Pesticide Detox by Design

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.

Herbicide Safeners: From Molecular Structure Design to Safener Activity

Herbicide safeners, highly effective antidotes, find widespread application in fields for alleviating the phytotoxicity of herbicides to crops. Designing new herbicide safeners remains a notable issue in pesticide research. This review focuses on discussing and summarizing the structure-activity relationships, molecular structures, physicochemical properties, and molecular docking of herbicide safeners in order to explore how different structures affect the safener activities of target compounds. It also provides insights into the application prospects of computer-aided drug design for designing and synthesizing new safeners in the future.

Target and non-target site mechanisms of fungicide resistance and their implications for the management of crop pathogens

Fungicides are indispensable for high-quality crops, but the rapid emergence and evolution of fungicide resistance have become the most important issues in modern agriculture. Hence, the sustainability and profitability of agricultural production have been challenged due to the limited number of fungicide chemical classes. Resistance to site-specific fungicides has principally been linked to target and non-target site mechanisms. These mechanisms change the structure or expression level, affecting fungicide efficacy and resulting in different and varying resistance levels. This review provides background information about fungicide resistance mechanisms and their implications for developing anti-resistance strategies in plant pathogens. Here, our purpose was to review changes at the target and non-target sites of quinone outside inhibitor (QoI) fungicides, methyl-benzimidazole carbamate (MBC) fungicides, demethylation inhibitor (DMI) fungicides, and succinate dehydrogenase inhibitor (SDHI) fungicides and to evaluate if they may also be associated with a fitness cost on crop pathogen populations. The current knowledge suggests that understanding fungicide resistance mechanisms can facilitate resistance monitoring and assist in developing anti-resistance strategies and new fungicide molecules to help solve this issue. © 2023 Society of Chemical Industry.

A Study in Scaffold Hopping: Discovery and Optimization of Thiazolopyridines as Potent Herbicides That Inhibit Acyl-ACP Thioesterase

In the search for new chemical entities that can control resistant weeds by addressing novel modes of action (MoAs), we were interested in further exploring a compound class that contained a 1,8-naphthyridine core. By leveraging scaffold hopping methodologies, we were able to discover the new thiazolopyridine compound class that act as potent herbicidal molecules. Further biochemical investigations allowed us to identify that the thiazolopyridines inhibit acyl-acyl carrier protein (ACP) thioesterase (FAT), with this being further confirmed via an X-ray cocrystal structure. Greenhouse trials revealed that the thiazolopyridines display excellent control of grass weed species in pre-emergence application coupled with dose response windows that enable partial selectivity in certain crops.

A new series of acylhydrazones derived from metribuzin with modulated herbicidal activity

This paper reports the preparation and herbicidal evaluation of a small library of acylhydrazones based on the synthetic herbicide metribuzin. The hydrazone linkage easily obtained by reaction of metribuzin with aliphatic and aromatic aldehydes, masks efficiently the exocyclic amino group, thereby altering significantly H-bonding with the receptor and increasing the lipophilicity relative to the parent herbicide. The structures of all compounds, including key stereochemical issues on conformation and E/Z configuration around the C[bond, double bond]N bond were thoroughly elucidated by spectroscopic methods, and unambiguously corroborated by X-ray diffraction analysis. The herbicidal assays using an aliphatic and an aromatic acylhydrazone were performed on tomato and rapeseed plants grown in greenhouse. Our results demonstrate, regardless of rate application, that such acylhydrazone formulations do not alter the selectivity of metribuzin. Moreover, the herbicide activity was even higher in the alkyl derivative than that achieved by commercial metribuzin, thus suggesting that this substance can be applied with no need of combination with chemical coadjuvants, unlike most formulations of commercially available herbicides. Therefore, the study shows the promising effect of chemical derivatization of a common herbicide as metribuzin, to improve the herbicide activity without compromising selectivity, and allowing the farmers its use in crop protection safely and effectively.

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.

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.

Crude Extracts and Secondary Metabolites of Epichloë bromicola against Phytophthora infestans

Potato late blight caused by Phytophthora infestans is still one of the main factors limiting potato production. Epichloë spp. can provide host plants with various resistances, which makes them show great potential in the biological control of diseases. In this study, we explored the potential biological activity of crude extracts of 20 strains of Epichloë bromicola to control P. infestans. The crude extracts of strains 1 and 8 showed significant antifungal activity with an inhibition rate of 88 % and 81 %, respectively, and showed different effects on the mycelium morphology of P. infestans observed by scanning electron microscopy. Moreover, the two crude extracts demonstrated an interesting therapeutic and protective effect on potato late blight, and none of the extracts had an adverse effect against zebrafish embryos. A total of 13 metabolites were isolated from the crude extract of strain 8, and these tested compounds showed a weak antifungal effect and the inhibition rate was less than 80 %. These findings suggested that strains 1 and 8 have potential for biocontrol of late potato blight.

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.

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.

The Role of Cytochrome P450s in Insect Toxicology and Resistance

Insect cytochrome P450 monooxygenases (P450s) perform a variety of important physiological functions, but it is their role in the detoxification of xenobiotics, such as natural and synthetic insecticides, that is the topic of this review. Recent advances in insect genomics and postgenomic functional approaches have provided an unprecedented opportunity to understand the evolution of insect P450s and their role in insect toxicology. These approaches have also been harnessed to provide new insights into the genomic alterations that lead to insecticide resistance, the mechanisms by which P450s are regulated, and the functional determinants of P450-mediated insecticide resistance. In parallel, an emerging body of work on the role of P450s in defining the sensitivity of beneficial insects to insecticides has been developed. The knowledge gained from these studies has applications for the management of P450-mediated resistance in insect pests and can be leveraged to safeguard the health of important beneficial insects.

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 Biological Evaluation of Novel Thienylpyridyl- and Thioether-Containing Acetamides and Their Derivatives as Pesticidal Agents

Referring to the structural information of the "hit" compound A from the reported pharmacophore-based virtual screening, a series of novel thienylpyridyl- and thioether/sulfoxide/sulfone-containing acetamide derivatives have been designed and synthesized. The structures of new compounds were confirmed by 1H NMR, 13C NMR and HRMS. The single-crystal structure of A was firstly reported. All the new synthesized compounds were evaluated for insecticidal activities on Mythimna separata Walker and Plutella xylostella L. Through a step-by-step structural optimization, the high insecticidal agents, especially towards Plutella xylostella L., have been found, and thienylpyridyl- and sulfone/thioether-containing acetamides Iq, Io, Ib and A, which are comparable with the control insecticides cartap, triflumuron and chlorantraniliprole in the present study, can be used as novel lead structures for new insecticides innovation research. In addition, some of the compounds, e.g., A, Ih, Id, Io and Iq, also exhibited favourable fungicidal activities against Physalospora piricola, Rhizoctonia cerealis and Sclerotinia sclerotiorum and would provide useful guidance for the design and development of new fungicides.

Non-Target Site Mechanisms of Fungicide Resistance in Crop Pathogens: A Review

The rapid emergence of resistance in plant pathogens to the limited number of chemical classes of fungicides challenges sustainability and profitability of crop production worldwide. Understanding mechanisms underlying fungicide resistance facilitates monitoring of resistant populations at large-scale, and can guide and accelerate the development of novel fungicides. A majority of modern fungicides act to disrupt a biochemical function via binding a specific target protein in the pathway. While target-site based mechanisms such as alternation and overexpression of target genes have been commonly found to confer resistance across many fungal species, it is not uncommon to encounter resistant phenotypes without altered or overexpressed target sites. However, such non-target site mechanisms are relatively understudied, due in part to the complexity of the fungal genome network. This type of resistance can oftentimes be transient and noninheritable, further hindering research efforts. In this review, we focused on crop pathogens and summarized reported mechanisms of resistance that are otherwise related to target-sites, including increased activity of efflux pumps, metabolic circumvention, detoxification, standing genetic variations, regulation of stress response pathways, and single nucleotide polymorphisms (SNPs) or mutations. In addition, novel mechanisms of drug resistance recently characterized in human pathogens are reviewed in the context of nontarget-directed resistance.

Design, Synthesis and Evaluation of Novel Trichloromethyl Dichlorophenyl Triazole Derivatives as Potential Safener

The dominance of safener can unite with herbicides acquiring the efficient protection of crop and qualifying control of weeds in agricultural fields. In order to solve the crop toxicity problem and exploit the novel potential safener for fenoxaprop-P-ethyl herbicide, a series of trichloromethyl dichlorobenzene triazole derivatives were designed and synthesized by the principle of active subunit combination. A total of 21 novel substituted trichloromethyl dichlorobenzene triazole compounds were synthesized by substituted aminophenol and amino alcohol derivatives as the starting materials, using cyclization and acylation. All the compounds were unambiguously characterized by IR, 1H-NMR, 13C-NMR, and HRMS. A greenhouse bioassay indicated that most of the title compounds could protect wheat from injury caused by fenoxaprop-P-ethyl at varying degrees, in which compound 5o exhibited excellent safener activity at a concentration of 10 μmol/L and was superior to the commercialized compound fenchlorazole. A structure-activity relationship for the novel compounds was determined, which demonstrated that those compounds containing benzoxazine groups showed better activity than that of oxazole-substituted compounds. Introducing a benzoxazine fragment and electron-donating group to specific positions could improve or maintain the safener activity for wheat against attack by the herbicide fenoxaprop-P-ethyl. A molecular docking model suggested that a potential mechanism between 5o and fenoxaprop-P-ethyl is associated with the detoxication of the herbicide. Results from the present work revealed that compound 5o exhibited good crop safener activities toward wheat and could be a promising candidate structure for further research on wheat protection.