JP2647420B2 - Method for producing N-protected-α-L-aspartyl-L-phenylalanine methyl ester - Google Patents

Description

The present invention relates to N-protected-L-aspartic anhydride and L-aspartic anhydride.
A phenylalanine methyl ester mineral acid salt in an organic carboxylic acid, an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylate, or ammonium carbonate of these metals; ,
N-protected-α-L-aspartyl-L-phenylalanine methyl ester (hereinafter referred to as N-protected-α-AP), characterized by reacting with addition of an ammonium ammonium carboxylate.
M).

The N-protected-α-APM of the present invention is an important compound as an intermediate of α-L-aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as α-APM) used as a sweetener. α-APM is widely known as a dipeptide-based sweetener, has good sweetness properties and a high sweetness nearly 200 times higher than that of sucrose, and its demand as a diet sweetener is greatly growing.

[Conventional technology and problems to be solved] α-APM is a dipeptide compound composed of L-aspartic acid and L-phenylalanine methyl ester. Are known.

The method generally uses N-protected-L-aspartic anhydride as a starting material.
A method of condensing aspartic anhydride and L-phenylalanine methyl ester in an organic solvent and then removing the protecting group by a conventional method (US Pat. No. 3,786,039)
), A method of using L-phenylalanine methyl ester as a reaction raw material and reacting with N-protected-L-aspartic anhydride in an inert reaction medium (JP-A-46-1370).
No.) are known.

According to this method, N-benzyloxycarbonyl-
Ethyl acetate solution of L-aspartic anhydride and L-
A solution of phenylalanine methyl ester hydrochloride in ethyl acetate is mixed, and a 1N aqueous sodium carbonate solution is added to the ethyl acetate solution to react while neutralizing the hydrochloride of L-phenylalanine methyl ester.

As a method not using L-phenylalanine methyl ester, N-formyl-L-aspartic anhydride and L-phenylalanine are condensed in acetic acid, and then subjected to deformylation in the presence of hydrohalic acid, and A method is known in which esterification is carried out by treating the mixture with an alcohol and a hydrohalic acid, and α-APM is isolated as a hydrohalide (JP-A-55-26133).

Also known is a method of reacting N-benzyloxycarbonyl-L-aspartic anhydride with L-phenylalanine methyl ester hydrochloride in an inert organic solvent in the presence of a base (JP-A-46-7068). Specifically, the hydrochloride of N-benzyloxycarbonyl-L-aspartic anhydride and L-phenylalanine methyl estil is dissolved in ethyl acetate, and then the reaction is performed while adding an aqueous solution of sodium carbonate or potassium carbonate to the solution. Is the way. In this reaction, tertiary amines are also used as an organic base. However, in these cases, since the reaction is carried out using an hydrochloride of L-phenylalanine methyl ester in an organic solvent while neutralizing with an aqueous alkaline solution or the like, hydrolysis of the ester with an aqueous alkaline solution of L-phenylalanine methyl ester, and furthermore, L-phenylalanine methyl ester is self-cyclized under alkaline conditions or basic conditions such as tertiary amines to form a diketopiperazine compound which is by-produced, and the N-protected-L-aspartic anhydride is opened with water. The disadvantage that a ring reaction or the like occurs cannot be avoided.

On the other hand, N-formyl-L-aspartic anhydride and L
-Reaction with phenylalanine methyl ester in a solvent,
A method in the presence of acetic acid or formic acid (Japanese Patent Laid-Open No. 62-14 / 1987)
9699) is known.

However, this method is a method in which L-phenylalanine methyl ester is reacted in an organic solvent in the presence of acetic acid or formic acid, and the raw material used is an isolated L-phenylalanine methyl ester solution. Operations such as extraction, dehydration, and the like are complicated. Further, the use of the isolated L-phenylalanine methyl ester solution has the same drawbacks as in the above method.

As described above, the conventionally known methods for producing N-protected-α-APM have disadvantages, and they have not always been satisfactory as industrial methods.

[Means for solving the problem]

Means for Solving the Problems The present inventors have intensively studied a method which does not have the above-mentioned disadvantages of the conventional method and is satisfactory as an industrial production method in the reaction between N-protected-L-aspartic anhydride and L-phenylalanine methyl ester. As a result,
In the reaction of N-protected-L-aspartic anhydride with L-phenylalanine methyl ester, L-phenylalanine methyl ester is converted in the form of a mineral salt,
The mineral acid salt is neutralized, extracted, dehydrated, etc. and isolated as L-phenylalanine methyl ester as in the conventional method, and further, in an organic carboxylic acid, an alkali metal, an alkaline earth metal, or By adding a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylate of these metals, or ammonium carbonate or ammonium organic carboxylate, and condensing with N-protected-L-aspartic anhydride, The present inventors have found a method for producing N-protected-α-APM, and have completed the present invention.

That is, the present invention relates to a method in which an N-protected-L-aspartic anhydride and a mineral acid salt of L-phenylalanine methyl ester are used in an organic carboxylic acid in an alkali metal, an alkaline earth metal, or a hydroxide or an oxidized metal of these metals. A product, a carbonate, a bicarbonate, or an organic carboxylate, or ammonium carbonate or an organic carboxylate, in an amount of at least equimolar to the L-phenylalanine methyl ester mineral acid salt and react. N-protection-α-AP
This is a method for manufacturing M.

The method of the present invention relates to a method in which a mineral acid salt of L-phenylalanine methyl ester is dissolved in an organic carboxylic acid in an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylic acid of these metals. By adding an acid salt, ammonium carbonate or an organic ammonium carboxylate, the compound substantially reacts as L-phenylalanine methyl ester. It has the characteristic that no ring-closure reaction occurs.

The N-protecting group used in the method of the present invention may be a benzoyl group,
Acetyl group, formyl group, and halogen-substituted acetyl group, trifluoroacetyl group, trichloroacetyl group,
An alkoxybenzyloxycarbonyl group such as a triphenylmethyl group, a p-toluenesulfonyl group, or a p-methoxybenzyloxycarbonyl group; a halogenobenzyloxycarbonyl group such as a p-chlorobenzyloxycarbonyl group; and p-nitrobenzyloxycarbonyl Examples include a substituted or unsubstituted benzyloxycarbonyl group such as a group, and a formyl group, a trifluoroacetyl group, and a benzyloxycarbonyl group are particularly preferred.

These N-protected-L-aspartic anhydrides can be produced by various methods, and the following production methods can be adopted.

For example, N-formyl-L-aspartic anhydride is L
-It can be easily produced by reacting aspartic acid with formic acid in acetic anhydride.

In addition, N-trifluoroacetyl-L-aspartic anhydride can be produced by cooling L-aspartic acid, then slowly adding trifluoroacetic anhydride to cause a reaction, and further adding N-acetyl. −
L-aspartic anhydride, N-trichloroacetyl-
L-aspartic anhydride and the like can also be synthesized according to the above method (J. Med. Chem. 11b, 163 (1973)).

Further, N-benzyloxycarbonyl-L-aspartic anhydride is reacted with L-aspaarginic acid and carbobenzoxyl chloride to obtain N-benzyloxycarbonyl-L-aspartic acid, and then a dehydrating agent such as acetic anhydride is used. It is known that they can be obtained by acting.

Further, the L-phenylalanine methyl ester mineral salt used in the present invention can be produced by esterifying L-phenylalanine in methanol in the presence of a mineral acid in a conventional manner.

The organic carboxylic acid used in the method of the present invention is formic acid,
Although carboxylic acids such as acetic acid and propionic acid can be mentioned, acetic acid and propionic acid are preferably used.

The amount of these organic carboxylic acids to be used is not particularly limited, but in operation, usually, the N-protected-L-
It is preferably used in a range of 2 to 50 times by weight of aspartic anhydride.

Examples of the alkali metal and alkaline earth metal used in the method of the present invention include sodium and magnesium.

Examples of hydroxides of alkali metals and alkaline earth metals include, for example, hydroxides of sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide and the like. Examples of the oxide include oxides such as calcium oxide and magnesium oxide.Examples of the alkali metal and alkaline earth metal carbonates include lithium carbonate, sodium carbonate, potassium carbonate, calcium carbonate, and magnesium carbonate. Also, ammonium carbonate can be used. Examples of the alkali metal and alkaline earth metal bicarbonates include bicarbonates such as lithium bicarbonate, sodium bicarbonate, potassium bicarbonate, and calcium bicarbonate. The organic carboxylate may be any salt formed from an organic carboxylic acid and an alkali metal, an alkaline earth metal, ammonium, etc., for example, lithium acetate, sodium acetate, potassium acetate, calcium acetate, magnesium acetate, Examples thereof include ammonium acetate, sodium formate, and potassium formate. Preferably, sodium acetate and potassium acetate are used.

The amount of the alkali metal, alkaline earth metal, or hydroxide, oxide, carbonate, bicarbonate, or organic carboxylate, or ammonium carbonate or ammonium organic carboxylate of these metals is L-phenylalanine methyl ester An equimolar amount to the mineral acid salt is sufficient, but usually it is in the range of 1.0 to 3.0 molar ratio.

To carry out the process of the present invention, N
Suspending or dissolving protected L-aspartic anhydride to form an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylate, or carbonate of these metals; After adding ammonium and ammonium organic carboxylate, a mineral acid salt of L-phenylalanine methyl ester is added, or L-phenylalanine methyl ester is added.
After adding the mineral acid salt of phenylalanine methyl ester, an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate, or organic carboxylate of these metals, or ammonium carbonate, organic carboxylic acid Ammonium may be added.

In the present invention, the reaction temperature is not particularly limited, and may be generally in the range of -15 to 80C, preferably in the range of -5 to 25C.

 A reaction time of usually 0.5 to 10 hours is sufficient.

After the reaction, the N-protected-α-APM generally precipitates as a precipitate in the reaction system. In addition, since N-protected-β-aspartyl-L-phenylalanine methyl ester (hereinafter abbreviated as N-protected-β-APM) is relatively soluble in organic carboxylic acids, the precipitated crystals are filtered and washed. By doing so, the desired N-protected-α-APM can be easily isolated.

On the other hand, N-protected-β-APM contained in a small amount in the isolated N-protected-α-APM is easily removed with water or an organic solvent by a conventional method.

[Action and effect]

According to the method of the present invention, mineral acids of N-protected-L-aspartic anhydride and L-phenylalanine methyl ester are used in the production of N-protected-α-APM, an important compound as an intermediate of α-APM. Using a salt and an organic carboxylic acid as a solvent, various metals, and various metal compounds are added and reacted, under mild conditions, can be efficiently obtained in a short time, and is a valuable production method as an industrial production method. is there.

〔Example〕

Hereinafter, the method of the present invention will be described in detail with reference to examples.

Example 1 N-trifluoroacetyl-L-aspartic anhydride (21.1 g, 0.1 mol) was added to 63.3 g of acetic acid, and the mixture was suspended.
Under stirring, 9.2 g (0.11 mol) of sodium acetate was added at 10 to 15 ° C., and then 21.6 g (0.1 mol) of L-phenylalanine methyl ester hydrochloride was added at the same temperature. After stirring and reacting at the same temperature for 2 hours, the precipitated crystals are filtered, washed,
By drying, N-trifluoroacetyl-α-L
-Crystals of aspartyl-L-phenylalanine methyl ester were obtained.

Yield: 31.2 g (yield: 80.0% / vs. L-phenylalanine methyl ester hydrochloride) The obtained crystals were analyzed by high performance liquid chromatography to find that they were only α-forms.

Melting point 150-151 ° C Elemental analysis value (%) As C ₁₆ H ₁₇ N ₂ O ₆ F ₃ CH NF actually measured value 49.10 4.45 7.17 14.56 calculated value 49.24 4.39 7.18 14.60 Example 2 In Example 1, an organic carboxylic acid was used. The procedure was performed in the same manner as in Example 1 except that the organic carboxylate was changed.

 The results are shown in Table 1.

Example 3 25.18 (0.1 mol) of N-benzyloxycarbonyl-L-aspartic anhydride was added to 100.4 g of acetic acid and suspended, and then 9.2 g (0.11 mol) of sodium acetate was stirred at 10 to 15 ° C.
Then, at the same temperature, 21.6 g (0.1 mol) of L-phenylalanine methyl ester hydrochloride was added. 4 at the same temperature
After stirring and reacting for hours, 75.3 g of water was added at the same temperature,
After cooling to 5 ° C., the precipitated crystals were filtered, washed and dried to obtain crystals.

Yield 31.2 g (yield: 72.9% / pair L- phenylalanine methyl ester hydrochloride salt) mp 123.8 to 124.8 ° C. Elemental analysis (%) as _{C 22 H 23 N 2 O 7} C H N Found 61.58 5.70 6.53 Calculated 61.68 5.65 6.54 Example 4 14.3 g (0.1 mol) of N-formyl-L-aspartic anhydride was added to 28.6 g of acetic acid and suspended.
C., 9.2 g (0.11 mol) of sodium acetate were added thereto, and then L-phenylalanine methyl ester hydrochloride 21.6 g was added at the same temperature.
g (0.1 mol) was added. After stirring and reacting at the same temperature for 5 hours, the mixture was concentrated and 57.2 g of water was added. The precipitated crystals are filtered, washed and dried to give N-formyl-α-L.
-Crystals of aspartyl-L-phenylalanine methyl ester were obtained. Yield: 30.6 g. The obtained crystals were analyzed by high performance liquid chromatography. As a result, the ratio of α-form: β-form was 81.0: 19.0. The result was purified by a conventional method to obtain high-purity N-formyl-α-L
-Crystals of asparatyl-L-phenylalanine methyl ester were obtained.

Yield: 22.3 g (Yield: 69.3% / based on L-phenylalanine methyl ester hydrochloride) Melting point: 123.5 to 124 ° C Elemental analysis (%): CH N as C ₁₅ H ₁₈ N ₂ O ₆ Actual measured value 55.85 5.69 8.6 Calculated value 55.90 5.63 8.69 Example 5 After 25.1 g (0.1 mol) of N-benzyloxycarbonyl-L-aspartic anhydride was added to 75.3 g of acetic acid and suspended, 9.2 g (0.11 mol) of sodium acetate was stirred at 20 to 25 ° C.
And then cooled to 15-20 ° C., and at the same temperature, 21.6 g (0.1 mol) of L-phenylalanine methyl ester hydrochloride
64.8 g of an acetic acid solution in which is dissolved is added, and the mixture is stirred and reacted at the same temperature for 2 hours. Then, 110.1 g of water at the same temperature in the reaction solution
After cooling to 0 to 5 ° C., the precipitated crystals were filtered,
The crystals of N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester were obtained by washing and drying.

Yield: 29.5 g (68.9% yield / based on L-phenylalanine methyl ester hydrochloride) Melting point: 123.8 to 124.9 ° C. Example 6 L-phenylalanine methyl ester sulfate, 22.7 g (0.1%) instead of L-phenylalanine methyl ester hydrochloride
Mol) and increasing the amount of sodium acetate to 17.6 g (0.21 mol) in the same manner as in Example 1 to obtain crystals of N-trifluoroacetyl-α-L-aspartyl-L-phenylalanine methyl ester.

Yield: 31.1 g (yield: 79.9% / based on L-phenylalanine methyl ester hydrochloride) Melting point: 150 to 151 ° C. Example 7 To 100.4 g of acetic acid was added 25.1 g (0.1 mol) of N-benzyloxycarbonyl-L-aspartic anhydride. After the suspension, 21.6 g (0.1 mol) of L-phenylalanine methyl ester hydrochloride was added at 10 to 15 ° C. Then, at the same temperature, 9.2 g (0.11 mol) of sodium acetate was added over a period of 30 minutes, and the mixture was stirred and reacted at the same temperature for 3 hours. Then add 75.3 g of water
After cooling to 5 ° C., the precipitated crystals were filtered, washed and dried to obtain crystals of N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester.

Yield 30.0 g (Yield 70.1% / based on L-phenylalanine methyl ester hydrochloride) Melting point 123-124 ° C. Example 8 To 100.4 g of acetic acid was added 25.1 g (0.1 mol) of N-benzyloxycarbonyl-L-aspartic anhydride. After suspending, 27.7 g (0.1 mol) of sulfate of L-phenylalanine methyl ester was added at 10 to 15 ° C. Further, at the same temperature, 11.1 g (0.105 mol) of sodium carbonate was added. After reacting for 4 hours with stirring, 75.3 g of water was added, and the reaction solution was cooled to 0 to 5 ° C. The precipitated crystals were filtered, washed and dried to obtain crystals of N-benzyloxycarbonyl-α-L-aspartyl-L-phenylalanine methyl ester. Yield 29.9g
(Yield 69.9% / l-phenylalanine methyl ester sulfate) Melting point 123-124 ° C Example 9 Same as Example 8 except that 11.1 g (0.105 mol) of sodium carbonate was replaced by 4.8 g (0.12 mol) of magnesium oxide. went.

Yield: 26.0 g (yield: 60.7% / l-phenylalanine methyl ester sulfate) Melting point: 123.5 to 124.5 ° C Example 10: 9.2 g (0.11 mol) of sodium acetate was added to sodium formate 7.
The same operation as in Example 7 was carried out except that the amount was changed to 5 g (0.11 mol).

Yield 28.5 (Yield 66.6% / vs. L-fenlualanine methyl ester hydrochloride)

Claims (1)

(57) [Claims] (1) N-protected L-aspartic anhydride and L
-A mineral acid salt of phenylalanine methyl ester in an organic carboxylic acid, an alkali metal, an alkaline earth metal, or a hydroxide, oxide, carbonate, bicarbonate of these metals,
Or N-protected-α-L-aspartyl characterized by adding an organic carboxylate, ammonium carbonate, or ammonium ammonium carboxylate to a mineral salt of L-phenylalanine methyl ester in an equimolar amount or more and reacting it. -A method for producing L-phenylalanine methyl ester.