Cellular antioxidant activities of polyphenols isolated from Eucalyptus leaves (Eucalyptus grandis × Eucalyptus urophylla GL9)

An activity-guided isolation process was performed to identify the antioxidant constituents of Eucalyptus leaves (Eucalyptus grandis × Eucalyptus urophylla GL9). The ethyl acetate extract showed the highest activity in scavenging DPPH radical among five different fractions extracted from 70% aqueous ethanol extract of Eucalyptus leaves. Nine known compounds possessing radical scavenging activity, which included gallic acid (1), quercetin-3-O-β-d-glucuronide (Q-3-G-A) (2), ethyl gallate (3), tellimagrandin II(4), chlorogenic acid (5), 3-O-galloyl-4,6-O-[(S)-hexahydroxydiphenoyl]-d-glucose (gemin D) (6), pedunculagin (7), tellimagrandin I (8), and 1,2,3,4,6-penta-O-galloyl-β-d-glucose (PGG) (9) were isolated and identified from the ethyl acetate extract. Our results indicated that ethyl acetate extract and hydrolysable tannins among nine compounds exhibited great antioxidant activity in both chemical-based (e.g. DPPH and ABTS assays) and cellular-based (i.e., Hep G2) antioxidant assays, and PGG showed the highest cellular antioxidant activity. This study suggested that ethyl acetate extract and the hydrolysable tannins in Eucalyptus leaves would be promising natural antioxidants in pharmaceutical, feed and food supplement industries.