High Herbicidal Activity Research Articles

Enzymatic Degradation toward Herbicides: The Case of the Sulfonylureas.

Commercial herbicides, particularly sulfonylureas, are used worldwide and pose a significant challenge to environmental sustainability. The efficient degradation of sulfonylurea herbicides is critical. SulE, an esterase isolated from the bacterial strain Hansschlegelia zhihuaiae S113, shows degradation activity toward sulfonylurea herbicides. However, the detailed catalytic mechanism remains vague to a large extent. Herein, we decipher the SulEP44R-catalyzed degradation mechanism of sulfonylurea herbicides using hybrid quantum mechanics and molecular mechanics approaches. Our results show that the degradation of sulfonylureas catalyzed by SulEP44R involves four concerted elementary steps. The rate-determining step has an energy barrier range of 19.7-21.4 kcal·mol-1, consistent with the experimentally determined range of 16.0-18.0 kcal·mol-1. Distortion/interaction analysis demonstrates that active-site amino acids play a vital role in the enzymatic catalytic efficacy. The unique architecture of SulEP44R's active site can serve as an excellent template for designing artificial catalysts. Key structural and charge parameters affecting catalytic activity were systematically screened and identified. Based on the elucidated degradation mechanism, several new herbicides with both high herbicidal activity and biodegradability were developed with the aid of a high-throughput strategy. Our findings may advance the application of sulfonylurea herbicides within the framework of environmental sustainability.

Phytopathogenic Fungi and Their Active Metabolites With Bioherbicidal Potential Against the Invasive Alligator Weed, Alternanthera philoxeroides

ABSTRACTAlligator weed (Alternanthera philoxeroides), originally from South America, is a notorious semi‐aquatic invasive species in many countries, including India. Due to its amphibious nature, it not only damages the aquatic environment but is also detrimental to the terrestrial ecosystem. To seek an environmentally sound control option for alligator weed, this study focused on selecting an appropriate mycoherbicidal agent. A series of steps from field survey‐based collection, isolation and selection of promising fungal strains, followed by host range determination to biocontrol potential studies against the weed were undertaken. Twenty‐three phytopathogenic fungi were isolated, and among these, the fungi with the highest herbicidal activity (> 90% disease severity) were subjected to morphological and molecular characterisation and identified as Alternaria alternantherae (= Nimbya alternanthera). The fungus and its crude metabolites were tested against 76 plant species, showing a relatively narrow host range. This fungal species is being reported from West Bengal, India, for the first time. Although the fungus has been considered as a potential biocontrol tool against alligator weed in countries such as Australia, Brazil and China, long‐term, detailed research for A. alternantherae and its active metabolites to be developed as bioherbicides against alligator weed remains indispensable.

Validation of shikimate dehydrogenase as the herbicidal target of drupacine and screening of target-based compounds with high herbicidal activity

The discovery of new targets and lead compounds is the key to developing new pesticides. The herbicidal target of drupacine has been identified as shikimate dehydrogenase (SkDH). However, the mechanism of interaction between them remains unclear. This study found that drupacine specifically binds to SkDH with a dissociation equilibrium constant (KD) of 8.88 μM and a Kd value of 2.15 μM, as confirmed by surface plasmon resonance and microscale thermophoresis. Site-directed mutagenesis coupled with fluorescence quenching analysis indicated that residue THR431 was the key amino acid site for drupacine binding to SkDH. Nine compounds with the best binding ability to SkDH were identified by virtual screening from about 120,000 compounds. Among them, compound 8 showed the highest inhibition rate with values of 41.95% against SkDH, also exhibiting the strongest herbicidal activity. This research identifies a novel potential target SkDH and a candidate lead compound with high herbicidal activity for developing new herbicides.

Bioactivity evaluation and active compounds identification of Symphoricarpos orbiculatus as potential botanical herbicide.

Evaluation of herbicidal activity and identification of active compounds are important bases for the development of new botanical herbicides. This study confirmed that Symphoricarpos orbiculatus has high herbicidal activities against mono-dicotyledonous weeds, including Echinochloa crusgalli, Digitaria sanguinalis, Amaranthus retroflexus and Portulaca oleracea. By bioassay-guided isolation, 12 compounds were isolated and identified from S. orbiculatus for the first time, including iridoids: naucledal (K1), loganin (K2), loganigenin (K3), loganin acid (K4), glucologanin (K5) and vogeloside (K6), as well as flavonoids: quercetine (K7), luteolin (K8), nobiletin (K9), astragalin (K10), isorhamnetin 3-d-glucoside (K11) and rutin (K12). Biological assays showed that iridoids are the main active ingredients of S. orbiculatus. The compounds of K5 and K6 could inhibit both the root (IC50 = 37.54 and 38.91 μg mL-1, respectively) and shoot (IC50 = 42.78 and 45.72 μg mL-1, respectively) of Portulaca oleracea, which have a weeding toxicity similar to that of the commercialized plant-based herbicide pelargonic acid. In addition, the results of pot culture assay showed that S. orbiculatus ethanol extracts had high fresh weight control effect against Digitaria sanguinalis and P. oleracea at the concentration of 40 g L-1. After 7 days, both the soil treatment and the stem and leaf spray method resulted in severe leaf necrosis and significant leaf etiolation. Symphoricarpos orbiculatus and its herbicidal active compounds have the potential to develop into botanical herbicides, and are first reported in the present study. © 2024 Society of Chemical Industry.

Discovery of Novel N-Phenyltriazinone Derivatives Containing Oxime Ether or Oxime Ester Moieties as Promising Protoporphyrinogen IX Oxidase Inhibitors.

Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is one of the most important targets for the discovery of green herbicides. In order to find novel PPO inhibitors with a higher herbicidal activity, a series of novel N-phenyltriazinone derivatives containing oxime ether and oxime ester groups were designed and synthesized based on the strategy of pharmacophore and scaffold hopping. Bioassay results revealed that some compounds showed herbicidal activities; especially, compound B16 exhibited broad-spectrum and excellent 100% herbicidal effects to Echinochloa crusgalli, Digitaria sanguinalis, Setaria faberii, Abutilon juncea, Amaranthus retroflexus, and Portulaca oleracea at a concentration of 37.5 g a.i./ha, which were comparable to trifludimoxazin. Nicotiana tabacum PPO (NtPPO) enzyme inhibitory assay indicated that B16 showed an excellent enzyme inhibitory activity with a value of 32.14 nM, which was similar to that of trifludimoxazin (31.33 nM). Meanwhile, compound B16 revealed more safety for crops (rice, maize, wheat, peanut, soybean, and cotton) than trifludimoxazin at a dose of 150 g a.i./ha. Moreover, molecular docking and molecular dynamics simulation further showed that B16 has a very strong and stable binding to NtPPO. It indicated that B16 can be used as a potential PPO inhibitor and herbicide candidate for application in the field.

An enantioselective study of the behavior of the herbicide ethofumesate in agricultural soils: Impact of the addition of organoclays and biochar

Chiral pesticides that are still commercialized and incorporated into the environment as racemic mixtures of enantiomers require evaluation of the enantioselectivity of their biological activity and environmental fate processes for a better prediction of their field efficacy and environmental risks. In this work, we successfully separated the enantiomers of the chiral herbicide ethofumesate (ETFM), determined their absolute configuration, and characterized their herbicidal activity as well as their adsorption, degradation, enantiomerization, and leaching in Mediterranean agricultural soils. While the herbicidal activity of R-ethofumesate to the sensitive species Portulaca grandiflora was greater than that of S-ethofumesate, the adsorption, degradation, and leaching of the herbicide showed negligible enantioselectivity and enantiomer interconversion did not occur in soils. The adsorption of both enantiomers showed a positive correlation with the soil organic carbon content (r = 0.856, P = 0.015), and their degradation in soils occurred slowly (DT50 > 60 days) and at similar rates independent of their application as individual enantiomers or as a racemic mixture of enantiomers. The addition of three highly adsorptive materials to a scarcely adsorptive soil increased the adsorption of the enantiomers of ETFM and delayed their degradation without affecting the non-enantioselective character of the processes. As a result of their high adsorption capacity, the materials were highly effective in reducing the leaching of both enantiomers of ETFM through soil columns. The results of this work indicate that the application of single-enantiomer ETFM formulations, based on a higher herbicidal activity or a lower toxicity to non-target organisms of the formulated enantiomer, would reduce considerable exposure risks associated with incorporating into the environment the less favorable enantiomer, as this would show long persistence and high leaching potential in soils similar to its optical isomer.

Design, Synthesis and Bioactivity Evaluation of Heterocycle-Containing Mono- and Bisphosphonic Acid Compounds.

Fosmidomycin (FOS) is a naturally occurring compound active against the 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) enzyme in the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway, and using it as a template for lead structure design is an effective strategy to develop new active compounds. In this work, by replacing the hydroxamate unit of FOS with pyrazole, isoxazole and the related heterocycles that also have metal ion binding affinity, while retaining the monophosphonic acid in FOS or replacing it with a bisphosphonic acid group, heterocycle-containing mono- and bisphosphonic acid compounds as FOS analogs were designed. The key steps involved in the facile synthesis of these FOS analogs included the Michael addition of diethyl vinylphosphonate or tetraethyl vinylidenebisphosphonate to β-dicarbonyl compounds and the subsequent cyclic condensation with hydrazine or hydroxylamine. Two additional isoxazolinone-bearing FOS analogs were synthesized via the Michaelis-Becker reaction with diethyl phosphite as a key step. The bioactivity evaluation on model plants demonstrated that several compounds have better herbicidal activities compared to FOS, with the most active compound showing a 3.7-fold inhibitory activity on Arabidopsis thaliana, while on the roots and stalks of Brassica napus L. and Echinochloa crus-galli in a pre-emergence inhibitory activity test, the activities of this compound were found to be 3.2- and 14.3-fold and 5.4- and 9.4-fold, respectively, and in a post-emergency activity test on Amaranthus retroflexus and Echinochloa crus-galli, 2.2- and 2.0-fold inhibition activities were displayed. Despite the significant herbicidal activity, this compound exhibited a DXR inhibitory activity lower than that of FOS but comparable to that of other non-hydroxamate DXR inhibitors, and the dimethylallyl pyrophosphate rescue assay gave no statistical significance, suggesting that a different target might be involved in the inhibiting process. This work demonstrates that using bioisosteric replacement can be considered as a valuable strategy to discover new FOS analogs that may have high herbicidal activities.

Synthesis, Herbicidal Activity, Mode of Action, and In Silico Analysis of Novel Pyrido[2,3-d]pyrimidine Compounds.

Natural products are a main source of new chemical entities for use in drug and pesticide discovery. In order to discover lead compounds with high herbicidal activity, a series of new pyrido[2,3-d] pyrimidine derivatives were designed and synthesized using 2-chloronicotinic acid as the starting material. Their structures were characterized with 1H NMR, 13C NMR and HRMS, and the herbicidal activities against dicotyledonous lettuce (Lactuca sativa), field mustard (Brassica campestris), monocotyledonous bentgrass (Agrostis stolonifera) and wheat (Triticum aestivum) were determined. The results indicated that most of the pyrido[2,3-d] pyrimidine derivatives had no marked inhibitory effect on lettuce at 1 mM. However, most of the pyrido[2,3-d] pyrimidine derivatives possessed good activity against bentgrass at 1 mM. Among them, the most active compound, 3-methyl-1-(2,3,4-trifluorophenyl)pyrido[2,3-d]pyrimidine-2,4(1H,3H)-dione (2o), was as active as the positive controls, the commercial herbicides clomazone and flumioxazin. Molecular simulation was performed with molecular docking and DFT calculations. The docking studies provided strong evidence that 2o acts as an herbicide by inhibition of protoporphyrinogen oxidase. However, the physiological results indicate that it does not act on this target in vivo, implying that it could be metabolically converted to a compound with a different molecular target.

2,4-Di-tert-butylphenol and 7-hydroxy-3-(2-methylpropyl)-2,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-1,4-dione: two natural products from Serratia marcescens Ha1 and their herbicidal activities.

Weeds are one of the critical factors that negatively affect crop yield and quality. Microbial herbicides are a research hotspot for novel herbicides owing to their environmental safety and lack of weed resistance. In the current study, the active ingredients of Serratia marcescens Ha1, a new microbial herbicide, were investigated for their effectiveness against agricultural weeds using bioassay-guided fractionation. The results revealed that petroleum ether and ethyl acetate extracts of S. marcescens Ha1 had high herbicidal activity. Forty-nine compounds were identified from the petroleum ether extract, including 2,4-di-tert-butylphenol (DB; C14 H22 O, 38.82%), ethyl 14-methyl-hexadecanoate, 1-nonadecene, and [1,1'-biphenyl]-2,3'-diol, 3,4',5,6'-tetrakis. Of these, DB showed significant inhibitory effects on root and shoot growth in Amaranthus retroflexus, with half-maximal inhibitory concentration (IC50 ) values of 389.17 and 832.44 mg L-1 , respectively. In addition, 7-hydroxy-3-(2-methylpropyl)-2,3,6,7,8,8a-hexahydropyrrolo[1,2-a]pyrazine-1,4-dione (HPD) was identified as the major active ingredient in the ethyl acetate extract of S. marcescens Ha1 using bioassay-guided fractionation, with IC50 values of 439.86 and 476.95 mg L-1 against A. retroflexus shoot and root growth, respectively. Scanning electron microscopy indicated that DB and HPD exert destructive effects on A. retroflexus root, and the damage is gradually aggravated with increasing treatment time and concentration. The S. marcescens Ha1 extract and its active compounds DB and HPD exhibit significant herbicidal activity, which could be utilized further for the development of microbial herbicides. © 2023 Society of Chemical Industry.

АНАЛИЗ ГЕРБИЦИДНОЙ АКТИВНОСТИ ПРЕПАРАТИВНЫХ ФОРМ ПРОТРАВИТЕЛЕЙ НА ОСНОВЕ БЕНТАЗОНА

The study is devoted to the analysis of the herbicidal activity of preparative forms of disinfectants based on the sodium salt of bentazone, as well as the oxy-forms of bentazone in comparison with the commercial herbicide Octapon Extra, CE. It was found that all studied samples exhibit high herbicidal activity against the dicotyledonous weeds field mustard (Sinapis arvensis L.) and blue cornflower (Centauréa cyánus L.). It was revealed that all samples based on the sodium salt of bentazone were 5% more effective than the commercial herbicide. Of the studied oxy-forms of bentazone, the drug with an active substance concentration of 480 g/l showed the maximum effectiveness, while its effectiveness was 3% higher than that of a commercial herbicide. It was shown that all tested samples did not exhibit herbicidal activity against spring wheat (Triticum aestivum L.). Based on the data obtained, it was concluded that the studied formulations are promising for the development of herbicides for use for guard of cereal crops.

Modelling and spectroscopic investigation of 2,4-D adsorption in soil amended with pine sawdust, paunch grass and sewage sludge biochars

2,4-Dichlorophenoxyacetic acid (2,4-D) is a widely used herbicide possessing high herbicidal activity; however, it is potentially toxic to humans and quite persistent in the environment. We investigated the adsorption of 2,4-D in two pasture soils amended with pine sawdust (PSD), paunch grass (PG) and sewage sludge (SS) biochars using batch studies. The results showed that PSD biochar produced at 700 oC exhibited the highest adsorption capacity for 2,4-D among the waste-derived biochars tested, which is 200-fold greater than the control and other biochar-amended soils. In general, the sorption affinity of 2,4-D for biochar amended soils followed an order: PSD > > PG > SS. The high adsorption capacity of the PSD may be attributed to its significantly higher specific surface area of 795 m2·g-1 as compared to other soils and biochars. Moreover, the results of the physicochemical characterization showed no difference in surface oxygen functional groups among the PSD, PG and SS. These findings indicate that oxygen-containing surface functional groups have a negligible role in 2,4-D adsorption, as evident from the spectroscopic investigation, thus emphasizing the role of surface area in the 2,4-D adsorption. Lastly, pore intrusion/filling, hydrogen bonding and π-π EDA interactions are postulated to be the plausible adsorption mechanisms for 2,4-D onto biochar amended soils.

Efficient Total Synthesis and Herbicidal Activity of 3-Acyltetramic Acids: Endogenous Abscisic Acid Synthesis Regulators.

An efficient synthesis method will allow a large number of tetramic acid analogues to be synthesized for property and potency optimization. In this study, a facile and efficient method was described for the synthesis of 3-acyltetramic acids. The synthesis was accomplished mainly via (1) mild intramolecular cyclization and (2) the formation of β-ketoamides between nucleophiles and acyl Meldrum's acids. 3-Acyltetramic acid exhibited phytotoxicity against Echinochloa crusgalli and Portulaca oleracea. At a dosage of 750 g ha-1, 6k and 6a showed high herbicidal activity against E. crusgalli, Digitaria sanguinalis and P. oleracea, Amaranthus retroflexus, respectively. 6k inhibited the synthesis of endogenous abscisic acid, thus seedling germination and plant growth. The incorporation of various acyl Meldrum's acids and amino acid esters was applicable to the parallel synthesis of 3-acyltetramic acids. The mode of action and herbicidal activity indicate that 3-tetramic acid had good herbicidal performance and was a promising herbicide candidate. This study will provide a reference for novel herbicide development.

The Foliar Fungal Pathogenic Metabolites as Promising Alternatives to Chemical Herbicides: Recent Developments, Future Perspective and Commercialization

Weeds harbour wide variety of microorganisms having beneficial, neutral and phytopathogenic effects. Weed microbiome discoveries could fuel progress in sustainable agriculture, such as the development of microbial herbicide products. Weed infecting phytopathogenic living fungal cells (mycelia or spores) and their natural products have been studied as producers of mycoherbicides. The application of biological and biochemical (natural or biorational) herbicides based on specific weed pathogens and natural products, respectively, is believed to assist the decreasing harmful impact of the chemicals. Cell free broth of several plant pathogenic fungi have been enthusiastically investigated for substitutes of synthetic agrochemicals against weeds. However, all such studies conducted on pure compound with high purity which have limitations due to high costs. It was found that herbicide in cell-free culture broth of fungi were largely composed of various nature of different metabolites with the ratio varying with culture time. Crude broth in a form of cell-free culture broth showed high herbicidal activity against weeds. So, cell-free culture broth as a crude product could be serve as a potential cost-effective and environmental-friendly herbicide in agriculture. The application of mycometabolites in agricultural weed management are safer to the user and the environment. They were formulated and applied in the same manner as chemical herbicides. This review aims at summarizing the studies on the application of mycometabolites as a lucrative, novel source of secondary herbicidal compounds for management of weeds. More effort should be expended in this area of research in the future, despite the obstacles that exist.

Alkaline Soil Degradation and Crop Safety of 5-Substituted Chlorsulfuron Derivatives.

Sulfonylurea herbicides can lead to serious weed resistance due to their long degradation times and large-scale applications. This is especially true for chlorsulfuron, a widely used acetolactate synthase inhibitor used around the world. Its persistence in soil often affects the growth of crop seedlings in the following crop rotation, and leads to serious environmental pollution all over the world. Our research goal is to obtain chlorsulfuron-derived herbicides with high herbicidal activities, fast degradation times, as well as good crop safety. On account of the slow natural degradation of chlorsulfuron in alkaline soil, based on the previously reported results in acidic soil, the degradation behaviours of 5-substituted chlorsulfuron analogues (L101–L107) were investigated in a soil with pH 8.39. The experimental data indicated that 5-substituted chlorsulfuron compounds could accelerate degradation rates in alkaline soil, and thus, highlighted the potential for rational controllable degradation in soil. The degradation rates of these chlorsulfuron derivatives were accelerated by 1.84–77.22-fold, compared to chlorsulfuron, and exhibited excellent crop safety in wheat and corn (through pre-emergence treatment). In combination with bioassay activities, acidic and alkaline soil degradation, and crop safety, it was concluded that compounds L104 and L107, with ethyl or methyl groups, are potential green sulfonylurea herbicides for pre-emergence treatment on wheat and corn. This paper provides a reference for the further design of new sulfonylurea herbicides with high herbicidal activity, fast, controllable degradation rates, and high crop safety.

Synthesis, Herbicidal Activity, Crop Safety and Soil Degradation of Pyrimidine- and Triazine-Substituted Chlorsulfuron Derivatives.

Chlrosulfuron, a classical sulfonylurea herbicide that exhibits good safety for wheat but causes a certain degree of damage to subsequent corn in a wheat–corn rotation mode, has been suspended field application in China since 2014. Our previous study found that diethylamino-substituted chlorsulfuron derivatives accelerated the degradation rate in soil. In order to obtain sulfonylurea herbicides with good crop safety for both wheat and corn, while maintaining high herbicidal activities, a series of pyrimidine- and triazine-based diethylamino-substituted chlorsulfuron derivatives (W102–W111) were systematically evaluated. The structures of the synthesized compounds were confirmed with 1H NMR, 13C NMR, and HRMS. The preliminary biological assay results indicate that the 4,6-disubstituted pyrimidine and triazine derivatives could maintain high herbicidal activity. It was found that the synthesized compounds could accelerate degradation rates, both in acidic and alkaline soil. Especially, in alkaline soil, the degradation rate of the target compounds accelerated more than 22-fold compared to chlorsulfuron. Moreover, most chlorsulfuron analogs exhibited good crop safety for both wheat and corn at high dosages. This study provided a reference for the further design of new sulfonylurea herbicides with high herbicidal activity, fast degradation rates, and high crop safety.

Stereoselective degradation pathway of amide chiral herbicides and its impacts on plant and bacterial communities in integrated vertical flow constructed wetlands

This study demonstrates the stereoselective degradation patterns and biodegradation mechanisms of metolachlor (MET) and napropamide (NAP) in integrated vertical flow constructed wetlands (IVCW). The higher interphase transferability of NAP resulted in higher degradation rates of 90.60 ± 4.09%. The enantiomeric fraction (EF) values of 0.38 ± 0.02 and 0.54 ± 0.03, respectively, recorded for the enantiomers S-MET and R-NAP, with higher herbicidal activities, demonstrated their highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants showed positive correlations with the degradation efficiency and enantioselectivity of MET and NAP. Adaptive regulations by plants promoted the proliferation of microbial genera like Enterobacter and unclassified_Burkholderiales, which could facilitate plant growth. Moreover, enrichment of the herbicide-degrading functional bacteria Terrimonas (5.10%), Comamonas (4.05%) Pseudoxanthomonas (4.49%) and Mycobacterium (1.42%) demonstrably promoted the preferential degradation of S-MET and R-NAP. Furthermore, the abundance of Ferruginibacter favored the use of R-NAP as carbon source to achieve co-removal of R-NAP and NO3–-N.

Synthesis and herbicidal activities of 2‐phenylpyridine compounds containing alkenyl moieties

AbstractIn order to find new heterocyclic compounds with high herbicidal activity, a series of novel 2‐phenylpyridine derivatives were designed and synthesized by incorporating alkenyl into 2‐phenylpyridine moieties. The structures of the title compounds were characterized by 1H NMR, 13C NMR, 19F NMR, and HRMS. The herbicidal activities assay demonstrated that most of the title compounds showed 100% inhibition against Abutilon theophrasti and Amaranthus retroflexus at 150 g a.i./ha. At 37.5 g a.i./ha, compounds 6f and 6g exhibited comparable inhibition (>80%) against Abutilon theophrasti, Amaranthus retroflexus, and Eclipta prostrate, when compared with the positive control mesotrione at 150 g a.i./ha.

Degradation of 5-Dialkylamino-Substituted Chlorsulfuron Derivatives in Alkaline Soil.

Sulfonylurea herbicides are widely used as acetolactate synthase (ALS) inhibitors due to their super-efficient activity. However, some sulfonylurea herbicides show toxicity under crop rotation due to their long degradation time, for example, chlorsulfuron. Our research goal is to obtain chlorsulfuron-derived herbicides with controllable degradation time, good crop safety and high herbicidal activities. Based on our previously reported results in acidic soil, we studied the degradation behaviors of 5-dialkylamino-substituted chlorsulfuron derivatives (NL101–NL108) in alkaline soil (pH 8.39). The experimental data indicate that addition of the 5-dialkylamino groups on the benzene ring of chlorsulfuron greatly accelerated degradation in alkaline soil. These chlorsulfuron derivatives degrade 10.8 to 51.8 times faster than chlorsulfuron and exhibit excellent crop safety on wheat and corn (through pre-emergence treatment). With a comprehensive consideration of structures, bioassay activities, soil degradation and crop safety, it could be concluded that 5-dialkylamino-substituted chlorsulfuron derivatives are potential green sulfonylurea herbicides for pre-emergence treatment on both wheat and corn. The study also provides valuable information for the discovery of new sulfonylurea herbicides for crop rotation.

Structure-based ligand design and discovery of novel tenuazonic acid derivatives with high herbicidal activity

IntroductionComputer-aided design has become an important tool to develop novel pesticides based on natural lead compounds. Tenuazonic acid (TeA), a typical representative of the natural tetramic acid family, was patented as a potential bioherbicide. However, its herbicidal efficacy is still not up to the ideal standard of commercial products. ObjectivesWe aim to find new TeA’s derivatives with improved potency. MethodsMolecular docking was used to build ligand-acceptor interaction models, design and screen new derivatives. Phytotoxicity, oxygen evolution rate, chlorophyll fluorescence and herbicidal efficacy were determined to estimate biological activity of compounds. ResultsWith the aid of a constructed molecular model of natural lead molecule TeA binding to the QB site in Arabidopsis D1 protein, a series of derivatives differing in the alkyl side chain were designed and ranked according to free energies. All compounds are stabilized by hydrogen bonding interactions between their carbonyl oxygen O2 and D1-Gly256 residue; moreover, hydrogen bond distance is the most important factor for maintaining high binding affinity. Among 54 newly designed derivatives, D6, D13 and D27 with better affinities than TeA were screened out and synthesized to evaluate their photosynthetic inhibitory activity and herbicidal efficacy. Analysis of structure-activity relationship indicated that D6 and D13 with sec-pentyl and sec-hexyl side chains, respectively, were about twice more inhibitory of PSII activity and effective as herbicide than TeA with a sec-butyl side chain. ConclusionD6 and D13 are promising compounds to develop TeA-derived novel PSII herbicides with superior performance.

Synthesis and herbicidal activity of pyrimidyl‐1,2,4‐triazole derivatives containing aryl sulfonyl moiety

AbstractTo discover novel heterocyclic compounds with high herbicidal activity, a series of new pyrimidyl‐1,2,4‐triazole derivatives (Ι‐1 to Ι‐41) was designed and synthesized by incorporating the activating 1,2,4‐triazole, pyrimidine, and phenyl sulfonyl structural templets. Their structures were clearly identified by proton nuclear magnetic resonance (1H NMR), carbon‐13 nuclear magnetic resonance (13C NMR), high‐resolution mass spectroscopy (HRMS), and X‐ray single‐crystal diffraction (compound Ι‐3). Their herbicidal activities against monocotyledons (Echinochloa crusgalli, Sorghum bicolor) and dicotyledons (Raphanus sativus, Brassica campestris, Cucumis sativus, and Medicago sativa) were evaluated using a Petri dish culture method. The results indicated that most of title compounds exhibited significant herbicidal potencies against the plant growth at 100 mg·L−1, while some of them, such as Ι‐2 and Ι‐4, showed remarkable inhibitory effects on weed control at 10 mg·L−1 and 100 mg·L−1. On the whole, compound Ι‐3, which was found to possess an even broader spectrum of inhibitory activities against the roots and stalks of Echinochloa crusgalli, Raphanus sativus, Brassica campestris, Cucumis sativus, and Medicago sativa at 10 and 100 mg·L−1 than that of the commercial herbicide Flumetsulam, could be employed as a new lead structure for further optimization to find more potent herbicides.