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Background: Succinate dehydrogenase inhibitor (SDHI) fungicides are an important class of agricultural fungicides with the advantages of high efficiency and a broad bactericidal spectrum. To pursue novel SDHIs, a series of N-substituted dithiin tetracarboximide derivatives were designed, synthesized, and characterized by 1 H NMR, 13 C NMR, and high resolution mass spectrum (HRMS)., Results: These engineered compounds displayed potent fungicidal activity against phytopathogens, including Sclerotinia sclerotiorum, Botrytis cinerea, and Rhizoctonia solani, comparable with that of the commercial SDHI fungicide boscalid. In particular, compound 18 stood out with prominent activity against S. sclerotiorum with a half-maximal effective concentration (EC 50 ) value of 1.37 μg ml -1 . Compound 1 exhibited the most potent antifungal activity against B. cinerea with EC 50 values of 5.02 μg ml -1 . As for R. solani, 12 and 13 exhibited remarkably inhibitory activity with EC 50 values of 4.26 and 5.76 μg ml -1 , respectively. In the succinate dehydrogenase (SDH) inhibition assay, 13 presented significant inhibitory activity with a half-maximal inhibitory concentration (IC 50 ) value of 15.3 μm, which was approximately equivalent to that of boscalid (14.2 μm). Furthermore, molecular docking studies revealed that 13 could anchor in the binding site of SDH., Conclusion: Taken together, results suggested that the dithiin tetracarboximide scaffold possessed a huge potential to be developed as novel fungicides and SDHIs. © 2023 Society of Chemical Industry., (© 2023 Society of Chemical Industry.)

Antibacterial peptides are a class of naturally occurring peptides produced by eukaryotes and prokaryotes. Some of them exhibit broad-spectrum antifungal activity. Antifungal peptides (AFPs) can be developed as antibiotic to control fungal infections in agriculture due to their different antifungal mechanisms. As actinomycetes are still one of the most important sources of novel antibiotics, in this review, the mechanisms of action of AFPs are explained. Characterization of several AFPs produced by actinomycetes and their biological activities against plant diseases are summarized. Furthermore, the pathway for total synthesis of naturally occurring cyclodepsipeptide, valinomycin, is proposed. Finally, the pathway for biosynthesis of kutzneride 2 is proposed and the structure-activity relationship of kutznerides is discussed.

A novel strain with antifungal activity against Sclerotinia sclerotiorum was isolated from soil, and identified as Streptomyces sp. ZJUT-IFE-354 using morphological and 16S rDNA sequence analysis. The bioactive metabolite produced by strain ZJUT-IFE-354 was identified and characterized as valinomycin by spectroscopic and chemical methods. The yield of valinomycin was 191.26 mg/L from the culture of Streptomyces sp. ZJUT-IFE-354, which was the highest yield to our knowledge. The in vitro antifungal activity of valinomycin against S. sclerotiorum was investigated as 0.056 ± 0.012 (EC50) and 0.121 ± 0.023 μg/mL (EC95), respectively, which was approximately 10.696- and 30.960-fold more active than that of carbendazim. The results from scanning electron microscopy, cell membrane permeability, and D-sorbitol and ergosterol assay indicated that valinomycin exerted the antifungal activity probably by increasing permeability of fungal cell membrane, leading to mycelial electrolyte leakage, and eventually resulting in the death of S. sclerotiorum. Thus, valinomycin may be a promising antifungal agent to control S. sclerotiorum. [ABSTRACT FROM AUTHOR]

A novel strain with antifungal activity against Sclerotinia sclerotiorum was isolated from soil, and identified as Streptomyces sp. ZJUT-IFE-354 using morphological and 16S rDNA sequence analysis. The bioactive metabolite produced by strain ZJUT-IFE-354 was identified and characterized as valinomycin by spectroscopic and chemical methods. The yield of valinomycin was 191.26 mg/L from the culture of Streptomyces sp. ZJUT-IFE-354, which was the highest yield to our knowledge. The in vitro antifungal activity of valinomycin against S. sclerotiorum was investigated as 0.056 ± 0.012 (EC50) and 0.121 ± 0.023 μg/mL (EC95), respectively, which was approximately 10.696- and 30.960-fold more active than that of carbendazim. The results from scanning electron microscopy, cell membrane permeability, and D-sorbitol and ergosterol assay indicated that valinomycin exerted the antifungal activity probably by increasing permeability of fungal cell membrane, leading to mycelial electrolyte leakage, and eventually resulting in the death of S. sclerotiorum. Thus, valinomycin may be a promising antifungal agent to control S. sclerotiorum. [ABSTRACT FROM AUTHOR]

Chitin is an important part of the fungal cell wall, but is not found in plants and mammals, so chitin synthase (CHS) can be a green fungicide target. In this paper, 35 maleimide compounds were designed and synthesized as CHS inhibitors. All the screened compounds showed different degrees of CHS inhibitory activity and antifungal activity in vitro. In particular, the half–inhibitory concentration (IC50) value of compound 20 on CHS was 0.12 mM, and the inhibitory effect was better than that of the control polyoxin B (IC50 = 0.19 mM). At the same time, this compound also showed good antifungal activity and has further development value. [ABSTRACT FROM AUTHOR]