Pyridine Ring System Research Articles

Crystal structure and Hirshfeld surface analysis of 5-oxo-7-phenyl-2-(phenyl-amino)-1H-[1,2,4]triazolo[1,5-a]pyridine-6,8-dicarbo-nitrile dimethyl sulfoxide monosolvate.

In the title compound, C20H12N6O·C2H6OS, the [1,2,4]triazolo[1,5-a]pyridine ring system is almost planar and makes dihedral angles of 16.33 (7) and 46.80 (7)°, respectively, with the phenyl-amino and phenyl rings. In the crystal, mol-ecules are linked by inter-molecular N-H⋯O and C-H⋯O hydrogen bonds into chains along the b-axis direction through the dimethyl sulfoxide solvent mol-ecule, forming C(10)R 2 1(6) motifs. These chains are connected via S-O⋯π inter-actions, π-π stacking inter-actions between the pyridine rings [centroid-to-centroid distance = 3.6662 (9) Å] and van der Waals inter-actions. A Hirshfeld surface analysis of the crystal structure indicates that the most important contributions to the crystal packing are from H⋯H (28.1%), C⋯H/H⋯C (27.2%), N⋯H/H⋯N (19.4%) and O⋯H/H⋯O (9.8%) inter-actions.

Synthesis of Palladium-Catalysed C-C Bond Forming 5-Chloro Quinolines via Suzuki-Miyaura Coupling; Anti-Pancreatic Cancer Screening on PANC-1 Cell Lines.

Pancreatic cancer is the most severe among other cancers due to its late detection and less chance of survivability. Heterocycles are proven ring systems in the treatment of various cancers and this is due to the presence of two biodynamic molecules combined, which have a greater synergistic efficacy in many anticancer drugs. Quinoline and pyridine ring systems are brought together to obtain greater potency and this is achieved by coupling both using Pd-catalyst, and in the present investigation, Suzuki-Miyaura coupling (SMC) reactions are adopted to generate potent molecular entities. Pancreatic cancer is difficult to treat due to overexpression of the VEGFR2 protein. VEGFR2 is targeted to design the molecules of quinoline-coupled pyridine moieties and is docked to evaluate the protein-ligand interaction at the binding site. The binding affinity of conjugates revealed the potency and capability of ligands to inhibit the VEGFR2 pathway. The in-silico ADMET properties determined their inherent pharmacokinetic feasibility. The synthesized conjugates have been evaluated by MTT assay against the human pancreatic cancer cell lines (PANC-1). Among the series, compounds 5d, 5e, and 5h exhibited a greater inhibitory activity against the cell lines with an IC50 value of 82.32±1.38, 54.74±1.18 and 80.35±1.68 μM. In the present exploration, 5e exhibited greater inhibitory activity and it could be a promising lead for the development of new chemotherapeutics against pancreatic cancer.

Cellulose Supported Propylamine/Molybdate Complex: A Novel and Recyclable Nanocatalyst for the Synthesis of Pyranopyrimidine Derivatives

Background: Carbon-based materials, due to their unique properties such as lightweight, different forms, doping capability with hetero atoms, low cost, and ease of processability, are suitable support, for heterogeneous catalysts. Among them, cellulose, as one of the most abundant and renewable organic polymers, preserves a key position in many organic raw materials. Pyranopyrimidine derivatives, due to their high biological activity are of interest to both medicinal chemists and biochemists. Moreover, they play the most fundamental structural role in many natural compounds and are medicinally useful molecules. Owing to the great variety of biologically active pyridines, it is not surprising that the pyridine ring system has become a vital basic component in many pharmaceutical agents. Method: In this study, cellulose as a heterogeneous support was used to prepare an efficient solid catalyst. Cellulose, as the most abundant organic polymer, is a suitable material for this purpose. Then, by immobilizing polyoxomolybdate by a linker on the surface of this carbon-based material, we succeeded in producing Cell@(CH2)3N=Mo[Mo5O18] nanocatalyst. The structure and properties of this catalyst were confirmed by various analyses including FT-IR, XRD, EDS-map, FESEM, and TGA, and its efficacy was evaluated by its use in the preparation of Pyrano[2,3- d]pyrimidine derivatives through a multicomponent reaction between aryl aldehydes, malononitrile, and barbituric acid. Results: The results of this study showed that this new and non-toxic organo-inorganic hybrid nanocatalyst provides the desired products in a short time and with appropriate efficiency. Conclusion: The key features of the present protocol include reusability of the catalyst, ease of recovery, ambient reaction conditions, and simple work-up procedure that make it economic and sustainable.

Crystal structure and Hirshfeld surface analysis of 5-amino-5'-bromo-2'-oxo-2,3-di-hydro-1H-spiro-[imidazo[1,2-a]pyridine-7,3'-indoline]-6,8-dicarbo-nitrile dimethyl sulfoxide disolvate.

In the title compound, C16H11BrN6O·2C2H6OS, the 1,2,3,7-tetra-hydro-imid-azo[1,2-a]pyridine ring system and the oxindole moiety are both nearly planar [maximum deviations= 0.042 (2) and 0.115 (2) Å, respectively] and their planes form a dihedral angle of 86.04 (5)° with each other. Inter-molecular N-H⋯O, C-H⋯O and C-H⋯N hydrogen bonds link mol-ecules in the crystal through the O atoms of the solvent mol-ecules, generating a three-dimensional network. A Hirshfeld surface analysis was performed to further analyse the inter-molecular inter-actions.

Construction of Pyridine Ring Systems by Mn(OAc)2‐Promoted Formal Dehydrative Dehydroaromatizing [4+2] Cycloaddition of Enamides with Maleimides

AbstractHerein, we report a Mn(OAc)2‐promoted formal dehydrative dehydroaromatizing [4+2] cycloaddition of enamides with maleimides for the construction of pyridine rings to access the diverse synthetically valuable pyrrolo[3,4‐c]‐pyridine derivatives. This protocol allows two C−C bond formation for the assembly of pyridine derivatives from enamides synthesizable in two steps and inexpensive maleimides, which exhibits broad substrate scope and good functional group compatibility.magnified image

Crystal structure and Hirshfeld surface analysis of 2-oxo-2-phenyl-ethyl 3-nitroso-2-phenyl-imidazo[1,2-a]pyridine-8-carboxyl-ate.

The title compound, C22H15N3O4, is built up from a central imidazo[1,2-a]pyridine ring system connected to a nitroso group, a phenyl ring and a 2-oxo-2-phenyl-ethyl acetate group. The imidazo[1,2-a] pyridine ring system is almost planar (r.m.s. deviation = 0.017 Å) and forms dihedral angles of 22.74 (5) and 45.37 (5)°, respectively, with the phenyl ring and the 2-oxo-2-phenyl-ethyl acetate group. In the crystal, the mol-ecules are linked into chains parallel to the b axis by C-H⋯O hydrogen bonds, generating R 2 1 (5) and R 4 4 (28) graph-set motifs. The chains are further linked into a three-dimensional network by C-H⋯π and π-stacking inter-actions. The inter-molecular inter-actions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the most important contributions for the crystal packing are from H⋯H (36.2%), H⋯C/C⋯H (20.5%), H⋯O/O⋯H (20.0%), C⋯O/O⋯C (6.5%), C⋯N/N⋯C (6.2%), H⋯N/N⋯H (4.5%) and C⋯C (4.3%) inter-actions.

Bis(furazano)pyridinone N,N'-dioxide: a new high-density insensitive explosive

The synthesis and properties of novel high-dense energetic material based on new 4H,8H-bis(furazano)[3,4-b:3',4'-e]-pyridine ring system are described. An operationally simple, efficient and scalable protocol towards 4H,8H-bis(furazano)-[3,4-b:3',4'-e]pyridin-8-one 1,7-dioxide from commercially available 4-amino-2,6-dichloropyridine in three steps, namely, nitration–azidation–cascade ring closure, has been developed.

Crystal structure and Hirshfeld surface analysis of 5,7-diphenyl-1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine-6,6,8-tricarbo-nitrile methanol mono-solvate.

In the title compound, C22H17N5·CH4O, the imidazolidine ring of the 1,2,3,5,6,7-hexa-hydro-imidazo[1,2-a]pyridine ring system is a twisted envelope, while the 1,2,3,4-tetra-hydro-pyridine ring adopts a twisted boat conformation. In the crystal, pairs of mol-ecules are linked by O-H⋯N and N-H⋯O hydrogen bonds via two methanol mol-ecules, forming a centrosymmetric R 4 4(16) ring motif. These motifs are connected to each other by C-H⋯N hydrogen bonds and form columns along the a axis. The columns form a stable mol-ecular packing, being connected to each other by van der Waals inter-actions. A Hirshfeld surface analysis indicates that the most significant contributions to the crystal packing are from H⋯H (43.8%), N⋯H/H⋯N (31.7%) and C⋯H/H⋯C (18.4%) contacts.

The Exploration of Novel Pharmacophore Characteristics and Multidirectional Elucidation of Structure-Activity Relationship and Mechanism of Sesquiterpene Pyridine Alkaloids from Tripterygium Based on Computational Approaches.

Sesquiterpene pyridine alkaloids are a large group of highly oxygenated sesquiterpenoids, which are characterized by a macrocyclic dilactone skeleton containing 2-(carboxyalkyl) nicotinic acid and dihydro-β-agarofuran sesquiterpenoid, and are believed to be the active and less toxic components of Tripterygium. In this study, 55 sesquiterpene pyridine alkaloids from Tripterygium were subjected to identification of pharmacophore characteristics and potential targets analysis. Our results revealed that the greatest structural difference of these compounds was in the pyridine ring and the pharmacophore model-5 (Pm-05) was the best model that consisted of three features including hydrogen bond acceptor (HBA), hydrogen bond donor (HBD), and hydrophobic (HY), especially hydrophobic group located in the pyridine ring. It was proposed that 2-(carboxyalkyl) nicotinic acid part possessing a pyridine ring system was not only a pharmacologically active center but also a core of structural diversity of alkaloids from Tripterygium wilfordii. Furthermore, sesquiterpene pyridine alkaloids from Tripterygium were predicted to target multiple proteins and pathways and possibly played essential roles in the cure of Alzheimer's disease, breast cancer, Chagas disease, and nonalcoholic fatty liver disease (NAFLD). They also had other pharmacological effects, depending on the binding interactions between pyridine rings of these compounds and active cavities of the target genes platelet-activating factor receptor (PTAFR), cannabinoid receptor 1 (CNR1), cannabinoid receptor 1 (CNR2), squalene synthase (FDFT1), and heat shock protein HSP 90-alpha (HSP90AA1). Taken together, the results of this present study indicated that sesquiterpene pyridine alkaloids from Tripterygium are promising candidates that exhibit potential for development as medicine sources and need to be promoted.

Ni-catalyzed enantioselective [2 + 2 + 2] cycloaddition of malononitriles with alkynes

Summary Efficient strategies to assemble enantioenriched pyridine derivatives are highly important, given their significance in both synthetic and medicinal chemistry. Here, we report an enantioselective nickel-catalyzed intermolecular [2 + 2 + 2] cycloaddition of alkyne-tethered malononitriles with alkynes for the synthesis of densely substituted pyridines. The α-all-carbon quaternary center adjacent to pyridine is introduced by desymmetrizing the two cyano groups of disubstituted malononitriles. Notably, terminal alkynes are also tolerated with good regioselectivity to afford tetrasubstituted pyridines. Zinc halide is essential to enable the occurrence of the transformation by promoting the hetero-cyclometallation step. The reaction uses bio-renewable 2-MeTHF as the solvent and features mild reaction conditions, good functional group compatibilities, and enantioselectivities. This study offers a straightforward approach to the valuable enantioenriched heteroarenes from feedstock chemicals by forming three bonds and one quaternary stereocenter simultaneously in a single reaction step.

Synthesis and Antibacterial Activity of New Imidazo[1,2-a]pyridines Festooned with Pyridine, Thiazole or Pyrazole Moiety

A series of new 6,8-dichloro-imidazo[1,2-a]pyridine derivatives incorporating pyridine, thiazole, and pyrazole ring systems was synthesized. The synthetic strategy of imidazopyridinyl-pyridine hybrids 2 and 3 involves one pot reaction of the precursor 3-acetyl-6,8-dichloro-2-methylimidazo[1,2-a] pyridine (1) with aldehydes, malononitrile, and/or ethyl cyanoacetate. Treatment of 1 with thiosemicarbazide and/or bromine followed by subsequent cyclization with ethyl bromoacetate, chloroacetone, phenacyl chloride, and/or thiourea was applied as synthetic routes for accessing the imidazopyridinyl-thiazole hybrids 5, 6, and 8–10. The reaction of 1 with dimethylformamide-dimethylacetal followed by subsequent treatment with hydrazine was employed to prepare the imidazopyridinyl-pyrazole motif 12. The antibacterial potency of these imidazopyridine hybrids has been evaluated against some model bacteria. The results indicated that the imidazopyridine-thiazole hybrids revealed remarkable antibacterial activities.

Crystal structure and Hirshfeld surface analysis of phen-yl(5,7,8a-triphenyl-1,2,3,7,8,8a-hexa-hydro-imidazo[1,2-a]pyridin-6-yl)methanone with an unknown solvent.

In the title compound, C32H28N2O, the imidazolidine and pyridine rings of the central hexa-hydro-imidazo[1,2-a]pyridine ring system adopt envelope and screw-boat conformations, respectively. The mol-ecule exhibits two weak intra-molecular π-π inter-actions between phenyl rings. In the crystal, mol-ecules are linked via pairs of C-H⋯ O hydrogen bonds, forming inversion dimers. The dimers are further linked by pairs of C-H⋯π inter-actions, forming infinite chains along the c-axis direction. A Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (73.4%), C⋯H/H⋯C (18.8%) and O⋯H/H⋯O (5.7%) contacts. The contribution of some disordered solvent to the scattering was removed using the SQUEEZE routine [Spek (2015 ▸). Acta Cryst. C71, 9-18] in PLATON. The solvent contribution was not included in the reported mol-ecular weight and density.

Synthesis and antioxidant assay of new nicotinonitrile analogues clubbed thiazole, pyrazole and/or pyridine ring systems

AbstractA series of novel nicotinonitrile derivatives were synthesized by hybridization with thiazole, pyrazole, and pyridine ring systems using 4‐aminobenzohydrazide as link‐bridge. The synthetic strategy of nicotinonitrile‐thiazole analogues involves cyclization of the precursor N‐phenyl thiosemicarbazide derivative 4 with chloroacetic acid and phenacyl bromide. The reaction of hydrazide 3 with acetylacetone and/or ethyl acetoacetate was applied as a synthetic route for accessing 2‐((4‐(pyrazole‐1‐carbonyl)phenyl)amino)‐nicotinonitrile derivatives 9–10. The 2‐((4‐(4‐thiazolylidene‐pyrazole‐1‐carbonyl)‐phenyl)amino)nicotinonitriles 14–15 were obtained via a nucleophilic addition of pyrazolone 10 to phenyl isothiocyanate followed by cyclization with chloroacetone, phenacyl chloride, and/or ethyl bromoacetate. The 6‐amino‐4‐aryl‐3,5‐dicyano‐2‐oxo‐1‐(4‐substitutedbenzamido)‐pyridines 19 were synthesized by Knoevenagel condensation N′‐(2‐cyanoacetyl)‐benzohydrazide derivative 16 with substituted benzaldehydes followed by heating with malononitrile. All synthesized products were evaluated for their antioxidant potentialities using of 2,2′‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid) (ABTS) radical cation delcolorization assay. The nicotinonitrile‐thiazole hybrid 6b was found the most promising antioxidant agent with inhibition activity 86.27%.

Synthesis, Reactions, and Antimicrobial Activity of Novel Heterocyclic Compounds Containing Cyclopenta[d]thieno[2,3-b]pyridine Moiety and Related Fused Heterocycles

We describe a simple method to synthesize novel 4-cyano-1-morpholin-4-yl-6,7-dihydro-5H-cyclopenta[c]pyridine-3-thione by the reaction of 3-amino-1-thioxo-1,5,6,7-tetrahydrocyclopenta[c]thiopyran-4-carbonitrile with morpholine through Dimroth rearrangement. The 1-amino-5-morpholin-4-yl-7,8-dihydro-6H-cyclopenta[d]thieno[2,3-b]pyridine-2-carboxamide, which was synthesized by two methods, was used as a versatile precursor for synthesis of new thienopyrimidines fused to cyclopenta[d]pyridine ring system. Consequently, reaction of the amino-carboxamide with diethylmalonate, triethyl orthoformate, and cycloalkanones afforded the corresponding fused pyrimidine heterocycles. On the other hand, chloroacetylation of the amino-carboxamide using chloroacetyl chloride in dioxane produced the chloroacetyl amino derivative that in turn underwent cyclocondensation upon reaction with acetic anhydride to give the chloromethyl pyrimidinone. The latter compound was subjected to react with various nitrogen nucleophiles by nucleophilic substitution reactions to yield the akyl (aryl)amino methyl pyrimidinones. Subsequently, treatment of the phenyl aminomethyl derivative with formaldehyde under Mannich conditions produced the imidazopyridothienopyrimidine ring system. Similarly, reaction of the phenyl aminomethyl pyrimidonone with chloroacetyl chloride afforded a new heterocyclic system namely, cyclopentapyridothienopyrimidopyrazine. On the other hand, reaction of the amino-carboxamide with carbon disulfide in pyridine led to the formation of oxopyrimidine thione, which was alkylated by the reaction with different α-halo carbonyl compounds. The newly synthesized compounds were fully characterized on the basis of elemental and spectral analyses. Alternatively, some of these compounds revealed promising antibacterial and antifungal activities through the in vitro screening.

Crystal structure, Hirshfeld surface analysis and contact enrichment ratios of 1-(2,7-di-methyl-imidazo[1,2-a]pyridin-3-yl)-2-(1,3-di-thio-lan-2-yl-idene)ethanone monohydrate.

In the title hydrated hybrid compound C14H14N2OS2·H2O, the planar imidazo[1,2-a]pyridine ring system is linked to the 1,3-di-thiol-ane moiety by an enone bridge. The atoms of the C-C bond in the 1,3-di-thiol-ane ring are disordered over two positions with occupancies of 0.579 (14) and 0.421 (14) and both disordered rings adopt a half-chair conformation. The oxygen atom of the enone bridge is involved in a weak intra-molecular C-H⋯O hydrogen bond, which generates an S(6) graph-set motif. In the crystal, the hybrid mol-ecules are associated in R 2 2(14) dimeric units by weak C-H⋯O inter-actions. O-H⋯O hydrogen bonds link the water mol-ecules, forming infinite self-assembled chains along the b-axis direction to which the dimers are connected via O-H⋯N hydrogen bonding. Analysis of inter-molecular contacts using Hirshfeld surface analysis and contact enrichment ratio descriptors indicate that hydrogen bonds induced by water mol-ecules are the main driving force in the crystal packing formation.

6-Bromo-2-(4-chlorophenyl)-3-[(1-octyl-1H-1,2,3-triazol-4-yl)methyl]-3H-imidazo[4,5-b]pyridine

In the title compound, C23H26BrClN6, the imidazo[4,5-b]pyridine ring system (r.m.s. deviation = 0.012 Å) is inclined at angles of 19.37 (12) and 89.27 (13)° to the phenyl and triazole rings, respectively, while the phenyl and triazole rings subtend a dihedral angle of 71.23 (15)°. In the crystal, the molecules are linked by C—H...NI and bifurcated C—H...(NT,NT) (I = imidazo[4,5-b]pyridine and T = triazole) hydrogen bonds into a double-column structure propagating along the b-axis direction.

Crystal structure and Hirshfeld surface analysis of 4-allyl-6-bromo-2-(4-chloro-phen-yl)-4H-imidazo[4,5-b]pyridine.

The title compound, C15H11BrClN3, is built up from a planar imidazo[4,5-b]pyridine unit linked to phenyl and allyl substituents. The allyl substituent is rotated significantly out of the imidazo[4,5-b]pyridine plane, while the benzene ring is inclined by 3.84 (6)° to the ring system. In the crystal, mol-ecules are linked via a pair of weak inter-molecular C-H⋯N hydrogen bonds, forming an inversion dimer with an R 2 2(20) ring motif. The dimers are further connected by π-π stacking inter-actions between the imidazo[4,5-b]pyridine ring systems [centroid-centroid distances = 3.7161 (13) and 3.8478 (13) Å]. The important contributions to the Hirshfeld surface are H⋯H (35.9%), H⋯Cl/Cl⋯H (15.0%), H⋯C/C⋯H (12.4%), H⋯Br/Br⋯H (10.8%), H⋯N/N⋯H (7.5%), C⋯Br/Br⋯C (5.9%), C⋯C (5.5%) and C⋯N/N⋯C (4.0%) contacts.

Synthesis, crystal structure, 1H, 13C and 15N NMR studies, and biological evaluation of a new amidrazone-derived Au(III) complex

A new Au(III) complex was synthesized from an amidrazone derivative and HAuCl4. Cyclization of amidrazone moiety lead to the 1,2,4-triazolo[1,5a]pyridine ring system, followed by Au(III) chelation. The crystal and molecular structure of the final compound was studied by single crystal X-ray diffraction as well as by 1H13C and 1H15N HMQC- and HMBC-NMR spectroscopy, which resulted in the assignment of all detected signals. This species was tested in vitro as an antibacterial and antiproliferative agent. It exhibited good antibacterial activity against Staphylococcus aureus and was proved to be more potent than amoxicillin against Bacillus subtilis and the drug resistant strain of Klebsiella pneumoniae. In contrast, its antiproliferative properties against cancer cell lines A549, HT-29, MV-4-11 and MCF-7 were relatively low.

An investigation of molecular mechanism and the role of Te-bridged-atom in the formation of polysubstituted pyridines via Hetero-Diels–Alder reaction of isotellurazole with acetylenic dienophile: a molecular electron density study

An electron localization function (ELF) analysis and a detailed computational study of the hetero-Diels-Alder (HDA) reaction between isotellurazole and acetylenic dienophile have been performed. Then, B3LYP/Lanl2dz + 6-31+g(d) basis set level has been used to characterize the molecular mechanism and reactivity. The conceptual and computational DFT show that the most favorable regioisomeric product is the ortho/endo adduct, for which the energetic cost is 39.4 kcal/mol. Furthermore, ELF topological analysis envisages that the electron density of the pseudo-radical centers of the most electrophilic and nucleophilic atoms of the molecules come mainly from the charge transfer which takes place along the reaction pathway. The high asynchronicity of the bond formation means that two-stage one-step is the most appropriate mechanism for this reaction. However, the weak electronic contribution of the heavy chalcogen-bridged Tellurium atom in the C1-Te-N2 sequence has increased the activation barrier of the reaction. Otherwise, it has assisted the easy removal of the atom in the intermediary cycloadduct in the end of the reaction leading to the polysubstituted pyridine. So, despite the fact that Te atom is electronically rich, it plays a marginal role for improving reactivity of this [4+2] cycloaddition process. Synopsis. The mechanism of the Hetero-Diels-Alder (HDA) reaction of isotellurazole with acetylenic dienophile has been studied carefully. The quantum chemical calculations and an electron localization function analysis show that the weak electronic contribution of the heavy chalcogen-bridged Tellurium atom in the C1-Te-N2 sequence has decreased the activation barrier of the reaction. Besides, it has assisted the easy removal of this atom in the intermediary cycloadduct at the end of the reaction to make possible the synthesis of pyridine ring system (high polarized bonds). Equally, the electronic density analysis of several formed radicals permits us to conclude that two-stage one-step is the mechanism of the HDA reaction

Oxidative Cascade Reaction of N-Aryl-3-alkylideneazetidines and Carboxylic Acids: Access to Fused Pyridines.

A versatile silver-promoted oxidative cascade reaction of N-aryl-3-alkylideneazetidines with carboxylic acids is reported, providing a very efficient pathway to functionalized fused pyridines. This method allows introduction of fused pyridine ring systems to heterocycles, drugs, and natural products. A mechanistic study revealed that silver salt is essential for the chemo- and regioselective ring expansion, sequential oxidative nucleophilic additions, and oxidative aromatization. This approach represents the first example of the strained N-heterocycles undergoing a cascade reaction with a π bond and a nucleophile together.