Method for preparing L-BPA

Abstract

Provided is a method for preparing L-BPA, which includes steps of: reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether to obtain a reaction mixture, wherein the reaction mixture comprises N-protected (S)-4-boronophenylalanine of Formula II and the R.sup.2 group represents a protecting group; ##STR00001## isolating the N-protected (S)-4-boronophenylalanine from the reaction mixture; and deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA, wherein the L-BPA has a structure of Formula III.

Claims

1. A method for preparing L-BPA comprises steps of: reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether to obtain a reaction mixture, wherein the R.sup.1 group of N-protected (S)-4-halophenylalanine of Formula I is iodide or bromide, the Grignard reagent is tert-butylmagnesium chloride (t-BuMgCl), the reaction mixture comprises N-protected (S)-4-boronophenylalanine of Formula II and the R.sup.2 group represents a protecting group; ##STR00018## isolating the N-protected (S)-4-boronophenylalanine from the reaction mixture; and deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA, wherein the L-BPA has a structure of Formula III.

2. The method according to claim 1, wherein the R.sup.2 group of N-protected (S)-4-halophenylalanine of Formula I and N-protected (S)-4-boronophenylalanine of Formula II is selected from the group consisting of: tert-butoxycarbonyl (t-Boc) group, trityl (Trt) group, 3,5-dimethoxyphenylisopropoxycarbonyl (Ddz) group, 2-(4-Biphenyl)isopropoxycarbonyl (Bpoc) group, and 2-nitrophenylsulfenyl (Nps) group, the boronating agent is trialkyl borate.

3. The method according to claim 1, wherein the step of reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether to obtain a reaction mixture comprises reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether at a temperature ranging from 0 C. to 60 C. to obtain the reaction mixture.

4. The method according to claim 1, wherein the step of deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA comprises deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine at a temperature ranging from 30 C. to 60 C. to obtain L-BPA.

5. The method according to claim 1, wherein the boronating agent has a .sup.10B purity not less than 95%, the N-protected (S)-4-boronophenylalanine is N-protected (S)-4-(.sup.10B)boronophenylalanine of Formula IV and the L-BPA is L-.sup.10BPA of Formula V ##STR00019##

6. The method according to claim 1, wherein the method for preparing L-BPA further comprises a step of: ##STR00020## protecting the amine terminal of (S)-4-halophenylatermilanine of Formula VI to obtain N-protected (S)-4-halophenylalanine of Formula I.

7. The method according to claim 6, wherein the step of protecting the amine terminal of (S)-4-halophenylalanine of Formula VI to obtain N-protected (S)-4-halophenylalanine of Formula I comprises: adding the (S)-4-halophenylalanine, 1,4-dioxane, water, sodium hydroxide and di-t-butyl dicarbonate into reaction vessel to perform the reaction; adjusting the pH value to less than 2 to crystallize the N-protected (S)-4-boronophenyl alanine; adding a first extractive solvent so as to obtain N-protected (S)-4-boronophenylalanine.

8. The method according to claim 2, wherein trialkyl borate is tributyl borate, the method of preparing L-BPA further comprises a step of reacting the boronic acid with sulfuric acid and butan-1-ol in a first organic solvent, to prepare the tributyl borate.

9. The method according to claim 1, wherein the step of isolating the N-protected (S)-4-boronophenylalanine from the reaction mixture comprises: adding an organic solvent and acid solution into the reaction mixture, adjusting pH value to less than 5, and extractive, to obtain organic phase; adding alkaline solution to said organic phase, adjusting the pH value to 7.1-14; adding an extractive solvent so as to obtain the N-protected (S)-4-boronophenylalanine.

10. The method according to claim 1, wherein the step of deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA comprises: adding the N-protected (S)-4-borono-L-phenylalanine, water, acid solution and an organic solvent into a reaction vessel; adjusting the pH value to 6.15-6.25 so as to obtain L-BPA.

11. A method for preparing L-BPA comprises steps of: reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent and Grignard reagent to obtain a reaction mixture, wherein the R.sup.1 group of N-protected (S)-4-halophenylalanine of Formula I is iodide or bromide, the Grignard reagent is tert-butylmagnesium chloride (t-BuMgCl), the reaction mixture comprises N-protected (S)-4-boronophenylalanine of Formula II and the R.sup.2 group represents a protecting group; ##STR00021## isolating the N-protected (S)-4-boronophenylalanine from the reaction mixture; and deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA, wherein the L-BPA has a structure of Formula III.

12. The method according to claim 11, wherein the R.sup.2 group of N-protected (S)-4-halophenylalanine of Formula I and N-protected (S)-4-boronophenylalanine of Formula II is selected from the group consisting of: tert-butoxycarbonyl (t-Boc) group, trityl (Trt) group, 3,5-dimethoxyphenylisopropoxycarbonyl (Ddz) group, 2-(4-Biphenyl)isopropoxycarbonyl (Bpoc) group, and 2-nitrophenylsulfenyl (Nps) group, the boronating agent is trialkyl borate.

13. The method according to claim 11, wherein the step of reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent and Grignard reagent to obtain a reaction mixture comprises reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent and Grignard reagent at a temperature ranging from 0 C. to 30 C. to obtain the reaction mixture.

14. The method according to claim 11, wherein the boronating agent has a .sup.10B purity not less than 95%, the N-protected (S)-4-boronophenylalanine is N-protected (S)-4-(.sup.10B)boronophenylalanine of Formula IV and the L-BPA is L- BPA of Formula V ##STR00022##

15. A method for preparing L-BPA comprises steps of: reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether to obtain a reaction mixture, wherein the Grignard reagent is tert-butylmagnesium chloride (t-BuMgCl), the reaction mixture comprises N-protected (S)-4-boronophenylalanine of Formula II and the R.sup.2 group represents a protecting group; ##STR00023## isolating the N-protected (S)-4-boronophenylalanine from the reaction mixture; and deprotecting the R.sup.2 group of the N-protected (S)-4-boronophenylalanine to obtain L-BPA, wherein the L-BPA has a structure of Formula III; wherein the R.sup.1 group of N-protected (S)-4-halophenylalanine of Formula I is iodide or bromide, the R.sup.2 group of N-protected (S)-4-halophenylalanine of Formula I and N-protected (S)-4-boronophenylalanine of Formula II is selected from the group consisting of: tert-butoxycarbonyl (t-Boc) group, trityl (Trt) group, 3,5-dimethoxyphenylisopropoxycarbonyl (Ddz) group, 2-(4-Biphenyl)isopropoxycarbonyl (Bpoc) group, and 2-nitrophenylsulfenyl (Nps) group, the boronating agent is trialkyl borate.

16. The method according to claim 15, wherein the step of reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether to obtain a reaction mixture comprises reacting N-protected (S)-4-halophenylalanine of Formula I, a boronating agent, Grignard reagent and bis(2-dimethylaminoethyl)ether at a temperature ranging from 0 C. to 60 C. to obtain the reaction mixture.

17. The method according to claim 15, wherein the R.sup.1 group of N-protected (S)-4-halophenylalanine of Formula I is iodide.

Description

DETAILED DESCRIPTION

(1) As well known by one skilled in the art, the method for preparing L-BPA is basically the same as the method for preparing L-.sup.10BPA. The difference lies in the use of boronating agent as the raw material, which has different contents of .sup.10boron and .sup.10boron. The boron content in the boronating agent as the raw material using for the preparation of L-BPA, can be the content of boron element existed in nature, which is about 19.9% .sup.10boron and about 80.1% .sup.11boron. The L-.sup.10BPA with 95% .sup.10boron content (i.e., element .sup.10boron enriched L-BPA, normally called L-.sup.10BPA) can also be used. Therefore, the method for preparing L-.sup.10BPA disclosed by the embodiments of the present disclosure is also applicable to the method for preparing L-BPA. The Embodiment 1 of the present disclosure shows an Embodiment, in which boronating agent with 95% .sup.10boron content, bis(2-dimethylaminoethyl)ether, and tert-butylmagnesium chloride as the Grignard reagent are used as the raw material for the preparation of L-.sup.10BPA. The one with another ratio of .sup.10boron content can also be prepared by the same preparation method; the Embodiment 2 of the present disclosure discloses the steps of preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine, and the steps of deprotecting the amine terminal of (S)N-Boc-4-borono-L-phenylalanine to prepare L-BPA, using boronating agent with common .sup.10boron content, bis(2-dimethylaminoethyl)ether and tert-butylmagnesium chloride as the Grignard reagent as the raw material; the Embodiment 3 of the present disclosure discloses the steps of preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine, using boronating agent with common .sup.10boron content, bis(2-dimethylaminoethyl)ether and tert-butylmagnesium chloride as the Grignard reagent as the raw material; the Embodiment 4 of the present disclosure discloses the steps of preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine, using boronating agent with common .sup.10boron content, bis(2-dimethylaminoethyl)ether and cyclohexylmagnesium chloride as the Grignard reagent as the raw material; the Embodiment 5 of the present disclosure discloses the steps of preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine, using boronating agent with common .sup.10boron content, bis(2-dimethylaminoethyl)ether and tert-pentylmagnesium chloride as the Grignard reagent as the raw material; the Embodiments 6-7 of the present disclosure discloses the steps of preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine, using boronating agent with common .sup.10boron content and tert-butylmagnesium chloride as the Grignard reagent as the raw material, without the addition of bis(2-dimethylaminoethyl)ether.

(2) In the Embodiments 2-7 of the present disclosure, the prior steps of the preparation of L-BPA are basically the same as those described in Embodiment 1, except the difference of .sup.10boron content, therefore those steps will not be repeated in detail in those Embodiments. In the Embodiments 3-7 of the present disclosure, the steps of amine terminal deprotection of the preparation of L-BPA are basically the same as those described in Embodiment 2, therefore those steps will not be repeated in detail in those Embodiments.

(3) In the Embodiments below, (S)N-Boc-4-iodophenylalanine is used as the preferred Embodiment of N-protected (S)-4-halophenylalanine, and (S)N-Boc-4-iodophenylalanine is used to prepare L-BPA or L-.sup.10BPA, to explain that the embodiments of the present disclosure overcome the technical defects of the prior art. Through the contents of the present specification, one skilled in the art can easily realize the advantages and effects achieved by the present disclosure, and give out various modifications and changes without departing the spirit of the present disclosure, to implement or apply the contents of the present disclosure. It is also known that the Embodiments cited herein are not used to limit the scope of the claims of the present disclosure.

Embodiment 1

(4) Before preparing (S)N-Boc-4-boronophenylalanine from (S)N-Boc-4-iodophenylalanine, it is necessary to disclose the method for preparing (S)N-Boc-4-iodophenylalanine from (S)-4-iodophenylalanine as the raw material, and the method for preparing tributyl .sup.10B borate from .sup.10Boronic acid.

1. Preparing (S)N-Boc-4-iodophenylalanine from (S)-4-iodophenylalanine

(5) With reference to the following Reaction Formula I, it is the chemical reaction formula of reaction between (S)-4-iodophenylalanine and sodium hydroxide (NaOH) and di-t-butyl dicarbonate (Boc.sub.2O) in the solvents of 1,4-dioxane and water (H.sub.2O) to prepare (S)N-Boc-4-iodophenylalanine.

(6) ##STR00009##

(7) During the preparation process, two reaction vessels were selected to perform the reaction.

(8) The specific operation method is as follows:

(9) A reaction was set up, using 3 L three-necked flask. (S)-4-iodo-L-phenylalanine (200.00 g, 687.10 mmol, 1.00 eq), 1,4-dioxane (1.00 L) and water (1.00 L) were separately added into the reaction system, followed by sodium hydroxide (68.71 g, 1.72 mol, 2.50 eq), then the solution gradually became clear, and the temperature rose slightly to 19 C. When the system was cooled down to 0-10 C., di-t-butyl dicarbonate (254.93 g, 1.17 mol, 268.35 mL, 1.70 eq) was added into the reaction system, then the temperature of the reaction system naturally rose to 1030 C. After addition, the reaction system was stirred at room temperature (about 30 C.) for eight hours. High performance liquid chromatography (HPLC) was used to detect the reaction, until the reaction of the raw material was completed. Then the system temperature was controlled below 40 C., and 1,4-dioxane was concentrated. The reaction mixture was quenched with 100 mL water after the temperature of reaction system was cooled down to room temperature (about 25 C.), and the pH was adjusted to 1.8-2 by hydrochloric acid (2M (i.e., molarity (M))). The result reaction mixture was extracted three times with ethyl acetate (2 L). The obtained organic phases were combined, and washed twice with saturated salt water (1 L), dried by sodium sulfate (200 g) and rotary evaporating, to give a crude product as a yellowish solid. The crude product was subsequently dried in an oven (40-45 C.), to give a white solid (S)N-Boc-4-iodo-L-phenylalanine (250.00 g, 626.28 mmol, analyzed by HPLC, 93.00% yield, 98% purity).

(10) The analysis results of the resulting (S)N-Boc-4-iodo-L-phenylalanine by .sup.1Hydrogen nuclear magnetic resonance spectroscopy (.sup.1HNMR) were described as follows:

(11) .sup.1HNMR: (400 MHz DMSO-d.sub.6)

(12) 7.49 (d, J=7.8 Hz, 2H), 6.88 (d, J=7.8 Hz, 2H), 5.80 (d, J=5.9 Hz, 1H), 3.68 (d, J=5.5 Hz, 1H), 3.00-2.90 (m, 1H), 2.87-2.75 (m, 1H), 1.35-1.15 (m, 9H).

2. Preparation of Tributyl 10B Borate from 10Boronic Acid

(13) With reference to the following Reaction Formula II, it is the chemical reaction formula of reaction between .sup.10Boronic acid and sulfuric acid (H.sub.2SO.sub.4) in the solvents of butan-1-ol and toluene to prepare tributyl .sup.10B borate (.sup.10B(OBu).sub.3).

(14) ##STR00010##

(15) The specific operation method is as follows:

(16) The reaction device R1 was set up, using 3 L three-necked flask, equipped with a water segregator. .sup.10Boronic acid (150.00 g, 2.46 mol, 1.00 eq), butan-1-ol (1.00 L) was added into the reaction R1 and stirred, and most of boronic acid cannot be dissolved. Then toluene (1.00 L) was added into the reaction R1 and stirred at room temperature (about 25 C.). Concentrated sulfuric acid (4.82 g, 49.16 mmol, 2.62 mL, 0.02 eq) was dropwise added into the reaction at room temperature (about 25 C.), a large number of solids were still remained undissolved. After that, the temperature of reaction system was risen to 130 C., and stirred for 3.5 hours while keeping segregating the water out. The water generated in the water segregator (about 140 g) was separated, all of solids were dissolved, and the solution was changed from colorless to brown. TLC analysis (DCM:MeOH=5:1, Rf=0.43, coloured by bromocresol green) of the mixture showed the completion of the reaction. Most of the toluene was distilled off under normal pressure. After that, the system temperature was cooled down to 2030 C. The reaction liquids from two reactions were combined, and the device was changed for distillation. With an outer temperature of the oil bath of 108-110 C., the butan-1-ol was distilled off by water pump vacuum distillation, at 45 C. measured by the Kelvin thermometer, and the residual butanol was distilled off by oil pump vacuum distillation. Raise the temperature to 118-120 C., the product began to be distilled off by oil pump vacuum distillation at 55 C. measured by the Kelvin thermometer, and continue to raise the temperature to 135-140 C. until the product was distilled off. The resulting product was tributyl .sup.10B borate as a colorless liquid (830.00 g, 3.62 mol, 73.58% yield).

(17) The analysis results of the resulting tributyl .sup.10B borate by .sup.1HNMR were described as follows:

(18) .sup.1H NMR: (400 MHz CDCl.sub.3)

(19) 3.82-3.68 (m, 6H), 1.57-1.42 (m, 6H), 1.34 (qd, J=7.4, 14.9 Hz, 6H), 0.95-0.80 (m, 9H).

3. Preparation of (S)N-Boc-4-10borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(20) With reference to the following Reaction Formula III, it is the chemical reaction formula of reaction between (S)NBoc-4-iodophenylalanine, tributyl .sup.10B borate, tert-butylmagnesium chloride (t-BuMgCl) and bis(2-dimethylaminoethyl)ether (BDMAEE) to prepare (S)N-Boc-4-(.sup.10B)borono-L-phenylalanine.

(21) ##STR00011##

(22) During the preparation process, two reaction vessels were selected to perform the reaction.

(23) The specific operation method is as follows:

(24) A reaction was set up, using 3 L three-necked flask. Tributyl .sup.10B borate (187.60 g, 817.98 mmol, 3.20 eq), sodium hydride (20.45 g, 511.24 mmol, 60% purity, 2.00 eq) was added all at once into the reaction system, at that time, the reaction liquid was a suspension, which was stirred for 5 minutes at room temperature (about 22 C.). Then bis(2-dimethylaminoethyl)ether (327.73 g, 2.04 mol, 8.00 eq) and N-Boc-4-iodo-L-phenylalanine (100.00 g, 255.62 mmol, 1.00 eq) was added into the reaction system at room temperature (about 22 C.), and a large number of solids were not dissolved. After that, the temperature of reaction system was cooled down to 0-5 C., and tert-butylmagnesium chloride (1.7 M, 1.20 L, 2.04 mol, 8.00 eq) was dropwise added into the reaction. Mainwhile, the temperature was controlled to be 0-10 C., and the dropping time was about 1.5 hours. After the material addition was completed, the temperature of reaction system naturally rose to room temperature (2030 C.), continue stirred under this temperature for 12 hours. High performance liquid chromatography (HPLC) was used for detection, and the remaining of raw material was about 9.00%. When the temperature of reaction system was cooled down to 5-0 C., the reaction was quenched by dropwise addition of 500 mL water. Methyl tert-butyl ether (500 mL) was added into the reaction system at 0-5 C., and the pH was adjusted to 2.9-3.1 (by pH meter) by 37% HCl (about 500 mL). During the pH adjusting process, the system temperature was controlled to be 0-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (500 mL), the resulting organic phases were combined, to give about 1.1 L organic phases. Sodium hydroxide aqueous solution (1M, 400 mL) was dropwise added into the resulting organic phase slowly. During the dropwise addition process, the system temperature was controlled to be 0-15 C. After the dropwise addition was completed, the pH value of the system was about 10, then adjusted the pH value to 12.1-12.6 (determined by pH meter) by sodium hydroxide aqueous solution (4M). The resulting aqueous phase 1 was obtained by separating the mixture, the extracted once with butan-1-ol (500 ml) to give the aqueous phase 2. The resulting aqueous phases of the reaction in the two reaction vessels were combined, and then the pH value of the resulting aqueous phases was adjusted to 2.9-3.1 by 37% HCl. After stirred for about 40 minutes, a large amount of solids were precipitated. The white solid was collected by filtration and drip washed once with methylene chloride (50 mL). At 25 C., the precipitated solid was slurried with methylene chloride (150 mL), and stirred for 10 minutes. The resulting white solid was filtrated to give (S)N-Boc-4-(.sup.10B) borono-L-phenylalanine (75.00 g, 240.82 mmol, analyzed by HPLC, 47.11% yield, 99% purity).

(25) The analysis results of the resulting (S)N-Boc-4-(.sup.10B) borono-L-phenylalanine by .sup.1HNMR were described as follows:

(26) .sup.1HNMR: (400 MHz DMSO-d.sub.6)

(27) 2.55 (br. s., 1H), 7.91 (s, 2H), 7.66 (d, J=7.5 Hz, 2H), 7.17 (d, J=7.5 Hz, 2H), 4.08-4.01 (m, 1H), 3.61-3.53 (m, 1H), 2.98 (dd, J=4.2, 13.9 Hz, 1H), 2.79 (dd, J=10.4, 13.5 Hz, 1H), 1.79-1.67 (m, 1H), 1.35-1.17 (m, 9H).

4. Preparing L-10BPA from (S)N-Boc-4-borono-L-phenylalanine

(28) With reference to the following Reaction Formula IV, it is the chemical reaction formula of deprotecting the amine terminal of (S)N-Boc-4-(.sup.10B)borono-L-phenylalanine to prepare L-.sup.10BPA.

(29) ##STR00012##

(30) The specific operation method is as follows:

(31) A reaction was set up, using 1 L three-necked flask. (S)N-Boc-4-(.sup.10B) borono-L-phenylalanine (67.00 g, 217.31 mmol, 1.00 eq), water (23.75 mL) and acetone (420.00 mL) was added into the reaction system and stirred at room temperature (20-30 C.). Then concentrated hydrochloric acid (23.93 g, 656.28 mmol, 23.46 mL, 3.02 eq) was dropwise added into the reaction system. After the dropwise addition was completed, the temperature of reaction system was risen to 55-60 C., and the reaction system was stirred for 4.5 hours. HPLC analysis of the mixture showed the completion of the reaction. The acetone in the reaction system was concentrated with the temperature below 40 C. After the concentration, the system was cooled down to below 15 C., and the pH value of the system was adjusted to about 1.5 (detected by pH meter) by sodium hydroxide solution (4M). After stirring for 40 minutes, the pH value of the system was adjusted to 6.156.25 by continuously adding sodium hydroxide solution (4M), and a large amount of white solids were precipitated. The white solid was collected by filtration and drip washed with acetone (200 mL). The white solid L-.sup.10BPA was obtained (36.00 g, 171.17 mmol, analyzed by HPLC, 78.77% yield, 99% purity).

(32) The analysis results of the resulting L-.sup.10BPA by .sup.1HNMR were described as follows:

(33) .sup.1H NMR: (400 MHz D.sub.2O, CF.sub.3COOH)

(34) 7.44 (d, J=7.9 Hz, 1H), 7.03 (d, J=7.9 Hz, 1H), 4.06 (dd, J=5.7, 7.5 Hz, 1H), 3.11-3.01 (m, 1H), 2.98-2.87 (m, 1H).

Embodiment 2

1. Preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(35) With reference to Reaction Formula III, it is the chemical reaction formula of reaction between (S)N-Boc-4-iodophenylalanine, tributyl borate, tert-butylmagnesium chloride (t-BuMgCl) and bis(2-dimethylaminoethyl)ether (BDMAEE) to prepare (S)N-Boc-4-borono-L-phenylalanine.

(36) ##STR00013##

(37) The specific operation method is as follows:

(38) A reaction device was set up, using 100 mL three-necked flask. At the temperature of 2030 C., tributyl borate (5.65 g, 24.54 mmol, 3.20 eq), sodium hydride (613.50 mg, 15.34 mmol, 2.00 eq), bis(2-dimethylaminoethyl)ether (9.83 g, 61.35 mol, 8.00 eq) and (S)N-Boc-4-iodophenylalanine (3.00 g, 7.67 mmol, 1.00 eq) was added into the 100 mL flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., tert-butylmagnesium chloride (1.7 M in tetrahydrofuran, 36 mL, 8.00 eq) was dropwise added into the reaction, the dropping time was about 30 minutes, and the temperature was controlled to be 0 C.-10 C. Then the reaction system was stirred for 16 hours at 2030 C. Detected by HPLC, the reaction of the raw material was not completed, and the remaining of raw material was about 13%. At the temperature of 0 C., 1.5 mL water was dropwise added into the reaction for quenching. After the quenching was completed, the stirring continued for 10 minutes. Methyl tert-butyl ether (15 mL) was added into the reaction at 0 C., and the pH value was adjusted to 3 (detected by pH meter) by 37% HCl (about 15 mL). During the pH adjusting process, the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (15 mL). The two organic phases were combined. NaOH solution (1M, 17 mL) was dropwise added into the resulting organic phase, and the pH value was adjusted to 12.1-12.6. During this process, the temperature was controlled to be 0 C.-15 C. The liquids were separated, and the resulting aqueous phase was extracted once with butan-1-ol (15 ml), to remove most of the impurities by extraction. The resulting aqueous phase from liquid separating was adjusted by 37% HCl to pH=3, stirred for about 30 minutes, and large amount of white solids were precipitated. The white solid was collected by filtration and drip washed once with methylene chloride (15 mL). The precipitated solid was slurried with 8 mL methylene chloride, and stirred for 10 minutes at 25 C. The white solid(S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (1.80 g, 5.82 mmol, analyzed by HPLC, 75.92% yield, 100% purity).

(39) The analysis results of the resulting(S)N-Boc-4-borono-L-phenylalanine by .sup.1HNMR were described as follows:

(40) .sup.1H NMR: (400 MHz DMSO-d.sub.6)

(41) =7.95 (s, 2H), 7.69 (d, J=7.7 Hz, 2H), 7.19 (d, J=7.7 Hz, 2H), 7.07 (d, J=8.4 Hz, 1H), 4.14-4.04 (m, 1H), 3.00 (br dd, J=4.4, 13.7 Hz, 1H), 2.82 (br dd, J=10.5, 13.8 Hz, 1H), 1.32 (s, 9H).

2. Preparing L-BPA from (S)N-Boc-4-borono-L-phenylalanine

(42) With reference to the following Reaction Formula IV, it is the chemical reaction formula of deprotecting the amine terminal of (S)N-Boc-4-borono-L-phenylalanine to prepare L-BPA.

(43) ##STR00014##

(44) The specific operation method is as follows:

(45) A reaction device was set up, using 100 mL three-necked flask. At the temperature of 2030 C., (S)N-Boc-4-borono-L-phenylalanine (1.80 g, 5.82 mmol, 1.00 eq), water (0.63 mL) and acetone (11.30 mL) were separately added into the flask. Then HCl (17.46 mmol, 1.46 mL, 3.00 eq) was dropwise added into the reaction. After the dropwise addition was completed, the temperature of reaction was risen to 60 C., and the reaction was stirred for 4 hours. HPLC detection indicated that the reaction was already completed. The reaction liquid was concentrated under reduced pressure at 40 C. with most of acetone was rotary evaporated. The temperature was cooled down to 015 C., and the pH value was adjusted to 1.5 by NaOH solution (4M), and the solids started precipitated. The pH value was adjusted continuously to 6.2, and a large amount of white solids were precipitated, stirred for 15 minutes. The white solid was collected by filtration and drip washed with acetone (6 mL), then transferred and dried by rotary evaporating. The resulting white solid L-BPA was obtained (0.85 g, 4.07 mmol, analyzed by HPLC, 70.18% yield, 98% purity).

(46) The analysis results of the resulting L-BPA by .sup.1HNMR were described as follows:

(47) .sup.1H NMR: (400 MHz D.sub.2O)

(48) =7.62 (d, J=7.5 Hz, 2H), 7.22 (d, J=7.9 Hz, 2H), 3.86 (dd, J=5.5, 7.5 Hz, 1H), 3.20-3.13 (m, 1H), 3.05-2.97 (m, 1H).

Embodiment 3

Preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(49) With reference to Reaction Formula III once more, the specific operation method is as follows:

(50) A reaction device was set up, using 1 L three-necked flask. At 2030 C., tributyl borate (56.48 g, 245.40 mmol, 3.20 eq), sodium hydride (6.13 g, 153.37 mmol, 2.00 eq), bis(2-dimethylaminoethyl)ether (98.32 g, 613.50 mol, 8.00 eq) and (S)N-Boc-4-iodophenylalanine (30.00 g, 76.69 mmol, 1.00 eq) was added into the 1 L flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., tert-butylmagnesium chloride (1.7 M in tetrahydrofuran, 360 mL, 8.00 eq) was dropwise added into the reaction, the dropping time was about 1 hour, and the temperature was controlled to be 0 C.-10 C. Then the reaction system was stirred for 16 hours at 2030 C. Detected by HPLC, the reaction of the raw material was not completed, and the remaining of raw material was about 8%. 15 mL water was dropwise added into the reaction for quenching at the temperature of 0 C. After the quenching completely, the stirring continued for 10 minutes. Methyl tert-butyl ether (150 mL) was added into the reaction at 0 C., and the pH was adjusted to 3 (detected by pH meter) by 37% HCl (about 160 mL). During the pH adjusting process, the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (150 mL), and the two organic phases were combined. After that, NaOH solution (1M, 190 mL) was dropwise added into the resulting organic phase, and the pH value was adjusted to 12.1-12.6. During this process, the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase, separated from the liquids, was extracted once with butan-1-ol (150 ml), to remove most of the impurities by extraction. The resulting aqueous phase from liquid separating was adjusted by 37% HCl to pH=3, and stirred for 30 minutes, and a large amount of white solids were precipitated. The white solid was collected by filtration and drip washed once with methylene chloride (150 mL). Then, the precipitated solid was slurried with 80 mL methylene chloride, and stirred for 10 minutes at 25 C. The resulting white solid (S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (15.00 g, 48.52 mmol, analyzed by HPLC, 63.27% yield, 100% purity).

(51) The analysis results of the resulting (S)N-Boc-4-borono-L-phenylalanine by .sup.1HNMR were described as follows:

(52) .sup.1H NMR: (400 MHz DMSO-d.sub.6)

(53) =7.97 (s, 2H), 7.68 (d, J=7.9 Hz, 2H), 7.23-7.16 (m, 2H), 7.08 (d, J=8.4 Hz, 1H), 4.12-4.04 (m, 1H), 3.00 (dd, J=4.4, 13.7 Hz, 1H), 2.81 (dd, J=10.4, 13.7 Hz, 1H), 1.34-1.23 (m, 9H).

Embodiment 4

Preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(54) With reference to the following Reaction Formula V, it is the chemical reaction formula of reaction between (S)N-Boc-4-iodophenylalanine, tributyl borate, cyclohexylmagnesium chloride (c-HexMgCl) and bis(2-dimethylaminoethyl)ether (BDMAEE) to prepare (S)N-Boc-4-borono-L-phenylalanine.

(55) ##STR00015##

(56) The specific operation method is as follows:

(57) A reaction device was set up, using 100 mL three-necked flask. At 2030 C., tributyl borate (2.82 g, 12.27 mmol, 3.20 eq), bis(2-dimethylaminoethyl)ether (4.92 g, 30.67 mol, 8.00 eq), (S)N-Boc-4-iodo-L-phenylalanine (1.50 g, 3.83 mmol, 1.00 eq) was added into the 100 mL flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., cyclohexylmagnesium chloride (2 M in diethyl ether, 15 mL, 8.00 eq) was dropwise added into the reaction, the dropping time was about 20 minutes, and the temperature was controlled to be 0 C.-10 C. After addition, the reaction system was stirred for 24 hours at 2030 C., then stirred for 24 hours at 605 C. Detected by HPLC, the reaction of the raw material was not completed, and the remaining of raw material was about 83%. 0.75 mL water was dropwise added into the reaction for quenching at 0 C. After the quenching was completed, the stirring continued for 10 minutes. After that, methyl tert-butyl ether (7.5 mL) was added into the reaction at 0 C., and the pH value was adjusted to 3 (detected by pH meter) by 37% HCl (about 7.5 mL). Heat was released. During the pH adjusting process, the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (7.5 mL). The two organic phases were combined. NaOH solution (1M, 8.5 mL) was dropwise added into the resulting organic phase, and the pH was adjusted to 12.1-12.6. Heat was released. During this process, the temperature was controlled to be 0 C.-15 C. The liquids were separated, and the resulting aqueous phase was extracted once with butan-1-ol (7.5 ml), to remove most of the impurities by extraction. The resulting aqueous phase from liquid separating was adjusted by 37% HCl to pH=3, and stirred for about 30 minutes. The white solid was precipitated, collected by filtration, and drip washed once with methylene chloride (7.5 mL). The precipitated solid was slurried with 4 mL methylene chloride, and stirred for 10 minutes at 25 C. Finally, the white solid (S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (0.2 g, analyzed by HPLC, 14.83% yield, 99% purity).

(58) The analysis results of the resulting (S)N-Boc-4-borono-L-phenylalanine by .sup.1HNMR were described as follows:

(59) .sup.1H NMR: (400 MHz DMSO-d.sub.6)

(60) =7.96 (s, 2H), 7.67 (d, J=7.9 Hz, 2H), 7.21 (d, J=7.7 Hz, 2H), 7.09 (d, J=8.4 Hz, 1H), 4.12-4.04 (m, 1H), 3.00 (br dd, J=4.4, 13.7 Hz, 1H), 2.83 (dd, J=10.4, 13.7 Hz, 1H), 1.33-1.21 (m, 9H).

Embodiment 5

Preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(61) With reference to the following Reaction Formula VI, it is the chemical reaction formula of reaction between (S)N-Boc-4-iodophenylalanine, tributyl borate, tert-pentylmagnesium chloride (t-PenMgCl) and bis(2-dimethylaminoethyl)ether (BDMAEE) to prepare (S)N-Boc-4-borono-L-phenylalanine.

(62) ##STR00016##

(63) The specific operation method is as follows:

(64) A reaction device was set up, using 100 mL three-necked flask. At 2030 C., tributyl borate (2.82 g, 12.27 mmol, 3.20 eq), bis(2-dimethylaminoethyl)ether (4.92 g, 30.67 mol, 8.00 eq), (S)N-Boc-4-iodo-L-phenylalanine (1.50 g, 3.83 mmol, 1.00 eq) was added in batches into the 100 mL flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., tert-pentylmagnesium chloride (1.0 M in 2-MeTHF, 31 mL, 8.00 eq) was dropwise added into the reaction, the dropping time was about 20 minutes, and the temperature was controlled to be 0 C.-10 C. After addition, the reaction system was stirred for 24 hours at 2030 C., and stirred for 24 hours at 605 C. Then detected by HPLC, the reaction of the raw material was not completed, and the remaining of raw material was about 47%. 0.75 mL water was dropwise added into the reaction for quenching at 0 C. After the quenching was completed, the stirring continued for 10 minutes. Methyl tert-butyl ether (7.5 mL) was added into the reaction at 0 C., and the pH value was adjusted to 3 (detected by pH meter) by 37% HCl (about 7.5 mL). Heat was released during the pH adjusting process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (7.5 mL). The two organic phases were combined. NaOH solution (1M, 8.5 mL) was dropwise added into the resulting organic phase, and the pH value was adjusted to 12.1-12.6. Heat was released during this process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase, separated from the liquids, was extracted once with butan-1-ol (7.5 ml), to remove most of the impurities by extraction. The resulting aqueous phase from liquid separating was adjusted by 37% HCl to pH=3, and stirred for about 30 minutes. The white solid were precipitated, collected by filtration and drip washed once with methylene chloride (7.5 mL). The precipitated solid was slurried with 4 mL methylene chloride, and stirred for 10 minutes at 25 C. The white solid (S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (0.5 g, analyzed by HPLC, 46.25% yield, 98% purity).

(65) The analysis results of the resulting (S)N-Boc-4-borono-L-phenylalanine by .sup.1HNMR were described as follows:

(66) .sup.1H NMR: (400 MHz DMSO-d.sub.6)

(67) =7.98 (s, 2H), 7.70 (d, J=7.9 Hz, 2H), 7.23 (d, J=7.7 Hz, 2H), 7.10 (d, J=8.4 Hz, 1H), 4.13-4.04 (m, 1H), 3.00 (br dd, J=4.4, 13.7 Hz, 1H), 2.84 (dd, J=10.4, 13.7 Hz, 1H), 1.33-1.24 (m, 9H).

Embodiment 6

Preparing (S)N-Boc-4-borono-L-phenylalanine from (S)N-Boc-4-iodophenylalanine

(68) With reference to the following Reaction Formula VII, it is the chemical reaction formula of reaction between (S)N-Boc-4-iodophenylalanine, tributyl borate and tert-butylmagnesium chloride (t-BuMgCl) to prepare (S)N-Boc-4-borono-L-phenylalanine.

(69) ##STR00017##

(70) The specific operation method is as follows:

(71) A reaction device was set up, using 250 mL three-necked flask. At 2030 C., tributyl borate (17.65 g, 76.68 mmol, 3.00 eq), sodium hydride (1.02 g, 25.56 mmol, 1.00 eq), (S)N-Boc-4-iodo-L-phenylalanine (10.00 g, 25.56 mmol, 1.00 eq) was added into the flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., tert-butylmagnesium chloride (1.7 M in THF, 120 mL, 8.00 eq) was dropwise added into the reaction slowly, the dropping time was about 30 minutes, and the temperature was controlled to be 0 C.-10 C. Then the reaction system was stirred for 20 hours at 2030 C. Detected by HPLC, the reaction of the raw material was almost completed, and the remaining of raw material was only about 0.7%. 5 mL water was dropwise added into the reaction for quenching at 0 C. After the quenching was completed, the stirring continued for 10 minutes. Methyl tert-butyl ether (50 mL) was added into the reaction at 0 C., and the pH value was adjusted to 3 (detected by pH meter) by 37% HCl (about 50 mL). Heat was released during the pH adjusting process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (50 mL). The two organic phases were combined. NaOH solution (1M, 55 mL) was dropwise added into the resulting organic phase, and the pH value was adjusted to 12.1-12.6. Heat was released during this process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase, separated from the liquids, was extracted once with butan-1-ol (50 mL), to remove most of the impurities by extraction. Then adjusted by 37% HCl to pH=3, and stirred for about 30 minutes. The white solid was precipitated, collected by filtration and drip washed once with methylene chloride (50 mL). After that, the precipitated solid was slurried with 25 mL methylene chloride, and stirred for 10 minutes at 25 C. Finally, The white solid (S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (6.8 g, analyzed by HPLC, 83.15% yield, 98% purity).

Embodiment 7

(72) With reference to Reaction Formula VII once more, the specific operation method is as follows:

(73) A reaction device was set up, using 250 mL three-necked flask. At 2030 C., tributyl borate (8.82 g, 38.34 mmol, 3.00 eq), sodium hydride (511.25 mg, 12.78 mmol, 1.00 eq), (S)N-Boc-4-iodo-L-phenylalanine (5.00 g, 12.78 mmol, 1.00 eq) was added into the 250 mL flask. Under nitrogen atmosphere, the temperature of reaction system was cooled down to 0 C., tert-butylmagnesium chloride (1.7 M in THF, 60 mL, 8.00 eq) was dropwise added into the reaction, the dropping time was about 30 minutes, and the temperature was controlled to be 0 C.-10 C. Then the reaction system was stirred for 22 hours at 2030 C. Detected by HPLC, the reaction of the raw material was completed. 2.5 mL water was dropwise added into the reaction for quenching at 0 C. After the quenching was completed, the stirring continued for 10 minutes. Methyl tert-butyl ether (25 mL) was added into the reaction at 0 C., and the pH value was adjusted to 3 (detected by pH meter) by 37% HCl (about 25 mL). Heat was released during the pH adjusting process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase from liquid separating was extracted once with methyl tert-butyl ether (25 mL). The two organic phases were combined. NaOH solution (1M, 30 mL) was dropwise added into the resulting organic phase, and the pH value was adjusted to 12.1-12.6. Heat was released during this process, and the temperature was controlled to be 0 C.-15 C. The resulting aqueous phase, separated from the liquids, was extracted once with butan-1-ol (25 ml), to remove most of the impurities by extraction. Then adjusted by 37% HCl to pH=3, and stirred for about 30 minutes. The white solid was precipitated, collected by filtration and drip washed once with methylene chloride (25 mL). Then the precipitated solid was slurried with 15 mL methylene chloride, and stirred for 10 minutes at 25 C. Finally, the white solid (S)N-Boc-4-borono-L-phenylalanine was obtained by filtration (3.4 g, analyzed by HPLC, 85.26% yield, 98% purity).

(74) The bis(2-dimethylaminoethyl)ether is the complexing agent of Mg, which can reduce the occurrence of side reaction in the reaction. Embodiments 6 and 7 can also carry out the reactions smoothly, without the addition of bis(2-dimethylaminoethyl)ether. By analysis, in the reaction of Embodiment 6, the iodine-dropped impurity is about 17%, and in the reaction of Embodiment 7, the iodine-dropped impurity is about 28%. Therefore, it is laterally demonstrated that, the addition of bis(2-dimethylaminoethyl)ether to the reaction can protect the reaction and reduce the drop of iodine.

(75) The obtained BPA or .sup.10BPA in the above Embodiments was analyzed by chiral HPLC, indicating the ratio of L to D isomers to be 100 to 0 (100% enantiomeric excess).

(76) The above illustrates and describes basic principles, main features and advantages of the present disclosure. Those skilled in the art should appreciate that the above embodiments do not limit the present disclosure in any form. Technical solutions obtained by equivalent substitution or equivalent variations all fall within the scope of the present disclosure.