Hit-to-lead optimization of 2-aminoquinazolines as anti-microbial agents against Leishmania donovani.

Visceral leishmaniasis is a potentially fatal disease caused by infection by the intracellular protist pathogens Leishmania donovani or Leishmania infantum. Present therapies are ineffective because of high costs, variable efficacy against different species, the requirement for hospitalization, toxicity and drug resistance. Detailed analysis of previously published hit molecules suggested a crucial role of 'guanidine' linkage for their efficacy against L. donovani. Here we report the design of 2-aminoquinazoline heterocycle as a basic pharmacophore-bearing guanidine linkage. The introduction of various groups and functionality at different positions of the quinazoline scaffold results in enhanced antiparasitic potency with modest host cell cytotoxicity using a physiologically relevant THP-1 transformed macrophage infection model. In terms of the ADME profile, the C7 position of quinazoline was identified as a guiding tool for designing better molecules. The good ADME profile of the compounds suggests that they merit further consideration as lead compounds for treating visceral leishmaniasis.

Mitigating hERG Liability of Toll-Like Receptor 9 and 7 Antagonists through Structure-Based Design.

hERG is considered to be a primary anti-target in the drug development process, as the K+ channel encoded by hERG plays an important role in cardiac re-polarization. It is desirable to address the hERG safety liability during early-stage development to avoid the expenses of validating leads that will eventually fail at a later stage. We have previously reported the development of highly potent quinazoline-based TLR7 and TLR9 antagonists for possible application against autoimmune disease. Initial experimental hERG assessment showed that most of the lead TLR7 and TLR9 antagonists suffer from hERG liability rendering them ineffective for further development. The present study herein describes a coordinated strategy to integrate the understanding from structure-based protein-ligand interaction to develop non- hERG binders with IC50 >30 µM with retention of TLR7/9 antagonism through a single point change in the scaffold. This structure-guided strategy can serve as a prototype for abolishing hERG liability during lead optimization.

Hit-to-lead optimization of novel phenyl imidazole carboxamides that are active against Leishmania donovani.

Visceral leishmaniasis is a potentially fatal disease caused by the parasitic protists, Leishmania donovani and L. infantum. Current treatments remain unsuitable due to cost, the need for hospitalization, variable efficacy against different species, toxicity and emerging resistance. Herein, we report the SAR exploration of the novel hit 4-Fluoro-N-(5-(4-methoxyphenyl)-1-methyl-1H-imidazole-2-yl)benzamide [1] previously identified from a high throughput screen against Trypanosoma brucei, Trypanosoma cruzi and Leishmania donovani. An extensive and informative set of analogues were synthesized incorporating key modifications around the scaffold resulting in improved potency, whilst the majority of compounds maintained low cytotoxicity against human THP-1 macrophages that are target cells for these pathogens. New lead compounds identified within this study also maintained desirable physicochemical properties, improved metabolic stability in vitro and displayed no significant mitotoxicity against HepG2 cell lines. This compound class warrants continued investigation towards development as a novel treatment for Visceral Leishmaniasis.