New, more effective drugs for the treatment of lung disease caused by non-tuberculous mycobacteria (NTM) are needed. Among NTM opportunistic pathogens, Mycobacterium abscessus is the most difficult to cure and intrinsically multidrug resistant. In a whole-cell screen of a compound collection active against M. tuberculosis, we previously identified the piperidine-4-carboxamide (P4C) MMV688844 (844) as a hit against M. abscessus. Here, we identified a more potent analog of 844 and showed that both the parent and improved analog retain activity against strains representing all three subspecies of the M. abscessus complex. Furthermore, P4Cs showed bactericidal and anti-biofilm activity. Spontaneous resistance against the P4Cs emerged at a frequency of 10−8/CFU and mapped to gyrA and gyrB encoding the subunits of DNA gyrase. Biochemical studies with recombinant M. abscessus DNA gyrase showed that P4Cs inhibit the wild type enzyme but not the P4C resistant mutant. P4C resistant strains showed limited cross-resistance to the fluoroquinolone moxifloxacin, which is in clinical use for the treatment of macrolide resistant M. abscessus disease, and no cross-resistance to the benzimidazole SPR719, a novel DNA gyrase inhibitor in clinical development for the treatment of mycobacterial diseases. Analyses of P4Cs in recA promotor-based DNA damage reporter strains showed induction of recA promoter activity in wild type but not in P4C resistant mutant background. This indicates that P4Cs, similar to fluoroquinolones, cause DNA gyrase-mediated DNA damage. Together, our results show that P4Cs present a novel class of mycobacterial DNA gyrase inhibitors with attractive antimicrobial activities against the M. abscessus complex.

The synthesis of ethyl 2-[(4-methylpyridin-2-yl)amino)-4-(pyridin-2-yl)thiazole- 5-carboxylate via the Hantzsch reaction and partial in situ transesterification during recrystallization from methanol-d 4 to the d 3-methyl ester, resulting in the title solid solution, ethyl 2-[(4-methylpyridin-2-yl)amino)-4-(pyridin-2-yl)thiazole-5-carboxylate–d 3-methyl 2-[(4-methylpyridin-2-yl)amino)-4-(pyridin-2-yl)thiazole-5-carboxylate (0.88/0.12), 0.88C17H16N4O2S·0.12C16D3H11N4O2S, is reported. The refined ratio of ethyl to d 3-methyl ester in the crystal is 0.880 (6):0.120 (6). The pyridine ring is significantly twisted out of the plane of the approximately planar picoline thiazole ester moiety. N—H...N hydrogen bonds between the secondary amino group and the pyridine nitrogen atom of an adjacent symmetry-related molecule link the molecules into polymeric hydrogen-bonded zigzag tapes extending by glide symmetry in the [001] direction. There is structural evidence for intramolecular N...S chalcogen bonding and intermolecular weak C—H...O hydrogen bonds between adjacent zigzag tapes.

The synthesis and structural characterization of N-(6-methoxypyridin-3-yl)-4-(pyridin-2-yl)thiazol-2-amine mono-hydrobromide monohydrate (3) and N-(6-methoxypyridin-3-yl)-4-(pyrazin-2-yl)thiazol-2-amine mono-hydrobromide 0.35 methanol solvate (4) are reported. The crystal structures of 3 (monoclinic, space group P21/n, Z = 4) and 4 (monoclinic, space group, C2/c, Z = 8) feature N,4-diheteroaryl 2-aminothiazoles showing similar molecular conformations but different sites of protonation and thus distinctly different intermolecular hydrogen bonding patterns. In 3, Namine–H⋯Br−, N+pyridine–H⋯Owater, and Owater–H⋯Br− hydrogen bonds link protonated N-(6-methoxypyridin-3-yl)-4-(pyridin-2-yl)thiazol-2-amine and water molecules and bromide anions into a three-dimensional hydrogen-bonded network, whereas intermolecular N+methoxypyridine–H⋯Npyrazine hydrogen bonds result in hydrogen-bonded zigzag chains of protonated N-(6-methoxypyridin-3-yl)-4-(pyrazin-2-yl)thiazol-2-amine molecules in 4.

Mycobacterium abscessus causes difficult-to-cure pulmonary infections. The bacterium is resistant to most anti-infective agents, including first line antituberculosis (anti-TB) drugs. MMV688844 (844) is a piperidine-4-carboxamide (P4C) with bactericidal properties against M. abscessus. We recently identified DNA gyrase as the molecular target of 844. Here, we present in silico docking and genetic evidence suggesting that P4Cs display a similar binding mode to DNA gyrase as gepotidacin. Gepotidacin is a member of the Novel Bacterial Topoisomerase Inhibitors (NBTIs), a new class of nonfluoroquinolone DNA gyrase poisons. Thus, our work suggests that P4Cs present a novel structural subclass of NBTI. We describe structure–activity relationship studies of 844 leading to analogues showing increased antibacterial activity. Selected derivatives were tested for their inhibitory activity against recombinant M. abscessus DNA gyrase. Further optimization of the lead structures led to improved stability in mouse plasma and increased oral bioavailability.

Two polymorphic forms of 1-(4-methylpyridin-2-yl)thiourea (1) and the crystal and molecular structures of the 2-aminothiazoles N-(4-methylpyridin-2-yl)-4-(pyridin-2-yl)thiazol-2-amine (2) and N-(4-methylpyridin-2-yl)-4-(pyrazin-2-yl)thiazol-2-amine (3), derived from 1 and the respective α-bromoketone via the Hantzsch reaction, are described. Both polymorphic forms 1α (space group P21/c, Z = 4) and 1β (space group P21/n, Z = 8) crystallize in the monoclinic system but exhibit distinctly different intermolecular hydrogen bonding patterns. Compound 2 (orthorhombic, space group Pca21, Z = 8) forms polymeric N–H⋯N hydrogen-bonded zigzag tapes in the polar crystal structure, with a significant twisting between the thiazole and pyridine rings. In contrast, the crystal structure of 3 (monoclinic, space group P21/c, Z = 4) features nearly planar centrosymmetric N–H⋯N hydrogen-bonded dimers, which are laterally joined through long C–H⋯N contacts, affording a π⋯π stacked layered structure. Graphic Abstract Two polymorphs of 1-(4-methylpyridin-2-yl)thiourea and the crystal and molecular structures of two 2-aminothiazoles, derived from 1-(4-methylpyridin-2-yl)thiourea and α-bromoketones via Hantzsch reaction, are reported.