Antioxidant activity and cytotoxicity study of Leucaena leucocephala (Lam.) de wit leaf extract constituents

Abstract

Antioxidant activity of the solvent fractions obtained from a 20% aqueous methanol dried leaf extract of Leucaena leucocephala was evaluated using a 1, 1-diphenyl-2-picrylhydrazyl (DPPH) TLC assay. The more polar fractions ethyl acetate and butanol fractions demonstrated strong activity. A DPPH activity-guided fractionation procedure was used to isolate the antioxidant constituents of these active fractions. Separate fractionation of the fractions led to the isolation of epicatechin-3-O-gallate (1) along with two quercetin glycosides: quercetin-3-O-arabinofuranoside (2) and quercetin-3-O-rhamnoside (3) together with apigenin (4). The structures of the isolated compounds were elucidated using spectroscopic techniques NMR (1D and 2D) and mass spectrometry. Compounds 1 and 4 are reported for the first time from this species. In the qualitative antioxidant TLC assay, isolated compounds instantly bleached the DPPH (0.2% in MeOH) purple colour indicating strong antioxidant activity. The antioxidant quercetin glycosides were not cytotoxic at the highest concentration tested (200 ìg/ml), and apigenin was not isolated in sufficient quantity to test for cytotoxicity. Epicatechin-3-O-gallate showed slight cytotoxicity against Vero cells (LC₅₀ = 92 μg/ml).

Keywords: Leucaena leucocephala, Fabaceae, antioxidant, DPPH, cytotoxicity.