Spontaneous resolution of diastereomeric glycosyl isoxazolines: a combined theoretical and experimental study in solution and in the crystalline form.

Abstract

In this study, a glycosyl isoxazoline has been prepared by cycloaddition of phenyl nitrile oxide to 6-O-allyl galactopyranose. Crystallization of the galactosyl isoxazoline resulted in the spontaneous resolution of its two diastereomers. Their conformational behavior has been studied in solution and in crystalline form by NMR and X-ray diffraction analysis showing that both diastereomers have essentially the same OS2 conformation. To complete the study of the diastereomeric isoxazolines, Density Functional Theory was applied. The theoretical and experimental 1H NMR, as well as 13C NMR chemical shifts, showed very good correlation. Furthermore, structures resulting from X-ray analysis provided excellent starting points for DFT calculations.