**6. Acknowlegments**

This project was supported by the National Basic Research Program of China (973 Program) (No.2010CB735601) and National Key Technology Support Program during the 12th Five-Year Plan Period (No. 2011BAE06B03-03). We would like to thank Professor Huazheng Yang (Nankai University ) for the guidance and help in the Pharmacophore and CoMFA analysis.
