Pyrazinamide-derived 1,2,3-triazoles: Antimicrobial evaluation, selective antimycobacterial activity and mechanism of action insights

A series of pyrazinamide-derived 1,2,3-triazoles featuring systematic chlorination of the pyrazine ring and diverse aryl substituents was synthesized and evaluated for antimycobacterial activity. Biological activity screening revealed broad-spectrum antimycobacterial activity and good selectivity toward mycobacteria over other pathogens, with 11 of the prepared compounds showing activity against Mycobacterium tuberculosis (Mtb) H37Ra and/or Mtb H37Rv (MIC ≤62.5 μg/mL). Structure-activity relationship analysis showed that 5-Cl substitution on the pyrazine ring was associated with improved antimycobacterial activity, with the best MIC values observed for compound 7 against Mtb H37Ra (MIC = 1.98 μg/mL) and compound 37 against Mtb H37Rv (MIC = 1.56 μg/mL). The tested compounds retained activity against drug-resistant Mtb isolates and partially against naturally resistant Mycobacterium abscessus, while showing low in vitro cytotoxicity in the HepG2 cell line and favorable selectivity indices. During advanced cytotoxicity testing, both compounds 7 and 37 displayed substantially lower hemolytic activity than bedaquiline, indicating a favorable erythrocyte safety profile within the tested concentration ranges. In vivo toxicity testing on Galleria mellonella showed low acute toxicity for both compounds. Mechanistic studies on compounds 7, 27, 31, and 37 revealed reduced biosynthesis of fatty acids and derived lipids, a phenotype consistent with interference with the Fatty Acid Synthase I (FAS I) system.