For two decades, it housed many of the City of Philadelphia's attorneys. Soon, the former YMCA building on Arch Street will become home to a posh hotel.

Great West Mutual Life has sold part of the building, at 1421 Arch St., to Arch Street Hotel Partners L.P., a subsidiary of Development Services Group Inc. of Memphis.

The $8.5 million sale, negotiated by CB Richard Ellis Inc., includes the main lobby and floors five through 10 of the condominium building.

DSG said it planned to redevelop the property into a luxury hotel for a chain that has not yet been announced. The rest of the building houses Sweat Health Club, offices, and retail space.

Preliminary plans for the hotel include 194 rooms, a 90-seat restaurant with a 40-seat bar at the lobby level, and meeting space. Also, a ballroom would be restored.

"We are bullish on downtown Philadelphia," Gary Prosterman of DSG said in a statement yesterday. "This is a spectacular building.

"The planned expansion of the Convention Center is icing on the cake," he said. "We are thrilled that we can bring this high-quality European-styled hotel to the city center of Philadelphia."

Renowned Philadelphia architect Horace Trumbauer designed the 10-story, 125,000-square-foot, Georgian Revival building. It was built in 1911 as the Elkins Memorial YMCA. Last renovated in 1985, it housed the Philadelphia District Attorney's Office from 1986 to 2006.

A key attraction was the location, a half-block from the Convention Center's planned Broad Street entrance, said CB Richard Ellis vice president Christian Dyer, who represented Great West Mutual Life in the deal. The center's scheduled $631 million expansion is expected to be completed in 2009.

Contact staff writer Suzette Parmley at 215-854-2594 or sparmley@phillynews.com.