Hybridization Approach Toward Novel Antituberculars: Design, Synthesis, and Biological Evaluation of Compounds Combining Pyrazinamide and 4-Aminosalicylic Acid.

Apart from the SARS-CoV-2 virus, tuberculosis remains the leading cause of death from a single infectious agent according to the World Health Organization. As part of our long-term research, we prepared a series of hybrid compounds combining pyrazinamide, a first-line antitubercular agent, and 4-aminosalicylic acid (PAS), a second-line agent. Compound was found to be the most potent, with a broad spectrum of antimycobacterial activity and selectivity toward mycobacterial strains over other pathogens. It also retained its in vitro activity against multiple-drug-resistant mycobacterial strains. Several structural modifications were attempted to improve the in vitro antimycobacterial activity. The δ-lactone form of compound () had more potent in vitro antimycobacterial activity against H37Rv. Compound was advanced for in vivo studies, where it was proved to be nontoxic in and zebrafish models, and it reduced the number of colony-forming units in spleens in the murine model of tuberculosis. Biochemical studies showed that compound targets mycobacterial dihydrofolate reductases (DHFR). An in silico docking study combined with molecular dynamics identified a viable binding mode of compound in mycobacterial DHFR. The lactone opens in human plasma to its parent compound ( = 21.4 min). Compound was metabolized by human liver fraction by slow hydrolysis of the amidic bond ( = 187 min) to yield PAS and its starting 6-chloropyrazinoic acid. The long of compound overcomes the main drawback of PAS (short necessitating frequent administration of high doses of PAS).