Image courtesy of Architectural Resources Cambridge

Leggat McCall Properties is proposing a 330,000-square-foot office-lab tower in Somerville as the next phase of its Boynton Yards master-planned development.

The 11-story One Boynton at 121 South St. would occupy a nearly 1-acre building lot at the corner of South and Windsor streets, according to a site plan application submitted this week to the city of Somerville.

Replacing a 2-story commercial building, the 204-foot-tall tower would include 332,500 square feet of lab, R&D and office space, 9,500 square feet of retail space and 242 below-grade parking spaces. 

Boston-based Leggat McCall and DLJ Real Estate Partners of New York are partnering on the 6.5-acre development site near the future Union Square station on the MBTA Green Line.

The approved master plan for the development includes nearly 1 million square feet of office, lab and R&D space, 338,000 square feet of housing, 42,500 square feet of retail and over two acres of open space.

Leggat McCall and DLJ Real Estate developed the project’s first building, the 9-story, 289,000-square-foot 101 South St., on speculation and landed Cambridge biotech platform Flagship Pioneering as its anchor tenant in April.