The conformation of tetrafluorinated methyl galactoside anomers: crystallographic and NMR studies.

Carbohydrate research

PubMedID: 21531398

Linclau B, Golten S, Light M, Sebban M, Oulyadi H. The conformation of tetrafluorinated methyl galactoside anomers: crystallographic and NMR studies. Carbohydr Res. 2011;346(9):1129-39.
The first single-crystal X-ray diffraction study of tetrafluorinated monosaccharide derivatives is presented. Both a- and ß-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 ß-anomer shows a clear segregation between fluorinated and hydrophilic domains, while for the a-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)).