Cornerstone buys 99 Summer St.

Cornerstone Real Estate Advisers is purchasing the 20-story office building at 99 Summer Street in Boston for $110.8 million.

The firm, a subsidiary of MassMutual Financial Group, is buying the top-rated office building from Normandy Real Estate Partners, which acquired the property in 2006 and has since renovated its lobby and other common areas.

The sale of 99 Summer comes at a time of increasing activity in the Boston office market, which is experiencing increases in rent and renewed interest from national and international investors.

Advertisement - Continue Reading Below

Cornerstone, which has offices in the U.S., U.K. Europe and Asia, is among the world’s largest global real estate managers. It is also a major investor in the Fan Pier development in the South Boston Innovation District.

The building at 99 Summer includes 272,614 square feet of top-rated office space and is 93 percent leased. Its exterior features flame finish granite with an original red pyramidal roof and stepped office design. Eastdil Secured served as the broker in the transaction.