Conformational properties of alkyl glucosyl sulfones in solution†

The conformational properties of ester-protected alkyl glucosyl sulfones were studied by means of nuclear magnetic resonance (NMR) and circular dichroism (CD). The equilibrium about the C5–C6 rotational axis (hydroxymethyl group) in polar and apolar media is distributed between the gg and gt rotamers, and the equilibrium contributions of each rotamer are modulated by the steric properties of the aglycone, where an increment in the alkyl substituent's bulkiness leads to progressive increments in gt contributions at the expense of gg. The equilibrium about the glycosidic bond is also dependent on the aglycone's bulkiness and appears more sensitive to the media polarity. Glucosyl sulfones carrying small aglycones, e.g, those substituted with methyl and ethyl groups, show a ϕ torsion predominated by the g+ conformer in apolar media (C₆D₆) and distributed between g− and g+ conformers in a polar solvent (CD₃CN). Compounds substituted with larger alkyl groups, such as iso-propyl and tert-butyl groups, show glycosidic bond conformations predominated by the g− conformer.