Unizo Holdings, a Japanese company that has become one of the most active buyers of office space on the East Coast, could add another New York City office tower to its portfolio.

Unizo is in negotiations to buy 685 Third Ave. from current owner TH Real Estate, a subsidiary of TIAA, for close to $450M, Crain's New York Business reports. That pencils out to roughly $700/SF for the 646K SF office building, which TIAA bought from a then-distressed Pfizer for $190M in 2010. The tower lost its anchor tenant when Salesforce decided to move to 3 Bryant Park, now known as Salesforce Tower.

Unizo owns a handful of Manhattan properties, including 370 Lexington Ave. and 440 Ninth Ave., but the firm has recently been most active in Washington, D.C., where it has earned a reputation as the market's dominant buyer and one of its most secretive.

CBRE's Darcy Stacom and Bill Shanahan are marketing 685 Third on behalf of TH, and Crain's reports another buyer could swoop in and beat Unizo's offer. A deal would boost New York City's flagging investment sales market.

CORRECTION, AUG. 17, 5:20 P.M. ET: A previous version of this story incorrectly used an image of a nearby building. This story has been updated.