Enantioseparation and stereoselective dissipation of the novel chiral fungicide pydiflumetofen by ultra-high-performance liquid chromatography tandem mass spectrometry

Stereoselective Bioactivity and Action Mechanism of the Fungicide Isopyrazam

Understanding the stereoselective bioactivity of chiral pesticides is crucial for accurately evaluating their effectiveness and optimizing their use. Isopyrazam, a widely used chiral SDHI fungicide, has been studied for its antifungal activity only at the racemic level. Therefore, to clarify the highly bioactive isomers, the stereoselective bioactivity of isopyrazam isomers against four typical phytopathogens was studied for the first time. The bioactivity ranking of the isomers was trans-1S,4R,9R-(+)-isopyrazam > cis-1R,4S,9R-(+)-isopyrazam > trans-1R,4S,9S-(-)-isopyrazam > cis-1S,4R,9S-(-)-isopyrazam. SDH activity was assessed by molecular docking simulation and actual detection to confirm the reasons for stereoselective bioactivity. The results suggest that the stereoselective bioactivity of isopyrazam is largely dependent on the differential binding ability of each isomer to the SDH ubiquitin-binding site, located within a cavity formed by the iron-sulfur subunit, the cytochrome b560 subunit, and the cytochrome b small subunit. Moreover, to reveal the molecular mechanism of isopyrazam stereoselectively affecting mycelial growth, the contents of succinic acid, fumaric acid, and ATP were measured. Furthermore, by measuring exospore polysaccharides and oxalic acid content, it was determined that 1S,4R,9R-(+)- and 1R,4S,9R-(+)-isopyrazam more strongly inhibited the ability of Sclerotinia sclerotiorum to infect plants. The findings provided essential data for the development of high-efficiency isopyrazam fungicides and offered a methodological reference for analyzing the enantioselective activity mechanism of SDHI fungicides.

Various amino acid substitutions in succinate dehydrogenase complex regulating differential resistance to pydiflumetofen in Magnaporthe oryzae

Rice blast, caused by Magnaporthe oryzae, is a devastating fungal disease worldwide. Pydiflumetofen (Pyd) is a new succinate dehydrogenase inhibitor (SDHI) that exhibited anti-fungal activity against M. oryzae. However, control of rice blast by Pyd and risk of resistance to Pyd are not well studied in this pathogen. The baseline sensitivity of 109 M. oryzae strains to Pyd was determined using mycelial growth rate assay, with EC50 values ranging from 0.291 to 2.1313 μg/mL, and an average EC50 value of 1.1005 ± 0.3727 μg/mL. Totally 28 Pyd-resistant (PydR) mutants with 15 genotypes of point mutations in succinate dehydrogenase (SDH) complex were obtained, and the resistance level could be divided into three categories of very high resistance (VHR), high resistance (HR) and moderate resistance (MR) with the resistance factors (RFs) of >1000, 105.74-986.13 and 81.92-99.48, respectively. Molecular docking revealed that all 15 mutations decreased the binding-force score for the affinity between Pyd and target subunits, which further confirmed that these 15 genotypes of point mutations were responsible for the resistance to Pyd in M. oryzae. There was positive cross resistance between Pyd and other SDHIs, such as fluxapyroxad, penflufen or carboxin, while there was no cross-resistance between Pyd and carbendazim, prochloraz or azoxystrobin in M. oryzae, however, PydR mutants with SdhBP198Q, SdhCL66F or SdhCL66R genotype were still sensitive to the other 3 SDHIs, indicating lack of cross resistance. The results of fitness study revealed that the point mutations in MoSdhB/C/D genes might reduce the hyphae growth and sporulation, but could improve the pathogenicity in M. oryzae. Taken together, the risk of resistance to Pyd might be moderate to high, and it should be used as tank-mixtures with other classes of fungicides to delay resistance development when it is used for the control of rice blast in the field.

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.

Nano-selenium repaired the damage caused by fungicides on strawberry flavor quality and antioxidant capacity by regulating ABA biosynthesis and ripening-related transcription factors

Recently, studies have shown that pesticides may have adverse effects on the flavor quality of the fruits, but there is still a lack of appropriate methods to repair the damage. This study investigated the effects and mechanism of applying the emerging material, nano‑selenium, and two fungicides (Boscalid and Pydiflumetofen) alone or together on the flavor quality and antioxidant capacity of strawberries. The results showed that the two fungicides had a negative impact on strawberry color, flavor, antioxidant capacity and different enzymatic systems. The color damage was mainly attributed to the impact on anthocyanin content. Nano‑selenium alleviated the quality losses by increasing sugar-acid ratio, volatiles, anthocyanin levels, enzyme activities and DPPH scavenging ability and reducing ROS levels. Results also showed that these damage and repair processes were related to the regulation of flavor and ripening related transcription factors (including FaRIF, FaSnRK1, FaMYB10, FaMYB1, FaSnRK2.6 and FaABI1), the upregulation of genes on sugar-acid, volatile, and anthocyanin synthesis pathways, as well as the increase of sucrose and ABA signaling molecules. In addition, the application of nano-Se supplemented the selenium content in fruits, and was harmless to human health. This information is crucial for revealing the mechanisms of flavor damage caused by pesticides to strawberry and the repaired of nano‑selenium, and broadens the researching and applying of nano‑selenium in repairing the damage caused by pesticides.

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.

Simultaneous separation and determination of several chiral antidepressants and their enantiomers in wastewater by online heart-cutting two-dimensional liquid chromatography

A novel method for simultaneous separation and detection of the racemates and the enantiomers of common chiral antidepressants in wastewater matrix was developed by online heart-cutting two-dimensional liquid chromatography (2D-LC) coupled to solid-phase extraction (SPE). Screening of chiral stationary phases (CSPs) and chromatographic conditions was investigated for complete enantioseparation to be compatible with RP-HPLC in 1st D-LC. Using methanol-0.1 % (v/v) ammonia solution as mobile phase, a 2D-LC system was configured by reversed mode with a combination of C18 column and the serially CPS columns as 2D-LC stationary phases respectively. The target analytes could achieve satisfactory transformation between 2D-LCs with transfer rate of 90.57-98.58 %. By means of freeze-drying and SPE, three antidepressants in wastewater were greatly preconcentrated under the optimized conditions, improving the method performance. The racemates and the enantiomers of mirtazapine, bupropion and fluoxetine exhibited good linearity in the range of 0.10-30.00 ng/mL (R2≥0.9986), and LODs and LOQs ranged in 0.0183-0.0549 ng/mL and 0.0661-0.1831 ng/mL, respectively. By this way, the method was successfully applied to simultaneous determination of the racemates and the enantiomers of mirtazapine, bupropion and fluoxetine in wastewater samples. Among them, three samples contained bupropion at level of 0.401-0.822 ng/mL, and mirtazapine at level of 0.328 and fluoxetine at level of 0.381 ng/mL were detected respectively in the other two samples. The enantiomers were at level of 0.140-0.189 ng/mL for mirtazapine, 0.182-0.419 ng/mL for bupropion and 0.179-0.204 ng/mL for fluoxetine, respectively. The proposed method providing an efficient approach to monitoring chiral drugs and their enantiomers in wastewater, facilitating to pollution assessment of chiral drugs in the environment and regional survey of illicit abuse in drug control.

Enantioselective uptake, translocation, and biotransformation of pydiflumetofen in wheat (Triticum aestivum L.): Insights from chiral profiling and molecular simulation

Pydiflumetofen (PYD), a highly effective and broad-spectrum fungicide, is commonly employed for the control of fungal diseases. In this study, the uptake, translocation, and biotransformation of PYD by wheat (Triticum aestivum L.) were firstly investigated at a chiral level. The findings revealed that the residue concentration of R-PYD in wheat was higher than that of S-PYD, because of its higher uptake rate (k1 = 0.0421 h-1) and lower elimination rate (k2 = 0.0459 h-1). Additionally, R-PYD exhibited higher root bioconcentration factors and translocation factors compared with S-enantiomer, indicating R-PYD was more easily accumulating in roots and translocating to shoots. Furthermore, a total of 9 metabolites, including hydroxylated, demethylated, demethoxylated, dechlorinated, hydrolyzed, and glycosylated-conjugated products, were detected qualitatively in wheat roots or shoots. Symplastic pathway-mediated uptake, which predominantly relied on aquaporins and anion channels, was confirmed by root adsorption and inhibition experiments, without displaying any enantioselective effect. Molecular simulations demonstrated that R-PYD exhibited stronger binding affinity with TaLTP 1.1 with a lower grid score (-6.79 kcal/mol), whereas weaker interaction with the metabolic enzyme (CYP71C6v1) compared to the S-enantiomer. These findings highlight the significance of plant biomacromolecules in the enantioselective bioaccumulation and biotransformation processes. Importantly, a combination of experimental and theoretical evidence provide a comprehensive understanding of the fate of chiral pesticides in plants from an enantioselective perspective.

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.

Assessment of the Hydrolysis of Pydiflumetofen and Its Degradation Characteristics in Agricultural Soils

Pydiflumetofen is a potent fungicide that effectively inhibits pathogenic fungal growth by regulating succinate dehydrogenase activity. It effectively prevents and treats various fungal diseases, including leaf spot, powdery mildew, grey mold, bakanae, scab, and sheath blight. Pydiflumetofen's hydrolytic and degradation properties were investigated indoors in four distinct soil types (phaeozems, lixisols, ferrosols, and plinthosols) to assess its risks in aquatic and soil environments. The effect of soil physicochemical properties and external environmental conditions on its degradation was also explored. Hydrolysis experiments found that pydiflumetofen's hydrolysis rate decreased with increasing concentration, regardless of the initial concentration. Furthermore, an increasing temperature significantly enhances the hydrolysis rate, with neutral conditions having higher degradation rates than acidic and alkaline conditions. Pydiflumetofen showed a degradation half-life of 10.79-24.82 days and a degradation rate of 0.0276-0.0642 in different soils. Phaeozems soils had the fastest degradation, while ferrosols soils had the slowest. Sterilization significantly reduced its soil degradation rate and extended its half-life, which confirmed that microorganisms were the primary cause. Therefore, when using pydiflumetofen in agricultural production activities, the characteristics of water bodies, soil, and environmental factors must be considered, while minimizing the emissions and environmental impact.

Isolation of Sphingomonas sp. AJ-1 and its enantioselective S-methylation of the triazole fungicide prothioconazole

Prothioconazole is a widely used chiral triazole fungicide, and its residue pollution has attracted wide attention in recent years. However, little is known about microbial metabolic processes of prothioconazole enantiomers. In this study, a prothioconazole-degrading strain, Sphingomonas sp. AJ-1, was isolated from activated sludge. The optimal temperature and pH for prothioconazole degradation by strain AJ-1 were 30 °C and 6.0, respectively, and the degradation rate of prothioconazole by strain AJ-1 was negatively correlated with the initial concentration. When supplemented with additional carbon source, the degradation rates of 10 mg/L (Rac)-/(S)-/(R)-prothioconazole by strain AJ-1 were 76.0 %, 100.0 % and 64.8 % within 6 d, respectively. The CS bond of prothioconazole was methylated to produce (S)-/(R)-prothioconazole-S-methyl by strain AJ-1, but the degradation rate of prothioconazole by strain AJ-1 with (S)-enantiomer was 2.54-fold of that with (R)-enantiomer. Moreover, the toxicity of (Rac)-prothioconazole-S-methyl was 5.57 times lower than that of (Rac)-prothioconazole to Pseudokirchneriella subcapitata. The results showed that strain AJ-1 had obvious enantioselective metabolism for prothioconazole, and this metabolism was a detoxification process. This study provides new insights into the enantioselective metabolism of the chiral fungicide prothioconazole in microorganisms.

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.

Effect of formulation on the indoxacarb and lufenuron dissipation in maize and risk assessment

The supervised field trials were conducted in maize crops using nano-microemulsion (NM) and a commercial formulation of indoxacarb and lufenuron to evaluate the effect of nano-formulation on the dissipation pattern. A modified QuEChERS (Quick Easy Cheap Effective Rugged and Safe)-UPLC-MS/MS (ultra-performance liquid chromatography tandem mass spectrometry) method was utilized for sample analysis. Results showed that the initial deposits of indoxacarb and lufenuron in plants using nano-microemulsion were 0.98 mg/kg and 8.18 mg/kg at recommended dosage, while using the commercial formulation, they were 0.85 mg/kg and 5.53 mg/kg, respectively. Moreover, half-life (t_1/2) values of using nano-microemulsion were 1.25 days and 2.51 days, which were shorter than indoxacarb (1.87 days) and lufenuron (3.00 days) from the commercial formulation, suggesting that pesticide formulations have a moderate impact on the initial deposit and dissipation rate. The terminal residue test showed that indoxacarb and lufenuron residues in maize grain and maize straw were below the available maximum residue limit (MRL, 0.01 mg/kg), suggesting 2% indoxacarb NM and 5% lufenuron NM are safe to use under the recommended dosage. The risk quotient value (RQ of indoxacarb and lufenuron equal to 17.7% and 2.4%, respectively) also revealed an acceptable risk for human consumption. These findings provide scientific evidence of the proper application of 2% indoxacarb NM and 5% lufenuron NM on maize crops.

Comprehensive study of pydiflumetofen in Danio rerio: Enantioselective insight into the toxic mechanism and fate

Pydiflumetofen (PYD) is primarily used to control fungal disease. The potential risks posed by PYD enantiomers to the aquatic ecosystem are currently unclear. In this study, the enantioselective toxicity and fate of PYD in Danio rerio were investigated, and the enantioselective toxic mechanism and metabolic pathway were explored. The acute toxicity of R-PYD was 10.7-14.7-fold than that of S-PYD against Danio rerio embryos, larvae, and adults. Meanwhile, R-PYD presented a stronger effect on embryo hatching and abnormalities, adult tissue damage and oxidative stress. R-PYD inhibited the succinate dehydrogenase (SDH) activity more than S-PYD because of its better interaction with SDH with a lower binding free energy (-59.35 kcal/mol), explaining the mechanism of enantioselective toxicity. Remarkable enantioselectivity was observed in uptake, distribution, and elimination. R-PYD showed preferential uptake with the higher uptake rate constants and slow metabolism with a longer half-life, resulting in the bioaccumulation of R-PYD with higher BCF_k (7.37 at 0.05 mg/L and 14.69 at 0.2 mg/L). Besides, muscle is an important tissue for PYD accumulation, existing potential food risk. Eleven PYD metabolites were qualitatively identified, and the metabolic pathway was proposed, including hydroxylation, N-demethylation, demethoxylation, hydrolysation (phase Ⅰ), and acetylation and glucuronidation (phase Ⅱ). The predicted toxicity of the metabolite indicated that several highly toxic metabolites need to be considered in the future. This study provides a new perspective for evaluating the ecological and human health risks of chiral pesticides.

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

The spatial structures of chiral pesticide enantiomers can affect their activity, toxicity and behavior, thereby altering exposure risk. Identifying enantiomer differences and developing high-efficiency green enantiopure pesticide is an important strategy for reducing the negative effects of pesticides. In this study, after confirming the absolute configuration of pydiflumetofen enantiomers, fungicidal activity evaluation indicated that the activity of S-(+)-pydiflumetofen was 81.3-421 times higher than R-(-)-pydiflumetofen on three kinds of phytopathogens that control Fusarium wilt (Fusarium spp.), Alternaria rot (Alternaria alternata) and Southern blight (Sclerotinia rolfsii), which might be caused by the stronger binding ability of S-(+)-pydiflumetofen with the active site of the target protein. The coexistence of R-(-)-pydiflumetofen would enhance the toxicity of S-(+)-pydiflumetofen on zebrafish through synergistic effect. Low-activity R-(-)-pydiflumetofen was preferentially dissipated in soybean, soybean plants, cabbage and celery, which was opposite in soil. The persistence of S-(+)-pydiflumetofen in crops and degradability in soil were advantageous for pesticide effects and environmental protection. Based on the maximum residue limit (MRL) and hazard quotient (HQ), the dietary risks were determined to be acceptable for all crops. Thus, developing enantiopure S-(+)-pydiflumetofen products might be a high-efficiency and low-risk strategy, and more studies should be conducted in this aspect.

A Novel Enantioseparation Method and Enantioselective Dissipation of Novaluron in Tomatoes Using Ultrahigh-Performance Liquid Chromatography Tandem Mass Spectrometry via a Box-Behnken Design

Enantioseparation parameters of novaluron were optimized on a Chiralpak IG-3 column by ultrahigh-performance liquid chromatography tandem mass spectrometry via response surface methodology. The absolute configuration and elution order were identified as R-(+)-novaluron and S-(-)-novaluron by polarimetry and X-ray diffraction. A modified QuEChERS method was developed for enantioselective determination of novaluron in eight food and environmental samples. Under optimal conditions, the mean recoveries of the novaluron enantiomers in the eight matrices were 74.4-108.1% with intraday relative standard deviations (RSDs) of 0.3-9.7% and interday RSDs of 0.1-4.1%. Enantioselective dissipation was observed in tomatoes. The dissipation of S-(-)-novaluron was faster than that of R-(+)-novaluron with a half-life of 7.1 and 7.9 days, and the enantiomer fraction value changed from 0.49 to 0.53 in 21 days. An effective method for monitoring novaluron enantiomer residues in food and the environment was established for the first time and had been successfully applied to real samples. This study is of great significance for strengthening the risk assessment and supervision level of chiral pesticides.

Enantioselective Metabolic Mechanism and Metabolism Pathway of Pydiflumetofen in Rat Liver Microsomes: In Vitro and In Silico Study

Pydiflumetofen (PYD) has been used worldwide. However, the enantioselective fate of PYD within mammals is not clear. Thus, the enantioselective metabolism and its potential mechanisms of PYD were explored via in vitro and in silico. Consistent results were observed between metabolism and enzyme kinetics experiments, with S-PYD metabolizing faster than R-PYD in rat liver microsomes. Moreover, CYP3A1 and carboxylesterase 1 were found to be major enzymes participating in the metabolism of PYD. Based on the computational results, S-PYD bound with CYP3A1 and carboxylesterase 1 more tightly with lower binding free energy than R-PYD, explaining the mechanism of enantioselective metabolism. Nine phase I metabolites of PYD were identified, and metabolic pathways of PYD were speculated. This study is the first to clarify the metabolism of PYD in mammals, and further research to evaluate the toxicological implications of these metabolites will help in assessing the risk of PYD.

Enantioselective separation, analysis and stereoselective dissipation of the chiral pesticide cloquintocet-mexyl using a modified QuEChERS method by high-performance liquid chromatography tandem mass spectrometry

An efficient and novel enantioseparation method was successfully developed and validated to quantify the enantiomers of cloquintocet-mexyl in soil, millet, enoki mushroom, oilseed rape, and watermelon using a modified QuEChERS technique combined with HPLC-MS/MS. This method showed reliable performances for determining both enantiomers of cloquintocet-mexyl in all five matrices. The limits of detection and limits of quantification were in the range of 0.06-0.15 μg kg^-1 and 0.2-0.5 μg kg^-1, respectively. Good linearities were obtained with correlation coefficients ≥0.9954. The mean recoveries were between 84.1% and 111.5%, with relative standard deviations ranging from 1.2% to 9.8% at three spiked levels. Additionally, the study of stereoselective dissipation of cloquintocet-mexyl in soil indicated that (R)-cloquintocet-mexyl was preferentially degraded. This work is the first to describe a chiral analytical method and enantioselective behavior of cloquintocet-mexyl and provide basic data for the risk evaluation of cloquintocet-mexyl in food and environmental safety.

Systemic Stereoselectivity Study of Fenobucarb: Environmental Behaviors in Greenhouse Vegetables, Fruits, Earthworms, and Soils and Its Cytotoxicity

Fenobucarb (2-sec-butylphenyl methylcarbamate, BPMC) is a potent carbamate pesticide with high insecticidal activity. In this study, the enantioselective accumulation of BPMC in earthworms (Eisenia foetida) and dissipation in cabbage, Chinese cabbage, strawberry, and soils were investigated. The samples were prepared using the QuEChERS method and analyzed using fast and sensitive chiral high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) analysis. The stereoselective accumulation of BPMC enantiomers revealed that S-(+)-BPMC was preferentially accumulated in earthworms rather than its antipode. However, the dissipation studies showed that S-(+)-BPMC degraded faster than the R-(-)-isomer in cabbage, Chinese cabbage, strawberry, and soils. Furthermore, the cytotoxic effect of BPMC enantiomers toward PC12 and N9 neuronal, A549 lung cancer, and MRC5 lung fibroblast cell lines was evaluated using an 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Compared with R-(-)- and rac-isomers, S-(+)-BPMC exhibited lower cytotoxicity in neuronal cells and a weaker proliferating effect on lung cancer and lung fibroblast cells. Altogether, the findings suggest the use of the pure S-(+)-enantiomer in agricultural management rather than the use of the racemate or the R-(-)-isomer, which might reduce the environmental risk.

Enantioselective Bioactivity, Toxicity, and Degradation in Vegetables and Soil of Chiral Fungicide Mandipropamid

Mandipropamid (MDP) is a widely used chiral fungicide to control oomycete pathogens with two enantiomers. In this study, the enantioselective bioactivity, toxicity, and degradation of MDP were investigated for the first time. The bioactivity of S-MDP was 118-592 times higher than that of R-MDP and 1.14-1.67 times higher than that of Rac-MDP against six phytopathogens. Molecular docking found that S-MDP formed a strong halogen bond with HIS 693 of cellulose synthase and possessed a lower binding energy, which validated the results of the bioactivity assay. S-MDP showed lower toxicity toward Spirodela polyrhiza, while it exhibited higher toxicity in Danio rerio embryo and larva. S-MDP preferentially degraded in cowpea and pepper, while R-MDP preferentially degraded in soil. There is no significant difference between the two enantiomers in the toxicity of adult D. rerio and in cucumber degradation. Therefore, the development of the S-enantiomer was considered as a better option to exhibit high efficiency, which could reduce the residual risk of the pesticide and ensure environmental safety.

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.

Simultaneous determination of penthiopyrad enantiomers and its metabolite in vegetables, fruits, and cereals using ultra-high performance liquid chromatography-tandem mass spectrometry

Penthiopyrad is a novel succinate dehydrogenase inhibitor that has one chiral center and exists a metabolite, 1-methyl-3-trifluoromethyl-1H-pyrazole-4-carboxamide in its residue definition. An efficient analytical method for the simultaneous determination of penthiopyrad enantiomers and its metabolite in eight matrices were developed using modified quick, easy, cheap, effective, rugged, safe method, coupled with chiral stationary phase and ultra-high performance liquid chromatography-tandem mass spectrometry. The absolute configuration of penthiopyrad enantiomers was confirmed by polarimetry and electronic circular dichroism. Eight polysaccharide-based chiral stationary phases were evaluated in terms of the enantioseparation of penthiopyrad and separation-related factors (the mobile phase, flow rate and the column temperature) were optimized. To obtain an optimal purification, different sorbent combinations were assessed. The linearities of this method were acceptable in the range of 0.005 to 1 mg/L with R²  > 0.998, while the limits of detection and quantification were 0.0015 mg/kg and 0.01 mg/kg for two enantiomers and its metabolite. The average recoveries of R-(-)-penthiopyrad, S-(+)-penthiopyrad and the metabolite ranged from 75.4 to 109.1, 69.5 to 112.8, and 70.0 to 108.5%, respectively. The intra-day and inter-day relative standard deviations were less than 18.8%. The analytical method was accurate and convenient, which can support their further research on stereoselective degradation, residual monitoring and risk assessment.

Evaluation of exploitive potential for higher bioactivity and lower residue risk enantiomer of chiral fungicide pydiflumetofen

BACKGROUND

Pydiflumetofen, as a new succinate dehydrogenase inhibitor (SDHI) chiral fungicide, has been used in crop production because of its broad-spectrum and high-efficiency antifungal activity. However, little is known about pydiflumetofen at the chiral level. The stereoselective bioactivity and degradation of pydiflumetofen enantiomers were therefore investigated.

RESULTS

Pydiflumetofen presented effective bioactivity against the eight tested phytopathogens, and its enantiomers showed significant differences in activity. The bioactivity of R-pydiflumetofen was 9.0-958.8 times higher than that of the S enantiomer. Treatment with R-pydiflumetofen increased the cell membrane permeability of Sclerotinia sclerotiorum and decreased exopolysaccharide and oxalic acid production more than treatment with S-pydiflumetofen. Furthermore, R-pydflumetofen exhibited better inhibitory activity against the succinate dehydrogenase enzyme of S. sclerotiorum than S-pydiflumetofen by 584-fold. According to homology modeling and molecular docking studies, the binding affinities of the R and S enantiomers were -7.0 and -5.3 kcal mol^-1 , respectively. Additionally, the degradation half-lives of S- and R-pydiflumetofen in three vegetables (cucumber, eggplant, and cowpea) under field conditions were 2.56-3.12 days and 2.48-2.76 days, respectively, which reveals that R-pydiflumetofen degrades faster than S-pydiflumetofen.

CONCLUSION

Based on the results obtained, R-pydiflumetofen not only exhibited a higher bactericidal activity, but also posed fewer residual risks in the environment. The mechanism of the stereoselective bioactivity was correlated with the stereoselective inhibition activity of the target enzyme and affected the cell membrane permeability and the production of exopolysaccharide and oxalic acid. This research could provide a foundation for the systematic evaluation of pydiflumetofen from an enantiomeric view. © 2021 Society of Chemical Industry.

Enantioselective metabolism of phenylpyrazole insecticides by rat liver microsomal CYP3A1, CYP2E1 and CYP2D2

The stereoselective difference of chiral pesticide enantiomers is an important factor of risk evaluation and the subject has received wide attention. In the present work, enantioselective metabolism of chiral phenylpyrazole insecticides including fipronil, ethiprole and flufiprole in rat liver microsomes was investigated in vitro. The result showed remarkable enantioselectivity for fipronil and ethiprole with the EF values of 0.11-0.58. The metabolite fipronil-sulfone was formed with the degradation of fipronil. R-Ethiprole to S-ethiprole transformation was observed, but not S-ethiprole to R-ethiprole. No enantioselective metabolism was observed for flufiprole with the EF values of 0.49-0.51. The enzymatic assays showed that the inhibition ratio of R-fipronil and S-ethiprole was 1.5-2.1times that of the corresponding enantiomers on CYP2E1 and CYP2D2 activity, leading to the enantioselective metabolism. The result of the homology modeling and molecular docking further revealed that S-fipronil (-7.56 kcal mol^-1) and R-ethiprole (-6.45 kcal mol^-1) performed better binding with CYP2E1 and CYP2D2, respectively. The results provided useful data for the risk evaluation of chiral phenylpyrazole insecticides on ecological safety and human health.

Enantioselective Detection, Bioactivity, and Degradation of the Novel Chiral Fungicide Oxathiapiprolin

Oxathiapiprolin is a novel chiral piperidine thiazole isooxazoline fungicide that contains a pair of enantiomers. An effective analytical method was established for the enantioselective detection of oxathiapiprolin in fruit, vegetable, and soil samples using ultraperformance liquid chromatography-tandem triple quadrupole mass spectrometry. The optimal enantioseparation was achieved on a Chiralpak IG column at 35 °C using acetonitrile and 0.1% formic acid aqueous solution (90:10, v/v) as the mobile phase. The absolute configuration of the oxathiapiprolin enantiomers was identified with the elution order of R-(-)-oxathiapiprolin and S-(+)-oxathiapiprolin by electron circular dichroism spectra. The bioactivity of R-(-)-oxathiapiprolin was 2.49 to 13.30-fold higher than that of S-(+)-oxathiapiprolin against six kinds of oomycetes. The molecular docking result illuminated the mechanism of enantioselectivity in bioactivity. The glide score (-8.00 kcal/mol) for the R-enantiomer was better with the binding site in Phytophthora capsici than the S-enantiomer (-7.50 kcal/mol). Enantioselective degradation in tomato and pepper under the field condition was investigated and indicated that R-(-)-oxathiapiprolin was preferentially degraded. The present study determines the enantioselectivity of oxathiapiprolin about enantioselective detection, bioactivity, and degradation for the first time. The R-enantiomer will be a better choice than racemic oxathiapiprolin to enhance the bioactivity and reduce the pesticide residues at a lower application rate.