1. College of Horticulture and Landscape Architecture, Tianjin Agricultural University, Tianjin 300384, P. R. China
2. College of Chinese Materia Medica, Tianjin University of Traditional Chinese Medicine, Tianjin 300193, P. R. China
3. State Key Laboratory of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, P. R. China
4. Frontiers Science Center for New Organic Matter, College of Chemistry, Nankai University, Tianjin 300071, P. R. China