JPH0615518B2 - How to make protected amino acids - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing a protected amino acid. More specifically, it relates to a method for producing a protected amino acid useful as a synthetic intermediate for peptides or antibiotics.

[Prior art]

When synthesizing peptides using amino acids, a method of preliminarily reacting the starting amino acid with an amino group-protecting agent to protect the amino group is often adopted. Examples of the amino group protecting agent include tert-butyl-4,6-dimethoxy-s-
Triazyl-2-thiol carbonate (JP-A-54-
160390), 2- (4-methoxybenzyloxycarbonylthio) -4,6-dimethoxy-1,3,5-triazine (JP-A-60-109576) and the like are known. On the other hand, Japanese Patent Publication No. 51-18942 discloses the following general formula which is an amino group protecting agent. (In the formula, R ₁ and R ₂ represent hydrogen or a methyl group, and R ₃ represents hydrogen or a methoxy group) and an aralkyl 4 and / or 6-methyl-substituted or unsubstituted pyrimidyl-2-thiol carbonate and an amine. The following general formula (Wherein R ₃ has the same meaning as defined above, Z is a group formed by removing a hydrogen atom from nitrogen of amines), and a method for producing alkyloxycarbonylamines is described.

Usually, the reaction between an amino acid and an amino group-protecting agent is carried out in the presence of caustic alkali in an aqueous medium because it is necessary to dissolve the amino acid, but generally the reaction rate is slow and the amino group during the reaction is In addition to the decomposition of the protective agent,
The produced protected amino acid also tends to decompose, and it is difficult to obtain the protected amino acid in high yield. On the other hand, when a mixed solvent of water and a water-soluble organic solvent such as dioxane, tetrahydrofuran, N, N-dimethylformamide, methanol ethanol, and t-butanol is used as the solvent, the reaction rate is high, and Since the decomposition of the amino group protecting agent is small, the protected amino acid can be obtained in a relatively high yield. However, in this case, it takes time and effort to recover the organic solvent from the mixture after completion of the reaction, and it is hard to say that the yield is still sufficient.

[Problems to be solved by the invention]

The present invention comprises reacting an amino acid of the general formula [I] shown above with an amino group-protecting agent of the general formula [II] shown above,
In the production of the protected amino acid of I], the reaction proceeds favorably, and the produced protected amino acid is hardly decomposed, and an industrially advantageous production method is obtained in which the target compound can be obtained in a high yield.

[Means for solving problems]

The gist of the present invention is to provide an amino acid represented by the following general formula [I] R ¹ NH ₂ ... [I] (wherein R ¹ represents a residue obtained by removing one amino group from an amino acid) and the following general formula [II] (In the formula, A is a substituent R ² and R ⁴ represent a hydrogen atom or a lower alkyl group, and R ³ represents a lower alkyl group or a phenyl group which may be substituted at the para-position with a lower alkoxy group, a lower alkyl group or a nitro group. However, in the substituent A, X ^{1 to} X ⁴
Is a hydrogen atom, a lower alkyl group or a lower alkoxy group) and is reacted with an amino group protecting agent represented by the following general formula [III] in the presence of a caustic alkali in an aqueous medium. In the method for producing a protected amino acid represented by the formula (wherein R ^{1 to} R ⁴ have the same meaning as in the general formula shown above), the reaction is carried out while maintaining the pH in the reaction system within the range of 10 to 13. It exists in the manufacturing method of the protected amino acid characterized by the above.

Hereinafter, the present invention will be described in detail.

The reaction between the amino acid represented by the above general formula [I] and the amino group protecting agent represented by the above general formula [II] proceeds according to the following reaction formula.

The amino acid of the above-mentioned general formula [I] which is the object of the present invention is not particularly limited and various amino acids can be mentioned, for example, glycine, alanine, valine, norvaline, leucine, norleucine, isoleucine, Neutral amino acids such as phenylalanine, tyrosine, jodhtyrosine, thrinamine, threonine, serine, proline, hydroxyproline, tryptophan, thyroxine, methionine, cystine, cystine, α-aminobutyric acid,
Acidic amino acids such as aspartic acid, glutamic acid, asparagine, glutamine, lysine, hydroxylysine,
Examples include basic amino acids such as arginine and histidine.

On the other hand, the amino group protecting agent is not particularly limited as long as it satisfies the general formula [II] shown above, and for example, p-methoxybenzyloxylcarbonyl-4,6-
Dimethyl-2-mercaptopyrimidine, p-ethylbenzyloxycarbonyl-4,6-dimethyl-2-mercaptopyrimidine, p-nitrobenzyloxycarbonyl-
4,6-Dimethyl-2-mercaptopyrimidine, benzyloxycarbonyl-4,6-dimethyl-2-mercaptopyrimidine, t-butyloxycarbonyl-4,6-dimethyl-2-mercaptopyridine, t-butyloxycarbonyl-4 , 6-ditomex-2-mercapto-1,3,5, -triazine and the like. The amount of these amino group protecting agents used is 0.8 to 1.3 mole times, preferably 0.9 to 1.2 mole times, relative to the amino group of the amino acid.

In the present invention, the above-mentioned amino acid and amino group protecting agent are reacted in the presence of caustic alkali in an aqueous medium. As the caustic alkali, caustic soda or caustic potash is usually used. As the aqueous medium, substantially a single solvent of water or a mixed solvent of water and a water-soluble organic solvent is used. Examples of the organic solvent used in the case of the mixed solvent include dioxane, tetrahydrofuran, methanol,
Ethanol, isopropanol, t-butanol, N, N
-Dimethylformamide and the like can be mentioned, and the usage ratio thereof with respect to water is usually 0.1 to 3 times by weight. In addition, the amount of the aqueous medium used is usually 4 to 20 times by weight the amount of the amino acid of the general formula [I] shown above.

In the present invention, it is an essential requirement to carry out the reaction while maintaining the pH in the reaction system within the range of 10 to 13, preferably 10.5 to 12.5. When the reaction between the amino acid of the general formula shown above and the amino group-protecting agent is carried out in the presence of caustic, A-SH is by-produced as the reaction progresses, so the pH in the reaction system gradually decreases. However, the present invention is characterized in that the reaction is allowed to proceed while maintaining the pH within the above specified range. If the pH during the reaction becomes higher than the above range, the amount of free caustic will increase, resulting in the decomposition of the amino group protecting agent and the protected amino acid generated in the reaction, and conversely, lowering than the above range. In such a case, the production rate of the protected amino acid is extremely reduced, and the amino group protecting agent is decomposed during this period, so that the desired protected amino acid cannot be obtained in a high yield.

Therefore, in order to carry out the reaction of the present invention, the amino acid and the amino group-protecting agent are usually charged in an aqueous medium, and the reaction proceeds while adding caustic alkali so that the pH in the system becomes a desired value. Alternatively, the amino acid is charged in an aqueous medium, and a caustic alkali is added dropwise to the system so that the pH of the system becomes a desired value, and an amino group protecting agent is supplied to allow the reaction to proceed.

The reaction temperature of the present invention is usually 10 to 40 ° C., preferably 1
The reaction time is usually about 2 to 10 hours.

After the reaction, the mixture is usually acidified and then extracted with an organic solvent such as ethyl acetate to extract the protected amino acid in the organic phase, and then the organic solvent is distilled off from the organic phase to remove the protected amino acid. Can be isolated.

〔Example〕

Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

Example 1 131.1 g (1 mol) of L-leucine as an amino acid was placed in a 2 glass reactor equipped with a stirrer, a pH meter and a temperature controller.
And 940 g of water were added, and 160 g of a 25% aqueous sodium hydroxide solution (1 mol as NaOH) was added to the mixture to adjust the pH of the system to 1
After setting to 2, t-butyloxycarbonyl-4,6-dimethyl- as an amino group protecting agent at a temperature of 20 ° C. under stirring.
2-Mercaptopyrimidine (hereinafter abbreviated as BOCS) 264.4
g (1.1 mol) was mixed over 5 minutes, and then,
The reaction was carried out by continuing stirring for 5 hours. During this reaction, the pH in the reaction system was maintained between 11.8 and 12.2 by dropping a 15% aqueous sodium hydroxide solution. In addition,
The amount of caustic soda used for this pH adjustment was 1.1 mol as NaOH.

After completion of the reaction, the mixture was analyzed by high performance liquid chromatography to determine the yield of the protected amino acid as the target product (relative to amino acid). The results shown in Table 1 were obtained.

Comparative Example 1 Table 1 shows the results of the case where the caustic soda used for pH adjustment was all present in the reaction system at the initial stage of the reaction in Example 1 and the same reaction was carried out.

The pH of the reaction system at this time is from 13.8 (at the start of the reaction) to 9
(At the end of the reaction).

Comparative Examples 2 to 3 Table 1 shows the results when the same reaction was carried out by adjusting the pH in the reaction system to the value shown in Table 1 in Example 1.

Example 2 Table 2 shows the results of the same reaction as in Example 1 except that a mixture of 550 g of dioxane and 390 g of water was used as the solvent instead of 940 g of water.

Comparative Examples 4 to 5 Table 2 shows the results obtained when the pH in the reaction system was adjusted to the values shown in Table 2 and the same reaction was performed in Example 2.

Examples 3 to 4 and Comparative Examples 6 to 7 Reactions were performed in the same manner as in Example 1 except that the amino acid and amino group protecting agent shown in Table 3 were used and the pH of the reaction system was adjusted to the values shown in Table 3. Table 3 shows the results of the above.

Examples 5 to 6 and Comparative Examples 8 to 9 The reaction was performed in the same manner as in Example 2 except that the pH of the reaction system was adjusted to the values shown in Table 3 by using the amino acids shown in Table 4 and the amino group protecting agent. Table 4 shows the results of the tests performed.

[Effects of the Invention] According to the present invention, when a protected amino acid is produced by reacting an amino acid with a specific amino group-protecting agent, by keeping the pH in the reaction system within a specific range, water alone as a solvent In particular, the yield is remarkably improved as compared with the case where pH is not adjusted, and the target product can be obtained in high yield. Further, even when a mixed solvent of a water-soluble organic solvent and water is used, the yield can be further increased.

Claims (3)

[Claims] 1. An amino acid represented by the following general formula [I] R ¹ NH ₂ ... [I] (wherein R ¹ represents a residue obtained by removing one amino group from an amino acid) and the following general formula [I II) (In the formula, A is a substituent R ² and R ⁴ represent a hydrogen atom or a lower alkyl group, and R ³ represents a lower alkyl group or a phenyl group which may be substituted at the para-position with a lower alkoxy group, a lower alkyl group or a nitro group. However, in the substituent A, X ^{1 to} X ⁴
Is a hydrogen atom, a lower alkyl group or a lower alkoxy group) and is reacted with an amino group protecting agent represented by the following general formula [III] in the presence of a caustic alkali in an aqueous medium. In the method for producing a protected amino acid represented by the formula (wherein R ^{1 to} R ⁴ have the same meaning as in the general formula shown above), the reaction is carried out while maintaining the pH in the reaction system within the range of 10 to 13. A method for producing a protected amino acid, which is characterized in that 2. The method according to claim 1, wherein the reaction temperature is 10 to 40 ° C. 3. The method according to claim 1, wherein the amount of the amino group-protecting agent used is 0.8 to 1.3 mol times that of the amino group of the amino acid.