Functional glucosylation of kojic acid and daidzein with the Eucalyptus membrane-associated UDP-glucosyltransferase reaction system

Regioselective Enzymatic Synthesis of Kojic Acid Monoesters

Kojic acid is a fungal metabolite and one of the strongest tyrosinase inhibitors. Its esters are used as lipid-compatible skin whitening components in cosmetic formulations. In this study, lipase PS, lipase AK, Lipolyve AN and pig pancreatic lipase catalyzed the acetylation of kojic acid under selective formation of the same product, kojic 7-acetate. However, the enzymes differed in their regioselectivity when catalyzing the alcoholysis of kojic acid diacetate. While lipase PS and lipase AK produced mixtures of both monoacetate regioisomers (7-acetate and 5-acetate of kojic acid), the pancreatic lipase almost exclusively produced 5-acetate. The enzyme displayed the same regioselectivity in the palmitoylation of kojic acid and in the alcoholysis of kojic acid dipalmitate. Simple reaction engineering with PPL as a catalyst thus provides the complementary monoesters of kojic acid. Kojic 7-acetate, 5-acetate, 7-palmitate and 5-palmitate were prepared with yields after purification of 57.3%, 38.2%, 31.7% and 31.4%, respectively.

Enzymatic synthesis of kojic acid esters and their potential industrial applications

In this paper, enzymatic methods for the synthesis of 5-hydroxy-2-(hydroxymethyl)-4H-pyran-4-one (kojic acid) esters are reviewed. Important process parameters related to the synthesis of kojic acid esters such as the type of immobilized lipase, solvent, temperature, initial water activity, water content, pH, metal salts, enzyme loading, substrates mole ratio, and acyl donors are highlighted and discussed. The properties of kojic acid esters related to their solubility, stability, cytotoxicity, depigmenting activity, tyrosinase inhibitory, metal-chelating, anti-oxidant, and other biological activities are also highlighted. At present, kojic acid and its esters are widely used in cosmetic and skin health industries as skin whitening agents. The advantages and disadvantages of various kojic acid esters are compared and possible industrial applications of these derivatives are also discussed.

Aromatic O-glycosylation

Carbohydrates carrying an aromatic aglycon are important natural products and thus key synthetic targets. However, due to the electron-withdrawing properties of aromatic rings, phenols are difficult to glycosylate. This review covers the most common carbohydrate donors used for aromatic O-glycosylation (anomeric acetates, halides, trichloroacetimidates and thioglycosides) as well as some less common donors. The scope of the review is to give practical examples of aromatic O-glycosylations and to offer guidelines for glycosylation of typical aromatic residues. Anomeric acetates or trichloroacetimidates, activated under acidic conditions, are preferred for electron rich aromatic aglycons, while glycosyl halides, activated using basic conditions, are preferred for electron deficient aromatic residues.