Synthesis of alternatingly 6-O-methylated cellulose via enzymatic polymerization of a substituted cellobiosyl fluoride monomer catalyzed by cellulase

Novel cellobiose derivatives, 6-O-methyl, 6′-O-methyl, 6,6′-di-O-methyl-β-cellobiosyl fluorides, have been prepared and their hydrolytic behaviour as well as polymerizability by a purified cellulase from Trichoderma viride were investigated. Among these compounds, 6-O-methyl-β-cellobiosyl fluoride was found to polymerize by the cellulase catalysis in a mixed solvent of acetonitrile and acetate buffer (pH 5.0), giving rise to an alternatingly 6-O-methylated cellulose derivative. The stereoselective formation of the β(1 → 4) glycosidic bond is explained by a mechanism involving double inversion at the C1 carbon of the substrate. Another cellobiose derivative, 6′-O-methyl-β-cellobiosyl fluoride, gave a mixture of low molecular weight oligomers. The difference in the observed polymerizability was explained by assuming a difference in steric repulsions between the methyl groups and an amino acid residue at the enzyme catalytic site.