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

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 degrees C for 20 h in SC-CO2. The yield of arbutin palmitate increased with increasing temperature over the range of 40-60 degrees 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.

Automated summary

A novel one-step enzymatic acylation method was developed for the synthesis of hydrophobic arbutin ester using supercritical carbon dioxide as the reaction solvent, achieving a high transesterification yield with immobilized Novozym 435 catalyst. The yield of arbutin palmitate increased with temperature, but decreased at a certain molar ratio, indicating inhibitory effects of high acyl donor concentrations on the enzyme. Novozym 435 maintained 38% of its original enzyme activity after 3 cycles of use under optimized conditions.