6-Azido-6-deoxy-α-l-galactose (6-azido-l-fucose) monohydrate

Although 6-azido-6-deoxy-l-galactose in aqueous solution is in equilibrium between the open-chain, furanose and pyranose forms, it crystallizes solely as 6-azido-6-deoxy-α-l-galactopyranose monohydrate, C6H11N3O5·H2O, with the six-membered ring adopting a chair conformation. The structure exists as hydrogen-bonded chains, with each molecule acting as a donor and acceptor of five hydrogen bonds. There are no unusual crystal packing features and the absolute configuration was determined from the use of 1-azido-1-deoxy-d-galactitol as the starting material.

This work was supported in part by the Programme for the Promotion of Basic Research Activities for Innovative Biosciences (PROBRAIN). The authors also thank the Oxford University Chemical Crystallography Service for use of the instruments.
The methodology developed by Izumori (2002Izumori ( ,2006 for the interconversion of tetroses, pentoses and hexoses by enzymatic oxidation, inversion at C3 with a single epimerase, and reduction to the aldose has been seen to be generally applicable for the 1-deoxy ketohexoses (Yoshihara et al., 2008). The viability of the methodology for the corresponding azido substituted systems was investigated with the synthesis 6-azido-6-deoxy-L-galactose 3 by microbial oxidation of 1-azido-1-deoxy-D-galactitol 1 with K.Pneumoniae 40bR followed by isomerization to the aldose 3 using D-arabinose isomerase ( Fig. 1).
6-Azido-6-deoxy sugars have been little investigated and may have similar interesting properties. They are also of interest as Click Chemistry substrates, allowing a wide range of novel sugar substituted triazoles to be synthesized quickly, utilizing a few easy and reliable reactions. A click reaction should be wide in scope and easy to perform, use only readily available reagents, and be insensitive to oxygen and water. Reaction work-up and purification uses benign solvents and avoids chromatography. In many cases the reaction can be performed in, or on top of water; (Kolb and Sharpless, 2003) presenting an obvious environmental benefit to many existing precedures.
6-Azido-6-deoxy-L-galactose monohydrate crystallized solely in the α-pyranose form with the 6-membered ring adopting a chair conformation (Fig. 2). Each molecule acts as a donor and acceptor for 5 hydrogen bonds. A non standard hydrogen bond to the terminal azide nitrogen has been removed from the packing diagrams. The structure exists as discrete chains of molecules run ning parallel to the a-axis and exhibits no unusual crystal packing features. As is common with these materials, the azide group is non linear [N12-N13-N14 171.91° (6)] (Chesterton et al. 2006).

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged. The relatively large ratio of minimum to maximum corrections applied in the multiscan process (1:1.15) 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).

supplementary materials sup-2
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 (C-H in the range 0.93-0.98, O-H = 0.82 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints.
A few very weak reflections were ignored in the refinement, and was therefore carried out on only 1095 reflections, not the full 1296 originally collected. Fig. 1. Synthetic scheme.