Walgreens Boots Alliance, Inc. has sold shares of AmerisourceBergen Corporation common stock pursuant to variable prepaid forward transactions executed in reliance on Rule 144 of the Securities Act of 1933, as amended, for current proceeds of approximately $644 million.    In addition, and subject to the closing of the Rule 144 transaction, Walgreens Boots Alliance entered into a concurrent share repurchase by AmerisourceBergen for proceeds of approximately $50 million.   Walgree...