The hex-5-enose degradation: Cleavage of modified glycosiduronic acid linkages in methylated Khaya ivorensis gum

Abstract

Reduction of uronic acid residues in permethylated polysaccharide A from Khaya ivorensis gum, followed by transformation of the resulting hexose into 6-deoxy-6-iodohexose residues, affords a modified polysaccharide which undergoes depolymerization on treatment with zinc dust. The main products after reduction with sodium borohydride are hexenitol-terminated oligosaccharides whose structures have been established on the basis of n.m.r. and mass-spectral data and compositional analysis as members of a series of O-α- l-rhamnopyranosyl-(1→3)-1,2-di-deoxyhex-1-enitol derivatives, with and without β- d-galactopyranosyl substituents. The major portion of the polysaccharide may be formulated as a backbone of alternating 4-linked α- d-galacturonic acid and 2-linked α- l-rhamnopyranose residues with side chains of β- d-galactopyranosyl or 4- O-(4- O-methyl-α- d-glucopyranosyl-uronic acid)-β- d-galactopyranosyl units attached to O-4 of rhamnose residues.