New York real estate firm Madison International Realty announced Wednesday that it had purchased a 49 percent interest in One California Plaza, a 42-story office tower at 300 S. Grand Ave. in downtown Los Angeles.

The $295 million paid by Madison values the 1.03 million-square-foot building at more than $600 million, or about $582 a square foot. The sale closed Sept. 26.

Madison purchased the minority interest from Boston real estate investment firm Beacon Capital Partners, which acquired the trophy tower for just under $208 million about 18 months ago with joint venture partner MPG Office Trust Inc. MPG sold its stake to Beacon in December.

Ronald M. Dickerman, president of Madison, said the firm was pleased to partner with Beacon on the class A office property in downtown Los Angeles, where no new office towers have been constructed for 20 years.

“We have acquired a substantial interest in a top-tier asset with prominent tenants located in a premier West Coast office market,” he said in a statement.

The Bunker Hill building, built in 1985, is now about 78 percent occupied, according to CoStar Group Inc. Major tenants include law firms Skadden Arps Slate Meagher & Flom and Morgan Lewis & Bockius, as well as Bank of the West.