Allen & Overy (A&O), Simpson Thacher & Bartlett, Wachtell Lipton Rosen & Katz and Gibson Dunn & Crutcher have snared the key advisory roles on the £5.6bn takeover of UK pharmacy chain Alliance Boots by US drugs giant Walgreens.

Walgreens will take full control of Boots in early 2015, acquiring the 55% share in the company it did not already own.

Simpson Thacher New York M&A partner Mark Pflug is leading a team of lawyers across New York and London for Boots' private equity owner Kohlberg Kravis Roberts (KKR), which took over the chain in 2007.

On that £9.7bn takeover, Clifford Chance staged a major coup by grabbing the mandate for KKR, despite the US buyout house's ongoing relationship with Simpson Thacher. Slaughter and May represented Boots Alliance on the 2007 deal, though it is unclear whether the magic circle has a role this time round.

Corporate work for Walgreens was carried out by an A&O team in Amsterdam led by partner Justin Steer with senior associate Emily Barker. Amsterdam competition head Paul Glazener acted on anti-trust matters.

An A&O team in London handled specialist work such as pensions, employment and environment matters. In total, according to a source at A&O, the firm has had more than 50 lawyers in different jurisdictions acting for Walgreens on the deal.

The US buyer has also instructed Wachtell, with the New York powerhouse fielding a team led by corporate partners Andrew Brownstein and Benjamin Roth. 

Gibson Dunn is representing Lazard, the financial advisor to Walgreens. The firm's team includes New York corporate partners Eduardo Gallardo and Dennis Friedman.

Upon closure of the deal, the new company will operate under the name Walgreens Boots Alliance and will remain headquartered in the US. A number of other recent cross-border mergers have seen companies relocate to the UK for tax purposes.