Molecular and crystal structure of galactinol dihydrate [1-O-(α-d-galactopyranosyl)-myo-inositol dihydrate]

The crystal structure of galactinol dihydrate has been determined by X-ray diffraction. The crystal belongs to the orthorhombic system, space group P21212, a=15.898(6), b=19.357(5), c=5.104(4) Å, and Z=4. The structure was refined to R=0.044 for 1818 observed structure amplitudes. The primary hydroxyl group exhibits twofold orientational disorder. The linkage conformation is close to those of α-(1→4) linkages in methyl α-maltotrioside tetrahydrate and erlose trihydrate. Although there is no interring hydrogen bond in galactinol, an indirect interring hydrogen bond including a water molecule is present. The observed conformation is additionally stabilized by the indirect interring hydrogen bond. The global minimum in the relaxed-residue energy map based on the MM3(92) force-field is close to the observed conformation in the crystal structure. All hydroxyl, ring and water oxygen atoms are involved in a complex three-dimensional hydrogen-bonding network.