A preparation method of chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid
The preparation process of trans-chiral 1-aminocyclopentane-3-carboxylic acid is simplified by double bond migration and reduction, which solves the problems of difficult separation and high cost in the prior art and achieves high-yield and low-cost industrial production.
Patent Information
- Application Number
- CN202311771775.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-12-21
- Publication Date
- 2025-09-30
- Estimated Expiration
- 2043-12-21
AI Technical Summary
The existing method for preparing trans-chiral 1-aminocyclopentane-3-carboxylic acid has the problems of difficult separation, high cost, and difficulty in achieving industrial production.
The invention adopts a double bond migration and reduction method, wherein (1R,4S)-4-((tert-butoxycarbonyl)amino)cyclopent-2-enecarboxylic acid reacts with a base, di-tert-butyl dicarbonate, potassium carbonate, sodium borohydride and a specific catalyst, thereby simplifying the reaction steps and improving the overall yield.
The method effectively avoids separation difficulties, reduces production costs, is suitable for industrial production, and improves optical purity and overall yield.
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Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of organic synthesis, and specifically relates to a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, and in particular relates to a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with high yield. Background Art
[0002] Trans-chiral 1-aminocyclopentane-3-carboxylic acid is a key fragment of nucleoside analog reverse transcriptase inhibitors and also a key fragment of many new anticancer drugs. The conventional preparation method uses the following steps:
[0003]
[0004] The third step, the differentiation process, involves preparing and isolating the trans-isomer, but this separation process is difficult and expensive, making it difficult to commercialize and hindering the large-scale application of trans-chiral 1-aminocyclopentane-3-carboxylic acid. Therefore, a method for preparing trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with high yield, simplicity, low cost, and high optical purity has become an urgent challenge. Summary of the Invention
[0005] To address the shortcomings of the prior art, the present invention aims to provide a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, particularly a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid in high yield. Compared to the prior art, the preparation method provided by the present invention significantly reduces the number of reaction steps and processes, resulting in a simpler overall process, a higher total yield, and significantly reduced production costs, making it suitable for industrial production.
[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:
[0007] The present invention provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, which comprises the following steps:
[0008] (1) (1R,4S)-4-((tert-butoxycarbonyl)amino)cyclopent-2-enecarboxylic acid and methanol are mixed and esterified to obtain compound 1;
[0009] (2) Compound 1 is mixed with a base and di-tert-butyl dicarbonate to react to obtain Compound 2;
[0010] (3) Compound 2 is mixed with potassium carbonate to react to obtain compound 3;
[0011] (4) Compound 3 is mixed with sodium borohydride and a catalyst to react to obtain compound 4;
[0012] (5) Compound 4 is mixed with a base and hydrolyzed to obtain the chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid.
[0013] The reaction process is as follows:
[0014]
[0015] The above method effectively avoids the separation difficulty caused by the differentiation process in the prior art by adopting the double bond migration and subsequent reduction. The reaction steps and processes are significantly reduced, the overall process is simpler, the total yield is higher, the production cost is greatly reduced, and it is suitable for industrial production.
[0016] Preferably, the reaction temperature in step (1) is 10-80°C, and the reaction time is 2-8h, wherein the temperature can be 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, and the reaction time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h or 8h, but are not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0017] Preferably, the reaction temperature in step (2) is 10-30°C, and the reaction time is 8-16h, wherein the temperature can be 10°C, 15°C, 20°C, 25°C or 30°C, and the reaction time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or 16h, but are not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0018] Preferably, the molar ratio of compound 2 to potassium carbonate in step (3) is 1:(1.5-2.5), for example 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, etc., but is not limited to the values listed above, and other values not listed within the above numerical range are also applicable.
[0019] Preferably, the reaction temperature in step (3) is 50-80°C, and the reaction time is 8-15h, wherein the temperature can be 50°C, 55°C, 60°C, 65°C, 70°C, 75°C or 80°C, etc., and the reaction time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h or 15h, etc., but are not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0020] Preferably, the catalyst in step (4) comprises any one of L-pyroglutamic acid, L-proline, L-alanine or L-hydroxyproline, or a combination of at least two thereof, preferably L-pyroglutamic acid.
[0021] The above-mentioned specific catalyst can effectively catalyze the reaction to generate the target chiral product. At the same time, the selection of a specific catalyst can further improve the optical purity of the product.
[0022] Preferably, the molar ratio of compound 3 to the catalyst and sodium borohydride in step (4) is 1:(0.3-0.5):(1-5), wherein the number of parts of the catalyst can be 0.3, 0.35, 0.4, 0.45 or 0.5, etc., and the number of parts of sodium borohydride can be 1, 2, 3, 4 or 5, etc., but are not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0023] Preferably, the reaction temperature in step (4) is 10-30°C, and the reaction time is 8-16h, wherein the temperature can be 10°C, 15°C, 20°C, 25°C or 30°C, and the reaction time can be 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h or 16h, but are not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0024] Preferably, the base in step (5) comprises any one of lithium hydroxide, sodium hydroxide or lithium hydroxide, or a combination of at least two thereof.
[0025] Preferably, the molar ratio of compound 4 to the base in step (5) is 1:(1.5-2.5), for example 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4 or 1:2.5, etc., but is not limited to the values listed above, and other values not listed within the above numerical range are also applicable.
[0026] Preferably, the reaction temperature in step (5) is -10 to 5°C, and the reaction time is 2-5h, wherein the temperature can be -10°C, -9°C, -8°C, -7°C, -6°C, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, 1°C, 2°C, 3°C, 4°C or 5°C, and the reaction time can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h, but is not limited to the values listed above. Other values not listed within the above numerical range are also applicable.
[0027] Compared with the prior art, the present invention has the following beneficial effects:
[0028] The present invention provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid. By adopting a double bond migration followed by reduction, the separation difficulty caused by the differentiation process in the prior art is effectively avoided. The reaction steps and processes are significantly reduced, the overall process is simpler, the total yield is higher, the production cost is greatly reduced, and the method is suitable for industrial production. DETAILED DESCRIPTION
[0029] In order to further illustrate the technical means and effects adopted by the present invention, the technical solutions of the present invention are further described below in conjunction with the preferred embodiments of the present invention, but the present invention is not limited to the scope of the embodiments.
[0030] Example 1
[0031] This embodiment provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, and the specific steps are as follows:
[0032]
[0033] (1) Add (1R, 4S)-N-tert-butyloxycarbonyl-1-aminocyclopent-2-ene-4-carboxylic acid (100 g, 0.44 mol) and anhydrous methanol (440 mL) to a 1 L three-necked flask, cool to 0°C in an ice bath with stirring, and begin to add thionyl chloride (62 g, 0.52 mol) dropwise. After the addition of thionyl chloride, stir at 20°C for 2 hours, heat (70°C) and reflux for 4 hours, and then concentrate under reduced pressure to obtain a large amount of solid, namely, compound 1, with a yield of 98%;
[0034] (2) Compound 1 (76 g, 0.43 mol) and 1 L of dichloromethane were added to a 2 L three-necked flask and stirred. The mixture was cooled in an ice bath (0°C) and triethylamine (66.6 g, 0.65 mol) was added dropwise. After the addition was complete, the mixture was stirred for 20 minutes. Di-tert-butyl dicarbonate (105 g, 0.48 mol) was added dropwise. After the addition was complete, the mixture was stirred at 10°C for 12 hours. After TLC showed that the starting material disappeared, 1 M hydrochloric acid solution was added dropwise and the pH was adjusted to 1. The layers were separated and the aqueous phase was extracted once with 200 mL of dichloromethane. The organic phase was washed once with 200 mL of saturated brine, dried over anhydrous magnesium sulfate, and concentrated to obtain compound 2 with a yield of 95%.
[0035] (3) 1 L of dichloromethane was added to a 2 L three-necked flask, and compound 2 (97.7 g, 0.40 mol) was added with stirring, followed by potassium carbonate (111 g, 0.8 mol). After the addition of potassium carbonate, the mixture was stirred for 30 minutes, heated at 66 ° C. and refluxed for 10 hours. After TLC showed that the starting material disappeared, the mixture was concentrated under reduced pressure. After concentration, the mixture was dissolved in dichloromethane, 1 M hydrochloric acid solution was added dropwise, and the pH was adjusted to 1. The layers were separated, and the aqueous phase was extracted once with 200 mL of dichloromethane. The organic phase was washed once with 200 mL of saturated brine, dried over anhydrous magnesium sulfate, concentrated, and crystallized from petroleum ether to obtain a white solid, thereby obtaining compound 3 with a yield of 90%;
[0036] (4) Add 4 L of anhydrous methanol and L-pyroglutamic acid (321 g, 2.48 mol) to a 2 L three-necked flask, add sodium borohydride (31 g, 0.79 mol) in portions at -10 ° C, raise the temperature to 0 ° C and stir for 1 hour. The temperature is then lowered to -10 ° C, the obtained compound 3 (87 g, 0.36 mol) is dissolved in dichloromethane (1 L) and added dropwise to the above mixture, slowly raised to 0 ° C, stirred for 1 hour, and then naturally raised to 20 ° C and stirred for 12 hours. After LC shows that the raw material disappears, 1 M hydrochloric acid solution is added dropwise to adjust the pH to 1, and then 2 L of water is added. The layers are separated and extracted twice with 4 L of dichloromethane. The organic phases are combined and washed with saturated sodium carbonate until alkaline. The organic phases are dried over anhydrous magnesium sulfate, concentrated, and crystallized from petroleum ether:ethyl acetate = 1:1 to obtain solid compound 4 with a yield of 80% and an ee of 95.8%.
[0037] (5) Compound 4 (70 g, 0.288 mol) was added to a 2 L three-necked flask and dissolved in tetrahydrofuran (800 mL) and water (400 mL). Lithium hydroxide (12.4 g, 0.518 mol) was added portionwise under ice bath. The reaction was continued for 2 hours after the addition of lithium hydroxide. After TLC showed that the starting material disappeared, water (300 mL) was added, the layers were separated, and the aqueous phase was extracted once with dichloromethane. The pH of the separated aqueous phase was adjusted to 2 with 1 M hydrochloric acid, and then extracted three times with dichloromethane (2 L). The organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and concentrated to an organic phase. Petroleum ether:ethyl acetate|=1:1 (300 mL) was added for crystallization. The mixture was stirred at 20°C for 1 hour, filtered, and dried to obtain 60 g of trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with a yield of 90% and an ee of 96.2%.
[0038] The characterization data are as follows:
[0039] 1H NMR (400MHz, DMSO) δ6.89 (dd, J=13.8, 7.3Hz, 1H), 3.93–3.68 (m, 1H), 2.90–2.62 (m, 1H), 2.13–1.88 (m, 1H) ,1.86–1.74(m,2H),1.65(ddd,J=23.3,13.7,7.8Hz,1H),1.56(dt,J=12.6,9.3Hz,1H),1.48–1.37(m,11H).
[0040] Example 2
[0041] This example provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid. The specific steps are the same as those in Example 1 except for step (4).
[0042] (4) 4 L of anhydrous methanol and L-hydroxyproline (94.5 g, 2.48 mol) were added to a 2 L three-necked flask. Sodium borohydride (31 g, 0.79 mmol) was added portionwise at -10 °C. After addition, the temperature was raised to 0 °C and stirred for 1 h. The temperature was then lowered to -10 °C, and the obtained compound 3 (87 g, 0.36 mol) was dissolved in dichloromethane (1 L) and added dropwise to the above mixture. The temperature was slowly raised to 0 °C and stirred for 1 h. The temperature was then naturally raised to 20 °C and stirred for 12 h. After LC showed that the starting material disappeared, 1 M hydrochloric acid solution was added dropwise to adjust the pH to 1. 2 L of water was added, the layers were separated, and the mixture was extracted twice with 4 L of dichloromethane. The combined organic phases were washed with saturated sodium carbonate until alkaline, dried over anhydrous magnesium sulfate, concentrated, and crystallized from petroleum ether:ethyl acetate = 1:1 to obtain solid compound 4 with a yield of 60% and an ee of 85.2%.
[0043] Example 3
[0044] This example provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid. The specific steps are the same as those in Example 1 except for step (4).
[0045] (4) 4 L of anhydrous methanol and L-alanine (2.48 mmol) were added to a 2 L three-necked flask. Sodium borohydride (31 g, 0.79 mmol) was added portionwise at -10 °C. The temperature was raised to 0 °C and stirred for 1 h. The temperature was then lowered to -10 °C. Compound 3 (87 g, 0.36 mmol) was dissolved in dichloromethane (1 L) and added dropwise to the above mixture. The temperature was slowly raised to 0 °C and stirred for 1 h. The temperature was then naturally raised to 20 °C and stirred for 12 h. After LC showed that the starting material disappeared, 1 M hydrochloric acid solution was added dropwise to adjust the pH to 1. 2 L of water was added, the layers were separated, and the mixture was extracted twice with 4 L of dichloromethane. The combined organic phases were washed with saturated sodium carbonate until alkaline. The organic phases were dried over anhydrous magnesium sulfate, concentrated, and crystallized from petroleum ether:ethyl acetate = 1:1 to obtain solid compound 4 with a yield of 70% and an ee of 83.7%.
[0046] Example 4
[0047] This example provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid. The specific steps are the same as those in Example 1 except for step (5).
[0048] (5) Compound 4 (70 g, 0.288 mol) was added to a 2 L three-necked flask and dissolved in tetrahydrofuran (800 mL) and water (400 mL). Aqueous sodium hydroxide solution (25 g, 0.518 mol) was added portionwise under ice bath. The mixture was reacted for 2 hours after the addition was complete. After TLC showed that the starting material disappeared, water (300 mL) was added, the layers were separated, and the aqueous phase was extracted once with dichloromethane. The pH of the separated aqueous phase was adjusted to 2 with 1 M hydrochloric acid, and then extracted three times with dichloromethane (2 L). The organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and concentrated to an organic phase. Petroleum ether:ethyl acetate|=1:1 (300 mL) was added for crystallization. The mixture was stirred at 20°C for 1 hour, filtered, and dried to obtain 46.3 g of trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with a yield of 71%.
[0049] Example 5
[0050] This example provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid. The specific steps are the same as those in Example 1 except for step (5).
[0051] (5) Compound 4 (70 g, 0.288 mol) was added to a 2 L three-necked flask and dissolved in tetrahydrofuran (800 mL) and water (400 mL). Aqueous potassium hydroxide solution (23 g, 0.518 mol) was added portionwise under ice bath. The mixture was reacted for 2 hours after the addition was complete. After TLC showed that the starting material disappeared, water (300 mL) was added, the layers were separated, and the aqueous phase was extracted once with dichloromethane. The pH of the separated aqueous phase was adjusted to 2 with 1 M hydrochloric acid, and then extracted three times with dichloromethane (2 L). The organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and concentrated to an organic phase. Petroleum ether:ethyl acetate|=1:1 (300 mL) was added for crystallization. The mixture was stirred at 20°C for 1 hour, filtered, and dried to obtain 39.7 g of trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with a yield of 61%.
[0052] Comparative Example 1
[0053] This comparative example provides a method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, and the specific steps are as follows:
[0054]
[0055] (1) Add (1R, 4S)-N-tert-butyloxycarbonyl-1-aminocyclopent-2-ene-4-carboxylic acid (100 g, 0.44 mol) and anhydrous methanol (440 mL) to a 1 L three-necked flask, cool to 0°C in an ice bath with stirring, and begin to add thionyl chloride (62 g, 0.52 mol) dropwise. After the addition of thionyl chloride, stir at 20°C for 2 hours, heat (70°C) and reflux for 4 hours, and then concentrate under reduced pressure to obtain a large amount of solid, namely compound 1', with a yield of 98%;
[0056] (2) Compound 1' (76 g, 0.43 mol) and 1 L of dichloromethane were added to a 2 L three-necked flask and stirred. The mixture was cooled in an ice bath (0°C) and triethylamine (66.6 g, 0.65 mol) was added dropwise. After the addition was complete, the mixture was stirred for 20 minutes. Di-tert-butyl dicarbonate (105 g, 0.48 mol) was added dropwise. After the addition was complete, the mixture was stirred at 10°C for 12 hours. After TLC showed that the starting material disappeared, 1 M hydrochloric acid solution was added dropwise and the pH was adjusted to 1. The layers were separated and the aqueous phase was extracted once with 200 mL of dichloromethane. The organic phase was washed once with 200 mL of saturated brine, dried over anhydrous magnesium sulfate, and concentrated to obtain compound 2' with a yield of 95%.
[0057] (3) Add 600 mL of ethyl acetate to a 1 L hydrogenation reactor, stir and add compound 2' (97.7 g, 0.40 mol), then add 10 g of 10% palladium on carbon. Press forty times, refill the air three times, and observe the reaction after 24 hours. After the reaction is complete by TLC, the palladium on carbon is filtered, the ethyl acetate is concentrated under reduced pressure, and crystallized from petroleum ether to obtain compound 3' as a white solid in a 70% yield.
[0058] (4) Compound 3' (68.8 g, 0.28 mol) was added to a 2 L three-necked flask, and 1 L of anhydrous methanol was added. Sodium methoxide (22.9 g, 0.42 mol) was added and refluxed at 55°C for 5 h. The mixture was separated into two spots on a plate and cooled to room temperature. The reaction was complete by TLC. Acetic acid (28 g, 0.46 mol) was added to neutralize the mixture. 500 ml of water was added, and the aqueous phase was extracted with dichloromethane several times. The dichloromethane phase was washed with sodium bicarbonate until it was weakly alkaline, then dried, concentrated, and the sample was passed through a column to obtain compound 4' with a yield of 20%.
[0059] (5) Compound 4' (13.6 g, 0.056 mol) was dissolved in tetrahydrofuran (300 mL) and water (150 mL) in a 1 L three-necked flask. Lithium hydroxide (2.68 g, 0.112 mol) was added portionwise under ice-cooling. The reaction was continued for 2 hours after the addition of lithium hydroxide. After TLC showed the disappearance of the starting material, water (300 mL) was added. The layers were separated and the aqueous phase was extracted once with dichloromethane. The pH of the separated aqueous phase was adjusted to 2 with 1 M hydrochloric acid and then extracted three times with dichloromethane (2 L). The organic phases were combined, dried over anhydrous magnesium sulfate, filtered, and concentrated to an organic phase. Petroleum ether:ethyl acetate (1:1) (300 mL) was added for crystallization. The mixture was stirred at 20°C for 1 hour, filtered, and dried to obtain 7.6 g of trans-N-BOC-1-aminocyclopentane-3-carboxylic acid with a yield of 59%. ee = 96%.
[0060] Comparison of total yield:
[0061] The total yields of Examples 1-5 and Comparative Example 1 were calculated and statistically analyzed as follows:
[0062]
[0063] From the above results, it can be found that the preparation method provided by the present invention has significantly fewer reaction steps and processes than the existing method, the overall process is simpler, the total yield is higher, the production cost is greatly reduced, and it is suitable for industrial production; by comparing Examples 1-3, it can be found that the present invention can further improve the optical purity of the product and the total yield by adopting a specific catalyst; by comparing Examples 1, 4-5, it can be found that the present invention effectively improves the yield of hydrolysis by selecting a specific base.
[0064] The applicant declares that while the above-described examples illustrate the method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, the present invention is not limited to these examples. This does not necessarily mean that the present invention must rely on these examples for implementation. Those skilled in the art will appreciate that any improvements to the present invention, equivalent substitutions for raw materials in the product, addition of auxiliary ingredients, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.
[0065] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the scope of protection of the present invention.
[0066] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.
Claims
1. A method for preparing chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid, characterized in that: The preparation method comprises the following steps: (1) (1R,4S)-4-((tert-butoxycarbonyl)amino)cyclopent-2-enecarboxylic acid and methanol are mixed and esterified to obtain compound 1; (2) Compound 1 is mixed with a base and di-tert-butyl dicarbonate to react to obtain Compound 2; (3) Compound 2 is mixed with potassium carbonate to react to obtain compound 3; (4) Compound 3 is mixed with sodium borohydride and a catalyst to react to obtain Compound 4; the catalyst comprises any one or a combination of at least two of L-pyroglutamic acid, L-proline, L-alanine or L-hydroxyproline; (5) mixing compound 4 with a base and hydrolyzing it to obtain the chiral trans-N-BOC-1-aminocyclopentane-3-carboxylic acid; The reaction process is as follows:
2. The preparation method according to claim 1, characterized in that The reaction temperature of step (1) is 10-80° C. and the reaction time is 2-8 hours.
3. The preparation method according to claim 2, characterized in that The reaction temperature in step (2) is 10-30° C. and the reaction time is 8-16 h.
4. The preparation method according to claim 1, characterized in that The molar ratio of compound 2 to potassium carbonate in step (3) is 1:(1.5-2.5).
5. The preparation method according to claim 1, characterized in that The reaction temperature in step (3) is 50-80° C. and the reaction time is 8-15 h.
6. The preparation method according to claim 1, characterized in that The catalyst is L-pyroglutamic acid.
7. The preparation method according to claim 1, characterized in that The molar ratio of the compound 3 to the catalyst and sodium borohydride in step (4) is 1:(0.3-0.5):(1-5).
8. The preparation method according to claim 1, characterized in that The reaction temperature in step (4) is 10-30° C. and the reaction time is 8-16 h.
9. The preparation method according to claim 1, characterized in that The base in step (5) includes any one of lithium hydroxide, sodium hydroxide or lithium hydroxide or a combination of at least two thereof.
10. The preparation method according to claim 1, characterized in that The molar ratio of compound 4 to base in step (5) is 1:(1.5-2.5).
11. The preparation method according to claim 1, characterized in that The reaction temperature in step (5) is -10 to 5°C and the reaction time is 2 to 5 hours.