Application of the Intermediate Derivatization Approach in Agrochemical Discovery

Discovery, Isolation, and Characterization of 23-Spirocholestane Derivatives as Novel Plant Root Growth Inhibitors from Ypsilandra thibetica

In the present study, we first discovered that the 70% ethanol extract of Ypsilandra thibetica significantly inhibited Arabidopsis root growth. Through a bioactivity-guided strategy, 18 rare 23-spirocholestane derivatives (1-18), including 12 new ones (1-12), featuring a dioxane ring between C-24/C-23 of the aglycone moiety and C-1'/C-2' of the d-fucose ligand, were obtained from the strongest active elution fraction. Their structures were elucidated via a comprehensive method of MS and NMR spectroscopy, single-crystal X-ray diffraction, and chemical methods. Evaluation of their inhibitory effects of all isolates on Arabidopsis root growth revealed that 5/6, 3/4, 1, and 2 exhibited pronounced activity, with EC50 values of 6.89, 9.13, 18.01, and 26.83 μM, respectively. Then, a preliminary structure-activity relationship (SAR) analysis of these compounds was conducted. Furthermore, transcriptome data indicated that Arabidopsis responded to the stress caused by these bioactive compounds through the modulation of ethylene and auxin signaling pathways and the activation of various detoxification-related genes. Finally, the herbicidal evaluation showed that 3/4 and 5/6 significantly inhibited the root growth of Echinochloa crusgalli, while 3/4 remarkably suppressed the root growth of Lolium multiflorum. These findings highlight that 23-spirocholestane derivatives represent promising candidates for the development of new bioherbicides.

Assessment of the Microbiological Potential and Spectroscopic Properties of New Imino-1,3,4-Thiadiazoles Showing the ESIPT Effect Strongly Enhanced by Aggregation

There is currently a growing interest in imino derivatives of compounds such as thiadiazoles and other groups of compounds whose extended π-electron systems enhance their photophysical properties. These compounds also show low toxicity and strong antifungal activity, making them effective against fungal pathogens in crops. For the above reasons, in the first part of the paper, the structure of the selected analogs was considered, and detailed spectroscopic analyses were conducted focusing on the excited state intramolecular proton transfer (ESIPT) process taking place in the same. Measurements were taken in terms of absorption spectroscopy and electron fluorescence, synchronous spectra, and fluorescence lifetimes, as well as calculations of fluorescence quantum efficiency in selected solvents and concentrations. In the spectral observations, the ESIPT process was manifested in several solvents as very distinct dual fluorescence. Moreover, in selected molecules, this phenomenon was strongly related to molecular aggregation, which was associated with not very efficient but nonetheless visible fluorescence of the AIE (Aggregation-Induced Emission) type. In the second part of the paper, a detailed preliminary study is presented exploring the microbiological properties of selected imino-1,3,4-thiadiazole derivatives in the context of their potential applicability as inhibitors affecting the development and growth of some of the most important fungal pathogens attacking cereal crops and posing an increasing threat to modern agriculture. Overall, the research presented in this article provides a detailed, experimental analysis of the spectroscopic properties of selected imino-thiadiazoles and points to their potential use as novel and effective solutions capable of limiting the growth and development of fungal pathogens in cereals.

Cobalt-based Photocatalysis: From Fundamental Principles to Applications in the Generation of C-X (X=C, O, N, H, Si) Bond

Over the past few decades, the merger of photocatalysis and transition metal-based catalysis or self-photoexcitation of transition metals has emerged as a useful tool in organic transformations. In this context, cobalt-based systems have attracted significant attention as sustainable alternatives to the widely explored platinum group heavy metals (iridium, rhodium, ruthenium) for photocatalytic chemical transformations. This review encompasses the basic types of cobalt-based homogeneous photocatalytic systems, their working principles, and the recent developments (2018-2024) in C-X (X=C, N, O, H, Si) bond formations. Noteworthy to mention that cobalt-based heterogeneous photocatalysis is beyond the scope of the present review. An elaborate presentation on the mechanistic intricacies of cobalt-based photocatalysis, without any external photocatalyst, and cobalt-based dual organophotoredox catalysis have been provided in this comprehensive review, excluding the dual-metal photoredox catalysis. To the best of our knowledge, this is the only contemporary review encompassing the aforementioned two major types of cobalt-based photocatalysis, in general synthetic chemistry, covering all types of C-X bond formations spanning a range of the last six years.

Carboxylations of (Hetero)Aromatic C-H Bonds Using an Alkyl Silyl Carbonate Reagent

In this paper, we report that the use of an alkyl silyl carbonate reagent combined with CsF and 18-crown-6 facilitates efficient direct carboxylations of (hetero)aromatic C-H bonds. This system also enables benzylic carboxylation of a toluene derivative and double carboxylation of methyl heteroarene. The carbonate reagent is characterized by its ease of handling and storage. Moreover, we demonstrate the application of this system in 13C-labeling experiments.

Carbonylation Reactions at Carbon-Centered Radicals with an Adjacent Heteroatom

Heteroatoms are essential to living organisms and present in almost all molecules with medicinal usage. The catalytic functionalization at the carbon-centered radical with an adjacent heteroatom provides an effective way to value added moiety while retaining the unique physicochemical and pharmacological properties of heteroatoms, which can promote the development of pharmaceutical and fine chemical production. Carbonylative transformation was discovered nearly a century ago which is an efficient method for the synthesis of carbonyl-containing molecules with potent applications in both industry and academia. Despite numerous advances in new reaction development, carbonylative transformation involving adjacent heteroatom carbon radical remain a subject that deserves to be discussed. In this minireview, we systematically summarized and discussed the recent advances in carbonylative transformations involving carbon-centered radicals with an adjacent heteroatom, including oxygen (O), nitrogen (N), phosphorus (P), silicon (Si), sulfur (S), boron (B), fluorine (F), and chlorine (Cl). The related reaction mechanism was also discussed.

Design, Synthesis, and Assessment of Fungicidal Activity of Active Substructure 1,2,4-Triazole Containing Coumarin

Fragment splicing and molecular docking are important techniques in the design of new agrochemicals. Based on our former discovery of 4-(3,4-dichloroisothiazole)-7-hydroxycumarins 1a and 1b as fungicidal leads, following fragment splicing and molecular docking, a series of bioactive substructure 1,2,4-triazole containing coumarins were designed and synthesized. In vitro fungicidal bioassay indicated that compound 7e was more active than 1b against Botrytis cinereal, Cercospora arachidicola, and Sclerotinia sclerotiorum, with a corresponding EC50 value of 4.02 vs 5.90, 6.03 vs 8.31, and 3.81 vs 5.37 μg/mL, respectively. Compound 7e also showed an EC50 value of 4.15 μg/mL against Fusarium graminearum. Moreover, compound 7e demonstrated a stronger inhibition than flutriafol against F. graminearum 14-α demethylase, with an IC50 value of 0.59 and 0.97 μM, respectively. Calculation results based on density functional theory calculation (DFT), molecular dynamics (MD), and molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) studies gave a rational explanation between the activity of compound 7e and its structure. This study demonstrates that fragment splicing of 1,2,4-triazole and coumarin is a good technique for discovering a novel fungicide lead.

Synthesis of Unsymmetrical Urea Derivatives via PhI(OAc)2 and Application in Late-Stage Drug Functionalization

Unsymmetrical urea derivatives are essential structural motifs in a wide array of biologically significant compounds. Despite the well-established methods for synthesizing symmetrical ureas, efficient strategies for the synthesis of unsymmetrical urea derivatives remain limited. In this study, we present a novel approach for the synthesis of unsymmetrical urea derivatives through the coupling of amides and amines. Utilizing hypervalent iodine reagent PhI(OAc)2 as a coupling mediator, this method circumvents the need for metal catalysts, high temperatures, and inert atmosphere. The reaction proceeds under mild conditions and demonstrates broad substrate scope, including various primary and secondary amines and primary benzamides. This protocol not only offers a practical and versatile route for synthesizing unsymmetrical ureas but also shows significant potential for the late-stage functionalization of complex molecules in drug development.

Copper(II)-Mediated Dual Reactivity of 2-(5-Phenylisoxazol-3-yl)aniline: Directed Amination and Oxidative C(═O)─C Cleavage of Amides Enabling Direct Access to Urea Derivatives

The dual reactivity of amides fused to 2-(5-phenylisoxazol-3-yl)aniline as a directing group for the formation of urea derivatives via chemospecific cleavage of the C(═O)─C bond and C(sp2)-H amination is reported here. Employing inexpensive copper as the catalyst and O2 in air as the oxidant, this protocol exhibited broad functional group tolerance for both the transformations. Detailed mechanistic studies and DFT calculations were performed to gain insights into a plausible mechanism for the formation of urea derivatives.

Fungicidal Activity of Novel 6-Isothiazol-5-ylpyrimidin-4-amine-Containing Compounds Targeting Complex I Reduced Nicotinamide Adenine Dinucleotide Oxidoreductase

To discover novel inhibitors of the complex I reduced nicotinamide adenine dinucleotide (NADH) oxidoreductase as fungicides, a series of 6-isothiazol-5-ylpyrimidin-4-amine-containing compounds were designed using a computer-aided pesticide design method and splicing of substructures from diflumetorim and isotianil. In vitro fungicidal bioassays indicated that compounds T17-T24 showed high inhibitory activity against Rhizoctonia solani with an effective concentration (EC50) value falling between 2.20 and 23.85 μg/mL, which were more active than or equivalent to the lead diflumetorim with its EC50 of 19.80 μg/mL. In vivo antifungal bioassays demonstrated that, at a concentration of 200 μg/mL, T7 and T21 showed higher inhibition against Pseudoperonospora cubensis than all other compounds, while T23 exhibited the highest inhibition against Sphaerotheca fuliginea. T23 showed an approximately twofold lower inhibition potency against R. solani complex I NADH oxidoreductase than diflumetorim. Molecular docking and transcriptomic analyses indicated that T23 and diflumetorim both might share the same mode of action, targeting NADH oxidoreductase. T23 as a good fungicidal candidate against R. solani is worthy of further investigation.

Metal-Free Synthesis of Pharmaceutically Relevant Sulfonylureas via Direct Reaction of Sulfonamides with Amides

A metal-free process has been developed for the sustainable synthesis of medicinally important sulfonylureas in one pot via the direct reaction of sulfonamides with amides in green solvent (DMC). The reaction proceeded efficiently at room temperature, and the products were obtained in good to excellent yields. The use of readily accessible, inexpensive, and environmentally benign starting materials and reagents, metal-free mild reaction conditions, wide substrate scope, tolerance to air and moisture, operational simplicity, and good atom economy are the salient features of this reaction protocol. Gram-scale synthesis of antidiabetic drugs tolbutamide and chlorpropamide in excellent yields further revealed the practical utility of this procedure. Additionally, the synthetic value of this straightforward method is showcased by the late-stage modification of drug molecules, including drug-drug conjugation with good yields. Preliminary mechanistic studies indicated the in situ generation of an isocyanate intermediate, which further reacts with sulfonamide to form sulfonylurea. As compared to other related methods reported for sulfonylurea synthesis, the current method obviates the requirement of traditional multistep protocols involving isolation of hazardous isocyanates and avoids the use of toxic phosgene.

Oxime chemistry in crop protection

An overview is given on the significance of the oxime moiety in crop protection chemistry. This review focuses on the two most important aspects of agrochemical oximes, which are the occurrence and role of oxime groups in compounds with herbicidal, fungicidal and insecticidal activity, as well as the application of oxime derivatives as intermediates in the synthesis of crop protection agents not bearing any oxime function. Especially noteworthy is the fact, that in the synthesis of agrochemicals, oximes can be cyclized to isooxazoline, isoxazole, oxadiazole, oxazine, pyrrole, isothiazole and imidazole rings. © 2024 Society of Chemical Industry.

Design, Synthesis, and Acaricidal Activity of 2,5-Diphenyl-1,3-oxazoline Compounds

By using a scaffold hopping/ring equivalent and intermediate derivatization strategies, a series of compounds of 2,5-diphenyl-1,3-oxazoline with substituent changes at the 5-phenyl position were prepared, and their acaricidal activity was studied. However, the synthesized 2,5-diphenyl-1,3-oxazolines showed lower activity against mite eggs and larvae compared to the 2,4-diphenyl-1,3-oxazolines with the same substituents. We speculate that there is a significant difference in the spatial extension direction of the substituents between the two skeletons of compounds, resulting in differences in their ability to bind to the potential target chitin synthase 1. This work is helpful in inferring the internal structure of chitin synthase binding pockets.

Diastereoselective Palladaelectro-Catalyzed Construction of Bromomethyl Morpholines as Key Step To Access Morpholino Homonucleosides

A synthetic protocol for the preparation of a new class of morpholino homonucleosides in enantiopure form starting from readily available 1,2-aminoalcohols or glycidol has been developed. Key intermediates of the synthetic sequence are 2-bromomethyl morpholines, diastereoselectively achieved from the corresponding alkenols by palladaelectro-catalyzed alkoxybromination of unactivated alkenes. The so obtained bromo derivatives are in turn susceptible to functionalization with nucleic bases for easy access to morpholino homonucleosides.

Synthesis and herbicidal activities of 2-((3-pyridinyl-2-oxo-2,3-dihydrobenzo[d]thiazol-6-yl)oxy)propionates

BACKGROUND

The discovery of lead compounds is fundamental to herbicide innovation, yet the limited availability of valuable lead compounds has impeded their progress in recent years. The study presents a novel molecular scaffold that exhibits remarkably potent herbicidal activity.

RESULTS

Through a scaffold-hopping strategy, a highly potent lead compound for herbicides, namely 3-(2-pyridinyl)-benzothiazol-2-one, was unexpectedly discovered during attempts to structurally modify haloxyfop, a commercial aryl-oxy-phenoxy-propionate herbicide. To investigate the structure-activity relationship (SAR) of the newly discovered herbicidal chemicals, a series of 2-(2-oxo-3-(pyridin-2-yl)-2,3-dihydrobenzo[d]thiazol-6-yloxy)propanoic acid derivatives, I-01 ~ I-27, were designed and synthesized. SAR analysis revealed that trifluoromethyl at the 5-position of pyridine is crucial for herbicidal activity, whereas additional fluorine or Cl atom at the 3-position of pyridine significantly enhances activity. Carboxylic ester derivatives exhibit superior herbicidal activity compared with amide derivatives. Moreover, the activity of carboxylic ester derivatives decreases with C chain extension, but the introduction of O atoms in the side chain benefits activity enhancement. Pot experiments conducted in a glasshouse demonstrated that I-01 and I-09 exhibited potent postemergence herbicidal activity against broadleaf weeds, and completely inhibited growth of Amaranthus retroflex, Abutilon theophrasti and Portulaca oleracea at a dosage of 75 g ha-1.

CONCLUSION

Despite the initial goal of scaffold-hopping not being achieved, we have successfully identified a novel molecular scaffold exhibiting exceptional herbicidal activity, thereby presenting innovative prospects for herbicide development. © 2024 Society of Chemical Industry.

Fungicidal Activity of New Pyrrolo[2,3-d]thiazoles and Their Potential Action on the Tryptophan Metabolic Pathway and Wax Biosynthesis

The main challenge in the development of agrochemicals is the lack of new leads and/or targets. It is critical to discover new molecular targets and their corresponding ligands. YZK-C22, which contains a 1,2,3-thiadiazol-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole skeleton, is a fungicide lead compound with broad-spectrum fungicidal activity. Previous studies suggested that the [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole scaffold exhibited good antifungal activity. Inspired by this, a series of pyrrolo[2,3-d]thiazole derivatives were designed and synthesized through a bioisosteric strategy. Compounds C1, C9, and C20 were found to be more active against Rhizoctonia solani than the positive control YZK-C22. More than half of the target compounds provided favorable activity against Botrytis cinerea, where the EC50 values of compounds C4, C6, C8, C10, and C20 varied from 1.17 to 1.77 μg/mL. Surface plasmon resonance and molecular docking suggested that in vitro potent compounds C9 and C20 have a new mode of action instead of acting as pyruvate kinase inhibitors. Transcriptome analysis revealed that compound C20 can impact the tryptophan metabolic pathway, cutin, suberin, and wax biosynthesis of B. cinerea. Overall, pyrrolo[2,3-d]thiazole is discovered as a new fungicidal lead structure with a potential new mode of action for further exploration.

Discovery of Novel Pyrazole Acyl Thiourea Skeleton Analogue as Potential Herbicide Candidates

To discover novel transketolase (TKL, EC 2.2.1.1) inhibitors with potential herbicidal applications, a series of pyrazole acyl thiourea derivatives were designed based on a previously obtained pyrazolamide acyl lead compound, employing a scaffold hopping strategy. The compounds were synthesized, their structures were characterized, and they were evaluated for herbicidal activities. The results indicate that 7a exhibited exceptional herbicidal activity against Digitaria sanguinalis and Amaranthus retroflexus at a dosage of 90 g ai/ha, using the foliar spray method in a greenhouse. This performance is comparable to that of commercial products, such as nicosulfuron and mesotrione. Moreover, 7a showed moderate growth inhibitory activity against the young root and stem of A. retroflexus at 200 mg/L in the small cup method, similar to that of nicosulfuron and mesotrione. Subsequent mode-of-action verification experiments revealed that 7a and 7e inhibited Setaria viridis TKL (SvTKL) enzyme activity, with IC50 values of 0.740 and 0.474 mg/L, respectively. Furthermore, they exhibited inhibitory effects on the Brassica napus acetohydroxyacid synthase enzyme activity. Molecular docking predicted potential interactions between these (7a and 7e) and SvTKL. A greenhouse experiment demonstrated that 7a exhibited favorable crop safety at 150 g ai/ha. Therefore, 7a is a promising herbicidal candidate that is worthy of further development.

Synthesis and Herbicidal Activity of 2-(2-Oxo-3-pyridyl-benzothiazol-6-yloxy)hexanoic Acids

The discovery of a lead compound is fundamental to herbicide innovation, but the limited availability of valuable lead compounds has hindered their development in recent years. By utilizing the structural diversity-oriented inactive group strategy, 3-(2-pyridyl)-benzothiazol-2-one was identified as a promising lead scaffold for herbicides, starting from benzothiazole which is an inactive moiety commonly found in herbicides such as mefenacet, benazolin, benzthiazuron, and fenthiaprop-ethyl. To investigate the structure-activity relationship (SAR) of these chemicals, a series of 2-(2-oxo-3-pyridyl-benzothiazol-6-yloxy)hexanoic acid derivatives (VI01 ∼ VI28) were synthesized through classical nucleophilic SNAr reaction using halogenated pyridines and 6-methoxybenzothiazole-2-one. The chemical structures of all the title compounds were confirmed by NMR and MS analysis. Petri dish assays indicated that many compounds exhibited potent herbicidal activity against both broad-leaf weeds and grass weeds at 1.0 mg/L. The SAR analysis revealed that the presence of a trifluoromethyl group at the 5-position of pyridine is essential for herbicidal activity. Furthermore, carboxylic esters exhibit higher herbicidal activity compared to carboxylic amides and free acids, and the activity decreased with the extension of the carbon chain. The postemergence herbicidal activity of VI03 against 16 species of weeds was tested by pot experiments in a greenhouse. VI03 demonstrated comparable efficacy in controlling broadleaf weeds and superior efficacy in controlling grass weeds compared to carfentrazone ethyl. The present study has unveiled a novel molecular scaffold exhibiting remarkably potent herbicidal activity. These findings are anticipated to provide valuable insights for the advancement of new herbicides and offer an alternative approach for managing resistant weeds.

Design, Synthesis, and Biological Activities of Novel Coumarin Derivatives as Pesticide Candidates

Food security is an important issue in the 21st century; preventing and controlling crop diseases and pests are the key to solve this problem. The creation of new pesticides based on natural products is an important and effective method. Herein, coumarins were selected as parent structures, and a series of their derivatives were designed, synthesized, and evaluated for their antiviral activities, fungicidal activities, and insecticidal activities. We found that coumarin derivatives exhibited good to excellent antiviral activities against tobacco mosaic virus (TMV). The antiviral activities of I-1, I-2a, I-4b, II-2c, II-2g, II-3, and II-3b are better than that of ribavirin at 500 μg/mL. Molecular docking research showed that these compounds had a strong interaction with TMV CP. These compounds also showed broad-spectrum fungicidal activities against 14 plant pathogenic fungi. The EC50 values of I-1, I-2a, I-3c, and II-2d are in the range of 1.56-8.65 μg/mL against Rhizoctonia cerealis, Physalospora piricola, Sclerotinia sclerotiorum, and Pyricularia grisea. Most of the compounds also displayed good insecticidal activities against Mythimna separata. Pesticide-likeness analysis showed that these compounds are following pesticide-likeness and have the potential to be developed as pesticide candidates. The present work lays a foundation for the discovery of novel pesticide lead compounds based on coumarin derivatives.

Discovery of Arylfluorosulfates as Novel Fungicidal Agents against Plant Pathogens

A series of arylfluorosulfates were synthesized as fungicide candidates through a highly efficient sulfur fluoride exchange (SuFEx) reaction. A total of 32 arylfluorosulfate derivatives with simple structures have been synthesized, and most of them exhibited fungal activities in vitro against five agricultural pathogens (Rhizoctonia solani, Botrytis cinerea, Fusarium oxysporum, Pyricularia oryzae, and Phytophthora infestans). Among the target compounds, compound 31 exhibited great antifungal activity against Rhizoctonia solani (EC50 = 1.51 μg/mL), which was comparable to commercial fungicides carbendazim and thiabendazole (EC50 = 0.53 and 0.70 μg/mL, respectively); compounds 17 and 30 exhibited antifungal activities against Pyricularia oryzae (EC50 = 1.64 and 1.73 μg/mL, respectively) comparable to carbendazim (EC50 = 1.02 μg/mL). The in vitro antifungal effect of compound 31 was also evaluated on rice plants against Rhizoctonia solani. Significant preventive and curative efficacies were observed (89.2% and 91.8%, respectively, at 200 μg/mL), exceeding that of thiabendazole. Primary study on the mechanism of action indicated that compound 31 could suppress the sclerotia formation of Rhizoctonia solani even at a very low concentration (1.00 μg/mL), destroy the cell membrane and mitochondria, trigger the release of cellular contents, produce excessive reactive oxygen species (ROS), and suppress the activity of several related enzymes. This work could bring new insights into the development of arylfluorosulfates as novel fungicides.

Sativene Sesquiterpenoids from the Plant Endophytic Fungus Bipolaris victoriae S27 and Their Potential as Plant-Growth Regulators

Thirteen new sativene sesquiterpenoids (1 and 3-14), one new natural product (2), and 16 known compounds (15-30) were isolated from the endophytic fungus Bipolaris victoriae S27. Their structures were elucidated by extensive spectroscopic analysis, NMR and ECD calculations, and X-ray crystal diffractions. Compound 1 represented the first example of sativene sesquiterpenoids with a 6/5/3/5-caged tetracyclic ring system. All obtained compounds were evaluated for their plant-growth regulatory activity. The results showed that 1, 3, 4, 6, 8, 11, 12, 17, 19, 26, and 27 could suppress the growth of Arabidopsis thaliana, while 2, 5, 13, 15, 18, and 25 showed promoting effects. Among them, compound 3 showed the most potent plant-growth inhibitory activity, which is obviously superior to that of the marked herbicide glyphosate.

Antifungal activity of Ligusticum chuanxiong essential oil and its active composition butylidenephthalide against Sclerotium rolfsii

BACKGROUND

Peanut stem rot caused by Sclerotium rolfsii is an epidemic disastrous soil-borne disease. Recently, natural products tend to be safe alternative antifungal agents to combat pathogens.

RESULTS

This work determined the preliminary antifungal activity of 29 essential oils against S. rolfsii and found that Ligusticum chuanxiong essential oil (LCEO) showed the best antifungal activity, with an EC50 value of 81.79 mg L-1 . Sixteen components (98.78%) were identified in LCEO by gas chromatography-mass spectrometry analysis, the majority by volume comprising five phthalides (93.14%). Among these five phthalides, butylidenephthalide was the most effective compound against S. rolfsii. Butylidenephthalide not only exhibited favorable in vitro antifungal activity against the mycelial growth, sclerotia production and germination of S. rolfsi, but also presented efficient in vivo efficacy in the control of peanut stem rot. Seven days after application in the glasshouse, the protective and curative efficacy of butylidenephthalide at 300 mg L-1 (52.02%, 44.88%) and LCEO at 1000 mg L-1 (49.60%, 44.29%) against S. rolfsii were similar to that of the reference fungicide polyoxin at 300 mg L-1 (54.61%, 48.28%). Butylidenephthalide also significantly decreased the oxalic acid and polygalacturonase content of S. rolfsii, suggesting a decreased infection ability on plants. Results of biochemical actions indicated that butylidenephthalide did not have any effect on the cell membrane integrity and permeability but significantly decreased nutrient contents, disrupted the mitochondrial membrane, inhibited energy metabolism and induced reactive oxygen species (ROS) accumulation of S. rolfsii.

CONCLUSION

Our results could provide an important reference for understanding the application potential and mechanisms of butylidenephthalide in the control of S. rolfsii. © 2023 Society of Chemical Industry.

Isosteric Ring Exchange as a Useful Scaffold Hopping Tool in Agrochemistry

Replacing one ring in a molecule by a different carba- or heterocycle is an important scaffold hopping manipulation, because biologically active compounds and their analogues, which underwent such a transformation, are often similar in size, shape, and physicochemical properties and, therefore, likely in their potency as well. This review will demonstrate, how isosteric ring exchange led to the discovery of highly active agrochemicals and which ring interchanges have proven to be most successful.

Ring Closure and Ring Opening as Useful Scaffold Hopping Tools in Agrochemistry

Ring closing acyclic parts of a molecular scaffold or the opposite manipulation, opening rings to produce pseudo-ring structures, is an important scaffold hopping manipulation. Analogues derived from biologically active compounds through the utilization of such strategies are often similar in shape and physicochemical properties and, therefore, likely to exhibit similar potency. This review will demonstrate how several different ring closure techniques, such as replacing carboxylic functions by cyclic peptide mimics, incorporating double bonds into aromatic rings, tying back ring substituents to a bicyclic structure, cyclizing adjacent ring substituents to an annulated ring, bridging annulated ring systems to tricyclic scaffolds, and exchanging gem-dimethyl groups by cycloalkyl rings, but also ring opening led to the discovery of highly active agrochemicals.

CoMFA Directed Molecular Design for Significantly Improving Fungicidal Activity of Novel [1,2,4]-Triazolo-[3,4-b][1,3,4]-thiadizoles

Target based molecular design via the aid of computation is one of the most efficient methods in the discovery of novel pesticides. Here, a combination of the comparative molecular field analysis (CoMFA) and molecular docking was applied for discovery of potent fungicidal [1,2,4]-triazolo-[3,4-b][1,3,4]-thiadiazoles. Bioassay results indicated that the synthesized target compounds 3a, 3b, and 3c exhibited good activity against Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Fusarium graminearum, Physalospora piricola, Rhizoctonia solani, and Sclerotinia sclerotiorum with an EC50 value falling between 0.64 and 16.10 μg/mL. Specially, 3c displayed excellent fungicidal activity against C. arachidicola and R. solani, which was 5 times more potent than the lead YZK-C22. The enzymatic inhibition assay and fluorescence quenching analysis with R. solani pyruvate kinase (RsPK) showed a weaker binding affinity between RsPK and 3a, 3b, or 3c. Transcriptomic analyses showed that 3c exerted its fungicidal activity by disrupting steroid biosynthesis and ribosome biogenesis in eukaryotes. These findings support that 3c is a promising fungicide candidate, and a fine modification from a lead may lead to a totally different mode of action.

Structural optimization based on 4,5-dihydropyrazolo[1,5-a]quinazoline scaffold for improved insecticidal activities

The long-term and irrational application of insecticides has increased the rate of development of pest resistance and caused numerous environmental issues. To address these problems, our previous work reported that 4,5-dihydropyrazolo[1,5-a]quinazoline (DPQ) is a class of gelled heterocyclic compounds that act on insect γ-aminobutyric acid receptors (GABAR). DPQ scaffold has no cross-resistance to existing insecticides, so the development of this scaffold is an interesting task for integrated pest management. In the present study, a novel series of 4,5-dihydropyrazolo[1,5-a]quinazolines (DPQs) were designed and synthesized based on pyraquinil, a highly insecticidal compound discovered in our previous work. Insecticidal activities of the target compounds against diamondback moth (Plutella xylostella), beet armyworm (Spodoptera exigua), fall armyworm (Spodoptera frugiperda), and red imported fire ant (Solenopsis invicta Buren) were evaluated. Compounds 6 and 12 showed the best insecticidal activity against Plutella xylostella (P. xylostella) (LC50 = 1.49 and 0.97 mg/L), better than pyraquinil (LC50 = 1.76 mg/L), indoxacarb and fipronil (LC50 = 1.80 mg/L). Meanwhile, compound 12 showed slow toxicity to Solenopsis invicta Buren (S. invicta), with a 5 d mortality rate of 98.89% at 0.5 mg/L that is similar to fipronil. Moreover, Electrophysiological studies against the PxRDL1 GABAR heterologously expressed in Xenopus oocytes indicated that compound 12 could act as a potent GABA receptor antagonist (2 μΜ, inhibition rate, 68.25%). Molecular docking results showed that Ser285 (chain A) and Thr289 (chain D) of P. xylostella GABAR participated in hydrogen bonding interactions with compound 12, and density functional theory (DFT) calculations suggested the importance of pyrazolo[1,5-a]quinazoline core in potency. This systematic study provides valuable clues for the development of DPQ scaffold in the field of agrochemicals, and compound 12 can be further developed as an insecticide and bait candidate.

Design, Synthesis and Fungicidal Activity of Ester Derivatives of 4-(3,4-Dichloroisothiazole) 7-Hydroxy Coumarin

The development of new fungicides is vital for safeguarding crops and ensuring sustainable agriculture. Building on our previous finding that 4-(3,4-dichloroisothiazole)-7-hydroxy coumarins can be used as fungicidal leads, 44 novel coumarin ester derivatives were designed and synthesized to evaluate whether esterification could enhance their fungicidal activity. In vitro fungicidal bioassays indicated that compound 2ai displayed good activity against Alternaria solani, Botrytis cinereal, Cercospora arachidicola, Physalospora piricola and Sclerotinia sclerotiorum, with an EC₅₀ value ranging from 2.90 to 5.56 μg/mL, comparable to the lead compound 1a, with its EC₅₀ value ranging from 1.92 to 9.37 μg/mL. In vivo bioassays demonstrated that compounds 1a, 2ar and 2bg showed comparable, excellent efficacy against Pseudoperonospora cubensis at a dose of 25 µg/mL. Our research shows that the esterification of 4-(3,4-dichloroisothiazole) 7-hydroxycoumarins results in a fungicidal activity equivalent to that of its lead compounds. Furthermore, our density functional theory (DFT) calculations and 3D-QSAR modeling provide a rational explanation of the structure-activity relationship and offer valuable insights to guide further molecular design.

The Effect of Terbinafine and Its Ionic Salts on Certain Fungal Plant Pathogens

Terbinafine, an inhibitor of squalene epoxidase in ergosterol biosynthesis, is chiefly utilized as an antifungal medication with potential uses in pesticide applications. This study explores the fungicidal efficacy of terbinafine against prevalent plant pathogens and confirms its effectiveness. To augment its water solubility, five ionic salts of terbinafine were synthesized by pairing them with organic acids. Among these salts, TIS 5 delivered the most impressive results, amplifying the water solubility of terbinafine by three orders of magnitude and lessening its surface tension to facilitate better dispersion during spraying. The in vivo experiments on cherry tomatoes showed that TIS 5 had a superior therapeutic activity compared to its parent compound and two commonly used broad-spectrum fungicides, pyraclostrobin and carbendazim. The results highlight the potential of terbinafine and its ionic salts, particularly TIS 5, for use as fungicides in agriculture due to their synergistic effects with furan-2-carboxylate.

Ni-Catalyzed Mild Synthesis of Sulfonylurea via Tandem Coupling of Sulfonyl Azide, Isocyanide, and Water

An efficient, mild, and novel route is developed to synthesize sulfonylurea via the nickel-catalyzed tandem coupling of sulfonyl azide, isocyanide, and water in aqueous media. The sulfonyl azide is expected to act as a nitrene precursor, which upon reaction with isocyanide generates carbodiimide. Herein, water acts as a nucleophile and reacts with carbodiimide to deliver the product. The protocol uses an inexpensive nickel catalyst, environmentally friendly water (as the nucleophile), and room temperature and provides products in moderate to good yields.

Facile synthesis, crystal structure, quantum calculation, and biological evaluations of novel selenenyl sulfide compounds as potential agrochemicals

BACKGROUND

In order to design compounds with fresh molecular skeleton to break through the limitation of available agrochemicals, a series of 36 novel selenenyl sulfide compounds were chemically synthesized, and their biological activities were fully evaluated against tobacco mosaic virus (TMV), 14 plant pathogenic fungi, three insect species and plant acetohydroxyacid synthase (AHAS).

RESULTS

All the target compounds were characterized by proton nuclear magnetic resonance (¹ H-NMR), carbon-13 (¹³ C)-NMR, selenium-77 (⁷⁷ Se)-NMR, and high-resolution mass spectrometry (HRMS). The crystal structure of 10j indicated that the Se-S bond was successfully constructed. Compounds 10d, 10h, 10s, 10u, 10aa, 10ac, 10ae, 10ag, and 10ai exhibited 40%, 43%, 39%, 41%, 47%, 46%, 47%, 42%, and 39% anti-TMV activities at 500 mg L^-1 , better than that of ribavirin. The median effective concentration (EC₅₀ ) against Sclerotinia sclerotiorum of 10ac was 6.69 mg L^-1 and EC₅₀ values against Physalospora piricola and Pyricularia grisea of 10z were 12.25 mg L^-1 and 15.27 mg L^-1 , respectively, superior to the corresponding values of chlorothalonil. Compounds 10c and 10v demonstrated 100% larvicidal activity against Culex pipiens pallens at 5 mg L^-1 , while 10a displayed 100% insecticidal activity against Mythimna separata at 200 mg L^-1 . Compounds 10c, 10j, and 10o showed > 60% inhibitions against plant AHAS at 10 μmol L^-1 . From the quantum calculation, highest occupied molecular orbital (HOMO) was considered as a factor that affects the anti-TMV activity.

CONCLUSION

The preliminary results suggested that more efforts should be devoted to exploring the selenenyl sulfides for the discovery of new leads of antiviral agent, fungicide, insecticide or AHAS inhibitors as potential agrochemicals for crop protection. © 2023 Society of Chemical Industry.

Ethylidene-Tethered Chromene-Pyrone Hybrids as Potential Plant-Growth Regulators from an Endolichenic Phaeosphaeria Species

Phaeosphaeria sp., a lichen-associated fungus, produced six skeletally new dimeric spiciferones (1-6) and four known metabolites (7-10). The new structures were elucidated by spectroscopic analysis, and their absolute configurations were determined by electronic circular dichroism calculations. Compounds 1 and 3-6 represent the first examples of ethylidene-bridged dimers from the building blocks 4H-chromene-4,7(8H)-dione and α-pyrone, and 2 is a unique homodimer of spiciferone. Compounds 1, 2, and 5-9 significantly inhibited the growth of weed-like dicot Arabidopsis thaliana at 100.0 μM. Notably, 8 showed the strongest inhibitory activity against the fresh weight and root elongation of A. thaliana with the IC₅₀ values of 32.04 and 26.78 μM, respectively, whereas 1, 8, and 9 stimulated the growth of A. thaliana at lower concentrations. Meanwhile, compounds 2 and 6 exhibited weak inhibitory effects on the root elongation of monocot rice, while 1 and 8 exhibited growth-promoting effects on the shoot and root elongation of rice in a roughly dose-dependent manner.

3D-QSAR-Based Molecular Design to Discover Ultrahigh Active N-Phenylpyrazoles as Insecticide Candidates

Three-dimensional quantitative structure-activity relationship (3D-QSAR) is one of the most important and effective tools to direct molecular design in new pesticide development. Chlorantraniliprole is an anthranilic diamide ryanodine receptor (RyR) agonist with ultrahigh activity, high selectivity, and mammalian safety. To continue our studies on new insecticide development, here, we designed new insecticidal N-phenylpyrazoles by using 3D-QSAR of chlorantraniliprole analogues as a guide. Most of the target compounds synthesized exhibited medium to excellent activity against Mythimna separata, Plutella xylostella, and Spodoptera frugiperda. Compounds III b and III y showed similar activity against M. separata as chlorantraniliprole (LC₅₀ values: 0.21, 0.25, and 0.16 μg mL^-1 respectively). Compounds III b exhibited a 3-fold higher potency against P. xylostella than chlorantraniliprole. For S. frugiperda, the potency of III a and III b was 2.9 and 2.0 times higher than that of the positive control, respectively. The mode of action of the title compounds was validated by calcium imaging experiments and molecular docking using their target RyRs. III b can dock well with mutated P. xylostella RyRs, implying a potentially lower cross-resistance risk as compared with commercial RyR agonists. Density functional theory calculations suggested the feasibility of higher potency with the structural modifications. Compound III b was found to be an ultrahigh active insecticidal candidate with a broad spectrum for integrated pest management.

Design, Synthesis, and Metabolism Studies of N-1,4-Diketophenyltriazinones as Protoporphyrinogen IX Oxidase Inhibitors

Protoporphyrinogen IX oxidase (PPO, EC 1.3.3.4) is an established site for green herbicide discovery. In this work, based on structural analysis, we develop an active fragment exchange and link (AFEL) approach to designing a new class of N-1,4-diketophenyltriazinones I-III as potent Nicotiana tabacum PPO (PPO) inhibitors. After systematic structure-activity relationship optimizations, a series of new compounds with Ki values in the single-digit nanomolar range toward NtPPO and promising herbicidal activity were discovered. Among them, Ii (Ki = 0.11 nM) displays 284- and 90-fold improvement in NtPPO inhibitory activity over trifludimoxazin (Ki = 31 nM) and saflufenacil (Ki = 10 nM), respectively. In addition, Ip (Ki = 2.14 nM) not only exhibited good herbicidal activity at 9.375-37.5 g ai/ha but also showed high crop safety to rice at 75 g ai/ha by the postemergence application, indicating that Ip could be developed as a potential herbicide for weed control in rice fields. Additionally, our molecular dynamic simulation clarified the molecular basis for the interactions of these molecules with NtPPO. The metabolism studies in planta showed that IIIc could be converted to Ic, which displayed higher herbicidal activity than IIIc. The density functional theory analysis showed that due to the effect of two sulfur atoms at the triazinone moiety, IIIc is more reactive than Ic, making it more easily degraded in planta. Our work indicates that the AFEL strategy could be used to design new molecules with improved bioactivity.

Lactate anion catalyzes aminolysis of polyesters with anilines

Chemical transformation of spent polyesters into value-added chemicals is substantial for sustainable development but still challenging. Here, we report a simple, metal-free, and efficient aminolysis strategy to upcycle polylactic acid by anilines over lactate-based ionic liquids (e.g., tetrabutylammonium lactate), accessing a series of N-aryl lactamides under mild conditions. This strategy is also effective for degradation of poly(bisphenol A carbonate), affording bisphenol A and corresponding diphenylurea derivatives. It is found that, with the assistance of water, lactate anion as hydrogen-bond donor can efficiently activate carbonyl C atom of polyesters via hydrogen bonding with carbonyl O atom; meanwhile, as hydrogen-bond acceptor, it can enhance nucleophilicity of the N atom of anilines via hydrogen bonding with amino H atom. The nucleophilic attack of N atom of anilines on carbonyl C atom of polyesters results in cleavage of C─O bond of polymers and formation of the target products.

Modern Approaches for the Development of New Herbicides Based on Natural Compounds

Weeds are a permanent component of anthropogenic ecosystems. They require strict control to avoid the accumulation of their long-lasting seeds in the soil. With high crop infestation, many elements of crop production technologies (fertilization, productive varieties, growth stimulators, etc.) turn out to be practically meaningless due to high yield losses. Intensive use of chemical herbicides (CHs) has led to undesirable consequences: contamination of soil and wastewater, accumulation of their residues in the crop, and the emergence of CH-resistant populations of weeds. In this regard, the development of environmentally friendly CHs with new mechanisms of action is relevant. The natural phytotoxins of plant or microbial origin may be explored directly in herbicidal formulations (biorational CHs) or indirectly as scaffolds for nature-derived CHs. This review considers (1) the main current trends in the development of CHs that may be important for the enhancement of biorational herbicides; (2) the advances in the development and practical application of natural compounds for weed control; (3) the use of phytotoxins as prototypes of synthetic herbicides. Some modern approaches, such as computational methods of virtual screening and design of herbicidal molecules, development of modern formulations, and determination of molecular targets, are stressed as crucial to make the exploration of natural compounds more effective.

The power of cross-indication testing: agrochemicals originally stemming from a different indication

Cross-indication testing is the assaying of final compounds, but also their intermediates or side products, from one agrochemical indication against target species of other product lines. This approach has proven to be a highly successful source of lead compounds, which led to several important crop protection products. This review article describes, which herbicides came from fungicides and insecticides, how fungicides have been obtained from herbicide and insecticide leads and which insecticides have their roots in herbicide and fungicide chemistry. © 2022 Society of Chemical Industry.

Insertion of Small Flexible Linkers as a Useful Scaffold Hopping Tool in Agrochemistry

Inserting small flexible linkers of only one- to three-atom chain lengths into a molecular backbone is an important scaffold hopping manipulation. Analogues derived from biologically active compounds through the utilization of such a strategy are often similar in shape and physicochemical properties and, therefore, likely to exhibit similar potency. This review will demonstrate how the elongation with oxygen, amino, methylene, ethylene, vinyl, ethynyl, and CH₂O bridges led to the discovery of highly active agrochemicals.

Bioisosterism and Scaffold Hopping in Modern Nematicide Research

The application of agrochemicals is critical to global food safety. Nowadays, environmentally friendly green agrochemicals are the trend in field crop protection. The research and development of nematicides absorbed more attention as a typical representation of agrochemicals. This review describes the origin of recently commercialized nematicides, the application of bioisosterism and scaffold hopping in the discovery and optimization of agrochemicals, especially nematicides, and novel bioisosteric design strategies for the identification of fluensulfone analogues. Pesticide repurposing, high-throughput screening, computer-aided drug design, and incorporation of known pharmacophoric fragments have been the most successful approach for the discovery of new nematicides. As outlined, the strategies of bioisosteric replacements and scaffold hopping have been very successful approaches in the search for new nematicides for sustainable crop protection. In the exploration of novel fluensulfone analogues with nematicidal activity, bioisosteric replacement of sulfone by amide, chain extension by insertion of a methylene group, and reversal of the amide group have proven to be successful approaches and yielded new and highly active fluensulfone analogues. These attempts might result in compounds with an optimal balance of steric, hydrophobic, electronic, and hydrogen-bonding properties and contribute to deal with the complex problem during the research and development of new nematicides. Further ideas are also put forward to provide new approaches for the molecular design of nematicides.

Reversal of Functional Groups as a Useful Scaffold Hopping Tool in Agrochemistry

Reverting the orientation of a functional group by exchanging molecular parts of it is an important scaffold hopping manipulation, as biologically active compounds and their analogs, which underwent such a transformation, are often similar in shape and physicochemical properties and therefore likely in their potency as well. This review will demonstrate, how the inversion of carboxamides, sulfonamides, carbamates, oximes, hydrazones, O,S-acetals, and ethers led to the discovery of highly active agrochemicals.

Green Design, Synthesis, and Molecular Docking Study of Novel Quinoxaline Derivatives with Insecticidal Potential against Aphis craccivora

An efficient and environmentally friendly method was established for designing novel 3-amino-1,4-dihydroquinoxaline-2-carbonitrile (1) via the reaction of bromomalononitrile and benzene-1,2-diamine under microwave irradiation in an excellent yield (93%). This targeted amino derivative was utilized for the construction of a series of Schiff bases (8-13). A new series of thiazolidinone derivatives (15-20) were synthesized in high yields (89-96%) via treatment of thioglycolic acid with Schiff bases (8-13) under microwave irradiation in high yields (89-96%). Moreover, new pyrimidine derivatives (26-30 and 35-38) were prepared by treatment of compound 1 with arylidenes (21-25) and/or alkylidenemalononitriles (31-34) using piperidine as a basic catalyst under microwave conditions. Based on elemental analyses and spectral data, the structures of the new assembled compounds were determined. The newly synthesized quinoxaline derivatives were screened and studied as an insecticidal agent against Aphis craccivora. The obtained results indicate that compound 16 is the most toxicological agent against nymphs of cowpea aphids (Aphis craccivora) compared to the other synthesized pyrimidine and thiazolidinone derivatives. The molecular docking study of the new quinoxaline derivatives registered that compound 16 had the highest binding score (-10.54 kcal/mol) and the thiazolidinone moiety formed hydrogen bonds with Trp143.

Design, Synthesis, and Evaluation of Novel 4-Chloropyrazole-Based Pyridines as Potent Fungicide Candidates

A rational molecular design approach was developed in our laboratory to guide the discovery of novel sterol biosynthesis inhibitors. Based on the application of bioactivities of heterocyclic rings and molecular docking targeting the sterol biosynthesis 14α-demethylase, a series of 4-chloropyrazole-based pyridine derivatives were rationally designed, synthesized, and characterized and their fungicidal activities were also evaluated. Bioassay results showed that 7e, 7f, and 7m exhibited commendable, diverse antifungal actions that are comparable to those of the positive controls imazalil and triadimefon. The active compounds' mode of action was further studied by microscopy observations, Q-PCR, and enzyme inhibition assay and discovered that target compounds affect fungal sterol biosynthesis via disturbing RcCYP51 enzyme system. These findings support that their fungicidal mode of action still targets the cytochrome P450-dependent 14α-demethylase as the molecular design did at first. The above results strongly suggest that our rational molecular design protocol is not only practical but also efficient.

Synthesis of unsymmetrical urea derivatives via Cu-catalysed reaction of acylazide and secondary amine

The synthesis of unsymmetrical urea generally requires toxic reagent, solvent and harsh reaction condition. Herein, we introduce Cu-catalyzed greener and safer unsymmetrical urea derivatives synthesis in ethyl acetate. This method minimized utilization of toxic reagent. A variety of indole, amines, and azides with bis-indole successfully employed leading to high yields and gram scale synthesis of isolated urea.

Synthesis, Anticancer Activities, and Mechanism of N-Heptyl-Containing Biguanide Derivatives

BACKGROUND

In recent years, the anticancer effects of biguanide drugs have received considerable attention. However, the effective concentration of biguanide drugs to kill cancer cells is relative high. Thus, we focus on structural modification of biguanides to obtain better antitumor candidates. Previous study in our laboratory has found that a biguanide compound containing n-heptyl group has the potent anticancer activity. However, the effect of different substituents on the benzene ring side of the biguanides on the anti-proliferative activity is unknown.

OBJECTIVE

A series of n-heptyl-containing biguanide derivatives whose benzene rings were modified by halogen substitution based on the intermediate derivatization method were further synthesized to find new compounds with improved antiproliferative activities.

METHOD

Ten n-heptyl-containing biguanide derivatives were synthesized via established chemical procedures. The activities of these derivatives were explored by MTT assay, clonogenic assay, and scratch assay. The protein levels were detected via Western blotting to explore the mechanisms underlying.

RESULTS

The optimal biguanide derivatives 10a-10c, 11d exhibited IC50 values of 2.21-9.59µΜ for five human cancer cell lines, significantly better than the control drug proguanil. The results of clonogenic and scratch wound healing assays also confirmed the inhibitory effects of derivatives 10a-10c, 11d on the proliferation and migration of human cancer cell lines. Western blot results demonstrated that one representative derivative, 10c upregulates AMPK signal pathway and downregulates mTOR/4EBP1/p70S6K.

CONCLUSION

All biguanide derivatives containing n-heptyl group are more active than proguanil, indicating that the modification of n-heptyl-containing biguanide derivatives provides a novel approach for the development of novel high efficient antitumor drugs.