High resolution nuclear magnetic resonance spectroscopy of glycosphingolipids. I: 360 MHz 1H and 90.5 MHz 13C NMR analysis of galactosylceramides

Abstract

The high resolution 1H and 13C nuclear magnetic resonance (NMR) spectra of galactosylceramides containing n-fatty acids and alpha-hydroxy fatty acids were recorded in dimethylsulfoxide solution with and without addition of D2O. From the coupling constants of the sugar ring protons, a 4C1 conformation can be deduced. In contrast to the conformation in aqueous solution, the C6 hydroxymethylene group is freely rotating around the C6--C5 bond. In the ceramide residue all signals produced by protons linked to carbons bearing electronegative substituents could be attributed. The large difference in coupling constants of the methylene protons of C1' to the C2' methine proton of the sphingosine indicates a restricted rotation around the C1'--C2' bond. The assignments of the hydroxy and amino protons follow from the decoupling of the corresponding methine protons.