Norcantharidin derivatives, and preparation method and application thereof

Abstract

The application discloses a norcantharidin derivative, a preparation method and application thereof, and belongs to the field of organic synthesis. The bactericidal performance of the derivative is improved by chiral modification of the oxygen ring on the left. Experiments show that part of the norcantharidin derivatives in the series has good bactericidal activity on Sclerotinia sclerotiorum and Botrytis cinerea, and the activity is significantly improved compared with the parent norcantharidin, so that the norcantharidin derivative can be used for preparing a high-efficiency, environment-friendly and low-toxicity bactericide.

Description

Technical Field

[0001] The invention belongs to the field of organic synthesis, and particularly relates to a norcantharidin derivative and a preparation method and application thereof. Background Art

[0002] Cantharidin (CTD) is a compound containing a six-membered oxygen-bridged ring structure, extracted from the traditional Chinese medicine Mylabris blister beetle. It was mentioned in the Shennong Bencao Jing, the earliest extant treatise on Chinese medicine. It is cold in nature, pungent in flavor, and highly toxic. Its primary effects include dispersing swelling, dissolving blood stasis, and attacking toxins and ulcers. As a pesticide, it exhibits insecticidal, bactericidal, and algaecidal activity. Modifying cantharidin with high enantioselectivity is of great significance. Summary of the Invention

[0003] The present invention provides a norcantharidin derivative, its preparation method, and its application. Experiments have shown that some of the norcantharidin derivatives have good fungicidal activity against Sclerotinia sclerotiorum and Botrytis cinerea, significantly improving their activity compared to the parent norcantharidin. Therefore, these derivatives are expected to be used in the preparation of highly effective, environmentally friendly, and low-toxic fungicides.

[0004] The norcantharidin derivatives of the present invention have a general structural formula as shown in Formula I below:

[0005]

[0006] in:

[0007] R1 is selected from one of alkyl, alkanoyl, aryl-substituted alkyl, heterocycle-substituted alkyl, and halogen-substituted alkyl; R2 is selected from phenyl or substituted phenyl, and the substituent of the substituted phenyl is halogen.

[0008] Further, R1 and R2 are selected from the following groups:

[0009]

[0010] Furthermore, compounds 6, 7, 8, and 13 are preferred, and compound 7 is most preferred.

[0011] The preparation method of the norcantharidin derivatives of the present invention comprises the following steps:

[0012] Step 1: reacting norcantharidin with substituted aniline to obtain intermediate a;

[0013]

[0014] R represents monohalogen or dihalogen substitution.

[0015] Step 2: Intermediate a is subjected to metal-catalyzed hydroalkylation to obtain the target product represented by formula I.

[0016] Further, in step 1, norcantharidin and substituted aniline are subjected to imidization reaction in the presence of a catalyst in DCM, and after the reaction is completed, the intermediate a is separated by column chromatography.

[0017] In step 1, the catalyst is one or more of DCC, EDCI.

[0018] In step 1, the reaction temperature is 0-5℃.

[0019] In step 1, the substituted aniline is selected from the group consisting of single-halogen-substituted or double-halogen-substituted aromatic amine structures at positions 2, 3, 4, and 5, and the structures are as shown below:

[0020] .

[0021] Further, in step 2, the intermediate a obtained in step 1, alkyl iodide, catalyst, ligand, and base are placed in a Schlenk tube, and the Schlenk tube is subjected to 3 times of inert gas exchange, and under inert gas protection, a solvent and a hydrogen source are added thereto, and the reaction is carried out at a certain temperature for 1-12h.

[0022] The alkyl iodide is selected from one of methyl iodide, deuterated methyl iodide, ethyl iodide, n-propyl iodide, and n-butyl iodide.

[0023] The solvent is selected from one of ethylene glycol dimethyl ether, ethyl acetate, and tetrahydrofuran.

[0024] In step 2, the catalyst is selected from one of CoCl2, CoBr2, CoBr2(DME), CoI2, Co(acac)2, or CoF3.

[0025] In step 2, the ligand is selected from one of the following ligands L1-L18:

[0026] .

[0027] In step 2, the reaction temperature is -40 to 40℃, and preferably -20 to 0℃.

[0028] In step 2, the base is one or a combination of one or more of CsF, KF, K3PO4, NaHCO3, KH2PO4, Cs2CO3, Na2CO4, KHCO3, and K2CO3, and further preferably CsF and K3PO4.

[0029] In step 2, the hydrogen source is one or a combination of one or more of DEMS, (MeO)3SiH, (MeO)2MeSiH, and PHMS.

[0030] The norcantharidin derivative of the present application is used for preparing a preparation for inhibiting plant pathogenic fungi.

[0031] The plant pathogens include common agricultural pathogens such as rapeseed sclerotinia and tomato gray mold. The cantharidin derivatives of the present invention have good fungicidal activity against rapeseed sclerotinia and tomato gray mold.

[0032] It is important to note that previous modifications of cantharidin and norcantharidin have focused on the anhydride ring on the right side of the norcantharidin structure. Unlike these prior art approaches, the present invention enhances the fungicidal properties of derivatives by chirally modifying the oxygen ring on the left side. Compound 7, obtained by methylation and deuterated methylation, exhibits excellent antibacterial activity. Its antibacterial efficacy is 2-fold higher than that of the commercially available drug procymidone and approximately 40-fold higher than that of its backbone structure.

[0033] In addition, the methylation of existing structures is not a simple matter. For example, there is no precedent for methylation of the six-membered oxygen-containing ring in the structure of norcantharidin. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the H NMR spectrum of compound 6.

[0035] Figure 2 is the H NMR spectrum of compound 7.

[0036] Figure 3 is the H NMR spectrum of compound 8.

[0037] Figure 4 Pymol 2.1 was used to visualize the complexes between proteins and small molecules. Figure A shows a molecular diagram of compound 7, Figure B shows the 3D structure of HK protein, Figure C shows the electron cloud density simulation of compound 7 after embedding into HK protein, and Figure D shows a schematic diagram of the interaction between compound 7 and different amino acid residues in HK protein.

[0038] Figure 5 Scanning electron microscopy images of mycelial morphology of S. sclerotiorum after 48 hours of culture on PDA medium containing 1.0 mg / L compound 7. Figures a and b show the SEM images of mycelial morphology at different magnifications of the blank control group; and c and d show the SEM images of mycelial morphology at different magnifications of mycelial morphology after treatment with 1 ppm of the drug.

[0039] Figure 6 This is the in vitro activity experiment of compound 7 against Sclerotinia sclerotiorum (100 mg / L and 200 mg / L).

[0040] The present invention is further described in detail below through the accompanying drawings and embodiments given by the inventor. DETAILED DESCRIPTION

[0041] Unless otherwise specified, the terms used herein are understood by those skilled in the art.

[0042] The synthetic route of the derivatives of the present invention is as follows:

[0043] Example 1:

[0044]

[0045] 1. Weigh 10 mmol of nordehydrocantharidin and 7.5 mmol of aniline and dissolve them in 100 mL of DCM. Stir in an ice bath for 30 min. Add 10 mmol of EDCI and stir at room temperature for 12 h. Detect by TLC. After the reaction is complete, remove DCM, dry, concentrate, and separate by column chromatography using PE:EA = 2:1 (V / V) as the eluent to obtain intermediate a1 in 60% yield.

[0046] 2. Weigh intermediate a1 (0.1 mmol), iodomethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, and DEMS 0.3 mmol. React at -20°C for 12 h. Separate by thin-layer chromatography to obtain compound 1 as a white solid with a yield of 60% and an ee value of 94%.

[0047] Example 2:

[0048]

[0049] 1. For the preparation of intermediate a1, see Example 1.

[0050] 2. Weigh intermediate a1 (0.1 mmol), deuterated iodomethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, and DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 2 as a white solid with a yield of 62% and an ee value of 94%.

[0051] Example 3:

[0052]

[0053] 1. For the preparation of intermediate a1, see Example 1.

[0054] 2. Intermediate a1 (0.1 mmol), iodoethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 3 as a white solid with a yield of 61% and an ee value of 92%.

[0055] Example 4:

[0056]

[0057] 1. For the preparation of intermediate a1, see Example 1.

[0058] 2. Intermediate a1 (0.1 mmol), iodinated n-propane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 4 as a white solid with a yield of 65% and an ee value of 92%.

[0059] Example 5:

[0060]

[0061] 1. For the preparation of intermediate a1, see Example 1.

[0062] 2. Intermediate a1 (0.1 mmol), n-butyl iodide (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 5 as a white solid with a yield of 60% and an ee value of 90%.

[0063] Example 6:

[0064]

[0065] 1. Weigh 10 mmol of nordehydrocantharidin and 7.5 mmol of 3-F-aniline and dissolve them in 100 mL of DCM. Stir in an ice bath for 30 min. Add 10 mmol of EDCI and stir at room temperature for 12 h. Monitor by TLC. After the reaction is complete, remove DCM, dry, concentrate, and separate by column chromatography to obtain intermediate a2 in a 65% yield.

[0066] 2. Weigh intermediate a2 (0.1 mmol), iodomethane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, and DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 6 as a white solid with a yield of 66% and an ee value of 95%. 1 H NMR (400 MHz, Chloroform-d) δ7.61-7.32 (m, 1H), 7.16-6.90 (m, 3H), 4.97 (d, J = 5.3 Hz, 1H), 4.58 (s, 1H),3.35-2.78 (m, 2H), 2.13-1.97 (m, 1H), 1.98-1.79 (m, 1H), 1.48-1.38 (m, 1H), 1.07 (d, J = 6.9 Hz, 3H).

[0067] Example 7:

[0068]

[0069] 1. For the preparation of intermediate a2, see Example 6.

[0070] 2. Weigh intermediate a2 (0.1 mmol), deuterated iodomethane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, and DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 7 as a white solid with a yield of 50% and an ee value of 95%. 1 H NMR (400 MHz, Chloroform-d) δ7.50-7.36 (m, 1H), 7.16-6.95 (m, 3H), 4.97 (d, J = 5.3 Hz, 1H), 4.58 (s, 1H),3.27-2.60 (m, 2H), 2.11-1.97 (m, 1H), 1.95-1.79 (m, 1H), 1.46-1.37 (m, 1H).

[0071] Example 8:

[0072]

[0073] 1. For the preparation of intermediate a2, see Example 6.

[0074] 2. Intermediate a2 (0.1 mmol), iodoethane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 8 as a white solid with a yield of 45% and an ee value of 90%. 1 H NMR (400 MHz, Chloroform-d) δ7.55-7.35 (m, 1H), 7.15-6.94 (m, 3H), 4.95 (d, J = 5.3 Hz, 1H), 4.69 (s, 1H),3.03 (d, J = 1.7 Hz, 2H), 1.94-1.74 (m, 2H), 1.58-1.41 (m, 2H), 1.37-1.16 (m,1H), 0.93 (t, J = 7.4 Hz, 3H).

[0075] Example 9:

[0076]

[0077] 1. For the preparation of intermediate a2, see Example 6.

[0078] 2. Intermediate a2 (0.1 mmol), iodinated n-propane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 9 as a white solid with a yield of 45% and an ee value of 88%.

[0079] Example 10:

[0080]

[0081] 1. For the preparation of intermediate a2, see Example 6.

[0082] 2. Intermediate a2 (0.1 mmol), n-iodobutane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 10 as a white solid with a yield of 42% and an ee value of 87%.

[0083] Example 11:

[0084]

[0085] 1. Weigh 10 mmol of nordehydrocantharidin and 7.5 mmol of 3,4-difluoroaniline and dissolve them in 100 mL of DCM. Stir in an ice bath for 30 min. Add 10 mmol of EDCI and stir at room temperature for 12 h. Monitor by TLC. After the reaction is complete, remove DCM, dry, concentrate, and separate by column chromatography to obtain intermediate a3 in a 61% yield.

[0086] 2. Intermediate a3 (0.1 mmol), iodomethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 11 as a white solid with a yield of 56% and an ee value of 90%.

[0087] Example 12:

[0088]

[0089] 1. For the preparation of intermediate a3, see Example 11.

[0090] 2. Intermediate a3 (0.1 mmol), deuterated iodomethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 12 as a white solid with a yield of 54% and an ee value of 90%.

[0091] Example 13:

[0092]

[0093] 1. For the preparation of intermediate a3, see Example 11.

[0094] 2. Intermediate a3 (0.1 mmol), iodoethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 13 as a white solid with a yield of 58% and an ee value of 91%.

[0095] Example 14:

[0096]

[0097] 1. For the preparation of intermediate a3, see Example 11.

[0098] 2. Intermediate a3 (0.1 mmol), iodinated n-propane (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 14 as a white solid with a yield of 58% and an ee value of 86%.

[0099] Example 15:

[0100]

[0101] 1. For the preparation of intermediate a3, see Example 11.

[0102] 2. Intermediate a3 (0.1 mmol), n-butyl iodide (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 15 as a white solid with a yield of 55% and an ee value of 85%.

[0103] Example 16:

[0104]

[0105] 1. Weigh 10 mmol of nordehydrocantharidin and 7.5 mmol of 3-chloroaniline and dissolve them in 100 mL of DCM. Stir in an ice bath for 30 min. Add 10 mmol of EDCI and stir at room temperature for 12 h. Monitor by TLC. After the reaction is complete, remove DCM, dry, concentrate, and separate by column chromatography to obtain intermediate a4 in a 63% yield.

[0106] 2. Intermediate a4 (0.1 mmol), iodomethane (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, and DEMS 0.3 mmol were reacted at -20°C for 12 h. Compound 16 was separated by thin-layer chromatography as a white solid with a yield of 60% and an ee value of 92%.

[0107] Example 17:

[0108]

[0109] 1. Preparation of intermediate a4, see example 16.

[0110] 2. Intermediate a4 (0.1 mmol), deuterated methyl iodide (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, -20 °C for 12 h, TLC separation to give compound 17 as a white solid in 55% yield with 92% ee value.

[0111] Example 18:

[0112]

[0113] 1. Preparation of intermediate a4, see example 16.

[0114] 2. Intermediate a4 (0.1 mmol), ethyl iodide (0.5 mmol), CoBr2(DME) 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, -20 °C for 12 h, TLC separation to give compound 18 as a white solid in 58% yield with 90% ee value.

[0115] Example 19:

[0116]

[0117] 1. Preparation of intermediate a4, see example 16.

[0118] 2. Intermediate a4 (0.1 mmol), n-propyl iodide (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, -20 °C for 12 h, TLC separation to give compound 19 as a white solid in 55% yield with 88% ee value.

[0119] Example 20:

[0120]

[0121] 1. Preparation of intermediate a4, see example 16.

[0122] 2. Intermediate a4 (0.1 mmol), n-butane iodide (0.5 mmol), CoBr2 0.01 mmol, ligand L1 0.012 mmol, CsF 0.1 mmol, K3PO4 0.2 mmol, DME 0.8 mL, DEMS 0.3 mmol, react at -20°C for 12 h, and separate by thin-layer chromatography to obtain compound 20 as a white solid with a yield of 56% and an ee value of 86%.

[0123] Example 21:

[0124] Test strains: There are two test strains, Sclerotinia scleotiorum and Botrytis cinerea.

[0125] Test compounds: compounds 1-20 and positive control commercial drugs sclerotinol and procymidone, and control natural products norcantharidin, olefin skeleton, and nor skeleton.

[0126] Others: glucose, agar powder, cutting board, kitchen knife, gauze, potato, cotton wool, sealing film, marker, etc.

[0127] Antibacterial activity determination method:

[0128] Growth rate method - Refer to "Research Methods of Plant Chemical Protection" edited by Mu Liyi. The growth rate method, also known as the inhibition zone method or agar plate method, involves mixing different concentrations of a solution with melted culture medium to create a toxic medium. Pathogens are inoculated onto the medium surface and the toxicity of the agent is determined by the growth rate of the pathogens. The toxicity is expressed as the diameter of the colonies within a certain period of time.

[0129] Potato dextrose agar (PDA) is typically prepared as follows for sterile culture: 200 g of peeled potatoes, diced, added to 1000 mL of distilled water, and boiled for 30 minutes. Filter through four layers of gauze. Pour the filtrate into a clean pan, add an appropriate amount of water, then add 20 g of glucose and 18 g of agar powder. Heat and stir constantly with a glass rod until completely dissolved. Once completely dissolved, dilute to 1000 mL with distilled water and dispense the calculated amount into 300 mL Erlenmeyer flasks.

[0130] First, a dimethyl sulfoxide (DMSO) solution containing the test compound was added to a sterile Petri dish containing approximately 10 mL of potato dextrose agar (PDA). A 6 mm diameter mycelial cake was then excised from the fungal colony and placed in the center of the PDA dish at 28°C for 3–7 days. Three antifungal experiments were performed for each compound. In addition, pure DMSO and the commercial fungicides cypermethrin and procymidone served as negative and positive controls, respectively. The inhibition rate (I) of the test compound was calculated according to the following formula:

[0131]

[0132] In this formula, C represents the average hyphal diameter of the negative control, and T represents the average hyphal diameter of the compound-treated PDA. Finally, some selected compounds were further tested at different concentrations using probabilistic analysis based on the SPSS 23.0 software package to calculate their EC50 (half-maximal effective concentration) values.

[0133]

[0134] Example 22: Molecular docking simulation

[0135] 1. Preparation of compound structure

[0136] The docking compound, compound 7, was constructed using ChemDraw and imported into Chem3D for optimization and energy minimization using the MM2 module. The resulting file was saved as an .sdf file, serving as the ligand for molecular docking. The file was then imported into Maestro 12.8 and optimized using the LigPrep module, with OPLS3e as the force field.

[0137] 2. Preparation of target protein structure

[0138] Since HK proteins are commonly used as receptors for phthalimide drugs, we selected them for simulation. The HK protein structure (PDB ID: 2C2A) was obtained from the RCSB database (https: / / www.rcsb.org / ). The protein structure was processed using Maestro 11.9 to remove any structurally unreasonable structures. The protein was then processed using Schrodinger's Protein Preparation Wizard for energy minimization and geometry optimization.

[0139] 3. Molecular docking

[0140] Molecular docking and optimization were performed using the Glide module within Schrödinger Maestro software. Protein preparation was performed using the Protein Preparation Wizard module. Receptors were preprocessed, optimized, and minimized (using the OPLS3e force field for constrained minimization). Compound structures were prepared using the default settings of the LigPrep module. For screening in the Glide module, the prepared receptors were imported, and the box size was set to 10 Å × 10 Å × 10 Å, with the protein ligand as the active site center. Finally, molecular docking and screening were performed using the standard precision docking (SP) method.

[0141] 4. Screening and analysis of docking results

[0142] Analyze the interaction mode between the compound and the target protein to obtain the interaction between the compound and the protein residue, such as the hydrogen bonding, π-π interaction, hydrophobic interaction, etc., and then refer to the docking score of the compound to infer whether the compound to be screened has a certain active effect.

[0143] 5. Docking results

[0144] The molecular docking results are shown in Table 2. In addition, the complexes of proteins and small molecules were visualized and analyzed using Pymol 2.1. Figure 4 .

[0145]

[0146] 6. Protein interaction analysis

[0147] In this experiment, compound 7 was molecularly docked with the HK target protein. The docking results showed that the compound and the target protein bind well, with a binding energy of -8.545 kcal / mol, less than -6.0 kcal / mol. The complex formed after docking was visualized using Pymol 2.1 software, revealing the binding mode of the compound and protein. The binding mode clearly revealed the amino acid residues that bind to the protein pocket. For example, compound 7 formed strong hydrogen bonds with key residues in the HK protein's active site, VAL-431 (valine) and TYR-384 (tyrosine), and also formed weak hydrogen bonds with ARG-430 (arginine). This strong binding ability plays a crucial role in anchoring small molecules in the protein pocket. In addition, the compound can also form hydrophobic interactions with TYR-384 (tyrosine) and ILE-416 (isoleucine), especially the benzene ring of the compound forms a π-π conjugated interaction with the amino acid benzene ring of TYR-384 (tyrosine), which makes an important contribution to the stabilization of small molecules. These interactions can promote the formation of stable complexes between the compound and proteins, and have a strong correlation with proteins.

[0148] Then, the S. sclerotiorum was cultured on PDA medium containing 1.0 mg / L compound 7 for 48 hours. The mycelial morphology was observed using a scanning electron microscope. Figure 5 Scanning electron microscopy revealed that the hyphae of S. sclerotiorum were wrinkled, proving that the growth of the hyphae was indeed inhibited.

[0149] We then conducted an in vitro activity test on rapeseed leaves. The inhibitory effect of compound 7 on Sclerotinia sclerotiorum was tested at 100 ppm and 200 ppm, respectively, and 100 ppm and 200 ppm of Sclerotinia net were used as the control groups. The results showed that the leaves of the experimental group and the blank group showed significant differences. 72 hours after inoculation, the blank group was severely infected with the pathogen, with large areas of wilting and a large number of white hyphae. The wilting area of ​​the experimental group and the positive control group using 100 ppm compound 7 and 100 ppm of Sclerotinia net was significantly smaller than that of the blank group. The inhibition rate of compound 7 was calculated to be 44.2%, and the inhibition rate of the positive control group was 31.9%. Subsequently, the concentration was increased to 200 ppm, and there was no disease on the leaves of compound 7 or the positive control group. The inhibition rate of both was 100%, showing excellent antibacterial effect.

Claims

1. A norcantharidin derivative, characterized in that It is selected from the compounds of the following structures: 。 2. A method for preparing a norcantharidin derivative, characterized in that The steps include: Step 1: In the presence of a catalyst, norcantharidin and substituted aniline are subjected to imidization reaction in DCM. After the reaction is completed, intermediate a is obtained by separation by column chromatography; ； R represents monohalogen or dihalogen substitution; The catalyst is one or more of DCC and EDCI; Step 2: Place the intermediate a obtained in step 1, an alkyl iodide, a catalyst, a ligand, and a base in a Shrek tube under inert gas protection, add a solvent and a hydrogen source to the system, and perform a hydroalkylation reaction to obtain the target product represented by formula I; The alkyl iodide is selected from one of methyl iodide, deuterated methyl iodide, ethyl iodide, n-propane iodide, and n-butane iodide; The catalyst is selected from one of CoCl2, CoBr2, CoBr2(DME), CoI2, Co(acac)2, and CoF3; The ligand is L1, and its structure is shown below: 。 3. The preparation method according to claim 2, wherein: The base is one or more of CsF, KF, K3PO4, NaHCO3, KH2PO4, Cs2CO3, Na2CO4, KHCO3, and K2CO3.

4. The preparation method according to claim 2, wherein: The hydrogen source is a combination of one or more of DEMS, (MeO)3SiH, (MeO)2MeSiH, and PHMS.

5. Use of the norcantharidin derivatives according to claim 1 in the preparation of a preparation for inhibiting plant pathogens, wherein the plant pathogen is Sclerotinia sclerotiorum.

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