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

An approach for discriminating the threo and erythro configurations of polyacetylene glycosides by H-1 NMR spectroscopy was developed. Using acetic acid-d(4)/D2O as the solvent, a relatively larger (3)J(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.