D-Mannosamine hydrochloride (2-amino-2-deoxy-D-mannose hydrochloride): ionic hydrogen bonding in saccharides...

D-Mannosamine hydrochloride (2-amino-2-deoxy-D-mannose hydrochloride), C₆H₁₄NO₅⁺·Cl^-, (I), crystallized from a methanol/ethyl acetate/n-hexane solvent mixture at room temperature in a ⁴C₁ chair conformation that is slightly distorted towards the ^C3,O5B form. A comparison of the structural parameters of (I) with the corresponding parameters in α-D-glucosamine hydrochloride, (II), and β-D-galactosamine hydrochloride, (III)/(III'), was undertaken to evaluate the effects of ionic hydrogen bonding on structural properties. Three types of ionic hydrogen bonds are present in the crystals of (I)-(III)/(III'), i.e. N⁺-H...O, N⁺-H...Cl^-, and O-H...Cl^-. The exocyclic structural parameters in (I), (II), and (III)/(III') appear to be most influenced by this bonding, especially the exocyclic hydroxy groups, which adopt eclipsed conformations enabled by ionic hydrogen bonding to the chloride anion. Anomeric disorder was observed in crystals of (I), with an α:β ratio of 37:63. However, anomeric configuration appears to exert minimal structural effects; that is, bond lengths, bond angles, and torsion angles are essentially identical in both anomers. The observed disorder at the anomeric C atom of (I) appears to be caused by the presence of the chloride anion and atom O3 or O4 in proximal voids, which provide opportunities for hydrogen bonding to atom O1 in both axial and equatorial orientations.