Walgreens Boots Alliance has agreed to be acquired by Sycamore Partners, a private equity firm, in a $10 billion deal.Walgreens has been facing declining prescription reimbursements and falling sales, amid competition from retail giants like Amazon and Walmart.The buyout follows a 50% drop in Walgreens' share price, and Sycamore will pay $11.45 per share for the acquisition.Walgreens has been closing stores and reported a net loss of $8.6 billion in the previous fiscal year.