Protease-catalyzed synthesis of disaccharide amino acid esters in organic media

Abstract

An enzymatic synthesis of sugar amino acid esters has been developed in pyridine by using a commercial protease, Optimase M-440, from Bacillus licheniformis. Optimase M-440 showed broad substrate specificity toward amino acid esters as acyl donors and disaccharides as nucleophiles. Analysis of acylation sites indicated sucrose was acylated only at three primary hydroxyls. Trehalose, consisting of two glucose units, was acylated at two primary (6-OH and 6′-OH) and one secondary (3-OH). With sucrose and trehalose, diesters along with monoesters were enzymatically synthesized. In both cases, no triester was formed. Molecular size of nucleophiles, glucose and sucrose, have effects on the extent of acylation with d-amino acids. N-blocked phenylalanine, leucine, and methionine exhibited higher activity toward sucrose than lysine, aspartic acid, and tyrosine. Various leaving groups of tBoc- l-phenylalanine were used and cyanomethyl ester gave the highest rate of reaction. Optimization of initial water activity of Optimase M-440 ( A w = 0.2–0.3) was necessary to maintain catalytic activity and to prevent undesirable hydrolysis of activated esters.