Synthesis and herbicidal activity of diphenyl ether derivatives containing unsaturated carboxylates

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.

Carane-3,4-diol Derivatives as Potential Water-Based Herbicides

Twelve novel carane-3,4-diol derivatives were designed, synthesized, and evaluated for their herbicidal activities against Lolium multiflorum Lam. and Brassica campestris for the first time. The relationships between the chemical structural factors, including types, the number or the carbon chain length of functional groups, associated with the lipophilicity and the herbicidal activity of the tested compounds were also discussed. The results showed that most of newly synthesized compounds had a dose-dependent, herbicidal activity against the root and shoot growths of Lolium multiflorum Lam. and Brassica campestris. Compared to carane-3,4-diol, most of the target derivatives possessed improved lipophilicity and certain solubilities in representative solvents with different polarities. Particularly, ester derivatives 3a-3b and 3e can be dissolved or dispersed in water, but also displayed higher herbicidal activity against Lolium multiflorum Lam. and Brassica campestris than other ester derivatives. The 50 % inhibitory concentration (IC50) value of compound 3e against shoot growth of Brassica campestris (0.485 mmol/L) was superior to that of commercial herbicide glyphosate (1.14 mmol/L), indicating that the potential application as a water-based herbicide for Brassica campestris control.

Synthesis and Evaluation of New Phytotoxic Fluorinated Chalcones as Photosystem II and Seedling Growth Inhibitors

The development of novel phytotoxic compounds has been an important aim of weed control research. In this study, we synthesized fluorinated chalcone derivatives featuring both electron-donating and electron-withdrawing groups. These compounds were evaluated both as inhibitors of the photosystem II (PSII) electron chain as well as inhibitors of the germination and seedling growth of Amaranthus plants. Chlorophyll a (Chl a) fluorescence assay was employed to evaluate their effects on PSII, while germination experiments were conducted to assess their impact on germination and seedling development. The results revealed promising herbicidal activity for (E)-3-(4-bromophenyl)-1-(4-fluorophenyl)prop-2-en-1-one (7 a) and (E)-1-(4-fluorophenyl)-3-phenylprop-2-en-1-one (7 e). Compounds 7 a and 7 e exhibited a reduction in Chl a parameters associated with performance indexes and electron transport per reaction center. This reduction suggests a decrease in PSII activity, attributed to the blockage of electron flow at the quinone pool. Molecular docking analyses of chalcone derivatives with the D1 protein of PSII revealed a stable binding conformation, wherein the carbonyl and fluorine groups interacted with Phe265 and His215 residues, respectively. Additionally, at a concentration of 100 μM, compound 7 e demonstrated pre- and post-emergent herbicidal activity, resulting in a reduction of the seed germination index, radicle and hypocotyl lengths of Amaranthus weeds.

Resistance-driven innovations in the discovery of bactericides: novel triclosan derivatives decorating isopropanolamine moiety as promising anti-biofilm agents against destructive plant bacterial diseases

BACKGROUND

Controlling bacterial infections in plants is a major challenge owing to the appearance of resistant strains. As a physical barrier, the bacterial biofilm helps bacterial infections acquire drug resistance by enabling bacteria to accommodate complex and volatile environmental conditions and avoid bactericidal effects. Thus, developing new antibacterial agents with antibiofilm potency is imperative.

RESULTS

A series of simple triclosan derivatives containing isopropanolamine moiety were elaborately designed and assessed for their antibacterial behavior. Bioassay results showed that some title compounds had excellent bioactivity against three destructive bacteria Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac) and Pseudomonas syringae pv. actinidiae (Psa). Notably, compound C₈ displayed high bioactivities toward Xoo and Xac, with EC₅₀ values were 0.34 and 2.11 μg mL^-1 , respectively. In vivo trials revealed that compound C₈ exhibited excellent protective activities against rice bacterial blight and citrus bacterial canker at 200 μg mL^-1 , with control effectivenesses of 49.57% and 85.60%, respectively. Compound A₄ had remarkably inhibitory activity toward Psa, with an EC₅₀ value of 2.63 μg mL^-1 , and demonstrated outstanding protective activity with a value of 77.23% against Psa in vivo. Antibacterial mechanisms indicated that compound C₈ dose-dependently prevented biofilm formation and extracellular polysaccharide production. C₈ also significantly weakened the motility and pathogenicity of Xoo.

CONCLUSION

This study contributes to the development and excavation of novel bactericidal candidates with broad-spectrum antibacterial activity by targeting bacterial biofilm to control refractory plant bacterial diseases. © 2023 Society of Chemical Industry.

Cypyrafluone, a 4-Hydroxyphenylpyruvate Dioxygenase Inhibitor to Control Weed in Wheat Fields

As a bleaching herbicide, cypyrafluone was applied postemergence in wheat fields for annual weed control; especially, this herbicide possesses high efficacy against cool-season grass weed species such as Alopecurus aequalis and Alopecurus japonicus. In this study, the target of action of cypyrafluone on 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibition was confirmed. This herbicide caused severe foliar whitening symptoms at 5-7 days after treatment (DAT) and death of the whole plant within 10 DAT. Significant increases in phytoene content and significant decreases in kinds of carotenoid and chlorophyll pigments were observed. The content of chlorophyll pigments in cypyrafluone-treated Spirodela polyrhiza decreased upon the addition of homogentisic acid (HGA), which indicated that cypyrafluone prevents the HGA production, possibly by inhibiting the catalytic activity of 4-HPPD. Indeed, cypyrafluone strongly inhibited the catalytic activity of Arabidopsis thaliana HPPD produced by Escherichia coli, which was approximately 2 times less effective than mesotrione. In addition, overexpression of Oryza sativa HPPD in rice and A. thaliana both conferred a high tolerance level to cypyrafluone on them. Molecular docking found that cypyrafluone bonded well to the active site of the HPPD and formed a bidentate coordination interaction with the Fe²⁺ atom, with distances of 2.6 and 2.7 Å between oxygen atoms and the Fe²⁺ atom and a binding energy of -8.0 kcal mol^-1.

Discovery of novel phenoxypyridine as promising protoporphyrinogen IX oxidase inhibitors

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

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Expedient Discovery for Novel Antifungal Leads Targeting Succinate Dehydrogenase: Pyrazole-4-formylhydrazide Derivatives Bearing a Diphenyl Ether Fragment

The pyrazole-4-carboxamide scaffold containing a flexible amide chain has emerged as the molecular skeleton of highly efficient agricultural fungicides targeting succinate dehydrogenase (SDH). Based on the above vital structural features of succinate dehydrogenase inhibitors (SDHI), three types of novel pyrazole-4-formylhydrazine derivatives bearing a diphenyl ether moiety were rationally conceived under the guidance of a virtual docking comparison between bioactive molecules and SDH. Consistent with the virtual verification results of a molecular docking comparison, the in vitro antifungal bioassays indicated that the skeleton structure of title compounds should be optimized as an N'-(4-phenoxyphenyl)-1H-pyrazole-4-carbohydrazide scaffold. Strikingly, N'-(4-phenoxyphenyl)-1H-pyrazole-4-carbohydrazide derivatives 11o against Rhizoctonia solani, 11m against Fusarium graminearum, and 11g against Botrytis cinerea exhibited excellent antifungal effects, with corresponding EC₅₀ values of 0.14, 0.27, and 0.52 μg/mL, which were obviously better than carbendazim against R. solani (0.34 μg/mL) and F. graminearum (0.57 μg/mL) as well as penthiopyrad against B. cinerea (0.83 μg/mL). The relative studies on an in vivo bioassay against R. solani, bioactive evaluation against SDH, and molecular docking were further explored to ascertain the practical value of compound 11o as a potential fungicide targeting SDH. The present work provided a non-negligible complement for the structural optimization of antifungal leads targeting SDH.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Design, Synthesis, and Herbicidal Activity of Novel Diphenyl Ether Derivatives Containing Fast Degrading Tetrahydrophthalimide

To seek new protoporphyrinogen oxidase (PPO) inhibitors with better biological activity, a series of novel diphenyl ether derivatives containing tetrahydrophthalimide were designed based on the principle of substructure splicing and bioisomerization. PPO inhibition experiments exhibited that 6c is the most potential compound, with the half-maximal inhibitory concentration (IC₅₀) value of 0.00667 mg/L, showing 7 times higher activity than Oxyfluorfen (IC₅₀ = 0.0426 mg/L) against maize PPO and similar herbicidal activities to Oxyfluorfen in weeding experiments in greenhouses and field weeding experiments. In view of the inspected bioactivities, the structure-activity relationship (SAR) of this series of compounds was also discussed. Crop selection experiments demonstrate that compound 6c is safe for soybeans, maize, rice, peanuts, and cotton at a dose of 300 g ai/ha. Accumulation analysis experiments showed that the accumulation of 6c in some crops (soybeans, peanuts, and cotton) was significantly lower than Oxyfluorfen. Current work suggests that compound 6c may be developed as a new herbicide candidate in fields.

Potentials of Diphenyl Ether Scaffold as a Therapeutic Agent: A Review

Diphenyl ethers (DPE) and its analogs have exhibited excellent potential for therapeutic and industrial applications. Since the 19th century, intensive research is perpetuating on the synthetic routes and biological properties of DPEs. Few well-known DPEs are Nimesulide, Fenclofenac, Triclosan, Sorafenib, MK-4965, and MK-1439 which have shown the potential of this moiety as a lead scaffold for different pharmacological properties. In this review, we recapitulate the diverse synthetic route of DPE moiety inclusive of merits and demerits over the classical synthetic route and how this moiety sparked an interest in researchers to discern the SAR (Structure Activity Relationship) for the development of diversified biological properties of DPEs such as antimicrobial, antifungal, antiinflammatory & antiviral activities.

Bacterial Biodegradation of 4-Monohalogenated Diphenyl Ethers in One-Substrate and Co-Metabolic Systems

The use of diphenyl ether (DE) and its 4-monohalogenated derivatives (4-HDE) as flame retardants, solvents, and substrates in biocide production significantly increases the risk of ecosystem contamination. Their removal is important from the point of view of environmental protection. The aim of this study was to evaluate the degradation processes of DE and 4-HDE by enzymes of the environmental bacterial strains under one-substrate and co-metabolic conditions. The study is focused on the biodegradation of DE and 4-HDE, the enzymatic activity of microbial strains, and the cell surface properties after contact with compounds. The results show that the highest biodegradation (96%) was observed for 4-chlorodiphenyl ether in co-metabolic culture with P. fluorescens B01. Moreover, the activity of 1,2-dioxygenase during degradation of 4-monohalogenated diphenyl ethers was higher than that of 2,3-dioxygenase for each strain tested. The presence of a co-substrate provoked changes in dioxygenase activity, resulting in the increased activity of 1,2-dioxygenase. Moreover, the addition of phenol as a co-substrate allowed for increased biodegradation of the diphenyl ethers and noticeable modification of the cell surface hydrophobicity during the process. All observations within the study performed have led to a deeper understanding of the contaminants’ biodegradation processes catalyzed by environmental bacteria.

Flumioxazin metabolism in pregnant animals and cell-based protoporphyrinogen IX oxidase (PPO) inhibition assay of fetal metabolites in various animal species to elucidate the mechanism of the rat-specific developmental toxicity

Flumioxazin, an N-phenylimide herbicide, inhibits protoporphyrinogen oxidase (PPO), a key enzyme in heme biosynthesis in mammals, and causes rat-specific developmental toxicity. The mechanism has mainly been clarified, but no research has yet focused on the contribution of its metabolites. We therefore conducted in vivo metabolism studies in pregnant rats and rabbits, and found 6 major known metabolites in excreta. There was no major rat-specific metabolite. The most abundant component in rat fetuses was APF, followed by flumioxazin and 5 identified metabolites. The concentrations of flumioxazin and these metabolites in fetuses were lower in rabbits than in rats. In vitro PPO inhibition assays with rat and human liver mitochondria showed that flumioxazin is a more potent PPO inhibitor than the metabolites. There were no species differences in relative intensity of PPO inhibition among flumioxazin and these metabolites. Based on the results of these in vivo and in vitro experiments, we concluded that flumioxazin is the causal substance of the rat-specific developmental toxicity. As a more reliable test system for research on in vitro PPO inhibition, cell-based assays with rat, rabbit, monkey, and human hepatocytes were performed. The results were consistent with those of the mitochondrial assays, and rats were more sensitive to PPO inhibition by flumioxazin than humans, while rabbits and monkeys were almost insensitive. From these results, the species difference in the developmental toxicity was concluded to be due to the difference in sensitivity of PPO to flumioxazin, and rats were confirmed to be the most sensitive of these species.

Design, synthesis and herbicidal activities of novel 4-(1H-pyrazol-1-yl)-6-(alkynyloxy)-pyrimidine derivatives as potential pigment biosynthesis inhibitors

BACKGROUND

With the objective of finding novel valuable herbicidal candidates, a series of novel 4-(1H-pyrazol-1-yl)-6-(alkynyloxy)-pyrimidine derivatives were synthesised and their herbicide activities were evaluated in vivo.

RESULTS

The results showed that many target compounds expressed bleaching activities. Among these, compound 5 h showed the best bleaching activity to gramineous weeds, being able to produce the highest inhibition of chlorophyll level in seedlings of Pennisetum alopecuroides L. (IC50 = 3.48 mg L(-1) ). Moreover, compound 5 h expressed good selective toxicity between gramineous P. alopecuroides L. and broadleaf plant Brassica campestris L.

CONCLUSIONS

The present work demonstrates that pyrimidine derivatives containing pyrazole can be used as potential lead compounds for developing novel pigment biosynthesis inhibitors.

Synthesis of rubrolide analogues as new inhibitors of the photosynthetic electron transport chain

Many natural products have been used as a model for the development of new drugs and agrochemicals. Following this strategy 11 rubrolide analogues, bearing electron-withdrawing and -donating groups at both benzene rings, were prepared starting from commercially available mucobromic acid. The ability of all compounds to inhibit the photosynthetic electron transport chain in the chloroplast was investigated. The rubrolide analogues were effective in interfering with the light-driven ferricyanide reduction by isolated chloroplasts. The IC(50) values of the most active derivatives are in fact only 1 order of magnitude higher than those of commercial herbicides sharing the same mode of action, such as Diuron (0.27 μM). QSAR studies indicate that the most efficient compounds are those having higher ability to accept electrons, either by a reduction process or by an electrophilic reaction mechanism. The results obtained suggest that the rubrolide analogues represent promising candidates for the development of new active principles targeting photosynthesis to be used as herbicides.