Enzymatic acylation of isoorientin isolated from antioxidant of bamboo leaves with palmitic acid and antiradical activity of the acylated derivatives

Abstract

The utilization of bamboo-leaf extracts is limited by their weak solubility in lipidic media. As such, this study established an effective and relatively cheap method for preparation of ester of isoorientin isolated from bamboo-leaf extracts. Acylation of isoorientin with palmitic acid was efficient in a system containing dried tert-amyl alcohol and molecular sieves, yielding from 22 to 90 % bioconversion with different conditions; in detail, several factors (the origin and the amount of the lipase, temperature and water content of the system) were investigated in depth with the effect on the performance of the acylation reaction in this paper. Thereafter high purity ester (95 %) was obtained following a two-step solvent purification procedure and a chromatographic separation. With 1H and 13C nuclear magnetic resonance spectroscopy analysis, single product was detected to be 6″-O-palmitate isoorientin ester. Introducing an acyl group into isoorientin significantly improved its lipophilicity yet slightly reduced their antioxidant activity.