Synthesis of glycero amino acid-based surfactants. Part 1. Enzymatic preparation of rac-1-O-(Nα-acetyl-l-aminoacyl)glycerol derivatives

Abstract

An enzymatic procedure for the selective synthesis of a number of Nα-protected amino acid glyceryl esters is presented. Using Nα-Boc-arginine as a model substrate, changes in product yield are examined for the following reaction variables: aqueous buffer content, pH, biocatalyst configuration (free or deposited), enzyme concentration and synthetic approach (thermodynamically or kinetically controlled synthesis). The best yields (61–89%) are obtained at 50 °C in glycerol containing a range of aqueous buffer from 0 to 10% (v/v). Readily available industrial proteases and lipases are used as catalysts. The method allowed us to selectively acylate one of the primary hydroxy groups of the glycerol with the carboxylate groups of the amino acid. In the case of aspartic acid and glutamic acid, selective esterification of the α-carboxylate group is achieved. None of the enzymes tested could differentiate between the two enantiotopic hydroxymethyl groups of glycerol, giving diastereoisomeric mixtures in all cases.