New bioactive flavonoid glycosides with antioxidant activity from the stem bark of Olax subscorpioidea Oliv

A previously unreported gallocatechin glycoside, (2 R,3S) 4′-O-methyl-gallocatechin-3-O-α-ʟ-rhamnopyranoside (1) and an unseparable mixture of two previously undescribed dihydromyricetin glycosides, (2 R,3R) 4′-O-methyl-dihydromyricetin-3-O-α-ʟ-rhamnopyranoside (2a) and (2 R,3S) 4′-O-methyl-dihydromyricetin-3-O-α-ʟ-rhamnopyranoside (2 b) along with three known compounds were isolated from the n-butanol soluble fraction of the stem bark of Olax subscorpioidea Oliv. Their structures were elucidated by detailed spectroscopic analyses, including ¹H NMR, ¹³C NMR, ¹H-¹H COSY, HSQC, HMBC, NOESY, HR-ESI-MS and chemical methods. The crude ethanol extract, the fractions, and some of the isolated compounds were screened for their antioxidant and antibacterial activities. They showed significant antioxidant activities with EC₅₀ ranging from 6.29 to 18.19 µg/mL in 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and EC₅₀ ranging from 85.77 to 86.39 mmol FeSO₄/g in ferric reducing antioxidant power (FRAP) methods compared with 2.29 µg/mL and 3.52 mmol FeSO₄/g for the positive control (ʟ-ascorbic acid). Nevertheless, no inhibition was observed against the tested bacterial strains at a MIC less than 256 μg/mL.