A preparation method of (S)-3-amino-2-pentanone hydrochloride

Abstract

The invention discloses a preparation method of (S)-3-amino-2-pentanone hydrochloride, belonging to the field of pharmaceutical intermediate processing technology. Its preparation method comprises the following steps: (1) L-2-aminobutyric acid, solvent, alkaline solution and Boc anhydride solution are mixed and stirred to obtain L-2-Boc-aminobutyric acid; (2) the product of step (1) is mixed and stirred with solvent, dimethylhydroxylamine hydrochloride, organic base and coupling agent to obtain N-methoxy-N-methylamide; (3) the product of step (2), solvent and methylmagnesium bromide are mixed and reacted to obtain S-(2-oxopentan-3-yl) tert-butyl carbamate; (4) the product of step (3) is reacted with concentrated hydrochloric acid to obtain. The reagents used in this preparation method have little environmental pollution, meet the requirements of green chemistry, the required raw materials are simple and easy to obtain, the cost is low, the preparation route is concise, the operation is simple, easy to control and the yield is high.

Description

Technical Field

[0001] The invention relates to the technical field of pharmaceutical intermediate processing, and in particular to a method for preparing (S)-3-amino-2-pentanone hydrochloride. Background Art

[0002] (S)-3-Amino-2-pentanone hydrochloride is an important intermediate in the synthesis of innovative drugs. It has the potential to be used in the research and development of drugs for treating a variety of diseases or symptoms, and is used in the research and development of drugs for treating a variety of diseases or symptoms.

[0003] At present, there are only reports on the preparation method of its precursor S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester. Among them, US200942967 discloses a method for preparing S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester by using L-aminobutyric acid as raw material, protecting it with Boc anhydride, preparing Weinreb amide, and reacting the amide with methyl lithium at -78 degrees to generate ketone. On the one hand, this method uses methyl lithium and Weinreb amide to react to prepare S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester, which is costly, has high temperature requirements (-78°C), and is difficult to control. On the other hand, the ether used in the reaction belongs to a precursor chemical with poor safety. The synthesis scheme of S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester reported in EP2589592 involves column chromatography purification, which is not suitable for industrial application and scale-up production.

[0004] In summary, since the preparation of S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester, a precursor of (S)-3-amino-2-pentanone hydrochloride in the prior art, has the problems of complex operation, low yield, use of easily made-toxin and environmentally unfriendly reagents, and is not conducive to large-scale industrial production, it is urgent to develop a preparation method of (S)-3-amino-2-pentanone hydrochloride that meets the requirements of green chemistry, has simple and easy-to-obtain raw materials, is convenient for industrial production, is simple to operate, easy to control, and has a high yield. Summary of the invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a method for preparing (S)-3-amino-2-pentanone hydrochloride, so as to solve the problems that the preparation of S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester, a precursor of (S)-3-amino-2-pentanone hydrochloride in the prior art, has complex operation, low yield, use of easily made poisons and environmentally unfriendly reagents, and is not conducive to large-scale industrial production.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A method for preparing (S)-3-amino-2-pentanone hydrochloride comprises the following steps:

[0008] (1) Preparation of L-2-Boc-aminobutyric acid: L-2-aminobutyric acid is mixed with a solvent, an alkaline solution and a Boc anhydride solution and stirred to obtain a product;

[0009] (2) Preparation of N-methoxy-N-methylamide: dissolving the L-2-Boc-aminobutyric acid obtained in step (1) in a solvent, adding dimethylhydroxylamine hydrochloride, an organic base and a coupling agent, and mixing and stirring to obtain;

[0010] (3) Preparation of tert-butyl S-(2-oxopentan-3-yl)carbamate: dissolving the N-methoxy-N-methylamide obtained in step (2) in a solvent, mixing and reacting with methylmagnesium bromide to obtain;

[0011] (4) Preparation of (S)-3-amino-2-pentanone hydrochloride: Dissolve the S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester prepared in step (3) in a solvent, add concentrated hydrochloric acid to react, and prepare.

[0012] The beneficial effects of the present invention are as follows: the present invention provides a preparation method of (S)-3-amino-2-pentanone hydrochloride, which specifically involves four-step reactions: amino protection reaction, Weinreb amide preparation reaction, substitution reaction and amino deprotection reaction. The preparation method has small environmental pollution, a simple route and a high yield; each step of the reaction is simple to operate, easy to control, does not require harsh reaction conditions, etc., and is convenient for industrial large-scale production.

[0013] Furthermore, in step (1), the mass volume ratio of L-2-aminobutyric acid to the solvent, alkaline solution and Boc anhydride solution is 30-40g:40-60mL:50-150mL:20-40mL; the solvent includes any one of methanol, ethanol and water; the alkaline solution includes any one of NaOH aqueous solution, Na2CO3 aqueous solution and NaHCO3 aqueous solution, the concentration of NaOH aqueous solution is 3-5mol / L, the concentration of Na2CO3 aqueous solution is 5-10mol / L, and the concentration of NaHCO3 aqueous solution is 5-10mol / L; the concentration of Boc anhydride solution is 10-15mol / L.

[0014] Preferably, in step (1), the mass volume ratio of L-2-aminobutyric acid to the solvent, the alkaline solution and the Boc anhydride solution is 34 g: 50 mL: 100 mL: 30 mL; the solvent is water; the alkaline solution is a NaOH aqueous solution with a concentration of 4 mol / L; and the concentration of the Boc anhydride solution is 13.33 mol / L.

[0015] Furthermore, the solvent of the Boc anhydride solution includes any one of methanol, ethanol and isopropanol.

[0016] Preferably, the solvent of the Boc anhydride solution is methanol.

[0017] Furthermore, the mixing and stirring in step (1) is carried out at a temperature of 20-30° C. and for a time of 1-3 h.

[0018] Preferably, the mixing and stirring in step (1) is carried out at a temperature of 25° C. and for 2 hours.

[0019] The beneficial effect of adopting the above further technical scheme is: the present invention uses L-2-aminobutyric acid and Boc anhydride as reaction substances, mixes L-2-aminobutyric acid and Boc anhydride at room temperature in an alkaline environment, so that the amino group of L-2-aminobutyric acid is protected by Boc anhydride to generate L-2-Boc-aminobutyric acid, the reaction conditions are mild, and the solvents and alkaline substances used during the process are simple and easy to obtain, low in cost, and meet the requirements of green chemistry.

[0020] Furthermore, after the mixing and stirring reaction in step (1) is completed, the reaction of the raw materials is monitored by TLC, and then ethyl acetate is added for liquid separation, the pH of the aqueous phase is adjusted to 5-6, extracted with ethyl acetate, the organic phases are combined, dried over anhydrous sodium sulfate, and concentrated in vacuo to complete purification and collect to obtain a colorless viscous liquid L-2-Boc-aminobutyric acid.

[0021] The beneficial effect of adopting the above further technical scheme is: the present invention monitors the reaction of the raw materials in step (1) by TLC, and uses ethyl acetate as a liquid separation and extraction solvent, the purification method is simple, the purification speed is fast, and the collected colorless viscous liquid L-2-Boc-aminobutyric acid has a high yield.

[0022] Further, in step (2), the mass volume ratio of L-2-Boc-aminobutyric acid to the solvent is 50-60 g: 150-250 mL, and the solvent includes dichloromethane; the molar ratio of L-2-Boc-aminobutyric acid, dimethylhydroxylamine hydrochloride, organic base and coupling agent is 250-300: 300-500: 800-1200: 300-500, and the organic base includes triethylamine, N,N-diisopropylethylamine (DIPEA), 4- Any one of dimethylaminopyridine (DMAP) and pyridine, and the coupling agent includes any one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI hydrochloride), dicyclohexylcarbodiimide (DCC), 1,3-diisopropylcarbodiimide (DIC), N,N'-carbonyldiimidazole (CDI) and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate (HATU).

[0023] Preferably, in step (2), the mass volume ratio of L-2-Boc-aminobutyric acid to the solvent is 55 g:200 mL, and the solvent is dichloromethane; the molar ratio of L-2-Boc-aminobutyric acid, dimethylhydroxylamine hydrochloride, organic base and coupling agent is 270:400:1000:400, the organic base is triethylamine, and the coupling agent is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDCI hydrochloride).

[0024] Furthermore, the mixing and stirring in step (2) is carried out at a temperature of 20-30° C. and for a time of 3-7 h.

[0025] Preferably, the mixing and stirring in step (2) is carried out at a temperature of 25° C. and for 5 hours.

[0026] The beneficial effects of adopting the above further technical scheme are as follows: the present invention uses L-2-Boc-aminobutyric acid and dimethylhydroxylamine hydrochloride as reaction substances, adds a coupling agent, and reacts under alkaline conditions at room temperature to successfully prepare Weinreb amide. The reaction conditions are mild, and the solvents and alkaline substances used during the reaction are simple and easy to obtain, low in cost, and meet the requirements of green chemistry.

[0027] Furthermore, after the mixing and stirring reaction in step (2) is completed, TLC is monitored until the starting material disappears, water is added to quench the reaction, and then the liquids are separated, the organic phase is washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to complete purification and collect to obtain white solid N-methoxy-N-methylamide.

[0028] The beneficial effect of adopting the above further technical scheme is: the present invention monitors the mixing and stirring reaction in step (2) by TLC, and quenches the reaction and separates the liquids by adding water. The purification method is simple and the purification speed is fast. The yield of the collected white solid N-methoxy-N-methylamide is high.

[0029] Furthermore, in step (3), the mass volume ratio of N-methoxy-N-methylamide to the solvent is 7-8 g:80-120 mL, and the solvent includes at least one of tetrahydrofuran and toluene; and the molar ratio of N-methoxy-N-methylamide to methylmagnesium bromide is 200-400:800-1200.

[0030] Preferably, in step (3), the mass volume ratio of N-methoxy-N-methylamide to the solvent is 7.2 g:100 mL, and the solvent is tetrahydrofuran; the molar ratio of N-methoxy-N-methylamide to methylmagnesium bromide is 292:1000.

[0031] Furthermore, in step (3), the temperature of the mixed reaction is -30 to 0°C, and the time is 3 to 7 hours.

[0032] Preferably, the temperature of the mixed reaction in step (3) is -30°C and the time is 5 hours.

[0033] The beneficial effects of adopting the above further technical scheme are as follows: the present invention uses N-methoxy-N-methylamide and methylmagnesium bromide as reaction raw materials, and reacts at -30 to 0°C. During the reaction, no other reagents are needed except the solvent. The reaction conditions are mild, the cost is low, and it meets the requirements of green chemistry.

[0034] Furthermore, after the mixing reaction in step (3) is completed, the reaction is continued at room temperature until the reaction of the raw materials is completed as monitored by TLC, and then poured into a 5% by mass citric acid solution or a 1N HCl solution for quenching, extracted with ethyl acetate three times, the organic phases are combined, washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to complete the purification and collect solid S-(2-oxopentane-3-yl)carbamic acid tert-butyl ester.

[0035] The beneficial effects of adopting the above further technical scheme are as follows: the present invention monitors the mixing and stirring reaction of step (2) by TLC, quenches by adding into a citric acid solution or an HCl solution, and extracts by ethyl acetate. The purification method is simple and the purification speed is fast. The yield of the collected solid S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester is high.

[0036] Furthermore, in step (4), the mass volume ratio of S-(2-oxopentane-3-yl)carbamic acid tert-butyl ester, solvent and concentrated hydrochloric acid is 4-6 g:10-20 mL:3-8 mL, and the solvent includes any one of dichloromethane, ethyl acetate, tetrahydrofuran and dioxane.

[0037] Preferably, in step (4), the mass volume ratio of S-(2-oxopentyldan-3-yl)carbamic acid tert-butyl ester, solvent and concentrated hydrochloric acid is 5g:15mL:5mL, and the solvent is dichloromethane.

[0038] Furthermore, in step (4), the reaction temperature is 20-30° C. and the reaction time is 1-5 h.

[0039] Preferably, the reaction temperature in step (4) is 25° C. and the reaction time is 3 h.

[0040] The beneficial effect of adopting the above further technical scheme is as follows: the present invention uses S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester as a raw material, carries out an amino deprotection reaction with concentrated hydrochloric acid, and successfully prepares (S)-3-amino-2-pentanone hydrochloride. The preparation conditions are mild, the yield is high, the cost is low, and it meets the requirements of green chemistry.

[0041] Furthermore, after the reaction in step (4) is completed, TLC is used to monitor until the reaction of the raw materials is complete, and the precipitate is collected by filtration to obtain white crystals of (S)-3-amino-2-pentanone hydrochloride.

[0042] The beneficial effect of adopting the above further technical scheme is that the purification and separation of the final product of the present invention can be achieved by simply filtering and collecting the precipitate, the separation method is simple and fast, and the obtained white crystal (S)-3-amino-2-pentanone hydrochloride has a high yield and high purity.

[0043] The present invention has the following beneficial effects:

[0044] The invention provides a preparation method of (S)-3-amino-2-pentanone hydrochloride, which specifically involves four-step reactions: amino protection reaction, Weinreb amide preparation reaction, substitution reaction and amino deprotection reaction. The reagents used in the preparation method have little environmental pollution and meet the requirements of green chemistry. The required raw materials are simple and easy to obtain, the cost is low, and the industrial production is convenient. The preparation route is concise, the operation is simple, the control is easy and the yield is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 The present invention is a flow chart for the preparation of (S)-3-amino-2-pentanone hydrochloride;

[0046] Figure 2 This is the H NMR spectrum of tert-butyl S-(2-oxopentan-3-yl)carbamate prepared in Example 1 of the present invention;

[0047] Figure 3 This is the H NMR spectrum of (S)-3-amino-2-pentanone hydrochloride prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not used to limit the scope of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0049] Embodiment 1:

[0050] A method for preparing (S)-3-amino-2-pentanone hydrochloride (preparation flow chart as shown in Figure 1 As shown), comprising the following steps:

[0051] (1) Preparation of L-2-Boc-aminobutyric acid

[0052] Weigh L-2-aminobutyric acid (34 g, 330 mmol) and add it to 50 mL of water, then add NaOH aqueous solution (4 mol / L, 100 mL), then drop Boc anhydride methanol solution (400 mmol, 30 mL), stir and react at 25 ° C for 2 h, and monitor by TLC until the reaction of the raw materials is complete. After adding 30 mL of ethyl acetate for separation, adjust the pH of the aqueous phase to 5.5, extract with ethyl acetate, combine the organic phases, dry over anhydrous sodium sulfate, and concentrate in vacuo to obtain colorless viscous liquid L-2-Boc-aminobutyric acid.

[0053] (2) Preparation of Weinreb amide

[0054] The L-2-Boc-aminobutyric acid (55 g, 270 mmol) prepared in step (1) was dissolved in 200 mL of dichloromethane, dimethylhydroxylamine hydrochloride (400 mmol) and triethylamine (1.0 mol) were added to the solution system, and then EDCI hydrochloride (76.7 g, 400 mmol) was added, and the reaction was stirred at 25°C for 5 h, and monitored by TLC until the raw material point disappeared. 100 mL of water was added to quench the reaction, and the liquid was separated, and then the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to obtain white solid Weinreb amide.

[0055] (3) Preparation of tert-butyl S-(2-oxopentan-3-yl)carbamate

[0056] The Weinreb amide (7.20 g, 292 mmol) obtained in step (2) was dissolved in 100 mL THF, and then the system was cooled to -30 ° C by ice-salt bath, and methylmagnesium bromide solution (1.0 mol) was added dropwise, and the reaction was maintained at low temperature for 5 h, and the reaction was monitored by TLC until the reaction of the raw materials was completed. After the reaction was completed, the reaction product was poured into a 1N HCl solution for quenching, and then extracted with 50 mL of ethyl acetate for 3 times, and the organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and then concentrated in vacuo to obtain 5.60 g of solid S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester, with a yield of 95%.

[0057] The H NMR spectrum of tert-butyl S-(2-oxopentan-3-yl)carbamate is as follows Figure 2 As shown, the results of H NMR spectrum are: 1 HNMR(CDCl3)0.82(3H),1.37(9H),1.55(1H),1.86(1H),2.13(3H),4.23(1H),5.16(1H).

[0058] (4) Preparation of (S)-3-amino-2-pentanone hydrochloride

[0059] The tert-butyl S-(2-oxopentan-3-yl)carbamate obtained in step (3) was dissolved in 15 mL of dichloromethane, 5 mL of concentrated hydrochloric acid was added, and the mixture was reacted at 25° C. for 3 h to generate a large amount of white precipitate. After the reaction of the raw materials was completed by monitoring by TLC, the precipitate was collected by filtration to obtain 3.40 g of white crystals of (S)-3-amino-2-pentanone hydrochloride, with a yield of 99%.

[0060] The H NMR spectrum of (S)-3-amino-2-pentanone hydrochloride is as follows Figure 3 As shown, the results of H NMR spectrum are: 1 HNMR (400MHz, CD3OD): δ1.01(3H), 1.93(1H), 2.08(1H), 2.28(3H), 4.16(1H).

[0061] Embodiment 2:

[0062] A method for preparing (S)-3-amino-2-pentanone hydrochloride comprises the following steps:

[0063] (1) Preparation of L-2-Boc-aminobutyric acid

[0064] Weigh L-2-aminobutyric acid (34 g, 330 mmol) and add it to 50 mL of water, then add Na2CO3 aqueous solution (8 mol / L, 50 mL), then drop Boc anhydride methanol solution (400 mmol, 30 mL), stir and react at 25°C for 2 h, and monitor by TLC until the reaction of the raw materials is complete. After adding 30 mL of ethyl acetate for separation, adjust the pH of the aqueous phase to 5.5, extract with ethyl acetate, combine the organic phases, dry over anhydrous sodium sulfate, and concentrate in vacuo to obtain a colorless viscous liquid L-2-Boc-aminobutyric acid.

[0065] (2) Preparation of Weinreb amide

[0066] The L-2-Boc-aminobutyric acid (55 g, 270 mmol) prepared in step (1) was dissolved in 200 mL of dichloromethane, dimethylhydroxylamine hydrochloride (400 mmol) and EDCI hydrochloride (76.7 g, 400 mmol) were added to the solution system, and then DIPEA (1.0 mol) was added, and the reaction was stirred at 25°C for 5 h, and monitored by TLC until the raw material point disappeared. 100 mL of water was added to quench the reaction, and the liquid was separated, and then the organic phase was washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to obtain white solid Weinreb amide.

[0067] (3) Preparation of tert-butyl S-(2-oxopentan-3-yl)carbamate

[0068] The Weinreb amide (7.00 g, 284 mmol) obtained in step (2) was dissolved in a mixed solvent of 100 mL toluene and tetrahydrofuran in a volume ratio of 1:1, and then the system was cooled to -315°C by an ice-salt bath, and methylmagnesium bromide solution (1.1 mol) was added dropwise, and the reaction was maintained at low temperature for 5 hours, and the reaction of the raw materials was monitored by TLC. After the reaction was completed, the reaction product was poured into a citric acid solution with a mass fraction of 5% to quench, and then extracted with 50 mL of ethyl acetate for 3 times, the organic phases were combined, washed with saturated brine and dried over anhydrous sodium sulfate, and then concentrated in vacuo to obtain 5.0 g of solid S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester.

[0069] (4) Preparation of (S)-3-amino-2-pentanone hydrochloride

[0070] The tert-butyl S-(2-oxopentan-3-yl)carbamate obtained in step (3) was dissolved in 15 mL of ethyl acetate, and 5 mL of concentrated hydrochloric acid was added. The mixture was reacted at 25° C. for 3 h to generate a large amount of white precipitate. After the reaction of the raw materials was completed by monitoring by TLC, the precipitate was collected by filtration to obtain 3.40 g of white crystals of (S)-3-amino-2-pentanone hydrochloride, with a yield of 99%.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing (S)-3-amino-2-pentanone hydrochloride, characterized in that: The following steps are involved: (1) Preparation of L-2-Boc-aminobutyric acid: L-2-aminobutyric acid is mixed with a solvent, an alkaline solution and a Boc anhydride solution and stirred to obtain a product; (2) Preparation of N-methoxy-N-methylamide: dissolving the L-2-Boc-aminobutyric acid obtained in step (1) in a solvent, adding dimethylhydroxylamine hydrochloride, an organic base and a coupling agent, and mixing and stirring to obtain; (3) Preparation of tert-butyl S-(2-oxopentan-3-yl)carbamate: dissolving the N-methoxy-N-methylamide obtained in step (2) in a solvent, mixing and reacting with methylmagnesium bromide to obtain; (4) Preparation of (S)-3-amino-2-pentanone hydrochloride: dissolving the S-(2-oxopentan-3-yl)carbamic acid tert-butyl ester obtained in step (3) in a solvent, adding concentrated hydrochloric acid to react, and obtaining; Wherein, in step (1), the mass volume ratio of L-2-aminobutyric acid to solvent, alkaline solution and Boc anhydride solution is 30-40g:40-60mL:50-150mL:20-40mL; the solvent comprises any one of methanol, ethanol and water; the alkaline solution comprises any one of NaOH aqueous solution, Na2CO3 aqueous solution and NaHCO3 aqueous solution, the concentration of the NaOH aqueous solution is 3-5mol / L, the concentration of the Na2CO3 aqueous solution is 5-10mol / L, the concentration of the NaHCO3 aqueous solution is 5-10mol / L; the concentration of the Boc anhydride solution is 10-15mol / L; the temperature of the mixed stirring is 20-30°C, and the time is 1-3h; After the mixing and stirring reaction in step (1) is completed, the reaction of the raw materials is monitored by TLC, and then ethyl acetate is added for separation, the pH of the aqueous phase is adjusted to 5-6, and ethyl acetate is extracted, the organic phases are combined, dried over anhydrous sodium sulfate, and concentrated in vacuo to complete purification and collection to obtain a colorless viscous liquid L-2-Boc-aminobutyric acid; The mixing and stirring temperature in step (2) is 20-30° C., and the time is 3-7 h. After the mixing and stirring reaction is completed, the reaction is monitored by TLC until the starting material disappears, water is added to quench the reaction, and then the liquids are separated, the organic phase is washed with saturated brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to complete purification and collect to obtain white solid N-methoxy-N-methylamide; In step (3), the mixed reaction is carried out in an ice-salt bath at a temperature of -30°C for 3-7 hours.

2. The method for preparing (S)-3-amino-2-pentanone hydrochloride according to claim 1, characterized in that: In the step (2), the mass volume ratio of L-2-Boc-aminobutyric acid to the solvent is 50-60 g: 150-250 mL, and the solvent includes dichloromethane; the molar ratio of L-2-Boc-aminobutyric acid, dimethylhydroxylamine hydrochloride, organic base and coupling agent is 250-300: 300-500: 800-1200: 300-500, the organic base includes any one of triethylamine, N,N-diisopropylethylamine, 4-dimethylaminopyridine and pyridine, and the coupling agent includes any one of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, dicyclohexylcarbodiimide, 1,3-diisopropylcarbodiimide, N,N'-carbonyldiimidazole and 2-(7-azobenzotriazole)-N,N,N',N'-tetramethyluronium hexafluorophosphate.

3. The method for preparing (S)-3-amino-2-pentanone hydrochloride according to claim 1, characterized in that: In the step (3), the mass volume ratio of N-methoxy-N-methylamide to the solvent is 7-8 g:80-120 mL, and the solvent includes at least one of tetrahydrofuran and toluene; the molar ratio of N-methoxy-N-methylamide to methylmagnesium bromide is 200-400:800-1200.

4. The method for preparing (S)-3-amino-2-pentanone hydrochloride according to claim 1, characterized in that: In the step (4), the mass volume ratio of S-(2-oxopentane-3-yl)carbamic acid tert-butyl ester, solvent and concentrated hydrochloric acid is 4-6 g:10-20 mL:3-8 mL, and the solvent includes any one of dichloromethane, ethyl acetate, tetrahydrofuran and dioxane.

5. The method for preparing (S)-3-amino-2-pentanone hydrochloride according to claim 1, characterized in that: The reaction temperature in step (4) is 20-30°C and the reaction time is 1-5h.

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