Syntheses o f Substituted Polysaccharides by Ring-Opening Polymerization of 1, 6-Anhydro-D-glucose and -mannose Derivati v e s

Abstract

Cationic ring-opening polymerizations of 1, 6-anhydro sugars which were derived from levglucosan(1, 6-anhydro-*β-D-glucopyranose) and levomannosan (1, 6-anhydro-*β-D-mannopyranose)by protecting the hydroxyl groups with various substituents were investigated. The structures and physical properties of the polymers obtained were also examined. Tri-O-benzyllevoglucosan was polymerized with such catalysts as PF₅, NbF₅, TaF₅, and 2-iodopropane. AgPF₆ complex to give stereoregular dextran derivatives. Although tri-O- (methyl and ethyl)levoglucosans showed high polymerizabilities, tri-O-(2-butenyl)levoglucosan did not polymerize under these conditions. A levoglucosan derivative in which the C-2 carbon had a tosylamino group instead of a hydroxyl group gave oligomers even by the action of strong Lewis acid. Although triO-(methyl and ethyl)levomannosans showed high polymerizabilities, a 2, 3-O-benzylidenelevominnosan derivative showed very low reactivity. As a result, a large influence of substituent of C-2 carbon of the 1, 6-anhydro sugars on the polymerizability was deduced. Polymers obtained from tri-O-methyllevoglucosan and -levomannosan and tri-O-ethyllevoglucosan were f ound to have high crystallinity by X-ray diffractiometry. The methylated polysaccharides were insoluble in all the solvents examined.¹H-NMR spectra (400 MHz) of 2, 3, 4-tri-O-benzyl-(1+6) α-D-glucopyranan and -mannopyranan revealed highly stereoregular stru ctures with α-configuration,