1. College of Chemistry, Nankai University, Tianjin 300071, P. R. China
2. Department of Chemical Sciences, Bernal Institute University of Limerick, Limerick V94T9PX, Republic of Ireland
3. Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, Tampa, Florida 33620, United States
4. State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin 300071, P. R. China
5. College of Pharmacy, Nankai University, Tianjin 300071, P. R. China