1. School of Pharmaceutical Sciences, Hangzhou Medical College, Hangzhou, Zhejiang 311399, China
2. Department of Pharmacy, School of Medicine, Zhejiang University City College, No. 48, Huzhou Road, Hangzhou 310015, P. R. China
3. Roy and Diana Vagelos Laboratories, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA