LONG-RANGE (4)J AND (5)J 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 (4)J and (5)J long-range interactions. Intraresidue correlations, involving all H-1 resonances of a given pyranose ring with its anomeric proton, are consistently observed in alpha-pyranosyl residues at approximatel y 5 to 10 times lower intensities than vicinal (3)J correlation cross peaks. beta-Anomers, pyranosyl residues with axial H1 protons, show ve ry few such effects. Both alpha and beta anomers do, however, exhibit interresidue (4)J 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 t he envelope of pyranosyl ring protons located in the typically very cr owded 3 to 4 ppm region. These effects depend on the strength and dura tion of the applied gradients. (C) 1995 Academic Press, Inc.