STEREOCHEMICAL ASSIGNMENT OF TERTIARY HYDROXYL GROUP IN DITERPENE FURAN GLYCOSIDES BY PYRIDINE INDUCED SHIFTS, C-13-NMR AND 2D-NMR SPECTROSCOPY

The stereochemistry of the tertiary hydroxyl group in diterpene furan glycosides viz. cordifolisides D (1) and cordifoliside E (2) has been assigned on the basis of pyridine solvent induced shifts (PIS) in the H-1 and C-13 NMR spectra. The methyl and the methylene groups occupyin g positions vicinal, 1,3-diaxial and geminal to the tertiary hydroxyl group were deshielded to different extent depending on the dihedral an gle. The stereochemical assignments are well supported by C-13-gamma s hifts and 2D Overhauser spectroscopy.