Crystal structure of methyl α- L -rhamnopyranosyl-(1→2)-α- l -rhamnopyranoside monohydrate

Abstract

The title compound, C13H24 O9·H2O, a structural model for part of bacterial O-antigen polysaccharides from Shigella flexneri and Escherichia coli, crystallizes with four independent disaccharide molecules and four water molecules in the asymmetric unit. The conformation at the glycosidic linkage joining the two rhamnosyl residues is described by the torsion angles H oF39, 30, 37 and 37°, and ψ H of -32, -35, -31 and -32°, which are the major conformation region known to be populated in an aqueous solution. The hexopyranose rings have the 1 C4chair conformation. In the crystal, the disaccharide and water molecules are associated through O - H...O hydrogen bonds, forming a layer parallel to the bc plane. The layers stack along the a axis via hydrophobic interactions between the methyl groups.