Spiro brassinolide as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of botanical herbicides, and provides spirobrassinolide as well as a preparation method and application thereof. The preparation method comprises the following steps: mixing isatin, nitromethane, a chiral catalyst and tetrahydrofuran, and performing asymmetric Henry reaction to obtain an intermediate 1; mixing the intermediate 1, methanol and a palladium-carbon catalyst, and performing catalytic hydrogenation reduction reaction to obtain an intermediate 2; mixing the intermediate 2, carbon disulfide, a sodium hydroxide solution and methyl iodide, and carrying out an addition methylation reaction to obtain an intermediate 3; and mixing the intermediate 3, dichloromethane, pyridine and methylsulfonyl chloride, and carrying out a substitution cyclization reaction to obtain the spirobrassinolide. The process route is efficient and excellent in stereoselectivity, the problem of low efficiency of traditional natural product separation is avoided, and the prepared spirobrassinolide is high in weed inhibition activity, has a remarkable inhibition effect on growth of gramineous weed millet and broadleaf weed chenopodium album and has the potential of becoming a novel plant source herbicide.

Description

Technical Field

[0001] The present invention relates to the technical field of plant-derived herbicides, and particularly to a spirobrassinolide and its preparation method and application. Background Art

[0002] In agricultural production, the types of weeds in farmland are complex and their distribution areas are extensive. Given the high morphological similarity between weeds and crops and the overlap of their growth cycles with those of crops, the losses caused by weeds are immeasurable. Therefore, the prevention and control of weeds face severe challenges. The development and application of highly active chemical herbicides have brought benefits to agricultural production and reduced the harm of weeds. However, with the misuse, overuse, and improper mixing of chemical herbicides, not only the crop yield is affected, but also drug resistance is easily generated. Currently, the herbicides targeting acyl-CoA carboxylase produce the largest number of resistant weeds. The herbicide with the most resistant weeds is atrazine, followed by glyphosate. The resistance problems of Amaranthaceae and Chenopodiaceae weeds to photosynthesis inhibitor herbicides such as fomesafen and branched-chain amino acid biosynthesis inhibitor herbicides such as imazethapyr are becoming increasingly prominent, and the control effect has decreased significantly. Long-residual herbicides such as imazethapyr have a greater impact on subsequent crops and the environment, causing problems such as soil pollution and ecological imbalance, posing threats to the ecological environment, food security, farmland weed management, and agricultural sustainable development. To solve the above problems, safer, more efficient, and environmentally friendly herbicides are needed.

[0003] Plant-derived herbicides are an environmentally friendly type of herbicide, which have the characteristics of easy biodegradability, low toxicity, low development costs, novel chemical structures, unique modes of action, and high target selectivity, and have advantages that synthetic herbicides cannot match. Current research shows that the research and development of plant-derived herbicides are extremely rapid, and the secondary metabolites of more than 2,000 plants have been reported to have herbicidal activity. However, the research on plant secretions and allelopathic effects of plant decomposition mainly focuses on crops or green manure, and there is still a large research space for allelochemicals. In the development process of herbicides, plant-derived herbicides based on allelochemicals have great potential to break through economic limitations and reduce synthesis costs. However, the effective components of natural products are complex, with low content and difficult to enrich. Using traditional separation methods is not only cumbersome, consuming a large amount of energy and materials, but also with low yield and purity, especially difficult to separate components with similar structures and properties. Summary of the Invention

[0004] In view of this, the present invention provides a spirobrassinolide and its preparation method and application, aiming to fully utilize natural resources to develop an environmentally friendly herbicide.

[0005] To achieve the above invention purposes, the present invention provides the following technical solutions:

[0006] The present invention provides a spiro brassinolide, and the structural formula of the spiro brassinolide is as follows:

[0007]

[0008] The present invention provides a preparation method of the above-mentioned spiro brassinolide, comprising the following steps:

[0009] S1. Mix isatin, nitromethane, a chiral catalyst and tetrahydrofuran, and then carry out an asymmetric Henry reaction to obtain intermediate 1;

[0010] S2. Mix intermediate 1, methanol and a palladium-carbon catalyst, and then carry out a catalytic hydrogenation reduction reaction to obtain intermediate 2;

[0011] S3. Mix intermediate 2, carbon disulfide, a sodium hydroxide solution and iodomethane, and then carry out an addition methylation reaction to obtain intermediate 3;

[0012] S4. Mix intermediate 3, dichloromethane, pyridine and methanesulfonyl chloride, and then carry out a substitution cyclization reaction to obtain spiro brassinolide.

[0013] Further, in the step S1, the molar ratio of isatin to nitromethane is 1:1 to 1.5; the mass-volume ratio of isatin to the amount of tetrahydrofuran used is 1 g:5 to 15 mL; the amount of the chiral catalyst used is 1 to 10 mol%;

[0014] The temperature of the asymmetric Henry reaction is 0 to 2 °C, and the time is 10 to 15 h.

[0015] Further, in the step S2, the mass-volume ratio of intermediate 1 to methanol is 1 g:8 to 15 mL; the amount of the palladium-carbon catalyst used is 1 to 10 mol%;

[0016] The temperature of the catalytic hydrogenation reduction reaction is 20 to 30 °C, the time is 5 to 8 h, and the hydrogen pressure is 1 to 5 atm.

[0017] Further, in the step S3, intermediate 2, carbon disulfide and the sodium hydroxide solution first carry out an addition reaction, and the obtained reaction product carries out a methylation reaction with iodomethane.

[0018] Further, the molar ratio of intermediate 2 to sodium hydroxide is 1:1.5 to 2.5; the amount of carbon disulfide used is 1 to 2 equivalents, the pH value of the sodium hydroxide solution is 9 to 11; the temperature of the addition reaction is 0 to 2 °C, and the time is 1 to 3 h.

[0019] Further, the amount of iodomethane used is 1 to 5 equivalents; the temperature of the methylation reaction is 20 to 30 °C, and the time is 3 to 5 h.

[0020] Further, in the step S4, the mass-volume ratio of intermediate 3 to dichloromethane is 1 g: 8 - 12 mL; the dosage of pyridine is 1 - 3 equivalents, and the dosage of methanesulfonyl chloride is 1 - 1.5 equivalents.

[0021] Further, in the step S4, the substitution cyclization reaction is divided into two stages. The temperature of the first stage is 0 - 2 °C and the time is 1 - 2 h; the temperature of the second stage is 20 - 30 °C and the time is 10 - 15 h.

[0022] The present invention also provides the application of the above-mentioned spirobrassinolide in the preparation of herbicides.

[0023] As can be seen from the above technical solutions, compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. The spirobrassinolide provided by the present invention has a strong inhibitory effect on the roots of weeds. From this point of view, the synthesized spirobrassinolide can be popularized and applied in the form of a soil sealant. The roots of wild foxtail seedlings are strongly inhibited by spirobrassinolide, showing no difference from the positive control tribenuron-methyl.

[0025] 2. The spirobrassinolide provided by the present invention is a yellow oily compound at room temperature. Without adding spray adjuvants, it can resist evaporation and degradation when carried by an oily medium, which helps to reduce the usage frequency and total amount, thus reducing the potential impact on the environment. In addition, other natural products or synthetic compounds can be compounded with spirobrassinolide to achieve a synergistic effect. Spirobrassinolide has a high lipophilicity with a LogP of 1.7. There is only one position for the hydrogen bond donor, which is the unsaturated amino group on the indole ring. Spirobrassinolide has three hydrogen bond acceptor groups and has a certain flexibility.

[0026] 3. The preparation method of the spirobrassinolide provided by the present invention overcomes the research difficulty of the low content of natural products and is conducive to the large-scale production of spirobrassinolide. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the technical route diagram for preparing spirobrassinolide of the present invention;

[0028] Figure 2 It is the hydrogen spectrum diagram of the spirobrassinolide prepared in Example 1 of the present invention;

[0029] Figure 3 It is the high performance liquid chromatography diagram of the spirobrassinolide prepared in Example 1 of the present invention;

[0030] Figure 4 It is the mass spectrum diagram of the product obtained in Example 1 of the present invention;

[0031] Figure 5 It is the chromatography diagram of the product obtained in Example 1 of the present invention;

[0032] Figure 6 Effect diagram of the inhibitory effect of the spirobrassinolide prepared in Example 1 on the root length of weeds as a herbicide. Detailed implementation manners

[0033] The present invention provides a spirobrassinolide, and the structural formula of the spirobrassinolide is as follows:

[0034]

[0035] The present invention provides a preparation method of the above-mentioned spirobrassinolide, which comprises the following steps:

[0036] S1. Mix isatin, nitromethane, a chiral catalyst and tetrahydrofuran, and carry out an asymmetric Henry reaction to obtain intermediate 1;

[0037] S2. Mix intermediate 1, methanol and a palladium-carbon catalyst, and carry out a catalytic hydrogenation reduction reaction to obtain intermediate 2;

[0038] S3. Mix intermediate 2, carbon disulfide, a sodium hydroxide solution and iodomethane, and carry out an addition methylation reaction to obtain intermediate 3;

[0039] S4. Mix intermediate 3, dichloromethane, pyridine and methanesulfonyl chloride, and carry out a substitution cyclization reaction to obtain spirobrassinolide.

[0040] In the present invention, in step S1, the molar ratio of isatin to nitromethane is 1:1 to 1.5, preferably 1:1.2; the mass-volume ratio of isatin to the amount of tetrahydrofuran used is 1 g:5 to 15 mL, preferably 1 g:10 mL; the amount of the chiral catalyst used is 1 to 10 mol%, preferably 5 mol%;

[0041] The temperature of the asymmetric Henry reaction is 0 to 2 °C, preferably 0 °C, and the time is 10 to 15 h, preferably 12 h.

[0042] In the present invention, in step S1, after the asymmetric Henry reaction is completed, the reaction solution is concentrated under reduced pressure and then purified by silica gel column chromatography (eluent: ethyl acetate / n-hexane = 1:3) to obtain a yellow solid intermediate 1.

[0043] In the present invention, in step S2, the mass-volume ratio of intermediate 1 to methanol is 1 g:8 to 15 mL, preferably 1 g:10 mL; the amount of the palladium-carbon catalyst used is 1 to 10 mol%, preferably 5 mol%;

[0044] The temperature of the catalytic hydrogenation reduction reaction is 20 to 30 °C, preferably 25 °C, the time is 5 to 8 h, preferably 6 h; the hydrogen pressure is 1 to 5 atm, preferably 3 atm.

[0045] In the present invention, in step S2, after the catalytic hydrogenation reduction reaction is completed, the reaction solution is filtered through diatomaceous earth to remove the catalyst, and the filtrate is concentrated under reduced pressure to obtain a white solid intermediate 2.

[0046] In the present invention, in step S3, intermediate 2, carbon disulfide and sodium hydroxide solution first undergo an addition reaction, and the resulting reaction product undergoes a methylation reaction with iodomethane.

[0047] In the present invention, the molar ratio of intermediate 2 to sodium hydroxide is 1:1.5 - 2.5; preferably 1:2; the amount of carbon disulfide used is 1 - 2 equivalents, the pH value of the sodium hydroxide solution is 9 - 11, preferably 10; the temperature of the addition reaction is 0 - 2°C, preferably 0°C, and the time is 1 - 3 h, preferably 2 h.

[0048] In the present invention, the amount of iodomethane used is 1 - 5 equivalents, preferably 3 equivalents; the temperature of the methylation reaction is 20 - 30°C, preferably 25°C, and the time is 3 - 5 h, preferably 4 h.

[0049] In the present invention, in step S3, after the methylation reaction is completed, the reaction solution is extracted with dichloromethane, the organic phase is dried over anhydrous sodium sulfate and then concentrated, and purified by recrystallization (ethanol / water) to obtain a pale yellow crystal intermediate 3.

[0050] In the present invention, in step S4, the mass-volume ratio of intermediate 3 to dichloromethane is 1 g:8 - 12 mL, preferably 1 g:10 mL; the amount of pyridine used is 1 - 3 equivalents, preferably 2 equivalents, and the amount of methanesulfonyl chloride used is 1 - 1.5 equivalents, preferably 1.2 equivalents.

[0051] In the present invention, in step S4, the substitution cyclization reaction is divided into two stages. The temperature of the first stage is 0 - 2°C and the time is 1 - 2 h; the temperature of the second stage is 20 - 30°C and the time is 10 - 15 h.

[0052] In the present invention, in step S4, after the substitution cyclization reaction is completed, the reaction solution is washed with dilute hydrochloric acid, the organic phase is dried and then concentrated, and purified by silica gel column chromatography (eluent: dichloromethane / methanol = 20:1) to obtain the final product.

[0053] In the present invention, the technical route is shown in Figure 1 , and the reaction principle of step S1 is: isatin and nitromethane undergo an asymmetric Henry reaction under the action of a chiral organic catalyst to generate a β-nitro alcohol intermediate (intermediate 1). This reaction achieves high enantioselectivity through the stereoselective induction of the catalyst;

[0054] The reaction principle of step S2 is as follows: The nitro group (-NO2) of intermediate 1 is reduced to an amino group (-NH2) under the action of a palladium-carbon (Pd / C) catalyst and hydrogen (H2), generating intermediate 2.

[0055] The reaction principle of step S3 is as follows: The amino group of intermediate 2 reacts with carbon disulfide (CS2) to form thiocarbamic acid (-NH-CSSH), and then a methylation reagent (such as methyl iodide) converts it into methyl thiocarbamate (-NH-CSSCH3), obtaining intermediate 3.

[0056] The reaction principle of step S4 is as follows: Intermediate 3 is sulfonylated under the action of methanesulfonyl chloride (MsCl) and pyridine to form an intermediate sulfonate ester, and then a spiro ring structure is formed through an intramolecular S N 2 substitution reaction to finally obtain spirobrassinolide.

[0057] The technical solutions provided by the present invention will be described in detail below with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0058] Example 1

[0059] Isatin and nitromethane were mixed at a molar ratio of 1:1.2, 5 mol% of a chiral catalyst was added, and the reaction was carried out in tetrahydrofuran at 0 °C for 12 hours. After the reaction solution was concentrated under reduced pressure, it was purified by silica gel column chromatography (eluent: ethyl acetate / n-hexane = 1:3) to obtain a yellow solid intermediate 1. Recovery rate and purity: The yield was 99%, the ee value measured by HPLC was 99%, the production rate was 99%, and the purity was ≥98% (confirmed by nuclear magnetic resonance hydrogen spectrum ( 1 1H NMR) and high performance liquid chromatography (HPLC)).

[0060] Intermediate 1 was dissolved in methanol, 10 wt% Pd / C catalyst (the catalyst dosage was 5 mol%) was added, and the reaction was stirred at 3 atm hydrogen pressure and 25 °C for 6 hours. The reaction solution was filtered through diatomaceous earth to remove the catalyst, and the filtrate was concentrated under reduced pressure to obtain a white solid intermediate 2. Recovery rate and purity: The yield was 95% (based on intermediate 1), and the purity was ≥97% (confirmed by 1 1H NMR and mass spectrometry (MS)).

[0061] Intermediate 2 and CS2 (1.5 equivalents) were reacted in a sodium hydroxide solution (pH 10) at 0 °C for 2 h, methyl iodide (1.2 equivalents) was added, and the mixture was stirred at room temperature for 4 h. Then the reaction solution was extracted with dichloromethane, the organic phase was dried over anhydrous sodium sulfate and concentrated, and purified by recrystallization (ethanol / water) to obtain a pale yellow crystal intermediate 3. Recovery rate and purity: The yield was 90%, and the purity was ≥96% (confirmed by 1 1H NMR and HPLC).

[0062] Intermediate 3 was dissolved in dichloromethane, pyridine (2 equivalents) and MsCl (1.2 equivalents) were added. The reaction was first carried out at 0 °C for 1 hour, then the temperature was raised to room temperature and stirred for 12 hours to complete the cyclization. The reaction solution was washed with dilute hydrochloric acid, the organic phase was dried and concentrated, and purified by silica gel column chromatography (eluent: dichloromethane / methanol = 20:1) to obtain spirobrassinin, named: S-(-)-Spirobrassinin. Recovery rate and purity: The yield was 85%, and the purity was ≥99% (confirmed by 1 1H NMR and HPLC, see Figure 2 and Figure 3 ), and the specific rotation [α]D 25 = -68.42° (CH3OH), which was consistent with the natural product.

[0063] Figure 4 This is the mass spectrum of the product obtained in this example; Figure 5 This is the chromatogram of the product obtained in this example; from Figure 4 and Figure 5 it can be seen that the retention times of the main peaks in the two figures are close, indicating the same component, verifying the main existence form of the product. The mass spectrometry data shows that the main product accounts for a significant proportion (ion count is much higher than other peaks), and the response value of the main peak in the chromatographic data is much higher than that of the secondary peak, further indicating that the purity of the main product is relatively high. Thus, it can be obtained that the spirobrassinin prepared by the present invention has a very high purity.

[0064] The physical and chemical properties of the S-(-)-Spirobrassinin prepared in this example are shown in Table 1.

[0065] Table 1 Physical and Chemical Properties of S-(-)-Spirobrassinin

[0066] Name Lipophilicity-hydrophilicity partition coefficient Hydrogen bond donor Hydrogen bond acceptor Rotatable bond S-(-)-Spirobrassinin 1.7 1 3 1

[0067] Example 2

[0068] Isatin and nitromethane were mixed at a molar ratio of 1:1.3, and 6 mol% of a chiral catalyst was added. The reaction was carried out in tetrahydrofuran at 0 °C for 11 hours. After the reaction solution was concentrated under reduced pressure, it was purified by silica gel column chromatography (eluent: ethyl acetate / n-hexane = 1:3) to obtain a yellow solid intermediate 1.

[0069] Intermediate 1 was dissolved in methanol, and 20 wt% Pd / C catalyst (the catalyst dosage was 1 mol%) was added. The reaction was stirred at 3 atm hydrogen pressure and 25 °C for 6 hours. The reaction solution was filtered through diatomaceous earth to remove the catalyst, and the filtrate was concentrated under reduced pressure to obtain a white solid intermediate 2.

[0070] Intermediate 2 was reacted with CS2 (1.3 equivalents) in a sodium hydroxide solution (pH 10) at 0 °C for 2 h, then methyl iodide (1.3 equivalents) was added, and the mixture was stirred at room temperature for 4 h. Then the reaction solution was extracted with dichloromethane, the organic phase was dried over anhydrous sodium sulfate and concentrated, and purified by recrystallization (ethanol / water) to obtain pale yellow crystal Intermediate 3.

[0071] Intermediate 3 was dissolved in dichloromethane, pyridine (2.2 equivalents) and MsCl (1.4 equivalents) were added, the reaction was first carried out at 0 °C for 1 h, then the temperature was raised to 30 °C and stirred for 10 h to complete the cyclization. The reaction solution was washed with dilute hydrochloric acid, the organic phase was dried and concentrated, and purified by silica gel column chromatography (eluent: dichloromethane / methanol = 20:1) to obtain spirobrassinin.

[0072] Performance test

[0073] The S-(-)-Spirobrassinin prepared in Example 1 was used in the form of a soil sealant. The weed selected was Echinochloa crusgalli. Using blank control and tribenuron-methyl as a comparison, both were used at 2 g per mu. The test results are shown in Figure 6 . From Figure 6 it can be seen that the roots of Echinochloa crusgalli seedlings were strongly inhibited by S-(-)-Spirobrassinin, only 0.4 cm, showing no difference from the positive control tribenuron-methyl.

[0074] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A spiro brassinolide, characterized in that, The structural formula of the spiro brassinolide is as follows:

2. The preparation method of the spirolactone brassinolide according to claim 1, characterized in that, It includes the following steps: S1. Mix isatin, nitromethane, a chiral catalyst and tetrahydrofuran, and carry out an asymmetric Henry reaction to obtain intermediate 1; S2. Mix intermediate 1, methanol and a palladium-carbon catalyst, and carry out a catalytic hydrogenation reduction reaction to obtain intermediate 2; S3. Mix intermediate 2, carbon disulfide, a sodium hydroxide solution and methyl iodide, and carry out an addition methylation reaction to obtain intermediate 3; S4. Mix intermediate 3, dichloromethane, pyridine and methanesulfonyl chloride, and carry out a substitution cyclization reaction to obtain spiro brassinolide.

3. The preparation method according to claim 2, characterized in that In step S1, the molar ratio of isatin to nitromethane is 1:1 - 1.5; the mass-volume ratio of the dosage of isatin to tetrahydrofuran is 1 g:5 - 15 mL; the dosage of the chiral catalyst is 1 - 10 mol%; The temperature of the asymmetric Henry reaction is 0 - 2 °C, and the time is 10 - 15 h.

4. The preparation method according to claim 3, characterized in that, In step S2, the mass-volume ratio of intermediate 1 to methanol is 1 g:8 - 15 mL; the dosage of the palladium-carbon catalyst is 1 - 10 mol%; The temperature of the catalytic hydrogenation reduction reaction is 20 - 30 °C, the time is 5 - 8 h, and the hydrogen pressure is 1 - 5 atm.

5. The preparation method according to claim 3 or 4, characterized in that, In step S3, intermediate 2, carbon disulfide and the sodium hydroxide solution first carry out an addition reaction, and the obtained reaction product carries out a methylation reaction with methyl iodide.

6. The preparation method according to claim 5, characterized in that, The molar ratio of intermediate 2 to sodium hydroxide is 1:1.5 - 2.5; The dosage of carbon disulfide is 1 - 2 equivalents, the pH value of the sodium hydroxide solution is 9 - 11; the temperature of the addition reaction is 0 - 2 °C, and the time is 1 - 3 h.

7. The preparation method according to claim 5, wherein The dosage of methyl iodide is 1 - 5 equivalents; the temperature of the methylation reaction is 20 - 30 °C, and the time is 3 - 5 h.

8. The preparation method according to claim 7, characterized in that, In step S4, the mass-volume ratio of intermediate 3 to dichloromethane is 1 g:8 - 12 mL; the dosage of pyridine is 1 - 3 equivalents, and the dosage of methanesulfonyl chloride is 1 - 1.5 equivalents.

9. The preparation method according to claim 5 or 8, characterized in that, In step S4, the substitution cyclization reaction is divided into two stages. The temperature of the first stage is 0 - 2 °C, and the time is 1 - 2 h; the temperature of the second stage is 20 - 30 °C, and the time is 10 - 15 h.

10. The application of the spiro brassinolide according to claim 1 in the preparation of herbicides.

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