The office and retail property giant said the net initial yield is 4.1%, topped up to 5.8%.
The 10-storey building is located at 55 Old Broad Street, near Liverpool Street station, and wraps around Landsec’s City office tower Dashwood.
It is 87% let by income to businesses including Ecom Agrotrade, GB Rail Freight and Barclays.
The deal is expected to complete in January.
“The development potential of this asset, combined with the potential for Dashwood, offers Landsec the opportunity to deliver a compelling, best-in-class destination over the medium term,” said Landsec’s head of investment Nick de Mestre.
“This acquisition demonstrates our commitment to optimising our central London portfolio through the reinvestment of capital, as set out in our strategy.”
Shares shed 4% to 695.69p on Monday morning.