Proton nuclear magnetic resonance analysis of anomeric structure of glycosphingolipids. Lewis-active and Lewis-like substances.

High resolution nuclear magnetic resonance spectra were recorded in a chloroform solution of six Lewis-active or Lewis-like glycosphingolipids in permethylated and permethylated-reduced (LiAlH₄) form. The samples were selected to cover the presently known structural variants of α-fucose linked to galactose and N-acetylglucosamine. Fucα1 → 2Gal, Fucα1 → 3GlcNAc, and Fucα1 → 4GlcNAc gave characteristic and well-separated anomeric resonances. Furthermore, upon reduction there was a strong deshielding effect on Fucα1 → 3GlcNAc and Galβ1 → 3GlcNAc (linkage vicinal to reduced amide), which makes it possible to differentiate type 1 (Galβ1 → 3GlcNAc) and type 2 (Galβ1 → 4GlcNAc) saccharide chains. This improved method of nuclear magnetic resonance spectroscopy is discussed in relation to sequence analysis by mass spectrometry, two microscale structural methods using the same type of derivatives and needing no degradations before analysis.