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

Abstract

α-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 α- and β-arbutin-α-D-glycosides through transglycosylation reactions catalyzed by a recombinant amylomaltase, using tapioca starch and α- and β-arbutin as donor and acceptor molecules, respectively. The catalytic yield of products by the amylomaltase was greater with α-arbutin than with β-arbutin. The highest glycoside yield (83%) was achieved by adjusting the following six parameters: starch and α-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, α-arbutin-α-d-glucopyranoside (α-Ab-α-G1) and α-arbutin-α-d-maltopyranoside (α-Ab-α-G2). Both α-Ab-α-G1 and α-Ab-α-G2 are more water soluble than α-arbutin. Like α-arbutin, α-Ab-α-G1 and α-Ab-α-G2 showed competitive inhibition of human tyrosinase. However, their Ki values were 0.53 and 1.40 mM, respectively, which are slightly higher than that of α-arbutin (0.25 mM). The addition of glucosyl residues to α-arbutin improved its water solubility. Therefore, α-Ab-α-G1 and α-Ab-α-G2 could be easily absorbed by the skin and used as skin-whitening agents in pharmaceutical and cosmetic industries.