Synthesis of glycosyl (thio) ureido sugars via carbodiimides and their conformational behaviour in water

摘要

The preparation of sugar ureas and thioureas by nucleophilic addition of water or hydrogen sulfide, respectively, to sugar-derived carbodiimides has been examined. Acetic acid efficiently catalysed the formation of ureas, whereas silica gel was found to be a more convenient catalyst in the case of the thioxo analogues. The procedures have been exploited in the development of an amine-and isocyanate-free synthesis of urea -and thiourea-tethered pseudooligosaccharides via the corresponding glycosylcarbodiimido sugars. The fully unprotected compounds adopted,preferentially, the (Z,Z) configuration at the pseudoamide bonds in water solution.