Hantzsch 1,4-dihydropyridine synthesis in aqueous ethanol by visible light

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, crystal structure and Hirshfeld surface analysis of tert-butyl 4-[4-(di-fluoro-meth-oxy)phen-yl]-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexa-hydro-quinoline-3-carboxyl-ate

The 1,4-di-hydro-pyridine ring of the title compound, C24H29F2NO4, adopts a distorted boat conformation, while the cyclo-hexene ring is in an almost twist-boat conformation. In the crystal, N-H⋯O and C-H⋯O hydrogen bonds as well as C-H⋯π inter-actions connect mol-ecules, forming layers parallel to the (100) plane. These layers are linked by van der Waals forces and C-H⋯F inter-actions, which consolidate the crystal structure. Hirshfeld surface analysis shows the major contributions to the crystal packing are from H⋯H (54.1%), F⋯H/H⋯F (16.9%), O⋯H/H⋯O (15.4%) and C⋯H/H⋯C (12.6%) contacts.

Ultrasound-Promoted preparation and application of novel bifunctional core/shell Fe3O4@SiO2@PTS-APG as a robust catalyst in the expeditious synthesis of Hantzsch esters

In this work, D-(-)-α-phenylglycine (APG)-functionalized magnetic nanocatalyst (Fe₃O₄@SiO₂@PTS-APG) was designed and successfully prepared in order to implement the principles of green chemistry for the synthesis of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives under ultrasonic irradiation in EtOH. After preparing of the nanocatalyst, its structure was confirmed by different spectroscopic methods or techniques including Fourier transform infrared (FTIR) spectroscopy, energy-dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and thermal gravimetric analysis (TGA). The performance of Fe₃O₄@SiO₂@PTS-APG nanomaterial, as a heterogeneous catalyst for the Hantzsch condensation, was examined under ultrasonic irradiation and various conditions. The yield of products was controlled under various conditions to reach more than 84% in just 10 min, which indicates the high performance of the nanocatalyst along with the synergistic effect of ultrasonic irradiation. The structure of the products was identified by melting point as well as FTIR and ¹H NMR spectroscopic methods. The Fe₃O₄@SiO₂@PTS-APG nanocatalyst is easily prepared from commercially available, lower toxic and thermally stable precursors through a cost-effective, highly efficient and environmentally friendly procedure. The advantages of this method include simplicity of the operation, reaction under mild conditions, the use of an environmentally benign irradiation source, obtaining pure products with high efficiency in short reaction times without using a tedious path, which all of them address important green chemistry principles. Finally, a reasonable mechanism is proposed for the preparation of polyhydroquinoline (PHQ) and 1,4-dihydropyridine (1,4-DHP) derivatives in the presence of Fe₃O₄@SiO₂@PTS-APG bifunctional magnetic nanocatalyst.

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.

Synthesis, molecular docking and extensive structure activity relationship of substituted DHP derivatives: a new class of herbicides

In the present study, twenty-two derivatives of dihydropyridine (DHP) have been synthesized using the Boric acid catalyst in solventless conditions. The synthesis was confirmed by FTIR analysis, 1HNMR, and 13CNMR analysis. The quantitative structure-activity relationship for all the synthesized derivatives was performed using an artificial neural network with correlation coefficient (R²) 0.8611, mean standard error 0.19, and Comparative molecular field analysis (CoMFA) with correlation coefficient (R²) 0.713, mean standard error 0.27. The molecular docking activity of synthesized compounds was tested using "AUTODOCK VINA" against "Acetohydroxyacid synthase protein receptors (PDB code 1YHZ)" acquired from the "RCSB Protein Data Bank". Docking experiments demonstrated favorable interaction among synthesized DHP derivatives and protein receptors with significant binding energy values. These synthesized derivatives have been screened for their pre-emergence herbicidal bioassay against weed species Echinochola crus galli, and the IC50 value were calculated and activity was compared with Butachlor, significant activity was exhibited by all the derivatives. All the synthesized compounds were also screened for their post emergence herbicidal activity against Echinochola crus galli, and the activity of DHPs were compared with penoxulum. All the synthesized compounds show good to moderate activity. Thus, it is concluded that substituted DHP derivatives may be developed as potential herbicides.

Anticancer activity of a 1,4-dihydropyridine in DMBA-induced mouse skin tumor model

Antitumor potential of a 1,4-dihydropyridine derivative (DHP-8) has been successfully studied previously in a number of cancer cell lines including the human melanoma cells, A375. In order to validate its anticancer activity, DMBA induced tumor in Swiss Albino mice was considered for this study. DMBA causes skin carcinoma in murine systems and is an important in vivo model for evaluating the efficacy of any new chemical entity against skin cancer. Topical administration of DHP-8 at the dose rate of 33.3 and 50.0 mg/kg body weight showed a significant reduction in tumor parameters. It also prevented the progression and differentiation of squamous cell carcinoma, as evidenced from histopathological studies. Immunohistochemical analysis for the expression of Ki67 indicated that it also reduced cancer cell proliferation. Additionally, it induced apoptosis in the tumor cells by activation of Caspase3. Our results indicated that DHP-8 efficiently attenuated DMBA induced tumor progression and it could be a potent therapeutic agent for skin cancer treatment.

Dendrons containing boric acid and 1,3,5-tris(2-hydroxyethyl)isocyanurate covalently attached to silica-coated magnetite for the expeditious synthesis of Hantzsch esters

A new multifunctional dendritic nanocatalyst containing boric acid and 1,3,5-tris(2-hydroxyethyl)isocyanurate covalently attached to core-shell silica-coated magnetite (Fe3O4@SiO2@PTS-THEIC-(CH2)3OB(OH)2) was designed and properly characterized by different spectroscopic or microscopic methods as well as analytical techniques used for mesoporous materials. It was found that the combination of both aromatic π-π stacking and boron-oxygen ligand interactions affords supramolecular arrays of dendrons. Furthermore, the use of boric acid makes this dendritic catalyst a good choice, from corrosion, recyclability and cost points of view. The catalytic activity of Fe3O4@SiO2@PTS-THEIC-(CH2)3OB(OH)2, as an efficient magnetically recoverable catalyst, was investigated for the synthesis of polyhydroacridines (PHAs) as well as polyhydroquinolines (PHQs) via one-pot multicomponent reactions of dimedone and/or ethyl acetoacetate, different aldehydes and ammonium acetate in EtOH under reflux conditions. Very low loading of the catalyst, high to quantitative yields of the desired PHAs or PHQs products, short reaction times, wide scope of the substrates, eliminating any toxic heavy metals or corrosive reagents for the modification of the catalyst, and simple work-up procedure are remarkable advantages of this green protocol. An additional advantage of this magnetic nanoparticles catalyst is its ability to be separated and recycled easily from the reaction mixture with minimal efforts in six subsequent runs without significant loss of its catalytic activity. This magnetic and dendritic catalyst can be extended to new two- and three-dimensional covalent organic frameworks with different applications.

Green synthesis and characterization of novel Mn-MOFs with catalytic and antibacterial potentials

The synthesis and characterization of novel Mn-MOF nanostructures (UoB-4) with high performance as catalysts and antibacterial agents.

Novel 1,4-dihydropyridine induces apoptosis in human cancer cells through overexpression of Sirtuin1

1,4-Dihydropyridines (1,4-DHPs) are important as a class of heterocyclic compounds that exhibit wide range of biological actions. Many of its derivatives are already characterized as medicinally important drugs and used worldwide. In this study, we have screened some novel Hantzsch 1,4-DHP compounds using both in silico (QSAR and Pharmacophore) and in vitro (cytotoxic screening). 1,4-DHP showed selective cytotoxicity against five human cancerous cell lines; A375, A549, HeLa, HepG2 and SH-SY5Y but limited effect towards normal skin keratinocyte (HaCaT), lung fibroblast (WL-38) and healthy peripheral blood mononuclear cells. In A375 and HepG2 cells, one of the 1,4-DHP derivative (DHP-8) was found to inhibit cell proliferation, and simultaneously increased the apoptotic population as well as mitochondrial membrane depolarization. Furthermore, the mitochondrial signal was triggered with the activation of cleaved Caspase9, Caspase3 and PARP. The treatment with DHP-8 also increased the expression level of SIRT1, subsequently decreasing the level of pAKT^ser473 and survivin. Reduced pAKT^ser473 expression led to decrease the phosphorylated inactive form of GSK3β^ser9 and as a result, proteasomal degradation of Mcl-1 occurred in both the cell lines. Here, we suggest that the apoptotic effect of DHP-8 in A375 and HepG2 cells was mediated by AKT and survivin pathways through SIRT1 activation. The involvement of DHP-8 in SIRT1 activation was further verified by co-treatment of nicotinamide with DHP-8 in both A375 and HepG2 cells. Overall, this study emphasizes the possible potential and therapeutic role of DHP-8 in skin and liver cancer.

Replication of the Enzymatic Temperature Dependency of the Primary Hydride Kinetic Isotope Effects in Solution: Caused by the Protein-Controlled Rigidity of the Donor-Acceptor Centers?

The change from the temperature independence of the primary (1°) H/D kinetic isotope effects (KIEs) in wild-type enzyme-catalyzed H-transfer reactions (ΔE_a = E_aD - E_aH ∼ 0) to a strong temperature dependence with the mutated enzymes (ΔE_a ≫ 0) has recently been frequently observed. This has prompted some enzymologists to develop new H-tunneling models to correlate ΔE_a with the donor-acceptor distance (DAD) at the tunneling-ready state (TRS) as well as the protein thermal motions/dynamics that sample the short DAD_TRS's for H-tunneling to occur. While extensive evidence supporting or disproving the thermally activated DAD sampling concept has emerged, a comparable study of the simpler bimolecular H-tunneling reactions in solution has not been carried out. In particular, small ΔE_a's (∼0) have not been found. In this paper, we report a study of the hydride-transfer reactions from four NADH models to the same hydride acceptor in acetonitrile. The ΔE_a's were determined: 0.37 (small), 0.60, 0.99, and 1.53 kcal/mol (large). The α-secondary (2°) KIEs on the acceptor that serve as a ruler for the rigidity of reaction centers were previously reported or determined. All possible productive reactant complex (PRC) configurations were computed to provide insight into the structures of the TRS's. Relationships among structures, 2° KIEs, DAD_PRC's, and ΔE_a's were discussed. The more rigid system with more suppressed 2° C-H vibrations at the TRS and more narrowly distributed DAD_PRC's in PRCs gave a smaller ΔE_a. The results replicated the trend observed in enzymes versus mutated enzymes and appeared to support the concepts of different thermally activated DAD_TRS sampling processes in response to the rigid versus flexible donor-acceptor centers.

Organophotoredox Catalysis: Visible-light-induced Multicomponent Synthesis of Chromeno[4, 3-b]chromene and Hexahydro-1H-xanthene Derivatives

Background:

In recent years, photoredox catalysis using eosin Y has gained considerable significance in organic chemistry. It is evolving as a powerful approach in modern organic synthesis for the activation of small molecules.

Objective:

The use of organic dyes to convert visible light into chemical energy by involving a single-electron transfer with organic substrates has innumerable applications.

Method and Results:

The present strategy is the first example of visible light promoted, aerobic, oxidative cyclization of chromeno[4,3-b]chromenes and hexahydro-1H-xanthenes via the formation of C–O and C–C bonds to afford excellent yield of the products in a simple one-pot operation under mild reaction conditions.

Conclusion:

The major advantages of the present methodology include short reaction time, cost effectiveness, easy work-up, broad substrate scope and high atom economy.

A green and clean pathway: one pot, multicomponent, and visible light assisted synthesis of pyrano[2,3-c]pyrazoles under catalyst-free and solvent-free conditions

Visible light mediated, an eco-friendlier synthetic protocol for dihydropyrano[2,3-c]pyrazoles via catalyst-free and solvent-free conditions at room temperature.

A multicomponent reaction on a ‘free’ KCC-1 catalyst at room temperature under solvent free conditions by visible light

A green and efficient method for the synthesis of various triazolo[1,2-a]indazoletrione under mild conditions is reported, that making it a genuinely green protocol.

One-pot pseudo three-component reaction of nitroketene-N,S-acetals and aldehydes for synthesis of highly functionalized hexa-substituted 1,4-dihydropyridines

Pseudo three-component condensation of aliphatic/aromatic/α,β-unsaturated aldehydes and nitroketene-N,S-acetals to afford diversely functionalized hexa-substituted 1,4-dihydropyridines under 2-aminopyridine catalysis was achieved.