Structure–Activity Relationships of 3-Hydroxypropanamidines (HPAs) with Potent In Vivo Antimalarial Activity

New treatment strategies are required to combat the spread of drug-resistant <i>Plasmodium falciparum</i> malaria. The synthesis and preclinical evaluation of novel 3-hydroxy-propanamidines (HPAs), with modifications of the phenanthrene and the 4-fluorobenzamidine moieties, has yielded several analogs exhibiting excellent in vitro growth inhibition of drug-sensitive or resistant <i>P. falciparum</i> fresh clinical isolates and culture-adapted strains. No cytotoxicity in the human HepG2 cell line was observed, demonstrating notable parasite selectivity. The most active HPA <b>7d</b>, which features a 4-bromobenzamidine moiety, inhibited the formation of synthetic hemozoin (β-hematin) with IC₅₀ values lower than chloroquine and the lead compound <b>TKK130</b>. Additionally, <b>7d</b> showed a killing rate comparable to chloroquine. In initial in vivo pharmacokinetics, <b>7d</b> displayed a favorable pharmacokinetic profile, with a fast onset and slow elimination phase. In vivo, <b>7d</b> demonstrated dose-dependent curative activity after oral administration in the <i>Plasmodium berghei</i> mouse model, without apparent signs of toxicity.