PREPARATION AND CRYSTAL AND MOLECULAR-STRUCTURE OF 6-O-[(2S)-2,3-EPOXYPROPYL]-1,2/3,4-DI-O-ISOPROPYLIDENE-ALPHA-D-GALACTOPYRANOSE - PYRANOID RING CONFORMATION IN 1,2/3,4-DI-O-ISOPROPYLIDENE-GALACTOPYRANOSE AND RELATED SYSTEMS

The title compound was isolated by several recrystallisations from a 1:1 mixture of diastereomers which was obtained in 75% yield from the reaction of 1,2:3,4-di-O-isopropylidene-alpha-D-galactopyranose with epichlorohydrin. The absolute configuration of this isomer (30% yield) was established by X-ray crystallography. The conformation of the pyranoid ring in this compound is compared to those in related situations. In all these cases the pyranoid ring adopts a heavily distorted conformation which is described on average as between the screw-boat S-O(5) and the twist-boat (''skew''-boat) T-O(2) with deviations in the direction of the boat B-2,B-5 in most cases. The puckering parameters for all such reported pyranoid rings were calculated or recalculated, and are given within expanded conventions of carbohydrate nomenclature.