A hit expansion of 3-benzamidopyrazine-2-carboxamide: Toward inhibitors of prolyl-tRNA synthetase with antimycobacterial activity.

This study presents an exploration of the chemical space around derivatives of 3-benzamidopyrazine-2-carboxamides, previously identified as potent antimycobacterial compounds with predicted binding to mycobacterial prolyl-transfer RNA synthetase. New urea derivatives (Series-1) were generally inactive, probably due to their preference for cis-trans conformation (confirmed by density functional theory calculations and experimentally by nuclear overhauser effect spectroscopy NMR). Series-2 (3-benzamidopyrazine-2-carboxamides with disubstituted benzene ring) demonstrated that substituents larger than fluorine are not tolerated in the ortho position of the benzene ring. This series brought two new compounds (21: R = 2-F, 4-Cl and 22: R = 2-F, 4-Br) with in vitro activity against Mycobacterium tuberculosis H37Rv as well as multidrug-resistant clinical isolates, with minimum inhibitory concentration ranging from 6.25 to 25 µg/mL. The lactone-type derivatives 4H-pyrazino[2,3-d][1,3]oxazin-4-ones (Series-3) were inactive, but solvent stability studies of compound 29 indicated that they might be developed to usable lactone prodrugs of inhibitors of mycobacterial aspartate decarboxylase (PanD).

Adenosine-Mimicking Derivatives of 3-Aminopyrazine-2-Carboxamide: Towards Inhibitors of Prolyl-tRNA Synthetase with Antimycobacterial Activity.

Multidrug-resistant tuberculosis (MDR-TB) poses a significant threat to mankind and as such earned its place on the WHO list of priority pathogens. New antimycobacterials with a mechanism of action different to currently used agents are highly required. This study presents the design, synthesis, and biological evaluation of 3-acylaminopyrazine-2-carboxamides derived from a previously reported inhibitor of human prolyl-tRNA synthetase. Compounds were evaluated in vitro against various strains of mycobacteria, pathogenic bacteria, and fungi of clinical significance. In general, high activity against mycobacteria was noted, while the antibacterial and antifungal activity was minimal. The most active compounds were 4'-substituted 3-(benzamido)pyrazine-2-carboxamides, exerting MIC (Minimum Inhibitory Concentration) from 1.95 to 31.25 µg/mL. Detailed structure-activity relationships were established and rationalized in silico with regard to mycobacterial ProRS as a probable target. The active compounds preserved their activity even against multidrug-resistant strains of Mycobacterium tuberculosis. At the same time, they were non-cytotoxic against HepG2 human hepatocellular carcinoma cells. This project is the first step in the successful repurposing of inhibitors of human ProRS to inhibitors of mycobacterial ProRS with antimycobacterial activity.