IDENTIFICATION OF THE ACIDIC DEGRADATION PRODUCTS OF HEXENURONIC ACIDAND CHARACTERIZATION OF HEXENURONIC ACID-SUBSTITUTED XYLOOLIGOSACCHARIDES BY NMR-SPECTROSCOPY

A 4-O-methylglucuronoxylan was converted into a hexenuronoxylan at hig h temperature and alkalinity similar to the conditions used during kra ft pulping. The hexenuronoxylan was hydrolysed with enzymes, and acidi c xylooligosaccharides were separated from the hydrolysate by anion-ex change and size-exclusion chromatography. The primary structure of the two main hexenuronic acid-substituted xylooligosaccharides (a tetrame r and a pentamer) was determined by two-dimensional H-1 and C-13 NMR s pectroscopy. The 4-deoxy-hexenuronic acid is not stable under the acid hydrolysis step of conventional carbohydrate analysis. Here, we have identified the acidic degradation products of 4-deoxy-hexenuronic acid by NMR spectroscopy. Two degradation pathways were observed, both res ulting in a furan derivative.