Pyridazinone: an important element of pharmacophore possessing broad spectrum of activity

Bacterial Hydrazine Biosynthetic Pathways Featuring Cupin/Methionyl tRNA Synthetase-like Enzymes

Nitrogen-Nitrogen (N-N) bond-containing functional groups in natural products and synthetic drugs play significant roles in exerting biological activities. The mechanisms of N-N bond formation in natural organic molecules have garnered increasing attention over the decades. Recent advances have illuminated various enzymatic and nonenzymatic strategies, and our understanding of natural N-N bond construction is rapidly expanding. A group of didomain proteins with zinc-binding cupin/methionyl-tRNA synthetase (MetRS)-like domains, also known as hydrazine synthetases, generates amino acid-based hydrazines, which serve as key biosynthetic precursors of diverse N-N bond-containing functionalities such as hydrazone, diazo, triazene, pyrazole, and pyridazinone groups. In this review, we summarize the current knowledge on hydrazine synthetase mechanisms and the various pathways employing this unique bond-forming machinery.

Dinuclear Zn-Catalytic System as Brønsted Base and Lewis Acid for Enantioselectivity in Same Chiral Environment

Zinc (Zn) is a crucial element with remarkable significance in organic transformations. The profusion of harmless zinc salts in the Earth's outer layer qualifies zinc as a noteworthy contender for inexpensive and eco-friendly reagents and catalysts. Recently, widely recognized uses of organo-Zn compounds in the field of organic synthesis have undergone extensive expansion toward asymmetric transformations. The ProPhenol ligand, a member of the chiral nitrogenous-crown family, exhibits the spontaneous formation of a dual-metal complex when reacted with alkyl metal (R-M) reagents, e.g., ZnEt2. The afforded Zn complex possesses two active sites, one Lewis acid and the other Brønsted base, thereby facilitating the activation of nucleophiles and electrophiles simultaneously within the same chiral pocket. In this comprehensive analysis, we provide a thorough account of the advancement and synthetic potential of these diverse catalysts in organic synthesis, while emphasizing the reactivity and selectivities, i.e., dr and ee due to the design/structure of the ligands employed.

Selective and Stepwise Functionalization of the Pyridazine Scaffold by Using Thio-Substituted Pyridazine Building Blocks

We described a regioselective tri- and tetra-functionalization of the pyridazine scaffold using two readily available building blocks: 3-alkylthio-6-chloropyridazine and 3,4-bis(methylthio)-6-chloropyridazine by performing selective metalations with TMPMgCl ⋅ LiCl and catalyst-tuned cross-coupling reactions with arylzinc halides. Several of the resulting pyridazines were converted into more elaborated N-heterocycles such as thieno[2,3-c]pyridazines and 1H-pyrazolo[3,4-c]pyridazines.

Anti-inflammatory activity of novel derivatives of pyrazolo [3,4d] pyridazine against digestive system inflammation

The digestive system is exposed to severe inflammation as a result of taking some medications that have gastrointestinal side effects. Sixty Swiss-albino male mice were randomly distributed into six groups to treat inflammations of the colon, stomach, and small intestine caused by taking high doses of diclofenac (D), with two novel synthesized compounds, pyrazolo [3,4 d] pyridazine derivatives (Co1 and Co2). Myeloperoxidase enzyme activity was determined in the colon and small intestinal tissues. Serum contents of TNF-α, IL-22, IgG, and IgM were determined by ELISA. Histopathological examinations of the colon, small intestinal, and stomach tissues were microscopically analyzed. TNF-α, IL-22, and TNFSF11 gene expression were measured in the colon, intestinal, and spleen using qRT-PCR. Diclofenac caused surface columnar epithelial cell loss, focal necrosis of the gastric mucosa, inflammatory cell infiltration, and congested blood vessels in the stomach, colon, and small intestinal tissues. Co1 component was found to be better than Co2 component in reducing the focal necrosis of gastric mucosa and improving the histological structures of the stomach, colon, and small intestinal tissues. After 14 days, the activity of the myeloperoxidase enzyme was increased in group D and decreased in groups DCo1, DCo2, Co1, and Co2. Serum concentrations of TNF-α and IgG were increased, while IL-22 and IGM were reduced in the D, DCo1, and DCo2 groups compared with the Co1 and control groups. TNF-α gene was upregulated in the D group and downregulated in the Co1 group, while the IL-22 gene was downregulated in the D group and upregulated in the Co1 group compared with the control group. The CO1 component may be useful in reducing digestive system inflammation.

Exploring Three Avenues: Chemo- and Regioselective Transformations of 1,2,4-Triketone Analogs into Pyrazoles and Pyridazinones

A convenient approach to substituted pyrazoles and pyridazinones based on 1,2,4-triketones is presented. Chemo- and regiocontrol in condensations of t-Bu, Ph-, 2-thienyl-, and CO2Et-substituted 1,2,4-triketone analogs with hydrazines are described. The direction of preferential nucleophilic attack was shown to be switched depending on the substituent nature in triketone as well as the reaction conditions. The acid and temperature effects on the selectivity of condensations were revealed. Regiochemistry of heterocyclic core formation was confirmed by NMR and XRD studies. The facile construction of heterocyclic motifs bearing acetyl and (or) carbethoxy groups suggests them as promising mono- or bifunctional building blocks for subsequent transformations.

Discovery of the Diphenyl 6-Oxo-1,6-dihydropyridazine-3-carboxylate/carboxamide Analogue J27 for the Treatment of Acute Lung Injury and Sepsis by Targeting JNK2 and Inhibiting the JNK2-NF-κB/MAPK Pathway

Acute lung injury (ALI) and sepsis are both serious and complex conditions associated with high mortality, yet there are no effective treatments. Herein, we designed and synthesized a series of diphenyl 6-oxo-1,6-dihydropyridazine-3-carboxylate/carboxamide analogues exhibiting anti-inflammatory activity. The optimal compound J27 decreased the release of TNF-α and IL-6 in mouse and human cells J774A.1 and THP-1 (IL-6 IC50 = 0.22 μM) through the NF-κB/MAPK pathway. J27 demonstrated remarkable protection against ALI and sepsis in vivo and exhibited good safety in subacute toxicity experiments. Pharmacokinetic study indicated that J27 had good bioavailability (30.74%). To our surprise, J27 could target JNK2 with a totally new molecular skeleton compared with the only few JNK2 inhibitors reported. Moreover, there is no report that JNK2 inhibitors could apply for ALI and sepsis. Therefore, this work provides a new lead structure for the study of JNK2 inhibitors and a new target of JNK2 to treat ALI and sepsis.

Synthesis, Characterization and Cytotoxic Evaluation of New Pyrrolo[1,2-b]pyridazines Obtained via Mesoionic Oxazolo-Pyridazinones

New pyrrolo[1,2-b]pyridazines were synthesized by 3 + 2 cycloaddition reaction between mesoionic oxazolo-pyridazinones and methyl/ethyl propiolate. The mesoionic compounds were generated in situ by action of acetic anhydride on 3(2H)pyridazinone acids obtained from corresponding esters by alkaline hydrolysis followed by acidification. The structures of the compounds were confirmed by elemental analyses and IR, ¹H-NMR, ¹³C-NMR, and X-ray diffraction data. The regioselectivity of cycloaddition was evidenced by NMR spectroscopy and confirmed by X-ray analysis. The compounds were evaluated for their cytotoxicity on plant cells (Triticum aestivum L.) and crustacean animal cells (Artemia franciscana Kellogg and Daphnia magna Straus). The results indicated that the tested compounds exhibited low toxicity on the plant cell (IC₅₀ values higher than 200 µM), while on Artemia nauplii no lethality was observed. Daphnia magna assay showed that pyrrolo[1,2-b]pyridazines 5a and 5c could exhibit toxic effects, whereas, for the other compounds, toxicity was low to moderate. Also, the cytotoxic effects of the compounds were tested on three human adenocarcinoma-derived adherent cell lines (colon LoVo, ovary SK-OV-3, breast MCF-7). The in vitro compound-mediated cytotoxicity assays, performed by the MTS technique, demonstrated dose- and time-dependent cytotoxic activity for several compounds, the highest anti-tumor activity being observed for 5a, 2c, and 5f, especially against colon cancer cells.

Copper-Catalyzed Hydroamination: Enantioselective Addition of Pyrazoles to Cyclopropenes

Chiral N-cyclopropyl pyrazoles and structurally related heterocycles are prepared using an earth-abundant copper catalyst under mild reaction conditions with high regio-, diastereo-, and enantiocontrol. The observed N2:N1 regioselectivity favors the more hindered nitrogen of the pyrazole. Experimental and DFT studies support a unique mechanism that features a five-centered aminocupration.

Discovery of (S)-N-(2-Amino-4-fluorophenyl)-4-(1-(3-(4-((dimethylamino)methyl)phenyl)-6-oxopyridazin-1(6H)-yl)ethyl)benzamide as Potent Class I Selective HDAC Inhibitor for Oral Anticancer Drug Candidate

A novel series of benzamide derivatives were successively designed and synthesized prepared from the pyridazinone scaffold. Among them, (S)-17b, demonstrated potent inhibitory activity in vitro toward human class I HDAC isoforms and human myelodysplastic syndrome (SKM-1) cell line. Also, (S)-17b strongly increased the intracellular level of acetyl-histone H3 and P21 simultaneously and effectively induced G1 cell cycle arrest and apoptosis. Through oral dosing in SKM-1 xenograft models, (S)-17b exhibited excellent in vivo antitumor activity. In addition, compound (S)-17b showed better antitumor efficacy on mouse models with intact immune system than those with thymus deficiencies. Furthermore, this compound displayed a favorable pharmacokinetic profile in ICR mice and SD rat, respectively, minimal metabolic property differences among hepatocytes from five species, and a low inhibition upon the human ether-a-go-go (hERG) channel with an IC₅₀ value of 34.6 μΜ. This novel compound (S)-17b may serve as a new drug candidate for further investigation.

Ribosome-mediated biosynthesis of pyridazinone oligomers in vitro

The ribosome is a macromolecular machine that catalyzes the sequence-defined polymerization of L-α-amino acids into polypeptides. The catalysis of peptide bond formation between amino acid substrates is based on entropy trapping, wherein the adjacency of transfer RNA (tRNA)-coupled acyl bonds in the P-site and the α-amino groups in the A-site aligns the substrates for coupling. The plasticity of this catalytic mechanism has been observed in both remnants of the evolution of the genetic code and modern efforts to reprogram the genetic code (e.g., ribosomal incorporation of non-canonical amino acids, ribosomal ester formation). However, the limits of ribosome-mediated polymerization are underexplored. Here, rather than peptide bonds, we demonstrate ribosome-mediated polymerization of pyridazinone bonds via a cyclocondensation reaction between activated γ-keto and α-hydrazino ester monomers. In addition, we demonstrate the ribosome-catalyzed synthesis of peptide-hybrid oligomers composed of multiple sequence-defined alternating pyridazinone linkages. Our results highlight the plasticity of the ribosome's ancient bond-formation mechanism, expand the range of non-canonical polymeric backbones that can be synthesized by the ribosome, and open the door to new applications in synthetic biology.

A Natural Dihydropyridazinone Scaffold Generated from a Unique Substrate for a Hydrazine-Forming Enzyme

Nitrogen-nitrogen bond-containing functional groups are rare, but they are found in a considerably wide class of natural products. Recent clarifications of the biosynthetic routes for such functional groups shed light onto overlooked biosynthetic genes distributed across the bacterial kingdom, highlighting the presence of yet-to-be identified natural products with peculiar functional groups. Here, the genome-mining approach targeting a unique hydrazine-forming gene led to the discovery of actinopyridazinones A (1) and B (2), the first natural products with dihydropyridazinone rings. The structure of actinopyridazinone A was unambiguously established by total synthesis. Biosynthetic studies unveiled the structural diversity of natural hydrazines derived from this family of N-N bond-forming enzymes.

Anti-inflammatory activity of pyridazinones: A review

The pyridazinone core has emerged as a leading structure for fighting inflammation, with low ulcerogenic effects. Moreover, easy functionalization of various ring positions of the pyridazinone core structure makes it an attractive synthetic and therapeutic target for the design and synthesis of anti-inflammatory agents. The present review surveys the recent advances of pyridazinone derivatives as potential anti-inflammatory agents to provide insights into the rational design of more effective anti-inflammatory pyridazinones.

N-Heterocyclic Carbene-Promoted [4+2] Annulation of α-Chloro Hydrazones with α-Chloro Aliphatic Aldehydes to Access Enantioenriched Dihydropyridazinones

An expeditious protocol for the assembly of chiral 4,5-dihydropyridazin-3(2H)-ones from α-chloro hydrazones and α-chloro aliphatic aldehydes via N-heterocyclic carbene (NHC) catalysis is outlined. These in situ-generated 1,2-diaza-1,3-dienes undergo asymmetric [4+2] annulation with NHC-bound enolates to afford the desired products bearing a stereogenic center at the C4 position. The notable features of this approach include good to excellent enantioselectivities, high functional group tolerance, mild reaction conditions, simple operating procedures, and compatibility with gram-scale synthesis.

Carbene-catalyzed enantioselective annulation of dinucleophilic hydrazones and bromoenals for access to aryl-dihydropyridazinones and related drugs

4,5-Dihydropyridazinones bearing an aryl substituent at the C6-position are important motifs in drug molecules. Herein, we developed an efficient protocol to access aryl-dihydropyridazinone molecules via carbene-catalyzed asymmetric annulation between dinucleophilic arylidene hydrazones and bromoenals. Key steps in this reaction include polarity-inversion of aryl aldehyde-derived hydrazones followed by chemo-selective reaction with enal-derived α,β-unsaturated acyl azolium intermediates. The aryl-dihydropyridazinone products accessed by our protocol can be readily transformed into drugs and bioactive molecules.

Polarity inversion of arylidene hydrazones to react with bromoenals via carbene organic catalysis is disclosed. The reaction enantioselectively affords 6-aryl-4,5-dihydropyridazinones and related drugs with proven commercial applications.

Novel Ring Systems: Spiro[Cycloalkane] Derivatives of Triazolo- and Tetrazolo-Pyridazines

In orderto synthesize new pyridazine derivatives anellated with different nitrogen heterocyclic moieties, spiro[cycloalkane]pyridazinones were transformed into the corresponding thioxo derivatives via a reaction with phosphorus pentasulfide. The reaction of the formed 2,3-diazaspiro[5.5]undec-3-ene-1-thiones with hydrazine provided the corresponding 1-hydrazono-2,3-diazaspiro[5.5]undec-3-ene, whose diazotization led to the desired spiro[cyclohexane-1,8′-tetrazolo[1,5-b]pyridazines. The reaction of dihydropyridazinethiones with benzhydrazide afforded the corresponding 7H-spiro[[1,2,4]triazolo[4,3-b]pyridazin-8,1′-cyclohexanes]. As a result of our work, seven new pyridazinethione intermediates were prepared, which served as starting materials for the synthesis of two kinds of new ring systems: tetrazolo-pyridazines and triazolo-pyridazines. The six new annulated derivatives were characterized by physicochemical parameters. The new N-heterocycles are valuable members of the large family of pyridazines.

Crystal structure and Hirshfeld surface analysis of 4-(2,6-di-chloro-benz-yl)-6-[(E)-2-phenyl-ethen-yl]pyridazin-3(2H)-one

The title pyridazinone derivative, C19H14Cl2N2O, an important pharmacophore with a wide variety of biological applications is not planar, the chloro-phenyl and pyridazinone rings being almost perpendicular, subtending a dihedral angle of 85.73 (11)°. The phenyl ring of the styryl group is coplanar with the pyridazinone ring [1.47 (12)°]. In the crystal, N-H⋯O hydrogen bonds form inversion dimers with an R 2 2(8) ring motif and C-H⋯Cl hydrogen bonds also occur. The roles of the inter-molecular inter-actions in the crystal packing were clarified using Hirshfeld surface analysis, and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (37.9%), C⋯H/H⋯C (18.7%), Cl⋯H/ H⋯Cl (16.4%) and Cl⋯C/C⋯Cl (6.7%) contacts.

Azolo[d]pyridazinones in medicinal chemistry

Azolo[d]pyridazinone is a privileged structure and versatile pharmacophore whose derivatives are associated with diverse biological activities, in particular antidiabetic, antiasthmatic, anticancer, analgesic, anti-inflammatory, antithrombotic, antidepressant and antimicrobial activities. The importance of this scaffold against some targets like PDE, COX and DPP-4 has been reviewed in detail previously. In the present review, we have summarized comprehensive information on azolo[d]pyridazinone derivatives investigated by many researchers for their diverse pharmacological activities, structure-activity relationship and molecular modeling studies since 2000. The review may lead scientists in the research fields of organic synthesis, medicinal chemistry and pharmacology to the strategic design and development of azolo[d]pyridazinone-based drug candidates in the future.

Design, Synthesis, and Biological Evaluation of Pyridazinones Containing the (2-Fluorophenyl) Piperazine Moiety as Selective MAO-B Inhibitors

Twelve pyridazinones (T1–T12) containing the (2-fluorophenyl) piperazine moiety were designed, synthesized, and evaluated for monoamine oxidase (MAO) -A and -B inhibitory activities. T6 was found to be the most potent MAO-B inhibitor with an IC₅₀ value of 0.013 µM, followed by T3 (IC₅₀ = 0.039 µM). Inhibitory potency for MAO-B was more enhanced by meta bromo substitution (T6) than by para bromo substitution (T7). For para substitution, inhibitory potencies for MAO-B were as follows: -Cl (T3) > -N(CH₃)₂ (T12) > -OCH₃ (T9) > Br (T7) > F (T5) > -CH₃ (T11) > -H (T1). T6 and T3 efficiently inhibited MAO-A with IC₅₀ values of 1.57 and 4.19 µM and had the highest selectivity indices (SIs) for MAO-B (120.8 and 107.4, respectively). T3 and T6 were found to be reversible and competitive inhibitors of MAO-B with K_i values of 0.014 and 0.0071, respectively. Moreover, T6 was less toxic to healthy fibroblast cells (L929) than T3. Molecular docking simulations with MAO binding sites returned higher docking scores for T6 and T3 with MAO-B than with MAO-A. These results suggest that T3 and T6 are selective, reversible, and competitive inhibitors of MAO-B and should be considered lead candidates for the treatment of neurodegenerative disorders like Alzheimer’s disease.

Pyridazine as a privileged structure: An updated review on anticancer activity of pyridazine containing bioactive molecules

Identification of potent anticancer agents with high selectivity and low toxicity remains on the way to human health. Pyridazine featuring advantageous physicochemical properties and antitumor potential usually is regarded as a central core in numerous anticancer derivatives. There are several approved pyridazine-based drugs in the market and analogues currently going through different clinical phases or registration statuses, suggesting pyridazine as a promising drug-like scaffold. The current review is intended to provide a comprehensive and updated overview of pyridazine derivatives as potential anticancer agents. In particular, we focused on their structure-activity relationship (SAR) studies, design strategies, binding modes and biological activities in the hope of offering novel insights for further rational design of more active and less toxic anticancer drugs.

[4 + 2] Annulation Reaction of In Situ Generated Azoalkenes with Azlactones: Access to 4,5-Dihydropyridazin-3(2H)-Ones

An unprecedented [4 + 2] annulation reaction between in situ formed azoalkenes and azlactones has been developed. This reaction provides a facile access to an array of 4,5-dihydropyridazin-3(2H)-one derivatives, which are very promising in medicinal applications as potential biologically active candidates. Notably, these dihydropyridazinones could also be synthesized via a one-pot reaction protocol by using the in situ formed azlactones from N-acyl amino acids and in situ generated azoalkenes from α-halogeno hydrazones. The potential applications of the methodology were also demonstrated by gram-scale experiments and the versatile conversions of the products into other nitrogen-containing compounds.

2-Butyl-6-phenyl-4,5-dihydropyridazin-3(2H)-one: Synthesis, In Silico Studies and In Vitro Cyclooxygenase-2 Inhibitory Activity

Pyridazinone derivatives are a great template for developing cyclooxygenase-2 (COX-2) inhibitors. The 2-butyl-6-phenyl-4,5-dihydropyridazin-3(2H)-one was prepared by reacting 6-phenyl-4,5-dihydropyridazin-3(2H)-one with n-butyl bromide in the presence of potassium carbonate. The structure of the compound was confirmed based on its FTIR, 1H-NMR, 13C-NMR, and Mass data. The molecular docking studies assessed the COX-2 binding capability of the synthesized compound. The in silico physicochemical and pharmacokinetic parameters of this compound concerning selected drugs were also calculated. The COX-2/COX-1 analysis revealed the synthesized compound as a novel potent COX-2 inhibitor, in comparison to indomethacin, with a promising physicochemical and pharmacokinetic profile.

Crystal structure, Hirshfeld surface analysis and DFT studies of 2-[5-(4-methyl-benz-yl)-6-oxo-3-phenyl-1,6-di-hydro-pyridazin-1-yl]acetic acid

In the title compound, the phenyl and pyridazine rings are inclined to each other by 10.55 (12)°, whereas the 4-methyl­benzyl ring is nearly orthogonal to the pyridazine ring with a dihedral angle of 72.97 (10)°.

The title pyridazinone derivative, C₂₀H₁₈N₂O₃, is not planar. The phenyl ring and the pyridazine ring are inclined to each other by 10.55 (12)°, whereas the 4-methyl­benzyl ring is nearly orthogonal to the pyridazine ring, with a dihedral angle of 72.97 (10)°. In the crystal, mol­ecules are linked by pairs of O—H⋯O hydrogen bonds, forming inversion dimers with an R₂²(14) ring motif. The dimers are linked by C—H⋯O hydrogen bonds, generating ribbons propagating along the c-axis direction. The inter­molecular inter­actions were additionally investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots. They revealed that the most significant contributions to the crystal packing are from H⋯H (48.4%), H⋯O/O⋯H (21.8%) and H⋯C/C⋯H (20.4%) contacts. Mol­ecular orbital calculations providing electron-density plots of HOMO and LUMO mol­ecular orbitals and mol­ecular electrostatic potentials (MEP) were also computed, both with the DFT/B3LYP/6–311 G++(d,p) basis set.

Crystal structure and Hirshfeld surface analysis of (E)-6-(4-hy-droxy-3-meth-oxy-styr-yl)-4,5-di-hydro-pyridazin-3(2H)-one

In the title com­pound, inter­molecular C—H⋯O, O—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional supra­molecular network.

In the title com­pound, C₁₃H₁₄N₂O₃, the dihydropyridazine ring (r.m.s. deviation = 0.166 Å) has a screw-boat conformation. The dihedral angle between its mean plane and the benzene ring is 0.77 (12)°. In the crystal, inter­molecular O—H⋯O hydrogen bonds generate C(5) chains and N—H⋯O hydrogen bonds produce R₂²(8) motifs. These types of inter­actions lead to the formation of layers parallel to (12). The three-dimensional network is achieved by C—H⋯O inter­actions, including R₂⁴(8) motifs. Inter­molecular inter­actions were additionally investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots. The most significant contributions to the crystal packing are by H⋯H (43.3%), H⋯C/C⋯H (19.3%), H⋯O/H⋯O (22.6%), C⋯N/N⋯C (3.0%) and H⋯N/N⋯H (5.8%) contacts. C—H⋯π inter­actions and aromatic π–π stacking inter­actions are not observed.

Crystal structures and Hirshfeld surface analyses of 4-benzyl-6-phenyl-4,5-di-hydro-pyridazin-3(2H)-one and methyl 2-[5-(2,6-di-chloro-benz-yl)-6-oxo-3-phenyl-1,4,5,6-tetra-hydropyridazin-1-yl]acetate

In each asymmetric unit of the title compounds, one independent mol­ecule is present. In the crystal structure of 4-benzyl-6-phenyl-4,5-di­hydro­pyridazin-3(2H)-one, adjacent mol­ecules are linked by a pair of N—H⋯O hydrogen bonds, forming inversion dimers with an (8) ring motif. The crystal structure of methyl 2-[5-(2,6-di­chloro­benz­yl)-6-oxo-3-phenyl-1,6-di­hydro-pyridazin-1-yl]acetate displays inter­molecular C—H⋯O inter­actions.

The asymmetric units of the title compounds both contain one nonplanar mol­ecule. In 4-benzyl-6-phenyl-4,5-di­hydro­pyridazin-3(2H)-one, C₁₇H₁₄N₂O, (I), the phenyl and pyridazine rings are twisted with respect to each other, making a dihedral angle of 46.69 (9)°; the phenyl ring of the benzyl group is nearly perpendicular to the plane of the pyridazine ring, the dihedral angle being 78.31 (10)°. In methyl 2-[5-(2,6-di­chloro­benz­yl)-6-oxo-3-phenyl-1,4,5,6-tetra­hydropyridazin-1-yl]acetate, C₂₀H₁₆Cl₂N₂O₃, (II), the phenyl and pyridazine rings are twisted with respect to each other, making a dihedral angle of 21.76 (18)°, whereas the phenyl ring of the di­chloro­benzyl group is inclined to the pyridazine ring by 79.61 (19)°. In the crystal structure of (I), pairs of N—H⋯O hydrogen bonds link the mol­ecules into inversion dimers with an R₂²(8) ring motif. In the crystal structure of (II), C—H⋯O hydrogen bonds generate dimers with R₁²(7), R₂²(16) and R₂²(18) ring motifs. The Hirshfeld surface analyses of compound (I) suggests that the most significant contributions to the crystal packing are by H⋯H (48.2%), C⋯H/H⋯C (29.9%) and O⋯H/H⋯O (8.9%) contacts. For compound (II), H⋯H (34.4%), C⋯H/H⋯C (21.3%) and O⋯H/H⋯O (16.5%) inter­actions are the most important contributions.

Crystal structure and Hirshfeld surface analysis of 4-(4-methyl-benz-yl)-6-phenyl-pyridazin-3(2H)-one

In this paper, we describe the synthesis of a new di-hydro-2H-pyridazin-3-one derivative. The mol-ecule, C18H16N2O, is not planar; the benzene and pyridazine rings are twisted with respect to each other, making a dihedral angle of 11.47 (2)°, and the toluene ring is nearly perpendicular to the pyridazine ring, with a dihedral angle of 89.624 (1)°. The mol-ecular conformation is stabilized by weak intra-molecular C-H⋯N contacts. In the crystal, pairs of N-H⋯O hydrogen bonds link the mol-ecules into inversion dimers with an R 2 2(8) ring motif. The inter-molecular inter-actions were investigated using Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots, revealing that the most important contributions for the crystal packing are from H⋯H (56.6%), H⋯C/C⋯H (22.6%), O⋯H/H⋯O (10.0%) and N⋯C/C⋯N (3.5%) inter-actions.

Synthesis and biological evaluation of pyridazinone derivatives as potential anti-inflammatory agents

Cyclic nucleotide phosphodiesterase type 4 (PDE4), that controls intracellular level of cyclic nucleotide cAMP, has aroused scientific attention as a suitable target for anti-inflammatory therapy in respiratory diseases. Here we describe the development of two families of pyridazinone derivatives as potential PDE4 inhibitors and their evaluation as anti-inflammatory agents. Among these derivatives, 4,5-dihydropyridazinone representatives possess promising activity, selectivity towards PDE4 isoenzymes and are able to reduce IL-8 production by human primary polymorphonuclear cells.

An isothiourea-catalyzed asymmetric formal [4 + 2] cycloaddition of in situ generated azoalkenes with C1 ammonium enolates

An efficient isothiourea-catalyzed stereoselective formal [4 + 2] cycloaddition of α-chloro cyclic hydrazones with carboxylic acids has been developed.

Analysis of Fluorescence Quenching for Newly Synthesized Biologically Active 3(2H)-pyridazinone Derivative by Aniline

Herein, we have studied the analysis of fluorescence quenching for newly synthesized biologically active 3(2H)-pyridazinone derivative 5-(5-bromo-2-hydroxy-phenyl)-2-phenyl-2H-pyridazin-3-one [BHP] by various concentrations of aniline using UV-Visible spectroscopy, fluorescence spectroscopy and time-correlated single photon counting technique in five different solvents namely, methanol, ethanol, propan-2-ol, dimethylsulfoxide and ethyl acetate at room temperature. The fluorescence intensity of BHP molecule decrease with increasing in the aniline concentration and it is studied using the Stern-Volmer relation. The obtained Stern-Volmer plots were found to be linear in all the five solvents. The various parameters responsible for the fluorescence quenching such as quenching rate parameters (k _q ), diffusion rate parameter (k _d ) and the probability of quenching per encounter (p) were experimentally calculated in all five solvents. An activation energy of quenching (E _a ) was calculated using the values of activation energy of diffusion (E _d ) and p. It was found that the values of E _a are greater than E _d in all five solvents studied. Further, it is inferred that the fluorescence quenching reactions in BHP molecule are more significantly affected by activation energy processes.

Pyridazinone: an attractive lead for anti-inflammatory and analgesic drug discovery

In spite of the availability of a large number of anti-inflammatory and analgesic agents, fighting pain and inflammation remains a common problem. The current review article discusses the need of novel therapeutic targets for risk-free anti-inflammatory and analgesic therapy and summarizes some new agents in various stages of drug discovery pipeline. Pyridazin-3(2H)-ones are nitrogen-rich heterocyclic compounds of considerable medicinal interest due to their diverse biological activities. The current review article focuses on progressive development of this attractive scaffold for the design and synthesis of new pyridazinone-based anti-inflammatory and analgesic agents. Mechanistic insights into the anti-inflammatory and analgesic properties of pyridazinone derivatives and various synthetic techniques used for their synthesis are also described.

Nucleophilic ring-opening reactions of trans-2-aroyl-3-aryl-cyclopropane-1,1-dicarboxylates with hydrazines

trans-2-Aroyl-3-aryl-cyclopropane-1,1-dicarboxylates gave dihydropyrazoles when treated with arylhydrazines in refluxing EtOH, whereas they afforded cyclopropane-fused pyridazinones upon treatment with hydrazines in refluxing AcOH.