1. Chemistry and Life Sciences, Research Triangle Institute, Research Triangle Park, North Carolina 27709, Clinical Psychopharmacology Section, NIDA Addiction Research Section, P.O. Box 5180, Building C, 4980 Eastern Avenue, Baltimore, Maryland 21224, Laboratory for the Structure of Matter, Naval Research Laboratory, Building 35, Room 455, Overlook Avenue, Washington, D.C., 20375, and Lilly Research Laboratories, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, Indiana 46285