Methyl α-l-rhamnosyl-(1→2)[α-l-rhamnosyl-(1→3)]-α-l-rhamnoside penta-hydrate: synchrotron study

Abstract

The title hydrate, C(19)H(34)O(13)·5H(2)O, contains a vicinally disubstituted tris-accharide in which the two terminal rhamnosyl sugar groups are positioned adjacent to each other. The conformation of the tris-accharide is described by the glycosidic torsion angles ϕ2 = 48 (1)°, ψ2 = -29 (1)°, ϕ3 = 44 (1)° and ψ3 = 4 (1)°, whereas the ψ2 torsion angle represents a conformation from the major state in solution, the ψ3 torsion angle conformation may have been caught near a potential energy saddle-point when compared to its solution structure, in which at least two but probably three conformational states are populated. Extensive inter-molecular O-H⋯O hydrogen bonding is present in the crystal and a water-containing channel is formed along the b-axis direction.

Fig. 1.

A view of the molecule with displacement ellipsoids drawn at the 50% probablity level.

Fig. 2.

Four unit cells viewed along the b axis with the water molecules symbolized by the large blue discs. The water molecules mediate intermolecular hydrogen bonds between the sugar molecules and along the b axis.

Fig. 3.

Stereoview of the hydrogen bonded water structure of approximately two unit-cell lengths along the b axis. The water O atoms are shown with blue color and the hydroxyl O atoms are shown with red color.