Gradient-enhanced, two-dimensional, homonuclear correlation numerous instances of long-range 4 J and 5 J couplings in techniques (GCOSY) of carbohydrates provide numerous correlainstances of favorable geometry ( 6 -8 ) . However, the intions based on 4 J and 5 J long-range interactions. Intraresidue corcident of long-range coupling across heteroatoms such as relations, involving all 1 H resonances of a given pyranose ring oxygen has, in general, received scant attention in multidiwith its anomeric proton, are consistently observed in a-pyranosyl mensional NMR of carbohydrates ( 9) .
residues at approximately 5 to 10 times lower intensities than
The spectral analysis of carbohydrates almost always vicinal 3 J correlation cross peaks. b-Anomers, pyranosyl residues starts from the anomeric proton ( H1 ) and follows the with axial H1 protons, show very few such effects. Both a and b spin network through the entire pyranose ring by means anomers do, however, exhibit interresidue 4 J correlations across of two-dimensional correlation techniques ( 10 ) such as the glycosidic linkage as shown for several linear and branched COSY and TOCSY ( 11,12 ) or one-dimensional equivaoligosaccharides ranging from three to five residues and are especially useful for spectral assignments in the envelope of pyranosyl lents ( 13) with shaped-selective excitation pulses ( 14) . ring protons located in the typically very crowded 3 to 4 ppm However, in common carbohydrate structures, the overlap region. These effects depend on the strength and duration of the of resonances between 3 and 4 ppm is most often very applied gradients.