JP2001181247A - Method of producing inorganic acid salt of amino acid ester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of efficiently and simply producing an inorganic acid salt of protected or unprotected amino acid esters useful as a raw material for peptide synthesis, raw materials for medicine and the like. SOLUTION: In this method for producing an inorganic acid salt of protected or unprotected amino acid salt by subjecting a protected or unprotected amino acid or their inorganic acid salt and an alcohol to the esterification reaction to produce inorganic acid salt of protected or unprotected amino acid ester, the reaction process characteristically comprises: (1) the step where the esterification reaction is carried out in the presence of thionyl chloride; (2) the step where the crystals of the inorganic acid of the protected or unprotected amino acid ester is filtered after completion of the esterification reaction; (3) in addition, the filtrate is additionally subjected to the following esterification reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an inorganic acid salt of an amino acid ester protected or unprotected by a protecting group useful as a raw material for peptide synthesis, a raw material for a medicament or the like.

[0002]

2. Description of the Related Art As a method for producing an amino acid ester inorganic acid salt, a method comprising subjecting an amino acid and an alcohol to an esterification reaction in the presence of an inorganic acid catalyst, precipitating crystals by cooling, and separating the precipitated crystals by filtration. It has been known. In this method, the filtrate obtained after removing the crystals of the obtained amino acid ester inorganic acid salt contains unreacted alcohol, and thus it is desirable to reuse this as a raw material.

[0003] However, when the alcohol in the recovered filtrate is reused as a raw material, the purity of the amino acid ester inorganic acid salt and the yield are reduced because the filtrate contains water generated during the esterification reaction. . In order to solve this problem, an approximately equal amount of glycine is added to hydrogen chloride remaining in the filtrate after filtering the crystals of glycine ethyl ester hydrochloride to form glycine hydrochloride, and the water present in the filtrate is replaced with ethanol. A method for producing glycine ethyl ester hydrochloride which is removed by azeotropic distillation with benzene is known (Japanese Patent Application Laid-Open No.
53-127412).

[0004] However, the above-mentioned method has problems that benzene is required, and benzene, ethanol and water must be separated by distillation or the like in order to reuse benzene and ethanol. Also,
After subjecting the amino acid and methanol to an esterification reaction in the presence of a mineral acid, the crystals are precipitated by cooling, isolating the amino acid methyl ester mineral acid salt, and controlling the water content during the reaction to 20% by weight or less. In addition, a method has been reported in which a filtrate is circulated through a reaction system to carry out an esterification reaction again (Japanese Patent No. 2928564).

However, in this method, water generated by esterification accumulates in the reaction solution when recycling is repeated. Therefore, in order to maintain a high esterification reaction rate, the amount of circulating filtrate is reduced or the filtrate is recycled. A complicated operation such as an operation of reducing the amount of water contained in the filtrate by concentrating the solution before the operation is required.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for efficiently and easily producing an inorganic acid salt of an amino acid ester protected or unprotected by a protecting group.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides an amino acid protected or unprotected by a protecting group or an amino acid salt thereof with an alcohol by subjecting it to an esterification reaction. In the method for producing an ester inorganic acid salt, 1) a step of performing the esterification reaction in the presence of thionyl chloride, 2) an amino acid ester inorganic acid salt protected or unprotected from the reaction solution by a protecting group after the esterification reaction is completed And 3) further comprising the step of subjecting the filtrate to an esterification reaction.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As amino acids, natural amino acids or unnatural amino acids can be used.
Both the isomer and the DL form, and a mixture of the L form and the D form in any ratio can be used. Specific examples of the amino acid include glycine, alanine, valine, leucine, isoleucine, phenylalanine, lysine, arginine, ornithine, aspartic acid, and glutamic acid. Of these, ornithine is preferably used.

The amino acid protected by the protecting group may be a known protecting group whose functional group is used at the time of peptide synthesis or the like [for example, Protective Groups in Japan]
Organic Synthesis (Protective Groups in Org)
anic Synthesis), TW Greene, John Wiley & Sons, Inc. (1981), etc.], and the like. Is an amino acid protected with a benzyloxycarbonyl group, a t-butyloxycarbonyl group, or an acidic amino acid such as aspartic acid or glutamic acid, one of the carboxyl groups of which is a methyl group, an ethyl group, a propyl group, an isopropyl group, etc. And amino acids protected by the above.

As the inorganic acid salt of an amino acid inorganic acid salt protected or unprotected by a protecting group, hydrochloride, sulfate, nitrate, phosphate and the like are used, and among them, hydrochloride is preferably used. Examples of the inorganic acid salts of inorganic acid salts of amino acid esters protected or unprotected by a protecting group include hydrochlorides, sulfates, nitrates, phosphates and the like, and mixtures of the above-mentioned inorganic acid salts.

Examples of the alcohol include alcohols having 1 to 6 carbon atoms. Specific examples include methanol, ethanol, propanol, isopropanol, butanol, pentanol and hexanol. The amount of the alcohol to be used is not limited, but is usually 1 to 20 times (by weight) the amino acid protected or unprotected by a protecting group or an inorganic acid salt thereof.

In the esterification reaction, a reaction solvent may be used if necessary. Examples of the reaction solvent in this case include hydrocarbon solvents such as toluene, xylene and hexane, ether solvents such as tetrahydrofuran and dioxane, aliphatic halogenated hydrocarbon solvents such as methylene chloride, ethylene chloride, trichloroethylene and tetrachloroethylene, and acetic acid. Examples thereof include aliphatic ester solvents such as methyl, ethyl acetate and methyl propionate, and phosphate ester solvents such as trimethyl phosphate.

In the esterification reaction, thionyl chloride is preferably used in an amount of 0.5 times or more, and more preferably 0.9 to 5 times by mole, of the amino acid protected or unprotected by a protecting group or an inorganic acid salt thereof. Is more preferred. The esterification reaction is usually performed at a temperature between 0 and 150 ° C, but is preferably performed at a temperature between 30 and 80 ° C.

The reaction time is not particularly limited, but is usually 5 minutes to 24 hours. In the esterification reaction, the esterification rate of an amino acid protected or unprotected by a protecting group of a raw material or an inorganic acid salt thereof is preferably 6 or more.
The process is terminated when it becomes 0% or more, more preferably 80% or more. The esterification rate is determined by the following equation.

[0015]

(Equation 1)

When the reaction solution after the esterification reaction is usually concentrated or cooled, crystals of the amino acid ester inorganic acid salt protected or unprotected by the protecting group are precipitated. The cooling temperature in this case is not particularly limited by the type of amino acid, the type and amount of alcohol, and the like. For example, in the case of L-ornithine ethyl ester dihydrochloride, it is preferably cooled to 0 to 80 ° C.

The filtrate obtained after isolating the target substance from the reaction solution by filtration or the like is further subjected to an esterification reaction. In this case, the filtrate can be directly subjected to an esterification reaction without requiring any operation such as purification such as dehydration or removal of impurities. As the esterification reaction, a method other than the method performed in the presence of thionyl chloride, for example, a method using an azeotropic agent, a method performed in the presence of an inorganic acid catalyst, and the like can be applied. Is preferred.

In the case of the method carried out in the presence of thionyl chloride, it is preferable to further add an amino acid protected or unprotected by a protecting group or an inorganic acid salt thereof and thionyl chloride to the filtrate and subject it to an esterification reaction. Preferred and esterification reaction conditions (reaction temperature, amount of alcohol used,
The amount of thionyl chloride used, etc.) can be set to the same conditions as in the above-mentioned method.

Further, after the esterification reaction in the presence of thionyl chloride is completed, the filtrate obtained after isolating the target substance from the reaction solution by filtration or the like can be further subjected to the esterification reaction in the same manner as described above. In addition, the above-mentioned operations [2) and 3)] can be performed repeatedly and continuously two or more times. When the steps 2) and 3) are repeated twice or more as described above, the esterification reaction is preferably performed by a method performed in the presence of thionyl chloride.

Hereinafter, the present invention will be described more specifically with reference to examples.

[0021]

The HPLC analysis conditions in Examples and Comparative Examples are as follows. HPLC conditions Column: CROWNPACK CR (+) manufactured by Daicel Chemical Co., Ltd. Mobile phase: 44.8 g / L perchloric acid aqueous solution Detector: RI Flow rate: 0.7 ml / min Column temperature: 30 ° C

Example 1 (1) Crude crystals of L-ornithine hydrochloride (purity 94.4%, moisture 4.4)
%) 169.5 g (0.95 mol) was suspended in 685 g of ethanol, and 124.4 g (1.05 mol) of thionyl chloride was added thereto. 7
The reaction was carried out by heating and refluxing at 8 ° C for 4 hours, and then cooled to 20 ° C, and the precipitated crystals were filtered. The obtained filtrate was dried under reduced pressure at 50 ° C. to obtain 206.6 g of L-ornithine ethyl ester dihydrochloride having a purity of 98.5% (yield 91.9%). The crystal purity of L-ornithine ethyl ester dihydrochloride is HP
It was determined from the result of analysis by LC (analysis conditions were as described above). Further, the purity of the crystals of the following examples and comparative examples was determined in the same manner.

(2) The obtained filtrate (149.8 g) was recycled, and after adding 49.3 g of ethanol, 53.6 g (0.30 mol) of crude crystals of L-ornithine hydrochloride and 25.7 g of thionyl chloride were added.
g (0.23 mol) was added. The esterification reaction was carried out in the same manner as above, and after cooling, filtration and drying yielded crystals of L-ornithine ethyl ester dihydrochloride having a purity of 94.7% in a yield of the second esterification reaction of 83.3%. The total yield of the first and second esterification reactions was 87.6%.

The yield of the second esterification reaction was determined by the following equation (2).

[0025]

(Equation 2)

The total yield of the first and second esterification reactions was determined by the following equation (3).

[0027]

(Equation 3)

Comparative Example 1 Crude crystals of L-ornithine hydrochloride (purity 94.4%, moisture 4.4%) 17
6.4 g (0.99 mol) was suspended in 285 g of ethanol, and 18.
1% by weight hydrogen chloride ethanol solution (hydrogen chloride 2.19mol) 4
40.7 g was added. The mixture was heated and refluxed at 78 ° C. for 5 hours to react, and then cooled to 20 ° C., and the precipitated crystals were filtered. By drying the obtained filtrate under reduced pressure at 50 ° C,
207.3 g of crystals of 95.5% pure L-ornithine ethyl ester dihydrochloride were obtained (86.0% yield).

Using 155.2 g of the filtrate obtained above, a solution of 18.1% by weight of hydrogen chloride in ethanol (hydrogen chloride: 1.09 mol) 220.
After adding 5 g, 87.9 g of crude L-ornithine hydrochloride (0.49 mol
l) was added. The esterification reaction was carried out in the same manner as above, and after cooling, filtration and drying were performed to obtain crystals of L-ornithine ethyl ester dihydrochloride having a purity of 91.3% (yield of the second esterification reaction) of 74.9%. The total yield of the first and second esterification reactions was 80.5%. The yield of the second esterification reaction was determined by the above formula 2, and the total yield of the first and second esterification reactions was determined by the above formula 3.

Example 2 20.7 g (0.12 mol) of L-ornithine hydrochloride (purity 97.8%) was suspended in 79.9 g of ethanol, and 14.2 g (0.1%) of thionyl chloride was added thereto.
2 mol) was added. The mixture was heated and refluxed at 78 ° C. for 5 hours to react, and then cooled to 20 ° C., and the precipitated crystals were filtered. By drying the obtained filtrate under reduced pressure at 50 ° C,
25.2 g of crystals of L-ornithine ethyl ester dihydrochloride having a purity of 97.8% were obtained (yield: 88.3%).

Example 1 using the filtrate obtained here
The same operation as in (2) was repeated three times to carry out an esterification reaction, followed by cooling, filtration and drying to obtain crystals of L-ornithine ethyl ester dihydrochloride (purity: 95.9%). The yields of the second, third and fourth esterification reactions were 88.9% and 91.2%, respectively.
89.0%. The yield of the second esterification reaction was determined by the above formula 2, and the yield of the third and fourth esterification reactions was determined in the same manner as the above formula 2.

[0032]

According to the present invention, there is provided a method for efficiently and conveniently producing an amino acid ester inorganic acid salt protected or unprotected by a protecting group.

Continued on the front page (72) Inventor Kenji Mutoh 2-3-3, Daikyo-cho, Yokkaichi-shi, Mie Kyowa Yuka Co., Ltd. Yokkaichi Research Laboratory F-term (reference) 4H006 AA02 AC48 AD15 AD17 BB11 BB12 BB15 BB17 BB25 BC10 BC19 BC51 BE51 BS10 BU32 NB14

Claims (5)

[Claims] A method for producing an inorganic acid salt protected or unprotected by a protecting group by subjecting an amino acid protected or unprotected by a protecting group or an inorganic acid salt thereof to an alcohol and subjecting it to an esterification reaction. 1) a step of performing an esterification reaction in the presence of thionyl chloride; 2) a step of filtering crystals of an inorganic acid salt of an amino acid ester protected or unprotected by a protecting group from the reaction solution after completion of the esterification reaction; 3) A method further comprising a step of subjecting the filtrate to an esterification reaction. 2. The method according to claim 1, wherein the alcohol is an alcohol having 1 to 6 carbon atoms. 3. The method according to claim 1, wherein step 3) is performed in the presence of thionyl chloride. 4. The method according to claim 3, wherein the steps 2) and 3) are repeated at least twice. 5. The method according to claim 1, wherein the amino acid is ornithine.
4. The production method according to any one of 4.