Reagents and solvents were purchased from Beijing Chemical Reagents Company and were used without further purification. Column chromatography was performed on silica gel 200-300 mesh obtained from Qingdao Haiyang Chemical Co., Ltd. Analytical thin-layer chromatography was performed on silica gel plates, and the plots were visualized under UV light at 254 nm or iodine vapor. Elemental analyses (C, H, N, P, S) were performed at the ...
