1. School of Chinese Materia Medica, Beijing University of Chinese Medicine, Beijing 102488, China
2. Department of Chemistry, Renmin University of China, Beijing 100872, China
3. Roy and Diana Vagelos Laboratories, Penn/Merck Laboratory for High-Throughput Experimentation, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA