1. Center for Drug Discovery and Design, State Key Laboratory of New Drug Research, Shanghai Institute of Materia Medica, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 294 Taiyuan Road, Shanghai 200031, P. R. China, School of Chemical & Life Sciences, Singapore Polytechnic, 500 Dover Road, Singapore 139651, Singapore, and Technology Centre for Life Sciences, Singapore Polytechnic, 500 Dover Road, Singapore 139651, Singapore