Synthetic method of isoxazoline anti-parasitic drug lotirasodium

Abstract

The invention relates to the field of chemistry or medicinal chemistry, in particular to a synthesis method of isoxazoline anti-parasitic drug lotirasodium. The synthesis method comprises the following steps: firstly, synthesizing an intermediate 1 (1, 2, 3-trichloro-5-(1-trifluoromethyl-vinyl) benzene); then synthesizing an intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxime); the preparation method comprises the following steps: carrying out a 1, 3 dipolar cycloaddition reaction on an intermediate 1 and an intermediate 2 in sequence to obtain an intermediate 3, carrying out a Grignard reaction to obtain racemic acid, and finally carrying out chemical resolution and amide condensation in sequence to obtain lotirasodium. According to the novel synthesis method of the isoxazoline anti-parasitic drug lotirazine, wittig reaction is adopted for the first time to obtain the intermediate 1, operation is simpler and more convenient, and reaction conditions are mild. Besides, the synthesis method of the intermediate 2 is improved, so that the reaction conditions are milder, the operation is simpler, the cost is greatly reduced on the basis of reported reaction conditions, and the method is suitable for industrialization.

Description

Technical Field

[0001] The present invention relates to the field of chemistry or medicinal chemistry, and particularly relates to a method for synthesizing lotilaner, an isoxazoline anti-parasitic drug. Background Art

[0002] Lotilaner is an isoxazoline anti-ectoparasitic drug. It was developed by Eli Lilly and Company in 2017. In December 2019, the FDA approved its listing. It is mainly used for the treatment of tick and flea infections in dogs and cats. Its chemical name is: 5-[5-(3,4,5-trichlorophenyl)-5-trifluoromethyl-4,5-dihydro-isoxazol-3-yl]-3-methyl-thiophene-2-carboxylic acid-[2,2,2-trifluoro-ethyl-carbamoyl)-methyl]-amide. The biologically active structure of lotilaner is the S-enantiomer. In the reports so far, the IC50 value of lotilaner for the Drosophila γ-aminobutyric acid receptor is 23.84 nM. It is the most effective oral isoxazoline anti-tick agent for cats, with an oral bioavailability of almost 100%, a half-life of about 33 days, and better safety than traditional in vitro anti-parasitic drugs.

[0003] The mechanism of action of lotilaner is similar to that of other isoxazoline drugs. Isoxazoline drugs play a role in preventing and killing by inhibiting the γ-aminobutyric acid-gated chloride channel (GABACls) and the glutamate-gated chloride channel (GluCls). By binding to the GABA receptor and the Glu receptor, the chloride channel is closed, causing the cells of the parasite to be overly excited, thereby killing the parasite.

[0004] The main key points of the existing synthesis methods of lotilaner lie in the construction of the isoxazoline ring, the Grignard reaction, and the amide condensation. Among them, the main innovation lies in the construction of the isoxazoline ring. The main existing methods for synthesizing lotilaner include the following several:

[0005] Route 1: As Figure 1 shown, Patent WO 2014 / 090918 reported that 2-bromo-3-methyl-5-acetylthiophene (Compound 2) undergoes an aldol condensation reaction with trifluoro-3,4,5-trichlorobenzophenone (Compound 1) to obtain Compound 3, which is dehydrated with thionyl chloride to obtain Compound 4, cyclized with hydroxylamine hydrochloride to obtain Compound 5, undergoes a Grignard reaction to obtain Compound 6, and then is resolved with the resolving agent (R)-1-(4-methylphenyl)ethylamine to obtain the S-type Compound 7. Finally, it undergoes chlorination and condensation reactions to obtain Lotilaner (Compound 9).

[0006] Route 2: As Figure 2As shown in Patent CN115504971A, 2-acetyl-4-methylthiophene and 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone are used as starting materials. Through aldol condensation and dehydration with thionyl chloride, intermediate I is obtained. Then, it is condensed with hydroxylamine hydrochloride to obtain intermediate II. Intermediate II is prepared into intermediate III through the Vilsmeier reaction, and then lotilaner is prepared through one-pot oxidation and amide condensation.

[0007] Route 3: As Figure 3 shown, Patent CN117800960A reports a method for preparing lotilaner by using 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone and 2-acetyl-5-bromo-4-methylthiophene as starting materials, through condensation dehydration, cyclization, Grignard reaction, resolution, and finally condensation reaction with 2-amino-N-(2,2,2-trifluoroethyl)acetamide.

[0008] Route 4: As Figure 4 shown, Patent CN109879826A reports a method for preparing lotilaner by using 5-formyl-3-methylthiophene-2-carboxylic acid as a starting compound, through hydroxylamine oximation and amide condensation to obtain intermediate 2, and then through NCS cyclization.

[0009] Route 5: As Figure 5 shown, Patent CN117447443A reports a method for preparing lotilaner (Formula b) by using 5-acetyl-3-methylthiophene-2-carboxylic acid, 2-amino-trifluoroethyl-acetamide, and 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone through one-pot method.

[0010] However, in the above synthetic methods of lotilaner, the overall operation is relatively complex and the preparation cost is relatively high. Summary of the Invention

[0011] The main object of the present invention is to provide a synthetic method of an isoxazoline anti-parasitic drug lotilaner, aiming to improve the technical problems of relatively complex operation process and relatively high preparation cost in the existing synthetic methods of lotilaner.

[0012] To achieve the above object, the present invention provides a synthetic method of an isoxazoline anti-parasitic drug lotilaner. First, intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene) is synthesized; then intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime) is synthesized; then, the 1,3-dipolar cycloaddition reaction of intermediate 1 and intermediate 2 is carried out to obtain intermediate 3, and then the Grignard reaction is carried out to obtain the racemic acid. Finally, lotilaner is obtained through chemical resolution and amide condensation in sequence. The synthetic route is as follows:

[0013]

[0014] Preferably, it includes the following steps:

[0015] (1) Synthesis of Intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethylvinyl)benzene):

[0016] Add a base to a suspension of the Wittig reagent in an anhydrous solvent, keep the reaction in an ice bath at -5 to 0 °C for 0.5 - 2 h, then add 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone of formula (I) thereto, warm up to room temperature and react for 2 - 6 h. After the reaction is completed, quench with water, extract and separate with ethyl acetate, wash, concentrate under reduced pressure, separate by column chromatography, and after concentration and drying under reduced pressure, obtain Intermediate 1 of formula (II);

[0017]

[0018] (2) Synthesis of Intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime):

[0019] Under nitrogen protection, cool to -78 °C with a dry ice-acetone bath, add n-butyllithium to a suspension of diisopropylamine in an anhydrous solvent, keep warm for 15 - 45 min, then add an anhydrous solvent solution of 2-bromo-3-methylthiophene of formula (III) to the system, continue to keep warm and react at -78 °C for 0.5 - 1.5 h, then add methyl formate or N,N-dimethylformamide to the system, keep warm and react for 5 - 30 min. After the reaction is completed, quench the reaction with a saturated ammonium chloride solution or 1.0 - 2.0 M hydrochloric acid solution, extract and separate with ethyl acetate, wash, concentrate under reduced pressure with a rotary evaporator (wherein, the preferred temperature for concentration under reduced pressure is 35 °C), use a tetrahydrofuran solution containing 10% - 50% water as the solvent to dissolve the above product. After the system is stirred evenly, add hydroxylamine hydrochloride and sodium acetate to the system, keep warm and react at 25 - 55 °C for 0.5 - 2 h. After the reaction is completed, add water to the system to cool to room temperature to terminate the reaction, extract the aqueous phase with ethyl acetate, wash, dry with anhydrous sodium sulfate, concentrate under reduced pressure, recrystallize, filter, and after drying under reduced pressure, obtain Intermediate 2 of formula (IV);

[0020]

[0021] (3) 1,3-Dipolar cycloaddition reaction:

[0022] Dissolve Intermediate 1 of formula (II) and Intermediate 2 of formula (IV) with a solvent, then add water, potassium peroxymonosulfate and a halide salt, react at room temperature for 2 - 8 h. After the reaction is completed, wash with water, extract, dry with anhydrous sodium sulfate, concentrate under reduced pressure, purify by column chromatography, recrystallize, filter, and after drying under reduced pressure, obtain Intermediate 3 of the cyclization product of formula (V);

[0023]

[0024] (4) Grignard reaction:

[0025] After nitrogen replacement, an anhydrous solvent is added to Intermediate 3 of Formula (V), and a Grignard reagent is added at room temperature. The reaction is carried out under heat preservation, carbon dioxide gas is introduced, and the reaction is monitored by HPLC. After completion, water is added, and the pH value is adjusted to 1-3 with an acid. It is left to stand, the aqueous layer is separated, the organic layer is concentrated under reduced pressure to dryness, n-hexane is added, the temperature is lowered for crystallization, suction filtration is carried out, and drying is carried out to obtain the racemic acid of Formula (VI);

[0026]

[0027] (5) Chemical resolution:

[0028] In an organic solvent, the racemic acid of Formula (VI) and a resolving agent are added, the temperature is raised to reflux, the temperature is lowered for crystallization, and drying is carried out to obtain the S-type resolving salt;

[0029] (6) Amide condensation:

[0030] In a mixed system of water and one solvent selected from dichloromethane, ethyl acetate, N,N-dimethylformamide, and toluene in a ratio of 10%-80%, the S-type resolving salt obtained in step (5) is added, the pH is adjusted to acidic with an acid, the temperature is raised to reflux and stirred for 0.5-1.5 h, then extraction and liquid separation are carried out, anhydrous sodium sulfate drying is carried out, the organic layer is concentrated under reduced pressure, vacuum drying is carried out for 4-12 h, then it is dissolved in dichloromethane or N,N-dimethylformamide, a condensing agent, 2-amino-N-(2,2,2-trifluoroethyl)acetamide hydrochloride and a catalyst are added, after reaction at room temperature, extraction and liquid separation are carried out, the organic layer is washed, dried with anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized, suction filtered, and vacuum dried at 30-80 °C for 6 hours to obtain lotilaner of Formula (VII);

[0031]

[0032] Preferably, in steps (1), (2) and (4), the anhydrous solvent is at least one of methanol, dichloromethane, ethanol, N,N-dimethylformamide, ether and tetrahydrofuran.

[0033] Preferably, in step (1), the Wittig reagent is one of methyltriphenylphosphonium chloride, methyltriphenylphosphonium bromide, and methyltriphenylphosphonium iodide; the base is one of sodium hydride, calcium hydride, n-butyllithium or potassium tert-butoxide.

[0034] Preferably, in step (3), the solvent is one of tetrahydrofuran, acetonitrile, dichloromethane, ethyl acetate, chloroform, ethanol or methanol.

[0035] Preferably, in step (3), the halide salt is one of potassium chloride, sodium chloride, ammonium chloride, potassium bromide, sodium bromide, potassium iodide or sodium iodide.

[0036] Preferably, in step (4), the Grignard reagent is one of methylmagnesium chloride, ethylmagnesium chloride, methylmagnesium bromide, ethylmagnesium bromide, isopropylmagnesium chloride or isopropylmagnesium bromide.

[0037] Preferably, in step (4) or step (6), the acid is one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, sulfurous acid, phosphoric acid, pyruvic acid, carbonic acid, citric acid, hydrofluoric acid, malic acid, formic acid, acrylic acid, acetic acid, propionic acid or boric acid.

[0038] Preferably, in step (5), the resolving agent is one of (R)-1-(4-methylphenyl)ethylamine, (R)-1-(4-bromophenyl)ethylamine, (S)-1-(4-nitrophenyl)ethylamine hydrochloride, glucosamine, (R)-p-nitrobenzylamine, (S)-1-(4-bromophenyl)ethylamine.

[0039] Preferably, in step (6), the condensing agent is one of EDCI, HATU, HBTU, DCC, and the catalyst is 4-dimethylaminopyridine.

[0040] Compared with the prior art, the synthesis method of the isoxazoline anti-parasitic drug lotilaner in the present invention has the following beneficial effects:

[0041] 1. The present invention proposes a new synthesis method of the isoxazoline anti-parasitic drug lotilaner, and for the first time uses the Wittig reaction to obtain intermediate 1. This method has not been reported in the literature. Compared with the reported synthesis methods of intermediate 1, the reaction reagents used in this method are stable, easy to obtain, and have lower costs. Moreover, the one-pot reaction makes the operation more convenient and the reaction conditions milder.

[0042] 2. In addition, the present invention has also improved the synthesis method of intermediate 2, making the reaction conditions milder and the operation simpler. Moreover, on the basis of the reported reaction conditions, the operation steps are simplified, the reaction time is reduced, and the raw material and time costs are reduced, which is suitable for industrialization.

[0043] 3. The present invention creatively uses the water-soluble oxidant - potassium peroxymonosulfate to carry out the 1,3-dipolar cycloaddition reaction in water. The reaction conditions of the 1,3-dipolar cycloaddition method are mild, the post-treatment is simple, and because the used oxide is a salt, the cost is lower. It avoids the use of more organic reagents and causes less environmental pollution, being more economical and environmentally friendly.

[0044] 4. In the synthesis method of lotilaner in the present invention, when the preferred amide condensing agent used is EDCI, compared with other condensing agents, this reagent has a lower cost, and the by-products generated during the reaction are water-soluble products, which are easy to remove. The reaction operation is simple, the yield is high, and the loss is less. Description of the Drawings

[0045] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other relevant accompanying drawings can also be obtained based on these drawings.

[0046] Figure 1 It is the synthetic route diagram of lotilaner for Route 1 in the traditional synthetic method;

[0047] Figure 2 It is the synthetic route diagram of lotilaner for Route 2 in the traditional synthetic method;

[0048] Figure 3 It is the synthetic route diagram of lotilaner for Route 3 in the traditional synthetic method;

[0049] Figure 4 It is the synthetic route diagram of lotilaner for Route 4 in the traditional synthetic method;

[0050] Figure 5 It is the synthetic route diagram of lotilaner for Route 5 in the traditional synthetic method;

[0051] Figure 6 It is the 1H NMR spectrum of Intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethylvinyl)benzene) of this solution;

[0052] Figure 7 It is the 13C NMR spectrum of Intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethylvinyl)benzene) of this solution;

[0053] Figure 8 It is the 1H NMR spectrum of Intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime) of this solution;

[0054] Figure 9 It is the 13C NMR spectrum of Intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime) of this solution;

[0055] Figure 10 It is the 1H NMR spectrum of Intermediate 3 (3-(5-bromo-4-methylthiophen-2-yl)-5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazole) of this solution;

[0056] Figure 11 It is the 1H NMR spectrum of Intermediate 3 (3-(5-bromo-4-methylthiophen-2-yl)-5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazole) of this solution;

[0057] Figure 12 1H NMR spectrum of the racemic acid (3-methyl-5-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)thiophene-2-carboxylic acid) of this solution

[0058] Figure 13 13C NMR spectrum of the racemic acid (3-methyl-5-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)thiophene-2-carboxylic acid) of this solution

[0059] Figure 14 1H NMR spectrum of lotilaner of this solution

[0060] Figure 15 13C NMR spectrum of lotilaner of this solution

[0061] Figure 16 Infrared spectrum of lotilaner of this solution

[0062] Figure 17 High resolution mass spectrum of lotilaner of this solution

[0063] Figure 18 HPLC chromatogram of lotilaner of this solution

[0064] The realization, functional features and advantages of the purpose of this application will be further described with reference to the embodiments and the accompanying drawings. Detailed implementation manners

[0065] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0066] In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions appears to be contradictory or unable to be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the protection scope required by the present invention.

[0067] A synthetic method of the isoxazoline anti-parasitic drug lotilaner, which first synthesizes intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene); then synthesizes intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime); then successively performs a 1,3-dipolar cycloaddition reaction of intermediate 1 and intermediate 2 to obtain intermediate 3, then performs a Grignard reaction to obtain a racemic acid, and finally obtains lotilaner through chemical resolution and amide condensation in sequence. The synthetic route is as follows:

[0068]

[0069] Furthermore, it includes the following steps:

[0070] (1) Synthesis of intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene):

[0071] Suspend the Wittig reagent in an anhydrous solvent to obtain a suspension of the Wittig reagent in the anhydrous solvent. Assemble the reaction device according to the requirements of anhydrous reaction. Add the base to the suspension of the Wittig reagent in the anhydrous solvent. After ice-bath insulation for 0.5 - 2 h, then add 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone of formula (I) to the system, heat up to room temperature and react for 2 - 6 h. After the reaction is completed, quench with water, extract and separate with ethyl acetate, wash, concentrate under reduced pressure, purify by column chromatography, and dry by concentration under reduced pressure to obtain intermediate 1 of formula (II);

[0072]

[0073] (2) Synthesis of intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime):

[0074] Under a dry ice - acetone bath, in a dry flask under nitrogen protection, drop a certain amount of n-butyllithium into a suspension of diisopropylamine in an anhydrous solvent. After maintaining the temperature for 15 - 45 min, drop a solution of 2-bromo-3-methylthiophene in an anhydrous solvent of formula (III) into the system. Continue to maintain the temperature for 0.5 - 1.5 h, then drop methyl formate or N,N-dimethylformamide into the system, and maintain the temperature for 5 - 30 min. After the reaction is completed, quench the reaction with saturated ammonium chloride solution or 1.0 - 2.0 M hydrochloric acid solution. Extract and separate with ethyl acetate, wash, concentrate under reduced pressure, and without treatment, use a tetrahydrofuran solution containing 10% - 50% water as the solvent to dissolve the above product. After the system is stirred evenly, add hydroxylamine hydrochloride and sodium acetate to the system, maintain the temperature at 25 - 55 °C for 0.5 - 2 h. After the reaction is completed, add water to the system to lower the temperature to room temperature to terminate the reaction. Extract the aqueous phase with ethyl acetate, wash, dry with anhydrous sodium sulfate, concentrate under reduced pressure, recrystallize, filter, and dry under reduced pressure to obtain intermediate 2 of formula (IV);

[0075]

[0076] (3) 1,3-Dipolar cycloaddition reaction:

[0077] In a flask, the intermediate 1 of formula (II) and the intermediate 2 of formula (IV) are dissolved in a solvent selected from tetrahydrofuran, acetonitrile, dichloromethane, ethyl acetate, chloroform, and methanol. Then, water, a potassium hydrogen persulfate, and a halide salt selected from potassium chloride, sodium chloride, ammonium chloride, potassium bromide, sodium bromide, potassium iodide, and sodium iodide are added to the flask. The reaction is carried out at room temperature for 2 - 8 h. After the reaction is completed, it is washed with water, extracted, dried over anhydrous sodium sulfate, concentrated under reduced pressure, purified by column chromatography, recrystallized, filtered, and dried under reduced pressure to obtain the intermediate 3 of the cyclized product of formula (V).

[0078]

[0079] (4) Grignard reaction:

[0080] After purging with nitrogen, an anhydrous solvent is added to the intermediate 3 of formula (V) obtained in step (3). At room temperature, a Grignard reagent is added, and the reaction is kept warm. Carbon dioxide gas is introduced. After the reaction is monitored by HPLC and completed, water is added, and the pH value is adjusted to 1 - 3 with an acid. It is left to stand, and the aqueous layer is separated. The organic layer is concentrated to dryness under reduced pressure, n - hexane is added, the temperature is lowered for crystallization, suction filtration is carried out, and drying is performed to obtain the racemic acid of formula (VI).

[0081]

[0082] (5) Chemical resolution:

[0083] In an organic solvent, the racemic acid of formula (VI) and a resolving agent are added. The temperature is raised to reflux, then lowered for crystallization, and drying is carried out to obtain the S - type resolved salt.

[0084] (6) Amide condensation:

[0085] In a mixed system of water and a solvent selected from dichloromethane, ethyl acetate, N,N - dimethylformamide, and toluene in a proportion of 10% - 80%, the S - type resolved salt obtained in step (5) is added. The pH is adjusted to acidic with an acid. After heating to reflux and stirring for 0.5 - 1.5 h, extraction and liquid separation are carried out, followed by drying over anhydrous sodium sulfate. The organic layer is concentrated under reduced pressure and vacuum - dried for 4 - 12 h. Then, it is dissolved in dichloromethane or N,N - dimethylformamide, a condensing agent, 2 - amino - N - (2,2,2 - trifluoroethyl)acetamide hydrochloride, and a catalyst are added. After reacting at room temperature, extraction and liquid separation are carried out. The organic layer is washed, dried over anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized, suction - filtered, and vacuum - dried at 30 - 80 °C for 6 h to obtain lotilaner of formula (VII).

[0086]

[0087] Among them, the anhydrous solvents in step (1), step (2) and step (4) are at least one of methanol, dichloromethane, ethanol, N, N-dimethylformamide, diethyl ether and tetrahydrofuran. The Wittig reagent in step (1) is one of methyltriphenylphosphonium chloride, methyltriphenylphosphonium bromide, and methyltriphenylphosphonium iodide; the base is one of sodium hydride, calcium hydride, n-butyllithium or potassium tert-butoxide. In step (4), the Grignard reagent is one of methylmagnesium chloride, ethylmagnesium chloride, methylmagnesium bromide, ethylmagnesium bromide, isopropylmagnesium chloride or isopropylmagnesium bromide. The acid in step (4) or step (6) is one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, sulfurous acid, phosphoric acid, pyruvic acid, carbonic acid, citric acid, hydrofluoric acid, malic acid, formic acid, acrylic acid, acetic acid, propionic acid or boric acid. The resolving agent in step (5) is one of (R)-1-(4-methylphenyl)ethylamine, (R)-1-(4-bromophenyl)ethylamine, (S)-1-(4-nitrophenyl)ethylamine hydrochloride, glucosamine, (R)-p-nitrophenylethylamine, (S)-1-(4-bromophenyl)ethylamine. The condensing agent in step (6) is one of EDCI, HATU, HBTU, DCC, and the catalyst is 4-dimethylaminopyridine.

[0088] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0089] Example 1 Synthesis of Intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene)

[0090] The following schemes selected different Wittig reagents and bases to participate in the reaction. After screening, Scheme III was the optimal one.

[0091] Scheme I: Under a nitrogen atmosphere, 8.73 g (0.021 mol) of methyltriphenylphosphonium iodide was put into a dried reaction flask that had been treated for water removal, dissolved in 40 ml of anhydrous tetrahydrofuran, and 2.83 g (0.025 mol) of potassium tert-butoxide was added under ice bath conditions. After maintaining the reaction for 0.5 h, the temperature was raised to room temperature. 5.00 g (0.018 mol) of 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone was added to the system, and the reaction was carried out for 4 h. The reaction was monitored by TLC and quenched with water after completion. After extraction and separation with ethyl acetate, washing, the organic phase was concentrated under reduced pressure, and flash column chromatography was carried out with petroleum ether or n-hexane, and dried under reduced pressure to obtain 3.47 g of Intermediate 1 liquid, with a yield of 69.9% and an HPLC purity of 99.8%.

[0092] Scheme 2: Under a nitrogen atmosphere, 8.61 g (0.024 mol) of methyltriphenylphosphonium bromide was put into a dried reaction flask that had been treated for water removal, dissolved in 40 mL of anhydrous tetrahydrofuran, 3.14 g (0.028 mol) of potassium tert-butoxide was added under ice bath conditions, after maintaining the temperature for reaction for 0.5 h, the temperature was raised to room temperature, 5.00 g (0.018 mol) of 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone was added to the system, reacted for 4 h, quenched with water after monitoring the reaction by TLC, extracted and separated with ethyl acetate, washed, the organic phase was concentrated under reduced pressure, and purified by flash column chromatography with petroleum ether or n-hexane, and dried under reduced pressure to obtain 3.47 g of intermediate 1 as a liquid, with a yield of 69.9% and an HPLC purity of 99.8%.

[0093] Scheme 3: Under a nitrogen atmosphere, 8.73 g (0.021 mol) of methyltriphenylphosphonium iodide was put into a dried reaction flask that had been treated for water removal, dissolved in 40 mL of anhydrous tetrahydrofuran, 13.5 mL of 2.0 M n-butyllithium solution was added dropwise to the system under a dry ice-acetone bath, after maintaining the temperature for reaction for 0.5 h, the temperature was raised to room temperature, 5.00 g (0.018 mol) of 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone was added to the system, reacted for 3 h, quenched with water after monitoring the reaction by TLC, extracted and separated with ethyl acetate, washed, the organic phase was concentrated under reduced pressure, and purified by flash column chromatography with petroleum ether or n-hexane, and dried under reduced pressure to obtain 3.96 g of intermediate 1 as a liquid, with a yield of 79.9% and an HPLC purity of 99.8%. Among them, the base and Wittig reagent used in Scheme 3 are the most preferred, so the yield of this scheme is higher.

[0094] Scheme 4: Under a nitrogen atmosphere, 8.73 g (0.021 mol) of methyltriphenylphosphonium iodide was put into a dried reaction flask that had been treated for water removal, dissolved in 40 mL of anhydrous tetrahydrofuran, 0.6 g (0.025 mol) of sodium hydride was added under ice bath conditions, after maintaining the temperature for reaction for 1 h, the temperature was raised to room temperature, 5.00 g (0.018 mol) of 2,2,2-trifluoro-1-(3,4,5-trichlorophenyl)ethanone was added to the system, reacted for 6 h, quenched with water after monitoring the reaction by TLC, extracted and separated with ethyl acetate, washed, the organic phase was concentrated under reduced pressure, and purified by flash column chromatography with petroleum ether or n-hexane, and dried under reduced pressure to obtain 3.16 g of intermediate 1 as a liquid, with a yield of 63.7% and an HPLC purity of 99.8%.

[0095] Nuclear magnetic resonance results: 1 HNMR(600 MHz, DMSO-d6) δ: 7.74 (s, 2H), 6.36 (t, 1H), 6.27 (t, 1H).

[0096] 13CNMR(151MHz, DMSO-d6) δ: 134.22, 134.02, 134.01, 133.82, 133.75, 133.62, 131.38, 128.13, 126.39, 126.36, 126.32, 126.28, 125.96, 124.14, 122.33, 120.51.

[0097] HR-MS(ESI) Calcd for C 9 H 4 Cl 3 F 3 (M + H + ): 274.9331; Found: 274.9543.

[0098] Synthesis of Intermediate 2 (5-Bromo-4-methyl-2-thiophenecarboxaldehyde oxime) in Example 2

[0099] Under a dry ice - acetone bath and in a nitrogen atmosphere, 13.72 g (0.14 mol) of diisopropylamine and 100 mL of tetrahydrofuran were added to a dried flask that had been treated for water removal. Then, 59 mL of 2.5 M n - butyllithium was added dropwise. After maintaining the temperature for 30 min, a solution of 20 g (0.11 mol) of 2 - bromo - 3 - methylthiophene in tetrahydrofuran (20 mL) was added dropwise to the system. After continuing to maintain the temperature and react for 1 h, 8.15 g (0.14 mol) of methyl formate was added dropwise to the system, and the reaction was maintained for 30 min. After the reaction was completed, the reaction was quenched with saturated ammonium chloride solution. After extraction and separation with ethyl acetate, washing, and concentration under reduced pressure, without further treatment, the above - mentioned product was dissolved using a solvent of tetrahydrofuran and water with a volume ratio of 4:1. After the system was stirred evenly, 9.76 g (0.14 mol) of hydroxylamine hydrochloride and 14.40 g (0.18 mol) of sodium acetate were added to the system. The reaction was maintained at 55 °C for 2 h. After the reaction was completed, a certain amount of water was added to the system, and the aqueous phase was extracted with ethyl acetate. The organic phase was washed, dried over anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized from petroleum ether, filtered, and dried under reduced pressure to obtain 21.83 g of solid Intermediate 2, with a yield of 90.2% and an HPLC purity of 99.6%.

[0100] Nuclear magnetic resonance results: 1 HNMR(600MHz, DMSO - d6) δ: 12.07(d, J = 12.0, 1H), 7.76(d, J = 1.8, 1H), 7.26(d, J = 13.8, 1H), 2.16(s, 3H).

[0101] 13CNMR(151 MHz, DMSO-d6) δ: 140.08, 140.02, 136.55, 133.94, 132.52, 130.87, 115.48, 15.04, 13.43.

[0102] HR-MS (ESI) Calcd for C 6 H 6 BrNOS (M + H + ): 219.9353; Found: 219.9627. Synthesis of Intermediate 3 (3-(5-Bromo-4-methylthiophen-2-yl)-5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazole) in Example 3

[0103] Scheme 1: Dissolve 33.06 g (0.12 mol) of Intermediate 1 and 22 g (0.1 mol) of Intermediate 2 in 120 mL of acetonitrile in a flask. Add 40 mL of water, 109.65 g of potassium peroxymonosulfate and a catalytic amount of potassium chloride to the flask. React at room temperature for 4 hours. After the reaction is completed, wash with water, extract, dry over anhydrous sodium sulfate, concentrate under reduced pressure, perform column chromatography on petroleum ether, recrystallize with water and ethanol, filter, and dry under reduced pressure to obtain 36.57 g of the cyclized product Intermediate 3 as a solid, with a yield of 74.1% and an HPLC purity of 99.4%.

[0104] Scheme 2: Dissolve 33.06 g (0.12 mol) of Intermediate 1 and 22 g (0.1 mol) of Intermediate 2 in 120 mL of acetonitrile in a flask. Add 40 mL of water, 109.65 g of potassium peroxymonosulfate and a catalytic amount of potassium iodide to the flask. React at room temperature for 4 hours. After the reaction is completed, wash with water, extract, dry over anhydrous sodium sulfate, concentrate under reduced pressure, perform column chromatography on petroleum ether, recrystallize with water and ethanol, filter, and dry under reduced pressure to obtain 35.49 g of the cyclized product Intermediate 3 as a solid, with a yield of 71.9% and an HPLC purity of 99.4%.

[0105] Nuclear magnetic resonance results: 1 HNMR (600 MHz, DMSO-d6) δ: 7.80 (s, 2H), 7.31

[0106] (s, 1H), 4.36 - 4.26 (dd, J = 42.0, 18.0 Hz, 2H, C-CH 2 -C=N), 2.17 (s, 3H).

[0107] 13CNMR (151 MHz, DMSO-d6) δ: 153.56, 138.66, 136.18, 134.18, 134.11, 132.21, 128.44, 127.99, 124.97, 103.09, 113.94, 87.09, 86.89, 43.39, 15.24.

[0108] HR-MS (ESI) Calcd for C 15 H 8 BrCl 3 F 3 NOS (M + H + ): 491.8528; Found: 491.8966.

[0109] Synthesis of racemic acid (3-methyl-5-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)thiophene-2-carboxylic acid) in Example 4

[0110] Dissolve 20 grams (0.04 mol) of Intermediate 3 in anhydrous tetrahydrofuran and add it to a three-necked flask that has been treated to remove water. Dropwise add 30 mL of 2.0 M ethylmagnesium chloride at room temperature. After maintaining the temperature for 0.5 h, introduce carbon dioxide gas and maintain the temperature for another 0.5 h. Monitor the reaction by LC-MS. After the reaction is complete, add water, adjust the pH value to 1 - 3 with 1.0 M acid, let it stand, separate the aqueous layer, concentrate the organic layer under reduced pressure to dryness, add n-hexane, cool to crystallize, filter by suction, and dry to obtain 17.62 grams of racemic acid solid, with a yield of 96.0% and an HPLC purity of 99.6%.

[0111] Results of nuclear magnetic resonance: 1 HNMR (600 MHz, DMSO-d6) δ: 13.39 (s, 1H), 7.82

[0112] (s, 2H), 7.40 (s, 1H), 4.41 - 4.31 (dd, J = 42.0, 18.0 Hz, 2H, C-CH 2 -C=N), 2.48 (s, 3H).

[0113] 13 CNMR (151 MHz, DMSO-d6) δ: 163.54, 153.92, 145.19, 136.14, 135.94, 134.12, 132.23, 131.46, 131.13, 127.99, 126.83, 124.95, 123.06, 121.18, 87.57, 87.37, 87.17, 86.97, 43.52, 15.86.

[0114] HR-MS(ES I)Calcd for C 16 H 9 Cl 3 F 3 NO 3 S(M+Na + ):479.9362;

[0115] Found:479.9792。

[0116] Resolution of racemic acid (3-methyl-5-(5-(3,4,5-trichlorophenyl)-5-(trifluoromethyl)-4,5-dihydroisoxazol-3-yl)thiophene-2-carboxylic acid) in Example 5

[0117] Charge 30 g (0.065 mol) of racemic acid, 13.5 g (0.0975 mol) of (R)-p-nitrobenzylamine, 490 mL of acetonitrile, 110 mL of n-butanol, and 30 g of water into a reaction flask. Start stirring, heat up to 81 °C for reflux, and keep refluxing for 0.5 h. Cool down for crystallization, cool down to 25 °C, filter by suction, and obtain 17.11 g of off-white resolution salt solid after drying. The yield is 41.3%. The purity detected by HPLC is 99.2%. The optical purity detected by HPLC is 99.8%.

[0118] Synthesis of S-lotilaner in Example 6

[0119] Scheme 1: Add 30 g (0.047 mol) of resolution salt into a water and toluene solution with a weight ratio of 1:1, adjust the pH to 3 - 5 with hydrochloric acid, stir for 0.5 h, then let it stand for liquid separation, dry with anhydrous sodium sulfate, concentrate the organic layer under reduced pressure, vacuum dry overnight, dissolve it in 120 mL of dichloromethane, add 10.82 g (0.056 mol) of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, 12.41 g (0.096 mol) of N,N-diisopropylethylamine, 7.57 g (0.056 mol) of 1-hydroxybenzotriazole, stir for one hour in an ice bath, then add 10.78 g (0.056 mol) of 2-amino-N-(2,2,2-trifluoroethyl)acetamide hydrochloride and 2.80 g (0.023 mol) of 4-dimethylaminopyridine to the reaction system to react at room temperature. After the reaction is completed, extract and separate the liquid. The organic layer is washed, dried with anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized with dichloromethane and n-hexane, filtered by suction, and the filter cake is vacuum dried to obtain 25.52 g of lotilaner, with a yield of 90.9% and an HPLC purity of 99.8%.

[0120] Scheme 2: Add 30 g (0.047 mol) of the resolving salt to a water and toluene solution with a weight ratio of 1:1, adjust the pH to 3 - 5 with hydrochloric acid, stir for 0.5 h, then let it stand for liquid separation, dry with anhydrous sodium sulfate, concentrate the organic layer under reduced pressure, dry in vacuum overnight, dissolve it in 100 mL of N,N - dimethylformamide, add 10.82 g (0.056 mol) of 1-(3 - dimethylaminopropyl)-3 - ethylcarbodiimide hydrochloride, 12.41 g (0.096 mol) of N,N - diisopropylethylamine, 7.57 g (0.056 mol) of 1 - hydroxybenzotriazole, stir in an ice bath for one hour, then add 10.78 g (0.056 mol) of 2 - amino - N-(2,2,2 - trifluoroethyl)acetamide hydrochloride and 2.80 g (0.023 mol) of 4 - dimethylaminopyridine to the reaction system and react at room temperature. After the reaction is completed, pour the system into water to precipitate a solid, filter and collect the filter cake, recrystallize with dichloromethane and n - hexane, filter by suction, and dry in vacuum to obtain 25.52 g of lotilaner, with a yield of 90.9% and an HPLC purity of 99.8%.

[0121] Nuclear magnetic resonance results: 1 HNMR(600MHz,DMSO - d6)δ:8.63(t,1H),8.39

[0122] (t,1H), 7.82(s,2H), 7.35(s,1H), 4.41 - 4.31(dd,J=42.0,18.0Hz,2H,C - CH 2 -C=N), 3.94 - 3.91(m,4H), 2.44(s,3H).

[0123] 13 CNMR(151MHz,DMSO - d6)δ:169.91(C=O),162.26(C=O),153.92,(C=N - O)140.69,136.14,135.79,134.79,134.08,132.18,128.98,127.99,126.84,126.05,124.96,

[0124] 124.20,123.07,87.22,87.02,86.83,43.54,42.80,40.48,15.67(CH 3 ).

[0125] HR - MS(ESI)Cal cd for C 20 H 14 Cl 3 F 6 N 3 O3 S(M + Na + ): 617.9276; Found: 617.9626.

[0126] IR: (KBr, cm -1 ): 3329.14 (-CONH-), 2920.23 (-CH 2 -), 2850.79 (-CH 2 -), 1693.50 (-C=O), 1620.21 (C=C), 1550.77, 1519.91, 1435.04, 1388.75, 1292.31, 1157.29, 1095.57, 1022.27, 995.27, 898.83, 844.82, 806.25, 597.93.

[0127] The above embodiments are only the preferred embodiments of the present invention and do not limit the patent scope of the present invention. The synthetic methods of lotilaner mentioned in the present invention are not limited to the above several. Therefore, the above embodiments cannot be regarded as a limitation of the protection scope of the present invention. Any equivalent structural transformation made by using the content of the specification of the present invention under the inventive concept of the present invention, or direct / indirect application in other related technical fields is included in the patent protection scope of the present invention.

Claims

1. A method for synthesizing the isoxazoline antiparasitic drug lotiranab, characterized in that: First, the intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene) is synthesized, and then the intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime) is synthesized, and then the intermediate 1 and the intermediate 2 are subjected to a 1,3 dipolar cycloaddition reaction to obtain the intermediate 3, and then a Grignard reaction is performed to obtain the racemic acid, and finally chemical resolution and amide condensation are performed in sequence to obtain Lotiranab. The synthetic route is as follows:

2. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 1, characterized in that: The steps include: (1) Synthesis of Intermediate 1 (1,2,3-trichloro-5-(1-trifluoromethyl-vinyl)benzene): Add a base to a suspension of the Wittig reagent in an anhydrous solvent, keep the mixture in an ice bath for 0.5-2 hours, then add 2,2,2-trifluoromethyl-1-(3,4,5-trichlorophenyl)ethanone of formula (I), raise the temperature to room temperature and react for 2-6 hours, add water to quench the reaction after completion, extract with ethyl acetate, separate the liquids, wash, concentrate under reduced pressure, separate by column chromatography, concentrate under reduced pressure and dry, to obtain intermediate 1 of formula (II); (2) Synthesis of intermediate 2 (5-bromo-4-methyl-2-thiophenecarboxaldehyde oxime): Under nitrogen protection, after cooling with a dry ice acetone bath, n-butyl lithium is added to the suspension of diisopropylamine in anhydrous solvent, and after keeping the temperature for 15-45 minutes, a 2-bromo-3-methylthiophene anhydrous solvent solution of formula (III) is added to the system, and the reaction is continued for 0.5-1h. After that, methyl formate or N, N-dimethylformamide is added to the system, and the reaction is kept warm for 5-30 minutes. After the reaction is completed, a saturated ammonium chloride solution or a 1.0-2.0M hydrochloric acid solution is used to quench the reaction, and the liquid is separated by ethyl acetate extraction, washed, and concentrated under reduced pressure to obtain product A, and a water-tetrahydrofuran mixed solution is used as a solvent to dissolve product A. After the system is stirred uniformly, hydroxylamine hydrochloride and sodium acetate are added to the system, and the reaction is kept warm at 25-55°C for 0.5-2h. After the reaction is completed, water is added to the system and the temperature is lowered to room temperature to terminate the reaction, and the aqueous phase is extracted with ethyl acetate, washed, dried over anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized, filtered, and dried under reduced pressure to obtain intermediate 2 of formula (IV); (3) 1,3-dipolar cycloaddition reaction: The intermediate 1 of formula (II) and the intermediate 2 of formula (IV) are dissolved in a solvent, and then water, potassium persulfate and a halide salt are added to react at room temperature for 2-8 hours. After the reaction is completed, the intermediate 3 of formula (V) is obtained after washing with water, extraction, drying over anhydrous sodium sulfate, concentrating under reduced pressure, purifying by column chromatography, recrystallizing, filtering and drying under reduced pressure; (4) Grignard reaction: After nitrogen replacement, anhydrous solvent is added to the intermediate 3 of formula (V), Grignard reagent is added at room temperature, the reaction is kept warm, carbon dioxide gas is introduced, the reaction is completed by HPLC, water is added, the pH value is adjusted to 1-3 with acid, the reaction is allowed to stand, the water layer is separated, the organic layer is concentrated to dryness under reduced pressure, n-hexane is added, the temperature is reduced for crystallization, suction filtration is performed, and drying is performed to obtain the racemic acid of formula (VI); (5) Chemical separation: Add the racemic acid of formula (VI) and a resolving agent to an organic solvent, raise the temperature to reflux, cool down for crystallization, and dry to obtain an S-type resolved salt; (6) Amide condensation: In a mixed system of water and a solvent selected from dichloromethane, ethyl acetate, N,N-dimethylformamide and toluene, the S-type resolved salt obtained in step (5) is added, the pH is adjusted to acidic with an acid, the temperature is raised to reflux and stirred for 0.5-1.5 hours, the liquid is separated by extraction, dried over anhydrous sodium sulfate, the organic layer is concentrated under reduced pressure, dried under vacuum for 4-12 hours, dissolved in dichloromethane or N,N-dimethylformamide, a condensing agent, 2-amino-N-(2,2,2-trifluoroethyl)acetamide hydrochloride and a catalyst are added, the reaction is carried out at room temperature, the liquid is separated by extraction, the organic layer is washed, dried over anhydrous sodium sulfate, concentrated under reduced pressure, recrystallized, filtered, and dried under vacuum at 30-80°C for 6 hours to obtain lotirana of formula (VII); 3. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (1), step (2) and step (4), the anhydrous solvent is at least one of methanol, dichloromethane, ethanol, N,N-dimethylformamide, ether and tetrahydrofuran.

4. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (1), the Wittig reagent is one of methyltriphenylphosphonium chloride, methyltriphenylphosphonium bromide or methyltriphenylphosphonium iodide; and the base is one of sodium hydride, calcium hydride, n-butyl lithium or potassium tert-butoxide.

5. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (3), the solvent is one of tetrahydrofuran, acetonitrile, dichloromethane, ethyl acetate, chloroform, ethanol or methanol.

6. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (3), the halide salt is one of potassium chloride, sodium chloride, ammonium chloride, potassium bromide, sodium bromide, potassium iodide or sodium iodide.

7. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (4), the Grignard reagent is one of methylmagnesium chloride, ethylmagnesium chloride, methylmagnesium bromide, ethylmagnesium bromide, isopropylmagnesium chloride or isopropylmagnesium bromide.

8. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (4) or step (6), the acid is one of phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, oxalic acid, sulfurous acid, phosphoric acid, pyruvic acid, carbonic acid, citric acid, hydrofluoric acid, malic acid, formic acid, acrylic acid, acetic acid, propionic acid or boric acid.

9. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (5), the resolving agent is one of (R)-1-(4-methylphenyl)ethylamine, (R)-1-(4-bromophenyl)ethylamine, (S)-1-(4-nitrophenyl)ethylamine hydrochloride, glucosylamine, (R)-p-nitrophenylethylamine, and (S)-1-(4-bromophenyl)ethylamine.

10. The method for synthesizing the isoxazoline antiparasitic drug lotirana according to claim 2, characterized in that: In step (6), the condensation agent is one of EDCI, HATU, HBTU, and DCC, and the catalyst is 4-dimethylaminopyridine.

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