A historic Back Bay building home to Boston magazine has found a buyer, and its new owner is promising a multimillion-dollar renovation.

Marcus Partners, a real estate investment firm, has purchased 300 Massachusetts Ave., also known as Horticultural Hall, at Huntington and Massachusetts avenues for an undisclosed sum. The 45K SF mixed-use property is across the street from Symphony Hall. While exact details of the renovation are unknown, Marcus said the building is well-suited for retail, office and institutional uses.

Back Bay’s western edge has become popular for tenants and developers. Boston’s second Four Seasons Hotel, which will become the city’s third-tallest tower, is under construction across Christian Science Plaza from Horticultural Hall. The 15-acre plaza is in the middle of an extensive renovation, and developer Weiner Ventures is proposing 566-foot and 283-foot towers nearby at 1000 Boylston on air rights over the Massachusetts Turnpike.

“300 Mass Avenue offers all of those adjacencies and a wholly unique and architecturally significant environment that will be dramatically upgraded,” Marcus Partners Principal Pete Cameron said.