Walgreen (WAG) stock is retreating after a number of research firms reacted negatively to the company's acquisition of a 45% stake in British drugstore chain Alliance Boots yesterday. The deal, which gives Walgreen the option to acquire a 100% stake in Alliance Boots in about three years, will not solve Walgreen's problems in the U.S., research firms Citigroup and Macquarie contended. The transaction creates execution risks, as Walgreen has limited integration experience and U.S. retailers have not historically acquired international companies, Citigroup said in a note to investors this morning. Moreover, the deal increases Walgreen's exposure to Europe, added the firm, which lowered its price target for Walgreen shares to $27 from $29 while maintaining a Sell rating on the stock. Similarly, research firm Macquarie contends that the transaction doesn't address Walgreen's deteriorating U.S. traffic trends and declining pharmacy volumes. The firm downgraded the stock to Neutral from Outperform and reduced its target on the shares to $34 from $38. In mid-morning trading, Walgreen fell $1.14, or 3.79%, to $28.95.