The Citadel Center reportedly is up for sale — for as much as $750 million, according to media sources.

New York-based Angelo Gordon & Co. and Houston-based Hines Interests hired HFF, a real estate capital markets firm, to market the 37-story Loop office tower at 131 S Dearborn St., according to the Real Estate Alert newsletter.

Through a joint venture, the companies infused $50 million in equity to take control of the building three years ago, when owners Robert Gans and Dearborn Capital were about to default on a $472 million mortgage.

The JV is seeking between $700 million and $750 million for the building, according to Crain's Chicago Business. They reportedly spent more than $100 million upgrading the building last year.