Synergy Investments purchased a 21-story Downtown Crossing office tower, the largest commercial property to sell in Boston since before the pandemic.

The Boston-based developer, which has made a string of recent acquisitions, bought the building at 101 Arch St. for $78M from an entity linked to Clarion Partners, according to property records.

The building on top of the Downtown Crossing MBTA stop last sold for $121.7M in 2005.

“Adding 101 Arch Street to our portfolio aligns perfectly with our strategy of investing in high-quality assets in prime locations,” Synergy CEO David Greaney said in a release. “With its modern design, exceptional amenities, and unmatched commuter accessibility, 101 Arch Street represents a prime opportunity for Synergy to create value for our tenants and stakeholders.”

The 407K SF office tower is 82% leased with over 30 tenants, including Rockland Trust, KP Law, PC and Thorton Tomasetti.

The transaction is the largest commercial property to sell in Boston since 2019, when Rockpoint Group paid $800M to acquire the 1.1M SF 100 Summer St. office building, the Boston Business Journal reported.

JLL’s Coleman Benedict, Chris Angelone, Scott Carpenter, Brooke Howard, Scott Tully Jr. and Rachel Bliss brokered the deal.

The deal comes after Synergy last week purchased the 221K SF building at 179 Lincoln St. from Blackstone by assuming $76.5M in debt. The developer has also acquired Boston's One Liberty Square and One India mixed-use buildings within the last year.

Synergy hasn't shown interest in converting any of these buildings into residential, but the company is working on one of the largest conversion projects in the state at Chestnut Place in Worcester. The two-building complex is planned to become 198 market-rate units and 22 affordable condos.

Synergy's portfolio totals 7M SF across office, retail, multifamily and hospitality assets, according to the release.