Antimalarial Dibenzannulated Medium-Ring Keto Lactams.

Area of Science:

• Medicinal Chemistry
• Parasitology
• Drug Discovery

Background:

• The urgent need for novel antimalarial agents is driven by widespread drug resistance.
• Exploring new chemical scaffolds is crucial for identifying compounds with unique mechanisms of action.
• Dibenzannulated medium-ring keto lactams represent an unexplored class of compounds for antimalarial drug development.

Purpose of the Study:

• To discover and characterize a new class of antimalarial compounds, dibenzannulated medium-ring keto lactams.
• To evaluate the in vitro antimalarial activity, pharmacokinetic properties, and cytotoxicity of these novel compounds.
• To investigate the potential mechanism of action, including metabolic conversion to active species.

Main Methods:

• Synthesis and purification of a series of dibenzannulated medium-ring keto lactams.
• Assessment of antimalarial activity against Plasmodium falciparum using in vitro assays (IC50 determination).
• Evaluation of physicochemical properties (LogD7.4, kinetic solubility) and metabolic stability (CLint in human liver microsomes).
• Cytotoxicity testing against mammalian cell lines and activity profiling against other protozoal pathogens.
• Investigation of in vitro and in vivo metabolic conversion to identify potential active metabolites.

Main Results:

• Dibenzannulated medium-ring keto lactams were identified as a novel antimalarial chemotype.
• Compounds exhibited a range of LogD7.4 values (<0 to 3) and good kinetic solubilities.
• More polar compounds (<2 LogD7.4) showed enhanced metabolic stability (<50 μL/min/mg protein).
• Most compounds displayed low cytotoxicity (>30 μM IC50) with no correlation to antiplasmodial activity.
• Four potent compounds achieved Plasmodium falciparum IC50 values of 4.2–9.4 nM with high in vitro selectivity indices (>670).
• These compounds were significantly less potent against Trypanosoma brucei rhodesiense, Trypanosoma cruzi, and Leishmania donovani, but potent against Toxoplasma gondii (80–200 nM IC50).
• Keto lactams were converted to poorly soluble 4(1H)-quinolone transannular condensation products in vitro and in vivo.
• Similar antimalarial potencies of keto lactam-quinolone pairs suggest quinolones contribute to activity.

Conclusions:

• Dibenzannulated medium-ring keto lactams represent a promising new class of antimalarial drug candidates.
• The compounds possess favorable drug-like properties, including good solubility, metabolic stability, and low cytotoxicity.
• The observed antimalarial activity is likely mediated, in part, by their conversion to active quinolone metabolites.