A method for preparing a side-chain isomer impurity of nemonoxacin

Abstract

This invention belongs to the field of organic synthesis technology and discloses a side-chain isomer impurity of nemonoxacin, its preparation method, and its application. The impurity is N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate (Formula 3). The preparation method uses N-Boc-L-pyroglutamic acid methyl ester (compound 1) as a raw material, and obtains an intermediate (compound 2) through a methylation reaction under alkaline conditions; compound 2 undergoes ring-opening and methyl esterification reactions to obtain compound 3; compound 3 undergoes ammonolysis, dehydration, and hydrogenation reactions to finally obtain the target product. The preparation method provided by this invention can synthesize specific stereoisomers, which can be used as standards for quality control and impurity detection of nemonoxacin side-chain products, and are of great significance for improving drug safety.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a method for preparing a key intermediate of nemonoxacin. Background Technology

[0002] Fluoroquinolone antibiotics are commonly used to treat infectious diseases such as respiratory tract infections and urinary tract infections due to their advantages such as broad antibacterial spectrum, strong antibacterial activity, fewer adverse reactions, good tissue penetration, high oral bioavailability, and convenient administration. The structural feature of this class of drugs is the introduction of a fluorine atom at the 6-position of the quinolone core. However, in the past decade, the selective pressure brought about by the widespread use of these drugs has led to a gradual increase in drug-resistant strains, especially quinolone-resistant Streptococcus pneumoniae, which has shown cross-resistance to penicillin, macrolides, and quinolones in recent years. Furthermore, some fluoroquinolones also cause adverse reactions such as QTc interval prolongation, hepatotoxicity, and phototoxicity. To overcome these shortcomings, the development of novel quinolone compounds with good activity against multidrug-resistant bacteria, a broad antibacterial spectrum, and fewer adverse reactions is particularly urgent. Against this backdrop, nemonoxacin, as a novel quinolone drug, has emerged, with the following structure: .

[0003] Nemonoxacin side chain (MAP), namely N-[(3S,5S)-5-methyl-3-piperidinyl]-tert-butyl carbamate (as shown in Formula 2), is a key intermediate in the production of the quinolone antibiotic nemonoxacin. This compound contains two chiral centers.

[0004] .

[0005] Drug impurity research is a crucial aspect of drug development, significantly impacting the pharmacological activity and adverse reactions of drugs. Therefore, controlling impurities within a safe and reasonable range directly affects the quality and safety of marketed drugs. Currently, related substances for nemonoxac are expensive to purchase, and some lack literature reports. However, related substance standards are indispensable for nemonoxac quality research.

[0006] Impurities typically originate from process impurities, degradation products, and impurities introduced from reactants and reagents. Nemonoxacin's side chain has two chiral centers. Since chiral drugs and their isomers may produce different or even opposite pharmacological effects in the human body, synthesizing the stereoisomers of the nemonoxacin side chain is of great significance for the quality research and control of nemonoxacin. Summary of the Invention

[0007] The purpose of this invention is to provide a nemonoxacin side chain isomer, its preparation method and application, and a method for detecting impurities in the nemonoxacin side chain isomer. The nemonoxacin side chain isomer, as an impurity in the nemonoxacin side chain, can be used as a standard to detect impurities in the nemonoxacin side chain.

[0008] This invention provides a nemonoxacin side-chain isomer having the structure shown in Formula 3: .

[0009] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0010] Dissolve reagent 1 in solvent 1, add compound 1 dropwise, add reagent 2 dropwise, and carry out the first reaction to obtain compound 2; Compound 2 and reagent 3 were added to solvent 2 to carry out a second reaction, and then reagents 4 and 5 were added to carry out a third reaction to obtain compound 3. Compound 3 was subjected to ammonolysis with reagent 6, followed by dehydration with reagent 7 and solvent 4, and finally hydrogenation with solvent 5, reagent 8 and reagent 9 to obtain the numonoxacin isomer impurity.

[0011] The structural formula of compound 1 is: Reagent 1 is bis(trimethylsilyl)aminolithium; reagent 2 is iodomethane; the structural formula of compound 2 is: Reagent 3 is lithium hydroxide, sodium hydroxide, and sodium carbonate; reagent 4 is sodium bicarbonate, sodium carbonate, and sodium hydroxide; reagent 5 is iodomethane; the structural formula of compound 3 is: The reagent 6 is ammonia; the reagent 7 is cyanuric chloride; the reagent 8 is palladium on carbon; the reagent 9 is benzylamine; the structural formula of compound 4 is: .

[0012] Further, the mass ratio of compound 1 to solvent 1 is 1:3 to 10; the molar ratio of compound 1 to reagent 1 is 1:1.2 to 2; the molar ratio of reagent 2 is 1:1.0 to 1.8; solvent 1 includes at least one of toluene, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, n-hexane, and diethyl ether; the conditions for the first reaction are: temperature -80 to -60°C, and time 10 to 24 hours.

[0013] Furthermore, the molar ratio of compound 2 to reagent 3 is 1:1~3; the mass ratio of compound 2 to solvent 2 is 1:5~10; the molar ratio of compound 2 to reagent 4 is 1:4~10; the molar ratio of compound 2 to reagent 5 is 1:2~5; and solvent 2 and solvent 3 include tetrahydrofuran, N,N-dimethylformamide, toluene, dichloromethane, dichloroethane, trichloromethane, 2-methyltetrahydrofuran, acetonitrile, and 1,4-dioxane.

[0014] The conditions for the second and third reactions are: temperature 0~30℃ and time 1~10 hours.

[0015] Furthermore, the molar ratio of compound 3 to reagent 6 is 1:5~15; the molar ratio of compound 3 to reagent 7 is 1:2~3; the mass ratio of compound 3 to solvent 4 is 1:3~10; the mass ratio of compound 3 to reagent 8 is 1:0.03~0.1; the molar ratio of compound 3 to reagent 9 is 1:1~2; and the mass ratio of compound 3 to solvent 5 is 1:8~15.

[0016] The solvent 4 is tetrahydrofuran, N,N-dimethylformamide, toluene, dichloromethane, dichloroethane, trichloromethane, 2-methyltetrahydrofuran, acetonitrile, or 1,4-dioxane. N,N-dimethylformamide is preferred.

[0017] The solvent 5 is one or a mixture of tetrahydrofuran, 2-methyltetrahydrofuran, acetonitrile, methanol, anhydrous ethanol, ethyl acetate, isopropyl acetate, dimethyl sulfoxide, 1,4-dioxane, N,N-dimethylformamide, N-methylpyrrolidone, etc.; preferably methanol.

[0018] The conditions for the ammonolysis reaction are: temperature 10~30℃, time 3~12 hours; the conditions for the dehydration reaction are: temperature 0~10℃, time 4~6 hours; and the conditions for the hydrogenation reaction are: temperature 25~60℃, time 2~8 hours.

[0019] This invention provides the application of the nanofloxacin side chain optical isomer described in the above technical solution or the nanofloxacin side chain optical isomer prepared by the above technical solution as a standard in the detection of impurities in nanofloxacin side chain products. Attached Figure Description

[0020] Figure 1 The image shows the LC-MS chromatogram of N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate obtained in Example 1 of this invention.

[0021] Figure 2The image shows the 1H NMR spectrum of N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate obtained in Example 1 of this invention.

[0022] Figure 3 This is a comparison diagram of the liquid chromatography internal standard between N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate obtained in Example 1 of the present invention and commercially available N-[(3S,5S)-5-methyl-3-piperidinyl]-tert-butyl carbamate. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0025] This invention provides a method for synthesizing a side-chain isomer impurity of nemonoxacin, wherein the side-chain isomer impurity of nemonoxacin is N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate, and the method includes the following steps: Step 1: ; Using N-Boc-L-pyroglutamic acid methyl ester as a raw material, a methylation reaction was carried out in solvent 1 to generate (2S,4R)-1-Boc-4-methylpyroglutamic acid methyl ester.

[0026] In step 1, solvent 1 is one or more of dichloromethane, dichloroethane, trichloromethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, etc.; tetrahydrofuran is preferred.

[0027] In step 1, the mass ratio of compound 1 to solvent 1 is 1:3~10; preferably 1:5~8.

[0028] In step 1, the molar ratio of compound 1 to LiHMDS is 1:1~2, preferably 1:1.2~1.8. In step 1, the reaction temperature is -80~-60℃, preferably -78℃.

[0029] In step 1, the reaction time is 5 to 30 hours, preferably 10 to 20 hours.

[0030] Step 2: ; Compound 2 was dissolved in solvent 2, and then hydrolyzed by adding an aqueous lithium hydroxide solution. Subsequently, iodomethane was added under alkaline conditions to carry out a methyl esterification reaction to generate compound 3.

[0031] In step 2, solvent 2 is one or a mixture of tetrahydrofuran, N,N-dimethylformamide, toluene, dichloromethane, dichloroethane, chloroform, 2-methyltetrahydrofuran, acetonitrile, 1,4-dioxane, etc.

[0032] In step 2, the mass ratio of compound 2 to solvent 2 is 1:5~10.

[0033] In step 2, the molar ratio of compound 2 to reagent 3 is 1:1~3.

[0034] In step 2, the molar ratio of compound 2 to reagent 4 is 1:4~10.

[0035] In step 2, the molar ratio of compound 2 to reagent 5 is 1:2~5.

[0036] In step 2, the hydrolysis reaction is carried out at a temperature of 0~30℃ for 1~10 hours.

[0037] In step 2, the temperature of the methyl esterification reaction is 0~30℃ and the time is 1~10 hours.

[0038] Step 3: ; Using compound 3 as a raw material, it first reacts with reagent 6 to generate a diamide intermediate, and then reacts with reagent 7 to generate a dinitrile intermediate. Finally, it is hydrogenated under the action of reagents 8 and 9 to obtain the nemonoxacin isomer impurity.

[0039] In step 3, solvent 4 is preferably N,N-dimethylformamide; solvent 5 is preferably methanol.

[0040] In step 3, the mass ratio of compound 3 to solvent 4 is 1:3~10; and the mass ratio of compound 3 to solvent 5 is 1:8~15.

[0041] In step 3, the molar ratio of compound 3 to ammonia (reagent 6) is 1:5~15.

[0042] In step 3, the molar ratio of compound 3 to cyanuric chloride (reagent 7) is 1:2~3.

[0043] In step 3, the mass ratio of compound 3 to palladium on carbon (reagent 8) is 1:0.03~0.1.

[0044] In step 3, the molar ratio of compound 3 to benzylamine (reagent 9) is 1:1~2.

[0045] In step 3, the ammonolysis reaction is carried out at a temperature of 10-30°C for 3-12 hours.

[0046] In step 3, the dehydration reaction is carried out at a temperature of 0-10°C for 4-6 hours.

[0047] In step 3, the hydrogenation reaction is carried out at a temperature of 25-60°C for 2-8 hours. Example

[0048] This example provides a method for synthesizing a side-chain isomer impurity of nemonoxacin, wherein the nemonoxacin isomer impurity is N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate, and the synthesis method includes the following steps: .

[0049] Under nitrogen protection, a solution of bis(trimethylsilyl)aminolithium (LiHMDS) (1.2–1.8 equivalents) was added to the reaction flask, and the temperature was maintained at -78°C. Subsequently, a tetrahydrofuran solution of compound 1 (N-Boc-L-methyl pyroglutamate) (compound to solvent mass ratio 1:5–8) was slowly added dropwise at a temperature below -60°C. After the addition was complete, the mixture was stirred at -78°C for approximately 1.5 hours.

[0050] Add a tetrahydrofuran solution of iodomethane (1.0~1.8 equivalents) dropwise to the obtained solution at a temperature below -60°C. After the addition is complete, stir the reaction solution at -80~-60°C (preferably -78°C) for 10~20 hours.

[0051] After the reaction was complete, methanol was carefully added dropwise at approximately -60°C to quench the reaction, followed by the addition of dilute hydrochloric acid (e.g., 2M HCl) at -10°C to adjust the pH. Toluene (or ethyl acetate) was added to the resulting mixture for extraction, and the organic layer was separated. The organic layer was washed with a 17% sodium thiosulfate aqueous solution and stirred (for approximately 30 minutes) to remove excess iodomethane and color until the solution color lightened (from dark to pale yellow). After drying and filtration, the organic phase was concentrated under reduced pressure to remove the solvent, yielding compound 2 ((2S,4R)-1-Boc-4-methylpyroglutamic acid methyl ester).

[0052] .

[0053] Compound 2 was dissolved in tetrahydrofuran, and an aqueous lithium hydroxide solution was added dropwise at -10°C to -5°C with stirring. Stirring was continued at 0-30°C for 1-10 hours, and the reaction progress was monitored by LC / MS. After the reaction was complete, the pH of the reaction solution was adjusted by treating with dilute hydrochloric acid, and the aqueous phase was extracted with an organic solvent (such as ethyl acetate). The organic phases were then combined.

[0054] Sodium bicarbonate solid was added as an acid-binding agent to the obtained organic phase at 0-10°C, followed by the slow dropwise addition of iodomethane. The reaction was stirred at 0-30°C for 1-10 hours. After the reaction was complete, water was added to quench the reaction, the organic layer was separated, and the mixture was treated with sodium thiosulfate solution to remove excess iodomethane (if applicable), with stirring for 30 minutes, during which the solution color changed. The organic layer was evaporated under vacuum to give compound 3.

[0055] .

[0056] 3.1 Ammonolysis Reaction: Compound 3 was suspended in ammonia solution (5-15 eq) and stirred at 10-30°C (room temperature). The mixture gradually changed from a particulate suspension to a solid suspension over 3 to 12 hours. After stirring, the solid was filtered, washed with water, and dried under vacuum to obtain the ammonolysis product (amide intermediate).

[0057] 3.2 Dehydration Reaction: The above-mentioned amide intermediate (1 eq) was dissolved in an ice-cooled solution of DMF (3-10 times by mass), and cyanuric chloride (2-3 eq) was added in a single batch at 0-10°C. The mixture was stirred at 0-10°C for 4-6 hours. Subsequently, the mixture was slowly poured into ice water over 5 minutes and stirred for 10 minutes, allowing the solid to precipitate in needle-like form. The slurry was filtered, the solid was washed with water, and dried to obtain the dehydrated product (nitrile intermediate).

[0058] 3.3 Hydrogenation reaction: Methanol (8-15 times by mass) and benzylamine (1-2 eq) were added to a high-pressure reactor. Then, under nitrogen protection, the above-mentioned nitrile intermediate and 10% palladium on carbon (0.03-0.1 times by mass) were added. Nitrogen / vacuum exchange was performed three times, followed by hydrogen / vacuum exchange once. Finally, the reactor was pressurized to 10 bar with hydrogen.

[0059] The mixture was stirred at 20-25°C under 10 bar pressure, and the disappearance of the starting material was confirmed by gas chromatography or liquid chromatography. Depending on the reaction, the temperature could be gradually increased to 40-45°C with stirring, and finally increased to 45°C (within the range of 25-60°C) with stirring until the reaction was complete. After the reaction was complete, the temperature was lowered to 20-25°C, and nitrogen / vacuum exchange was performed three times. The reaction solution was filtered to remove palladium on carbon, and the filtrate was concentrated under vacuum to obtain the final product, the numonoxacin side-chain isomer impurity.

[0060] In summary, the embodiments of the present invention provide a method for synthesizing the side chain isomer impurity of nemonoxacin. The present invention adopts a completely innovative method for synthesizing N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate.

Claims

1. A side-chain isomer of nemonoxacin, characterized in that, The isomer is N-[(3S,5R)-5-methyl-3-piperidinyl]-tert-butyl carbamate, having the chemical structure shown in Formula 3: (Note: This refers to the structure of Formula 3 in the specification).

2. A method for preparing the nemonoxacin side chain isomer according to claim 1, characterized in that, Includes the following steps: (1) Compound 1 (N-Boc-L-pyroglutamic acid methyl ester) is dissolved in solvent 1 and reacted with reagent 2 under the action of reagent 1 to obtain compound 2; (2) Compound 2 is reacted with reagent 3 in solvent 2, and then reagent 4 and reagent 5 are added to react to obtain compound 3; (3) Compound 3 is subjected to ammonolysis reaction with reagent 6, and then reagent 7 and solvent 4 are added to carry out dehydration reaction, and finally reagent 8 and reagent 9 are added to solvent 5 to carry out hydrogenation reaction to obtain the side chain isomer of nemonoxacin; wherein, the structure of compound 1 is N-Boc-L-pyroglutamic acid methyl ester; reagent 1 is bis(trimethylsilyl)aminolithium; reagent 2 is iodomethane; reagent 3 is selected from lithium hydroxide, sodium hydroxide, and sodium carbonate; reagent 5 is iodomethane; reagent 6 is ammonia; reagent 7 is cyanuric chloride; reagent 8 is palladium on carbon; and reagent 9 is benzylamine.

3. The preparation method according to claim 2, characterized in that, In step (1), solvent 1 is selected from at least one of toluene, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, n-hexane, and diethyl ether; the mass ratio of compound 1 to solvent 1 is 1:3~10; the molar ratio of compound 1 to reagent 1 is 1:1.2~2; the molar ratio of compound 1 to reagent 2 is 1:1.0~1.8; and the reaction temperature is -80~-60℃.

4. The preparation method according to claim 2, characterized in that, In step (2), solvent 2 is selected from one or more of tetrahydrofuran, N,N-dimethylformamide, toluene, dichloromethane, dichloroethane, chloroform, 2-methyltetrahydrofuran, acetonitrile, and 1,4-dioxane; the molar ratio of compound 2 to reagent 3 is 1:1~3; the molar ratio of compound 2 to reagent 5 is 1:2~5; the temperature of both the hydrolysis reaction and the methyl esterification reaction is 0~30℃.

5. The preparation method according to claim 2, characterized in that, In step (3), the molar ratio of compound 3 to reagent 6 is 1:5~15; the molar ratio of compound 3 to reagent 7 is 1:2~3; the mass ratio of compound 3 to reagent 8 is 1:0.03~0.1; and the molar ratio of compound 3 to reagent 9 is 1:1~2.

6. The preparation method according to claim 2, characterized in that, In step (3), solvent 4 is N,N-dimethylformamide; solvent 5 is preferably methanol; the temperature of the ammonolysis reaction is 10~30℃; the temperature of the dehydration reaction is 0~10℃; and the temperature of the hydrogenation reaction is 25~60℃.

7. The preparation method according to claim 2, characterized in that, The pressure of the hydrogenation reaction in step (3) is 10 bar.

8. The application of the nemonoxacin side-chain isomer according to claim 1 or the nemonoxacin side-chain isomer prepared by any one of claims 2-7 in the detection of impurities in nemonoxacin side-chain products, characterized in that, It is used as a standard for the analysis of related substances in the side chain of nemonoxacin and its formulations.

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