1. School of Pharmacy; Guangdong Medical University; Dongguan 523808 P. R. China
2. Guangdong Key Laboratory for Research and Development of Natural Drugs; Guangdong Medical University; Zhanjiang 524023 P. R. China
3. Key Laboratory of Synthetic; and Natural Functional Molecule Chemistry of the Ministry of Education; Shaanxi Key Laboratory of Physico-Inorganic Chemistry; College of Chemistry & Materials Science; Northwest University; Xi'an 710069 P. R. China
4. School of Chemistry; University of Melbourne; Melbourne VIC 3010 Australia
5. School of Chemistry; Monash University; Melbourne VIC 3800 Australia