The initial $240 million phase of the Fenway Center development is finally under way with groundbreaking for 315 apartments in two buildings off Brookline Avenue.

Original developer John Rosenthal of Newton-based Meredith Management Co. formed a partnership with Oregon developer Gerding Edlen and TH Real Estate that provided the impetus to begin construction after 15 years of progress and setbacks. The group contributed a combined $104 million in equity, Rosenthal said. Union Labor Life Insurance Co. and Sun Trust Bank provided $136 million in debt financing.

“The primary attraction for us has always been the phenomenal location right next to Fenway Park, Boston University and Kenmore Square,” said Kelly Saito, managing partner at Gerding Edlen. A groundbreaking ceremony was held Tuesday morning.

Under a 99-year ground lease signed last year with the Massachusetts Department of Transportation, the developers paid $20.6 million up front in base rent.

The Architectural Team of Chelsea designed the phase one complex including 200 underground parking spaces and 37,000 square feet of ground floor retail, to be built on the south side of the Massachusetts Turnpike between the Beacon Street and Brookline Avenue overpasses. The current phase also includes 12,500 square feet of air rights development above the Turnpike for a pedestrian deck above Yawkey station on the MBTA commuter rail.

The development team includes interior designer Planeta Design Group and construction manager John Moriarty & Assoc.

The second phase would include more than 430,000 square feet of offices and residences in two buildings and a 750-space parking garage, subject to a development agreement with the Massachusetts Department of Transportation for construction of an estimated $80 million deck above the Turnpike.

“You have to know how to price and finance it and that’s the next big challenge,” Rosenthal said.