Linclau, Bruno, Golten, Samuel, Light, Mark, Sebban, Muriel and Oulyadi, Hassan
The conformation of tetrafluorinated methyl galactoside anomers: crystallographic and NMR studies
Carbohydrate Research, 346, (9), . (doi:10.1016/j.carres.2011.04.007). (PMID:21531398).
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The first single-crystal X-ray diffraction study of tetrafluorinated monosaccharide derivatives is presented.
Both a- and b-methyl 2,3-dideoxy-2,2,3,3-tetrafluoro-D-galactopyranoside anomers adopt the
4C1 conformation. The values for the C1–O1 and C1–O5 bond lengths and the O5–C1–O1–CH3 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 b-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 4C1 conformation in solution (D2O, CDCl3).
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