Enzymatically derived aldouronic acids from Eucalyptus globulus glucuronoxylan

Abstract

A glucuronoxylan was extracted from the holocellulose of Eucalyputus globulus wood with 10% KOH and subjected to hydrolysis by a commercial cellulase preparation “Meicelase”. Neutral xylooligosaccharides liberated were analyzed by size exclusion chromatography. Aldouronic acids liberated were purified by preparative anion exchange chromatography. Their structures were studied by monosaccharide analysis, comparison of volume distribution coefficients ( Dvs) in anion exchange chromatography with those of the authentic samples, and 1H and 13C NMR spectroscopy, resulting in the characterization of seven aldouronic acids including a novel one containing galactose residue. O-β- d-Xyl p-(1 → 4)-[ O-(4- O-Me-α- d-GlcA p)-(1 → 2)]- O-β- d-Xyl p-(1 → 4)- O-β- d-Xyl p-(1 → 4)- d-Xyl O-(4- O-Me-α- d-GlcA p)-(1 → 2)- O-β- d-Xyl p-(1 → 4)- O-β- d-Xyl p-(1 → 4)- d-Xyl O-(4- O-Me-α- d-GlcA p)-(1 → 2)- O-β- d-Xyl p-(1 → 4)- d-Xyl O-β- d-Xyl p-(1 → 4)- O-β- d-Xyl p-(1→3)- O-α- l-Rha p-(1 → 2)- O-α- l-GalA p-(1 → 4)- d-Xyl O-β- d-Xyl p-(1 → 4)- O-β- d-Xyl p-(1 → 3)- O-α- l-Rha p-(1 → 2)- d-GalA O-β- d-Xyl p-(1 → 3)- O-α- l-Rha p-(1 → 2)- O-α- d-GalA p-(1 → 4)- d-Xyl O-β- d-Gal p-(1 → 2)- O-(4- O-Me-α- d-GlcA p)-(1 → 2)- O-β- d-Xyl p-(1 → 4)- O-β- d-Xyl p-(1 → 4)- d-Xyl. The oligosaccharides liberated provide information on multiplicity of xylanases secreted by Trichoderma viride. The presence of the last aldouronic acid shows a structural feature of E. globulus xylan.