Evidence of the presence of 2-O-β-d-xylopyranosyl-α-l-arabinofuranose side chains in barley husk arabinoxylan

(Glucurono)arabinoxylans were extracted from barley husks and degraded with endo-beta-xylanase or subjected to periodate oxidation. The released oligosaccharide fragments were separated and isolated on Biogel-P2, and their structures were determined by NMR spectroscopy. The oligosaccharides identified consisted Of beta-D-(1-4)-linked xylopyranosyl residues, of which some were substituted at O-3 with alpha-L-arabinofuranosyl groups or at O-2 with 4-0-methylglucuronic acid. In addition to these substituents, a disaccharide side chain, 2-O-beta-D-Xylopyranosyl-alpha-L-arabinofuranose, attached at position O-3 of the main chain, was proved to exist in arabinoxylan from barley husks. The compound was fully characterized with NMR, and all H-1 and C-13 NMR signals were assigned. The arabinose to xylose ratio was low (similar to 0.2) and no 2,3 -disubstitution existed. No blocks of substituted xylose residues could be observed along the main chain. (c) 2006 Elsevier Ltd. All rights reserved.