Synthesis, Crystal Structure, Antifungal Activity, and Docking Study of Difluoromethyl Pyrazole Derivatives

Synthesis of Fully Substituted Difluoromethylpyrazoles by Cyclization of Difluoroacetohydrazonoyl Bromides with 2-Acylacetonitriles or Malononitrile

A concise and efficient method for the construction of fully substituted difluoromethylpyrazoles is achieved by a cyclization reaction between difluoroacetohydrazonoyl bromides and 2-acylacetonitrile or malononitrile. The method features advantages such as mild reaction conditions, broad substrate scope, good product yields, and high regioselectivity.

Development of 1,5-diarylpyrazoles as EGFR/JNK-2 dual inhibitors: design, synthesis, moleecular docking, and bioactivity evaluation

The eradication of multifactorial diseases, such as cancer, requires the design of drug candidates that attack multiple targets that contribute to the progression and proliferation of such diseases. Here, 1,5-diarylpyrazole derivatives bearing vanillin or sulfanilamide are developed as potential dual inhibitors of epidermal growth factor receptor (EGFR)/c-Jun N-terminal kinase 2 (JNK-2) for possible anticancer activity. These derivatives inhibited the growths of DLD-1, HeLa, K-562, SUIT-2 and HepG2 cancer cell lines, with minimum concentration required to inhibit half of the cellular growth (IC50) values of 2.7-63 μM. The tests confirmed that 5b and 5d were potent JNK-2 inhibitors, with IC50 of 2.0 and 0.9 μM, respectively, whereas 6 h selectively inhibited EGFR protein kinase (EGFR-PK) (IC50 = 1.7 μM). Notably, 6c inhibited both kinases, with IC50 values of 2.7 and 3.0 μM against EGFR-PK and JNK-2, respectively, offering a reference for designing mutual inhibitors of EGFR/JNK-2. The docking studies revealed the ability of the pyrazole ring to bind to the hinge region of the ATP binding site, thereby supporting the experimental inhibitory results. Furthermore, the developed compounds could induce apoptosis and induce cell cycle arrest at different cell phases.

Novel Pyrazole Acyl(thio)urea Derivatives Containing a Biphenyl Scaffold as Potential Succinate Dehydrogenase Inhibitors: Design, Synthesis, Fungicidal Activity, and SAR

As part of a program to discover novel succinate dehydrogenase inhibitor fungicides, a series of new pyrazole acyl(thio)urea compounds containing a diphenyl motif were designed and synthesized. Their structures were confirmed by 1H NMR, HRMS, and single X-ray crystal diffraction analysis. Most of these compounds possessed excellent activity against 10 fungal plant pathogens at 50 μg mL-1, especially against Rhizoctonia solani, Alternaria solani, Sclerotinia sclerotiorum, Botrytis cinerea, and Cercospora arachidicola. Interestingly, compounds 3-(difluoromethyl)-1-methyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9b, EC50 = 0.97 ± 0.18 μg mL-1), 1,3-dimethyl-N-((3',4',5'-trifluoro-[1,1'-biphenyl]-2-yl)carbamoyl)-1H-pyrazole-4-carboxamide (9a, EC50 = 2.63 ± 0.41 μg mL-1), and N-((4'-chloro-[1,1'-biphenyl]-2-yl)carbamoyl)-1,3-dimethyl-1H-pyrazole-4-carboxamide (9g, EC50 = 1.31 ± 0.15 μg mL-1) exhibited activities against S. sclerotiorum that were better than the commercial fungicide bixafen (EC50 = 9.15 ± 0.05 μg mL-1) and similar to the positive control fluxapyroxad (EC50 = 0.71 ± 0.11 μg mL-1). These compounds were not significantly phytotoxic to monocotyledonous and dicotyledonous plants. Structure-activity relationships (SAR) are discussed by substituent effects/molecular docking, and density functional theory analysis indicated that these compounds are succinate dehydrogenase inhibitors.

Applications of Bioisosteres in the Design of Biologically Active Compounds

The design of bioisosteres represents a creative and productive approach to improve a molecule, including by enhancing potency, addressing pharmacokinetic challenges, reducing off-target liabilities, and productively modulating physicochemical properties. Bioisosterism is a principle exploited in the design of bioactive compounds of interest to both medicinal and agricultural chemists, and in this review, we provide a synopsis of applications where this kind of molecular editing has proved to be advantageous in molecule optimization. The examples selected for discussion focus on bioisosteres of carboxylic acids, applications of fluorine and fluorinated motifs in compound design, some applications of the sulfoximine functionality, the design of bioisosteres of drug-H2O complexes, and the design of bioisosteres of the phenyl ring.

Design, Synthesis, Insecticidal Activity, and SAR of Aryl Isoxazoline Derivatives Containing Pyrazole-5-carboxamide Motif

It is important to develop new insecticides with a new mode of action because of increasing pesticide resistance. In this study, a series of novel aryl isoxazoline derivatives containing the pyrazole-5-carboxamide motif were designed and synthesized. Their structures were confirmed by 1H NMR, 13C NMR, and HRMS. Bioassays indicated that the 24 compounds synthesized possessed excellent insecticidal activity against Mythimna separate and no activity against Aphis craccivora and Tetranychus cinnabarinus. Among these aryl isoxazoline derivatives, 3-(5-(3,5-dichlorophenyl)-5-(trifluoromethyl)-4,5-dihydrozol-3-yl)-N-(4-fluorophenyl)-1-methyl-1H-pyrazole-5-carboxamide (IA-8) had the best insecticidal activity against M. separate, which is comparable with the positive control fluralaner. The molecular docking results of compound IA-8 and fluralaner with the GABA model demonstrated the same docking mode between compound IA-8 and positive control fluralaner in the active site of GABA. Molecular structure comparisons and ADMET analysis can potentially be used to design more active compounds. The structure-activity relationships are also discussed. This work provided an excellent insecticide for further optimization.

Antifungal Activities of Fluorinated Pyrazole Aldehydes on Phytopathogenic Fungi, and Their Effect on Entomopathogenic Nematodes, and Soil-Beneficial Bacteria

Fluoro-substituted pyrazoles have a wide range of biological activities, such as antibacterial, antiviral, and antifungal activities. The aim of this study was to evaluate the antifungal activities of fluorinated 4,5-dihydro-1H-pyrazole derivatives on four phytopathogenic fungi: Sclerotinia sclerotiorum, Macrophomina phaseolina, Fusarium oxysporum f. sp. lycopersici, and F. culmorum. Moreover, they were tested on two soil beneficial bacteria-Bacillus mycoides and Bradyrhizobium japonicum-as well as two entomopathogenic nematodes (EPNs)-Heterorhabditis bacteriophora and Steinernema feltiae. The molecular docking was performed on the three enzymes responsible for fungal growth, the three plant cell wall-degrading enzymes, and acetylcholinesterase (AChE). The most active compounds against fungi S. sclerotiorum were 2-chlorophenyl derivative (H9) (43.07% of inhibition) and 2,5-dimethoxyphenyl derivative (H7) (42.23% of inhibition), as well as H9 against F. culmorum (46.75% of inhibition). Compounds were shown to be safe for beneficial soil bacteria and nematodes, except for compound H9 on EPN H. bacteriophora (18.75% mortality), which also showed the strongest inhibition against AChE (79.50% of inhibition). The molecular docking study revealed that antifungal activity is possible through the inhibition of proteinase K, and nematicidal activity is possible through the inhibition of AChE. The fluorinated pyrazole aldehydes are promising components of future plant protection products that could be environmentally and toxicologically acceptable.

Rational Exploration of Novel SDHI Fungicide through an Amide-β-ketonitrile Bioisosteric Replacement Strategy

The identification of succinate dehydrogenase inhibitor (SDHI) fungicides bearing a novel scaffold is of great importance to control pathogenic fungi. Difluoromethyl-pyrazole β-ketonitrile derivatives were rationally designed through an innovative amide-β-ketonitrile bioisosteric replacement strategy and evaluated for their antifungal activities. In preliminary fungicidal screening, our new β-ketonitrile compounds showed outstanding in vitro activity. Compounds A7 and A14 exhibited EC₅₀ values of 0.116 and 0.165 μg/mL against Sclerotinia sclerotiorum, respectively, and A14 also displayed an EC₅₀ of 0.0774 μg/mL against Rhizoctonia solani. Furthermore, A14 exhibited moderate in vivo protective activity against rice sheath blight on rice plants. Results from SDH enzymatic assays demonstrated that A14 possesses significant inhibitory effect toward porcine heart SDH, with an IC₅₀ value of 0.183 μM, which was 20-fold more potent than that of fluxapyroxad (IC₅₀ = 3.76 μM). A docking study indicated that H-bonds, cation-π interactions, and edge-to-face π-π interactions play key roles in the binding of A14 with R. solani SDH. The CoMSIA model guided the approach to further structural optimizations and indicated that hydrophobic and steric substituents on the benzene ring have decisive effects on the fungicidal activity against R. solani. The present work describes for the first time the successful bioisosteric replacement of the common SDHI amide moiety by a β-ketonitrile group and highlights the potential of β-ketonitriles as an innovative novel SDHI subclass.

Synthesis, Structure, and Antifungal Activities of 3-(Difluoromethyl)-Pyrazole-4-Carboxylic Oxime Ester Derivatives

Fifteen new pyrazole-4-carboxylic oxime ester derivatives were conveniently synthesized, and their structures were confirmed by 1H NMR, 13C NMR, HRMS, and X-ray diffraction. Antifungal assays indicated that some of these compounds possessed good activity against S. sclerotiorum, B. cinerea, R. solani, P. oryae, and P. piricola at 50 ppm. Structure-activity relationships (SAR) were studied by molecular docking simulation.

Comprehensive Overview of Carboxamide Derivatives as Succinate Dehydrogenase Inhibitors

Up to now, a total of 24 succinate dehydrogenase inhibitors (SDHIs) fungicides have been commercialized, and SDHIs fungicides were also one of the most active fungicides developed in recent years. Carboxamide derivatives represented an important class of SDHIs with broad spectrum of antifungal activities. In this review, the development of carboxamide derivatives as SDHIs with great significances were summarized. In addition, the structure-activity relationships (SARs) of antifungal activities of carboxamide derivatives as SDHIs was also summarized based on the analysis of the structures of the commercial SDHIs and lead compounds. Moreover, the cause of resistance of SDHIs and some solutions were also introduced. Finally, the development trend of SDHIs fungicides was prospected. We hope this review will give a guide for the development of novel SDHIs fungicides in the future.

Synthesis of Difluoromethylated Pyrazoles by the [3 + 2] Cycloaddition Reaction of Difluoroacetohydrazonoyl Bromides

As novel and efficient difluoromethyl building blocks, difluoroacetohydrazonoyl bromides have been synthesized for the first time. The synthetic utility of this reagent for the construction of difluoromethyl organic compounds is demonstrated by their effective regioselective [3 + 2] cycloaddition reactions with ynones, alkynoates, and ynamides. The reactions provide a novel and efficient protocol to access difluoromethyl-substituted pyrazoles in good to excellent yields.

Synthesis and Fungicidal Activity of Hydrated Geranylated Phenols against Botrytis cinerea

Botrytis cinerea is a ubiquitous fungus that affects hundreds of plants, resulting in economic losses to the horticulture and fruit industry. The search for new antifungal agents is a matter of current interest. Thus, in this work a series of geranylated phenols in which the side alkyl chain has been hydrated have been synthesized, and their activity against B. cinerea has been evaluated. The coupling of phenol and geraniol has been accomplished under microwave irradiation obtaining the highest reaction yields in the shortest reaction times. Hydration of the side chain was carried out in dioxane with p-toluenesulfonic acid polymer-bound as the catalyst. All synthesized compounds were tested against B. cinerea using the growth inhibition assay and EC50 values were determined. The results show that activity depends on the number and nature of functional groups in the phenol ring and hydration degree of the geranyl chain. The most active compound is 1,4-dihydroquinone with one hydroxyl group attached at the end of the alkyl chain. Results from a molecular docking study suggest that hydroxyl groups in the phenol ring and alkyl chain are important in the binding of compounds to the active site, and that the experimental antifungal activity correlates with the number of H-bond that can be formed in the binding site.

Photodegradation of an Anilide Fungicide Inpyrfluxam in Water and Nitrate Aqueous Solution

The photodegradation behavior of a new anilide fungicide, inpyrfluxam [3-difluoromethyl-N-[(R)-2,3-dihydro-1,1,3-trimethyl-1H-inden-4-yl]-1-methylpyrazole-4-carboxamide] (1), was investigated in aqueous buffer and nitrate solutions under irradiation with artificial sunlight (λ > 290 nm). In both media, 1 mainly photodegraded via oxidation at the 3'-position of the Indane ring, cleavage of the C-N bond of the amide linkage and N-phenyl ring bond, and finally mineralization to carbon dioxide. No isomerization of 1 occurred at the 3'-position of the Indane ring. In the presence of nitrate ion, which originates from fertilizer in agricultural fields, the degradation of 1 was significantly accelerated as compared with buffer solution, and the reaction rate was strongly correlated with the concentration of hydroxyl radicals derived from the photolysis of nitrate ions. The reaction rate constant of hydroxyl radicals with 1 was determined to be 3.0 × 10¹⁰ /M/s, which was higher than that of hydroxyl radicals with other pesticides possessing aromatic rings.

Synthesis and herbicidal activity of novel pyrazole aromatic ketone analogs as HPPD inhibitor

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) has been a good target for herbicide discovery. In order to discover novel HPPD herbicides, a series of pyrazole aromatic ketone analogs were designed and synthesized.

RESULTS

The 25 pyrazole aromatic ketone analogs synthesized were tested for herbicidal activity and compounds A1, A3, A4, A17, A20 and A25 displayed excellent herbicidal activity against Chenopodium serotinum, Stellaria media and Brassica juncea at 37.5 g ha^-1 . In addition, compounds A1, A5, A9, A10, A16, A17, A20 and A25 exhibited good crop selectivity for wheat, maize and rice at 150 g ha^-1 . Inhibition activities against AtHPPD proved the compounds were HPPD inhibitors. The structure-activity relationship of these pyrazole aromatic ketone analogs was studied using molecular docking.

CONCLUSION

These pyrazole aromatic ketone derivatives could be used as lead structures for development of HPPD herbicides against dicotyledonous weeds with further structure modification. © 2019 Society of Chemical Industry.