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

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.

Discovery of Triketone-Indazolones as Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibiting-Based Herbicides

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a crucial herbicide target in current research, playing an important role in the comprehensive management of resistant weeds. However, the limited crop selectivity and less effectiveness against grass weeds of many existing HPPD inhibitors, limit their further application. To address these issues, a series of novel HPPD inhibitors with fused ring structures were designed and synthesized by introducing an electron-rich indazolone ring and combining it with the classical triketone pharmacophore structure. The cocrystal structure of representative compound III-7 complexed with Arabidopsis thaliana HPPD (AtHPPD) was obtained at 2.0 Å resolution to guide the optimization of the designed inhibitor. The optimization results showed that 5-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,4-dimethyl-2-(3-(methylthio)phenyl)-1,2-dihydro-3H-indazol-3-one, III-15, was the most active AtHPPD inhibitor, with an IC50 value of 12 nM, nearly 30 times higher efficacy than mesotrione. Greenhouse herbicidal activity tests demonstrated that compound III-15 exhibited excellent herbicidal potency at 30-120 g ai/ha. Notably, it maintained high safety for peanuts even at 120 g ai/ha. Our results showed that compound III-15 is promising as a new candidate HPPD herbicide for use in the peanut fields.

A Novel AIE-Active Salicylaldehyde-Schiff Base Probe with Carbazole Group for Al3+ Detection in Aqueous Solution

A donor-acceptor Schiff-base fluorescent probe BKS with chelation enhanced fluorescence (CHEF) mechanism was designed and synthesized via benzophenone(Acceptor), salicylaldehyde and carbazole(Donor) for Al3+ detection, which exhibited typical aggregation-induced emission (AIE) characteristic. BKS probe could provide outstanding selectivity to Al3+ with a prominent fluorescence "turn-on" at 545 nm in a wide pH range from 2 to 11. By the Job's plot, the binding stoichiometry ratio of probe BKS to Al3+ was determined 1:1. The proposed strategy offered a very low limit of detection at 1.486 µM in THF/H2O(V/V = 1:4, HEPBS = 10 mM, pH = 7.40), which was significantly lower than the standard of WHO (Huang et al., Microchem J 151:104195, 2019)-(Yongjie Ding et al., Spectrochim Acta Mol Biomol Spectrosc 167:59-65, 2021) guidelines for drinking water. BKS probe could provide a wider linear detection range of 50 to 500 µM. Furthermore, the probe could hardly be interfered by other examined metal ions. The analysis of Al3+ in real water samples with appropriate recovery (100.72 to 102.85) with a relative standard deviation less than 2.82% indicated the accuracy and precision of BKS probe and the great potential in the environmental monitoring of Al3+.

4-Hydroxyphenylpyruvate Dioxygenase Inhibitors: From Molecular Design to Synthesis

Weed resistance is a critical issue in crop production. Among the known herbicides, 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors are crucial for addressing weed resistance. HPPD inhibitors constitute a pivotal aspect of contemporary crop protection strategies. The advantages of these herbicides are their broad weed spectrum, flexible application, and excellent compatibility with other herbicides. They also exhibit satisfactory crop selectivity and low toxicity and are environmentally friendly. An increasing number of new HPPD inhibitors have been designed by combining computer-aided drug design with conventional design approaches. Herein, the molecular design and structural features of innovative HPPD inhibitors are reviewed to guide the development of new HPPD inhibitors possessing an enhanced biological efficacy.

Design, Synthesis, and Herbicidal Activity of Novel Tetrahydrophthalimide Derivatives Containing Oxadiazole/Thiadiazole Moieties

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) has a high status in the development of new inhibitors. To develop novel and highly effective PPO inhibitors, active substructure linking and bioisosterism replacement strategies were used to design and synthesize novel tetrahydrophthalimide derivatives containing oxadiazole/thiadiazole moieties, and their inhibitory effects on Nicotiana tobacco PPO (NtPPO) and herbicidal activity were evaluated. Among them, compounds B11 (Ki = 9.05 nM) and B20 (Ki = 10.23 nM) showed significantly better inhibitory activity against NtPPO than that against flumiclorac-pentyl (Ki = 46.02 nM). Meanwhile, compounds A20 and B20 were 100% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 37.5 g a.i./ha. It was worth observing that compound B11 was more than 90% effective against three weeds (Abutilon theophrasti, Amaranthus retroflexus, and Portulaca oleracea) at 18.75 and 9.375 g a.i./ha. It was also safer to rice, maize, and wheat than flumiclorac-pentyl at 150 g a.i./ha. In addition, the molecular docking results showed that compound B11 could stably bind to NtPPO and it had a stronger hydrogen bond with Arg98 (2.9 Å) than that of flumiclorac-pentyl (3.2 Å). This research suggests that compound B11 could be used as a new PPO inhibitor, and it could help control weeds in agricultural production.

Ferulic Acid Dimers as Potential Antiviral Agents by Inhibiting TMV Self-Assembly

A series of ferulic acid dimers were designed, synthesized, and evaluated for anti-TMV activity. Biological assays demonstrated that compounds A6, E3, and E5 displayed excellent inactivating against tobacco mosaic virus (TMV) with EC50 values of 62.8, 94.4, and 85.2 μg mL-1, respectively, which were superior to that of ningnanmycin (108.1 μg mL-1). Microscale thermophoresis indicated that compounds A6, E3, and E5 showed strong binding capacity to TMV coat protein with binding affinity values of 1.862, 3.439, and 2.926 μM, respectively. Molecular docking and molecular dynamics simulation revealed that compound A6 could firmly bind to the TMV coat protein through hydrogen and hydrophobic bonds. Transmission electron microscopy and self-assembly experiments indicated that compound A6 obviously destroyed the integrity of the TMV particles and blocked the virus from infecting the host. This study revealed that A6 can be used as a promising leading structure for the development of antiviral agents by inhibiting TMV self-assembly.

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.

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.

Integrated Virtual Screening and Validation toward Potential HPPD Inhibition Herbicide

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27, HPPD) is one of the most widely studied herbicide targets and has gained significant attention. To identify potential effective HPPD inhibitors, a rational multistep virtual screening workflow was built, which included CBP models (based on the receptor-ligand interactions in the crystal complex), Hypogen models with activity prediction ability (according to the derivation of structure-activity relationships from a set of molecules with reported activity values), and a consensus docking procedure (consisting of LibDock, Glide, and CDOCKER). About 1 million molecules containing diketone or β-keto-enol substructures were filtered by Lipinski's rules, CBP model, and Hypogen model. A total of 12 compounds with similar docking postures were generated by consensus docking. Eventually, four molecules were screened based on the specific binding pattern and affinity of the HPPD inhibitor. The biological evaluation in vivo displayed that compounds III-1 and III-2 exhibited comparable herbicidal activity to isoxaflutole and possessed superior safety on various crops (wheat, rice, sorghum, and maize). The ADMET prediction (absorption, distribution, metabolism, excretion, and toxicity) showed that compound III possessed relatively good toxicological results. This work provides a theoretical basis and valuable reference for the virtual screening and molecular design of novel HPPD inhibition herbicides.

Discovery of Novel Cinnamic Acid Derivatives as Fungicide Candidates

Structural diversity derivatization from natural products is an important and effective method of discovering novel green pesticides. Cinnamic acids are abundant in plants, and their unparalleled structures endow them with various excellent biological activities. A series of novel cinnamic oxime esters were designed and synthesized to develop high antifungal agrochemicals. The antifungal activity, structure-activity relationship, and action mechanism were systematically studied. Compounds 7i, 7u, 7v, and 7x exhibited satisfactory activity against Gaeumannomyces graminis var. tritici, with inhibition rates of ≥90% at 50 μg/mL. Compounds 7z and 7n demonstrated excellent activities against Valsa mali and Botrytis cinerea, with median effective concentration (EC50) values of 0.71 and 1.41 μg/mL, respectively. Compound 7z exhibited 100% protective and curative activities against apple Valsa canker at 200 μg/mL. The control effects of 7n against gray mold on tomato fruits and leaves were all >96%, exhibiting superior or similar effects to those of the commercial fungicide boscalid. Furthermore, the quantitative structure-activity relationship was established to guide the further design of higher-activity compounds. The preliminary results on the action mechanism revealed that 7n treatment could disrupt the function of the nucleus and mitochondria, leading to reactive oxygen species accumulation and cell membrane damage. Its primary biochemical mechanism may be inhibiting fungal ergosterol biosynthesis. The novel structure, simple synthesis, and excellent activity of cinnamic oxime esters render them promising potential fungicides.

Discovery and Development of 4-Hydroxyphenylpyruvate Dioxygenase as a Novel Crop Fungicide Target

Plant pathogenic fungi pose a significant threat to crop yields and quality, and the emergence of fungicide resistance has further exacerbated the problem in agriculture. Therefore, there is an urgent need for efficient and environmentally friendly fungicides. In this study, we investigated the antifungal activity of (+)-Usnic acid and its inhibitory effect on crop pathogenic fungal 4-hydroxyphenylpyruvate dioxygenases (HPPDs) and determined the structure of Zymoseptoria tritici HPPD (ZtHPPD)-(+)-Usnic acid complex. Thus, the antifungal target of (+)-Usnic acid and its inhibitory basis toward HPPD were uncovered. Additionally, we discovered a potential lead fungicide possessing a novel scaffold that displayed remarkable antifungal activities. Furthermore, our molecular docking analysis revealed the unique binding mode of this compound with ZtHPPD, explaining its high inhibitory effect. We concluded that HPPD represents a promising target for the control of phytopathogenic fungi, and the new compound serves as a novel starting point for the development of fungicides and dual-purpose pesticides.

A New Class of Diaryl Ether Herbicides: Structure-Activity Relationship Studies Enabled by a Rapid Scaffold Hopping Approach

We report on the development of a novel class of diaryl ether herbicides. After the discovery of a phenoxybenzoic acid with modest herbicidal activity, optimization led to several molecules with improved control of broadleaf and grass weeds. To facilitate this process, we first employed a three-step combinatorial approach, then pivoted to a one-step Ullmann-type coupling that provided faster access to new analogs. After determining that the primary target site of our benchmark diaryl ethers was acetolactate synthase (ALS), we further leveraged this copper-catalyzed methodology to conduct a scaffold hopping campaign in the hope of uncovering an additional mode of action with fewer documented cases of resistance. Our comprehensive and systematic investigation revealed that while the herbicidal activity of this area seems to be exclusively linked to ALS inhibition, our molecules represent a structurally distinct class of Group 2 herbicides. The structure-activity relationships that led us to this conclusion are described herein.

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.

Design, synthesis and biological activity determination of novel phenylpyrazole protoporphyrinogen oxidase inhibitor herbicides

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is the last common enzyme in the biosynthetic pathway in the synthesis of heme and chlorophyll. The high-frequency use of PPO inhibitor herbicides has led to the gradual exposure of pesticide damage and resistance problems. In order to solve this kind of problem, there is an urgent need to develop new PPO inhibitor herbicides. In this paper, 16 phenylpyrazole derivatives were designed by the principle of active substructure splicing through the electron isosterism of five-membered heterocycles. Greenhouse herbicidal activity experiments and in vitro PPO activity experiments showed that the inhibitory effect of compound 9 on weed growth was comparable to that of pyraflufen-ethyl. Crop safety experiments and cumulative concentration experiments in crops showed that when the spraying concentration was 300 g ai/ha, wheat, corn, rice and other cereal crops were more tolerant to compound 9, among which wheat showed high tolerance, which was comparable to the crop safety of pyraflufen-ethyl. Herbicidal spectrum experiments showed that compound 9 had inhibitory activity against most weeds. Molecular docking results showed that compound 9 formed one hydrogen bond interaction with amino acid residue ARG-98 and two π-π stacking interactions with amino acid residue PHE-392, indicating that compound 9 had better herbicidal activity than pyraflufen-ethyl. It shows that compound 9 is expected to be a lead compound of phenylpyrazole PPO inhibitor herbicide and used as a herbicide in wheat field.

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.

Novel cinnamic acid derivatives as a versatile tool for developing agrochemicals for controlling plant virus and bacterial diseases by enhancing plant defense responses

BACKGROUND

Plant pathogens have led to large yield and quality losses in crops worldwide. The discovery and study of novel agrochemical alternatives based on the chemical modification of bioactive natural products is a highly efficient approach. Here, two series of novel cinnamic acid derivatives incorporating diverse building blocks with alternative linking patterns were designed and synthesized to identify their antiviral capacity and antibacterial activity.

RESULTS

The bioassay results demonstrated that most cinnamic acid derivatives had excellent antiviral competence toward tobacco mosaic virus (TMV) in vivo, especially compound A₅ (median effective concentration [EC₅₀ ] = 287.7 μg mL^-1 ), which had a notable protective effect against TMV when compared with the commercial virucide ribavirin (EC₅₀  = 622.0 μg mL^-1 ). In addition, compound A₁₇ had a protective efficiency of 84.3% at 200 μg mL^-1 against Xac in plants. Given these outstanding results, the engineered title compounds could be regarded as promising leads for controlling plant virus and bacterial diseases. Preliminary mechanistic studies suggest that compound A₅ could enhance the host's defense responses by increasing the activity of defense enzymes and upregulating defense genes, thereby suppressing phytopathogen invasion.

CONCLUSION

This research lays a foundation for the practical application of cinnamic acid derivatives containing diverse building blocks with alternative linking patterns in pesticide exploration. © 2023 Society of Chemical Industry.

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.

Structure-Based Design of 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor as a Potential Herbicide for Cotton Fields

4-Hydroxyphenylpyruvate dioxygenase (HPPD, EC 1.13.11.27) is one of the most promising herbicide targets for the development of agricultural chemicals owing to its unique mechanism of action in plants. We previously reported on the co-crystal structure of Arabidopsis thaliana (At) HPPD complexed with methylbenquitrione (MBQ), an inhibitor of HPPD that we previously discovered. Based on this crystal structure, and in an attempt to discover even more effective HPPD-inhibiting herbicides, we designed a family of triketone-quinazoline-2,4-dione derivatives featuring a phenylalkyl group through increasing the interaction between the substituent at the R¹ position and the amino acid residues at the active site entrance of AtHPPD. Among the derivatives, 6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,5-dimethyl-3-(1-phenylethyl)quinazoline-2,4(1H,3H)-dione (23) was identified as a promising compound. The co-crystal structure of compound 23 with AtHPPD revealed that hydrophobic interactions with Phe392 and Met335, and effective blocking of the conformational deflection of Gln293, as compared with that of the lead compound MBQ, afforded a molecular basis for structural modification. 3-(1-(3-Fluorophenyl)ethyl)-6-(2-hydroxy-6-oxocyclohex-1-ene-1-carbonyl)-1,5-dimethylquinazoline-2,4(1H,3H)-dione (31) was confirmed to be the best subnanomolar-range AtHPPD inhibitor (IC₅₀ = 39 nM), making it approximately seven times more potent than MBQ. In addition, the greenhouse experiment showed favorable herbicidal potency for compound 23 with a broad spectrum and acceptable crop selectivity against cotton at the dosage of 30-120 g ai/ha. Thus, compound 23 possessed a promising prospect as a novel HPPD-inhibiting herbicide candidate for cotton fields.

Discovery of Bis-5-cyclopropylisoxazole-4-carboxamides as Novel Potential 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (EC 1.13.11.27; HPPD) represents a potential target for novel herbicide development. To discover the more promising HPPD inhibitor, we designed and synthesized a series of bis-5-cyclopropylisoxazole-4-carboxamides with different linkers using a multitarget pesticide design strategy. Among them, compounds b9 and b10 displayed excellent herbicidal activities versus Digitaria sanguinalis (DS) and Amaranthus retroflexus (AR) with the inhibition of about 90% at the concentration of 100 mg/L in vitro, which was better than that of isoxaflutole (IFT). Furthermore, compounds b9 and b10 displayed the best inhibitory effect versus DS and AR with the inhibition of about 90 and 85% at 90 g (ai)/ha in the greenhouse, respectively. The structure-activity relationship study showed that the flexible linker (6 carbon atoms) is responsible for increasing their herbicidal activity. The molecular docking analyses showed that compounds b9 and b10 could more closely bind to the active site of HPPD and thus exhibited a better inhibitory effect. Altogether, these results indicated that compounds b9 and b10 could be used as potential herbicide candidates targeting HPPD.

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.

Discovery of Novel Pyrazole Derivatives with Improved Crop Safety as 4-Hydroxyphenylpyruvate Dioxygenase-Targeted Herbicides

As one of the essential herbicide targets, 4-hydroxyphenylpyruvate dioxygenase (HPPD) has recently been typically used to produce potent new herbicides. In continuation with the previous work, several pyrazole derivatives comprising a benzoyl scaffold were designed and synthesized, and their inhibitory effects on Arabidopsis thaliana hydroxyphenylpyruvate dioxygenase (AtHPPD) and herbicidal activities were comprehensively evaluated in this study. Compound Z9 showed top-rank inhibitory activity to AtHPPD with an half-maximal inhibitory concentration (IC₅₀) value of 0.05 μM, which was superior to topramezone (1.33 μM) and mesotrione (1.76 μM). Compound Z21 exhibited superior preemergence inhibitory activity against Echinochloa crusgalli, with stem and root inhibition rates of 44.3 and 69.6%, respectively, compared to topramezone (16.0 and 53.0%) and mesotrione (12.8 and 41.7%). Compounds Z5, Z15, Z20, and Z21 showed excellent postemergence herbicidal activities at a dosage of 150 g ai/ha, along with distinct bleaching symptoms and higher crop safety than topramezone and mesotrione, and they all were safe for maize, cotton, and wheat with injury rates of 0 or 10%. In addition, the molecular docking analysis also revealed that these compounds formed hydrophobic π-π interactions with Phe360 and Phe403 to AtHPPD. This study suggests that pyrazole derivatives containing a benzoyl scaffold could be used as new HPPD inhibitors to develop pre- and postemergence herbicides and be applied to additional crop fields.

A novel isophorone-based fluorescent probe for recognition of Al3+ and its bioimaging in cells and plants

In this work, a novel isophorone-based fluorescent probe H-1 was designed and synthesized. The probe H-1 could achieve highly selective detection of Al³⁺ through forming a 1:1 complex, with a recognition mechanism based on intramolecular charge transfer (ICT). The detection limit of the probe H-1 for Al³⁺ is as low as 8.25 × 10^-8 M which was determined by fluorescent titration. It is confirmed that H-1 could be used not only for fluorescence spectrometry to detect Al³⁺ ions in actual water samples, but also for biological imaging to detect Al³⁺ ions in cells and plants.

Phytochemical Screening and Evaluation of Pesticidal Efficacy in the Oleoresins of Globba sessiliflora Sims and In Silico Study

Globba sessiliflora Sims is an aromatic rhizomatous herb of family Zingiberaceae which is endemic to Peninsular India. This study first reports the phytochemical profile and pesticidal potential of oleoresins obtained from the aerial and rhizome parts of Globba sessiliflora Sims. The oleoresins were prepared by the cold percolation method and were analyzed by a gas chromatography-mass spectrometry (GC-MS) method. Both the oleoresins varied greatly in composition, the major compounds identified in aerial part oleoresin (GSAO) were methyl linoleate, methyl palmitate, and phytol, while the major compounds present in rhizome part oleoresin (GSRO) were γ-sitosterol, 8 (17),12-labdadiene-15, 16-dial, methyl linoleate, and methyl palmitate. In order to evaluate the biological activities, the oleoresins were tested under laboratory conditions for nematicidal action and inhibition of egg hatching potential against root knot nematode, where GSRO was more effective. Insecticidal activity was performed against mustard aphid, Lipaphis erysimi and castor hairy caterpillar, Selepa celtis. In case of mustard aphid, GSRO (LC₅₀ = 154.8 ppm) was more effective than GSAO (LC₅₀ = 263.0 ppm), while GSAO (LC₅₀ = 346.7.0 ppm) was more effective against castor hairy caterpillar than GSRO (LC₅₀ = 398.1 ppm). The herbicidal activity was performed in the receptor species Raphanus raphanistrum subsp. sativus, and the oleoresins showed different intensities for seed germination inhibition and coleoptile and radical length inhibition. Molecular docking studies were conducted to screen the in vitro activities and through molecular docking, it was found that the major oleoresins components were able to interact with the binding pocket of HPPD and AChE with γ-sitosterol showing the best binding affinity.

Design, Synthesis, and Herbicidal Activity of Naphthalimide-Aroyl Hybrids as Potent Transketolase Inhibitors

Transketolase (TK) was identified as a new target for the development of novel herbicides. In this study, a series of naphthalimide-aroyl hybrids were designed and prepared based on TK as a new target and tested for their herbicidal activities. In vitro bioassay showed that compounds 4c and 4w exhibited stronger inhibitory effects against Digitaria sanguinalis (DS) and Amaranthus retroflexus (AR) with the inhibition over 90% at 200 mg/L and around 80% at 100 mg/L. Also, compounds 4c and 4w exhibited excellent postemergence herbicidal activity against DS and AR with the inhibition around 90% at 90 g [active ingredient (ai)]/ha and 80% at 50 g (ai)/ha in the greenhouse, which was comparable with the activity of mesotrione. The fluorescent quenching experiments of At TK revealed the occurrence of electron transfer from compound 4w to At TK and the formation of a strong exciplex between them. Molecular docking analyses further showed that compounds 4w exhibited profound affinity with At TK through the interaction with the amino acids in the active site, which results in its strong inhibitory activities against TK. These findings demonstrated that compound 4w is potentially a lead candidate for novel herbicides targeting TK.

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.

Phytochemical Profile, In Vitro Bioactivity Evaluation, In Silico Molecular Docking and ADMET Study of Essential Oils of Three Vitex Species Grown in Tarai Region of Uttarakhand

A comparative study of volatiles, antioxidant activity, phytotoxic activity, as well as in silico molecular docking and ADMET study, was conducted for essential oils from three Vitex species, viz., V. agnus-castus, V. negundo, and V. trifolia. Essential oils (OEs) extracted by hydrodistillation were subjected to compositional analysis using GC-MS. A total number of 37, 45, and 43 components were identified in V. agnus-castus, V. negundo, and V. trifolia, respectively. The antioxidant activity of EOs, assessed using different radical-scavenging (DPPH, H₂O₂ and NO), reducing power, and metal chelating assays, were found to be significant as compared with those of the standards. The phytotoxic potential of the EOs was performed in the receptor species Raphanusraphanistrum (wild radish) and the EOs showed different levels of intensity of seed germination inhibition and root and shoot length inhibition. The molecular docking study was conducted to screen the antioxidant and phytotoxic activity of the major and potent compounds against human protein target, peroxiredoxin 5, and 4-hydroxyphenylpyruvate dioxygenase protein (HPPD). Results showed good binding affinities and attributed the strongest inhibitory activity to 13-epi-manoyl oxide for both the target proteins.

Computer-Aided and AILDE Approaches to Design Novel 4-Hydroxyphenylpyruvate Dioxygenase Inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is a pivotal enzyme in tocopherol and plastoquinone synthesis and a potential target for novel herbicides. Thirty-five pyridine derivatives were selected to establish a Topomer comparative molecular field analysis (Topomer CoMFA) model to obtain correlation information between HPPD inhibitory activity and the molecular structure. A credible and predictive Topomer CoMFA model was established by "split in two R-groups" cutting methods and fragment combinations (q² = 0.703, r² = 0.957, ONC = 6). The established model was used to screen out more active compounds and was optimized through the auto in silico ligand directing evolution (AILDE) platform to obtain potential HPPD inhibitors. Twenty-two new compounds with theoretically good HPPD inhibition were obtained by combining the high-activity contribution substituents in the existing molecules with the R-group search via Topomer search. Molecular docking results revealed that most of the 22 fresh compounds could form stable π-π interactions. The absorption, distribution, metabolism, excretion and toxicity (ADMET) prediction and drug-like properties made 9 compounds potential HPPD inhibitors. Molecular dynamics simulation indicated that Compounds Y12 and Y14 showed good root mean square deviation (RMSD) and root mean square fluctuation (RMSF) values and stability. According to the AILDE online verification, 5 new compounds with potential HPPD inhibition were discovered as HPPD inhibitor candidates. This study provides beneficial insights for subsequent HPPD inhibitor design.

Fabrication and Characterization of Antifungal Hydroxypropyl-β-Cyclodextrin/Pyrimethanil Inclusion Compound Nanofibers Based on Electrospinning

Pyrimethanil (PMT) is an anilinopyrimidine bactericide with poor water solubility, which limits its applications. To improve the physical and chemical properties of PMT, hydroxypropyl-β-cyclodextrin/pyrimethanil inclusion compound nanofibers (HPβCD/PMT-IC-NFs) were fabricated via electrospinning. A variety of analytical techniques were used to confirm the formation of the inclusion compound. Scanning electron microscopy image displayed that HPβCD/PMT-IC-NF was homogeneous without particles. Thermogravimetric analysis indicated that the formation of the inclusion compound improved the thermostability of PMT. In addition, the phase solubility test illustrated that the inclusion compound formed by PMT and HPβCD had a stronger water solubility. The antifungal effect test exhibited that HPβCD/PMT-IC-NF had better antifungal properties. The release experiment confirmed that HPβCD/PMT-IC-NF had a sustained-release effect, and the release curve conformed to the first-order kinetic model equation. In short, the fabrication HPβCD/PMT-IC-NF inhibited improved solubility and thermostability of PMT, thus promoting the development of pesticide dosage form to water-based and low-pollution direction.

Survey on the Recent Advances in 4-Hydroxyphenylpyruvate Dioxygenase (HPPD) Inhibition by Diketone and Triketone Derivatives and Congeneric Compounds: Structural Analysis of HPPD/Inhibitor Complexes and Structure-Activity Relationship Considerations

The serendipitous discovery of the HPPD inhibitors from allelopathic plants opened the way for searching new and effective herbicidal agents by application of classical hit-to-lead optimization approaches. A plethora of active and selective compounds were discovered that belong to three major classes of cyclohexane-based triketones, pyrazole-based diketones, and diketonitriles. In addition, to enhance inhibitory constant and herbicidal activity, many efforts were also made to gain broader weed control, crop safety, and eventual agricultural applicability. Moreover, HPPD inhibitors emerged as therapeutic agents for inherited and metabolic human diseases as well as vector-selective insecticides in the control of hematophagous arthropods. Given the large set of experimental data available, structure-activity relationship analysis could be used to derive suggestions for next generation optimized compounds.

Virtual screening based on pharmacophore model for developing novel HPPD inhibitors

4-Hydroxyphenylpyruvate dioxygenase (HPPD) is an important target for herbicide design. A multilayered virtual screening workflow was constructed by combining two pharmacophore models based on ligand and crystal complexes, molecular docking, molecular dynamics (MD), and biological activity determination to identify novel small-molecule inhibitors of HPPD. About 110, 000 compounds of Bailingwei and traditional Chinese medicine databases were screened. Of these, 333 were analyzed through docking experiments. Five compounds were selected by analyzing the binding pattern of inhibitors with amino acid residues in the active pocket. All five compounds could produce stable coordination with cobalt ion, and form favorable π-π interactions. MD simulation demonstrated that Phe381 and Phe424 made large contributions to the strength of binding. The enzyme activity experiment verified that compound-139 displayed excellent potency against AtHPPD (IC₅₀ = 0.742 μM), however, compound-5222 had inhibitory effect on human HPPD (IC₅₀ = 6 nM). Compound-139 exhibited herbicidal activity to some extent on different gramineous weeds. This work provided a strong insight into the design and development of novel HPPD inhibitor using in silico techniques.

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, and Herbicidal Activity of Diphenyl Ether Derivatives Containing a Five-Membered Heterocycle

Protoporphyrinogen oxidase (PPO, EC 1.3.3.4) is an important target for discovering novel herbicides, and it causes bleaching symptoms by inhibiting the synthesis of chlorophyll and heme. In this study, the active fragments of several commercial herbicides were joined by substructure splicing and bioisosterism, and a series of novel diphenyl ether derivatives containing five-membered heterocycles were synthesized. The greenhouse herbicidal activity and the PPO inhibitory activity in vitro were discussed in detail. The results showed that most compounds had good PPO inhibitory activity, and target compounds containing trifluoromethyl groups tended to have higher activity. Among them, compound G4 showed the best inhibitory activity, with a half-maximal inhibitory concentration (IC₅₀) of 0.0468 μmol/L, which was approximately 3 times better than that of oxyfluorfen (IC₅₀ = 0.150 μmol/L). In addition, molecular docking indicated that compound G4 formed obvious π-π stacking interactions and hydrogen bond interactions with PHE-392 and ARG-98, respectively. Remarkably, compound G4 had good safety for corn, wheat, rice, and soybean, and the cumulative concentration in crops was lower than that of oxyfluorfen. Therefore, compound G4 can be used to develop potential lead compounds for novel PPO inhibitors.