Wachtell Lipton Rosen & Katz, Sullivan & Cromwell and Ropes & Gray have grabbed lead roles on US pharmaceutical company Alexion's $8.4bn (£5.5bn) purchase of fellow US drugmaker Synageva.

The deal is the latest in a string of high-profile pharma deals this year and will see Alexion pay more than twice the market value for Synageva.

Alexion turned to Wachtell on the deal, which is fielding a team led by corporate partners Daniel Neff and Mark Gordon.

The firm is also fielding partners acting across antitrust, executive compensation, finance and tax aspects of the deal.

Sullivan's team advising Synageva is headed by New York corporate partners Matthew Hurd and Krishna Veeraraghavan.

Ropes & Gray is also acting for Synageva. The firm's Boston office has acted as Synageva's legal adviser on multiple deals over the last few years, including its $117m (£76.9m) stock offering in 2013 and its merger with biotech company Trimeris in 2011.

The pharmaceutical sector has experienced a slew of deal activity in recent months. Most recently, Chinese e-commerce giant Alibaba Group agreed to transfer its online pharmacy business to its Hong Kong-listed sister company Alibaba Health Information.

In March Wachtell led alongside Wilson Sonsini Goodrich & Rosati on US drugs manufacturer AbbVie's acquisition of cancer treatment specialist Pharmacyclics for $21bn (£13.9bn). In the same month Slaughter & May and Cleary Gottlieb Steen & Hamilton were instructed by GlaxoSmithKline on the sale of half of its stake in South African drugmaker Aspen.

Earlier this year Ropes & Gray took on another big role as part of a trio of firms called up for Pfizer's $17bn (£11bn) acquisition of injectable drugmaker Hospira, while Sullivan also acted on a merger deal between medical device companies Sorin Group and Cyberonics.