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

The preparation of sugar ureas and thioureas by nucleophilic addition of wa ter or hydrogen sulfide, respectively, to sugar-derived carbodiimides has b een examined. Acetic acid efficiently catalysed the formation of ureas, whe reas silica gel was found to be a more convenient catalyst in the case of t he thioxo analogues. The procedures have been exploited in the development of an amine- and isocyanate-free synthesis of urea- and thiourea-tethered p seudooligosaccharides via the corresponding glycosylcarbodiimido sugars. Th e fully unprotected compounds adopted, preferentially, the (Z,Z) configurat ion at the pseudoamide bonds in water solution. (C) 2000 Elsevier Science L td. All rights reserved.