1. Division of Medicinal and Natural Products Chemistry, The University of Iowa, Iowa City, Iowa 52242, Departments of Pharmacology and Psychiatry, The Ohio State University College of Medicine, Columbus, Ohio 43210, Department of Medicinal Chemistry, The University of Kansas, Lawrence, Kansas 66045, and Clinical Psychopharmacology Section, IRP, NIDA, NIH, DHHS, Baltimore, Maryland 21224