Isolation, structural elucidation and conformational analysis of sesquiterpene pyridine alkaloids from Maytenus ebenifolia Reiss. X-Ray molecular structure of ebenifoline W-I

Abstract

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 ¹H and ¹³C 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 ¹³C NMR spectroscopy.