title: The conformation of tetrafluorinated methyl galactoside anomers: crystallographic and NMR studies.
abstract: The first single-crystal X-ray diffraction study of tetrafluorinated monosaccharide derivatives is presented. Both α- and β-methyl 2,3-dideoxy-2,2,3,3-tetrafluoro-d-galactopyranoside anomers adopt the (4)C(1) conformation. The values for the C1-O1 and C1-O5 bond lengths and the O5-C1-O1-CH(3) dihedral angles are in line with what can be expected from the anomeric and exo-anomeric effects. The chair conformations are slightly distorted, presumably due to repulsion between 1,3-diaxial C-O and C-F bonds. The asymmetric unit of both compounds contains up to three independent molecules, which differ in the conformation of the hydroxymethyl group (including in one case a 'forbidden'gg rotamer). The molecular packing of the β-anomer shows a clear segregation between fluorinated and hydrophilic domains, while for the α-anomer the regions of fluorine segregation are broken by interleafing of OMe groups. There is one close OH⋯F contact, which is likely to arise from the crystal packing. NMR studies show that the two anomers also adopt a (4)C(1) conformation in solution (D(2)O, CDCl(3)).
authors.affiliation: School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom. bruno.linclau@soton.ac.uk
authors.forename: Bruno
authors.initials: B
authors.lastname: Linclau
authors.forename: Samuel
authors.initials: S
authors.lastname: Golten
authors.forename: Mark
authors.initials: M
authors.lastname: Light
authors.forename: Muriel
authors.initials: M
authors.lastname: Sebban
authors.forename: Hassan
authors.initials: H
authors.lastname: Oulyadi
mesh_terms: D002236:Carbohydrate Conformation; D018360:Crystallography, X-Ray; D005697:Galactosides / Q000138:chemical synthesis / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular
chemical_list: D005697:Galactosides