Aryldiones incorporating a [1,4,5]oxadiazepane ring. Part 2: chemistry and biology of the cereal herbicide pinoxaden

A smartphone-adaptable chromogenic and fluorogenic sensor for rapid visual detection of toxic hydrazine in the environment

Hydrazine is an essential chemical in industries, but its high toxicity poses great threats to human health and environmental safety. Hence, it is of great significance to monitor the hydrazine in environment. In this work, we presented a chromogenic and fluorogenic dual-mode sensor RA for the detection of hydrazine based on nucleophilic substitution reaction. A linear relationship was obtained between the fluorescence intensity and the concentrations of N₂H₄ ranging from 0 to 35 μM (R² = 0.9936). The sensor can determine hydrazine with fast response (within 12 min), low limit of detection (0.129 μM) and high selectivity. RA was successfully used to detect N₂H₄ in real water samples with good recoveries and the results corresponded to the standard method. Furthermore, the sensor-coated portable test papers were fabricated, which can visually quantify hydrazine solutions with obvious fluorescence transformation from colorless to red. Moreover, RA-loaded papers were used to create a smartphone-adaptable RGB values analytical method for quantitative N₂H₄ detection.

Finding the Missing Property Concepts in Pesticide-Likeness

Poor bioavailability of pesticides is one of the major bottlenecks in the development of pesticides. Applications of the concept of pesticide-likeness have been widely accepted as one of the ways to break the bottleneck. At present, the evaluation of pesticide-likeness is mainly based on absorption, distribution, metabolism, excretion, and toxicity (ADME-T) property concepts of pesticides. However, a few significant property concepts of pesticides are ignored in the research of pesticide-likeness. Herein, we summarize the current study of ADME-T and other property concepts and analyze physicochemical properties for pesticides in the last 30 years, such as Fsp³, log P, and chiral centers. On the basis of these analyses, we propose that molecular complexity and residual property concepts of pesticides should be considered in the pesticide-likeness study. We hope that this work can help pesticide researchers and students, who are less knowledgeable in the field, to assess pesticide-likeness.

Bioinspired Synthesis of Pinoxaden Metabolites Using a Site-Selective C-H Oxidation Strategy

A bioinspired synthesis of Pinoxaden metabolites 2-5 is described herein. A site-selective C-H oxidation strategy validated by density functional theory (DFT) calculations was devised for preparing metabolites 2-4. Oxidation of the benzylic C-H bond in tertiary alcohol 7 using K₂S₂O₈ and catalytic AgNO₃ formed the desired metabolite 2 that enabled access to metabolites 3 and 4 in a single step. Unlike most metal/persulfate-catalyzed transformations reported for the C-C and C-O bond formation reactions wherein the metal acts as a catalyst, we propose that Ag(I)/K₂S₂O₈ plays the role of an initiator in the oxidation of intermediate 7 to 2. Metabolite 2 was subjected to a ruthenium tetroxide-mediated C-H oxidation to form metabolites 3 and 4 as a mixture that were purified to isolate pure standards of these metabolites. Metabolite 5 was synthesized from readily available advanced intermediate 9 via a House-Meinwald-type rearrangement in one step using a base.

Catalytic System-Controlled Divergent Reaction Strategies for the Construction of Diversified Spiropyrazolone Skeletons from Pyrazolidinones and Diazopyrazolones

A catalytic system-controlled divergent reaction strategy was here reported to construct four types of intriguing spiroheterocyclic skeletons from simple and readily available starting materials via a precise chemical bond activation/[n+1] annulation cascade. The tetraazaspiroheterocyclic and trizazspiroheterocyclic scaffolds could be independently constructed by a selective N-N bond activation/[n+1] annulation cascade, a C(sp² )-H activation/[4+1] annulation and a novel tandem C(sp² )-H/C(sp³ )-H bond activation/[4+1] annulation strategy, along with a broad scope of substrates, moderate to excellent yields and valuable transformations. More importantly, in these transformations, we are the first time to capture a N-N bond activation and a C(sp³ )-H bond activation of pyrazolidinones under different catalytic system.

Dissipation, adsorption-desorption, and potential transformation products of pinoxaden in soil

This study established and validated a simple and sensitive analytical approach for determining pinoxaden residues in soil. The dissipation and adsorption-desorption of pinoxaden in four kinds of Chinese soil were comprehensively investigated for the first time, and the possible metabolic products and pathways were identified. The developed method was successfully applied in dissipation and adsorption-desorption trials. Several influential factors, including temperature, organic matter, and moisture content, affected the dissipation rate of pinoxaden in soil. During the dissipation process, 1 hydrolytic intermediate and 13 possible transformation products were identified, and predicted metabolic pathways were composed of electron rearrangement, oxidation, cyclization, carboxylation, and so on. Both the adsorption and desorption isotherms of pinoxaden in four kinds of Chinese soil followed the Freundlich equation, and the Freundlich K_f values were positively correlated with the soil cation exchange capacity. According to the calculated Gibbs free energies, the adsorption of pinoxaden was an endothermic reaction and mainly a physical process. These results could provide some useful data for the determination of pinoxaden in other matrices and the evaluation of the environmental fate of pinoxaden in soil and other ecosystems.

Stimulation action of mefenpyr-diethyl on soybean, wheat, and signal grass plants

Mefenpyr-diethyl is a safener used for protection of cereal plants under applications of ACCase and ALS inhibitor herbicides. Current studies are describing safeners using a new approach, relating these products to stimulation action on plants. The objective of this work was to evaluate the stimulation action of mefenpyr-diethyl on soybean, wheat, and signal grass plants. The experiment was conducted in a greenhouse, under a completely randomized design, with four replications, in two seasons. Mefenpyr-diethyl (50 g a.i. ha-1) was applied on soybean plants (at V4 stage), and wheat and signal grass plants (both with 15 cm height). The variables evaluated were plant height, dry matter, and lipid content of the three species, and number of tillers of wheat and signal grass plants. The application of mefenpyr-diethyl in the first season increased the number of tillers of wheat and height of soybean plants. The soybean presented 24 and 14% more dry matter than the control in the first and second season, respectively, and 0.5% more lipid content in plants treated with mefenpyr-diethyl. These results show the stimulation action of mefenpyr-diethyl on wheat and soybean plants, denoting its potential for growth promotion and indicating the need for studies with this approach. No effect was found for the signal grass plants.

Target-Site and Metabolic Resistance Mechanisms to Penoxsulam in Barnyardgrass (Echinochloa crus-galli (L.) P. Beauv)

Herbicide resistance identification is essential for effective chemical weed control. In this study, we quantified the differences in growth response between penoxsulam resistant (R) and sensitive (S) Echinochloa crus-galli populations, explored the changes in ALS, and performed genetic analyses to identify metabolic genes that are up-regulated by the application of penoxsulam and other common herbicides. The R population showed a 26.0-fold higher resistance to penoxsulam and varied resistance to most tested herbicides with indices ranging from 4.9 to 145.9. A Trp-574-Arg amino acid mutation in ALS and low penoxsulam ALS sensitivity were the main mechanisms underlying herbicide resistance. The penoxsulam resistance can be significantly reversed by two P450s inhibitors and one GST inhibitor. By RNA-Seq, thirty-six highly expressed contigs were selected, and 30 of them were up-regulated in the R population treated by penoxsulam. Many of these genes were significantly expressed when treated with pyroxsulam, metamifop, and quinclorac. These upregulated genes appear to be complementary for plant resistance to penoxsulam and other common herbicides.

Palladium-Catalyzed Cross-Coupling Reactions: A Powerful Tool for the Synthesis of Agrochemicals

Pd-catalyzed cross-coupling reactions have become essential tools for the construction of carbon-carbon and carbon-heteroatom bonds. Over the last three decades, great efforts have been made with cross-coupling chemistry in the discovery, development, and commercialization of innovative new pharmaceuticals and agrochemicals (mainly herbicides, fungicides, and insecticides). In view of the growing interest in both modern crop protection and cross-coupling chemistry, this review gives a comprehensive overview of the successful applications of various Pd-catalyzed cross-coupling methodologies, which have been implemented as key steps in the synthesis of agrochemicals (on R&D and pilot-plant scales) such as the Heck, Suzuki, Sonogashira, Stille, and Negishi reactions, as well as decarboxylative, carbonylative, α-arylative, and carbon-nitrogen bond bond-forming cross-coupling reactions. Some perspectives and challenges for these catalytic coupling processes in the discovery of agrochemicals are briefly discussed in the final section. The examples chosen demonstrate that cross-coupling chemistry approaches open-up new, low-cost, and more efficient industrial routes to existing agrochemicals, and such methods also have the capability to lead the new generation of pesticides with novel modes of action for sustainable crop protection.

The Mode of Action of Adjuvants-Relevance of Physicochemical Properties for Effects on the Foliar Application, Cuticular Permeability, and Greenhouse Performance of Pinoxaden

We comprehensively studied the complexity of the mode of action of adjuvants by uncoupling the parameters contributing to the spray process during foliar application of agrochemicals. The ethoxylated sorbitan esters Tween 20 and Tween 80 improved the efficiency of pinoxaden (PXD) in controlling grass-weed species in greenhouse experiments by aiding retention, having humectant properties, maintaining the bioavailability, and increasing the cuticular penetration of PXD. The nonethoxylated sorbitan esters Span 20 and Span 80 showed minimal effects on retention, droplet hydration, or cuticular penetration, resulting in reduced PXD effects in the greenhouse. Tris(2-ethylhexyl)phosphate (TEHP) does not contribute much to retention and spreading but strongly enhances the diffusion of PXD across isolated P. laurocerasus cuticular membranes. As TEHP was most efficient in controlling the growth of grass-weed species, we propose that the direct effect of penetration aids on cuticular permeation plays a key role in the efficiency of foliar-applied agrochemicals.

Herbicidal aryldiones incorporating a 5-methoxy-[1,2,5]triazepane ring

Novel 2-aryl-cyclic-1,3-diones containing a 5-methoxy-[1,2,5]triazepane unit were explored towards an effective and wheat safe control of grass weeds. Their preparation builds on the ease of synthetic access to 7-membered heterocyclic [1,2,5]triazepane building blocks. Substitution and pattern hopping in the phenyl moiety revealed structure-activity relationships in good agreement with previously disclosed observations amongst the pinoxaden family of acetyl-CoA carboxylase inhibitors. In light of basic physicochemical, enzyme inhibitory and binding site properties, the N-methoxy functionality effectively acts as a bioisostere of the ether group in the seven-membered hydrazine ring.

Catalytic asymmetric synthesis of diphenylbutazone analogues

The asymmetric Michael addition of diphenylbutazone and its analogues to α,β-unsaturated 2-acyl imidazoles has been developed with a chiral-at-metal Rh(iii) complex as a catalyst.

Climate change increases the risk of herbicide-resistant weeds due to enhanced detoxification

Global warming will increase the incidence of metabolism-based reduced herbicide efficacy on weeds and, therefore, the risk for evolution of non-target site herbicide resistance. Climate changes affect food security both directly and indirectly. Weeds are the major biotic factor limiting crop production worldwide, and herbicides are the most cost-effective way for weed management. Processes associated with climatic changes, such as elevated temperatures, can strongly affect weed control efficiency. Responses of several grass weed populations to herbicides that inhibit acetyl-CoA carboxylase (ACCase) were examined under different temperature regimes. We characterized the mechanism of temperature-dependent sensitivity and the kinetics of pinoxaden detoxification. The products of pinoxaden detoxification were quantified. Decreased sensitivity to ACCase inhibitors was observed under elevated temperatures. Pre-treatment with the cytochrome-P450 inhibitor malathion supports a non-target site metabolism-based mechanism of herbicide resistance. The first 48 h after herbicide application were crucial for pinoxaden detoxification. The levels of the inactive glucose-conjugated pinoxaden product (M5) were found significantly higher under high- than low-temperature regime. Under high temperature, a rapid elevation in the level of the intermediate metabolite (M4) was found only in pinoxaden-resistant plants. Our results highlight the quantitative nature of non-target-site resistance. To the best of our knowledge, this is the first experimental evidence for temperature-dependent herbicide sensitivity based on metabolic detoxification. These findings suggest an increased risk for the evolution of herbicide-resistant weeds under predicted climatic conditions.

Determination of Stability from Multicomponent Pesticide Mixes

A study was conducted to evaluate the stability of 528 pesticides, metabolites, and contaminants prepared in large multicomponent mixes to enhance laboratory efficiency by allowing maximum use of the useful shelf life of the mixtures. Accelerated aging at 50 °C simulated 6 month, 1 year, and 2 year storage periods at -20 °C. Initial mixture composition was based on the instrument of analysis. After preliminary stability data had been obtained, mixtures were reformulated and re-evaluated. In all, 344 compounds showed satisfactory stability across all treatment groups, 100 compounds showed statistically significant changes between the control and the 6 month simulated storage period (27 with losses >20%), and the remainder showed borderline stability or were tested in one protocol. Stability behavior for organophosphates agreed with the proposed reaction mechanism responsible for acetylcholinesterase inhibition. A small number of compounds increased in response over time, suggesting the occurrence of degradation of precursor pesticides into these respective compounds.

Progress of modern agricultural chemistry and future prospects

Agriculture is facing an enormous challenge: it must ensure that enough high-quality food is available to meet the needs of a continually growing population. Current and future agronomic production of food, feed, fuel and fibre requires innovative solutions for existing and future challenges, such as climate change, resistance to pests, increased regulatory demands, renewable raw materials or requirements resulting from food chain partnerships. Modern agricultural chemistry has to support farmers to manage these tasks. Today, the so-called 'side effects' of agrochemicals regarding yield and quality are gaining more importance. Agrochemical companies with a strong research and development focus will have the opportunity to shape the future of agriculture by delivering innovative integrated solutions. This review gives a comprehensive overview of the innovative products launched over the past 10 years and describes the progress of modern agricultural chemistry and its future prospects.

Propesticides and their use as agrochemicals

The synthesis of propesticides is an important concept in design of modern agrochemicals with optimal efficacy, environmental safety, user friendliness and economic variability. Based on increasing knowledge of the biochemistry and genetics of major pest insects, weeds and agricultural pathogens, the search for selectivity has become an ever more important part of pesticide development and can be achieved by appropriate structural modifications of the active ingredient. Propesticides affect the absorption, distribution, metabolism and excretion parameters, which can lead to biological superiority of these modified active ingredients over their non-derivatised analogues. Various selected commercial propesticides testify to the successful utilisation of this concept in the design of agrochemicals. This review describes comprehensively the successful utilisation of propesticides and their role in syntheses of modern agrochemicals, exemplified by selected commercial products coming from different agrochemical areas.

Evolution of herbicide resistance mechanisms in grass weeds

Herbicide resistant weeds are becoming increasingly common, threatening global food security. Here, we present BrIFAR: a new model system for the functional study of mechanisms of herbicide resistance in grass weeds. We have developed a large collection of Brachypodium accessions, the BrI collection, representing a wide range of habitats. Wide screening of the responses of the accessions to four major herbicide groups (PSII, ACCase, ALS/AHAS and EPSPS inhibitors) identified 28 herbicide-resistance candidate accessions. Target-site resistance to PSII inhibitors was found in accessions collected from habitats with a known history of herbicide applications. An amino acid substitution in the psbA gene (serine264 to glycine) conferred resistance and also significantly affected the flowering and shoot dry weight of the resistant accession, as compared to the sensitive accession. Non-target site resistance to ACCase inhibitors was found in accessions collected from habitats with a history of herbicide application and from a nature reserve. In-vitro enzyme activity tests and responses following pre-treatment with malathion (a cytochrome-P450 inhibitor) indicated sensitivity at the enzyme level, and give strong support to diclofop-methyl and pinoxaden enhanced detoxification as NTS resistance mechanism. BrIFAR can promote better understanding of the evolution of mechanisms of herbicide resistance and aid the implementation of integrative management approaches for sustainable agriculture.