1. Department of Chemistry, National University of Singapore, 3, Science Drive 3, Singapore 117543 (Singapore), 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