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

Enantioselective metabolism of fenpropathrin enantiomers by carboxyl/choline esterase 6 in Tetranychus cinnabarinus

BACKGROUND

Tetranychus cinnabarinus is a polyphagous pest mite commonly found in agriculture. As an excellent acaricide, fenpropathrin (FEN) is frequently used to control T. cinnabarinus in agriculture. However, commercial FEN is a racemate with two enantiomers, R-FEN and S-FEN. Considering that investigations on the metabolism of FEN by T. cinnabarinus are based on racemate FEN, it is important to investigate the enantioselective metabolism of FEN in T. cinnabarinus.

RESULTS

S-FEN was more toxic to T. cinnabarinus than R-FEN by more than 68.8-fold. Moreover, the synergist bioassay revealed that carboxylesterase and cytochrome P450 were the primary enzymes engaged in the detoxification of FEN in T. cinnabarinus, with carboxylesterase playing a leading role. Seven genes were substantially different after the induction of S-FEN and R-FEN. TcCCE06 was screened and selected as a key gene that related to FEN metabolism in T. cinnabarinus. The metabolic results showed that the recombinant TcCCE06 effectively metabolized 32.1% of the R-FEN and 13.8% of the S-FEN within 4 h of incubation. Moreover, R-FEN was demonstrated to have a higher affinity for the TcCCE06 protein than S-FEN based on molecular docking.

CONCLUSION

Our results indicated that TcCCE06 mediates the enantioselective metabolism of FEN in T. cinnabarinus. Our findings will contribute to a more comprehensive understanding of the mechanisms underlying the differential toxicity of the FEN enantiomers against T. cinnabarinus. Furthermore, they also provide a new perspective for the development of enantiomer-enriched acaricides with higher activity and lower pesticide dosage and pollution risks. © 2023 Society of Chemical Industry.

Screening for a Fenpropidin Enantiomer with High Activity and Low Toxicity

Fenpropidin has been extensively used for managing fungal diseases in different crops. There is a lack of literature on the enantioselective bioactivity and toxicity of fenpropidin. This study aims to explore the enantioselective bioactivity and toxicity of fenpropidin. R-Fenpropidin exhibited more potent bioactivity against seven plant pathogens than S-fenpropidin. R-Fenpropidin was more effective than S-fenpropidin in inhibiting sclerotial production, affecting mycelial growth and morphology, increasing cell membrane permeability, and decreasing the ergosterol content of Rhizoctonia solani. R-Fenpropidin exhibited a tighter binding affinity and formed hydrogen bonds with two target proteins. Fenpropidin also has enantioselective toxicity to Selenastrum capricornutum, with the toxicity of S-fenpropidin being seven times that of R-fenpropidin. S-Fenpropidin significantly reduced the content of the photosynthetic pigments. The results showed that R-fenpropidin was a highly active enantiomer with low toxicity. This study can provide a basis for the development of enantiomers with high activity and low toxicity.

Enantioselective Behaviors of Chiral Pesticides and Enantiomeric Signatures in Foods and the Environment

Unreasonable application of pesticides may result in residues in the environment and foods. Chiral pesticides consist of two or more enantiomers, which may exhibit different behaviors. This Review intends to provide progress on the enantioselective residues of chiral pesticides in foods. Among the main chiral analytical methods, high performance liquid chromatography (HPLC) is the most frequently utilized. Most chiral pesticides are utilized as racemates; however, due to enantioselective dissipation, bioaccumulation, biodegradation, and chiral conversion, enantiospecific residues have been found in the environment and foods. Some chiral pesticides exhibit strong enantioselectivity, highlighting the importance of evaluation on an enantiomeric level. However, the occurrence characteristics of chiral pesticides in foods and specific enzymes or transport proteins involved in enantioselectivity needs to be further investigated. This Review could help the production of some chiral pesticides to single-enantiomer formulations, thereby reducing pesticide consumption as well as increasing food production and finally reducing human health risks.

Design and Synthesis of Novel Oxathiapiprolin Derivatives as Oxysterol Binding Protein Inhibitors and Their Application in Phytopathogenic Oomycetes

Oomycetes, particularly those from the genus Phytophthora, are significant threats to global food security and natural ecosystems. Oxathiapiprolin (OXA) is an effective oomycete fungicide that targets an oxysterol binding protein (OSBP), while the binding mechanism of OXA is still unclear, which limits the pesticide design, induced by the low sequence identity of Phytophthora and template models. Herein, we generated the OSBP model of the well-reported Phytophthora capsici using AlphaFold 2 and studied the binding mechanism of OXA. Based on it, a series of OXA analogues were designed. Then, compound 2l, the most potent candidate, was successfully designed and synthesized, showing a control efficiency comparable to that of OXA. Moreover, field trial experiments showed that 2l exhibited nearly the same activity (72.4%) as OXA against cucumber downy mildew at 25 g/ha. The present work indicated that 2l could be used as a leading compound for the discovery of new OSBP fungicides.

Enantiomeric Separation and Degradation of Benoxacor Enantiomers in Horticultural Soil by Normal-Phase and Reversed-Phase High Performance Liquid Chromatography

The separation of benoxacor enantiomers on six commercial chiral columns was investigated by high-performance liquid chromatography (HPLC) under normal-phase and reversed-phase conditions. The mobile phases included hexane/ethanol, hexane/isopropanol, acetonitrile/water, and methanol/water. The effects of the chiral stationary phases (CSPs), temperature, and mobile phase composition and ratio on the separation of benoxacor enantiomers were examined. Under normal-phase conditions, the two benoxacor enantiomers were completely separated on Chiralpak AD, Chiralpak IC, Lux Cellulose-1, and Lux Cellulose-3 columns and partially separated on a Lux Cellulose-2 column. Under reversed-phase conditions, benoxacor enantiomers were completely separated on a Lux Cellulose-3 column and partially separated on Chiralpak IC and Lux Cellulose-1 columns. Normal-phase HPLC performed better than reversed-phase HPLC for the separation of benoxacor enantiomers. As the column temperature increased from 10 °C to 4 °C, the enthalpy (ΔH) and entropy (ΔS) results indicated that the resolution was strongly affected by the temperature and that the lowest temperature did not always produce the best resolution. An optimized separation method on the Lux Cellulose-3 column was used to investigate the stability of benoxacor enantiomers in solvents and the degradation of benoxacor enantiomers in three types of horticultural soil. Benoxacor enantiomers were stable, and degradation or racemization were not observed in methanol, ethanol, isopropanol, acetonitrile, hexane, or water (pH = 4.0, 7.0, and 9.0). In three horticultural soils, the degradation rate of S-benoxacor was faster than that of R-benoxacor, resulting in soil enrichment with R-benoxacor. The results of this study will help to improve the risk assessment of enantiomer levels of benoxacor in the environment.

Synthesis, Antifungal Evaluation, 3D-QSAR, and Preliminarily Mechanism Study of Novel Chiral Mandelic Acid Derivatives

To investigate the effect of spatial configuration on the biological activity of the compounds, a series of chiral mandelic acid derivatives with a moiety of 1,3,4-oxadiazole thioether have been designed and synthesized. Bioassay results demonstrated that most title compounds with the S-configuration exhibited better in vitro antifungal activity against three plant fungi, such as H3' (EC₅₀ = 19.3 μg/mL) against Gibberella saubinetii, which was approximately 16 times higher than that of H3 (EC₅₀ = 317.0 μg/mL). CoMFA and CoMSIA models were established for 3D-QSAR analysis and provided an important support for further optimization of this series of compounds. Comparing the preliminary mechanism studies between enantiomers (H3 and H3') found that the S-configuration compound (H3') exhibited a stronger ability to destroy the surface structure of G. saubinetii mycelia, causing the leakage of intracellular substances to accelerate and the growth of the hyphae to be inhibited. The results provided a novel view for the further optimization of this series of active compounds and deep mechanism study of chiral pesticides.

Application of Chiral Piperidine Scaffolds in Drug Design

Chiral piperidine scaffolds are prevalent as the common cores of a large number of active pharmaceuticals in medical chemistry. This review outlined the diversity of chiral piperidine scaffolds in recently approved drugs, and also covers the scaffolds in leads and drug candidates. The significance of chiral piperidine scaffolds in drug design is also discussed in this article. With the introduction of chiral piperidine scaffolds into small molecules, the exploration of drug-like molecules can be benefitted from the following aspect: (1) modulating the physicochemical properties; (2) enhancing the biological activities and selectivity; (3) improving pharmacokinetic properties; and (4) reducing the cardiac hERG toxicity. Given above, chiral piperidine-based discovery of small molecules will be a promising strategy to enrich our molecules' library to fight against diseases.

Design, Synthesis, Biological Activity Evaluation and Action Mechanism of Myricetin Derivatives Containing Thiazolebisamide

The plant diseases caused by a variety of pathogens such as viruses, bacteria and fungi pose a great threat to global food production and food safety. Therefore, the search for green, efficient and pollution-free pesticides has become an important task. In this article, 23 myricetin derivatives containing thiazolebisamides active groups have been designed and synthesized. Their activities were evaluated by performing in vitro antibacterial and in vivo antiviral assays, microscale thermophoresis (MST) and molecular docking assays. The results of in vivo antiviral assays showed that compounds A4 and A23 exhibited good antiviral activity with EC50 values of 79.0 and 54.1 μg/mL for therapeutic activity and 103.3 and 91.2 μg/mL for protective activity, respectively. The dissociation constants (Kd) values of compounds A4 and A23 against TMV-CP were 0.021 and 0.018 μM, respectively, determined by microscale thermophoresis (MST), which were much smaller than those of the commercial drug ningnanmycin (NNM), which were 2.84 μM. The interaction of compounds A4, A23 with TMV-CP was further verified at the molecular level. In addition, in vitro antifungal assays of this series of compounds showed that they exhibited some inhibitory activity against a variety of fungi, especially against the phytophthora capsici. Among them, A13 and A20 showed similar inhibitory activity to the control drug azoxystrobin at 100 μg/mL against the phytophthora capsici.

Systematic evaluation of chiral pesticides at the enantiomeric level: A new strategy for the development of highly effective and less harmful pesticides

Over the past few decades, pesticides have been used in large quantities, and they pose potential risks to organisms across various environments. Reducing the use of pesticides and their environmental risks has been an active research focus and difficult issue worldwide. As a class of pesticides with special structures, chiral pesticides generally exhibit enantioselectivity differences in biological activity, ecotoxicity, and environmental behavior. At present, replacing the racemates of chiral pesticides by identifying and developing their individual enantiomers with high efficiency and environmentally friendly characteristics is an effective strategy to reduce the use of pesticides and their environmental risks. In this study, we review the stereoselective behaviors of chiral pesticide, including their environmental behavior, stereoselective biological activity, and ecotoxicity. In addition, we emphasize that the systematic evaluation of chiral pesticides at the enantiomeric level is a promising novel strategy for developing highly effective and less harmful pesticides, which will provide important data support and an empirical basis for reducing pesticide application.

Enantiomer-Specific Study of Fenpropathrin in Soil-Earthworm Microcosms: Enantioselective Bioactivity, Bioaccumulation, and Toxicity

In this study, the enantiomer-specific bioactivity, bioaccumulation, and toxicity of fenpropathrin (FEN) enantiomers were investigated in soil-earthworm microcosms. The bioactivity order was S-FEN > rac-FEN > R-FEN for Spodoptera litura and Conogethes punctiferalis. Moreover, S-FEN was 12.0 and 32.2 times more toxic than rac-FEN and R-FEN to earthworms, respectively. S-FEN degraded faster than R-FEN with the enrichment of R-FEN in the soil environment. Furthermore, the peak-shaped accumulation curves for FEN enantiomers were observed, and R-FEN was preferentially bioaccumulated by earthworms. As compared to R-FEN, S-FEN induced greater changes in the activities of detoxification enzymes, antioxidant enzymes, and malondialdehyde content, which suggested that earthworms exhibited enantioselective defense responses to S-FEN and R-FEN. Integrated biomarker response results indicated that S-FEN exhibited higher toxic effects on earthworms than R-FEN. Finally, molecular simulation revealed that the greater interaction forces between S-FEN and sodium channel protein could be the primary reason for the enantioselective bioactivity and toxicity of FEN enantiomers. This study comprehensively highlights the enantiomer-specific bioactivity, bioaccumulation, toxicity, and mechanism of FEN in soil-earthworm microcosms at the enantiomer level. Our findings will contribute to a better risk assessment of FEN in the soil ecosystem.

Toxicokinetics of Two Oxathiapiprolin Enantiomers in Rats and Their Stereoselective Interaction with Oxysterol Binding Protein

Oxathiapiprolin is a chiral fungicide, and it can affect the metabolism of the cholesterol compounds by inhibiting oxysterol binding protein (OSBP) to exert its fungicidal effect. The application of oxathiapiprolin in agriculture is widespread, and its residue in the environment is a threat to both human and animal health. The two oxathiapiprolin enantiomers differ in their fungicidal activity, biotoxicity, and degradation by environmental forces. However, their biotoxicity has not been reported in animals. The toxicokinetics of a pesticide should be a crucial component for the evaluation of its toxicity in vivo. In this study, we investigated the absorption, bioavailability, tissue distribution, and excretion of the two oxathiapiprolin enantiomers in rats to verify their toxicokinetic process in animals. An ultrahigh-performance liquid chromatography triple quadrupole tandem mass spectrometry (UHPLC-QQQ/MS) method was established to quantify the two oxathiapiprolin enantiomers in vivo. The two oxathiapiprolin enantiomers were found to have approximately the same absorption rate and bioavailability, and both were excreted mainly in the feces. The half-life of R-(-)-oxathiapiprolin was nearly twice that of S-(+)-oxathiapiprolin. R-(-)-oxathiapiprolin also had greater distribution than S-(+)-oxathiapiprolin in the liver, lungs, heart, spleen, kidneys, stomach, large intestine, small intestine, brain, and pancreas, supporting the notion that R-(-)-oxathiapiprolin could better bind with OSBP. The stereoselectivity of S-(+)-oxathiapiprolin in these tissues may be responsible for it being readily metabolized in vivo. The molecular docking technique was subsequently used to verify the more superior binding between R-(-)-oxathiapiprolin and OSBP compared with the binding between S-(+)-oxathiapiprolin and OSBP. The findings of this study could provide more reliable data for determining the toxicokinetics of a single enantiomer of oxathiapiprolin in animals, thereby providing some theoretical basis for its subsequent toxicological study.

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.

Enantioselective aquatic toxicity and degradation in soil of the chiral fungicide oxathiapiprolin

Oxathiapiprolin is an efficient and chiral fungicide for peronosporomycetes. The enantioselective environmental behavior and ecotoxicity of oxathiapiprolin are still unclear. The enantioselectivity of oxathiapiprolin enantiomers was explored, including their acute toxicity toward aquatic plants (Auxenochlorella pyrenoidosa and Soirodela polyrhiza) along with their influence on photosynthetic pigment production, the acute toxicity and morphological differences for the embryos, larvae and adult stages of zebrafish (Danio rerio), and the degradation in four typical soils (aerobic, anaerobic and sterilized conditions). The enantioselective toxicity of oxathiapiprolin showed that the toxicity of R-oxathiapiprolin was 1.8-2.1 times higher than that of S-oxathiapiprolin toward the two aquatic plants. In particular, the content of photosynthetic pigments decreased significantly stronger after exposure to R-oxathiapiprolin compared with S-oxathiapiprolin. The LC₅₀ values of R-oxathiapiprolin in zebrafish in the different life stages were 1.6-2.1 times higher than those of S-oxathiapiprolin. The zebrafish embryos were most sensitive to the oxathiapiprolin enantiomers. After exposure to R-oxathiapiprolin, zebrafish embryos showed noticeable hatching delays, inhibition or deformation. R-oxathiapiprolin degraded preferentially in all four soils, with an enantiomeric fraction (EF) ranging from 0.28 to 0.42 under aerobic conditions. Enantioselective degradation was not found under anaerobic and sterilized conditions. The enantioselectivity of new chiral pesticides should be fully considered in risk assessments to provide a basis for the development and preparation of pure optical enantiomers.

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.

Simultaneous determination of nereistoxin insecticides in foods of animal origins by combining pH-dependent reversible partitioning with hydrophilic interaction chromatography-mass spectrometry

Although nereistoxin insecticides (NIs) are banned for animal husbandry operations, they are still used because of their high insecticidal activities. Therefore, a reliable residue analysis method for the simultaneous detection of cartap, bensultap, thiocyclam, and nereistoxin in foods of animal origins, including beef, pork, chicken, milk, and eggs, was developed using hydrophilic interaction liquid chromatography-mass spectrometry (HILIC-LC-MS/MS). The NIs were extracted with an acidic cysteine and formate buffer solution and hydrolyzed to nereistoxin. The molarity and pH of the buffer were optimized at 20 mM and 3, respectively, to keep the pH of the extracts at 4-5. pH-dependent acid-base partitioning coupled with salting-out-assisted liquid-liquid extraction using acetonitrile was performed for purification and for the direct introduction of the extracts to LC. The optimal pH values were 5 and 9 for the acid-base partitioning. Nereistoxin quantitation was achieved with consistent column retention (RSD < 0.6%) and a high degree of separation (N > 10⁶). The matrix-dependent method limit of quantitation was 2 μg nereistoxin/kg, and the calibration curve showed good linearity (R² > 0.998). The recovery efficiencies were in the range of 89.2-109.9% with relative standard deviations less than 10%, and matrix effects did not exceed ± 10%, which satisfied the criteria outlined in the European SANTE/12682/2019 guidelines.

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.

Resistance Risk and Novel Resistance-Related Point Mutations in Target Protein PiORP1 of Fluoxapiprolin in Phytophthora infestans

Fluoxapiprolin is a new oxysterol binding protein inhibitor (OSBPI), which showed excellent inhibitory activity to plant pathogenic oomycetes. Its resistance risk and mechanism in Phytophthora infestans are unclear. In the current study, the sensitivities of 103 P. infestans isolates to fluoxapiprolin were investigated, and a unimodal distribution with a mean EC₅₀ value of 0.00035 μg/mL was observed. Four types of resistant mutants, with a resistance factor from 14 to more than 1000, and point mutations S768I+N837I, S768I+L860I, S768I, and I877F in PiORP1, were acquired using fungicide adaption. The fitness of the mutants was similar to or lower than that of the corresponding parental isolate. Positive cross-resistance was detected between fluoxapiprolin and oxathiapiprolin. The point mutations were verified in P. sojae homologue positions using the CRISPR/Cas9 genome editing system. Transformants containing S768I+N837I or S768I+L860I, showed high fluoxapiprolin resistance (RF > 1000). In conclusion, the risk of P. infestans resistance to fluoxapiprolin is moderate, and novel point mutation types S768I+N837I or S768I+L860I could cause high fluoxapiprolin resistance in P. infestans.

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.

Developments in the Catalytic Asymmetric Synthesis of Agrochemicals and Their Synthetic Importance

Catalytic asymmetric synthesis has become an essential tool for the enantioselective synthesis of pharmaceuticals, natural products, and agrochemicals (mainly fungicides, herbicides, insecticides, and pheromones). With continuous growing interest in both modern agricultural chemistry and catalytic asymmetric synthesis chemistry, this review provides a comprehensive overview of some earlier reports as well as the recent successful applications of various catalytic asymmetric syntheses methodologies, such as enantioselective hydroformylation, enantioselective hydrogenation, asymmetric Sharpless epoxidation and dihydroxylation, asymmetric cyclopropanation or isomerization, organocatalyzed asymmetric synthesis, and so forth, which have been used as key steps in the preparation of chiral agrochemicals (on R&D, piloting, and commercial scales). Chiral agrochemicals can also lead the new generation of such chemicals having specific and novel modes of action for achieving sustainable crop protection and production. Some perspectives and challenges for these catalytic asymmetric methodologies in the synthesis of chiral agrochemicals are also briefly discussed in the final section of the manuscript. This review will provide the insight regarding understanding, development, and evaluation of catalytic asymmetric systems for the synthesis of chiral agrochemicals among the agrochemists.

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.

Biochar decreased enantioselective uptake of chiral pesticide metalaxyl by lettuce and shifted bacterial community in agricultural soil

A 35-day microcosmic experiment was conducted with lettuce (Lactuca sativa L.) and two metalaxyl (MET) enantiomers (R-MET and S-MET) to understand the roles of biochar in the enantioselective fate of chiral pesticides in soil-plant ecosystems. Wood waste-derived biochar (WBC) amendment effectively decreased the shoot concentrations of R-MET/S-MET and their metabolites R-MET/S-MET acid by 57.7-86.3% and 13.3-32.5%, respectively. The reduced uptake was mainly attributed to the decreased bioavailability of R-MET and S-MET. A lower fraction of R-MET was accumulated by the lettuce in the WBC-amended soils relative to the control, suggesting a decrease in the enantioselective uptake of the chiral pesticide MET in the presence of biochar. Regardless of the WBC amendment, no enantiomerization of MET or MET acid occurred. The application of WBC stimulated soil bacterial diversity, shifted the bacterial community, and enhanced the abundance of pesticide degrading bacteria (e.g., Luteimonas, Methylophilus, and Hydrogenophaga), which were responsible for the enantioselective degradation of MET in the soil. This work expands our understanding of the enantioselective fate of chiral pesticides in the biochar-amended soil ecosystems. These findings can be used to develop biochar-based technologies to remediate soils contaminated with these chiral pesticides to ensure food safety.