Assignment of the 1H and 13C NMR spectra of 2-aminobenzamide-labeled xylo-oligosaccharides

Xylose, xylo-oligosaccharides with a degree of polymerization (DP) from 2 to 6, xylo-oligosaccharides carrying a single arabinofuranosyl, glucosyluronic acid, or 4-O-methyl glucosyluronic acid residues and 4-β-d-Xylp-(1 → 4)-d-Xylp-(1 → 3)-α-l-Rhap-(1 → 2)-α-d-GalpA-(1 → 4)-d-Xylp were labeled at their reducing ends with 2-aminobenzamide (2AB) in the presence of sodium cyanoborohydride (NaBH3CN). These derivatives were then analyzed by high-performance anion-exchange chromatography (HPAEC) and structurally characterized by electrospray-ionization mass spectrometry (ESI-MS) and by 1H and 13C NMR spectroscopy. Reacting Xyl3-Xylitol-2AB with UDP-Xyl in the presence of rice microsomes resulted in the formation of small amounts of Xyl4–6-Xylitol-2AB showing that the 2AB-labeled compound is an acceptor for xylosyltransferase. The 2AB-labeled xylo-oligosaccharides and the 2AB-labeled xylo-oligosaccharides carrying 4-O-methyl glucuronic acid are fragmented by xylanase and α-glucuronidase present in the culture filtrate of Fomitopsis palustris FFPRI 0507. Thus, the 2AB-labeled xylo-oligosaccharides are useful for studying enzymes involved in xylan degradation and biosynthesis.