The preferred conformation of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride. An X-ray crystallographic and 2-dimensional proton nuclear magnetic resonance study

The preferred conformation of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride has been determined in the solid state by X-ray crystallography and in aqueous solution by 2-dimensional J-resolved proton nuclear magnetic resonance. Crystals of 2-fluoro-2-deoxy β-D-mannopyranosyl fluoride are monoclinic, a = 4 10.9150(8), b = 4 4.9079(4), c = 4 6.9902(6) Å, β = 105.158(4)°, Z = 2, space group P21. The structure was solved by direct methods and was refined by full-matrix least-squares procedures to R = 0.028 and Rw = 0.031 for 797 reflections with I ≥ 3σ(I). The sugar ring was present in an essentially undistorted 4C1 chair conformation. Weak, but significant interactions, presumably hydrogen bonding of the type OH … F and CH … F, are observed within the crystal lattice. Coupling constants observed in the proton nmr were consistent only with a 4C1 chair conformation in solution. These observations are briefly discussed in terms of recent findings concerning the interaction of fluorodeoxy sugars with enzymic binding sites.