2,6-Dideoxy-2,6-imino-l-glycero-d-ido-heptitol

The title molecule, C7H15NO5, the major product from selective enzymatic oxidation followed by hydrogenolysis of the corresponding azidoheptitol, was found by X-ray crystallography to exisit in a chair conformation with three axial hydroxyl groups. One of the hydroxymethyl groups is disordered over two sets of sites in a 0.590 (3):0.410 (3) ratio. In the crystal, O—H⋯O, O—H⋯(O,O), O—H⋯N and N—H⋯O hydrogen bonding occurs.

The azido heptitol 1 was synthesized from readily available D-glycero-D-gulo-heptono-1,4-lactone and underwent selective enzymatic oxidation to the ketose 2 followed by hydrogenation with closure on either face of the ketone to generate the imino sugars 3 and 4 (Fig. 1). The major product was found to be the symmetrical homonorjirimycin 3 and its structure was confirmed by X-ray crystallography.
The X-ray structure shows that the compound adopts a chair conformation with 3 axial hydroxyl substituents (Fig. 2).
There is significant disorder in the structure with one of the equatorial hydroxymethyl groups occupying two possible sites each of which is able to form a hydrogen bond.The crystal exists as an extensively hydrogen bonded lattice with each molecule acting as a donor and an acceptor for 8 hydrogen bonds (Fig. 3).

Refinement
The relatively large ratio of minimum to maximum corrections applied in the multiscan process (1:1.21) reflect changes in the illuminated volume of the crystal. Changes in illuminated volume were kept to a minimum, and were taken into account (Görbitz, 1999) by the multi-scan inter-frame scaling (DENZO/SCALEPACK, Otwinowski & Minor, 1997).
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (