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Boston-based developer Synergy added to its office portfolio with acquisition of a 159,273-square-foot West End complex that includes medical offices affiliated with Mass General Hospital.

Synergy acquired 101 Merrimac St. in exchange for assuming $22.5 million in outstanding mortgage payments, according to a Suffolk County deed.

The property previously traded for $22.9 million in 1997, when it was acquired by Boston-based H.N. Gorin and Artemis Real Estate Partners. The previous owners received $64.6 million in floating rate refinancing from French investment bank Societe Generale in 2019.

Completed in 1989, the building is currently valued at $64.3 million, according to Boston assessors’ records.

Synergy continues to expand its portfolio through acquisitions of office buildings at deep discounts in the downtown area.

The firm previously acquired 179 Lincoln St. last year for 51 percent below its pre-COVID transaction price and 101 Arch St. for a 36 percent discount on its 2005 purchase price.

Synergy recently completed upgrades to another large downtown office building that it acquired for $238 million before the pandemic, 10 Post Office Square.

This fall, Synergy completed a lobby redesign and new amenities floor including a conference center, tenant lounge and fitness club at the 451,947 square-foot building.