Alexion Pharmaceuticals, Inc.  has entered into a definitive agreement to acquire Achillion Pharmaceuticals, Inc., a clinical-stage biopharmaceutical company, for approximately $930 million. Achillion is focused on the development of oral small molecule Factor D inhibitors to treat people with complement alternative pathway-mediated rare diseases, such as paroxysmal nocturnal hemoglobinuria (PNH) and C3 glomerulopathy (C3G). Achillion currently has two candidates in development, including dan...