Structural analysis of 6-S-(benzoxazol-2-yl)-6-deoxy1,2:3,4-di-O-isopropylidene-6-thio-α-d-galactopyranose by means of X-ray diffraction, high resolution NMR spectroscopy, and molecular modelling

The conformational behaviour of a representative azaheterocycle/thiosugar hybrid: 6-S-(benzoxazol-2-yl)-6-deoxy-1,2:3,4-di-O-isopropylidene-6-thio-α-d-galactopyranose, 1, has been characterised by X-ray crystallography, molecular modelling and NMR studies. The crystal of 1 (C19H23NO6S) belongs to the monoclinic space group P21, with α = 8.4330(4), b = 10.287(3), c = 11.417(4) Å, β = 101.66(5)°, V = 970.0(5) Å3, and Z = 2. The structure has been determined by X-ray diffraction at 299 K using an area detector. Least-squares refinement based on 2352 reflections yielded a final wR2 of 0.098, with R1 = 0.040 [for 2210 reflections with Fo > 4σ(Fo)]. The pyranose ring adopts a conformation between that of the screw-boat, OS5, and the twist-boat, OT2 forms. Proton NMR chemical shifts have been assigned by measurement of ID and 2D spectra. The C-5-C-6 conformer populations in CDC13 solution have been estimated. In parallel, a