JP2735778C - - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an N-alkoxycarbonyl amino acid. [0002] N-alkoxycarbonyl amino acids in which the amino group of an amino acid is protected can be selected when forming a peptide bond in the chemical synthesis of antibiotics, peptides, polypeptides, proteins and aminoglycosides. It is a compound that is important as a starting material or an intermediate for obtaining a target product. Conventionally, as a method for synthesizing N-alkoxycarbonylamino 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, Then, 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) 63 is known.
Vol. 160-170, 1985). [0004] However, in the above 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 of N-alkoxycarbonyl amino acid or in water. About 3 to 7% by weight of water is dissolved when brought into contact with the suspension. 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. [0005] 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 during the dehydration operation, It was found that the N-alkoxycarbonyl amino acid was decomposed to release the starting material amino acid. 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, the aqueous solution or aqueous suspension after the N-alkoxycarbonyl amino acid salt was neutralized and converted into the acid form was brought into contact with a specific organic solvent to extract the N-alkoxycarbonyl amino acid into the organic phase. Later, they found that an N-alkoxycarbonyl amino acid could be synthesized by azeotropically dehydrating the organic phase without releasing the starting material amino acid, and completed the present invention. That is, the present invention provides a method comprising reacting an amino acid salt with a dialkyl dicarbonate.
An azeotropic mixture is formed with water and an aqueous solution or aqueous suspension of N-alkoxycarbonylamino acid obtained by neutralization, and the content of water in the azeotropic composition is 10% by volume or more and 60% by volume or less. After extracting the N-alkoxycarbonylamino acid into the organic phase by contacting with an organic solvent, the organic phase is separated from the aqueous phase, and then the azeotropic dehydration of the organic phase is carried out. It is a manufacturing method. [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 that can be suitably used in the present invention include, for example, glycine, alanine, β-alanine, valine, norvaline, leucine, norleucine, isoleucine, phenylalanine, tyrosine, diiodotyrosine, and 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) ) Purobion acid, N- methylglycine, taurine, .gamma.-formyl -N- methyl-nor-valine, N ^g - tosyl-arginine, N ^g - benzyloxycarbonyl arginine, S- Asetoamidomechi Cysteine, S- benzyl cysteine, N ^im - benzyloxycarbonyl ornithine, N ⁶ - benzyloxycarbonyl-lysine, N ⁵
-Benzyloxycarbonylornithine, 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 can be mentioned. 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. Further, as the organic base, pyridine, 4-dimethylaminopyridine, triethylamine, tributylamine, 1-methylpiperidine,
1-methylpyrrolidine and the like can be mentioned. The amount of the base used is 0 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 to 2.0 equivalents, more preferably 0.5 to 1.5 equivalents. Next, the dialkyl dicarbonate to be reacted with the above-described amino acid salt can be represented by the following general formula. Embedded image (However, R ₁ and R ₂ are the same or different alkyl groups.) Specific examples of dialkyl dicarbonates that can be suitably used in the present invention include di-t-butyl dicarbonate and di-t -Amyl dicarbonate, diisopropyl dicarbonate, diisobutyl dicarbonate and the like. The amount of the dialkyl dicarbonate relative to the amino acid salt prevents the crystallization of the N-alkoxycarbonyl amino acid and, from the viewpoint of economy, is usually equivalent to 1 equivalent of the amino group or imino group of the amino acid to be protected. 0.5 to 2.0 equivalents,
Further, it is preferable to select in the range of 0.8 to 1.2 equivalents. The reaction temperature between the amino acid salt and 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 alcohols such as t-butyl alcohol, t-amyl alcohol, isopropyl alcohol, isobutyl alcohol, ethanol, and methanol; ethers such as tetrahydrofuran and dioxane; nitriles such as acetonitrile; Ketones; 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. To maintain the water 1
100 parts by weight of the organic solvent in the range of 10 parts by weight to 900 parts by weight,
It is preferable to select in the range of parts by weight to 400 parts by weight. In order to maintain a high reaction rate as the concentration of the amino acid salt in the mixed solvent of the above organic solvent and water, and to suppress the production of N-alkoxycarbonylamino acid ester as a by-product, the mixed solvent 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 if the distillation temperature is high.
It is preferred that the solvent be distilled off under reduced pressure at a temperature of not more than ° C. In the operation of neutralizing an amino acid salt, an ordinary 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 amino acid and cannot be specified unconditionally. However, it is usually preferable to add the acid until the pH of the aqueous solution is in the range of 1 to 4, and the optimal amount is N-alkoxycarbonylamino acid. It may be determined according to the pKa value. 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 N-alkoxycarbonyl amino acid is extracted into the organic solvent by contacting the aqueous solution or suspension of the N-alkoxycarbonyl amino acid thus obtained 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 organic solvents that 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 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. Can not be specified in
In order to minimize the decomposition of N-alkoxycarbonyl amino acids, the temperature is -5 ° C to 40 ° C.
It is preferable to carry out in the range of ° C. Although the amount of the organic solvent is not particularly limited for the same reason as described above, the amount of the organic solvent is generally about 20 to 50 parts by volume with respect to 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, a method of vigorously mixing the aqueous solution or the aqueous suspension and the organic solvent by shaking or stirring or the like, allowing the mixture to stand, separating into two phases, and separating the organic phase 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. However, it may be determined while observing the state of the interface in the range of 10 minutes to 100 minutes. The organic phase from which the N-alkoxycarbonyl amino acid has been extracted as described above is subjected to reduced pressure, for example, from 1 to 4 to prevent decomposition of the ruvonyl amino acid unless the amino acid as a starting material is detected by analysis such as thin layer chromatography. 500 Torr, and-
It is preferably performed at 5 ° C to 40 ° C. When an amino acid is detected by analysis such as thin layer chromatography, the amino acid is detected in 10 to 40 parts by volume of water or a saline solution having a concentration of 10% or less based on 100 parts by volume of the organic solvent. After washing the organic phase until it is no longer possible, the same operation as described above may be performed. After performing azeotropic dehydration in this way, the organic solvent is distilled off and concentrated, and hexane,
The N-alkoxycarbonyl amino acid can be crystallized by adding an aliphatic hydrocarbon solvent such as heptane, or by performing a recrystallization operation after concentrating the organic solvent. According to the present invention, as an organic solvent for extracting N-alkoxycarbonylamino acid from an aqueous solution or aqueous suspension of N-alkoxycarbonylamino acid, an azeotropic mixture with water is formed and azeotropic The content of water in the mixed composition is 10% by volume or more and 60% by volume.
By using the following organic solvent, it can be produced without decomposing the N-alkoxycarbonyl amino acid during the dehydration operation. Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to these examples. Example 1 A four-necked flask equipped with a stirrer and a thermometer was charged with 75.07 g of glycine (1 mo).
l), 44 g (1.1 mol) of sodium hydroxide, 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 (1 mol) of di-t-butyl dicarbonate 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. The pH of the aqueous suspension at this time was 2.20 (6.5 ° C.). This aqueous suspension is treated with butyl acetate (water content 29% in an azeotropic composition with water).
) Extracted three times with 1.2 L. At this time, the water content in the butyl acetate phase was 320
It was 00 ppm. For separation, butyl acetate was added at 25 ° C., and the mixture was stirred for 10 minutes with a stirrer. When the butyl acetate phase was analyzed by thin-layer chromatography, a trace amount of glycine remained. For the purpose of completely removing this, it was washed twice with 400 ml of ion-exchanged water. The butyl acetate phase was azeotropically dehydrated at 35 ° C. and 40 Torr to remove 1 L of butyl acetate. 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. When the white crystals separated by filtration were dried under reduced pressure at 20 ° C.,
160.3 g (91.5%) of Nt-butoxycarbonylglycine was obtained.
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. Table 1 shows the results. Glycine in the obtained Nt-butoxycarbonylglycine was 0.005% by weight or less. [Table 1] Example 7 89.09 g of alanine (1 mo) was placed in a four-necked flask equipped with a stirrer and a thermometer.
1), 44 g (1.1 mol) of sodium hydroxide, 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 (1 mol) of di-t-butyl dicarbonate 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. The pH of the aqueous suspension at this time was 2.18 (5.5 ° C.). The 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, trace amounts of alanine remained. After washing twice with 400 ml of ion-exchanged water for the purpose of completely removing this, alanine was completely removed. The butyl acetate phase was azeotropically dehydrated at 35 ° C. and 40 Torr, and 1.2 L of butyl acetate was distilled off. The water content at this time was 400 ppm. Heptane was added to the obtained butyl acetate solution.
After adding 00 ml, the mixture was cooled to 5 ° C. and stirred for 1 hour, and white crystals were precipitated. The white crystals separated by filtration were dried under reduced pressure at 20 ° C. to obtain 171.6 g (91.0%) of Nt-butoxycarbonylalanine. The obtained Nt-
Alanine in butoxycarbonylalanine was 0.005% by weight or less. Examples 8 to 12 The same operation as in Example 7 was performed except that the amino acids shown in Table 2 were used. Table 2 shows the results. The amino acids in the obtained Nt-butoxycarbonyl amino acids were all 0.005% by weight or less. [Table 2] Comparative Example 1 The same operation as in Example 1 was performed, except that ethyl acetate (water content of 8% in an azeotropic composition with water) was used as the organic solvent. As a result, Nt-butoxycarbonylglycine was 85.0% and glycine was 0.02%.

Claims (1)

[Claim 1] After reacting an amino acid salt with a dialkyl dicarbonate,
An aqueous solution or aqueous suspension of the N-alkoxycarbonyl amino acid obtained by the addition ,
After extracting an N-alkoxycarbonyl amino acid into an organic phase by contacting with an organic solvent which forms an azeotrope with water and whose content of water in the azeotropic composition is 10% by volume or more and 60% by volume or less, A method for producing an N-alkoxycarbonyl amino acid, comprising separating the organic phase from the aqueous phase and then subjecting the organic phase to azeotropic dehydration.