Efficient analoging around ethionamide to explore thioamides bioactivation pathways triggered by boosters in Mycobacterium tuberculosis
Résumé
Ethionamide is a key antibiotic prodrug of the second-line chemotherapy regimen to treat tuberculosis. It targets the biosynthesis of mycolic acids thanks to a mycobacterial bioactivation carried out by the Baeyer-Villiger monooxygenase EthA, under the control of a transcriptional repressor called EthR. Recently, the drug-like molecule SMARt-420, which triggers a new transcriptional regulator called EthR2, allowed the derepression a cryptic alternative bioactivation pathway of ethionamide. In order to study the bioactivation of a collection of thioisonicotinamides through the two bioactivation pathways, we developed a new two-step chemical pathway that led to the efficient synthesis of eighteen ethionamide analogues. Measurements of the antimycobacterial activity of these derivatives, used alone and in combination with boosters BDM41906 or SMARt-420, suggest that the two different bioactivation pathways proceed via the same mechanism, which implies the formation of similar metabolites. In addition, an electrochemical study of the aliphatic thioisonicotinamide analogues was undertaken to see whether their oxidation potential correlates with their antitubercular activity measured in the presence or in the absence of the two boosters.