Shares of Walgreens Boots Alliance rallied 6.4% toward a 7-month high in morning trading Monday, after Bloomberg News reported that the private equity giant KKR & Co. had approached the pharmacy chain about a buyout. If the deal moves forward, which could be valued at north of $70 billion, it would be the largest leveraged buyout ever. Like other pharmacy retailers, Walgreens is facing pressure from a combination of weak retail shares and drug reimbursement pressure. Reuters first reported last week that the company was considering going private.