New York-based SL Green Realty Corp. has agreed to sell its 43.7 percent interest in a Southern California office portfolio of 28 properties, including six San Diego buildings, for $100 million.

Officials of the real estate investment trust said the buyer is an affiliate of New York-headquartered Blackstone Group LP, a current joint venture partner which will now take full ownership of the portfolio.

SL Green said the deal includes buildings in San Diego, Los Angeles and Orange counties, totaling 3.7 million square feet The San Diego properties include buildings in Sorrento Valley, Governor Park, Rancho Bernardo and Carmel Mountain Ranch.

Properties in the deal were originally part of a 31-property, 4.5 million-square-foot portfolio that SL Green acquired through foreclosure in 2012 and later recapitalized through its venture with Blackstone.

“While Blackstone stands to enjoy additional success with the portfolio, we are now ready to exit this noncore investment at a significant gain and intend to redeploy the proceeds back into New York City assets," said David Schonbraun, SL Green’s co-chief investment officer, in a statement.

SL Green (NYSE: SLG) is New York City’s largest office landlord, with interests in 92 Manhattan buildings.

Blackstone Group (NYSE: BX), among the world’s largest investment companies, is majority owner of Hotel Del Coronado. Its portfolio companies include SeaWorld Entertainment, operator of SeaWorld San Diego; and Merlin Entertainments Group, which operates Legoland California Resort in Carlsbad.

Blackstone also owns, manages or franchises several local hotel properties through its Hilton Worldwide.