Effect of substitution pattern on 1H, 13C NMR chemical shifts and 1JCH coupling constants in heparin derivatives

1H, 13C NMR chemical shifts and 1JCH coupling constants were measured for derivatives of heparin containing various sulfation patterns. 1H and 13C chemical shifts varied considerably after introducing electronegative sulfate groups. Chemical shifts of protons linked to carbons changed by up to 1 ppm on substitution with O- and N-sulfate or acetyl groups. Differences up to 10 ppm were detected for 13C chemical shifts in substituted glucosamine, but a less clear dependence was found in iduronate. 1JCH values formed two groups, corresponding to either sulfation or non-sulfation at positions 2 and 3 of glucosamine. O-sulfation caused increases up to 6 Hz in 1JCH and N-sulfation decreases up to 4 Hz. N-acetylation gave similar 1JCH values to N-sulfation. At positions 2 and 3 of iduronate the trend was less marked; 1JCH for O-sulfated positions usually increasing. Introduction of sulfate groups influences chemical shift and 1JCH values at the position of substitution, but also at more remote positions. 1JCH at the glycosidic linkage positions varied between free-amino and N-sulfated compounds, by up to 9 Hz. These results and changes in chemical shift values suggest that iduronate residues and the glycosidic linkages are affected, indicating overall conformational change. This may have important implications for biological activities.