Kushenol A and 8-prenylkaempferol, tyrosinase inhibitors, derived from Sophora flavescens

Tyrosinase is known for an Enzyme that plays a key role in producing the initial precursor of melanin biosynthesis. Inhibition of the catalytic reaction of this Enzyme led to some advantage such as skin-whitening and anti-insect agents. To find a natural compound with inhibitory activity towards Tyrosinase, the five Flavonoids of kushenol A (1), 8-prenylkaempferol (2), kushenol C (3), formononetin (4) and 8-prenylnaringenin (5) were isolated by column chromatography from a 95% methanol extract of Sophora flavescens. The ability of these Flavonoids to block the conversion of L-tyrosine to L-DOPA by Tyrosinase was tested in vitro. Compounds 1 and 2 exhibited potent inhibitory activity, with IC50 values less than 10 µM. Furthermore, Enzyme kinetics and molecular docking analysis revealed the formation of a binary encounter complex between compounds 1-4 and the Enzyme. Also, all of the isolated compounds (1-5) were confirmed to possess antioxidant activity.