NEW YORK CITY — Ariel Property Advisors has negotiated the $15.9 million sale of a 71-unit multifamily portfolio in the Flatbush neighborhood of Brooklyn. The portfolio is made up of nine buildings and spans 79,932 square feet. Victor Sozio, Alexander McGee and Michael A. Tortorici of Ariel Property Advisors represented the undisclosed seller in the transaction. The buyer was also undisclosed. The properties in the portfolio are located at 90-92 E. 18th St.; 25 E. 21st St.; 369 E. 21st St.; 600 E. 22nd St.; 2102, 2108, 2112 and 2116 Regent Place; and 2322 Bedford Ave.