The bioisosteric modification of pyrazinamide derivatives led to potent antitubercular agents: Synthesis via click approach and molecular docking of pyrazine-1,2,3-triazoles.

Tuberculosis remains as a major public health risk which causes the highest mortality rate globally and an improved regimen is required to treat the drug-resistant strains. Pyrazinamide is a first-line antitubercular drug used in combination therapy with other anti-TB drugs. Herein, we describe the modification of pyrazinamide structure using bioisosterism and rational approaches by incorporating the 1,2,3-triazole moiety. Three sets of pyrazine-1,2,3-triazoles (3a-o, 5a-o and 9a-l) are designed, synthesized and evaluated for their in vitro inhibitory potency against mycobacterium tuberculosis H37Rv. The pyrazine-1,2,3-triazoles synthesized through the bioisosteric modification displayed improved activity as compared to rationally modified pyrazine-1,2,3-triazoles. Among 42 title compounds, seven derivatives demonstrated significant anti-tubercular activity with the MIC of 1.56 µg/mL, which are two-fold more potent than the parent compound pyrazinamide. Further, the synthesized pyrazinamide analogs demonstrated moderate inhibition activity against several bacterial strains and possessed an acceptable in vitro cytotoxicity profile as well. Additionally, the activity profile of pyrazine-1,2,3-triazoles was validated by performing the molecular docking studies against the Inh A enzyme. Furthermore, in silico ADME prediction revealed good oral bioavailability for the potent molecules.

Pyrazinoates as antiparasitic agents against Trypanosoma cruzi.

This work reports a repurposing study of pyrazinoic acid (1) and methyl (2), ethyl (3) and 2-chloroethyl (4) ester derivatives with antimycobacterial activity, in assays against Trypanosoma cruzi. The compounds and benznidazole, the standard antitrypanosoma drug, were evaluated in concentrations ranging from 100 to 6.25 µg/mL. The results showed that compounds 2 and 3 (EC50 = 182 and 447 µM) significantly reduced the infection rate of the parasite into the mammalian cells at 100 µg/mL (p < 0.05) in a similar way to benznidazole. In addition, all the compounds also significantly reduced the number of intracellular parasites (compound 1 at 50 µg/mL, and compounds 2-4 at 100 µg/mL, p < 0.05) in comparison to the control. Compounds 1 and 2 were more effective than benznidazole at 50 µg/mL (p < 0.001). Moreover, compounds 1-4 did not show significant cytotoxicity against THP-1, J774, and HeLa cells (>1000 µM), indicating that they possess considerable selectivity against the parasites. This report represents the first study of such compounds against T. cruzi, indicating the potential of pyrazinoates as antiparasitic agents.

Design, synthesis and biological activity of pyrazinamide derivatives for anti-Mycobacterium tuberculosis.

A total of 11 pyrazinamide derivatives were designed and synthesised using pyrazinamide as the lead compound, which was optimised by structural modification with alkyl chains, six-membered rings, and bioisosterism, respectively. The target compounds were synthesised using pyrazinecarboxylic acid as the starting material by acylation, amidation, and alkylation, respectively. Their structures were confirmed by 1H NMR, 13C NMR, HRESIMS, and elemental analysis, respectively. The bioactivities of derivatives were assayed using bacteriostatic experiment and minimum inhibitory concentration experiment. It was showed that the derivatives had good inhibitory effect on Mycobacterium tuberculosis. The biological activity of derivative 1f was the best among all compounds, its antibacterial activity was 99.6%, and the minimum inhibitory concentration was 8.0 µg/mL.

Discovery of a novel prolyl-tRNA synthetase inhibitor and elucidation of its binding mode to the ATP site in complex with l-proline.

Prolyl-tRNA synthetase (PRS) is a member of the aminoacyl-tRNA synthetase family of enzymes and catalyzes the synthesis of prolyl-tRNAPro using ATP, l-proline, and tRNAPro as substrates. An ATP-dependent PRS inhibitor, halofuginone, was shown to suppress autoimmune responses, suggesting that the inhibition of PRS is a potential therapeutic approach for inflammatory diseases. Although a few PRS inhibitors have been derivatized from natural sources or substrate mimetics, small-molecule human PRS inhibitors have not been reported. In this study, we discovered a novel series of pyrazinamide PRS inhibitors from a compound library using pre-transfer editing activity of human PRS enzyme. Steady-state biochemical analysis on the inhibitory mode revealed its distinctive characteristics of inhibition with proline uncompetition and ATP competition. The binding activity of a representative compound was time-dependently potentiated by the presence of l-proline with Kd of 0.76 nM. Thermal shift assays demonstrated the stabilization of PRS in complex with l-proline and pyrazinamide PRS inhibitors. The binding mode of the PRS inhibitor to the ATP site of PRS enzyme was elucidated using the ternary complex crystal structure with l-proline. The results demonstrated the different inhibitory and binding mode of pyrazinamide PRS inhibitors from preceding halofuginone. Furthermore, the PRS inhibitor inhibited intracellular protein synthesis via a different mode than halofuginone. In conclusion, we have identified a novel drug-like PRS inhibitor with a distinctive binding mode. This inhibitor was effective in a cellular context. Thus, the series of PRS inhibitors are considered to be applicable to further development with differentiation from preceding halofuginone.

Synthesis of Novel Pyrazinamide Derivatives Based on 3-Chloropyrazine-2-carboxamide and Their Antimicrobial Evaluation.

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.

Antimycobacterial activity of pyrazinoate prodrugs in replicating and non-replicating Mycobacterium tuberculosis.

Tuberculosis (TB) is an important infectious disease caused by Mycobacterium tuberculosis (Mtb) and responsible for thousands of deaths every year. Although there are antimycobacterial drugs available in therapeutics, just few new chemical entities have reached clinical trials, and in fact, since introduction of rifampin only two important drugs had reached the market. Pyrazinoic acid (POA), the active agent of pyrazinamide, has been explored through prodrug approach to achieve novel molecules with anti-Mtb activity, however, there is no activity evaluation of these molecules against non-replicating Mtb until the present. Additionally, pharmacokinetic must be preliminary evaluated to avoid future problems during clinical trials. In this paper, we have presented six POA esters as prodrugs in order to evaluate their anti-Mtb activity in replicating and non-replicating Mtb, and these showed activity highly influenced by medium composition (especially by albumin). Lipophilicity seems to play the main role in the activity, possibly due to controlling membrane passage. Novel duplicated prodrugs of POA were also described, presenting interesting activity. Cytotoxicity of these prodrugs set was also evaluated, and these showed no important cytotoxic profile.

Esters of Pyrazinoic Acid Are Active against Pyrazinamide-Resistant Strains of Mycobacterium tuberculosis and Other Naturally Resistant Mycobacteria In Vitro and Ex Vivo within Macrophages.

Pyrazinamide (PZA) is active against major Mycobacterium tuberculosis species (M. tuberculosis, M. africanum, and M. microti) but not against M. bovis and M. avium. The latter two are mycobacterial species involved in human and cattle tuberculosis and in HIV coinfections, respectively. PZA is a first-line agent for the treatment of human tuberculosis and requires activation by a mycobacterial pyrazinamidase to form the active metabolite pyrazinoic acid (POA). As a result of this mechanism, resistance to PZA, as is often found in tuberculosis patients, is caused by point mutations in pyrazinamidase. In previous work, we have shown that POA esters and amides synthesized in our laboratory were stable in plasma (M. F. Simões, E. Valente, M. J. Gómez, E. Anes, and L. Constantino, Eur J Pharm Sci 37:257-263, 2009, http://dx.doi.org/10.1016/j.ejps.2009.02.012). Although the amides did not present significant activity, the esters were active against sensitive mycobacteria at concentrations 5- to 10-fold lower than those of PZA. Here, we report that these POA derivatives possess antibacterial efficacy in vitro and ex vivo against several species and strains of Mycobacterium with natural or acquired resistance to PZA, including M. bovis and M. avium. Our results indicate that the resistance probably was overcome by cleavage of the prodrugs into POA and a long-chain alcohol. Although it is not possible to rule out that the esters have intrinsic activity per se, we bring evidence here that long-chain fatty alcohols possess a significant antimycobacterial effect against PZA-resistant species and strains and are not mere inactive promoieties. These findings may lead to candidate dual drugs having enhanced activity against both PZA-susceptible and PZA-resistant isolates and being suitable for clinical development.

Synthesis and anti-infective evaluation of 5-amino-N-phenylpyrazine-2-carboxamides.

A series of eleven novel 5-amino-N-phenylpyrazine-2-carboxamides were synthesized and evaluated for in vitro anti-infective properties. Prepared compounds were characterized by IR, 1H NMR and 13C NMR spectra, elementary analysis and melting points. Lipophilicity parameters Log P and ClogP were calculated. None of the compounds was effective against any of tested mycobacterial strains (Mycobacterium tuberculosis H37Rv, M. kansasii, M. avium) up to concentration of 100 µg/mL. 5-amino-N-(2,5-dimethylphenyl) pyrazine-2-carboxamide (3) exerted moderate antibacterial activity against Staphylococcus aureus (MIC = 62.5 µM). No antifungal activity was detected. Several compounds exerted moderate antiviral activity against influenza A viruses at the level of tens of µM.Key words: pyrazinamide antimycobacterial activity antibacterial activity antifungal activity antiviral activity.

Synthesis and Biological Evaluation of N-Alkyl-3-(alkylamino)-pyrazine-2-carboxamides.

A series of N-alkyl-3-(alkylamino)pyrazine-2-carboxamides and their N-alkyl-3-chloropyrazine-2-carboxamide precursors were prepared. All compounds were characterized by analytical methods and tested for antimicrobial and antiviral activity. The antimycobacterial MIC values against Mycobacterium tuberculosis H37Rv of the most effective compounds, 3-(hexylamino)-, 3-(heptylamino)- and 3-(octylamino)-N-methyl-pyrazine-2-carboxamides 14‒16, was 25 µg/mL. The compounds inhibited photosystem 2 photosynthetic electron transport (PET) in spinach chloroplasts. This activity was strongly connected with the lipophilicity of the compounds. For effective PET inhibition longer alkyl chains in the 3-(alkylamino) substituent in the N-alkyl-3-(alkylamino)pyrazine-2-carboxamide molecule were more favourable than two shorter alkyl chains.

Synthesis, antimycobacterial and antifungal evaluation of some new 1-ethyl-5-(hetero)aryl-6-styryl-1,6-dihydropyrazine-2,3-dicarbonitriles.

The Petasis reaction of 6-hydroxy adducts of 1-alkyl-2,3-dicyano-5-arylpyrazinium salts with trans-styrylboronic acids proved to proceed smoothly at room temperature to give the corresponding 5-(hetero)aryl-6-styryl substituted 1,6-dihydropyrazine derivatives. Also it has been found that C(6) unsubstituted 1,6-dihydro- or 1,4,5,6-tetrahydropyrazine derivatives can be easy prepared in high yields from the corresponding pyrazinium salts by reduction with triethylsilane. All synthesized compounds were screened in vitro for their antifungal activities against seven pathogenic fungal strains and antimycobacterial activities against Mycobacterium tuberculosis H37Rv, avium, terrae and multi-drug-resistant strains isolated from tuberculosis patients in the Ural region (Russia).

Synthesis and antimycobacterial evaluation of 5-alkylamino-N-phenylpyrazine-2-carboxamides.

Substitution of chlorine in 5-chloro-N-phenylpyrazine-2-carboxamide (1) with simple n-alkylamines yielded a series of 5-alkylamino-N-phenylpyrazine-2-carboxamides (propylamino to octylamino derivatives), which possessed similar or increased activity against Mycobacterium tuberculosis H37Rv compared to parent 5-chloro derivative (1), with MIC ranging from 2.5 to 12.2 µM. 5-Butylamino to 5-heptylamino derivatives exerted similar activity also against Mycobacterium kansasii. Importantly, the substitution led also to significant decrease of in vitro cytotoxicity in HepG2 cell line. 5-Heptylamino-N-phenylpyrazine-2-carboxamide (1e) exerted MIC=2.5 µM (M.tbc) and IC50 >250 µM (HepG2). Further modification of alkylamino chain with terminal methoxy or hydroxy group lead to compounds with decreased or none activity, the decrease was proportional to the decrease of lipophilicity. 5-(2-Phenylethylamino) and 5-(3-phenylpropylamino) derivatives were also of decreased activity. On contrary to alkylamino derivatives derived from 1, alkylamino derivatives derived from 5-chloro-N-2-chlorophenylpyrazine-2-carboxamide (2) possessed substantially decreased or none activity. None of the prepared compounds was active against Mycobacterium avium.

New potentially active pyrazinamide derivatives synthesized under microwave conditions.

A series of 18 N-alkyl substituted 3-aminopyrazine-2-carboxamides was prepared in this work according to previously experimentally set and proven conditions using microwave assisted synthesis methodology. This approach for the aminodehalogenation reaction was chosen due to higher yields and shorter reaction times compared to organic reactions with conventional heating. Antimycobacterial, antibacterial, antifungal and photosynthetic electron transport (PET) inhibiting in vitro activities of these compounds were investigated. Experiments for the determination of lipophilicity were also performed. Only a small number of substances with alicyclic side chain showed activity against fungi which was the same or higher than standards and the biological efficacy of the compounds increased with rising lipophilicity. Nine pyrazinamide derivatives also inhibited PET in spinach chloroplasts and the IC50 values of these compounds varied in the range from 14.3 to 1590.0 µmol/L. The inhibitory activity was connected not only with the lipophilicity, but also with the presence of secondary amine fragment bounded to the pyrazine ring. Structure-activity relationships are discussed as well.

Synthesis and evaluation of [(11)C]PyrATP-1, a novel radiotracer for PET imaging of glycogen synthase kinase-3ß (GSK-3ß).

INTRODUCTION: The dysfunction of glycogen synthase kinase-3ß (GSK-3ß) has been implicated in a number of diseases, including Alzheimer's disease. The ability to non-invasively quantify GSK-3ß activity in vivo is therefore of critical importance, and this work is focused upon development of inhibitors of GSK-3ß radiolabeled with carbon-11 to examine quantification of the enzyme using positron emission tomography (PET) imaging. METHODS: (11)C PyrATP-1 was prepared from the corresponding desmethyl-piperazine precursor in an automated synthesis module. In vivo rodent and primate imaging studies were conducted on a Concorde MicroPET P4 scanner to evaluate imaging properties and in vitro autoradiography studies with rat brain samples were carried out to examine specific binding. RESULTS: 2035±518MBq (55±14mCi) of [(11)C]PyrATP-1 was obtained (1%-2% non-corrected radiochemical yield at end-of-synthesis based upon [(11)C]CO2) with high chemical (>95%) and radiochemical (>99%) purities, and good specific activities (143±52GBq/µmol (3874±1424Ci/mmol)), n=5. In vivo microPET imaging studies revealed poor brain uptake in rodents and non-human primates. Pretreatment of rodents with cyclosporin A resulted in moderately increased brain uptake suggesting Pgp transporter involvement. Autoradiography demonstrated high levels of specific binding in areas of the rodent brain known to be rich in GSK-3ß. CONCLUSION: (11)C PyrATP-1 is readily synthesized using standard carbon-11 radiochemistry. However the poor brain uptake in rodents and non-human primates indicates that the radiotracer is not suitable for the purposes of quantifying GSK-3ß in neurological and psychiatric disorders.

Alkylamino derivatives of pyrazinamide: synthesis and antimycobacterial evaluation.

A series of pyrazinamide derivatives with alkylamino substitution was designed, synthesized and tested for their ability to inhibit the growth of selected mycobacterial, bacterial and fungal strains. The target structures were prepared from the corresponding 5-chloro (1) or 6-chloropyrazine-2-carboxamide (2) by nucleophilic substitution of chlorine by various non-aromatic amines (alkylamines). To determine the influence of alkyl substitution, corresponding amino derivatives (1a, 2a) and compounds with phenylalkylamino substitution were prepared. Some of the compounds exerted antimycobacterial activity against Mycobacterium tuberculosis H37Rv significantly better than standard pyrazinamide and corresponding starting compounds (1 and 2). Basic structure-activity relationships are presented. Only weak antibacterial and no antifungal activity was detected.

Synthesis, antimycobacterial activity and in vitro cytotoxicity of 5-chloro-N-phenylpyrazine-2-carboxamides.

5-Chloropyrazinamide (5-Cl-PZA) is an inhibitor of mycobacterial fatty acid synthase I with a broad spectrum of antimycobacterial activity in vitro. Some N-phenylpyrazine-2-carboxamides with different substituents on both the pyrazine and phenyl core possess significant in vitro activity against Mycobacterium tuberculosis. To test the activity of structures combining both the 5-Cl-PZA and anilide motifs a series of thirty 5-chloro-N-phenylpyrazine-2-carboxamides with various substituents R on the phenyl ring were synthesized and screened against M. tuberculosis H37Rv, M. kansasii and two strains of M. avium. Most of the compounds exerted activity against M. tuberculosis H37Rv in the range of MIC = 1.56-6.25 µg/mL and only three derivatives were inactive. The phenyl part of the molecule tolerated many different substituents while maintaining the activity. In vitro cytotoxicity was decreased in compounds with hydroxyl substituents, preferably combined with other hydrophilic substituents. 5-Chloro-N-(5-chloro-2-hydroxyphenyl)pyrazine-2-carboxamide (21) inhibited all of the tested strains (MIC = 1.56 µg/mL for M. tuberculosis; 12.5 µg/mL for other strains). 4-(5-Chloropyrazine-2-carboxamido)-2-hydroxybenzoic acid (30) preserved good activity (MIC = 3.13 µg/mL M. tuberculosis) and was rated as non-toxic in two in vitro models (Chinese hamster ovary and renal cell adenocarcinoma cell lines; SI = 47 and 35, respectively).

Development and characterization of ligand-appended liposomes for multiple drug therapy for pulmonary tuberculosis.

Tuberculosis (TB) remains one of the oldest and deadliest diseases in the current scenario. The intracellular organism Mycobacterium tuberculosis, which mainly resides in mononuclear phagocytes, is responsible for tuberculosis in humans. A few therapies are available for the treatment of tuberculosis but they have many hurdles. To overcome these hurdles, a combination of chemotherapeutic agent-loaded vesicular systems have been prepared to overcome tuberculosis. To investigate the role of novel drug delivery systems for the treatment of pulmonary tuberculosis, ligand appended liposomals have been developed. In the present study, drug-loaded, ligand-appended liposomes and their DPI (Dry Powder Inhaler) forms have been prepared and characterized using various in vitro and in vivo parameters. The prepared ligand-appended liposomal formulation showed good entrapment efficiency, prolonged drug release, improved recovery of drugs from the target site, and proved to be more suitable for use as DPI, justifying their potential for improved drug delivery. Thus we tried our best by our project to reduce the national burden of tuberculosis, which is still a global health challenge.

Synthesis and antimycobacterial evaluation of pyrazinamide derivatives with benzylamino substitution.

A series of 19 new compounds related to pyrazinamide were synthesized, characterized with analytical data and screened for in vitro whole cell antimycobacterial activity against Mycobacterium tuberculosis H37Rv, Mycobacterium kansasii and two types of Mycobacterium avium. The series consisted of 3-(benzylamino)-5-cyanopyrazine-2-carboxamides and 3-(benzylamino)pyrazine-2,5-dicarbonitriles with various substituents on the phenyl ring. RP-HPLC method was used to determine the lipophilicity of the prepared compounds. Nine compounds exerted similar or better activity against Mycobacterium tuberculosis compared to pyrazinamide (MIC=6.25-12.5 µg/mL). 3-(Benzylamino)pyrazine-2,5-dicarbonitrile inhibited all of the tested mycobacterial strains with MIC within the range 12.5-25 µg/mL. Although not the most active, 4-NH(2) substituted compounds possessed the lowest in vitro cytotoxicity (hepatotoxicity), leading to selectivity index SI=5.5 and SI >21.

Exploration of the pyrazinamide polymorphism at high pressure.

We report the high-pressure response of three forms (α, δ, and γ) of pyrazinamide (C(5)H(5)N(3)O, PZA) by in situ Raman spectroscopy and synchrotron X-ray diffraction techniques with a pressure of about 14 GPa. These different forms are characterized by various intermolecular bonding schemes. High-pressure experimental results show that the γ phase undergoes phase transition to the ß phase at a pressure of about 4 GPa, whereas the other two forms retain their original structures at a high pressure. We propose that the stabilities of the α and δ forms upon compression are due to the special dimer connection that these forms possess. On the other hand, the γ form, which does not have this connection, prefers to transform to the closely related ß form when pressure is applied. The detailed mechanism of the phase transition together with the stability of the three polymorphs is discussed by taking molecular stacking into account.

Synthesis and antimycobacterial evaluation of N-substituted 3-aminopyrazine-2,5-dicarbonitriles.

A series of 14 new compounds related to pyrazinamide were synthesized, characterized with analytical data and screened for in vitro antimycobacterial activity against Mycobacterium tuberculosis, Mycobacterium kansasii and two types of Mycobacterium avium. The series comprised of N-substituted 3-aminopyrazine-2,5-dicarbonitriles derived from 3-chloropyrazine-2,5-dicarbonitrile by nucleophilic substitution of chlorine by various non-aromatic amines (alkylamines, cycloalkylamines and heterocyclic amines). Noteworthy antimycobacterial activity against M. tuberculosis was found among the alkylamino derivatives, for example, 3-(heptylamino)pyrazine-2,5-dicarbonitrile inhibited M. tuberculosis at MIC=51 µmol/L. 3-(Hexylamino)pyrazine-2,5-dicarbonitrile inhibited M. kansasii at MIC=218 µmol/L. Basic structure-activity relationships are discussed. A comparison between calculated and experimentally determined lipophilicity parameters within the series is included.

Synthesis, antimycobacterial, antifungal and photosynthesis-inhibiting activity of chlorinated N-phenylpyrazine-2-carboxamides.

A series of sixteen pyrazinamide analogues with the -CONH- linker connecting the pyrazine and benzene rings was synthesized by the condensation of chlorides of substituted pyrazinecarboxylic acids with ring-substituted (chlorine) anilines. The prepared compounds were characterized and evaluated for their antimycobacterial and antifungal activity, and for their ability to inhibit photosynthetic electron transport (PET). 6-Chloro-N-(4-chlorophenyl)pyrazine-2-carboxamide manifested the highest activity against Mycobacterium tuberculosis strain H37Rv (65% inhibition at 6.25 µg/mL). The highest antifungal effect against Trichophyton mentagrophytes, the most susceptible fungal strain tested, was found for 6-chloro-5-tert-butyl-N-(3,4-dichlorophenyl)pyrazine-2-carboxamide (MIC=62.5 µmol/L). 6-chloro-5-tert-butyl-N-(4-chlorophenyl)pyrazine-2-carboxamide showed the highest PET inhibition in spinach chloroplasts (Spinacia oleracea L.) chloroplasts (IC50=43.0 µmol/L). For all the compounds, the relationships between the lipophilicity and the chemical structure of the studied compounds as well as their structure-activity relationships are discussed.