Structure of a new arabinoxylan from the bark of Cinnamomum iners

Two polysaccharide fractions, water-soluble (24%) composed of d-xylose and l-arabinose, and alkali-soluble (15%) composed of l-arabinose, d-xylose, and d-glucose, have been isolated from the delignified bark of Cinnamomum zeylanicum. The water-soluble fraction gave an arabinoxylan (60%) composed of l-arabinose and d-xylose in the molar ratio 1.45: 1.00. Methylation analysis, together with the isolation of the oligosaccharides 3-O-α-d-xylopyranosyl-l-arabinose, 4-O-β-d-xylopyranosyl-d-xylose, O-β-d-xylopyranosyl-(1→4)-O-β-d-xylopyranosyl-(1→4)-d-xylose, and O-β-d-xylopyranosyl-(1→4)-O-β-d-xylopyranosyl-(1→4)-d-xylose after partial hydrolysis with acid, suggested that the polysaccharide contained a backbone of (1 →4)-linked β-d-xylosyl residues each of which was substituted both at O-2 and O-3 with l-arabinofuranosyl and 3-O-α-d-xylopyranosyl-l-arabinofuranosyl groups. Very mild hydrolysis with acid gave a degraded polysaccharide, containing 10% of l-arabinose and 90% of d-xylose, which was essentially a (1→)-linked β-d-xylan carrying a limited number of branches at O-2 and O-3. These results together with those from periodate-oxidation and Smith-degradation studies support the proposed structure.