Pyridazine and pyridazinone derivatives: Synthesis and in vitro investigation of their anti-inflammatory potential in LPS-induced RAW264.7 macrophages.

New pyridazine and pyridazinone derivatives 3a-g, 4a-f, 6a, and 6b were designed and synthesized. Cell viability of all compounds was established based on the viability of lipopolysaccharide-induced RAW264.7 macrophage cells determined via the MTT assay. In vitro inhibition assays on human COX-1 and COX-2 enzymes were conducted to probe the newly synthesized compounds' anti-inflammatory activity. The half maximal inhibitory concentration values for the most active compounds, 3d, 3e, and 4e towards COX-2 were 0.425, 0.519, and 0.356 µM, respectively, in comparison with celecoxib. The newly synthesized compounds' ability to inhibit the production of certain proinflammatory cytokines, such as inducible nitric oxide synthase, tumor necrosis factor-α, interleukin-6, and prostaglandin-E2, was also estimated in lipopolysaccharide-induced macrophages (RAW264.7 cells). Compounds 3d and 3e were identified as the most potent cytokine production inhibitors. The results of molecular modeling studies suggested that these compounds were characterized by a reasonable binding affinity toward the active site of COX-2, when compared to a reference ligand. These results might be taken into consideration in further investigations into new anti-inflammatory agents.

Monofluoromethylation of N-Heterocyclic Compounds.

The review focuses on recent advances in the methodologies for the formation or introduction of the CH2F moiety in N-heterocyclic substrates over the past 5 years. The monofluoromethyl group is one of the most versatile fluorinated groups used to modify the properties of molecules in synthetic medical chemistry. The review summarizes two strategies for the monofluoromethylation of N-containing heterocycles: direct monofluoromethylation with simple XCH2F sources (for example, ICH2F) and the assembly of N-heterocyclic structures from CH2F-containing substrates. The review describes the monofluoromethylation of pharmaceutically important three-, five- and six-membered N-heterocycles: pyrrolidines, pyrroles, indoles, imidazoles, triazoles, benzothiazoles, carbazoles, indazoles, pyrazoles, oxazoles, piperidines, morpholines, pyridines, quinolines and pyridazines. Assembling of 6-fluoromethylphenanthridine, 5-fluoromethyl-2-oxazolines, C5-monofluorinated isoxazoline N-oxides, and α-fluoromethyl-α-trifluoromethylaziridines is also shown. Fluoriodo-, fluorchloro- and fluorbromomethane, FCH2SO2Cl, monofluoromethyl(aryl)sulfoniummethylides, monofluoromethyl sulfides, (fluoromethyl)triphenylphosphonium iodide and 2-fluoroacetic acid are the main fluoromethylating reagents in recent works. The replacement of atoms and entire functional groups with a fluorine atom(s) leads to a change and often improvement in activity, chemical or biostability, and pharmacokinetic properties. The monofluoromethyl group is a bioisoster of -CH3, -CH2OH, -CH2NH2, -CH2CH3, -CH2NO2 and -CH2SH moieties. Bioisosteric replacement with the CH2F group is both an interesting task for organic synthesis and a pathway to modify drugs, agrochemicals and useful intermediates.

The Application of Microwaves, Ultrasounds, and Their Combination in the Synthesis of Nitrogen-Containing Bicyclic Heterocycles.

The use of alternative energy sources, such as microwaves (MW) or ultrasounds (US), and their mutual cross-combination have been widely described in the literature in the development of new synthetic methodologies in organic and medicinal chemistry. In this review, our attention is focused on representative examples, reported in the literature in the year range 2013-2023 of selected N-containing bicyclic heterocycles, with the aim to highlight the advantages of microwave- and ultrasound-assisted organic synthesis.

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.

A Multifield Study on Dimethyl Acetylenedicarboxylate: A Reagent Able to Build a New Cycle on Diaminoimidazoles.

A new effective method for the synthesis of imidazo[1,5-b]pyridazines derivatives (yields = 68-89%) by the interaction of 1,2-diamino-4-phenylimidazole with DMAD, in methanol and in the presence of a catalytic amount of acetic acid, is proposed. The course of reaction has been examined by classical organic methods, HPLC-MS analysis, and quantum-chemical calculations.

Azimuthal Dipolar Rotor Arrays on Surfaces.

A set of dipolar molecular rotor compounds was designed, synthesized and adsorbed as self-assembled 2D arrays on Ag(111) surfaces. The title molecules are constructed from three building blocks: (a) 4,8,12-trioxatriangulene (TOTA) platforms that are known to physisorb on metal surfaces such as Au(111) and Ag(111), (b) phenyl groups attached to the central carbon atom that function as pivot joints to reduce the barrier to rotation, (c) pyridine and pyridazine units as small dipolar units on top. Theoretical calculations and scanning tunneling microscopy (STM) investigations hint at the fact that the dipoles of neighboring rotors interact through space through pairs of energetically favorable head-to-tail arrangements.

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.

A One-Pot Approach to Novel Pyridazine C-Nucleosides.

The synthesis of glycosides and modified nucleosides represents a wide research field in organic chemistry. The classical methodology is based on coupling reactions between a glycosyl donor and an acceptor. An alternative strategy for new C-nucleosides is used in this approach, which consists of modifying a pre-existent furyl aglycone. This approach is applied to obtain novel pyridazine C-nucleosides starting with 2- and 3-(ribofuranosyl)furans. It is based on singlet oxygen [4+2] cycloaddition followed by reduction and hydrazine cyclization under neutral conditions. The mild three-step one-pot procedure leads stereoselectively to novel pyridazine C-nucleosides of pharmacological interest. The use of acetyls as protecting groups provides an elegant direct route to a deprotected new pyridazine C-nucleoside.

Hydrazides in the reaction with hydroxypyrrolines: less nucleophilicity - more diversity.

Expedient protocols for the synthesis of three types of highly functionalized azaheterocyclic scaffolds (dihydropyridazines, tetrahydropyridazines, and partially saturated tricyclic systems) from readily available hydroxypyrrolines and hydrazides are described. The directions of the transformation of a common initial intermediate, namely a Brønsted acid-activated hydroxypyrroline, depend on the reaction conditions and the structure of the hydrazides.

Synthesis of dibenzosuberenone-based novel polycyclic π-conjugated dihydropyridazines, pyridazines and pyrroles.

The synthesis of novel polycyclic π-conjugated dihydropyridazines, pyridazines, and pyrroles was studied. Dihydropyridazine dyes were synthesized by inverse electron-demand Diels-Alder cycloaddition reactions between a dibenzosuberenone and tetrazines that bear various substituents. The pyridazines were synthesized in high yields by oxidation of dihydropyridazine-appended dibenzosuberenones with PIFA or NO. p-Quinone derivatives of pyridazines were also obtained by H-shift isomerization following the inverse electron-demand Diels-Alder reaction of tetrazines with p-quinone dibenzosuberenone. Then these pyridazines were converted to the corresponding pyrroles by reductive treatment with zinc. It was observed that all the dihydropyridazines obtained gave absorbance and emission at long wavelengths.

Antimicrobial Pyridazines: Synthesis, Characterization, Cytotoxicity, Substrate Promiscuity, and Molecular Docking.

A facile and convenient synthesis of new pyridazines suitable for use as antimicrobial agents was reported. The hydrazide intermediate was coupled with various benzaldehydes and/or acetophenones and cyclized instantaneously to afford target pyridazine derivatives. The structures of new pyridazines were confirmed by IR, 1 H- and 13 C-NMR, elemental analysis in addition to representative LC/MS. Antimicrobial activity was screened against 10 bacterial and fungal strains. The new pyridazines showed strong to very strong antibacterial activity against Gram-negative (GNB) bacteria, while none of them showed significant antifungal activity at the same concentration range. Chloro derivatives exhibited the highest antibacterial activity with MICs (0.892-3.744 µg/mL) lower than that of chloramphenicol (2.019-8.078 µg/mL) against E. coli, P. aeruginosa, and S. marcescens. Prediction of ADME parameters, pharmacokinetics, and substrate promiscuity revealed that these new pyridazines could be promising drug candidates. Cytotoxic studies on rat hepatocytes showed how much safe these new pyridazines on living organisms (IC50 >64 µg/mL). MOE docking studies showed a good overlay of these new pyridazines with co-crystallized ligand within an E. coli DNA gyrase subunit B active sites (4KFG).

Triazolopyridazine derivatives: Synthesis, cytotoxic evaluation, c-Met kinase activity and molecular docking.

Novel series of some triazolo[4,3-b]pyridazine derivatives were designed and synthesized. All the newly synthesized compounds were evaluated for their cytotoxic activity at 10-5 M concentration towards 60 cancer cell lines according to USA NCI protocol. Most of the synthesized compounds showed good activity against SR (leukemia) cell panel. The most active compounds, 2f and 4a were subjected for further evaluation at a five dose level screening and their efficacy for c-Met kinase inhibition was determined in vitro. Binding mode of these derivatives was explored via molecular docking.

Synthesis and bioevaluation of 6-chloropyridazin-3-yl hydrazones and 6-chloro-3-substituted-[1,2,4]triazolo[4,3-b]pyridazines as cytotoxic agents.

An efficient synthesis of a series of 6-chloro-3-substituted-[1,2,4]triazolo[4,3-b]pyridazines is described via intramolecular oxidative cyclization of various 6-chloropyridazin-3-yl hydrazones with iodobenzene diacetate. The structures of the newly synthesized compounds were assigned on the basis of elemental analysis, IR, NMR (1H and 13C) and mass spectral data. All the thirty three compounds 3a-q and 4b-q synthesized in the present study were evaluated for their in vitro cytotoxic activities against two Acute Lymphoblastic Leukemia (ALL) cell lines named, SB-ALL and NALM-6, and a human breast adenocarcinoma cell lines (MCF-7). The results revealed that triazoles 4 exhibit better cytotoxicity than their hydrazone precursors 3. Among triazoles, compounds 4f, 4j and 4q exhibited potent cytotoxic activity against SB-ALL and NALM-6 with IC50 values in the range of ∼1.64-5.66 µM and ∼1.14-3.7 µM, respectively, compared with doxorubicin (IC50 = 0.167 µM, SB-ALL). Compounds 4f, 4j and 4q were subjected to apoptosis assay after 48 h treatment and these compounds induced apoptosis of NALM-6 cells via caspase 3/7 activation. Results revealed that compound 4q represents potential promising lead.

Energetic 1,2,5-Oxadiazolo-Pyridazine and its N-Oxide.

Achieving an energetic compound, which exhibits high performance and insensitivity, is important in the field of energetic materials and remains a major challenge. Herein, we found that oxidation of 4,7-diaminopyridazino[4,5-c]furoxan (5) with a mixture of 50 % hydrogen peroxide and trifluoroacetic anhydride gave 6-amino-7-nitro-[1,2,5]oxadiazolo[3,4-c]pyridazine (7) and its N-oxide derivative (8). The oxidation of 5 with hypofluorous acid (HOF) was also studied. Compound 8 displayed an energetic performance compared to triaminotrinitrobenzene (TATB) and insensitive properties (impact sensitivity (IS) 36 J and friction sensitivity (FS)>360 N). Such excellent properties make 8 attractive for high-performance applications, in which insensitivity is important.

Multi Component Reactions under Increased Pressure: On the Mechanism of Formation of Pyridazino[5,4,3-de][1,6]naphthyridine Derivatives by the Reaction of Malononitrile, Aldehydes and 2-Oxoglyoxalarylhydrazones in Q-Tubes.

Efficient synthesis of phenanthridin-6(5H)-one derivatives 12a-n in a four-component reaction of aldehyde hydrazone, aromatic aldehydes and malononitrile in Q-Tubes is reported. The results showed that the methodology has the advantage of being a one-pot synthesis of tricyclic systems in good yields. Potential routes leading to formation of compounds 12 are discussed. The structures of the synthesized compounds could be unequivocally established via X-ray crystal structure determination and spectroscopic methods.

A novel synthetic approach to hydroimidazo[1,5-b]pyridazines by the recyclization of itaconimides and HPLC-HRMS monitoring of the reaction pathway.

The novel cascade two-stage reaction between itaconimides and 1,2-diamino-4-phenylimidazole proceeds regio- and chemoselectively to form tetrahydroimidazo[1,5-b]pyridazines and includes nucleophilic C-addition by the activated C=C double bond and subsequent intramolecular recyclization of the intermediate with the amino group involved.

Organocatalytic one-pot synthesis of highly substituted pyridazines from Morita-Baylis-Hillman carbonates and diazo compounds.

A biologically inspired organocatalytic one-pot synthesis of highly functionalized pyridazines, which are ubiquitous structural units in a number of biologically active compounds, has been developed by starting from readily available diazo compounds and Morita-Baylis-Hillman (MBH) carbonates. Under mild reaction conditions, this synthetic route tolerated significant substrate variation to deliver a broad range of substituted products, including CF3 -substituted pyridazines derivatives. Moreover, the introduction of trifluoromethyl groups into the ring of pyridazine could be completed conveniently from 2,2,2-trifluorodiazoethane.

Imidazo[1,2-b]pyridazines as inhibitors of DYRK kinases.

Selective inhibitors of DYRK1A are of interest for the treatment of cancer, Type 2 diabetes and neurological disorders. Optimization of imidazo [1,2-b]pyridazine fragment 1 through structure-activity relationship exploration and in silico drug design efforts led to the discovery of compound 17 as a potent cellular inhibitor of DYRK1A with selectivity over much of the kinome. The binding mode of compound 17 was elucidated with X-ray crystallography, facilitating the rational design of compound 29, an imidazo [1,2-b]pyridazine with improved kinase selectivity with respect to closely related CLK kinases.

Thiophene Ring-opening Reactions III: One-Pot Synthesis and Antitumor Activity of 1,3,4-Thiadiazoline-Benzothiazolo[3,2-b]pyridazine Hybrids†.

INTRODUCTION: The preparation of model 6-chloro-5-nitrothieno[2,3-c]pyridazines incorporating (2'-halo-5'-nitrophenyl) entity is described. Interaction of these substrates with N'-(aryl)benzothiohydrazides, in the presence of triethylamine, followed a formal [4+1] annulation, furnishing the respective 1,3,4-thiadiazoline-benzothiazolo [3,2-b]pyridazine hybrids directly. This one-pot synthesis implies thiophene ring-opening and two consecutive intramolecular cyclizations. The structures of the synthesized new hybrids are supported by MS, NMR, and IR spectral data and further confirmed by single-crystal X-ray diffraction. These hybrids exhibit antiproliferative activity with notable selectivity against solid tumor cell lines (IC50: 4-18 µM). AIMS: This study aimed at exploring the scope and applicability of thiophene ring-opening reaction towards the synthesis of new thiadiazoline-[fused]tricyclic conjugates. BACKGROUND: α-Chloro-ß-nitrothienopyridazine underwent ring-opening upon reacting with N'-(aryl)benzothiohydrazides generating 1,3,4-thiadiazoline-benzothiazolo[3,2-b]pyridazines. OBJECTIVE: This new thiophene ring-opening reaction is applied to the one-pot synthesis of thiadiazoline-benzothiazolo[3,2-b]pyridazine couples. METHOD: A direct interaction of α-chloro-ß-nitrothienopyridazine with N'-(aryl)benzothio-hydrazide at room temperature for 1-2 h occurred. RESULT: a-Chloro-ß-nitrothieno[2,3-c]pyridazines are suitable substrates for the facile synthesis of thiadiazoline-benzothiazolo[3,2-b]pyridazine hybrids. CONCLUSION: This novel ring-opening reaction proceeds via formal [4+1] annulation and provides a versatile approach to various conjugated and/or fused five-membered heterocycles.

DFT study of structural and electronic properties of 1,4-diarylcyclopenta[d] pyridazines and oxazines for non-linear optical applications.

Polymer and molecular-based electronic materials incorporating heterocycles like thiophenes and pyrroles are attractive possibilities as substitutes for semimetal materials. Heterocyclic materials are heavily studied in this regard due to the large variations in possible substrates. Herein we evaluated four different 5,6-fused ring heterocycles to gain a better understanding of any favorable optical and electronic properties that were due to incorporation of certain moieties. The molecules chosen would highlight the effects that the central ring (pyridazine versus oxazine), aromatic substituent, and heterocyclic side group may have on electronic and optical properties. Computational analysis of these four molecules was done using density functional theory (B3LYP and PBEPBE) with 6-31G(d,p), 6-311 ++G(d,p), and cc-pVTZ basis sets. The constituent molecules were optimized, and calculations were done for the dipole moment, polarizability, first-order hyperpolarizability (ß), HOMO and LUMO orbitals, and a natural bonding order (NBO) analysis. These calculations allow for the study of charge density via electrostatic potential mapping and bonding orbitals. The results indicated that the pyridazine molecules presented here are more favorable than the oxazines for non-linear optical (NLO) applications. It is also noted that side ring substituents (thienyl and furyl) in the two pyridazines studied showed very little calculated differences. Finally, heterocyclic rings showed more favorable properties when incorporated as substituents for NLO applications over hydrocarbon aromatics. Graphical abstract.