Carbon‐13 as a tool for the study of carbohydrate structures, conformations and interactions

Abstract

Abstract The application of 13 C‐NMR spectroscopy to problems involving the structures and interactions of carbohydrates is described. Both 13 C‐enriched and natural abundance compounds were used and some advantages of the use of the stable isotope are described. Carbon‐carbon and carbon‐proton coupling constants obtained from 1‐ 13 C enriched carbohydrates were employed in the assignment of their chemical shifts and to establish solution conformation. In all cases studied thus far, C‐3 couples to C‐1 only in the β‐anomers while C‐5 couples to C‐1 only in the α‐anomers. C‐6 and C‐2 always couple to C‐1 in both anomeric species. The alkaline degradation of glucose [1‐ 13 C] to saccharinic acids was followed by 13 C‐NMR. The conversion of glucose [1‐ 13 C] to fructose‐1,6‐bisphosphate [1,6‐ 13 C] by enzymes of the glycolytic pathway was shown as an example of the use of 13 C‐enriched carbohydrates to elucidate biochemical pathways. In a large number of glycosyl phosphates the 31 P to H‐1 and 31 P to C‐2 coupling constants demonstrate that in the preferred conformation the phosphate group lies between the O‐5 and the H‐1 of the pyranose ring. The influence of paramagnetic Mn 2+ ions on the proton decoupled 13 C‐NMR spectra of uridine diphosphate N‐acetylglucosamine indicates that the Mn 2+ interacts strongly with the pyrophosphate moiety and with the carbonyl groups of the uracil and N‐acetyl groups.