1. Laboratory of Medicinal Chemistry, Building 8, Room B1-23, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0815, Clinical Psychopharmacology Section, National Institute on Drug Abuse, Addiction Research Center, Baltimore, Maryland 21224, and Laboratory for the Structure of Matter, Naval Research Laboratory, Washington, D.C. 20375