Synthesis and structural studies of anomeric 2,3,4,6-tetra-O-acetyl-5-thio-d-glucopyranosyl azides

Two methods are presented for the preparation of the α and β anomers of 2,3,4,6-tetra-O-acetyl-5-thio-d-glucopyranosyl azide. These methods are comparable in yield, but the one that converts a glucopyranosyl bromide into the azide is preferable because of easier purification. After chromatographic separation, the α and β anomers were analysed by NMR spectroscopy. The crystal and molecular structure of the β anomer was determined by X-ray diffraction. It crystallises in space group P21 [a=11.729(3), b=7.305(3), c=11.363(3)Å, β=107.63(5)°, Z=2]. The hexopyranose ring of the β anomer assumes a 4C1 conformation and the orientation of the azido group is compatible with the requirements of the exo-anomeric effect. This geometry is compared to that of other similar structures.