Circular dichroism of naphthyltetrahydroisoquinoline alkaloids: calculation of CD spectra by semiempirical methods

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

“…It turns out that all major peaks of the calculated spectra are shifted by 10-20 nm to longer wavelengths as compared with the measured ones, which was also observed and discussed in previous work [7][8][9]. The calculated spectrum of isoancistrocladine (Fig.…”

“…As already described in earlier papers [7,8], we perform the geometry optimization and the calculation of the CD spectra of isoancistrocladine (2a) and isohamatine (2b) using the semiempirical method AMI [13] included in the program package MOPAC 6.0 [14]. Starting from the structures containing bond lengths and bond angles taken from the literature [15], we calculated the global energetic minimum structure by optimizing all internal coordinates, i.e.…”

“…Regarding ancistrocladine (la), one of the most widespread naphthylisoquinoline alkaloids [11, we have established a theoretical procedure for the calculation of CD spectra as an efficient analytic tool for the elucidation of the absolute stereostructure at the biaryl axis [7], and we have subsequently applied it to a broad variety of further related but also structurally most different chiral compounds [8,9]. Another diastereomer of ancistrocladine (la) is the Cl-epimeric and thus cisconfigured related alkaloid, isoancistrocladine (2a), an oxidation-sensitive, and thus relatively unstable compound, recently isolated from the tropical liana, A. heynenaus [10].…”

The Assignment of Absolute Stereostructures through Quantum Chemical Circular Dichroism Calculations

“…[45] A detailed computational analysis of these natural biaryls revealed that the CD spectra expected for different conformational species -just differing in the dihedral angles at the biaryl axis -gave nearly opposite CD spectra, even if belonging to the very same atropodiastereomer! It was thus only by taking all of these structures into account by Boltzmann weighting that a reliable prediction of the CD behavior succeeded.…”

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

“…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…”