Optimization of amylomaltase for the synthesis of α-arbutin derivatives as tyrosinase inhibitors

alpha-Arbutin is widely used as a skin-whitening agent in the pharmaceutical and cosmetic industries because of its inhibitory effect on tyrosinase, an important enzyme for generating melanin pigments. Given the increasing demand for such products, we synthesized alpha-and beta-arbutin-alpha-D-glycosides through transglycosylation reactions catalyzed by a recombinant amylomaltase, using tapioca starch and alpha-and beta-arbutin as donor and acceptor molecules, respectively. The catalytic yield of products by the amylomaltase was greater with alpha-arbutin than with beta-arbutin. The highest glycoside yield (83%) was achieved by adjusting the following six parameters: starch and alpha-arbutin concentration, enzyme concentration, pH, temperature, and incubation time. The glycoside products were isolated and analyzed by HPLC, and two major products were identified by mass spectrometry and nuclear magnetic resonance spectroscopy, namely, alpha-arbutin-alpha-D-glucopyranoside (alpha-Ab-alpha-G(1)) and alpha-arbutin-alpha-D-maltopyranoside (alpha-Ab-alpha-G(2)). Both alpha-Ab-alpha-G(1) and alpha-Ab-alpha-G(2) are more water soluble than alpha-arbutin. Like alpha-arbutin, alpha-Ab-alpha-G(1) and alpha-Ab-alpha-G(2) showed competitive inhibition of human tyrosinase. However, their K-i values were 0.53 and 1.40 mM, respectively, which are slightly higher than that of alpha-arbutin (0.25 mM). The addition of glucosyl residues to alpha-arbutin improved its water solubility. Therefore, alpha-Ab-alpha-G(1) and alpha-Ab-alpha-G(2) could be easily absorbed by the skin and used as skin-whitening agents in pharmaceutical and cosmetic industries.