Re-evaluating pretomanid analogues for Chagas disease: Hit-to-lead studies reveal both in vitro and in vivo trypanocidal efficacy.

Phenotypic screening of a 900 compound library of antitubercular nitroimidazole derivatives related to pretomanid against the protozoan parasite Trypanosoma cruzi (the causative agent for Chagas disease) identified several structurally diverse hits with an unknown mode of action. Following initial profiling, a first proof-of-concept in vivo study was undertaken, in which once daily oral dosing of a 7-substituted 2-nitroimidazooxazine analogue suppressed blood parasitemia to low or undetectable levels, although sterile cure was not achieved. Limited hit expansion studies alongside counter-screening of new compounds targeted at visceral leishmaniasis laid the foundation for a more in-depth assessment of the best leads, focusing on both drug-like attributes (solubility, metabolic stability and safety) and maximal killing of the parasite in a shorter timeframe. Comparative appraisal of one preferred lead (58) in a chronic infection mouse model, monitored by highly sensitive bioluminescence imaging, provided the first definitive evidence of (partial) curative efficacy with this promising nitroimidazooxazine class.

Development of (6 R)-2-Nitro-6-[4-(trifluoromethoxy)phenoxy]-6,7-dihydro-5 H-imidazo[2,1- b][1,3]oxazine (DNDI-8219): A New Lead for Visceral Leishmaniasis.

Discovery of the potent antileishmanial effects of antitubercular 6-nitro-2,3-dihydroimidazo[2,1- b][1,3]oxazoles and 7-substituted 2-nitro-5,6-dihydroimidazo[2,1- b][1,3]oxazines stimulated the examination of further scaffolds (e.g., 2-nitro-5,6,7,8-tetrahydroimidazo[2,1- b][1,3]oxazepines), but the results for these seemed less attractive. Following the screening of a 900-compound pretomanid analogue library, several hits with more suitable potency, solubility, and microsomal stability were identified, and the superior efficacy of newly synthesized 6 R enantiomers with phenylpyridine-based side chains was established through head-to-head assessments in a Leishmania donovani mouse model. Two such leads ( R-84 and R-89) displayed promising activity in the more stringent Leishmania infantum hamster model but were unexpectedly found to be potent inhibitors of hERG. An extensive structure-activity relationship investigation pinpointed two compounds ( R-6 and pyridine R-136) with better solubility and pharmacokinetic properties that also provided excellent oral efficacy in the same hamster model (>97% parasite clearance at 25 mg/kg, twice daily) and exhibited minimal hERG inhibition. Additional profiling earmarked R-6 as the favored backup development candidate.

Synthesis and structure-activity studies of biphenyl analogues of the tuberculosis drug (6S)-2-nitro-6-{[4-(trifluoromethoxy)benzyl]oxy}-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazine (PA-824).

A series of biphenyl analogues of the new tuberculosis drug PA-824 was prepared, primarily by coupling the known (6S)-2-nitro-6,7-dihydro-5H-imidazo[2,1-b][1,3]oxazin-6-ol with iodobenzyl halides, followed by Suzuki coupling of these iodides with appropriate arylboronic acids or by assembly of the complete biaryl side chain prior to coupling with the above alcohol. Antitubercular activity was determined under both replicating (MABA) and nonreplicating (LORA) conditions. para-Linked biaryls were the most active, followed by meta-linked and then ortho-linked analogues. A more detailed study of a larger group of para-linked analogues showed a significant correlation between potency (MABA) and both lipophilicity (CLOGP) and the electron-withdrawing properties of terminal ring substituents ( summation operatorsigma). Selected compounds were evaluated for their efficacy in a mouse model of acute Mycobacterium tuberculosis infection. In vivo activity correlated well with the stability of compounds to microsomal metabolism. Three compounds bearing combinations of lipophilic, electron-withdrawing groups achieved >200-fold higher efficacies than the parent drug.