1. Contribution from the Department of Medicinal Chemistry, The University of Kansas, 1251 Wescoe Hall Drive, Malott Hall 4070, Lawrence, Kansas 66045-7563, Urologic Oncology Branch, National Cancer Institute, National Institutes of Health, Rockville, Maryland 20850, and Department of Biological Chemistry, John Innes Centre, Colney, Norwich NR4 7UH, United Kingdom