Isolation and Characterisation of the Antioxidant Phenolic Metabolites of Boerhaavia erecta L. Leaves

Boerhaavia erecta L. (Nyctaginaceae) is a medicinal weed, indigenous to tropical America, but presently pantropical and appear to constitute a functional leafy vegetable of certain communities. The taxon is reported to possess antiparasitic, antifungal, antibacterial, antiviral, antihistaminic, antioxidant and hepatoprotective properties. The residue of the ethanolic leaf-extract was fractionated into diethyl ether, acetone and methanol solubles. All the three fractions of the leaf extract scavenged reactive oxygen and nitrogen species effectively. The most polar methanol fraction was determined to possess Vitamin C equivalent antioxidant capacity (VCEAC) of 64.57±1.07%, which is about 78.4% of the dietary flavonol, rutin. The acetone and ether fractions were determined to possess respectively, 51.5 and 47.1% of the rutin VCEAC. The percent nitric oxide inhibitions of the fractions were respectively found to be 84.0, 56.4 and 51.9% of the rutin capacity for the methanol, acetone and ether fractions. The per cent Fe chelating capacities of the leaf-extract were found to be in the order methanol > acetone > ether (viz., 73.4, 63.1 and 59.4% of the chelating capacities of the standard trihydroxamic siderophoric drug, deferoxamine). Chemical analysis of the leafy matter has led to the isolation and characterisation of two potentially antioxidant flavan-3-ols, [(+)-catechin] (1) and [(-)-epicatechin] (2) and two dietary flavonols, quercetin (3) and isorhamnetin (4) together with their glycosides, rutin (5), narcissin (6) isoquercitrin (7) and isorhamnetin