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

his 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).