Rapid and unambiguous assignment of proton-deficient N-acyl amidine indole alkaloid by a combination of calculation methods

Abstract

The unprecedently rearranged 6/5/8/6/5 pentacyclic monoterpenoid indole alkaloid voafriamidine from Voacanga africana contains an uncommon N-acyl amidine structural motif that forms a unique 2,4-diazatricycle-[6,5,11,8,03,7] tetradecane skeleton. Despite the lack of proper NMR correlations for the related quaternary carbon and nitrogen, the complex structure was finally elucidated by the combination of ACD/Structure Elucidator, density functional theory (DFT) calculations of the NMR spectra and electronic circular dichroism (ECD) analyses.