Glycosidic bond formation by glycosidase in organic solvent

Abstract

To develop enzymatic methods of glycosidic-bonds formation, glycosidases in organic solvents were utilized as a catalyst of condensation betweem sugars, and sugar and alcohol. In these system, organoboronic acids, for example, phenylboric acids and butylboric acid were introduced to solubilize sugars in organic solvents. Organobornic acids in these system were condensated with sugars to give sugar-boronic esters and conedlnsing water. The condensation in microaqueous two-phase system was critically influenced by the amount of water and organoboronic acids. It has been investigated the effects of water and organoboronic acids on the formations of disaccharides and alkyl-$\beta$-D-glycosides by the quantitative HPLC analysis and Karl-Fisher titration of water cotents in organic phase. Various organic solvents having different water solubilities were examined to find optimal reaction medium in the syntheses of ethyl-$\beta$-D-glucoside and ethyl-$\beta$-D-galactoside. Also, optimal water contents in aqueous phase were evaluted in terms of the Q value defined as following : mole of water divided by mole of sugar in aqueous phase. Q values of optimal condensation increased on the increase of solubility of solvent in water. Q values of optimal condensation were different according to alcohols i.e., in cass of (1) water miscible alcohol : Q value slightly increased on the increase of nucleophilicity, and (2) water immiscible alcohol : Q value increased greatly on the increase of hydrophobicity. As a whole, Q values were dependent on the activity of water and alcohols. The concentration of products and reactants concentration in organic phases were affercted by the amounts organoboronic acid water in the reaction system. In the presence of phenylboronic acid, glucose was more soluble in organic solvents than alkyl-$\beta$-D-glucoside, whereas less soluble galactose than alkyl-$\beta$-D-galactoside. Organoboronic acids in the formation of ethyl-$\beta$-D-galactoside inc...