Assignment of the absolute configuration of zwitterionic and neutral macropodumines by means of TDDFT CD calculations

Abstract

Macropodumines B and C (1, 2) are fused pentacyclic alkaloids previously isolated from the Chinese medicinal plant Daphniphyllum macropodum. Macropodumine B (1) possesses an amazing structural feature of a cyclopentadienyl carbanion, stabilized as a zwitterion by an internal iminium cation, which was confirmed by X-ray diffraction analysis. On the basis of the X-ray geometry, the absolute configuration of 1 was determined by employing the solid-state CD/TDDFT approach. The absolute configuration of 2 was instead determined by using TDDFT CD calculations on DFT-optimized geometries, in comparison with CD spectra recorded in solution.

Solution‐Processed, Undoped, Deep‐Blue Organic Light‐Emitting Diodes Based on Starburst Oligofluorenes with a Planar Triphenylamine Core

“…To determine the absolute configuration of 2 , the ECD spectrum was measured in acetonitrile and compared with the Boltzmann‐averaged spectrum calculated with TD‐DFT for the solution conformers 23. Because of the presence of several flexible torsions, the number of low‐energy minima obtained by a preliminary MMFF conformational analysis for compound 2 was quite large.…”

Curvularin‐Type Metabolites from the Fungus Curvularia sp. Isolated from a Marine Alga

“…[23] Because of the presence of several flexible torsions, the number of low-energy minima obtained by a preliminary MMFF conformational analysis for compound 2 was quite large. However, several structures, which did not fit the NMR spectroscopic data (especially the two different 3 J HH coupling constants between protons 10-H and 11-H), could be discarded.…”

Electronic Circular Dichroism

“…As an example of application of the ss-ECD/TDDFT approach, let us consider macropodumine B (13, Figure 9.6) a unique zwitterionic natural compound containing a rare cyclopentadienyl anion and an iminio counterion [68]. It was isolated from Daphniphyllum macropodum, a Chinese medicinal plant, along with several related metabolites including macropodumine C (14), and its solid-state structure was determined by X-ray analysis.…”

“…Their weighted average was in agreement with the ECD of 14 measured in solution in the low-energy region, while some discrepancy was obtained at high energies (Figure 9.6b). Moreover, the AC assignment required a considerable computational effort, about 4.5 times longer than for 13 [68].…”