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

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.

Efficient detection of flusilazole by an electrochemical sensor derived from MOF MIL-53(Fe) for food safety

Flusilazole is a triazole fungicide with residues that are potentially toxic to humans. It enters the human body mainly through food, although its bactericidal activity is substantial. In this study, an electrochemical sensor Fe/Fe2O3@C with a core-shell structure was constructed to efficiently detect flusilazole by annealing MIL-53(Fe) which was prepared by a simple solvothermal method. Transmission electron microscopy and scanning electron microscopy were used to characterize the apparent morphology of MIL-53(Fe) and Fe/Fe2O3@C, and their structures were further characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, powder X-ray diffraction, and the mapping of elements by energy dispersive spectroscopy. The electrochemical behavior of Fe/Fe2O3@C in the detection of flusilazole was evaluated by differential pulse voltammetry under optimal conditions. The results of the study indicate that the Fe/Fe2O3@C electrochemical sensor displayed excellent detection capabilities for flusilazole, where the sensor exhibited a wide detection range from 1.00 × 10-4 to 1.00 × 10-12 mol/L with an incredibly low LOD of 593 fM, making it highly sensitive to trace amounts of flusilazole. Moreover, Fe/Fe2O3@C demonstrated superior reproducibility, stability, and resistance to interference, highlighting its reliability in practical applications. The sensor was also successfully utilized to quantitatively detect flusilazole in various real samples, which suggests that Fe/Fe2O3@C has broad-spectrum environmental resistance and can effectively and rapidly detect flusilazole residues in different types of food items and environmental matrices. The study also delved into the mechanism of Fe/Fe2O3@C for the detection of flusilazole, providing a deeper understanding of the functionality of this sensor. Overall, these findings emphasize the practical significance of Fe/Fe2O3@C as an electrochemical sensor, showcasing its potential for real-world applications in food safety and environmental monitoring.

Overexpressing CYP81D11 enhances 2,4,6-trinitrotoluene tolerance and removal efficiency in Arabidopsis

Phytoremediation is a promising technology for removing the high-toxic explosive 2,4,6-trinitrotoluene (TNT) pollutant from the environment. Mining dominant genes is the key research direction of this technology. Most previous studies have focused on the detoxification of TNT rather than plants' TNT tolerance. Here, we conducted a transcriptomic analysis of wild type Arabidopsis plants under TNT stress and found that the Arabidopsis cytochrome P450 gene CYP81D11 was significantly induced in TNT-treated plants. Under TNT stress, the root length was approximately 1.4 times longer in CYP81D11-overexpressing transgenic plants than in wild type plants. The half-removal time for TNT was much shorter in CYP81D11-overexpressing transgenic plants (1.1 days) than in wild type plants (t1/2 = 2.2 day). In addition, metabolic analysis showed no difference in metabolites in transgenic plants compared to wild type plants. These results suggest that the high TNT uptake rates of CYP81D11-overexpressing transgenic plants were most likely due to increased tolerance and biomass rather than TNT degradation. However, CYP81D11-overexpressing plants were not more tolerant to osmotic stresses, such as salt or drought. Taken together, our results indicate that CYP81D11 is a promising target for producing bioengineered plants with high TNT removing capability.

Design, Synthesis, and Biological Evaluation of Novel Purine Derivatives as Herbicide Safeners

Mesosulfuron-methyl, an inhibitor of acetolactate synthase (ALS), has been extensively used in wheats. However, it can damage wheat (Triticum aestivum) and even lead to crop death. Herbicide safeners selectively shield crops from such damage without compromising weed control. To mitigate the phytotoxicity of mesosulfuron-methyl in crops, several purine derivatives were developed based on active substructure splicing. The synthesized title compounds underwent thorough characterization using infrared spectroscopy, 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry. We evaluated chlorophyll and glutathione contents as well as various enzyme activities to evaluate the safer activity of these compounds. Compounds III-3 and III-7 exhibited superior activity compared with the safener mefenpyr-diethyl. Molecular structure analysis, along with predictions of absorption, distribution, metabolism, excretion, and toxicity, indicated that compound III-7 shared pharmacokinetic traits with the commercial safener mefenpyr-diethyl. Molecular docking simulations revealed that compound III-7 competitively bound to the ALS active site with mesosulfuron-methyl, elucidating the protective mechanism of the safeners. Overall, this study highlights purine derivatives as potential candidates for novel safener development.

Design, Synthesis, and Biological Activity of Novel Phenyltriazolinone PPO Inhibitors Containing Five-Membered Heterocycles

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) catalyzes the oxidation of protoporphyrinogen IX to protoporphyrin IX, which is a key step in the synthesis of porphyrins in vivo. PPO inhibitors use protoporphyrinogen oxidase as the target and block the biosynthesis process of porphyrin by inhibiting the activity of the enzyme, eventually leading to plant death. In this paper, phenyl triazolinone was used as the parent structure, and the five-membered heterocycle with good herbicidal activity was introduced by using the principle of substructure splicing. According to the principle of bioisosterism, the sulfur atoms on the thiophene ring were replaced with oxygen atoms. Finally, 33 phenyl triazolinones and their derivatives were designed and synthesized, and their characterizations and biological activities were investigated. The in vitro PPO inhibitory activity and greenhouse herbicidal activity of 33 target compounds were determined, and compound D4 with better activity was screened out. The crop safety determination, field weeding effect determination, weeding spectrum determination, and crop metabolism study were carried out. The results showed that compound D4 showed good safety to corn, soybean, wheat, and peanut but poor selectivity to cotton. The field weeding effect of this compound is comparable to that of the commercial herbicide sulfentrazone. The herbicidal spectrum experiment showed that compound D4 had a wide herbicidal spectrum and a good growth inhibition effect on dicotyledonous weeds. Molecular docking results showed that compound D4 forms a hydrogen bond with amino acid residue Arg-98 in the tobacco mitochondria (mtPPO)-active pocket and forms two π-π stacking interactions with Phe-392. This indicates that compound D4 has stronger PPO inhibitory activity. This indicates that compound D4 has wide prospects for development.

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.

Improving U-net network for semantic segmentation of corns and weeds during corn seedling stage in field

Introduction

Weeds are one of the main factors affecting crop growth, making weed control a pressing global problem. In recent years, interest in intelligent mechanical weed-control equipment has been growing.

Methods

We propose a semantic segmentation network, RDS_Unet, based on corn seedling fields built upon an improved U-net network. This network accurately recognizes weeds even under complex environmental conditions, facilitating the use of mechanical weeding equipment for reducing weed density. Our research utilized field-grown maize seedlings and accompanying weeds in expansive fields. We integrated the U-net semantic segmentation network, employing ResNeXt-50 for feature extraction in the encoder stage. In the decoder phase, Layer 1 uses deformable convolution with adaptive offsets, replacing traditional convolution. Furthermore, concurrent spatial and channel squeeze and excitation is incorporated after ordinary convolutional layers in Layers 2, 3, and 4.

Results

Compared with existing classical semantic segmentation models such as U-net, Pspnet, and DeeplabV3, our model demonstrated superior performance on our specially constructed seedling grass semantic segmentation dataset, CGSSD, during the maize seedling stage. The Q6mean intersection over union (MIoU), precision, and recall of this network are 82.36%, 91.36%, and 89.45%, respectively. Compared to those of the original network, the proposed network achieves improvements of 5.91, 3.50, and 5.49 percentage points in the MIoU, precision, and recall, respectively. The detection speed is 12.6 frames per second. In addition, ablation experiments further confirmed the impactful contribution of each improvement component on the overall semantic segmentation performance.

Discussion

This study provides theoretical and technical support for the automated operation of intelligent mechanical weeding devices.

Soil enzyme activities, physiological indicators, agronomic traits and yield of common buckwheat under herbicide combined with safeners

In the pursuit of green agricultural development, alleviating the harmful effects of herbicides is critical. Herbicide safeners have been identified as an effective solution to safeguard crops without compromising the herbicidal efficacy. However, the impact of combined applications of herbicide and safeners on the physiological characteristics, growth, yield of common buckwheat, and soil enzyme activities remains unclear. Therefore, a two-year (2021 and 2022) field experiment was conducted in the Loess Plateau region of Northwest China under seven treatments: herbicide metolachlor application alone (H1); herbicide metolachlor combined with gibberellin (H1S1); herbicide metolachlor combined with brassinolide (H1S2); herbicide metolachlor combined with naian (H1S3); herbicide metolachlor combined with jiecaotong (H1S4); manual weeding (CK1) and spraying the same volume of water (CK2). The results indicated that H1S3 minimized herbicide toxicity while sustaining the herbicide control efficacy. H1S2 treatment significantly increased the chlorophyll content (SPAD value), superoxide dismutase (SOD), peroxidase (POD) activities, and decreased the malondialdehyde (MDA) content of the leaves compared to H1 treatment. Additionally, the safeners helped restore the biochemical homeostasis of the soil by preventing the inhibition of invertase and urease activities and increasing soil catalase activity. Furthermore, H1S2 promotion of dry matter accumulation, alleviation of herbicide inhibition on plant height, stem diameter, grainnumber per plant and thousand-grain weight resulted in a significant increase in grain yield (14.36 % in 2021 and 27.78 % in 2022) compared to other safener treatments. Overall, this study demonstrates that brassinolide as a safener can effectively mitigate the negative effects of herbicide on the growth and development of common buckwheat while also improving grain yield. These findings provide valuable technical guidance for sustainable and intensive production of common buckwheat in the Loess Plateau of Northwest China.

Integrating transcriptome and physiological analyses to elucidate the molecular responses of sorghum to fluxofenim and metolachlor herbicide

The extensive use of herbicides has raised concerns about crop damage, necessitating the development of effective herbicide safeners. Fluxofenim has emerged as a promising herbicide safener; however, it's underlying mechanism remains unclear. Here, we screened two inbred lines 407B and HYZ to investigate the detoxication of fluxofenim in mitigating metolachlor damage in sorghum. Metolachlor inhibited seedling growth in both 407B and HYZ, while, fluxofenim could significantly restore the growth of 407B, but not effectively complement the growth of HYZ. Fluxofenim significantly increased the activities of glutathione-S-transferase (GST) to decrease metolachlor residue in 407B, but not in HYZ. This implys that fluxofenim may reduce metolachlor toxicity by regulating its metabolism. Furthermore, metolachlor suppressed AUX-related and JA-related genes expression, while up-regulated the expression of SA-related genes. Fluxofenim also restored the expression of AUX-related and JA-related genes inhibited by metolachlor and further increased expression of SA-related genes. Moreover, we noted a significant increase in the content of trans-zeatin O-glucoside (tZOG) and Gibberellin1 (GA1) after the fluxofenim treatment. In conclusion, fluxofenim may reduce the injury of herbicide by affecting herbicide metabolism and regulating hormone signaling pathway.

A pH-responsive MOF-functionalized hollow mesoporous silica controlled herbicide delivery system exhibits enhanced activity against ACCase-herbicide-resistant weeds

BACKGROUND

Weeds grow aggressively in agricultural fields, leading to reduced crop yields and an inability to meet the growing demand for food. Herbicides are currently the most effective method for weed control. However, the overuse of herbicides has resulted in the evolution of resistance mutants and has caused environmental pollution. Therefore, new technologies are urgently required to address this global challenge.

RESULTS

We report a copper-benzene-1,4-dicarboxylate metal organic framework (Cu-BDC MOF)-functionalized carboxyl hollow mesoporous silica (HMS-COOH) delivery system for the pH-controlled release of the acetyl-CoA carboxylase (ACCase)-inhibiting herbicide quizalofop-p-ethyl (QE). The delivery system (QE@HMS@Cu-BDC) enabled the efficient control of barnyard grasses that are susceptible and resistant to ACCase-inhibiting herbicides, which showed 93.33% and 88.33% FW control efficacy at 67.5 g ha-1 , respectively. With the lowest pH value (3), QE and copper ion were released slowly to total 70.30% and 78.55% levels (respectively) from QE@HMS@Cu-BDC after 89 h. QE@HMS@Cu-BDC showed better absorption, conduction, transportation and ACCase activity inhibition performance than that of QE emulsifiable concentrate (EC) in both susceptible and ACCase-herbicide resistant barnyard grasses. In addition, with the safener effect of carrier HMS@Cu-BDC and the aid of the safener fenchlorazole-ethyl (FE), the application of QE@HMS@Cu-BDC was shown to mitigate the damage caused by QE to rice plants.

CONCLUSION

This work found that the new material HMS-COOH@Cu-BDC can be used to mitigate herbicide-induced oxidative stress and improve rice plant safety. Futhermore, the QE@HMS-COOH@Cu-BDC constructed in this research might be used as an efficient nanopesticide formulation for weed controls in paddy rice fields. © 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.

Synthesis and Biological Activity Evaluation of Benzoxazinone-Pyrimidinedione Hybrids as Potent Protoporphyrinogen IX Oxidase Inhibitor

Protoporphyrinogen IX oxidase (PPO/Protox, E.C. 1.3.3.4) is recognized as one of the most important targets for herbicide discovery. In this study, we report our ongoing research efforts toward the discovery of novel PPO inhibitors. Specifically, we identified a highly potent new compound series containing a pyrimidinedione moiety and bearing a versatile building block-benzoxazinone scaffold. Systematic bioassays resulted in the discovery of compound 7af, ethyl 4-(7-fluoro-6-(3-methyl-2,6-dioxo-4-(trifluoromethyl)-3,6-dihydropyrimidin-1(2H)-yl)-3-oxo-2,3-dihydro-4H-benzo[b][1,4]oxazin-4-yl)butanoate, which exhibited broad-spectrum and excellent herbicidal activity at the dosage of 37.5 g a.i./ha through postemergence application. The inhibition constant (Ki) value of 7af to Nicotiana tabacum PPO (NtPPO) was 14 nM, while to human PPO (hPPO), it was 44.8 μM, indicating a selective factor of 3200, making it the most selective PPO inhibitor to date. Moreover, molecular simulations further demonstrated the selectivity and the binding mechanism of 7af to NtPPO and hPPO. This study not only identifies a candidate that showed excellent in vivo bioactivity and high safety toward humans but also provides a paradigm for discovering PPO inhibitors with improved performance through molecular simulation and structure-guided optimization.

Design, Synthesis, and Biological Activity Determination of Novel Phenylpyrazole Protoporphyrinogen Oxidase Inhibitor Herbicides Containing Five-Membered Heterocycles

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitor herbicides have attracted widespread attention in recent years as ideal herbicides due to their high efficiency, low toxicity, and low pollution. In this article, 30 phenylpyrazole derivatives containing five-membered heterocycles were designed and synthesized according to the principle of bioelectronic isoarrangement and active substructure splicing. A series of structural characterizations were performed on the synthesized compounds. The herbicide activity in greenhouse was evaluated to determine their growth inhibition effect on weeds, their IC50 value through in vitro PPO enzyme activity measurement was calculated, and target compounds 2i and 3j that have herbicide effects comparable to pyraflufen-ethyl were selected. Crop safety experiments have shown that when the spraying concentration is 300 g of ai/ha, gramineous crops such as wheat, corn, and rice are more tolerant to compound 2i, with wheat exhibiting high tolerance, which is equivalent to the crop safety of pyraflufen-ethyl. Compound 2i can be used as a candidate herbicide for wheat, corn, and paddy fields, and the results are consistent with the cumulative concentration experiment. Molecular docking results showed that compound 2i interacted with the amino acid residue ARG-98 by forming two hydrogen bonds and interacted with the amino acid residue PHE-392 by forming two π-π stacking interactions, indicating that compound 2i has more excellent herbicidal activity than pyraflufen-ethyl and is expected to become a potential lead compound of phenylpyrazole PPO inhibitor herbicides.

Design, synthesis and biological activity of novel triketone herbicides containing natural product fragments

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) belongs to the non-heme Fe2+ - containing enzyme family and is an important enzyme in tyrosine decomposition. HPPD is crucial to the discovery of novel bleaching herbicides. To develop novel HPPD inhibitor herbicides containing the β-triketone motif, a series of 4-hydroxyl-3-(substituted aryl)-pyran-2-one derivatives were designed using the active fragment splicing method. The title compounds were synthesized and characterized through infrared spectroscopy (IR), 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry (HRMS). The X-ray diffraction method determined the single crystal structure of I-17. Preliminary bioassay data revealed that several novel compounds, especially I-12 and II-3, showed excellent herbicidal activity against broadleaf and monocotyledonous weeds at a dose of 150 g ai/ha. The results of crop selectivity and carotenoids determination indicated that compound I-12 is more suitable for wheat and cotton fields than mesotrione. Additionally, compound II-3 is safer for soybeans and peanuts than mesotrione. The inhibitory activity of Arabidopsis thaliana HPPD (AtHPPD) verified that compound II-3 showed the most activity with an IC50 value of 0.248 μM, which was superior to that of mesotrione (0.283 μM) in vitro. The binding mode of compound II-3 and AtHPPD was confirmed through molecular docking and molecular dynamics simulations. This study provides insights into the future development of natural and efficient herbicides.

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.

Discovery of novel HPPD inhibitors: Virtual screening, molecular design, structure modification and biological evaluation

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD, a Fe(II)/α-ketoglutarate dependent oxygenases), is a popular herbicide target. In this work, two pharmacophore models based on common molecular characteristics (HipHop) and receptor-ligand complex (CBP) were generated for virtual screening for HPPD inhibitors. About 1,000,000 molecules containing diketone structure from PubChem were filtered by Lipinski's rules to build a 3D database. Then the database was screened through combining HipHop model, CBP model, ADMET (absorption, distribution, metabolism, excretion and toxicity) prediction and molecular docking. Subsequently, based on the specific binding mode and affinity of HPPD inhibitors, 4 molecules with high -CDOCKER energy, good aqueous solubility and human safety predicative properties values were screened. From the screening results and combined with previous work, three novel HPPD inhibitors were designed and synthesized through fragment splicing and bioisosterism strategies. Compound IV-a exhibited similar inhibition of Arabidopsis thaliana HPPD (AtHPPD) and herbicidal activity as mesotrione. Crop selectivity showed that compound IV-a had better crop safety than mesotrione. Comparing the molecular properties, ADMET and molecular docking studies indicated that compounds IV-a exhibited better properties than mesotrione, which could be further modified as novel HPPD inhibitor herbicides.

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.