1H‐NMR studies at 500 MHz of a neutral disaccharide and sulphated di‐, tetra‐, hexa‐ and larger oligosaccharides obtained by endo‐β‐galactosidase treatment of keratan sulphate

Abstract

In the preceding paper in this journal, the major oligosaccharides obtained by endo‐β‐galactosidase digestion of bovine corneal keratan sulphate were identified as a neutral disaccharide, GlcNAcβ1‐3Gal, and sulphated di‐, tetra‐, hexa‐, octa‐ and decasaccharides based on the sequence (‐3/4GlcNAcβ1‐3Galβ1‐)n having 1, 3, 5, 7 and 9 sulphate groups, respectively. In the present study, these oligosaccharides have been analysed by 500‐MHz 1H‐NMR spectroscopy using spin‐decoupling and two‐dimensional correlated spectroscopy experiments. The NMR data confirm the β‐configuration of all the interglycosidic linkages and are consistent with an alternating sequence of →4GlcNAc and →3Gal, a non‐reducing‐end N‐acetylglucosamine residue and a reducing‐end galactose residue. The NMR data have also established that a sulphate group is linked to the C6 position of all sugar residues except the reducing‐end galactose as follows: (Formula Presented.) The signals of the protons attached to the sulphated carbon atoms show marked downfield shifts (apprximately 0.4 ppm from equivalent protons of non‐sulphated carbon atoms), while the protons at C5 vicinal to sulphated atoms show a change of 0.1–0.2 ppm and other protons of the sulphated monosaccharides show smaller changes in chemical shift (0.01–0.1 ppm). The proton at C4 of the non‐sulphated reducing‐end galactose linked at C3 also shows a significant change in chemical shift (0.03 ppm). Copyright © 1986, Wiley Blackwell. All rights reserved