Methanolic extract from leaves of Karwinskia humboldtiana (Schult.) Zucc. was subjected to fractionation with a pair of immiscible solvents and subsequently tested for antioxidant activity. Using DPPH the order of scavenging activities of the extracts in comparison with standards of L-ascorbic acid and quercetin was as follows: ethyl acetate fraction > L-ascorbic acid > quercetin > butan-1-ol > light petrol > chloroform > water. The capability of scavenging OH radicals determined by EPR was as follows: ethyl acetate, chloroform > light petrol > butan-1-ol > water fractions. On the basis of availability and antioxidant activity of these fractions, isolation of constituents from butanol fractions was achieved. Separation of this fraction led to the isolation of (+)-epicatechin and flavonol derivatives – quercetin, quercetin 3-O-glucoside (isoquercitrin), quercetin-3-O-galactoside (hyperosid), quercetin-3-O-arabinoside, quercetin 3-O-rutinoside (rutin), kaempferol 3-O-arabinoside and kaempferol 3-O-rutinoside. All of them might be responsible for the observed antioxidant effects.
