1. Research Centre for Natural Medicinal Chemistry, College of Science, Northwest A & F University, Yangling, Shaanxi 712100, China.
2. Department of Chemistry, Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S 5B6, Canada.
3. Chemical Biology Group, Biotechnology Research Institute, 6100 Royalmount Av., Montreal, QC H4J 1P2, Canada.
4. Department of Organic and Bioorganic chemistry, Lund University, Box 124, SE-221 00 Lund, Sweden.