N-(t-butyloxycarboryl)-S-(3-nitro-2-pyridylthio)-L-cysteine as well as preparation method and application thereof

Abstract

The invention discloses N-(t-butyloxycarboryl)-S-(3-nitro-2-pyridylthio)-L-cysteine as well as a preparation method and application thereof, and relates to the technical field of chemical synthesis. Comprising the following steps: adding a diluent of 3-nitro-2-pyridylsulfuryl chloride into a dispersion liquid of N-t-butyloxycarboryl-L-cysteine, adding a first solvent, mixing, and carrying out a substitution reaction. The molar ratio of the 3-nitro-2-pyridylsulfuryl chloride to the N-t-butyloxycarboryl-L-cysteine is (0.5 to 2.0): 1. The first solvent comprises tetrahydrofuran and / or dichloromethane. 3-nitro-2-pyridylsulfuryl chloride and N-t-butyloxycarboryl-L-cysteine are used as raw materials, the molar ratio of the 3-nitro-2-pyridylsulfuryl chloride and the N-t-butyloxycarboryl-L-cysteine is controlled, and the selection of the first solvent is matched, so that the N-(t-butyloxycarboryl)-S-(3-nitro-2-pyridylsulfuryl)-L-cysteine with relatively high purity can be obtained, the reaction conditions are mild, the reaction efficiency is high, and the method is suitable for industrial production. And large-scale production can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of chemical synthesis, in particular to N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, a preparation method and application thereof. BACKGROUND

[0002] 3-nitro-2-pyridylthio (Npys) group is a group for protecting alcohol and amine functional groups in the process of peptide synthesis. The introduction of the group provides an important orthogonal protection supplement for the widely used Fmoc (9-fluorenylmethoxycarbonyl) and Boc (tert-butoxycarbonyl) protection strategy. In addition, the deprotection conditions of the Npys group are mild, and it can also specifically react with thiol groups to form asymmetric disulfide bonds, so it has an important position in the field of thiol protection. However, in the process of reaction of the Npys group with amino acids, there are many side reactions, which easily affect the yield and / or purity of the product.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The present application relates to the technical field of chemical synthesis, in particular to N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, a preparation method and application thereof.

[0005] The present application is implemented as follows: In a first aspect, the present application provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, comprising: adding a dilute solution of 3-nitro-2-pyridylthioyl chloride to a dispersion of N-tert-butoxycarbonyl-L-cysteine, and then adding a first solvent to mix and perform a substitution reaction.

[0006] The molar ratio of 3-nitro-2-pyridylthioyl chloride to N-tert-butoxycarbonyl-L-cysteine is 0.5-2.0:1.

[0007] The first solvent comprises tetrahydrofuran and / or dichloromethane.

[0008] In an optional embodiment, the dilute solution of 3-nitro-2-pyridylthioyl chloride comprises dissolving 3-nitro-2-pyridylthioyl chloride in a diluent, and the diluent comprises tetrahydrofuran and / or dichloromethane.

[0009] Preferably, the diluent is dichloromethane.

[0010] Preferably, the volume of the diluent is 4-6 times the mass of N-tert-butoxycarbonyl-L-cysteine. Preferably, the first solvent is tetrahydrofuran.

[0011] Preferably, the volume of the first solvent is 4-6 times the mass of the N-tert-butoxycarbonyl-L-cysteine.

[0012] In an optional embodiment, the temperature of the dispersion of N-tert-butoxycarbonyl-L-cysteine is less than 5℃ before the dilute solution of 3-nitro-2-pyridine sulfonyl chloride is added; and the temperature of the reaction system is 15-25℃ after the dilute solution of 3-nitro-2-pyridine sulfonyl chloride and the first solvent are added, and the substitution reaction is maintained for 20-40 min.

[0013] Preferably, the reaction atmosphere of the substitution reaction is an inert atmosphere.

[0014] Preferably, the molar ratio of 3-nitro-2-pyridine sulfonyl chloride to N-tert-butoxycarbonyl-L-cysteine is 0.8-1.2:1, preferably 1:1.

[0015] In an optional embodiment, the process further comprises separating and purifying the final reaction solution obtained from the substitution reaction; the process of separating and purifying comprises filtering the final reaction solution to obtain a filtrate, extracting and drying the filtrate to obtain a solid crude product; and the solid crude product is subjected to slurry purification.

[0016] Preferably, the extraction solvent used for extracting the filtrate of the final reaction solution is a combination of water and an organic solvent; and the organic solvent comprises dichloromethane or ethyl acetate.

[0017] Preferably, the process of extracting the filtrate of the final reaction solution comprises adding the extraction solvent to the filtrate, adjusting the pH to be alkaline, allowing the mixture to stand and separate into layers, taking the aqueous phase, adding an organic solvent to the aqueous phase, adjusting the pH to be acidic, allowing the mixture to stand and separate into layers, and taking the organic phase.

[0018] Preferably, in the process of extracting the filtrate of the final reaction solution, the pH is adjusted to be alkaline by adjusting the pH to 8-9, and the pH is adjusted to be acidic by adjusting the pH to 2-3.

[0019] Preferably, the process of drying the filtrate of the final reaction solution after extraction comprises using a desiccant for concentration and drying; the concentration and drying temperature is 40-50℃; and the desiccant comprises at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate, or molecular sieves.

[0020] Preferably, the process of slurry purification of the solid crude product comprises slurry purification of the solid crude product using a crude product purification solvent; and the crude product purification solvent comprises at least one of methyl tert-butyl ether, anhydrous methanol, petroleum ether, n-heptane, ethyl acetate, tetrahydrofuran, or dichloromethane.

[0021] In an optional embodiment, the preparation method of the dispersion of N-tert-butoxycarbonyl-L-cysteine comprises mixing N,N'-bis(tert-butoxycarbonyl)-L-cystine, triphenylphosphine, and a second solvent, and then heating and reacting.

[0022] Preferably, the molar ratio of N,N'-bis(tert-butoxycarbonyl)-L-cystine to triphenylphosphine is 1:1-1.2.

[0023] Preferably, the volume of the second solvent is 5.5-7 times the mass of N,N'-bis(tert-butoxycarbonyl)-L-cystine.

[0024] Preferably, the second solvent comprises at least one of tetrahydrofuran, water, dichloromethane and toluene.

[0025] Preferably, the conditions of the warming reaction comprise warming to 40-50°C, a reaction time of 2-5h and an inert atmosphere.

[0026] In an alternative embodiment, the method for preparing 3-nitro-2-pyridine sulfonyl chloride comprises: mixing 2-chloro-3-nitropyridine, benzyl mercaptan and an acid binding agent and then warming to react, and then purifying the obtained first reaction solution to obtain 2-(benzylthio)-3-nitropyridine; mixing 2-(benzylthio)-3-nitropyridine, a third solvent, a catalyst and sulfuryl chloride and then reacting below 0°C to obtain 3-nitro-2-pyridine sulfonyl chloride.

[0027] In an alternative embodiment, the molar ratio of 2-chloro-3-nitropyridine, benzyl mercaptan and an acid binding agent is 1:1.3-1.8:1.3-1.8.

[0028] Preferably, the acid binding agent comprises any one of triethylamine, diisopropylethylamine, pyridine, sodium carbonate, potassium carbonate or sodium acetate.

[0029] Preferably, the temperature of the reaction of 2-chloro-3-nitropyridine, benzyl mercaptan and an acid binding agent is 60-70°C, the reaction time is 1-3h and the solvent added during the reaction comprises any one of anhydrous methanol, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, tetrahydrofuran or N-methylpyrrolidone.

[0030] Preferably, the purification process of the first reaction solution comprises: drying the first reaction solution after concentration, and then separately extracting with a good solvent and a poor solvent.

[0031] Preferably, the good solvent comprises any one of ethyl acetate, dichloromethane or isopropyl acetate.

[0032] Preferably, the poor solvent comprises any one of petroleum ether, n-heptane or cyclohexane.

[0033] Preferably, after extraction with the good solvent, the extract is dried and then extracted with the poor solvent.

[0034] In an alternative embodiment, the molar ratio of 2-(benzylthio)-3-nitropyridine, a catalyst and sulfuryl chloride is 1:0.1-0.2:1.1-1.5.

[0035] Preferably, the third solvent comprises at least one of dichloromethane, dichloroethane and dioxane.

[0036] Preferably, the volume of the third solvent is 4-6 times the mass of 2-(benzylthio)-3-nitropyridine.

[0037] Preferably, the catalyst comprises any one of pyridine, triethylamine, 4-dimethylaminopyridine or N-methylmorpholine.

[0038] Preferably, the reaction time of 2-(benzylthio)-3-nitropyridine and sulfuryl chloride is 20-40 min.

[0039] In a second aspect, the present application provides N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine prepared by the preparation method of any one of the preceding embodiments.

[0040] In a third aspect, the present application provides use of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine as in any one of the preceding embodiments in preparation of an amino acid drug or an amino acid derivative drug.

[0041] The present application has the following beneficial effects: The present application provides N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, a preparation method and use thereof. By using 3-nitro-2-pyridylsulfonyl chloride and N-tert-butoxycarbonyl-L-cysteine as reaction raw materials, controlling the molar ratio of the two, and selecting the first solvent, it is beneficial to obtain N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine with high purity, and the reaction conditions are mild and the reaction efficiency is high, which is beneficial to realize large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0043] Figure 1 High performance liquid chromatogram of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine prepared by the method provided in Embodiment 1 of the present application; Figure 2The N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine prepared by the method provided in Embodiment 1 of the present application has a nuclear magnetic resonance hydrogen spectrum as shown in the following figure. DETAILED DESCRIPTION

[0044] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conditions are implemented according to conventional conditions or the conditions recommended by the manufacturers. If the manufacturers of the reagents or instruments are not specified, the reagents or instruments are conventional products that can be purchased in the market.

[0045] The features and performances of the present application will be further described in detail below in combination with the embodiments.

[0046] It should be noted that the “purity” and “yield” mentioned below are obtained by high performance liquid chromatography detection, and the detection conditions include: HPLC ≥ 99% (Shimadzu Essentia LC-16), column type (C18), mobile phase composition (0.1% H3PO4), flow rate (1.0 mL / min), wavelength (210 nm).

[0047] In a first aspect, the present application provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, comprising: adding a dilute solution of 3-nitro-2-pyridyl chloride to a dispersion solution of N-tert-butoxycarbonyl-L-cysteine, and then adding a first solvent to mix and perform a substitution reaction.

[0048] The molar ratio of 3-nitro-2-pyridyl chloride to N-tert-butoxycarbonyl-L-cysteine is 0.5-2.0.

[0049] The first solvent includes tetrahydrofuran and / or dichloromethane.

[0050] By using 3-nitro-2-pyridyl chloride and N-tert-butoxycarbonyl-L-cysteine as the reaction raw materials, and controlling the molar ratio of the two, and selecting the first solvent, it is beneficial to obtain N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine with high purity, and the reaction conditions are mild and the reaction efficiency is high, which is beneficial to realize large-scale production.

[0051] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. If specific conditions are not specified in the embodiments, the conditions are implemented according to conventional conditions or the conditions recommended by the manufacturers. If the manufacturers of the reagents or instruments are not specified, the reagents or instruments are conventional products that can be purchased in the market. S01, synthesis of 2-(benzylthio)-3-nitropyridine In an optional embodiment, the first reaction solution is obtained by mixing 2-chloro-3-nitropyridine, benzyl mercaptan and an acid-binding agent and then warming the mixture to react. The 2-(benzylthio)-3-nitropyridine is separated after the first reaction solution is purified.

[0052] S011, reaction process of 2-chloro-3-nitropyridine and benzyl mercaptan: In an optional embodiment, in order to ensure that 2-chloro-3-nitropyridine and benzyl mercaptan can uniformly react, the fourth solvent is first added into the reaction container before the reaction, and then 2-chloro-3-nitropyridine, benzyl mercaptan and an acid-binding agent are sequentially added into the fourth solvent to ensure that the raw materials and the auxiliary agent are uniformly dispersed in the fourth solvent, which is conducive to the stable synthesis of 2-(benzylthio)-3-nitropyridine and reduces the probability of side reactions.

[0053] Preferably, the fourth solvent includes any one of anhydrous methanol, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, tetrahydrofuran or N-methyl pyrrolidone, and is preferably anhydrous methanol.

[0054] Preferably, in order to ensure that 2-chloro-3-nitropyridine, benzyl mercaptan and an acid-binding agent are uniformly dispersed in the fourth solvent and conducive to the stable synthesis of 2-(benzylthio)-3-nitropyridine, the volume of the fourth solvent is 4-5 times the mass of 2-chloro-3-nitropyridine.

[0055] Preferably, the molar ratio of 2-chloro-3-nitropyridine, benzyl mercaptan and an acid-binding agent is 1:1.3-1.8:1.3-1.8, more preferably 1:1.4-1.6:1.4-1.6, and more preferably 1:1.5:1.5. By adding an excess of benzyl mercaptan, 2-chloro-3-nitropyridine can be completely converted, the purification is simple, and the yield of 2-(benzylthio)-3-nitropyridine is improved.

[0056] Preferably, the reaction temperature of 2-chloro-3-nitropyridine, benzyl mercaptan and an acid-binding agent is 60-70°C, and the reaction time is 1-3h. By reacting at a medium-high temperature, the conversion of 2-(benzylthio)-3-nitropyridine is facilitated.

[0057] Preferably, the acid-binding agent includes any one of triethylamine, diisopropyl ethylamine, pyridine, sodium carbonate, potassium carbonate or sodium acetate, and is more preferably triethanolamine.

[0058] Preferably, whether the reaction is complete can be determined by TLC spotting plate to show whether the raw material 2-chloro-3-nitropyridine is completely reacted.

[0059] S012, purification process of the first reaction solution: In an optional embodiment, after confirming that the reaction is completed, the purification process of the obtained first reaction solution comprises: after the first reaction solution is concentrated and dried, obtaining 2-(benzylthio)-3-nitropyridine crude product, and then extracting the 2-(benzylthio)-3-nitropyridine crude product with a good solvent and a poor solvent, respectively.

[0060] The selection of different extraction solvents will affect the yield and purity of 2-(benzylthio)-3-nitropyridine, and when the purity of 2-(benzylthio)-3-nitropyridine is low, for example, the purity of 2-(benzylthio)-3-nitropyridine is ≤95%, it will affect the purity of the final product N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine.

[0061] In order to improve the yield and purity of 2-(benzylthio)-3-nitropyridine and avoid affecting the purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, preferably, the good solvent includes any one of ethyl acetate, dichloromethane or isopropyl acetate; and the poor solvent includes any one of petroleum ether, n-heptane or n-hexane.

[0062] More preferably, the good solvent is ethyl acetate, and the poor solvent is petroleum ether. By using the combination of ethyl acetate as the good solvent and petroleum ether as the poor solvent, the high polarity of ethyl acetate can dissolve 2-(benzylthio)-3-nitropyridine, separate 2-(benzylthio)-3-nitropyridine from impurities, and then use petroleum ether to dissolve low-polarity impurities, thereby further improving the purity of 2-(benzylthio)-3-nitropyridine, and at the same time, reducing the loss of 2-(benzylthio)-3-nitropyridine.

[0063] Preferably, in order to ensure the smooth progress of the above extraction process, after extraction with the good solvent, the extraction liquid is dried to remove most of the good solvent, and then extracted with the poor solvent.

[0064] Specifically, the above extraction process is as follows: the 2-(benzylthio)-3-nitropyridine crude product is diluted and dissolved in a good solvent, then washed with ultrapure water, and the organic phase is collected. After the organic phase is concentrated and dried, it is added to a poor solvent to form a slurry, and then filtered to collect the solid.

[0065] Preferably, in order to ensure the extraction effect, the volume of the good solvent is 1.5-2.0 times, more preferably 1.8-2.0 times, the mass of the 2-(benzylthio)-3-nitropyridine crude product.

[0066] Preferably, the volume of the poor solvent is 1.5-2.0 times, more preferably 1.8-2.0 times, the mass of the concentrated and dried organic phase.

[0067] Preferably, the above-mentioned concentration and drying comprises drying the organic phase obtained after washing with ultra-pure water at 40-50°C using anhydrous sodium sulfate.

[0068] In an alternative embodiment, the solid obtained after beating and filtering the poor solvent is dried to ensure the subsequent reaction to proceed smoothly; the drying temperature is 40-50°C.

[0069] Preferably, the purity of 2-(benzylthio)-3-nitropyridine is ≥98% and the yield is ≥65%.

[0070] S02, synthesis of 3-nitro-2-pyridine sulfonyl chloride In an alternative embodiment, 2-(benzylthio)-3-nitropyridine, a third solvent, a catalyst and sulfonyl chloride are mixed and reacted below 0°C to obtain 3-nitro-2-pyridine sulfonyl chloride.

[0071] Preferably, 2-(benzylthio)-3-nitropyridine can be synthesized in S01 or purchased; to control costs, it is preferred to be synthesized in S01.

[0072] Preferably, to reduce the occurrence of side reactions, the process of synthesizing 3-nitro-2-pyridine sulfonyl chloride is carried out under the protection of an inert atmosphere, and the reaction temperature is controlled below 0°C.

[0073] Preferably, the inert atmosphere includes any one of nitrogen or helium.

[0074] Preferably, to ensure that the reaction of 2-(benzylthio)-3-nitropyridine and sulfonyl chloride proceeds stably, the process of synthesizing 3-nitro-2-pyridine sulfonyl chloride comprises: first adding a third solvent to the reaction vessel, then adding 2-(benzylthio)-3-nitropyridine under stirring, cooling the system to below 0°C, then sequentially adding a catalyst and sulfonyl chloride to the system, and controlling the system temperature to be below 0°C for 20-40 min.

[0075] In an alternative embodiment, the molar ratio of 2-(benzylthio)-3-nitropyridine, catalyst and sulfonyl chloride is 1:0.1-0.2:1.1-1.5, more preferably 1:0.12-0.18:1.2-1.4, and more preferably 1:0.15:1.3. By adding excess sulfonyl chloride, it is ensured that 2-(benzylthio)-3-nitropyridine is completely converted to 3-nitro-2-pyridine sulfonyl chloride, and the yield of 3-nitro-2-pyridine sulfonyl chloride is ensured.

[0076] Preferably, the third solvent comprises at least one of dichloromethane, dichloroethane and dioxane, more preferably dichloroethane. By selecting the third solvent as described above, the yield of 3-nitro-2-pyridine sulfonyl chloride can be significantly improved, especially when dichloroethane is used as the third solvent, the yield of 3-nitro-2-pyridine sulfonyl chloride is significantly improved, and the purity is also high, which is beneficial to the subsequent reaction.

[0077] Preferably, in order to facilitate the dispersion of the reaction raw materials in the third solvent, the volume of the third solvent is 4-6 times the mass of 2-(benzylthio)-3-nitropyridine.

[0078] Preferably, the catalyst comprises any one of pyridine, triethylamine, 4-dimethylaminopyridine or N-methylmorpholine. The catalyst can induce the generation of chloride anion by sulfonyl chloride, thereby promoting the generation of 3-nitro-2-pyridine sulfonyl chloride.

[0079] Preferably, after the TLC point plate shows that the reaction of the raw material 2-(benzylthio)-3-nitropyridine is complete, the reaction mixture is concentrated and dried under the protection of an inert atmosphere, and is temporarily stored under the inert atmosphere.

[0080] S03, synthesis of N-tert-butoxycarbonyl-L-cysteine In an optional embodiment, the method for preparing a dispersion of N-tert-butoxycarbonyl-L-cysteine comprises: mixing N,N'-bis(tert-butoxycarbonyl)-L-cystine, triphenylphosphine and a second solvent, and then heating to react.

[0081] Preferably, an inert atmosphere is used to protect the process of synthesizing N-tert-butoxycarbonyl-L-cysteine, so as to avoid side reactions.

[0082] Preferably, the inert atmosphere comprises any one of nitrogen or helium.

[0083] Preferably, the molar ratio of N,N'-bis(tert-butoxycarbonyl)-L-cystine to triphenylphosphine is 1:1-1.2, more preferably 1:1.1.

[0084] Preferably, the heating condition comprises heating to 40-50°C, and the reaction time is 2-5h.

[0085] Preferably, the second solvent comprises at least one of tetrahydrofuran, water, dichloromethane and toluene; preferably, the second solvent is a combination of tetrahydrofuran and water, and the water is ultrapure water, so as to avoid side reactions.

[0086] Preferably, in order to ensure the stable reaction of N,N'-bis(tert-butoxycarbonyl)-L-cysteine ​​and triphenylphosphine, the process of synthesizing N-tert-butoxycarbonyl-L-cysteine ​​includes: first adding a portion of the second solvent to the reaction vessel, then adding N,N'-bis(tert-butoxycarbonyl)-L-cysteine, triphenylphosphine and the remaining second solvent in sequence under stirring, mixing and then heating to react.

[0087] Preferably, the second solvent added twice can be the same or different. For example, tetrahydrofuran can be added twice, or tetrahydrofuran can be added first and water can be added second.

[0088] Preferably, the total volume of the added second solvent is 5.5 to 7 times the mass of N,N'-bis(tert-butoxycarbonyl)-L-cysteine. The volume ratio of the first added second solvent to the second added second solvent is 4 to 5: 0.5 to 1.

[0089] Preferably, after the reaction of the raw material N,N'-bis(tert-butoxycarbonyl)-L-cysteine ​​is completed as shown by TLC plate dot plot, the temperature is lowered to ≤5°C, and the resulting reaction solution can be directly used as a dispersion of N-tert-butoxycarbonyl-L-cysteine ​​for the next step.

[0090] S04, Synthesis of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridinylthio)-L-cysteine The reaction process of S041, 3-nitro-2-pyridinethioyl chloride and N-tert-butoxycarbonyl-L-cysteine: A diluted solution of 3-nitro-2-pyridinethioyl chloride was added to a dispersion of N-tert-butoxycarbonyl-L-cysteine, and then the first solvent was added and mixed before the substitution reaction was carried out.

[0091] In an optional embodiment, the diluent for 3-nitro-2-pyridinethioyl chloride comprises dissolving 3-nitro-2-pyridinethioyl chloride in a diluent, the diluent comprising tetrahydrofuran and / or dichloromethane.

[0092] Preferably, the diluent is dichloromethane.

[0093] By selecting the above-mentioned raw materials as solvents for diluting 3-nitro-2-pyridinethioyl chloride, and by using the diluent as a solvent system in the subsequent reaction process, a stable environment was provided for the reaction process of 3-nitro-2-pyridinethioyl chloride and N-tert-butoxycarbonyl-L-cysteine, effectively reducing the generation of impurities.

[0094] In addition, diluting 3-nitro-2-pyridinethioyl chloride with a diluent before reacting it with N-tert-butoxycarbonyl-L-cysteine ​​can control the reaction process and facilitate temperature control during the reaction, thus avoiding excessively vigorous local reactions that could lead to side reactions.

[0095] Preferably, the volume of the diluent is 4-6 times the mass of N-tert-butoxycarbonyl-L-cysteine.

[0096] Further, the dispersion of N-tert-butoxycarbonyl-L-cysteine can be directly obtained from the reaction solution at the end of the S03 step.

[0097] Preferably, the molar ratio of 3-nitro-2-pyridine sulfonyl chloride to N-tert-butoxycarbonyl-L-cysteine is 0.5-2.0:1, more preferably 0.8-1.2:1, and more preferably 1:1.

[0098] By controlling the molar ratio of 3-nitro-2-pyridine sulfonyl chloride to N-tert-butoxycarbonyl-L-cysteine within the above range, the generation of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine is facilitated; when the molar ratio is too low, the raw materials do not react completely, and the yield is reduced; when the molar ratio is too high, the auxiliary materials are wasted, and the cost is increased.

[0099] Preferably, the first solvent includes tetrahydrofuran and / or dichloromethane.

[0100] More preferably, the first solvent is tetrahydrofuran.

[0101] Preferably, the volume of the first solvent is 4-6 times the mass of N-tert-butoxycarbonyl-L-cysteine.

[0102] By selecting the above first solvent and combining it with the diluent to form the reaction system of 3-nitro-2-pyridine sulfonyl chloride and N-tert-butoxycarbonyl-L-cysteine, by the preferred combination of the first solvent being tetrahydrofuran and the diluent being dichloromethane, the yield of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine can be significantly improved, while ensuring that the purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine is relatively high.

[0103] In an optional embodiment, in order to further ensure the yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, the reaction atmosphere is an inert atmosphere, and the temperature of the entire process system needs to be controlled.

[0104] Specifically, the temperature of the dispersion of N-tert-butoxycarbonyl-L-cysteine is first reduced to less than 5°C, preferably 0°C; then the diluted solution of 3-nitro-2-pyridine sulfonyl chloride is added, the temperature is gradually increased to near room temperature level, then the first solvent is added, and the temperature of the reaction system is maintained at room temperature (15-25°C) for 20-40 min.

[0105] Preferably, the cooling process of the dispersion of N-tert-butyloxycarbonyl-L-cysteine can be performed by using an ice bath, such as an ice-salt bath or an ice-water bath, etc.

[0106] S042, purification process of the final reaction solution: In order to improve the purity of N-(tert-butyloxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, after the TLC point plate shows that the raw material N-tert-butyloxycarbonyl-L-cysteine has been completely reacted, the final reaction solution obtained by the substitution reaction is further separated and purified.

[0107] The separation and purification include filtering the final reaction solution, extracting and drying the filtrate to obtain a solid crude product, and beating the solid crude product for purification.

[0108] Preferably, the extraction of the filtrate of the final reaction solution includes adding water and an organic solvent to the filtrate to adjust the pH to be alkaline, standing and separating the layers to obtain the water phase, continuously adding the organic solvent to the water phase to adjust the pH to be acidic, standing and separating the layers to obtain the organic phase.

[0109] The water is ultrapure water, and the organic solvent includes any one of dichloromethane or ethyl acetate, and preferably, the organic solvent is dichloromethane.

[0110] Preferably, in the process of extracting the filtrate of the final reaction solution, the pH is adjusted to be alkaline to 8-9, and the pH is adjusted to be acidic to 2-3.

[0111] Specifically, the pH can be adjusted to be alkaline by adding an alkaline substance to the filtrate, such as sodium carbonate, sodium bicarbonate, and sodium hydroxide, etc.; preferably, the pH can be adjusted to be alkaline by adding 15% sodium carbonate to the filtrate.

[0112] The pH can be adjusted to be acidic by adding an acidic substance to the filtrate, such as phosphoric acid aqueous solution, and preferably, the pH can be adjusted to be acidic by adding 10% phosphoric acid aqueous solution to the filtrate.

[0113] By selecting the above-mentioned extraction solvent and controlling the pH of the extraction, various impurities can be removed, which is conducive to improving the purity of N-(tert-butyloxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine.

[0114] Preferably, the drying of the filtrate of the final reaction solution after extraction includes concentrated drying by using a hygroscopic agent, and the concentrated drying temperature is 40-50°C; the hygroscopic agent includes at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate, or molecular sieves.

[0115] Preferably, the beating purification of the solid crude product comprises beating the solid crude product with a crude product purification solvent; the crude product purification solvent comprises at least one of methyl tert-butyl ether, anhydrous methanol, petroleum ether, n-heptane, ethyl acetate, tetrahydrofuran or dichloromethane.

[0116] Preferably, the beating time is 1-3 h, and the volume of the crude product purification solvent is 5-6 times the mass of the solid crude product. After the beating, the filter cake is filtered and washed with the crude product purification solvent.

[0117] In a second aspect, the present application provides N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine prepared by the preparation method of any one of the preceding embodiments.

[0118] In a third aspect, the present application provides use of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine as in any one of the preceding embodiments in preparation of an amino acid drug or an amino acid derivative drug.

[0119] Example 1 The present embodiment provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, and the process is as follows: .

[0120] The specific steps and reaction parameters are as follows: S01, synthesis of 2-(benzylthio)-3-nitropyridine S011, reaction process of 2-chloro-3-nitropyridine and benzyl mercaptan: Into a 2 L three-necked flask, anhydrous methanol (675 mL, 4.5 V) was added at room temperature, and magnetic stirring was started, followed by sequential addition of 2-chloro-3-nitropyridine (150 g, 946.1 mmol, 1.0 eq), benzyl mercaptan (176.3 g, 1419.1 mmol, 1.5 eq) and triethylamine (14.36 g, 1419.1 mmol, 1.5 eq). The temperature was raised to 65 ℃ and kept for 2 h until TLC point plate showed that the raw material 2-chloro-3-nitropyridine was completely reacted, and a first reaction liquid was obtained.

[0121] S012, purification process of the first reaction liquid: The first reaction solution of step S011 was concentrated and dried at 45 °C to obtain 484.5 g of bright yellow solid, which was 2-(benzylthio)-3-nitropyridine crude product. The 2-(benzylthio)-3-nitropyridine crude product was diluted with 900 mL of ethyl acetate and washed twice with 450 mL of ultrapure water each time. After washing, the organic phase was collected. The organic phase was dried with anhydrous sodium sulfate (300 g), and concentrated and dried at 45 °C to obtain 298.5 g of brownish yellow oil. Then, the brownish yellow oil was slurried with petroleum ether (600 mL) for 0.5 h, filtered at room temperature, and the collected solid was dried in a blast oven at 45 °C to obtain 205.5 g of yellow solid, which was 2-(benzylthio)-3-nitropyridine. Yield: 88%, purity 99%. S02, synthesis of 3-nitro-2-pyridine sulfonyl chloride Nitrogen was replaced three times, and under nitrogen protection, dichloroethane (850 mL, 5 V) was added to a 2 L three-necked flask, magnetic stirring was started, then 2-(benzylthio)-3-nitropyridine (170 g, 690.2 mmol, 1.0 eq) obtained from step S01 was added, and the ice-salt bath was cooled to below 0 °C. Under nitrogen protection, pyridine (8.2 g, 103.5 mmol, 0.15 eq) and sulfonyl chloride (121.1 g, 897.3 mmol, 1.3 eq) were added to the above reaction system in turn, and the temperature was controlled below 0 °C for 0.5 h.

[0122] After TLC point plate showed that the raw material 2-(benzylthio)-3-nitropyridine was completely reacted, the product was transferred to a single-necked flask under nitrogen protection, concentrated and dried at 45 °C, evacuated under nitrogen, and the product was stored in a nitrogen environment. The product was 131.6 g of yellow solid, which was 3-nitro-2-pyridine sulfonyl chloride, yield: 100%, purity 99%.

[0123] S03, synthesis of N-tert-butoxycarbonyl-L-cysteine Nitrogen was replaced three times, and under nitrogen protection, tetrahydrofuran (756 mL, 5.4 V) was added to a 2 L three-necked flask, magnetic stirring was started, and N,N'-bis(tert-butoxycarbonyl)-L-cystine (140 g, 317.8 mmol, 1.0 eq), triphenylphosphine (91.7 g, 349.6 mmol, 1.1 eq) and ultrapure water (116.2 mL, 0.83 V) were added in turn; the temperature was increased to 40-50 °C and the reaction was kept for 4 h.

[0124] TLC spot plate showed that after the reaction of raw material N,N'-bis(tert-butoxycarbonyl)-L-cystine was completed, the reaction solution was cooled to 0-5 ℃ and could be directly used for the next step. The yield of N-tert-butoxycarbonyl-L-cysteine was 100%, and the purity was 99%.

[0125] S04, synthesis of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine S041, reaction process of 3-nitro-2-pyridine sulfonyl chloride and N-tert-butoxycarbonyl-L-cysteine: Under nitrogen protection, N-tert-butoxycarbonyl-L-cysteine (140 g, 632.7 mmol, 1.0 eq) was added to the reaction vessel containing the reaction solution of S03 step, and 3-nitro-2-pyridine sulfonyl chloride (120.6 g, 632.7 mmol, 1.0 eq) diluted with dichloromethane (350 mL, 2.5 V) was added dropwise to the system under an ice-salt bath. The temperature rose, and tetrahydrofuran (350 mL, 2.5 V) was added to disperse the system, and the reaction was stirred at room temperature for 0.5 h.

[0126] S042, purification process of the final reaction solution: When TLC spot plate showed that the reaction of raw material N-tert-butoxycarbonyl-L-cysteine was completed, the final reaction solution was filtered at room temperature, and the filtrate was reserved. Ultra-pure water (1.5 L) and dichloromethane (0.5 L) were added to the filtrate, and 15% sodium carbonate aqueous solution (600 g) was added dropwise to adjust the pH to 8-9. The water phase was reserved after standing and layering. Dichloromethane (1.5 L) was added to the water phase, 10% phosphoric acid aqueous solution (850 mL) was used to adjust the pH to 2-3, and the organic phase was reserved after standing and liquid separation. Anhydrous sodium sulfate (350 g) was used for drying, and the yellow solid crude product was obtained by concentrating at 45 ℃. The solid was slurried with methyl tert-butyl ether (1000 mL) and anhydrous methanol (20 mL) at room temperature for 2 h, filtered, and the filter cake was rinsed with methyl tert-butyl ether (200 mL). The filter cake after rinsing was dried in a blast oven for 3 h to obtain 131.16 g of yellow solid, which was N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine. The yield was 55%, and the purity was 99%.

[0127] In the method provided in the embodiment, the high performance liquid chromatogram of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine is as shown in Figure 1 , and as can be seen from Figure 1 , the purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine is 99%, and the single impurity is <0.4%.

[0128] The N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine prepared in this example was detected by a nuclear magnetic resonance hydrogen spectrum, and the results as shown in Figure 2 Figure 2 The structure of the N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine was confirmed as

[0129] Example 2 This example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that the petroleum ether in S012 step is replaced by n-heptane.

[0130] Comparative Example 1 This comparative example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that the ethyl acetate in S012 step is replaced by methyl tert-butyl ether.

[0131] Comparative Example 2 This comparative example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that the ethyl acetate in S012 step is replaced by a mixture of ethyl acetate and isopropanol, and the volume ratio of ethyl acetate to isopropanol is 1:1.

[0132] Comparative Example 3 This comparative example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that the ethyl acetate in S012 step is replaced by a mixture of methyl tert-butyl ether and isopropanol, and the volume ratio of methyl tert-butyl ether to isopropanol is 1:1.

[0133] Test Example 1 The yield of 2-(benzylthio)-3-nitropyridine obtained in S01 step of the methods of Examples 1, 2 and Comparative Examples 1 to 3 was calculated, and its purity was detected, and the results as shown in Table 1 were obtained.

[0134] ​​Meanwhile, the 2-(benzylthio)-3-nitropyridine obtained in the above examples and comparative examples was further prepared to obtain N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine according to the method of Example 1, and whether the 2-(benzylthio)-3-nitropyridine obtained after purification of different reagents had an effect on the purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine was checked; if HPLC≤99%, it was indicated that there was an effect, and if HPLC≥99%, it was indicated that there was no effect, and the effect was also recorded in Table 1.

[0135] Table 1 Yield, purity and effect of 2-(benzylthio)-3-nitropyridine

[0136] As can be seen from Table 1, in the S01 step, the combination of ethyl acetate and petroleum ether was used to extract the first reaction liquid obtained in the reaction in Example 1, and 2-(benzylthio)-3-nitropyridine with high yield and purity could be obtained, and the purity of the final product would not be affected. Although the combination of ethyl acetate and n-heptane was used in Example 2, 2-(benzylthio)-3-nitropyridine with high purity could also be obtained, and the purity of the final product would not be affected, but the yield was low, so it could be used as a process method for small-scale synthesis. In the purification process of the step, methyl tert-butyl ether and / or isopropanol were introduced in Comparative Examples 1 to 3, which resulted in low purity of 2-(benzylthio)-3-nitropyridine. Using 2-(benzylthio)-3-nitropyridine with low purity to continue to synthesize N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine would cause the purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine to decrease significantly. Therefore, the selection of the extraction solvent in the S012 step has an important influence on the purity and yield of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, and the purity of the intermediate 2-(benzylthio)-3-nitropyridine is very important for the purity control of the final product.

[0137] Example 3 This example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, and the only difference is that dichloroethane is replaced by dioxane in the S02 step.

[0138] Example 4 This example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, and the only difference is that dichloroethane is replaced by dichloromethane in the S02 step.

[0139] Comparative Example 4 This comparative example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, except that in the S02 step, dichloroethane is replaced by chloroform.

[0140] Comparative Example 5 This comparative example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, except that in the S02 step, dichloroethane is replaced by toluene.

[0141] Test Example 2 The yield of 3-nitro-2-pyridylthiochloride obtained in the S02 step of the methods of Examples 1, 3, 4, and Comparative Examples 4 and 5 was calculated, and the purity was detected, obtaining the results shown in Table 2.

[0142] Table 2 Yield and Purity of 3-nitro-2-pyridylthiochloride

[0143] As can be seen from Table 2, in the S02 step, Example 1 used dichloroethane as the third solvent, the yield of 3-nitro-2-pyridylthiochloride reached 100%, and the purity reached 99%, which had a very significant advantage in the subsequent reaction process. Examples 3 and 4 used dioxane and dichloromethane to replace dichloroethane, respectively, and obtained 3-nitro-2-pyridylthiochloride with higher purity, but the yield decreased slightly, which can be used as a process method for small-scale synthesis. Comparative Example 4 used chloroform, and the yield of 3-nitro-2-pyridylthiochloride further decreased, and the economic benefit was lower. Comparative Example 5 used toluene to replace dichloroethane, and the purity decreased significantly, which easily affected the purity of the final product.

[0144] It is shown that in the reaction process of 2-(benzylthio)-3-nitropyridine and thionyl chloride, the selection of the solvent of the reaction system has a great influence on the purity and yield of the reactant.

[0145] Example 5 This example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, except that in the S03 step, both tetrahydrofuran and ultrapure water are replaced by dichloromethane.

[0146] Example 6 This example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to Example 1, except that in the S03 step, ultrapure water is replaced by tetrahydrofuran.

[0147] Example 7 This example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that in S03 step, the combination of tetrahydrofuran and ultrapure water is replaced by toluene.

[0148] Test Example 3 The yield of N-tert-butoxycarbonyl-L-cysteine obtained in S03 step of the method of Example 1 and Examples 5-7 is calculated, and its purity is detected, and the reaction time is recorded, and the results shown in Table 3 are obtained.

[0149] Table 3 Yield, purity and reaction time of N-tert-butoxycarbonyl-L-cysteine

[0150] As can be seen from Table 3, in S03 step, the combination of tetrahydrofuran and ultrapure water used in Example 1 as the solvent system for synthesizing N-tert-butoxycarbonyl-L-cysteine can ensure high yield and high purity of the product, while obtaining the shortest reaction time, which is conducive to improving the economic benefit of the process. Examples 5-7 can also obtain N-tert-butoxycarbonyl-L-cysteine with relatively high purity, and the yield is slightly lower than that of Example 1, and the reaction time is prolonged. It is shown that the solvent system of tetrahydrofuran and ultrapure water is more conducive to the efficient synthesis of N-tert-butoxycarbonyl-L-cysteine with high purity and high yield.

[0151] Example 8 This example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that in S041 step, dichloromethane is replaced by tetrahydrofuran.

[0152] Example 9 This example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that in S041 step, tetrahydrofuran is replaced by dichloromethane.

[0153] Comparative Example 6 This comparative example provides a method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that in S041 step, tetrahydrofuran is replaced by N,N-dimethylformamide, and dichloromethane is also replaced by N,N-dimethylformamide.

[0154] Comparative Example 7 The comparative example provides a preparation method of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, which is similar to that of Example 1, except that in the S041 step, tetrahydrofuran is replaced by dimethyl sulfoxide, and dichloromethane is also replaced by dimethyl sulfoxide.

[0155] Test Example 4 The yield of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine obtained in the S04 step of the methods of Examples 1, 8, 9 and Comparative Examples 6 and 7 was calculated, and its purity was detected, obtaining the results shown in Table 4.

[0156] Table 4 Yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine

[0157] As can be seen from Table 2, in the S04 step, Example 1 uses a solvent system of dichloromethane and tetrahydrofuran to carry out the reaction of N-tert-butoxycarbonyl-L-cysteine and 3-nitro-2-pyridylthiochloride, and the purity of the final product reaches 99%, while the yield is as high as 55%, significantly improving the yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, and the synthesis method is simple and mild, and the synthesis conditions are easy to control, which is suitable for large-scale production.

[0158] Examples 8 and 9 use pure dichloromethane solvent system and pure tetrahydrofuran solvent system, and still can obtain N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine with relatively high purity, which meets the use requirements of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine, but the yield is slightly lower than that of Example 1, indicating that the composite solvent system of dichloromethane and tetrahydrofuran is beneficial to improving the yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine.

[0159] Comparative Example 6 uses N,N-dimethylformamide as the reaction system of S041 step, and the yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine obtained are reduced, and Comparative Example 7 uses dimethyl sulfoxide as the reaction system of S041 step, and the yield and purity of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine obtained are too low to affect the further application of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridylthio)-L-cysteine.

[0160] The above merely provides the preferred embodiments of the present application, and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the principles and technical scope of the present application shall fall into the scope of the present application.

Claims

1. A method for preparing N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridinylthio)-L-cysteine, characterized in that, include: A diluted solution of 3-nitro-2-pyridinethioyl chloride was added to a dispersion of N-tert-butoxycarbonyl-L-cysteine, and then the first solvent was added and mixed to carry out the substitution reaction. The molar ratio of 3-nitro-2-pyridinethioyl chloride to N-tert-butoxycarbonyl-L-cysteine ​​is 0.5~2.0:1; The first solvent includes at least one of tetrahydrofuran and / or dichloromethane.

2. The preparation method according to claim 1, characterized in that, The diluent for the 3-nitro-2-pyridinethioyl chloride comprises dissolving the 3-nitro-2-pyridinethioyl chloride in a diluent comprising tetrahydrofuran and / or dichloromethane; Preferably, the diluent is dichloromethane; Preferably, the volume of the diluent is 4 to 6 times the mass of the N-tert-butoxycarbonyl-L-cysteine; Preferably, the first solvent is tetrahydrofuran; Preferably, the volume of the first solvent is 4 to 6 times the mass of the N-tert-butoxycarbonyl-L-cysteine.

3. The preparation method according to claim 1, characterized in that, Before adding the diluent of 3-nitro-2-pyridinethioyl chloride, the temperature of the dispersion of N-tert-butoxycarbonyl-L-cysteine ​​is less than 5°C; after adding the diluent of 3-nitro-2-pyridinethioyl chloride and the first solvent, the temperature of the reaction system is 15~25°C, and the substitution reaction is carried out for 20~40 minutes. Preferably, the reaction atmosphere for the substitution reaction is an inert atmosphere; Preferably, the molar ratio of 3-nitro-2-pyridinethioyl chloride to N-tert-butoxycarbonyl-L-cysteine ​​is 0.8 to 1.2, more preferably 1.

0.

4. The preparation method according to claim 1, characterized in that, It also includes separating and purifying the final reaction solution obtained from the substitution reaction; the separation and purification process includes filtering the final reaction solution, taking the filtrate, extracting and drying the filtrate to obtain a solid crude product; and purifying the solid crude product by pulping. Preferably, the extraction solvent used to extract the filtrate of the final reaction solution is a combination of water and an organic solvent; the organic solvent includes dichloromethane or ethyl acetate. Preferably, the extraction of the filtrate of the final reaction solution includes: adding an extraction solvent to the filtrate, adjusting the pH to alkaline, allowing it to stand and separate into layers, taking the aqueous phase, adding the organic solvent to the aqueous phase, adjusting the pH to acidic, allowing it to stand and separate into layers, and taking the organic phase. Preferably, during the extraction of the filtrate of the final reaction solution, adjusting the pH to alkaline means adjusting the pH to 8-9, and adjusting the pH to acidic means adjusting the pH to 2-3. Preferably, drying the filtrate of the final reaction solution after extraction includes: concentrating and drying with a hygroscopic agent at a temperature of 40-50°C, wherein the hygroscopic agent includes at least one of anhydrous sodium sulfate, anhydrous magnesium sulfate, and molecular sieve. Preferably, the purification of the crude solid product by pulping includes pulping the crude solid product using a crude product purification solvent; the crude product purification solvent includes at least one of methyl tert-butyl ether, anhydrous methanol, petroleum ether, n-heptane, ethyl acetate, tetrahydrofuran, or dichloromethane.

5. The preparation method according to claim 1, characterized in that, The method for preparing the dispersion of N-tert-butoxycarbonyl-L-cysteine ​​includes: mixing N,N'-bis(tert-butoxycarbonyl)-L-cysteine, triphenylphosphine, and a second solvent, and then heating the mixture to react. Preferably, the molar ratio of N,N'-bis(tert-butoxycarbonyl)-L-cysteine ​​to triphenylphosphine is 1:1 to 1.2; Preferably, the volume of the second solvent is 5.5 to 7 times the mass of N,N'-bis(tert-butoxycarbonyl)-L-cysteine; Preferably, the second solvent comprises at least one of tetrahydrofuran, water, dichloromethane, and toluene; Preferably, the conditions for the heating reaction include heating to 40~50°C, a reaction time of 2~5 hours, and an inert atmosphere.

6. The preparation method according to claim 1, characterized in that, The preparation method of the 3-nitro-2-pyridinethioyl chloride includes: mixing 2-chloro-3-nitropyridine, benzyl thiol and an acid-binding agent and then heating the mixture to react; purifying the first reaction solution to obtain 2-(benzylthio)-3-nitropyridine; mixing the 2-(benzylthio)-3-nitropyridine, a third solvent, a catalyst and thioyl chloride and then reacting the mixture below 0°C to obtain the 3-nitro-2-pyridinethioyl chloride.

7. The preparation method according to claim 6, characterized in that, The molar ratio of the 2-chloro-3-nitropyridine, the benzyl thiol, and the acid-binding agent is 1:1.3~1.8:1.3~1.8; Preferably, the acid-binding agent includes any one of triethylamine, diisopropylethylamine, pyridine, sodium carbonate, potassium carbonate, or sodium acetate; Preferably, the reaction temperature of 2-chloro-3-nitropyridine, benzyl thiol and acid-binding agent is 60~70℃, the reaction time is 1~3h, and the solvent added during the reaction includes any one of anhydrous methanol, dimethyl sulfoxide, N,N-dimethylformamide, acetonitrile, tetrahydrofuran or N-methylpyrrolidone. Preferably, the purification process of the first reaction solution includes: concentrating and drying the first reaction solution, and then extracting it with a good solvent and a poor solvent, respectively; Preferably, the good solvent includes any one of ethyl acetate, dichloromethane, or isopropyl acetate; Preferably, the undesirable solvent includes any one of petroleum ether, n-heptane, or cyclohexane; Preferably, after extraction with the good solvent, the extract is dried before extraction with the poor solvent.

8. The preparation method according to claim 6, characterized in that, The molar ratio of the 2-(benzylthio)-3-nitropyridine, the catalyst, and the thioyl chloride is 1:0.1~0.2:1.1~1.5; Preferably, the third solvent includes at least one of dichloromethane, dichloroethane, and dioxane; Preferably, the volume of the third solvent is 4 to 6 times the mass of the 2-(benzylthio)-3-nitropyridine shown. Preferably, the catalyst comprises any one of pyridine, triethylamine, 4-dimethylaminopyridine, or N-methylmorpholine; Preferably, the reaction time of the 2-(benzylthio)-3-nitropyridine with the thioyl chloride is 20-40 min.

9. An N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridinylthio)-L-cysteine, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. The use of N-(tert-butoxycarbonyl)-S-(3-nitro-2-pyridinylthio)-L-cysteine ​​as described in claim 9 in the preparation of amino acid drugs or amino acid derivative drugs.

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