On the anomeric preference of the isothiocyanato group

This work is aimed at providing a systematic and comprehensive analysis of the anomeric effect exerted by the isothiocyanato (N&z.dbd;C&z.dbd;S) group taking the xylopyranose ring as a scaffold because enhanced effects have been detected in that ring-bearing halogen and pseudohalogen substituents. To this end, both α- and β-anomers of tri- O -acetoxypyranosyl- d -xylose have been prepared and thoroughly characterized. The axial preference of the isothiocyanato group reflects a dominant anomeric effect, whose origin could be determined through DFT calculations with identification of the stereoelectronic interactions as revealed by Natural Bond Orbital (NBO) analysis. In this way, this study expands the repertoire of groups biasing the conformation and reactivity of monosaccharides and related heterocycles. Anomeric effect of the isothiocyanato group has been quantified for the first time in xylopyranose triacetates; both anomers being synthesized.