1. Department of Natural Medicinal Chemistry, China Pharmaceutical University, Nanjing 210009, People's Republic of China, R & D Center, Zhongxin Pharmaceuticals, Tianjin 300458, People's Republic of China, Department of Chemistry, The Hong Kong University of Science and Technology, Hong Kong, People's Republic of China, and Department of Biochemistry and Biotechnology Research Institute, The Hong Kong University of Science and Technology, Hong Kong, People's Republic of China