FOURTH AMENDMENT TO REAL ESTATE PURCHASE CONTRACT

Exhibit 2.5

FOURTH AMENDMENT TO REAL ESTATE PURCHASE CONTRACT

THIS FOURTH AMENDMENT TO REAL ESTATE PURCHASE CONTRACT (the “Fourth Amendment”) is attached to and made a part of that certain Real Estate Purchase Contract effectively dated February 9, 2006, by and between CNLR DC ACQUISITIONS I, LLC, a Delaware limited liability company (hereinafter referred to as “Seller”), and BROOKFIELD FINANCIAL PROPERTIES, L.P., a Delaware limited partnership (hereinafter referred to as “Purchaser”), as amended by (i) the Amendment to Real Estate Purchase Contract dated February 14, 2006, (ii) the Second Amendment to Real Estate Purchase dated February 15, 2006, and (iii) the Third Amendment to Real Estate Purchase dated April 18, 2006 (as amended, the “Agreement”).

WITNESSETH:

WHEREAS, Seller and Purchaser have heretofore entered into the Agreement, whereby Purchaser agreed to purchase that certain real and personal property located at 601 and 701 South 12^th Street, Arlington, Virginia as more particularly described therein (collectively referred to herein as the “Property”), and Seller agreed to sell the Property to Purchaser on the terms and conditions set forth therein; and

WHEREAS, Seller and Purchaser desire to modify certain terms of the Agreement for their mutual benefit as set forth below.

NOW, THEREFORE, for and in consideration of the premises, the payment of Ten and No/100 ($10.00) Dollars in hand paid by Purchaser to Seller, the mutual covenants and agreements herein set forth, and other good and valuable consideration, the receipt, adequacy and sufficiency of which are hereby expressly acknowledged by the parties thereto, the parties hereto do hereby covenant and agree as follows:

1. Recitals. The foregoing recitals are true and correct and are incorporated herein by this reference.

2. Lender Approval Period. The Lender Approval Period is hereby extended through May 12, 2006 at 5:00 p.m. EDT. Purchaser shall have no right to extend the Lender Approval Period beyond this date.

3. Closing Date. The Closing Date is hereby agreed by the parties to be May 16, 2006.

4. Counterparts. This Fourth Amendment may be executed in one or more counterparts, all of which shall be considered one and the same agreement, and shall become a binding agreement when one or more counterparts have been signed by each of the parties and delivered to the other party, which may be by facsimile.

5. Capitalized terms. Capitalized terms used in this Fourth Amendment shall, unless otherwise defined, have the meaning ascribed to them in the Agreement.

6. No Other Amendment. Except as herein amended, the terms and conditions of the Agreement remain in full force and effect. In the event of a conflict between the terms and conditions of this Fourth Amendment and the terms and conditions of the Agreement, the terms and conditions contained in this Fourth Amendment shall control.

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IN WITNESS WHEREOF, Purchaser and Seller have caused this Fourth Amendment to be executed and effective as of May 10, 2006.