Tyrosinase inhibitors of Galla Rhois and its derivative components

Two hundred forty-three oriental herbs were screened for their tyrosinase inhibitory activity. Among them, methanol extract of Galla Rhois was shown to be the most potent tyrosinase inhibitory activity. The IC50 values for Galla Rhois, kojic acid, ascorbic acid, arbutin and 5 HMF were 0.163, 0.019, 0.316, 1.520 and 2.511 mg/mL, respectively. Anti-tyrosinase activity of Galla Rhois is higher about two, nine and 15-fold of anti-tyrosinase activity of ascorbic acid, arbutin and 5-HMF while lesser than kojic acid. To isolate active compounds, the 50% aqueous methanol extracts was evaporated to vacuo, and the fractionated by the Diaion HP-20, Sepadex LH-20 column chromatography and repeated the preparative HPLC procedure. Three major phenolic compounds were isolated, and characterized, one of them exhibiting tyrosinase inhibitory activity stronger than L-ascorbic acid (IC50 = 90 μg/mL) was identified as Methyl gallate ((IC50 = 40 μg/mL) by UV, IR, C-NMR, and FAB-MS spectroscopy. The compound isolated from Galla Rhois exhibited non-competitive inhibition against oxidation of l-3-4-dihydroxyphenylalanine (l-DOPA) by mushroom tyrosinase. As a naturally occurring tyrosinase inhibitor, methyl gal-late may be useful as a new agent to inhibit the oxidation of l-DOPA by mushroom tyrosinase. This is the first HPLC analysis containing ascorbic acid, 5-HMF and arbutin, Galla Rhois exert varying degrees of inhibition on tyrosinase-dependent and these result suggesting that Galla Rhois may serve as candidates for depigmenting agents. Further studies on the application of Methyl gallate is needed in cosmetics and as anti-melanogenic agents.