DPPH Radical Scavengers from Dried Leaves of Oregano (Origanum vulgare)

Abstract

  1,1-Dipehnyl-2-picrylhydrazyl (DPPH) radical scavenging activities were found in the extract of dried leaves of oregano (Origanum vulgare). The water-soluble active ingredients were isolated, and their structures were determined to be 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybenzyl protocatechuate and 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybenzyl 4-O-methylprotocatechuate by ¹H-, ¹³C-NMR, DEPT, HMQC, and HMBC spectral analyses, and by NOE experiments. The DPPH radical scavenging activities of these compounds were compared with those of rutin, quercetin and rosmarinic acid at a concentration of 2×10^-5 M. The scavenging activity of 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybenzyl protocatechuate was almost the same as that of quercetin and rosmarinic acid, but that of 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybennzyl 4-O-methylprotocatechuate was less than that of quercetin, rosmarinic acid and 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybenzyl protocatechuate. The amount of 4′-O-β-D-glucopyranosyl-3′,4′-dihydroxybenzyl protocatechuate was estimated to be 3.8 mg/1 g of dried leaves by an HPLC analysis.