Phase transfer catalyzed synthesis of bis-quinolines: Antileishmanial activity in experimental visceral leishmaniasis and in vitro antibacterial evaluation

Quinoline as a Privileged Structure: A Recent Update on Synthesis and Biological Activities

Among heterocyclic compounds, quinoline is one of the best ubiquitous heterocyclic rings for medicinal chemistry purposes. Quinoline appears to be a powerful chemical structure to develop new drug entities. The quinoline derivatives own a wide array of biological activities such as anticancer, antimalarial, antimicrobial, anti-inflammatory, anti-leishmanial, etc. Because of the wide spectrum of bioactivities, the scientific communities are still looking for more efficient synthetic routes to form quinoline derivatives. Therefore, the primary focus of this review is to provide a thorough and inclusive, updated report on quinoline analogs that may pave the way for more efficient drug development.

Synthesis, DFT, and eco-friendly insecticidal activity of some N-heterocycles derived from 4-((2-oxo-1,2-dihydroquinolin-3-yl)methylene)-2-phenyloxazol-5(4H)-one

A new series of nitrogen heterocycles encompassing a quinoline scaffold such as imidazolone, benzimidazole, triazinone, triazole, and thiazole derivatives was synthesized utilizing the readily obtainable building block synthon, 4-((2-oxo-1,2-dihydroquinolin-3-yl)methylene)-2-phenyloxazol-5(4H)-one (3). It was interesting that the fused heterocycle, pyranoquinoline derivative 15 was successfully synthesized by different routes of reactions. The synthesized compounds were evaluated for their insecticidal activity and compounds 6, 17, and 20 were the most potent against both Mythimna separata and Nilaparvata lugens. The DFT study was performed for the most potent compounds.

The Role of Nitro (NO2-), Chloro (Cl), and Fluoro (F) Substitution in the Design of Antileishmanial and Antichagasic Compounds

Neglected tropical diseases (NTDs) are responsible for over 500,000 deaths annually and are characterized by multiple disabilities. Leishmaniasis and Chagas diseases are among the most severe NTDs, and are caused by the Leishmania sp and Trypanosoma cruzi, respectively. Glucantime, pentamidine, and miltefosine are commonly used to treat leishmaniasis, whereas nifurtimox, benznidazole are current treatments for Chagas disease. However, these treatments are associated with drug resistance and severe side effects. Hence, the development of synthetic products, especially those containing N0₂, F, or Cl, are known to improve biological activity. The present work summarizes the information on the antileishmanial and antitrypanosomal activity of nitro-, chloro-, and fluorosynthetic derivatives. Scientific publications referring to halogenated derivatives in relation to antileishmanial and antitrypanosomal activities were hand-searched in databases such as SciFinder, Wiley, Science Direct, PubMed, ACS, Springer, Scielo, and so on. According to the literature information, more than 90 compounds were predicted as lead molecules with reference to their IC₅₀/EC₅₀ values in in vitro studies. It is worth mentioning that only active compounds with known cytotoxic effects against mammalian cells were considered in the present study. The observed activity was attributed to the presence of nitro-, fluoro-, and chloro-groups in the compound backbone. All in all, nitro and halogenated derivatives are active antileishmanial and antitrypanosomal compounds and can serve as the baseline for the development of new drugs against leishmaniasis and Chagas disease. However, efforts in in vitro and in vivo toxicity studies of the active synthetic compounds is still needed. Pharmacokinetic studies and the mechanism of action of the promising compounds need to be explored. The use of new catalysts and chemical transformation can afford unexplored halogenated compounds with improved antileishmanial and antitrypanosomal activity.

Crystal structure, Hirshfeld surface analysis, DFT and mol-ecular docking investigation of 2-(2-oxo-1,3-oxazolidin-3-yl)ethyl 2-[2-(2-oxo-1,3-oxazolidin-3-yl)eth-oxy]quinoline-4-carboxyl-ate

In the mol-ecular structure of the title compound, C20H21N3O7, the quinoline ring system is slightly bent, with a dihedral angle between the phenyl and the pyridine rings of 3.47 (7)°. In the crystal, corrugated layers of mol-ecules extending along the ab plane are generated by C-H⋯O hydrogen bonds. The inter-molecular inter-actions were qu-anti-fied by Hirshfeld surface analysis and two-dimensional fingerprint plots. The most significant contributions to the crystal packing are from H⋯H (42.3%), H⋯O/O⋯H (34.5%) and H⋯C/ C⋯H (17.6%) contacts. Mol-ecular orbital calculations providing electron-density plots of the HOMO and LUMO as well as mol-ecular electrostatic potentials (MEP) were computed, both with the DFT/B3LYP/6-311 G++(d,p) basis set. A mol-ecular docking study between the title mol-ecule and the COVID-19 main protease (PDB ID: 6LU7) was performed, showing that it is a good agent because of its affinity and ability to adhere to the active sites of the protein.

Evaluation of catacholase mimicking activity and apoptosis in human colorectal carcinoma cell line by activating mitochondrial pathway of copper(II) complex coupled with 2-(quinolin-8-yloxy)(methyl)benzonitrile and 8-hydroxyquinoline

To evaluate the cytotoxic potential of metal-based chemotherapeutic candidate towards the colorectal cancer, we have synthesized a new copper(II) complex [Cu(qmbn)(q)(Cl)] (1) (where, qmbn = 2-(quinolin-8-yloxy)(methyl)benzonitrile and q = 8-hydroxyquinoline) and structurally characterized by single crystal X-ray, Powder-XRD, FTIR and thermogravimetric analysis (TGA). The structural analysis reveals that copper(II) ions exist in a distorted square pyramidal (τ = ~0.1), with ligation of a chloride ion, oxygen atom and two nitrogen atoms at equatorial position and one oxygen atom at apical position. The cytotoxicity potential of complex 1 was executed against human colorectal cell lines (HCT116), which showed that 1 induces mitochondrion-mediated apoptotic cell death via activation of the Bax (pro-apoptotic protein) caspases-3 and 9 proteins. Interestingly, complex 1 was found to be a good candidate as electron-transfer catalyst which mimics catacholase with high turnover frequency (k_cat = 1.03 × 10² h^-1) for the conversion of the model substrate 3,5-di-tertbutylcatechol (3,5-DTBC) to 3,5-di-tertbutylquinone (3,5-DTBQ). Furthermore, molecular docking studies revealed that complex 1 was successfully localized inside the binding pocket of protein kinase (Akt), which validate the mechanism and mode of interaction of 1 that displayed cytotoxic activity experimentally. The obtained outcomes reveal that the complex 1 could be utilized as an encouraging perspective in the development of new therapeutic candidate for colon cancer.

Crystal structure and Hirshfeld surface analysis of hexyl 1-hexyl-2-oxo-1,2-di-hydro-quinoline-4-carboxyl-ate

The asymmetric unit of the title compound, C22H31NO3, comprises of one mol-ecule. The mol-ecule is not planar, with the carboxyl-ate ester group inclined by 33.47 (4)° to the heterocyclic ring. Individual mol-ecules are linked by aromaticC-H⋯Ocarbon-yl hydrogen bonds into chains running parallel to [001]. Slipped π-π stacking inter-actions between quinoline moieties link these chains into layers extending parallel to (100). Hirshfeld surface analysis, two-dimensional fingerprint plots and mol-ecular electrostatic potential surfaces were used to qu-antify the inter-molecular inter-actions present in the crystal, indicating that the most important contributions for the crystal packing are from H⋯H (72%), O⋯H/H⋯O (14.5%) and C⋯H/H⋯C (5.6%) inter-actions.

Crystal structure, DFT study and Hirshfeld surface analysis of ethyl 6-chloro-2-eth-oxy-quinoline-4-carboxyl-ate

In the title quinoline derivative, C14H14ClNO3, there is an intra-molecular C-H⋯O hydrogen bond forming an S(6) graph-set motif. The mol-ecule is essentially planar with the mean plane of the ethyl acetate group making a dihedral angle of 5.02 (3)° with the ethyl 6-chloro-2-eth-oxy-quinoline mean plane. In the crystal, offset π-π inter-actions with a centroid-to-centroid distance of 3.4731 (14) Å link inversion-related mol-ecules into columns along the c-axis direction. Hirshfeld surface analysis indicates that H⋯H contacts make the largest contribution (50.8%) to the Hirshfeld surface.

Synthesis, Characterization, and Antileishmanial Activity of Certain Quinoline-4-carboxylic Acids

Leishmaniasis is a fatal neglected parasitic disease caused by protozoa of the genusLeishmaniaand transmitted to humans by different species ofphlebotominesandflies. The disease incidence continues to increase due to lack of vaccines and prophylactic drugs. Drugs commonly used for the treatment are frequently toxic and highly expensive. The problem of these drugs is further complicated by the development of resistance. Thus, there is an urgent need to develop new antileishmanial drug candidates. The aim of this study was to synthesize certain quinoline-4-carboxylic acids, confirm their chemical structures, and evaluate their antileishmanial activity. Pfitzinger reaction was employed to synthesize fifteen quinoline-4-carboxylic acids (Q1-Q15) by reacting equimolar mixtures of isatin derivatives and appropriateα-methyl ketone. The products were purified, and their respective chemical structures were deduced using various spectral tools (IR, MS,1H NMR, and13C NMR). Then, they were investigated againstL. donovanipromastigote (clinical isolate) in different concentration levels (200 μg/mL to 1.56 μg/mL) against sodium stibogluconate and amphotericin B as positive controls. The IC50for each compound was determined and manipulated statistically. Among these compounds,Q1(2-methylquinoline-4-carboxylic acid) was found to be the most active in terms of IC50.

Synthesis and activity of benzopiperidine, benzopyridine and phenyl piperazine based compounds against Leishmania infantum

In the present study, anti-leishmanial evaluation of twenty four structurally diverse compounds based on benzopiperidine, benzopyridine and phenylpiperazine nucleuses against Leishmania infantum has been reported. Cytotoxicity studies of all the compounds were performed on murine non-infected splenocytes. Tested compounds exhibited weak to potent activity against promastigote (IC₅₀ 3.21 ± 1.40 to >100 μM) as well as amastigote (IC₅₀ 6.84 ± 2.5 to 92.47 ± 17.61 μM) forms of tested strains. Moreover, two compounds F13 and F15 exhibited potent activity (IC₅₀ < 10 μM) against both forms of the parasite with selectivity index ranges from 11.40 to 22.10. Overall, the current study afforded few hits with novel anti-leishmanial activity in low micromolar concentration, further hit optimization studies can be performed to get more potent candidates against the selected species of parasite.

Fe3+chelating quinoline–hydrazone hybrids with proven cytotoxicity, leishmanicidal, and trypanocidal activities

Neglected tropical diseases cause great concern in developing countries where there are millions of reported infected humans. Our calculations support a direct relationship between biological activity and the Fe³⁺chelating ability of the shown set of quinoline–hydrazone hybrids.

A rapid and sensitive UHPLC-MS/MS method for quantification of 83b1 in plasma and its application to bioavailability study in rats

Great attentions have been drawn by quinoline for its broad bioactivity as anti-fungal, anti-bacterial and anti-tumor activities. Compared with cisplatin, 83b1, a quinoline derivative, showed equal activity in anti-tumor and lower cyctotoxicity in normal cell. In this study, a simple, rapid and sensitive method for determination of 83b1 in rat plasma using UHPLC-MS/MS was developed for the first time. Loratadine was used as an internal standard (IS). Separation was performed on an Xterra MS C₁₈ column by isocratic elution using acetonitrile: water solution with 1‰ formic acid (90:10, v/v) as mobile phase at a flow rate of 0.3mL/min. A triple quadrupole mass spectrometer operating in the positive ion-switching electron spray ionization mode with selection reaction monitoring (SRM) was employed to determine 83b1 and IS transitions of m/z 321.82→147.84, 382.71→258.76 for 83b1 and Loratadine, respectively. The values of specificity, linearity and lower limit of quantification, intra- and inter- day precision and accuracy, extraction recovery, matrix effect and stability for this method satisfied the acceptable limits. The lower limit of quantification was 0.5ng/mL with a linear range of 0.5-1500ng/mL. The validated method was employed to study the bioavailability of 83b1 in rat by dosing with intravenous injection (1mg/kg) and gavage (10mg/kg), and the oral bioavailability of 83b1 in rat was calculated as 20.9±8.8%.

Crystal structure of bis-{μ-(E)-2-[(2-oxido-phenyl-imino)-meth-yl]quinolin-8-olato-κ4O,N,N',O'}bis-[di-butyl-tin(IV)]

Condensation of 8-hy-droxy-quinoline-2-carbaldehyde with 2-amino-phenol gave the (E)-2-[(2-hy-droxy-phenyl-imino)-meth-yl]quinolin-8-ol derivative that reacted with di-n-butyl-tin oxide with release of H2O to yield the chelate title complex, [Sn2(C4H9)4(C16H10N2O2)2]. The compound crystallizes in the triclinic space group P-1, with two independent centrosymmetric dimers in the unit cell. Each features a typical pincer-type structure where the dianionic ligand is tetra-dentate, coordinating to the central tin atom through both phenolate oxygen atoms, as well as through the quinoline and imine N atoms. Each metal atom adopts a distorted penta-gonal-bipyramidal SnC2N2O3 coordination arising from the N,N',O,O'-tetra-dentate deprotonated Schiff base, one bridging phenolate O atom of the neighbouring ligand and two butyl groups in the axial sites.

Cutaneous and mucocutaneous leishmaniasis: Differential diagnosis, diagnosis, histopathology, and management

The diagnosis of leishmaniasis can be challenging because it mimics both infectious and malignant conditions. A misdiagnosis may lead to an unfavorable outcome. Using culture, histologic, and/or polymerase chain reaction study results, a diagnosis of leishmaniasis can be established and treatment initiated. Appropriate management requires an accurate diagnosis, which often includes identification of the specific etiologic species. Different endemic areas have varying sensitivities to the same medication, even within individual species. Species identification may be of practical value, because infections with select species have a substantial risk of visceral involvement. In addition, HIV and otherwise immunocompromised patients with leishmaniasis have a propensity for diffuse cutaneous leishmaniasis. For most New World Leishmania species, parenteral antimonial drugs remain the first line of therapy, while Old World species are easily treated with physical modalities. Historically, live organism vaccination has been used and is effective in preventing leishmaniasis, but results in an inoculation scar and an incubation period that may last for years. A more effective method of vaccination would be welcome.

Antigiardial activity of novel triazolyl-quinolone-based chalcone derivatives: when oxygen makes the difference

Giardiasis is a common diarrheal disease worldwide caused by the protozoan parasite Giardia intestinalis. It is urgent to develop novel drugs to treat giardiasis, due to increasing clinical resistance to the gold standard drug metronidazole (MTZ). New potential antiparasitic compounds are usually tested for their killing efficacy against G. intestinalis under anaerobic conditions, in which MTZ is maximally effective. On the other hand, though commonly regarded as an ‘anaerobic pathogen,’ G. intestinalis is exposed to relatively high O₂ levels in vivo, living attached to the mucosa of the proximal small intestine. It is thus important to test the effect of O₂ when searching for novel potential antigiardial agents, as outlined in a previous study [Bahadur et al. (2014) Antimicrob. Agents Chemother. 58, 543]. Here, 45 novel chalcone derivatives with triazolyl-quinolone scaffold were synthesized, purified, and characterized by high resolution mass spectrometry, ¹H and ¹³C nuclear magnetic resonance and infrared spectroscopy. Efficacy of the compounds against G. intestinalis trophozoites was tested under both anaerobic and microaerobic conditions, and selectivity was assessed in a counter-screen on human epithelial colorectal adenocarcinoma cells. MTZ was used as a positive control in the assays. All the tested compounds proved to be more effective against the parasite in the presence of O₂, with the exception of MTZ that was less effective. Under anaerobiosis eighteen compounds were found to be as effective as MTZ or more (up to three to fourfold); the same compounds proved to be up to >100-fold more effective than MTZ under microaerobic conditions. Four of them represent potential candidates for the design of novel antigiardial drugs, being highly selective against Giardia trophozoites. This study further underlines the importance of taking O₂ into account when testing novel potential antigiardial compounds.

Palladium catalyzed one-pot synthesis of 2-(pyridin-4-yl) quinolines via a multicomponent unprecedented reaction of pyridine-4-carbaldehyde, 2-iodoaniline and triethylamine

Palladium catalyzed synthesis of 2-(pyridin-4-yl) quinoline with an unprecedented participation of Et₃N was achieved in a novel multicomponent reaction of pyridine-4-carbaldehyde, 2-iodoaniline and triethylamine.

Preparation of 8-hydroxyquinoline derivatives as potential antibiotics against Staphylococcus aureus

This work describes the preparation of quinoline compounds as possible anti-bacterial agents. The synthesized quinoline derivatives show anti-bacterial activity towards Staphylococcus aureus. It is interesting to observe that the synthetic 5,7-dibromo-2-methylquinolin-8-ol (4) shows a similar minimum inhibitory concentration of 6.25μg/mL as compared to that of methicillin (3.125μg/mL) against Staphylococcus aureus.

Synthesis of 8-hydroxyquinoline derivatives as novel antitumor agents

This letter describes the preparation of quinoline derivatives and their cytotoxic potentials toward human carcinoma cell lines. Among the selected compounds, 8-hydroxy-2-quinolinecarbaldehyde (3) showed the best in vitro cytotoxicity against the human cancer cell lines, including MDA231, T-47D, Hs578t, SaoS2, K562, SKHep1 (with a MTS50 range of 12.5-25 μg/mL) and Hep3B (with a MTS50 range of 6.25±0.034 μg/mL). The in vivo antitumor activity of compound 3 on subcutenaous Hep3B hepatocellular carcinoma xenograft in athymic nude mice was then studied. The results showed that the dose of 10 mg/kg/day of compound 3 with intraperitoneal injection for 9 days totally abolished the growth of the xenograft tumor of Hep3B with no histological damage on vital organs as compared with the control. The experimental results suggested that compound 3 has a good potential as an antitumor agent.

The concept of privileged structures in rational drug design: focus on acridine and quinoline scaffolds in neurodegenerative and protozoan diseases

INTRODUCTION

For nearly 20 years, privileged structures have offered an optimal source of core scaffolds and capping fragments for the design of combinatorial libraries directed at a broad spectrum of targets. From describing structures promiscuous within a given target family, the concept has evolved to include frameworks that can modulate proteins lacking a strict target class relation.

AREAS COVERED

Based on a literature search from 2000 to 2010, we discuss how two privileged motifs, quinolines and acridines, are particularly recurrent in compounds active against two quite different pathologies, neurodegenerative and protozoan diseases.

EXPERT OPINION

As privileged structures, quinolines and acridines could improve the productivity of drug discovery projects in the field of neurodegenerative and protozoan diseases. They could be particularly relevant for protozoan diseases because of the importance of cost-effective strategies and less stringent intellectual property concerns. Furthermore, because of their inherent affinity for various targets, privileged structures could offer a viable starting point in the search for novel multi-target ligands. Finally, from a broader perspective, they can serve as effective probes for investigating unknown but interrelated mechanisms of action.