JP2735778B2 - Method for producing N-alkoxycarbonyl amino acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing N-alkoxycarbonyl amino acids.

[0002]

2. Description of the Related Art N-Alkoxycarbonyl amino acids in which the amino group of an amino acid is protected are selectively used for forming peptide bonds in the chemical synthesis of antibiotics, peptides, polypeptides, proteins and aminoglycosides. It is an important compound as a starting material or intermediate for obtaining a product.

Conventionally, as a method for synthesizing N-alkoxycarbonyl amino acids, a mixed solvent system of water and a water-miscible organic solvent such as t-butyl alcohol is used. After reacting with a basic substance to form a water-soluble salt, and then reacting with a dialkyl dicarbonate, the obtained N-alkoxycarbonyl amino acid salt is neutralized and converted into an acid to obtain an aqueous solution or suspension thereof, Next, a method of extracting with an organic solvent such as diethyl ether or ethyl acetate, and further dehydrating the extract with a solid dehydrating agent such as sodium sulfate or magnesium sulfate (Organic synthesis (Or)) is known.
Ganical Synthesis) 63 volumes, 160-1
70, 1985).

[0004]

However, in the above-mentioned method, diethyl ether or ethyl acetate, which is an organic solvent used for extraction of N-alkoxycarbonyl amino acid, is dissolved in an aqueous solution or aqueous suspension of N-alkoxycarbonyl amino acid. When contacted, about 3 to 7% by weight of water is dissolved. For this reason, when producing a large amount of N-alkoxycarbonyl amino acid, a large amount of solid dehydrating agent must be used for dehydrating the organic phase in which the extracted N-alkoxycarbonyl amino acid is dissolved, which is very industrial. It could not be said to be an advantageous method.

Usually, an azeotropic dehydration method is employed as a method for dehydrating a large amount of an organic solvent. However, when the present inventors applied this azeotropic dehydration method to the above method, it was found that the It was found that the N-alkoxycarbonyl amino acid was decomposed to release the starting material amino acid.

[0006]

Means for Solving the Problems In view of the above circumstances, the present inventors have made intensive studies to produce N-alkoxycarbonyl amino acids without decomposing them. As a result, N-
The aqueous solution or aqueous suspension obtained by neutralizing the alkoxycarbonyl amino acid salt to convert it to the acid form is brought into contact with a specific organic solvent to extract the N-alkoxycarbonyl amino acid into the organic phase. Was found to be able to synthesize an N-alkoxycarbonyl amino acid by azeotropic dehydration without releasing an amino acid as a starting material, and completed the present invention.

That is, the present invention provides an azeotropic mixture of water and an aqueous solution or suspension of an N-alkoxycarbonyl amino acid, wherein the water content in the azeotropic composition is from 10% by volume to 60% by volume. After extracting the N-alkoxycarbonylamino acid into the organic phase by contacting the organic phase with an organic solvent, the organic phase is separated from the aqueous phase, and the organic phase is azeotropically dehydrated. This is a method for producing an amino acid.

[0008] The N-alkoxycarbonyl amino acid used in the present invention can be obtained by reacting an amino acid salt with a dialkyl dicarbonate and then neutralizing it. As a specific method, a known method can be adopted without any limitation. For example, the starting amino acid is not particularly limited as long as it is a compound having at least one amino group or imino group and a carboxyl group in the molecule. However, in the case of an amino acid having two or more amino groups or imino groups in one molecule, as long as it has at least one amino group or imino group, other amino groups or imino groups are It may be substituted by an alkyl group or the like. In the case of an amino acid having two or more carboxyl groups in one molecule, other carboxyl groups may be in an ester or amide state as long as they have at least one carboxyl group. .

Specific examples of amino acids which can be suitably used in the present invention include, for example, glycine, alanine, β-alanine, valine, norvaline, leucine, norleucine, isoleucine, phenylalanine, tyrosine, diiodotyrosine, threonone, serine. , Homoserine, isoserine, proline, hydroxyproline, tryptophan, thyroxine, methionine, homomethionine, cystine, homocystine, cysteine, homocysteine, α-
Aminobutyric acid, β-aminobutyric acid, γ-aminobutyric acid, α-aminoisobutyric acid, aspartic acid, aspartic acid-β-
Cyclohexyl ester, aspartic acid-β-methyl ester, aspartic acid-β-isopropyl ester, aspartic acid-β-benzyl ester, glutamic acid, glutamic acid-γ-cyclohexyl ester, glutamic acid-γ-methyl ester, glutamic acid-γ-
Isopropyl ester, glutamic acid-γ-benzyl ester, lysine, ornithine, hydroxylysine, arginine, histidine, anticapsin, N ⁵ -iminomethylornithine, α-amino-β- (2-imidazolidyl) propionic acid, N-methylglycine, taurine , Γ
-Formyl-N-methylnorvaline, N ^g -tosylarginine, N ^g -benzyloxycarbonylarginine,
S-acetamidomethylcysteine, S-benzylcysteine, N ^im -benzyloxycarbonylortinine,
N ⁶ -benzyloxycarbonyl lysine, N ⁵ -benzyloxycarbonyl ornithine, O-benzylserine, O
-Benzylthreonine, N ⁱⁿ -formyltryptophan, 2- (2-amino-4-thiazolyl) -2-methoxyiminoacetic acid, 2- (2-amino-4-thiazolyl)-
2-hydroxyiminoacetic acid, 2- (2-amino-4-thiazolyl) -2-glyoxyacetic acid, 2- (2-amino-
4-thiazolyl) -2-pentenoic acid, phenylglycine, 4-hydroxyphenylglycine and the like. These amino acids may be optical isomers or racemic mixtures.

In order to convert these amino acids into water-soluble salts, a general acid-alkali neutralization reaction operation can be used without any limitation. For example, there are a method using an aqueous solution of an inorganic base such as a hydroxide or a carbonate of an alkali metal or an alkaline earth metal, and a method of converting an ammonium salt with an organic base. Specific examples of the base used include, as inorganic bases, sodium hydroxide, potassium hydroxide, lithium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, sodium hydrogen carbonate,
Potassium hydrogen carbonate and the like can be mentioned. Examples of the organic base include pyridine, 4-dimethylaminopyridine, triethylamine, tributylamine, 1-methylpiperidine, 1-methylpyrrolidine and the like. The amount of the base used is 0.2 to 1 equivalent of the amino acid in order to maintain the reaction rate with the dialkyl dicarbonate and to reduce the amount of acid required for neutralization after the reaction with the dialkyl dicarbonate. It is preferable to select in the range of -2.0 equivalents, more preferably 0.5-1.5 equivalents.

Next, the dialkyl dicarbonate to be reacted with the above-mentioned amino acid salt can be represented by the following general formula.

[0012]

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(However, R ₁ and R ₂ are the same or different alkyl groups.) Dialkyl dicarbonate which can be suitably used in the present invention is specifically exemplified by di-t-
Butyl dicarbonate, di-t-amyl dicarbonate, diisopropyl dicarbonate, diisobutyl dicarbonate and the like can be mentioned.

The amount of the above dialkyl dicarbonate relative to the amino acid salt prevents crystallization inhibition of the N-alkoxycarbonyl amino acid and, from the viewpoint of economy, is usually 1 equivalent of the amino group or imino group of the amino acid to be protected. It is preferable to select from 0.5 to 2.0 equivalents, more preferably from 0.8 to 1.2 equivalents.

The reaction temperature of the amino acid salt with the dialkyl dicarbonate is not particularly limited, but is usually selected from the range of -20 ° C. to 60 ° C. in order to prevent the decomposition of the dialkyl dicarbonate at a high temperature and the reaction with water. Is preferred.

As a reaction solvent in the reaction between the amino acid salt and the dialkyl dicarbonate, the amino acid salt is water-soluble and hardly soluble in an organic solvent, and the dialkyl dicarbonate is hardly water-soluble and soluble in an organic solvent. It is preferable to use a mixed solvent. The organic solvent used at this time can be used without any particular limitation as long as it is an organic solvent soluble in water. Specific examples of these organic solvents include t-butyl alcohol, t-amyl alcohol, isopropyl alcohol, isobutyl alcohol,
Alcohols such as ethanol and methanol; ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile; ketones such as acetone; amides such as N, N-dimethylformamide; dimethyl sulfoxide; .

The mixing ratio of these organic solvents and water cannot be determined unequivocally because it varies depending on the type of amino acid used in the reaction. However, both the solubility of the amino acid and the solubility of the dialkyl dicarbonate are increased to increase the reaction rate. In order to maintain the organic solvent, it is preferable to select the organic solvent in the range of 10 parts by weight to 900 parts by weight, and more preferably in the range of 30 parts by weight to 400 parts by weight with respect to 100 parts by weight of water.

In order to maintain a high reaction rate as the concentration of the amino acid salt in the above-mentioned mixed solvent of the organic solvent and water, and to suppress the production of N-alkoxycarbonylamino acid ester as a by-product, the mixed solvent is used. It is good to select from the range of 5 to 100 parts by weight, preferably 10 to 70 parts by weight with respect to 100 parts by weight.

After the reaction of the amino acid salt with the dialkyl dicarbonate, the organic solvent is distilled off and the amino acid salt is neutralized. The temperature in the distillation operation of the organic solvent is not particularly limited, but is usually selected from the range of 0 ° C to 100 ° C. Particularly, when an optically active amino acid is used as a raw material, racemization may occur at a high distillation temperature.
It is preferable to perform distillation under reduced pressure below.

In the neutralization operation of an amino acid salt, a normal operation of an acid-base neutralization reaction is generally employed. Examples of the acid used include mineral acids such as hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid; alkali metal salts such as potassium hydrogen sulfate, sodium hydrogen sulfate, potassium hydrogen phosphate, and sodium hydrogen phosphate; and acetic acid, formic acid, and oxalic acid. Organic acids can be mentioned. The amount of the acid used depends on the type of the amino acid and cannot be unconditionally specified.
It is preferable to add up to the range of ~ 4, and the optimal amount may be determined according to the pKa value of the N-alkoxycarbonylamino acid. If the temperature of the neutralization operation is too high, an elimination reaction of the N-alkoxycarbonyl group occurs. Therefore, the neutralization operation is preferably performed at 40 ° C. or lower, preferably 30 ° C. or lower.

The above-mentioned distillation and neutralization operations are preferably performed in the order of distillation and neutralization in order to minimize the decomposition of N-alkoxycarbonyl amino acids.

In the present invention, the thus obtained N-
The N-alkoxycarbonyl amino acid is extracted into the organic solvent by contacting an aqueous solution or suspension of the alkoxycarbonyl amino acid with a specific organic solvent. The organic solvent must be an organic solvent that forms an azeotrope with water and has a water content in the azeotropic composition of 10% by volume or more and 60% by volume or less. The azeotropic dehydration ability of the organic solvent is weak when the water content of the organic solvent is lower than the above composition, and the boiling point of the organic solvent itself is high when the water content of the organic solvent is higher than the above composition. Therefore, in any case, the time required for azeotropic dehydration becomes long, and the N-alkoxycarbonylamino acid is decomposed during the azeotropic dehydration operation.

Specific examples of the organic solvent which can be suitably used in the present invention include esters such as propyl acetate, butyl acetate, isobutyl acetate, ethyl butyrate, isobutyl butyrate and propyl propionate; toluene, o-xylene, m -Aromatic hydrocarbons such as xylene, p-xylene and chlorobenzene; 2-pentanone, 3-pentanone,
Examples thereof include ketones such as 3-methyl-2-butanone and methyl isobutyl ketone, and carbonates such as diethyl carbonate. Among these organic solvents, esters, ketones, and aromatic hydrocarbons are preferably used because of the ease of solvent distillation and the high solubility of N-alkoxycarbonyl amino acids.

The temperature at which these organic solvents are brought into contact with an aqueous solution or aqueous suspension of N-alkoxycarbonylamino acids is generally determined by the solubility of the amino acids in the organic solvents or the presence or absence of meniscus during phase separation. However, in order to minimize the decomposition of N-alkoxycarbonylamino acid, the temperature is preferably set to -5 ° C to 40 ° C.
It is preferable to carry out within the range.

Although the amount of the organic solvent is not particularly limited for the same reason as above, it is generally about 20 to 50 parts by volume of the organic solvent per 100 parts by volume of the aqueous solution or suspension of N-alkoxycarbonylamino acid. It is enough to extract about three times.

For the extraction operation, a conventional general method can be used without any limitation. For example, after vigorously mixing the aqueous solution or aqueous suspension and the organic solvent by shaking or stirring,
A method in which this is allowed to stand and separated into two phases and the organic phase is separated can be used. As the mixing time, 1 to 30 minutes is sufficient because the N-alkoxycarbonylamino acid has high solubility in an organic solvent. The standing time cannot be determined unconditionally because it varies depending on the specific gravity of the solvent used and the presence or absence of meniscus.
What is necessary is just to determine while observing the state of an interface in the range of 0 to 100 minutes.

The organic phase from which the N-alkoxycarbonyl amino acid has been extracted in this manner is directly dehydrated by azeotropic dehydration unless the amino acid as a starting material is detected by analysis such as thin layer chromatography. A known method can be used for the azeotropic dehydration operation without any limitation. The temperature in the azeotropic dehydration operation is, for example, 1 under reduced pressure to suppress the decomposition of N-alkoxycarbonyl amino acid.
It is preferable to perform the heating at 500 Torr and -5 ° C. to 40 ° C.

When an amino acid is detected by analysis such as thin layer chromatography, 10 to 40 parts by volume of water or 10%
The same operation as described above may be performed after washing the organic phase with the following saline solution or the like until no amino acid is detected.

After the azeotropic dehydration as described above, the organic solvent is distilled off and concentrated, and an aliphatic hydrocarbon solvent such as hexane or heptane is added, or the organic solvent is concentrated and then recrystallized. Is carried out to crystallize the N-alkoxycarbonyl amino acid.

[0030]

According to the present invention, as an organic solvent for extracting N-alkoxycarbonylamino acid from an aqueous solution or suspension of N-alkoxycarbonylamino acid, an azeotropic mixture with water is formed and the azeotropic composition is determined. By using an organic solvent having a water content of 10% by volume or more and 60% by volume or less, it can be produced without decomposing the N-alkoxycarbonyl amino acid during the dehydration operation.

[0031]

Hereinafter, the present invention will be described with reference to examples.
The present invention is not limited to these embodiments.

Example 1 75.07 g (1 mol) of glycine and 44 g of sodium hydroxide were placed in a four-necked flask equipped with a stirrer and a thermometer.
(1.1 mol), 370 ml of water and 370 ml of t-butyl alcohol were added, and the mixture was cooled to 20 ° C. with stirring. After cooling, 218.25 g of di-t-butyl dicarbonate (1
mol) was added dropwise while maintaining the internal temperature at 25 ° C. or lower.
After reacting at room temperature for 14 hours, t-butyl alcohol was distilled off under reduced pressure, and the resulting aqueous solution was cooled to 5 ° C or lower. When 2.7 L of 2N hydrochloric acid was added dropwise over 4 hours under cooling, white crystals of Nt-butoxycarbonylglycine were precipitated. At this time, the pH of the aqueous suspension was 2.2.
0 (6.5 ° C.).

This aqueous suspension was extracted three times with 1.2 L of butyl acetate (water content of azeotropic composition with water: 29%). At this time, the water content in the butyl acetate phase was 3
2000 ppm. Separation was performed by adding butyl acetate at 25 ° C. and stirring with a stirrer for 10 minutes, and then allowed to stand for 30 minutes to separate a butyl acetate phase. When the butyl acetate phase was analyzed by thin-layer chromatography, a trace amount of glycine remained. For the purpose of completely removing this, 400 m
After washing twice with 1 liter of ion-exchanged water, glycine could be completely removed.
After azeotropic dehydration at 40 ° C. and 40 Torr, 1 L of butyl acetate was distilled off. At this time, the water content was 600 ppm. The obtained butyl acetate solution was cooled to 5 ° C. and stirred for 1 hour, and white crystals were precipitated. The filtered white crystals were dried under reduced pressure at 20 ° C. to obtain 160.3 g (91.5%) of Nt-butoxycarbonylglycine. Glycine in the obtained Nt-butoxycarbonylglycine was 0.005% by weight or less.

Examples 2 to 6 The same operation as in Example 1 was performed except that the organic solvents shown in Table 1 were used.

The results are shown in Table 1. Nt obtained
Glycine in butoxycarbonylglycine was 0.005% by weight or less.

[0036]

[Table 1]

EXAMPLE 7 89.09 g (1 mol) of alanine and 44 g of sodium hydroxide were placed in a four-necked flask equipped with a stirrer and a thermometer.
(1.1 mol), 370 ml of water and 370 ml of t-butyl alcohol were added, and the mixture was cooled to 20 ° C. with stirring. After cooling, 218.25 g of di-t-butyl dicarbonate (1
mol) was added dropwise while maintaining the internal temperature at 25 ° C. or lower.
After reacting at room temperature for 14 hours, t-butyl alcohol was distilled off under reduced pressure, and the resulting aqueous solution was cooled to 5 ° C or lower. When 1.35 L of 1N hydrochloric acid was added dropwise over 4 hours under cooling, white crystals of Nt-butoxycarbonylalanine were precipitated. At this time, the pH of the aqueous suspension was 2.
18 (5.5 ° C.).

This aqueous suspension was extracted three times with 1.4 L of butyl acetate. At this time, the water content in the butyl acetate phase was 24000 ppm. Separation was performed by adding butyl acetate at 25 ° C. and stirring with a stirrer for 10 minutes, and then allowed to stand for 30 minutes to separate a butyl acetate phase. When the butyl acetate phase was analyzed by thin-layer chromatography, a trace of alanine remained.
After washing twice with 0 ml of ion-exchanged water, alanine could be completely removed.
Azeotropically dehydrate at 5 ° C. and 40 Torr, butyl acetate 1.2 L
Was distilled off. The water content at this time was 400 ppm.
600 ml of heptane was added to the obtained butyl acetate solution,
After cooling to 5 ° C. and stirring for 1 hour, white crystals precipitated, which were filtered off. The filtered white crystals were dried under reduced pressure at 20 ° C. to obtain 171.6 g (91.0%) of Nt-butoxycarbonylalanine. Nt obtained
Alanine in butoxycarbonylalanine is 0.0
It was not more than 05% by weight.

Examples 8 to 12 The same operation as in Example 7 was performed except that the amino acids shown in Table 2 were used.

The results are shown in Table 2. Nt obtained
-The amino acids in the butoxycarbonyl amino acids were all 0.005% by weight or less.

[0041]

[Table 2]

Comparative Example 1 The same operation as in Example 1 was carried out except that ethyl acetate (water content in the azeotropic composition with water: 8%) was used as the organic solvent. As a result, Nt-butoxycarbonylglycine was 85.0% and glycine was 0.02%.

Claims (1)

(57) [Claims] 1. An organic solvent which forms an azeotrope with an aqueous solution or suspension of an N-alkoxycarbonylamino acid and water and has a water content of 10 to 60% by volume in an azeotropic composition. And extracting the N-alkoxycarbonylamino acid into the organic phase, separating the organic phase from the aqueous phase, and then azeotropically dehydrating the organic phase. .