Recent developments in the nanomaterial-catalyzed green synthesis of structurally diverse 1,4-dihydropyridines

The Use of 5-Hydroxymethylfurfural (5-HMF) in Multi-Component Hantzsch Dihydropyridine Synthesis

The renewable 5-hydroxymethylfurfural (5-HMF) has gained a wide interest from the chemistry community as a valuable biobased platform opening the way to many applications. Despite an impressive number of publications reporting either its preparation or its functionalization, its direct use in fine chemistry, and especially in multi-component reaction (MCR), is less reported. Here, we report a complete study of the use of 5-HMF in the Hantzsch dihydropyridines synthesis. The strategy was applied to a scope of β-dicarbonyl molecules (including β-ketoesters and 1,3-diketones) in a 3-component procedure leading to a series of symmetrical 1,4-dihydropyridines derived from 5-HMF in excellent yields. The study was extended to the 4-component protocol using one equivalent of a β-ketoester and one equivalent of 5,5-dimethyl-1,3-cyclohexanedione (dimedone), which efficiently provided the corresponding unsymmetrical dihydropyridines.

Montmorillonite K-10 catalyzed synthesis of Hantzsch dihydropyridine derivatives from methyl arenes via in situ generated ammonia under microwave irradiation in neat conditions

An expeditious, efficient, and environmentally friendly approach has been established for the synthesis of diverse Hantzsch 1,4-dihydropyridine derivatives utilizing montmorillonite K-10 as a catalyst in solvent-free conditions. The procedure entails the reaction of methyl arynes as a sustainable surrogate of aryl aldehydes, active methylene compounds, and urea hydrogen peroxide (UHP) as an oxidising agent as well as a source of ammonia under microwave irradiation, facilitated by montmorillonite K-10.

Revisiting Biginelli-like reactions: solvent effects, mechanisms, biological applications and correction of several literature reports

This study critically reevaluates reported Biginelli-like reactions using a Kamlet-Abboud-Taft-based solvent effect model. Surprisingly, structural misassignments were discovered in certain multicomponent reactions, leading to the identification of pseudo three-component derivatives instead of the expected MCR adducts. Attempts to replicate literature conditions failed, prompting reconsideration of the described MCRs and proposed mechanisms. Electrospray ionization (tandem) mass spectrometry, NMR, melting points, elemental analyses and single-crystal X-ray analysis exposed inaccuracies in reported MCRs and allowed for the proposition of a complete catalytic cycle. Biological investigations using both pure and "contaminated" derivatives revealed distinctive features in assessed bioassays. A new cellular action mechanism was unveiled for a one obtained pseudo three-component adduct, suggesting similarity with the known dihydropyrimidinone Monastrol as Eg5 inhibitors, disrupting mitosis by forming monoastral mitotic spindles. Docking studies and RMSD analyses supported this hypothesis. The findings described herein underscore the necessity for a critical reexamination and potential corrections of structural assignments in several reports. This work emphasizes the significance of rigorous characterization and critical evaluation in synthetic chemistry, urging a careful reassessment of reported synthesis and biological activities associated with these compounds.

Synthesis of hydrazone-based polyhydroquinoline derivatives - antibacterial activities, α-glucosidase inhibitory capability, and DFT study

In recent years, polyhydroquinolines have gained much attention due to their widespread applications in medicine, agriculture, industry, etc. Here, we synthesized a series of novel hydrazone-based polyhydroquinoline derivatives via multi-step reactions. These molecules were characterized by modern spectroscopic techniques (1H-NMR, 13C NMR, and LC-HRMS) and their antibacterial and in vitro α-glucosidase inhibitory activities were assessed. Compound 8 was found to be the most active inhibitor against Listeria monocytogenes NCTC 5348, Bacillus subtilis IM 622, Brevibacillus brevis, and Bacillus subtilis ATCC 6337 with a zone of inhibition of 15.3 ± 0.01, 13.2 ± 0.2, 13.1 ± 0.1, and 12.6 ± 0.3 mm, respectively. Likewise, compound 8 also exhibited the most potent inhibitory potential for α-glucosidase (IC50 = 5.31 ± 0.25 μM) in vitro, followed by compounds 10 (IC50 = 6.70 ± 0.38 μM), and 12 (IC50 = 6.51 ± 0.37 μM). Furthermore, molecular docking and DFT analysis of these compounds showed good agreement with experimental work and the nonlinear optical properties calculated here indicate that these compounds are good candidates for nonlinear optics.

Facile One-Pot Synthesis and Anti-Microbial Activity of Novel 1,4-Dihydropyridine Derivatives in Aqueous Micellar Solution under Microwave Irradiation

The current study describes a novel and eco-conscious method to synthesize 1,4-dihydropyridine derivatives utilizing an aqueous micellar solution containing aluminum dodecyl sulfate, Al(DS)3, using readily available starting material. The final products were synthesized with excellent yields within remarkably quick reaction durations, promoting remarkable atom economy and minimizing environmental impacts. The present protocol has several advantages over other methodologies in terms of high yield (up to 97%) with excellent purity. Further, the synthesized 1,4-DHPs exhibit favorable to excellent resistance against examined bacterial and fungal species. Intriguingly, polar groups on the phenyl ring (5b, 5c, 5i and 5j) make the 1,4-DHPs equally potent against the microbes as compared to the standard drugs.

Construction of 1,4-Dihydropyridines: The Evolution of C4 Source

The field of cascade cyclization for the construction of 1,4-dihydropyridines (1,4-DHPs) has been continuously expanding during the last decades because of their broad-spectrum biological and synthetic importance. To date, many methods have been developed, mainly including the Hantzsch reaction, Hantzsch-like reaction and newly developed cascade cyclization, in which various synthons have been successively developed as C4 sources of 1,4-DHPs. This review presents the cascade cyclization synthesis strategy for the construction of 1,4-DHPs according to various C4 sources from carbonyl compounds, alkenyl fragments, alcohols, aliphatic amines, glycines and other C4 sources.

Synthesis of 4-Alkylated 1,4-Dihydropyridines: Fe(II)-Mediated Oxidative Cascade Cyclization Reaction of Cyclic Ethers with Enaminones

Syntheses of highly functionalized 4-alkylated 1,4-dihydropyridines (1,4-DHPs) from cyclic ethers and enaminones via iron(II)-mediated oxidative free radical cascade C(sp3)-H bond functionalization/C(sp3)-O bond cleavage/cyclization reaction have been first developed. This novel synthetic strategy offers an alternative method for the construction of 1,4-DHPs by using esters as the C4 sources, as well as expands the application of ethers in heterocycle synthesis.

Tandem Protocol of Hexahydroquinoline Synthesis Using [H2-DABCO][HSO4]2 Ionic Liquid as a Green Catalyst at Room Temperature

Green, eco-benign, and sustainable synthesis is paramount in present chemistry. Here, a facile, efficient, and [H₂-DABCO][HSO₄]₂ ionic-liquid-catalyzed one-pot multicomponent synthesis of hexahydroquinolines was reported under ambient reaction conditions. The reaction of 1,3-dicarbonyls, malononitrile, and ammonium acetate with various aldehydes in the presence of an ionic liquid catalyst and EtOH solvent at room temperature afforded excellent yields (76-100%) of hexahydroquinolines under a short reaction time (5-15 min). Mild reaction conditions, broad substrate scope (28 derivatives), and column-chromatography-free synthesis with excellent catalytic efficiency and good recyclability rendered this protocol superior and practical. The greenness of the present method was assessed through eco-score and E-factor. The significant results in gram-scale synthetic conditions validate its applicability in industries as well as academia in the near future.

Solid-state silica gel-catalyzed synthesis of fluorescent polysubstituted 1,4- and 1,2-dihydropyridines

We present the green, highly atom-economical, solid-state silica gel-catalyzed synthesis of polysubstituted 1,4- and 1,2-dihydropyridines (DHPs) from commercially available materials, amines and ethyl propiolate. The DHP skeleton was assembled by heating the reactants and silica gel in a closed vessel. Aliphatic amines provided 1,4-isomers as the main or only DHP products, but the reactions of aromatic amines yielded a mixture of 1,4- and 1,2-isomers. To the best of our knowledge, this is the first example of the formation of a 1,2-DHP structure by the reaction of an amine with propiolic ester. Addition of 1 mass percent of H₂SO₄ to silica gel shifted the product distribution to 1,4-DHP as the main or the only isomer obtained. Experimental and theoretical analyses led to the identification of two key intermediates en route to DHPs and the explanation of the observed regioisomeric ratios. 1,2-DHPs show blue-cyan fluorescence in MeOH with the quantum yield Φ = 0.10-0.22 relative to quinine sulfate Φ = 0.58 and 1,4-DHPs show blue-violet fluorescence with Φ = 0.09-0.81.

Binding Properties of Photosynthetic Herbicides: Photosynthetic Activity and Molecular Docking Approach towards 1,4-Dihydropyridines Derivatives

In the current work, we describe the synthesis of 1,4-dihydropyridine (1,4-DHP) derivatives via Hantzsch multicomponent reaction and their evaluation as photosystem II (PSII) inhibitors through chlorophyll a fluorescence bioassay. Among all the compounds tested, 1,1'-(2,4,6-trimethyl-1,4-dihydropyridine-3,5-diyl)bis(ethan-1-one) (4b) showed best results, reducing the parameters performance index on absorption basis (PI_abs ) and electron transport per reaction center by 61 % and 49 %, respectively, as compared to the control. These results indicate the inhibitory activity of PSII over the electron transport chain. Additionally, a molecular docking approach using the protein D1 (PDB code 4V82) was performed in order to assess the structure-activity relationship among the 1,4-DHP derivatives over the PSII, which revealed that both, size of the group at position 4 and the carbonyl groups at the dihydropyridine ring are important for the ligand's interaction, particularly for the hydrogen-bonding interaction with the residues His215, Ser264, and Phe265. Thus, the optimization of these molecular features is the aim of our research group to extend the knowledge of PSII electron chain inhibitors and the establishment of new potent bioactive molecular scaffolds.

1,4-Dihydropyridine: synthetic advances, medicinal and insecticidal properties

1,4-Dihydropyridine (1,4-DHP) is one of the foremost notable organic scaffolds with diverse pharmaceutical applications. This study will highlight recent accomplishments in the construction of 1,4-DHP with structural and functional modifications using multi-component one-pot and green synthetic methodologies. The various intrinsic therapeutic applications, ranging from calcium channel blocker, anti-oxidative, anticancer, anti-inflammatory, anti-microbial, anti-hypertensive, anti-diabetic, anticoagulants, anti-cholinesterase, neuro-protective, and other miscellaneous activities, have been summarized with a focus on their structure-activity relationship (SAR) investigations. In addition, the insecticidal properties have been collated and discussed. Researchers in the fields of medicinal chemistry and drug development will find the summarized conclusions of this study incredibly informative, instructional, and valuable.

1,1′-{[3,5-Bis((dodecyloxycarbonyl)-4-phenyl-1,4-dihydropyridine-2,6-diyl]bis(methylene)}bis[4-(anthracen-9-yl)pyridin-1-ium] Dibromide

A synthesis of a cationic moiety and fluorescent moieties containing amphiphilic 1,4-dihydropyridine (1,4-DHP) derivatives was performed starting with the Hantzsch-type cyclization of dodecyl acetoacetate, phenylaldehyde and ammonium acetate. Bromination of the 2,6-dimethyl groups of a parent 1,4-DHP compound, followed by nucleophilic substitution of bromine with 4-(anthracen-9-yl)pyridine, produced the desired 1,1′-{[3,5-bis((dodecyloxycarbonyl)-4-phenyl-1,4-dihydropyridine-2,6-diyl]bis(methylene)}bis[4-(anthracen-9-yl)pyridin-1-ium] dibromide. The obtained target compound was fully characterized by the IR, 1H NMR, 13C NMR and HRMS data. Studies of the self-assembling properties and characterization of the nanoparticles obtained by the ethanol injection method were performed using dynamic light scattering (DLS) measurements. DLS measurement data showed that 1,1′-{[3,5-bis((dodecyloxycarbonyl)-4-phenyl-1,4-dihydropyridine-2,6-diyl]bis(methylene)}bis[4-(anthracen-9-yl)pyridin-1-ium] dibromide produced liposomes that had average diameters of 200 nm when the samples were freshly prepared, and 140 nm after 7 days or 1 month storage. The PDI values of the samples were approximately 0.50 and their zeta-potential values were approximately 41 mV when the samples were freshly prepared, and 33 mV after storage. The obtained nanoparticles were stored at room temperature for one month and remained stable during that period. The mean molecular area of the cationic 1,4-DHP-anthracene hybrid 4 was 118 Å2, while the mean molecular area of the cationic 1,4-DHP 5 without anthracene substituents was only 83 Å2. The photoluminescence quantum yield (PLQY) value for the EtOH solution of the 1,4-DHP derivative 4 was 10.8%, but for the 1,4-DHP derivative 5 it was only 1.8%. These types of compounds could be used as synthetic lipids in the further development of prospective theranostic delivery systems.

Progress in the Synthesis of Heterocyclic Compounds Catalyzed by Lipases

Heterocyclic compounds are representative of a larger class of organic compounds, and worthy of attention for many reasons, chief of which is the participation of heterocyclic scaffolds in the skeleton structure of many drugs. Lipases are enzymes with catalytic versatility, and play a key role in catalyzing the reaction of carbon–carbon bond formation, allowing the production of different compounds. This article reviewed the lipase-catalyzed aldol reaction, Knoevenagel reaction, Michael reaction, Mannich reaction, etc., in the synthesis of several classes of heterocyclic compounds with important physiological and pharmacological activities, and also prospected the research focus in lipase-catalyzed chemistry transformations in the future.