Comprehensive evaluation of chiral pydiflumetofen from the perspective of reducing environmental risks

Stereoselective study on chiral fungicide metconazole in four kinds of fruits: Absolute configuration, SFC-MS/MS enantioseparation, degradation and risk assessment

Metconazole is a novel chiral fungicide with two chiral carbon atoms, but the research on its stereoselective behavior is limited. Therefore, the stereoselective behaviors of metconazole in four fruits, including grape, peach, pear and jujube, were summarized in this study. After determining the absolute configuration of metconazole stereoisomers, a chiral separation method through supercritical fluid chromatography/tandem triple quadrupole mass spectrometry was first developed, which combined an improved QuEChERS method obtained the recoveries of 71.6-113 % with RSD ≤ 19.8 %. The LOD and LOQ were 4.30-95.9 and 10.5-143.2 ng/kg, respectively. Different stereoselective and diastereoselective behaviors were observed in four fruits. Dietary risk assessments of rac-metconazole were performed in populations with different ages and genders. Both acute (RQa, 0.0124-0.140 %) and chronic (HQ, 0.0234-0.0794 %) intake risks were acceptable. The results of this study would contribute to more complete risk assessments of metconazole and provide data for chiral studies.

Enantioselective fate and risk assessment of chiral fungicide pydiflumetofen in rice-fish and wheat farming systems

Fungicides have been widely used for reducing the losses caused by plant diseases. Rice and wheat are the most basic food crops, and the potential risks after applying fungicides are worthy of attention. Especially rice-fish farming system is an ecological symbiosis system that is beneficial to both environmental and ecological protection. However, the application of pesticides will stress the ecosystem, and the pesticide residues in rice and fish would be transmitted along the food chain, which is harmful to human health. Here, the enantioselective behaviors of chiral pydiflumetofen in rice-fish and wheat farming systems were clarified. In the rice-fish farming system, pydiflumetofen enantiomers were preferentially attached to the plants, entering the paddy water and settling into the paddy soil, and then accumulating and dissipating in the fish. With the growth of rice, it was transported to rice fruits. The wheat farming system was similar. Enantioselective dissipation occurred in carp (Cyprinus carpio), brown rice and wheat soil, and S-(+)-pydiflumetofen was preferentially dissipated. In other words, R-(-)-pydiflumetofen showed higher concentrations, especially in carp, which meant R-(-)-pydiflumetofen was more easily accumulated in the environment, and posed a greater potential risk to the farming system. The pydiflumetofen residues in brown rice and wheat were lower than MRLs from the EFSA (0.02 mg/kg) and eCFR (0.3 mg/kg), respectively. What deserves attention is that the MRL of pydiflumetofen in fish is not clear. Meanwhile, pydiflumetofen in paddy soil and wheat soil had a persistent residual effect, and the risks could not be ignored. Combined with the previous research, developing S-(+)-pydiflumetofen products will help to reduce the dosage and reduce the risks to environment and people. This study evaluated the environmental fate and risk of chiral pydiflumetofen from the perspective of farming system, and would provide data support for its rational use and risk assessment.

Rational understanding of chiral fungicide penthiopyrad stereoselectivity: Bioactivity, aquatic toxicity and cytotoxicity

Penthiopyrad is a novel chiral succinate dehydrogenase inhibitor (SDHI) fungicide with two enantiomers. However, enantioselective information on the biological activity, nontarget organisms and human health risk of penthiopyrad is not comprehensive, which may cause inaccurate risk assessment. In this study, the enantioselective bioactivity to three kinds of phytopathogens (Rhizoctonia solani, Botrytis cinerea and Sclerotinia sclerotiorum) was first disclosed, and the antifungal activity of S-(+)-penthiopyrad was higher than that of R-(-)-penthiopyrad by 12-37 times. Moreover, its enantioselective toxicity to Raphidocelis subcapitata and Daphnia magna was also clarified, and the order of toxicity was S-(+)-penthiopyrad > rac-penthiopyrad >R-(-)-penthiopyrad, with 1.8- and 5.3-fold differences between the two enantiomers. Furthermore, the enantioselectivity of penthiopyrad on HepG2 cytotoxicity was studied. The data showed that the cytotoxicity of S-(+)-penthiopyrad was 1.8 times higher than that of R-(-)-penthiopyrad, and S-(+)-penthiopyrad had a stronger impact on cell proliferation, oxidative stress and lipid peroxidation. In summary, due to the enantioselectivity of the activity and toxicity of the chiral pesticide, the efficacy and risk evaluation of penthiopyrad should be considered at the enantiomer level.

Multiomics Sequencing and AlphaFold2 Analysis of the Stereoselective Behavior of Mefentrifluconazole for Bioactivity Improvement and Risk Reduction

As the first isopropanol chiral triazole fungicide, mefentrifluconazole has broad prospects for application. In this study, the stereoselective stability, bioactivity, fate, and biotoxicity were systematically investigated. Our results indicated that the stability of mefentrifluconazole enantiomers differed between environmental media, and they were stable in water and sediment in the dark. The bactericidal activity of R-mefentrifluconazole against the four target pathogens was 4.6-43 times higher than that of S-mefentrifluconazole. In the water-sediment system, S-mefentrifluconazole dissipated faster than R-mefentrifluconazole in water; however, its accumulation capacity was higher than that of R-mefentrifluconazole in sediment and zebrafish. S-Mefentrifluconazole induced more differentially expressed genes (DEGs) and differentially expressed proteins (DEPs) in zebrafish than did R-mefentrifluconazole. Multiomics sequencing results showed that S-mefentrifluconazole enhanced the antioxidant, detoxification, immune, and metabolic functions of zebrafish by interacting with related proteins. Based on AlphaFold2 modeling and molecular docking, mefentrifluconazole enantiomers had different binding modes with key target proteins in pathogens and zebrafish, which may be the main reason for the stereoselective differences in bioactivity and biotoxicity. Based on its excellent bioactivity and low biotoxicity, the R-enantiomer can be developed to improve the bioactivity and reduce the risk of mefentrifluconazole.

Stereoselective, Diastereoselective Dissipation and Risk Assessment of Chiral Metconazole in Soybean, Peanut, Cabbage, Celery, Tomato, and Soil

The stereoselective behaviors and dietary risks of metconazole (MZE) in soil and five vegetables were investigated. The results showed that there was species-specific stereoselective and diastereoselective dissipation, and the half-lives ranged from 0.69 to 8.17 days. cis-(+)-1S,5R-MZE was preferentially dissipated in soybean pods, cabbages, celeries, and tomatoes, which was contrary to soybean plants and soil. trans-(+)-1R,5R-MZE was preferentially dissipated in peanut plants, peanut shells, celeries, and tomatoes, while trans-(-)-1S,5S-MZE was preferentially dissipated in soybean plants. cis-MZE was preferentially dissipated in the test vegetables and soil, except celery. The stereoisomeric excess changes were higher than 10%, indicating that the stereoselectivity and diastereoselectivity should be considered in the risk assessment of MZE in soybean plants, pods, and peanut plants. The acute and chronic dietary intake risks of rac-MZE for different groups of people were acceptable. The preferentially dissipated and high activity cis-(+)-1S,5R-MZE with lower toxicity might be suitable for application as monocase.

Discovery of Benzothiazolylpyrazole-4-Carboxamides as Potent Succinate Dehydrogenase Inhibitors through Active Fragment Exchange and Link Approach

Succinate dehydrogenase (SDH) is an attractive target for developing green fungicides to manage agricultural pathogens in modern agriculture research. Herein, in this work, we report the discovery of benzothiazolylpyrazole-4-carboxamides I-III as potent SDH inhibitors using active fragment exchange and link approach. The results of the fungicidal activity assays showed that some of the synthesized compounds exhibited excellent inhibition against the tested fungi. Systematic structure-activity relationship studies led to the discovery of compound Ip, N-(1-((4,6-difluorobenzo[d]thiazol-2-yl)thio)propan-2-yl)-3-(difluoromethyl)-N-methoxy-1-methyl-1H-pyrazole-4-carboxamide, which showed higher fungicidal activity against Fusarium graminearum Schw (EC50 = 0.93 μg/mL) than the commercial fungicides thifluzamide (EC50 > 50 μg/mL) and boscalid (EC50 > 50 μg/mL). The molecular simulation studies suggested that hydrophobic interactions were the primary driving forces between ligands and SDH. Promisingly, we found that Ip could stimulate the growth of wheat seedlings and Arabidopsis thaliana and increase the biomass of the treated plants. Preliminary studies on the plant growth promoter mechanism of Ip indicated that it could increase nitrate reductase activity in planta, that, in turn, stimulates the growth of plants.

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.

Development and Validation of a HTS Platform for the Discovery of New Antifungal Agents against Four Relevant Fungal Phytopathogens

Fungal phytopathogens are the major agents responsible for causing severe damage to and losses in agricultural crops worldwide. Botrytis cinerea, Colletotrichum acutatum, Fusarium proliferatum, and Magnaporthe grisea are included in the top ten fungal phytopathogens that impose important plant diseases on a broad range of crops. Microbial natural products can be an attractive alternative for the biological control of phytopathogens. The objective of this work was to develop and validate a High-throughput Screening (HTS) platform to evaluate the antifungal potential of chemicals and natural products against these four important plant pathogens. Several experiments were performed to establish the optimal assay conditions that provide the best reproducibility and robustness. For this purpose, we have evaluated two media formulations (SDB and RPMI-1640), several inoculum concentrations (1 × 106, 5 × 105 and 5 × 106 conidia/mL), the germination curves for each strain, each strain's tolerance to dimethyl sulfoxide (DMSO), and the Dose Response Curves (DRC) of the antifungal control (Amphotericin B). The assays were performed in 96-well plate format, where absorbance at 620 nm was measured before and after incubation to evaluate growth inhibition, and fluorescence intensity at 570 nm excitation and 615 nm emission was monitored after resazurin addition for cell viability evaluation. Quality control parameters (RZ' Factors and Signal to Background (S/B) ratios) were determined for each assay batch. The assay conditions were finally validated by titrating 40 known relevant antifungal agents and testing 2400 microbial natural product extracts from the MEDINA Library through both HTS agar-based and HTS microdilution-based set-ups on the four phytopathogens.

Stereoselective analysis of chiral succinate dehydrogenase inhibitors (SDHIs) in foods of plant origin and animal origin by supercritical fluid chromatography-tandem mass spectrometry (SFC-MS/MS)

The stereoisomers of chiral SDHIs were prepared using Autoprep HPLC and chiral columns. The method of combining theoretical calculation with experimental determination was used to confirm the absolute configuration of stereoisomer. SFC-MS/MS and four kinds of chiral columns were used to separate the eight chiral SDHIs, and they could be separated simultaneously using OD-3 column in 6.5 min. The integrated QuEChERS strategy was used to analyse the chiral SDHIs in foods of plant and animal origin, and the average recoveries ranged from 71 % to 119 % with RSD ≤ 18 %, and the LOQ was 1 ng/g. There were 99.2 % and 63.6 % matrix effects were in the range of 0.8-1.2 in foods of plant and animal origin, respectively, showing weak matrix effects. The study provided methods for monitoring chiral SDHIs stereoisomers residues, which were crucial for stereoselective evaluations and improving risk assessments.

Systemic enantioselectivity study of penthiopyrad: enantioselective bioactivity, acute toxicity, degradation and influence on tomato

BACKGROUND

In order to promote the green development of agriculture, it is important to study the enantioselective effect of chiral pesticides. The bioactivity of the chiral fungicide penthiopyrad (PEN) racemate and enantiomers against phytopathogens, toxicity to non-target organisms, effect on tomato fruit growth and maturation, and environmental fate in tomato cultivation were evaluated at an enantioselective level in this study.

RESULTS

The results indicated that at the same efficacy, the optically pure S-(+)-PEN could lower the dosage of racemate by 20-96%. The S-enantiomer had low toxicity to earthworms. Besides, the S-(+)-PEN did not cause significant abiotic stress to the tomato and increased fruit fresh weight and size via modulating the contents of plant hormones. However, the content of hydrogen peroxide (H₂ O₂ ), superoxide (O₂ ^- ) and malondialdehyde in the R-enantiomer treatment group was significantly higher than the control group. The effect of the racemate on tomato fruit was between the enantiomers. Furthermore, compared to R-(-)-PEN and racemate, the S-enantiomer degraded more quickly in tomato fruit, leaves, and soil, reducing the danger of human exposure.

CONCLUSION

The S-enantiomer is highly effective and less toxic. The development of enantiomer pure S-(+)-PEN products might be an efficient and low-risk strategy. The results lay the foundation for comprehensive evaluation and proper application of PEN. © 2023 Society of Chemical Industry.

Comprehensive evaluation of novel fungicide benzovindiflupyr at the enantiomeric level: Bioactivity, toxicity, mechanism, and dissipation behavior

Racemates in the environment can lead to inaccurate risk assessment. To obtain the enantiomeric level information of benzovindiflupyr for accurate risk assessment, the absolute configuration of benzovindiflupyr was first confirmed, and the enantioseparation method was developed by supercritical fluid chromatography tandem mass spectrometry. The enantioselectivity for bioactivity and toxicity was investigated, and the mechanism was explored by molecular docking and detecting succinate dehydrogenase (SDH) activity and content of succinate acid. 1S,4R-(-)-benzovindiflupyr was identified as the most active against the six targeted phytopathogens, which showed higher 1.7-54.5 times than 1R,4S-(+)-benzovindiflupyr. Additionally, 1S,4R-(-)-benzovindiflupyr (LD₅₀: 21.54 μg L^-1) was 103.7 times more toxic than 1R,4S-(+)-benzovindiflupyr against Daphnia magna. 1S,4R-(-)-benzovindiflupyr had a stronger affinity for SDH and significantly inhibited SDH activity, resulting in an increase in succinate acid in the tricarboxylic acid cycle, while its downstream products, fumaric and L-malic acid were significantly reduced. Moreover, the dissipation behavior of benzovindiflupyr on three vegetables was evaluated. 1S,4R-(-)-benzovindiflupyr was preferentially degraded in tomato, but opposite in leaves. The enantioselectivity in pepper and cucumber leaves was the same as in tomato, while there was no enantioselectivity in pepper and cucumber. The study provides a basis for accurate risk assessment and the development of high-effective and low-risk fungicides.

Comprehensive evaluation of chiral penflufen metabolite (penflufen-3-hydroxy-butyl): Identification, synthesis, enantioseparation, toxicity and enantioselective metabolism

Identification and evaluations of pesticide metabolites are necessary for risk assessment and toxicological research. In this study, the metabolites of penflufen (a widely used chiral pesticide) in rat liver microsomes were identified using liquid chromatography Q-Exactive Plus mass spectrometry. In total, 17 penflufen metabolites were identified, and most of them were hydroxylation products, which were generated by oxygenation at different candidate sites of penflufen. The relative abundance of metabolite M12 (penflufen-3-hydroxy-butyl, 32 %) was the largest, followed by M8 (15.6 %) and M2 (12.8 %). The major metabolite penflufen-3-hydroxy-butyl was first synthesized by 11 reactions with a 99.73 % purity. The absolute configuration of M12 enantiomers were confirmed after preparing enantiomers, and establishing the enantioseparation method. The M12 enantiomers toxicity to Danio rerio (LC₅₀, >10 mg/L) and four kinds of phytopathogens (EC₅₀, 148-34969 mg/L) were significantly lower than parents (LC₅₀, 0.449-24.3 mg/L; EC₅₀, 0.027-92.0 mg/L). In rat liver microsomes, approximately 40-47 % of the penflufen enantiomers were metabolized to M12 enantiomers, and R-penflufen was preferentially metabolized. The generation concentrations of S-M12 were higher than R-M12 after 10 min, and the metabolic half-lives of R-M12 (29.0-32.5 min) were shorter than S-M12 (35.2-38.1 min), and were approximately 4 times longer than parent penflufen enantiomers (4.5-9.5 min). Simultaneously, the generated contents (relative contents) of M8 (27.1-57 %) and M10 (2.22-8.36 %) from S-penflufen were lower than those from R-penflufen (M8, 24.7-92.4 %; M10, 27.4-69.5 %). The enantioselective evaluations of M12, M10 and M8 deserve further study. These findings were helpful in understanding the fate and risks of chiral penflufen.

Enantioselective Degradation and Bioactivity Mechanism of a New Chiral Fungicide Fluindapyr in Paddy Ecosystems

Fluindapyr is a novel chiral succinate dehydrogenase inhibitor used to control fungal diseases. The enantioselective effects of fluindapyr in paddy ecosystems are unknown. We developed a new chiral determination method of fluindapyr using ultrahigh performance liquid chromatography tandem mass spectrometry. The absolute configuration of the fluindapyr enantiomers was identified by an electron circular dichroism model. A new husk-based biochar material was used to optimize and establish a QuEchERs method for paddy soil determination. Under anaerobic conditions, the half-lives of R-fluindapyr and S-fluindapyr in paddy soil were 69.6 and 101.8 days, respectively. R-fluindapyr degraded more rapidly than S-fluindapyr. S-fluindapyr was 87.8 times more active against Rhizoctonia solani than R-fluindapyr. The enantioselective bioactivity mechanism was illustrated by molecular docking between the fluindapyr enantiomers and SDH of R. solani. The binding powers of R-fluindapyr and S-fluindapyr to proteins were -32.12 and - 42.91 kcal/mol, respectively. This study reports the stereoselectivity of fluindapyr about determination, degradation, bioactivity, and its mechanism. It provides a foundation for an in-depth study of fluindapyr at the enantiomer level.

Dissipation and Dietary Risk Assessment of Pydiflumetofen Residues in Soybean

In this study, the quick, easy, cheap, effective, rugged, and safe (QuEChERS) method, combined with high-performance liquid chromatography−tandem mass spectrometry, was chosen for detecting pydiflumetofen residues in soybean plants, soybeans and soil, and assessing the risk of short- and long-term dietary intake. Pydiflumetofen concentrations ranging from 0.001−0.5 mg/L exhibited good linearity (r > 0.997). At varying doses, the average pydiflumetofen recovery rates and relative standard deviations among soybean plants, soybeans, and soil ranged from 83.9 ± 1.1% to 99.5 ± 3.3% and from 0.77 to 7.77%, respectively. The sensitivity, accuracy, and precision of the chosen methodology met the requirements of pesticide residue analysis. The results of the degradation dynamics test showed that the half-life of pydiflumetofen (t1/2) in soybean plants and in soil were 3.6 to 5.7 and from 7.9 to 25.7 d, respectively. Assessment of the concentration of pydiflumetofen residues in soybeans revealed acute and chronic dietary exposure risks of 0.06 and 7.54%, respectively. As these values are very low, pydiflumetofen residues in soybeans present an acceptable risk to public health. The results of this study will help to guide the practical application of pydiflumetofen and minimize the environmental risks associated with its use.

Antifungal Peptide P852 Controls Fusarium Wilt in Faba Bean (Viciafaba L.) by Promoting Antioxidant Defense and Isoquinoline Alkaloid, Betaine, and Arginine Biosyntheses

Green pesticides are highly desirable, as they are environmentally friendly and efficient. In this study, the antifungal peptide P852 was employed to suppress Fusarium wilt in the Faba bean. The disease index and a range of physiological and metabolomic analyses were performed to explore the interactions between P852 and the fungal disease. The incidence and disease index of Fusarium wilt were substantially decreased in diseased Faba beans that were treated with two different concentrations of P852 in both the climate chamber and field trial. For the first time, P852 exhibited potent antifungal effects on Fusarium in an open field condition. To explore the mechanisms that underlie P852′s antifungal effects, P852 treatment was found to significantly enhance antioxidant enzyme capacities including guaiacol peroxidase (POD), superoxide dismutase (SOD), catalase (CAT), and the activities of antifungal enzymes including chitinase and β-1,3-glucanase, as well as plant dry and fresh weights, and chlorophyll content compared to the control group (p ≤ 0.05). Metabolomics analysis of the diseased Faba bean treated with P852 showed changes in the TCA cycle, biological pathways, and many primary and secondary metabolites. The Faba bean treated with a low concentration of P852 (1 μg/mL, IC₅₀) led to upregulated arginine and isoquinoline alkaloid biosynthesis, whereas those treated with a high concentration of P852 (10 μg/mL, MFC) exhibited enhanced betaine and arginine accumulation. Taken together, these findings suggest that P852 induces plant tolerance under Fusarium attack by enhancing the activities of antioxidant and antifungal enzymes, and restoring plant growth and development.

Stereoselective bioactivity, toxicity and degradation of novel fungicide sedaxane with four enantiomers under rice-wheat rotation mode

Sedaxane was a novel chiral fungicide that contains four enantiomers. Unfortunately, the stereoselective bioactivity, toxicity and degradation of sedaxane have not been clarified. In this study, we identified the absolute configuration of the four sedaxane enantiomers at first time. The stereoselective bioactivity toward three wheat and rice pathogens, stereoselective acute toxicity to aquatic organisms (Selenastrum capricornutum and Daphnia magna), and stereoselective degradation of sedaxane were studied. The 1 S,2S-(+)-sedaxane possessed 5.4-7.3 times greater bioactivity than 1 R,2R-(-)-sedaxane to Rhizoctonia solani and Rhizoctonia cerealis. Contrarily, the 1 R,2S-(+)-sedaxane had 4.2 times greater activity than 1 S,2S-(+)-sedaxane against Fusarium graminearum. The 1 R,2R-(-)-sedaxane had 2.8 times greater toxicity than 1 S,2S-(+)-sedaxane to S. capricornutum. The chiral determination method used ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The recovery of sedaxane stereoisomers ranged from 83.1 % to 98.2 %, with RSDs (Relative standard deviations) of 1.2 %- 8.4 %. The trans-sedaxane existed stereoselective degradation phenomenon in the rice-wheat rotation mode, and 1 S,2S-(+)-sedaxane was preferentially degraded. Our results would provide scientific importance and practical guidance to the safety evaluation of chiral pesticides.