1. Department of Pharmacology, Case School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106-4965, Departamento de Química Orgánica, Facultad de Química, Universidade de Vigo, 36310 Vigo, Spain, and Division of Endocrinology, Diabetes, and Metabolism, Department of Medicine and Department of Genetics, and The Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104