Long-range 4J and 5J, including interglycosidic correlations in gradient-enhanced homonuclear COSY experiments of oligosaccharides.

Gradient-enhanced, two-dimensional, homonuclear correlation techniques (GCOSY) of carbohydrates provide numerous correlations based on 4J and 5J long-range interactions. Intraresidue correlations, involving all 1H resonances of a given pyranose ring with its anomeric proton, are consistently observed in alpha-pyranosyl residues at approximately 5 to 10 times lower intensities than vicinal 3J correlation cross peaks. beta-Anomers, pyranosyl residues with axial H1 protons, show very few such effects. Both alpha and beta anomers do, however, exhibit interresidue 4J correlations across the glycosidic linkage as shown for several linear and branched oligosaccharides ranging from three to five residues and are especially useful for spectral assignments in the envelope of pyranosyl ring protons located in the typically very crowded 3 to 4 ppm region. These effects depend on the strength and duration of the applied gradients.