KR860001047B1 - Process for the preparation of aspartyl-phenylalanine methyl ester - Google Patents

Abstract

Methylester of dipeptide, Asp-Phe, was prepd. by reacting Asp -Phe with pentaformaldehyde in an anhydro aprotic solvent in the presence of an acidic catalyst. Thus, 5g Asp-Phe was reacted with 0.6g p- formaldehyde in 47 ml anhyd. ethylacetate at 45≰C for 6 hr, and cooled to room temp. This reaction mixt. was treated with methanolic HCl. This resulting material was dissolved in ethylacetate-NaOH soln. and the organic layer was extd. with H2O to give 62.9% .-L-aspartyl- L-phenylalanine methyl ester.

Description

Method for preparing asphaltene-phenylalanine methyl ester

The present invention relates to a new industrial production method of methyl ester of α-L-asphatyl-L-phenylalanine represented by the following structural formula (1).

Α-L-Asphaltyl-L-phenylalaninemethyl ester of the above structure is a sweetener having a sweetness corresponding to 160-200 times the sugar of general name is called aspaltam as Korean Patent Publication No. 79-216, US Patent 3492131, By 3901871,3933781,4173562 the synthesis method is already known.

According to Korean Patent Publication No. 79-216 of the conventional synthetic method, L-asphatylic acid is reacted with phosphorus trichloride and acetic anhydride to prepare L-asphatylic anhydride hydrochloride by a general synthetic method, By reacting L-phenylalanine methyl ester to prepare α-L-asphaltyl-L-phenylalanine methyl ester, and dipeptide ester containing water and 1-5 carbon atoms for the purpose of removing impurities contained therein. Dipeptide esters were separated by distribution between alkanols. However, this method is a by-product of various impurities such as β-dipeptide esters, tripeptipiperopiferazil, and free asphatylic acid. The method of separation is complex and involves many difficulties in industrial implementation.

In addition, US Pat. Nos. 393781 and 4173562 disclose N-formyl-L-asphatyl-L-phenylalanine (IV) by reacting L-phenylalanine (III) with N-formyl-L-asphaltonic anhydride (II). Α-L-asfaltyl-L-phenylalanine (V) was prepared by removing N-formyl group from hydrochloric acid.

Only the carboxyl group in the produced phenylalanine group of the general formula (V) is esterified to prepare a compound of the general formula (1).

However, α-L-asphatyl-L-phenylalanine (V) has two carboxyl groups in the aspartic acid group and the phenylalanine group, and is esterified without protecting the carboxyl group in the aspartic acid group. Many reactive substances, including unreacted substances, are produced, and it is difficult to separate only monoesters from these various composite materials.

The present invention, which improves this disadvantage, is to selectively protect only the carboxyl group in the asphaltene acid group in the esterification of α-L-asphatyl-L-phenylalanine (V) to prepare the target compound of general formula (I), and then phenylalanine. It is a convenient and industrial method that improves the conventional esterification reaction of α-L-asphaltyl-L-phenylalanine (V) by esterifying only the carboxyl group in the group and removing the protecting group to prepare the substance of formula (1). It provides a practical method that can be implemented.

When the present invention is represented by the chemical formula is as follows.

The α-L-asfaltyl-L-phenylalanine, which is a general formula (V) used as a starting material for carrying out the present invention, has already been known in the above-mentioned US Patent No. It can be made as a starting material.

The present invention will be described in more detail by reacting α-L-asphatyl-L-phenylalanine (V) prepared by known methods with paraformaldehyde under an acid catalyst such as acetyl chloride, acetic anhydride or P-toluenesulfonic acid chloride. Ring 6 ring of the lactone ring through the intermediate (V ') compound to produce the general formula (VI). As the solvent for forming the lactone ring, anhydrous aprotic solvents such as topruel, benzel, 1,2-dichloroethane and dioxane are used, and the amount of paraformaldehyde is calculated as the amount of formaldehyde, and α-L-asphaltyl is used. It is suitable to use 1.0-1.2 moles per mole of -L-phenylalanine. At this time, the reaction intermediate (V ′) compound may form a Schiff base by dehydration, thus protecting the amino group and forming a lactone ring to prepare an amino group-protected lactone ring chemical, as in the present invention. When the produced lactone ring is 6 rings, the lactone ring is very stable, and thus the compound can be prepared without protecting the amino group.

In addition, when the amino group is protected, a large decrease in yield occurs in the step of removing the protecting group. Formula (VII) of the reaction-produced lactone ring was reacted with methyl alcohol in HCL acid or diazomethane in an aprotic solvent to selectively esterify only carboxyl groups of the phenylalanine group to prepare a compound of formula (VII). do.

At this time, since the lactone ring of the general formula is stable in acidity, no diester is produced by the ring-opening of the lactone ring, and only the carboxyl group of the phenylalanine group can be esterified.

Alkyl solution and acid treatment in general formula (IV) open | release a lactone ring and a protecting group is removed simultaneously, and the target (alpha) -L-asphathyl-L-phenylalanine methyl ester (1) is obtained in high yield. At this time, the substance of Formula (I) produced contains a small amount (within 5%) of the starting formula (VN) as an impurity. Therefore, the domestic patent notification 79-216 was revised to be used for food and medicine. Purification is carried out according to known methods using ion exchange resins.

Japanese Patent Publication No. 52-35660, US Patent No. 4309341 discloses a method for purifying General Formula (1) by basic anion exchange resin, and Japanese Patent Publication Nos. 48-67243, 47-42643 Purification by strong acid formation of c) is known, and an appropriate method may be used depending on the nature and type of the by-products produced during the production reaction.

Example 1

To 50 milliliters of anhydrous toluene were added 5.6 grams (0.02 mol) of α-L-asphatyl-L-phenylalanine, 0.7 grams of paraformaldehyde, and 1 milliliter of acetic anhydride, and stirred at 45-55 ° C. for 3 hours to form a clear solution. Cool the temperature to 20 degrees and stir for an additional hour. After the reaction, the mixture was distilled under reduced pressure to remove the solvent, followed by repeated distillation several times with 30 milliliters of toluene to remove all the acid in the reaction solution. The light yellow residue is dissolved in ethyl acetate and stirred in an ice bath at 0-5 ° C. 10 milliliters of ether containing diazomethane is added and stirred in an ice bath for 3 hours.

After the reaction was completed, the ice bath was removed to raise the temperature of the reactant to room temperature, and while stirring, the excess diazomethane was removed through dry nitrogen gas, and 50 milliliters of a 5% NaOH solution was added to the reaction solution and stirred at room temperature for 4 hours. After the reaction, an aqueous layer is taken, and the ethyl acetate layer is extracted once with 30 milliliters of water. The extract was combined with the water bath layer and the contents were made acidic with strong hydrochloric acid while stirring in an ice bath at 0-5 ° C. After stirring for 1 hour, white crystals were precipitated by adjusting the liquidity to neutral with aqueous NaOH solution. After filtration, washed with cold water and dried to obtain 3.4 grams (57.6%) of α-L-asphatyl-L-phenylalanine methyl ester, and the filtrate was concentrated under reduced pressure until it became 30 milliliters and 1.3 grams (22.0%) when standing in an ice bath. Get more.

Melting Point: 244-248 °

Example 2

To 47 milliliters of anhydrous ethyl acetate, 5 grams (0.018 mol) of α-L-asphatyl-L-phenylalanine, 1.3 milliliters of acetyl chloride, and 0.6 grams of paraformaldehyde were added thereto, stirred at 45 ° C for 6 hours, cooled to room temperature, and stirring continued. While a small amount of 14 ml of 10% methanolic hydrochloric acid was added dropwise, and after the addition was completed, the reaction solution was raised to 40 degrees, continued stirring for 4 hours at constant temperature, and the reaction solution was distilled under reduced pressure. The residue was dissolved in a mixed solution of ethyl acetate-5% NaOH (50 milliliters; 50 milliliters), stirred at room temperature for 4 hours, and then operated in Example 1). The same α-L-Asphaltyl-L as in Example 1) was performed. -3.3 grams of phenylalanine methyl esters (yield: 62.9%) were obtained.

Example 3

5 grams of α-L-asphatyl-L-phenylalanine methyl ester prepared above were dissolved in a mixed solvent of 300 milliliters of water and 100 milliliters of methanol and passed through a column filled with 20 grams of basic anion exchange resin.

The solution passed through the ion exchange resin is combined and the solvent is distilled off under reduced pressure. The residue is recrystallized from a mixed solvent of isopropyl alcohol and water to obtain 3.8 grams of pure α-L-asphatyl-L-phenylalanine methyl ester.

Melting Point: 245-247 °

Elemental Analysis (C ₁₄ H ₁₈ N ₁₂ O ₅ )

Theoretic Value: C57.14%, H6.12%, N: 9.52%

Found: C: 56.88%, H: 6.21%, N: 9.68%

Claims (5)

Next, a compound of formula (VI) having a lactone ring formed by reacting α-L-asphatyl-L-phenylalanine of general formula (V) with paraformaldehyde and methyl esterified with only carboxyl groups in the phenylalanine group A method of preparing α-L-asphatyl-L-phenylalamine methyl ester of the general formula (1) by preparing a formula (VII), then ring opening and removing a protecting group of a lactone ring.

The reaction of the compound of formula (V) and paraformaldehyde in the preparation of the formula (VI) of the lactone ring in the presence of an acid catalyst such as acetyl chloride, acetic anhydride, P-toluenesulfonic acid chloride Reaction using an aprotic solvent. The process of claim 1 wherein the esterification reaction uses methyl alcohol in HCl acid. The process of claim 1 wherein the esterification reaction uses diazomethane in a mousse protic solvent. The method of claim 1 wherein the protecting group is removed in an alkaline solution.