Syntheses of arbutin-alpha-glycosides and a comparison of their inhibitory effects with those of alpha-arbutin and arbutin on human tyrosinase

The effects of 4-hydroxyphenyl alpha-glucopyranoside (alpha-arbutin) and 4-hydroxyphenyl beta-glucopyranoside (arbutin) on the activity of tyrosinase from human malignant melanoma cells were examined. The inhibitory effect of alpha-arbutin on human tyrosinase was stronger than that of arbutin. The K(i) value for alpha-arbutin was calculated to be 1/20 that for arbutin. We then synthesized arbutin-alpha-glycosides by the transglycosylation reaction of cyclomaltodextrin glucanotransferase using arbutin and starch, respectively, as acceptor and donor molecules. The structural analyses using 13C- and 1H-NMR proved that the transglycosylated products were 4-hydroxyphenyl beta-maltoside (beta-Ab-alpha-G1) and 4-hydroxyphenyl beta-maltotrioside (beta-Ab-alpha-G2). These arbutin-alpha-glycosides exhibited competitive type inhibition on human tyrosinase, and their K(i) values were calculated to be 0.7 mM and 0.9 mM, respectively. These arbutin-alpha-glycosides possessed stronger inhibitory activity than arbutin, but less activity than alpha-arbutin. These results suggested that the alpha-glucosidic linkage of hydroquinone-glycosides plays an important role in the inhibitory effect on human tyrosinase.