1. Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 Department of Pharmaceutical Chemistry, University of California at San Francisco, San Francisco, California 94158 Merck-Frosst Canada Ltd., 16711 TransCanada Highway, Kirkland, Quebec, Canada H9H 3L1, and Department of Chemical Engineering, University of Virginia, P.O. Box 400741, Charlottesville, Virginia 22904-4741