1. Department of Medicinal Chemistry, 308 Harvard Street SE, 8-101 Weaver-Densford Hall, University of Minnesota, Minneapolis, Minnesota 55455-0353, and Laboratory of Integrative and Medical Biophysics, National Institute of Child Health and Human Development, National Institutes of Health, 9 Memorial Drive, Building 9, Room 1E129, Bethesda, Maryland 20892-0924