Seattle

SALESFORCE.COM Inc, which has agreed to lease what will be San Francisco's tallest office tower, now plans to buy its first building in the city to expand its headquarters.

The company agreed to purchase 50 Fremont St for about US$640 million, according to a regulatory filing. That ranks as the city's most expensive office deal this year. Salesforce already leases about 60 per cent of the 41-storey building in the South of Market area. The deal includes the office tower and two retail buildings totalling 817,000 square feet (75,900 square metres), the company said.