Circular dichroism of michellamines: Independent assignment of axial chirality by calculated and experimental CD spectra

Abstract

The circular dichroic behavior of the michellamines, dimeric naphthylisoquinoline alkaloids, was investigated. Due to the molecular size and conformational flexibility, which makes direct calculations of the CD spectra very difficult, and because of the lack of direct standards for an empirical comparison, there is no simple possibility for the interpretation of the CD spectra of such quateraryls. The chiroptical contributions of the particular stereogenic elements were shown to behave largely additively and thus allow comparison of spectra of the quateraryls with those of the corresponding ‘monomeric’ naphthylisoquinolines. This comparison was performed first of all with the experimental and theoretical CD spectra of ancistrobrevine B, then with the predicted spectra of the authentic molecular ‘halves’ of the michellamines.