Synthesis and Anti-tumor Activity of Derivatives of Ring A of Ursolic Acid

Ten derivatives were successfully synthesized by the introduction of nitrogenand oxygencontaining heterocyclic compounds at ring A and the modification of the amidation at C(28) position in the natural product ursolic acid, which structures were characterized by H NMR, C NMR, MS and elemental analysis. Their anti-tumor activities against KB and SGC7901 cells in vitro were evaluated by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay. These results indicated that all of derivatives can inhibit cell proliferation of KB and SGC7901 cells better than ursolic acid (UA), and UA4-1 (IC50=0. 289 μmol/L) and UA4-2 (IC50=0. 04 μmol/L) were also found to have especially more potent inhibitory activity on SGC7901 tumor cells than that of the positive control drug gefitinib (IC50=1. 03 μmol/L).