ISOLATION, STRUCTURAL ELUCIDATION AND CONFORMATIONAL-ANALYSIS OF SESQUITERPENE PYRIDINE ALKALOIDS FROM MAYTENUS-EBENIFOLIA REISS - X-RAY MOLECULAR-STRUCTURE OF EBENIFOLINE-W-I

The structures of seven novel alkaloids, ebenifolines W-I, W-II, E-I, E-II, E-III, E-IV and E-V, isolated from Maytenus ebenifolia Reiss., were determined by means of H-1 and C-13 NMR spectroscopic studies, mainly 2D experiments, to be sesquiterpene pyridine alkaloids having either a fifteen- or sixteen-membered ring structure. The conformation of one of these alkaloids, ebenifoline W-I 1, was determined by homodecoupling experiments, NOESY spectra in NMR, and X-ray analysis. The flexibility of the two types of macrocyclic ring systems was studied by their T1-values of C-13 NMR spectroscopy.