NMR characterization of acidic xylo-oligosaccharides containing two methylglucuronic acid residues from Japanese cedar and Hinoki cypress

Xylo-oligosaccharides containing 4-O-methyl glucuronic acid (MeGlcA) residues attached to two adjacent xylosyl residues and those with a single MeGlcA residue were isolated from partial acid hydrolyzates of the arabinoglucuronoxylans (AGX) from Japanese cedar (Sugi, Cryptomaria japonica) and Hinoki cypress (Chamaecyparis obtusa). The ratio of xylo-oligosaccharides with two MeGlcA residues and those with a single MeGlcA residue was about 1:3 for both Sugi and Hinoki. Four xylo-oligosaccharides with two MeGlcA residues were labeled at their reducing end with 2-aminobenzamide (2AB). The 2AB-labeled oligosaccharides (1–4) were structurally characterized using normal-phase liquid chromatography, electrospray-ionization mass spectrometry (ESI-MS), and nuclear magnetic resonance (NMR) spectroscopy. The signals in the 1H and 13C NMR spectra of the 2AB-labeled oligosaccharides were fully assigned using one- and two-dimensional NMR spectroscopy.