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Preparation and crystal and molecular structure of 6-O-[(2S)-2,3-epoxypropyl]-1, 2:3,4-di-O-isopropylidene-α-d-galactopyranose. Pyranoid ring conformation in 1,2:3,4-di-O-isopropylidene galactopyranose and related systems

✍ Scribed by Peter Köll; Wolfgang Saak; Siegfried Pohl; Bohumil Steiner; Miroslav Koóš

Publisher
Elsevier Science
Year
1994
Tongue
English
Weight
858 KB
Volume
265
Category
Article
ISSN
0008-6215

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✦ Synopsis

The title compound was isolated by several recrystallisations from a 1:l mixture of diastereomers which was obtained in 75% yield from the reaction of 1,2:3,4-di-O-isopropylidene-c~-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 OS, and the twist-boat ( "skew''-boat)

OT, with deviations in the direction of the boat & 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.

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The structures of the title compounds (2b and 3) have been investigated in the solid state by X-ray methods. The crystals of 2b are monoclinic, space group P2,, and of 3 orthorhombit, space grtup P2,2,2,. The cell dimensions are: for 2b, a = 9.910(2), b = 11;745W, c = 11.810(3) A, /3 = 97.32(l)"; a