Despite the established treatment regimens, tuberculosis remains an alarming threat to public health according to WHO. Novel agents are needed to overcome the increasing rate of resistance and perhaps achieve eradication. As part of our long-term research on pyrazine derived compounds, we prepared a series of their ortho fused derivatives, N-phenyl- and N-benzyl quinoxaline-2-carboxamides, and evaluated their in vitro antimycobacterial activity. In vitro activity against Mycobacterium tuberculosis H37Ra (represented by minimum inhibitory concentration, MIC) ranged between 3.91-500 µg/mL, with most compounds having moderate to good activities (MIC < 15.625 µg/mL). The majority of the active compounds belonged to the N-benzyl group. In addition to antimycobacterial activity assessment, final compounds were screened for their in vitro cytotoxicity. N-(naphthalen-1-ylmethyl)quinoxaline-2-carboxamide (compound 29) was identified as a potential antineoplastic agent with selective cytotoxicity against hepatic (HepG2), ovarian (SK-OV-3), and prostate (PC-3) cancer cells lines. Molecular docking showed that human DNA topoisomerase and vascular endothelial growth factor receptor could be potential targets for 29.

• Keywords
• Mycobacterium tuberculosis, antimycobacterial, cytotoxicity, molecular docking, pyrazinamide, quinoxaline, tuberculosis,
• Publication type
• Journal Article MeSH

According to the World Health Organization, tuberculosis is still in the top ten causes of death from a single infectious agent, killing more than 1.7 million people worldwide each year. The rising resistance developed by Mycobacterium tuberculosis against currently used antituberculars is an imperative to develop new compounds with potential antimycobacterial activity. As a part of our continuous research on structural derivatives of the first-line antitubercular pyrazinamide, we have designed, prepared, and assessed the in vitro whole cell growth inhibition activity of forty-two novel 5-alkylamino-N-phenylpyrazine-2-carboxamides with various length of the alkylamino chain (propylamino to octylamino) and various simple substituents on the benzene ring. Final compounds were tested against Mycobacterium tuberculosis H37Ra and four other mycobacterial strains (M. aurum, M. smegmatis, M. kansasii, M. avium) in a modified Microplate Alamar Blue Assay. We identified several candidate molecules with micromolar MIC against M. tuberculosis H37Ra and low in vitro cytotoxicity in HepG2 cell line, for example, N-(4-hydroxyphenyl)-5-(pentylamino)pyrazine-2-carboxamide (3c, MIC = 3.91 µg/mL or 13.02 µM, SI > 38) and 5-(heptylamino)-N-(p-tolyl)pyrazine-2-carboxamide (4e, MIC = 0.78 µg/mL or 2.39 µM, SI > 20). In a complementary screening, we evaluated the in vitro activity against bacterial and fungal strains of clinical importance. We observed no antibacterial activity and sporadic antifungal activity against the Candida genus.

• Keywords
• alkylamino derivatives, antibacterial, antifungal, antimycobacterial, cytotoxicity, pyrazinamide,
• MeSH
• Antitubercular Agents chemical synthesis   chemistry   isolation & purification   pharmacology   MeSH
• Humans MeSH
• Microbial Sensitivity Tests MeSH
• Mycobacterium tuberculosis drug effects   MeSH
• Pyrazinamide chemistry   MeSH
• Pyrazines chemistry   MeSH
• Drug Design MeSH
• Drug Development MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antitubercular Agents MeSH
• Pyrazinamide MeSH
• Pyrazines MeSH

We report the design, synthesis, and in vitro antimicrobial activity of a series of N-substituted 3-aminopyrazine-2-carboxamides with free amino groups in position 3 on the pyrazine ring. Based on various substituents on the carboxamidic moiety, the series is subdivided into benzyl, alkyl, and phenyl derivatives. The three-dimensional structures of the title compounds were predicted using energy minimization and low mode molecular dynamics under AMBER10:EHT forcefield. Compounds were evaluated for antimycobacterial, antibacterial, and antifungal activities in vitro. The most active compound against Mycobacterium tuberculosis H37Rv (Mtb) was 3-amino-N-(2,4-dimethoxyphenyl)pyrazine-2-carboxamide (17, MIC = 12.5 µg/mL, 46 µM). Antimycobacterial activity against Mtb and M. kansasii along with antibacterial activity increased among the alkyl derivatives with increasing the length of carbon side chain. Antibacterial activity was observed for phenyl and alkyl derivatives, but not for benzyl derivatives. Antifungal activity was observed in all structural subtypes, mainly against Trichophyton interdigitale and Candida albicans. The four most active compounds (compounds 10, 16, 17, 20) were evaluated for their in vitro cytotoxicity in HepG2 cancer cell line; only compound 20 was found to exert some level of cytotoxicity. Compounds belonging to the current series were compared to previously published, structurally related compounds in terms of antimicrobial activity to draw structure activity relationships conclusions.

• Keywords
• aminopyrazine, antibacterial activity, antifungal activity, antimycobacterial activity, cytotoxicity, pyrazinamide derivatives,
• MeSH
• Anti-Bacterial Agents chemical synthesis   chemistry   pharmacology   MeSH
• Antifungal Agents pharmacology   MeSH
• Bacteria drug effects   MeSH
• Cell Death drug effects   MeSH
• Hep G2 Cells MeSH
• Fungi drug effects   MeSH
• Humans MeSH
• Microbial Sensitivity Tests MeSH
• Molecular Conformation MeSH
• Pyrazines chemical synthesis   chemistry   pharmacology   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Anti-Bacterial Agents MeSH
• Antifungal Agents MeSH
• Pyrazines MeSH

Aminodehalogenation of 3-chloropyrazine-2-carboxamide with variously substituted benzylamines yielded a series of fifteen 3-benzylaminopyrazine-2-carboxamides. Four compounds possessed in vitro whole cell activity against Mycobacterium tuberculosis H37Rv that was at least equivalent to that of the standard pyrazinamide. MIC values ranged from 6 to 42 μM. The best MIC (6 μM) was displayed by 3-[(4-methylbenzyl)amino]pyrazine-2-carboxamide (8) that also showed low cytotoxicity in the HepG2 cell line (IC50 ≥ 250 μM). Only moderate activity against Enterococcus faecalis and Staphylococcus aureus was observed. No activity was detected against any of tested fungal strains. Molecular docking with mycobacterial enoyl-ACP reductase (InhA) was performed to investigate the possible target of the prepared compounds. Active compounds shared common binding interactions of known InhAinhibitors. Antimycobacterial activity of the title compounds was compared to the previously published benzylamino-substituted pyrazines with differing substitution on the pyrazine core (carbonitrile moiety). The title series possessed comparable activity and lower cytotoxicity than molecules containing a carbonitrile group on the pyrazine ring.

• Keywords
• antibacterials, antifungals, benzylamines, cytotoxicity, microwave-assisted, pyrazinamide, tuberculosis,
• MeSH
• Amides chemistry   MeSH
• Anti-Bacterial Agents chemical synthesis   pharmacology   MeSH
• Antifungal Agents chemical synthesis   pharmacology   MeSH
• Anti-Infective Agents chemical synthesis   pharmacology   MeSH
• Antitubercular Agents chemical synthesis   pharmacology   MeSH
• Humans MeSH
• Microbial Sensitivity Tests MeSH
• Molecular Structure MeSH
• Pyrazinamide chemical synthesis   pharmacology   MeSH
• Pyrazines chemistry   MeSH
• Molecular Docking Simulation MeSH
• Structure-Activity Relationship MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Amides MeSH
• Anti-Bacterial Agents MeSH
• Antifungal Agents MeSH
• Anti-Infective Agents MeSH
• Antitubercular Agents MeSH
• Pyrazinamide MeSH
• Pyrazines MeSH