Phenylpropanoid esters of lesquerella and castor oil

Abstract

Lesquerella (LO) and castor oil (CO) were esterified at the secondary hydroxyl groups of their 14-hydroxyeicos-cis-11-enoic fatty acids and 12-hydroxyoctadec-cis-9-enoic fatty acids, respectively, with 4-acetoxy-3-methoxycinnamic acid (acetoxyferulic acid). The unconventional esterifications were conducted under inert nitrogen atmospheres without solvent at 175–200°C in sealed ampules. 1H NMR was used to measure the degree of acetoxyferuloyl esterification using a modified esterification number (EN). Reactions at 200°C resulted in ∼43% conversions to the acetoxyferuloylated LO and CO but promoted significant degradation/loss of the acetoxyferulic acid as evidenced by the low quantity of acetoxyferulic acid found in the reaction products as determined by HPLC. Reactions at 175°C resulted in significantly lower conversions to the acetoxyferuloylated LO and CO, 9–17%, but did not result in as severe acetoxyferulic acid degradation. The addition of tin (II) 2-ethylhexanoate catalyst to the 175°C reactions increased esterification conversion to ∼45% without significant loss of acetoxyferulic acid to degradation. The aromatic acetate of the acetoxyferuloylated LO and CO was selectively deacylated using excess pyrrolidine without affecting the aliphatic esters to give feruloylated LO and CO. The feruloylated LO and CO absorbed ultraviolet (UV) radiation from 280 to 360nm with a λmax at 327nm, bridging the absorbance gap of commercial UV absorbing ingredients. The feruloylated LO and CO are also presumably good antioxidants and are potential candidates for incorporation into lipid bilayers to protect liposomes and their contents from reactive oxygen species.