JPH11228512A - Production of d-alloisoleucine and intermediate therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain D-alloisoleucine useful as an intermediate for a medicine for a circulatory system, by treating an epimer mixture of L-isoleucine and D-alloisoleucine with a specific tartaric acid derivative to precipitate the complex of D-alloisoleucine and the tartaric acid derivative. SOLUTION: An epimer mixture of L-isoleucine and D-alloisoleucine in an amount of 1 mol is treated with 0.1-0.7 mol of a (2S,3S)-tartaric acid derivative of the formula (R is a 1-3C lower alkyl, a lower alkoxy, a chlorine atom, a bromine atom or nitro; (n) is 0, 1 or 2) as a reagent for optical resolution in a solvent composed of water, a lower alcohol such as methanol, ethanol or the like or their mixture. The formed complex of D alloisoleucine and the tartaric acid derivative is precipitated as an intermediate and the solid complex separated from the solution is decomposed to isolate D-alloisoleucine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an improvement in a method for producing D-alloisoleucine, which is useful as an intermediate for the production of drugs, particularly circulatory drugs (eg, WO94 / 28,901). The present invention also encompasses the novel complexes formed as intermediates during their preparation.

[0002] In the description of this specification, the RS notation was used for the configuration of tartaric acid and its derivatives. This is because the DL (or dl) display tends to be confusing, and in the old days, the same isomer was used in some cases as a D-form and another as the L-form.
As for amino acids, since there is no such problem, a convenient DL display is used.

[0003]

BACKGROUND OF THE INVENTION D-alloisoleucine, a (2R, 3S) -2-amino-3-methylpentanoic acid of formula II, is

[0004]

Embedded image

Although it is a stereoisomer of L-isoleucine, which is one of the essential amino acids, no industrially feasible production method has been known so far, so it is extremely expensive and cannot be obtained in large quantities. It was difficult.

[0006] Among the known production methods, there are two powerful ones, one is to resolve the racemate of alloisoleucine, and the other is L-isoleucine of the formula III.

[0007]

Embedded image

[0008] This is to separate the D-allo form from the epimer mixture obtained by epimerization of the compound [see, for example, Takeo Kaneko, "Amino Acid Industry-Synthesis and Utilization", Kodansha Scientific (1973), p.133]. . It is known that resolution of a racemate can be performed using an N-acetyl derivative using quinine as a resolving agent [WA Huffmann, AW In
gersoll, J .; Am. Chem. Soc. , 73, 3366 (19
51)] However, in this method, it is necessary to derive an N-acetyl form, and it is not easy to obtain a racemic form.

[0009] On the other hand, epimerization of L-isoleucine produced in large quantities can be carried out relatively easily [for example, Japanese Patent Publication No. 63-55505 of Tanabe Seiyaku].
However, all known methods for splitting an epimer mixture use the epimer mixture as a derivative and then split, and there is no known method for splitting the epimer mixture as it is. That is, a method of recrystallizing an N-formyl form from methyl ethyl ketone [Dow Chemical, Bri.
t. 704983 (1954)], a method in which the epimer mixture is Z- or Boc-formed and separated as a salt with an optically active α-phenethylamine with a difference in solubility [G. Flouret, SH
Nagasawa, J. Org. Chem. 40, 2635 (197
5)], a method of removing L-isoleucine by asymmetric hydrolysis of an N-acetyl form using an enzyme to obtain the remaining N-acetyl-D-alloisoleucine [P. Lloyd
-Williams et al., J.A. Chem. Soc. , Perkin T
rans. I, vol. 1994, 1969].
In any of these methods, the split product is obtained as a derivative in any case, and further steps such as removal of substituents are required until the desired optically active substance is obtained, which is complicated and practical. This is not a typical manufacturing method.

On the other hand, although the optical resolution of amino acids has been well studied, it is often the case that the amino acids are converted into derivatives such as N-acyl derivatives or esters. Few. Some examples of using strongly acidic sulfonic acids, tartaric acid, or mandelic acid as the optical resolving agent are known, but there have been no successful examples of neutral aliphatic amino acids such as leucine and isoleucine.

There are known several examples of deriving a neutral amino acid, that is, an amino acid having no functional group other than an amino group and a carboxyl group, into an ester thereof and optically resolving dibenzoyltartaric acid or a substituted derivative thereof as a resolving agent. I have. For example, the benzyl ester of alanine is (2
R, 3R) -Dibenzoyltartaric acid, D
-Salts with alanine precipitate as poorly soluble salts [W. Lange
nbeck, O. Herbst, Chem. Ber. , 86, 1524 (195
3)]. In the case of the ethyl ester of leucine, a salt of the L-ester and (2R, 3R) -dibenzoyltartaric acid precipitates similarly [W. Langenbeck, G. Zimmermann,
Chem. Ber. , 84,524 (1951); G. Losse, H. Jesc
hkeit, Chem. Ber. , 90,1275 (1957)]. As an example of resolving an amino acid without a protecting group using dibenzoyltartaric acid as an optical resolving agent, see lysine resolution [FJ Kearley, AW Ingersoll, J. Am. Am. Ch
em. Soc. , 73, 5783 (1951)] and the resolution of asparagine [E. Fogassy, M. Acs, J. Gressay, Periodi.
ca Polytechnica, 20,179 (1976)]. However, no attempt has been made to optically resolve a neutral aliphatic amino acid such as alanine, valine, leucine or isoleucine directly by dibenzoyltartaric acid or a substituted derivative thereof without deriving an ester.

The present inventors have found that D-isomerization of D-isoleucine is achieved by optical resolution of an epimer mixture obtained by epimerization.
Investigations aimed at improving the method of producing alloyosorosine and searching for a method of optical resolution without converting the epimeric mixture into derivatives, surprisingly showed that (2S, 3S) -tartaric acid of formula I O, O'-dialoyl esters of L-isoleucine are precipitated by forming a poorly soluble complex with D-alloisoleucine in water or a lower alcohol such as methanol or ethanol, or a mixed solution thereof. And easy separation.

[0013]

Embedded image

The complex of the compound of the formula I with L-isoleucine has remarkably higher solubility than the complex with D-alloisoleucine, and therefore, the complex with D-alloisoleucine having high optical purity is separated by solid-liquid separation. And can be isolated in almost quantitative yield.

[0015]

SUMMARY OF THE INVENTION An object of the present invention is to utilize the above-mentioned novel findings of the present inventors to directly optically resolve an epimeric mixture of L-isoleucine and D-alloisoleucine without converting it into a derivative. Is possible,
Therefore, in a simple process, and with high yield and high purity, D
-To provide a method capable of obtaining alloisoleucine.

[0016]

The process for producing D-alloisoleucine according to the present invention comprises reacting an epimeric mixture of L-isoleucine and D-alloisoleucine with a compound of the formula (2S, 3S)-represented by the formula I in a solvent. Act on tartaric acid derivatives,

[0017]

Embedded image

(Wherein R represents a hydrogen atom, a C ₁ -C ₃ lower alkyl group, a lower alkoxy group, a chlorine atom, a bromine atom or a nitro group, and n is 0, 1 or 2). Separating the complex of D-alloisoleucine and the compound of formula I from the solution and decomposing the separated solid complex to isolate D-alloisoleucine.

The above-mentioned complex of the compound of formula I and D-alloisoleucine, which is an intermediate formed during the production of D-alloisoleucine of the present invention, also forms part of the present invention.

The complex of the obtained compound of the formula I and D-alloisoleucine is added to a lower alcohol such as methanol or ethanol, and the resolving agent tartaric acid-O,
It is possible to separate O'-dialoyl ester, and by this operation, high-purity D-alloisoleucine is precipitated as a crystal. Therefore, a pure product can be obtained by a simple purification operation.

[0021]

DETAILED DESCRIPTION OF THE INVENTION The epimer mixture consisting of L-isoleucine and D-alloisoleucine used as starting materials in the process of the present invention is commercially available L-isoleucine.
It is obtained by isomerizing isoleucine by a conventional method. Isoleucine has an amino group bonded to 2-
There are a 3-position where a methyl group is bonded to the 3-position, and two asymmetric carbon atoms, but the 3-position asymmetric carbon atom is not isomerized at all under normal conditions, Only the asymmetric carbon atom isomerizes to form an epimeric mixture with D-alloisoleucine. For this isomerization, that is, epimerization, any method commonly used for racemizing optically active amino acids can be employed. Specific examples include heating with mixing with an acid or base catalyst, and heating with a neutral, pressurized, if necessary. Since the isomerization of isoleucine is relatively slow, it is practical to use a method of heating in the presence of an aldehyde such as salicylaldehyde and isomerizing via a Schiff base.

Such isomerization, that is, epimerization, has been reported (Japanese Patent Publication No. 63-55505, supra).
No. 93), heating isoleucine to a catalytic amount of salicylaldehyde in glacial acetic acid at 100 ° C. for 1 hour leads to 93% epimerization (the absence of aldehyde under the same reaction conditions reduces epimerization to 4%). Just). The disadvantage of this method is that it is difficult to separate the epimer mixture from the reaction solution obtained by epimerization. As a solution to this problem, the inventors have found that it is preferable to use an inert solvent having a relatively low solubility in aromatic hydrocarbons or water as a solvent for performing the epimerization reaction. If such a solvent is used and the mixture of amino acids that crystallizes upon cooling after the reaction is filtered off, a high-purity epimer mixture can be obtained in good yield only by washing with the solvent.

[0023] (2)
Specific examples of the O, O′-dialoyl ester of (S, 3S) -tartaric acid include dibenzoyltartaric acid, di (p-toluoyl)
Benzoyltartaric acid, di (3,4-dimethylbenzoyl)
And tartaric acid and di (2-chlorobenzoyl) tartaric acid. These compounds are prepared according to a conventional method (2S, 3
It can be easily synthesized by heating S) -tartaric acid with the corresponding chloride or anhydride of benzoic acid or substituted benzoic acid and hydrolyzing the resulting diaroyltartaric anhydride [CL Butler, LH Cretcher,
J. Am. Chem. Soc. , 55, 2605 (1933); Toray, JP-A-7-138206]. Among these tartaric acid derivatives, particularly useful ones are dibenzoyl form (R = H, hereinafter abbreviated as “DBTA”) and (p-toluoyl) form (R = p-Me, n) which are easily available industrially. =
1, hereinafter abbreviated as “DTTA”).

The amount of the tartaric acid derivative used as a resolving agent for the epimer mixture is 0.1 to 0.7 in molar ratio.
Choose from a range. This is because, as described later, D-alloisoleucine is the O, O'- of (2S, 3S) -tartaric acid.
This is because they form a 1: 1 complex with diaroyl esters. When the molar ratio of the tartaric acid derivative is low, the amount of the complex to be crystallized decreases, and the yield decreases. On the other hand, if the molar ratio exceeds 0.6, a complex of the tartaric acid derivative and L-isoleucine tends to crystallize, and as a result, the optical purity of D-alloisoleucine obtained decreases. For this reason, the preferred range of the amount of the resolving agent is from 0.3 to 0.5, more preferably from 0.4 to 0.5, as a molar ratio to the epimer mixture. The optical purity of D-alloisoleucine in the complex crystallized under these conditions is 90% de or more, and may reach 97 to 98% de.

In the crystallization of the complex, an achiral acid is added to the system in addition to the tartaric acid derivative as a resolving agent.
More favorable results are obtained. The molar ratio with respect to the epimer mixture is 0.05 to 0.7, preferably 0.4 to 0.1.
By adding the achiral acid of No. 6, D-
The optical purity of the complex of alloisoleucine and the tartaric acid derivative can be improved, and the amount of the required solvent can be significantly reduced. As the achiral acid, inorganic acids such as hydrochloric acid, sulfuric acid and phosphoric acid and organic acids such as formic acid, acetic acid and propionic acid can be used. Inorganic acids, especially hydrochloric acid, are preferred.

In an optical resolution for forming a diastereomer salt by using an optically active acid or amine as a resolving agent, an amount of the resolving agent smaller than the equivalent amount is used without using an equivalent amount of the resolving agent with the racemic form. The use of an amount of an achiral acid or base to offset the totality and neutralize the whole is widely used and is called the Pope and Peachey method [J. Chem. Soc. , 75,1066 (1899)]. This aspect of the present invention is also apparently understood as an example, but one mole of the amino acid epimer and one mole of the tartaric acid derivative, which is a dibasic acid, combine to form a poorly soluble complex, and this complex itself It is not possible to simply equate it with known methods, because it adds extra acid to where it is acidic and has not been neutralized.

As a medium for forming a complex, water, lower alcohol or a mixture thereof can be suitably used. Examples of lower alcohols include methanol, ethanol,
1- and 2-propanol are mentioned. Using only water as solvent gives good results as far as the yield of the complex and the optical purity of D-alloisoleucine are concerned, but requires a relatively large amount of solvent. In this regard, the use of a mixed solvent obtained by adding a small amount of methanol to water is advantageous in terms of efficiency because the amount of the solvent can be reduced from 2/3 to 1/2. Complexes formed using a water-methanol solvent are also advantageous in that crystals are easily filtered. The amount of methanol occupying 10 to 30% by weight in the mixed solvent is appropriate. If the amount is less than 10%, the effect of using less solvent is poor,
When the amount exceeds 30%, the yield of the complex decreases.

The preparation of the system for forming the complex, including the mixture of the epimer mixture, the tartaric acid derivative and the solvent, and when achiral acid is added, may be performed in any order. Tartaric acid derivatives have low solubility in water and are easily hydrolyzed under strong acidity. Therefore, first, the epimer mixture is put in a solvent, and when added, a part of achiral acid is added and dissolved here, and the resolving agent is added directly or preferably in a solution of a lower alcohol, and then added. It is preferable to mix the whole, and then add the remaining achiral acid to obtain a predetermined composition. At this time, it is not necessary to form a uniform solution, and the solid may be partially suspended.

The composition (solution or suspension) thus prepared is stirred well. Heating at this time is preferable in order to stably obtain high-quality products. After heating, slowly cool to room temperature or lower,
The complex crystallizes out well. The crystals are separated and obtained by a method such as filtration and centrifugation.

This complex contains an amino acid and a resolving agent at a ratio of 1: 1 according to elemental analysis and ¹ H-NMR spectrum, as shown in the following working data. From the analysis value of the water content (by the Karl-Fischer method), it was also found that depending on the type of the resolving agent, one or two water molecules were bound to the amino acid. That is, when unsubstituted DBTA is used as a resolving agent, an anhydrous complex is obtained, and when DTTA substituted with a p-methyl group is used, one to two molecules of water are bound.

The mode of binding between D-alloisoleucine and the tartaric acid derivative in the complex is understood to be weaker than that of the usual diastereomeric salt in view of the fact that it is easily decomposed in alcohol. Fogassy et al. Reported that cycloaliphatic amines and D
He studies diastereomeric salts with BTA and proposes to determine whether the bond is a typical ionic bond or a loose bond such as a hydrogen bond by infrared absorption spectra [Tetrahedron,
52 (5), 1637-42 (1996)]. According to that, when ionic bonds are present, the absorption of ionized amino groups is 3400-
2500 cm ^-1 and the absorption of carboxyl groups is 1610-30 cm ^-1
And 1320-80 cm ^-1 , whereas when there is no ionic bond, the absorption of amino groups around 3400 cm ^-1 and 1720 cm ^-1
Strong absorption of carboxyl groups appears around ^-1 .

The complex of the present invention is not a complex with alicyclic amines studied by Fogassy et al., But a complex with an amino acid, and the amino acid itself may have a carboxyl group and may form an internal salt. Therefore, it is difficult to determine the binding mode of the complex based on the infrared absorption spectrum. In the complex of the present invention, there are three carboxyl groups for one amino group, and the composition is not ionically neutralized at all. Because of this and the fact that the complex is easily decomposed when put in alcohol, it is highly likely that the complex is not a salt strongly bound by ionic bonds but a weakly bound one by hydrogen bonds or the like.

Since L-isoleucine is dissolved in the mother liquor after the complex separation, it is recovered, epimerized by the method described above, and reused. Specifically, when alcohol is added to the solvent, the solvent is heated to evaporate and remove the alcohol, then the mixture is acidified and extracted with an appropriate organic solvent to separate a resolving agent that is hardly soluble in water, that is, a tartaric acid derivative. Isoleucine is crystallized by neutralizing the remaining aqueous solution to the isoelectric point.

In order to obtain the desired optically active D-alloisoleucine from the crystals of the complex separated as described above, according to a conventional method, the complex is put into an acidic aqueous solution to dissolve the amino acid, and then dissolved in water. After extraction and separation of a slightly soluble tartaric acid derivative with an organic solvent immiscible with water, the acidic aqueous solution of the amino acid is neutralized so that the pH becomes the isoelectric point, and the crystallized D-alloisoleucine is solid-liquid separated. Will be.
For the amino acid separation following the solvent extraction of the resolving agent, ion exchange can also be used.

However, the complex of the present invention is a substance which is easily decomposed as described above, and the tartaric acid derivative as a resolving agent can be dissolved by a simple operation of adding it to a highly polar solvent such as methanol, ethanol or isopropanol. And
It has the advantageous property that D-alloisoleucine crystallizes out and separates naturally. To ensure this separation, a base such as triethylamine, which is well soluble in alcohol, is preferably added in an amount of 1 to 2 equivalents to the amino acid.
A more effective method is to use a solvent containing 2 to 20% of water in alcohol. When isopropanol containing about 10% of water was used, it was found that D-alloisoleucine having high optical purity and containing almost no tartaric acid derivative as a resolving agent could be isolated with a recovery rate of 90% or more based on the complex. . The optical purity of the amino acid thus obtained is higher than that of the amino acid in the complex,
The purification-crystallization operation itself has a refining effect.

As a solvent for decomposing the complex, besides the above-mentioned lower alcohol, use is made of a highly polar solvent such as esters such as methyl acetate and ethyl acetate and ketones such as acetone and methyl ethyl ketone. Can be. In any case, it is preferable to use water by adding 5 to 10%.

In the mother liquor after separation of the amino acids crystallized by decomposing the complex, a tartaric acid derivative as a resolving agent is dissolved together with a small amount of amino acids. If the mother liquor is concentrated and the solvent is evaporated off, the resolving agent remains as a solid. This can be used as it is or, if necessary, after purification, in the next complex formation cycle.

[0038]

EXAMPLES The determination of the optical purity of the epimer mixture and of D-alloisoleucine in the following examples was carried out by HPLC under the following conditions: Column: Daicel Chiralpak MA (+) 0.46φ × 5 cm Mobile phase: 2 mmol CuSO ₄ + MeOH (85:15) Flow rate: 0.5 mL / min. Column temperature: 30 ° C. Detector: JASCO Corporation UV-975 wavelength: 254 nm.

[Raw material production example] A reaction vessel was charged with 60.0 g (0.45 mol) of L-isoleucine, 300 mL of toluene, 110.0 g (1.8 mol) of glacial acetic acid, and 11.2 g (0.09 mol) of salicylaldehyde. While stirring,
Heat at reflux (104 ° C.) for 3 hours. After cooling to room temperature, the precipitated solid was separated by filtration, washed three times with 30 mL portions of toluene, and dried to obtain 54.0 g of an epimer mixture.

The yield of the starting material relative to L-isoleucine was 90%, and the epimeric composition (L-isoleucine: D-alloisoleucine) by HPLC was 49:51 to 51:
49, which was completely epimerized.

Example 1 5 g (38.1 mmol) of the epimer mixture produced in the raw material production example was mixed with water 90 in a reaction vessel.
It was suspended in mL. To this, (2S, 3S) -DBTA
6.83 g (19.1 mmol) was added, heated to 70 ° C., and held for 1 hour with stirring. The resulting slurry was allowed to cool, solid-liquid separated at 25 ° C., and the solid was washed twice with 10 mL portions of water.
7.77 g of a 1: 1 complex of D-alloisoleucine and (2S, 3S) -DBTA was obtained as white crystals. The yield (based on the epimer mixture) is 41.7%, and the optical purity is 9
It was 5.6% de.

The analysis results of this complex are shown below: Melting point: 175.5-176.5 ° C. IR KBr pellet (cm ⁻¹ ): 3156, 2972, 2942,
2882, 1733 (S), 1692 (S), 1601 (m), 1528 (m), 1320, 126
6 (S), 1118 (S), 719 (S) ¹ H-NMR (270 MHz, MeOH-d ₄ ) δ: 0.97 (t,
3H, J = 4.0 Hz); 1.00 (t, 3H, J = 4.0)
Hz); 1.24-1.40 (m, 1H); 1.43-
1.59 (m, 1H); 2.01-2.14 (m, 1H)
H); 3.71 (d, 1H, J = 3.5 Hz); 4.90
(S, 7.5H); 5.94 (s, 2H); 7.50
(T, 4H); 7.64 (m, 2H); 8.1 (m,
4H). Elemental analysis value: measured value C 59.0% H 5.6% N 3.1% calculated value (C ₂₄ H ₂₇ NO ₁₀ ) C 58.9% H 5.6% N 2.9% moisture (Karl- Fischer method): 0.53% (calculated monohydrate 3.55%).

A mixed solution of 27 mL of 2-propanol and 3 mL of water was prepared, and 3 g of the above complex was added thereto. After heating to reflux for 1 hour, the mixture was cooled, separated into solid and liquid at 25 ° C., and the obtained solid was washed three times with 4 mL of 2-propanol. 0.71 g of D-alloisoleucine was obtained as white crystals. The yield was 88.3% (based on the complex), and the optical purity (HPLC) was 100% de.

Example 2 5 g (38.1 mmol) of the epimer mixture produced in the raw material production example was mixed with water 49 in a reaction vessel.
suspended in mL, and 1.98 g (19.1 mmol) of 35% hydrochloric acid
added. Next, as in the first embodiment, (2S, 3S) −
6.83 g (19.1 mmol) of DBTA was added, heated to 70 ° C., and kept for 1 hour with stirring. Thereafter, the same treatment as in Example 1 was carried out, and D-alloisoleucine and (2
8.21 g of a 1: 1 complex with (S, 3S) -DBTA was obtained as white crystals. The yield (based on the epimer mixture) is 4
The optical purity was 4.0% and the optical purity was 96.2% de.

To a mixture of 72 mL of 2-propanol and 8 mL of water was added 8.0 g of the above complex.
Decomposition of the complex was performed. 1.90 g of the obtained D-alloisoleucine, the yield was 88.4% (based on the complex),
The optical purity (HPLC) was 100% de.

Example 3 5 g (38.1 mmol) of the epimer mixture produced in the raw material production example was added to water 75 in a reaction vessel.
suspended in 10 mL of methanol (2S, 3
After dropwise adding a solution in which 6.83 g (19.1 mmol) of S) -DBTA was dissolved, the mixture was heated to 70 ° C. and maintained for 1 hour with stirring. Thereafter, the same treatment as in Example 1 was performed to obtain 7.39 g of a complex. The yield (based on the epimer mixture) was 39.6%, and the optical purity was 95.6% de.

Example 4 5 g (38.1 mmol) of the epimer mixture produced in the raw material production example was added to 40 mL of water in a reaction vessel.
And 1.98 g of 35% hydrochloric acid as in Example 2.
(19.1 mmol) were added. In addition, (2S, 3S)-
6.83 g (19.1 mmol) of DBTA was added to methanol 10
The solution dissolved in mL was added dropwise, heated to 70 ° C., and kept for 1 hour with stirring. After allowing to cool, the mixture was further stirred at 25 ° C. for 1 hour, then separated into solid and liquid, and washed with 10 mL of water. The obtained complex was 8.47 g, the yield (based on the epimer mixture) was 45.4%, and the optical purity was 9%.
It was 5.4% de.

Example 5 50 g (380 mmol) of the epimer mixture produced by the method shown in the raw material production example was suspended in 360 mL of water in a reaction vessel, and 8.0 g of 35% hydrochloric acid was obtained.
(77 mmol) and stirred to form a slurry. Next, 61.3 g of (2S, 3S) -DBTA (171 mmo)
A solution of l) dissolved in a mixture of 100 mL of methanol and 80 mL of water was added dropwise. Furthermore, 11.9 g of 35% hydrochloric acid
(114 mmol) diluted with 50 mL of water and added.
C. and kept at this temperature for 1 hour. The reaction solution was allowed to cool, stirred at 25 ° C. for 1 hour, and then subjected to solid-liquid separation.
The solid was washed twice with 100 mL of water and dried to obtain 84.7 g of a complex. The yield (based on the epimer mixture) was 45.5%, and the optical purity was 94.8% de.

The mother liquor from which the complex was separated by filtration and the washing liquid were combined, concentrated by distilling off methanol, and then the concentrated liquid was extracted with 200 mL of methyl tert-butyl ether to remove the resolving agent. The remaining aqueous solution was further concentrated, neutralized to the isoelectric point (pH 5.94), and the crystallized isoleucine was recovered.

80.0 g of the complex obtained as described above (1
63 mmol) was placed in a mixture of 720 mL of 2-propanol and 80 mL of water, heated under reflux for 1 hour, cooled, and solid-liquid separated at 25 ° C. After washing with 80 mL of 2-propanol three times and drying, D-alloisoleucine was obtained as white crystals. Yield 19.0 g, yield (based on complex) 8
The optical purity was 9.0% and the optical purity was 99.9% de.

The filtrate from which D-alloisoleucine was separated was combined with the washing solution, 2-propanol was distilled off, and the mixture was concentrated. To the remaining solution, 100 mL of methanol was added to form a solution.
This solution contained about 58 g of (2S, 3S) -DBTA and a small amount of isoleucine, and could be used for the next optical resolution cycle.

Example 6 In the same manner as in Example 1, 5 g (38.1 mmol) of the epimer mixture produced in the raw material production example was used.
It was suspended in 90 mL of water in a reaction vessel. In addition, (2
7.36 g (19.0 mmol) of (S, 3S) -DTTA was added, heated to 70 ° C., and held for 1 hour with stirring. The resulting slurry was allowed to cool, solid-liquid separated at 25 ° C., and the solid was washed twice with 10 mL portions of water. The obtained white crystals weighed 9.2 g. From the following analytical data, D-alloisoleucine:
It is considered to be a complex of (2S, 3S) -DTTA: water 1: 1: 1-2. The yield (based on the epimer mixture) is 44.
The optical purity was 34.8% and the optical purity was 94.8% de.

The analytical data for this complex is shown below. The results show that the ratio of amino acid to DTTA is 1: 1. Although the results of the moisture analysis and the elemental analysis do not match, it is estimated that one or two molecules of water are bound.

Melting point: 157 to 161 ° C. IR KBr pellet (cm ⁻¹ ): 3526, 2966, 2924,
1717 (S), 1609 (S), 1546 (m), 1259 (S), 1176, 1123, 110
8 (S), 755 (S). ¹ H-NMR (270 MHz, MeOH-d ₄ ) δ: 0.97 (t,
3H, J = 4.0 Hz); 1.00 (t, 3H, J = 4.0)
Hz); 1.26-1.40 (m, 1H); 1.43-
1.58 (m, 1H); 2.03-2.13 (m, 1
H); 2.42 (s, 6H); 3.70 (d, 1H, J
= 3.5 MHz); 4.89 (s, 11H); 5.91
(S, 2H); 7.31 (d, 4H); 8.03
(D, 4H). Elemental analysis value: measured value C 58.9% H 6.1% N 2.8% calculated value (C ₂₆ H ₃₁ NO ₁₀ .H ₂ O) C 58.3% H 6.2% N 2.6% (C ₂₆ H ₃₁ NO ₁₀ .2H ₂ O) C 56.4% H 6.4% N 2.5% Moisture (Karl-Fischer method): 6.47% (calculated dihydrate 6.51% ).

8.0 g of the above complex was added to 80 mL of methanol, 1.6 g of triethylamine was added, and the mixture was heated under reflux for 1 hour. The mixture was cooled, separated into solid and liquid at 25 ° C., and the obtained solid was washed with 2 mL of methanol. The amount of the obtained white crystals (D-alloisoleucine) was 1.48 g, the yield was 76.8% (based on the complex), and the optical purity (HP
LC) was 99.4% de.

[0056]

As described above, the known method for producing D-alloisoleucine is a method for producing an N-acyl derivative by converting a racemate or an epimeric mixture of L-isoleucine and D-alloisoleucine into an N-acyl derivative, and using a resolving agent. A complicated step of splitting-hydrolysis or enzymatic asymmetric hydrolysis had to be performed.

On the other hand, according to the method of the present invention, L-
By using isoleucine as a starting material, D-alloisoleucine having high optical purity can be produced in a high yield by a relatively simple operation of epimerization, formation of a complex with a tartaric acid derivative, and decomposition of the formed complex. It can be manufactured in a special way. Examples of optical resolution of amino acids that can be optically resolved with a resolving agent without protecting the amino group or carboxyl group as described above include:
Extremely limited. In particular, DBTA and DTTA
Only two cases of asparagine and lysine have been reported as examples of direct resolution using a tartaric acid derivative as described above as a resolving agent. The direct resolution of neutral aliphatic amino acids such as alanine, valine and leucine is not limited to tartaric acid derivatives, and no examples using other resolving agents are known. Under such circumstances, the present invention, which enables the direct resolution of the epimeric mixture of L-isoleucine and D-alloisoleucine, can be said to be a breakthrough.

Since L-isoleucine is produced in large quantities, it can be easily and inexpensively obtained. Diaroyl- (2S, 3S) -tartaric acid as a resolving agent is also easily available, and its use amount can be as small as about 0.5 with respect to the epimer mixture, and can be recovered from the complex at a high recovery rate. Can be used.

In a preferred embodiment, in the production of the complex, by adding a small amount of an inorganic acid or an organic acid, particularly an inorganic acid, together with the resolving agent, the amount of the solvent used can be greatly reduced, and the productivity is remarkably reduced. Can be improved.

The decomposition of the complex can be realized very easily only by adding the complex to a lower alcohol, preferably a lower alcohol to which an appropriate amount of water has been added, and the desired D-alloisoleucine can be separated in high yield. it can.

The L-isoleucine remaining after separating D-alloisoleucine from the epimer mixture is epimerized again and can be reused as a raw material, and the raw material can be used effectively.

As described above, the present invention realizes, for the first time, the industrial production of D-alloisoleucine, which enables the production of optically active functions such as physiologically active substances such as various pharmaceuticals and agricultural chemicals. The use of conductive materials has been opened.

Claims (8)

[Claims] 1. An epimeric mixture of L-isoleucine and D-alloisoleucine, in a solvent, a (2S, 3S) -tartaric acid derivative represented by the formula I acting as an optical resolving agent, (Wherein, R represents a hydrogen atom, a C ₁ -C ₃ lower alkyl group, a lower alkoxy group, a chlorine atom, a bromine atom or a nitro group, and n is 0, 1 or 2). A process for producing D-alloisoleucine, comprising precipitating a complex of isoleucine and a compound represented by the formula I, separating the complex from a solution, and decomposing the separated solid complex to isolate D-alloisoleucine. 2. The method of claim 1, wherein R of the formula I is a hydrogen atom or a methyl group substituted at the p-position (n = 1). Production method. 3. A solvent comprising water or methanol;
The method for producing D-alloisoleucine according to claim 1, wherein the complex is formed using lower alcohols such as ethanol or a mixture thereof. 4. The method for producing D-alloisoleucine according to claim 1, wherein 0.1 to 0.7 mol of the compound represented by the formula I is allowed to act on 1 mol of the epimer mixture to form a complex. 5. The method according to claim 1, wherein 0.1 to 0.7 mol of the compound of the formula I is allowed to act on 1 mol of the epimer mixture, and 0.05 to 0.7 equivalent of an inorganic acid is added. 1
Production method of D-alloisoleucine. 6. Isolation of D-alloisoleucine by decomposition of the complex is performed by placing the complex in a lower alcohol, dissolving only the tartaric acid derivative as an optical resolving agent, and leaving D-alloisoleucine as a solid. The method for producing D-alloisoleucine according to claim 1, which is carried out. 7. The method for producing D-alloisoleucine according to claim 6, wherein isopropanol is selected as a lower alcohol, and 2 to 20% by weight of water is added thereto. 8. A complex of D-alloisoleucine and a compound of the formula I.