CHICAGO-KBS Realty Advisors LLC has agreed to acquire the Citigroup Center office tower at 500 W. Madison St. here for $435 million.

The purchase price for the 1.5-million-square-foot building is the highest paid for an office property since the Newport Beach, CA-based firm purchased 300 N. LaSalle St. in July 2010 for $655 million, according to Crain’s Chicago Business.

The deal with KBS, which is not yet finalized, is being brokered by the Chicago office of HFF Inc. A deal to sell the building to Los Angeles-based CIM Group fell apart recently, The property is owned by GE Asset Management of Stamford, CT and a group of German investors. See story in Crain’s Chicago Business.