1. Laboratory of Drug Discovery Research and Development, Developmental Therapeutics Program, Division of Cancer Treatment and Diagnosis, National Cancer Institute−Frederick Cancer Research and Development Center, Building 1052, Room 121, Maryland 21702-1201, SAIC−Frederick, Frederick Cancer Research and Development Center, Frederick, Maryland 21702-1201, and Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892-0805