Synthesis and study of organometallic PGM complexes containing 2-(2-pyridyl)benzimidazole as antiplasmodial agents

Abstract

Six half-sandwich complexes of iridium (III), rhodium (III), and ruthenium (II) (C1-C6) bearing the N,N’-chelated ligand 2-(2-pyridyl)benzimidazole (L) were synthesized and characterized, three of which, bearing the iodido ligand are new. The complexes were isolated as yellow or orange solids in moderate to good yields. The complexes were tested for their ability to catalyse the hydrogenation of NAD+ to NADH at pH 7 at 37 °C. The iridium complexes (C1 and C2) were found to perform the best with NADH yields of up to 74% after one hour. All of the complexes and the ligand were screened for their ability to inhibit growth of the drug-sensitive strain of malaria-causing parasite Plasmodium falciparum, NF54. The complexes containing the rhodium (III) metal centre had the highest activity with the IC50 values for the chlorido (C3) and iodido (C4) complexes determined to be 11.4 µM and 9.65 µM respectively. Both complexes performed better than the ligand (IC50 = 55.9 µM). Complexes bearing the iodido ligand were found to be favourable in both the catalysis as well as the antimalarial assays.