Cyrhetrenyl chalcones: Synthesis, characterization and antimalarial evaluation

A new series of hybrid organometallic-organic and dinuclear organometallic chalcones containing the cyrhetrenyl fragment were synthesised and characterised. 1H and 13C NMR spectra indicate that these compounds adopt in solution an E-stereochemistry at the Cdouble bond; length as m-dashC bond, as well as the s-cis conformation of the enone moiety. A similar structure was also found for 1-ferrocenyl-3-cyrhetrenyl-2-propen-1-one (2i) by X-ray crystallography in the solid state. The electron-withdrawing capability of the cyrhetrenyl group on the ketonic carbonyl and olefinic (Cβ) carbons correlate properly with the 13C shift of the carbon nuclei of the enone moiety. Evaluation of in vitro antimalarial activity of the compounds against the chloroquine-susceptible strain 3D7 and the chloroquine-resistant strain W2 of Plasmodium falciparum, indicates that these cyrhetrene conjugates are more active compared to their ferrocenic analogues.