Antioxidant and antiproliferative properties of methylated metabolites of anthocyanins

•Phase II methylation of anthocyanins originates new 4′-methyl metabolites.•The catechol and pyrogallol group are metabolised in a different way.•The synthesised metabolites retain antiradicalar and reduction power.•All compounds inhibited the proliferation of all cell lines tested.•Dp3glc was the anthocyanin with the better inhibitory activity. Anthocyanins are major flavonoids in many plant foods and have been related to health promotion. In the human organism anthocyanins are metabolised to different metabolites. One of the most important phase II reactions of flavonoids is the methylation of the catechol group. This feature is expected to have an effect on the antioxidant and antiproliferative properties of flavonoids including anthocyanins. In this work, delphinidin-3-glucoside, cyanidin-3-glucoside and petunidin-3-glucoside methylated metabolites were obtained by enzymatic hemi-synthesis. The compounds were identified as monomethylated products by HPLC–MS and NMR. The methylated metabolites were found to still retain significant radical scavenging activity and reducing activity, suggesting that they could act as potential antioxidants in vivo. The antiproliferative activity of the metabolites in comparison with the parental anthocyanins was also evaluated in three cancer cell lines by sulforhodamine B assay. The conjugation with methyl groups decreased or did not alter the antiproliferative effect of the original anthocyanin.