CONCERTED USE OF HOMONUCLEAR AND HETERONUCLEAR 2D-NMR IN THE ELUCIDATION OF THE STRUCTURE OF A NOVEL PENTAESTER OF 19-HYDROXYINGOL FROM EUPHORBIA-MARGINATA SEEDS

Homo- and heteronuclear 2D NMR techniques were used to elucidate the structure of a novel pentaester of 19-hydroxyingol from Euphorbia marginata seeds. The diterpene skeleton was identified by H-1 1D and 2D COSY spectra. Heteronuclear 2D C-13-H-1 shift correlation spectroscopy was used to assign the C-13 signals. The position of the esterified hydroxymethyl group at C-10 was identified by NOE difference spectroscopy. The nature of the five ester groups and their corresponding positions on the diterpene skeleton were identified by a combination of long-range 2D C-13-H-1 correlation experiments and C-13 spectra with H-1 selective decoupling.