1. Chemistry Research and Discovery, Department of Molecular Structure, Department of Neuroscience, Department of Protein Science, Amgen Inc., One Amgen Center Drive, Thousand Oaks, California 91320, Chemistry Research and Discovery, Department of HTS and Molecular Pharmocology, Department of Pharmacokinetics and Drug Metabolism, Amgen Inc., 1 Kendall Square Building 1000, Cambridge, Massachusetts 02139