1. Molecular Targets Development Program, Center for Cancer Research, National Cancer Institute, Building 1052, Room 121, Frederick, Maryland 21702-1201, Intramural Research Support Program, SAIC-Frederick, Frederick, Maryland 21702-1201, Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Disease, Bethesda, Maryland 20892-0805, and USA Cancer Research Institute, College of Medicine, University of South Alabama, 307 University Boulevard, MSB 2310, Mobile, Alabama 36688