Safeners Improve Maize Tolerance under Herbicide Toxicity Stress by Increasing the Activity of Enzymes in Vivo

Detoxification Strategy of Titanium Oxide Nanoparticles Driving Endogenous Molecules Metabolism to Modulate Atrazine Conversion in Lactuca sativa L

Nanoparticles (NPs) exhibit the potential to enhance plant tolerance to organic pollutant stress, but how they drive endogenous molecules to detoxify contaminants remains to be further investigated. This study clarified the modulatory mechanisms by which foliar or root application of biosynthesized titanium oxide NPs (g-nTiO2) alleviated atrazine (ATZ) toxicity to Lactuca sativa L. Compared with the ATZ-alone group, 10 mg/L g-nTiO2 intensified light-harvesting, photoelectron transfer, and reduced oxidative damage, thereby improving growth and inducing metabolic reprogramming. Specifically, g-nTiO2 activated pathways related to energy supply and defense detoxification, while stabilizing membrane lipid and nitrogen metabolism. Furthermore, the modulation of biomarkers involved in balancing cellular homeostasis and stimulating growth by g-nTiO2 ultimately boosted lettuce resistance to ATZ and physiological performance. Molecular docking analysis revealed that g-nTiO2 enhanced the Phase II metabolism of ATZ by glutathione and amino acids through increasing detoxification enzyme activities by 23-44%, which confirmed the driving role of NPs in alleviating ATZ phytotoxicity to lettuce. Collectively, these findings provide a prospective nanoenabled strategy for mitigating crop sensitivity to pesticide residues for safe and sustainable agricultural production.

Pharmacophore Recombination Design, Synthesis, and Bioactivity of Ester-Substituted Pyrazole Purine Derivatives as Herbicide Safeners

Mesosulfuron-methyl, an acetolactate synthase (ALS) inhibitor primarily applied to wheat and rye, can injure or even kill wheat crops. Herbicide safeners can improve the herbicide resistance of crops without reducing the herbicidal effect on targeted weed species. Herein, we present a series of pyrazole purine derivatives with the primary structure of the natural product cytokinin and commercialized safener mefenpyridyl, designed using the pharmacophore recombination method. The title compounds were synthesized and characterized using infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. A bioactivity assay proved that most of the target compounds can reduce the wheat phytotoxicity of mesosulfuron-methyl. Measurements of chlorophyll and glutathione contents, along with other enzyme activity assays, confirmed that compounds I-15 and I-13 exhibit higher safety activities compared with the mefenpyr-diethyl safener. Molecular structure comparisons demonstrated that I-15 is more readily absorbed and disseminated through the crop than the commercialized safener mefenpyr-diethyl. Molecular docking models and molecular dynamics simulations elucidated the protective mechanism of safeners; specifically, compound I-15 competitively binds to the ALS active site with mesosulfuron-methyl. The current study reveals the potential of pyrazole purine derivatives in the future discovery of novel herbicide safeners.

Developing fluorescence hyperspectral imaging methods for non-invasive detection of herbicide safeners action mechanism and effectiveness

Herbicide safeners are considered key agents for plant protection that reduce the harmful impacts of herbicides on crops and the environment in general, but traditional evaluation methods for their effectiveness are time-consuming and labor-intensive. In this study, a rapid and non-destructive method was proposed using chlorophyll fluorescence and hyperspectral imaging that combined with machine learning models. Besides, chemometric analysis was utilized to reveal the action mechanism between the wheat crop (Triticum aestivum L.) understudy and the herbicide isoproturon (ISO) and safener gibberellin acid (GA3). The results showed that ISO caused oxidative stress and disrupted the photosynthesis mechanism in wheat by hindering the electron transport pathway from primary acceptor quinone to secondary acceptor. Meanwhile, GA3 stimulated wheat to synthesize more glutathione (GSH) that accelerated the herbicide action metabolism. It's worth noting that excessive GA3 has decreased significantly the GSH and photosynthetic pigment concentrations, while the malondialdehyde concentration was significantly (p < 0.05) increased. Additionally, competitive adaptive reweighted sampling proved the best performance when combined with partial least squares regression for predicting the phytochemical concentrations that characterized the effectiveness of GA3. In conclusion, the novelty of the current study came from the accurate real-time tracking method for GA3 action mechanism and its effectiveness on ISO toxicity. Where, that model holds great value for reducing the traditional methods' limitations in safener developments.

Efficacy and mechanism of cyprosulfamide in alleviating the phytotoxicity of clomazone residue on maize seedling

Introduction

The residues of clomazone (Clo) can lead to phytotoxic symptoms such as foliar bleaching, reduced plant height, and decreased maize yields. Herbicide safener represent one of the most economically efficient strategies for mitigating herbicide-induced damage.

Methods

In this study, various seed treatments were implemented, including the immersion of maize seeds in water (CK), immersion in Cyprosulfamide (CSA), soil supplemented with clomazone (ClO) and CSA+ClO, evaluated physiological indicators, chlorophyll content, and qRT-PCR analyses of the maize plants were evaluated under the different treatments.

Results and discussion

The objective of this study was to investigate the impact of CSA on mitigating residual damage caused by Clo on maize and elucidate its mechanism. Compared to the CK, treatment with Clo resulted in significant inhibition of maize plant height, fresh weight, chlorophyll content, and carotenoid levels by 19.0%, 29.9%, 92.5%, and 86.3% respectively. On the other hand, under CSA+Clo treatment, milder inhibition was observed with reductions of only 9.4% in plant height and 7.2% in fresh weight, as well as decreases of 35.7% and 21.8% respectively in chlorophyll and carotenoid contents. The findings revealed that the application of CSA effectively mitigated the inhibitory effects of Clo residues on maize plant height, fresh weight, carotenoids and chlorophyll content. Additionally, the combination of CSA and Clo reduced MDA levels by 13.4%, increased SOD activity by 9.7% and GST activity by 26.7%, while elevating GSSG content by 31.3% compared to Clo alone, ultimately mitigating oxidative damage in maize plants. qRT-PCR analysis showed that the expression of five P450 genes (CYP72A5, CYP81A4, CYP81Q32, CYP81A9, CYP81A36), nine GST genes (GST30, GST31, GSTIV, GSTVI, GST21, GST7, GST37, GST25, IN2-1), and two UGT genes (UGT76C2, UGT83A1) significantly high increased by 6.74-, 10.27-, 4.98-, 10.56-, 25.67-, 16.70-, 46.92-,7.53-, 5.10-, 238.82-, 143.50-, 4.58-, 31.51-, 39.3-, 4.20-, 10.47-fold after CSA+Clo treatment compared to that in the Clo treatment. The pre-treatment of CSA led to the upregulation of five P450 genes, nine GST genes, and two UGT genes, which may be associated with the metabolism of Clo in maize. Overall, this study suggests that CSA could be effectively mitigates Clo residual damage by up-regulating detoxification-related genes, enhancing chlorophyll content and activities of antioxidant enzymes.

A systematic review of herbicide safener toxicity

Herbicide safeners are agrochemicals added to herbicide formulations to protect crops from herbicide damage without reducing the effectiveness of the herbicide against weeds. While safeners are typically structurally similar to their co-formulated herbicides, they are classified as "inert" in the United States, meaning they are not held to the same regulatory standards as the herbicides. This review systematically examines the toxicity of safeners, which is important given their large-scale global use and potential for exposure to wildlife, livestock, and humans. A systematic review of peer-reviewed literature identified only seven studies examining safener toxicity. Regulatory toxicity data, compiled from the European Chemicals Agency (ECHA) database, included data for 9 of the 18 commercial safeners. Most safeners have low acute ecotoxicity and mammalian toxicity; however, chronic effects and the underlying mechanism are less clear. Benoxacor showed enantioselective metabolism and depletion by drug-metabolizing enzymes. In conclusion, despite the widespread use of safeners, significant knowledge gaps exist regarding their toxicity. More research is needed to fully characterize the potential risks of safeners to human health and the environment. Regulatory agencies should consider reclassifying safeners as active ingredients to ensure adequate toxicity testing and risk assessment.

Multiomics Analysis of the Mechanism by Which Gibberellin Alleviates S-Metolachlor Toxicity in Rice Seedlings

S-metolachlor is a selective pre-emergence herbicide used in dryland. However, it is challenging to employ in paddy fields due to its phytotoxic effects on rice. As a common phytohormone, Gibberellin-3 (GA3) is inferred to have the ability to alleviate herbicide phytotoxicity. This study first quantitatively verified the phytotoxicity of s-metolachlor to rice and then demonstrated the mitigative effect of GA3 on these adverse reactions. Furthermore, a transcriptome of rice seedlings subjected to different treatments was constructed to assemble the reference genes, followed by comparative metabolomics and proteomics analyses. Metabolomics revealed an enrichment of flavonoid metabolites in the group of adding GA3, and these flavonoids can eliminate ROS in plants. Proteomics analysis indicated that differential proteins were enriched in the phenylpropanoid biosynthesis pathway responsible for the synthesis of flavonoids and that the functions of most differential proteins are associated with peroxidase. The proteome, combined with the transcriptome, revealed that the expressions of proteins and genes was related to the POD activity in the group of adding GA3. It was speculated that the elimination of ROS is key to alleviating the stress of s-metolachlor on rice growth. It was inferred that the mechanism of GA3 in alleviating the phytotoxicity of the substance s-metolachlor is by increasing the activity of the POD and influencing the growth of rice seedlings through the restoration of flavonoid synthesis. In this study, we screened GA3 as a safener to alleviate the phytotoxicity of s-metolachlor on rice. On this basis, the mechanism of alleviating phytotoxicity was studied. The application range of s-metolachlor might be expanded, providing a new supplementary method for weed control and herbicide resistance management.

Design, Synthesis, and Biological Activity of Novel Triketone-Containing Phenoxy Nicotinyl Inhibitors of HPPD

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a crucial target enzyme in albino herbicides. The inhibition of HPPD activity interferes with the synthesis of carotenoids, blocking photosynthesis and resulting in bleaching and necrosis. To develop herbicides with excellent activity, a series of 3-hydroxy-2-(6-substituted phenoxynicotinoyl)-2-cyclohexen-1-one derivatives were designed via active substructure combination. The title compounds were characterized via infrared spectroscopy, 1H and 13C nuclear magnetic resonance spectroscopies, and high-resolution mass spectrometry. The structure of compound III-17 was confirmed via single-crystal X-ray diffraction. Preliminary tests demonstrated that some compounds had good herbicidal activity. Crop safety tests revealed that compound III-29 was safer than the commercial herbicide mesotrione in wheat and peanuts. Moreover, the compound exhibited the highest inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD), with a half-maximal inhibitory concentration of 0.19 μM, demonstrating superior activity compared with mesotrione (0.28 μM) in vitro. A three-dimensional quantitative structure-activity relationship study revealed that the introduction of smaller groups to the 5-position of cyclohexanedione and negative charges to the 3-position of the benzene ring enhanced the herbicidal activity. A molecular structure comparison demonstrated that compound III-29 was beneficial to plant absorption and conduction. Molecular docking and molecular dynamics simulations further verified the stability of the complex formed by compound III-29 and AtHPPD. Thus, this study may provide insights into the development of green and efficient herbicides.

Protective mechanisms of neral as a plant-derived safener against fenoxaprop-p-ethyl injury in rice

BACKGROUND

The use of herbicide safeners effectively minimises crop damage while maintaining the full efficacy of herbicides. The present study aimed to assess the potential protective effects of neral (NR) as a safener, in order to mitigate injury caused by fenoxaprop-p-ethyl (FE) on rice.

RESULTS

The alleviating effect of NR was similar to that of the safener isoxadifen-ethyl (IE). The root elongation of rice was significantly promoted under the FE + NR and FE + IE treatments, as compared to the FE treatment. The transcriptome analysis further suggested that the effects of NR treatment on plant metabolic pathways differed from those of IE treatment. In total, 895 and 47 up-differentially expressed genes induced by NR (NR-inducible genes) and IE (IE-inducible genes) were identified. NR-inducible genes were mainly enriched in phytohormone synthesis and signalling response, including 'response to brassinosteroid', 'response to jasmonic acid', 'response to ethylene', 'brassinosteroid metabolic process', 'brassinosteroid biosynthesis' and 'plant hormone signal transduction'. In contrast, IE-inducible genes were predominantly enriched in glutathione metabolism. The activity of glutathione S-transferase was found to be increased after IE treatment, whereas no significant increase was observed following NR treatment. Moreover, several transcription factor genes, such as those encoding AP2/ERF-ERF and (basic helix-loop-helix) bHLH were found to be significantly induced by NR treatment.

CONCLUSION

This is the first report of the utilisation of NR as an herbicide safener. The results of this study suggest the toxicity of FE to rice is mitigated by NR through a distinct mechanism compared to IE. © 2023 Society of Chemical Industry.

Design, Synthesis, and Bioactivity of Novel 2-(Arylformyl)cyclohexane-1,3-dione Derivatives as HPPD Inhibitors

4-Hydroxyphenylpyruvate dioxygenase inhibitors (Echinochloa crus-galli 1.13.11.27, HPPD) have gained significant popularity as one of the best-selling herbicides worldwide. To identify highly effective HPPD inhibitors, a rational design approach utilizing bioisosterism was employed to create a series of 2-(arylformyl)cyclohexane-1,3-dione derivatives. A total of 29 novel compounds were synthesized and characterized through various techniques, including IR, 1H NMR, 13C NMR, and HRMS. Evaluation of their inhibitory activity against Arabidopsis thaliana HPPD (AtHPPD) revealed that certain derivatives exhibited superior potency compared to mesotrione (IC50 = 0.204 μM). Initial herbicidal activity tests demonstrated that compounds 27 and 28 were comparable to mesotrione in terms of weed control and crop safety, with compound 28 exhibiting enhanced safety in canola crops. Molecular docking analyses indicated that the quinoline rings of compounds 27 and 28 formed more stable π-π interactions with the amino acid residues Phe-360 and Phe-403 in the active cavity of AtHPPD, surpassing the benzene ring of mesotrione. Molecular dynamics simulations and molecular structure comparisons confirmed the robust binding capabilities of compounds 27 and 28 to AtHPPD. This study provides a valuable reference for the development of novel triketone herbicide structures, serving as a blueprint for future advancements in this field.

Transcriptomic analysis of maize uncovers putative genes involved in metabolic detoxification under four safeners treatment

Isoxadifen-ethyl (IDF) and cyprosulfamide (CSA) can effectively protect maize from nicosulfuron (NIC) injury, while mefenpyr-diethyl (MPR) and fenchlorazole-ethyl (FCO) did not. Their chemical diversity and requirement to use them in combination with the corresponding herbicides suggest that their elicitation of gene expression are complex and whether it is associated with the safening activity remains elusive. In this study, our first objective was to determine whether or not the ability of four safeners to enhance the metabolic rate of nicosulfuron. It was found that nicosulfuron degradation in maize was accelerated by IDF and CSA, but not by FCO and MPR. Transcriptomic analysis showed that the number of genes induced by IDF and CSA were larger than that induced by FCO and MPR. Overall, 34 genes associated with detoxification were identified, including glutathione S-transferase (GST), cytochrome P450 (CYP450), UDP-glucosyltransferase (UGT), transporter and serine. Moreover, 14 detoxification genes were screened for further verification by real-time PCR in two maize inbred lines. Two maize inbred lines exhibited high expression levels of four genes (GST31, GST39, AGXT2 and ADH) after IDF treatment. GST6, GST19, MATE, SCPL18 and UF3GT were specifically up-regulated in telerant maize inbred line under IDF and IDF + NIC treatments. Seven genes, namely GST31, GST6, GST19, UF3GT, MATE, ADH and SCPL18, are induced by IDF and CSA to play a vital role in regulating the detoxification process of NIC. Accordingly, the GST activity in maize was accelerated by IDF and CSA, but not by FCO and MPR. This result is consistent with transcriptome and metabolic data.These results indicate that the mitigation of NIC damage is associated with enhanced herbicide metabolism. IDF and CSA were more effective in protecting maize from NIC injury due to their ability to enhance the detoxification of specific types of herbicides, compared to FCO and MPR. The chemical specificity of four safeners is attributed to the up-regulated genes related to the detoxification pathway.

Review on the Discovery of Novel Natural Herbicide Safeners

The phytotoxicity of herbicides on crops is a major dilemma in agricultural production. Fortunately, the emergence of herbicide safeners is an excellent solution to this challenge, selectively enhancing the performance of herbicides in controlling weeds while reducing the phytotoxicity to crops. But owing to their potential toxicity, only a tiny proportion of safeners are commercially available. Natural products as safeners have been extensively explored, which are generally safe to mammals and cause little pollution to the environment. They are typically endogenous signal molecules or phytohormones, which are generally difficult to extract and synthesize, and exhibit relatively lower activity than commercial products. Therefore, it is necessary to adopt rational design approaches to modify the structure of natural safeners. This paper reviews the application, safener effects, structural characteristics, and modifications of natural safeners and provides insights on the discovery of natural products as potential safeners in the future.

Design, Synthesis, and Structure-Activity Relationship of Novel Aryl-Substituted Formyl Oxazolidine Derivatives as Herbicide Safeners

Nicosulfuron is the leading herbicide in the global sulfonylurea (SU) herbicide market; it was jointly developed by DuPont and Ishihara. Recently, the widespread use of nicosulfuron has led to increasingly prominent agricultural production hazards, such as environmental harm and influence on subsequent crops. The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of existing herbicides. A series of novel aryl-substituted formyl oxazolidine derivatives were designed using the active group combination method. Title compounds were synthesized using an efficient one-pot method and characterized by infrared (IR) spectrometry, ¹H and ¹³C nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS). The chemical structure of compound V-25 was further identified by X-ray single crystallography. The bioactivity assay and structure-activity relationship proved that nicosulfuron phytotoxicity to maize could be reduced by most title compounds. The glutathione S-transferase (GST) activity and acetolactate synthase (ALS) in vivo were determined, and compound V-12 showed inspiring activity comparable to that of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound V-12 competed with nicosulfuron for the acetolactate synthase active site and that this is the protective mechanism of safeners. Absorption, distribution, metabolism, excretion, and toxicity (ADMET) predictions demonstrated that compound V-12 exhibited superior pharmacokinetic properties to the commercialized safener isoxadifen-ethyl. The target compound V-12 shows strong herbicide safener activity in maize; thus, it may be a potential candidate compound that can help further protect maize from herbicide damage.

Design, Synthesis, and Bioactivity of Novel Ester-Substituted Cyclohexenone Derivatives as Safeners

Tembotrione, a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, has been widely used in many types of plants. Tembotrione has been reported for its likelihood of causing injury and plant death to certain corn hybrids. Safeners are co-applied with herbicides to protect certain crops without compromising weed control efficacy. Alternatively, herbicide safeners may effectively improve herbicide selectivity. To address tembotrione-induced Zea mays injury, a series of novel ester-substituted cyclohexenone derivatives were designed using the fragment splicing method. In total, 35 title compounds were synthesized via acylation reactions. All the compounds were characterized using infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. The configuration of compound II-15 was confirmed using single-crystal X-ray diffraction. The bioactivity assay proved that tembotrione phytotoxicity to maize could be reduced by most title compounds. In particular, compound II-14 exhibited the highest activity against tembotrione. The molecular structure comparisons as well as absorption, distribution, metabolism, excretion, and toxicity predictions demonstrated that compound II-14 exhibited pharmacokinetic properties similar to those of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound II-14 could prevent tembotrione from reaching or acting with Z. mays HPPD (PDB: 1SP8). Molecular dynamics simulations showed that compound II-14 maintained satisfactory stability with Z. mays HPPD. This research revealed that ester-substituted cyclohexenone derivatives can be developed as potential candidates for discovering novel herbicide safeners in the future.

Research Progress on the Action Mechanism of Herbicide Safeners: A Review

Herbicide safeners are agricultural chemicals that protect crops from herbicide injury and improve the safety of herbicides and the effectiveness of weed control. Safeners induce and enhance the tolerance of crops to herbicides through the synergism of multiple mechanisms. The principal mechanism is that the metabolic rate of the herbicide in the crop is accelerated by safeners, resulting in the damaging concentration at the site of action being reduced. We focused on discussing and summarizing the multiple mechanisms of safeners to protect crops in this review. It is also emphasized how safeners alleviate herbicide phytotoxicity to crops by regulating the detoxification process and conducting perspectives on future research on the action mechanism of safeners at the molecular level.

The mechanism of exogenous gibberellin A3 protecting sorghum shoots from S-metolachlor Phytotoxicity

BACKGROUND

S-metolachlor (MET) was used to prevent weed infestation in sorghum fields, but inappropriate application could result in phytotoxicity on sorghum. Exogenous gibberellin A₃ (GA₃ ) has been applied for alleviating the phytotoxicity of MET. However, its detoxification mechanism is still not well known.

RESULTS

Leaf deformity of sorghum caused by 200 mg/L MET was alleviated by treating sorghum shoots with 800 mg/L GA₃ , and the injury recovery rate of growth index was over 73%. More importantly, GA₃ could not accelerate the metabolic rate of MET in sorghum. The result of phytohormone metabolomics showed that endogenous GA₃ content in sorghum decreased by 78.10% with MET treatment, while abscisic acid (ABA) content increased by 120.2%, resulting in 10.3-fold increase of ABA/GA₃ ratio. Content of ABA and GA₃ increased by 11.9- and 21.1-fold with MET and GA₃ treatment, respectively, leading to ABA/GA₃ ratio restoration. Moreover, MET inhibited the expression of genes encoding key enzymes related to GA synthesis including CPS1, KO2, KAO, GA20ox1D and ABA8ox gene related to ABA metabolism. The transcription levels of GA metabolism-related genes CYP714D1 and GA2ox were up-regulated by 11.2- and 7.2-fold, while ABA synthesis-related genes NCED and ZEP were up-regulated by 8.0- and 3.0-fold, respectively, with MET and GA₃ treatment.

CONCLUSION

In this study, exogenous GA₃ protecting sorghum shoots from MET phytotoxicity was due to supplement the MET-induced GA₃ deficiency by absorbing exogenous GA₃ , and restore homeostasis of ABA and GA₃ by promoting ABA synthesis, which provides novel insights for mechanism of GA₃ alleviating MET phytotoxicity. © 2022 Society of Chemical Industry.

Diazabicyclo derivatives as safeners protect cotton from injury caused by flumioxazin

Flumioxazin, a protoporphyrinogen oxidase (PPO; EC 1.3.3.4) inhibitor, has been used in soybean, cotton, grapes, and many other crops to control broad leaf weeds. Unfortunately, it can cause damage to cotton. To ameliorate phytotoxicity of flumioxazin to cotton, this work assessed the protective effects of diazabicyclo derivatives as potential safeners in cotton. A bioactivity assay proved that the phytotoxicity of flumioxazin on cotton was alleviated by some of the compounds. In particular, the activity of glutathione S-transferases (GSTs) was significantly enhanced by Compound 32, which showed good safening activity against flumioxazin injury. The physicochemical properties and absorption, distribution, metabolism, excretion and toxicity (ADMET) predictions proved that the pharmacokinetic properties of Compound 32 are similar to those of the commercial safener BAS 145138. The present work demonstrated that diazabicyclo derivatives are potentially efficacious as herbicide safeners, meriting further investigation.

Discovery of novel phenoxypyridine as promising protoporphyrinogen IX oxidase inhibitors

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is a significant target for the discovery of novel bleaching herbicides. Starting from the active fragments of several known commercial herbicides, a series of PPO inhibitors with diphenyl ether scaffolds were designed and synthesized by substructure splicing and bioisosterism methods. The greenhouse herbicidal activity and the PPO inhibitory activity in vitro were measured. The results showed that the novel synthesized compounds have good PPO inhibitory activity, and the IC₅₀ value against corn PPO ranges from 0.032 ± 0.008 mg/L to 3.245 ± 0.247 mg/L. Among all target compounds, compound P2 showed the best herbicidal activity, with a half inhibitory concentration (IC₅₀) of 0.032 ± 0.008 mg/L. In addition, the molecular docking results showed that the benzene ring part of compound P2 can form a π-π stacking with PHE-392, and the trifluoromethyl group and ARG-98 form two hydrogen bonds. Crop safety experiments and cumulative concentration analysis experiments indicated that compound P2 can be used for weed control in rice, wheat, soybean and corn. Therefore, compound P2 can be selected to develop potential lead compounds for novel PPO inhibitors.

The safener isoxadifen-ethyl confers fenoxaprop-p-ethyl resistance on a biotype of Echinochloa crus-galli

BACKGROUND

Some herbicides are commercially formulated with safeners to increase crop selectivity. Fenoxaprop-p-ethyl is formulated with the safener isoxadifen-ethyl for Echinochloa crus-galli control in rice. Safeners act on crops by increasing herbicide metabolism, but this effect may also occur in weeds. The objective of this study was to investigate the effect of the safener isoxadifen-ethyl on the resistance to fenoxaprop-p-ethyl in a biotype of E. crus-galli.

RESULTS

A screening of 52 biotypes identified lack of control in the biotype SANTPAT-R treated with the recommended dose of 69 g ha^-1 of the commercial formulation of fenoxaprop-p-ethyl with the safener isoxadifen-ethyl. While this biotype survived doses greater than 2208 g ha^-1 of the formulation fenoxaprop-p-ethyl + isoxadifen-ethyl, it was killed with 69 g ha^-1 of fenoxaprop-p-ethyl without the safener. A glutathione-s-transferase (GST) enzymes inhibitor reduced the resistance factor in two dose-response curves. A minor effect of a CytP450 inhibitor was observed. The previous spraying of the safener isoxadifen-ethyl followed by fenoxaprop-p-ethyl induced survival in the resistant but not in the susceptible biotype. The GST1 and GSTF1 genes were up-regulated in the resistant biotype. ACCase gene mutations were not found, and no cross-resistance to other ACCase inhibitors was identified.

CONCLUSION

The safener isoxadifen-ethyl present in the commercial herbicide formulation of fenoxaprop-p-ethyl is associated with resistance in the E. crus-galli SANTPAT-R biotype. This resistance is related with herbicide metabolization mediated by GST pathways. This is the first field-selected weed biotype with herbicide resistance due to safener presence in the sprayed formulation. © 2022 Society of Chemical Industry.

Research Progress in the Design and Synthesis of Herbicide Safeners: A Review

Detoxification plays an important role in herbicide action. Herbicide safeners selectively protect crops from herbicide injury without reducing the herbicidal efficiency against the target weeds. With the large-scale use of herbicides, herbicide safeners have been widely used in sorghum, wheat, rice, corn, and other crops. In recent years, an increasing number of unexpected new herbicide safeners have been designed. The varieties, structural characteristics, uses, and synthetic routes of commercial herbicide safeners are reviewed in this paper. The design ideas and structural characteristics of novel herbicide safeners are summarized, which provide a basis for the design of bioactive molecules as new herbicide safeners in the future.

Design, synthesis and biological activity of novel triketone-containing quinoxaline as HPPD inhibitor

BACKGROUND

4-Hydroxyphenyl pyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the important target enzymes used to address the issue of weed control. HPPD-inhibiting herbicides can reduce the carotenoid content in plants and hinder photosynthesis, eventually causing albinism and death. Exploring novel HPPD-inhibiting herbicides is a significant direction in pesticide research. In the process of exploring new high-efficiency HPPD inhibitors, a series of novel quinoxaline derivatives were designed and synthesized using an active fragment splicing strategy.

RESULTS

The title compounds were unambiguously characterized by infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectroscopy. The results of the in vitro tests indicated that the majority of the title compounds showed potent inhibition of Arabidopsis thaliana HPPD (AtHPPD). Preliminary bioevaluation results revealed that a number of novel compounds displayed better or excellent herbicidal activity against broadleaf and monocotyledonous weeds. Compound III-5 showed herbicidal effects comparable to those of mesotrione at a rate of 150 g of active ingredient (ai)/ha for post-emergence application. The results of molecular dynamics verified that compound III-5 had a more stable protein-binding ability. Molecular docking results showed that compound III-5 and mesotrione shared homologous interplay with the surrounding residues. In addition, the enlarged aromatic ring system adds more force, and the hydrogen bond formed can enhance the synergy with π-π stacking.

CONCLUSIONS

The present work indicates that compound III-5 may be a potential lead structure for the development of new HPPD inhibitors.

Design, Synthesis, Structure-Activity Relationship, Molecular Docking, and Herbicidal Evaluation of 2-Cinnamoyl-3-Hydroxycyclohex-2-en-1-one Derivatives as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

Cinnamic acid, isolated from cinnamon bark, is a natural product with excellent bioactivity, and it effectively binds with cyclohexanedione to form novel 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors. According to the active sub-structure combination principle, a series of novel 3-hydroxy-2-cinnamoyl-2-en-1-one derivatives were designed and synthesized. The title compounds were characterized by infrared, ¹H NMR, ¹³C NMR, and HRMS. The in vitro inhibitory activity of AtHPPD verified that compound II-13 showed the most activity with a half-maximal inhibitory concentration (IC₅₀) value of 0.180 μM, which was superior to that of mesotrione (0.206 μM) in vitro. The preliminary herbicidal activity tests demonstrated that some compounds had good herbicidal activity especially compound II-13 at a concentration of 150 g ai/ha. The binding mode of AtHPPD through molecular docking indicated that two oxygens of compounds II-13 formed bidentate interactions with metal ions, and the benzene ring formed π-π accumulation effects with Phe-381 and Phe-424. The results of molecular dynamics simulations showed that compound II-13 exhibited a more stable binding ability with AtHPPD than mesotrione. This study provided insights into the development of natural and efficient herbicides in the future.

Quinoxaline derivatives as herbicide safeners by improving Zea mays tolerance

Isoxaflutole (IXF), a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, causes injury to crops leading to reductions in grain yield. In order to solve the phytotoxicity caused by IXF, the present work evaluated the protective response of the substituted quinoxaline derivatives as potential safeners on Zea mays. The bioassay results showed that all of the test compounds displayed protection against IXF. In particular, safener I-6 exhibited excellent safener activity against IXF injury via enhancing glutathione (GSH) content, glutathione S transferases (GSTs) and cytochrome P450 monooxygenases (CYP450) activity. The tested compounds induced the activity of CYP450 and GSTs in Z. mays. The physicochemical properties and ADMET properties of safener I-6, benoxacor and diketonitrile (DKN, IXF metabolite) were compared to predict pharmaceutical behavior. The present work demonstrates that the safener I-6 could be considered as a potential candidate for developing novel safeners in the future.

Design, synthesis, and herbicidal activity of novel phenoxypyridine derivatives containing natural product coumarin

BACKGROUND

In recent years, protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors have been widely studied as important agricultural herbicides. Our research focused on the design and synthesis of novel PPO inhibitor herbicides, through linking of a diphenylether pyridine bioisostere structure to substituted coumarins, which aims to enhance environmental and crop safety while retaining high efficacy.

RESULTS

A total of 21 compounds were synthesized via acylation reactions and all compounds were characterized using infrared, ¹ H NMR, ¹³ C NMR, and high-resolution mass spectra. The respective configurations of compounds IV-6 and IV-12 were also confirmed using single crystal X-ray diffraction. The bioassay results showed that the title compounds displayed notable herbicidal activity, particularly compound IV-6 which displayed better herbicidal activity in greenhouse and field experiments, crop selectivity and safety for cotton and soybean compared with the commercial herbicide oxyfluorfen.

CONCLUSION

The work revealed that compound IV-6 deserves further attention as a candidate structure for a novel and safe herbicide. © 2021 Society of Chemical Industry.

NPA-Cu2+ Complex as a Fluorescent Sensing Platform for the Selective and Sensitive Detection of Glyphosate

Glyphosate is a highly effective, low-toxicity, broad-spectrum herbicide, which is extensively used in global agriculture to control weeds and vegetation. However, glyphosate has become a potential threat to human and ecosystem because of its excessive usage and its bio-concentration in soil and water. Herein, a novel turn-on fluorescent probe, N-n-butyl-4-(3-pyridin)ylmethylidenehydrazine-1,8-naphthalimide (NPA), is proposed. It efficiently detected Cu2+ within the limit of detection (LOD) of 0.21 μM and displayed a dramatic turn-off fluorescence response in CH3CN. NPA-Cu2+ complex was employed to selectively and sensitively monitor glyphosate concentrations in real samples accompanied by a fluorescence turn-on mode. A good linear relationship between NPA and Cu2+ of glyphosate was found in the range of 10-100 μM with an LOD of 1.87 μM. Glyphosate exhibited a stronger chelation with Cu2+ than NPA and the system released free NPA through competitive coordination. The proposed method demonstrates great potential in quantitatively detecting glyphosate in tap water, local water from Songhua River, soil, rice, millet, maize, soybean, mung bean, and milk with mild conditions, and is a simple procedure with obvious consequences and no need for large instruments or pretreatment.

Fragmenlt Recombination Design, Synthesis, and Safener Activity of Novel Ester-Substituted Pyrazole Derivatives

Fenoxaprop-p-ethyl (FE), a type of acetyl-CoA carboxylase (ACCase) inhibitor, has been extensively applied to a variety of crop plants. It can cause damage to wheat (Triticum aestivum) even resulting in the death of the crop. On the prerequisite of not reducing herbicidal efficiency on target weed species, herbicide safeners selectively protect crops from herbicide injury. Based on fragment splicing, a series of novel substituted pyrazole derivatives was designed to ultimately address the phytotoxicity to wheat caused by FE. The title compounds were synthesized in a one-pot way and characterized via infrared spectroscopy, ¹H nuclear magnetic resonance, ¹³C nuclear magnetic resonance, and high-resolution mass spectrometry. The bioactivity assay proved that the FE phytotoxicity to wheat could be reduced by most of the title compounds. The molecular docking model indicated that compound IV-21 prevented fenoxaprop acid (FA) from reaching or acting with ACCase. The absorption, distribution, metabolism, excretion, and toxicity predictions demonstrated that compound IV-21 exhibited superior pharmacokinetic properties to the commercialized safener mefenpyr-diethyl. The current work revealed that a series of newly substituted pyrazole derivatives presented strong herbicide safener activity in wheat. This may serve as a potential candidate structure to contribute to the further protection of wheat from herbicide injury.

Phenoxypyridine derivatives containing natural product coumarins with allelopathy as novel and promising proporphyrin IX oxidase-inhibiting herbicides: Design, synthesis and biological activity study

To seek novel and safe protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors with excellent herbicidal activity. A series of novel phenoxypyridine derivatives containing natural product coumarins with allelopathy were designed and synthesized based on bioisosterism and active subunit combination in this research. Compounds W3.1 and W3.4, with the half-maximal inhibitory concentration (IC₅₀) value of 0.02653 mg/L and 0.01937 mg/L, respectively, displayed excellent herbicidal activity in greenhouse. Their herbicidal activity was similar to commercial herbicide oxyfluorfen (IC₅₀ = 0.04943 mg/L). The best field inhibitory effect of compounds W3.1 and W3.4 recorded was at doses of 450 g ai/ha and 300 g ai/ha, respectively. Compound W3.4 had the best herbicidal activity among all the target compounds in this paper. Molecular docking analysis revealed that compounds W3.1 and W3.4 could form a hydrogen bonds with the amino acid AGR-98 and a π-π superposition with the amino acid PHE-398, respectively, which was similar to the oxyfluorfen. The crop selectivity tests results indicated that maize, cotton and soybean showed high tolerance to compound W3.4. Compound W3.4 reduced the C_a and C_b contents of wheat and rice, but had less effect on maize, cotton and soybean. Selectivity of compound W3.4 in maize, cotton and soybean were appeared to be due to reduced absorption of the herbicide compared to wheat and rice. Compound W3.4 deserves further attention as a candidate structure for new herbicides.

Electrospun Polymer-Free Nanofibers Incorporating Hydroxypropyl-β-cyclodextrin/Difenoconazole via Supramolecular Assembly for Antifungal Activity

In this study, flexible and self-standing hydroxypropyl-β-cyclodextrin/difenoconazole inclusion complex (HPβCD/DZ-IC) nanofibers were prepared by polymer-free electrospinning, which exhibited potential to be a new fast-dissolving pesticide formulation. Scanning electron microscopy and optical microscopy were applied to evaluate the morphology of nanofibers, which showed that the resulting HPβCD/DZ-IC nanofibers were bead-free and uniform. In addition, the proton nuclear magnetic resonance (¹H NMR) spectrum suggested a stoichiometric ratio of 1:0.9 (HPβCD/DZ). Other characterization methods, such as UV-vis absorption, fluorescence spectroscopy, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), were applied in this study. On the one hand, UV-vis absorption, fluorescence spectroscopy, FT-IR, XRD, and TGA provided useful information for the successful formation of an inclusion complex; on the other hand, the results of TGA indicated the thermal stability of DZ was enhanced after the formation of inclusion complexes. Besides, the phase solubility test could explain the increased water solubility of the nanofibers of inclusion complexes formed by DZ and HPβCD. The results of molecular docking studies demonstrated the most favorable binding interactions when HPβCD combined with DZ. The dissolution test and the antifungal performance test exhibited the characteristics of fast dissolution and the excellent antifungal performance of HPβCD/DZ-IC nanofibers, respectively.

Design, synthesis, herbicidal activity and CoMFA of aryl-formyl piperidinone HPPD inhibitors

Isoxazole, nicotinic acid and benzoic acid are important components in many natural products and useful synthons to build macrostructures having valuable biological activities. In continuation of our effort to discover 4-hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) inhibitors and search for active fragments from natural products, a series of substituted aryl-formyl piperidinone derivatives with natural product fragments was rationally designed, synthesized and tested for their herbicidal activity. Compound I-9 was considered the most effective candidate with an IC₅₀ value of 0.260 μM. The molecular docking results showed that the triketone group of compound I-9 forms a bidentate complex with a metal ion, and the benzene ring interacted with Phe424 and Phe381 via π-π stacking, which was similar to the mechanisms of mesotrione. The present work indicates that compound I-9 may serve as a potential lead compound for further development of green HPPD inhibitors.

Fragments recombination, design, synthesis, safener activity and CoMFA model of novel substituted dichloroacetylphenyl sulfonamide derivatives

BACKGROUND

Isoxaflutole (IXF), as a kind of 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, has been widely used in many kinds of plants. IXF can cause injury in corn including leaf and stem bleaching, plant height reduction or stunting, and reduced crop stand. Safeners are co-applied with herbicides to protect crops without compromising weed control efficacy. With the ultimate goal of addressing Zea mays injury caused by IXF, a series of novel substituted dichloroacetylphenyl sulfonamide derivatives was designed on the basis of scaffold hopping and active substructure splicing.

RESULTS

A total of 35 compounds were synthesized via acylation reactions. All the compounds were characterized by infrared (IR), proton and carbon-13 nuclear magnetic resonance (¹ H-NMR and ¹³ C-NMR), and high-resolution mass spectrometry (HRMS). The configuration of compound II-1 was confirmed by single crystal X-ray diffraction. The bioassay results showed that all the title compounds displayed remarkable protection against IXF via improved content of carotenoid. Especially compound II-1 which possessed better glutathione transferases (GSTs) activity and carotenoid content than the contrast safener cyprosulfamide (CSA). All the satisfied parameters suggested that the Comparative Molecular Field Analysis (CoMFA) model was reliable and stable [with a cross-validated coefficient (q² ) = 0.527, r² = 0.995, r² _pred = 0.931]. The molecular docking simulation indicated that the compound II-1 and CSA could compete with diketonitrile (DKN) at the active site of HPPD, which is a hydrolyzed product of IXF in plants, causing the herbicide to be ineffective.

CONCLUSIONS

The present work revealed that the compound II-1 deserves further attention as the candidate structure of safeners. © 2020 Society of Chemical Industry.

Cobalt (II) complex as a fluorescent sensing platform for the selective and sensitive detection of triketone HPPD inhibitors

4-Hydroxyphenylpyruvatedioxygenase (HPPD) is a Fe(II)/Co(II)-dependent enzyme which has become one of the most effective herbicide targets. HPPD inhibitors have been developed as efficient herbicides for resistant weed control. Developing a method for efficient and rapid HPPD inhibitors detection is still challenging. N-n-butyl-4-methylhydrazinecarbothioamide-1,8-naphthalimide (NMN) was synthesized and used to detect Co²⁺ efficiently with the limit of detection (LOD) of 7.82 nM with a turn-on fluorescence. Herein a novel fluorescent complex, NMN‒Co²⁺ was employed to determine HPPD inhibitors which performed a turn-off effect in the sensing process based on the competitive coordination between the probe and HPPD with Co²⁺. The LODs for three commercial triketone HPPD inhibitors (mesotrione, tembotrione and NTBC) were 6.60 nM, 7.37 nM and 10.22 nM with good sensitivity and selectivity. Furthermore, the present probe has potentials to quantitatively detect mesotrione and tembotrione in real samples.

Thiram/hydroxypropyl-β-cyclodextrin inclusion complex electrospun nanofibers for a fast dissolving water-based drug delivery system

The electrospinning of thiram/hydroxypropyl-β-cyclodextrin inclusion complex nanofiber (thiram/HPβCD-IC-NF) was produced for establishing a quick dissolving water-based drug delivery system. As a dithiocarbamate broad-spectrum fungicide, thiram is insoluble in water. High-concentration HPβCD solutions (180 %, w/v) were applied in thiram/HPβCD systems to implement electrospinning with no extra polymer matrix added. The formation of thiram/HPβCD-IC-NF was identified by Fourier transform infrared spectroscopy, X-ray diffraction as well as nuclear magnetic resonance. Phase solubility study proved HPβCD played a huge role in the improvement in solubility of thiram, and thiram/HPβCD-IC-NF showed an excellent dissolution rate. Scanning electron microscopy was used to examine the configuration of surface of thiram/HPβCD-IC-NF, which exhibited that thiram/HPβCD-IC-NF was uniform and beadless. In addition, thiram/HPβCD-IC-NF exhibited better antifungal activity and thermal stability than pure thiram. In summary, thiram/HPβCD-IC-NF drug delivery system contributed to water solubility, thermal stability and antifungal activity of thiram. It could provide a new idea for the development of new formulations of rapidly dissolving green pesticides, and made efforts to promote the sustainable development of agriculture.

Design, Synthesis, and SAR of Novel 1,3-Disubstituted Imidazolidine or Hexahydropyrimidine Derivatives as Herbicide Safeners

Herbicide safeners enhance herbicide detoxification in crops without reducing their herbicidal efficacy against target weeds. To alleviate maize injury caused by the sulfonylurea herbicide nicosulfuron, a series of 1,3-disubstituted imidazolidine or hexahydropyrimidine derivatives were rationally designed via bioisosterism and active subunit combinations. Thirty novel compounds were synthesized using an efficient one-pot method and low-cost raw materials and characterized by IR, ¹H NMR, ¹³C NMR, and high-resolution mass spectrometer (HRMS). Bioactivity and structure-activity relationship (SAR) were evaluated for herbicide safeners tested against nicosulfuron injury. Most of the compounds effectively protected sensitive maize against nicosulfuron damage. The parent skeletons and substituents of the target compounds both substantially influenced their safener activity. Compound I-3 exhibited superior bioactivity compared to the safener isoxadifen-ethyl. Molecular docking simulations disclosed that compound I-3 competed with nicosulfuron for the acetolactate synthase active site and demonstrated that this is the protective mechanism of safeners. The target compound I-3 presented with strong herbicide safener activity in maize and is, therefore, a potential candidate for the development of a novel herbicide safener.

Novel phenylpyrimidine derivatives containing a hydrazone moiety protect rice seedlings from injury by metolachlor

One strategy for solving the phytotoxicity of herbicides is to apply herbicide safeners that can efficiently alleviate the injuries of agricultural crops caused by herbicides. When metolachlor, a chloroacetamide herbicide, is applied with paddy rice, for example, the mechanisms associated with metolachlor and its residue negatively impact on the growth and yields of rice. To identify novel high-activity herbicide safener candidates for metolachlor, a series of (E)-4-(2-substituted hydrazinyl)-6-chloro-2-phenyl pyrimidines were synthesized and their structures were confirmed using IR (infrared radiation), ¹H NMR, ¹³C NMR, and HRMS (high resolution mass spectrometry). The herbicide safener activities were then evaluated via primary tests. Compounds 3i and 3t were found to have the best herbicide activity on plant height. These compounds were then further screened for their activities at lower concentrations and showed better or similar activities compared to the positive control fenclorim, a commercial herbicide safener. The compounds 3i and 3t significantly enhanced glutathione S-transferase (GST) activity related with the herbicide safener activity in both shoots and roots tissues. Moreover, a qPCR (Real-time quantitative polymerase chain reaction) analysis found that the 3i and 3t treatments enhanced the expressions of OsGSTU3, OsGsTU39, and OsGSTF5. Finally, the results of an acute toxicity assessment with zebrafish (Danio rerio) embryos using treatments 3i and 3t indicated they are relatively safe to aquatic organisms.

Protective efficacy of phenoxyacetyl oxazolidine derivatives as safeners against nicosulfuron toxicity in maize

BACKGROUND

Herbicide safeners mitigate crop damage without reducing herbicide efficacy. Here, the protective effects of phenoxyacetyl oxazolidine derivatives as potential safeners were evaluated with a view toward reducing injury caused by sulfonylurea herbicide nicosulfuron to sensitive maize varieties.

RESULTS

Growth indices demonstrated that the bioactivity of compound 9 (N-phenoxyacety-2-methyl-2,4-diethyl-1,3-oxazolidine) was superior to that of R-28725 and all other compounds tested. Compound 9 induced endogenous glutathione and upregulated glutathione-S-transferase (GST) in maize. Thus, it could enhance maize tolerance to nicosulfuron. Compared with the untreated water control group, the maximum reaction rate of GST was increased by 37.62%, while the maximum velocity of GST was decreased by 61.93% after treatment with compound 9. Acetolactate synthase relative activity was significantly enhanced in the case of treatment with compound 9, indicating the excellent protective effects of compound 9 against nicosulfuron in maize.

CONCLUSIONS

The present work demonstrates that phenoxyacetyl oxazolidine derivatives are potentially efficacious as herbicide safeners and merit further investigation.

Discovery of novel arylthioacetic acid derivatives as 4-hydroxyphenylpyruvate dioxygenase inhibitors

BACKGROUND

4-Hydroxyphenylpyruvate dioxygenase (HPPD) plays an important role in addressing the issue of plant protection research. In a continuing effort to discover novel HPPD inhibitors, we adopted a bioisosterism strategy to design a series of novel arylthioacetic acid scaffold based on the previously discovered aryloxyacetic acid scaffold. This study sheds new light on the discovery of novel HPPD inhibitors.

RESULTS

The compounds A1-A30 and B1-B39 were prepared through an efficient synthetic route for in vitro and glasshouse experiments (herbicidal activities, herbicidal activity spectrum, and crop selectivity). Preliminary bioassay results reveal that these derivatives are promising Arabidopsis thaliana HPPD inhibitors, compounds A11 (K_i = 0.021 μmol L^-1 ) and B20 (K_i = 0.022 μmol L^-1 ), which exhibit similar activities to that of mesotrione (K_i = 0.020 μmol L^-1 ). The glasshouse experiments data indicated that compounds B34 displayed excellent herbicidal activity, which was higher compared to that of mesotrione. Moreover, molecular simulation results show that the compounds B20, B34, and mesotrione shared similar interplay with surrounding residues, which led to a perfect interaction with the active site of Arabidopsis thaliana HPPD. Based on herbicidal results, compound B34 was selected for crop selectivity studies (corn injury ≤ 10%), indicating its potential for weed control in corn fields.

CONCLUSION

These bioassay results showed that the compound B34 could be used as a possible lead compound for the development of HPPD inhibitors. © 2020 Society of Chemical Industry.

Novel phenoxy-(trifluoromethyl)pyridine-2-pyrrolidinone-based inhibitors of protoporphyrinogen oxidase: Design, synthesis, and herbicidal activity

As important chemical pesticides, protoporphyrinogen oxidase (PPO, EC 1.3.3.4) herbicides play a vital role in weed management. Herein, in a search for novel PPO herbicides, a series of phenoxypyridine-2-pyrrolidinone derivatives were synthesized and their herbicidal activities were tested. To confirm the structures of the newly synthesized compounds, a colorless single crystal of compound 9d was obtained and crystallographic data collected. PPO inhibition experiments showed that most compounds have PPO inhibitory effects. The half-maximal inhibitory concentration (IC₅₀) of compound 9d and oxyfluorfen were 0.041 mg/L and 0.043 mg/L, respectively, which showed compound 9d was the most potent compound. Compound 9d reduced the Chlorophyll a (Chl a) and Chlorophyll b (Chl b) contents of Abutilon theophrasti (A. theophrasti), to 0.306 and 0.217 mg/g, respectively. Crop selectivity experiments and field trial indicated that compound 9d can potentially be used to develop post-emergence herbicides for weed control in rice, cotton, and peanut. Molecular docking studies showed that both oxyfluorfen and compound 9d can enter the PPO cavity to occupy the active site and compete with the porphyrin to block the chlorophyll synthesis process, affect photosynthesis, and eventually cause weed death. Compound 9d was found to be a promising lead compound for novel herbicide development.

Safening activity and metabolism of the safener cyprosulfamide in maize and wheat

BACKGROUND

Safeners extend the application of existing herbicides by selectively enhancing tolerance in large-grained cereal crops. While their activity is linked to enhanced herbicide metabolism, their exact mode of action and reasons for their crop specificity have yet to be determined. In this study, we investigated the selectivity of the recently developed sulfonamide safener cyprosulfamide (CSA) in maize (Zea mays L.) and wheat (Triticum aestivum), focusing on its uptake, distribution and metabolism in the two species.

RESULTS

CSA protected maize, but not wheat, from injury by thiencarbazone-methyl (TCM). This correlated with the selective enhanced detoxification of the herbicide in maize. CSA underwent more rapid metabolism in maize than in wheat, with the formation of a specific hydroxylated metabolite correlating with safening. Studies with the nsf1 mutant sweetcorn line showed that the hydroxylation of CSA was partly mediated by the cytochrome P450 CYP81A9. However, primary metabolites of CSA were chemically synthesised and tested for their ability to safen TCM in maize but when tested were inactive as safeners.

CONCLUSION

The results of this study suggest that the protection against TCM injury by CSA is linked to enhanced herbicide metabolism. This selective activity is due to the specific recognition of parent CSA in maize but not in wheat. Subsequent rapid oxidative metabolism of CSA led to its inactivation, demonstrating that cytochrome P450s regulate the activity of safeners as well as herbicides. © 2020 Society of Chemical Industry.

Design, Synthesis, and Bioevaluation of Substituted Phenyl Isoxazole Analogues as Herbicide Safeners

Herbicide safeners enhance herbicide detoxification in crops without affecting target weed sensitivity. To enhance crop tolerance to the toxicity-related stress caused by the herbicide acetochlor (ACT), a new class of substituted phenyl isoxazole derivatives was designed by an intermediate derivatization method as herbicide safeners. Microwave-assisted synthesis was used to prepare the phenyl isoxazole analogues, and all of the structures were confirmed via IR, ¹H NMR, ¹³C NMR, and HRMS. Compound I-1 was further characterized by X-ray diffraction analysis. Bioassay results showed that most of the obtained compounds provided varying degrees of safening against ACT-induced injury by increasing the corn growth recovery, glutathione content, and glutathione S-transferase activity. In particular, compound I-20 showed excellent safener activity against ACT toxicity, comparable to that of the commercial safener benoxacor. Gaussian calculations have been performed and the results indicated that the nucleophilic ability of compound I-20 is higher than that of benoxacor, thus the activity is higher than that of benoxacor. These findings demonstrate that phenyl isoxazole derivatives possess great potential for protective management in cornfields.

Synthesis of Novel 6-Aryloxy-4-chloro-2-phenylpyrimidines as Fungicides and Herbicide Safeners

Fenclorim is a commercial herbicide safener with fungicidal activity used for chloroacetanilide herbicides, which might be suitable as a lead compound for screening novel fungicides. However, little has been reported so far on the structure-activity relationship of fungicidal activities of fenclorim or its analogues. Here, a series of 4-chloro-6-substituted phenoxy-2-phenylpyrimidine derivatives was synthesized by a substructure splicing route using fenclorim as a lead compound. The structures of synthesized derivatives were characterized by ¹H NMR, ¹³C NMR, and HRMS. Their fungicidal and herbicide safening activities were then evaluated. The results revealed that compound 11 had the best fungicidal activity against Sclerotinia sclerotiorum and Thanatephorus cucumeris, which was better than that of the control pyrimethanil. Moreover, compounds 3, 5, and 25 exhibited excellent safening activities against fresh weight, plant height, and root length, respectively. Such activities were significantly improved when compared to fenclorim. In summary, these findings look promising for the preparation of new fungicides and herbicide safeners based on the structure of fenclorim.

A Highly Selective Perylenediimide-Based Chemosensor: "Naked-Eye" Colorimetric and Fluorescent Turn-On Recognition for Al3

A novel “turn-on” fluorescent probe (PCN) was designed, synthesized, and characterized with perylene tetracarboxylic disimide as the fluorophore and Schiff base subunit as the metal ion receptor. The probe demonstrated a considerable fluorescence enhancement in the presence of Al³⁺ in DMF with high selectivity and sensitivity. Furthermore, the considerably “off–on” fluorescence response simultaneously led to the apparent color change from colorless to brilliant yellow, which could also be identified by naked eye easily. The sensing capability of PCN to Al³⁺ was evaluated by the changes in ultraviolet–visible, fluorescence, Fourier transform–infrared, proton nuclear magnetic resonance, and high-resolution mass spectrometry spectroscopies. The linear concentration range for Al³⁺ was 0–63 μM with a detection limit of 0.16 μM, which allowed for the quantitative determination of Al³⁺.

Encapsulation of thiabendazole in hydroxypropyl-β-cyclodextrin nanofibers via polymer-free electrospinning and its characterization

BACKGROUND

Thiabendazole (TBZ) is a poorly water-soluble benzimidazole fungicide. However, the water solubility of TBZ can be significantly enhanced by inclusion complexation with cyclodextrins. In this study, a thiabendazole/hydroxypropyl-β-cyclodextrin (TBZ/HPβCD) complex was synthesized and electrospinning was performed to produce a TBZ/HPβCD nanofibrous (TBZ/HPβCD-NF) complex that improved water solubility and antifungal activity.

RESULTS

The formation of TBZ/HPβCD-NF was characterized by Fourier transform infrared spectroscopy, X-ray diffraction and nuclear magnetic resonance. The morphology of TBZ/HPβCD-NF was studied by scanning electron microscopy. A phase solubility experiment showed that HPβCD exerted a great solubilization effect on TBZ, and TBZ/HPβCD-NF had better antifungal activity compared to that of TBZ alone.

CONCLUSIONS

In summary, the solid fungicidal nanodispersion prepared in the present study is a new type of formulation that can enhance the water solubility of TBZ. This formulation, which demonstrated potential as a new fast dissolving formulation type with increased efficacy, is expected to be conducive to the sustainable development of agriculture. © 2020 Society of Chemical Industry.

Crystal structure of 2-(3,6-dimethyl-2,3-dihydro-4H-benzo[b][1,4]oxazin-4-yl)-2-oxoethyl acetate, C14H17NO4

C14H17NO4, monoclinic, P21/c (no. 14), a = 9.6719(19) Å, b = 13.529(3) Å, c = 11.094(2) Å, β = 112.31(3)°, V = 1342.9(5) Å3, Z = 4, R gt(F) = 0.0480, wR ref(F 2) = 0.1422, T = 293(2) K.

Based on the Virtual Screening of Multiple Pharmacophores, Docking and Molecular Dynamics Simulation Approaches toward the Discovery of Novel HPPD Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an iron-dependent non-heme oxygenase involved in the catabolic pathway of tyrosine, which is an important enzyme in the transformation of 4-hydroxyphenylpyruvic acid to homogentisic acid, and thus being considered as herbicide target. Within this study, a set of multiple structure-based pharmacophore models for HPPD inhibitors were developed. The ZINC and natural product database were virtually screened, and 29 compounds were obtained. The binding mode of HPPD and its inhibitors obtained through molecular docking study showed that the residues of Phe424, Phe381, His308, His226, Gln307 and Glu394 were crucial for activity. Molecular-mechanics-generalized born surface area (MM/GBSA) results showed that the coulomb force, lipophilic and van der Waals (vdW) interactions made major contributions to the binding affinity. These efforts will greatly contribute to design novel and effective HPPD inhibitory herbicides.

Identification of key residues determining the binding specificity of human 4-hydroxyphenylpyruvate dioxygenase

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is the second enzyme of the tyrosine catabolic pathway. Its physiological function is to catalyze the conversion of 4-hydroxyphenylpyruvic acid to homogentisic acid, which displays different physiological effects in mammals and plants. Insights on the selective inhibition of human HPPD (hHPPD) by triketone inhibitors were furnished by the integrated application of molecular simulation and biological testing. The binding free energy of hHPPD and inhibitors was obtained through molecular dynamics (MD) simulations, and the result was in agreement with the inhibition experiment in vitro. The binding free energy contribution demonstrated that the formation of hHPPD-inhibitor complexes was mainly driven by van der Waals energy. Ser226, Asn241, Gln265, Phe336, Phe359 and Phe364 made great contributions to binding affinities of all the systems. Among the residues involved in the interaction between nitisinone (NTBC) and hHPPD, Tyr221 and Leu224, whose mutation into Ala caused significant decrease of NTBC binding ability, were two key residues in determining the selective binding affinity of inhibitor and hHPPD. This work provides valuable theoretical basis for rational design of highly selective inhibitors targeting hHPPD.