debt instruments issued by
     a corporation organized and existing under the laws of any state of the
     United States of America or the District of Columbia and having a long term
     credit rating of BBB-or better from S&P or Baa3 or better from Moody's; and

          (ix)   Commercial Mortgage Loans and ABS originated, purchased or
     acquired by the Company in the ordinary course of its business, provided
     that any such Commercial Mortgage Loan or ABS shall comply with the
     investment guidelines set forth on Exhibit C hereto at the time of
                                        ---------                      
     origination, purchase, or acquisition by the Company; and further provided,
     that at all times the Company's portfolio of Investments, taken as a whole,
     shall be in compliance with such investment guidelines.

     6C(4).  MERGER AND CONSOLIDATION.  Merge or consolidate with any other
Person, except that the Company may consolidate or merge with any other
corporation if (A) the Company shall be the continuing or surviving corporation
and (B) no Default or Event of Default exists or would exist after giving effect
to such merger or consolidation.

     6C(5).  TRANSFER OF ASSETS.  Transfer, or agree or otherwise commit to
Transfer, a substantial portion of its assets.

     6C(6)   ISSUANCE OF ADDITIONAL UNSECURED NOTES.  Issue any unsecured notes
of the Company which are rated lower than the rating of the Notes on the date
hereof.

     7.   EVENTS OF DEFAULT.

     7A.  ACCELERATION.  If any of the following events shall occur and be
continuing for any reason whatsoever (and whether such occurrence shall be
voluntary or involuntary or come about or be effected by operation of law or
otherwise):

                                       10
<PAGE>
 
          (i)    the Company defaults in the payment of any principal of or
     Yield-Maintenance Amount payable with respect to any Note when the same
     shall become due, either by the terms thereof or otherwise as herein
     provided; or

          (ii)   the Company defaults in the payment of any interest on any Note
     for more than 10 days after the date due; or

          (iii)  the Company defaults (whether as primary obligor or as
     guarantor or other surety) in any payment of principal of or interest on
     any other Debt (other than secured Debt which is non-recourse to the
     Company) beyond any period of grace provided with respect thereto, or the
     Company fails to perform or observe any other agreement, term or condition
     contained in any agreement under which any such Debt is created (or if any
     other event thereunder or under any such agreement shall occur and be
     continuing) and the effect of such failure or other event is to cause, or
     to permit the holder or holders of such (or a trustee on behalf of such
     holder or holders) to cause, such Debt to become due (or to be repurchased
     by the Company) prior to any stated maturity, provided that the aggregate
     amount of all Debt as to which such a payment default shall occur and be
     continuing or such a failure or other event causing or permitting
     acceleration (or resale to the Company) shall occur and be continuing
     exceeds an amount equal to the lesser of (x) $10,000,000 and (y) 5% of the
     net assets of the Company as reflected on its most recent balance sheet at
     the time of determination; or

          (iv)   any representation or warranty made by or on behalf of the
     Company or any of its officers herein or in any other writing furnished in
     connection with or pursuant to this Agreement or the transactions
     contemplated hereby shall be false in any material respect on the date as
     of which made; or

          (v)    the Company fails to perform or observe any agreement contained
     in paragraph 6; or
        -----------    

          (vi)   the Company fails to perform or observe any other agreement,
     term or condition contained herein and such failure shall not be remedied
     within 30 days after the Company receives written notice of such default
     from any holder of a Note; or

          (vii)  the Company makes an assignment for the benefit of creditors or
     is generally not paying its debts as such debts become due; or

          (viii) any decree or order for relief in respect of the Company is
     entered under any bankruptcy, reorganization, compromise, arrangement,
     insolvency, readjustment of debt, dissolution or liquidation or similar
     law, whether now or hereafter in effect (herein called the "BANKRUPTCY
     LAW"), of any jurisdiction; or

                                       11
<PAGE>
 
          (ix)   the Company petitions or applies to any tribunal for, or
     consents to, the appointment of, or taking possession by, a trustee,
     receiver, custodian, liquidator or similar official of the Company, or of
     any substantial part of the assets of the Company, or commences a voluntary
     case under the Bankruptcy Law of the United States or any proceedings
     relating to the Company under the Bankruptcy Law of any other jurisdiction;
     or

          (x)    any such petition or application is filed, or any such
     proceedings are commenced, against the Company and the Company by any act
     indicates its approval thereof, consent thereto or acquiescence therein, or
     an order, judgment or decree is entered appointing any such trustee,
     receiver, custodian, liquidator or similar official, or approving the
     petition in any such proceedings, and such order, judgment or decree
     remains unstayed and in effect for more than 60 days; or

          (xi)   any order, judgment or decree is entered in any proceedings
     decreeing the dissolution of the Company and such order, judgment or decree
     remains unstayed and in effect for more than 60 days; or

          (xii)  one or more final judgments in an aggregate amount in excess of
     $10,000,000 is rendered against the Company and, within 60 days after entry
     thereof, a solvent insurance carrier or carriers have not confirmed in
     writing that each such judgment is fully insured or any such judgment is
     not discharged or execution thereof stayed pending appeal, or within 60
     days after the expiration of any such stay, any such judgment is not
     discharged;

     then (a) if such event is an Event of Default specified in clauses (i) or
                                                                -----------   
     (ii) of this paragraph 7A, the holder of any Note (other than the Company
     ----         ------------                                                
     or any of its Affiliates) may at its option during the continuance of such
     Event of Default, by notice in writing to the Company, declare such Note to
     be, and such Note shall thereupon be and become, immediately due and
     payable at par, together with interest accrued thereon, without
     presentment, demand, protest or other notice of any kind, all of which are
     hereby waived by the Company, (b) if such event is an Event of Default
     specified in clause (viii), (ix) or (x) of this paragraph 7A, all of the
                  -------------  ----    ---         ------------            
     Notes at the time outstanding shall automatically become immediately due
     and payable, together with interest accrued thereon and the Yield-
     Maintenance Amount, if any and to the extent permitted by law, with respect
     to each Note, without presentment, demand, protest or notice of any kind,
     all of which are hereby waived by the Company, and (c) with respect to any
     other event constituting an Event of Default, the Required Holder(s) may,
     at its or their option, by notice in writing to the Company, declare all of
     the Notes to be, and all of the Notes shall thereupon be and become,
     immediately due and payable together with interest accrued thereon and
     together with the Yield-Maintenance Amount, if any, with respect to each
     Note, without presentment, demand, protest or other notice of any kind, all
     of which are hereby waived by the Company (provided that, so long as any BP
                                                -------- ----                   
     Party holds any Note(s), such BP Party may declare its Note(s) to be
     immediately due and payable 

                                       12
<PAGE>
 
     with respect to any such other event constituting an Event of Default
     without the consent or approval of the other Holders).

          The Company acknowledges, and the parties hereto agree, that each
     holder of a Note has the right to maintain its investment in the Notes free
     from repayment by the Company (except as herein specifically provided for)
     and that the provision for payment of the Yield-Maintenance Amount by the
     Company in the event that the Notes are prepaid or are accelerated as a
     result of an Event of Default, is intended to provide compensation for the
     deprivation of such right under such circumstances.

     7B.  RESCISSION OF ACCELERATION.  At any time after any or all of the Notes
shall have been declared immediately due and payable pursuant to paragraph 7A,
                                                                 ------------ 
the Required Holder(s) may, by notice in writing to the Company, rescind and
annul such declaration and its consequences if (i) the Company shall have paid
all overdue interest on the Notes, the principal of and Yield-Maintenance
Amount, if any, payable with respect to any Notes which have become due
otherwise than by reason of such declaration, and interest on such overdue
interest and overdue principal and Yield-Maintenance Amount at the applicable
rate specified in the Notes, (ii) the Company shall not have paid any amounts
which have become due solely by reason of such declaration, (iii) all Events of
Default and Defaults, other than non-payment of amounts which have become due
solely by reason of such declaration, shall have been cured or waived pursuant
to paragraph 11C, and (iv) no judgment or decree shall have been entered for the
   -------------                                                                
payment of any amounts due pursuant to the Notes or this Agreement.
Notwithstanding the foregoing, so long as any BP Holder holds any Note(s), only
such BP Holder shall be permitted to rescind and annul any such declaration with
respect to the Note(s) that it holds.  No such rescission or annulment shall
extend to or affect any subsequent Event of Default or Default or impair any
right arising therefrom.

     7C.  NOTICE OF ACCELERATION OR RESCISSION.  Whenever any Note shall be
declared immediately due and payable pursuant to paragraph 7A or any such
                                                 ------------            
declaration shall be rescinded and annulled pursuant to paragraph 7B, the
                                                        ------------     
Company shall forthwith give written notice thereof to the holder of each Note
at the time outstanding.

     7D.  OTHER REMEDIES.  If any Event of Default shall occur and be
continuing, the holder of any Note may proceed to protect and enforce its rights
under this Agreement and such Note by exercising such remedies as are available
to such holder in respect thereof under applicable law, either by suit in equity
or by action at law, or both, whether for specific performance of any covenant
or other agreement contained in this Agreement or in aid of the exercise of any
power granted in this Agreement.  No remedy conferred in this Agreement upon the
holder of any Note is intended to be exclusive of any other remedy, and each and
every such remedy shall be cumulative and shall be in addition to every other
remedy conferred herein or now or hereafter existing at law or in equity or by
statute or otherwise.

     8.   REPRESENTATIONS, COVENANTS AND WARRANTIES.  The Company represents,
covenants and warrants as follows:

                                       13
<PAGE>
 
     8A.  ORGANIZATION.  The Company is a corporation duly organized and
existing in good standing under the laws of the State of Delaware, and is duly
qualified as a foreign corporation and is in good standing in each jurisdiction
in which such qualification is required by law, other than those jurisdictions
as to which the failure to be so qualified or in good standing would not,
individually or in the aggregate, reasonably be expected to have a Material
Adverse Effect.  The Company has the corporate power and authority to own or
hold under lease the properties it purports to own or hold under lease, to
transact the business it transacts and proposes to transact, to execute and
deliver this Agreement and the Notes and to perform the provisions hereof and
thereof.  The Company has no Subsidiaries.

     8B.  FINANCIAL STATEMENTS.  The Company has furnished you with the
unaudited financial statements, certified by a principal financial officer of
the Company:  a balance sheet of the Company as of June 30, 1998 and statements
of income, stockholders' equity and cash flows for the six-month period ended on
such date, prepared by the Company.  To the Company's knowledge, such financial
statements are true and correct in all material respects (subject, as to interim
statements, to changes resulting from audits and year-end adjustments), have
been prepared in accordance with GAAP consistently followed through  out the
periods involved and show all liabilities, direct and contingent, of the Company
required to be shown in accordance with such principles.  To the Company's
knowledge, the balance sheets fairly present the condition of the Company as at
the dates thereof, and the statements of income, stockholders' equity and cash
flows fairly present the results of the operations of the Company and its cash
flows for the periods indicated.  To the knowledge of the Company, there has
been no material adverse change in the business, condition (finan  cial or
otherwise) or operations of the Company since June 30, 1998.

     8C.  ACTIONS PENDING.  There is no action, suit, investigation or
proceeding pending or, to the knowledge of the Company, threatened against the
Company, or any properties or rights of the Company, by or before any court,
arbitrator or administrative or governmental body which (i) might result in a
Material Adverse Effect or (ii) purports to affect the validity or
enforceability of this Agreement, any Note issued hereunder or the transactions
contemplated hereby.

     8D.  TAXES.  The Company has filed all federal, state and other income tax
returns which, to the knowledge of the officers of the Company, are required to
be filed, and has paid all taxes as shown on such returns and on all assessments
received by it to the extent that such taxes have become due, except such taxes
as are subject to a Good Faith Contest.

     8E.  CONFLICTING AGREEMENTS AND OTHER MATTERS.  The Company is not a party
to any contract or agreement or subject to any charter or other corporate
restriction which materially and adversely affects its business, property or
assets, or financial condition. Neither the execution nor delivery of this
Agreement or the Notes, nor the offering, issuance and sale of the Notes, nor
fulfillment of nor compliance with the terms and provisions hereof and of the
Notes will materially conflict with, or result in a material breach of the
terms, conditions or provisions of, or constitute a default under, or result in
any material violation of, or result in the creation of any Lien upon any of the
properties or assets of the Company

                                       14
<PAGE>
 
pursuant to, the charter or by-laws of the Company, any award of any arbitrator
or any agree ment (including any agreement with stockholders), instrument,
order, judgment, decree, statute, law, rule or regulation to which the Company
is subject. Except as set forth in Schedule 8E attached hereto, the Company is
                                   -----------      
not a party to, or otherwise subject to any provision contained in, any
instrument evidencing Indebtedness of the Company, any agreement relating
thereto or any other contract or agreement (including its charter) which limits
the amount of, or otherwise imposes restrictions on the incurring of, Debt of
the Company of the type to be evidenced by the Notes.

     8F.  OFFERING OF NOTES.  Neither the Company nor any agent acting on its
behalf has, directly or indirectly, offered the Notes or any similar security of
the Company for sale to, or solicited any offers to buy the Notes or any similar
security of the Company from, or otherwise approached or negotiated with respect
thereto with, any Person other than Institutional Investors, and neither the
Company nor any agent acting on its behalf has taken or will take any action
which would subject the issuance or sale of the Notes to the provisions of
section 5 of the Securities Act or to the provisions of any securities or Blue
Sky law of any applicable  jurisdiction.

     8G.  USE OF PROCEEDS.  The Company does not own or have any present
intention of acquiring any "margin stock" as defined in Regulation U (12 CFR
Part 207) of the Board of Governors of the Federal Reserve System (herein called
"MARGIN STOCK").  The proceeds of sale of the Notes will be used to purchase
Commercial Mortgage Loans and/or marketable debt securities, including, but not
limited to, ABS.  None of such proceeds will be used, directly or indirectly,
for the purpose, whether immediate, incidental or ultimate, of purchasing or
carrying any margin stock or for the purpose of maintaining, reducing or retir
ing any Indebtedness which was originally incurred to purchase or carry any
stock that is currently a margin stock or for any other purpose which might
constitute this transaction a "purpose credit" within the meaning of such
Regulation U.  Neither the Company nor any agent acting on its behalf has taken
or will take any action which might cause this Agreement or the Notes to violate
Regulation U, Regulation T or any other regulation of the Board of Governors of
the Federal Reserve System or to violate the Exchange Act, in each case as in
effect now or as the same may hereafter be in effect.

     8H.  ERISA.  The Company has no retirement or employee benefit plans
subject to ERISA.

     8I.  GOVERNMENTAL CONSENT.  No circumstance in connection with the
offering, issuance, sale or delivery of the Notes is such as to require any
authorization, consent, approval, exemption or other action by or notice to or
filing with any court or administrative or governmental body in connection with
the execution and delivery of this Agreement, the offering, issuance, sale or
delivery of the Notes or fulfillment of or compliance with the terms and
provisions hereof or of the Notes, if the failure to obtain any such consent
would have a Material Adverse Effect.

                                       15
<PAGE>
 
     8J.  COMPLIANCE WITH LAWS.  The Company and all of its properties and
facilities have complied at all times in all material respects with all federal,
state, local and regional statutes, laws, ordinances and judicial or
administrative orders, judgments, rulings and regulations, except, in any such
case, where failure to comply would not result in a Material Adverse Effect on
the business, condition (financial or otherwise) or operations of the Company.

     8K.  INVESTMENT COMPANY STATUS.  Neither the Company nor any Subsidiary is
an "investment company" or a company "controlled" by an "investment company"
within the meaning of the Investment Company Act of 1940, as amended, or an
"investment adviser" within the meaning of the Investment Advisers Act of 1940,
as amended.

     8L.  DUE AUTHORIZATION, ETC.  This Agreement and the Notes have been duly
authorized by all necessary corporate action on the part of the Company, and
this Agreement constitutes, and upon execution and delivery thereof each Note
will constitute, a legal, valid and binding obligation of the Company
enforceable against the Company in accordance with its terms, except as such
enforceability may be limited by (i) applicable bankruptcy, insolvency,
reorganization, moratorium or other similar laws affecting the enforcement of
creditors' rights generally and (ii) general principles of equity (regardless of
whether such enforceability is considered in a proceeding in equity or at law).

     8M. DISCLOSURE.  Neither this Agreement nor any other document, certificate
or statement furnished to you by or on behalf of the Company in connection
herewith contains any untrue statement of a material fact or omits to state a
material fact necessary in order to make the statements contained herein and
therein not misleading.  There is no fact peculiar to the Company which
materially adversely affects or in the future may (so far as the Company can now
foresee) materially adversely affect the business, property or assets, or
financial condition of the Company and which has not been set forth in this
Agreement or in the other documents, certificates and written statements
furnished to you and Boston Properties Limited Partnership, a Delaware limited
partnership by or on behalf of the Company prior to the date hereof in
connection with the transactions contemplated hereby.

     8N.  INVESTMENTS.  All mortgage loans owned by the Company as of the date
of this Agreement are Commercial Mortgage Loans which are not in default beyond
any applicable cure periods pursuant to the terms thereof, and the Company has
not extended any of the cure periods provided in the loan documents governing,
evidencing and securing such Commercial Mortgage Loans and originally executed
in connection therewith beyond the applicable cure periods provided in such loan
documents.

     8O.  ENVIRONMENTAL MATTERS.  Except as disclosed on Schedule 8O hereto, the
                                                         -----------            
Company (i) has complied in all material respects with all applicable
Environmental Laws, and the Company has not received (A) notice of any material
failure so to comply, (B) any letter or request for information under Section
104 of CERCLA or comparable state laws or (C) any information that would lead it
to believe that it is the subject of any federal, state or local investigation
concerning Environmental Laws; (ii) does not manage, generate,

                                       16
<PAGE>
 
transport, discharge or store any Hazardous Material in material violation of
any material Environmental Laws; (iii) does not own, operate or maintain any
underground storage tanks; and (iv) is not aware of any conditions or
circumstances associated with its currently or previously owned or leased
properties or operations (or those of any tenants of such properties) which may
give rise to any liabilities under Environmental Laws which could have a
Material Adverse Effect.

     9.   REPRESENTATIONS OF THE PURCHASER.  You represent that you are not
acquiring the Notes to be purchased by you hereunder with a view to or for sale
in connection with any distribution thereof within the meaning of the Securities
Act, provided that the disposition of your property shall at all times be and
remain within your control. You understand that the Notes have not been
registered under the Securities Act and may be resold only if registered
pursuant to the provisions of the Securities Act or if an exemption from
registration is available, except under circumstances where neither such
registration nor such an exemption is required by law, and that the Company is
not required to register the Notes.

     10.  DEFINITIONS; ACCOUNTING MATTERS.  For the purpose of this Agreement,
the terms defined in paragraphs 10A and 10B (or within the text of any other
                     --------------     ---                                 
paragraph) shall have the respective meanings specified therein and all
accounting matters shall be subject to determination as provided in paragraph
                                                                    ---------
10C.
--- 

     10A. YIELD-MAINTENANCE TERMS.

               "BUSINESS DAY" shall mean any day other than a Saturday, a Sunday
     or a day on which commercial banks in New York City are required or
     authorized to be closed.

               "CALLED PRINCIPAL" shall mean, with respect to any Note, the
     princi pal of such Note that is to be prepaid pursuant to paragraph 4 or is
                                                               -----------      
     declared to be immediately due and payable pursuant to paragraph 7A, as the
                                                            ------------        
     context requires.

               "DISCOUNTED VALUE" shall mean, with respect to the Called
     Principal of any Note, the amount obtained by discounting all Remaining
     Scheduled Payments with respect to such Called Principal from their
     respective scheduled due dates to the Settlement Date with respect to such
     Called Principal, in accordance with accepted financial practice and at a
     discount factor (as converted to reflect the periodic basis on which
     interest on the Notes is payable, if interest is payable other than on a
     semi-annual basis) equal to the Reinvestment Yield with respect to such
     Called Principal.

               "REINVESTMENT YIELD" shall mean, with respect to the Called
     Princi pal of any Note, the offered-side yield to maturity, as of 10:00
     a.m. (New York City time) on the Business Day next preceding the Settlement
     Date with respect to such

                                       17
<PAGE>
 
     Called Principal, of the U.S. Treasury security that was used to determine
     the then Treasury of such Investment Note.

               "REMAINING AVERAGE LIFE" shall mean, with respect to the Called
     Principal of any Note, the number of years (calculated to the nearest one-
     twelfth year) obtained by dividing (i) such Called Principal into (ii) the
     sum of the products obtained by multiplying (a) each Remaining Scheduled
     Payment of such Called Principal (but not of interest thereon) by (b) the
     number of years (calculated to the nearest one-twelfth year) which will
     elapse between the Settlement Date with respect to such Called Principal
     and the scheduled due date of such Remaining Scheduled Payment.

               "REMAINING SCHEDULED PAYMENTS" shall mean, with respect to the
     Called Principal of any Note, all payments of such Called Principal and
     interest thereon that would be due on or after the Settlement Date through
     and including the Rate Reset Date (assuming that the entire principal
     balance and all accrued interest as of such Rate Reset Date will be repaid
     on such Rate Reset Date), if the Settlement Date precedes such Rate Reset
     Date, or alternatively, the Maturity Date if the Settlement Date occurs
     after the Rate Reset Date.

               "SETTLEMENT DATE" shall mean, with respect to the Called
     Principal of any Note, the date on which such Called Principal is to be
     prepaid pursuant to paragraph 4 or is declared to be immediately due and
                         -----------                                         
     payable pursuant to paragraph 7A, as the context requires.
                         ------------                          

               "YIELD-MAINTENANCE AMOUNT" shall mean, with respect to any Note,
     an amount equal to the excess, if any, of the Discounted Value of the
     Called Principal of such Note over the sum of (i) such Called Principal
     plus (ii) to the extent paid on the Settlement Date with the Called
     Principal, interest accrued thereon as of (including interest due on) the
     Settlement Date with respect to such Called Principal. The Yield-
     Maintenance Amount shall in no event be less than zero.

     10B.    OTHER TERMS.

               "ABS" shall mean mortgage, or other asset backed securities.

               "AFFILIATE" shall mean any Person directly or indirectly
     controlling, controlled by, or under direct or indirect common control
     with, the Company.  A Person shall be deemed to control a corporation if
     such Person possesses, directly or indirectly, the power to direct or cause
     the direction of the management and policies of such corporation, whether
     through the ownership of voting securities, by contract or otherwise.

               "BANKRUPTCY LAW" shall have the meaning specified in clause
                                                                    ------
     (viii) of paragraph 7A.
     -----     ------------

                                       18
<PAGE>
 
               "BIG FIVE ACCOUNTING FIRM" shall mean any of Arthur Andersen,
     Deloitte & Touche, KPMG Peat Marwick, PricewaterhouseCoopers and Ernst &
     Young.

               "BP PARTY" shall mean Boston Properties Limited Partnership, a
     Delaware limited partnership, and any Affiliate thereof, and shall also
     include, in all events, One Embarcadero Center Venture, a California
     general partnership.

               "CASH FLOW"  shall mean, in respect of any period, the sum of (a)
     Net Income for such period and (b) the amount of all depreciation and
     amortization allowances and other non-cash expenses of the Company but only
     to the extent deducted in the determination of Net Income for such period.

               "CERCLA" shall mean the Comprehensive Environmental Response,
     Compensation and Liability Act of 1980, as amended.

               "CODE" shall mean the Internal Revenue Code of 1986, as amended.

               "COMMERCIAL MORTGAGE LOANS" shall mean commercial mortgage loans
     made in substantial conformance with (x) standards prevailing in the
     commercial loan mortgage marketplace and (y) the guidelines contained in
     Exhibit C hereto.
     ---------        

               "CURRENT DEBT" shall mean, with respect to the Company, all
     Indebtedness for borrowed money which by its terms or by the terms of any
     instrument or agreement relating thereto matures on demand or within one
     year from the date of the creation thereof and is not directly or
     indirectly renewable or extendible at the option of the debtor to a date
     more than one year from the date of the creation thereof, provided that
     Indebtedness for borrowed money outstanding under a revolving credit or
     similar agreement which obligates the lender or lenders to extend credit
     over a period of more than one year shall constitute Funded Debt and not
     Current Debt, even though such Indebtedness by its terms matures on demand
     or within one year from the date of the creation thereof.

               "DEBT" shall mean Current Debt and Funded Debt.

               "DEBT SERVICE" shall mean, with respect to any period, the sum of
     the following: (a) Interest Charges for such period, and (b) all payments
     of principal in respect of Debt of the Company paid or payable during such
     period.

               "DEBT SERVICE COVERAGE RATIO" shall mean, at any time of
     determination, the ratio of (a) Cash Flow for the most recent fiscal
     quarter to (b) Debt Service for such fiscal quarter.

                                       19
<PAGE>
 
               "DEFAULT" shall mean any of the events specified in paragraph 7A,
                                                                   ------------ 
     whether or not any requirement for such event to become an Event of Default
     has been satisfied.

               "DUFF & PHELPS" shall mean Duff & Phelps Corporation.

               "ENVIRONMENTAL LAWS" shall mean all laws relating to pollution,
     the release or other discharge, handling, disposition or treatment of
     Hazardous Materials and other substances or the protection of the
     environment or of employee health and safety, including, without
     limitation, CERCLA, the Hazardous Material Transportation Act (49 U.S.C.
     Section 1801 et. seq.), the Resource Conservation and Recovery Act (42
     U.S.C. Section 7401 et. seq.), the Clean Air Act (42 U.S.C. Section 401 et.
     seq.), the Toxic Substances Control Act (15 U.S.C. Section 651 et. seq.)
     and the Emergency Planning and Community Right-To-Know Act (42 U.S.C.
     Section 11001 et. seq.), each as the same may be amended and supplemented.

               "EVENT OF DEFAULT" shall mean any of the events specified in 
     paragraph 7A, provided that there has been satisfied any requirement in
     ------------                                                           
     connection with such event for the giving of notice, or the lapse of time,
     or the happening of any further condition, event or act.

               "EQUITY REDEMPTION LOAN" shall mean that certain loan in the
     aggregate principal amount of $328,143,000 by Bankboston. N.A., The Chase
     Manhattan Bank, Fleet National Bank, PNC Bank, National Association,
     Dresdner Bank AG New York Branch and Grand Cayman Branch, The Bank of New
     York, Key Bank National Association and Citizens Bank (and other banks
     which may become parties to the Term Loan Agreement described immediately
     below) to you, One Embarcadero Center Venture, Embarcadero Center
     Associates and Four Embarcadero Center Venture pursuant to that certain
     Term Loan Agreement dated as of November 12, 1998.

               "EXCHANGE ACT" shall mean the Securities Exchange Act of 1934, as
     amended.

               "FITCH" shall mean Fitch IVCA, Inc.

               "FUNDED DEBT" shall mean, with respect to any Person, all
     Indebtedness of such Person which by its terms or by the terms of any
     instrument or agreement relating thereto matures, or which is otherwise
     payable or unpaid, more than one year from, or is directly or indirectly
     renewable or extendible at the option of the debtor to a date more than one
     year (including an option of the debtor under a revolving credit or similar
     agreement obligating the lender or lenders to extend credit over a period
     of more than one year) from, the date of the creation thereof, including
     current maturities of long-term debt that appear as current liabilities in
     accordance with GAAP.

                                       20
<PAGE>
 
               "GAAP" shall have the meaning set forth in paragraph 10C.
                                                          ------------- 

               "GOOD FAITH CONTEST" shall mean, with respect to any tax,
     assessment, Lien, obligation, claim, liability, judgment, injunction,
     award, decree, order, law, regulation, statute or similar item, any
     challenge or contest thereof by appropriate proceedings timely initiated in
     good faith by the Company for which adequate reserves therefor have been
     taken in accordance with GAAP.

               "GUARANTEE" shall mean, with respect to any Person, any direct or
     indirect liability, contingent or otherwise, of such Person with respect to
     any indebtedness, lease, dividend or other obligation of another,
     including, without limitation, any such obligation directly or indirectly
     guaranteed, endorsed (otherwise than for collection or deposit in the
     ordinary course of business) or discounted or sold with recourse by such
     Person, or in respect of which such Person is otherwise directly or
     indirectly liable, including, without limitation, any such obligation in
     effect guaranteed by such Person through any agreement (contingent or
     otherwise) to

            (i) purchase,repurchase or otherwise acquire such obligation or any
          security therefor, or to provide funds for the payment or discharge of
          such obligation (whether in the form of loans, advances, stock
          purchases, capital contributions or otherwise);

          (ii)  maintain the solvency or any balance sheet or other financial
          condition of the obligor of such obligation; or

          (iii) pay the purchase price for goods or services regardless of the
          non-delivery or non-furnishing thereof, in any such case if the
          purpose, intent or effect of such agreement is to provide assurance
          that such obligation will be paid or discharged, or that any
          agreements relating thereto will be complied with, or that the holders
          of such obligation will be protected against loss in respect thereof.

     The amount of any Guarantee shall be equal to the outstanding principal
     amount of the obligation guaranteed or such lesser amount to which the
     maximum exposure of the guarantor shall have been specifically limited.

               "HAZARDOUS MATERIALS"  shall mean (i) any material or substance
     defined as or included in the definition of "hazardous substances",
     "hazardous wastes", "hazardous material", "toxic substances" or any other
     formulations intended to define, list or classify substances by reason of
     their deleterious properties, (ii) any oil, petroleum or petroleum derived
     substance, (iii) any flammable substances or explosives, (iv) any
     radioactive materials, (v) asbestos in any form, (vi) electrical equipment
     that contains any oil or dielectric fluid containing levels or
     polychlorinated biphenyls in excess of 50 parts per million, (vii)
     pesticides or (viii)

                                       21
<PAGE>
 
     any other chemical, material or substance, exposure to which is prohibited,
     limited or regulated by any governmental agency or authority or which may
     or could pose a hazard to the health and safety of persons in the vicinity
     thereof.

               "INCLUDING" shall mean, unless the context clearly requires
     otherwise, "including without limitation".

               "INDEBTEDNESS" shall mean, with respect to any Person and without
     duplication (i) all items (excluding items of contingency reserves or of
     reserves for deferred income taxes) which in accordance with GAAP would be
     included in determining total liabilities as shown on the liability side of
     a balance sheet of such Person as of the date on which Indebtedness is to
     be determined, other than Preferred Stock of such Person except as set
     forth in clause (iv) below; (ii) all indebtedness secured by any Lien on,
              -----------                                                     
     or payable out of the proceeds or production from, any property or asset
     owned or held by such Person, whether or not the indebtedness secured
     thereby shall have been assumed, (iii) all indebtedness of third parties,
     including joint ventures and partnerships of which such Person is a
     venturer or general partner, recourse to which may be had against such
     Person, (iv) redemption obligations in respect of mandatorily redeemable
     Preferred Stock; and (v) all indebtedness and other obligations of others
     with respect to which such Person has become liable by way of a Guarantee.

               "INITIAL TREASURY" shall mean, for any Note, the yield to
     maturity implied by (i) the bid-side yields reported, as of 10:00am (New
     York City time) (or, at your election, at such other time as we may
     mutually agree) on the Business Day next preceding the date upon which such
     Note is funded, on the display designated as "Page 678" on the Telerate
     Access Service, for actively traded U.S. Treasury securities having a
     maturity equal to the Rate Reset Date of such Note, or if such bid-side
     yields shall not be reported as of such time or the yields reported as of
     such time shall not be ascertainable, (ii) the Treasury Constant Maturity
     Series bid-side yields reported, for the latest day for which such yields
     shall have been so reported as of the Business Day next preceding the date
     upon which such Note is funded in Federal Reserve Statistical Release H.15
     (519) (or any comparable successor publication) for actively traded U.S.
     Treasury securities having a constant maturity equal to the Rate Reset Date
     of such Note.  Such implied yields shall be determined, if necessary, by
     (a) converting U.S. Treasury bill quotations to bond-equivalent yields in
     accordance with accepted financial practice and (b) interpolating linearly
     between yields reported for various maturities.  Notwithstanding the
     foregoing, subject to the Company's written approval (which approval shall
     not be unreasonably withheld or delayed), you shall be entitled to select a
     different actively traded U.S. Treasury security (which shall have a
     maturity date approximately equal and reasonably comparable to the first
     Rate Reset Date of such Note) the bid-side yield to maturity of which shall
     be the Initial Treasury for purposes of such Note; provided, however, that
                                                        --------  -------      
     if you select a different U.S. Treasury security which is approved by the
     Company pursuant to the foregoing or if a time other than 10:00 a.m. is
     used to determine the Initial Treasury,

                                       22
<PAGE>
 
     then the Margin for such Note shall be adjusted so that the interest rate
     on such Investment Note is no different than if you had not exercised your
     rights pursuant to this sentence to select a different U.S. Treasury or to
     agree to a different time for determining the Initial Treasury. Schedule 1
                                                                     ----------
     sets forth the definitive Initial Treasury for each Note.

               "INSTITUTIONAL INVESTOR" shall mean any insurance company,
     commercial, investment or merchant bank, finance company, mutual fund,
     registered money or asset manager, savings and loan association, credit
     union, registered investment advisor, pension fund, investment company,
     licensed broker-dealer, "qualified institutional buyer" (as such term is
     defined under Rule 144A promulgated under the Securities Act, or any
     successor law, rule or regulation) or "accredited investor" (as such term
     is defined under Regulation D promulgated under the Securities Act, or any
     successor law, rule or regulation).

               "INTANGIBLES" shall mean, without duplication, all Intellectual
     Property and operating agreements, treasury stock, deferred or capitalized
     research and development costs, goodwill (including any amounts, however
     designated, representing the cost of acquisition of business and
     investments in excess of the book value thereof), unamortized debt discount
     and expense, any write-up of asset value after June 30, 1997 and any other
     amounts reflected in contra-equity accounts, and any other assets treated
     as intangible assets under GAAP.

               "INTELLECTUAL PROPERTY" shall mean all patents, trademarks,
     service marks, trade names, copyrights, brand names, mechanical or
     technical processes and paradigms, know-how, and similar intellectual
     property and applications, licenses and similar rights in respect of the
     same.

               "INTEREST CHARGES" shall mean, with respect to any period, the
     sum (without duplication) of the following: (a) all interest in respect of
     Debt of the Company deducted in determining Net Income for such period, and
     (b) all debt discount and expense amortized or required to be amortized in
     the determination of Net Income for such period.

               "INVESTMENTS" shall have the meaning provided in paragraph 6C(3).
                                                                --------------- 

               "LIEN" shall mean any mortgage, pledge, security interest,
     encumbrance, minimum or compensating deposit arrangement, lien (statutory
     or otherwise) or charge of any kind (including any agreement to give any of
     the foregoing, any conditional sale or other title retention agreement, any
     lease in the nature thereof, and the filing of or agreement to give any
     financing statement under the Uniform Commercial Code of any jurisdiction)
     or any other type of preferential arrangement for the purpose, or having
     the effect, of protecting a creditor against loss or securing the payment
     or performance of an obligation.

                                       23
<PAGE>
 
               "MARGIN" shall mean, for any Note, 165 basis points; provided
                                                                    --------
     that, if you select, for purposes of determining the Initial Treasury, a
     ----                                                                    
     different U.S. Treasury security from the U.S Treasury selected by the
     Company or if a time other than 10:00 a.m. is used to determine the Initial
     Treasury, in either case pursuant to your rights as described in the
     definition of Initial Treasury, then the Margin during the period of time
     commencing on the funding of the Investment Note until the first Rate Reset
     Date thereunder shall be adjusted as described in the last sentence of the
     definition of Initial Treasury and, from and after the first Rate Reset
     Date, the Margin shall again adjust to equal 165 basis points.  Schedule 1
                                                                     ----------
     sets forth the definitive initial Margin for each Note through the first
     Rate Reset Date of each Note.

               "MATERIAL ADVERSE EFFECT" shall mean (i) a material adverse
     effect on the business, assets, liabilities, operations, prospects or
     condition, financial or otherwise, of the Company, (ii) material impairment
     of the Company to perform any of its obligations under the Agreement and
     the Notes or (iii) material impairment of the validity or enforceability or
     the rights of, or the benefits available to, the holders of the Notes under
     this Agreement or the Notes.

               "MATURITY DATE" shall have the meaning set forth in paragraph 1
                                                                   -----------
     hereof.

               "MOODY'S" shall mean Moody's Investors Services, Inc., including
     the NCO/Moody's Commercial Division, or any successor Person.

               "NET INCOME" shall mean, as to any period, consolidated gross
     revenues of the Company less all operating and non-operating expenses of
     the Company for such period, including all charges of a proper character
     (including current and deferred taxes on income, provision for taxes on
     unremitted foreign earnings which are included in gross revenues, and
     current additions to reserves), but not including in gross revenues the
     following:

               (i)   any gains (net of expenses and taxes applicable thereto) in
               excess of losses resulting from the Transfer of capital assets
               (i.e., assets other than current assets);

               (ii)  any gains resulting from the write-up of assets;

               (iii) any equity of the Company in the undistributed earnings
               (but not losses) of any corporation which is not a Subsidiary;

               (iv)  any earnings or losses of any Person acquired by the
               Company through purchase, merger, consolidation or otherwise for
               any fiscal period prior to the fiscal period in which the
               acquisition occurs;

                                       24
<PAGE>
 
               (v)    gains or losses from the acquisition of securities or the
               retirement or extinguishment of Debt;

               (vi)   gains on collections from insurance policies or
               settlements;

               (vii)  any income or gain during such period from any change in
               accounting principles, from any discontinued operations or the
               disposition thereof, from any extraordinary items or from any
               prior period adjustment;

               (viii) in the case of a successor to the Company by consolidation
               or merger or as a transferee of its assets, any earnings of the
               successor corporation prior to such consolidation, merger or
               transfer of assets.

     If the preceding calculation results in a number less than zero, such
     amount shall be considered a net loss.

               "OFFICER'S CERTIFICATE" shall mean a certificate signed in the
     name of the Company by its President, one of its Vice Presidents or its
     Treasurer.

               "OTHER EC NOTES" shall mean those certain senior promissory notes
     of the Company issued by the Company on the date hereof to (a) One
     Embarcadero Center Venture in the aggregate principal amount of $88,200,000
     (b) Embarcadero Center Associates in the aggregate principal amount of
     $111,927,000 and (c) Four Embarcadero Center Venture in the aggregate
     principal amount of $143,119,000.

               "PERMITTED INVESTMENTS" shall have the meaning set forth in
     paragraph 6C(3).
     --------------- 

               "PERMITTED LIENS" shall have the meaning set forth in paragraph
                                                                     ---------
     6C(1).
     ----- 

               "PERSON" shall mean and include an individual, a partnership, a
     joint venture, a corporation, a limited liability company, a trust, an
     unincorporated organ  ization and a government or any department or agency
     thereof.

               "PHASE ONE" shall mean the closing and consummation of the
     transactions described in that certain Master Transaction Agreement dated
     as of September 28, 1998, by and among Prudential, PIC Realty Corporation,
     Fedmark Corporation, Embarcadero Center Investors Partnership, Pacific
     Property Services, L.P., the Persons listed on Exhibit A-1 attached
     thereto, Boston Properties Limited Partnership and Boston Properties, Inc.,
     which are to be consummated on the "Closing Date" (as defined in such
     Master Transaction Agreement).

                                       25
<PAGE>
 
               "PRUDENTIAL" shall mean The Prudential Insurance Company of
     America, a New Jersey mutual insurance company.

               "PRUDENTIAL GUARANTIED LOAN"  shall mean that certain loan in the
     aggregate principal amount of $92,000,000 by The Chase Manhattan Bank
     and/or any of its subsidiaries or affiliates (the "BANK") to you, One
     Embarcadero Center Venture, Embarcadero Center Associates and Four
     Embarcadero Center Venture pursuant to that certain Term Loan Agreement
     dated as of November 12, 1998.

               "RATE RESET DATE", with respect to any Note, shall have the
     meaning set forth in such Note.

               "RATED BANK" shall have the meaning set forth in paragraph
                                                                ---------
     6C(3)(ii).
     --------- 

               "RELEASE" shall mean any release, spill, emission, leaking,
     pumping, injection, deposit, disposal, discharge, leaching or migration
     into the indoor or outdoor environment, including, without limitation, the
     movement of Hazardous Materials through ambient air, soil, surface water,
     ground water, wetlands, land or subsurface strata, in violation of
     applicable law or prudent business practice.

               "REQUIRED HOLDER(S)" shall mean the holder or holders of at least
     51% of the aggregate principal amount of the Notes from time to time
     outstanding, but shall include, in any event, the BP Parties so long as any
     BP Party holds a direct or indirect interest in any Note.

               "RESET TREASURY" shall mean the yield to maturity implied by (i)
     the yields reported, as of 10:00am (New York City time) on the Business Day
     next preceding the Rate Reset Date for any Note, on the display designated
     as "Page 678" on the Telerate Access Service, for actively traded U.S.
     Treasury securities having a maturity equal to the earlier to occur of the
     next Rate Reset Date provided for in such Note (if any) and the Maturity
     Date of such Note, or if such yields shall not be reported as of such time
     or the yields reported as of such time shall not be ascertainable, (ii) the
     Treasury Constant Maturity Series yields reported, for the latest day for
     which such yields shall have been so reported as of the Business Day next
     preceding the Rate Reset Date in Federal Reserve Statistical Release H.15
     (519) (or any comparable successor publication) for actively traded U.S.
     Treasury securities having a constant maturity equal to the earlier to
     occur of the next Rate Reset Date provided for in such Note (if any) or the
     Maturity Date of such Note.  Such implied yields shall be determined, if
     necessary, by (a) converting U.S. Treasury bill quotations to bond-
     equivalent yields in accordance with accepted financial practice and (b)
     interpolating linearly between yields reported for various maturities.

               "RESPONSIBLE OFFICER" shall mean the chief executive officer,
     chief operating officer, chief financial officer or chief accounting
     officer of the Company 

                                       26
<PAGE>
 
     or any other officer of the Company involved principally in its financial
     administration or its controllership function.

               "RESTRICTED INVESTMENT" shall mean any Investment other than a
     Permitted Investment.

               "RESTRICTED PAYMENTS" shall mean any of the following (provided
     that, notwithstanding anything to the contrary stated below, the term
     "Restricted Payments" does not include any distribution of capital gains by
     the Company to its shareholders):

               (i)   any dividend on any class of the Company's capital stock at
               any time after the date hereof;

               (ii)  any other distribution on account of any class of the
               Company's capital stock;

               (iii) any redemption, purchase or other acquisition, direct or
               indirect, of any shares of the Company's capital stock;

               (iv)  any unscheduled payment of principal of, or retirement,
               redemption, purchase or other acquisition of, any subordinated
               debt, including subordinated debt that is convertible into equity
               of the Company;

               (v)   any Restricted Investment;

               "S&P" shall mean Standard and Poor's Corporation, or any
     successor Person.

               "SECURITIES ACT" shall mean the Securities Act of 1933, as
     amended.

               "SHAREHOLDER" shall mean and include any Person who owns,
     beneficially or of record, directly or indirectly, at any time during any
     year with respect to which a computation is being made 5% or more of the
     outstanding voting stock of the Company.

               "SIGNIFICANT HOLDER" shall mean (i) any BP Party, so long as any
     BP Party shall hold (or be committed under this Agreement to purchase) any
     Note, or (ii) any other holder of at least 5% of the aggregate principal
     amount of the Notes from time to time outstanding.

               "SUBSIDIARY" shall mean any corporation or other entity at least
     51% of the total combined voting power of all classes of Voting Stock or
     similar securities 

                                       27
<PAGE>
 
     of which shall, at the time as of which any determination is being made, be
     owned by the Company either directly or through Subsidiaries.

               "TOTAL ASSETS" shall mean, as at any time of determination, the
     total assets of a Person recorded on a balance sheet of such Person
     prepared in accordance with GAAP.

               "TRANSFER" shall mean, with respect to any item, the sale,
     exchange, conveyance, lease, transfer or other disposition of such item.

               "TRANSFEREE" shall mean any direct or indirect transferee of all
     or any part of any Note purchased by you under this Agreement.

               "TREASURY" shall mean, for any Note, the Initial Treasury or the
     then Reset Treasury, as the case may be, upon which the Margin under such
     Note is added to obtain the interest rate of such Note.

               "VOTING STOCK" shall mean, with respect to any corporation, any
     shares of stock of such corporation whose holders are entitled under
     ordinary circumstances to vote for the election of directors of such
     corporation (irrespective of whether at the time stock of any other class
     or classes shall have or might have voting power by reason of the happening
     of any contingency), and, with respect to any other entity, any similar
     security of such entity.

     10C. ACCOUNTING AND LEGAL PRINCIPLES, TERMS AND  DETERMINATIONS.  All
references in this Agreement to "GAAP" shall mean generally accepted accounting
principles, as in effect in the United States from time to time.  Unless
otherwise specified herein, all accounting terms used herein shall be
interpreted, all determinations with respect to accounting matters hereunder
shall be made, and all unaudited financial statements and certificates and
reports as to financial matters required to be furnished hereunder shall be
prepared, in accordance with GAAP (except as set forth in the next succeeding
sentence of this paragraph 10C), applied on a basis consistent with the most
                 -------------                                              
recent audited financial statements of the Company delivered pursuant to
paragraph 5A(i) or (ii) or, if no such statements have been so delivered, the
---------------    ----                                                      
most recent audited financial statements referred to in clause (i) of paragraph
                                                        ----------    ---------
8B.  Notwithstanding the foregoing, however, quarterly financial statements
--                                                                         
shall not include notes to financial statements and to that extent such
statements will not have been prepared in accordance with GAAP.  Any reference
herein to any specific citation, section or form of law, statute, rule or
regulation shall refer to such new, replacement or analogous citation, section
or form should citation, section or form be modified, amended or replaced.

     11.  MISCELLANEOUS.

     11A   NOTE PAYMENTS.  The Company agrees that, so long as you shall hold
any Note, it will make payments of principal of, interest on and any Yield-
Maintenance Amount 

                                       28
<PAGE>
 
payable with respect to such Note, which comply with the terms of this
Agreement, by wire transfer of immediately available funds for credit (not later
than 12:00 noon, New York City time, on the date due) to your account or
accounts as specified in the Purchaser Schedule attached hereto, or such other
account or accounts in the United States as you may designate in writing,
notwithstanding any contrary provision herein or in any Note with respect to the
place of payment. You agree that, before disposing of any Note, you will make a
notation thereon (or on a schedule attached thereto) of all principal payments
previously made thereon and of the date to which interest thereon has been paid.
Upon written request of the Company made concurrently with or reasonably
promptly after payment or prepayment in full of any Note, you shall surrender
such Note for cancellation, reasonably promptly after any such request, to the
Company at its principal executive office. The Company agrees to afford the
benefits of this paragraph 11A to any Transferee which shall have
                 -------------                                   
made the same agreement as you have made in this paragraph 11A.
                                                 ------------- 

     11B. EXPENSES. The Company agrees, whether or not the transactions
contemplated hereby shall be consummated, to pay, and save you and any
Transferee harmless against liability for the payment of, all reasonable out-of-
pocket costs and expenses arising in connection with such transactions,
including:

          (i)    (A) all stamp and documentary taxes and similar charges and (B)
          costs of obtaining a private placement number for the Notes in each
          case as a result of the execution and delivery of this Agreement or
          the issuance of the Notes;

          (ii)   document production and duplication charges and the reasonable
          fees and expenses of any special counsel engaged by you or such
          Transferee in connection with this Agreement and the transactions
          contemplated hereby;

          (iii)  the costs and expenses, including reasonable attorneys' fees,
          incurred by you or such Transferee in enforcing any rights under this
          Agreement or the Notes; and

          (iv)   any judgment, liability, claim, order, decree, cost, fee,
          expense, action or obligation resulting directly from the consummation
          of the transactions contemplated hereby, including the use of the
          proceeds of the Notes by the Company;

provided that the Company shall not be responsible for (1) any of your expenses
--------                                                                       
or those of a Transferee incurred solely in connection with any transfer of any
Note or (2) the fees and expenses of more than one counsel for the holders of
the Notes, except to the extent the Required Holders determine that (a) either
legal advice is needed in a jurisdiction other than that specified in paragraph
                                                                      ---------
11L or (b) there exists a conflict of interest amongst the holders of the Notes.
--- 
The obligations of the Company under this paragraph 11B shall survive the
                                          -------------                  
transfer of any Note or portion thereof or interest therein by you or any
Transferee and the payment of any Note.

                                       29
<PAGE>
 
     11C. CONSENT TO AMENDMENTS.  This Agreement may be amended, and the Company
may take any action herein prohibited, or omit to perform any act herein
required to be performed by it, if the Company shall obtain the written consent
to such amendment, action or omission to act, of the Required Holder(s); except
                                                                         ------
that, (i) without the written consent of the holder or holders of all Notes at
----                                                                          
the time outstanding, no amendment to this Agreement shall change the maturity
of any Note, or change the principal of, or the rate, method of computation or
time of payment of interest on or any Yield-Maintenance Amount payable with
respect to any Note, or affect the time, amount or allocation of any
prepayments, or change the proportion of the principal amount of the Notes
required with respect to any consent, amendment, waiver or declaration, and (ii)
so long as any BP Holder holds any Note(s), no amendment, action or omission to
act shall amend, modify or otherwise affect such BP Party's rights under the
Note(s) that it holds (or its rights under this Agreement to the extent relating
to such BP Party's Note(s)) without such BP Party's written consent.  Each
holder of any Note at the time or thereafter outstanding shall be bound by any
consent authorized by this paragraph 11C, whether or not such Note shall have
                           -------------                                     
been marked to indicate such consent, but any Notes issued thereafter may bear a
notation referring to any such consent.  No course of dealing between the
Company and the holder of any Note nor any delay in exercising any rights
hereunder or under any Note shall operate as a waiver of any rights of any
holder of such Note.  As used herein and in the Notes, the term "this Agree
ment" and references thereto shall mean this Agreement as it may from time to
time be amended or supplemented.

     11D. FORM, REGISTRATION, TRANSFER AND EXCHANGE OF NOTES; LOST NOTES.  The
Notes are issuable as registered notes without coupons in denominations of at
least $1,000,000, except as may be necessary to (i) reflect any principal amount
not evenly divisible by $1,000,000 or (ii) enable the registration of transfer
by a holder of its entire holding of Notes.  The Company shall keep at its
principal office a register in which the Company shall provide for the
registration of Notes and of transfers of Notes.  Upon surrender for
registration of transfer of any Note at the principal office of the Company, the
Company shall, at its expense, execute and deliver one or more new Notes of like
tenor and of a like aggregate principal amount, registered in the name of such
transferee or transferees. At the option of the holder of any Note, such Note
may be exchanged for other Notes of like tenor and of any authorized
denominations, of a like aggregate principal amount, upon surrender of the Note
to be exchanged at the principal office of the Company.  Whenever any Notes are
so surrendered for exchange, the Company shall, at its expense, execute and
deliver the Notes which the holder making the exchange is entitled to receive.
Every Note surrendered for registration of transfer or exchange shall be duly
endorsed, or be accompanied by a written instrument of transfer duly executed,
by the holder of such Note or such holder's attorney duly authorized in writing.
Any Note or Notes issued in exchange for any Note or upon transfer thereof shall
carry the rights to unpaid interest and interest to accrue which were carried by
the Note so exchanged or transferred, so that neither gain nor loss of interest
shall result from any such transfer or exchange.  Upon receipt of written notice
from the holder of any Note of the loss, theft, destruction or mutilation of
such Note and, in the case of any such loss, theft or destruction, upon receipt
of such holder's indemnity agreement (which shall be unsecured if such holder is
an Institutional Investor whose senior

                                       30
<PAGE>
 
debt securities are rated BBB- or Baa3 or better by S&P or Moody's,
respectively, and, otherwise, which shall be unsecured unless the Company
requests in writing that such indemnity agreement be secured), or in the case of
any such mutilation upon surrender and cancellation of such Note, the Company
will make and deliver a new Note, of like tenor, in lieu of the lost, stolen,
destroyed or mutilated Note. The Company shall give to any holder of a Note that
is an Institutional Investor promptly upon request therefor, a complete and
correct copy of the names and addresses of all registered holders of Notes.

     The Company may require payment of a sum sufficient to cover any stamp tax
or governmental charge imposed in respect of any such transfer of Notes.

     11E. TRANSFER OF NOTES; PERSONS DEEMED OWNERS.  Subject to the next
succeeding sentence, you may transfer any Note or portion thereof in your sole
discretion; provided, however, that any Transferee shall be an Institutional
Investor.  Prior to due presentment for registration of transfer, the Company
may treat the Person in whose name any Note is registered as the owner and
holder of such Note for the purpose of receiving payment of principal of,
interest on and any Yield-Maintenance Amount payable with respect to such Note
and for all other purposes whatsoever, whether or not such Note shall be
overdue, and the Company shall not be affected by notice to the contrary.

     11F. SURVIVAL OF REPRESENTATIONS AND WARRANTIES; ENTIRE AGREEMENT.  All
representations and warranties contained herein or made in writing by or on
behalf of the Company in connection herewith shall survive the execution and
delivery of this Agreement and the Notes, the transfer by you of any Note or
portion thereof or interest therein and the payment of any Note, and may be
relied upon by any Transferee, regardless of any investi  gation made at any
time by or on behalf of you or any Transferee.  Subject to the preceding
sentence, this Agreement and the Notes embody the entire agreement and
understanding between you and the Company and supersede all prior agreements and
understandings between you and the Company relating to the subject matter
hereof, and the Company shall not be affected by notice to the contrary.  No
provision of this Agreement shall be interpreted for or against any party
because that party or its legal representative drafted the provision.

     11G. SUCCESSORS AND ASSIGNS.  All covenants and other agreements in this
Agreement contained by or on behalf of either of the parties hereto shall bind
and inure to the benefit of the respective successors and assigns of the parties
hereto (including, without limitation, any Transferee) whether so expressed or
not.

     11H. NOTICES.  All written communications provided for hereunder shall be
sent by first class mail or nationwide overnight delivery service (with charges
prepaid) and (i) if to you, addressed to you at the address specified for such
communications in the Purchaser Schedule attached hereto, or at such other
address as you shall have specified to the Company in writing, (ii) if to any
other holder of any Note, addressed to such other holder at such address as such
other holder shall have specified to the Company in writing or, if any such
other holder shall not have so specified an address to the Company, then
addressed to such other holder in care of the last holder of such Note which
shall have so specified an 

                                       31
<PAGE>
 
address to the Company, and (iii) if to the Company, addressed to it at
Prudential Realty Group, 8 Campus Drive, Parsippany, New Jersey 07054,
Attention: John Triece, or at such other address as the Company shall have
specified to the holder of each Note in writing; provided, however, that any
such communication to the Company may also, at the option of the holder of any
Note, be delivered by any other means either to the Company at its address
specified above or to any officer of the Company.

     11I. PAYMENTS DUE ON NON-BUSINESS DAYS.  Anything in this Agreement or the
Notes to the contrary notwithstanding, any payment of principal of or interest
on any Note that is due on a date other than a Business Day shall be made on the
next succeeding Business Day.  If the date for any payment is extended to the
next succeeding Business Day by reason of the preceding sentence, the period of
such extension shall be included in the computation of the interest payable on
such Business Day.

     11J. SATISFACTION REQUIREMENT.  If any agreement, certificate or other
writing, or any action taken or to be taken, is by the terms of this Agreement
required to be satisfactory to you or to the Required Holder(s), the
determination of such satisfaction shall be made by you or the Required
Holder(s), as the case may be, in the reasonable judgment of the Person or
Persons making such determination.

     11K. INDEMNIFICATION.  The Company hereby agrees to indemnify you and
your directors, officers, employees and agents from, and hold each of them
harmless against, any and all losses, liabilities, claims, damages and expenses
arising out of or by reason of any investigation or litigation or other
proceeding relating to this Agreement, the Notes or the transactions
contemplated hereby, including, without limitation, the reasonable fees and
disbursements of counsel incurred in connection with any such investigation or
litigation or other proceedings (but excluding any such losses, liabilities,
claims, damages or expenses incurred by reason of the gross negligence or
willful misconduct of the Person to be indemnified).

     11L. GOVERNING LAW.  This Agreement shall be construed and enforced in
accordance with, and the rights of the parties shall be governed by, the law of
the State of New York.

     11M. SEVERABILITY.  Any provision of this Agreement which is prohibited
or unenforceable in any jurisdiction shall, as to such jurisdiction, be
ineffective to the extent of such prohibition or unenforceability without
invalidating the remaining provisions hereof, and any such prohibition or
unenforceability in any jurisdiction shall not invalidate or render
unenforceable such provision in any other jurisdiction.

     11N. DESCRIPTIVE HEADINGS.  The descriptive headings of the several
paragraphs of this Agreement are inserted for convenience only and do not
constitute a part of this Agreement.

                                       32
<PAGE>
 
     11O.   COUNTERPARTS.  This Agreement may be executed in any number of
counterparts, each of which shall be an original but all of which together shall
constitute one instrument.


                          [INTENTIONALLY LEFT BLANK]

                                       33
<PAGE>
 
     If you are in agreement with the foregoing, please sign the form of
acceptance on the enclosed counterpart of this letter and return the same to the
Company, whereupon this letter shall become a binding agreement between the
Company and you.



                                    Very truly yours,


                                    PRUDENTIAL REALTY
                                    SECURITIES, INC.

                                    By: /s/ Paul D. Egan
                                       -------------------------
                                    Name:  Paul D. Egan
                                    Title: Vice President


                                    By:________________________
                                    Name:______________________
                                    Title:_____________________

                                      S-1
<PAGE>
 
The foregoing Agreement is
hereby accepted as of the
date first above written:



THREE EMBARCADERO CENTER VENTURE,
a California general partnership

By: BOSTON PROPERTIES LLC,
    as Managing General Partner

    By: BOSTON PROPERTIES LIMITED
        PARTNERSHIP, as Manager

        By: BOSTON PROPERTIES, INC.,
            as General Partner


            By: /s/ Thomas J. O'Connor
               -------------------------
            Name: Thomas J. O'Connor
            Title: Vice President

                                      S-2
<PAGE>
 
                                   EXHIBIT A
                                   ---------

                                [FORM OF NOTES]

                      PRUDENTIAL REALTY SECURITIES, INC.

                       SENIOR NOTE DUE __________, 200_

No. _____                                                     [Date]
$________


     FOR VALUE RECEIVED, the undersigned, PRUDENTIAL REALTY SECURITIES, INC.
(the "COMPANY"), a corporation organized and existing under the laws of the
State of Delaware, hereby promises to pay to THREE EMBARCADERO CENTER VENTURE, a
California general partnership, or registered assigns, the principal sum of
_____________  ______________ DOLLARS ($______________) on _____________, ____
(the "Maturity Date"), with interest (computed on the basis of a 360-day year
comprised of 12 30-day months) on the unpaid balance thereof at the rate of
____% per annum from the date hereof through and including _______, ___ (the
"RATE RESET DATE") and thereafter through and including the Maturity Date, at a
rate of interest per annum equal to the sum of (i) ________ basis points, and
(ii) the Reset Treasury, as defined in the Note Agreement.  All such interest
shall be payable semiannually on the 15/th/ day of June and December in each
year, commencing with the first such date next succeeding the date hereof, until
the principal hereof shall have become due and payable, and shall be payable on
any overdue payment (including any overdue prepayment) of principal, any overdue
payment of interest and any overdue payment of any Yield-Maintenance Amount (as
defined in the Note Agreement), payable semiannually as aforesaid (or, at the
option of the registered holder hereof, on demand), at a rate per annum from
time to time equal to the lesser of (a) the maximum rate permitted by applicable
law and (b) 2.0% over the interest rate then in effect under this Note in
accordance with the foregoing terms and provisions.

     Payments of principal of, interest on and any Yield-Maintenance Amount
payable with respect to this Note are to be made in immediately available funds,
in lawful money of the United States of America, by wire transfer to [_______]
at [NAME OF BANK] in [New York City], ABA #________, Account # __________, or to
such other account or place as the registered holder hereof shall designate to
the Company in writing.

     This Note is one of a series of Senior Notes (the "NOTES") issued pursuant
to a Note Agreement, dated as of November 12, 1998 (the "NOTE AGREEMENT"),
between the Company and One Embarcadero Center Venture and is entitled to the
benefits thereof.

     This Note is a registered Note and, as provided in the Note Agreement, upon
surrender of this Note for registration of transfer, duly endorsed, or
accompanied by a written instrument of transfer duly executed, by the registered
holder hereof or such holder's attorney duly authorized in writing, a new Note
for a like principal amount will be issued to, and registered in the name of,
the transferee. 

                                      A-1
<PAGE>
 
Prior to due presentment for registration of transfer, the Company may treat the
person in whose name this Note is registered as the owner hereof for the purpose
of receiving payment and for all other purposes, and the Company shall not be
affected by any notice to the contrary.

     This Note is subject to optional prepayment, in whole or from time to time
in part, on the terms specified in the Note Agreement.

     If an Event of Default, as defined in the Note Agreement, shall occur and
be continuing, the principal of this Note may be declared or otherwise become
due and payable in the manner and with the effect provided in the Note
Agreement.

     The Company and any and all endorsers, guarantors and sureties severally
waive grace, demand, presentment for payment, notice of dishonor or default,
notice of intent to accelerate, notice of acceleration (to the extent set forth
in the Note Agreement), protest and diligence in collecting.

     THIS NOTE IS INTENDED TO BE PERFORMED IN THE STATE OF NEW YORK AND SHALL BE
CONSTRUED AND ENFORCED IN ACCORDANCE WITH THE LAW OF SUCH STATE.

                              PRUDENTIAL REALTY SECURITIES, INC.



                              By_________________________
                                    [Vice] President


                              By_________________________
                                    Treasurer

                                      B-1
<PAGE>
 
                                   EXHIBIT C
                                   ---------

                             INVESTMENT GUIDELINES
                             ---------------------


1. Invest only in investment grade fixed income assets that:

a) are current in payment and not in default (subject to cure periods):

b) minimally provide for interest payments which are (i) monthly in the case of
"non securities" investments (i.e., whole mortgage loans) or (ii) semi-annually
in the case of "securities" investments (i.e. ABS):

c) have a maturity date which is at least thirty months beyond the asset
purchase date:

d) include prepayment premiums providing for yield maintenance or the
substantial equivalent: and

e) on an individual basis, do not exceed 7% of the total portfolio.

2. Make more than 80% of all investment in assets directly secured by first
mortgages.  In addition: (a) no such assets may have a "loan to value" ratio
which exceeds 80%, and at least 90% of such assets shall have a "loan to value"
ratio which is 75% or less and (b) the overall portfolio of such assets shall be
geographically diverse.

                                      C-1
