1. School of Chinese Pharmacy; Beijing University of Chinese Medicine; Beijing 100102 China
2. The State Key Laboratory of Elemento-organic Chemistry; Nankai University; Tianjin 300071 China
3. Department of Geological Sciences; University of Saskatchewan; 114 Science Place Saskatoon SK S7N 5E2 Canada
4. The Key Laboratory for Chemical Biology of Fujian Province, Department of Chemistry; Xiamen University; Xiamen 361005 China