2-((3,5-Dinitrobenzyl)thio)quinazolinones: Potent Antimycobacterial Agents Activated by Deazaflavin (F)-Dependent Nitroreductase (Ddn).

Swapping the substituents in positions 2 and 4 of the previously synthesized but yet undisclosed 5-cyano-4-(methylthio)-2-arylpyrimidin-6-ones , ring closure, and further optimization led to the identification of the potent antitubercular 2-thio-substituted quinazolinone . Structure-activity relationship (SAR) studies indicated a crucial role for both -nitro substituents for antitubercular activity, while the introduction of polar substituents on the quinazolinone core allowed reduction of bovine serum albumin (BSA) binding (, ). While most of the tested quinazolinones exhibited no cytotoxicity against MRC-5, the most potent compound was found to be mutagenic via the Ames test. This analogue exhibited moderate inhibitory potency against thymidylate kinase, the target of the 3-cyanopyridones that lies at the basis of the current analogues, indicating that the whole-cell antimycobacterial activity of the present -substituted thioquinazolinones is likely due to modulation of alternative or additional targets. Diminished antimycobacterial activity was observed against mutants affected in cofactor F biosynthesis (), cofactor reduction (), or deazaflavin-dependent nitroreductase activity (), indicating that reductive activation of the 3,5-dinitrobenzyl analogues is key to antimycobacterial activity.