Biocatalytic preparation of alkyl esters of citrus flavanone glucoside prunin in organic media

Abstract

The biocatalytic preparation of alkyl esters of prunin, a flavanone glucoside derivative of citric flavonoid naringin, was performed in organic media using two commercial immobilized lipases: Novozym 435 (Candida antarctica lipase B immobilized on an acrylic resin) and Lipozyme RM IM (Rhizomucor miehei lipase immobilized on an anion exchange resin). The influence of several reaction parameters on the performance and regioselectivity of the biocatalytic process was investigated using four solvents (acetone, acetonitrile, tetrahydrofurane and t-butanol) and vinyl laurate as a donor. The biocatalytic modification of prunin was strongly dependant on the solvent, the molar ratio of the substrates, the enzyme and the chain length of the donor. The acylation was highly regioselective, obtaining 6"-O-acyl monoesters except when the donor was vinyl acetate in which case a diester seemed to be formed. Novozym 435 proved to be a more efficient biocatalyst than Lipozyme RM IM. In acetone and acetonitrile, derivatives with a 100% conversion yield were synthesized after only 6 h of reaction at 50 °C. The modified derivatives preserved the antiradical activity of the flavanone glucoside and their solubility notably increased in the hydrophobic medium 1-octanol.