1. Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania,
Philadelphia, Pennsylvania 19104-6323, UMR 8601 CNRS, Université Paris V, 45 Rue des Saints-Pères,
75270 Paris Cedex 06, France, Department of Chemistry, University of Toledo, Toledo, Ohio 43606, and
Department of Biochemistry, Temple University School of Medicine, Philadelphia, Pennsylvania 19140