Determination of Carbohydrate Structure by Using NMR

The proton-decoupled C-NMR spectrum of carbohydrates gives a signal for each of the specific types of carbons present. For highly asymmetric carbohydrate units, this usually means a signal for each of the carbons in the asynmietric unit. This has been demonstrated for a number of saccharides, such as amylose [40], cyclomaltodextrins [41], dextrans [42], and many others [18]. It is most clearly demonstrated for sucrose in which 12 distinct signals are produced, one for each of the 12 carbons (see Fig. 12.4A). 

0- substituted C-6. In the B-742 dextran spectrum, there is also a signal at 81.7 ppm for the C-3 0-substituted branch linkage, which is in high amount in B-742 dextran. A very similar spectrum was observed for S. mutans dextran [45], which is an alternating comb dextran whose structure is similar to that of L mesen-teroides B-742 regular comb dextran but with approximately 50% fewer a- 

1 - 3 linkages at 98.7, 97.2, and 96.4 ppm, respectively. There also were two signals for C-6 at 66.5 ppm for the 0-substituted C-6, and at 61.5 ppm for the unsubstituted C-6 single-branch glucose residue. One of the several signals in the range of 76-70 ppm probably represents the C-2 0-substituted carbon that is in this dextran [42]. 

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