1. State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China, Graduate School of Pharmaceutical Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku 113-0033, Japan, and Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan