Quinoline-triazole half-sandwich iridium(III) complexes: synthesis, antiplasmodial activity and preliminary transfer hydrogenation studies

Dalton Trans. 2020 Aug 25;49(33):11543-11555. doi: 10.1039/d0dt01935f.

Abstract

Iridium(iii) half-sandwich complexes containing 7-chloroquinoline-1,2,3-triazole hybrid ligands were synthesised and their inhibitory activities evaluated against the Plasmodium falciparum malaria parasite. Supporting computational analysis revealed that metal coordination to the quinoline nitrogen occurs first, forming a kinetic product that, upon heating over time, forms a more stable cyclometallated thermodynamic product. Single crystal X-ray diffraction confirmed the proposed molecular structures of both isolated kinetic and thermodynamic products. Complexation with iridium significantly enhances the in vitro activity of selected ligands against the chloroquine-sensitive (NF54) Plasmodium falciparum strain, with selected complexes being over one hundred times more active than their respective ligands. No cross-resistance was observed in the chloroquine-resistant (K1) strain. No cytotoxicity was observed for selected complexes tested against the mammalian Chinese Hamster Ovarian (CHO) cell line. In addition, speed-of-action assays and β-haematin inhibition studies were performed. Through preliminary qualitative and quantitative cell-free experiments, it was found that the two most active neutral, cyclometallated complexes can act as transfer hydrogenation catalysts, by reducing β-nicotinamide adenine dinucleotide (NAD+) to NADH in the presence of a hydrogen source, sodium formate.

MeSH terms

  • Animals
  • Antimalarials / chemical synthesis*
  • Antimalarials / pharmacology
  • CHO Cells
  • Chloroquine / chemistry
  • Coordination Complexes / chemical synthesis*
  • Coordination Complexes / pharmacology
  • Cricetulus
  • Hemeproteins / metabolism
  • Humans
  • Hydrogenation
  • Iridium / chemistry*
  • Ligands
  • Models, Molecular
  • NAD / metabolism
  • Plasmodium falciparum / drug effects
  • Quinolines / chemistry*
  • Triazoles / chemistry*

Substances

  • Antimalarials
  • Coordination Complexes
  • Hemeproteins
  • Ligands
  • Quinolines
  • Triazoles
  • NAD
  • hemozoin
  • Iridium
  • Chloroquine