Received 25 August 2006
aDepartment of Organic Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, England, and bChemical Crystallography Laboratory, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, England
Correspondence e-mail: email@example.com
The crystalline form of 1-deoxy-D-sorbose, C6H12O5, is shown to be 1-deoxy--D-sorbopyranose. This is the first reported crystal structure of a 1-deoxyketose. The absolute configuration was determined by the use of D-xylose as the starting material. The crystal structure has a three-dimensional hydrogen-bonded network.
Although the driving force for the large-scale production of rare sugars by biotechnological (Izumori, 2002; Granström et al., 2004) and chemical (Beadle et al., 1992) methods is driven by the demand for alternative foodstuffs (Skytte, 2002), rare monosaccharides such as D-psicose (Takata et al., 2005; Matsuo et al., 2006) and D-allose (Sui et al., 2005; Hossain et al., 2006) have significant chemotherapeutic properties. As well as being useful for their potential biological properties, the 1-deoxyketoses are likely to provide a new set of building blocks for the synthesis of a wide variety of complex biomolecules. However, the properties of 1-deoxyketoses have been little studied to date; there are no reports of the crystal structure of any of the four diastereomers. As part of our work to extend the range of simple monosaccharide derivatives, 1-deoxy-D-sorbose, (4), was synthesized. Although the compound has been prepared previously (James & Angyal, 1972; Dills & Meyer, 1976), a solution of the compound contains a mixture of equilibrating structures (Angyal et al., 1976). 1-Deoxy-D-sorbose was readily crystallized and this paper firmly establishes that it exists in the crystalline state as the -anomer of the pyranose ring form, (5), in a chair conformation.
In summary, 1-deoxy-D-sorbose, (4), exists in the crystalline state as 1-deoxy--D-sorbopyranose, (5). The absolute configuration was determined by the use of D-xylose as the starting material. A D-sugar is defined by the absolute stereochemistry at C-5 (relative to D-glyceraldehyde); see http://www.chem.qmw.ac.uk/iupac/2carb/ for an explanation of carbohydrate nomenclature (IUPAC-IUBMB, 1996). The present X-ray crystal structure determined the stereochemistry at the anomeric position (C1) as being , with the hydroxyl group in the axial position.
The crystal structure of (5) has a three-dimensional hydrogen-bonded network, with each molecule interacting with six neighbours (Fig. 2). The hydrogen bonds themselves form a discrete continuous chain: O10O7, O7O9, O9O8 and O8O6, with O10 at the head of the chain as a donor and O6 at the tail as an acceptor (Fig. 3).
| || Figure 1 |
The molecular structure of the title compound, with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radii.
| || Figure 2 |
The crystal structure of (5), projected along the b axis, showing the three-dimensional hydrogen-bonding network (dotted lines). The hydrogen-bond chain involving atoms O6, O7, O8, O9 and O10 is highlighted in orange.
| || Figure 3 |
A projection of the crystal structure along the c axis, showing the five molecules linked by the discrete hydrogen-bond chain, in which the HO hydrogen bonds are shown in orange.
For the synthesis of 1-deoxy-D-sorbose, the tribenzylated derivative of D-xylose, (1) (Barker & Fletcher, 1961; Postema et al., 2000), was oxidized to the lactone, (2), with acetic anhydride and dimethyl sulfoxide (Calzada et al., 1995). Addition of methyl lithium to the protected lactone, (2), afforded the lactol, (3). Subsequent hydrogenation yielded 1-deoxy-D-sorbose, (4) (Jones et al., in preparation). The title compound, (5), was recrystallized from a mixture of ethyl acetate and methanol (3:1) to give colourless crystals (m.p. 425-427 K). D20 50.2 (c 1.0 in H2O).
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the known starting materials. The H atoms were all located in a difference map, but those attached to C 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 Å and O-H = 0.82 Å and Uiso(H) in the range 1.2-1.5Ueq(C,O)], after which they were refined with riding constraints.
Data collection: COLLECT (Nonius, 2001); cell refinement: DENZO/SCALEPACK (Otwinowski & Minor, 1997); data reduction: DENZO/SCALEPACK; program(s) used to solve structure: SIR92 (Altomare et al., 1994); program(s) used to refine structure: CRYSTALS (Betteridge et al., 2003); molecular graphics: CAMERON (Watkin et al., 1996); software used to prepare material for publication: CRYSTALS.
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