1. School of Pharmaceutical Sciences and Chongqing Key Laboratory of Natural Drug Research, Chongqing University, Chongqing 401331, P. R. China
2. Chongqing Key Laboratory of Development and Utilization of Genuine Medicinal Materials in Three Gorges Reservoir Area, Chongqing Three Gorges Medical College, Chongqing 404120, P. R. China
3. Department of Chemistry, Zhejiang Sci-Tech University, Hangzhou 310018, P. R. China