1. Division of Medicinal Chemistry & Pharmacology, College of Pharmacy, The Ohio State University, Columbus, Ohio 43210, Department of Pharmaceutical Sciences, College of Pharmacy, University of Tennessee, Memphis, Tennessee 38163, U.S. Army Edgewood Research Development and Engineering Center, Aberdeen P.G., Maryland 21010-5423, and Laboratory of the Structure of Matter, Naval Research Laboratory, Code 6030, Washington, D.C. 20375