4-Aminoquinoline Antimalarials Containing a Benzylmethylpyridylmethylamine Group Are Active against Drug Resistant Plasmodium falciparum and Exhibit Oral Activity in Mice.

Emergence of drug resistant Plasmodium falciparum including artemisinin-tolerant parasites highlights the need for new antimalarials. We have previously shown that dibemequines, 4-amino-7-chloroquinolines with dibenzylmethylamine (dibemethin) side chains, are efficacious. In this study, analogues in which the terminal phenyl group of the dibemethin was replaced with a 2-pyridyl group and in which the 4-amino-7-chloroquinoline was either maintained or replaced with a 4-aminoquinoline-7-carbonitrile were synthesized in an effort to improve druglikeness. These compounds exhibited significantly improved solubility and decreased lipophilicity and were potent against chloroquine-sensitive (NF54) and -resistant (Dd2 and 7G8) P. falciparum strains with 5/6 having IC50 < 100 nM against the NF54 strain. All inhibited both ß-hematin (synthetic hemozoin) formation and hemozoin formation in the parasite. Parasitemia was reduced by over 90% in P. berghei infected mice in 3/6 derivatives following oral dosing at 4 × 30 mg/kg, with microsomal metabolic stability data suggesting that this could be attributed to highly active metabolites.

Structure-activity relationships for ferriprotoporphyrin IX association and ß-hematin inhibition by 4-aminoquinolines using experimental and ab initio methods.

In order to probe structure-activity relationships of association with ferriprotoporphyrin IX (logK) and inhibition of ß-hematin formation, a series of 4-aminoquinolines with varying substituents at the 7-position (X) have been synthesized. These have been further elaborated by introduction of two different R groups on the 4-amino nitrogen atom in the form of methyl (R=Me) and ethylamine (R=EtNH2) side chains. Data for a previously investigated series containing an N,N-diethyl-ethylamine side chain were also compared with the findings of this study. Experimentally, logK values for the simple 4-aminoquinoline series (R=H) were found to correlate with the hydrophobicity constant (π) of the group X. The logK values for the series with R=Me and EtNH2 were found to correlate with those of the series with R=H. The log of the 50% ß-hematin inhibitory activity (logBHIA50) was found to correlate with logK and either meta (σm) or para (σp) Hammett constants for the series with R=Me and EtNH2, but not the simple series with R=H. To further improve predictability, correlations with ab initio electrostatic parameters, namely Mulliken and CHelpG charges were investigated. The best correlations were found with CHelpG charges which indicated that logK values can be predicted from the charges on atom H-8 and the group X in the quinolinium species computed in vacuum, while logBHIA50 values can be predicted from the CHelpG charges on C-7, C-8 and N-1 for the neutral species in vacuum. These correlations indicate that association and inhibition of ß-hematin formation are separately determined. They also suggest that electron withdrawing groups at the 7-position, but not necessarily hydrophobic groups are required for hemozoin inhibition. The upshot is that the correlations imply that considerably more hydrophilic hemozoin inhibitors are feasible.