C-P Natural Products as Next-Generation Herbicides: Chemistry and Biology of Glufosinate

Synthetic versatility: the C-P bond odyssey

C-P bond formation reactions have garnered significant attention due to the widespread presence of organophosphorus compounds in pharmaceuticals, phosphine-containing ligands, pesticides, and materials science. Consequently, various efficient methodologies have been established in recent decades for constructing C-P bonds. This review article traces the historical evolution of C-P bond research and explores the prospects of C-P bond formation. It contrasts biotechnological approaches with chemical synthesis, emphasizing the critical importance of precision and innovation in developing novel C-P structures. A forward-looking perspective is provided on the role of computational tools and machine learning in optimizing C-P bond synthesis and discovering new compounds. The article explores prospective avenues for reactions that form C-P bonds and advocates for enhanced interdisciplinary collaboration to propel scientific and technological advancements.

Computer-Aided Flexible Loops Engineering of Glutamate Dehydrogenase for Asymmetric Synthesis of Chiral Pesticides l-phosphinothricin

The access to the enantiopure noncanonical amino acid l-phosphinothricin (l-PPT) by applying biocatalysts is highly appealing in organic chemistry. In this study, a NADH-dependent glutamate dehydrogenase from Lachnospiraceae bacterium (LbGluDH) was chosen for the asymmetric synthesis of l-PPT. Three flexible loops undergoing big conformational shifts during the catalysis were identified and rationally engineered following the initial mutagenesis. The enzyme's specific activity toward the key precursor of l-PPT, 2-oxo-4-[(hydroxy) (methyl) phosphinyl] butyric acid (PPO), was improved from negligible to 9 U/mg, and the Km value was reduced to 17 mM. The computational analysis showed that the modified loops broadened the enzyme's narrow tunnels, allowing the substrate to access the binding pocket and get closer to the crucial residue D165, thereby enhancing the catalytic process. Utilizing the variant as the catalyst, the preparation of l-PPT achieved a 100% conversion rate within 60 min, coupled with a stereoselectivity exceeding 99.9%, demonstrating its practical capacity for industrial application. Similar enhancement in catalytic activity was obtained applying the same strategy to a typical NADH-dependent GluDH from Pyrobaculum islandicum (PisGluDH), indicating the effectiveness of our strategy for the protein engineering of GluDHs targeted to the biosynthesis of unnatural compounds.

Asymmetric Conjugate Addition of Phosphine Sulfides to α-Substituted β-Nitroacrylates Using Cinchona Alkaloid Amide Catalysts

Chiral phosphine-containing amino acids are useful motifs in pharmaceutical compounds. In this study, we developed the asymmetric conjugate addition of phosphine sulfides with α-substituted β-nitroacrylates to synthesize phosphine-containing amino acid precursors with chiral tetrasubstituted carbon centers. This method showed a wide substrate scope, and the obtained products were converted into various chiral compounds. The origin of the enantioselectivity was clarified by computational analysis.

Through virtual saturation mutagenesis and rational design for superior substrate conversion in engineered d-amino acid oxidase

The d-amino acid oxidase (DAAO) is pivotal in obtaining optically pure l-glufosinate (l-PPT) by converting d-glufosinate (d-PPT) to its deamination product. We screened and designed a Rasamsonia emersonii DAAO (ReDAAO), making it more suitable for oxidizing d-PPT. Using Caver 3.0, we delineated three substrate binding pockets and, via alanine scanning, identified nearby key residues. Pinpointing key residues influencing activity, we applied virtual saturation mutagenesis (VSM), and experimentally validated mutants which reduced substrate binding energy. Analysis of positive mutants revealed elongated side-chain prevalence in substrate binding pocket periphery. Although computer-aided approaches can rapidly identify advantageous mutants and guide further design, the mutations obtained in the first round may not be suitable for combination with other advantageous mutations. Therefore, each round of combination requires reasonable iteration. Employing VSM-assisted screening multiple times and after four rounds of combining mutations, we ultimately obtained a mutant, N53V/F57Q/V94R/V242R, resulting in a mutant with a 5097% increase in enzyme activity compared to the wild type. It provides valuable insights into the structural determinants of enzyme activity and introduces a novel rational design procedure.

Chemodivergent phosphonylation of diazocarboxylates: light-on vs. light-off reactions

By tapping into the divergent reactivity of diazocarboxylates under thermal and photocatalytic conditions, we could develop chemodivergent phosphonylation protocols for α-diazocarboxylates with trialkyl phosphites. While the thermal reaction led to N-P bond formation affording phosphonylated hydrazones, the visible light-mediated reaction furnished phosphonylated aryl carboxylates through C-P bond formation. Both reactions are notable for their operational simplicity and mild conditions affording products in good yields without the requirement of a metal, base or photocatalyst.

Sensitive fluorescence detection of glyphosate and glufosinate ammonium pesticides by purine-hydrazone-Cu2+ complex

Organophosphorus pesticides play an important role as broad-spectrum inactivating herbicides in agriculture. Developing a method for rapid and efficient organophosphorus pesticides detection is still urgent due to the increasing concern on food safety. An organo-probe (ZDA), synthesized by purine hydrazone derivative and 2,2'-dipyridylamine derivative, was applied in sensitive recognition of Cu2+ with detection limit of 300 nM. Mechanism study via density functional theory (DFT) and job's plot experiment revealed that ZDA and Cu2+ ions form a 1:2 complex quenching the fluorescence emission. Moreover, this fluorescent complex ZDA-Cu2+ was applicable for detecting glyphosate and glufosinate ammonium following fluorescence enhancement mechanism, with detection limits of 11.26 nM and 11.5 nM, respectively. Meanwhile, ZDA-Cu2+ was effective and sensitive when it is used for pesticide detection, reaching the maximum value and stabilizing in 1 min. Finally, the ZDA-Cu2+ probe could also be tolerated in cell assay environment, implying potential bio-application.

Recent progress on the functionalization of white phosphorus in China

Direct synthesis of organophosphorus compounds from white phosphorus represents a significant but challenging subject, especially in the context of ongoing efforts to comprehensively improve the phosphorus-derived chemical industry driven by sustainability and safety concerns. China is the world's largest producer of white phosphorus, creating a significant demand for the green transformation of this crucial feedstock. This review provides an overview of advancements in white phosphorus activation by Chinese research teams, focusing on the direct construction of P‒C/N/O/S/M bonds from white phosphorus. Additionally, we offer some insights into prospective directions for the activation and transformation of white phosphorus in the future. This review paper aims to attract more researchers to engage in this area, stimulating follow-up exploration and fostering enduring advances.

Palladium-catalyzed (Z)-selective allylation of phosphine oxides with vinylethylene carbonates to construct phosphorus allyl alcohols

Allylphosphine oxide compounds are important building blocks with broad applications in organic synthesis and pharmaceutical science. Herein, we report an unprecedented palladium-catalyzed allylation of phosphine oxides with vinylethylene carbonates, producing various phosphorus allyl alcohols in excellent yields with high Z-selectivity. In addition, gram-scale synthesis and further functional group transformations demonstrate the practical utility of this synthetic method.

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

BACKGROUND

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.

RESULTS

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.

CONCLUSION

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.

A review of organophosphonates, their natural and anthropogenic sources, environmental fate and impact on microbial greenhouse gases emissions - Identifying knowledge gaps

Organophosphonates (OPs) are a unique group of natural and synthetic compounds, characterised by the presence of a stable, hard-to-cleave bond between the carbon and phosphorus atoms. OPs exhibit high resistance to abiotic degradation, excellent chelating properties and high biological activity. Despite the huge and increasing scale of OP production and use worldwide, little is known about their transportation and fate in the environment. Available data are dominated by information concerning the most recognised organophosphonate - the herbicide glyphosate - while other OPs have received little attention. In this paper, a comprehensive review of the current state of knowledge about natural and artificial OPs is presented (including glyphosate). Based on the available literature, a number of knowledge gaps have been identified that need to be filled in order to understand the environmental effects of these abundant compounds. Special attention has been given to GHG-related processes, with a particular focus on CH4. This stems from the recent discovery of OP-dependent CH4 production in aqueous environments under aerobic conditions. The process has changed the perception of the biogeochemical cycle of CH4, since it was previously thought that biological methane formation was only possible under anaerobic conditions. However, there is a lack of knowledge on whether OP-associated methane is also formed in soils. Moreover, it remains unclear whether anthropogenic OPs affect the CH4 cycle, a concern of significant importance in the context of the increasing rate of global warming. The literature examined in this review also calls for additional research into the date of OPs in waste and sewage and in their impact on environmental microbiomes.

Design, Synthesis, and Herbicidal Activity of Pyrazole Amide Derivatives as Potential Transketolase Inhibitors

The design and synthesis of new herbicidal active compounds based on a new target are of great significance for the development of new herbicides. Transketolase (TK) plays a key role in the Calvin cycle of plant photosynthesis and has been confirmed as a potential candidate target to develop and discover new herbicides. To obtain compounds with ultraefficient targeting of TK, a series of pyrazole amide derivatives were designed and synthesized through structural optimization for lead compound 4u based on TK as the new target. The bioassay results showed that compounds 6ba and 6bj displayed a highly inhibitory effect with the root inhibition of about 90% against Digitaria sanguinalis (DS) and 80% against Amaranthus retroflexus (AR) and Setaria viridis (SV) by the small cup method, which was better than the positive control mesotrione and nicosulfuron. Furthermore, compounds 6ba and 6bj exhibited an excellent inhibitory effect with the inhibition of about 80% (against DS) and over 80% (against SV) at the dosage of 150 g of active ingredient/ha by the foliar spray method. The TK enzyme activity inhibition test showed that the inhibition effect of target compounds against TK was consistent with the results of herbicidal activities. Also, molecular docking analysis showed that compounds 6ba and 6bj went deep into the active cavity of TK, bound to TK by a strong interaction, and might act on the enzyme TK. Above of all, compounds 6ba and 6bj are promising herbicide lead compounds targeting TK. Hence, they could be developed into more efficient herbicides by further structural optimization.

Quantitation of glyphosate, glufosinate, and AMPA in drinking water and surface waters using direct injection and charged-surface ultra-high performance liquid chromatography-tandem mass spectrometry

Herbicides glyphosate (N-(phosphonomethyl)glycine) and glufosinate (2-amino-4-(hydroxymethylphosphinyl)butanoic acid) and the main transformation product of glyphosate, aminomethanephosphonic acid (AMPA), are challenging to analyze for in environmental samples. The quantitative method developed by this study adapts previously standardized dechlorination procedures coupled to a novel charged surface C18 column, ultra-high performance liquid chromatography-tandem mass spectrometry, polarity switching, and direct injection. The method was applied to chlorinated tap water, as well as river samples, collected in the City of Winnipeg and rural Manitoba, Canada. Using only syringe filtration without derivatization, the validated method resulted in good accuracies in both tap and surface water, at both 2 and 20 μg L-1. Method limits of detection (MLD) and quantification (MLQ) ranged from 0.022/0.074 to 0.11/0.36 μg L-1, with precisions of 0.46-2.2% (intraday) and 1.3-7.3% (interday). The mean (SEM) of the pesticides in μg L-1 for tap water were 0.11 (0.007) (AMPA), glufosinate and glyphosate < MLDs; and for Red River water were 0.56 (0.045) (AMPA), glufosinate < MLQ, and glyphosate 0.40 (0.072). For the smaller tributaries, glufosinate was >MLD but < MLQ once and that was for Shannon Creek at 0.2 μg L-1. For the remaining rivers, the mean concentrations ranged from 0.31 to 3.1 μg L-1 for AMPA, and 0.087-0.53 μg L-1 for glyphosate. The method will be ideal for supporting monitoring and risk assessment programs that require high throughput sampling and quantitative methods capable of producing robust results that leverages chromatographic and mass spectrometric paradigms instead of being extraction technology focused.

Enhancement of the substrate specificity of D-amino acid oxidase based on tunnel-pocket engineering

D-Amino acid oxidase (DAAO) selectively catalyzes the oxidative deamination of  D-amino acids, making it one of the most promising routes for synthesizing optically pure  L-amino acids, including  L-phosphinothricin ( L-PPT), a chiral herbicide with significant market potential. However, the native DAAOs that have been reported have low activity against unnatural acid substrate  D-PPT. Herein, we designed and screened a DAAO from Rhodotorula taiwanensis (RtwDAAO), and improved its catalytic potential toward  D-PPT through protein engineering. A semirational design approach was employed to create a mutation library based on the tunnel-pocket engineering. After three rounds of iterative saturation mutagenesis, the optimal variant M3rd -SHVG was obtained, exhibiting a >2000-fold increase in relative activity. The kinetic parameters showed that M3rd -SHVG improved the substrate binding affinity and turnover number. This is the optimal parameter reported so far. Further, molecular dynamics simulation revealed that the M3rd -SHVG reshapes the tunnel-pocket and corrects the direction of enzyme-substrate binding, allowing efficiently catalyze unnatural substrates. Our strategy demonstrates that the redesign of tunnel-pockets is effective in improving the activity and kinetic efficiency of DAAO, which provides a valuable reference for enzymatic catalysis. With the M3rd -SHVG as biocatalyst, 500 mM D, L-PPT was completely converted and the yield reached 98%. The results laid the foundation for further industrial production.

Eleusine indica Cytochrome P450 and Glutathione S-Transferase Are Linked to High-Level Resistance to Glufosinate

Eleusine indica has become a global nuisance weed and has evolved resistance to glufosinate. The involvement of target-site resistance (TSR) in glufosinate resistance in E. indica has been elucidated, while the role of nontarget-site resistance (NTSR) remains unclear. Here, we identified a glufosinate-resistant (R) population that is highly resistant to glufosinate, with a resistance index of 13.5-fold. Molecular analysis indicated that the resistance mechanism of this R population does not involve TSR. In addition, pretreatment with two known metabolic enzyme inhibitors, the cytochrome P450 (CYP450) inhibitor malathion and the glutathione S-transferase (GST) inhibitor 4-chloro-7-nitrobenzoxadiazole (NBD-Cl), increased the sensitivity of the R population to glufosinate. The results of subsequent RNA sequencing (RNA-seq) and quantitative real-time PCR (RT-qPCR) suggested that the constitutive overexpression of a GST gene (GSTU3) and three CYP450 genes (CYP94s and CYP71) may play an important role in glufosinate resistance. This study provides new insights into the resistance mechanism of E. indica.

Chemodiversity of Cyanobacterial Toxins Driven by Future Scenarios of Climate Warming and Eutrophication

Climate change and eutrophication are two environmental threats that can alter the structure of freshwater ecosystems and their service functions, but we know little about how ecosystem structure and function will evolve in future scenarios of climate warming. Therefore, we created different experimental climate scenarios, including present-day conditions, a 3.0 °C increase in mean temperature, and a "heatwaves" scenario (i.e., an increase in temperature variability) to assess the effects of climate change on phytoplankton communities under simultaneous stress from eutrophication and herbicides. We show that the effects of climate warming, particularly heatwaves, are associated with elevated cyanobacterial abundances and toxin production, driven by a change from mainly nontoxic to toxic Microcystis spp. The reason for higher cyanobacterial toxin concentrations is likely an increase in abundances because under the dual pressures of climate warming and eutrophication individual Microcystis toxin-producing ability decreased. Eutrophication and higher temperatures significantly increased the biomass of Microcystis, leading to an increase in the cyanobacterial toxin concentrations. In contrast, warming alone did not produce higher cyanobacterial abundances or cyanobacterial toxin concentrations likely due to the depletion of the available nutrient pool. Similarly, the herbicide glyphosate alone did not affect abundances of any phytoplankton taxa. In the case of nutrient enrichment, cyanobacterial toxin concentrations were much higher than under warming alone due to a strong boost in biomass of potential cyanobacterial toxin producers. From a broader perspective our study shows that in a future warmer climate, nutrient loading has to be reduced if toxic cyanobacterial dominance is to be controlled.

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.

Adverse health effects of emerging contaminants on inflammatory bowel disease

Inflammatory bowel disease (IBD) is becoming increasingly prevalent with the improvement of people's living standards in recent years, especially in urban areas. The emerging environmental contaminant is a newly-proposed concept in the progress of industrialization and modernization, referring to synthetic chemicals that were not noticed or researched before, which may lead to many chronic diseases, including IBD. The emerging contaminants mainly include microplastics, endocrine-disrupting chemicals, chemical herbicides, heavy metals, and persisting organic pollutants. In this review, we summarize the adverse health effect of these emerging contaminants on humans and their relationships with IBD. Therefore, we can better understand the impact of these new emerging contaminants on IBD, minimize their exposures, and lower the future incidence of IBD.

Deamination of 1-Aminoalkylphosphonic Acids: Reaction Intermediates and Selectivity

Deamination of 1-aminoalkylphosphonic acids in the reaction with HNO₂ (generated "in situ" from NaNO₂) yields a mixture of substitution products (1-hydroxyalkylphosphonic acids), elimination products (vinylphosphonic acid derivatives), rearrangement and substitution products (2-hydroxylkylphosphonic acids) as well as H₃PO₄. The variety of formed reaction products suggests that 1-phosphonoalkylium ions may be intermediates in such deamination reactions.

Copper-Catalyzed Radical Hydrazono-Phosphorylation of Alkenes

An efficient copper-catalyzed radical hydrazono-phosphorylation of alkenes with hydrazine derivatives and diarylphosphine oxides is described. The reaction provides a general and convenient method toward the synthesis of diverse β-hydrazonophosphine oxides in satisfactory yields. Based on conducted mechanistic experiments, a mechanism involving Ag-catalyzed oxidative generation of phosphinoyl radicals and subsequent addition to alkenes followed by Cu-assisted hydrazonation is proposed. Moreover, the practicability of the reaction is successfully demonstrated by its successful application on a gram scale.

Involvement of glutamine synthetase 2 (GS2) amplification and overexpression in Amaranthus palmeri resistance to glufosinate

Amplification and overexpression of the target site glutamine synthetase, specifically the plastid-located isoform, confers resistance to glufosinate in Amaranthus palmeri. This mechanism is novel among glufosinate-resistant weeds. Amaranthus palmeri has recently evolved resistance to glufosinate herbicide. Several A. palmeri populations from Missouri and Mississippi, U.S.A. had survivors when sprayed with glufosinate-ammonium (GFA, 657 g ha^-1). One population, MO#2 (fourfold resistant) and its progeny (sixfold resistant), were used to study the resistance mechanism, focusing on the herbicide target glutamine synthetase (GS). We identified four GS genes in A. palmeri; three were transcribed: one coding for the plastidic protein (GS2) and two coding for cytoplasmic isoforms (GS1.1 and GS1.2). These isoforms did not contain mutations associated with resistance. The 17 glufosinate survivors studied showed up to 21-fold increase in GS2 copies. GS2 was expressed up to 190-fold among glufosinate survivors. GS1.1 was overexpressed > twofold in only 3 of 17, and GS1.2 in 2 of 17 survivors. GS inhibition by GFA causes ammonia accumulation in susceptible plants. Ammonia level was analyzed in 12 F1 plants. GS2 expression was negatively correlated with ammonia level (r =  - 0.712); therefore, plants with higher GS2 expression are less sensitive to GFA. The operating efficiency of photosystem II (ϕPSII) of Nicotiana benthamiana overexpressing GS2 was four times less inhibited by GFA compared to control plants. Therefore, increased copy and overexpression of GS2 confer resistance to GFA in A. palmeri (or other plants). We present novel understanding of the role of GS2 in resistance evolution to glufosinate.

In(OTf)3-catalyzed N-α phosphonylation of N,O-acetals with triethyl phosphite

A practical approach to α-aminophosphonates has been developed through an In(OTf)₃-catalyzed N-α phosphonylation of N,O-acetals with triethyl phosphite 7. Indoline and isoindoline N,O-acetals 6a-6j and 9a-9j and chain N,O-acetals 11a-11p were subjected to a Lewis acid catalyzed N-α phosphonylation process. As a result, the desired α-aminophosphonates 8a-8j, 10a-10j and 12a-12p were obtained in moderate to good yields.

Domain Fusion of Two Oxygenases Affords Organophosphonate Degradation in Pathogenic Fungi

Proteins of the HD-domain superfamily employ a conserved histidine-aspartate (HD) dyad to coordinate diverse metallocofactors. While most known HD-domain proteins are phosphohydrolases, new additions to this superfamily have emerged such as oxygenases and lyases, expanding their functional repertoire. To date, three HD-domain oxygenases have been identified, all of which employ a mixed-valent FeIIFeIII cofactor to activate their substrates and utilize molecular oxygen to afford cleavage of C-C or C-P bonds via a diferric superoxo intermediate. Phylogenetic analysis reveals an uncharacterized multidomain protein in the pathogenic soil fungus Fonsecaea multimorphosa, herein designated PhoF. PhoF consists of an N-terminal FeII/α-ketoglutarate-dependent domain resembling that of PhnY and a C-terminal HD-domain like that of PhnZ. PhnY and PhnZ are part of an organophosphonate degradation pathway in which PhnY hydroxylates 2-aminoethylphosphonic acid, and PhnZ cleaves the C-P bond of the hydroxylated product yielding phosphate and glycine. Employing electron paramagnetic resonance and Mössbauer spectroscopies in tandem with activity assays, we determined that PhoF carries out the O2-dependent degradation of two aminophosphonates, demonstrating an expanded catalytic efficiency with respect to the individual, but mechanistically coupled PhnY and PhnZ. Our results recognize PhoF as a new example of an HD-domain oxygenase and show that domain fusion of an organophosphonate degradation pathway may be a strategy for disease-causing fungi to acquire increased functional versatility, potentially important for their survival.

Green and Effective Preparation of α-Hydroxyphosphonates by Ecocatalysis

A green and effective approach for the synthesis of structurally diversed α-hydroxyphosphonates via hydrophosphonylation of aldehydes under solventless conditions and promoted by biosourced catalysts, called ecocatalysts "Eco-MgZnOx" is presented. Ecocatalysts were prepared from Zn-hyperaccumulating plant species Arabidopsis halleri, with simple and benign thermal treatment of leaves rich in Zn, and without any further chemical treatment. The elemental composition and structure of Eco-MgZnOx were characterized by MP-AES, XRPD, HRTEM, and STEM-EDX techniques. These analyses revealed a natural richness in two unusual and valuable mixed zinc-magnesium and iron-magnesium oxides. The ecocatalysts were employed in this study to demonstrate their potential use in hydrophosphonylation of aldehydes, leading to various α-hydroxyphosphonate derivatives, which are critical building blocks in the modern chemical industry. Computational chemistry was performed to help discriminate the role of some of the constituents of the mixed oxide ecocatalysts. High conversions, broad substrate scope, mild reaction conditions, and easy purification of the final products together with simplicity of the preparation of the ecocatalysts are the major advantages of the presented protocol. Additionally, Eco-MgZnOx-P could be recovered and reused for up to five times.

The adjuvant effects of rosin and coconut oil on nicosulfuron and mesotrione to control weeds

Natural adjuvants are novel options to reduce the doses of chemical herbicides. The aim of the current study was to examine the compositions and adjuvant effects of rosin and coconut oil on herbicides using a combination of indoor experiment and field trial. The GC-MS results showed that the main component of rosin was abietic acid (40.02%), and the main components of coconut oil were 2-pentanone, 4-hydroxy-4-methyl- (21.45%) and dodecanoic acid (14.59%). In greenhouse experiment, rosin showed a significant adjuvant effect on nicosulfuron against Digitaria sanguinalis and Amaranthus retroflexus, with the GR₅₀ ratios of 1.47 and 1.69, respectively. The GR₅₀ values of nicosulfuron in the present of coconut oil were 3.99 and 10.13 g a.i./hm² against D. sanguinalis and A. retroflexus, lower than that of individual application. The adjuvant effect of rosin and coconut oil on mesotrione was also found. In field trial, the fresh weight control efficiency of nicosulfuron (45 g a.i./hm²) and mesotrione (112.5 g a.i./hm²) was significantly improved after the addition of rosin and coconut oil, similar with that of recommended dose. Rosin and coconut oil could reduce the contact angle of nicosulfuron, with the results of 56.68° and 53.90°, respectively, lower than that of individual application. Furthermore, rosin and coconut oil could decrease the surface tension, wetting and penetration time; and increase the spreading diameter and maximum retention. Both rosin and coconut oil have adjuvant effects on herbicides in the lab & field with multiple mechanisms. Thus, they have the potential to be developed into natural adjuvants for herbicide formulation to control weeds.

Design, Synthesis, and Biological Activity of Novel Ferulic Amide Ac5c Derivatives

A total of 34 novel ferulic amide Ac5c derivatives were designed and synthesized and their antipest activities were investigated. The results showed that some compounds exhibited excellent in vitro antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo) and X. oryzae pv. oryzicola (Xoc), such as compounds 4q and 5n demonstrated excellent in vitro activity against Xoo, with EC₅₀ values of 4.0, and 1.9 μg/mL, respectively. Compounds 4c, 4h, 4m, 4p, 4q, and 5a had significant in vitro activities against Xoc, with EC₅₀ values of 12.5, 13.9, 9.8 15.0, 9.2, and 19.8 μg/mL, respectively. Moreover, the antibacterial activity in vivo against rice bacterial leaf blight was also evaluated. Scanning electron microscopy (SEM) showed that compound 5n significantly reduced the cell membrane of Xoo, and resulted in cell surface wilting, deformation, breakage, and increased porous attributes. In addition, some of the target compounds also showed moderate biological activity against fungi and acted as potential insecticides.

Design, Synthesis, and Herbicidal Activity of Thioether Containing 1,2,4-Triazole Schiff Bases as Transketolase Inhibitors

Transketolase (TK) represents a potential target for novel herbicide development. To discover novel TK inhibitors with potency against resistant weeds, 36 thioether compounds containing 1,2,4-triazole Schiff bases were designed and synthesized for herbicidal activity evaluation. The results demonstrated that compounds 5av and 5aw provided excellent weed control with inhibition of over 90% against the tested weeds, even at concentrations as low as 100 mg/L in vitro. In addition, compounds 5av and 5aw exhibited higher postemergence herbicidal activity than all of the positive controls against the tested weeds at 50-90 g [active ingredient (ai)]/ha in a greenhouse, while being safe for crops of maize and wheat at 90 g (ai)/ha. Fluorescent binding experiments of At TK indicated that compounds 5av and 5aw had strong TK inhibitory activity and could tightly bind with the enzyme At TK. Also, molecular docking analyses revealed that the structures of compounds 5av and 5aw were suitable for TK inhibitory activity. Taken together, these results suggested that compounds 5av and 5aw were promising herbicide candidates for weed control in wheat and maize fields targeting TK.

Biosynthesis of the Fungal Organophosphonate Fosfonochlorin Involves an Iron(II) and 2-(Oxo)glutarate Dependent Oxacyclase

The fungal metabolite Fosfonochlorin features a chloroacetyl moiety that is unusual within known phosphonate natural product biochemistry. Putative biosynthetic genes encoding Fosfonochlorin in Fusarium and Talaromyces spp. were investigated through reactions of encoded enzymes with synthetic substrates and isotope labelling studies. We show that early biosynthetic steps for Fosfonochlorin involves the reduction of phosphonoacetaldehyde to form 2-hydroxyethylphosphonic acid, followed by oxidative intramolecular cyclization of the resulting alcohol to form ( S )-epoxyethylphosphonic acid. The latter reaction is catalyzed by FfnD, a rare example of a non-heme iron / 2-(oxo)glutarate dependent oxacyclase. In contrast, FfnD behaves as a more typical oxygenase with ethylphosphonic acid, producing ( S )-1-hydroxyethylphosphonic acid. FfnD thus represents a new example of a ferryl generating enzyme that can suppress the typical oxygen rebound reaction that follows abstraction of a substrate hydrogen by a ferryl oxygen, thereby directing the substrate radical towards a fate other than hydroxylation.

Asymmetric synthesis of organophosphorus compounds using H-P reagents derived from chiral alcohols

Chiral organophosphorus compounds, especially those containing C-stereogenic carbons in the proximity of the phosphorus atom, are known for their unique properties and have found wide applications that span from medicinal chemistry to enantioselective catalysis. However, the synthesis of such chiral molecules, especially with the precise control of stereochemistry at chiral carbon atoms, still remains a very challenging task. This review summarizes recent advances in the highly stereoselective formation of C- and, in some cases, also P-stereogenic organophosphorus compounds. The presented synthesis strategy is based on the use of H-P reagents bearing TADDOL, BINOL or a menthol moiety attached to the phosphorus atom and serving as a chiral auxiliary. Reactions of such chiral H-P species with different partners, e.g., alkenes, alkynes, imines, and carbonyl compounds, leading to structurally diverse chiral organophosphorus compounds with up to five chiral centers are comprehensively discussed. In each case, the stereochemical outcome of the reaction is influenced by the presence of the chiral alcohol used; therefore, the content of this review is compiled into sections with respect to the type of chiral alcohol attached to the phosphorus atom in the H-P species applied.

High bioremediation potential of strain Chenggangzhangella methanolivorans CHL1 for soil polluted with metsulfuron-methyl or tribenuron-methyl in a pot experiment

Soil contamination caused by long-term application of metsulfuron-methyl and tribenuron-methyl has become an issue of increasing concern. In our previous study, strain Chenggangzhangella methanolivorans CHL1, capable of efficiently degrading sulfonylurea herbicides, was isolated. Here, the bioremediation potential of strain CHL1 was assessed for soil polluted with metsulfuron-methyl or tribenuron-methyl in a pot experiment. The growth parameters of waxy maize were measured on day 21 of the pot experiment. Additionally, the residues of metsulfuron-methyl and tribenuron-methyl in soils were analyzed, and the soil microbial community was investigated using a phospholipid fatty acids (PLFAs) method on days 1, 7, 14, and 21. The results indicated that strain CHL1 greatly accelerated the degradation of metsulfuron-methyl and tribenuron-methyl in soils. The degradation rates in the treatments inoculated with strain CHL1were all more than 91% after 7 days, significantly higher than the 25-36% degradation measured in non-inoculated treatments. Furthermore, strain CHL1 reduced the negative effects of tribenuron-methyl and metsulfuron-methyl on waxy maize growth, especially the primary root length. Moreover, inoculation with strain CHL1 also reduced the effects of tribenuron-methyl and metsulfuron-methyl on soil microbial biomass, diversity, and community structure. The present study demonstrates that strain CHL1 has great potential application to remediate soil contaminated with metsulfuron-methyl or tribenuron-methyl.

Glufosinate-ammonium: a review of the current state of knowledge

Glufosinate is a key herbicide to manage glyphosate-resistant weeds mainly because it is a broad-spectrum herbicide, and transgenic glufosinate-resistant crops are available. Although glufosinate use has increased exponentially over the past decade, the treated area with this herbicide is far less than that with glyphosate. This is because glufosinate often provides inconsistent performance in the field, which is attributed to several factors including environmental conditions, application technology, and weed species. Glufosinate is also highly hydrophilic and does not translocate well in plants, generally providing poor control of grasses and perennial species. In the soil, glufosinate is rapidly degraded by microorganisms, leaving no residual activity. While there have been concerns regarding glufosinate toxicology, its proper use can be considered safe. Glufosinate is a fast-acting herbicide that was first discovered as a natural product, and is the only herbicide presently targeting glutamine synthetase. The mode of action of glufosinate has been controversial, and the causes for the rapid phytotoxicity have often been attributed to ammonia accumulation. Recent studies indicate that the contact activity of glufosinate results from the accumulation of reactive oxygen species and subsequent lipid peroxidation. Glufosinate disrupts both photorespiration and the light reactions of photosynthesis, leading to photoreduction of molecular oxygen, which generates reactive oxygen species. The new understanding of the mode of action provided new ideas to improve the herbicidal activity of glufosinate. Finally, a very few weed species have evolved glufosinate resistance in the field, and the resistance mechanisms are generally not well understood requiring further investigation. © 2020 Society of Chemical Industry.

Enzyme cascade for biocatalytic deracemization of D,L-phosphinothricin

Deracemization of D,L-phosphinothricin (D,L-PPT) is one of the most promising routes for preparation of optically pure L-PPT. In this work, an efficient multi-enzyme redox cascade was developed for deracemization ofPPT, which includes oxidative reaction and reductive reaction. The oxidative reaction catalyzing oxidative deamination of D-PPT to 2-oxo-4-[(hydroxy)(-methyl)phosphinyl]butyric acid (PPO) was performed by a D-amino acid oxidase and a catalase for removing H₂O₂. The reductive reaction catalyzing amination of PPO to L-PPT is achieved by a glufosinate dehydrogenase and a glucose dehydrogenase for cofactor regeneration. To avoid the inhibitory effect of glucose on the oxidative reaction, a "two stages in one-pot" strategy was developed to combine these two reactions in deracemization process. By using this strategy, the L-PPT was obtained with a high yield (89 %) and > 99 % enantiomeric excess at substrate loading of 300 mM in absence of addition of extra NADP⁺. These encouraging results demonstrated that the developed enzyme cascade deracemization process exhibits great potential and economical competitiveness for manufacture of L-PPT from D,L-PPT.

Engineered biosynthesis of thaxtomin phytotoxins

Herbicide-resistant weeds are a growing problem worldwide. Thaxtomin phytotoxins are a group of nitrated diketopiperazines produced by the potato common scab-causing pathogen Streptomyces scabies and other actinobacterial plant pathogens. They represent a unique class of microbial natural products with distinctive structural features and promising herbicidal activity. The biosynthesis of thaxtomins proceeds through multiple steps of unusual enzymatic reactions. Advances in understanding of thaxtomins biosynthetic machinery have provided the basis for precursor-directed biosynthesis, pathway refactoring, and one-pot biocombinatorial synthesis to generate thaxtomin analogues. We herein summarize recent findings on the biosynthesis of thaxtomins and highlight recent advances in the rational generation of novel thaxtomins for the development of potent herbicidal agents.