Isolation of a bioactive flavonoid from Spilanthes calva D.C. in vitro xanthine oxidase assay and in silico study

An isoprenylated flavonoid was isolated from the aerial parts of the Spilanthes calva D.C. The structure of the isolated compound was ascertained by UV, IR, ¹H NMR, ¹³C NMR and mass analyses. The structure was elucidated as 6-(3-methylbut-1-enyl)-5,7-dimethoxy-4′-hydroxy flavone. The isolated compound was further evaluated by in vitro xanthine oxidase enzyme activity. Molecular docking study was carried out to establish the binding mode of isolated compound in the inhibitor-binding cavity of enzyme. The isoprenylated flavonoid was found to be possess potent xanthine oxidase inhibition activity with an IC₅₀ of 16.56 μM. Molecular docking study revealed that the potent action of the compound was due to the hydrogen bonding to ALA 1079 and π–π stacking interaction with PHE 914 in the inhibitor-binding cavity of xanthine oxidase.