Synthesis and Insecticidal Activity Evaluation of Virtually Screened Phenylsulfonamides

In-Depth Structural Simplification of Celangulin V: Design, Synthesis, and Biological Activity

Celangulin V is a novel botanical insecticide with significant bioactivity and a unique molecular target, but its complex polyol ester structure hinders its broader application in agriculture. To discover new analogues of celangulin V with a simpler structure and enhanced biological activities, we initiated a research project aimed at simplifying its structure and assessing insecticidal efficacy. In this study, a series of novel 1-tetralone derivatives were designed via a structure-based rational design approach and synthesized by a facile method. The biological activities of the target compounds were determined against Mythimna separata (M. separata), Plutella xylostella, and Rhopalosiphum padi. The results revealed that most of the synthesized compounds exhibited superior activities compared to celangulin V. Remarkably, the insecticidal activity of compound 6.16 demonstrated 102-fold greater stomach toxicity than celangulin V against M. separata. In addition, certain compounds showed significant contact toxicity against M. separata, a finding not reported previously in the structural optimization studies of celangulin V. Molecular docking analysis illustrated that the binding pocket of compound 6.16 with the H subunit of V-ATPase was the same as celangulin V. This study presents novel insights into the structural optimization of botanical pesticides.

Design, synthesis, and evaluation of novel arecoline-linked amino acid derivatives for insecticidal and antifungal activities

A series of arecoline derivatives with amino acid moieties were designed and synthesised using an acylamide condensation strategy, taking arecoline as the foundational structure. The insecticidal efficacy of these compounds against Aphis craccivora and Tetranychus cinnabarinus was evaluated. Notably, derivatives 3h and 3i demonstrated superior insecticidal activity compared with arecoline. Additionally, 3h and 3i showed good fungicidal effectiveness against two types of plant fungi. Moreover, molecular docking analyses suggested that 3h and 3i could affect the nervous systems of A. craccivora and T. cinnabarinus by binding to neuronal nicotinic acetylcholine receptors. These findings suggest that compounds 3h and 3i represent promising leads for further development in insecticide and fungicide research.

Synthesis, and Insecticidal Activities of Propargyloxy-Diphenyl Oxide-Sulfonamide Derivatives

Agricultural pests are the primary contributing factor to crop yield reduction, particularly in underdeveloped regions. Despite the significant efficacy of pesticides in pest control, their extensive use has led to the drug-fast of insecticide resistance. Developing of new environmentally friendly plant-based pesticides is an urgent necessity. In this study, a series of diaryl ether compounds containing propargyloxy and sulfonamide groups were designed. The synthesis of these 36 compounds primarily relied on nuclear magnetic resonance for structure determination, while single-crystal X-ray diffraction was employed for certain compounds. Meanwhile, the insecticidal activities against Mythimna separata were also assessed. Some of the compounds exhibited significantly enhanced activity, the LC50 value of the highest activity compound TD8 (0.231 mg/mL) demonstrating respective increases by 100-fold compared to the plant pesticide celangulin V (23.9 mg/mL), and a 5-fold increase with the positive control L-1 (1.261 mg/mL). The interaction between the target compound and the target, as well as the consistency of the target, were verified through symptomological analysis and molecular docking. The structure-activity relationships were also conducted. This study offered a novel trajectory for the advancement and formulation of future pesticides.

Diversifying the benzenesulfonamide scaffold for potential V-ATPase inhibitors: synthesis and insecticidal activity evaluation

Celangulin V is a natural β-dihydroagarofuran derivative isolated from Celastrus angulatus which shows insecticidal activity in many agricultural pests. Using celangulin V as a molecular probe, we find out a new pesticide target: subunit H of V-ATPase. To explore the potential application of this novel target, lead sulfonamides have been found through virtual screening. Combined with the previous work, 46 sulfonamide derivatives are designed and synthesized. All target compounds are first screened for their insecticidal activities against Mythimna separata. The results of bioassay reveal that most of the designed compounds exhibit significant insecticidal activities against third-instar larvae of M. separata under the concentration of 10 mg/mL, and compound 8.4 shows the highest activity with LC50 value of 1.72 mg/mL, 15-fold smaller than that of celangulin V (25.89 mg/mL). Molecular docking results further indicated that compound 8.4 might serve as a potential inhibitor of the subunit H of V-ATPase. This study provides a potential sulfonamide candidate compound for the M. separata control.

Bactericidal bissulfone B7 targets bacterial pyruvate kinase to impair bacterial biology and pathogenicity in plants

The prevention and control of rice bacterial leaf blight (BLB) disease has not yet been achieved due to the lack of effective agrochemicals and available targets. Herein, we develop a series of novel bissulfones and a novel target with a unique mechanism to address this challenge. The developed bissulfones can control Xanthomonas oryzae pv. oryzae (Xoo), and 2-(bis(methylsulfonyl)methylene)-N-(4-chlorophenyl) hydrazine-1-carboxamide (B7) is more effective than the commercial drugs thiodiazole copper (TC) and bismerthiazol (BT). Pyruvate kinase (PYK) in Xoo has been identified for the first time as the target protein of our bissulfone B7. PYK modulates bacterial virulence via a CRP-like protein (Clp)/two-component system regulatory protein (regR) axis. The elucidation of this pathway facilitates the use of B7 to reduce PYK expression at the transcriptional level, block PYK activity at the protein level, and impair the interaction within the PYK-Clp-regR complex via competitive inhibition, thereby attenuating bacterial biology and pathogenicity. This study offers insights into the molecular and mechanistic aspects underlying anti-Xoo strategies that target PYK. We believe that these valuable discoveries will be used for bacterial disease control in the future.

Design, synthesis and insecticidal activity of benzenesulfonamide derivatives containing various alkynyl, alkenyl and cyclopropyl groups in para position

Celangulin V is a natural β-dihydrofuran sesquiterpene polyester with anti Mythimna separate activity and unique mechanism of action. Further study showed that its target was the H subunit of V-ATPase in the midgut of M. separate. Thus, combined with the previous work, thirty-two benzene sulfonamide derivatives were systematically synthesised to discover efficient and low-budget insecticidal candidates for the H subunit of V-ATPase. Screening results showed that compounds C2, C4, C5, C6 and C8 could significantly cause death of tested third-instar larvae of M. separate, and provided the corresponding LC50 values of 0.844, 0.953, 0.705, 0.599 and 0.887 mg/mL, which were extremely better than Celangulin V (LC50 = 11.5 mg/mL). The docking results indicated that this novel framework might target H subunit of V-ATPase. Given these excellent bioactivity results, this kind of sulfonamide framework could provide a suitable point for exploring highly efficient insecticidal agents.

Green synthesis, characterization, and biochemical impacts of new bioactive isoxazoline-sulfonamides as potential insecticidal agents against the Sphodroxia maroccana Ley

BACKGROUND

Sphodroxia maroccana Ley is a pest of cork oak crops that damages the roots of seedlings and can severely impair cork oak regeneration. Since the banning of carbosulfan and chlorpyriphos, which were widely used against the larvae of Sphodroxia maroccana because of their harmful impact on the environment, until now there has been no pesticide against these pests. Therefore, it is particularly urgent to develop highly effective insecticidal molecules with novel scaffolds. Isoxazolines are a class of insecticides that act on γ-aminobutyric acid (GABA)-gated chloride channel allosteric modulators. In this work, a green synthesis of novel 3,5-disubstituted isoxazoline-sulfonamide derivatives was achieved in water via ultrasound-assisted four-component reactions, and their insecticidal activities against fourth-instar larvae of S. maroccana were evaluated.

RESULTS

Most of the tested compounds showed insecticidal activity compared to fluralaner as positive control and commercially available insecticide. Especially, the isoxazoline-secondary sulfonamides containing halogens (Br and Cl) on the phenyl group attached to the isoxazoline, 6g (LC50  = 0.31 mg/mL), 6j (LC50  = 0.38 mg/mL), 6k (LC50  = 0.18 mg/mL), 6L (LC50  = 0.49 mg/mL), 6m (LC50  = 0.24 mg/mL), 6q (LC50  = 0.46 mg/mL), exhibited much higher larvicidal activity than fluralaner (LC50  = 0.99 mg/mL).

CONCLUSION

Novel isoxazolines containing sulfonamide moieties were designed, synthesized and confirmed by two single-crystal structures of 4e and 6q. Their bioassay results showed significant larvicidal activity with significant morphological changes in vivo. These results will lay the foundation for the further discovery and development of isoxazoline-sulfonamide derivatives as novel crop protection larvicides of cork oak. © 2023 Society of Chemical Industry.

Applying molecular docking to pesticides

Pesticide creation is related to the development of sustainable agricultural and ecological safety, and molecular docking technology can effectively help in pesticide innovation. This paper introduces the basic theory behind molecular docking, pesticide databases, and docking software. It also summarizes the application of molecular docking in the pesticide field, including the virtual screening of lead compounds, detection of pesticides and their metabolites in the environment, reverse screening of pesticide targets, and the study of resistance mechanisms. Finally, problems with the use of molecular docking technology in pesticide creation are discussed, and prospects for the future use of molecular docking technology in new pesticide development are discussed. © 2023 Society of Chemical Industry.

Insights into a class of natural eugenol and its optimized derivatives as potential tobacco mosaic virus helicase inhibitors by structure-based virtual screening

Plant diseases caused by malignant and refractory phytopathogenic viruses have considerably restricted crop yields and quality. To date, drug design targeting functional proteins or enzymes of viruses is an efficient and viable strategy to guide the development of new pesticides. Herein, a series of novel eugenol derivatives targeting the tobacco mosaic virus (TMV) helicase have been designed using structure-based virtual screening (SBVS). Structure-activity relationship indicated that 2 t displayed the most powerful bonding capability (Kd = 0.2 μM) along with brilliant TMV helicase ATPase inhibitory potency (IC50 = 141.9 μM) and applausive anti-TMV capability (EC50 = 315.7 μg/mL), ostentatiously outperforming that of commercial Acyclovir (Kd = 23.0 μM, IC50 = 183.7 μM) and Ribavirin (EC50 = 624.3 μg/mL). Molecular dynamics simulations and docking suggested ligand 2 t was stable and bound in the active pocket of the TMV helicase by multiple interactions. Given these superior properties, eugenol-based derivatives could be considered as the novel potential plant viral helicase inhibitors. Furthermore, this effective and feasible SBVS strategy established a valuable screening platform for helicase-targeted drug development.

Design, synthesis and insecticidal activities of 4-propargyloxybenzene sulfonamide derivatives substituted with amino acids

Sixty-nine 4-propargyloxybenzene sulfonamide derivatives with different amino acids as amino substituent were synthesized and evaluated for their insecticidal activity against third-instar Mythimna separate. The bioassay results revealed that some derivatives bearing amino acid ester group performed good insecticidal activity against third-instar M.separata, such as the LC₅₀ values of D18 and D19 were 4.28 and 2.96 mg/ml after 48 h, in particular, the LC₅₀ of D16 was 2.38 mg/ml and the activity was improved by 14 times compared to celangulin V (34.48 mg/ml). The above results provided theoretical and experimental basis for the discovery of novel insecticidal active compounds.

Ensemble-based, high-throughput virtual screening of potential inhibitor targeting putative farnesol dehydrogenase of Metisa plana (Lepidoptera: Psychidae)

Metisa plana (Lepidoptera: Psychidae) bagworm is a leaf-eater caterpillar ubiquitously found as a damaging pest in oil palm plantations, specifically in Malaysia. Various strategies have been implemented, including the usage of chemical insecticides. However, the main challenges include the development of insecticide resistance and its detrimental effects on the environment and non-target organisms. Therefore, a biorational insecticide is introduced by targeting the juvenile hormone (JH) biosynthetic pathway, which is mainly present in the insect and vital for the insect's growth, diapause, metamorphosis, and adult reproduction. This study aimed to investigate the potential inhibitor for the rate-limiting enzyme involved in the JH pathway known as farnesol dehydrogenase. A 255 amino acids sequence encoded for the putative M. plana farnesol dehydrogenase (MpFolDH) open reading frame had been identified and isolated. The three-dimensional structure of MpFolDH was predicted to have seven β- sheets with α-helices at both sides, showing typical characteristics for classical short-chain dehydrogenase and associated with oxidoreductase activity. Then, the ensemble-based virtual screening was conducted based on the ZINC20 database, in which 43 768 compounds that fulfilled pesticide-likeness criteria were screened by site-specific molecular docking. After a short molecular dynamics simulation (5 ns) was conducted towards 102 compounds, only the top 10 compounds based on their most favourable binding energy were selected for a more extended simulation (100 ns). Based on the protein-ligand stability, protein compactness, residues rigidity, binding interaction, binding energy throughout the 100 ns simulation, and physicochemical analysis, ZINC000408743205 was selected as a potential inhibitor for this enzyme. Amino acids decomposition analysis indicates Ile18, Ala95, Val198 and Val202 were the critical contributor residues for MpFolDH-inhibitors(s) complex.

Design, Synthesis, Insecticidal Activities and Molecular Docking of Sulfonamide Derivatives Containing Propargyloxy or Pyridine Groups

The discovery of new highly active molecules from natural products is a common method to create new pesticides. Celangulin V targeting Mythimna separate (M. separate) midgut V-ATPase  H subunit, has received considerable attention for its excellent insecticidal activity and unique mechanism of action. Therefore, combined with our preliminary work, thirty-seven sulfonamide derivatives bearing propargyloxy or pyridine groups were systematically synthesized to search for insecticidal candidate compounds with low cost and high efficiency on the  H subunit of V-ATPase. Bioactive results showed that compounds A2-A4 and A6-A7 exhibited a better bioactivity with median effective concentration (LC₅₀ ) values (2.78, 3.11, 3.34, 3.54 and 2.48 mg/mL, respectively) against third-instar larvae of M. separate than Celangulin V (LC₅₀ =18.1 mg/mL). Additionally, molecular docking experiments indicated that these molecules may act on the H subunit of V-ATPase. Based on the above results, these compounds provide new ideas for the discovery of insecticides.

Identification of sulfonamide compounds active on the insect nervous system: Molecular modeling, synthesis and biological evaluation

Insect nicotinic acetylcholine receptors (nAChRs) are a recognized target for insecticide design. In this work, we have identified, from a structure-based approach using molecular modeling tools, ligands with potential selective activity for pests versus pollinators. A high-throughput virtual screening with the Openeye software was performed using a library from the ZINC database, thiacloprid being used as the target structure. The top sixteen molecules were then docked in α6 cockroach and honeybee homomeric nAChRs to check from a theoretical point of view relevant descriptors in favor of pest selectivity. Among the selected molecules, one original sulfonamide compound has afterward been synthesized, together with various analogs. Two compounds of this family have been shown to behave as activators of the cockroach cholinergic synaptic transmission.

Synthesis and insecticidal activities of 4-(propargyloxy) benzenesulfonamide derivatives

A series of 4-(propargyloxy) benzenesulfonamide derivatives with different substituents on the benzene ring were synthesized and evaluated for their insecticidal activity. Some of the compounds showed good insecticidal activity against Mythimna separata, and the LC₅₀ value of the most active compound B2.5 was 0.235 mg/ml. Ultrastructural changes in the midgut epithelial cells of Mythimna separata were observed using transmission electron microscopy, and severe structural damage was found in microvilli, mitochondria and rough endoplasmic reticulum. It indicates that the possible site of action of these benzenesulfonamides is the cytoplasmic membrane and endomembrane system of the midgut epithelial cells. The above provides a basis for the development of novel insecticidal active compounds with a novel mechanism of action.

Synthesis and Antibacterial Activities of 2-Oxo-N-phenylacetamide Derivatives Containing a Dissulfone Moiety Target on Clp

Rice bacterial blight and rice bacterial streak are two serious rice diseases and have caused great harm to the production of rice all over the world. To develop an efficient antibacterial agent with a novel target, a series of novel 2-oxo-N-phenylacetamide derivatives containing a dissulfone moiety were synthesized, and their antibacterial activities were evaluated. Among them, compound D₁₄ exhibited the best antibacterial activities, especially against Xoo and Xoc with EC₅₀ values of 0.63 and 0.79 mg/L, respectively, which were much better than the commercial control of bismerthiazol (BT) (76.59 and 83.35 mg/L, respectively) and thiodiazole copper (TC) (91.72 and 114.00 mg/L, respectively). Meanwhile, compound D₁₄ can interact with a CRP-like protein (Clp) of Pxo99^A and show strong binding activity with Xoo-Clp with a K_d value of 0.52 μM, which was far superior to the corresponding K_d values of BT (183.94 μM) and TC (222.58 μM). Treatment of D₁₄ and deletion of the clp gene could significantly reduce the expression of the clp gene and attenuate the virulence of pathogenic bacteria. These results indicated that compound D₁₄ could be used as a potential novel agricultural bactericide and Clp can be used as a target protein for the control of plant bacterial diseases. This work provided reliable support for developing novel antibacterial agents based on Clp as a target protein.

Classifying the toxicity of pesticides to honey bees via support vector machines with random walk graph kernels

Pesticides benefit agriculture by increasing crop yield, quality, and security. However, pesticides may inadvertently harm bees, which are valuable as pollinators. Thus, candidate pesticides in development pipelines must be assessed for toxicity to bees. Leveraging a dataset of 382 molecules with toxicity labels from honey bee exposure experiments, we train a support vector machine (SVM) to predict the toxicity of pesticides to honey bees. We compare two representations of the pesticide molecules: (i) a random walk feature vector listing counts of length- L walks on the molecular graph with each vertex- and edge-label sequence and (ii) the Molecular ACCess System (MACCS) structural key fingerprint (FP), a bit vector indicating the presence/absence of a list of pre-defined subgraph patterns in the molecular graph. We explicitly construct the MACCS FPs but rely on the fixed-length- L random walk graph kernel (RWGK) in place of the dot product for the random walk representation. The L-RWGK-SVM achieves an accuracy, precision, recall, and F1 score (mean over 2000 runs) of 0.81, 0.68, 0.71, and 0.69, respectively, on the test data set—with L = 4 being the mode optimal walk length. The MACCS-FP-SVM performs on par/marginally better than the L-RWGK-SVM, lends more interpretability, but varies more in performance. We interpret the MACCS-FP-SVM by illuminating which subgraph patterns in the molecules tend to strongly push them toward the toxic/non-toxic side of the separating hyperplane.

Design, synthesis, and insecticidal activities of propargyloxy-naphthalene-sulfonamide derivatives

In our previous studies, a kind of novel benzenesulfonamides was found to be a candidate insecticidal compounds. It was shown that propargyloxy and sulfonamide groups are pharmacodynamic groups. One hundred and twenty-six (126) naphthalenesulfonamides derivatives with propargyloxy functionality were designed and synthesized, and their insecticidal activities were determined. Some of them showed outstanding activity, with LC₅₀ values as low as 0.202 mg ml^-1, much lower than that of the positive control celangulin V (23.9 mg ml^-1). In addition, the structure-activity relationships were discussed, and molecular docking was used to verify the binding mode of the compound and the target receptor.

Primary Mode of Action of the Novel Sulfonamide Fungicide against Botrytis cinerea and Field Control Effect on Tomato Gray Mold

Botrytis cinerea is considered an important plant pathogen and is responsible for significant crop yield losses. With the frequent application of commercial fungicides, B. cinerea has developed resistance to many frequently used fungicides. Therefore, it is necessary to develop new kinds of fungicides with high activity and new modes of action to solve the increasingly serious problem of resistance. During our screening of fungicide candidates, one novel sulfonamide compound, N-(2-trifluoromethyl-4-chlorphenyl)-2-oxocyclohexyl sulfonamide (L13), has been found to exhibit good fungicidal activity against B. cinerea. In this work, the mode of action of L13 against B. cinerea and the field control effect on tomato gray mold was studied. L13 had good control against B. cinerea resistant to carbendazim, diethofencarb, and iprodione commercial fungicides in the pot culture experiments. SEM and TEM observations revealed that L13 could cause obvious morphological and cytological changes to B. cinerea, including excessive branching, irregular ramification or abnormal configuration, and the decomposition of cell wall and vacuole. L13 induced more significant electrolyte leakage from hyphae than procymidone as a positive control. L13 had only a minor effect on the oxygen consumption of intact mycelia, with 2.15% inhibition at 50 μg/mL. In two locations over 2 years, the field control effect of L13 against tomato gray mold reached 83% at a rate of 450 g ai ha⁻¹, better than the commercial fungicide of iprodione. Moreover, toxicological tests demonstrated the low toxicological effect of L13. This research seeks to provide technical support and theoretical guidance for L13 to become a real commercial fungicide.

Discovery of Biphenyl-Sulfonamides as Novel β-N-Acetyl-d-Hexosaminidase Inhibitors via Structure-Based Virtual Screening

Novel insecticidal targets are always in demand due to the development of resistance. OfHex1, a β-N-acetyl-d-hexosaminidase identified in Ostrinia furnacalis (Asian corn borer), is involved in insect chitin catabolism and has proven an ideal target for insecticide development. In this study, structure-based virtual screening, structure simplification, and biological evaluation are used to show that compounds with a biphenyl-sulfonamide skeleton have great potential as OfHex1 inhibitors. Specifically, compounds 10k, 10u, and 10v have K_i values of 4.30, 3.72, and 4.56 μM, respectively, and thus, they are more potent than some reported nonglycosyl-based inhibitors such as phlegmacin B₁ (K_i = 26 μM), berberine (K_i = 12 μM), 2 (K_i = 11.2 μM), and 3 (K_i = 28.9 μM). Furthermore, inhibitory kinetic assessments reveal that the target compounds are competitive inhibitors with respect substrate, and based on toxicity predictions, most of them have potent drug properties. The obtained results indicate that the biphenyl-sulfonamide skeleton characterized by simple chemical structure, synthetic tractability, potent activity, and low toxicity has potential for further development in pest management targeting OfHex1.