New ferrocenic pyrrolo[1,2-a]quinoxaline derivatives: synthesis, and in vitro antimalarial activity

Bioorg Med Chem. 2008 Oct 15;16(20):9133-44. doi: 10.1016/j.bmc.2008.09.038. Epub 2008 Sep 17.

Abstract

Following our search for antimalarial compounds, novel series of ferrocenic pyrrolo[1,2-a]quinoxaline derivatives 1-2 were synthesized from various substituted nitroanilines and tested for in vitro activity upon the erythrocytic development of Plasmodiumfalciparum strains with different chloroquine-resistance status. The pyrrolo[1,2-a]quinoxalines 1 were prepared in 6-8 steps through a regioselective palladium-catalyzed monoamination by coupling 4-chloropyrrolo[1,2-a]quinoxalines with 1,3-bis(aminopropyl)piperazine or -methylamine using Xantphos as the ligand. The ferrocenic bispyrrolo[1,2-a]quinoxalines 2 were prepared by reductive amination of previously described bispyrrolo[1,2-a]quinoxalines 9 with ferrocene-carboxaldehyde, by treatment with NaHB(OAc)(3). The best results were observed with ferrocenic pyrrolo[1,2-a]quinoxalines linked by a bis(3-aminopropyl)piperazine. Moreover, it was observed that a methoxy group on the pyrrolo[1,2-a]quinoxaline nucleus and no substitution on the terminal N-ferrocenylmethylamine function enhanced the pharmacological activity. Selected compounds 1b, 1f-h, 1l and 2a were tested for their ability to inhibit beta-haematin formation, the synthetic equivalent of hemozoin, by using the HPIA (heme polymerization inhibitory activity) assay. Of the tested compounds, only 2a showed a beta-haematin formation inhibition, but no inhibition of haem polymerization was observed with the other selected ferrocenic monopyrrolo[1,2-a]quinoxaline derivatives 1b, 1f-h and 1l, as the IC(50) values were superior to 10 equivalents.

MeSH terms

  • Amines / chemistry
  • Animals
  • Antimalarials / chemical synthesis*
  • Antimalarials / chemistry
  • Antimalarials / pharmacology*
  • Cell Line
  • Cell Survival / drug effects
  • Ferrous Compounds / chemistry*
  • Humans
  • Hydrophobic and Hydrophilic Interactions
  • Metallocenes
  • Molecular Structure
  • Plasmodium falciparum / drug effects
  • Pyrroles / chemical synthesis*
  • Pyrroles / chemistry
  • Pyrroles / pharmacology*
  • Quinoxalines / chemical synthesis*
  • Quinoxalines / chemistry
  • Quinoxalines / pharmacology*
  • Structure-Activity Relationship

Substances

  • Amines
  • Antimalarials
  • Ferrous Compounds
  • Metallocenes
  • Pyrroles
  • Quinoxalines
  • pyrrolo(1,2-a)quinoxaline
  • ferrocene