1. State Key Laboratory of Natural and Biomimetic Drugs, Department of Natural Medicines, School of Pharmaceutical Sciences Peking University, 38 Xueyuan Road, Haidian District Beijing 100191 China
2. State Key Laboratory of Bioorganic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences 345 Lingling Road Shanghai 200032 China