With Alexion Pharmaceuticals Inc.'s acquisition of Achillion Pharmaceuticals Inc. for about $930 million up front, Alexion expands and diversifies its pipeline into familiar territory – treating complement-mediated diseases. Blue Bell, Pa.-based Achillion is developing oral, small-molecule factor D inhibitors for treating complement alternative pathway-mediated rare diseases, including paroxysmal nocturnal hemoglobinuria and C3 glomerulopathy.