Recent advances in the synthesis of pharmaceutically active 4-quinolone and its analogues: a review

Electrochemical Synthesis of 3-(Sulfonyl)quinol-4-ones from o-Alkynyl-N-(formyl)anilides and Sulfinates

Electrolysis of o-alkynyl-N-(formyl)anilides and sodium sulfinates on graphite electrodes delivers biologically sound 3-(sulfonyl)quinol-4-ones with moderate to good yields. The reaction is carried out in an undivided cell in the presence of silver(I) oxide with potassium iodide or sodium tetrafluoroborate as the supporting electrolyte. The reaction tolerates variously substituted anilides as well as aryl and alkyl sulfinates. The transformation proceeds as a domino sequence of oxysulfonylation and cyclocondensation steps.

Methoxyquinolone-Benzothiazole Hybrids as New Aggregation-Induced Emission Luminogens and Efficient Fluorescent Chemosensors for Cyanide Ions

This work describes the synthesis and characterization of new quinolone-benzothiazole hybrids, the study of their aggregation-induced emission (AIE) properties, and the use of these systems as efficient fluorescent probes for cyanide ions. These conjugated derivatives are linked through a double bond favoring electronic communication, and together with their planar geometry, can strongly aggregate under solvophobic environments, leading to aggregation and exhibiting significant AIE behavior. The double bond between electroactive units is prone to nucleophilic addition reactions by cyanide ions, selectively, conducive to turning off the fluorescence properties, making this hybrid system an efficient probe for cyanide ions. These studies were theoretically explained using DFT and TD-DFT calculations.

One-Pot Synthesis of N-Fused Quinolone-4 Tetracyclic Scaffolds from 2,2-Disubstituted Indolin-3-ones

A cascade transformation of C2-quaternary indoxyls leading to an efficient assembly of complex (dihydro)indolo[1,2-a]quinolin-5-one ring systems is reported. The method involves the gram-scale preparation of 2-(2-aryl-3-oxoindolin-2-yl)-2-phenylacetonitriles which are then converted with methyl ketones to the corresponding 2-(2-oxo-2-aryl(alkyl)ethyl)-2-phenylindolin-3-ones. The latter can either be isolated with good yields (75-96%) or, in the case of o-nitroacetophenone, used in situ for further base-assisted intramolecular SNAr cyclization resulting in indoxyl-fused quinolone-4 hybrids (up to 95%).

Advances in the Synthesis and Biological Applications of Enoxacin-Based Compounds

A comprehensive review of advances in the synthesis and biological applications of enoxacin (1, referred to as ENX)-based compounds is presented. ENX, a second-generation fluoroquinolone (FQ), is a prominent 1,8-naphthyridine containing compounds studied in medicinal chemistry. Quinolones, a class of synthetic antibiotics, are crucial building blocks for designing multi-biological libraries due to their inhibitory properties against DNA replication. Chemical modifications at positions 3 and 7 of the quinolone structure can transform antibacterial FQs into anticancer analogs. ENX and its derivatives have been examined for various therapeutic applications, including anticancer, antiviral, and potential treatment against COVID-19. Several synthetic methodologies have been devised for the efficient and versatile synthesis of ENX and its derivatives. This review emphasizes all-inclusive developments in the synthesis of ENX derivatives, focusing on modifications at C3 (carboxylic acid, Part A), C7 (piperazinyl, Part B), and other modifications (Parts A and B). The reactions considered were chosen based on their reproducibility, ease of execution, accessibility, and the availability of the methodology reported in the literature. This review provides valuable insights into the medicinal properties of these compounds, highlighting their potential as therapeutic agents in various fields.

Highly Selective Electrosynthesis of 1H-1-Hydroxyquinol-4-ones-Synthetic Access to Versatile Natural Antibiotics

1H-1-Hydroxyquinolin-4-ones represent a broad class of biologically active heterocycles having an exocyclic N,O motif. Electrosynthesis offers direct, highly selective, and sustainable access to 1-hydroxyquinol-4-ones by nitro reduction. A versatile synthetic route starting from easily accessible 2-nitrobenzoic acids was established. The broad applicability of this protocol was demonstrated on 26 examples with up to 93% yield, highlighted by the naturally occurring antibiotics Aurachin C and HQNO. The practicability and technical relevance were underlined by multigram scale electrolysis.

Modular synthesis of pentacyclic-fused pyranoquinoliziniums as organelle-selective fluorescent probes

On basis of their unique chemical and photophysical properties, and excellent biological activities, quinoliziniums have been widely used in various research fields. Herein, modular synthetic strategies for efficient synthesis of novel fluorescent quinoliziniums by using one-pot and stepwise rhodium(III)-catalyzed C-H annulations were developed. In the one-pot synthesis, the reaction between 2-aryl-4-quinolones (1) and 1,2-diarylalkynes (2) proceeded in a chemo- and regioselective manner to give quinolinone-fused isoquinolines (3) and pentacyclic-fused pyranoquinoliziniums (4). The structural diversity of pentacyclic-fused pyranoquinoliziniums (4) was expanded by the stepwise synthesis from 3 and 2, allowing the strategic incorporation of electron-donating (OMe and OH) and electron-withdrawing (Cl) substituents on the top and bottom parts of the pyranoquinoliziniums (4). These newly synthesized pyranoquinoliziniums (4) exhibited tunable absorptions (455-532 nm), emissions (520-610 nm), fluorescence lifetime (0.3-5.6 ns), large Stokes shifts (up to 120 nm), and excellent fluorescence quantum yields (up to 0.73) upon adjusting the different substituents. The the unique arrangement of N and O atoms and extended π-conjugation of 4 could cause the relocation of HOMO comparing with our previous quinoliziniums. Importantly, pyranoquinoliziniums (4a-4g and 4i) targeted the mitochondria, while 4h was localized in lysosome. Due to the remarkable photophysical properties and the potential for organelle targeting of the novel class of quinoliziniums, they could be further applied for biological, chemical and material applications.

Reagent-Free Intramolecular Hydroamination of Ynone-Tethered Aryl-sulfonamide: Synthesis of Polysubstituted 4-Quinolones

An efficient reagent-free method for the synthesis of polysubstituted 4-quinolone from 2-substituted alkynoyl aryl-sulfonamide was developed. This developed method tolerates various functional groups and gives the corresponding 4-quinolones. We have successfully extended this method to the synthesis of dihydro-4-quinolones from 2-alkenoyl aryl sulfonamide derivatives.

Synthesis and antibacterial medicinal evaluation of carbothioamido hydrazonyl thiazolylquinolone with multitargeting antimicrobial potential to combat increasingly global resistance

The global microbial resistance is a serious threat to human health, and multitargeting compounds are considered to be promising to combat microbial resistance. In this work, a series of new thiazolylquinolones with multitargeting antimicrobial potential were developed through multi-step reactions using triethoxymethane and substituted anilines as start materials. Their structures were confirmed by 1H NMR, 13C NMR and HRMS spectra. Antimicrobial evaluation revealed that some of the target compounds could effectively inhibit microbial growth. Especially, carbothioamido hydrazonyl aminothiazolyl quinolone 8a showed strong inhibitory activity toward drug-resistant Staphylococcus aureus with MIC value of 0.0047 mM, which was 5-fold more active than that of norfloxacin. The highly active compound 8a exhibited negligible hemolysis, no significant toxicity in vitro and in vivo, low drug resistance, as well as rapidly bactericidal effects, which suggested its favorable druggability. Furthermore, compound 8a was able to effectively disrupt the integrity of the bacterial membrane, intercalate into DNA and inhibit the activity of topoisomerase IV, suggesting multitargeting mechanism of action. Compound 8a could form hydrogen bonds and hydrophobic interactions with DNA-topoisomerase IV complex, indicating the insertion of aminothiazolyl moiety was beneficial to improve antibacterial efficiency. These findings indicated that the active carbothioamido hydrazonyl aminothiazolyl quinolone 8a as a chemical therapeutic candidate demonstrated immense potential to tackle drug-resistant bacterial infections.

Direct catalytic photodecarboxylative amination of carboxylic acids with diazirines for divergent access to nitrogen-containing compounds

Amines, hydrazines, and nitrogen-containing heterocycles are pivotal species in medicine, agriculture, fine chemicals, and materials. Diazirines have been recently reported to serve as versatile electrophilic amination reagents for the synthesis of building blocks or late-stage C-N bond formation. Here, we report the catalytic photodecarboxylative amination of carboxylic acids with diazirines under mild conditions. The substrate scope includes broad functional group tolerance, such as ketones, esters, olefins, and alcohols, along with the late-stage amination of naproxen, ibuprofen, gemfibrozil, and gibberellic acid. Synthetic applications leverage the versatility of the intermediate diaziridines and include the regioselective preparation of a suite of 1H-indazoles, 2H-indazoles, and fluoroquinolones.

Cu-Catalyzed Tandem C-N and C-C Bond Formation Leading to 4(1H)-Quinolones: A Scaffold with Diverse Biological Properties from Totally New Raw Materials in a Single Step

A novel Cu-catalyzed tandem C-N and C-C bond-formation reaction has been developed to furnish 2-substituted-4-(1H)-quinolones. 4-(1H)-quinolones play an important role in medicinal chemistry. Many 2-aryl(alkyl)-4(1H)-quinolones are found to exhibit diverse biological properties. While traditional methods have inherent issues [like starting materials with incompatible functional groups (NH2 and keto groups)], many modern methods either require activated starting materials (like Ynones) or employ expensive metals (Pd, Rh, Au, etc.) involving carbonylation using CO or metal complexes. Our protocol presents an environmentally friendly one-step method for the construction of these useful 2-substituted-4-(1H)-quinolones from easily available aryl boronic acid (or pinacolate ester) and nitriles as new raw materials, using a cheap Cu-catalyst and O2 (air) as a green oxidant. We further extended its application to the synthesis of various natural products, including the first formal total synthesis of punarnavine. A plausible mechanism involving an aryl nitrilium ion (formed due to the intermolecular C-N bond-forming coupling between aryl boron species and the nitrile group) followed by tandem intramolecular C-C bond formation has been proposed.

Synthesis, molecular docking analysis and in vitro evaluation of new heterocyclic hybrids of 4-aza-podophyllotoxin as potent cytotoxic agents

Two different synthetic approaches to novel heterocyclic hybrid compounds of 4-azapodophyllotoxin were investigated. The obtained products were characterized by infrared spectroscopy, nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. MTT protocol was then performed to examine the cytotoxic activity of these products against KB, HepG2, A549, MCF7, and Hek-293 cell lines. The cytotoxic assessment indicated that all products displayed moderate to high cytotoxicity against all tested cancer cell lines. The most active compound 13k containing the 2-methoxypyridin-4-yl group exhibited selective cytotoxicity against KB, A549, and HepG2 cell lines with the IC50 values ranging from 0.23 to 0.27 μM, which were between 5- to 10-fold more potent than the positive control ellipticine. Compounds 13a (HetAr = thiophen-3-yl) and 13d (HetAr = 5-bromofuran-2-yl) displayed high cytotoxic selectivity for A549 and HepG2 cancer cell lines when compared to the other cancer cell lines and low toxicity to the normal Hek-293 cell line. Molecular docking study was conducted to evaluate the interaction of new synthesized compounds with the colchicine-binding-site of tubulin. Besides that, physicochemical and pharmacokinetic properties of the most active compounds 13h,k were predicted.

Quinolone Derivatives as Anticancer Agents: Importance in Medicinal Chemistry

Quinolone is a heterocyclic compound containing carbonyl at the C-2 or C-4 positions with nitrogen at the C-1 position. The scaffold was first identified for its antibacterial properties, and the derivatives were known to possess many pharmacological activities, including anticancer. In this review, the quinolin-2(H)-one and quinolin-4(H)-one derivatives were identified to inhibit several various proteins and enzymes involved in cancer cell growth, such as topoisomerase, microtubules, protein kinases, phosphoinositide 3-kinases (PI3K) and histone deacetylase (HDAC). Hybrids of quinolone with curcumin or chalcone, 2-phenylpyrroloquinolin-4-one and 4-quinolone derivatives have demonstrated strong potency against cancer cell lines. Additionally, quinolones have been explored as inhibitors of protein kinases, including EGFR and VEGFR. Therefore, this review aims to consolidate the medicinal chemistry of quinolone derivatives in the pipeline and discuss their similarities in terms of their pharmacokinetic profiles and potential target sites to provide an understanding of the structural requirements of anticancer quinolones.

Effective Synthesis of 4-Quinolones by Reductive Cyclization of 2'-Nitrochalcones Using Formic Acid as a CO Surrogate

4-Quinolones are the structural elements of many pharmaceutically active compounds. Although several approaches are known for their synthesis, the introduction of an aryl ring in position 2 is problematic with most of them. The reductive cyclization of o-nitrochalcones by pressurized CO, catalyzed by ruthenium or palladium complexes, has been previously reported to be a viable synthetic strategy for this aim, but the need for pressurized CO lines and autoclaves has prevented its widespread use. In this paper, we describe the use of the formic acid/acetic anhydride mixture as a CO surrogate, which allows us to perform the reaction in a cheap and commercially available thick-walled glass tube without adding any gaseous reagent. The obtained yields are often high and compare favorably with those previously reported by the use of pressurized CO. The procedure was applied to a three-step synthesis from commercially available and cheap reagents of the alkaloid Graveoline.