1. Department of Chemistry, Yunnan Normal University, Kunming 650092, People's Republic of China, Department of Traditional Chinese Herbs, Yunnan Institute of Traditional Chinese Medicine, Kunming 650011, People's Republic of China, Shanghai Institute of Materia Medica, Shanghai Institutes of Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, People's Republic of China, and Department of Chemistry and Biochemistry, South Dakota State University, Brookings, South Dakota 57007