Application of nano-probe NMR for structure determination of low nanomole amounts of arabinoxylan oligosaccharides fractionated by analytical HPAEC-PAD

A methodology for NMR analysis of low nanomole amounts of oligosaccharides fractionated by analytical HPAEC is presented. Arabinoxylan derived oligosaccharides purified by HPAEC-PAD on an analytical column, by single injections, were analyzed with nano-probe NMR and MALDI-TOF MS to provide full structural assignment. The NMR data were obtained with a 500 MHz NMR spectrometer equipped with a H-1-observe nano-probe. Both one- and two-dimensional experiments on arabinoxylan samples in the low nanomole range were performed, including H-1-H-1 DQF-COSY,H-1-H-1 TOCSY and H-1-H-1 ROESY. These experiments allowed, in combination with MALDI-TOF MS and literature NMR data, a complete structural determination of several tetra-, penta-, hexa-and heptasaccharides. Two new structures: alpha-L-araf-(1-->2)-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-D-Xylp and alpha-L-Araf-(1-->2)[alpha-L-Araf-(1-->3)]-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-beta-D-Xylp-(1-->4)-D-Xylp) were characterized, as well as some previously published structures. (C) 2000 Elsevier Science Ltd. All rights reserved.