Theoretical VCD response in the C-H stretching region of methyl α and β L-Fucopyranoside: a different behavior from monosaccharides

Abstract

Vibrational circular dichroism (VCD) band near 2840 cm−1 in the C-H stretching region is likely to play an important role as an alternative approach to extract stereochemical information namely, glycosidic O-linkages α or β for monosaccharides. Indeed, the experimental results attribute a positive sign for the S absolute configuration (α-anomers for D-sugars and β-anomers for L-sugars) and a negative sign for the R absolute configuration (β-anomers for D-sugar and α-anomers for L-sugar) at C-1 anomeric carbon site. This band was assigned as a symmetric stretching motion of glycosidic methyl group. The idea was to reproduce and explain these experimental results by using theoretical powerful methods and go farther, by studying how to extract stereochemical information from polysaccharides. The obtained theoretical VCD spectra for six monosaccharides were in good agreement with the experiment, except for methyl L-Fucopyranoside. Truly, for this particular sugar, two VCD bands with different signs were obtained for the S-configuration (β form) and assigned both to the symmetric stretching of the methyl glycosidic group. It becomes more interesting to explore this VCD response, to allow us, possibly to examine another way to differentiate between the alpha and the beta forms for this molecule.