1. Department of Pharmacology and Toxicology, Virginia Commonwealth University, Richmond, Virginia 23298-0613, Laboratory of Medicinal Chemistry, Building 8, Room B1-22, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0815, and Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan 48109