1. Laboratory of Bioorganic Chemistry, Institute of Biomedical Sciences, Academia Sinica, Taipei 115, Taiwan, Molecular Pharmacology and Chemistry Program, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, and Department of Pharmacology, University of Medicine and Dentistry of New Jersey − Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, New Jersey 08854