Synthesis of fungicidally active succinate dehydrogenase inhibitors with novel difluoromethylated heterocyclic acid moieties

Application of Difluoromethyl Isosteres in the Design of Pesticide Active Molecules

Difluoromethyl (CF2H) groups have been found in many listed pesticides due to their unique physical and chemical properties and outstanding biological activity. In pesticide molecules, compared with the drastic changes brought by trifluoromethyl, difluoromethyl usually moderately regulates the metabolic stability, lipophilicity, bioavailability, and binding affinity of compounds. Therefore, difluoromethylation has become an effective means to modify the biological activity of pesticide molecules. This paper reviews the representative literatures and patents containing difluoromethyl groups in the past 10 years, and introduces the research progress. The aim is to provide an effective reference value for the study of difluoromethyl in pesticides.

Tandem Addition/Cyclization/Halogenation Reaction of Difluoromethylated N-Acylhydrazones with Allyltrimethylsilanes

As novel difluoromethyl building blocks, difluoromethylated N-acylhydrazones react with allyltrimethylsilanes and the halogen source via a tandem addition/cyclization/halogenation strategy, which produces various difluoromethylpyrazoline compounds in good yields. The method features mild reaction conditions, broad substrate scopes, and a transition metal-free process with easy operation. It also proves that difluoromethylated N-acylhydrazones are useful difluoromethyl building blocks for the construction of difluoromethylated nitrogen heterocycles.

Development of S-penthiopyrad for bioactivity improvement and risk reduction from the systemic evaluation at the enantiomeric level

For the purpose of screening high-efficiency and low-risk green pesticides, a systematic study on fungicide penthiopyrad was conducted at the enantiomeric level. The bioactivity of S-(+)-penthiopyrad (median effective concentration (EC50), 0.035 mg/L) against Rhizoctonia solani was 988 times higher than R-(-)-penthiopyrad (EC50, 34.6 mg/L), which would reduce 75% usage of rac-penthiopyrad under the same efficacy. Furthermore, their antagonistic interaction (toxic unit (TUrac), 2.07) indicated the existence of R-(-)-penthiopyrad would reduce the fungicidal activity of S-(+)-penthiopyrad. AlphaFold2 modeling and molecular docking illustrated that S-(+)-penthiopyrad had the higher binding ability with the target protein than R-(-)-penthiopyrad, showing higher bioactivity. For model organism Danio rerio, S-(+)-penthiopyrad (median lethal concentrations (LC50), 3.02 mg/L) and R-(-)-penthiopyrad (LC50, 4.89 mg/L) were both less toxic than rac-penthiopyrad (LC50, 2.73 mg/L), and the existence of R-(-)-penthiopyrad could synergistically enhance the toxicity of S-(+)-penthiopyrad (TUrac, 0.73), using S-(+)-penthiopyrad would reduce at least 23% toxicity to fish. The enantioselective dissipation and residues of rac-penthiopyrad were tested in three kinds of fruits, and their dissipation half-lives ranged from 1.91 to 23.7 d. S-(+)-penthiopyrad was dissipated preferentially in grapes, which was R-(-)-penthiopyrad in pears. On the 60th d, the residue concentrations of rac-penthiopyrad in grapes were still higher than its maximum residue limit (MRL), but the initial concentrations were lower than their MRL values in watermelons and pears. Thus, more tests in different cultivars of grapes and planting environments should be encouraged. Based on the acute and chronic dietary intake risk assessments, the risks in the three fruits were all acceptable. In conclusion, S-(+)-penthiopyrad is a high-efficiency and low-risk alternative to rac-penthiopyrad.

Synthesis Strategies and Medicinal Value of Pyrrole and its Fused Heterocyclic Compounds

For several decades, interest in pyrrole and pyrrolopyrimidine derivatives increases owing to their biological importance, such as anti-tumor, anti-microbial, anti-inflammatory, anti-diabetic, anti-histaminic, anti-malarial, anti-Parkinson, antioxidant and anti-viral, specially recently against COVID-19. These tremendous biological features motivated scientists to discover more pyrrole and fused pyrrole derivatives, owing to the great importance of the pyrrole nucleus as a pharmacophore in many drugs, and motivated us to present this article, highlighting on the different synthetic pathways of pyrrole and its fused compounds specially pyrrolopyrimidine, as well as their medicinal value from 2017 till 2021.

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.

The research progress in and perspective of potential fungicides: Succinate dehydrogenase inhibitors

Succinate dehydrogenase inhibitors (SDHIs) have become one of the fastest growing classes of new fungicides since entering the market, and have attracted increasing attention as a result of their unique structure, high activity and broad fungicidal spectrum. The mechanism of SDHIs is to inhibit the activity of succinate dehydrogenase, thereby affecting mitochondrial respiration and ultimately killing pathogenic fungi. At present, they have become popular varieties researched and developed by major pesticide companies in the world. In the review, we focused on the mechanism, the history, the representative varieties, structure-activity relationship and resistance of SDHIs. Finally, the potential directions for the development of SDHIs were discussed. It is hoped that this review can strengthen the individuals' understanding of SDHIs and provide some inspiration for the development of new fungicides.

Multicomponent reactions in crop protection chemistry

An overview is given of the significance of multicomponent reactions in the synthesis of agrochemicals. The most important applications of multicomponent condensations, such as the Biginelli reaction, Bucherer-Bergs reaction, Hantzsch dihydropyridine synthesis, Kabachnik-Fields reaction, Mannich reaction, Passerini reaction, Petasis reaction, Strecker reaction, Ugi reaction and Willgerodt-Kindler reaction, to the synthesis of herbicidally, fungicidally and insecticidally active compounds are presented. Also the mode of action and biological activity of these multicomponent reaction products are reported.

Novel 4-pyrazole carboxamide derivatives containing flexible chain motif: design, synthesis and antifungal activity

BACKGROUND

In recent years, carboxamide fungicides, targeting succinate dehydrogenase (SDH), have shown highly efficient and broad spectrum fungicidal activity. Structure-activity relationship (SAR) results for these commercial fungicides show that the carboxamide group was a key active group. This is useful information for the discovery of new pyrazole carboxamide derivatives with fungicidal activity.

RESULTS

Twenty-seven novel pyrazole carboxamides were designed and synthesized. Their fungicidal activities against Gibberella zeae, Phytophthora infestans, Phytophthora capsici, Rhizoctonia solani, Alternaria solani, Botrytis cinerea, Fusarium oxysporum, Cercospora arachidicola, Sclerotinia sclerotiorum and Physalospora piricola were tested; derivatives possessed excellent inhibitory at 50 mg L^-1 in particular. Furthermore, some pyrazole carboxamides exhibited remarkably high activities against Sclerotinia sclerotiorum in vitro with EC₅₀ values of 2.04 to 15.2 μg mL^-1 . In addition, some compounds also exhibited high activities against Physalospora piricola, Cercospora arachidicola and Phytophthora capsici. Inhibition activities against SDH proved that the designed analogues were effective at the enzyme level. The SAR of these pyrazole carboxamides was studied by using the docking method.

CONCLUSION

It is possible that pyrazole carboxamides, which exhibit good activity against Sclerotinia sclerotiorum, can be further optimized as a lead compounds of carboxamide fungicides. © 2019 Society of Chemical Industry.

Design, Synthesis, and Antifungal Activities of Novel Aromatic Carboxamides Containing a Diphenylamine Scaffold

A series of novel N-(2-(phenylamino)-4-fluorophenyl)-pyrazole-4-carboxamides 1-15 and aromatic carboxamides with a diphenylamine scaffold 16-29 were designed, synthesized, and evaluated for their antifungal activities. In vitro experiments showed that compound 6 (EC₅₀ = 0.03 mg/L) was superior to bixafen (EC₅₀ = 0.04 mg/L) against Rhizoctoinia solani and compound 6 (IC₅₀ = 1.41 mg/L) was close to bixafen (IC₅₀ = 1.22 mg/L) against succinate dehydrogenase from R. solani. Additionally, in vivo pot experiments showed that compound 6 (EC₅₀ = 1.93 mg/L) was better than bixafen (EC₅₀ = 3.72 mg/L) and close to thifluzamide (EC₅₀ = 1.83 mg/L) against R. solani. In vivo field trials showed that compound 6 at 200 g ai ha^-1 had 64.10% control efficacy against rice sheath blight after 21 days with two sprayings, close to thifluzamide (71.40%). Furthermore, molecular docking showed that compound 6 anchors in the binding site of SDH.

Regiocontrolled Halogen Dance of Bromothiophenes and Bromofurans

The LDA (lithium diisopropylamide)-promoted regiocontrolled halogen dance of α-bromothiophenes and α-bromofurans is described. Bromothiophenes bearing a diethyl acetal moiety undergo selective deprotonation at the β-position adjacent to the bromo group. In contrast, oxazoline, ester, and amide groups act as directing groups in the initial lithiation step to generate a carbanion at the β-position neighboring the directing group to exclusively give the other regioisomer. These results can be applied to the regiocontrolled halogen dance of bromofuran derivatives.

Synthesis of Multi-Substituted Pyrrole Derivatives Through [3+2] Cycloaddition with Tosylmethyl Isocyanides (TosMICs) and Electron-Deficient Compounds

Pyrrole and its polysubstituted derivatives are important five-membered heterocyclic compounds, which exist alone or as a core framework in many pharmaceutical and natural product structures, some of which have good biological activities. The Van Leusen [3+2] cycloaddition reaction based on tosylmethyl isocyanides (TosMICs) and electron-deficient compounds as a substrate, which has been continuously developed due to its advantages such as operationally simple, easily available starting materials, and broadly range of substrates, is one of the most convenient methods to synthetize pyrrole heterocycles. In this review, we discuss the different types of two carbon synthons in the Van Leusen pyrrole reaction and give a summary of the progress of these synthesis methods in the past two decades.