JPH11302244A - Production of n-hydrocarbonoxycarbonylamino acid ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an N-hydrocarbonoxycarbonylamino acid ester by quickly and safely neutralizing an acidic reaction solution containing an amino acid ester with an inorganic carbonic acid base while suppressing hydrolysis of the ester and carrying out successive N-hydrocarbonoxycarbonylation. SOLUTION: This method for producing an N-hydrocarbonoxycarbonylamino acid ester comprises using an inorganic carboxylic acid base having >=0.8 m<2> /g specific surface area as a neutralizing agent used for neutralization step in a series of reaction steps reacting an amino acid with an alcohol in the presence of strong acid or thionyl chloride, neutralizing the resultant acidic reaction solution containing the ester of the amino acid, mixing the neutralized compound with a dicarbonate compound represented by the general formula [R<1> is an alkyl group, alkenyl group or aralkyl group which may have a substituent group] to obtain the objective N-hydrocarbonoxycarbonylamino acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing N-hydrocarbon oxycarbonyl amino acid esters useful as pharmaceutical intermediates in high purity.

[0002]

[0002] N-hydrocarbon oxycarbonyl amino acid esters are extremely important compounds as intermediates for HIV protease inhibitors and other physiologically active substances.

As a conventional method for producing N-hydrocarbon oxycarbonyl amino acid ester, for example, an amino acid ester salt is prepared in an organic solvent in the presence of a stoichiometric amount of an organic base such as triethylamine or diisopropylethylamine in the presence of di-t-butyl. A method of reacting with dicarbonate is known (Journal of Medicinal Chemistry (J. Med. Chem.) Vol. 26, No. 4, 549-).
554, 1986).

The amino acid ester salt used in such a reaction is obtained by reacting an amino acid with an alcohol and a strong acid or thionyl chloride.

[0005]

However, in the above-mentioned method, a large amount of by-produced ammonium salt must be treated, and the reaction step involves the steps of preparing an amino acid ester salt and N-hydrocarbon oxycarbonylation reaction. Since the process was divided into steps, it was necessary to perform an isolation operation of the amino acid ester salt. In order to solve this problem, a one-step synthesis method using an inorganic base as a base has been previously proposed (Japanese Patent Application Laid-Open No. 7-101928).

According to such a method, the step of isolating the amino acid ester salt could be omitted, but the method of adding the inorganic base had some problems. That is, in the above method, since the inorganic base is added as an aqueous solution or used after being suspended in an organic medium, hydrolysis of the amino acid ester occurs as a side reaction in the former case, which causes a reduction in yield. . In the latter method, although hydrolysis can be suppressed, the neutralization reaction does not proceed sufficiently, so that a relatively large amount of inorganic base is used, and it is difficult to determine the end point of the neutralization reaction. Was. Further, when the compound is added together with the dicarbonate compound as the N-hydrocarbon oxycarbonylating agent in the next step, the neutralization reaction and the N-hydrocarbon oxycarbonylation reaction by the dicarbonate compound proceed in parallel, so that the neutralization reaction When the reaction proceeded rapidly, the N-hydrocarbon oxycarbonylation reaction also proceeded rapidly at the same time, and there was a risk that the reaction solution would be ejected from the reaction vessel.

[0007]

Means for Solving the Problems In view of the above situation, the present inventors have intensively studied a production method in which the hydrolysis reaction is suppressed and the reaction proceeds suitably. As a result, the hydrolysis reaction can be suppressed by adding an inorganic carbonate base having a specific surface area of 0.8 m ² / g or more as a neutralizing agent, and the amino acid ester salt can be reduced in the same manner as when an aqueous solution of an inorganic base is used. Since instantaneous neutralization occurs, it has been found that the neutralization reaction and the N-hydrocarbon oxycarbonylation reaction can be performed separately, and the present invention has been completed.

That is, the present invention is to neutralize an acidic reaction solution containing an ester of the amino acid obtained by reacting an amino acid with an alcohol in the presence of a strong acid or thionyl chloride.
The following general formula (I)

[0009]

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(Where R ¹ represents an alkyl group, an alkenyl group or an aralkyl group which may have a substituent) and a mixture of dicarbonate compound represented by the formula (1) to obtain N-hydrocarbonoxycarbonyl amino acid ester: In the reaction step, an inorganic carbonate having a specific surface area of 0.8 m ² / g or more is used as a neutralizing agent used in the neutralization step.

As the amino acid used in the present invention, a known compound having at least one amino group and at least one carboxyl group in the molecule is used without any limitation. Here, the amino group is a general term for a so-called amino group (—NH ₂ ) and an imino group (> NH), for example, a monosubstituted amino group substituted with a hydrocarbon residue such as an alkyl group or an aralkyl group, a pyrrolidyl group, It is a group in which at least one hydrogen atom is bonded to a nitrogen atom such as a piperidyl group.

The carboxyl group is a so-called carboxyl group (—COOH), salts and ester groups thereof, and includes a carboxyl group capable of undergoing an esterification reaction and a derivative group thereof in the present invention.

Specific examples of amino acids that can be suitably used in the present invention include, for example, glycine, phenylglycine, N-methylglycine, N-ethylglycine, N-benzylglycine, hydroxyphenylglycine, alanine, N-methyl. Alanine, N-ethylalanine, N-benzylalanine, β-alanine, N-methyl-β-alanine, N-ethyl-β-alanine, N-benzyl-β-alanine, serine, homoserine, isoserine, O-benzyl- Serine, cysteine, S-acetamido-cysteine, cystine, homocystine, threonine, O-benzyl-threonine, methionine, homomethionine, valine, N-methylvaline, N-ethylvaline, N-benzylvaline, norvaline, N-methylnorvaline, N-ethylnorvaline, N Benzyl-nor-valine, leucine,
N-methylleucine, N-ethylleucine, N-benzylleucine, norleucine, N-methylnorleucine,
N-ethylnorleucine, N-benzylnorleucine,
Isoleucine, N-methylisoleucine, N-ethylisoleucine, N-benzylisoleucine, phenylalanine, N-methylphenylalanine, N-ethylphenylalanine, N-benzylphenylalanine, hydroxyphenylalanine, tyrosine, O-benzyl-tyrosine, tyrosine, O- Benzyl-thyronine, proline,
Hydroxyproline, O-benzyl-hydroxyproline, tryptophan, aspartic acid, asparagine,
Glutamic acid, homoglutamic acid, glutamine, arginine, N-tosylarginine, N-benzylarginine, lysine, ornithine, histidine, α-aminobutyric acid, β-aminobutyric acid, γ-aminobutyric acid, α-aminoisobutyric acid, lysine, etc. Can be. Each of these amino acids may have a substituent, may be protected, may be a racemic mixture containing optical isomers, or may be a mixture of different amino acids.

In the present invention, the alcohol used for the esterification reaction of the amino acid is not particularly limited, but preferably has 1 to 10 carbon atoms in view of the reactivity of the esterification reaction. Specifically, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, n-amyl alcohol, isoamyl alcohol, t-amyl alcohol, n
-Hexyl alcohol, cyclohexyl alcohol, allyl alcohol, benzyl alcohol and the like. Among them, methyl alcohol, ethyl alcohol, n-propyl alcohol, which can be easily converted to an ester,
Preferred are isopropyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, benzyl alcohol and the like. These alcohols may be used in combination of two or more, and are selectively used according to the purpose.

The amount of the alcohol used in the present invention may be 1 to 1 per carboxyl group of the amino acid since the esterification reaction is an equivalent reaction of the amino acid and the alcohol.
There is no restriction as long as it is equal to or more than the equivalent. Generally, an excess amount is used to also have a role of a solvent. However, if the amount is too large, the yield per batch decreases and it is not economical, so that the concentration of amino acid in alcohol is usually 0.1 to 9%.
The amount is preferably 0% by weight, preferably 1 to 80% by weight.

In this reaction, only an alcohol may be used as a solvent, but another solvent may be mixed and used. Those are organic solvents which do not react with solutes such as amino acids and alcohols. Specifically, halogenated aliphatic hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, carbon tetrachloride, and trichloroethylene, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, and acetic acid t-butyl, ethyl formate, n-propyl formate,
Isobutyl formate, ethyl propionate, n-propionate
Esters such as -butyl, t-butyl propionate, benzene, toluene, o-xylene, m-xylene, p-
Aromatic hydrocarbons such as xylene, halogenated aromatic hydrocarbons such as chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, diethyl ether, tetrahydrofuran, 1,4-dioxane, butyl ethyl ether, diisopropyl ether Ethers such as acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone, carbonates such as dimethyl carbonate, nitriles such as acetonitrile and propionitrile, n-pentane, n-hexane, n-heptane and trimethylpentane. Examples thereof include aliphatic hydrocarbons, cycloaliphatic hydrocarbons such as cyclohexane, amides such as dimethylformamide and dimethylacetamide, and dimethyl sulfoxide. These organic solvents may be used in combination of two or more.

Since the amount of the organic solvent used varies depending on the amount of the alcohol used and the type of the organic solvent, it cannot be specified unconditionally.
Generally, the total amount of the alcohol and the organic solvent is determined so as to be 90 to 90% by weight, preferably 1 to 80% by weight.

Since the esterification reaction of amino acids is greatly inhibited by water, the content of water in the alcohol and organic solvent used in this reaction is 1% by weight or less, preferably 0.5% by weight, based on the amino acid. % Or less. As the dehydration method of alcohol and organic solvent,
Although it cannot be said unconditionally because it varies greatly depending on the type of compound, in general, azeotropic dehydration, calcium chloride, calcium oxide, calcium sulfate, magnesium sulfate, calcium hydride, sodium hydride, sodium, phosphorus pentoxide, etc. A method using a dehydrating agent is employed.

In the present invention, when the amino acid is reacted with an alcohol in the presence of a strong acid or thionyl chloride, a reaction solution containing an amino acid ester salt can be obtained.

As the strong acid used in this reaction, any known strong acid used for the esterification reaction of amino acids can be used without any limitation. Preferably, pKa in aqueous solution
It is preferable to use an acid having a value of 2.0 or less, preferably 1.0 or less. Here, if the acid is a polybasic acid such as sulfuric acid, the pKa of the acid refers to the value at the first stage of dissociation at which the value is minimized. In addition, such a small pK
Even a compound having an acidic group as a and having a basic group such as an amino group at the same time as an amino acid does not exhibit strong acidity as a whole molecule, and thus is distinguished from the strong acid in the present invention.

Specific examples of the strong acid preferably used in the present invention include mineral acids such as hydrogen chloride, sulfuric acid, nitric acid and phosphoric acid, and organic acids such as p-toluenesulfonic acid, benzenesulfonic acid and methanesulfonic acid. Is mentioned. Among these, it is most preferable to use hydrogen chloride or sulfuric acid, which can be expected to have a high esterification rate.

The amount of the strong acid or thionyl chloride used is not particularly limited, but is preferably at least equivalent to the amino group of the amino acid. When hydrogen chloride is used as the strong acid, it is preferable to use the alcohol used as a reaction solvent or the alcohol and an organic solvent by blowing at least an equivalent amount to the amino group.

In the esterification reaction of the amino acid, the method of adding the amino acid, alcohol, and strong acid or thionyl chloride is not particularly limited. However, when the esterification reaction is carried out using thionyl chloride, especially when using an amino acid having a hydroxyl group in the molecule such as serine, the amino acid is added after mixing thionyl chloride and an alcohol in advance. The method is preferred from the viewpoint of improving the yield of the desired esterification reaction.

The reaction in the present reaction can be carried out at any of normal pressure, increased pressure and reduced pressure.

This reaction can be usually carried out in the atmosphere. In such a case, the progress of the reaction may be hindered by moisture in the atmosphere. It is preferable to open to the atmosphere through the agent, or in an atmosphere of an inert gas such as nitrogen, argon, or helium, or in a sealed state.

Further, depending on the type and amount of the acid used, as the esterification reaction proceeds, the esterification reaction may be affected by the by-produced water and the reaction may stop. In such a case, it is possible to appropriately remove the by-produced water by distillation or the like, and to promote the reaction by adding a new alcohol or an alcohol and an organic solvent, often giving a favorable result.

The temperature of this reaction is not particularly limited, but if it is too high, amino acid racemization occurs, and if it is too low, the esterification reaction rate is remarkably reduced, so that it is usually between the freezing point of the system and the pressure at the time of the reaction. The boiling point is selected, for example, in the range of 100 ° C, preferably in the range of -20 to 80 ° C. The time required for this reaction varies depending on the reaction temperature, the type of alcohol and amino acid used, but is usually in the range of 1 to 120 hours.

This reaction can be carried out in a batch system or a continuous system.

In the reaction solution obtained by the above esterification reaction, in addition to the target amino acid ester salt, unreacted strong acid or hydrogen chloride and sulfur dioxide by-produced when thionyl chloride is used coexist. It is acidic.

In the present invention, after the formation of the amino acid ester salt, the acidic reaction solution is neutralized with an inorganic carbonate base.

As the inorganic carbonate base used in the present invention, any known inorganic carbonate base can be used without any limitation as long as it reacts with an acidic substance to neutralize the same and to produce carbon dioxide as a by-product. Specifically, alkali metal carbonates and acid carbonates such as lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate and potassium hydrogen carbonate; and alkaline earth metals such as magnesium carbonate, calcium carbonate and barium carbonate. Carbonates and basic carbonates are used. Preferably, lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, magnesium carbonate, calcium carbonate, and the like are used.

The most important feature of the present invention is that the inorganic carbonate base used in the neutralization step is B.I. E. FIG. T. Those having a specific surface area of 0.8 m ² / g or more according to the formula are used. In general, the crystal particles of the inorganic carbonate base are dense and have a specific surface area of usually 0.1.
It is about 5 m ² / g or less. Therefore, when used as a neutralizing agent in the present invention, pulverization is also performed as necessary. Such pulverization can be performed by a known pulverizer, for example, a rod mill, a roll mill, a ball mill, a vibration mill, a tower mill, a colloid mill, various jet pulverizers, and the like. Above all, an impact-pulverization type pulverizer using an aerial force is preferably used.

Of course, in some cases, a specific surface area suitable as the neutralizing agent of the present invention can be obtained by a method of controlling the reaction and the precipitation conditions in the production process of the inorganic carbonate base, or by classification.

Thus, an inorganic carbonate base having a specific surface area of 0.8 m ² / g or more, preferably 1.0 m ² / g or more was obtained, and this was used in the neutralization step of the present invention to use an inorganic base aqueous solution. The neutralization reaction proceeds almost instantaneously, as in the case of the above, and since there is no water, there is little possibility of hydrolysis. In addition, there is an advantage that the end point of neutralization can be easily confirmed based on the point at which the generation of carbon dioxide bubbles stops.

The neutralizing agent has a specific surface area of 0.7 m ² /
g or less of an inorganic carbonate base, the neutralization reaction does not proceed instantaneously, and it is difficult to determine the end point,
In many cases, the neutralization reaction continues even after mixing the N-hydrocarbon oxycarbonylating agent in the next step, and as shown in FIG. A long time is required for the conversion process. Further, one of the problems in the case where the neutralization reaction and the N-hydrocarbon oxycarbonylation reaction proceed in parallel is that if the neutralization reaction proceeds abruptly due to some trigger, it may cause generation of carbon dioxide due to decomposition of the inorganic carbonate base. In addition, there is a danger that double foaming will occur due to carbon dioxide produced as a by-product of the N-hydrocarbon oxycarbonylation, the level of the reaction solution will rise, and jetting from the reaction vessel will occur.

Conversely, the use of an inorganic carbonate base having a specific surface area of not less than 3.0 m ² / g has no technical advantage anymore. It is difficult to say that it is a neutralizer.

Therefore, in the present invention, the specific surface area is generally set at 0.1.
The neutralization reaction is allowed to proceed instantaneously with the inorganic carbonate base in the range of 8 to 3.0 m ² / g, and the end point of the neutralization reaction is determined by visually checking the presence or absence of carbon dioxide generated by the decomposition of the inorganic carbonate base used. Can be confirmed, and the neutralization reaction and the N-hydrocarbon oxycarbonylation reaction can be separated to safely carry out the reaction.

In the neutralization step, the inorganic carbonate base itself may be brought into contact with the acidic reaction solution as it is, or the inorganic carbonate base may be suspended in an organic solvent and brought into contact with the reaction solution. In that case, the organic solvent is not particularly limited, but specifically, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, n-amyl alcohol, isoamyl alcohol , T
Alcohols such as amyl alcohol, n-hexyl alcohol, cyclohexyl alcohol, and benzyl alcohol; halogenated aliphatic hydrocarbons such as dichloromethane, chloroform, 1,2-dichloroethane, carbon tetrachloride, and trichloroethylene; ethyl acetate; Propyl, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, ethyl formate, n-propyl formate,
Isobutyl formate, ethyl propionate, n-propionate
Esters such as -butyl, t-butyl propionate, benzene, toluene, o-xylene, m-xylene, p-
Aromatic hydrocarbons such as xylene, halogenated aromatic hydrocarbons such as chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, diethyl ether, tetrahydrofuran, 1,4-dioxane, butyl ethyl ether, diisopropyl ether Ethers such as acetone, methyl ethyl ketone, ketones such as methyl isobutyl ketone, carbonates such as dimethyl carbonate, nitriles such as acetonitrile and propionitrile, n-pentane, n-hexane, n-heptane and trimethylpentane. Aliphatic hydrocarbons, cycloaliphatic hydrocarbons such as cyclohexane, amides such as dimethylformamide and dimethylacetamide, and dimethyl sulfoxide are used. Preferably, the same methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, t-butyl alcohol, n-amyl alcohol, n- alcohol as used in the esterification reaction of the amino acid are used. Hexyl alcohol, cyclohexyl alcohol, benzyl alcohol are used. Further, these organic solvents may be used alone or in combination of two or more.

If the amount of the inorganic carbonate base used in the neutralization reaction is too large, it is uneconomical. If the amount is too small, the N-hydrocarbon oxycarbonylation reaction in the next step does not proceed. 0.8 to the equivalent of the component
It may be selected from a range of 2.0 equivalents, preferably 1.0 to 1.5 equivalents.

The neutralization temperature in the present invention is not particularly limited. However, if the temperature is too high, a side reaction such as hydrolysis is promoted, and if the temperature is too low, the viscosity of the reaction system increases and hinders a stirrer or the like. In general, it is preferable to carry out the reaction at a temperature in the range of -40 to 80C, more preferably -20 to 40C.

As a feature of the present reaction, carbon dioxide is instantaneously generated when the inorganic carbonate base is brought into contact with the reaction solution because the neutralization rate is high. For this reason, when neutralizing, it is necessary to carry out the neutralization while paying sufficient attention to the rise in the liquid level due to the bubbling of carbon dioxide.

The thus obtained solution of the amino acid ester is subjected to the next N-hydrocarbon oxycarbonylation reaction. At this time, the salt by-produced by the neutralization may be separated by solid-liquid separation, but is generally used in the next reaction as a slurry solution. In the present invention, the reactant used for the N-hydrocarbon oxycarbonylation reaction includes:
General formula (I)

[0043]

Embedded image

(Wherein, R ¹ represents an alkyl group, alkenyl group or aralkyl group which may have a substituent).

That is, two R ^{1 in the} dicarbonate compound (I) used in the present invention may be the same or different, and may be an alkyl group, an alkenyl group or an aralkyl group. It is preferably selected from hydrocarbon residues having 10 or less carbon atoms. These hydrocarbon residues may have a substituent, for example, a halogen atom such as a fluorine atom, a chlorine atom and a bromine atom; a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-group.
Alkyl groups such as -butyl group and t-amyl group; cycloalkyl groups such as cyclohexyl group; alkenyl groups such as allyl group and glycidyl group; aryl groups such as phenyl group; aralkyl groups such as benzyl group; It may have one or more acyl groups; ester groups such as methoxycarbonyl groups and acetoxy groups; dialkylamino groups; carbamoyl groups and the like.

The alkyl group represented by R ¹ is a methyl group,
An ethyl group, a n-propyl group, an isopropyl group, a n-butyl group, an isobutyl group, a t-butyl group, a lower alkyl group having 1 to 10 carbon atoms such as a t-amyl group is preferable, and an alkenyl group is an allyl group, A glycidyl group is preferred, and an aralkyl group is preferably a benzyl group.

Specific examples of the dicarbonate compound suitably used in the present invention include dimethyl dicarbonate, diethyl dicarbonate, diisopropyl dicarbonate, di-i-butyl dicarbonate and di-t-carbonate.
Butyl dicarbonate, di-t-amyl dicarbonate, diallyl dicarbonate, dibenzyl dicarbonate and the like can be mentioned.

The amount of the dicarbonate compound used in the N-hydrocarbon oxycarbonylation reaction is not economical if it is used in an excessively large amount. Therefore, it is usually 1.0 to 5 based on the amino group of the amino acid ester to be protected. 1.0 equivalent, preferably 1.0 to 2.5 equivalent, more preferably 1.0 to 2.5 equivalent.
What is necessary is just to select in the range of 1.5 equivalents.

The reaction temperature in this reaction is not particularly limited, but if the temperature is too high, the starting dicarbonate compound and the product are decomposed.
It is suitable to be in the range of 0 ° C, preferably in the range of 0 to 80 ° C.

The reaction pressure in this reaction is normal pressure, pressurization,
The reaction can be performed under any reduced pressure, and the time required for the reaction varies depending on the reaction temperature and the kind of the amino acid used as the raw material, but is usually in the range of 1 to 120 hours. The reaction can be performed in either a batch system or a continuous system.

By the way, the alcohol used for the reaction throughout the entire reaction process is used as a solvent, the neutralization reaction of the esterification reaction solution of the amino acid is carried out without using any other organic solvent, and the inorganic carbonate base is reacted in powder form. When added to the system or when the solvent component is used by suspending in the same alcohol as the alcohol used as a raw material in the esterification reaction of the amino acid, the reaction medium for the N-hydrocarbon oxycarbonylation reaction is large. A portion is occupied by the same alcohol used in the esterification reaction of the amino acid. Therefore, in such a case, before or after the start of the N-hydrocarbon oxycarbonylation reaction, an arbitrary amount of the alcohol in the reaction medium is recovered by distillation under reduced pressure or the like, and if necessary, after purification, again. It can be used as an alcohol raw material for the esterification reaction of amino acids. When the amino acid to be used is an amino acid having a hydroxyl group in a molecule such as serine, if alcohol is recovered before the reaction, there is a risk of a by-product of a dimer ester of the amino acid. It is preferably carried out after completion of the chemical reaction.

From the thus obtained solution of N-hydrocarbonoxycarbonyl amino acid ester in an organic solvent,
As a method for isolating the hydrocarbon oxycarbonyl amino acid ester, a known method can be used without any limitation.

More specifically, for example, a method of removing a salt by-produced by the above reaction and an excess inorganic carbonate base and then isolating the N-hydrocarbon oxycarbonyl amino acid ester by extracting it with an organic solvent. And the like.

As a method for removing salts produced as a by-product of the above reaction and excess inorganic carbonate, crystals precipitated in the reaction solution can be removed by a known method such as natural filtration, centrifugal filtration, pressure filtration or decantation. After the separation by a solid-liquid separation method, the alcohol is distilled off as much as possible, and water is added to the obtained solution to dissolve a water-soluble salt and an inorganic carbonate base in an aqueous phase, or from the above reaction solution. After distilling off the alcohol as much as possible, water may be added to dissolve all salts and inorganic carbonate bases in water.

The N-hydrocarbon oxycarbonyl amino acid ester is isolated from the aqueous solution thus obtained by extraction with an organic solvent.

As the organic solvent used for the extraction, N-
Dissolve the hydrocarbon oxycarbonyl amino acid ester,
Any organic solvent that is not compatible with water can be used without any limitation. Specifically, dichloromethane, chloroform, 1,2
-Halogenated aliphatic hydrocarbons such as dichloroethane, carbon tetrachloride, and trichloroethylene, ethyl acetate, and acetic acid n-
Esters such as propyl, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, benzene,
Aromatic hydrocarbons such as toluene, o-xylene, m-xylene, p-xylene, halogenated aromatic hydrocarbons such as chlorobenzene, o-dichlorobenzene, m-dichlorobenzene, p-dichlorobenzene, diethyl ether, butylethyl Ethers such as ether and diisopropyl ether; ketones such as methyl ethyl ketone and methyl isobutyl ketone; carbonates such as dimethyl carbonate; aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and trimethylpentane; cyclohexane; And the like. Among them, dichloromethane, chloroform, halogenated aliphatic hydrocarbons of 1,2-dichloroethane, ethyl acetate,
Esters such as n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, ethyl formate, propyl formate, isobutyl formate, ethyl propionate, n-butyl propionate, t-butyl propionate, Toluene, aromatic hydrocarbons such as m-xylene, halogenated aromatic hydrocarbons such as chlorobenzene, ethers such as diethyl ether and diisopropyl ether, ketones such as methyl ethyl ketone and methyl isobutyl ketone, carbonates such as dimethyl carbonate,
Aliphatic hydrocarbons such as n-hexane and n-heptane, and cycloaliphatic hydrocarbons such as cyclohexane are preferably used.

The temperature at the time of extraction varies depending on the type of N-hydrocarbon oxycarbonyl amino acid ester to be formed, and cannot be specified unconditionally. However, when the temperature is too high, the hydrolysis reaction is promoted. Takes a long time to form an emulsion, or causes a large amount of emulsion to be formed. Therefore, at a temperature of 0 ° C. to the boiling point of the solvent to be used or lower, usually 0 to 60 ° C., preferably 5 to 50 ° C. Good to do.

The N-hydrocarbon oxycarbonyl amino acid ester obtained by the above method can be sufficiently used as an industrially useful raw material as it is. However, in some cases, impurities such as amino acid ester or amino acid ester which is an intermediate may be used as a raw material. May be removed since they are contained in small amounts. As a method for removing impurities, a known method can be used without any limitation. For example, after washing the above solution with an acidic aqueous solution and removing impurities such as amino acids and amino acid esters into the aqueous phase, neutralize the acid with a basic aqueous solution,
Finally, a method of washing with water to remove trace amounts of dissolved salts and bases can be used.

As the acid used in the acidic aqueous solution, mineral acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid are preferably used, and more preferably, hydrochloric acid, sulfuric acid and nitric acid are used. When the concentration is too high, the N-hydrocarbon oxycarbonyl amino acid ester is decomposed, and when the concentration is too low, unreacted substances cannot be removed. Therefore, the concentration is usually selected from the range of 0.0001 to 12N, preferably 0.001 to 10N. Just do it.

Examples of the base used in the basic aqueous solution include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, calcium hydroxide and magnesium hydroxide, lithium hydrogen carbonate, sodium hydrogen carbonate and potassium hydrogen carbonate. Alkali metal carbonates such as alkali metal bicarbonate, sodium carbonate, potassium carbonate, magnesium carbonate, calcium carbonate and the like, and ammonia are used, preferably alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, and hydrogen carbonate Lithium, sodium bicarbonate, alkali metal bicarbonate such as potassium bicarbonate, sodium carbonate,
An alkali metal carbonate such as potassium carbonate is used. If the concentration is too high, the N-hydrocarbon oxycarbonyl amino acid ester is hydrolyzed, and if the concentration is too low, the acid is not sufficiently neutralized.
12N, preferably in the range of 0.001 to 10N.

By distilling off the organic solvent from the thus obtained extract, N-hydrocarbon oxycarbonyl amino acid ester can be obtained. When the target substance is a liquid or oil, it can be isolated as it is or as a solution of the organic solvent, but when it is recovered as crystals,
By a known method such as recrystallization or reprecipitation from such an extract,
The N-hydrocarbon oxycarbonyl amino acid ester may be crystallized.

Here, the solid-liquid separation method of the precipitated N-hydrocarbon oxycarbonyl amino acid ester may be a known method without any particular limitation.
Filtration method such as pressure filtration, filtration under reduced pressure, decantation,
Alternatively, a method such as centrifugation is used.

[0063]

According to the present invention, an acidic reaction solution containing an ester of an amino acid obtained by reacting an amino acid with an alcohol in the presence of a strong acid or thionyl chloride has a specific surface area of at least 0.8 m ² / g. By neutralizing with an inorganic carbonate base, the hydrolysis reaction is suppressed, and the neutralization reaction occurs instantaneously as in the case of using an aqueous solution of an inorganic base. Therefore, the neutralization reaction and N-hydrocarbon oxycarbonylation are performed. The reaction can be performed separately, and N-hydrocarbon oxycarbonyl amino acid ester can be produced safely. Therefore, the present invention is industrially extremely useful as a method for producing an N-hydrocarbon oxycarbonyl amino acid ester.

[0064]

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

Example 1 A 2 L four-necked flask equipped with a stirrer and a thermometer was
248 g of methanol (7.
74 mol) and 72.92 g (2.00 mol) of hydrogen chloride.
l) and 165.19 g of L-phenylalanine
(1.00 mol) was added. Then, the reaction solution was
The mixture was heated to 5 ° C and stirred for 12 hours. After the completion of the reaction, 222.6 sodium carbonate having a specific surface area of 0.8 m ² / g at 10 ° C. or less.
g (2.10 mol) was added dropwise over 30 minutes while controlling the liquid temperature to 15 ° C. or lower while paying attention to the rise in the liquid level of the reaction solution accompanying the generation of carbon dioxide. 14 after dropping
Within minutes the evolution of carbon dioxide stopped. At this time, the content of the hydrolyzate was determined by high performance liquid chromatography (HPLC) to be 0.3%. Further, the liquid temperature is 20 ° C.
Under the control described below, 216.1 g (0.99 mol) of di-t-butyl dicarbonate was added and Nt was added.
-Butoxycarbonyl-L-phenylalanine methyl ester was obtained. 35 minutes after completion of the dropwise addition, completion of the reaction was confirmed by HPLC. After completion of the reaction, 326 g of methanol and by-produced t-butyl alcohol were distilled off. Next, n-
400 ml of hexane and 1000 ml of water were added, and the desired product was extracted into the n-hexane phase.
00ml, 0.2N aqueous sodium carbonate solution 60ml,
The n-hexane phase was washed with water in the order of 60 ml, and n-hexane was distilled off to obtain Nt-butoxycarbonyl-L-.
The yield of phenylalanine methyl ester was 258.4 g.
(92.5% yield).

Comparative Example 1 As in Example 1, except that sodium carbonate having a specific surface area of 0.6 m ² / g was used as the inorganic carbonate base, and sodium carbonate and di-t-butyl dicarbonate were simultaneously added. went. As a result, Nt-butoxycarbonyl-L-phenylalanine methyl ester was obtained in a yield of 248.
6 g (yield 89.0%).
12 hours for the hydrocarbon oxycarbonylation reaction.

Comparative Example 2 As in Example 1, except that sodium carbonate having a specific surface area of 0.3 m ² / g was used as the inorganic carbonate base and sodium carbonate and di-t-butyl dicarbonate were added simultaneously. went. As a result, Nt-butoxycarbonyl-L-phenylalanine methyl ester was obtained in a yield of 245.
8 g (yield: 88.0%).
16 hours for the hydrocarbon oxycarbonylation reaction.

Examples 2 to 7 The same operation as in Example 1 was carried out except that the alcohol shown in Table 1 and the inorganic carbonate having the specific surface area shown in Table 1 were used. Table 1 shows the results. Further, in Examples 1 to 7 and Comparative Examples 1 and 2, plots of the neutralization time with respect to the specific surface area of the inorganic carbonate base and the total time required for N-hydrocarbon oxycarbonylation are shown in FIG.

[0069]

[Table 1]

Example 8 A 2 L four-necked flask equipped with a stirrer and a thermometer was placed
248 g of methanol (7.
74mol) and 392.4g (4.00mol) of sulfuric acid were injected, and 165.19g (1.0%) of L-phenylalanine was added.
0 mol) was added. Thereafter, the reaction solution was heated to 40 ° C. and stirred for 12 hours. After the completion of the reaction, 352.8 g of sodium hydrogencarbonate having a specific surface area of 1.3 m ² / g at 10 ° C. or less.
(4.20 mol) was added dropwise over 30 minutes while controlling the liquid temperature to 15 ° C. or lower while paying attention to the rise in the liquid level of the reaction solution accompanying the generation of carbon dioxide. 14 minutes after the completion of the dropping, the generation of carbon dioxide was stopped. At this time, when the hydrolyzate was quantified by HPLC, it was 0.4%. Further, 216.1 g (0.99 mol) of di-t-butyl dicarbonate was added while controlling the liquid temperature to 20 ° C. or lower.
It was added dropwise over 0 minutes, and Nt-butoxycarbonyl-L-
Phenylalanine methyl ester was obtained. After dropping 3
At 0 minutes, the completion of the reaction was confirmed by HPLC. Thereafter, 329 g of methanol and by-produced t-butyl alcohol were added.
Distilled off. Next, 400 ml of ethyl acetate and 600 ml of water were used.
Add the desired product to the ethyl acetate phase, and further add
The ethyl acetate phase was washed with 200 ml of 0.4N hydrochloric acid, 60 ml of a 0.2N aqueous sodium carbonate solution and 60 ml of water in that order, and the ethyl acetate was distilled off to obtain Nt-butoxycarbonyl-L-phenylalanine methyl ester in a yield of 2%.
60.6 g (93.3% yield) could be obtained.

Examples 9 to 17 The same procedures as in Example 8 were carried out except that the amino acids and alcohols shown in Table 2 and the inorganic carbonate base having the specific surface area shown in Table 2 were used. Table 2 shows the results.

[0072]

[Table 2]

Comparative Example 3 As an inorganic carbonate base, sodium bicarbonate having a specific surface area of 0.6 m ² / g was used.
Example 8 was repeated except that -butyl dicarbonate was added at the same time. As a result, Nt-butoxycarbonyl-L-phenylalanine methyl ester was obtained in a yield of 250.0 g (yield: 89.5%), but it took 11 hours for the neutralization reaction and the N-hydrocarbon oxycarbonylation reaction. did.

Example 18 In a 2 L four-necked flask equipped with a stirrer and a thermometer,
248 g of methanol (7.
74 mol), 165.19 g of D-phenylalanine
(1.00 mol), and 124.9 g of thionyl chloride was added.
(1.05 mol) was added. Then, the reaction solution was
The mixture was heated to 5 ° C and stirred for 10 hours. After completion of the reaction, sodium carbonate 183.4 having a specific surface area of 2.2 m ² / g at 10 ° C. or less.
g (1.73 mol) was added dropwise over 30 minutes while controlling the liquid temperature to 15 ° C. or lower while paying attention to the rise in the liquid level of the reaction solution accompanying the generation of carbon dioxide. 14 after dropping
Within minutes the evolution of carbon dioxide stopped. At this time, when the hydrolyzate was quantified by HPLC, it was 0.2% or less. Further, while controlling the liquid temperature to 20 ° C. or less,
-210.8 g of butyl dicarbonate (0.97 mo
1) was added dropwise over 30 minutes to obtain Nt-butoxycarbonyl-D-phenylalanine methyl ester. 35 minutes after completion of the dropwise addition, completion of the reaction was confirmed by HPLC. Further, 330 g of methanol and by-produced t-butyl alcohol were distilled off. Next, 400 ml of dichloromethane and 1200 ml of water were added, and the desired product was extracted into a dichloromethane phase.
Was washed with 60 ml of an aqueous sodium carbonate solution and 60 ml of water in that order, and dichloromethane was distilled off. As a result, 264.0 g of Nt-butoxycarbonyl-D-phenylalanine methyl ester was obtained (94.5 yield).
%).

Examples 19 to 22 The same procedures as in Example 18 were carried out except that the amino acids shown in Table 3 and the sodium carbonate having the specific surface area shown in Table 3 were used. Table 3 shows the results.

[0076]

[Table 3]

Example 23 In a 2 L four-necked flask equipped with a stirrer and a thermometer,
248 g of methanol (7.
74 mol) and 72.92 g (2.00 mol) of hydrogen chloride.
l) and 165.19 g of L-phenylalanine
(1.00 mol) was added. Then, the reaction solution was
The mixture was heated to 5 ° C and stirred for 12 hours. After the completion of the reaction, 222.6 sodium carbonate having a specific surface area of 1.1 m ² / g at 10 ° C. or less.
g (2.10 mol) was added dropwise over 30 minutes while controlling the liquid temperature to 15 ° C. or lower while paying attention to the rise in the liquid level of the reaction solution accompanying the generation of carbon dioxide. 35 after dropping
Within minutes the evolution of carbon dioxide stopped. At this time, the content of the hydrolyzate was determined by HPLC to be 0.3%. While controlling the liquid temperature below 20 ° C,
216.1 g of di-t-butyl dicarbonate (0.99 g)
mol) was added to obtain Nt-butoxycarbonyl-L-phenylalanine methyl ester. 35 after dropping
And the completion of the reaction was confirmed by HPLC. After the completion of the reaction, methanol and by-produced t-butyl alcohol were added to 326.
g was distilled off. Next, 400 ml of toluene and 100 ml of water
0 ml was added and the target substance was extracted into the toluene phase.
The toluene phase was washed in the order of 200 ml of 0.4N hydrochloric acid, 60 ml of a 0.2N aqueous sodium carbonate solution and 60 ml of water, and the toluene was distilled off.
8.4 g (92.5% yield) could be obtained.

Examples 24 to 28 Dicarbonate compounds and alcohols shown in Table 4
The operation was performed in the same manner as in Example 23 except that sodium carbonate having the specific surface area shown in Table 2 was used. Table 4 shows the results.

[0079]

[Table 4]

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the specific surface area of an inorganic carbonate base used for a neutralization reaction in the present invention, the neutralization time, and the N-hydrocarbon oxycarbonylation time.

Claims (1)

[Claims] 1. An acidic reaction solution containing an ester of an amino acid obtained by reacting an amino acid with an alcohol in the presence of a strong acid or thionyl chloride is neutralized, and then the following general formula (I): (Where R ¹ represents an alkyl group, an alkenyl group or an aralkyl group which may have a substituent). A series of reaction steps for obtaining an N-hydrocarbonoxycarbonyl amino acid ester by mixing with a dicarbonate compound represented by the formula: In the above, a specific surface area of 0.8 m ² /
A method for producing an N-hydrocarbon oxycarbonyl amino acid ester, wherein at least g of an inorganic carbonate base is used.