Novel quinoline and naphthalene derivatives as potent antimycobacterial agents

Eleutherlenes A-D, Diverse Types of Naphthalene Derivatives with Anti-inflammatory Activity from Eleutherine bulbosa

Eleutherlene A (1), an unprecedented carbon skeleton featuring an aryl-fused 6-methyl-2,7-dioxabicyclo[3.2.1]octane unit, and eleutherlene B (2), a naphthoquinone derivative with interesting ring fusion of an α,β-unsaturated γ-lactam and a tetrahydropyran moiety, along with two novel naphthoquinone alkaloids, eleutherlenes C (3) and D (4), were isolated from Eleutherine bulbosa and identified. Their structures were elucidated by spectroscopic analyses along with computer-assisted structure elucidation, including ACD/Structure Elucidator and computational calculations and X-ray crystal diffraction. A plausible biosynthetic route for 1 and 2 was proposed. Compound 1 showed significant anti-inflammatory activity with respect to the inhibition of pro-inflammatory mediators NO, IL-1β, iNOS, and COX-2. Mechanistically, compound 1 inhibited the inflammatory response by suppressing NF-κB/MAPK and activating the Nrf2/Keap1 signaling pathway in LPS-induced RAW 264.7 cells.

Efficacy of mefloquine and its enantiomers in a murine model of Mycobacterium avium infection

The treatment of Mycobacterium avium infections is still long, complex, and often poorly tolerated, besides emergence of resistances. New active molecules that are more effective and better tolerated are deeply needed. Mefloquine and its enantiomers ((+) Erythro-mefloquine ((+)-EMQ) and (-)-Erythro-mefloquine ((-)-EMQ)) have shown efficacy in both in vitro and in vivo, in a mouse model of M. avium intraveinous infection. However, no study reports aerosol model of infection or combination with gold standard treatment. That was the aim of our study. In an aerosol model of M. avium infection in BALB/c mice, we used five treatment groups as followed: Clarithromycin-Ethambutol-Rifampicin (CLR-EMB-RIF, standard of care, n = 15), CLR-EMB-MFQ (n = 15), CLR-EMB-(+)-EMQ (n = 15), CLR-EMB-(-)-EMQ (n = 15) and an untreated group (n = 25). To evaluate drug efficacy, we sacrificed each month over 3 months, 5 mice from each group. Lung homogenates were diluted and plated for colony forming unit count (CFU) expressed in Log10. At each time point, we found a significant difference between the untreated group and each of the treatment groups (p<0.005). The (+)-EMQ-CLR-EMB group was the group with the lowest CFU count at each time point but never reached statistical significance. The results of each group 3 months after treatment are: (+)-EMQ-CLR-EMB (4.43 ± 0.26), RIF-CLR-EMB (4.83 ± 0.37), (-)-EMQ-CLR-EMB (4.82 ± 0.18), MFQ-CLR-EMB (4.70 ± 0.21). In conclusion, MFQ and its enantiomers appear to be as effective as rifampicin in combination therapy. Further studies are needed to evaluate the ability of these drugs to prevent selection of clarithromycin resistant strains and potential for lung sterilization.

Generation of Aurachin Derivatives by Whole-Cell Biotransformation and Evaluation of Their Antiprotozoal Properties

The natural product aurachin D is a farnesylated quinolone alkaloid, which is known to possess activity against the causative agent of malaria, Plasmodium spp. In this study, we show that aurachin D inhibits other parasitic protozoa as well. While aurachin D had only a modest effect on Trypanosoma brucei rhodesiense, two other trypanosomatids, T. cruzi and Leishmania donovani, were killed at low micromolar and nanomolar concentrations, respectively, in an in vitro assay. The determined IC₅₀ values of aurachin D were even lower than those of the reference drugs benznidazole and miltefosine. Due to these promising results, we set out to explore the impact of structural modifications on the bioactivity of this natural product. In order to generate aurachin D derivatives with varying substituents at the C-2, C-6 and C-7 position of the quinolone ring system, we resorted to whole-cell biotransformation using a recombinant Escherichia coli strain capable of aurachin-type prenylations. Quinolone precursor molecules featuring methyl, methoxy and halogen groups were fed to this E. coli strain, which converted the substrates into the desired analogs. None of the generated derivatives exhibited improved antiprotozoal properties in comparison to aurachin D. Obviously, the naturally occurring aurachin D features already a privileged structure, especially for the inhibition of the causative agent of visceral leishmaniasis.

Development of Novel Isatin-Tethered Quinolines as Anti-Tubercular Agents against Multi and Extensively Drug-Resistant Mycobacterium tuberculosis

We describe the design and synthesis of two isatin-tethered quinolines series (Q6a-h and Q8a-h), in connection with our research interest in developing novel isatin-bearing anti-tubercular candidates. In a previous study, a series of small molecules bearing a quinoline-3-carbohydrazone moiety was developed as anti-tubercular agents, and compound IV disclosed the highest potency with MIC value equal to 6.24 µg/mL. In the current work, we adopted the bioisosteric replacement approach to replace the 3,4,5-trimethoxy-benzylidene moiety in the lead compound IV with the isatin motif, a privileged scaffold in the TB drug discovery, to furnish the first series of target molecules Q6a-h. Thereafter, the isatin motif was N-substituted with either a methyl or benzyl group to furnish the second series Q8a-h. All of the designed quinoilne-isatin conjugates Q6a-h and Q8a-h were synthesized and then biologically assessed for anti-tubercular actions towards drug-susceptible, MDR, and XDR strains. Superiorly, the N-benzyl-bearing compound Q8b possessed the best activities against the examined M. tuberculosis strains with MICs equal 0.06, 0.24, and 1.95 µg/mL, respectively.

Plant growth promoting endophyte Burkholderia contaminans NZ antagonizes phytopathogen Macrophomina phaseolina through melanin synthesis and pyrrolnitrin inhibition

The endophytic bacterium Burkholderia contaminans NZ was isolated from jute, which is an important fiber-producing plant. This bacterium exhibits significant growth promotion activity in in vivo pot experiments, and like other plant growth-promoting (PGP) bacteria fixes nitrogen, produces indole acetic acid (IAA), siderophore, and 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. B. contaminans NZ is considered to exert a promising growth inhibitory effect on Macrophomina phaseolina, a phytopathogen responsible for infecting hundreds of crops worldwide. This study aimed to identify the possibility of B. contaminans NZ as a safe biocontrol agent and assess its effectiveness in suppressing phytopathogenic fungi, especially M. phaseolina. Co-culture of M. phaseolina with B. contaminans NZ on both solid and liquid media revealed appreciable growth suppression of M. phaseolina and its chromogenic aberration in liquid culture. Genome mining of B. contaminans NZ using NaPDoS and antiSMASH revealed gene clusters that displayed 100% similarity for cytotoxic and antifungal substances, such as pyrrolnitrin. GC-MS analysis of B. contaminans NZ culture extracts revealed various bioactive compounds, including catechol; 9,10-dihydro-12'-hydroxy-2'-methyl-5'-(phenylmethyl)- ergotaman 3',6',18-trione; 2,3-dihydro-3,5- dihydroxy-6-methyl-4H-pyran-4-one; 1-(1,6-Dioxooctadecyl)- pyrrolidine; 9-Octadecenamide; and 2- methoxy- phenol. These compounds reportedly exhibit tyrosinase inhibitory, antifungal, and antibiotic activities. Using a more targeted approach, an RP-HPLC purified fraction was analyzed by LC-MS, confirming the existence of pyrrolnitrin in the B. contaminans NZ extract. Secondary metabolites, such as catechol and ergotaman, have been predicted to inhibit melanin synthesis in M. phaseolina. Thus, B. contaminans NZ appears to inhibit phytopathogens by apparently impairing melanin synthesis and other potential biochemical pathways, exhibiting considerable fungistatic activity.

Inhibitors of F1F0-ATP synthase enzymes for the treatment of tuberculosis and cancer

The spectacular success of the mycobacterial F₁F₀-ATP synthase inhibitor bedaquiline for the treatment of drug-resistant tuberculosis has generated wide interest in the development of other inhibitors of this enzyme. Work in this realm has included close analogues of bedaquiline with better safety profiles and 'bedaquiline-like' compounds, some of which show potent antibacterial activity in vitro although none have yet progressed to clinical trials. The search has lately extended to a range of new scaffolds as potential inhibitors, including squaramides, diaminoquinazolines, chloroquinolines, dihydropyrazolo[1,5-a]pyrazin-4-ones, thiazolidinediones, diaminopyrimidines and tetrahydroquinolines. Because of the ubiquitous expression of ATP synthase enzymes, there has also been interest in inhibitors of other bacterial ATP synthases, as well as inhibitors of human mitochondrial ATP synthase for cancer therapy. The latter encompass both complex natural products and simpler small molecules. The review seeks to demonstrate the breadth of the structural types of molecules able to effectively inhibit the function of variants of this intriguing enzyme.

Directed Ortho and Remote Metalation of Naphthalene 1,8-Diamide: Complementing SEAr Reactivity for the Synthesis of Substituted Naphthalenes

Mono- and dianion species of 1,8-naphthalene diamide 2 were generated under sec-BuLi/TMEDA conditions and trapped with a variety of electrophiles to give 2- and 2,7- substituted products 3 and 4. Using Suzuki-Miyaura cross-coupling, mono- and di-iodinated products were converted into the corresponding 2-aryl (5) and 2,7-diaryl (6) products, respectively. The amide-amide rotation barrier of 2 was established by VT NMR, and the structure of fluorenone structure 9, obtained by remote metalation, was secured.

Analysis of Approaches to Anti-tuberculosis Compounds

Mycobacterium tuberculosis (Mtb) remains a deadly pathogen two decades after the announcement of tuberculosis (TB) as a global health emergency by the World Health Organization. Medicinal chemistry efforts to synthesize potential drugs to shorten TB treatments have not always been successful. Here, we analyze physiochemical properties of 39 TB drugs and 1271 synthetic compounds reported in 40 publications from 2006 to early 2020. We also propose a new TB space of physiochemical properties that may provide more appropriate guidelines for design of anti-TB drugs.

SAR Analysis of Small Molecules Interfering with Energy-Metabolism in Mycobacterium tuberculosis

Tuberculosis remains the world's top infectious killer: it caused a total of 1.5 million deaths and 10 million people fell ill with TB in 2018. Thanks to TB diagnosis and treatment, mortality has been falling in recent years, with an estimated 58 million saved lives between 2000 and 2018. However, the emergence of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains is a major concern that might reverse this progress. Therefore, the development of new drugs acting upon novel mechanisms of action is a high priority in the global health agenda. With the approval of bedaquiline, which targets mycobacterial energy production, and delamanid, which targets cell wall synthesis and energy production, the energy-metabolism in Mtb has received much attention in the last decade as a potential target to investigate and develop new antimycobacterial drugs. In this review, we describe potent anti-mycobacterial agents targeting the energy-metabolism at different steps with a special focus on structure-activity relationship (SAR) studies of the most advanced compound classes.

Design, synthesis and biological evaluation of novel triaryldimethylaminobutan-2-ol derivatives against Mycobacterium tuberculosis

Bedaquiline (TMC207), a typical diarylquinoline anti-tuberculosis drug, has been approved by FDA to specifically treat MDR-TB. Herein we describe design, synthesis, and in vitro biological evaluation against Mycobacterium tuberculosis of a series of triaryldimethylaminobutan-2-ol derivatives obtaining from the structural modification of TMC207. Compounds 23, 25, 28, 32, 39 and 43 provided superior anti-mycobacterial activity than positive control PC01 which shows the same configuration and contains TMC207. Compounds 16, 20, 29, 34, 37, 45 and 47 exhibited the similar activity to positive control PC01. Most importantly, the series of compounds showed excellent activity against XDR-Mtb. The result of acute toxicity suggested that this class of triaryldimethylaminobutan-2-ol derivatives should be graded as low. Further SAR analysis indicates that a large steric bulk of triaryl and 7-Br, 3-OCH₃ on 1-naphthyl are critical.

Insight into antimicrobial activity of substituted phenylcarbamoyloxypiperazinylpropanols

3-[4-(Substituted)phenyl-/4-(diphenylmethyl)phenylpiperazin-1-yl]-2-hydroxypropyl-1-[(substituted)phenyl]carbamates and their salts with hydrochloric acid were synthesized, characterized, and tested in vitro against Staphylococcus aureus ATCC 29213 and Enterococcus faecalis ATCC 29212 as reference and quality control strains, against three methicillin-resistant isolates of S. aureus, and three isolates of vancomycin-resistant E. faecalis. All the compounds were evaluated against Mycobacterium tuberculosis H₃₇R_a/ATCC 25177, M. kansasii DSM 44162, and M. smegmatis ATCC 700084. All of the tested compounds demonstrated very good activity against all the tested strains/isolates comparable with or better than that of clinically used drugs (ampicillin, ciprofloxacin, vancomycin, isoniazid). 1-[{(3-Trifluoromethyl)phenyl}carbamoyloxy-2-hydroxypropyl]-4-(3,4-dichlorophenyl)piperazin-1-ium chloride demonstrated the highest potency against all the tested strains/isolates (MICs ranged from 3.78 to 30.2 µM), and 1-[{(3-trifluoromethyl)phenyl}carbamoyloxy-2-hydroxypropyl]-4-(diphenylmethyl)piperazin-1-ium chloride was the most effective against all the screened mycobacterial strains (MICs ranged from 3.64 to 14.5 µM). All the investigated derivatives had strong antibiofilm activity against S. aureus ATCC 29123 and a synergistic or additive effect with gentamicin against isolates of E. faecalis with both intrinsic and acquired resistance to gentamicin. The screening of the cytotoxicity of the compounds was performed using human monocytic leukemia THP-1 cells. The IC₅₀ values of the most effective compounds ranged from ca. 2.8 to 7.3 µM; thus, it can be stated that the antimicrobial effect is closely connected with their cytotoxicity. These observations disqualify these compounds from further development as antimicrobial agents, but they can be considered potential multi-target drugs with a preferred anticancer effect with good water solubility and additional anti-infectious activity.

Synthetic approaches towards bedaquiline and its derivatives

Bedaquiline is a diarylquinoline drug that demonstrates potent and selective inhibition of mycobacterial ATP synthase, and is clinically administered for the treatment of multi-drug resistant tuberculosis. Due to its excellent activity and novel mechanism of action, bedaquiline has been the focus of a number of synthetic studies. This review will discuss these synthetic approaches, as well as the synthesis and bioactivity of the numerous derivatives and molecular probes inspired by bedaquiline.

Activity of N-Phenylpiperazine Derivatives Against Bacterial and Fungal Pathogens

BACKGROUND

As the bacterial resistance to antibacterial chemotherapeutics is one of the greatest problems in modern medicine, efforts are made to develop new antimicrobial drugs. Compounds with a piperazine ring have proved to be promising agents against various pathogens.

OBJECTIVE

The aim of the study was to prepare a series of new N-phenylpiperazines and determine their activity against various pathogens.

METHOD

Target compounds were prepared by multi-step synthesis starting from an appropriate substituted acid to an oxirane intermediate reacting with 1-(4-nitrophenyl)piperazine. Lipophilicity and pKa values were experimentally determined. Other molecular parameters were calculated. The inhibitory activity of the target compounds against Staphylococcus aureus, four mycobacteria strains, Bipolaris sorokiniana, and Fusarium avenaceum was tested. In vitro antiproliferative activity was determined on a THP-1 cell line, and toxicity against plant was determined using Nicotiana tabacum.

RESULTS

In general, most compounds demonstrated only moderate effects. 1-(2-Hydroxy-3-{[4-(propan- 2-yloxy)benzoyl]oxy}propyl)-4-(4-nitrophenyl)piperazinediium dichloride and 1-{3-[(4-butoxybenzoyl)- oxy]-2-hydroxypropyl}-4-(4-nitrophenyl)piperazinediium dichloride showed the highest inhibition activity against M. kansasii (MIC = 15.4 and 15.0 µM, respectively) and the latter also against M. marinum (MIC = 15.0 µM). 1-(2-Hydroxy-3-{[4-(2-propoxyethoxy)benzoyl]oxy}propyl)-4-(4-nitrophenyl)piperazinediium dichloride had the highest activity against F. avenaceum (MIC = 14.2 µM). All the compounds showed only insignificant toxic effects on human and plant cells.

CONCLUSION

Ten new 1-(4-nitrophenyl)piperazine derivatives were prepared and analyzed, and their antistaphylococcal, antimycobacterial, and antifungal activities were determined. The activity against M. kansasii was positively influenced by higher lipophilicity, the electron-donor properties of substituent R and a lower dissociation constant. The exact mechanism of action will be investigated in follow-up studies.

Synthesis of thieno[2,3-b]quinoline and selenopheno[2,3-b]quinoline derivatives via iodocyclization reaction and a DFT mechanistic study

In this letter, we report the regioselective iodocyclization reaction of 3-alkynyl-2-(methylthio)quinolines and 3-alkynyl-2-(methylseleno)quinolines for the synthesis of thieno[2,3-b]quinoline and selenopheno[2,3-b]quinoline derivatives. Furthermore, by employing various palladium-catalyzed Sonogashira, Suzuki, and Heck reactions, the structural diversification of the resulting halide derivatives, which can act as the important intermediates for building other valuable compounds, was achieved. All compounds were fully characterized by the FT-IR, mass, ¹H NMR, and ¹³C NMR spectral data. Finally, the structure of the thieno[2,3-b]quinoline derivative was confirmed by X-ray crystallography. This methodology provided a novel pathway to access quinoline fused heterocycles via iodocyclization reaction. Furthermore, the reaction process was well elucidated by density functional theory calculations.

Synthesis and Cytotoxicity Studies on Novel Piperazinylacetamides

Background:

In this study, nine novel compounds, bearing N-[2-(4-substituted piperazine-1-yl)acetyl]-N’-[bis-(4-fluorophenyl)methyl]piperazine structures were synthesized.

Methods:

Their cytotoxic properties were evaluated in vitro by NCI-60 Sulforhodamine B (SRB) assay against human cancer cell lines: Huh7 (hepatocellular), MCF7 (breast) and HCT116 (colorectal).

Results and Conclusion:

According to the activity data, most of the compounds are more cytotoxic than 5-fluorouracil against Huh7 and HCT116 cancer cell lines.

Naphthalene, a versatile platform in medicinal chemistry: Sky-high perspective

Naphthalene, a cytotoxic moiety, is an extensively explored aromatic conjugated system with applications in various pathophysiological conditions viz. anticancer, antimicrobial, anti-inflammatory, antiviral, antitubercular, antihypertensive, antidiabetic, anti-neurodegenerative, antipsychotic, anticonvulsant, antidepressant. Naphthalene epoxides and naphthoquinones are most reactive metabolites of naphthalene and are responsible for the covalent interaction with cysteine amino acid of cellular proteins for cytotoxic nature. Many naphthalene derived bioactive phytoconstituents are present in nature including podophyllotoxins (Etoposide, teniposide), bis-ANS 82, Rifampicin, Justiprocumin A, B, Patentiflorin A. The naphthalene-based molecules, viz. Naphyrone, tolnaftate, naftifine, nafcillin, terbinafine, propranolol, nabumetone, nafimidone, naproxen, duloxetine, lasofoxifene, bedaquiline etc. have also been approved by FDA and are being marketed as therapeutics. Thus, the naphthalene scaffold emerges as an important building block in drug discovery owing to its broad spectrum of biological activities through varying structural modifications. This review incorporates the pharmacological aspects of different types of chemically modified naphthalene-based molecules along with their activity profile. This compiled information may serve as a benchmark for the alteration of existing ligands to design novel potent molecules with lesser side effects.

Probability-driven 3D pharmacophore mapping of antimycobacterial potential of hybrid molecules combining phenylcarbamoyloxy and N-arylpiperazine fragments

The current study examines in silico characterization of the structure-inhibitory potency for a set of phenylcarbamic acid derivatives containing an N-arylpiperazine scaffold, considering the electronic, steric and lipophilic properties. The main objective of the ligand-based modelling was the systematic study of classical comparative molecular field analysis (CoMFA)/comparative molecular surface analysis (CoMSA) performance for the modelling of in vitro efficiency observed for these phenylcarbamates, revealing their inhibitory activities against a virulent Mycobacterium tuberculosis H₃₇R_v strain. We compared the findings of efficiency modelling produced by a standard 3D methodology (CoMFA) and its neural counterparts (CoMSA) regarding multiple training/test subsets and variables used. Moreover, systematic space inspection, splitting values into the analysed training/test subsets, was performed to monitor statistical estimator performance while mapping the probability-driven pharmacophore pattern. Consequently, a 'pseudo-consensus' 3D-quantitative structure-activity relationship (3D-QSAR) approach was applied to retrieve an 'average' pharmacophore hypothesis by the investigation of the most densely populated training/test subpopulations to specify the potentially important factors contributing to the inhibitory activity of phenylcarbamic acid analogues. In addition, examination of descriptor-based similarity with a principal component analysis (PCA) procedure was employed to visualize noticeable variations in the performance of these molecules with respect to their structure and activity profiles.

Synthesis and Spectrum of Biological Activities of Novel N-arylcinnamamides

A series of sixteen ring-substituted N-arylcinnamamides was prepared and characterized. Primary in vitro screening of all the synthesized compounds was performed against Staphylococcus aureus, three methicillin-resistant S. aureus strains, Mycobacterium tuberculosis H37Ra, Fusarium avenaceum, and Bipolaris sorokiniana. Several of the tested compounds showed antistaphylococcal, antitubercular, and antifungal activities comparable with or higher than those of ampicillin, isoniazid, and benomyl. (2E)-N-[3,5-bis(trifluoromethyl)phenyl]-3-phenylprop-2-enamide and (2E)-3-phenyl-N-[3-(trifluoromethyl)phenyl]prop-2-enamide showed the highest activities (MICs = 22.27 and 27.47 µM, respectively) against all four staphylococcal strains and against M. tuberculosis. These compounds showed an activity against biofilm formation of S. aureus ATCC 29213 in concentrations close to MICs and an ability to increase the activity of clinically used antibiotics with different mechanisms of action (vancomycin, ciprofloxacin, and tetracycline). In time-kill studies, a decrease of CFU/mL of >99% after 8 h from the beginning of incubation was observed. (2E)-N-(3,5-Dichlorophenyl)- and (2E)-N-(3,4-dichlorophenyl)-3-phenylprop-2-enamide had a MIC = 27.38 µM against M. tuberculosis, while a significant decrease (22.65%) of mycobacterial cell metabolism determined by the MTT assay was observed for the 3,5-dichlorophenyl derivative. (2E)-N-(3-Fluorophenyl)- and (2E)-N-(3-methylphenyl)-3-phenylprop-2-enamide exhibited MICs = 16.58 and 33.71 µM, respectively, against B. sorokiniana. The screening of the cytotoxicity of the most effective antimicrobial compounds was performed using THP-1 cells, and these chosen compounds did not shown any significant lethal effect. The compounds were also evaluated for their activity related to the inhibition of photosynthetic electron transport (PET) in spinach (Spinacia oleracea L.) chloroplasts. (2E)-N-(3,5-dichlorophenyl)-3-phenylprop-2-enamide (IC₅₀ = 5.1 µM) was the most active PET inhibitor. Compounds with fungicide potency did not show any in vivo toxicity against Nicotiana tabacum var. Samsun. The structure–activity relationships are discussed.

Crystal structure and Hirshfeld surface analysis and energy frameworks of 1-(2,4-di-methyl-phen-yl)-4-(4-meth-oxy-phen-yl)naphthalene

In the title compound, C25H22O, the two rings of the naphthalene system are inclined to each other by 3.06 (15)°. The mean plane of the naphthalene ring system makes a dihedral angle of 65.24 (12)° with the di-methyl-phenyl ring and 55.82 (12)° with the meth-oxy-phenyl ring. The di-methyl-phenyl ring is inclined to the meth-oxy-phenyl ring by 59.28 (14)°. In the crystal, adjacent mol-ecules are linked via C-H⋯π inter-actions, forming chains along [100]. Using Hirshfeld surface and two-dimensional fingerprint plots, the presence of short inter-molecular inter-actions in the crystal structure were analysed. The inter-molecular inter-action energies were also calculated and their distribution over the crystal structure was visualized graphically using energy frameworks.

Recent advances of imidazole-containing derivatives as anti-tubercular agents

Tuberculosis still remains one of the most common, communicable, and leading deadliest diseases known to mankind throughout the world. Drug-resistance in Mycobacterium tuberculosis which threatens to worsen the global tuberculosis epidemic has caused great concern in recent years. To overcome the resistance, the development of new drugs with novel mechanisms of actions is of great importance. Imidazole-containing derivatives endow with various biological properties, and some of them demonstrated excellent anti-tubercular activity. As the most emblematic example, 4-nitroimidazole delamanid has already received approval for treatment of multidrug-resistant tuberculosis infected patients. Thus, imidazole-containing derivatives have caused great interests in discovery of new anti-tubercular agents. Numerous of imidazole-containing derivatives were synthesized and screened for their in vitro and in vivo anti-mycobacterial activities against both drug-sensitive and drug-resistant Mycobacterium tuberculosis pathogens. This review aims to outline the recent advances of imidazole-containing derivatives as anti-tubercular agents, and summarize the structure-activity relationship of these derivatives. The enriched structure-activity relationship may pave the way for the further rational development of imidazole-containing derivatives as anti-tubercular agents.

Crystal structure of dimethyl 1-oxo-2,4-di-phenyl-1,2-dihydronaphthalene-2,3-di-carboxyl-ate

In the title compound, C₂₆H₂₀O₅, a 1,2-di-hydro-naphthalene derivative, the cyclo-hexa-1,3-diene ring of the 1,2-di-hydro-naphthalene ring system adopts a half-chair conformation. The mean plane of the 1,2-di-hydro-napthalene ring system makes dihedral angles of 86.23 (6) and 64.80 (7)° with two phenyl rings. The carbonyl O atom attached to the di-hydro-naphthalene ring system deviates from the mean plane of the 1,2-di-hydro-naphthalene ring system by 0.618 (1) Å. In the crystal, the mol-ecules are linked into layers parallel to the bc plane via two kinds of C-H⋯O inter-actions, one of which forms a C(10) chain motif running along the c-axis direction and the other forms an R²₂(6) ring motif. Adjacent layers are further connected by C-H⋯π and offset π-π inter-actions [centroid-centroid distance = 3.6318 (9) Å].

Synthesis and In Vitro Antimycobacterial Activity of Novel N-Arylpiperazines Containing an Ethane-1,2-diyl Connecting Chain

Novel 1-(2-{3-/4-[(alkoxycarbonyl)amino]phenyl}-2-hydroxyethyl)-4-(2-fluorophenyl)-piperazin-1-ium chlorides (alkoxy = methoxy to butoxy; 8a-h) have been designed and synthesized through multistep reactions as a part of on-going research programme focused on finding new antimycobacterials. Lipophilic properties of these compounds were estimated by RP-HPLC using methanol/water mobile phases with a various volume fraction of the organic modifier. The log k_w values, which were extrapolated from intercepts of a linear relationship between the logarithm of a retention factor k (log k) and volume fraction of a mobile phase modifier (ϕ_M), varied from 2.113 (compound 8e) to 2.930 (compound 8h) and indicated relatively high lipophilicity of these salts. Electronic properties of the molecules 8a-h were investigated by evaluation of their UV/Vis spectra. In a next phase of the research, the compounds 8a-h were in vitro screened against M. tuberculosis CNCTC My 331/88 (identical with H₃₇R_v and ATCC 2794), M. kansasii CNCTC My 235/80 (identical with ATCC 12478), a M. kansasii 6 509/96 clinical isolate, M. avium CNCTC My 330/80 (identical with ATCC 25291) and M. avium intracellulare ATCC 13950, respectively, as well as against M. kansasii CIT11/06, M. avium subsp. paratuberculosis CIT03 and M. avium hominissuis CIT10/08 clinical isolates using isoniazid, ethambutol, ofloxacin, ciprofloxacin or pyrazinamide as reference drugs. The tested compounds 8a-h were found to be the most promising against M. tuberculosis; a MIC = 8 μM was observed for the most effective 1-(2-{4-[(butoxycarbonyl)amino]phen-ylphenyl}-2-hydroxyethyl)-4-(2-fluorophenyl)piperazin-1-ium chloride (8h). In addition, all of them showed low (insignificant) in vitro toxicity against a human monocytic leukemia THP-1 cell line, as observed LD₅₀ values > 30 μM indicated. The structure-antimycobacterial activity relationships of the analyzed 8a-h series are also discussed.

Triazole derivatives and their anti-tubercular activity

Tuberculosis (TB) remains one of the most widespread and leading deadliest diseases, threats one-third of the world's population. Although numerous efforts have been undertaken to develop new anti-TB agents, only a handful of compounds have entered human trials in the past 5 decades. Triazoles including 1,2,3-triazole and 1,2,4-triazole are one of the most important classes of nitrogen containing heterocycles that exhibited various biological activities. Triazole derivatives are regarded as a new class of effective anti-TB candidates owing to their potential anti-TB potency. Thus, molecules containing triazole moiety may show promising in vitro and in vivo anti-TB activities and might be able to prevent the drug resistant to certain extent. This review outlines the advances in the application of triazole-containing hybrids as anti-TB agents, and discusses the structure-activity relationship of these derivatives.

Structural Simplification of Bedaquiline: the Discovery of 3-(4-(N,N-Dimethylaminomethyl)phenyl)quinoline-Derived Antitubercular Lead Compounds

Bedaquiline (BDQ) is a novel and highly potent last-line antituberculosis drug that was approved by the US FDA in 2013. Owing to its stereo-structural complexity, chemical synthesis and compound optimization are rather difficult and expensive. This study describes the structural simplification of bedaquiline while preserving antitubercular activity. The compound's structure was split into fragments and reassembled in various combinations while replacing the two chiral carbon atoms with an achiral linkage instead. Four series of analogues were designed; these candidates retained their potent antitubercular activity at sub-microgram per mL concentrations against both sensitive and multidrug-resistant (MDR) Mycobacterium tuberculosis strains. Six out of the top nine MIC-ranked candidates were found to inhibit mycobacterial ATP synthesis activity with IC₅₀ values between 20 and 40 μm, one had IC₅₀ >66 μm, and two showed no inhibition, despite their antitubercular activity. These results provide a basis for the development of chemically less complex, lower-cost bedaquiline derivatives and describe the identification of two derivatives with antitubercular activity against non-ATP synthase related targets.

The Structure-Antimicrobial Activity Relationships of a Promising Class of the Compounds Containing the N-Arylpiperazine Scaffold

This research was focused on in silico characterization and in vitro biological testing of the series of the compounds carrying a N-arylpiperazine moiety. The in silico investigation was based on the prediction of electronic, steric and lipohydrophilic features. The molecules were screened against Mycobacterium avium subsp. paratuberculosis CIT03, M. smegmatis ATCC 700084, M. kansasii DSM 44162, M. marinum CAMP 5644, Staphylococcus aureus ATCC 29213, methicillin-resistant S. aureus 63718, Escherichia coli ATCC 25922, Enterococcus faecalis ATCC 29212, Candida albicans CCM 8261, C. parapsilosis CCM 8260 and C. krusei CCM 8271, respectively, by standardized microdilution methods. The eventual antiproliferative (cytotoxic) impact of those compounds was examined on a human monocytic leukemia THP-1 cell line, as a part of the biological study. Promising potential against M. kansasii was found for 1-[3-(3-ethoxyphenylcarbamoyl)oxy-2-hydroxypropyl]-4-(3-trifluoromethylphenyl)piperazin-1-ium chloride (MIC = 31.75 μM), which was comparable to the activity of isoniazid (INH; MIC = 29.17 μM). Moreover, 1-{2-hydroxy-3-(3-methoxyphenylcarbamoyl)oxy)propyl}-4-(4-fluorophenyl)piperazin-1-ium chloride was even more effective (MIC = 17.62 μM) against given mycobacterium. Among the tested N-arylpiperazines, 1-{2-hydroxy-3-(4-methoxyphenylcarbamoyl)oxy)propyl}-4-(3-trifluoromethylphenyl)piperazin-1-ium chloride was the most efficient against M. marinum (MIC = 65.32 μM). One of the common features of all investigated substances was their insignificant antiproliferative (i.e., non-cytotoxic) effect. The study discussed structure–antimicrobial activity relationships considering electronic, steric and lipophilic properties.

Design and Stereochemical Research (DFT, ECD and Crystal Structure) of Novel Bedaquiline Analogs as Potent Antituberculosis Agents

A series of bedaquiline analogs containing H-bond donors were designed as anti-Mycobacterium tuberculosis drugs. A pair of diastereoisomers (R/S- and S/S-isomers) was selected from these designed compounds for synthetic and stereochemical research. The title compounds were synthesized from chiral precursors for the first time and the absolute configurations (ACs) were determined by electronic circular dichroism (ECD) with quantum chemical calculations. Moreover, a single crystal of the S/S compound was obtained for X-ray diffraction analysis, and the crystal structure showed high consistency with the geometry, confirming the reliability of ACs obtained by ECD analyses and theoretical simulation. Furthermore, the effect of stereochemistry on the anti-tuberculosis activity was investigated. The MICs of the R/S- and S/S-isomers against Mycobacterium phlei 1180 are 9.6 and 32.1 μg·mL⁻¹, respectively. Finally, molecular docking was carried out to evaluate the inhibitory nature and binding mode differences between diastereoisomers.

Synthesis and evaluation of antibacterial and antioxidant activity of novel 2-phenyl-quinoline analogs derivatized at position 4 with aromatically substituted 4H-1,2,4-triazoles

A set of novel quinolone-triazole conjugates (12-31) were synthesized in three steps in good yields starting from 2-phenylquinoline-4-carboxylic acid. All the intermediates, as well as the final 1,2,4-triazolyl quinolines were fully characterized by their detailed spectral analysis utilizing different techniques such as IR, ¹H NMR, ¹³C NMR, and finally mass spectrometry. All the synthesized compounds were evaluated in vitro for their potential antibacterial activity and their preliminary safety profile was assessed through cytotoxicity assay. Additionally, six selected conjugates were evaluated for their antioxidative properties on the basis of density functional theory calculations, using radical scavenging assay (DPPH) and cellular antioxidant assay. The reported results encourage further investigation of selected compounds and are shading light on their potential pharmacological use.

A new route to naphthyl ketones via copper-mediated intramolecular aerobic oxidative cyclization of alkynes and sulfonylcrotonates

A copper-mediated intramolecular aerobic oxidative cyclization of alkynes and sulfonylcrotonates to a variety of highly functionalized naphthyl ketones was developed.

Asymmetric Synthesis and Absolute Configuration Assignment of a New Type of Bedaquiline Analogue

Bedaquiline is the first FDA-approved new chemical entity to fight multidrug-resistant tuberculosis in the last forty years. Our group replaced the quinoline ring with a naphthalene ring, leading to a new type of triarylbutanol skeleton. An asymmetric synthetic route was established for our bedaquiline analogues, and the goal of assigning their absolute configurations was achieved by comparison of experimental and calculated electronic circular dichroism spectra, and was confirmed by the combined use of circular dichroism and NMR spectroscopy.

Further study of oxazolidines derived from mefloquine and arenealdehydes: diastereoisomers and polymorphs

The reaction between racemic erythro [(R*,S*)-2,8-bis(trifluoromethyl)quinolin-4-yl]-(2-piperidyl)methanol] and 2-formyl-5-nitrothiene in toluene generates a reaction mixture containing two diastereoisomers of 4-[3-(5-nitrothien-2-yl)-hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline, 6, – namely (2S*,3R*,4S*5R*)-6 (6a) and (2R*,3S*,4S*,5R*)-6 (6b) in a ratio of 5:1 as indicated by 1H NMR spectroscopy (using the 1,3-oxazolidine ring numbering scheme for the chiral centres). Isolation of each product from the mefloquine/2-formyl-5-nitrothiene reaction mixture was achieved by fractional crystallisation of an ethanol solution, but not by column chromatography on silica, which led to the destruction of the minor product, 6b. A second polymorphic form, [monoclinic, P21/c] of (2S*,3R*,4S*,5R*)-4-[3-(2-hydroxyphenyl-hexahydro[1,3]oxazolo[3,4-a]pyridin-1-yl]-2,8-bis(trifluoromethyl)quinoline (monoclinic-7) has been isolated from MeOH solution: the previously reported orthorhombic form, space group Fdd2, had been isolated from an ethanolic solution.

Crystal structure of 2-meth-oxy-1-nitro-naphthalene

The asymmetric unit of the title compound, C11H9NO3, contains two mol-ecules, A and B. In mol-ecule A, the dihedral angle between the planes of the naphthalene ring system (r.m.s. deviation = 0.003 Å) and the nitro group is 89.9 (2)°, and the C atom of the meth-oxy group deviates from the naphthyl plane by 0.022 (2) Å. Equivalent data for mol-ecule B are 0.008 Å, 65.9 (2)° and -0.198 (2) Å, respectively. In the crystal, mol-ecules are linked by weak C-H⋯O inter-actions, forming [100] chains of alternating A and B mol-ecules. Weak aromatic π-π stacking contacts, with a range of centroid-centroid distances from 3.5863 (9) to 3.8048 (9) Å, are also observed.

Crystal structure of 2,2'-bis-[(2-chloro-benz-yl)-oxy]-1,1'-bi-naphthalene

In the title binaphthyl compound, C34H24Cl2O2, the dihedral angle between the two naphthyl ring systems (r.m.s. deviations = 0.016 and 0.035 Å) is 76.33 (8)°. The chloro-phenyl rings make dihedral angles of 58.15 (12) and 76.21 (13)° with the naphthyl ring to which they are linked. The dihedral angle between the planes of the two chloro-phenyl rings is 27.66 (16)°. In the crystal, C-H⋯O hydrogen bonds link mol-ecules into chains propagating along [1-10]. The chains are linked by C-H⋯π inter-actions, forming a three-dimensional framework.

Piperazine scaffold: A remarkable tool in generation of diverse pharmacological agents

Piperazine is one of the most sought heterocyclics for the development of new drug candidates. This ring can be traced in a number of well established, commercially available drugs. Wide array of pharmacological activities exhibited by piperazine derivatives have made them indispensable anchors for the development of novel therapeutic agents. The review herein highlights the therapeutic significance of piperazine derivatives. Various therapeutically active piperazine derivatives developed by several chemists are reported here.

Ring-substituted 8-hydroxyquinoline-2-carboxanilides as potential antimycobacterial agents

In this study, a series of twenty-two ring-substituted 8-hydroxyquinoline-2-carboxanilides was prepared and characterized. Primary in vitro screening of the synthesized compounds was performed against Mycobacterium tuberculosis H37Ra, Mycobacterium avium complex and M. avium subsp. paratuberculosis. Some of the tested compounds showed the antimycobacterial activity against M. avium subsp. paratuberculosis comparable with or higher than that of rifampicin. 8-Hydroxy-N-[3-(trifluoromethyl)phenyl]- and 8-hydroxy-N-[4-(trifluoromethyl)phenyl]quinoline-2-carboxamide showed MIC=24 μM against all tested mycobacterial strains. 3-Methoxyphenyl- and 3-methylphenyl derivatives expressed MIC=27 or 29 μM also against all the tested strains. Their activity against M. avium subsp. paratuberculosis was 4-fold higher than that of rifampicin. 2-Bromophenyl- and 2-(trifluoromethyl)phenyl derivatives had MIC=23 or 24 μM against M. tuberculosis. A significant decrease of mycobacterial cell metabolism (viability of M. tuberculosis H37Ra) was observed using MTT assay. Screening of cytotoxicity of the compounds was performed using the THP-1 cells, and no significant lethal effect was observed up to tested concentration 30 μM. The structure-activity relationships are discussed.

Crystal structure of 2-{[1-(4-bromo-benz-yl)-1H-1,2,3-triazol-4-yl]meth-oxy}naph-thalene-1,4-dione

In the title compound, C20H14BrN3O3, the benzene ring makes dihedral angles of 71.30 (11) and 68.95 (14)° with the naphthalene ring system and the triazole ring, respectively. The latter two ring systems are coplanar, with a dihedral angle of 2.92 (12)°. The O atoms deviate from the naphthalene ring system by 0.029 (2) and -0.051 (2) Å. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯N hydrogen bonds, forming ribbons parallel to (10-1). The ribbons are linked via C-H⋯O and π-π stacking inter-actions [centroid-centroid distance = 3.4451 (14) Å], forming slabs parallel to the bc plane.