Synthesis of ketopyranosyl glycosides and determination of their anomeric configuration on the basis of the three-bond carbon–proton couplings

Anomeric pairs of ketopyranosyl glycosides with various substituents at Cα, Cβ and Cγ were synthesized from the corresponding thioglycosides, and the influence of the Cα–Cβ–Cγ–Hγ torsion angle and substituent effects on the three-bond carbon–proton couplings was studied. The cis coupling constants range from 1 to 2 Hz. The trans couplings are generally as small as 2.3–2.6 Hz; however, for compounds bearing an unsubstituted γ-carbon, a relatively large trans coupling was measured (4.8 Hz). An S-ethyl group at the β-position increases the cis coupling (up to 3.2 Hz) compared to the corresponding O-glycosides.

Graphical abstractThe influence of the Cα–Cβ–Cγ–Hγ torsion angle and substituent effects on the three-bond carbon–proton couplings was studied for ketopyranosyl glycoside anomeric pairs.Figure optionsDownload full-size imageDownload as PowerPoint slide