C-13 NMR data of the pyrrolizidine alkaloid echimidine

The 13C NMR spectra of nine pyrrolizidine alkaloids of the macrocyclic diester type, seven of thecorresponding N-oxides and of the parent base retronecine have been recorded and the signals assigned. The13C NMR signals were found to be sensitive to structural variation in both the diester moiety and theheterocyclic ring system, providing useful information for structural elucidation, particularly when the ‘HNMR spectra may be difficult to interpre