Preparation method for l-6-hydroxytryptophan derivative and intermediate

Abstract

A preparation method for an L-6-hydroxytryptophan derivative and an intermediate, belonging to the technical field of organic synthesis. Provided is a preparation method for a plurality of intermediates of an L-6-hydroxytryptophan derivative; an L-6-hydroxytryptophan derivative can be prepared on this basis; and the product yield is high, and the production cost is low. Specifically, in the present invention, compound A6-0 having a structure as shown in formula 1 is used as an initial reaction raw material, and an L-6-hydroxytryptophan derivative is obtained by means of a TIPS protection reaction, a coupling reaction, a carbon-boron bond oxidation reaction, a benzyl protection reaction of hydroxyl, a TIPS protection group removal reaction, a Boc protection group removal reaction, a methyl ester hydrolysis reaction and a 9-fluorenylmethoxycarbonyl protection reaction of an amino. The initial reaction raw material is convenient to purchase in a commercialized way, and has a low price, a relatively high product yield, a short process flow, and convenient operation, which facilitate the realization of large-scale production.

Description

Preparation method of L-6-hydroxytryptophan derivatives and intermediates

[0001] This application claims priority to a Chinese patent application filed with the Patent Office of China on March 7, 2024, with application number CN202410256775.9 and invention name “Method for preparing L-6-hydroxytryptophan derivatives and intermediates”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present invention relates to the technical field of synthesis of pharmaceutical intermediates, in particular to a preparation method of L-6-hydroxytryptophan derivatives and intermediates. Background Art

[0003] Tryptophan, also known as aminoindolepropionic acid, exists in L-, D-, and DL-forms. Only the L-form can be absorbed by the human body. As an essential amino acid, it significantly impacts the growth, development, and metabolism of humans and animals. Humans and animals cannot synthesize L-tryptophan and are prone to deficiency, requiring it to be obtained from food. Consequently, the potential demand for L-tryptophan is enormous, and it is currently widely used in medicine, food, and feed. Currently, the production technology for L-tryptophan and its derivatives has matured after years of research and development. For example, it can be obtained through protein hydrolysis or microbial fermentation.

[0004] However, the synthetic production technology of L-hydroxytryptophan and its derivatives is still in urgent need of development. Among them, L-5-hydroxytryptophan (L-5-Hydroxytryptophan, L-5-HTP) is a natural amino acid and dietary supplement that can be used as an antidepressant, appetite suppressant and sleep aid. It is a precursor of the neurotransmitter serotonin and an antagonist of reserpine. L-6-Hydroxytryptophan (L-6-Hydroxytryptophan) is a key non-natural chiral amino acid building block of amanitin-type cyclic peptide toxins and has important applications in the efficient total synthesis of such cyclic peptide toxin payloads. L-6-Hydroxytryptophan has huge potential demand in the polypeptide drug, food and feed industries. Up to now, there is no microbial fermentation route for the preparation of L-6-hydroxytryptophan and its derivatives, and the chemical synthesis methods in the existing technology all have the problems of cumbersome routes, high production costs and low product yields.

[0005] Summary of the Invention

[0006] The present invention aims to provide a method for preparing L-6-hydroxytryptophan derivatives and intermediates. The method provided by the present invention is used to prepare L-6-hydroxytryptophan derivatives and intermediates, with a short process flow, convenient operation, low production cost and high product yield.

[0007] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0008] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate C, comprising the following steps:

[0009] Compound A6-0 is subjected to TIPS protection reaction to obtain L-6-hydroxytryptophan derivative intermediate A;

[0010] The L-6-hydroxytryptophan derivative intermediate A is subjected to a coupling reaction to obtain an L-6-hydroxytryptophan derivative intermediate B;

[0011] subjecting the L-6-hydroxytryptophan derivative intermediate B to a carbon-boron bond oxidation reaction to obtain the L-6-hydroxytryptophan derivative intermediate C;

[0012] The structural formulas of the compound A6-0, L-6-hydroxytryptophan derivative intermediate A, L-6-hydroxytryptophan derivative intermediate B and L-6-hydroxytryptophan derivative intermediate C are shown in Formula 1, Formula 2, Formula 3 and Formula 4 respectively:

[0013] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate D, comprising the following steps:

[0014] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate C is obtained;

[0015] Performing a benzyl protection reaction on the hydroxyl group of the L-6-hydroxytryptophan derivative intermediate C to obtain the L-6-hydroxytryptophan derivative intermediate D;

[0016] The structural formula of the L-6-hydroxytryptophan derivative intermediate D is shown in Formula 5:

[0017] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate E, comprising the following steps:

[0018] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate D is obtained;

[0019] The L-6-hydroxytryptophan derivative intermediate D is subjected to a TIPS protecting group removal reaction to obtain the L-6-hydroxytryptophan derivative intermediate E;

[0020] The structural formula of the L-6-hydroxytryptophan derivative intermediate E is shown in Formula 6:

[0021] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate F, comprising the following steps:

[0022] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate E is obtained;

[0023] Deprotecting the L-6-hydroxytryptophan derivative intermediate E by removing the Boc protecting group to obtain the L-6-hydroxytryptophan derivative intermediate F;

[0024] The structural formula of the L-6-hydroxytryptophan derivative intermediate F is shown in Formula 7:

[0025] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative, comprising the following steps:

[0026] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate F is obtained;

[0027] The L-6-hydroxytryptophan derivative intermediate F is subjected to a methyl ester hydrolysis reaction and a 9-fluorenylmethoxycarbonyl protection reaction of the amino group to obtain the L-6-hydroxytryptophan derivative;

[0028] The structural formula of the L-6-hydroxytryptophan derivative is shown in Formula 8:

[0029] Preferably, the raw material used in the TIPS protection reaction is triisopropylsilyl chloride, and the molar ratio of triisopropylsilyl chloride to compound A6-0 is 0.15-0.2:0.15;

[0030] The TIPS protection reaction is carried out in the presence of lithium hexamethyldisilazide and an organic solvent, and the usage ratio of lithium hexamethyldisilazide, organic solvent and compound A6-0 is 0.15-0.20 mol: 0.3-1 L: 0.15 mol.

[0031] Preferably, the temperature of the TIPS protection reaction is 0-50° C., and the time is 0.1-2 h.

[0032] Preferably, after the TIPS protection reaction, the process further comprises: adding a saturated NH4Cl solution to the obtained system to quench the reaction, followed by extraction, removing the solvent from the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate A.

[0033] Preferably, the raw materials used in the coupling reaction include pinacol borane and biboronic acid pinacol ester, and the molar ratio of the L-6-hydroxytryptophan derivative intermediate A, pinacol borane and biboronic acid pinacol ester is 1:0.2-0.3:3.5-4.5;

[0034] The coupling reaction is carried out in the presence of methoxy(cyclooctadiene)iridium(I) dimer ([Ir(cod)(OMe)]2), o-phenanthroline (phen) and an organic solvent, and the usage ratio of the L-6-hydroxytryptophan derivative intermediate A, methoxy(cyclooctadiene)iridium(I) dimer, o-phenanthroline and organic solvent is 1 mol: 0.04-0.06 mol: 0.08-0.12 mol: 3-7 L.

[0035] Preferably, the coupling reaction temperature is 70-90° C., and the time is 1-24 h.

[0036] Preferably, after the coupling reaction, the process further comprises: adding a saturated NaHCO3 solution to the obtained system to quench the reaction, followed by extraction, removing the solvent from the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate B.

[0037] Preferably, the carbon-boron bond oxidation reaction is carried out in the presence of sodium perborate tetrahydrate and potassium tert-butoxide.

[0038] Preferably, the molar ratio of the L-6-hydroxytryptophan derivative intermediate B, sodium borate tetrahydrate and potassium tert-butoxide is 1:2-10:1-5;

[0039] The carbon-boron bond oxidation reaction is carried out in the presence of an organic solvent and water, and the usage ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate B is 0.5-3L:0.5-3L:0.1mol.

[0040] Preferably, the carbon-boron bond oxidation reaction includes a first-stage reaction and a second-stage reaction in sequence; the temperature of the first-stage reaction is -10 to 10°C, and the time of the first-stage reaction is 1 to 2 hours; the temperature of the second-stage reaction is 0 to 25°C, and the time of the second-stage reaction is 1 to 24 hours.

[0041] Preferably, after the carbon-boron bond oxidation reaction, the process further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate C.

[0042] Preferably, the benzyl reagent used in the benzyl protection reaction of the hydroxyl group includes benzyl bromide, and the benzyl protection reaction of the hydroxyl group is carried out in the presence of potassium iodide and potassium carbonate.

[0043] Preferably, the molar ratio of the L-6-hydroxytryptophan derivative intermediate C, benzyl bromide, potassium iodide and potassium carbonate is 1:1-5:0.05-1:1-5;

[0044] The benzyl protection reaction of the hydroxyl group is carried out in the presence of an organic solvent, and the ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate C is 0.5-2 L:0.1 mol.

[0045] Preferably, the benzyl protection reaction of the hydroxyl group is carried out at a temperature of 30 to 100° C. and for a time of 2 to 24 hours.

[0046] Preferably, after the benzyl protection reaction of the hydroxyl group is completed, the process further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate D.

[0047] Preferably, the TIPS protecting group removal reaction is carried out in the presence of tetrabutylammonium fluoride.

[0048] Preferably, the molar ratio of the L-6-hydroxytryptophan derivative intermediate D to tetrabutylammonium fluoride is 1:1 to 5;

[0049] The TIPS protection group removal reaction is carried out in the presence of an organic solvent, and the ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate D is 0.5-2 L:1 mol.

[0050] Preferably, the temperature of the TIPS protection group removal reaction is 0-50° C., and the time is 0.2-6 h.

[0051] Preferably, after the TIPS protecting group removal reaction, the process further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate E.

[0052] Preferably, the Boc protecting group removal reaction is carried out in the presence of trifluoroacetic acid.

[0053] Preferably, the ratio of trifluoroacetic acid to L-6-hydroxytryptophan derivative intermediate E is 0.5-3 L:0.1 mol;

[0054] The Boc protecting group removal reaction is carried out in the presence of an organic solvent, and the volume ratio of the organic solvent to trifluoroacetic acid is 1 to 6:3.

[0055] Preferably, the temperature of the Boc protection group removal reaction is 0-50° C., and the time is 0.2-6 h.

[0056] Preferably, after the Boc protecting group removal reaction, the process further comprises: removing the solvent from the obtained product system, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate F.

[0057] Preferably, the methyl ester hydrolysis reaction is carried out in the presence of sodium hydroxide, an organic solvent and water; the molar ratio of the L-6-hydroxytryptophan derivative intermediate F to sodium hydroxide is 1:1-10, and the usage ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate F is 0.5-3L:0.5-2L:1mol.

[0058] Preferably, the temperature of the methyl ester hydrolysis reaction is 0-50° C., and the time is 0.5-6 h.

[0059] Preferably, the raw materials used in the 9-fluorenylmethoxycarbonyl protection reaction of the amino group include 9-fluorenylmethoxycarbonyl chloride, and the 9-fluorenylmethoxycarbonyl protection reaction of the amino group is carried out in the presence of sodium carbonate, an organic solvent and water; based on the amount of the L-6-hydroxytryptophan derivative intermediate F, the molar ratio of the L-6-hydroxytryptophan derivative intermediate F, 9-fluorenylmethoxycarbonyl chloride and sodium carbonate is 1:1~3:1~3; the amount ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate F is 0.5~3L:0.5~2L:1mol.

[0060] Preferably, the 9-Fmoc protection reaction is carried out at a temperature of 0 to 50° C. and for a time of 1 to 24 hours.

[0061] Preferably, after the 9-fluorenylmethoxycarbonyl protection reaction, the process further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative.

[0062] The present invention provides an intermediate for synthesizing L-6-hydroxytryptophan derivatives, including a compound having a structure shown in Formula 4, Formula 5 or Formula 6:

[0063] Beneficial technical effects: The present invention provides a method for preparing a variety of L-6-hydroxytryptophan derivative intermediates, based on which L-6-hydroxytryptophan derivatives can be prepared with high product yield and low production cost. Specifically, the present invention uses compound A6-0 having a structure shown in Formula 1 as a starting reaction raw material, which is easy to purchase through commercial channels and is inexpensive. After a TIPS protection reaction, an L-6-hydroxytryptophan derivative intermediate A having a structure shown in Formula 2 is obtained. Then, a coupling reaction is performed to obtain an L-6-hydroxytryptophan derivative intermediate B having a structure shown in Formula 3. Then, a carbon-boron bond oxidation reaction is performed to obtain an L-6-hydroxytryptophan derivative intermediate C having a structure shown in Formula 4. Then, a benzyl protection reaction of the hydroxyl group is performed to obtain an L-6-hydroxytryptophan derivative intermediate D having a structure shown in Formula 5. Then, a TIPS protecting group removal reaction is performed to obtain an L-6-hydroxytryptophan derivative intermediate E having a structure shown in Formula 6. Then, a Boc protecting group removal reaction is performed to obtain an L-6-hydroxytryptophan derivative intermediate F having a structure shown in Formula 7. Finally, a methyl ester hydrolysis reaction and a 9-fluorenylmethyloxycarbonyl protection reaction of the amino group are performed to obtain an L-6-hydroxytryptophan derivative having a structure shown in Formula 8. The product yield is high, the process flow is short, and the operation is convenient, which facilitates large-scale production.

[0064] Furthermore, the method provided by the present invention has mild reaction conditions, high selectivity, and a separation and purification process with good operability, which is convenient for further use in the synthesis of polypeptides and bioactive small molecules. DETAILED DESCRIPTION

[0065] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate C, comprising the following steps:

[0066] Compound A6-0 is subjected to TIPS protection reaction to obtain L-6-hydroxytryptophan derivative intermediate A;

[0067] The L-6-hydroxytryptophan derivative intermediate A is subjected to a coupling reaction to obtain an L-6-hydroxytryptophan derivative intermediate B;

[0068] subjecting the L-6-hydroxytryptophan derivative intermediate B to a carbon-boron bond oxidation reaction to obtain the L-6-hydroxytryptophan derivative intermediate C;

[0069] The structural formulas of the compound A6-0, L-6-hydroxytryptophan derivative intermediate A, L-6-hydroxytryptophan derivative intermediate B and L-6-hydroxytryptophan derivative intermediate C are shown in Formula 1, Formula 2, Formula 3 and Formula 4 respectively:

[0070] In the present invention, unless otherwise specified, the raw materials used are commercially available products well known to those skilled in the art.

[0071] In the present invention, compound A6-0 is subjected to a TIPS protection reaction to obtain L-6-hydroxytryptophan derivative intermediate A. In the present invention, the starting material used in the TIPS protection reaction is preferably triisopropylsilyl chloride, and the molar ratio of triisopropylsilyl chloride to compound A6-0 is preferably 0.15-0.2:0.15, more preferably 0.18:0.15. In the present invention, the TIPS protection reaction is preferably carried out in the presence of lithium hexamethyldisilazide and an organic solvent, preferably tetrahydrofuran. The ratio of lithium hexamethyldisilazide to organic solvent to compound A6-0 is preferably 0.15-0.20 mol:0.3-1 L:0.15 mol, more preferably 0.18 mol:0.48 L:0.15 mol.

[0072] The present invention preferably mixes compound A6-0 with tetrahydrofuran, then adds a tetrahydrofuran solution of lithium hexamethyldisilazide for a pre-reaction, and then adds a tetrahydrofuran solution of triisopropylsilyl chloride for a TIPS protection reaction. In the present invention, the temperature of the pre-reaction is preferably -70 to -85°C, more preferably -78°C, and the time is preferably 0.1 to 2 hours, more preferably 1 hour. In the present invention, the temperature of the TIPS protection reaction is preferably 0 to 50°C, more preferably room temperature; the time is preferably 0.1 to 2 hours, more preferably 1 hour. In the present invention, the pre-reaction and TIPS protection reaction are preferably carried out under nitrogen protection conditions.

[0073] After the TIPS protection reaction, the present invention preferably adds a saturated NH4Cl solution to the resulting system to quench the reaction, followed by extraction to remove the solvent from the resulting organic phase. The resulting crude product is separated by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate A. The organic reagent used in the extraction is preferably ethyl acetate; the extraction is preferably followed by drying, and the drying agent is preferably anhydrous sodium sulfate. In the present invention, the drying is preferably followed by filtration to remove the solvent from the resulting filtrate to obtain the crude product; the solvent is preferably removed by distillation under reduced pressure, and the solvent can be recovered and reused. In the present invention, the silica gel used for separation is preferably 200-300 mesh silica gel; the eluent used in the separation is preferably a mixture of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is preferably 95:5.

[0074] After obtaining the L-6-hydroxytryptophan derivative intermediate A, the present invention performs a coupling reaction on the L-6-hydroxytryptophan derivative intermediate A to obtain the L-6-hydroxytryptophan derivative intermediate B. In the present invention, the raw materials used in the coupling reaction preferably include pinacol borane and biboronic acid pinacol ester, and the molar ratio of the L-6-hydroxytryptophan derivative intermediate A, pinacol borane, and biboronic acid pinacol ester is preferably 1:0.2-0.3:3.5-4.5, and more preferably 1:0.25:4. The coupling reaction of the present invention is preferably carried out in the presence of methoxy(cyclooctadiene)iridium(I) dimer ([Ir(cod)(OMe)]2), o-phenanthroline (phen) and an organic solvent, and the organic solvent is preferably n-hexane; the amount ratio of the L-6-hydroxytryptophan derivative intermediate A, methoxy(cyclooctadiene)iridium(I) dimer, o-phenanthroline and organic solvent is preferably 1 mol: 0.04-0.06 mol: 0.08-0.12 mol: 3-7 L, and more preferably 1 mol: 0.05 mol: 0.1 mol: 6 L.

[0075] The present invention preferably mixes methoxy(cyclooctadiene)iridium(I) dimer, o-phenanthroline, and a portion of an organic solvent for complexation; then, pinacol borane, L-6-hydroxytryptophan derivative intermediate A, and biboronic acid pinacol ester are added for coupling reaction. In the present invention, the temperature of the complexation treatment is preferably 0 to 50°C, more preferably room temperature. In an embodiment of the present invention, the room temperature is specifically 25°C; the time is preferably 2 to 15 minutes, more preferably 10 minutes. In the present invention, the temperature of the coupling reaction is preferably 70 to 90°C, more preferably 80°C; the time is preferably 1 to 24 hours, more preferably 12 to 24 hours.

[0076] After the coupling reaction, the present invention preferably adds a saturated NaHCO solution to the resulting system to quench the reaction, followed by extraction, removing the solvent from the resulting organic phase, and separating the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate B. The organic reagent used in the extraction is preferably ethyl acetate; the extraction is preferably followed by drying, and the drying agent is preferably anhydrous sodium sulfate. In the present invention, the drying is preferably followed by filtration to remove the solvent from the resulting filtrate to obtain the crude product; the solvent is preferably removed by distillation under reduced pressure, and the solvent can be recovered and reused. In the present invention, the silica gel used for separation is preferably 200-300 mesh silica gel; the eluent used for separation is preferably a mixture of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate is preferably 95:5.

[0077] After obtaining the L-6-hydroxytryptophan derivative intermediate B, the present invention subjects the L-6-hydroxytryptophan derivative intermediate B to a carbon-boron bond oxidation reaction to obtain the L-6-hydroxytryptophan derivative intermediate C. In the present invention, the carbon-boron bond oxidation reaction is preferably carried out in the presence of sodium perborate tetrahydrate and potassium tert-butoxide. In the present invention, the molar ratio of the L-6-hydroxytryptophan derivative intermediate B, sodium borate tetrahydrate, and potassium tert-butoxide is preferably 1:2-10:1-5, more preferably 1:1.5:1.1. In the present invention, the carbon-boron bond oxidation reaction is preferably carried out in the presence of an organic solvent and water. The organic solvent preferably includes one or more of tetrahydrofuran, methanol, and dioxane, more preferably tetrahydrofuran. The ratio of the organic solvent, water, and L-6-hydroxytryptophan derivative intermediate B is preferably 0.5-3L:0.5-3L:0.1 mol, more preferably 1-3L:1-3L:0.1 mol.

[0078] The present invention preferably dissolves the L-6-hydroxytryptophan derivative intermediate B in an organic solvent, and then sequentially adds potassium tert-butoxide, sodium perborate tetrahydrate, and water to carry out a carbon-boron bond oxidation reaction. In the present invention, the carbon-boron bond oxidation reaction preferably comprises a first-stage reaction and a second-stage reaction in sequence. The temperature of the first-stage reaction of the present invention is preferably -10 to 10°C, more preferably 0°C; the time of the first-stage reaction is preferably ≤2 hours, more preferably 1 hour. The temperature of the second-stage reaction of the present invention is preferably 0 to 50°C, more preferably room temperature; the time of the second-stage reaction is preferably 1 to 24 hours, more preferably 12 to 24 hours. The carbon-boron bond oxidation reaction of the present invention is preferably carried out under stirring conditions.

[0079] After the carbon-boron bond oxidation reaction, the present invention preferably extracts the resulting product system, removes the solvent from the resulting organic phase, and separates the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate C. The present invention preferably sequentially adds water and ethyl acetate to the product system for extraction. The extraction preferably includes drying, and the drying agent is preferably anhydrous sodium sulfate. In the present invention, the drying preferably includes filtration to remove the solvent from the resulting filtrate to obtain the crude product. The solvent is preferably removed by vacuum distillation, and the solvent can be recovered and reused. In the present invention, the silica gel used for separation is preferably 200-300 mesh silica gel. The separation preferably includes a first stage separation and a second stage separation. The first eluent used in the first stage separation is preferably a mixture of petroleum ether and ethyl acetate, with the volume ratio of petroleum ether to ethyl acetate in the first eluent preferably being 95:5. The second eluent used in the second stage separation is preferably a mixture of petroleum ether and ethyl acetate, with the volume ratio of petroleum ether to ethyl acetate in the second eluent preferably being 92:8. The present invention preferably adds 200-300 mesh silica gel to a glass column and then adds the crude product, uses a first eluent for elution, collects the eluate of the first band, and distills under reduced pressure to recover the solvent to obtain impurities, then uses a second eluent for elution, collects the eluate of the second band, and distills under reduced pressure to recover the solvent to obtain a light yellow oily liquid, which is the L-6-hydroxytryptophan derivative intermediate C.

[0080] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate D, comprising the following steps:

[0081] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate C is obtained;

[0082] Performing a benzyl protection reaction on the hydroxyl group of the L-6-hydroxytryptophan derivative intermediate C to obtain the L-6-hydroxytryptophan derivative intermediate D;

[0083] The structural formula of the L-6-hydroxytryptophan derivative intermediate D is shown in Formula 5:

[0084] The method for preparing the L-6-hydroxytryptophan derivative intermediate C in the present invention is preferably consistent with the above technical solution, and will not be repeated here.

[0085] After obtaining the L-6-hydroxytryptophan derivative intermediate C, the present invention performs a benzyl protection reaction on the hydroxyl group of the L-6-hydroxytryptophan derivative intermediate C to obtain the L-6-hydroxytryptophan derivative intermediate D. In the present invention, the benzyl reagent used in the benzyl protection reaction of the hydroxyl group preferably includes benzyl bromide, and the benzyl protection reaction of the hydroxyl group is preferably carried out in the presence of potassium iodide and potassium carbonate. In the present invention, the molar ratio of the L-6-hydroxytryptophan derivative intermediate C, benzyl bromide, potassium iodide, and potassium carbonate is preferably 1:1-5:0-1:1-5, more preferably 1:1.2:0.05:2. In the present invention, the benzyl protection reaction of the hydroxyl group is preferably carried out in the presence of an organic solvent, preferably one or more of acetonitrile, dioxane, and methanol, more preferably acetonitrile; the ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate C is preferably 0.5-2L:0.1mol, more preferably 1-2L:0.1mol.

[0086] The present invention preferably dissolves the L-6-hydroxytryptophan derivative intermediate C in an organic solvent, and then sequentially adds potassium carbonate, potassium iodide, and benzyl bromide to perform a benzyl protection reaction of the hydroxyl group. In the present invention, the temperature of the benzyl protection reaction of the hydroxyl group is preferably 30 to 100°C, more preferably under reflux conditions, specifically at 70°C; the time of the benzyl protection reaction of the hydroxyl group is preferably 2 to 24 hours, more preferably 12 hours. The benzyl protection reaction of the hydroxyl group of the present invention is preferably performed under stirring conditions.

[0087] After the benzyl protection reaction of the hydroxyl group is completed, the present invention preferably extracts the resulting product system, removes the solvent from the resulting organic phase, and separates the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate D. The present invention preferably adds water and ethyl acetate sequentially to the product system for extraction. The extraction preferably includes drying, and the drying agent is preferably anhydrous sodium sulfate. In the present invention, the drying preferably includes filtration to remove the solvent from the resulting filtrate to obtain the crude product. The solvent is preferably removed by vacuum distillation, and the solvent can be recovered and reused. In the present invention, the silica gel used for separation is preferably 200-300 mesh silica gel. The eluent used for separation is preferably a mixture of petroleum ether and ethyl acetate, and the volume ratio of petroleum ether to ethyl acetate in the eluent is preferably 90:10. The present invention preferably adds 200-300 mesh silica gel to a glass column, then adds the crude product, elutes with the eluent, collects the first band of eluate, and recovers the solvent by vacuum distillation to obtain a light yellow oily liquid, which is the L-6-hydroxytryptophan derivative intermediate D.

[0088] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate E, comprising the following steps:

[0089] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate D is obtained;

[0090] The L-6-hydroxytryptophan derivative intermediate D is subjected to a TIPS protecting group removal reaction to obtain the L-6-hydroxytryptophan derivative intermediate E;

[0091] The structural formula of the L-6-hydroxytryptophan derivative intermediate E is shown in Formula 6:

[0092] The method for preparing the L-6-hydroxytryptophan derivative intermediate D in the present invention is preferably consistent with the above technical solution, and will not be repeated here.

[0093] After obtaining the L-6-hydroxytryptophan derivative intermediate D, the present invention removes the TIPS protecting group from the L-6-hydroxytryptophan derivative intermediate D to obtain the L-6-hydroxytryptophan derivative intermediate E. In the present invention, the TIPS protecting group removal reaction is preferably carried out in the presence of tetrabutylammonium fluoride; the molar ratio of the L-6-hydroxytryptophan derivative intermediate D to tetrabutylammonium fluoride is preferably 1:1-5, more preferably 1:1.5. In the present invention, the TIPS protecting group removal reaction is preferably carried out in the presence of an organic solvent, preferably one or more of tetrahydrofuran, methanol, and dioxane, more preferably tetrahydrofuran; the ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate D is preferably 0.5-2L:1 mol, more preferably 1L:1 mol.

[0094] In the present invention, the L-6-hydroxytryptophan derivative intermediate D is preferably dissolved in an organic solvent, and then tetrabutylammonium fluoride is added to perform a TIPS protecting group removal reaction. In the present invention, the TIPS protecting group removal reaction is preferably performed at a temperature of 0 to 50°C, more preferably at room temperature, and for a time of 0.2 to 6 hours, more preferably 0.5 hours. The TIPS protecting group removal reaction is preferably performed under stirring.

[0095] After the TIPS protecting group removal reaction, the present invention preferably extracts the resulting product system, removes the solvent from the resulting organic phase, and separates the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate E. The present invention preferably sequentially adds a saturated ammonium chloride solution and ethyl acetate to the product system for extraction. The extraction is preferably followed by drying, with the drying agent preferably being anhydrous sodium sulfate. In the present invention, the drying is preferably followed by filtration to remove the solvent from the resulting filtrate to obtain the crude product. The solvent is preferably removed by distillation under reduced pressure, and the solvent can be recovered and reused. In the present invention, the silica gel used for separation is preferably 200-300 mesh silica gel. The eluent used for separation is preferably a mixture of petroleum ether and ethyl acetate, with the volume ratio of petroleum ether to ethyl acetate in the eluent preferably being 95:5. The present invention preferably adds 200-300 mesh silica gel to a glass column, then adds the crude product, elutes with the eluent, collects the first band of eluate, and distills under reduced pressure to recover the solvent, yielding a light yellow oily liquid, the L-6-hydroxytryptophan derivative intermediate E.

[0096] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative intermediate F, comprising the following steps:

[0097] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate E is obtained;

[0098] Deprotecting the L-6-hydroxytryptophan derivative intermediate E by removing the Boc protecting group to obtain the L-6-hydroxytryptophan derivative intermediate F;

[0099] The structural formula of the L-6-hydroxytryptophan derivative intermediate F is shown in Formula 7:

[0100] The method for preparing the L-6-hydroxytryptophan derivative intermediate E in the present invention is preferably consistent with the above technical solution, which will not be described in detail here.

[0101] After obtaining the L-6-hydroxytryptophan derivative intermediate E, the present invention performs a Boc protection group removal reaction on the L-6-hydroxytryptophan derivative intermediate E to obtain the L-6-hydroxytryptophan derivative intermediate F. In the present invention, the Boc protection group removal reaction is preferably carried out in the presence of trifluoroacetic acid; the ratio of trifluoroacetic acid to L-6-hydroxytryptophan derivative intermediate E is preferably 0.5 to 3 L:0.1 mol, more preferably 1 to 3 L:0.1 mol. In the present invention, the Boc protection group removal reaction is preferably carried out in the presence of an organic solvent, the organic solvent preferably includes one or more of dichloromethane, ethyl acetate and methanol, more preferably dichloromethane; the volume ratio of the organic solvent to trifluoroacetic acid is preferably 0 to 6:3, more preferably 1:3.

[0102] In the present invention, the L-6-hydroxytryptophan derivative intermediate E is preferably dissolved in an organic solvent, and trifluoroacetic acid is then added to carry out a Boc-protecting group removal reaction. In the present invention, the Boc-protecting group removal reaction is preferably carried out at a temperature of 0 to 50° C., more preferably room temperature, and for a time of 0.2 to 6 hours, more preferably 0.5 hours. The Boc-protecting group removal reaction is preferably carried out under stirring.

[0103] After the Boc-protecting group removal reaction, the present invention preferably removes the solvent from the resulting product system and separates the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate F. In the present invention, the method for removing the solvent is preferably distillation under reduced pressure, and the solvent can be recovered and reused. In the present invention, the silica gel used for the separation is preferably 200-300 mesh silica gel; the eluent used for the separation is preferably a mixture of dichloromethane and methanol, and the volume ratio of dichloromethane to methanol in the eluent is preferably 98:2. In the present invention, it is preferred to add 200-300 mesh silica gel to a glass column, then add the crude product, elute with the eluent, collect the eluate of the first band, and recover the solvent by distillation under reduced pressure to obtain a light yellow oily liquid, which is the L-6-hydroxytryptophan derivative intermediate F.

[0104] The present invention provides a method for preparing an L-6-hydroxytryptophan derivative, comprising the following steps:

[0105] According to the preparation method described in the above technical solution, the L-6-hydroxytryptophan derivative intermediate F is obtained;

[0106] The L-6-hydroxytryptophan derivative intermediate F is subjected to a methyl ester hydrolysis reaction and a 9-fluorenylmethoxycarbonyl protection reaction of the amino group to obtain the L-6-hydroxytryptophan derivative;

[0107] The structural formula of the L-6-hydroxytryptophan derivative is shown in Formula 8:

[0108] The method for preparing the L-6-hydroxytryptophan derivative intermediate F in the present invention is preferably consistent with the above technical solution, and will not be repeated here.

[0109] After obtaining the L-6-hydroxytryptophan derivative intermediate F, the present invention subjects the L-6-hydroxytryptophan derivative intermediate F to a methyl ester hydrolysis reaction and a 9-fluorenylmethoxycarbonyl protection reaction of the amino group to obtain the L-6-hydroxytryptophan derivative. The present invention preferably subjects the L-6-hydroxytryptophan derivative intermediate F to a methyl ester hydrolysis reaction and a 9-fluorenylmethoxycarbonyl protection reaction of the amino group in sequence, each of which is described in detail below.

[0110] In the present invention, the methyl ester hydrolysis reaction is preferably carried out in the presence of sodium hydroxide, and the molar ratio of the L-6-hydroxytryptophan derivative intermediate F to sodium hydroxide is preferably 1:1-10, more preferably 1:5. In the present invention, the methyl ester hydrolysis reaction is preferably carried out in the presence of an organic solvent and water, and the organic solvent preferably includes one or more of tetrahydrofuran, methanol, and dioxane; the ratio of the organic solvent, water, and L-6-hydroxytryptophan derivative intermediate F is preferably 0.5-3L:0.5-2L:1mol, more preferably 1L:1L:1mol.

[0111] In the present invention, the L-6-hydroxytryptophan derivative intermediate F is preferably dissolved in an organic solvent, and then sodium hydroxide and water are sequentially added to carry out a methyl ester hydrolysis reaction. In the present invention, the methyl ester hydrolysis reaction is preferably carried out at a temperature of 0 to 50°C, more preferably at room temperature, and for a time of 0.5 to 6 hours, more preferably 1 hour. The methyl ester hydrolysis reaction is preferably carried out under stirring.

[0112] After the methyl ester hydrolysis reaction, the present invention preferably extracts the resulting product system, removes the solvent from the resulting organic phase, and directly subjects the resulting crude product to a subsequent 9-fluorenylmethoxycarbonyl protection reaction of the amino group. The present invention preferably sequentially adds water and ethyl acetate to the product system for extraction; the extraction preferably includes drying, preferably using anhydrous sodium sulfate as a desiccant. In the present invention, the drying preferably includes filtration to remove the solvent from the resulting filtrate to obtain a crude product; the solvent removal method is preferably vacuum distillation, and the solvent can be recovered and reused.

[0113] In the present invention, the raw materials used in the 9-fluorenylmethoxycarbonyl protection reaction of the amino group preferably include 9-fluorenylmethoxycarbonyl chloride, and the 9-fluorenylmethoxycarbonyl protection reaction of the amino group is preferably carried out in the presence of sodium carbonate; based on the amount of the L-6-hydroxytryptophan derivative intermediate F, the molar ratio of the L-6-hydroxytryptophan derivative intermediate F, 9-fluorenylmethoxycarbonyl chloride and sodium carbonate is preferably 1:1~3:1~3, more preferably 1:1.3:1.5. In the present invention, the 9-fluorenylmethoxycarbonyl protection reaction of the amino group is preferably carried out in the presence of an organic solvent and water. The organic solvent preferably includes one or more of 1,4-dioxane, tetrahydrofuran and methanol, and more preferably 1,4-dioxane. Based on the amount of the L-6-hydroxytryptophan derivative intermediate F, the amount ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate F is preferably 0.5-3L:0.5-2L:1mol, and more preferably 1L:1L:1mol.

[0114] The present invention preferably dissolves 9-Fmocyl chloride in a portion of the organic solvent used in the 9-Fmocyl protection reaction of the amino group to obtain a 9-Fmocyl chloride solution; the crude product obtained after the methyl ester hydrolysis reaction is dissolved in the remaining organic solvent used in the 9-Fmocyl protection reaction of the amino group, then sodium carbonate is added, followed by dropwise addition of the 9-Fmocyl chloride solution, and finally water is added to carry out the 9-Fmocyl protection reaction. In the present invention, the temperature of the 9-Fmocyl protection reaction is preferably 0-50°C, more preferably room temperature; the time of the 9-Fmocyl protection reaction is preferably 1-24 hours, more preferably 4 hours. The 9-Fmocyl protection reaction of the present invention is preferably carried out under stirring conditions.

[0115] After the 9-Fmocyl protection reaction, the present invention preferably extracts the resulting product system, removes the solvent from the resulting organic phase, and separates the resulting crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative. The present invention preferably sequentially adds water and ethyl acetate to the product system for extraction; the extraction preferably includes drying, and the drying agent used is preferably anhydrous sodium sulfate. In the present invention, the drying preferably includes filtration to remove the solvent from the resulting filtrate to obtain the crude product; the solvent removal method is preferably distillation under reduced pressure, and the solvent can be recovered and reused. In the present invention, the silica gel used for the separation is preferably 200-300 mesh silica gel; the separation preferably includes sequentially performing stage I separation and stage II separation; the first eluent used in the stage I separation is preferably a mixture of dichloromethane and methanol, the volume ratio of dichloromethane to methanol in the first eluent preferably being 99:1; the second eluent used in the stage II separation is preferably a mixture of dichloromethane and methanol, the volume ratio of dichloromethane to methanol in the second eluent preferably being 98:2. In the present invention, preferably, 200-300 mesh silica gel is added to a glass column followed by the crude product, elution is performed using the first eluent, the first eluate is collected, and the solvent is recovered by reduced pressure distillation to obtain impurities, and then the second eluent is used for elution, the first eluate is collected, and the solvent is recovered by reduced pressure distillation to obtain a colorless solid, which is the L-6-hydroxytryptophan derivative.

[0116] The present invention provides an intermediate for synthesizing the L-6-hydroxytryptophan derivative described in the above technical solution, including a compound having a structure shown in Formula 4, Formula 5 or Formula 6:

[0117] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0118] Example 1 Synthesis of Compound A6-2

[0119] Under nitrogen protection, 47.7 g (0.15 mol) of compound A6-0 was added to a reaction flask, 300 mL of dry tetrahydrofuran (THF) was added, and the mixture was stirred at -78 ° C for 15 min to obtain a solution of compound A6-0; then 139 mL of a 1.3 mol / L lithium hexamethyldisilazide (LiHMDS, 0.18 mol) THF solution was added dropwise to the compound A6-0 solution, and the mixture was heated at -78 ° C. The reaction was carried out for 1 hour; then, 41 mL of triisopropylsilyl chloride (34.7 g, 0.18 mol) in THF was added dropwise to the reaction solution with a syringe, and the temperature was raised to room temperature for 1 hour. After the reaction, 100 mL of saturated NH4Cl solution was added to the obtained system to quench the reaction, and the mixture was extracted three times with 300 mL of ethyl acetate. The organic phases were combined, dried over anhydrous sodium sulfate, filtered, and the solvent was removed by distillation under reduced pressure to obtain a crude product. The crude product was separated by column chromatography, specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 95:5 was used as the eluent. The eluate was collected and the solvent was removed by distillation under reduced pressure to obtain 63.55 g of a white solid powder, which was compound A6-1, with a yield of 89%.

[0120] The NMR data of the compound A6-1 are as follows:

[0121] 1 H NMR (600MHz, CDCl3) δ7.53(d,J=7.5Hz,1H),7.47(d,J=8.0Hz,1H),7.13(dt,J=14.7,7.0Hz,2H),7.03(s,1H),5.06(d,J=7.5Hz ,1H),4.65(d,J=6.9Hz,1H),3.63(s,3H),3.28(s,2H),1.68(dq,J=15.0,7.5Hz,3H),1.43(s,9H),1.14(dd,J=7.6,2.0Hz,18H). 13 C NMR (151MHz, CDCl3) δ172.8,155.3,141.4,131.2,129.9,121.7,119.8,118.8,114.1,112.2,79.8,54.2,52.2,28.5,28.2,18.3,12.9.

[0122] In a glove box, methoxy(cyclooctadiene)iridium(I) dimer ([Ir(cod)(OMe)]2, 3.3 g, 5 mmol) and o-phenanthroline (phen, 1.8 g, 10 mmol) were added to a round-bottom flask, and then 300 mL of n-hexane was added to the round-bottom flask for complexation at room temperature for 10 min; then, pinacol borane (HBPin, 3.2 g, 25 mmol), compound A6-1 (47.6 g, 0.1 mol) and 300 mL of n-hexane were added to the round-bottom flask and stirred for 5 min, followed by the addition of pinacol diboron (B2Pin2, 104.0 g, 0.4 mol) and 200 mL of n-hexane, and the round-bottom flask was sealed with a bottle cap. The bottom bottle was removed from the glove box and reacted at 80°C for 24h. After the reaction, 200mL of saturated NaHCO3 solution was added to quench the reaction, and the mixture was extracted with 500mL of ethyl acetate three times. The organic phases were combined, washed with saturated ammonium chloride solution three times, and then dried over anhydrous sodium sulfate, filtered, and the solvent was removed under reduced pressure to obtain a crude product. The crude product was separated by column chromatography, specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 95:5 was used as an eluent. The eluate was collected and the solvent was removed by distillation under reduced pressure to obtain 47.4g of a light yellow oily liquid, which was compound A6-2, with a yield of 79%.

[0123] The NMR data of compound A6-2 are as follows:

[0124] 1 H NMR (500MHz, CDCl3) δ7.92(s,1H),7.55(d,J=8.8Hz,1H),7.51(d,J=8.8Hz,1H),7.08(s,1H),5.04(d,J=8.1Hz,1H),4.65-4.6 3(m,1H),3.62(s,3H);3.27(d,J=5.5Hz,2H),1.71-1.68(m,3H),1.43(s,J=6.3Hz,9H),1.35(s,12H),1.13(d,J=7.2Hz,18H); 13 C NMR (151MHz, CDCl3) δ172.7,155.2,141.0,133.6,131.4,125.7,121.0,118.0,113.5,112.2,83.5,79.8,54.3,52.3,28.5,28.1,25.0,18.3,13.0.

[0125] Example 2 Synthesis of Compound A6-3

[0126] 66 g (0.1 mol) of compound A6-2 was added to a reaction flask, and then 1 L of tetrahydrofuran (THF) was added to fully dissolve compound A6-2. The reaction flask was transferred to a 0°C ice bath. After 3 minutes, 12.3 g (0.11 mol) of potassium tert-butoxide (tBuOK), 76.9 g (0.5 mol) of sodium perborate tetrahydrate (NaBO3·4H2O) and 3 L of water were added in sequence. The mixture was stirred at 0°C for 1 hour and then transferred to room temperature (25°C) for 24 hours. After the reaction was completed, 1 L of water and 1 L of ethyl acetate were added to the obtained product system in sequence for extraction. The extraction was performed three times with ethyl acetate, and the organic phases were finally combined. , anhydrous sodium sulfate was added to the organic phase and dried for 2 minutes, filtered, and the filtrate was distilled under reduced pressure and the solvent was recovered to obtain a crude product, which was separated by column chromatography. Specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 95:5 was used as an eluent, and the eluate of the first band was collected. The solvent was distilled under reduced pressure to recover the solvent to obtain impurities, and then a mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 92:8 was used as an eluent. The eluate of the second band was collected and the solvent was distilled under reduced pressure to recover the solvent to obtain 57.0 g of a light yellow oily liquid, which is compound A6-3, with a yield of 85%;

[0127] The chemical name of compound A6-3 is (S)-methyl 3-(6-(hydroxy)-1-(triisopropylsilyl)-1H-indol-3-yl)-2-((tert-butoxycarbonyl)amino)propanoate, and the NMR data are as follows:

[0128] 1 H NMR (600MHz, DMSO) δ8.92(s,1H),7.26(d,J=8.4Hz,1H),7.15(d,J=7.7Hz,1H),7.00(s,1H),6.89(s,1H),6.60(d,J=8.4Hz,1H),4.26-4.18(m ,1H),3.58(s,3H),3.05(dd,J=14.5,4.9Hz,1H),2.93(dd,J=14.3,9.5Hz,1H),1.64(dt,J=14.9,7.4Hz,3H),1.33(s,9H),1.11-1.07(m,18H). 13 C NMR (151MHz, DMSO) δ172.9,155.20,153.2,141.8,127.6,123.7,118.2,112.8,109.5,99.4,78.0,53.9,51.7,28.1,26.7,17.9,12.1.

[0129] Example 3 Synthesis of Compound A6-4

[0130] 49 g (0.1 mol) of compound A6-3 was added to the reaction flask, and then 2 L of acetonitrile was added to fully dissolve the compound A6-3. Then, 27.7 g (0.2 mol) of potassium carbonate (K2CO3), 0.9 g (0.005 mol) of potassium iodide (KI) and 20.5 g (0.12 mol) of benzyl bromide (BnBr) were added in sequence, and the mixture was stirred under reflux at 70 ° C for 12 h. After the reaction, 1 L of water and 1 L of ethyl acetate were added to the obtained product system in sequence for extraction. The mixture was extracted three times, and the organic phases were finally combined. Anhydrous sodium sulfate was added to the organic phase and dried for 2 minutes. The mixture was filtered, and the filtrate was distilled under reduced pressure and the solvent was recovered to obtain a crude product. The crude product was separated by column chromatography. Specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 90:10 was used as the eluent. The eluate of the first band was collected, and the solvent was recovered by distillation under reduced pressure to obtain 52.5 g of a light yellow oily liquid, which is compound A6-4, with a yield of 90%.

[0131] The chemical name of compound A6-4 is (S)-methyl 3-(6-(benzyloxy)-1-(triisopropylsilyl)-1H-indol-3-yl)-2-((tert-butoxycarbonyl)amino)propanoate, and the NMR data are as follows:

[0132] 1 H NMR (600MHz, CDCl3) δ7.45(d,J=7.5Hz,2H),7.41-7.37(m,3H),7.31(t,J=7.3Hz,1H),6.96(s,1H),6.91-6.89(m,2H),5.13(s,1H) ,5.07(s,1H),4.63(d,J=4.9Hz,1H),3.64(s,3H),3.23(s,2H),1.55(dt,J=14.8,7.4Hz,3H),1.44(s,9H),1.09(d,J=7.6Hz,18H). 13 C NMR (151MHz, CDCl3) δ173.0,155.4,152.1,142.3,128.5,125.5,119.0,111.9,109.7,100.2,80.0,54.1,52.3,28.5,27.0,18.3,12.9.

[0133] Example 4 Synthesis of Compound A6-5

[0134] 58 g (0.1 mol) of compound A6-4 was added to a reaction flask, and then 0.1 L of tetrahydrofuran (THF) was added to fully dissolve compound A6-4. After 3 minutes, 39 g (0.15 mol) of tetrabutylammonium fluoride (TBAF) was added, and the mixture was stirred at room temperature for 30 minutes. After the reaction, 0.1 L of saturated ammonium chloride (NH4Cl) solution and 0.1 L of ethyl acetate were added to the obtained system in sequence for extraction. The organic phase was extracted with 0.1 L of saturated ammonium chloride solution each time, for a total of 100% NH4Cl. The mixture was extracted three times, and finally anhydrous sodium sulfate was added to the organic phase and dried for 2 minutes. The mixture was filtered, and the filtrate was distilled under reduced pressure and the solvent was recovered to obtain a crude product. The crude product was separated by column chromatography. Specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of petroleum ether and ethyl acetate with a volume ratio of 95:5 was used as the eluent. The eluate of the first band was collected, and the solvent was recovered by distillation under reduced pressure to obtain 39.0 g of a light yellow oily liquid, which is compound A6-5, with a yield of 92%.

[0135] The chemical name of compound A6-5 is (S)-methyl 3-(6-(benzyloxy)-1H-indol-3-yl)-2-((tert-butoxycarbonyl)amino)propanoate, and the NMR data are as follows:

[0136] 1 H NMR (600MHz, CDCl3) δ8.27(s,1H),7.46(d,J=7.4Hz,2H),7.43(d,J=8.7Hz,1H),7.39(t,J=7.6Hz,2H),7.33(t,J=7.3Hz,1H),6.88(dt,J=6.0,3.0 Hz,1H),6.86(d,J=1.8Hz,1H),6.84(s,1H),5.07(s,2H),4.65(dd,J=12. 8,5.4Hz,1H),3.67(d,J=6.3Hz,3H),3.25(d,J=4.6Hz,2H),1.45(s,9H). 13 C NMR (151MHz, CDCl3) δ172.9,155.7,155.4,137.5,136.9,128.6,127.9,127.6,12 2.4,121.8,119.4,110.4,109.9,96.1,79.9,77.1,70.6,54.3,52.3,28.4,28.09.

[0137] Example 5 Synthesis of Compound A6-6

[0138] 42.4 g (0.1 mol) of compound A6-5 was added to a reaction flask, and then 1 L of dichloromethane (DCM) was added to fully dissolve compound A6-5, followed by adding 3 L of trifluoroacetic acid (TFA), and the reaction was stirred at room temperature for 30 minutes. After the reaction, the obtained product system was distilled under reduced pressure and the solvent was recovered to obtain a crude product, which was separated by column chromatography. Specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of dichloromethane and methanol with a volume ratio of 98:2 was used as an eluent. The eluate of the first band was collected, and the solvent was recovered by distillation under reduced pressure to obtain 27.4 g of a light yellow oily liquid, which is compound A6-6, with a yield of 85%.

[0139] The chemical name of compound A6-6 is (S)-2-amino-3-(6-(benzyloxy)-1-hydrogen-indol-3-yl)propanoic acid methyl ester, and the NMR data are as follows:

[0140] 1 H NMR (600MHz, DMSO) δ10.68(s,1H),7.47(d,J=7.5Hz,2H),7.41-7.36(m,3H),7.32(t,J=7.2Hz,1H),6.99(s,1H),6.94(s,1H),6.74(dd,J=8.6 ,1.9Hz,1H),5.10(s,2H),3.62(dd,J=8.7,3.5Hz,1H),3.56(s,3H),3.36(s,2H),2.99(dd,J=14.0,6.0Hz,1H),2.92(dd,J=14.1,6.3Hz,1H). 13 C NMR (151MHz, DMSO) δ175.7,154.5,137.7,136.7,128.4,127.6,127.5,122.4,122.1,118.9,109.9,109.2,96.0,69.6,55.2,51.4,30.8.

[0141] Example 6 Synthesis of Compound A6-7

[0142] 32.4 g (0.1 mol) of compound A6-6 was added to a reaction flask, followed by the addition of 0.1 L of tetrahydrofuran (THF) to fully dissolve compound A6-6. 20 g (0.5 mol) of sodium hydroxide (NaOH) and 0.1 L of water were then added in sequence, and the mixture was stirred at room temperature for 1 h. After the reaction, 0.1 L of water and 0.1 L of ethyl acetate were added to the resulting product system for extraction, and ethyl acetate was used for extraction three times. The organic phases were combined, anhydrous sodium sulfate was added to the organic phases, and the mixture was dried for 2 min. The mixture was filtered, and the filtrate was distilled under reduced pressure and the solvent was recovered to obtain a crude product.

[0143] The crude product was transferred to a reaction flask, and then 75 mL of 1,4-dioxane was added to fully dissolve the crude product, followed by adding 15.9 g (0.15 mol) of sodium carbonate (Na2CO3), and then a solution of 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl, 33.7 g, 0.13 mol) in 1,4-dioxane (1,4-dioxane, 25 mL) was added dropwise, and finally 0.1 L of water was added and stirred at room temperature for 4 h. After the reaction was completed, 1 L of water and 2 L of ethyl acetate were added to the obtained product system in sequence for extraction, and ethyl acetate was used for extraction 3 times. Finally, the 1 L of water and 2 L of ethyl acetate were added to the obtained product system for extraction. The organic phase was dried for 2 minutes by adding anhydrous sodium sulfate, filtered, and the filtrate was distilled under reduced pressure and the solvent was recovered to obtain a crude product. The crude product was separated by column chromatography, specifically, 200-300 mesh silica gel was added to a glass column and then the crude product was added. A mixed solvent of dichloromethane and methanol with a volume ratio of 99:1 was used as an eluent, and the eluate of the first band was collected. The solvent was distilled under reduced pressure to recover the solvent to obtain impurities. Then, a mixed solvent of dichloromethane and methanol with a volume ratio of 98:2 was used as an eluent, and the eluate of the first band was collected. The solvent was distilled under reduced pressure to recover the solvent to obtain 44.0 g of a colorless solid, which is compound A6-7, with a yield of 80%.

[0144] The chemical name of compound A6-7 is (S)-2-((((9-hydrogen-fluoren-9-yl)methoxy)carbonyl)amino)-3-(6-(benzyloxy)-1-hydrogen-indol-3-yl)propanoic acid, and the NMR data are as follows:

[0145] 1H NMR (600MHz, DMSO) δ12.70(s,1H),10.68(s,1H),7.88(d,J=6.9Hz,2H),7.68(dd,J=12.8,7.2Hz,2H),7.51-7.43(m,3H),7.44-7.35(m,4H),7 .35-7.24(m,3H),7.06(s,1H),6.94(s,1H),6.75(d,J=7.8Hz,1H),5.1 1(s,2H),4.36-4.04(m,4H),3.19(d,J=10.7Hz,1H),3.07-2.96(m,1H). 13 C NMR (151MHz, DMSO) δ173.7,155.9,154.5,143.8,140.7,137.7,136.7,128.4,127.6,127.4,127 .1,125.3,125.3,122.4,121.9,120.1,118.8,110.3,109.2,96.1,69.6,65.6,54.9,46.6,27.0.

[0146] As can be seen from the above examples, the raw materials used in the preparation of L-6-hydroxytryptophan derivative intermediates and L-6-hydroxytryptophan derivatives of the present invention are inexpensive and easily commercially available. The reaction conditions involved are mild, the operation is simple, the selectivity is high, the separation and purification process has good operability, and the product yield is high. The method has significant application value in the field of amino acid derivative synthesis.

[0147] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing an L-6-hydroxytryptophan derivative intermediate C, comprising the following steps: Compound A6-0 is subjected to TIPS protection reaction to obtain L-6-hydroxytryptophan derivative intermediate A; The L-6-hydroxytryptophan derivative intermediate A is subjected to a coupling reaction to obtain an L-6-hydroxytryptophan derivative intermediate B; The L-6-hydroxytryptophan derivative intermediate B is subjected to a carbon-boron bond oxidation reaction to obtain the L-6-hydroxytryptophan derivative intermediate C; The structural formulas of the compound A6-0, L-6-hydroxytryptophan derivative intermediate A, L-6-hydroxytryptophan derivative intermediate B and L-6-hydroxytryptophan derivative intermediate C are shown in Formula 1, Formula 2, Formula 3 and Formula 4 respectively:

2. A method for preparing an L-6-hydroxytryptophan derivative intermediate D, The following steps are involved: According to the preparation method of claim 1, the L-6-hydroxytryptophan derivative intermediate C is obtained; Performing a benzyl protection reaction on the hydroxyl group of the L-6-hydroxytryptophan derivative intermediate C to obtain the L-6-hydroxytryptophan derivative intermediate D; The structural formula of the L-6-hydroxytryptophan derivative intermediate D is shown in Formula 5:

3. A method for preparing an L-6-hydroxytryptophan derivative intermediate E, The following steps are involved: According to the preparation method of claim 2, the L-6-hydroxytryptophan derivative intermediate D is obtained; The L-6-hydroxytryptophan derivative intermediate D is subjected to a TIPS protecting group removal reaction to obtain the L-6-hydroxytryptophan derivative intermediate E; The structural formula of the L-6-hydroxytryptophan derivative intermediate E is shown in Formula 6:

4. A method for preparing an L-6-hydroxytryptophan derivative intermediate F, The following steps are involved: According to the preparation method of claim 3, the L-6-hydroxytryptophan derivative intermediate is obtained. Body E; The L-6-hydroxytryptophan derivative intermediate E is subjected to a Boc protecting group removal reaction to obtain the L-6-hydroxytryptophan derivative intermediate F; The structural formula of the L-6-hydroxytryptophan derivative intermediate F is shown in Formula 7:

5. A method for preparing an L-6-hydroxytryptophan derivative, The following steps are involved: According to the preparation method of claim 4, the L-6-hydroxytryptophan derivative intermediate F is obtained; The L-6-hydroxytryptophan derivative intermediate F is subjected to a methyl ester hydrolysis reaction and an amino group 9-fluorenylmethoxycarbonyl protection reaction to obtain the L-6-hydroxytryptophan derivative; The structural formula of the L-6-hydroxytryptophan derivative is shown in Formula 8:

6. The preparation method according to any one of claims 1 to 5, characterized in that: The raw material used in the TIPS protection reaction is triisopropylsilyl chloride, and the molar ratio of triisopropylsilyl chloride to compound A6-0 is 0.15-0.2:0.15; The TIPS protection reaction is carried out in the presence of lithium hexamethyldisilazide and an organic solvent, and the usage ratio of lithium hexamethyldisilazide, organic solvent and compound A6-0 is 0.15-0.20 mol: 0.3-1 L: 0.15 mol.

7. The preparation method according to claim 6, characterized in that The temperature of the TIPS protection reaction is 0-50° C. and the time is 0.1-2 h.

8. The preparation method according to claim 7, characterized in that After the TIPS protection reaction, the method further comprises: adding a saturated NH4Cl solution to the obtained system to quench the reaction, followed by extraction, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate A.

9. The preparation method according to any one of claims 1 to 5, characterized in that: The raw materials used in the coupling reaction include pinacol borane and biboric acid pinacol ester, and the molar ratio of the L-6-hydroxytryptophan derivative intermediate A, pinacol borane and biboric acid pinacol ester is 1:0.2-0.3:3.5-4.5; The coupling reaction is carried out in the presence of methoxy(cyclooctadiene)iridium(I) dimer, o-phenanthroline and an organic solvent, and the dosage ratio of the L-6-hydroxytryptophan derivative intermediate A, methoxy(cyclooctadiene)iridium(I) dimer, o-phenanthroline and the organic solvent is 1 mol: 0.04-0.06 mol: 0.08-0.12 mol: 3-7 L.

10. The preparation method according to claim 9, characterized in that: The coupling reaction is carried out at a temperature of 70 to 90° C. and for a time of 1 to 24 hours.

11. The preparation method according to claim 10, characterized in that: After the coupling reaction, the method further comprises: adding a saturated NaHCO3 solution to the obtained system to quench the reaction, then extracting, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate B.

12. The preparation method according to any one of claims 1 to 5, characterized in that: The carbon-boron bond oxidation reaction is carried out in the presence of sodium perborate tetrahydrate and potassium tert-butoxide.

13. The preparation method according to claim 12, characterized in that: The molar ratio of the L-6-hydroxytryptophan derivative intermediate B, sodium borate tetrahydrate and potassium tert-butoxide is 1:2-10:1-5; The carbon-boron bond oxidation reaction is carried out in the presence of an organic solvent and water, and the usage ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate B is 0.5-3L:0.5-3L:0.1mol.

14. The preparation method according to claim 13, characterized in that: The carbon-boron bond oxidation reaction includes a first stage reaction and a second stage reaction in sequence; the temperature of the first stage reaction is -10 to 10°C, and the time of the first stage reaction is 1 to 2 hours; the temperature of the second stage reaction is 0 to 25°C, and the time of the second stage reaction is 1 to 24 hours.

15. The preparation method according to claim 14, characterized in that: After the carbon-boron bond oxidation reaction, the method further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate C.

16. The preparation method according to any one of claims 2 to 5, characterized in that: The benzyl reagent used in the benzyl protection reaction of the hydroxyl group includes benzyl bromide, and the benzyl protection reaction of the hydroxyl group is carried out in the presence of potassium iodide and potassium carbonate.

17. The preparation method according to claim 16, characterized in that: The molar ratio of the L-6-hydroxytryptophan derivative intermediate C, benzyl bromide, potassium iodide and potassium carbonate is 1:1-5:0.05-1:1-5; The benzyl protection reaction of the hydroxyl group is carried out in the presence of an organic solvent, and the usage ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate C is 0.5-2L:0.1 mol.

18. The preparation method according to claim 17, characterized in that: The benzyl protection reaction of the hydroxyl group is carried out at a temperature of 30 to 100° C. and for a time of 2 to 24 hours.

19. The preparation method according to claim 18, characterized in that: After the benzyl protection reaction of the hydroxyl group is completed, the method further includes: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate D.

20. The preparation method according to any one of claims 3 to 5, characterized in that: The TIPS protecting group removal reaction is carried out in the presence of tetrabutylammonium fluoride.

21. The preparation method according to claim 20, characterized in that: The molar ratio of the L-6-hydroxytryptophan derivative intermediate D to tetrabutylammonium fluoride is 1:1-5; The TIPS protection group removal reaction is carried out in the presence of an organic solvent, and the ratio of the organic solvent to the L-6-hydroxytryptophan derivative intermediate D is 0.5-2L:1 mol.

22. The preparation method according to claim 21, characterized in that: The temperature of the TIPS protection group removal reaction is 0 to 50° C. and the time is 0.2 to 6 hours.

23. The preparation method according to claim 22, characterized in that: After the TIPS protection group removal reaction, the method further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate E.

24. The preparation method according to claim 4 or 5, characterized in that: The deprotection reaction of the Boc protecting group is carried out in the presence of trifluoroacetic acid.

25. The preparation method according to claim 24, characterized in that: The usage ratio of trifluoroacetic acid to L-6-hydroxytryptophan derivative intermediate E is 0.5-3L:0.1mol; The Boc protection group removal reaction is carried out in the presence of an organic solvent, and the volume ratio of the organic solvent to trifluoroacetic acid is 1 to 6:

3.

26. The preparation method according to claim 25, characterized in that: The temperature of the Boc protection group removal reaction is 0 to 50° C. and the time is 0.2 to 6 hours.

27. The preparation method according to claim 26, characterized in that: After the Boc protection group removal reaction, the method further comprises: removing the solvent in the obtained product system, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative intermediate F.

28. The preparation method according to claim 5, characterized in that: The methyl ester hydrolysis reaction is carried out in the presence of sodium hydroxide, an organic solvent and water; the molar ratio of the L-6-hydroxytryptophan derivative intermediate F to sodium hydroxide is 1:1-10, and the usage ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate F is 0.5-3L:0.5-2L:1mol.

29. The preparation method according to claim 5 or 28, characterized in that: The temperature of the methyl ester hydrolysis reaction is 0-50° C. and the time is 0.5-6 hours.

30. The preparation method according to claim 5, characterized in that: The raw materials used in the 9-fluorenylmethoxycarbonyl protection reaction of the amino group include 9-fluorenylmethoxycarbonyl chloride, and the 9-fluorenylmethoxycarbonyl protection reaction of the amino group is carried out in the presence of sodium carbonate, an organic solvent and water; based on the amount of the L-6-hydroxytryptophan derivative intermediate F, the molar ratio of the L-6-hydroxytryptophan derivative intermediate F, 9-fluorenylmethoxycarbonyl chloride and sodium carbonate is 1:1-3:1-3; the amount ratio of the organic solvent, water and L-6-hydroxytryptophan derivative intermediate F is 0.5-3L:0.5-2L:1mol.

31. The preparation method according to claim 5 or 30, characterized in that: The temperature of the 9-fluorenylmethoxycarbonyl protection reaction is 0 to 50° C. and the time is 1 to 24 hours.

32. The preparation method according to claim 31, characterized in that: After the 9-fluorenylmethoxycarbonyl protection reaction, the method further comprises: extracting the obtained product system, removing the solvent in the obtained organic phase, and separating the obtained crude product by column chromatography to obtain the L-6-hydroxytryptophan derivative.

33. An intermediate for synthesizing L-6-hydroxytryptophan derivatives, comprising a compound having a structure shown in Formula 4, Formula 5 or Formula 6:

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