Citizens Commercial Banking is leading the $435 million construction loan for Amazon’s new office building under construction in Boston’s Seaport District.

Newton-based WS Development broke ground this month on the 111 Harbor Way building, which contains 430,000 square feet of office space leased to Amazon and two stories of retail space totaling 81,000 square feet.

WS is partnering with PSP Investments, a Canadian pension investment manager, on the 7.6-million-square-foot master-planned Seaport development. Construction of 111 Harbor Way is scheduled for 2021.

A longtime Citizens client, WS Development has developed 98 properties comprising 23 million square feet in 10 states.

“Providing construction loans that fund projects, create jobs, and strengthen growing neighborhoods, is just one of the ways that Citizens delivers substantial value for our clients and invests in our host communities such as the Seaport,” Gary Magnuson, head of commercial real estate finance at Citizens, said in a statement.