(-)-Amarbellisine is none other than (-)-montanine: A CASE-3D and dereplication NMR study

The 2013 total synthesis of the putative structure of the (-)-amarbellisine lycorine alkaloid reported very significant differences between the 1H and 13C NMR spectra of the synthesized product and the originally isolated alkaloid, and it was hypothesized that the correct structure should be a diastereoisomer of the originally proposed one. The present CASE-3D configurational analysis, based on DFT predictions of 13C chemical shifts, provided very bad fits for all possible diastereoisomeric lycorine-type structures and reexamination of the NMR data reported for natural (-)-amarbellisine revealed several inconsistencies with the proposed lycorine-like structure. Dereplication of the original 13C shifts and literature searching showed that (-)-amarbellisine is none other than the well-known (-)-montanine alkaloid.