Affiliation: | 1. Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Fax: (+65)?6779‐1691;2. Provincial Key Laboratory of Natural Medicine and Immuno‐Engineering, Henan University, Jinming Campus, Kaifeng, Henan, 475004 (P.R. China), Fax: (+86)0378‐2864665 |