Design, Synthesis, Biological Evaluation, and Molecular Modeling of Novel 4H-Chromene Analogs as Potential Succinate Dehydrogenase Inhibitors

New 5,6-dihydrobenzo[h]quinoline derivatives as potential demethylase inhibitors (DMIs): design, synthesis, activity evaluation and molecular dynamics simulation

BACKGROUND

Bipolaris maydis is a serious plant fungus and strongly affects the yield and quality of crops. The main control strategy is the employment of fungicides. To research efficient fungicide with novel structure, a series of novel 5,6-dihydrobenzo[h]quinoline derivatives were designed and synthesized.

RESULTS

Thirty-six novel 5,6-dihydrobenzo[h]quinoline analogues were designed and synthesized. The assay results showed that most compounds exhibited significant fungicidal activity against Pyricularia oryzae, Bipolaris maydis, Sclerotinia sclerotiorum, Penicillium digitatum and Valsa mali at 16 μg mL-1. Compounds 4 h, 5e, 6a and 6b showed better antifungal activity than fluquinconazole against B. maydis. Their half maximal effective concentration (EC50) values were 0.732, 0.283, 0.529, 0.644 and 0.826 μg mL-1, respectively. Furthermore, the bioactive compounds were determined against sterol 14α-demethylase (CYP51). The results indicated that they displayed prominent inhibiting activities, 4 h, 5e, 6a and 6b also had better inhibitory activities than fluquinconazole against CYP51. Their half maximal inhibitory concentration (IC50) values were 0.840, 0.315, 0.601, 0.750 and 1.018 μg mL-1, respectively. The fluorescent quenching tests of proteins indicated that the quenching patterns of compounds 5e and 6a were analogous to fluquinconazole. The molecular dynamics (MD) simulations indicated that compound 5e possessed stronger affinity than fluquinconazole to CYP51.

CONCLUSION

The results of the present study displayed that novel 5,6-dihydrobenzo[h]quinoline derivatives could be one scaffold of potential CYP51 inhibitor and will provide some valuable information for the research and development of new fungicides. © 2024 Society of Chemical Industry.

Design, synthesis and antifungal activity of novel pyrazole-amide-isothiazole derivatives as succinate dehydrogenase inhibitors

To discover new fungicides to protect food safety and quality, thirty-four novel pyrazole-amide-isothiazole compounds were designed, synthesised by using scaffold hopping theory for the first time. The bioactivity of all the target compounds against five plant pathogens (Including Penicillium digitatum, Physalospora piricola, Helminthosporium maydis, Sclerotinia sclerotiorum and Botrytis cinerea) were determined, the results showed that most of the compounds exhibited certain biological activities against B. cinerea in vitro. Compounds 7-XHU-6 had better antifungal activities than fluopyram with the EC50 values were 1.02, 1.78 mg/L, respectively. Moreover, the SDH inhibiting activities results indicated that 7-XHU-6 possessed outstanding activities with an IC50 value of 0.47 mg/L which better than fluopyram (IC50 = 0.88 mg/L). Besides, the in vivo experiments indicated that compound 7-XHU-6 had excellent protection efficiency and therapeutic efficiency. In addition, molecular docking studies demonstrated that compound 7-XHU-6 (-10 kcal/mol) has superior binding energy compared to fluopyram (-8.6 kcal/mol).

Preparation, Antifungal Activity Evaluation, and Mechanistic Studies of Unique and Structurally Novel Pyrazole-Heterocyclic-Amide Analogues

Thirty-six novel pyrazole-heterocyclic-amide analogues were designed, synthesized, and characterized. The bioassay results showed that most target compounds exhibited good fungicidal activities against Rhizoctonia solani, Gibberella zeae, Pseudoperonospora cubensis, Helminthosporium maydis, and Coniothyrium diplodiella at 20 μg/mL. Compounds 6d, 6f, 6l, and 6j possessed better fungicidal activities than the commercial fungicide prochloraz against H. maydis. Their half maximal effective concentration (EC50) values were 0.47, 0.26, 0.58, and 0.69 μg/mL, respectively, and the EC50 value of prochloraz was 0.77 μg/mL. Furthermore, the inhibitory activities for the bioactive compounds were determined against sterol 14α-demethylase (CYP51), the results displayed that they had prominent activities, compounds 6d, 6f, 6l, and 6j also showed better inhibitory activities than prochloraz against CYP51, their half maximal inhibitory concentration (IC50) values were 0.543, 0.29, 0.77, 0.66, and 0.86 μg/mL, respectively. The results of molecular dynamics simulations exhibited that compound 6f displayed stronger affinity to CYP51 than prochloraz, and estimated ΔGbind values of -44.9 and -37.2 kcal/mol were found for 6f and prochloraz, respectively.

Synthesis and characterization of some new Schiff base azo disperse dyes based on chromene moiety for simultaneous dyeing and antimicrobial finishing

New azo Schiff base disperse dyes based on a chromene moiety were synthesized by reacting (2-amino-7-hydroxy-4-(4-methoxyphenyl)-4 H-chromene-3 carbonitrile) and(2-amino-4-(3,4-dimethoxyphenyl)-7-hydroxy-4 H-chromene-3-carbonitrile), with vanillin and ninhydrin, producing new chromene Schiff base derivatives, which in turn were coupled with 2-chloro-4-nitroaniline diazonium salt to give new 4 azo disperse dyes (1-4). The structures of the prepared dyes were confirmed using elemental analysis, 1HNMR spectroscopy, mass spectrometry, and IR. The synthesized dyes were applied to polyester and nylon fabrics using different dyeing techniques: high temperature- high pressure, and ultrasonic dyeing methods. The highest K/S values for all investigated dyes were achieved usinga high temperature-high pressure dyeing technique. Also, the color reflectance of all synthesized dyes with different dyeing shades (1%, 2%, and 3%) was obtained. The fastness properties of the dyed samples using the investigated dyes showed good color fastness toward light, washing, rubbing, and perspiration fastness. The presence of a chromene moiety and Schiff base in the investigated dyes promotes a higher antimicrobial activity on nylon and polyester fabrics against all tested bacteria (E. coli gram-negative and Staphylococcus aureus gram-positive) and two fungi, Aspergillus Niger and Candida albicans.

Recent Advances and Outlook of Benzopyran Derivatives in the Discovery of Agricultural Chemicals

Scaffold structures, new mechanisms of action, and targets present enormous challenges in the discovery of novel pesticides. The discovery of new scaffolds is the basis for the continuous development of modern agrochemicals. Identification of a good scaffold such as triazole, carbamate, methoxy acrylate, pyrazolamide, pyrido-pyrimidinone mesoionic, and bisamide often leads to the development of a new series of pesticides. In addition, pesticides with the same target, including the inhibitors of succinate dehydrogenase (SDH), oxysterol-binding-protein, and p-hydroxyphenyl pyruvate dioxygenase (HPPD), may have the same or similar scaffold structure. Recent years have witnessed significant progress in the discovery of new pesticides using natural products as scaffolds or bridges. In recent years, there have been increasing reports on the application of natural benzopyran compounds in the discovery of new pesticides, especially osthole and coumarin. A systematic and comprehensive review of benzopyran active compounds in the discovery of new agricultural chemicals is helpful to promote the discussion and development of benzopyran active compounds. Therefore, this work systematically reviewed the research and application of benzopyran derivatives in the discovery of agricultural chemicals, summarized the antiviral, herbicidal, antibacterial, fungicidal, insecticidal, nematicidal and acaricidal activities of benzopyran active compounds, and discussed the structural-activity relationship and mechanism of action. In addition, some active fragments were recommended to further optimize the chemical structure of benzopyran active compounds based on reference information.

Novel Pyrido[4,3-d]pyrimidine Derivatives as Potential Sterol 14α-Demethylase Inhibitors: Design, Synthesis, Inhibitory Activity, and Molecular Modeling

Thirty-four new pyrido[4,3-d]pyrimidine analogs were designed, synthesized, and characterized. The crystal structures for compounds 2c and 4f were measured by means of X-ray diffraction of single crystals. The bioassay results showed that most target compounds exhibited good fungicidal activities against Pyricularia oryzae, Rhizoctonia cerealis, Sclerotinia sclerotiorum, Botrytis cinerea, and Penicillium italicum at 16 μg/mL. Compounds 2l, 2m, 4f, and 4g possessed better fungicidal activities than the commercial fungicide epoxiconazole against B. cinerea. Their half maximal effective concentration (EC50) values were 0.191, 0.487, 0.369, 0.586, and 0.670 μg/mL, respectively. Furthermore, the inhibitory activities of the bioactive compounds were determined against sterol 14α-demethylase (CYP51). The results displayed that they had prominent activities. Compounds 2l, 2m, 4f, and 4g also showed better inhibitory activities than epoxiconazole against CYP51. Their half maximal inhibitory concentration (IC50) values were 0.219, 0.602, 0.422, 0.726, and 0.802 μg/mL, respectively. The results of molecular dynamics (MD) simulations exhibited that compounds 2l and 4f possessed a stronger affinity to CYP51 than epoxiconazole.

Design, Synthesis, Bioactive Evaluation, and Molecular Dynamics Simulation of Novel 4H-Pyrano[3,2-c]pyridine Analogues as Potential Sterol 14α-Demethylase (CYP51) Inhibitors

To discover potential sterol 14α-demethylase (CYP51) inhibitors, thirty-four unreported 4H-pyrano[3,2-c]pyridine derivatives were designed and synthesized. The assay results indicated that most compounds displayed significant fungicidal activity against Sclerotinia sclerotiorum, Colletotrichum lagenarium, Botrytis cinerea, Penicillium digitatum, and Fusarium oxysporum at 16 μg/mL. The half maximal effective concentration (EC50) values of compounds 7a, 7b, and 7f against B. cinerea were 0.326, 0.530, and 0.610, respectively. Namely, they had better antifungal activity than epoxiconazole (EC50 = 0.670 μg/mL). Meanwhile, their half maximal inhibitory concentration (IC50) values against CYP51 were 0.377, 0.611, and 0.748 μg/mL, respectively, representing that they also possessed better inhibitory activities than epoxiconazole (IC50 = 0.802 μg/mL). The fluorescent quenching tests of proteins showed that 7a and 7b had similar quenching patterns to epoxiconazole. The molecular dynamics simulations indicated that the binding free energy of 7a and epoxiconazole to CYP51 was -35.4 and -27.6 kcal/mol, respectively.

Design, Synthesis, Antifungal Activity, and Molecular Docking Studies of Novel Chiral Isoxazoline-Benzofuran-Sulfonamide Derivatives

Succinate dehydrogenase (SDH) is one of the most important molecular targets for the development of novel fungicides. With the emerging problem of resistance in plant fungal pathogens, novel compounds with high fungicidal activity need to be developed, but the study of chiral pesticides for the inhibition of highly destructive plant pathogens has been rarely reported in recent years. Therefore, a series of novel chiral isoxazoline-benzofuran-sulfonamide derivatives were designed to investigate potential novel antifungal molecules. The chiral target compound 3a was cultured as a single crystal and confirmed using X-ray diffraction. All the target compounds were tested for antifungal activity, and compounds 3c, 3i, 3s, and 3r were found to have significant antifungal effects against S. sclerotiorum with EC50 values of 0.42 mg/L, 0.33 mg/L, 0.37 mg/L, and 0.40 mg/L, respectively, which were superior to the commercial fungicide fluopyram (EC50 = 0.47 mg/L). The IC50 value of compound 3i against the SDH of S. sclerotiorum was 0.63 mg/mL, which was further demonstrated by enzyme activity assays. Scanning electron microscopy showed that 3i had a significant inhibitory effect on S. sclerotiorum. In addition, the fluorescence quenching analysis assay indicated that compound 3i had a similar effect with the positive control fluopyram. Molecular docking exhibited that target compounds with chiral configuration had better affinity than racemic configuration, and 3i possessed stronger action than fluopyram, which was in keeping with the in vitro test results. These results would provide a basis and reference for the development of novel chiral fungicides.

Design, Synthesis, Antifungal Evaluation, Structure-Activity Relationship (SAR) Study, and Molecular Docking of Novel Spirotryprostatin A Derivatives

Phytopathogenic fungi cause plant diseases and economic losses in agriculture. To efficiently control plant pathogen infections, a total of 19 spirotryprostatin A derivatives and 26 spirooxindole derivatives were designed, synthesized, and tested for their antifungal activity against ten plant pathogens. Additionally, the intermediates of spirooxindole derivatives were investigated, including proposing a mechanism for diastereoselectivity and performing amplification experiments. The bioassay results demonstrated that spirotryprostatin A derivatives possess good and broad-spectrum antifungal activities. Compound 4d exhibited excellent antifungal activity in vitro, equal to or higher than the positive control ketoconazole, against Helminthosporium maydis, Trichothecium roseum, Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium graminearum, Alternaria brassicae, Alternaria alternate, and Fusarium solan (MICs: 8-32 µg/mL). Compound 4k also displayed remarkable antifungal activity against eight other phytopathogenic fungi, including Fusarium oxysporium f. sp. niveum and Mycosphaerella melonis (MICs: 8-32 µg/mL). The preliminary structure-activity relationships (SARs) were further discussed. Moreover, molecular docking studies revealed that spirotryprostatin A derivatives anchored in the binding site of succinate dehydrogenase (SDH). Therefore, these compounds showed potential as natural compound-based chiral fungicides and hold promise as candidates for further enhancements in terms of structure and properties.

Synthesis and Characterization of a New Class of Chromene-Azo Sulfonamide Hybrids as Promising Anticancer Candidates with the Exploration of Their EGFR, hCAII, and MMP-2 Inhibitors Based on Molecular Docking Assays

In this study, novel selective antitumor compounds were synthesized based on their fundamental pharmacophoric prerequisites associated with EGFR inhibitors. A molecular hybridization approach was employed to design and prepare a range of 4H-chromene-3-carboxylates 7a-g, 8, and 11a-e derivatives, each incorporating a sulfonamide moiety. The structures of these hybrid molecules were verified using comprehensive analytical and spectroscopic techniques. During the assessment of the newly synthesized compounds for their anticancer properties against three tumor cell lines (HepG-2, MCF-7, and HCT-116), compounds 7f and 7g displayed remarkable antitumor activity against all tested cell lines, outperforming the reference drug Cisplatin in terms of efficacy. Consequently, these promising candidates were selected for further investigation of their anti-EGFR, hCAII, and MMP-2 potential, which exhibited remarkable effectiveness against EGFR and MMP2 when compared to Sorafenib. Additionally, docking investigations regarding the EGFR binding site were implemented for the targeted derivatives in order to attain better comprehension with respect to the pattern in which binding mechanics occur between the investigated molecules and the active site, which illustrated a higher binding efficacy in comparison with Sorafenib.

Novel aromatic carboxamide potentially targeting fungal succinate dehydrogenase: Design, synthesis, biological activities and molecular dynamics simulation studies

BACKGROUND

Succinate dehydrogenase inhibitors (SDHIs) emerging in fungicide markets are widely used in crop protection. Currently, the structural modification focusing on a structurally diverse 'core' moiety (aryl) of SDHIs is being gradually identified as one of the innovative strategies for developing novel, highly effective and low resistant fungicides.

RESULTS

By optimization of lead compound SCU2028, 30 novel aromatic carboxamides Ia-o and IIa-o without a pyrazol group were designed, synthesized and characterized by 1 H NMR, 13 C NMR and high resolution mass spectrum (HRMS). In vitro antifungal activities showed that most of the compounds Ia-o and IIa-o exhibited good antifungal activities against Rhizoctonia solani. Among them, compounds Ic and IIc (EC50  = 0.02 mg/L), with the 2-chloro-3-pyridyl moiety, and compounds Io (EC50  = 0.03 mg/L) and IIo (EC50  = 0.02 mg/L), with the 4-methyl-2-trifluoromethylthiazolyl moiety, all exhibited the equivalent antifungal activities against R. solani with compound SCU2028 (EC50  = 0.03 mg/L) and bixafen (EC50  = 0.04 mg/L). Additionally, in pot tests, compound IIc (EC50  = 3.63 mg/L) also had higher antifungal activity against R. solani than compound SCU2028 (EC50  = 7.63 mg/L). Furthermore, in vitro inhibitory activity against fungal SDH showed the inhibitory ability of compound IIc was equivalent with that of compound SCU2028, and molecular dynamics simulation of the SDH-compound IIc complex suggested that compound IIc could strongly bind to and interact with the binding site of SDH.

CONCLUSION

Novel aromatic carboxamides without a pyrazol group have potential as a class of SDHIs, and the strategy of replacing the pyrazol group with another aryl in the 'core' moiety might offer an alternative option in discovery of SDHI fungicides. © 2023 Society of Chemical Industry.

Novel quinolin-2(1H)-one analogues as potential fungicides targeting succinate dehydrogenase: design, synthesis, inhibitory evaluation and molecular modeling

BACKGROUND

Succinate dehydrogenase is an important target of fungicides. Succinate dehydrogenase inhibitors (SDHIs) have widely been used to combat destructive plant pathogenic fungi because they possess efficient and broad-spectrum antifungal activities and as well as unique mode of action. The research and development of novel SDHIs have been ongoing.

RESULTS

Thirty-six novel quinolin-2(1H)-one derivatives were designed, synthesized and characterized. The single crystal structure of compound 3c was determined through the X-ray diffraction of single crystals. The bioassay results displayed that most compounds had good antifungal activities at 16 μg mL-1 against Rhizoctonia cerealis, Erysiphe graminis, Botrytis cinerea, Penicillium italicum and Phytophthora infestans. Compounds 6o, 6p and 6r had better antifungal activities than the commercialized fungicide pyraziflumid against Botrytis cinerea. Their half maximal effective concentration (EC50 ) values were 0.398, 0.513, 0.205 and 0.706 μg mL-1 , respectively. Moreover, the inhibiting activities of the bioactive compounds were tested against succinate dehydrogenase. The results indicated that they possessed outstanding activities. Compounds 6o, 6p and 6r also exhibited better inhibiting activities than pyraziflumid against succinate dehydrogenase. Their half maximal inhibitory concentration (IC50 ) values were 0.450, 0.672, 0.232 and 0.858 μg mL-1 , respectively. The results of molecular dynamic (MD) simulations indicated that compound 6r displayed stronger affinity to succinate dehydrogenase than pyraziflumid.

CONCLUSION

The results of the present study displayed that quinolin-2(1H)-one derivative could be one scaffold of potential SDHIs and will provide some valuable information for the research and development of new SDHIs. © 2022 Society of Chemical Industry.

Potential Succinate Dehydrogenase Inhibitors Bearing a Novel Pyrazole-4-sulfonohydrazide Scaffold: Molecular Design, Antifungal Evaluation, and Action Mechanism

Aiming to develop novel antifungal agents with a distinctive molecular scaffold targeting succinate dehydrogenase (SDH), 24 N'-phenyl-1H-pyrazole-4-sulfonohydrazide derivatives were first devised, synthesized, and verified by ¹H NMR, ¹³C NMR, high-resolution mass spectrometry (HRMS), and single-crystal X-ray diffraction analysis. The bioassays revealed that the target compounds possessed highly efficient and broad-spectrum antifungal activities against four tested plant pathogenic fungi Rhizoctonia solani (R. solani), Botrytis cinerea, Fusarium graminearum, and Alternaria sonali. Strikingly, compound B6 was assessed as the selective inhibitor against R. solani, with an in vitro EC₅₀ value (0.23 μg/mL) that was similar to that of thifluzamide (0.20 μg/mL). The in vivo preventative effect of compound B6 (75.76%) at 200 μg/mL against R. solani was roughly comparable to thifluzamide (84.31%) under the same conditions. The exploration of morphological observations indicated that compound B6 could strongly damage the mycelium morphology, obviously increase the permeability of the cell membrane, and dramatically increase the number of mitochondria. Compound B6 also significantly inhibited SDH enzyme activity with an IC₅₀ value of 0.28 μg/mL, and its fluorescence quenching dynamic curves were similar to that of thifluzamide. Molecular docking and molecular dynamics simulations demonstrated that compound B6 could strongly interact with similar residues around the SDH active pocket as thifluzamide. The present study revealed that the novel N'-phenyl-1H-pyrazole pyrazole-4-sulfonohydrazide derivatives are worthy of being further investigated as the promising replacements of traditional carboxamide derivatives targeting SDH of fungi.

Design, Synthesis, and Study of the Dual Action Mode of Novel N-Thienyl-1,5-disubstituted-4-pyrazole Carboxamides against Nigrospora oryzae

Due to the single target but extensive application of commercialized succinate dehydrogenase inhibitors (SDHIs), resistance problems have gradually become apparent in recent years. To solve this problem, a series of novel N-thienyl-1,5-disubstituted-1H-4-pyrazole carboxamide derivatives were designed and synthesized in this work based on the active skeleton 5-trifluoromethyl-4-pyrazole carboxamide. The bioassay results indicated that some target compounds exhibited excellent in vitro antifungal activities against the eight phytopathogenic fungi tested. Among them, the EC₅₀ values of T₄, T₆, and T₉ against Nigrospora oryzae were 5.8, 1.9, and 5.5 mg/L, respectively. The in vivo protective and curative activities of 40 mg/L T₆ against rice infected with N. oryzae were 81.5% and 43.0%, respectively. Further studies revealed that T₆ not only significantly inhibited the growth of N. oryzae mycelia but also effectively hindered spore germination and germ tube elongation. Morphological studies using scanning electron microscopy (SEM), fluorescence microscopy (FM), and transmission electron microscopy (TEM) found that T₆ could affect the mycelium membrane integrity by increasing cell membrane permeability and causing peroxidation of cellular lipids, and these results were further verified by measuring the malondialdehyde (MDA) content. The IC₅₀ value of T₆ against succinate dehydrogenase (SDH) was 7.2 mg/L, lower than that of the commercialized SDHI penthiopyrad (3.4 mg/L). Further, ATP content detection and the results after docking T₆ and penthiopyrad suggested that T₆ was a potential SDHI. These studies demonstrated that active compound T₆ could both inhibit the activity of SDH and affect the integrity of the cell membrane at the same time via a dual action mode, which is different from the mode of action of penthiopyrad. Thus, this study provides a new idea for a strategy to delay resistance and diversify the structures of SDHIs.

Impairment of electron transport chain and induction of apoptosis by chrysin nanoparticles targeting succinate-ubiquinone oxidoreductase in pancreatic and lung cancer cells

BACKGROUND

Flavonoids may help ameliorate the incidence of the major causes of tumor-related mortality, such as pancreatic ductal adenocarcinoma (PDAC) and lung cancer, which are predicted to steadily increase between 2020 to 2030. Here we compared the effect of chrysin and chrysin nanoparticles (CCNPs) with 5-fluorouracil (5-FLU) on the activity and expression of mitochondrial complex II (CII) to induce apoptosis in pancreatic (PANC-1) and lung (A549) cancer cells.

METHODS

Chrysin nanoparticles (CCNPs) were synthesized and characterized, and the IC₅₀ was evaluated in normal, PANC-1, and A549 cell lines using the MTT assay. The effect of chrysin and CCNPs on CΙΙ activity, superoxide dismutase activity, and mitochondria swelling were evaluated. Apoptosis was assessed using flow cytometry, and expression of the C and D subunits of SDH, sirtuin-3 (SIRT-3), and hypoxia-inducible factor (HIF-1α) was evaluated using RT-qPCR.

RESULTS

The IC₅₀ of CII subunit C and D binding to chrysin was determined and used to evaluate the effectiveness of treatment on the activity of SDH with ubiquinone oxidoreductase. Enzyme activity was significantly decreased (chrysin < CCNPs < 5-FLU and CCNPs < chrysin < 5-FLU, respectively), which was confirmed by the significant decrease of expression of SDH C and D, SIRT-3, and HIF-1α mRNA (CCNPs < chrysin < 5-FLU). There was also a significant increase in the apoptotic effects (CCNPs > chrysin > 5-FLU) in both PANC-1 and A549 cells and a significant increase in mitochondria swelling (CCNPs < chrysin < 5-FLU and CCNPs > chrysin > 5-FLU, respectively) than that in non-cancerous cells.

CONCLUSION

Treatment with CCNPs improved the effect of chrysin on succinate-ubiquinone oxidoreductase activity and expression and therefore has the potential as a more efficient formulation than chemotherapy to prevent metastasis and angiogenesis by targeting HIF-1α in PDAC and lung cancer.

Design, Synthesis, Inhibitory Activity, and Molecular Modeling of Novel Pyrazole-Furan/Thiophene Carboxamide Hybrids as Potential Fungicides Targeting Succinate Dehydrogenase

To discover new fungicides targeting succinate dehydrogenase (SDH), 36 new furan/thiophene carboxamides containing 4,5-dihydropyrazole rings were designed, synthesized, and characterized. The crystal structure of compound 5l was determined with the X-ray diffraction (XRD) of single crystals. The antifungal activity of these compounds was studied against Botrytis cinerea, Pyricularia oryzae, Erysiphe graminis, Physalospora piricola, and Penicillium digitatum. Bioassay results were that most compounds had obvious inhibitory activity at 20 μg/mL. Compounds 5j, 5k, and 5l possessed outstanding inhibitory activity against B. cinerea. Their EC₅₀ values were 0.540, 0.676, and 0.392 μg/mL, respectively. They owned better effects than fluxapyroxad (EC₅₀ = 0.791 μg/mL). In the meantime, the inhibitory activity of 16 compounds was evaluated against SDH. It turned out that these compounds displayed excellent activity. The IC₅₀ values of compounds 5j, 5k, and 5l reached 0.738, 0.873, and 0.506 μg/mL, respectively, whereas the IC₅₀ value of fluxapyroxad was 1.031 μg/mL. The results of molecular dynamics (MD) simulation showed that compound 5l possessed a stronger affinity to SDH than fluxapyroxad.

Novel Pyrazole Carboxamide Containing a Diarylamine Scaffold Potentially Targeting Fungal Succinate Dehydrogenase: Antifungal Activity and Mechanism of Action

Succinate dehydrogenase (SDH) is known as an ideal target for the development of novel fungicides. Over the years, a series of novel pyrazole carboxamides containing a diarylamine scaffold have been reported as potent SDH inhibitors (SDHIs) in our laboratory. Among them, compound SCU3038 (EC₅₀ = 0.016 mg/L) against in vitro Rhizoctonia solani was better than fluxapyroxad (EC₅₀ = 0.033 mg/L). However, its mechanism of action is still unclear. In this paper, in pot tests, bioactivity evaluation indicated that in vivo antifungal activity of compound SCU3038 (EC₅₀ = 0.95 mg/L) against R. solani was better than that of fluxapyroxad (EC₅₀ = 2.29 mg/L) and thifluzamide (EC₅₀ = 1.88 mg/L). In field trials, control efficacy of compound SCU3038 (74.10%) at 200 g ai/ha against rice sheath blight was better than that of thifluzamide (71.40%). Furthermore, target evaluation showed that compound SCU3038 could inhibit the fungal SDH from R. solani and fix in the binding site of SDH by molecular docking, thereby it could dissolve and reduce mitochondria of R. solani as observed by electron microscopy. In addition, transcriptome results showed that compound SCU3038 affected the TCA cycle pathway in mitochondria, and this was manifested in the downregulation of eight genes and upregulation of one gene. The most important phenomenon was the repressed expression of SDH2 confirmed by qRT-PCR. It was observed that compound SCU3038 was a potent SDHI, and these results afforded further research on pyrazole carboxamides.

Design, Synthesis, and Fungicidal Evaluation of Novel 1,3-Benzodioxole-Pyrimidine Derivatives as Potential Succinate Dehydrogenase Inhibitors

A series of novel 1,3-benzodioxole-pyrimidine derivatives were designed and synthesized. The in vitro bioassay indicated that compounds 4e, 4g, 4n, 5c, and 5e displayed excellent fungicidal activities against test fungal strains. Especially, in the in vitro experiments, 5c exhibited a broad spectrum of fungicidal activity against Botrytis cinerea, Rhizoctonia solani, Fusarium oxysporum, Alternaria solani, and Gibberella zeae with EC₅₀ values of 0.44, 6.96, 6.99, 0.07, and 0.57 mg/L, respectively, which were significantly more potent than those of positive control boscalid (EC₅₀: 5.02, >50, >50, 0.16, and 1.28 mg/L). In vivo testing on tomato fruits and leaves showed that 5c displayed considerable protective and curative efficacy against A. solani. Scanning electron microscopy analysis indicated that 5c possessed a strong ability to destroy the surface morphology of mycelia and seriously interfere with the growth of the fungal pathogen. In the in vitro enzyme inhibition assay, 5c exhibited pronounced succinate dehydrogenase (SDH) inhibitory activity with an IC₅₀ value of 3.41 μM, equivalent to that of boscalid (IC₅₀: 3.40 μM). In addition, fluorescence quenching experiment further confirmed the strong interaction of 5c with SDH. Through chiral resolution, 5c was separated into two enantiomers. Among them, (S)-5c exhibited stronger fungicidal activity (EC₅₀: 0.06 mg/L) and SDH inhibitory (2.92 μM) activity than the R-enantiomer (EC₅₀: 0.17 mg/L and SDH IC₅₀: 3.68 μM), which was in accordance with the molecular docking study (CDOCKER Interaction Energy for (R)-5c and (S)-5c: -28.23 and -29.98 kcal/mol, respectively). These results presented a promising lead for the discovery of novel SDHIs as antifungal pesticides.

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.

N-Heterocyclic carbene-catalysed homoenolate addition reaction to 3-cyano-2-imino-2H-chromenes: synthesis of C4-functionalized 2-amino-3-cyano-4H-chromene

A NHC-catalyzed homoenolate addition reaction between enals and iminochromenes to yields of a new type of C4-functionalized 2-amino-4H-chromenes has been developed.