Friedlӓnder's synthesis of quinolines as a pivotal step in the development of bioactive heterocyclic derivatives in the current era of medicinal chemistry

In the current scenario of medicinal chemistry, quinoline plays a pivotal role in the design of new heterocyclic compounds with several pharmacological properties, so the search for new synthetic methodologies and their application in drug discovery has been widely studied. So far, many procedures have been performed for the preparation of quinoline scaffolds, among which Friedländer quinoline synthesis plays an important role in obtaining these heterocycles. The Friedländer reaction involves condensation between 2-aminobenzaldehydes and keto-compounds. The quinoline nucleus, once obtained through the Friedländer synthesis, has been extensively modified so that these derivatives can exhibit a large number of biological activities such as anticancer, antimalarial, antimicrobial, antifungal, antituberculosis, and antileishmanial properties. In this work, the focus is on the applicability of the Friedländer reaction in the synthesis of various types of bioactive heterocyclic quinoline compounds, which to date has not been reported in the context of medicinal chemistry. The main part of this review selectively focuses on research from 2010 to date and will present highlights of the Friedländer quinoline synthesis procedures and findings to address biological and pharmacological activities.

Synthesis of 1,8-Naphthyridines by the Ionic Liquid-Catalyzed Friedlander Reaction and Application in Corrosion Inhibition

A several of basic ionic liquids (ILs) were synthesized as green solvents and catalysts for the preparation of 1,8-naphthyridyl derivatives via the Friedlander reaction. [Bmmim][Im] exhibited remarkable catalytic activity to achieve the synthetic targets, and the reaction conditions were optimized. The model product 2,3-diphenyl-1,8-naphthyridine (1,8-Nap), with carboxyethylthiosuccinic acid (CETSA) to form an IL corrosion inhibitor ([1,8-Nap][CETSA]), and its corrosion inhibition performance for Q235 steel in 1 M HCl were researched by weight loss measurements, and the results showed that the inhibition efficiency was 96.95% when the concentration of [1,8-Nap][CETSA] was 1 mM at 35 °C. The electrochemical test verified that [1,8-Nap][CETSA] acted as a mixed-type inhibitor but mainly exhibited cathodic behavior. The inhibitor adsorbed on the metal surface was further proved by surface topography analysis.

Sulfonamides and Sulphonyl Ester of Quinolines as Non-Acidic, Non- Steroidal, Anti-inflammatory Agents

Background:

Quinolines are an important class of heterocyclic compounds possessing a wide range of biological activities. Previously, we had identified Schiff bases of quinoline as potential anti-inflammatory agents, thus the current work is the continuation of our previous study.

Objective:

In the current study, 3-, 5-, and 8-sulfonamide and 8-sulfonate derivatives of quinoline (1-50) were synthesized and their anti-inflammatory potential was evaluated. These synthetic analogs were evaluated for their anti-inflammatory activity via ROS (Reactive oxygen species) inhibitory effect produced from phagocytes from human whole blood.

Methods:

The sulfonamide and sulfonate derivatives of quinoline were synthesized via treating 5-, 3-, 8-amino, and 8-hydroxy quinolines with different substituted sulfonyl chlorides in pyridine. The synthetic molecules were characterized using various spectroscopic techniques and screened for their anti-inflammatory potential.

Results:

Among the synthetic derivatives 1-50, six compounds showed good to moderate antiinflammatory activity. Compounds 47 (IC50 = 2.9 ± 0.5 μg/mL), 36 (IC50 = 3.2 ± 0.2 μg/mL), and 24 (IC50 = 6.7 ± 0.3 μg/mL) exhibited enhanced activity as compared to the standard ibuprofen (IC50 = 11.2 ± 1.9 μg/mL). Compounds 20 (IC50 = 25.5 ± 0.7 μg/mL), 50 (IC50 = 42.9 ± 5.6 μg/mL), and 8 (IC50 = 53.9 ± 3.1 μg/mL) were moderately active, however, rest of the compounds were found to be inactive.

Conclusion:

The sulfonamide and sulfonate derivatives of quinoline were found to have promising anti-inflammatory activity. Further studies on the modification of these molecules may lead to the discovery of new and potential anti-inflammatory agents.

The catalytic influence of phosphotungstic acid-functionalized Fe3O4 MNPs blended with TiO2 on the synthesis of novel spiro-acridines and the evaluation of their medicinal potential through molecular docking studies

This manuscript describes an effective and rapid three-component synthesis of a novel series of spiro-acridine derivatives by integrating the pharmacologically dynamic hydantoin–phenytoin as the prime synthetic equivalent. The process was accelerated by Fe₃O₄@TiO₂-PTA magnetic nanoparticles (MNPs), which acted as the heterogeneous catalytic system, under ultrasonic conditions. The reaction was performed in the green PEG-200 solvent under aerophilic conditions to obtain products with excellent yields. The characteristics of the synthesized magnetic nano-catalysts were corroborated through powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDAX), FT-IR, and VSM techniques. In addition, the structures of the synthesized compounds were ascertained on the basis of elemental analyses and spectro-analytical data (¹H NMR, ¹³C NMR, and mass spectrometry). High yields, smaller E-factor, considerable atom economy, easy recovery, and recyclability of the catalyst and solvent are the captivating features of the developed protocol. Moreover, in view of the ongoing global research on COVID-19, herein, we tried to identify the potential sites of the synthesized moiety that can suitably fit the receptor sites of the main protease of SARS-CoV-2 (SARS-CoV-2 M^pro).

This manuscript describes an effective and rapid three-component synthesis of a novel series of spiro-acridine derivatives by integrating the pharmacologically dynamic hydantoin–phenytoin as the prime synthetic equivalent.

One-pot synthesis of benzopyrano[2,3-d]pyrimidine derivatives catalyzed by LDHs@Propyl-ANDSA

A general, effective, and operationally simple approach to highly substituted benzopyrano[2,3-d]pyrimidine through the annulation of salicylaldehydes, malononitrile, and secondary amines is explained. The reaction is promoted by the Brønsted–Lowry acid, furnishing a variety of benzopyrano[2,3-d]pyrimidine derivatives in synthetically useful yields.

Recent advances on the transition-metal-catalyzed synthesis of imidazopyridines: an updated coverage

A comprehensive account of recent advances in the synthesis of imidazopyridines, assisted through transition-metal-catalyzed multicomponent reactions, C-H activation/functionalization and coupling reactions are highlighted in this review article. The basic illustration of this review comprises of schemes with concise account of explanatory text. The schemes depict the reaction conditions along with a quick look into the mechanism involved to render a deep understanding of the catalytic role. At some instances optimizations of certain features have been illustrated through tables, i.e., selectivity of catalyst, loading of the catalyst and percentage yield with different substrates. Each of the reported examples has been rigorously analyzed for reacting substrates, reaction conditions and transition metals used as the catalyst. This review will be helpful to the chemists in understanding the challenges associated with the reported methods as well as the future possibilities, both in the choice of substrates and catalysts. This review would be quite appealing to a wider range of organic chemists in academia and industrial R&D sectors working in the field of heterocyclic syntheses. In a nutshell, this review will be a guiding torch to envisage: (i) the role of various transition metals in the domain dedicated towards method development and (ii) for the modifications needed thereof in the R&D sector.

Green recipes to quinoline: A review

The quinoline core possesses a vast number of biological activities such as anticancer, antimalarial, antimicrobial, antifungal, antitubercular and antileishmanial. The conventional classical synthetic methods require the use of expensive and harsh conditions such as high temperature. Currently the scientific communities are searching new methodology to eliminate the use of chemicals, solvents and catalysts, which are hazardous to human health as well as to environment. This review provides a concise overview of new dimensions of green chemistry approaches in designing quinoline scaffold that would encourage the researchers towards green chemistry as well as future application of these greener, non-toxic, environment friendly methods in designing quinoline scaffold.

Recent advances in research of natural and synthetic bioactive quinolines

Many natural products that consist of quinoline core are found to be bioactive and the versatility of quinoline and its derivatives have attracted great attention in the field of drug development. As a result, in recent years, many green and sustainable synthetic approaches for the synthesis of structurally diverse quinolines have been developed. This review covers four main aspects, namely bioactive quinoline alkaloids, the biological activity and mechanism of action of quinoline-based compounds as well as various quinoline syntheses.

A Simple, Efficient and Solvent-free Reaction for the Synthesis of Quinolines Using Caesium Iodide

A series of quinoline derivatives has been synthesised from the reactions of 2-aminoacetophenone and 2-aminobenzophenone with different ketones in the presence of caesium iodide under solvent-free and thermal conditions. This method has the advantages of good yields, a clean reaction, simple methodology, short reaction times, easy work-up and green conditions.

A new NBS/oxone promoted one pot cascade synthesis of 2-aminobenzimidazoles/2-aminobenzoxazoles: a facile approach

A rapid and transition metal free synthesis of 2-aminobenzazoles using readily available substrates.

Friedländer annulation: scope and limitations of metal salt Lewis acid catalysts in selectivity control for the synthesis of functionalised quinolines

In(OTf)₃ is the most effective catalyst among metal halides, tetrafluoroborates, perchlorates, and triflates for Friedländer quinoline synthesis in 75–92% yields.

A novel, facile, rapid, solvent free protocol for the one pot green synthesis of chromeno[2,3-d]pyrimidines using reusable nano ZnAl2O4– a NOSE approach and photophysical studies

The preparation of an eco-friendly, highly stable, reusable nano ZnAl₂O₄was used as an excellent catalyst for the pseudo four component synthesis of a library of fluorescent chromeno[2,3-d]pyrimidine derivatives.

Nickel nanoparticles: a highly efficient and retrievable catalyst for the solventless Friedlander annulation of quinolines and their in silico molecular docking studies as histone deacetylase inhibitors

Highly efficient, solvent-free protocol for the synthesis of polysubstituted quinolines via Friedlander annulation using nickel nanoparticles from Aegle Marmelos Correa aqueous leaf extract.