Dioscin: A synergistic tyrosinase inhibitor from the roots of Smilax china

In our study, we investigated the inhibition of mushroom tyrosinase in Smilax china. A methanol (MeOH) extract of S. china was partitioned into hexane, ethyl acetate (EtOAc) and water. Of the three fractions, EtOAc extract showed the strongest inhibition of tyrosinase activity with l-tyrosine or l-DOPA as a substrate. Two compounds were isolated from a final active fraction by activity-guided column chromatography. These compounds were identified as dioscin and oxyresveratrol by comparing their mass, ¹H- and ¹³C-NMR spectral data with those reported in the literature. Dioscin showed little inhibition activity of tyrosinase, whereas oxyresveratrol, a known tyrosinase inhibitor, showed a strong tyrosinase inhibitory activity. We discovered that a mixture of oxyresveratrol and dioscin (IC₅₀ = 5.1 and 5.7 μg/ml) highly increased the inhibition of tyrosinase activity with l-tyrosine or l-DOPA as the substrate as compared to either oxyresveratrol (IC₅₀ = 7.8 and 10.9 μg/ml) or dioscin (IC₅₀ > 100 and 100 μg/ml) alone.