Newly built Seaport office building sells for $455 million

A new office building in the Seaport sold Thursday for one of the highest prices on record in Boston’s hot office market.

American Realty Advisors and Norges Bank closed on a deal to buy 121 Seaport Blvd., a just-finished building that’s home to tech firm PTC and drug maker Alexion, from developer Skanska USA. Documents filed in Suffolk County show the deal worth $455 million. The sale did not include retail space on the lower two floors, but it ranks among the richest office space sales ever in Boston.

Skanska, which also built neighboring 101 Seaport, launched construction on the $281 million, 17-story tower in 2015 without tenants lined up, a rare and risky move in Boston’s typically conservative office development scene. But it inked huge leases with PTC and Alexion within a few weeks of each other last year, and the building opened 100 percent leased.