The properties are at 4400 MacArthur Blvd. and 5000 Birch St. and were developed by the Koll-Aetna partnership in the Airport Area submarket of Orange County.

The seller and the buyer were represented by Robert Smith, Michael Kane, John Weiner and Karen Scholte of CB Richard Ellis, which has been the manager and leasing agent since the buildings were constructed. The 4400 MacArthur property is a nine-story building, while 5000 Birch consists of two steel-frame and glass office towers, one of six stories and the other 10, that are connected by a two-story concourse.

The sale of the two Koll Center properties is one of the largest office development transactions in Orange County this year. The largest occurred this fall when Blackstone Real Estate Advisors bought the county's largest office campus, the 1.7 million-sf Park Place development along the I-405 Freeway, for about $200 million.

Don Koll, one of the sellers in the recent Newport Beach deal, is the founder of the Newport Beach-based Koll Co., which has developed more than 85 million sf of office, industrial and retail space in its 40 years. Aetna is one of the country's largest providers of health, dental, group life, disability and long-term care insurance. Cornerstone is an investment manager for a multi-billion-dollar portfolio of office buildings, warehouses, research and development properties, retail centers, apartment complexes and hotels.