Isolation of the pyrrolizidine alkaloid intermedine-N-oxide from Cerinthe glabra and ab initio calculation of its 13C NMR shifts

Abstract

The pyrrolizidine alkaloid intermedine-N-oxide was isolated from Cerinthe glabra for the first time. Due to the questionable assignments of NMR signals of this compound in previous literature reports ab initio calculations of the 13C NMR values based on the GIAO approach, using HF and B3LYP levels of theory and the four basis sets 6-31G(d), 6-311G(d), 6-31G(d,p), and 6-311G(d,p) were performed. The assignments obtained this way are in very good accordance with the experimental values. © 2012 Verlag der Zeitschrift für Naturforschung.