1. Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung 807, Taiwan, Republic of China, Pharmacological Institute, College of Medicine, National Taiwan University, Taipei 100, Taiwan, Republic of China, Faculty of Pharmaceutical Sciences, Chiba University, 1-33, Yayoi, Inage Chiba 263-8522, Japan, and Department of Pharmacy, Tajen Institute of Technology, Pingtung, Taiwan, Republic of China