3-[Benzimidazo- and 3-[benzothiadiazoleimidazo-(1,2-c)quinazolin-5-yl]-2H-chromene-2-ones as potent antimicrobial agents

A series of 3-[benzimidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one (6a-6f) and 3-[benzothiadiazole- imidazo(1,2-c)quinazolin-5-yl]-2H-chromene-2-one derivatives (7a-7f) that incorporate a variety of substituents at the 6- and/or 8-positions of the coumarin moieties have been synthesized utilizing cellulose sulfuric acid as an efficient catalyst under both conventional heating and microwave irradiation procedures. These analogs were evaluated for their antimicrobial activity against Bacillus subtilis, Staphylococcus aureus, Streptococcus pyogenes (Gram-positive bacteria), Escherichia Coli, Klebsiella pneumonia, Salmonella typhimurium (Gram-negative bacteria), and Aspergillus niger, Candida albicans, and Aspergillus flavus (Fungi). Two analogs, 6c (a 6,8-dichloro analog, MIC([SA]) = 2.5 μg/mL; MIC([ST]) = 2.5 μg/mL) and 7d (a 6,8-dibromo analog, MIC([ST]) = 2.5 μg/mL) were identified as potent antibacterial agents, and two analogs, 6b (a 6-bromo analog, MIC([AF]) = 10 μg/mL) and 6d (a 6,8-dibromo analog, MIC([AF]) = 15 μg/mL; MIC([CA]) = 15μg/mL), were identified as potent antifungal agents. Based on the MIC data, analogs 6b, 6c, 6d, and 7d were identified as the most potent antimicrobial agents in the series.     

Synthesis of novel 3-cyclohexylpropanoic acid-derived nitrogen heterocyclic compounds and their evaluation for tuberculostatic activity

A series of novel 3-cyclohexylpropanoic acid derivatives and 3-cyclohexylpropanoic acid-derived nitrogen heterocyclic compounds (1-8) have been synthesized and evaluated for tuberculostatic activity. Compounds 1a, 1c, 1e and 1f bearing benzimidazole or benzimidazole-like systems showed the most potent tuberculostatic activity against Mycobacterium tuberculosis strains with MIC values ranging from 1.5 to 12.5μg/mL. More importantly 1a (6-chloro-2-(2-cyclohexylethyl)-4-nitro-1H-benzo[d]imidazole) and 1f (2-(2-cyclohexylethyl)-1H-imidazo[4,5-b]phenazine) appeared selective for M. tuberculosis as compared with eukaryotic cells (human fibroblasts), and other antimicrobial strains. These compounds may thus represent a novel, selective class of antitubercular agents. Additionally compound 1a stimulated type I collagen output by fibroblasts, in vitro.     

Development of novel isatin–nicotinohydrazide hybrids with potent activity against susceptible/resistant Mycobacterium tuberculosis and bronchitis causing–bacteria

Joining the global fight against Tuberculosis, the world''s most deadly infectious disease, herein we present the design and synthesis of novel isatin-nicotinohydrazide hybrids (5a–m and 9a–c) as promising anti-tubercular and antibacterial agents. The anti-tubercular activity of the target hybrids was evaluated against drug-susceptible M. tuberculosis strain (ATCC 27294) where hybrids 5d, 5g and 5h were found to be as potent as INH with MIC = 0.24 µg/mL, also the activity was evaluated against Isoniazid/Streptomycin resistant M. tuberculosis (ATCC 35823) where compounds 5g and 5h showed excellent activity (MIC = 3.9 µg/mL). Moreover, the target hybrids were examined against six bronchitis causing-bacteria. Most derivatives exhibited excellent antibacterial activity. K. pneumonia emerged as the most sensitive strain with MIC range: 0.49–7.81 µg/mL. Furthermore, a molecular docking study has proposed DprE1 as a probable enzymatic target for herein reported isatin-nicotinohydrazide hybrids, and explored the binding interactions within the vicinity of DprE1 active site.     

Carboxylic acid and phosphate ester derivatives of fluconazole: synthesis and antifungal activities

Two classes of fluconazole derivatives, (a) carboxylic acid esters and (b) fatty alcohol and carbohydrate phosphate esters, were synthesized and evaluated in vitro against Cryptococcus neoformans, Candida albicans, and Aspergillus niger. All carboxylic acid ester derivatives of fluconazole (1a-l), such as O-2-bromooctanoylfluconazole (1g, MIC=111 microg/mL) and O-11-bromoundecanoylfluconazole (1j, MIC=198 microg/mL), exhibited higher antifungal activity than fluconazole (MIC > or = 4444 microg/mL) against C. albicans ATCC 14053 in SDB medium. Several fatty alcohol phosphate triester derivatives of fluconazole, such as 2a, 2b, 2f, 2g, and 2h, exhibited enhanced antifungal activities against C. albicans and/or A. niger compared to fluconazole in SDB medium. For example, 2-cyanoethyl-omega-undecylenyl fluconazole phosphate (2b) with MIC value of 122 microg/mL had at least 36 times greater antifungal activity than fluconazole against C. albicans in SDB medium. Methyl-undecanyl fluconazole phosphate (2f) with a MIC value of 190 microg/mL was at least 3-fold more potent than fluconazole against A. niger ATCC 16404. All compounds had higher estimated lipophilicity and dermal permeability than those for fluconazole. These results demonstrate the potential of these antifungal agents for further development as sustained-release topical antifungal chemotherapeutic agents.     

Discovery of novel methanone derivatives acting as antimycobacterial agents

A series of pyrazoline derivatives were synthesized and in vitro activity against Mycobacterium tuberculosis H37Rv was carried out. Among the synthesized compounds, compounds (4d) and (4f) 4-aminophenyl-3-(3,4-dimethoxyphenyl)-6,7-dimethoxy-2,3,3a,4-tetrahydroindeno[1,2-c]pyrazol-2-ylmethanone and 4-aminophenyl-6,7-dimethoxy-3-phenyl-2,3,3a,4-tetrahydroindeno[1,2-c]pyrazol-2-ylmethanone were found to be the most active agent against M. tuberculosis H37Rv with a minimum inhibitory concentration of 10 μg/mL.     

Novel imidazo[2,1-b][1,3,4]thiadiazole carrying rhodanine-3-acetic acid as potential antitubercular agents

The increase in the prevalence of multi drug-resistant and extensively drug-resistant strains of Mycobacteriumtuberculosis case demonstrates the urgent need of discovering new promising compounds with antimycobacterial activity. As part of our research program and with a aim of identifying new antitubercular drug candidates, a new class of 2-(trifluoromethyl)-6-arylimidazo[2,1-b][1,3,4]thiadiazole derivatives has been synthesized by both conventional as well as microwave assisted method and evaluated for their in vitro antitubercular activity against M. tuberculosis H(37)Rv. Moreover, various drug-likeness properties of new compounds were predicted. Seven compounds from the series exhibited good activity with MIC in range 3.12-1.56μg/ml. The present study suggests that compounds 6b, 6c, 6d, 6e and 6f may serve as promising lead scaffolds for further generation of new anti-TB agents.     

Synthesis and Antibacterial Activity Evaluation of Imidazole Derivatives Containing 6-Methylpyridine Moiety

A series of 2-cyclopropyl-5-(5-(6-methylpyridin-2-yl)-2-substituted-1H-imidazol-4-yl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazoles ( 15a – t and 16a – f ) were synthesized and their antibacterial activities were evaluated. More than half of the compounds showed moderate or strong antibacterial activity. Among them, compounds 15t (MIC=1–2 μg/mL) and 16d (MIC=0.5 μg/mL) showed the strongest antibacterial activities. Notably, compound 16d did not exhibit cytotoxicity in HepG2 cells and did not show hemolysis like the positive control compound Gatifloxacin. The results suggest that compound 16d should be further investigated as a candidate antibacterial agent.     

Design,Synthesis, Docking Study of Pyrazolohydrazinopyrimidin-4-one Derivatives and Their Application as Antimicrobials

New series of pyrazoles 4a – c and pyrazolopyrimidines 5a – f had been constructed. The newly synthesized compounds were assessed for their antimicrobial activity towards E. coli and P. aeruginosa (gram –ve bacteria), B. subtilis and S. aureus (gram +ve bacteria) and A. flavus and C. albicans (representative of fungi). The pyrazolylpyrimidine-2,4-dione derivative 5b is the most active candidate against B. subtilis (MIC=60 μg/mL) and P. aeruginosa (MIC=45 μg/mL). Regarding antifungal potential, compound 5f was the most effective against A. flavus (MIC=33 μg/mL). Similarly, compound 5c displayed strong antifungal activity towards C. Albicans (MIC=36 μg/mL) in reference to amphotericin B (MIC=60 μg/mL). Finally, the novel compounds had been docked inside dihydropteroate synthase (DHPS) to suggest the binding mode of these compounds.     

Discovery of novel 5-(ethyl or hydroxymethyl) analogs of 2'-'up' fluoro (or hydroxyl) pyrimidine nucleosides as a new class of Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium avium inhibitors

Discovery of novel antimycobacterial compounds that work on distinctive targets and by diverse mechanisms of action is urgently required for the treatment of mycobacterial infections due to the emerging global health threat of tuberculosis. We have identified a new class of 5-ethyl or hydroxy (or methoxy) methyl-substituted pyrimidine nucleosides as potent inhibitors of Mycobacterium bovis, Mycobacterium tuberculosis (H37Ra, H37Rv) and Mycobacterium avium. A series of 2'-'up' fluoro (or hydroxy) nucleosides (1, 2, 4-6, 9, 10, 13, 16, 18, 21, 24) was synthesized and evaluated for antimycobacterial activity. Among 2'-fluorinated compounds, 1-(3-bromo-2,3-dideoxy-2-fluoro-β-d-arabinofuranosyl)-5-ethyluracil (13) exhibited promising activity against M. bovis and Mtb alone, and showed synergism when combined with isoniazid. The most active compound emerging from these studies, 1-(β-d-arabinofuranosyl)-4-thio-5-hydroxymethyluracil (21) inhibited Mtb (H37Ra) (MIC(50)=0.5 μg/mL) and M. bovis (MIC(50)=0.5 μg/mL) at low concentrations, and was ten times more potent against Mtb (H37Ra) than cycloserine (MIC(50)=5.0 μg/mL), a second line drug. It also showed an additive effect when combined with isoniazid. Compound 21 retained sensitivity against a rifampicin-resistant (H37Rv) strain of Mtb (MIC(50)=1 μg/mL) at concentrations similar to that for a rifampicin-sensitive (H37Rv) strain, suggesting that it has no cross-resistance to a first-line anti-TB drug. In addition, the replication of M. avium was also inhibited by 21 (MIC(50)=10 μg/mL). No cellular toxicity of 13 or 21 was observed up to the highest concentration tested (CC(50)>100 μg/mL). These observations offer promise for a new drug treatment regimen to augment and complement the current chemotherapy of TB.     

Efficient synthesis and in vitro antitubercular activity of 1,2,3-triazoles as inhibitors of Mycobacterium tuberculosis

Efficient and rapid synthesis of 1,2,3-triazole derivatives has been achieved via Huisgen's 1,3-dipolar cycloaddition between alkyl/arylazides and diethyl/dimethyl acetylenedicarboxylate in excellent yields under solvent-free conditions. The environmentally friendly solvent-free protocol overcomes the limitations associated with the prevailing time-consuming solution phase protocols and affords the triazoles just in 1-3 min. In vitro antitubercular activity of these triazoles was screened against Mycobacterium tuberculosis H(37)Rv strain. Four of the compounds showed MIC in the range of 1.56-3.13 μg/mL proving their potential activity.     

Synthesis and antituberculosis activity of the derivatives of glycoside steviolbioside from the plant Stevia rebaudiana and diterpenoid isosteviol containing hydrazone, hydrazide and pyridinoyl moieties

Conjugates of antitubercular drug Isoniazid (hydrazide of isonicotinic acid), nicotinic and alpha-picolinic acid hydrazides and glycoside steviolbioside from the plant Stevia rebaudiana as well as the product of its acid hydrolysis, diterpenoid isosteviol, were synthesized. Besides, isosteviol hydrazide and hydrazone derivatives as well as conjugates containing two isosteviol moieties connected by dihydrazide linker were also obtained. Both initial compounds and their synthetic derivatives inhibit the growth of Mycobacterium tuberculosis (H37Rv in vitro). The minimum concentration at which the growth of M. tuberculosis was inhibited by 100% (MIC) for stevioside and steviolbioside equals 7.5 and 3.8 microg/mL, respectively. MIC values for conjugates of the hydrazides of pyridine carbonic acids and steviolbioside as well as isosteviol are in the ranges 5-10 and 10-20 microg/mL, respectively. Maximum inhibitory effect against M. tuberculosis showed the conjugates of isosteviol and adipic acid dihydrazide (MIC values ranged from 1.7 to 3.1 microg/mL). Antitubercular activity of the compounds studied is higher than the activity of antitubercular drug Pyrizanamide (MIC = 12.5-20 microg/mL) but lower than the activity of antitubercular drug Isoniazid (MIC = 0.02-0.04 microg/mL).     

Synthesis and biological evaluation of substituted 4-arylthiazol-2-amino derivatives as potent growth inhibitors of replicating Mycobacterium tuberculosis H₃₇Rv

In search of potential therapeutics for tuberculosis, we describe herein synthesis and biological evaluation of some substituted 4-arylthiazol-2-amino derivatives as modified analogues of the antiprotozoal drug Nitazoxanide (NTZ), which has recently been reported as potent inhibitor of Mtb H(37)Rv (Mtb MIC=52.12 μM) with an excellent ability to evade resistance. Among the synthesized derivatives, the two compounds 7a (MIC=15.28 μM) and 7c (MIC=17.03 μM) have exhibited about three times better Mtb growth inhibitory activity over NTZ and are free from any cytotoxicity (Vero CC(50) of 244 and 300 μM respectively). These two compounds represent promising leads for further optimization.     

Ring-substituted quinolines. Part 2: Synthesis and antimycobacterial activities of ring-substituted quinolinecarbohydrazide and ring-substituted quinolinecarboxamide analogues

Additional structural modifications of the new chemical entity, 2,8-dicyclopentyl-4-methylquinoline (DCMQ; MIC = 6.25 μg/mL, M. tuberculosis H37Rv) resulted in the synthesis of four new series of the ring-substituted quinolinecarbohydrazides (series 1–4) constituting 22 analogues. All new derivatives were evaluated for in vitro antimycobacterial activities against drug-sensitive M. tuberculosis H37Rv strain. Certain ring-substituted-2-quinolinecarbohydrazide analogues described herein showed good inhibitory activity. In particular, analogues 4-(1-adamantyl)-2-quinolinecarbohydrazide (2d), 4,5-dicyclopentyl-2-quinolinecarbohydrazide (2e), 4,8-dicyclopentyl-2-quinolinecarbohydrazide (2f), and 4,5-dicyclohexyl-2-quinolinecarbohydrazide (2g) have exhibited the MIC value of 6.25 μg/mL. Further investigation of the most suitable lead prototype, 4-(1-adamantyl)-2-quinolinecarbohydrazide (2d, series 1) led to the synthesis of N2-alkyl/N2,N2-dialkyl/N2-aryl-4-(1-adamantyl)-2-quinolinecarboxamides (series 5) consisting of 13 analogues. Some of the synthesized carboxamides 7a, 7h, and 7m reported herein have exhibited excellent antimycobacterial activities in the range of 6.25–3.125 μg/mL against drug-sensitive and drug-resistant M. tuberculosis H37Rv strains.     

Gatifloxacin derivatives: synthesis, antimycobacterial activities, and inhibition of Mycobacterium tuberculosis DNA gyrase

Sixteen 7-substituted gatifloxacin derivatives were synthesized and evaluated for antimycobacterial activity in vitro and in vivo against Mycobacterium tuberculosis H37Rv (MTB) and multi-drug resistant M. tuberculosis (MDR-TB), and also tested for the ability to inhibit the supercoiling activity of DNA gyrase from M. tuberculosis. Among the synthesized compounds, 1-cyclopropyl-6-fluoro-8-methoxy-7-[[[N4-[1'-(5-isatinyl-beta-semicarbazo)]methyl]3-methyl]N1-piperazinyl]-4-oxo-1,4-dihydro-3-quinoline carboxylic acid (3d) was found to be the most active compound in vitro with an MIC of 0.0125 microg/mL against MTB and MTR-TB. In the in vivo animal model 3d decreased the bacterial load in lung and spleen tissues with 3.62- and 3.76-log10 protections, respectively. Compound 3d was also found to be equally active as gatifloxacin in the inhibition of the supercoiling activity of wild-type M. tuberculosis DNA gyrase with an IC50 of 3.0 microg/mL. The results demonstrate the potential and importance of developing new quinolone derivatives against mycobacterial infections.     

Synthesis and in vitro antitubercular activity of 4-aryl/alkylsulfonylmethylcoumarins as inhibitors of Mycobacterium tuberculosis

A series of 4-aryl/alkylsulfonylmethylcoumarins have been synthesized and screened for in vitro antitubercular activity against Mycobacterium tuberculosis H(37)Rv (MTB). Four of the compounds showed MIC in the range of 0.78-3.13 μg/mL proving their potential activity.     

Synthesis, antimycobacterial and antibacterial activity of ciprofloxacin derivatives containing a N-substituted benzyl moiety

We report herein the design and synthesis of a series of novel ciprofloxacin (CPFX) derivatives with remarkable improvement in lipophilicity by introducing a substituted benzyl moiety to the N atom on the C-7 piperazine ring of CPFX. Antimycobacterial and antibacterial activity of the newly synthesized compounds was evaluated. Results reveal that compound 4f has good in vitro activity against all of the tested Gram-positive strains including MRSA and MRSE (MICs: 0.06-32μg/mL) which is two to eightfold more potent than or comparable to the parent drug CPFX (MICs: 0.25-128μg/mL), Gram-negative bacteria P. aeruginosa (MICs: 0.5-4μg/mL) and M. tuberculosis H37Rv ATCC 27294 (MIC: 1μg/mL).     

Synthesis and in vitro antitubercular activity of a series of quinoline derivatives

A series of 33 quinoline derivatives have been synthesized and evaluated for their in vitro antibacterial activity against Mycobacterium tuberculosis H₃₇Rv using the Alamar Blue susceptibility test and the activity expressed as the minimum inhibitory concentration (MIC) in μg/mL. Compounds 5e and 5f exhibited a significant activity at 6.25 and 3.12 μg/mL, respectively, when compared with first line drugs such as ethambutol and could be a good starting point to develop new lead compounds in the fight against multi-drug resistant tuberculosis.     

Benzofuran-isatin hybrids tethered via different length alkyl linkers and their in vitro anti-mycobacterial activities

A series of novel benzofuran-isatin hybrids 6a–m tethered through different length alkyl linkers propylene, butylene, pentylene and hexylene were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against both drug-susceptible and multi-drug resistant (MDR) Mycobacterium tuberculosis (MTB) and cytotoxicity towards VERO cells. All hybrids with acceptable cytotoxicity in VERO cells (CC₅₀: 64 to >1024 μg/mL) also exhibited considerable anti-mycobacterial activities against both drug-susceptible and MDR-MTB strains with MIC in a range of 0.125–4 μg/mL. The SAR indicated that the length of the linker played a pivotal role on the activity, and the longer linker could enhance the activity. The most active hybrid 6d (MIC: 0.125 and 0.125 μg/mL) was comparable to or better than rifampicin (MIC: 0.5 μg/mL) and isoniazid (MIC: 0.06 μg/mL) against MTB H₃₇Rv, and was ≥256 folds more potent than rifampicin (MIC: 64 μg/mL) and isoniazid (MIC: >128 μg/mL) against MDR-MTB strain, but was less active than TAM16 (MIC: <0.06 μg/mL against the tested two strains). The hybrid 6d also showed low cytotoxicity towards VERO cell (CC₅₀: 128 μg/mL), but it was inferior to TAM16 in metabolic stability and in vivo pharmacokinetic profiles.     

Mefloquine-oxazolidine derivatives, derived from mefloquine and arenecarbaldehydes: In vitro activity including against the multidrug-resistant tuberculosis strain T113

Ten new mefloquine-oxazolidine derivatives, 4-[(1S,8aR)-3-(aryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline (1: aryl=substituted phenyl) and 4-[(1S,8aR)-3-(heteroaryl)hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline [2: heteroaryl=5-nitrothien-2-yl (2a); 5-nitrofuran-2-yl (2b) and 4H-imidazol-2-yl) (2c)], have been synthesized and evaluated against Mycobacterium tuberculosis. Compounds 1f (aryl=3-ethoxyphenyl), 1g (Ar=3,4,5-(MeO)(3)-C(6)H(2)) and 2c were slightly more active than mefloquine (MIC=33μM) with MICs=24.5, 22.5 and 27.4, respectively, whereas compounds 1e (aryl=3,4-(MeO)(2)-C(6)H(3)) and 2a (MICs=11.9 and 12.1μM, respectively) were ca. 2.7 times more active than mefloquine, with a better tuberculostatic activity than the first line tuberculostatic agent ethambutol (MIC=15.9). The compounds were also assayed against the MDR strain T113 and the same MICs were observed. Thus the new derivatives have advantages over such anti-TB drugs as isoniazid, rifampicin, ethambutol and ofloxacin, for which this strain is resistant. The most active compounds were not cytotoxic to Murine Macrophages Cells in a concentration near their MIC values.     

Molecular weight and pH effects of aminoethyl modified chitosan on antibacterial activity in vitro

Aminoethyl modified chitosan derivatives (AEMCSs) with different molecular weight (Mw) were synthesized by grafting aminoethyl group on different molecular weight chitosans and chitooligosaccharide. FTIR, (1)H NMR, (13)C NMR, elemental analysis and potentiometric titration results showed that branched polyethylimine chitosan was synthesized. Clinical Laboratory Standard Institute (CLSI) protocols were used to determine MIC for Gram-negative strain of Escherichia coli under different pH. The antibacterial activity of the derivatives was significantly improved compared with original chitosans, with MIC values against E. coli varying from 4 to 64 μg/mL depending on different Mw and pH. High molecular weight seems to be in favor of stronger antibacterial activity. At pH 7.4, derivatives with Mw above 27 kDa exhibited equivalent antibacterial activity (16 μg/mL), while oligosaccharide chitosan derivative with lower Mw (~1.4 kDa) showed decreased MIC of 64 μg/mL. The effect of pH on antibacterial activity is more complicated. An optimal pH for HAEMCS was found around 6.5 to give MIC as low as 4 μg/mL, while higher or lower pH compromised the activity. Cell integrity assay and SEM images showed evident cell disruption, indicating membrane disruption may be one possible mechanism for antibacterial activity.