1. Contribution from the Faculty of Pharmaceutical Sciences, University of Tokushima, Shomachi 1-78, Tokushima 770, Japan, Institute of Materia Medica, Academia Sinica, Yue-yang Road 319, Shanghai 200031, China, and Biological Science and Technology, Faculty of Engineering, University of Tokushima, Minami-josanjima-cho 2-1, Tokushima 770, Japan