Direct Assignment of the <i>Threo</i> and <i>Erythro</i> Configurations in Polyacetylene Glycosides by ¹H NMR Spectroscopy

Abstract

An approach for discriminating the threo and erythro configurations of polyacetylene glycosides by ¹H NMR spectroscopy was developed. Using acetic acid-d₄/D₂O as the solvent, a relatively larger ³J_HH value (7.0 Hz) for the acyclic vicinal diol group was unambiguously assigned to the threo configuration, whereas the smaller value (3.5 Hz) was assigned to the erythro configuration. This convenient method requires no hydrolysis or derivatization and is suitable for micromolar concentrations of polyacetylene glycosides. The underlying mechanism is discussed via visualized conformations.