Phenolic metabolites from Acacia nilotica flowers and evaluation of its free radical scavenging activity

Reactive oxygen species (ROS) have been recognized as playing an important role in the initiation and/or progression of various diseases such as atherosclerosis, inflammatory injury, cancer and cardiovascular disease. Many antioxidant compounds, naturally occurring from plant sources, have been identified as a free radical or active oxygen scavengers. Additionally, it has been determined that the antioxidant effect of plant products is mainly due to phenolic compounds, such as simple phenolic acids, flavonoids, isoflavonoids, hydrolyzable tannins and condensed tannins. The present study deals with the isolation and identification of the phenolic metabolites from Acacia nilotica (L.) Delile (Leguminosae) flowers and evaluation of its free radical scavenging activity. The aqueous alcoholic extract (MeOH: H₂O, 8: 2) of Acacia nilotica flowers was subjected to extensive repeated column chromatography on polyamide, cellulose and Sephadex LH-20 resulted in catechin, catechin 7-O- gallate, gallic acid, naringenin 7-O-β- glucopyranoside, quercetin 3-O- β- glucoside (2→1) glucopyranoside, quercetin 3-O- β-glucopyranoside, chalconaringenin 4'-O-β-glucopyranoside, naringenin and quercetin. The structure of the isolated compounds was elucidated on the basis of spectral analysis (UV, HRESI, 1/2D NMR). The radical scavenging activity of the extract was quantified spectrophotometrically, using DPPH radical. The total polyphenols showed excellent antioxidant potency when tested by radical scavenging methods.

Keywords: Acacia nilotica, Phenolic compounds, antioxidant activity, DPPH