Synthesis, in vitro antimicrobial and cytotoxic activities of new carbazole derivatives of ursolic acid.

A series of new carbazole derivatives of ursolic acid were designed and synthesized in an attempt to develop potent antimicrobial or antitumor agents. Their structures were confirmed by using IR, HRMS and 1H NMR analysis. All the synthesized compounds were evaluated for their antimicrobial activity against four bacterial and three fungal strains using serial dilution method. Compounds 3a, 3b, 4a, 4b and 5a–f exhibited significant antibacterial activity against at least one tested bacteria with MIC values of 3.9–15.6μg/ml. In addition, the in vitro cytotoxicity of these compounds were also assayed against two human tumor cell lines (SMMC-7721 and HepG2) using MTT colorimetric method. From the results, compounds 5a–e and 5h displayed pronounced cytotoxic activity with IC50 values below 10μM. Specially, compound 5e was found to be the most potent compound with IC50 values of 1.08±0.22 and 1.26±0.17μM against SMMC-7721 and HepG2 cells, respectively, comparable to those of doxorubicin. In addition, compound 5e showed reduced cytotoxicity against noncancerous LO2 cells with IC50 value of 5.75±0.48μM.