Proton-nuclear magnetic resonance study of peracetylated derivatives of ten oligosaccharides isolated from human milk

Proton-nuclear magnetic resonance (NMR) spectra of peracetylated derivatives of ten structurally related oligosaccharides isolated from human milk were measured for solutions in CDCl 3 at 360 MHz. The following oligosaccharides were investigated: Galβ1 → 4Glc-ol ( 1), GlcNAcβ1 → 3Galβ1 → 4Glc-ol ( 2), Galβ1 → 4GlcNAcβ1 → 3Galβ1 → 4Glc-ol ( 3), Galβ1 → 3GlcNAcβ → 3Galβ1 → 4Glc-ol ( 4), Galβ1 → 3GlcNAc(4 ← 1Fucα)β1 → 3Galβ1 → 4Glc-ol ( 5), Fucα1 → 2Galβ1 → 3GlcNAcβ1 → 3Galβ1 → 4Glcol ( 6), Fucαl → 2Galβl → 3GlcNAc(4 ← 1Fucα)β1 → 3Galβ1 → 4Glc-ol ( 7), Fucαl → 2Galβ1 → 4Glc-ol(3 ← 1Fucα) ( 8), and a 1:3 mixture of Fucαl → 2Galβ1 → 4Glc-ol ( 9) and Galβ1 → 4Glc-ol(3 ← 1Fucα) ( 10). Owing to the strong downfield shifts of the resonances of protons linked to acetoxylated carbons, the problems of signal overlap are less severe and the spin systems of all constituent sugar residues can be assigned fully. The sites of glycosidic linkage can be recognized by the high-field position of the signals of protons linked to those sites; for example, type 1 (Galβ1 → 3GlcNAc) and type 2 (Galβ1 → 4GlcNAc) saccharide chains can be distinguished. The sequence can be established by observing a nuclear Overhauser effect involving the anomomeric and the aglyconic proton.