Walgreen says CEO Greg Wasson will retire when acquisition of UK's Alliance Boots closes

Walgreen says President and CEO Greg Wasson will retire after the drugstore chain completes its merger with health and beauty retailer Alliance Boots.

Walgreen expects that deal to close during the first quarter. The largest U.S. drugstore operator says Alliance Boots Chairman Stefano Pessina will become its acting CEO.

Wasson became CEO of Walgreen Co. in February 2009, and early in his tenure the company bought the New York City-based Duane Reade chain. In August Walgreen said it would buy full control of Alliance Boots, a Swiss company that runs the largest drugstore chain in the U.K.

Walgreen, based in Deerfield, Illinois, has more than 8,200 stores, and Alliance Boots has about 4,600.

Walgreen shareholders are scheduled to vote on the deal Dec. 29.