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

The title compound, C(13)H(24)O(9)·H(2)O, 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 φ(H) of 39, 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) C (4) chair 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.