1. Department of Chemistry, Developmental Therapeutics Program, Barbara Ann Karmanos Cancer Institute, Wayne State University School of Medicine, Detroit, Michigan 48201-1379; Department of Pediatrics, The University of Alabama at Birmingham, Birmingham, Alabama 35294; Department of Biologic and Materials Sciences, School of Dentistry, University of Michigan, Ann Arbor, Michigan 48019-1078; and Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06510-8066