1. Department of Natural Product Chemistry, School of Pharmaceutical Sciences, Hebei Medical University, 361 Zhongshan East Road, Shijiazhuang 050017 , P. R. China, (phone: +86‐311‐86265634)
2. Hebei United University Affiliated Hospital, Tangshan, P. R. China
3. Department of Chemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada
4. Jealott's Hill International Research Centre, Syngenta, Berkshire RG42 6EY, UK