NMR assignments of ellagic acid derivatives

HMBC spectroscopy optimized for small couplings was employed to determine the four-bend and two-bond proton carbon correlations on the aromatic rings of ellagic acid derivatives. Complete C-13 NMR assignments of 3'-O-methyl-3,4-methylenedioxyellagic acid 4'-O-beta-D-glucopyranoside (1), 3,3'-di-O-methylellagic acid 4'-O-beta-D-xylopyranoside (2), 3,3',4-tri-O-methylellagic acid 4'-O-beta-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 C-13 NMR signals of phenolic compounds with highly oxygenated quaternary carbons. Copyright (C) 1999 John Wiley & Sons, Ltd.