A simple and efficient approach for the synthesis of cholesterol esters of long-chain saturated fatty acids by using Ph3P·SO3 as a versatile organocatalyst

Abstract

Cholesteryl esters are more nonpolar compounds formed by the conjugation of cholesterol with fatty acids containing a long hydrocarbon chain. These ester molecules do not participate in the composition of the cell membranes and are found in lipid droplets. Because this form of cholesterol can be packaged in a larger amount in lipoproteins, the transport of cholesterol is more effective, and also, these esters play an important role in cholesterol metabolism. Moreover, some of their hydroperoxide derivatives are biologically active components of minimally modified low-density lipoprotein (mmLDL). In recent years, these esters have attracted attention in many industrial and medical applications. In this study, a triphenylphosphine-sulfur trioxide adduct efficiently catalyzed the esterification reactions between homologous long-chain saturated monocarboxylic or dicarboxylic fatty acids and cholesterol molecule in toluene. In these reactions, the triphenylphosphine-based adduct acts as a source of sulfur trioxide. Reactions were performed at 110 °C with equimolar amounts of the reagents except in the case of dicarboxylic acids, and two equimolar of cholesterol was used to afford the corresponding homologous cholesteryl esters in good to excellent yields. The present developed method has advantages such as being simpler, practical, and less toxic than the existing ones as well as enabling the synthesis of the related esters with higher yields.