Circular-dichroism studies on artemisinin and epiartemisinin and their beta-cyclodextrin complexes in solution

The circular dichroism (CD) spectra of the powerful antimalarian active principle artemisinin (ART; 1) from Artemisia annua, and of epiartemisinin (EPI, 2), its C(7) epimer, were studied in solution in the presence and absence of beta-cyclodextrin (beta-cd). A significant inversion of sign in the region of the second electronic transition was detected. The rotational strengths were successfully calculated within the time-dependent density functional theory (DFT), which enabled us to establish a correlation between the molecular recognition and the biological acitivities of the two isomers.