Antioxidant activity of column fractions and caryatin isolated from the ethyl acetate extract of dioscorea hirtiflora tuber

Abstract

The tubers of Dioscorea hirtifloraBenth. are widely used as food during famine and as medicine in South-western Nigeria. The aim of this study was to identify bioactive compound(s) from the tuber of Dioscorea hirtiflora. Bioactive constituents from the ethyl acetate extract and fractions of the tubers were identified using gas chromatography-mass spectrometry (GC-MS), and by reverse phase-high performance liquid chromatography (RP-HPLC). The extract was subjected to column chromatography (CC) and preparative thin layer chromatography (PTLC) for the isolation of constituent(s). Fractions from the column chromatography of the extract as well as an isolated compound from the sub-fraction of the extract were evaluated for their antioxidant activity using 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. The GC-MS of the derivatized ethyl acetate extract showed the presence of phenolics (benzoic acid, 4-hydroxybenzoic acid and 3,4-dihydroxybenzoic acid) while the RP-HPLC confirmed the presence of gallic acid, protocatechuic acid, catechin, isovanillic acid and quercetin in the fractions. CC and PTLC of the extract led to the isolation of compound I-24characterised as 3,5-dimethoxy-7, 3´, 4´-trihydroxy flavone (caryatin) by a combination of nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS), and by comparison of spectra data with literature. Fraction I and sub-fraction I-2 had the highest antioxidant activity with IC50 values of 2.11 ± 0.09 and 4.67 ± 0.06 µg/mL, respectively,while the isolated compound had IC50 value of 49.4 ± 2.18 µg/mL.The effect of these compounds as antioxidant could give credence to their traditional use as food and medicine.