
<PAGE>
 
                                                                   Exhibit 10.43






                            INDEMNIFICATION AGREEMENT
                            -------------------------

                   INDEMNIFICATION AGREEMENT (this "Agreement"), dated
                                                    ---------
         as of November __, 1997, made by BOSTON PROPERTIES LIMITED
         PARTNERSHIP ("Mortgagor"), a Delaware limited partnership, hav-
                       ---------
         ing an address at 599 Lexington Avenue, New York, New York
         10022, in favor of JOHN HANCOCK MUTUAL LIFE INSURANCE COMPANY
         ("Mortgagee"), a Massachusetts corporation, having its princi-
           ---------
         pal office at John Hancock Place, Post Office Box 111, Boston,
         Massachusetts 02117, Attention:  Real Estate Investment Group,
         T-52.


                                   WITNESSETH:
                                   ----------

                   WHEREAS, Mortgagor is, on the date hereof, (a) the
         owner of fee title to a parcel of land and the improvements
         thereon known as 875 Third Avenue, New York, New York and the
         easements appurtenant thereto (collectively, the "Original Fee
                                                           ------------
         Parcel"), all as more particularly described in Exhibit A-1
         ------                                          -----------
         hereto, and (b) the owner of fee title to the Corner Parcel and
         all Improvements thereon (as such terms are defined in the
         Mortgage, as hereinafter defined), which Corner Parcel is con-
         tiguous to the Original Fee Parcel and is more particularly de-
         scribed on Exhibit A-2 hereto (the Original Fee Parcel and the
                    -----------
         Corner Parcel are collectively described on Exhibit A-3
                                                     -----------
         hereto);

                   WHEREAS, Mortgagee is on the date hereof the owner
         and holder of certain mortgages which were consolidated, ex-
         tended and modified pursuant to that certain Consolidation,
         Extension and Modification Agreement (the "Consolidation Agree-
                                                    --------------------
         ment"), dated as of May 11, 1988, between Kenvic Associates, a
         ----
         New York general partnership ("Original Mortgagor") and Mort-
                                        ------------------
         gagee, recorded on May 18, 1988 in the Office of the City Reg-
         ister, New York County (the "Register's Office") in Reel 1403,
                                      -----------------
         Page 1793, so as to form a single first lien on the Mortgaged
         Premises (as such term is defined in the Mortgage, as herein-
         after defined) securing the original principal amount of
         $180,000,000, and were further modified (i) pursuant to that
         certain Modification Agreement, dated as of May 30, 1990, be-
         tween Original Mortgagor and Mortgagee, recorded on June 28,
         1990 in the Register's Office in Reel 1705, Page 1760 (the
         "1990 Modification Agreement"), (ii) pursuant to that certain
          ---------------------------
         Note and Mortgage Modification Agreement, dated as of July 23,
         1992, between Original Mortgagor and Mortgagee, recorded on
         July 30, 1992 in the Register's Office in Reel 1892, Page 434
         (the "1992 Modification Agreement"), (iii) pursuant to that
               ---------------------------
         certain Note and Mortgage Modification and Spreader Agreement,
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         dated as of December 29, 1995, between Original Mortgagor and
         Mortgagee, recorded on January 5, 1996 in the Register's Office
         in Reel 2279, Page 443 (the "1995 Modification Agreement"); and
                                      ---------------------------
         (iv) pursuant to that certain Note and Mortgage Modification
         and Spreader Agreement, dated as of the date hereof, between
         Mortgagor and Mortgagee, intended to be recorded in the
         Register's Office following the execution thereof (the "1997
                                                                 ----
         Modification Agreement"; the Consolidation Agreement as amended
         ----------------------
         by the 1990 Modification Agreement, the 1992 Modification
         Agreement, the 1995 Modification Agreement and the 1997 Modifi-
         cation Agreement is hereinafter referred to as the "Mortgage";
                                                             --------
         any capitalized terms used herein and not defined shall have
         the respective meanings assigned to them in the Mortgage);

                   WHEREAS, as of the date hereof, (i) Original Mort-
         gagor has, in exercise of its rights under Section 6 of the
         1995 Modification Agreement, conveyed to Mortgagor all of Orig-
         inal Mortgagor's right, title and interest in and to the Orig-
         inal Fee Parcel, (ii) Mortgagee and Original Mortgagor have
         terminated the Corner Parcel Lease, (iii) Mortgagee has con-
         veyed to Mortgagor Mortgagee's fee title in and to the Corner
         Parcel (the transaction described in subparagraph (ii) above
         and this subparagraph (iii) being collectively referred to
         herein as the "Corner Parcel Transfer"), and (iv) Mortgagor has
                        ----------------------
         agreed to assume all of Original Mortgagor's obligations aris-
         ing from and after the date hereof under the Notes, the Mort-
         gage and the other Loan Documents pursuant to that certain As-
         sumption, dated as of the date hereof, by Mortgagor for the
         benefit of Mortgagee and Original Mortgagor and their respec-
         tive successors and assigns (the transactions described in sub-
         paragraphs (i), (ii), (iii) and (iv) above shall hereinafter be
         collectively referred to as the "Transfer"); and
                                          --------
                   WHEREAS, Mortgagor, in consideration of the foregoing
         and of Mortgagee's agreement to consent to the Transfer, has
         agreed to execute and deliver this Agreement.

                   NOW, THEREFORE, in consideration of the premises and
         the mutual covenants herein contained and for other good and
         valuable consideration, the receipt of which is hereby acknowl-
         edged, the parties hereto agree as follows:

                   1.  Indemnification.  Notwithstanding any provision
                       ---------------
         in the Mortgage, the Notes or any other Loan Document limiting
         or negating the personal liability of Mortgagor, Mortgagor
         shall protect, indemnify, save harmless and defend Mortgagee
         from and against any and all transfer taxes, income taxes and
         all other costs, expenses, liabilities, obligations, claims,
         losses, damages, penalties, and causes of action, of any type
         whatsoever (collectively, "Claims"), imposed upon, suffered,


                                       -2-
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         incurred by or asserted against Mortgagee at any time by reason
         of the Corner Parcel Transfer, except to the extent that such
         Claims arise from Mortgagee's gross negligence or willful mis-
         conduct.

                   2.  Survival.  The obligations of Mortgagor under
                       --------
         Section 1 of this Agreement shall survive any payment of the
         Notes, any discharge, satisfaction, release or assignment of
         the Mortgage, any transfer of the Mortgaged Premises or any
         part thereof, any exercise of remedies by Mortgagee, including,
         without limitation, the appointment of a receiver, any foreclo-
         sure of the Mortgage or any transfer of the Mortgaged Premises
         (or any part thereof) by deed in lieu of foreclosure and any
         other event or circumstance whatsoever.

                   3.   Personal Liability.  In accordance with Sec-
                        ------------------
         tion 6 of the 1997 Modification Agreement, Mortgagor shall be
         personally liable for all of its obligations set forth in this
         Agreement.

                   4.   Binding Effect.  This Agreement shall inure to
                        --------------
         the benefit of Mortgagee and its successors and assigns, and
         shall be binding upon Mortgagor and its respective successors
         and assigns.

                   5.   Counterparts.  This Agreement may be executed in
                        ------------
         several counterparts, each of which shall constitute one and
         the same instrument.

                   6.   Notices.  All notices, demands, requests, con-
                        -------
         sents, approvals and other instruments under this Agreement
         shall be in writing and shall be deemed to have been actually
         or properly given if and when mailed by first-class registered
         or certified mail, return receipt requested, postage prepaid,
         or by personal delivery (with a receipt obtained therefor) or
         recognized overnight courier service, addressed (a) if to Mort-
         gagor, to Boston Properties Limited Partnership, 599 Lexington
         Avenue, New York, New York 10022, Attention, Robert Selsam, or
         at such other address as Mortgagor may have designated by no-
         tice to Mortgagee, with a copy to Goodwin, Proctor & Hoar, LLP,
         Exchange Place, Boston, Massachusetts 02109, Attention, Edward
         M. Schulman, Esq., with a copy to Weil, Gotshal & Manages LLP,
         767 Fifth Avenue, New York, New York 10153, Attention, Alan J.
         Pomerantz, Esq. or to such other firms as Mortgagor may direct
         in writing, and (b) if to Mortgagee originally named herein, to
         John Hancock Mutual Life Insurance Company, John Hancock Place,
         P.O. Box 111, Boston, Massachusetts 02117, Attention, Real Es-
         tate Investment Group, Floor T-52, or at such other address as
         Mortgagee may have designated by notice to Mortgagor.



                                       -3-
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                   7.   Miscellaneous.  Mortgagor agrees that:
                        -------------

                   (a)  If any term of this Agreement or any application
              thereof shall be declared invalid, illegal or unenforce-
              able, the remainder of this Agreement and any other ap-
              plication of such terms shall not be affected thereby.

                   (b)  No failure or delay on the part of Mortgagee to
              exercise any power, right or privilege under this Agree-
              ment shall impair any such power, right or privilege or be
              construed to be a waiver of any default or any acquies-
              cence therein, nor shall any single or partial exercise of
              such power, right or privilege preclude other or further
              exercise thereof or of any right, power or privilege.

                   (c)  No provision of this Agreement may be changed,
              waived, discharged or terminated except by an instrument
              in writing signed by the party against whom enforcement of
              the change, waiver, discharge or termination is sought.

                   (d)  This Agreement shall be governed and construed
              in accordance with the laws of the State of New York.

                   (e)  Mortgagor shall pay all reasonable attorneys'
              fees and other reasonable costs and expenses which may be
              incurred by Mortgagee in the enforcement of this Agree-
              ment.


                   [Remainder of Page Intentionally Left Blank]


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                   IN WITNESS WHEREOF, the undersigned has caused this
         Indemnification Agreement to be duly executed and delivered by
         its duly authorized officers as of the date first above writ-
         ten.


                                  MORTGAGOR:

                                  BOSTON PROPERTIES LIMITED PARTNERSHIP,
                                    A Delaware Limited Partnership

                                  By:  Boston Properties, Inc.,
                                       General Partner

                                       By:  /s/ Robert Selsam
                                            -------------------------------
                                            Name:  Robert Selsam
                                            Title: Senior Vice President
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         STATE OF NEW YORK   )
                             :    ss:
         COUNTY OF NEW YORK  )



                   On this ___ day of November, 1997, before me person-
         ally came ___________________, to me known to be the person(s)
         who executed the foregoing instrument, and who, being duly
         sworn by me, did depose and say that he/she is the
         _________________ of Boston Properties, Inc., a Delaware corpo-
         ration, the general partner of Boston Properties Limited Part-
         nership, a limited partnership duly organized under the laws of
         the State of Delaware, having an address at 599 Lexington Av-
         enue, New York, New York 10022; and that he/she has authority
         to sign the foregoing instrument for and on behalf of Boston
         Properties Limited Partnership, and he/she acknowledged to me
         that he/she executed the same as the act and deed of said part-
         nership for the use and purposes therein mentioned.



                                      ------------------------------------
                                                 Notary Public
