1. Guangdong Key Laboratory for Research and Development of Natural Drugs, and School of Pharmacy, Guangdong Medical University, Dongguan 523808, P. R. China
2. State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, China.
3. Department of Chemistry, University of Delhi, Delhi 110 007, India
4. Department of Chemistry, Faculty of Science, University of Lucknow, Lucknow 226 007, India