Cambridge-based Transatlantic Investment Management Inc. has purchased 151 Merrimac St. in Boston for $13.5 million.

Built in 1887, the six-story building is 80 percent leased to three long-term tenants. Massachusetts General Hospital leases 58 percent of the building.

"We have watched this area’s transformation and are bullish on its long-term prospects," Anthony Goschalk, president of Transatlantic Investment Management, said in a statement. "This investment matches our long-term strategy of acquiring high quality B+ assets in strong growth areas."

Avison Young Principals Karyn McFarland, Scott Jamieson and Michael Smith and Vice President Brandon Dickason represented the seller.

Located at the corner of Causeway and Merrimac streets, the building was recently renovated with a new granite lobby floor and energy-efficient lighting in common areas.