Newmark Knight Frank Chairman Jeffrey Gural and his partners have sold a stake in the Flatiron Building for $51.8 million, according to city records dated Oct. 28.

The buyer is listed as Michelangelo Flatiron Building Investment LLC, with an address at 805 Third Avenue. The LLC is 100 percent owned by the Michelangelo Fondo, which, in turn, is 100 percent owned by the Sorgente Group, headed in the United States by Veronica Mainetti. Sorgente already holds a…