The Irvine Co. has dropped its interest in buying the portfolio of Los Angeles-based CommonWealth Partners LLC.

“We think that it’s a very attractive portfolio, but for reasons we decline to discuss, we’ve decided not to submit a bid,” said Irvine Co. spokesman Bill Rams, reading a statement.

The buy would have been the biggest yet for the Irvine Co. and would have given the Newport Beach-based company a larger presence in Los Angeles and other Western U.S. markets.

Formal bids were expected to be submitted Tuesday to the portfolio’s broker, Secured Capital Corp. The 13 office-building portfolio could go for $1.5 billion or more, sources familiar with the sale have said.

Other serious contenders include J.P. Morgan & Co. and a partnership led by Equity Office Properties Trust. Houston-based Hines, Trizec Properties Inc. and possibly Maguire Properties Inc. also have shown interest.

It was unclear which firms had submitted formal bids.

Last month, CommonWealth listed its entire 6 million-square-foot portfolio, which includes the 53-story tower at 777 S. Figueroa St. in downtown L.A. and three high-profile Glendale office buildings.

CommonWealth owns its properties through a partnership with Rockefeller Group International Inc. and the California Public Employees Retirement System, which voted at the end of last year to cut back its overall real estate holdings. Calpers spurred the portfolio sale, sources said.