3-Deoxy-3-fluoro-d-glucopyranose crystallizes from acetone to give a unit cell containing two crystallographically independent molecules. One of these molecules (at site A) is structurally homogeneous and corresponds to 3-deoxy-3-fluoro--d-glucopyranose, C 6 H 11 FO 5 , (I). The second molecule (at site B) is structurally heterogeneous and corresponds to a mixture of (I) and 3-deoxy-3-fluoro--d-glucopyranose, (II); treatment of the diffraction data using partial-occupancy oxygen at the anomeric center gave a high-quality packing model with an occupancy ratio of 0.84:0.16 for (II):(I) at site B. The mixture of -and -anomers at site B appears to be accommodated in the lattice because hydrogen-bonding partners are present to hydrogen bond to the anomeric OH group in either an axial or equatorial orientation. CremerPople analysis of (I) and (II) shows the pyranosyl ring of (II) to be slightly more distorted than that of (I) [ (I) = 3.85 (15) and (II) = 6.35 (16) ], but the general direction of distortion is similar in both structures [' (I) = 67 (2) (B C1,C4 ) and ' (II) = 26.0 (15) ( C3 TB C1 ); B = boat conformation and TB = twistboat conformation]. The exocyclic hydroxymethyl (-CH 2 OH) conformation is gg (gauche-gauche) (H5 anti to O6) in both (I) and (II). Structural comparisons of (I) and (II) to related unsubstituted, deoxy and fluorine-substituted monosaccharides show that the gluco ring can assume a wide range of distorted chair structures in the crystalline state depending on ring substitution patterns.
CommentFluorosugars (Taylor, 1988) are saccharide derivatives in which one or more of the hydroxy groups or H atoms in the saccharide are substituted by fluorine. For example, substitution at the anomeric OH group, giving glycosyl fluorides, activates the anomeric center in chemical glycosylation reactions (Yokoyama, 2000). The altered internal electronic structure in fluorosugars relative to the parent (unsubstituted) saccharide renders them useful for the investigation of enzyme reaction mechanisms, since such substitution can be exploited for the stabilization of putative intermediates along a reaction trajectory (White et al., 1996). In addition, substitution of fluorine for hydroxy groups or H atoms alters the hydrogenbonding character of saccharides, thus affecting their binding properties with various receptors (Buchini et al., 2008).We have been preparing fluorosugars as tools to investigate the mechanisms of protein-bound saccharide rearrangements that accompany non-enzyme-catalyzed protein glycation (Chetyrkin et al., 2008). We reported recently the X-ray crystal structure of 4-deoxy-4-fluoro--d-glucopyranose (4DFG) and showed that its packing and that of the parent -dglucopyranose are very similar (Zhang et al., 2010). Furthermore, we showed that the anomeric configuration of 4DFG molecules in the crystal lattice is not completely homogeneous; careful fitting of the electron density at O1 showed that a small percentage (<5%) of the -anomer appears to be accommodated in the lattice. Labeling schem...