2-Deoxy-2,3-O-isopropylidene-2,4-di-C-methyl-β-l-arabinose

X-ray crystallography unequivocally confirmed the stereochemistry of the C atom at position 2 in the carbon scaffold of the title molecule, C10H18O4. The pyranose ring exists in a chair conformation with the methyl group on the C atom in the 2 position in an equatorial configuration. The absolute stereochemistry was determined from the starting material. The crystal structure consists of O—H⋯O hydrogen-bonded chains of molecules running parallel to the b axis.

X-ray crystallography unequivocally confirmed the stereochemistry of the C atom at position 2 in the carbon scaffold of the title molecule, C 10 H 18 O 4 . The pyranose ring exists in a chair conformation with the methyl group on the C atom in the 2 position in an equatorial configuration. The absolute stereochemistry was determined from the starting material. The crystal structure consists of O-HÁ Á ÁO hydrogen-bonded chains of molecules running parallel to the b axis.

Comment
Deoxy sugars play an important role in the natural world; 2-deoxy ribose forms the sugar backbone of DNA whilst L-fucose, 6-deoxy-L-galactose, is involved in a wide range of mammalian glycan mediated responses (Becker and Lowe, 2003).
Whilst the synthesis and biological evaluation of deoxy sugars is relatively common (Yoshihara et al., 2008;Gullapalli et al., 2007), examples of doubly branched analogues are to our knowledge, unknown.
Herein we report the structure of the novel deoxy aldose 3, generated by a short synthetic sequence from di-branched lactone 1 (Booth et al. 2007) (Fig. 1). Hydrogenation of the alkene functionality in 2 could give either epimer at position C-2 of lactone 3 or a mixture of both products. The reaction proved to be extremely stereospecific, generating only one product.
Direct crystallization of lactone 3 generated poor quality crystals, however, after reduction to the lactol, crystallization was facile and X-ray crystallography showed the product to be the arabino compound 4 rather than the ribo compound 5. The absolute stereochemistry was determined from the use of 2-C-methyl-D-ribono-1,4-lactone as starting material.
The pyranose ring adopts a chair conformation with methyl group at position 2 (atom C10 in the crystallogrphic labelling scheme) in the equatorial position (Fig. 2). The crystal structure exists O-H···O hydrogen-bonded chains of molecules lying parallel to the b-axis (Fig. 3). Only classical hydrogen bonding has been considered. There are no unusual crystal packing features.

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.