Synthesis and application of indolinone lactone analogues with oxime ether linkage

Abstract

This invention relates to the synthesis and application of indole-3-lactone analogs with oxime ether linkages. The general formula for this class of compounds is shown in (I), where R1 is methyl, ethyl, n-propyl, n-butyl, n-pentyl, isopropyl, isobutyl, phenyl, or benzyl. Starting with indigo as a raw material, the product is obtained through nucleophilic substitution, Wolff-Kishner-Huang Minglong reduction reaction, and Williamson ether synthesis reaction. Using *Trichosanthes kirilowii* seeds (… O. aegyptiaca As a target for control, this series of compounds were applied to test seed germination activity. These compounds exhibited good seed germination activity and can be applied to the seed germination of the parasitic weed *Orobanche deserticola*, for the development of a "suicidal" herbicide for *Orobanche deserticola*. This invention also includes its use in combination with agriculturally acceptable adjuvants, synergists, or commercial herbicides to prevent diseases caused by parasitic weeds such as *Orobanche deserticola* or *Orobanche spp.*.

Description

Technical Field

[0001] This invention relates to the synthesis and application of indole lactone analogs with oxime ether linkages, specifically the synthesis of lactone analogs with an indole ketone skeleton having bridged oxime ether linkages and their application in agriculture for controlling parasitic weeds such as broomrape and strigolactone. Background Technology

[0002] Strigolactones (SLs) were initially discovered as germination promoters of the parasitic plant *Striga*, and their name derives from their role in stimulating *Striga* germination and their distinctive lactone ring structure. Following auxins, gibberellins, cytokinins, abscisic acid, gibberellins, and ethylene, they were identified as a novel plant hormone in 2008. Strigolactones mediate plant development, trigger symbiosis with arbuscular mycorrhizal fungi, and help plants acquire resistance to environmental stresses. They can also induce seed germination in parasitic plants, such as *Orobanche* in Europe or Asia and *Striga* in Africa. This class of plant hormones plays a crucial regulatory role in plant growth and development. Due to their important physiological and biochemical functions, the study of these compounds has received widespread attention from chemists and biologists worldwide.

[0003] The first compound capable of stimulating the germination of the parasitic weed *Striga asiatica*, (+)-Strigol, was extracted by Cook from cotton root exudates in 1966. Its approximate configuration was determined in 1972, and its absolute configuration was finally determined by X-ray diffraction in 1985. Over the next 30 years, scientists successively extracted strigolactones from the exudates of higher plants such as corn, sorghum, and cowpea, finding natural products that stimulate the germination of seeds of root parasitic plants. Configurational studies of these natural products revealed that strigolactones all contain one tricyclic lactone (ABC ring) and one monocyclic lactone (D ring) linked by an enol ether bond. This molecular diversity primarily stems from the complexity of groups in different forms or positions on the ABC ring, limiting the chemical synthesis of natural strigolactones. GR24 is a widely used synthetic analog of strigolactones, exhibiting similar biological activities to endogenous strigolactones. Strigolactones with an ABC ring system are called typical strigolactones, while those lacking typical A, B, or C rings are atypical strigolactones. Avenaol, heliolactone, zealactone, and lotuslactone, isolated from root exudates of wild oats, sunflowers, maize, and Japanese lotus, are germination promoters for root-parasitic weeds; they are atypical strigolactones with unique structures.

[0004] Currently, typical strigolactone analogs isolated are mainly divided into strigolactone alcohols and broomrolides. The main difference between these two types of compounds lies in their stereochemical configuration at the BC ring. Both types of root parasitic weeds have a wide variety of host plants and spread rapidly, causing serious damage to crops and cash crops. According to statistics, the economic losses caused by strigolactones in Africa alone have reached more than US$3 billion. Broomrolides are mainly distributed in subtropical or temperate regions, such as Asia, Oceania, and the Mediterranean. According to surveys, in my country, broomrolides are mainly distributed in the Northwest region, with the largest concentration in Xinjiang. The host plants are mainly higher plants such as cereals, wormwood, and melons. In Xinjiang, the parasitism of melons and watermelons by broomrolides can cause yield reductions of up to 70% in severe cases. Because the growth cycle of parasitic weeds coincides with that of the host plants, common herbicides such as glyphosate are not effective in controlling the spread of these weeds and may even damage the host plants.

[0005] The germination of *Striga asiatica* and *Broomrape thunbergii* seeds depends on strigolactone analogs secreted by their host plants. Therefore, by applying synthetic analogs of natural strigolactones, the seeds of *Striga asiatica* and *Broomrape thunbergii* can be stimulated to detach from their host plants and germinate prematurely, ultimately leading to their suicidal death due to lack of nutrients and water, thus achieving the goal of weed control.

[0006] Therefore, finding highly active, structurally simplified analogs, as well as ensuring storage and soil stability, are urgent problems to be solved. Based on the mechanism of action of these compounds, the D ring is essential for binding with the receptor protein to form a triplet. Currently, the modification of strigolactone analogs mainly focuses on two aspects: ABC ring structural modification, which plays a stabilizing role in the molecule and adapts to the cavity requirements of the receptor protein; and modification of the bridging bonds connected by the D ring, whose natural structure is an ether bond.

[0007] Chinese patent CN 114369087 B discloses the synthesis and application of a lactone analog (II) with an indole-2-one skeleton. The general structural formulas of these two types of compounds are as follows: Compounds of this type all exhibit good seed germination activity in *Orobanche deserticola*. This invention modifies the bridged olefinic ether bond, providing a novel synthesis and application of indole lactone analogs with oxime ether linkages. Summary of the Invention

[0008] The purpose of this invention is to provide a novel synthesis and application of indole-2-one lactone analogs with oxime ether linkages. It is based on indole-2-one skeleton lactone compounds, where the olefinic ether linkage is replaced with an oxime ether linkage. Using indigo as a starting material, a series of lactone analogs with an indole-2-one core structure containing oxime ether linkages are synthesized through a three-step reaction. The seed germination activity of these compounds in broomrape seeds was tested, and the results showed that these compounds have good seed germination activity, especially in the germination of broomrape seeds, making them promising seed germinators for parasitic weeds.

[0009] The structure of the indole-3-lactone analog with an oxime ether linkage provided by this invention is shown in (I):

[0010] Wherein: R1 represents the methyl to n-pentyl and aromatic ring or benzyl substituents that are substituted on the N atom.

[0011] Preferably, R1 is an aromatic ring consisting of a C1-C5 alkyl substituent and an alkoxy-substituted benzyl or substituted phenyl group on the N-axis of indole. Preferred substituents include methyl, ethyl, n-propyl, n-butyl, n-pentyl, isopropyl, isobutyl, phenyl, and benzyl.

[0012] The specific compound is: an N-alkyl-substituted or N-aryl-substituted 3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one, systematically named in English. N -alkyl or arylsubstituted-3-(((4-methyl-5-oxo-2,5-dihydrofuran-2-yl)oxy)imino)indolin-2-one, wherein the N-alkyl substituted, N-aryl substituted, or other substituents are within the range described above (as described in claim 2).

[0013] The analogues of the indole-2-one skeleton having an oxime ether (linking) bond provided by this invention are as follows:

[0014] N -Methyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -Ethyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -propyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N-Butyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -pentyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -Isopropyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -Isobutyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -Phenyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; N -benzyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one.

[0015] The method for synthesizing lactone analogs with an indole-2-one skeleton provided by this invention includes the following steps:

[0016] Synthetic Route 1: Synthesis of Compounds I1-I9

[0017]

[0018] Synthetic Route 2: Synthesis of the D-ring

[0019]

[0020] The lactone analogues of indole-2-one cores with oxime ether linkages described in this invention can be applied to eco-friendly herbicides and seed germination agents for parasitic weeds. These compounds exhibit a significant inducing effect on the seeds of parasitic weeds in Chinese agricultural and economic crops, thereby inducing the seeds of parasitic weeds to germinate before the host plant, subsequently detaching from the host plant and ultimately causing the parasitic weeds to die. The aforementioned agricultural host plants are mainly selected from corn, sorghum, millet, rice, potato, cassava, soybean, sunflower, sugar beet, sugarcane, tomato, cucumber, watermelon, cantaloupe, honeydew melon, papaya, and papaya. The aforementioned parasitic weeds are selected from *Striga asiatica* and *Orobanche deserticola*.

[0021] The compounds involved in this invention and their acceptable salts are used as herbicides in agriculture.

[0022] The compounds involved in this invention and their agriculturally acceptable salts can also be used as active ingredients in combination with other ingredients to form pesticide compositions for use as herbicides.

[0023] This invention provides the synthesis and bioactivity of a novel class of compounds that induce suicidal germination of parasitic plant seeds. These compounds stimulate the seeds of parasitic weeds such as *Striga asiatica* or *Orobanche deserticola*, which parasitize common crop seeds, to germinate before the host plant seeds, thus preventing parasitism and causing the weeds to die. (1) The linkage type of the compounds involved in this invention is different: Compared with patent CN 114369087 B, this invention changes the ether linkage of indole-2-one lactone compounds to an oxime ether linkage, which has higher germination activity against parasitic weed seeds than the indole-2-one compounds described in the above patent and has better development prospects; (2) The synthesis cost is different: Compared with patent CN201911023549.1, the synthesis steps of this invention are simplified to 2-3 steps, and the raw materials are cheap and readily available, which greatly reduces the synthesis cost of this type of compound.

[0024] This invention provides the synthesis and application of a novel class of lactone analogs with an indole-2-one skeleton containing an oxime ether linkage. Using indole-2,3-dione as a starting material, a series of lactone analogs with an indole-2-one core structure containing an oxime ether linkage were synthesized through a two-step reaction. The seed germination activity of these compounds in *Orobanche deserticola* was tested, and the results showed that these compounds have good seed germination activity, especially against *Orobanche deserticola* seeds, making them promising seed germination agents for parasitic weeds. This invention relates to the use of oxime ether linkage indole-2-one lactone analogs, particularly in the agricultural control of parasitic weeds *Striga asiatica* and *Orobanche deserticola*. This invention also includes their use in combination with agriculturally acceptable adjuvants, synergists, or commercial herbicides in the prevention of diseases caused by parasitic weeds such as *Striga asiatica* and *Striga asiatica*. Detailed Implementation

[0025] The present invention will be described in detail below with reference to embodiments, but these embodiments are not intended to limit the present invention. Experimental methods not specifically described in the embodiments are generally performed under conventional conditions and conditions described in the manual, or as recommended by the manufacturer. Unless otherwise specified, the equipment, materials, reagents, etc. used are commercially available. Example

[0026] Synthesis Route 1:

[0027] In a dry 100 mL round-bottom flask, indigo (4 mmol, 558.5 mg, 1.0 eq), K₂CO₃ (10 mmol, 1.38 g, 2.5 eq), and iodomethane (4.8 mmol, 681.3 mg, 1.2 eq) were dissolved in 20 mL of DMF solution. The side reaction system was then stirred at 50 °C for 8 hours. After the reaction was complete, the reaction mixture was poured into cold saturated brine (200 mL) and filtered to obtain an orange solid. The filter cake was washed 2-3 times successively with water (100 mL) and hexane (150 mL) to obtain an orange-yellow solid of 517.7 mg N-methylindole-2,3-dione.

[0028] In a dry 100 mL round-bottom flask, N-methylindole-2,3-dione (3.2 mmol, 515.4 mg) and hydroxylamine hydrochloride (4 mmol, 277.9 mg) obtained in the previous step were added sequentially, followed by 20 mL of water and stirred until homogeneous. The reaction mixture was heated to 110 °C for 1 hour, after which potassium acetate (4 mmol, 392.6 mg) was added to the reaction mixture. The temperature was then maintained for another hour. After the reaction was complete, the system was cooled to room temperature, filtered to remove insoluble matter, and the filter cake was washed with water. The filter cake was dried in a vacuum drying oven to obtain 544.6 mg of a bright yellow solid, N-methyl-3-hydroxyimino-indole-2-one, which was directly proceeded to the next step without further purification.

[0029] 176.06 mg of N-methyl-3-hydroxyimino-indole-2-one intermediate (1.0 mmol) was dissolved in 6 mL of anhydrous tetrahydrofuran at room temperature, followed by the addition of 276 mg of potassium carbonate (2 mmol). After stirring at room temperature for 10 minutes, 193.5 mg of D ring (1.1 mmol) was added to the reaction system, and the reaction was continued at room temperature for 12 hours. After the reaction was completed, the system was filtered with diatomaceous earth to remove insoluble matter. The resulting filtrate was dried, filtered under vacuum, and desolventized to obtain the crude product. The crude product was purified by column chromatography (PE:EA = 8:1-4:1, v / v) to obtain the desired product I-1-I-9, with a yield of 43.4%-59.4%.

[0030] Synthesis Route 2:

[0031] In a 250 mL round-bottom flask, 15.06 mL of glyoxal (40% wt aqueous solution) and 9 g of methylmalonic acid were added sequentially, followed by the addition of 90 mL of water and stirring to dissolve. After the reaction system changed from turbid to clear, 20 drops of concentrated sulfuric acid were added, and the temperature was raised to 105 °C. oThe reaction was carried out at C for 16 hours. After the reaction was completed, the reaction system was cooled to room temperature, extracted with ethyl acetate, and the organic phase was collected. The organic phase was washed successively with water and saturated brine, dried over anhydrous sodium sulfate, filtered, and dissolved to obtain the crude product. The crude product was purified by column chromatography (PE:EA = 2:1, v / v) to give 4.66 g of the orange-yellow intermediate 5-hydroxy-3-methylfuran-2-one.

[0032] 1.14 g of the intermediate obtained in the previous step was dissolved in 20 mL of anhydrous dichloromethane. The reaction system was placed in an ice bath, and 4.64 g of carbon tetrabromide and 3.67 g of triphenylphosphine were slowly added in portions. The system was then brought to room temperature and stirred for 2.5 h. After the reaction was completed, the reaction system was evaporated to dryness to obtain a crude product. The crude product was purified by column chromatography (PE:EA = 6:1, v / v) to obtain 914.89 mg of a yellow oily liquid, which was the product D ring.

[0033] Compounds I1-9 were synthesized according to the above route, and their physicochemical data are shown in Table 1.

[0034]

[0035]

[0036]

[0037]

[0038] The following are the structures of synthesized indole-2-one lactone analogs with oxime ether linkages (Ⅰ1-Ⅰ9):

[0039]

[0040] Example 2

[0041] The germination activity of compounds I1-I9 in broomrape melon seeds was tested using the following method:

[0042] Take a disposable plastic petri dish with a diameter of 9cm. Place a sheet of filter paper at the bottom and moisten it with sterile distilled water. Then, cover the dish with small filter paper pieces with a diameter of 5mm. Evenly sprinkle the quail seeds onto the small filter paper pieces, with approximately 15-20 seeds on each piece. Seal the petri dish with sealing film and incubate at 25°C. o Pre-culture the seeds in a C-type seed culture incubator for 3 days. Take a 7cm diameter filter paper disc, place it in a 9cm plastic petri dish, and add 1mL of the test compound solution (1% acetone as solvent). Then, place small filter paper discs of the pre-cultured seeds on top of the dish (n = 4), and incubate for 23-25 ​​minutes. oSeeds were cultured in a sealed, dark incubator for 7 days. After 7 days, seed germination was observed under a microscope, and the germination rate was calculated. Each concentration of compound was tested in triplicate, with four sets of experiments per concentration. The mean and standard deviation were calculated, and the EC50 of the compounds was calculated using SPSS 19.0. 50 Values. The calculation results are shown in Table 3.

[0043] .

Claims

1. Application of a lactone analog with an indole-2-one core structure having an oxime ether linkage in inducing suicidal germination of parasitic weed seeds in farmland; The parasitic weed is *Striga asiatica* or *Orobanche deserticola*; the lactone analog is one of the following compounds: I-1: N-methyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-2: N-ethyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-3: N-n-propyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-4: N-n-butyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-6: N-Isopropyl-3-(((4'-Methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-7: N-Isobutyl-3-(((4'-Methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one; I-8: N-benzyl-3-(((4'-methyl-5'-oxo-2',5'-dihydrofuran-2'-yl)oxy)imino)indol-2-one.

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