Malaria remains one of the most deadly parasitic infectious
diseases in the world.12 The growing emergence of resistance
against conventional antimalarials, including ACT’s, urges the
search for novel and better antiplasmodial drugs, preferably directed
to new targets.13e15
The approval of Malarone for the treatment and prevention of
multidrug resistant malaria validated the bc1 protein complex of
Plasmodium falciparum as target for developing new antimalarial
drugs. The bc1 complex is a homodimeric transmembrane protein
responsible for the transfer of electrons from ubiquinol to cytochrome
c, concomitantly with the vectorial translocation of protons
across the inner mitochondrial membrane16,17 and has been considered
as an important target for antiplasmodial drug design. It
has been proposed that quinolone 3-esters 1 (Scheme 1) target the
Qo site of the enzyme in the bc1 complex, leading to a drop of
mitochondrial function (relevant to provide intermediates for pyrimidine
and ATP synthesis),18,19 collapse of the trans-membrane
electrochemical potential and parasite death.20 However, compounds
1 present some liabilities, such as poor solubility (poor
pharmacokinetic profile).
It is proposed that structure-based optimization of 1 may be
achieved by altering the nature of the substituent in position 7. As
such, a representative library of compounds 1 for SAR studies is
required, and these studies should provide compounds with improved
pharmacological profile that have the potential to be taken
forward as drug leads. Ethyl 4-chloro-7-iodoquinoline-3-
carboxylate (2, CIQCeScheme 2), proved to be instrumental as intermediate
for easy access to a range of new quinolone 3-esters 1.
We report the synthesis and detailed structure of CIQC. The
monomeric structure of CIQC was studied using the matrix isolation
technique coupled to infrared spectroscopy and contemporary
molecular orbital calculations. The structure of crystalline CIQC
was studied by X-ray crystallography and vibrational spectroscopy