Chicago-based real estate trust Equity Commonwealth is said to be under contract to sell 1600 Market St., the 39-story dark glass office tower in Center City once known as the PNC Bank Building, to American Real Estate Partners of Herndon, Va..

Equity Commonwealth, controlled by investor Sam Zell, entered into a contract to sell the 826,000-square-foot property last month and expects to close on the deal before the end of February, it said in a release on Tuesday.

American Real Estate Partners of Herndon, Va., the one-time owner of Center City's Two Liberty Place office tower, was identified as the buyer by two people familiar with the deal, but not authorized to discuss it publicly.

Spokeswomen for Equity Commonwealth and American Real Estate Partners did not immediately return phone messages seeking confirmation.

1600 Market St., now 84 percent leased, is the latest Philadelphia property to be sold by Equity Commonwealth as it thins out its holdings in the city.

Other transactions in recent years include the sale of the Centre Square, the 1500 Market St. office complex known for Claes Oldenburg's 45-foot-tall Clothespin sculpture in its front plaza, and the former One Franklin Plaza building, GlaxoSmithKline's past headquarters at 16th and Race Streets.

The company continues to own the 54-story 1735 Market St. tower, known as BNY Mellon Center.