A Solution NMR Approach To Determine the ChemicalStructures of Carbohydrates Using the Hydroxyl Groups as StartingPoints

摘要

An efficient NMR approach is described for determining the chemical structures of the monosaccharide glucose and four disaccharides, namely, nigerose, gentiobiose, leucrose and isomaltulose. This approach uses the ¹H resonances of the −OH groups, which are observable in the NMR spectrum of a supercooled aqueous solution, as the starting point for further analysis. The 2D-NMR technique, HSQC-TOCSY, is then applied to fully define the covalent structure (i.e., the topological relationship between C–C, C–H, and O–H bonds) that must be established for a novel carbohydrate before proceeding to further conformational studies. This process also leads to complete assignment of all ¹H and ¹³C resonances. The approach is exemplified by analyzing the monosaccharide glucose, which is treated as if it were an “unknown”, and also by fully assigning all the NMR resonances for the four disaccharides that contain glucose. It is proposed that this technique should be equally applicable to the determination of chemical structures for larger carbohydratesof unknown composition, including those that are only available inlimited quantities from biological studies. The advantages of commencingthe structure elucidation of a carbohydrate at the −OH groupsare discussed with reference to the now well-established 2D-/3D-NMRstrategy for investigation of peptides/proteins, which employs the−NH resonances as the starting point.