1. School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug ResearchChongqing University Chongqing 401331 P.R. China
2. Department of ChemistryZhejiang Sci-Tech University Hangzhou 310018 P.R. China
3. Department of ChemistryNational University of Singapore Singapore 117543 Singapore
4. National University of Singapore (Suzhou) Research Institute Suzhou 215123 P.R. China