Crystal and molecular structure of the beta-anomer of 6,7-dideoxy-1,2;3,4;9,10-tris-O-(1-methylethylidene)-D-erythro-alpha-D-galacto-undecopyranosid-8-ulose

摘要

6,7-dideoxy-1,2;3,4;9,10-tris-O-(1-methylethylidene)-d-erythro-alpha-d-galacto-undecopy- ranosid-8-ulose, 3, was formed by adding a D-galactose-derived dithiane nucleophile to a protected erythronolactone followed by reductive removal of the dithioacetal group. Its beta-anomer crystallizes in the chiral trigonal space group P3(2)21 with a=b=12.2649(19) angstrom, c=24.675(8) angstrom, and Z=6. The molecule is composed of an erythrofuranose and a galactopyranose moiety, linked by a flexible ethylene bridge. The pyranose part of the molecule is disordered over two positions with equal occupancy. The configuration of the two disordered moieties is the same and they are converted into each other by a slight rotation of 6 degrees around one of the C-C single bonds of the ethylene bridge. The disorder allows for a more effective packing in the solid state.