Microwave-Assisted Synthesis of Diversely Substituted Quinoline-Based Dihydropyridopyrimidine and Dihydropyrazolopyridine Hybrids

Recent developments on microwave-assisted organic synthesis of nitrogen- and oxygen-containing preferred heterocyclic scaffolds

In recent decades, the utilization of microwave energy has experienced an extraordinary surge, leading to the introduction of innovative and revolutionary applications across various fields of chemistry such as medicinal chemistry, materials science, organic synthesis and heterocyclic chemistry. Herein, we provide a comprehensive literature review on the microwave-assisted organic synthesis of selected heterocycles. We highlight the use of microwave irradiation as an effective method for constructing a diverse range of molecules with high yield and selectivity. We also emphasize the impact of microwave irradiation on the efficient synthesis of N- and O-containing heterocycles that possess bioactive properties, such as anti-cancer, anti-proliferative, and anti-tumor activities. Specific attention is given to the efficient synthesis of pyrazolopyrimidines-, coumarin-, quinoline-, and isatin-based scaffolds, which have been extensively studied for their potential in drug discovery. The article provides valuable insights into the recent synthetic protocols and trends for the development of new drugs using heterocyclic molecules.

Multicomponent Reactions Using C,N-Binucleophilic Nature of Aminopyrazoles: Construction of Pyrazole-Fused Heterocycles

Synthesis of pyrazole-fused heterocycles has gained considerable attention in recent years due to their wide applications in medicinal chemistry. Aminopyrazoles are versatile building blocks for the synthesis of pyrazole-fused heterocycles by multicomponent reactions. Due to the presence of multiple reaction sites, they have fascinating chemical reactivity. Thus, they have been extensively used in multicomponent reactions for the construction of pyrazole-fused heterocycles. Although few review articles on the preparation and applications of aminopyrazoles are known in the literature, to date there is no dedicated review article on the construction of pyrazole-fused heterocycles exploring the reactivity of amino pyrazoles as C,N-binucleophiles in multicomponent reactions. Considering this, herein the multicomponent reactions for the construction of pyrazole-fused heterocycles exploring C,N-binucleophilic nature of amino pyrazoles have been reported.

Preliminary Studies of Antimicrobial Activity of New Synthesized Hybrids of 2-Thiohydantoin and 2-Quinolone Derivatives Activated with Blue Light

Thiohydantoin and quinolone derivatives have attracted researchers' attention because of a broad spectrum of their medical applications. The aim of our research was to synthesize and analyze the antimicrobial properties of novel 2-thiohydantoin and 2-quinolone derivatives. For this purpose, two series of hybrid compounds were synthesized. Both series consisted of 2-thiohydantoin core and 2-quinolone derivative ring, however one of them was enriched with an acetic acid group at N3 atom in 2-thiohydantoin core. Antibacterial properties of these compounds were examined against bacteria: Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae. The antimicrobial assay was carried out using a serial dilution method to obtain the MIC. The influence of blue light irradiation on the tested compounds was investigated. The relative yield of singlet oxygen (1O2*, 1Δg) generation upon excitation with 420 nm was determined by a comparative method, employing perinaphthenone (PN) as a standard. Antimicrobial properties were also investigated after blue light irradiation of the suspensions of the hybrids and bacteria placed in microtitrate plates. Preliminary results confirmed that some of the hybrid compounds showed bacteriostatic activity to the reference Gram-positive bacterial strains and a few of them were bacteriostatic towards Gram-negative bacteria, as well. Blue light activation enhanced bacteriostatic effect of the tested compounds.

Recent Advances in the Development of Pyrazolopyridines as Anticancer Agents

Cancer, especially malignant tumor, is a serious threat to people's life and health. It is recognized as an enormous challenge in the 21st century. Continuous efforts are needed to overcome this problem. Pyrazolopyridine nucleus, similar in structure to purine, shows a variety of biological activities, which is mainly attributed to the antagonistic nature towards the natural purines in many biological processes. This has aroused enormous attention for many researchers. At present, a large number of new chemical entities containing pyrazolopyridine nucleus have been found as anticancer agents. In this review we summarize novel pyrazolopyridine-containing derivatives with biological activities. Furthermore, we outline the relationships between the structures of variously modified pyrazolopyridines and their anticancer activity.

Design, synthesis, and molecular docking study of novel quinoline-based bis-chalcones as potential antitumor agents

A novel series of quinoline-based symmetrical and unsymmetrical bis-chalcones was synthesized via a Claisen-Schmidt condensation reaction between 3-formyl-quinoline/quinolone derivatives with acetone or arylidene acetones, respectively, by using KOH/MeOH/H₂ O as a reaction medium. Twelve of the obtained compounds were evaluated for their in vitro cytotoxic activity against 60 different human cancer cell lines according to the National Cancer Institute protocol. Among the screened compounds, the symmetrical N-butyl bis-quinolinyl-chalcone 14g and the unsymmetrical quinolinyl-bis-chalcone 17o bearing a 7-chloro-substitution on the N-benzylquinoline moiety and 4-hydroxy-3-methoxy substituent on the phenyl ring, respectively, exhibited the highest overall cytotoxicity against the evaluated cell lines with a GI₅₀ range of 0.16-5.45 µM, with HCT-116 (GI₅₀  = 0.16) and HT29 (GI₅₀  = 0.42 μM) (colon cancer) representing best-case scenarios. Notably, several GI₅₀ values for these compounds were lower than those of the reference drugs doxorubicin and 5-FU. Docking studies performed on selected derivatives yielded very good binding energies in the active site of proteins that participate in key carcinogenic pathways.

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

Microwave-assisted (MWA) multicomponent reactions (MCRs) have successfully emerged as one of the useful tools in the synthesis of biologically relevant heterocycles. These reactions are strategically employed for the generation of a variety of heterocycles along with multiple point diversifications. Over the last few decades classical MCRs such as Ugi, Biginelli, etc. have witnessed enhanced yield and efficiency with microwave assistance. The highlights of MWA-MCRs are high yields, reduced reaction time, selectivity, atom economy and simpler purification techniques, such an approach can accelerate the drug discovery process. The present review focuses on the recent advances in MWA-MCRs and their mechanistic insights over the past decade and shed light on its advantage over the conventional approach.

Discovery of Anticancer Agents from 2-Pyrazoline-Based Compounds

As nitrogen-containing five-membered heterocyclic structural units, the substituted pyrazole derivatives have a broad spectrum of pharmacological activities, especially 4,5-dihydro-1H-pyrazoles that also commonly known as 2-pyrazolines. Since 2010, considerable studies have been found that the 2-pyrazoline derivatives possess potent anticancer activities. In the present review, it covers the pyrazoline derivatives reported by literature from 2010 till date (2010-2019). This review aims to establish the relationship between the anticancer activities variation and different substituents introduced into a 2-pyrazoline core, which could provide important pharmacophore clues for the discovery of new anticancer agents containing 2-pyrazoline scaffold.

Solvothermal Synthesis of Multiple Dihydropyrimidinones at a Time as Inhibitors of Eg5

Solvothermal synthesis of multiple dihydropyrimidinones at a time has been developed in inexpensive and green bio-based solvent lactic acid without any additional catalysts or additives. By this method, thirty new dihydropyrimidinone derivatives were synthesized in two batches and characterized. All of the compounds were screened by Eg5 motor protein ATPase assay, and the positive compounds were tested against the Caco-2 cell line, HeLa cell line, L929 cell line and T24 cell line in vitro. Among them, compound C9 exhibited the best inhibitory activity against motor protein ATPase with an IC₅₀ value of 30.25 μM and significant cytotoxic activity in the micromolar range against the cells above. The Lineweaver–Burk plot revealed that compound C9 was a mixed-type Eg5 inhibitor. A molecular modeling study using the Discovery Studio program was performed, where compound C9 exhibited good binding interaction with Eg5 motor protein ATPase, and this was consistent with the attained experimental results.

Potent Quinoline-Containing Combretastatin A-4 Analogues: Design, Synthesis, Antiproliferative, and Anti-Tubulin Activity

A novel series of quinoline derivatives of combretastatin A-4 incorporating rigid hydrazone and a cyclic oxadiazole linkers were synthesized and have demonstrated potent tubulin polymerization inhibitory properties. Many of these novel derivatives have shown significant antiproliferative activities in the submicromolar range. The most potent compound, 19h, demonstrated superior IC50 values ranging from 0.02 to 0.04 µM against four cancer cell lines while maintaining low cytotoxicity in MCF-10A non-cancer cells, thereby suggesting 19h's selectivity towards proliferating cancer cells. In addition to tubulin polymerization inhibition, 19h caused cell cycle arrest in MCF-7 cells at the G2/M phase and induced apoptosis. Collectively, these findings indicate that 19h holds potential for further investigation as a potent chemotherapeutic agent targeting tubulin.

Catalyst-free assembly of giant tris(heteroaryl)methanes: synthesis of novel pharmacophoric triads and model sterically crowded tris(heteroaryl/aryl)methyl cation salts

A series of giant tris(heteroaryl)methanes are easily assembled by one-pot three-component synthesis by simple reflux in ethanol without catalyst or additives. Diversely substituted indoles (Ar1) react with quinoline aldehydes, quinolone aldehydes, chromone aldehydes, and fluorene aldehydes (Ar2CHO) and coumarins (Ar3) in 1:1:1 ratio to form the corresponding tris(heteroaryl)methanes (Ar1Ar2Ar3)CH along with (Ar1Ar1Ar2)CH triads. A series of new 2:1 triads were also synthesized by coupling substituted indoles with Ar2CHO. The coupling reactions could also be carried out in water (at circa 80 °C) but with chemoselectivity favoring (Ar1Ar1Ar2)CH over (Ar1Ar2Ar3)CH. The molecular structure of a representative (Ar1Ar2Ar3)CH triad was confirmed by X-ray analysis. Model tris(heteroaryl/aryl)methylium salts were generated by reaction with DDQ/HPF6 and studied by NMR and by DFT and GIAO-DFT.

5-Aminopyrazole as precursor in design and synthesis of fused pyrazoloazines

The condensation of 5-aminopyrazole with various bielectrophilic moieties results in the formation of pyrazoloazines, an interesting array of fused heterocyclic systems. The development of new synthetic routes towards pyrazoloazines for their biological and medicinal exploration is an attractive area for researchers throughout the world. The present review focuses on various synthetic methods developed in the last decade for the synthesis of differently substituted pyrazoloazines by a broad range of organic reactions by means of 5-aminopyrazole as a precursor.

Design, synthesis and crystallographic study of novel indole-based cyano derivatives as key building blocks for heteropolycyclic compounds of major complexity

A four-stage reaction sequence has been designed and developed for the synthesis of highly functionalized enolate esters as key building blocks for the synthesis of novel heteropolycyclic compounds of potential pharmaceutical value. The sequence starts with simple commercially available indoles and proceeds via 3-(indol-3-yl)-3-oxopropanenitriles, which react with 2-bromobenzaldehyde to form the corresponding chalcones; these are readily reduced to dihydrochalcones, which are in turn acylated to form the enolate esters. The compounds in this sequence have been characterized by IR and ¹H and ¹³C NMR spectroscopy, by mass spectrometry and by elemental analysis. The molecular and supramolecular structures are reported for representative examples, namely (E)-3-(2-bromophenyl)-2-(1-methyl-1H-indole-3-carbonyl)acrylonitrile, C₁₉H₁₃BrN₂O, (Ib), (2RS)-2-(2-bromobenzyl)-3-(1-methyl-1H-indol-3-yl)-3-oxopropanenitrile, C₁₉H₁₅BrN₂O, (IIb), and (2RS)-3-(1-benzyl-1H-indol-3-yl)-2-(2-bromobenzyl)-3-oxopropanenitrile, C₂₅H₁₉BrN₂O, (IIc), the latter two of which crystallize with Z' = 2, and (E)-1-(1-acetyl-1H-indol-3-yl)-3-(2-bromophenyl)-2-cyanoprop-1-en-1-yl acetate, C₂₂H₁₇BrN₂O, (III), and (E)-1-(1-benzyl-1H-indol-3-yl)-3-(2-bromophenyl)-2-cyanoprop-1-en-1-yl benzoate, C₃₂H₂₃BrN₂O, (IV). The structure of the related chalcone (E)-2-benzoyl-3-(2-bromophenyl)prop-2-enenitrile, (V), has been redetermined at 100 K, where it is monoclinic, as opposed to the triclinic form reported at ambient temperature.