Metabolic products of microorganisms. 243. Pyridazomycin, a new antifungal antibiotic produced by Streptomyces violaceoniger

Synthesis of spiropyridazine-benzosultams by the [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes

A simple and efficient method for the synthesis of spiropyridazine-benzosultams has been developed by means of [4 + 2] annulation reaction of 3-substituted benzoisothiazole 1,1-dioxides with 1,2-diaza-1,3-dienes. This approach displays advantages such as mild reaction conditions, wide substrate range tolerance, simple operation, compatibility with gram-scale preparation.

Copper-catalysed dehydrogenative self-coupling/cyclization of 5-aminopyrazoles: synthesis and photophysical study of pyridazines

An interesting self-coupling/cyclization of 5-aminopyrazoles is revealed, which provides a variety of pyridazine cores in reasonable yields. In this reaction, C(sp²)-C(sp²) and N-N bond formation occurs simultaneously in one reaction vessel. The photophysical properties of the synthesized compounds were also studied and some of them exhibited fluorescence properties with good quantum yields. A radical mediated reaction mechanism is proposed with the help of control experiments.

Autoxidation of 4-Hydrazinylquinolin-2(1H)-one; Synthesis of Pyridazino[4,3-c:5,6-c']diquinoline-6,7(5H,8H)-diones

An efficient synthesis of a series of pyridazino[4,3-c:5,6-c']diquinolines was achieved via the autoxidation of 4-hydrazinylquinolin-2(1H)-ones. IR, NMR (¹H and ¹³C), mass spectral data, and elemental analysis were used to fit and elucidate the structures of the newly synthesized compounds. X-ray structure analysis and theoretical calculations unequivocally proved the formation of the structure. The possible mechanism for the reaction is also discussed.

Synthetic and biosynthetic routes to nitrogen-nitrogen bonds

The nitrogen-nitrogen bond is a core feature of diverse functional groups like hydrazines, nitrosamines, diazos, and pyrazoles. Such functional groups are found in >300 known natural products. Such N-N bond-containing functional groups are also found in significant percentage of clinical drugs. Therefore, there is wide interest in synthetic and enzymatic methods to form nitrogen-nitrogen bonds. In this review, we summarize synthetic and biosynthetic approaches to diverse nitrogen-nitrogen-bond-containing functional groups, with a focus on biosynthetic pathways and enzymes.

One-Pot and Two-Chamber Methodologies for Using Acetylene Surrogates in the Synthesis of Pyridazines and Their D-Labeled Derivatives

Acetylene surrogates are efficient tools in modern organic chemistry with largely unexplored potential in the construction of heterocyclic cores. Two novel synthetic paths to 3,6-disubstituted pyridazines were proposed using readily available acetylene surrogates through flexible C₂ unit installation procedures in a common reaction space mode (one-pot) and distributed reaction space mode (two-chamber): (1) an interaction of 1,2,4,5-tetrazine and its acceptor-functionalized derivatives with a CaC₂ -H₂ O mixture performed in a two-chamber reactor led to the corresponding pyridazines in quantitative yields; (2) [4+2] cycloaddition of 1,2,4,5-tetrazines to benzyl vinyl ether can be considered a universal synthetic path to a wide range of pyridazines. Replacing water with D₂ O and vinyl ether with its trideuterated analog in the developed procedures, a range of 4,5-dideuteropyridazines of 95-99% deuteration degree was synthesized for the first time. Quantum chemical modeling allowed to quantify the substituent effect in both synthetic pathways.

Synthesis of Pyridazine Derivatives via Aza-Diels-Alder Reactions of 1,2,3-Triazine Derivatives and 1-Propynylamines

A highly regioselective method was developed for the preparation of pyridazine derivatives via the aza-Diels-Alder reaction of 1,2,3-triazines with 1-propynylamines under neutral conditions. This methodology allowed direct access to a wide range of 6-aryl-pyridazin-3-amines in high yields with good functional group compatibility. Key features of this strategy included a broad substrate scope and simple, metal-free, and neutral reaction conditions.

Synthesis and antifungal activity of imidazo[1,2-b]pyridazine derivatives against phytopathogenic fungi

A series of 3,6-disubstituted imidazo[1,2-b]pyridazine derivatives have been synthesized and characterized with spectroscopic analyses. The antifungal activities of these compounds against nine phytopathogenic fungi were evaluated by the mycelium growth rate method. The in vitro antifungal bioassays indicated that most of compounds displayed excellent and broad-spectrum antifungal activities. Especially, compounds 4a, 4c, 4d, 4l and 4r exhibited 1.9-25.5 fold more potent than the commercially available fungicide hymexazol against Corn Curvalaria Leaf Spot (CL), Alternaria alternate (AA), Pyricularia oryzae (PO) and Alternaria brassicae (AB) strains. Structure-activity relationship analysis showed that the enhanced antifungal activity is significantly affected by the substituents on the benzene ring and pyridazine ring.

I2-Promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones: facile and efficient synthesis of 1,4-dihydropyridazines and pyridazines

A facile and efficient strategy for the synthesis of 1,4-dihydropyridazines and pyridazines through I2-promoted [4 + 2] cycloaddition of in situ generated azoalkenes with enaminones has been developed. The switch in selectivity is attributed to the judicious choice of different reaction temperatures. The key features of this work include controllable and selective synthesis, good functional group tolerance, good to excellent reaction yields, metal/base-free conditions, and also applicability to one-pot methodology.

Copper-Catalyzed Aerobic 6-Endo-Trig Cyclization of β,γ-Unsaturated Hydrazones for the Divergent Synthesis of Dihydropyridazines and Pyridazines

A divergent synthetic strategy to 1,6-dihydropyridazines and pyridazines through Cu(II)-catalyzed controllable aerobic 6-endo-trig cyclization was developed. The selectivity can be rationally tuned via the judicious choice of reaction solvent. It was found that the 1,6-dihydropyridazines were obtained in moderate to high yields with CH₃CN as the reaction solvent, whereas employment of AcOH directly afforded pyridazines in up to 92% yields, probably arising from the oxidation of the in situ generated 1,6-dihydropyridazines.

Synthesis of Two Key Fragments of the Complex Polyhalogenated Marine Meroterpenoid Azamerone

A concise route toward two advanced fragments in the context of the total synthesis of the unique natural product azamerone is reported. Key synthetic features include the enantioselective synthesis of an epoxysilane and its Lewis-acid-induced cyclization and the installation of the pyridazine ring via a formylation/condensation sequence. This route provides strategic insights into the chemistry of phthalazinediols, facilitating synthetic approaches toward this class of natural products.

Heteroatom-Heteroatom Bond Formation in Natural Product Biosynthesis

Natural products that contain functional groups with heteroatom-heteroatom linkages (X-X, where X = N, O, S, and P) are a small yet intriguing group of metabolites. The reactivity and diversity of these structural motifs has captured the interest of synthetic and biological chemists alike. Functional groups containing X-X bonds are found in all major classes of natural products and often impart significant biological activity. This review presents our current understanding of the biosynthetic logic and enzymatic chemistry involved in the construction of X-X bond containing functional groups within natural products. Elucidating and characterizing biosynthetic pathways that generate X-X bonds could both provide tools for biocatalysis and synthetic biology, as well as guide efforts to uncover new natural products containing these structural features.

Pharmacological and Predicted Activities of Natural Azo Compounds

This paper describes research on natural azo compounds isolated from fungi, plant, bacteria, and invertebrates. More than 120 biologically active diazene containing alkaloids demonstrate confirmed pharmacological activity, including antitumor, antimicrobial, and antibacterial effects. The structures, origin, and biological activities of azo compounds are reviewed. Utilizing the computer program PASS, some structure-activity relationship new activities are also predicted, pointing toward possible new applications of these compounds. This article emphasizes the role of natural azo compounds as an important source of drug prototypes and leads for drug discovery.

[3 + 3]-Cycloaddition of Donor-Acceptor Cyclopropanes with Nitrile Imines Generated in Situ: Access to Tetrahydropyridazines

Donor-acceptor cyclopropanes are reacted under the influence of a Lewis acid with hydrazonyl chlorides to afford tetrahydropyridazines. Formally, this transformation can be regarded as a [3 + 3]-cycloaddition of three-membered rings and nitrile imines generated in situ. This efficient method provides fast access to a variety of structurally diverse pyridazine derivatives. The structure of a typical product was confirmed by X-ray crystallography.

A Straightforward Approach toward Multifunctionalized Pyridazines via Imination/Electrocyclization

A facile synthesis of functionalized 3-carbamide pyridazines starting from readily available chlorovinyl aldehydes and oxamic acid thiohydrazides via cascade imination/electrocyclization is reported. In the presence of p-toluenesulfuric acid, various ketones have been efficiently incorporated into the pyridazine derivatives through a two-step sequence involving a Vilsmeier-Haack reaction and imination. The synthetic value of this method has been demonstrated by efficient synthesis of steroidal pyridazines.

[4 + 2] cycloaddition of in situ generated 1,2-diaza-1,3-dienes with simple olefins: facile approaches to tetrahydropyridazines

A catalyst-free [4 + 2] annulation process between in situ generated 1,2-diaza-1,3-butadienes and simple olefins has been developed. Under mild conditions, the reactions afforded 1,4,5,6-tetrahydropyridazines, which feature a wide range of bioactive compounds, with high yields (up to 99% yield).

Natural products containing a nitrogen-nitrogen bond

As of early 2013, over 200 natural products are known to contain a nitrogen-nitrogen (N-N) bond. This report categorizes these compounds by structural class and details their isolation and biological activity.

Are pyridazines privileged structures?

Compared to carbocyclic drug molecules, pyridazine-containing drugs present additional interaction possibilities, as illustrated here for the antirhinoviral agent R 61837.

A short synthesis of the triazolopyrimidine antibiotic essramycin

A short synthesis of the 1,2,4-triazolo[1,5-a]pyrimidine antibiotic essramycin is described involving condensation of aminoguanidine with ethyl benzoylacetate to give an amino-1,2,4-triazole, followed by condensation with ethyl acetoacetate to form the pyrimidone ring.

Estrogenic diazenes: heterocyclic non-steroidal estrogens of unusual structure with selectivity for estrogen receptor subtypes

Estrogens regulate many biological functions, often acting in a tissue-selective manner. Their tissue-selective action is believed to involve differential estrogen action through the two estrogen receptor (ER) subtypes, ERalpha and ERbeta, as well as differential interaction of the ligand-receptor complexes with promoters and coregulator proteins. In the latter case, selectivity is based on the induction of specific conformations of the ligand-ER complex, conformations that are influenced by the structure of the ligand. Estrogen pharmaceuticals having an ideal balance of tissue-selective activity are being sought for menopausal hormone replacement, breast cancer prevention and therapy, and other actions. To expand on the structural diversity of ER ligands that might show such tissue selectivity, we have prepared a series of diazenes (pyrazines, pyrimidines, and pyridazines) substituted with two to four aryl groups and various short-chain aliphatic substituents. All of the pyrazine and pyrimidines bind to ER, some with high affinity and with a considerable degree of preferential binding to either ERalpha or ERbeta. One pyrimidine and one pyrazine have ERalpha affinity preferences as high as 23 and 9, respectively, and one pyrimidine has an ERbeta affinity preference of 8. The pyridazines, by contrast, are quite polar and have only very low binding affinity for the ER. In cell-based transcription assays, several of the pyrimidines and a pyrazine were found to be considerably more agonistic on ERalpha than on ERbeta. Because these triaryl diazenes have the largest volumes among the ER ligands so far investigated, their high affinity demonstrates the flexibility of the ligand binding pocket of the ERs and its tolerance for large substituents. Thus, these novel heterocyclic ligands expand the repertoire of chemical structures that bind to the estrogen receptor, and they could prove to be useful in elucidating the biological behavior of the two ER subtypes and in forming the basis for new estrogen pharmaceuticals having desirable tissue selectivity.

Pyridazines, LXXII: On the synthesis of azinium and diazinium compounds structurally related to pyridazomycin

Preparation of series of pyridine-, pyridazine-, and pyrazine-derived carboxamides bearing at the ring N-atom an alkyl side-chain with a terminal carboxylic group (7-11) or with a terminal acetylamino malonic ester moiety (13-17, 19-23) is described. Two desaza-pyridazomycin derivatives (24, 26) and homologs thereof (25, 27) were synthesised. The novel compounds which are structurally related to the antifungal antibiotic pyridazomycin were screened for antifungal activity: preliminary in vitro tests showed no activity.