Current Topics in Medicinal Chemistry - Volume 19, Issue 8, 2019

Nowadays, tuberculosis (TB) is an important global public health problem, being responsible for millions of TB-related deaths worldwide. Due to the increased number of cases and resistance of Mycobacterium tuberculosis to all drugs used for the treatment of this disease, we desperately need new drugs and strategies that could reduce treatment time with fewer side effects, reduced cost and highly active drugs against resistant strains and latent disease. Considering that, 4H-1,3-benzothiazin-4-one is a promising class of antimycobacterial agents in special against TB-resistant strains being the aim of this review the discussion of different aspects of this chemical class such as synthesis, mechanism of action, medicinal chemistry and combination with other drugs.

DNA gyrase is a clinically validated drug target, currently targeted only by fluoroquinolone class of antibacterials. However, owing to increasing drug resistance as well as a concomitant reduction in the availability of newer classes of antibiotics, fluoroquinolones are increasingly being over-utilized in order to treat serious infections, including multi-drug resistant tuberculosis. This, in turn, increases the probability of resistance to fluoroquinolones, which is mediated by a single amino acid change in gyrA, leading to class-wide resistance. In this review, we provide an overview of the recent progress in identifying novel scaffolds which target DNA gyrase and provide an update on their discovery and development status.

Background: Tuberculosis is one of the leading causes of mortality worldwide. Resistance against the frontline anti-tubercular drugs has worsened the already alarming situation, which requires intensive drug discovery to develop new, more effective, affordable and accessible anti-tubercular agents possessing novel modes of action. Objective: Chemical transformation of dihydroartemisinin for anti-tubercular lead optimization. Methods: Dihydroartemisinin, a metabolite of artemisinin was chemically converted into eight acyl derivatives and were evaluated for anti-tubercular potential against H37Rv virulent strain of Mycobacterium tuberculosis by agar-based proportion assay. Further, synergistic activity of 12-O-m-anisoyl dihydroartemisinin was also studied with the front-line anti-TB drugs, isoniazid and rifampicin. Results: The results showed that all the derivatives were active but out of eight, 12-O-m-anisoyl dihydroartemisinin and 12-O-p-anisoyl dihydroartemisinin were significantly active (MIC 25.0 μg/mL). In synergistic activity evaluation, the 12-O-m-anisoyl dihydroartemisinin derivative showed reduction in MIC (by 1/8th, i.e. 3.12 μg/mL and that of rifampicin by ¼th, i.e. 0.05 μg/mL) with the front-line anti-TB drug, rifampicin. The sumfractional inhibitory concentration (Σ FIC) was 0.375. Conclusion: These results suggested a synergistic effect of the 12-O-m-anisoyl dihydroartemisinin with rifampicin and established its base for the development of anti-tubercular agents from an in-expensive and non-toxic natural product. To the best of our knowledge this is the first ever report on the anti-tubercular potential of dihydroartemisinin and its derivatives.

Background and Introduction: Tuberculosis (TB) is a leading infectious disease caused by Mycobacterium tuberculosiswith high morbidity and mortality. Isocitrate lyase (MtbICL), a key enzyme of glyoxylate pathway has been shown to be involved in mycobacterial persistence, is attractive drug target against persistent tuberculosis. Methods: Virtual screening, molecular docking and MD simulation study has been integrated for screening of phytochemical based anti-mycobacterial compounds. Docking study of reported MtbICL inhibitors has shown an average binding affinity score -7.30 Kcal/mol. In virtual screening, compounds exhibiting lower binding energy than calculated average binding energy were selected as top hit compounds followed by calculation of drug likeness property. Relationship between experimental IC50 value and calculated binding gibbs free energy of reported inhibitors was also calculated through regression analysis to predict IC50 value of potential inhibitors. Results: Docking and MD simulation studies of top hit compounds have identified shinjudilactone (quassinoid), lecheronol A (pimarane) and caniojane (diterpene) as potential MtbICL inhibitors. Conclusion: Phytochemical based anti-mycobacterial compound can further developed into effective drugs against persistence tuberculosis with lesser toxicity and side effects.

Background: High numbers of infection with resistant forms of Micobacterium tuberculosis (Mtb) contribute to a constant growing demand in new highly active and effective therapeutics. Current drug discovery efforts directed towards new antituberculosis agents include the development of new inhibitors of enoyl-acyl carrier protein reductase (InhA) that do not require activation by the specific enzymes. Tryptanthrin is a known inhibitor of Mtb InhA and its analogues are investigated as potential agents with antimycobacterial efficiency. Objective: The main objective of the presented research was to develop a new group of tryptanthrin analogues with good inhibition properties against Mtb. Methods: Synthesis of new derivatives of 5H-[1,3,4]thiadiazolo[2,3- b]quinazolin-5-one and evaluation of their activity against Mtb, as well as acute and chronic toxicity studies were carried out. Molecular modeling studies were performed to investigate the binding mechanisms of the synthesized ligands with InhA. Binding energies and non-covalent interactions stabilizing the ligand-receptor complexes were obtained from the results of molecular docking. Results: The most active compound in the obtained series, 2-(propylthio)-5H-[1,3,4]thiadiazolo[2,3- b]quinazolin-5-one, exhibited the superior inhibition activity (up to 100%) against mycobacterial growth at MIC 6.5 μg/mL, showed good affinity to the InhA enzyme in docking studies and demonstrated a very low per oral toxicity in animals falling under the category 5 according to GHS classification. Conclusion: 2-(propylthio)-5H-[1,3,4]thiadiazolo[2,3-b]quinazolin-5-one can be further explored for the development of a new series of compounds active against Mtb.

Background: Mycobacterium Tuberculosis (Mtb) is the causative pathogen of Tuberculosis (TB) and outbreaks are more common among immunosuppressed persons infected with HIV. The current treatment regimens are lengthy and toxic, yet the therapy has remained unchanged for many decades, so there is a need to find new structures with selective mechanism of action. Moreover, the increased incidence of severe disseminated infections produced by undiagnosed Multidrug-resistant (MDR), worsen clinical treatment and contribute the spread of the disease. Objective: The aim of our study was to evaluate the potential of imidazole and triazole moieties for antimycobacterial activity, by synthesizing some 1-(1-(aryl)-2-(2,6-dichlorophenyl)hydrazono)ethyl- 1H-imidazole and 1H-1,2,4-triazole derivatives 2a-l. Methods: The title compounds were obtained via classical organic synthesis. The antimicrobial activity was evaluated using the method of microdilution and the cytotoxicity assay was performed by MTT method. Results: The results indicated that the presence of both the imidazole ring and that of the 2,6- dichlorosubstituted phenyl moiety, is more relevant for inhibitory activity against Mtb than the triazole nucleus and the unsubstituted phenyl ring. Among the series, (E)-1-(2-(5-chlorothiophen-2-yl)-2-(2- (2,6-dichlorophenyl)hydrazono)ethyl)-1H-imidazole derivative 2f and (Z)-1-(2-([1,1’-biphenyl]-4-yl)- 2-(2-(2,6-dichlorophenyl)hydrazono)ethyl]-1H-imidazole derivatives 2e exhibited a promising antimycobacterial property and the latter also displayed a safe cytotoxic profile. Conclusion: The synthesized compounds were studied for their antitubercular activity. Among the series, the compounds 2e and 2f appeared to be the most promising agents and, according to the docking assessment, the compounds could be CYP51 inhibitors. These evidences could be useful for the future development of new antimycobacterial derivatives targeting CYP51 with more specificity for the mycobacterial cell enzyme.

Introduction: As a part of our drug discovery program for anti-tubercular agents, dihydroartemisinin (DHA-1) was screened against Mtb H37Rv, which showed moderate anti-tubercular activity (>25.0 μg/mL). These results prompted us to carry out the chemical transformation of DHA-1 into various derivatives and study their antitubercular potential. Materials and Methods: DHA-1 was semi-synthetically converted into four new acyl derivatives (DHA-1A – DHA-1D) and in-vitro evaluated for their anti-tubercular potential against Mycobacterium tuberculosis H37Rv virulent strain. The derivatives, DHA-1C (12-O-(4-nitro) benzoyl; MIC 12.5 μg/mL) and DHA-1D (12-O-chloro acetyl; MIC 3.12μg/mL) showed significant activity against the pathogen. Results: In silico studies of the most active derivative (DHA-1D) showed interaction with ARG448 inhibiting the mycobacterium enzymes. Additionally, it showed no cytotoxicity towards the Vero C1008 cells and Mouse bone marrow derived macrophages. Conclusion: DHA-1D killed 62% intracellular M. tuberculosis in Mouse bone marrow macrophage infection model. To the best of our knowledge, this is the first-ever report on the antitubercular potential of dihydroartemisinin and its derivatives. Since dihydroartemisinin is widely used as an antimalarial drug; these results may be of great help in anti-tubercular drug development from a very common, inexpensive, and non-toxic natural product.