1. Faculty of Pharmaceutical Sciences and Chemical Analysis Center, Chiba University, 1-33 Yayoi, Inage, Chiba 263-8522, Japan, R & D Division, Nippon Kayaku Co., Ltd., 3-31-12 Shimo, Kita, Tokyo 115-8588, Japan, and Department of Pharmacognosy, Faculty of Pharmaceutical Sciences, Chulalongkorn University, Bangkok 10330, Thailand