Application of Quinoline Ring in Structural Modification of Natural Products

Visible Light-Induced Tandem Radical Cyclization for the Synthesis of 2-(3-Cyanoalkyl)Substituted Quinoline Derivatives

A highly efficient 6-endo-trig radical cyclization reaction between cyclobutanone oximes and 1-isocyano-2-vinylbenzenes via visible light-induced photoredox catalysis has been realized in the presence of 2 mol % of fac-Ir(ppy)3 as the photocatalyst, which gave rise to a variety of 2-(3-cyanoalkyl)substituted quinoline derivatives with moderate to excellent yields under mild reaction conditions.

Ru-CNP Complex-Catalyzed Hydrogen Transfer/Annulation Reaction of 2-Nitrobenzylalcohol via an Outer-Sphere Mechanism

The development of efficient catalysts plays a central role in advancing chemical reactions. In this study, a ruthenium complex modified with a N-heterocyclic carbene-imine-phosphine ligand (CNP) was employed to enhance the hydrogen transfer/annulation process of 2-nitrobenzyl alcohols with various primary or secondary alcohols. The NMR and HRMS analyses of the reaction solution revealed the in situ formation of [fac-RuH(CO)(PPh3)(κ3-CN(H)P)]Cl through the transfer hydrogenation of the imine moiety within the CNP ligand under the reaction conditions. This species, a bifunctional Noyori-type ruthenium complex featuring facial coordination with a CN(H)P ligand, served as a key catalytic intermediate. By leveraging the outer-sphere mechanism facilitated by [fac-RuH(CO)(PPh3)(κ3-CN(H)P)]Cl, the synthesis of 75 quinolines from 2-nitrobenzyl alcohols and a wide range of alcohols has been achieved with yields as high as 95%.

Semi-Preparation and X-ray Single-Crystal Structures of Sophocarpine-Based Isoxazoline Derivatives and Their Pesticidal Effects and Toxicology Study

Recently, research and development of novel pesticides from natural plant products have received much attention. To accelerate the application of sophocarpine as the agrochemical candidate, a series of novel sophocarpine-based isoxazoline derivatives were prepared by the 1,3-dipolar [2 + 3] cycloaddition reaction of sophocarpine with different chloroximes. Their structures were well characterized by high-resolution mass spectra, infrared spectra, and proton/carbon-13 nuclear magnetic resonance spectra. Eight steric configurations of compounds 5a, 5e', 5f, 5g, 5h, 5i, 5r, and 5u' were further determined by X-ray single-crystallography. Against Aphis citricola Van der Goot, compounds 5n (LD50: 0.032 μg/nymph) and 5o (LD50: 0.024 μg/nymph) exhibited greater than 3.7- and 4.9-fold potent aphicidal activity compared to sophocarpine (LD50: 0.118 μg/nymph). Against Tetranychus cinnabarinus Boisduval, derivative 5g displayed the most promising acaricidal activity with the LC50 value of 0.247 mg/mL, which was 14.2-fold that of sophocarpine. Compounds 5d and 5g also exhibited good control efficacy against T. cinnabarinus. Scanning electron microscopy images indicated that compound 5g can destroy the mite cuticle layer. These results will provide the foundation for the structural modification and use of sophocarpine derivatives as agrochemicals in the future.

Transition Metal-Catalyzed C-H Activation/Functionalization of 8-Methylquinolines

8-Methylquinoline is regarded as an ideal substrate to participate in diversely C(sp3)-H functionalization reactions. The presence of the chelating nitrogen atom enables 8-methylquinoline to easily form cyclometallated complexes with various transition metals, leading to the selective synthesis of functionalized quinolines. Considering the great importance of quinoline cores in medicinal chemistry, in this review article, we have covered the publications related to the C-H activation and functionalization of 8-methylquinoline under transition metal catalysis during the last decade.

Synthesis of Indolo[2,3/3,2-c]quinoline through Complementary PIDA/BF3·OEt2 as Well as Pd(0)-Mediated Intramolecular Cyclization of Isomeric N-((Aryl)-N-(phenylsulfonyl)indolyl)methylbenzenesulfonamides

Herein, a straightforward facile synthesis of indolo[2,3-c]quinoline analogues was reported from 2-arylamino(phenylsulfonyl)methylindoles involving PIDA/BF3·OEt2-mediated intramolecular dehydrogenative coupling (IDC) as a key step. Even though isomeric 3-arylamino(phenylsulfonyl)methylindoles, upon interaction with PIDA/BF3·OEt2, led to complications, synthesis of the indolo[3,2-c]quinoline framework could be easily achieved from N-(2-iodoaryl)-N-indolylmethylbenzenesulfonamide by employing a Pd(0)-mediated intramolecular cyclization reaction. Under identical conditions, synthesis of indolo[2,3-c]quinolines was also accomplished from the respective N-(2-iodoaryl)-N-indolylmethylbenzenesulfonamides. The SRB assay of fluorine-bound indoloquinolines displayed nanomolar-level cytotoxicity against a nonsmall lung cancer cell line, NCI-H460.

2,4-Quinolinedione alkaloids: occurrence and biological activities

Natural products are an important source of chemical scaffolds that have diverse biological activities. They can be used directly or as starting templates for the development of innovative pharmaceutical agents. Among natural products, quinoline alkaloids are one of the most extensively studied groups. 2,4-Quinolinedione (2,4-QD) alkaloids, which are found in a variety of natural sources, possess valuable biological properties. This review examines the natural occurrence and bioactivities of 2,4-QD alkaloids, which have not been studied in as much depth in previous research.

Pallado-Catalyzed Cascade Synthesis of 2-Alkoxyquinolines from 1,3-Butadiynamides

A novel synthesis strategy to access 2-alkoxyquinoline derivatives via a palladium-driven cascade reaction is disclosed. Unlike classic methods based on the alkylation of 2-quinolones with alkyl halides, the present method benefits from the de novo assembly of the quinoline core starting from 1,3-butadiynamides. Palladium-catalyzed reaction cascades with N-(2-iodophenyl)-N-tosyl-1,3-butadiynamides and primary alcohols as external nucleophiles proceed under mild reaction conditions and selectively deliver a variety of differently functionalized 4-alkenyl 2-alkoxyquinolines in a single batch transformation.

Synthesis of a new 2-prenylated quinoline as potential drug for metabolic syndrome with pan-PPAR activity and anti-inflammatory effects

We have previously reported the total synthesis and structure-activity relationships (SAR) of 2-prenylated benzopyrans with PPAR agonist activity. Herein, we have described the synthesis and PPAR activity of 2-prenylated benzopyrans and 2-prenylated quinolines. The benzopyran nucleus was generated via enamine-catalyzed Kabbe condensation, and the quinoline nucleus via Friedländer condensation. Results demonstrated that both benzopyran (5a) and quinoline (4b) derivatives bearing a γ,δ-unsaturated ester displayed a pan-PPAR agonism. They were full PPARα agonists, but showed different preferences for PPARγ and PPARβ/δ activation. It was noteworthy that quinoline 4b displayed full hPPARα activation (2-fold than WY-14,643), weak PPARβ/δ and partial PPARγ activation. In addition, quinoline 4b showed anti-inflammatory effects on macrophages by reducing LPS-induced expression of both MCP-1 and IL-6. Therefore, 4b emerges as a first-in-class promising hit compound for the development of potential therapeutics aimed at treating metabolic syndrome, metabolic dysfunction-associated fatty liver disease (MAFLD), and its associated cardiovascular comorbidities.

Quinoline Derivatives in Discovery and Development of Pesticides

Finding highly active molecular scaffold structures is always the key research content of new pesticide discovery. In the research and development of new pesticides, the discovery of new agricultural molecular scaffold structures and new targets still faces great challenges. In recent years, quinoline derivatives have developed rapidly in the discovery of new agriculturally active molecules, especially in the discovery of fungicides. The unique quinoline scaffold has many advantages in the discovery of new pesticides and can provide innovative and feasible solutions for the discovery of new pesticides. Therefore, we reviewed the use of quinoline derivatives and their analogues as molecular scaffolds in the discovery of new pesticides since 2000. We systematically summarized the agricultural biological activity of quinoline compounds and discussed the structure-activity relationship (SAR), physiological and biochemical properties, and mechanism of action of the active compounds, hoping to provide ideas and inspiration for the discovery of new pesticides.

Recent advancement in the synthesis of quinoline derivatives via multicomponent reactions

The synthesis of quinoline derivatives through multicomponent reactions (MCRs) has emerged as an efficient and versatile strategy in organic synthesis. MCRs offer the advantage of constructing complex molecular architectures in a single step, utilising multiple starting materials in a convergent manner. This review provides an overview of recent advancements in the field of quinoline synthesis via MCRs. Various MCRs, such as the Povarov reaction, the Gewald reaction, and the Ugi reaction have been successfully employed for the synthesis of diverse quinoline scaffolds. These methodologies not only showcase high atom economy but also allow the incorporation of structural diversity into the final products. The versatility of MCRs enables the introduction of functional groups and substitution patterns tailored to specific applications. This review highlights the significance of quinoline derivatives in medicinal chemistry, materials science, and other interdisciplinary areas. The continuous innovation and development of novel MCR-based approaches for quinoline synthesis hold great promise for the rapid and efficient generation of valuable compounds with a wide range of biological and physicochemical properties.

Synthesis, Herbicidal Activity, Mode of Action, and In Silico Analysis of Novel Pyrido[2,3-d]pyrimidine Compounds

Natural products are a main source of new chemical entities for use in drug and pesticide discovery. In order to discover lead compounds with high herbicidal activity, a series of new pyrido[2,3-d] pyrimidine derivatives were designed and synthesized using 2-chloronicotinic acid as the starting material. Their structures were characterized with 1H NMR, 13C NMR and HRMS, and the herbicidal activities against dicotyledonous lettuce (Lactuca sativa), field mustard (Brassica campestris), monocotyledonous bentgrass (Agrostis stolonifera) and wheat (Triticum aestivum) were determined. The results indicated that most of the pyrido[2,3-d] pyrimidine derivatives had no marked inhibitory effect on lettuce at 1 mM. However, most of the pyrido[2,3-d] pyrimidine derivatives possessed good activity against bentgrass at 1 mM. Among them, the most active compound, 3-methyl-1-(2,3,4-trifluorophenyl)pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (2o), was as active as the positive controls, the commercial herbicides clomazone and flumioxazin. Molecular simulation was performed with molecular docking and DFT calculations. The docking studies provided strong evidence that 2o acts as an herbicide by inhibition of protoporphyrinogen oxidase. However, the physiological results indicate that it does not act on this target in vivo, implying that it could be metabolically converted to a compound with a different molecular target.