A regio- and stereoselective 1,3-dipolar cycloaddition for the synthesis of new-fangled dispiropyrrolothiazoles as antimycobacterial agents

A series of dispiropyrrolothiazoles compounds were synthesized using 1,3-dipolar cycloaddition and were screened for antimycobacterial activity against Mycobacterium tuberculosis H₃₇Rv and INH resistant M. tuberculosis strains. Two of them were showing good activity with MIC of less than 1 μM. Compound (5f) was found to be the most active with MIC of 0.210 and 8.312 μM respectively.     

In vitro synergistic activity between 8-methoxypsoralen and ethambutol, isoniazid, and rifampin when used in combination against Mycobacterium tuberculosis

8-Methoxypsoralen (8-MOP), a naturally occurring furocoumarin found in many plant species, has been reported to have antimycobacterial activity against Mycobacterium tuberculosis strain H37Rv (ATCC 27294). In the present study, we further test the in vitro synergistic activity of 8-MOP and ethambutol (EMB), isoniazid (INH), or rifampin (RMP) against M. tuberculosis. This study showed that 8-MOP has antimycobacterial activity against two drug-sensitive and six drug-resistant clinical isolates of M. tuberculosis, with the minimum inhibitory concentrations of 100–200 and 200–400 μg/mL, respectively. A synergistic antimycobacterial effect between 8-MOP and EMB, INH, or RMP against six drug-resistant strains was observed, with the fractional inhibitory concentration indices (FICIs) of 0.093–0.156, 0.138–0.285 and 0.093–0.262, respectively. The combination of 8-MOP/EMB, 8-MOP/INH, and 8-MOP/RMP displayed either synergistic activity or had no interaction when tested against the two clinical drug-sensitive strains and the standard strain. No antagonism was observed for any drug combination against any of the strains tested. To our knowledge, this is first report that 8-MOP has synergistic activity with first-line antimycobacterial agents.     

Synthesis and structure activity relationship of imidazo[1,2-a]pyridine-8-carboxamides as a novel antimycobacterial lead series

Imidazo[1,2-a]pyridine-8-carboxamides as a novel antimycobacterial lead were generated by whole cell screening of a focused library against Mycobacterium tuberculosis. Herein, we describe the synthesis and structure activity relationship evaluation of this class of inhibitors and the optimization of physicochemical properties. These are selective inhibitors of Mycobacterium tuberculosis with no activity on either gram positive or gram negative pathogens.     

Membrane-active and DNA binding related double-action antimycobacterial mechanism of antimicrobial peptide W3R6 and its synthetic analogs

The emergence of multidrug- or extremely drug-resistant M. tuberculosis strains has made very few drugs available for current tuberculosis treatment. Antimicrobial peptides can be employed as a promising alternative strategy for TB treatment. Here, we designed and synthesized a series of peptide sequences based on the structure-activity relationships of natural sequences of antimicrobial peptides. The peptide W3R6 and its analogs were screened and found to have potent antimycobacterial activity against M. smegmatis, and no hemolytic activity against human erythrocytes. The evidence from the mechanism of action study indicated that W3R6 and its analogs can interact with the mycobacterial membrane in a lytic manner and form pores on the outer membrane of M. smegmatis. Significant colocalization of D-W3R6 with mycobacterial DNA was observed by confocal laser scanning microscopy and DNA retardation assays, which suggested that the antimycobacterial mechanism of action of the peptide was associated with the unprotected genomic DNA of M. smegmatis. In general, W3R6 and its analogs act on not only the mycobacterial membrane but also the genomic DNA in the cytoplasm, which makes it difficult for mycobacteria to generate resistance due to the peptides having two targets. In addition, the peptides can effectively eliminate M. smegmatis cells from infected macrophages. Our findings indicated that the antimicrobial peptide W3R6 could be a novel lead compound to overcome the threat from drug-resistant M. tuberculosis strains in the development of potent AMPs for TB therapeutic applications.     

Design of hybrid molecules as antimycobacterial compounds: Synthesis of isoniazid-naphthoquinone derivatives and their activity against susceptible and resistant strains of Mycobacterium tuberculosis

Isoniazid-naphthoquinone hybrids were synthesized and evaluated against a susceptible (H₃₇Rv) strain and two isoniazid-resistant strains (INH_R1 and INH_R2) of Mycobacterium tuberculosis. The antimycobacterial activity of the derivatives was determined based on the resazurin microtiter assay and their cytotoxicity in adhered mouse monocyte macrophage J774.A1 cells (ATCC TIB-67). Of the twenty-two compounds evaluated against the three strains of M. tuberculosis, twenty-one presented some activity against the H₃₇Rv and INH_R1 (katG S315T) or INH_R2 (inhA C(−5)T) strains. Compounds 1a, 2a, and 8a were effective against the INH_R1 strain, and compounds 1a, 1b, 2a, 3a, 5a, 5b and 8a were effective against the INH_R2 strain, with MICs in the range of 3.12–6.25 µg/mL. Compounds 1b and 5b were the most active against H₃₇Rv, with MIC of 0.78 µg/mL. Based on the selectivity index, 1b and 5b can be considered safe as a drug candidate compounds. These results demonstrate that quinoidal compounds can be used as promising scaffolds for the development of new anti-TB drugs and hybrids with activity against M. tuberculosis-susceptible and INH-resistant strains.     

Synthesis and antimycobacterial activity of isoniazid derivatives from renewable fatty acids

This work describes the synthesis of a series of fatty acid hydrazide derivatives of isoniazid (INH). The compounds were tested against Mycobacterium tuberculosis H37Rv (ATCC 27294) as well as INH-resistant (ATCC 35822 and 1896 HF) and rifampicin-resistant (ATCC 35338) M. tuberculosis strains. The fatty acid derivatives of INH showed high antimycobacterial potency against the studied strains, which is desirable for a pharmaceutical compound, suggesting that the increased lipophilicity of isoniazid plays an important role in its antimycobacterial activity.     

1,3-Azoles from ortho-naphthoquinones: Synthesis of aryl substituted imidazoles and oxazoles and their potent activity against Mycobacterium tuberculosis

Twenty-three naphthoimidazoles and six naphthoxazoles were synthesised and evaluated against susceptible and rifampicin- and isoniazid-resistant strains of Mycobacterium tuberculosis. Among all the compounds evaluated, fourteen presented MIC values in the range of 0.78 to 6.25 μg/mL against susceptible and resistant strains of M. tuberculosis. Five structures were solved by X-ray crystallographic analysis. These substances are promising antimycobacterial prototypes.     

Synthesis of non-purine analogs of 6-aryl-9-benzylpurines,and their antimycobacterial activities. Compounds modified in the imidazole ring

Purine analogs modified in the five-membered ring have been synthesized and examined for antibacterial activity against Mycobacterium tuberculosis H₃₇Rv in vitro employing the microplate alamar blue assay (MABA). The 9-deaza analogs were only found to be weak inhibitors, but the 8-aza-, 7-deaza- and 8-aza-7-deazapurine analogs studied displayed excellent antimycobacterial activities, some even substantially better than the parent purine. In the 7-deazapurine series, MIC values between 0.08 and 0.35 μM, values comparable or better than the reference drugs used in the study (MIC rifampicin 0.09 μM, MIC isoniazid 0.28 μM and MIC PA-824 0.44 μM). The five most active compounds were also examined against a panel of drug-resistant Mtb strain, and they all retained their activity. The compounds examined were significantly less active against M. tuberculosis in a state of non-replicating persistence (NRP). MIC in the low-oxygen-recovery assay (LORA) ?60 μM. The 7-deazapurines were somewhat more toxic towards mammalian cells, but still the selectivity indexes were excellent. The non-purine analogs exhibit a selective antimycobacterial activity. They were essentially inactive against Staphylococcus aureus and Escherichia coli.     

Synthesis and biological evaluation of pyrimidine analogs of antimycobacterial purines

Pyrimidine analogs of antimycobacterial 6-aryl-9-benzylpurines have been synthesized and screened for antibacterial activity against Mycobacterium tuberculosis H₃₇Rv in vitro. Several active compounds were identified and the best results were observed for 5-formamidopyrimidines. These compounds generally displayed IC₉₀ values ≤1 μg/mL, and they exhibited low toxicity towards mammalian cells. Imidazolylpyrimidines, which may be regarded as fleximer analogs of the parent purines, were also synthesized and one of them was found to be quite a potent inhibitor of M. tuberculosis (IC₉₀ 14 μg/mL).     

Synthesis and biological evaluation of new enantiomerically pure azole derivatives as inhibitors of Mycobacterium tuberculosis

A series of novel enantiomerically pure azole derivatives was synthesized. The new compounds, bearing both an imidazole as well as a triazole moiety, were evaluated as antimycobacterial agents. One of them proved to have activity against Mycobaterium tuberculosis comparable to those of the classical antibacterial/antifungal drugs Econazole and Clotrimazole.     

Limonoids from Melia azedarach Fruits as Inhibitors of Flaviviruses and Mycobacterium tubercolosis

The biological diversity of nature is the source of a wide range of bioactive molecules. The natural products, either as pure compounds or as standardized plant extracts, have been a successful source of inspiration for the development of new drugs. The present work was carried out to investigate the cytotoxicity, antiviral and antimycobacterial activity of the methanol extract and of four identified limonoids from the fruits of Melia azedarach (Meliaceae). The extract and purified limonoids were tested in cell-based assays for antiviral activity against representatives of ssRNA, dsRNA and dsDNA viruses and against Mycobacterium tuberculosis. Very interestingly, 3-α-tigloyl-melianol and melianone showed a potent antiviral activity (EC₅₀ in the range of 3–11μM) against three important human pathogens, belonging to Flaviviridae family, West Nile virus, Dengue virus and Yellow Fever virus. Mode of action studies demonstrated that title compounds were inhibitors of West Nile virus only when added during the infection, acting as inhibitors of the entry or of a very early event of life cycle. Furthermore, 3-α-tigloyl-melianol and methyl kulonate showed interesting antimycobacterial activity (with MIC values of 29 and 70 μM respectively). The limonoids are typically lipophilic compounds present in the fruits of Melia azeradach. They are known as cytotoxic compounds against different cancer cell lines, while their potential as antiviral and antibacterial was poorly investigated. Our studies show that they may serve as a good starting point for the development of novel drugs for the treatment of infections by Flaviviruses and Mycobacterium tuberculosis, for which there is a continued need.     

Synthesis and antimycobacterial evaluation of novel 5,6-dimethoxy-1-oxo-2,5-dihydro-1H-2-indenyl-5,4-substituted phenyl methanone analogues

In present investigation, a series of substituted phenyl-5,6-dimethoxy-1-oxo-2,5-dihydro-1H-2-indenylmethanone analogues were synthesized and were evaluated for antimycobacterial activity against Mycobacterium tuberculosis H₃₇Rv and INH resistant M. tuberculosis. All the newly synthesized compounds were showing moderate to high inhibitory activities. The compound 5,6-dimethoxy-1-oxo-2,5-dihydro-1H-2-indenyl-4-fluorophenylmethanone (5g) was found to be the most promising compounds active against M. tuberculosis H₃₇Rv and isoniazid (INH) resistant M. tuberculosis with Minimum inhibitory concentration 0.10 and 0.10 μM.     

Synthesis,antimicrobial activity and acid dissociation constants of methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives

In this study, a series of polysubstituted methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives were designed and synthesized by the cyclization reaction of methyl 1-(benzoylcarbamothioyl)-5,5-diphenylpyrrolidine-2-carboxylates and 2-bromo-1-(4-substituted phenyl)ethanones in 70–96% yield. The starting pyrrolidine derivatives were synthesized via a 1,3-dipolar cycloaddition reaction in 83–88% yield. The stereochemistry of one of these methyl 5,5-diphenyl-1-(thiazol-2-yl)pyrrolidine-2-carboxylate derivatives was characterized by a single crystal X-ray diffraction study and the acid dissociation constants of these compounds were determined. An antimicrobial screening was performed against different bacterial and fungal strains and against the M. tuberculosis H37Rv strain. Interesting antibacterial activity was observed for two compounds against the A. baumannii strain with MIC values of 31.25?µg/mL (Ampicillin: 125?µg/mL) and against the M. tuberculosis H37Rv strain with MIC values of 0.98–1.96?µg/mL (Isoniazid: 0.98?µg/mL, Ethambutol: 1.96?µg/mL). Therefore, these structures can be considered as good starting points for the development of new powerful antimycobacterial agents.     

Piperidinols That Show Anti-Tubercular Activity as Inhibitors of Arylamine N-Acetyltransferase: An Essential Enzyme for Mycobacterial Survival Inside Macrophages

Latent M. tuberculosis infection presents one of the major obstacles in the global eradication of tuberculosis (TB). Cholesterol plays a critical role in the persistence of M. tuberculosis within the macrophage during latent infection. Catabolism of cholesterol contributes to the pool of propionyl-CoA, a precursor that is incorporated into cell-wall lipids. Arylamine N-acetyltransferase (NAT) is encoded within a gene cluster that is involved in the cholesterol sterol-ring degradation and is essential for intracellular survival. The ability of the NAT from M. tuberculosis (TBNAT) to utilise propionyl-CoA links it to the cholesterol-catabolism pathway. Deleting the nat gene or inhibiting the NAT enzyme prevents intracellular survival and results in depletion of cell-wall lipids. TBNAT has been investigated as a potential target for TB therapies. From a previous high-throughput screen, 3-benzoyl-4-phenyl-1-methylpiperidinol was identified as a selective inhibitor of prokaryotic NAT that exhibited antimycobacterial activity. The compound resulted in time-dependent irreversible inhibition of the NAT activity when tested against NAT from M. marinum (MMNAT). To further evaluate the antimycobacterial activity and the NAT inhibition of this compound, four piperidinol analogues were tested. All five compounds exert potent antimycobacterial activity against M. tuberculosis with MIC values of 2.3–16.9 µM. Treatment of the MMNAT enzyme with this set of inhibitors resulted in an irreversible time-dependent inhibition of NAT activity. Here we investigate the mechanism of NAT inhibition by studying protein-ligand interactions using mass spectrometry in combination with enzyme analysis and structure determination. We propose a covalent mechanism of NAT inhibition that involves the formation of a reactive intermediate and selective cysteine residue modification. These piperidinols present a unique class of antimycobacterial compounds that have a novel mode of action different from known anti-tubercular drugs.     

Antimicrobial activity of Brazilian propolis extracts against rumen bacteria in vitro

The antimicrobial activity of three Brazilian propolis extracts was evaluated on bacterial strains representing major rumen functional groups. The extracts were prepared using different concentrations of propolis and alcohol, resulting in different phenolic compositions. The propolis extracts inhibited the growth of Fibrobacter succinogenes S85, Ruminococcus flavefaciens FD-1, Ruminococcus albus 7, Butyrivibrio fibrisolvens D1, Prevotella albensis M384, Peptostreptococcus sp. D1, Clostridium aminophilum F and Streptococcus bovis Pearl11, while R. albus 20, Prevotella bryantii B₁4 and Ruminobacter amylophilus H18 were resistant to all the extracts. The inhibited strains showed also different sensitivity to propolis; the hyper-ammonia-producing bacteria (C. aminophilum F and Peptostreptococcus sp. D1) being the most sensitive. Inhibition of hyper-ammonia-producing bacteria by propolis would be beneficial to the animal. The extract containing the lowest amount of phenolic compounds (LLOS C3) showed the lowest antimicrobial activity against all the bacteria. The major phenolic compounds identified in the propolis extracts (naringenin, chrysin, caffeic acid, p-coumaric acid and Artepillin C) were also evaluated on four sensitive strains. Only naringenin showed inhibitory effect against all strains, suggesting that naringenin is one of the components participating to the antibacterial activity of propolis.     

Amino ether analogues of 4,4′-dihydroxy-3-methoxy-6,7′-cyclolignan and their activity against drug-resistant bacteria

Larrea tridentata antibacterial lignan 4,4′-dihydroxy-3-methoxy-6,7′-cyclolignan (1) was derivatized to obtain eleven new amino ether derivatives (2 A-12 C). The structural elucidation of compounds was performed by analysis of 1D- and 2D NMR spectral data and HRESIMS. The antibacterial activity of compounds was determined against nine drug-resistant bacteria and two strains of Mycobacterium tuberculosis (sensitive ATCC 27294 H37Rv and drug-resistant G122). Results showed that all derivatives were devoid of activity towards six gram-negative clinical isolates assayed. However, seven derivatives displayed antibacterial activity against three gram-positive drug-resistant bacteria. Further, enhancement of antibacterial activity was only observed for the compounds 2 A and 10 C-12 C (MIC of 12.5 µg/mL) which were two-fold more active than the starting material 1 against vancomycin-resistant Enterococcus faecium. All derivatives, except compound 9 B, showed antitubercular activity against both M. tuberculosis strains. Interestingly, all the compounds, except for 2 A and 11 A, were more active than the starting material 1 (MIC of 50 µg/mL). Compound 4 C was the only compound as active as the positive control ethambutol against the drug-resistant strain M. tuberculosis G122 (MIC of 6.25 µg/mL). In addition, the derivative 7 C was the most active compound against the sensitive strain M. tuberculosis H37Rv (MIC of 6.25 µg/mL)     

Design,synthesis and antimycobacterial activity of benzoxazinone derivatives and open-ring analogues: Preliminary data and computational analysis

This study examines in depth benzoxazine nucleus for antimycobacterial property. We synthesized some benzoxazin-2-one and benzoxazin-3-one derivatives, which were tested for activity against a panel of Mycobacterium tuberculosis (Mtb) strains, including H37Ra, H37Rv and some resistant strains. Several compounds displayed a high antimycobacterial activity and the three isoniazid analogue derivatives 8a-c exhibited a MIC range of 0.125–0.250 μg/mL (0.37–0.75 μM) against strain H37Ra, therefore lower than the isoniazid reference drug. Two benzoxazin-2-one derivatives, 1c and 5j, together with isoniazid-analogue compound 8a, also revealed low MIC values against resistant strains and proved highly selective for mycobacterial cells, compared to mammalian Vero cells. To predict whether molecule 8a is able to interact with the active site of InhA, we docked it into the crystal structure; indeed, during the molecular dynamic simulation the compound never left the protein pocket. The more active compounds were predicted for ADME properties and all proved to be potentially orally active in humans.     

Azurophil Granule Proteins Constitute the Major Mycobactericidal Proteins in Human Neutrophils and Enhance the Killing of Mycobacteria in Macrophages

Pathogenic mycobacteria reside in, and are in turn controlled by, macrophages. However, emerging data suggest that neutrophils also play a critical role in innate immunity to tuberculosis, presumably by their different antibacterial granule proteins. In this study, we purified neutrophil azurophil and specific granules and systematically analyzed the antimycobacterial activity of some purified azurophil and specific granule proteins against M. smegmatis, M. bovis-BCG and M. tuberculosis H37Rv. Using gel overlay and colony forming unit assays we showed that the defensin-depleted azurophil granule proteins (AZP) were more active against mycobacteria compared to other granule proteins and cytosolic proteins. The proteins showing antimycobacterial activity were identified by MALDI-TOF mass spectrometry. Electron microscopic studies demonstrate that the AZP disintegrate bacterial cell membrane resulting in killing of mycobacteria. Exogenous addition of AZP to murine macrophage RAW 264.7, THP-1 and peripheral blood monocyte-derived macrophages significantly reduced the intracellular survival of mycobacteria without exhibiting cytotoxic activity on macrophages. Immunofluorescence studies showed that macrophages actively endocytose neutrophil granular proteins. Treatment with AZP resulted in increase in co-localization of BCG containing phagosomes with lysosomes but not in increase of autophagy. These data demonstrate that neutrophil azurophil proteins may play an important role in controlling intracellular survival of mycobacteria in macrophages.     

Synthesis and antimycobacterial activity of 4-[5-(substituted phenyl)-4, 5-dihydro-3-isoxazolyl]-2-methylphenols

Compounds based on the isoxazoline moiety were screened for their antimycobacterial activity in vitro against Mycobacterium tuberculosis H37R (MTB), and INH (isoniazid) resistant Mycobacterium tuberculosis (INHR-MTB) using the agar dilution method and bactec 460. Among the synthesized compounds, 4-[5-(4-bromophenyl)-4,5-dihydro-3-isoxazolyl]-2-methylphenol (4l) was found to be the most active agent against MTB and INHR-MTB with minimum inhibitory concentration of 0.62 μM. When compared to INH, compound (4l) was 1.12 fold and 3.0 fold more active against MTB and INHR-MTB, respectively.