Inhibitors of Tyrosinase and Melanogenesis from Galla rhois

Previously, a 50% aqueous methanol extract of Galla rhois was shown to be the most potent tyrosinase inhibitory activity with an IC_(50)(the concentration causing 50% inhibition of tyrosinase activity) of 0.2mg/ml of 205 crude drug extracts. To isolate tyrosinase inhibitors, the methanol extract was evaporated to a small volume in vacuo, and then partitioned stepwise with benzene and ethyl acetate(EtOAc). The EtOAc fraction was solubilized in 10% MeOH solution, and then fractionated successively by Diaion HP-20 and Sephadex LH-20 column chromatography, and preparative HPLC. Three phenolic compounds were isolated, and characterized as gallic acid(GA), methyl gallate(MG) and l,2,3,4,6-penta-O-galloyl-β-D-glucose(PGG) by UV, IR, ¹H-&¹³C-NMR, and FAB- MS spectroscopy. PGG(IC_(50)=50㎍/ml) showed a considerable inhibitory effect against mushroom tyrosinase, while GA(IC(50)=1.6mg/ml) and MG(IC_(50)=234l㎍/ml) did not show an appreciable effect. Meanwhile, MG inhibited greatly melanogenesis in a murine melanocyte cell line, Mel-Ab. MG and PGG showed typical noncompetitive inhibition patterns against mushroom tyrosinase. These results suggest that PGG and MG may be potentially useful as either anti-browning or anti-melanogenic agents in foods and cosmetics.