1. R&D Institute of Health Science, Kayaku Co. Ltd., 560 Kashio-cho, Totsuka-ku, Yokohama 244-0812, Japan, School of Pharmaceutical Sciences, University of Shizuoka, 52-1, Yada, Shizuoka 422-8526, Japan, and Divison of Phytochemistry, Chengdu Institute of Biology, Academia Sinica, 4-9, Ren Ming Nan Lu, Chengdu, Sichuan, People's Republic of China