NMR assignments of ellagic acid derivatives

HMBC spectroscopy optimized for small couplings was employed to determine the four-bond and two-bond proton carbon correlations on the aromatic rings of ellagic acid derivatives. Complete 13C NMR assignments of 3′-O-methyl-3,4-methylenedioxyellagic acid 4′-O-β-D-glucopyranoside (1), 3,3′-di-O-methylellagic acid 4′-O-β-D-xylopyranoside (2), 3,3′,4-tri-O-methylellagic acid 4′-O-β-D-glucopyranoside (3) and ellagic acid (4) were achieved using this technique. This study indicates that optimization of the delay time in the HMBC spectrum is crucial in assigning the 13C NMR signals of phenolic compounds with highly oxygenated quaternary carbons.