In vitro potency of 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione against drug-resistant and non-replicating persisters of Mycobacterium tuberculosis.

OBJECTIVES: New antituberculosis agents active against drug-resistant and non-replicating tubercle bacilli are required. We evaluated a previously identified hit, 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione (PAMCHD), against several clinical Mycobacterium tuberculosis isolates, including multidrug-resistant (MDR) strains and non-replicating drug-tolerant persisters of M. tuberculosis H37Rv. METHODS: PAMCHD's potential against drug-resistant M. tuberculosis was investigated by broth microdilution. CFU enumeration was performed to determine PAMCHD's activity against five types of dormant bacilli. RESULTS: No significant differences in MICs of PAMCHD were observed against M. tuberculosis H37Rv (2.5-5 µg/mL) and eight drug-susceptible strains (1.25-5 µg/mL) as well as drug-resistant strains including six isoniazid (INH)-resistant (2.5-10 µg/mL), one INH + ethambutol (EMB)-resistant (5 µg/mL), one rifampicin (RIF) + EMB-resistant (5 µg/mL) and three MDR (2.5-10 µg/mL) strains. Thus, PAMCHD maintains activity against all kinds of clinical strains, especially MDR. Regarding drug-tolerant persisters, INH and RIF killed, respectively, 0.5 and 5.0 log10 CFU of non-replicating persisters developed by hypoxia and 1.5 and 2.5 log10 CFU developed by nutrient starvation at 64 × of their respective MIC against actively dividing cultures. In contrast, PAMCHD sterilised persister cultures developed by hypoxia (killed 6.5 log10 CFU) or starvation (killed 7.5 log10 CFU). PAMCHD sterilised RIF-tolerant (tolerance level up to 100 µg/mL of RIF) 100-day-old static persisters at 64 × MIC, while moxifloxacin killed only 1.0 log10 CFU of these persisters at 64 × MIC. CONCLUSION: PAMCHD offers significant potential against MDR-TB and exhibits notable potency against non-replicating drug-tolerant M. tuberculosis persisters. These findings warrant further studies of PAMCHD for further anti-TB drug development.

In vitro antimycobacterial activity of 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione: a new chemical entity against Mycobacterium tuberculosis.

This study reports on the in vitro antituberculosis potential of 2-(((2-hydroxyphenyl) amino)methylene)-5,5-dimethylcyclohexane-1,3-dione (PAMCHD) against Mycobacterium tuberculosis H37Rv. PAMCHD has been proven to be a tuberculostatic as well as a tuberculocidal agent by agar and broth dilution methods with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values equivalent to some standard antituberculosis drugs (ATDs). The dynamics of M. tuberculosis killing revealed the time- as well as concentration-dependent antituberculosis activity of PAMCHD and it sterilized M. tuberculosis culture at or above 10.0 µg/mL. PAMCHD acts either synergistically or additively with ATDs. Isoniazid (INH) and PAMCHD post-antibiotic effects increased with concentration from 16.18 ± 13.30 and 31.64 ± 13.30 to 127.9 ± 27.60 and 138.71 ± 16.42 h, respectively, from 1 × MIC to 8 × MIC; no significant difference was observed between INH and PAMCHD post-antibiotic effects. M. tuberculosis mutation frequency against PAMCHD is lower than that of INH. Mutant prevention concentration (MPC) of INH, rifampin (RIF) and PAMCHD were observed to be 40, 160 and 160 µg/mL, respectively, and their MPC/MIC values were 128, 2051 and 64, respectively; this lowest MPC/MIC highlights the advantage of PAMCHD over RIF and INH.

Oscimum sanctum extract inhibits growth of Gram positive and Gram negative bacterial strains.

In the present study petroleum ether, chloroform and methanolic extracts of Oscimum sanctum were prepared using soxhlet extractor. The extracts were evaluated for antibacterial activity against one Gram positive (Staphylococcus aureus) and one Gram negative (Escherichia coli) strain. The activity of the extracts was compared with the known antibacterial drugs, Oflaxacin and Penicillin G. Disc diffusion method revealed good antibacterial activity of the chloroform and methanol extracts compared to the petroleum ether extract. Methanolic extract was found to be most active against both Staphylococcus aureus and Escherichia coli bacterial strains. The zone of inhibition of methanolic extract against Staphylococcus aureus and Escherichia coli at 50 mg concentration was 16.0 and 18.0 mm, respectively. Chloroform extract also exhibited good antibacterial activity against Staphylococcus aureus and Escherichia coli bacterial strains. The zone of inhibition of chloroform extract against Staphylococcus aureus and Escherichia coli bacterial strains was 8.0 and 6.0 mm, respectively. The zone of inhibition of the drug Penicillin G against Escherichia coli and Staphylococcus aureus was18.0 and 17.0 mm, respectively. Oflaxacin showed zone of inhibition to be 19.0 and 20.0 against Escherichia coli and Staphylococcus aureus, respectively. The petroleum ether extract exhibited no activity against any of the two tested bacterial strains. These findings suggest that methanolic extract of Oscimum sanctum has anti-bacterial potential and therefore should be investigated for phytochemistry.

Preparation and evaluation of antibacterial potential of Pithecellobium dulce root extract against Gram positive and Gram negative bacteria.

In the present study hexane, benzene, ethyl acetate and ethanol extracts of Pithecellobium dulce root were prepared using soxhlet extractor. The extracts were evaluated for antibacterial activity against one Gram positive (Staphylococcus aureus) and three Gram negative (Acetobacter aceti, Acetobacter aceti, Klebsiella pneumoniae) strains. Disc diffusion method revealed promising antibacterial activity of the extracts prepared in polar solvents (ethyl acetate and ethanol) compared to non-polar solvents (hexane and benzene). Ethanolic root extract was found to be most active against Acetobacter aceti, Staphylococcus aureus, Klebsiella pneumonia and Enterobacter aerogenes bacterial strains. The zone of inhibition of ethanolic root extract against Acetobacter aceti, Staphylococcus aureus, Klebsiella pneumonia and Enterobacter aerogenes bacterial strains was 15.4, 11.0, 19.0 and 13.0 mm, respectively at 100 mg concentration. Ethyl acetate extract also exhibited good antibacterial activity against Entrobacter aerogenes, Klebsiella pneumonia and Acetobacter aceti. The zone of inhibition of ethyl acetate root extracts against Entrobacter aerogenes, Acetobacter aceti and Klebsiella pneumonia was 10.5, 18.0 and 10.0 mm, respectively. The benzene extract showed some activity against Acetobacter aceti with the zone of inhibition 10.0 mm. The antibacterial activity of Pithecellobium dulce root hexane extract was found to be negligible against all the four tested strains of bacteria. These findings suggest that ethanolic and ethyl acetate root extracts of Pithecellobium dulce has potential as effective anti-bacterial agent.

Synthesis and in vitro evaluation of 2-(((2-ether)amino)methylene)-dimedone derivatives as potential antimicrobial agents.

The study was designed with an aim to synthesize a series of 2-(((2-ether)amino)methylene)-dimedone derivatives and evaluate the synthesized compounds for antimicrobial activity. Compound library was synthesized by reaction with alkyl, alkenyl, alkynyl and alicyclic bromo-compounds. Characterization of the synthesized compounds was performed by 1H NMR, 13C NMR and mass spectral techniques. The compounds were evaluated for their antibacterial activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis, Clostridium sporogenes) and Gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli). The activity of these compounds was also evaluated against fungi (Aspergillus fumigatus, Penicillium chrysogenum, Fusarium oxysporum, Candida albicans) and molds (A. niger and A. oryzae). Broth microdilution method and CLSI guidelines with minor modification were used for the determination of anti-bacterial and antifungal activity, respectively. Although four compounds (4i, 4j, 4k and 4l) showed good antibacterial activity but compound 4k was found to be most active chemotype in the series. Compound 4k was found to be active against S. aureus, B. cereus and B. subtilis bacterial strains at one dilution lower compared to the control ciprofloxacin. Antibacterial activity of compound 4k was comparable to ciprofloxacin against S. pyogenes and M. luteus. The compound 4d, 4e and 4s showed good antifungal and antimold activity compared to other chemotypes. However, in comparison to fluconazole both the compounds showed lower activity. The results merit the antimicrobial promise of the 2-(((2-ether)amino)methylene)-dimedone analogs.

The synthesis, biological evaluation and structure-activity relationship of 2-phenylaminomethylene-cyclohexane-1,3-diones as specific anti-tuberculosis agents.

The present study utilised whole cell based phenotypic screening of thousands of diverse small molecules against Mycobacterium tuberculosis H37Rv (M. tuberculosis) and identified the cyclohexane-1,3-dione-based structures 5 and 6 as hits. The selected hit molecules were used for further synthesis and a library of 37 compounds under four families was synthesized for lead generation. Evaluation of the library against M. tuberculosis lead to the identification of three lead antituberculosis agents (37, 39 and 41). The most potential compound, 2-(((2-hydroxyphenyl)amino)methylene)-5,5-dimethylcyclohexane-1,3-dione (39) showed an MIC of 2.5 µg mL-1, which falls in the range of MICs values found for the known antituberculosis drugs ethambutol, streptomycin and levofloxacin. Additionally, this compound proved to be non-toxic (<20% inhibition at 50 µM concentration) against four human cell lines. Like first line antituberculosis drugs (isoniazid, rifampicin and pyrazinamide) this compound lacks activity against general Gram positive and Gram negative bacteria and even against M. smegmatis; thereby reflecting its highly specific antituberculosis activity.

Synthesis and screening of ursolic acid-benzylidine derivatives as potential anti-cancer agents.

Ursolic acid present abundantly in plant kingdom is a well-known compound with various promising biological activities including, anti-cancer, anti-inflammatory, hepatoprotective, antiallergic and anti-HIV properties. Herein, a library of ursolic acid-benzylidine derivatives have been designed and synthesized using Claisen Schmidt condensation of ursolic acid with various aromatic aldehydes in an attempt to develop potent antitumor agents. The compounds were evaluated against a panel of four human carcinoma cell lines including, A-549 (lung), MCF-7 (breast), HCT-116 (colon), THP-1 (leukemia) and a normal human epithelial cell line (FR-2). The results from MTT assay revealed that all the compounds displayed high level of antitumor activities compared with the triazole analogs (previously reported) and the parent ursolic acid. However, compound 3b, the most active derivative was subjected to mechanistic studies to understand the underlying mechanism. The results revealed that compound 3b induced apoptosis in HCT-116 cell lines, arrest cell cycle in the G1 phase, caused accumulation of cytochrome c in the cytosol and increased the expression levels of caspase-9 and caspase-3 proteins. Therefore, compound 3b induces apoptosis in HCT-116 cells through mitochondrial pathway.

Promise of Retinoic Acid-Triazolyl Derivatives in Promoting Differentiation of Neuroblastoma Cells.

Retinoic acid induces differentiation in various types of cells including skeletal myoblasts and neuroblasts and maintains differentiation of epithelial cells. The present study demonstrates synthesis and screening of a library of retinoic acid-triazolyl derivatives for their differentiation potential on neuroblastoma cells. Click chemistry approach using copper(I)-catalyzed azide-alkyne cycloaddition was adopted for the preparation of these derivatives. The neurite outgrowth promoting potential of retinoic acid-triazolyl derivatives was studied on neuroblastoma cells. Morphological examination revealed that compounds 8a, 8e, 8f, and 8k, among the various derivatives screened, exhibited promising neurite-outgrowth inducing activity at a concentration of 10 µM compared to undifferentiated and retinoic acid treated cells. Further on, to confirm this differentiation potential of these compounds, neuroblastoma cells were probed for expression of neuronal markers such as NF-H and NeuN. The results revealed a marked increase in the NF-H and NeuN protein expression when treated with 8a, 8e, 8f, and 8k compared to undifferentiated and retinoic acid treated cells. Thus, these compounds could act as potential leads in inducing neuronal differentiation for future studies.

Metal free stereoselective synthesis of functionalized enamides.

An efficient and expeditious DABCO-mediated synthesis of functionalized enamides from alkenes is delineated. The reaction proceeds through an unprecedented cascade involving an Aza-Michael addition/α-bromination/elimination and a Morita-Baylis-Hillman type reaction to generate functionalized enamides in a regio- & stereoselective fashion.