1. Graduate Institute of Natural Products, School of Pharmcy, Kaohsiung Medical University, Kaohsiung 807, Taiwan, Republic of China, Department of Chemistry, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, Republic of China, National Museum of Natural Science, Taichung, 404, Taiwan, Republic of China, and National Sun Yat-Sen University-Kaohsiung Medical University Joint Research Center, Kaohsiung 804, Taiwan, Republic of China