1. Center for Drug Design, Department of Chemistry and Biochemistry, University of North Carolina at Greensboro, Greensboro, North Carolina 27402, Computational Center for Molecular Structure and Design, Department of Chemistry, University of Georgia, Athens, Georgia 30602, and Laboratory for Molecular Modeling, Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599