Co-crystals of 3-deoxy-3-fluoro-α-D-glucopyranose and 3-deoxy-3-fluoro-β-D-glucopyranose

Abstract

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-β-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-α-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 α- and β-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. Cremer-Pople analysis of (I) and (II) shows the pyranosyl ring of (II) to be slightly more distorted than that of (I) [θ((I)) = 3.85 (15)° and θ((II)) = 6.35 (16)°], but the general direction of distortion is similar in both structures [ϕ((I)) = 67 (2)° (B(C1,C4)) and ϕ((II)) = 26.0 (15)° ((C3)TB(C1)); B = boat conformation and TB = twist-boat 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.