Xanthine oxidase inhibitory activity of flavonoids and tannins from Hexachlamys edulis (Myrtaceae)

Abstract

The acetone-water extract of Hexachlamys edulis (Myrtaceae) inhibited the enzyme xanthine oxidase (XO) in vitro. Bioassay-guided isolation led to the gallic acid ester in 2 of myricitrin (desmanthin-1), (-)-epigallocatechin-3-O-gallate (EGG) and pentagalloylglucose as the main XO inhibitors of H. edulis. Desmanthin-1 and EGG were mixed-type inhibitors of XO with Ki values of 1.6×10-4 M and 1.8×10-4 M, respectively. Pentagalloylglucose was an uncompetitive XO inhibitor with a KESI of 6.7×10-6M. From the active n-butanol soluble part of the aqueous acetone extract of H. edulis, several flavonoids were isolated. The flavonoids were mainly myricetin-3-O-monoglycosides with the quercetin glycoside avicularin as a minor compound displaying a weak inhibitory activity towards XO.