Synthesis of lipophilic arbutin ester by enzymatic transesterification in high pressure carbon dioxide

Scheme 1. Novozym 435 catalyzed transesterification of arbutin with palmitic acid ethyl ester in SC−CO2. [Display omitted] •This is the first report of enzymatic synthesis of arbutin palmitate in SC−CO2.•Enzymatic transesterification is less energy-intensive and more robust.•Various reaction parameters were studied and optimised to get maximum yield.•The strategy overcomes difficult transesterification of polar arbutin in SC−CO2.•Stability and activity of enzymes depend on the SC−CO2 operational conditions. In this study, a novel one-step enzymatic acylation was developed for the synthesis of hydrophobic arbutin ester, by using supercritical carbon dioxide (SC−CO2) as the reaction solvent. Immobilized Novozym 435 from Candida antarctica was identified as the best biocatalyst for producing arbutin palmitate through transesterification between arbutin and palmitic acid ethyl ester in SC−CO2. A transesterification yield of 85.21 % was obtained in batch operation using palmitic acid ethyl ester as the acyl donor, hexane/propylene glycol as the co-solvent and Novozym 435 as the enzyme at 10 MPa and 60 °C for 20 h in SC−CO2. The yield of arbutin palmitate increased with increasing temperature over the range of 40–60 °C in the current study. Operating at an arbutin/palmitic acid ethyl ester molar ratio of 5.0, the conversion of arbutin decreased, probably due to an inhibitory effect of the high concentration of palmitic acid ethyl ester on the enzyme. The 38 % original enzyme activity of Novozym 435 was maintained after being used for 3 cycles (60 h) under optimized conditions.