1. Key Laboratory of Tropical Medicinal Plant Chemistry of Ministry of Education, Hainan Normal University, Haikou 571158, P. R. China
2. State Key Laboratory of Natural Medicines, China Pharmaceutical University, Nanjing 210009, P. R. China
3. Key Laboratory of Southern Medicinal Plants Resources of Haikou City, Hainan Normal University, Haikou 571158, P. R. China