1. Bioinformatics and Drug Design Group, Departments of Pharmacy and Computational Science, National University of Singapore, Blk S16, Level 8, 3 Science Drive 2, Singapore 117543, Department of Biochemistry, The Yong Loo Lin School of Medicine, National University of Singapore, Blk MD7, #02-03, 8 Medical Drive, Singapore 117597, and College of Chemistry, Sichuan University, Chengdu, 610064, People's Republic of China