Kun Li

Guided by a 3D-QSAR hydrophobic field model, a series of ether-linked anthranilic diamides were synthesized for insecticidal screening. Bioassays identified that compounds N01 and N03 exhibited insecticidal activities against Mythimna separata with the LC₅₀ of 0.23 and 0.20 mg·L^–1, respectively. As compared with chlorantraniliprole, N01 demonstrated over 3-fold of significantly enhanced higher potency against Plutella xylostella with an LC₅₀ of 5.0 × 10^–4 mg·L^–1 and 1.6 × 10^–3 mg·L^–1, respectively. N01 showed safety to Apis mellifera and Danio rerio and lower toxicity to HEK293 cells. Transcriptomic and qRT-PCR analyses confirmed both N01 and chlorantraniliprole upregulate RyR gene expression in P. xylostella. Unlike chlorantraniliprole, N01 did not activate the insect resistance of Brassica oleracea var.botrytis Linnaeus, and its efficacy was mainly contributed to its physicochemical properties. Molecular docking and dynamics simulations demonstrated that N01 forms a more stable binding mode with P. xylostella RyR. The results showed that N01 is a promising high-efficacy insecticidal candidate.

To discover a novel succinate dehydrogenase (SDH) inhibition fungicide, a series of 4-(3,4,5-trifluorophenyl)but-3-en-2-amides were designed by a combination of 3D-QSAR and substructure splicing of fluxapyroxad and pydiflumetofen. In vitro fungicidal bioassays demonstrated that 5a exhibited a broad-spectrum of fungicidal activity against Alternaria solani, Cercospora arachidicola, Fusarium graminearum, Fusarium verticillioides, Rhizoctonia solani, and Sclerotinia sclerotiorum, with EC₅₀ values falling between 3.74 and 19.8 μg/mL. Enzymatic activity assays revealed that the inhibition of 5a was lower than that of fluxapyroxad, with an IC₅₀ of 12.5 vs 0.04 μg/mL, respectively. Scanning electron microscopy showed that 5a was effective in inhibiting fungal hyphae growth. Molecular docking and molecular dynamics (MD) simulations showed that 5a exhibited binding patterns similar to those of fluxapyroxad and pydiflumetofen. Binding free energy calculations and decomposition analyses provided insight into the residue interactions of 5a during the MD simulation. These findings suggest that 5a is a novel fungicidal candidate for further investigation.

Based on analyzing the pharmacophore model of commercial succinate dehydrogenase inhibitor (SDHI) fungicides, a molecular database was reasonably designed for computer-aided molecular design, and the potential heterocyclic oxime-ether-containing skeleton was found for derivation. A fungicidal bioassay indicated that the EC₅₀ values of the compounds I-5 (2.23 μg/mL), I-6 (2.15 μg/mL), I-9 (0.07 μg/mL), and I-11 (0.81 μg/mL) showed better in vitro activity against Rhizoctonia solani than that of trifloxystrobin (4.88 μg/mL). Especially, I-9 showed comparable activity to thifluzamide, with EC₅₀ of 0.07 μg/mL vs 0.06 μg/mL, and better activity than fluxapyroxad and boscalid, with EC₅₀ of 0.10 and 2.49 μg/mL, respectively. Like thifluzamide and fluxapyroxad, compounds I-1, I-3, and I-9 showed excellent in vivo activity against R. solani at 200 μg/mL. The IC₅₀ of the R. solani SDH (RsSDH) enzyme of compound I-9 was 0.35 μg/mL, which was near that of fluxapyroxad (0.28 μg/mL). The high potency of I-9 against RsSDH was also reflected in a steeper dose-response tendency in the fluorescence quenching assay, and it was well-docked into the active site of the target enzyme SDH. Molecular docking and molecular dynamics studies have provided a reasonable explanation for compound I-9 being able to act as a SDHI. Our studies supported that I-9 was a promising SDH-based fungicide highly active compound deserving of further study.

Succinate dehydrogenase (SDH) is an ideal fungicidal target. Here, a three-dimensional quantitative structure-activity relationship (3D-QSAR) was established based on the data of 74 compounds with activity against Rhizoctonia solani. By integrating our previously reported 3D-QSAR findings with the current model, a series of pyrazole-containing compounds were rationally designed and synthesized. Bioassay results demonstrated that B5, with an EC₅₀ of 0.002 μg/mL against R. solani, outperformed fluxapyroxad (0.01 μg/mL). Enzyme activity assays revealed that the IC₅₀ of B5 was 0.12 μM, significantly better than that of fluxapyroxad (0.35 μM). The in vivo fungicidal activity of B5 was 94.44% at 200 μg/mL, which was comparable to that of fluxapyroxad (88.89%). Transcriptomic analysis indicated that B5 affects the tricarboxylic acid cycle, sharing the same mode of action as the traditional succinate dehydrogenase inhibitors. Molecular docking and molecular dynamics simulations revealed that the binding modes of B5 were strongly correlated to its potent antifungal activity. Notably, B5, a lead compound without a thiazole substructure, is worthy of further investigation.

In this study, we developed a photoredox-catalyzed defluorinative cross-coupling method for trifluoroketones and alkyl boronic acids. The reaction afforded a series of novel α,α-difluoroketone derivatives, and in vitro fungicidal activity revealed that some of these compounds exhibited moderate to excellent activity against Rhizoctonia solani and Botrytis cinerea. In particular, compound 3d showed an EC₅₀ value of 4.27 μg/mL against B. cinerea and can be used as a fungicidal lead compound for further optimization.

The discovery of novel leads and new targets is an important approach to address the issue of fungicide resistance by new fungicide development. The indole skeleton has been widely utilized in agrochemicals due to its unique biological activity. YZK-C22 is a potent pyruvate kinase inhibitor with high antifungal activity. Several novel fungicide leads were developed based on YZK-C22. Inspired by these, the [1,2,4]triazino[4,5-a]indol-1(2H)-one derivatives were designed using a skeleton hopping strategy; however, these compounds exhibited moderate fungicidal activity. Unexpectedly, 2-(1H-indol-2-yl)-1,3,4-oxadiazole derivatives formed under controlled reaction conditions showed significantly higher fungicidal activity. Compounds 6c, 6d, 6f, and 6j exhibited excellent antifungal activity in vitro, with EC₅₀ values ranging from 0.120 to 0.310 μg/mL against Botrytis cinerea, more potent than commercial fungicide pyrimethanil (EC₅₀ = 0.990 μg/mL). In the field trials at 540 and 720 g of active ingredient (ai)/hm², compound 6c exhibited 81.46 and 86.58% efficacy against B. cinerea, higher than that of pyrimethanil at a rate of 540 g of ai/hm² (70.46%). The affinity constants of compounds 6c and 6d to pyruvate kinase from B. cinerea were lower than that of YZK-C22. Higher field efficacy but lower affinity to pyruvate kinase implies that these compounds may work as prodrugs or have a different mode of action. Thus, 2-(1H-indol-2-yl)-1,3,4-oxadiazole derivatives are worth being further investigated.

To discover novel inhibitors of pyruvate kinase (PK) as fungicidal candidates, a series of 2-thiazol-2-yl-1,3,4-oxadiazole derivatives were designed by a prediction model with Rhizoctonia solani PK (RsPK) as a protein target and YZK-C22 as a ligand. Fungicidal screening indicated that 5b, 5g, 5h, 5j, 5l, 5p, 5q, and 5s exhibited equal or higher activity compared to YZK-C22 against Botrytis cinerea, Cercospora arachidicola, or R. solani. To our surprise, 5s showed comparable activity to flutriafol with an EC₅₀ of 0.21 μg/mL vs 0.20 μg/mL, but over 14 times more active than the lead compound YZK-C22 against R. solani with its EC₅₀ of 0.21 μg/mL vs 3.14 μg/mL (mole ratio over 17-fold). Compound 5s also displayed 2.30-fold better inhibition potency against RsPK compared with YZK-C22. Moreover, this higher potency of 5s against RsPK was also reflected in a steeper dose-response tendency in the fluorescence quenching assay and a lower dissociation constant in the microscale thermophoresis (MST) assay when compared with YZK-C22. The results in this study not only broadened the structural diversity of PK inhibitors but also supported 5s as a promising PK-based highly active fungicide lead compound, with stronger binding ability to RsPK than YZK-C22.

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.

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.