Weil Gotshal & Manges and Wachtell Lipton Rosen & Katz are taking the key advisory roles as Sanofi-Aventis’s multibillion-dollar bid for US biotechnology company Genzyme goes hostile.

Weil Gotshal is acting for French pharma company Sanofi on its $18.5bn (£11.7bn) bid with a team including corporate partners Claude Serra in Paris and Michael Aiello in New York.