1. Laboratory of Molecular Modeling and Design, M/C 781, College of Pharmacy, University of Illinois at Chicago, 833 South Wood Street, Chicago, Illinois 60612-7231, Department of Pharmaceutical Chemistry, Pharmaceutical Institute, University of Kiel, Gutenbergstrasse 76, D-24118 Kiel, Germany, and Department of Pharmacology and Toxicology, Pharmaceutical Institute, University of Bonn, An der Immenburg 4, D-53121 Bonn, Germany