Direct Enantioseparation of Nitrogen-Heterocyclic Pesticides on Cellulose-Based Chiral Column by High-Performance Liquid Chromatography

Simultaneous Enantioseparation of Three Chiral Antifungal Pesticides by Hydroxypropyl-γ-CD-Modified Micellar Electrokinetic Chromatography

Simultaneous enantioseparation of three commonly used chiral antifungal pesticides (diniconazole, hexaconazole, and imazalil) was first studied based on micellar electrokinetic chromatography (MEKC) with hydroxypropyl-γ-CD (HP-γ-CD) as chiral selector. In this study, the importance of experimental parameters such as chiral selector type and concentration, sodium dodecyl sulfate (SDS) concentration, the ratio of methanol, and separation voltage in optimizing were investigated. The simultaneous enantioseparation of diniconazole, hexaconazole, and imazalil was successfully achieved in 30 mM borate buffer (pH 9.0) containing 10 mM HP-γ-CD and 20 mM SDS with methanol (8%) added as organic modifiers. The resolution of diniconazole, hexaconazole, and imazalil was 15.2, 2.12, and 2.78, respectively, and the peak efficiency (N) was over 566,825 plates/m. This study provides an alternative way to systematically separate chiral antifungal pesticides with high efficiency.

Dissipation, residue, stereoselectivity and dietary risk assessment of penthiopyrad and metabolite PAM on cucumber and tomato in greenhouse and field

Penthiopyrad is a broad-spectrum fungicide with wide application in agriculture with preferential degradation of the S (+)-stereoisomer in soil. An understanding of the stereoselective fate of penthiopyrad is crucial for accurate food safety risk assessment. In this study, the dissipation, distribution, and dietary intake risk of penthiopyrad and its main metabolite (PAM) was conducted in cucumber and tomato samples under greenhouse and open field conditions. The half-lives of penthiopyrad in cucumber and tomato samples were < 8 days and the dissipation rates were higher in the open field than in the greenhouse. Due to the enantiomeric fraction data > 0.5, S (+)-stereoisomer dissipated slightly faster than R-(-)-stereoisomer. The residues of total penthiopyrad (sum of rac-penthiopyrad and PAM) were lower than the maximum residue limits in cucumber and tomato samples (risk quotients ≪ 100%). Therefore, the recommended penthiopyrad spraying method does not threaten vegetable cultivations and has negligible dietary intake risk.

Simultaneous Enantiomeric Separation of Carfentrazone-Ethyl Herbicide and Its Hydrolysis Metabolite Carfentrazone by Cyclodextrin Electrokinetic Chromatography. Analysis of Agrochemical Products and a Degradation Study

The different activity and toxicity that the enantiomers of agrochemicals may have requires the development of stereoselective analytical methodologies enabling the individual determination of each enantiomer. The aim of this work was to develop the first Electrokinetic Chromatography methodology enabling the simultaneous enantiomeric separation of carfentrazone-ethyl herbicide and its hydrolysis metabolite carfentrazone. The use of an anionic cyclodextrin as chiral selector (captisol at 2.5% (w/v)) in a 25 mM acetate buffer, at a temperature of 30 °C, and an applied voltage (reverse polarity) of -30 kV, allowed the simultaneous separation of the four enantiomers of the two compounds studied in 6.8 min with enantiomeric resolutions of 5.0 for carfentrazone-ethyl and 5.1 for carfentrazone. Analytical characteristics of the developed method were evaluated and found adequate to achieve the quantitation of carfentrazone-ethyl and carfentrazone. Analysis of a commercial herbicide formulation showed the potential of the method for the quality control of these agrochemical products. Degradation studies for carfentrazone-ethyl revealed that no significant degradation took place in cleaned sand samples while a significant but not stereoselective degradation took place in soils for the whole period of time considered (seven days).

Stereoselective environmental behavior and biological effects of the chiral bitertanol

Bitertanol is a widely used chiral triazole fungicide. The stereoselective environmental behavior and biological effects of bitertanol are not clear. The present study evaluated the stereoselectivity of bitertanol, including its degradation in five typical soils (under laboratory controlled aerobic, anaerobic and sterilization conditions), metabolism in rat liver microsomes (RLM; in vitro), and the endocrine disruption effects on the estrogen receptor (ER) and thyroid hormone receptor (TR) using reporter gene assays. The results indicated that (1S,2R)-bitertanol and (1R,2S)-bitertanol had faster degradation rates in soil than the other stereoisomers. The half-lives of four bitertanol stereoisomers ranged from 9.1 d to 86.6 d in different soils under different conditions. (1S,2R)-bitertanol was preferentially metabolized in RLM. The molecular docking results confirmed the in vitro experiments that (1S,2R)-bitertanol had shortest binding distances and lowest energies with cytochrome P450 enzymes (CYPs). Four bitertanol stereoisomers showed stereoselective antagonistic effects on ER. Additionally, (1S,2R)-bitertanol and (1R,2S)-bitertanol exhibited antagonistic effects on TR. These results suggest that the use of pure (1S,2R)-bitertanol instead of the commercial stereoisomer mix, may help reduce environmental pollution and biological toxicity.

Stereoselective bioactivity, toxicity and degradation of the chiral triazole fungicide bitertanol

BACKGROUND

The chiral pesticide bitertanol has been widely used in the prevention and treatment of fungal diseases on many crops. However, research on bitertanol at the stereoisomer level has not been reported. Here, we study the stereoselective bioactivity, toxicity, and degradation of this pesticide under laboratory and field conditions.

RESULT

(1S,2R)-Bitertanol was the most effective stereoisomer, showing 4.3-314.7 times more potent bioactivity than other stereoisomers against eight target pathogenic fungi. (1S,2R)-Bitertanol showed 10.2 times greater inhibition of Botrytis cinerea spore germination than (1R,2S)-bitertanol. According to the receptor-drug docking results, the distances from the nitrogen atom in the heterocycle of (1S,2R)-, (1R,2S)-, (1R,2R)-, and (1S,2S)-bitertanol to the central Fe + atoms in the ferriporphyrin were 2.5, 3.8, 2.6, and 3.8 Å, respectively. (1S,2S)-Bitertanol was 1.6-2.7 times more toxic than (1R,2R)-bitertanol to Chlorella pyrenoidosa. The half-lives of (1R,2S)-, (1S,2R)-, (1R,2R)-, and (1S,2S)-bitertanol were 3.7, 4.1, 4.1, and 4.8 d, respectively, in tomato.

CONCLUSION

The stereoselective bioactivity, toxicity, and degradation for bitertanol were first studied here. (1S,2R)-Bitertanol was a high efficiency and low toxicity stereoisomer. Moreover, the stereoselective bioactivity among all stereoisomers correlated with the binding distances and calculated energy differences between stereoisomers and the target protein. This study also provides a foundation for a systematic evaluation of bitertanol at the stereoisomer level. © 2019 Society of Chemical Industry.

Preparation of a new benzylureido-β-cyclodextrin-based column and its application for the determination of phenylmercapturic acid and benzylmercapturic acid enantiomers in human urine by LC/MS/MS

A benzylureido-β-cyclodextrin was synthesized by the reaction of 6-amino-β-cyclodextrin with an active benzyl isocyanate. Then, it was bonded to silica gel by a thiol-ene addition reaction, obtaining a new benzylureido-β-cyclodextrin-based chiral stationary phase (BzCDP). Its chemical structure was characterized by infrared spectroscopy, elemental analysis, and solid-state nuclear magnetic resonance spectroscopy. The BzCDP was successfully used to separate phenylmercapturic acid (PMA) and benzylmercapturic acid (BMA) enantiomers, which were confirmed as biomarkers of exposure to benzene and toluene in human urine. The enantiomeric separations were also optimized through the investigation of related factors. The resolutions of PMA and BMA enantiomers could be up to 2.25 and 2.14, respectively, within 30 min under reversed-phase chromatography. Based on the optimal chromatographic and mass spectrometry conditions, a new LC-MS/MS quantitative method for the PMA and BMA enantiomers was established by negative ion multiple reaction monitoring (MRM) and an isotope-labeled PMA (d²-PMA) as an internal standard. The limits of detection (LODs) of enantiomers were less than 0.17 μg/L for PMA and 0.14 μg/L for BMA, and the averaged recoveries of enantiomers were in the range of 86~100% for PMA and 86~113% for BMA. The method had good reproducibility levels with the RSDs (3.5~11.3% for intra-day and 3.9~13.1% for inter-day). The method was successfully applied to urine testing of 60 painting and printing workers. The results showed that only L-PMA was detected in the urine of the Printers, while a high content of L-PMA (27.5~106 μg/L) and D-PMA (19.9~82.8 μg/L) can be detected simultaneously in the urine of the Painters, indicating that benzene pollution was more serious in this group. The positive rate of BMA was rather higher, indicating that toluene pollution was more common than benzene. BMA also existed in the form of two enantiomers (L-BMA and D-BMA), but the difference between the two types of occupational groups was small. It is a meaningful work to deeply study the existence and content of chiral markers in human urine, which will help to better understand and evaluate the harmful effects of benzene series on human beings. Graphical abstract.

Stereoselective Separation of the Fungicide Bitertanol Stereoisomers by High-Performance Liquid Chromatography and Their Degradation in Cucumber

Bitertanol is a widely used triazole fungicide and consists of four stereoisomers. A new high-performance liquid chromatography (HPLC) method was developed for simultaneous analysis of the four stereoisomers in apple, pear, tomato, cucumber, and soil. The mechanism of separation was explained with molecular docking and effects of thermodynamic parameters on the resolution. The absolute configuration and optical rotation of four stereoisomers were confirmed by X-ray diffraction and HPLC tandem circular dichroism, respectively. A good linearity ( R² ≥ 0.999) was obtained for four stereoisomers in all matrix-matched calibration curves in the range of 0.02-10 mg/L. The mean recoveries of four stereoisomers in five matrices ranged from 74.6% to 101.0% with an intraday and interday relative standard deviation from 0.6% to 9.9%. Stereoselective degradation of bitertanol in cucumber was observed: (1 R,2 S)-bitertanol and (1 R,2 R)-bitertanol were preferentially degraded with enantiomeric fraction values from 0.5 to 0.43 at 7 d and 0.42 at 5 d, respectively. This research provides a useful tool for the analysis of bitertanol stereoisomers.

Enantioselective Acute Toxicity and Bioactivity of Carfentrazone-ethyl enantiomers

The stereoselective herbicidal bioactivity and toxicity toward aquatic organisms of carfentrazone-ethyl enantiomers were investigated. The results showed that there was significant enantioselective acute toxicity toward Selenastrum bibraianum. In addition, S-(-)-carfentrazone-ethyl was 4.8 times more potent than R-(+)-isomer. However, a slight enantioselectivity was observed for Daphnia magna and Danio rerio. The stereoselective herbicidal bioactivity of carfentrazone-ethyl enantiomers was observed by assessing maize root-length inhibition. The results clarified that S-(-)-carfentrazone-ethyl (EC₅₀ 1.94 mg/L) > Rac-carfentrazone-ethyl (EC₅₀ 2.18 mg/L) > R-(+)-carfentrazone-ethyl (EC₅₀ 3.96 mg/L). The herbicidal bioactivity of S-(-)-carfentrazone-ethyl was 2 times higher more than R-(+)-isomer. The mechanism of enantioselective bioactivity was illustrated using molecular simulation software. The GlideScore energies of S-(-)-carfentrazone-ethyl and R-(+)-carfentrazone-ethyl were - 6.15 kcal/mol and - 5.59 kcal/mol, indicating that the S-form has a greater affinity to the active site of protoporphyrinogen oxidase, which is consistent with the results of the bioactive assay. This study can rise the significance of risk assessments for carfentrazone-ethyl herbicide.

Enantioseparation of Imazalil and Monitoring of Its Enantioselective Degradation in Apples and Soils Using Ultrahigh-Performance Liquid Chromatography-Tandem Mass Spectrometry

Imazalil is a widely used systemic chiral fungicide that is still being employed as a racemic mixture without distinguishing the difference between enantiomers, which often leads to its inaccurate risk assessment. In this study, a robust and highly sensitive chiral separation method was developed for imazalil enantiomers by ultrahigh-performance liquid chromatography-tandem mass spectrometry and was further applied to study the degradation dynamics of imazalil enantiomers in apples and field soils at three sites in China. The baseline enantioseparation for imazalil was achieved within 3.5 min on a Lux Cellulose-2 (CCMPC) column with acetonitrile (ACN)/water (65:35, v/v) with a mobile phase at 0.5 mL/min flow rate and a column temperature of 20 °C. The limit of quantitation (LOQ) for each enantiomer was <0.60 μg/kg, with a baseline resolution of approximately 1.75. The research showed that (S)-(+)-imazalil degraded more rapidly than (R)-(-)-imazalil in Gala apples, whereas (R)-(-)-imazalil preferentially degraded in Golden Delicious apples. No significant enantioselectivity was observed in OBIR-2T-47 apples and field soils from the three sites. Results of this study provide useful references for risk assessment and the rational use of imazalil in further agricultural produce practice.

Eluent Tolerance and Enantioseparation Recovery of Chiral Packing Materials Based on Chitosan Bis(Phenylcarbamate)-(n-Octyl Urea)s for High Performance Liquid Chromatography

The goal of the present work was to study the influence of the swelling of chitosan derivatives on the enantioseparation and the separation performance recovery of chiral stationary phases (CSPs) based on these derivatives. Therefore, six chitosan bis(phenylcarbamate)-(n-octyl urea)s were synthesized, which were coated on macroporous 3-aminopropyl silica gel affording new CSPs. Most of the CSPs demonstrated strong enantioseparation capability for the tested chiral compounds. The swelling capacity of the chitosan bis(phenylcarbamate)-(n-octyl urea)s in ethyl acetate, acetone and tetrahydrofuran (THF) was evaluated. Among the chitosan derivatives, the chitosan bis(3,5-dichlorophenylcarbamate)-(n-octyl urea) polymer showed the highest swelling capacity in ethyl acetate and THF. The polymer-based CSPs could be utilized with pure ethyl acetate and a normal phase containing 70% THF, but was damaged by pure THF. On the other hand, the separation performance of the damaged CSP could be recovered after it was allowed to stand for a period of time. The observations are important for the development and application of polysaccharide derivative-based CSPs.