Quinoline and quinolone dimers and their biological activities: An overview

Mechanochemical Synthesis of Functionalized Quinolines by Iodine Mediated Oxidative Annulation

An iodine-mediated environmentally benign synthesis of multi-substituted quinoline derivatives is developed using a solvent-free mechanochemical process. Appropriately designed and easily accessible protecting group-free aniline derivatives were used for the oxidative annulation reaction, and a series of quinoline derivatives with variable functionalities were synthesized up to 89 % isolated yield. Importantly, the activator iodine remains in the quinoline molecule and promotes further functionalizations. The present methodology is beneficial with regard to operational simplicity and mild reaction conditions.

Recent advances in isatin hybrids as potential anticancer agents

The isatin framework is a useful template for the development of novel anticancer agents. This is exemplified by the fact that several isatin-based anticancer agents, such as semaxanib, sunitinib, nintedanib, and hesperadin, are already in use or under clinical trials for the treatment of diverse kinds of cancers. Isatin-based hybrids could be obtained by incorporating other anticancer pharmacophores into the isatin skeleton and they have the potential to overcome drug resistance with reduced side effects. Thus, isatin-based hybrids may provide attractive scaffolds for the development of novel anticancer agents. This review covers the recent advances of isatin-based hybrids with anticancer activity, covering articles published between 2001 and 2019. The anticancer activities of these molecules and the structure-activity relationships are also discussed. The purpose of this review article is to set up the direction for the design and development of isatin-based hybrids with high efficacy and low toxicity.

The direct C–H alkenylation of quinoline N-oxides as a suitable strategy for the synthesis of promising antiparasitic drugs

This review highlights the direct C–H alkenylation of quinoline N-oxides covering the metal-free and transition-metal catalysed protocols, and the regioselectivity during the synthesis of antiparasitic drugs based on quinoline scaffold.

Synthesis of 3-sulfonylquinolines by visible-light promoted metal-free cascade cycloaddition involving N-propargylanilines and sodium sulfinates

A visible-light promoted radical cascade reaction of N-propargylanilines with sodium sulfinates as sulfonyl radical precursors was developed under metal-free conditions.

Synthesis and biological evaluation of novel 3-(quinolin-4-ylamino)benzenesulfonamidesAQ3 as carbonic anhydrase isoforms I and II inhibitors

Carbonic anhydrases (CAs, EC 4.2.1.1) are crucial metalloenzymes that are involved in diverse bioprocesses. We report the synthesis and biological evaluation of novel series of benzenesulfonamides incorporating un/substituted ethyl quinoline-3-carboxylate moieties. The newly synthesised compounds were in vitro evaluated as inhibitors of the cytosolic human (h) isoforms hCA I and II. Both isoforms hCA I and II were inhibited by the quinolines reported here in variable degrees: hCA I was inhibited with KIs in the range of 0.966-9.091 μM, whereas hCA II in the range of 0.083-3.594 μM. The primary 7-chloro-6-flouro substituted sulphfonamide derivative 6e (KI = 0.083 μM) proved to be the most active quinoline in inhibiting hCA II, whereas, its secondary sulfonamide analog failed to inhibit the hCA II up to 10 μM, confirming the crucial role of the primary sulphfonamide group, as a zinc-binding group for CA inhibitory activity.

Hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant Plasmodium falciparum

Malaria is a tropical disease, leading to around half a million deaths annually. Antimalarials such as quinolines are crucial to fight against malaria, but malaria control is extremely challenged by the limited pipeline of effective pharmaceuticals against drug-resistant strains of Plasmodium falciparum which are resistant toward almost all currently accessible antimalarials. To tackle the growing resistance, new antimalarial drugs are needed urgently. Hybrid molecules which contain two or more pharmacophores have the potential to overcome the drug resistance, and hybridization of quinoline privileged antimalarial building block with other antimalarial pharmacophores may provide novel molecules with enhanced in vitro and in vivo activity against drug-resistant (including multidrug-resistant) P falciparum. In recent years, numerous of quinoline hybrids were developed, and their activities against a panel of drug-resistant P falciparum strains were screened. Some of quinoline hybrids were found to possess promising in vitro and in vivo potency. This review emphasized quinoline hybrid molecules with potential in vitro antiplasmodial and in vivo antimalarial activity against drug-resistant P falciparum, covering articles published between 2010 and 2019.

Current scenario of ferrocene-containing hybrids for antimalarial activity

Hybrid molecules have the potential to enhance the efficacy against both drug-sensitive and drug-resistant organisms, and Ferroquine, a ferrocene hybrid, has demonstrated great potency in clinical trials against both drug-sensitive and drug-resistant malaria. Accordingly, hybridization of ferrocene with other antimalarial pharmacophores represents a promising strategy to develop novel antimalarial candidates. This work attempts to systematically review the recent study of ferrocene hybrids in the design and development of antimalarial agents, and the structure-activity relationship (SAR) is also discussed to provide an insight for rational design of more effective antibacterial candidates.

New insights into resistance of Helicobacter pylori against third- and fourth-generation fluoroquinolones: A molecular docking study of prevalent GyrA mutations

BACKGROUND

Fluoroquinolones hinder bacterial DNA replication by inhibiting DNA gyrase. However, mutations, in the QRDR segment of its A subunit (GyrA), cause antibiotic resistance. Here, the interactions of levofloxacin (LVX), gemifloxacin (GXN), and moxifloxacin (MXN) with Helicobacter pylori GyrA, in LVX-resistant vs -sensitive strains, were studied.

METHODS

Levoflixacin-sensitive (n = 4) and -resistant (n = 9) H pylori strains, randomly selected from another antibiotic susceptibility study, underwent PCR amplification of gyrA gene, spanning the QRDR segment. The amplified gene fragments were sequenced and aligned. The homology model of H pylori GyrA was built based on that of Escherichia coli, and energy minimization was done. The interaction patterns of LVX, GXN, and MXN with GyrA were analyzed via molecular docking studies.

RESULTS

Sequence alignment of the 13 studied strains, created 5 categories of strains: (A) wild type-like (H pylori ATCC26695), (B) N87K-only, (C) D91N-only, (D) N87K + V94L, and (E) D91N + A97V mutations. The minimum inhibitory concentrations (MIC) for LVX-sensitive (category A) and -resistant (categories B-E) strains were <1 mg/L and ≥32 mg/L, respectively. The binding mode of GyrA in category A with LVX identified G35/N87/Y90/D91/V94/G114/S115/I116/D117/G118/D119, as key residues, some residing outside the QRDR segment. Category B strains lost only one interaction (G35), which led to elevated binding free energy (∆G) and full LVX resistance. Categories C-E lost more contacts, with higher ∆G and again full LVX resistance. GXN bound to GyrA of categories A and B via a different set of key residues, while MXN retained the lost contact (G35) in LVX-resistant, category B strains.

CONCLUSION

Using molecular docking tools, we identified the key residues responsible for interaction of GyrA with LVX, GXN, and MXN. In the presence of N87K-only mutation, the loss of one of these contacts (ie, G35) led to full LVX resistance. Yet, GXN and MXN overcame this mutation, by retaining all key contacts with GyrA.

Recent advances in the synthetic and medicinal perspective of quinolones: A review

In the modern scenario, the quinolone scaffold has emerged as a very potent motif considering its clinical significance. Quinolones possess wide range of pharmacological activities such as anticancer, antibacterial, antifungal, antiprotozoal, antiviral, anti-inflammatory, carbonic anhydrase inhibitory and diuretic activity etc. The versatile synthetic approaches have been successfully applied and several of the resulted synthesized compounds exhibit fascinating biological activities in numerous fields. This has prompted to discover quinolone-based analogues among the researchers due to its great diversity in biological activities. In the past few years, various new, efficient and convenient synthetic approaches (including green chemistry and microwave-assisted synthesis) have been designed and developed to synthesize diverse quinolone-based scaffolds which represent a growing area of interest in academic and industry as well as to explore their biological activities. In this review, an attempt has been made by the authors to summarize (1) One of the most comprehensive listings of quinolone-based drugs or agents in the market or under various stages of clinical development; (2) Recent advances in the synthetic strategies for quinolone derivatives as well as their biological implications including insight of mechanistic studies. (3) Further, the biological data is correlated with structure-activity relationship studies to provide an insight into the rational design of more active agents.

Oxidative [4+2] Cycloaddition of α-(N-Arylamino) Carbonyls with Aryl Alkenes by Multiple C-H Functionalizations and [1,2]-Aryl Shifts

A new, general copper-catalyzed oxidative tandem [4+2] cycloaddition of α-(N-arylamino) carbonyl compounds with aryl alkenes to produce highly substituted quinolines has been developed, which allows the formation of three new C-C bonds through a sequence of multiple C-H functionalizations, annulation, and [1,2]-aryl shifts.

Coumarin-containing hybrids and their anticancer activities

Cancer is the second leading cause of death worldwide, and it results in around 9 million deaths annually. The anticancer agents play an intriguing role in the treatment of cancers, while the severe anticancer scenario and the emergence of drug-resistant especially multidrug-resistant cancers create a huge demand for novel anticancer drugs with different mechanisms of action. The coumarin scaffold is ubiquitous in nature and is a highly privileged motif for the development of novel drugs due to its biodiversity and versatility. Coumarin derivatives can exert diverse antiproliferative mechanisms, and some of them such as Irosustat are under clinical trials for the treatment of various cancers, revealing their potential as putative anticancer drugs. Hybridization of coumarin moiety with other anticancer pharmacophores is a promising strategy to reduce side effects, overcome the drug resistance, and may provide valuable therapeutic intervention for the treatment of cancers. Thus, coumarin-containing hybrids occupy an important position in the development of novel anticancer agents. This review aims to summarize the recent advances made towards the development of coumarin-containing hybrids as potential anticancer agents, covering articles published between 2015 and 2019, and the structure-activity relationship together with mechanisms of action are also discussed.

Close the ring to break the cycle: tandem quinolone-alkyne-cyclisation gives access to tricyclic pyrrolo[1,2-a]quinolin-5-ones with potent anti-protozoal activity

Expanding the chemical space of quinolones led to a tandem quinolone-alkyne-cyclisation reaction allowing chemoselective control of the synthesis of tricyclic pyrrolo[1,2-a]quinolin-5-ones. Importantly, we discovered anti-protozoal activity against Plasmodium and Toxoplasma with specific potency of one of the compounds against the liver stage of the malaria parasite in the nanomolar range.

Synthesis and biological evaluation of hybrid quinolone-based quaternary ammonium antibacterial agents

A series of novel fluoroquinolone-Safirinium dye hybrids was synthesized by means of tandem Mannich-electrophilic amination reactions from profluorophoric isoxazolones and antibiotics bearing a secondary amino group at position 7 of the quinoline ring. The obtained fluorescent spiro fused conjugates incorporating quaternary nitrogen atoms were characterized by ¹H NMR, IR, MS, and elemental analysis. All the synthetic analogues (3a-h and 4a-h) were evaluated for their in vitro antimicrobial, bactericidal, and antibiofilm activities against a panel of Gram positive and Gram-negative pathogenic bacteria. The most active Safirinium Q derivatives of lomefloxacin (4d) and ciprofloxacin (4e) exhibited molar-based antibacterial activities comparable to the unmodified drugs and displayed considerable inhibitory potencies in E. coli DNA gyrase supercoiling assays with IC₅₀ values in the low micromolar range. Zwiterionic hybrids were noticeably less lipophilic than the parent quinolones in micellar electrokinetic chromatography (MECK) experiments. The tests performed in the presence of phenylalanine-arginine β-naphthylamide (PAβN) or carbonyl cyanide m-chlorophenylhydrazone (CCCP) revealed that the conjugates are to some extent subject to bacterial efflux and cellular accumulation, respectively. Moreover, the hybrids did not exhibit notable cytotoxicity towards the HEK 293 control cell line and demonstrated low propensity for resistance development, as exemplified for compounds 3g and 4b. Finally, molecular docking experiments revealed that the synthesized compounds were able to bind in the fluoroquinolone-binding mode at S. aureus DNA gyrase and S. pneumoniae topoisomerase IV active sites.

A new exploration towards aminothiazolquinolone oximes as potentially multi-targeting antibacterial agents: Design, synthesis and evaluation acting on microbes, DNA, HSA and topoisomerase IV

This work did a new exploration towards aminothiazolquinolone oximes as potentially multi-targeting antimicrobial agents. A class of novel hybrids of quinolone, aminothiazole, piperazine and oxime fragments were designed for the first time, conveniently synthesized as well as characterized by ¹H NMR, ¹³C NMR and HRMS spectra. Biological activity showed that some of the synthesized compounds exhibited good antimicrobial activities in comparison with the reference drugs. Especially, O-methyl oxime derivative 10b displayed excellent inhibitory efficacy against MRSA and S. aureus 25923 with MIC values of 0.009 and 0.017 mM, respectively. Further studies indicated that the highly active compound 10b showed low toxicity toward BEAS-2B and A549 cell lines and no obvious propensity to trigger the development of bacterial resistance. Quantum chemical studies have also been conducted and rationally explained the structural features essential for activity. The preliminarily mechanism exploration revealed that compound 10b could not only exert efficient membrane permeability by interfering with the integrity of cells, bind with topoisomerase IV-DNA complex through hydrogen bonds and π-π stacking, but also form a steady biosupramolecular complex by intercalating into DNA to exert the efficient antibacterial activity. The supramolecular interaction between compound 10b and human serum albumin (HSA) was a static quenching, and the binding process was spontaneous, where hydrogen bonds and van der Waals force played vital roles in the supramolecular transportation of the active compound 10b by HSA.

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.

Choline Chloride-Based Deep Eutectic Systems in Sequential Friedländer Reaction and Palladium-Catalyzed sp3 CH Functionalization of Methyl Ketones

A volatile organic solvent-free and choline chloride (ChCl)-based deep eutectic system (DES)-mediated sp³-CH functionalization of acetophenones 1 with benzyl alcohols 2 to the corresponding α, β-saturated ketones 3 is accounted for. The domino dehydrogenation-aldol condensation (hydrogenation borrowing concept) has been successfully attempted with palladium-tetrakis(triphenylphosphine) [Pd(PPh₃)₄] catalyst-xantphos ligand combination. Furthermore, a sequential Friedländer reaction of 2-aminobenzophenone 4 and palladium-catalyzed α-alkylation of the quinolinyl methyl ketone with benzyl alcohols 2 in ChCl-based DES have been successfully investigated. The C-C bond formation through sp³-CH functionalization involves a wide scope of the substrates, high atom efficiency, chemoselectivity, and environmentally friendly strategy.

Quinolone derivatives and their antifungal activities: An overview

More than 300 million people suffer from the incidence of life-threatening invasive fungal infections, resulting in over 1.35 million deaths annually. Currently, the antifungal agents available in clinics are rather limited, and the rapid development of resistance to the existing antifungal drugs has further aggravated mortality. Quinolones possess a broad spectrum of chemotherapeutic properties and demonstrate considerable antifungal activities as well. Various quinolone derivatives have been screened for their antifungal activities, and some of them exhibit excellent potency against both drug-susceptible and drug-resistant fungi. This review aims to outline the recent advances in quinolone derivatives as potential antifungal agents and summarize the structure-activity relationship, to provide insights for the rational design of more active candidates.

Triazole derivatives and their antiplasmodial and antimalarial activities

Malaria, caused by protozoan parasites of the genus Plasmodium especially by the most prevalent parasite Plasmodium falciparum, represents one of the most devastating and common infectious disease globally. Nearly half of the world population is under the risk of being infected, and more than 200 million new clinical cases with around half a million deaths occur annually. Drug therapy is the mainstay of antimalarial therapy, yet current drugs are threatened by the development of resistance, so it's imperative to develop new antimalarials with great potency against both drug-susceptible and drug-resistant malaria. Triazoles, bearing a five-membered heterocyclic ring with three nitrogen atoms, exhibit promising in vitro antiplasmodial and in vivo antimalarial activities. Moreover, several triazole-based drugs have already used in clinics for the treatment of various diseases, demonstrating the excellent pharmaceutical profiles. Therefore, triazole derivatives have the potential for clinical deployment in the control and eradication of malaria. This review covers the recent advances of triazole derivatives especially triazole hybrids as potential antimalarials. The structure-activity relationship is also discussed to provide an insight for rational designs of more efficient antimalarial candidates.

A simple and convenient synthesis of 3-salicyloylquinoline-4-carboxylic esters from chromone and isatin

A simple and convenient synthesis of 3-salicyloylquinoline-4-carboxylic esters has been developed through AlCl₃-catalyzed reaction of Baylis–Hillman adducts from chromones and isatin-derivatives.

Quinolines and Quinolones as Antibacterial, Antifungal, Anti-virulence, Antiviral and Anti-parasitic Agents

Infective diseases have become health threat of a global proportion due to appearance and spread of microorganisms resistant to majority of therapeutics currently used for their treatment. Therefore, there is a constant need for development of new antimicrobial agents, as well as novel therapeutic strategies. Quinolines and quinolones, isolated from plants, animals, and microorganisms, have demonstrated numerous biological activities such as antimicrobial, insecticidal, anti-inflammatory, antiplatelet, and antitumor. For more than two centuries quinoline/quinolone moiety has been used as a scaffold for drug development and even today it represents an inexhaustible inspiration for design and development of novel semi-synthetic or synthetic agents exhibiting broad spectrum of bioactivities. The structural diversity of synthetized compounds provides high and selective activity attained through different mechanisms of action, as well as low toxicity on human cells. This review describes quinoline and quinolone derivatives with antibacterial, antifungal, anti-virulent, antiviral, and anti-parasitic activities with the focus on the last 10 years literature.

An efficient 3-acylquinoline synthesis from acetophenones and anthranilviaC(sp3)–H bond activation mediated by Selectfluor

An efficient method for the synthesis of 3-functionalized quinolines from commercially available acetophenones and anthranil has been described. Selectfluor propels the C(sp³)–H bond activation of the acetophenones and aza-Michael addition of anthranil resulting in annulated 3-acylquinolines in moderate to high yields. DMSO acts not only as a solvent but also as a one carbon donor in the reaction.

An efficient method for the synthesis of 3-functionalized quinolines from acetophenones and anthranil mediated by Selectfluor was achieved.