STRUCTURAL-ANALYSIS OF 6-S-(BENZOXAZOL-2-YL)-6-DEOXY 1,2 DI-O-ISOPROPYLIDENE-6-THIO-ALPHA-D-GALACTOPYRANOSE BY MEANS OF X-RAY-DIFFRACTION, HIGH-RESOLUTION NMR-SPECTROSCOPY, AND MOLECULAR MODELING/
Mt. Lakin et al., STRUCTURAL-ANALYSIS OF 6-S-(BENZOXAZOL-2-YL)-6-DEOXY 1,2 DI-O-ISOPROPYLIDENE-6-THIO-ALPHA-D-GALACTOPYRANOSE BY MEANS OF X-RAY-DIFFRACTION, HIGH-RESOLUTION NMR-SPECTROSCOPY, AND MOLECULAR MODELING/, Carbohydrate research, 290(2), 1996, pp. 125-136
The conformational behaviour of a representative azaheterocycle/thiosu
gar hybrid: 6-S-(benzoxazol-2-yl)-6-deoxy- di-O-isopropylidene-6-thio-
alpha-D-galactopyranose 1, has been characterised by X-ray crystallogr
aphy, molecular modelling and NMR studies, The crystal of 1 (C19H23NO6
S) belongs to the monoclinic space group P2(1), with a = 8.4330(4), b
= 10.287(3), c = 11.417(4) Angstrom, beta = 101.66(5)degrees, V = 970.
0(5) Angstrom(3), and Z = 2, The structure has been determined by X-ra
y diffraction at 299 K using an area detector. Least-squares refinemen
t based on 2352 reflections yielded a final wR2 of 0.098, with R1 = 0.
040 [for 2210 reflections with F-0 > 4 sigma(F-0)], The pyranose ring
adopts a conformation between that of the screw-boat, S-O(S), and the
twist-boat, T-O(2) forms. Proton NMR chemical shifts have been assigne
d by measurement of 1D and 2D spectra. The C-5-C-6 conformer populatio
ns in CDCl3 solution have been estimated, In parallel, a conformationa
l analysis using the crystal coordinates as the starting point has bee
n made using the Tripes force field. The resulting potential energy su
rface indicates a high flexibility about the C-5-C-6 and C-6-S-6 bonds
. The agreement between experimental and theoretical data is satisfact
ory and constitutes a validation of the conformational energy surface.
(C) 1996 Elsevier Science Ltd.