Circular Dichroism Studies on Anthracycline Antitumor Compounds. Relationship between the Molecular Structure and the Spectroscopic Data

Abstract

The band assignment of the circular dichroism (CD) spectra of anthracyclines can provide us with the tools to study the interaction of these molecules with biomolecules, such as DNA and membranes, and also with metal ions. This paper reports the CD spectra of 17 anthracycline derivatives and the tentative assignment of the bands to specific electronic transitions. The deprotonation of some anthracyclines, such as doxorubicin, daunorubicin, and idarubicin, have been also studied in order to characterize the electronic transitions involved in the acid-base process. Our evidence suggests the following assignment. The position of the band assigned to π→π* transition, polarized along the short axis of the molecule (~290nm), does not depend on the hydroxyl group at C(11) (presence and/or ionization state), whereas the position of the band assigned to the π→π* transition (~480nm), polarized along the long axis, is strongly dependent on it. Concerning the n→π* transitions, the bands at ~320 and ~350nm have a strong contribution of the n→π * C(12)=O transition and the n→π * C(5)=O transition, respectively.