The Absolute Configuration of Isoancistrocladine and 'Isohamatine' by Quantumchemical CD-Calculations

Abstract

The absolute configuration of the naphthylisoquinolines isoancistrocladine and isohamatine at the biaryl axis was determined by comparing the measured and the calculated CD spectra.In order to calculate these spectra we used the CNDO/S method in combination with a Boltzmann weighting of conformers with different dihedral angles at the biaryl axis. The Boltzmann factors were obtained with the AM 1 method.

MD‐based CD calculations for the assignment of the absolute axial configuration of the naphthylisoquinoline alkaloid dioncophylline A

“…In the CI calculation we used 169 singly excited singlet configurations, resulting from the excitation of one electron from the 13 highest occupied into one of the 13 lowest unoccupied molecular orbitals. The rotational strengths were obtained using the origin‐independent formalism,37 and were multiplied with Gaussian functions with the following half‐bandwidths: 6.02 nm for transitions below 180 nm, 6.72 nm for transitions between 180 and 235 nm, and 7.68 nm for transitions above 235 nm 18. Finally, the total spectrum was obtained by adding the single spectra after Boltzmann weighting them at a temperature of 289 K using the steric energy of the corresponding structure.…”

“…To get the overall theoretical CD spectrum we averaged the single CD spectra after Boltzmann weighting them. This well‐known procedure succeeded in the determination of the absolute configuration at the biaryl axis of molecules like 1a and 1b as described in earlier articles,18, 24, 25 but it fails for dioncophylline A ( 2 ), which has a rotationally more flexible biaryl framework compared to 1a and 1b due to the presence of only three ortho ‐substituents next to the stereogenic axis 26…”

“…For the assignment of the absolute configuration at the biaryl axis a comparison of the experimental and the semiempirically calculated CD spectrum has been shown to be a most helpful tool 15–22. To take into account the flexibility around the biaryl axis we first calculated in this article the single spectra of several rotamers of the molecule using the force field CVFF for geometry optimization and the semiempirical CNDO/2S method23 for calculation of the CD spectra.…”

Absolute Configuration in 4-Alkyl- and 4-Aryl-3,4-dihydro-2(1H)-pyrimidones: A Combined Theoretical and Experimental Investigation

“…Ab initio calculations of electronic excitation energies were also done by the single excitation configuration interaction (CIS) procedure (Gaussian 98). CD spectra were simulated 24,[47][48][49] as sums of Gaussians centered at the wavelengths of the corresponding electronic transitions and multiplied by the calculated rotational strength. An empirical half bandwidth of 7 nm at 1/e of the maximum 24,49…”

β-Phenylethylamines and the isoquinoline alkaloids (July 1998 to June 1999)

“…29 The absolute configurations of the known isoancistrocladine 19 and its rotamer, isohamatine, have been determined from their CD spectra. 31 Dionocophyllinol is the first 4-hydroxytetrahydroisoquinoline reported in this series, and korundamine A is the first unsymmetrical dimer of a 5-naphthyl and a 7-naphthylisoquinoline. The latter alkaloid shows antiviral activity against HIV-1 and antimalarial activity against Plasmodium falciparum.…”