JPS6138183B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is based on the formula () (In the formula, R ₁ is a hydrogen atom, a hydroxyl group or a lower alkylcarbonyloxy group, and R ₂ is a lower alkyl.) 2-acetoxy-4-aryl-3 represented by
-Relating to oxobutanoic acid derivatives and their production methods. Previously, Umezawa et al. cultivated bestatin-producing bacteria belonging to actinomycetes, and from the culture obtained bestatin [(2S,3R)--, which has a strong inhibitory effect on aminopeptidase B, leucine aminopeptidase, and bleomycin hydrolase. 3-amino-2
-Hydroxy-4-phenylbutanoyl-S-leucine]
(See Publication No. 7187). This bestatin is (2S,3R)-3-amino-
2-Hydroxy-4-phenylbutanoic acid () It is also known that it can be synthetically produced by reacting L-leucine with It is disclosed that analogous compounds are prepared in a similar manner. The present inventors have focused on the excellent physiological activity of bestatin, and are interested in the production of bestatin and its related compounds, especially derivatives having a hydroxyl group at the para-position on the phenyl nucleus of bestatin, by a synthetic method. 3-amino-2-hydroxy-4-phenylbutanoic acid (hereinafter referred to as "AHPA") and 3-amino-2-hydroxy-4-p-hydroxyphenylbutanoic acid (hereinafter referred to as "p-hydroxyAHPA"). ), various simple synthesis methods were investigated. Currently, the following steps are known to synthesize AHPA and nuclear-substituted AHPA. However, this method requires the use of an extremely toxic cyanide compound in the process of obtaining () from compound (), and in the actual reaction, high yields cannot be obtained unless the amino group is protected and the reaction is carried out. It has drawbacks such as not being as expected. Therefore, as a result of intensive research into a new manufacturing method that does not have these drawbacks, the inventors found that the general formula () When a derivative of 4-aryl-3-oxobutanoic acid represented by the formula (wherein R ₁ and R ₂ have the same meanings as above) is reacted with a metal acetate used as an acetoxylation reagent, it is possible to easily and with high yield. 2-acetoxy-4-aryl-3-oxobutanoic acid derivative represented by the above formula () is obtained at a certain rate, and () is reductively aminated,
When hydrolyzed with acid or alkali, it is useful as a raw material for the synthesis of bestatin and its derivatives.
We found that AHPA and nuclear substitution AHPA can be obtained. The present invention was completed based on the above findings. Next, the method of the present invention will be described in more detail. The method of the present invention can be shown by the following reaction formula. (In the formula, R ₁ and R ₂ have the same meanings as above.) That is, the present invention provides 4-
It is carried out by acetoxylating a derivative of aryl-3-oxobutanoic acid. The acetoxylation reagent used in this method may be any well-known acetoxylation agent that can acetoxylate active methylene, and metal acetate salts such as lead tetraacetate, mercury acetate, and thallium acetate are usually used to obtain the target compound in high yield. can get.
When lead tetraacetate is used, it is usually used in an amount of about 1 to 1.2 moles per mole of raw material. Further, the solvent used in the acetoxylation may be any solvent as long as it does not cause an undesirable side reaction with the reagent used, and benzene acetic acid is a typical example thereof. The reaction temperature can be arbitrarily selected within the range of 0 to 100°C, but room temperature is optimal. The reaction time varies depending on the reaction temperature, but at room temperature it takes 3~
6 hours is sufficient. There is no need to use any special method to separate and purify the target substance from the reaction mixture after the completion of the reaction, and this can be easily achieved by well-known means commonly used for such purposes. In formula (), the lower alkylcarbonyloxy group may be any hydroxyl group depending on the field of hydration, such as an acetyloxy group, an ethylcarbonyloxy group, and the like. The lower alkyl group _R2 , which is a protecting group for a carboxyl group, is a group necessary to stably exist a β-keto acid whose free acid is unstable, and is suitable for the purpose and has no inconvenience with the reagent used. Any group that does not cause any reaction may be used, such as methyl, ethyl, propyl, butyl groups, etc. Preferred from a practical standpoint are lower alkyl groups such as methyl and ethyl groups. The alkyl group and phenyl group in these protecting groups may have a substituent that does not inhibit their function as a protecting group. Representative examples of the compounds of the present invention are as follows. 2-acetoxy-3-oxo-4-phenylbutanoic acid methyl ester 2-acetoxy-3-oxo-4 phenylbutanoic acid ethyl ester 2-acetoxy-4-p-hydroxyphenyl-3-oxobutanoic acid methyl ester 2-acetoxy-4 -p-Acetetoxyphenyl-3-oxobutanoic acid methyl ester The novel 2-acetoxy-4-aryl-3-oxobutanoic acid derivatives produced by the method of the present invention are subjected to reductive amination followed by acid or By subjecting it to hydrolysis with alkali, it can be easily
Leading to AHPA and p-hydroxyAHPA.
This can be shown using the reaction formula as follows. (In the formula, R ₁ and R ₂ have the same meanings as above. R ₁ ' represents a hydrogen atom or a hydroxyl group.) The reductive amination reaction used in this reaction is a well-known ammonia/catalytic reduction method, Any method such as the ammonia/metal hydride reducing agent method is applicable and provides the target compound in good yield. Further, the acid or alkali used for hydrolysis may be any acid or alkali that is commonly used for hydrolysis of esters, and the type thereof is not particularly limited. Regarding the reaction time, when an aqueous solution having a concentration of about 5 to 7 normal is used, heating under reflux for about 1 hour is sufficient. To isolate the target AHPA and p-hydroxyAHPA from the reaction mixture, conventional methods used for isolating amino acids may be applied. That is, when a volatile acid such as hydrochloric acid is used for hydrolysis, the excess acid is distilled off under reduced pressure, water is added, the target substance is adsorbed through a strongly acidic ion exchange resin, and ammonia water is The solution is eluted with a volatile alkali, concentrated under reduced pressure, and if necessary, acetone or a hydrophilic organic solvent such as methanol or ethanol is added to collect the precipitated crystals. Instead of treatment with an ion exchange resin, a method may be used in which water is added, then neutralized with an alkali until the isoelectric point is reached, and if necessary, treated with a hydrophilic solvent. When a non-volatile acid such as sulfuric acid is used, it is diluted with water to a concentration of 1N or less, and then treated with a strongly acidic ion exchange resin in the same manner as in the case of a volatile acid. When an alkali such as caustic soda is used, a concentrated acid is added to make it strongly acidic, and the same treatment method as above is used thereafter. AHPA and p-hydroxy obtained above
Since AHPA is a mixture of erythro and threo bodies, if we sequentially perform operations such as separating the erythro body and threo body, inverting the erythro body to the threo body, and optically splitting the threo body (2S, 3R). )-AHPA
and (2S,3R)-p-hydroxyAHPA can be obtained. Compounds of the general formula (), which are raw materials for carrying out the production method of the present invention, include new compounds, but all of them can be prepared by the method described in Journal of Organic Chemistry, Vol. 43 (1978), p. 2087 to p. It is produced by reacting the aryl acetic acid chloride represented by ) with Meldrum's acid () to form acylated Meldrum's acid (), and then alcoholysing this. This can be shown using the reaction formula as follows. (In the formula, R ₁ and R ₂ have the same meanings as above.) The acylation reaction is carried out using an organic base such as pyridine in the presence of an organic solvent. Room temperature is sufficient for the reaction temperature. The next step, alcoholysis, can be carried out by refluxing for about 2 hours at the boiling point of the alcohol used, and in this way the target 4-aryl-3
-Oxobutanoic acid derivative () is obtained in high yield. As described above, the method of the present invention can easily produce AHPA and p- This method paved the way for the synthesis of hydroxyAHPA, and is an extremely superior method compared to conventional methods. The present invention will be specifically explained below with reference to Examples and Reference Examples. Example 1 Synthesis of 2-acetoxy-3-oxo-4-phenylbutanoic acid methyl ester 2 g of 3-oxo-4-phenyl butanoic acid methyl ester was dissolved in 20 ml of benzene, 5 g of lead tetraacetate was slowly added thereto, and the mixture was heated to room temperature. Stir for 3 hours. After the reaction was completed, the reaction solution was washed successively with water and saturated brine, and the organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure to give 2.7 g of a pale yellow oily substance.
get. Add this to 50g of silica gel [Merck]
(MERCK) Kieselgel 60] column chromatography, eluted with benzene-ethyl acetate (10:1), and when the solvent was distilled off, a pale yellow oily substance 2.3
get g. Yield 88% Elemental analysis value (as C ₁₃ H ₁₄ O ₅ ) Theoretical value C: 62.39% H: 5.64% Experimental value C: 62.66% H: 5.50% IRν ^film _nax 1750, 1730, 1600, 1500, 710cm ^-
1 NMR (CDCI ₃ ) δ: 2.20 (3H, s,

【formula】 3.93(2H,s,

【formula】) 5.57 (1H, s,

[Formula]) Example 2 Synthesis of 2-acetoxy-3-oxo-4-phenylbutanoic acid ethyl ester Same as Example 1 using 1 g of 3-oxo-4-phenylbutanoic acid ethyl ester, 2.5 g of lead tetraacetate, and 10 ml of benzene. After reaction and work-up, 1.1 g of pale yellow oil is obtained. Yield 85% Elemental analysis value (as C ₁₄ H ₁₆ O ₅ ) Theoretical value C: 63.62% H: 6.10% Experimental value C: 63.90% H: 5.92% IRν ^film _nax 1750, 1730, 1600, 1495, 705cm ^-
1 NMR (CDC1 ₃ ) δ: 2.17 (3H, s,

【formula】) 3.97(2H,s,

【formula】) 5.57 (1H, s,

[Formula]) Example 3 Synthesis of 2-acetoxy-4-p-acetoxyphenyl-3-oxobutanoic acid methyl ester 1 g of 4-p-acetoxyphenyl-3-oxobutanoic acid methyl ester, 2.5 g of lead tetraacetate, benzene Using 10 ml, the reaction and post-treatment were carried out in the same manner as in Example 1 to obtain 975 mg of a pale yellow oily substance.
Yield 79% Elemental analysis value (as C ₁₅ H ₁₆ O ₇ ) Theoretical value C: 58.44% H: 5.23% Experimental value C: 58.30% H: 5.47% IRν ^film _nax 1760, 1750, 1740, 1725,
1600, 1505, 915cm ^-1 NMR (CDC1 ₃ ) δ: 2.20 (3H, s,

[Formula]) 2.30 (3H, s,

[Formula]) 3.93 (2H, s,

【formula】) 5.58 (1H, s,

[Formula]) Reference Example 1 Synthesis of 4-p-acetoxyphenyl-3-oxobutanoic acid methyl ester Meldrum acid (2,2-dimethyl-1,3-dioxane-4,6-dione) 4.1 g and pyridine 5
A solution of 6 g of p-acetoxyphenyl acetic acid chloride dissolved in 10 ml of methylene chloride was added under ice cooling, and 1
The reaction is then allowed to proceed for 1 hour at room temperature. After the reaction is complete, pour the dark brown reaction solution into ice water and acidify with concentrated hydrochloric acid. The organic layer is washed successively with water and saturated brine, dried over anhydrous sodium sulfate, and concentrated under reduced pressure to obtain dark brown crystals of crude acylated Meldrum's acid. This is then converted into methanol30 without purification.
ml and heated under reflux for 2 hours. After the reaction, the mixture was concentrated under reduced pressure to obtain 8 g of a dark brown oil. This was subjected to column chromatography using 25 g of silica gel, eluted with benzene-ethyl acetate (10:1), and the solvent was distilled off to obtain 3.9 g of a colorless oil. Yield 55% Elemental analysis value (as C ₁₃ H ₁₄ O ₅ ) Theoretical value C: 62.39% H: 5.64% Experimental value C: 62.70% H: 5.48% IRν ^film _nax
1760, 1750, 1720, 1590, 1510, ^{915 cm -1} NMR (CDC1 ₃ ) δ: 2.28 (3H, s,

[Formula]) 3.45 (2H, s,

[Formula]) 3.80 (2H, s,

[Formula]) Reference Example 2 Synthesis of AHPA A solution of 1 g of 2-acetoxy-3-oxo-phenylbutanoic acid methyl ester, 504 mg of sodium cyanoborohydride, and 1.96 g of ammonium bromide in 5 ml of methanol is stirred at room temperature for 48 hours. . After the reaction, 3 ml of concentrated hydrochloric acid was added and stirred at room temperature for 1 hour. Methanol is distilled off under reduced pressure, and the remaining liquid is
Add 3 ml of 6N hydrochloric acid and heat under reflux for 1 hour. After the reaction was completed, the reaction solution was concentrated under reduced pressure, and 5 ml of water was added.
Strong acidic ion exchange resin DOWEX 50 (H type)
The target substance is adsorbed through a column filled with 20 ml.
After washing with water, elute with 2N ammonia water, and concentrate the eluate under reduced pressure to dryness to obtain 310 mg of crystals. Yield 40
%. Thin layer chromatography of the obtained crystals
(TLC) Rf value and high performance liquid chromatography (HPLC) Rt value are standard [Journal of
Medicinal Chemistry 20 510 (1977)]. The crystals obtained by HPLC were a mixture of erythro and threo forms. Reference Example 3 Synthesis of p-hydroxyAHPA Using 600 mg of 2-acetoxy-4-p-acetoxyphenyl-3-oxobutanoic acid methyl ester, 245 mg of sodium cyanoborohydride, 955 mg of ammonium bromide, and 5 ml of methanol, Reference Example 2
Perform the reaction and post-treatment in the same manner as above to obtain 135 mg of amorphous powder. Yield 33%. The TLC Rf value and HPLC Rt value of the obtained amorphous powder completely matched those of the standard product. The powder obtained by HPLC was a mixture of erythro and threo forms.

Claims (1)

[Claims] 1 formula (In the formula, R ₁ is a hydrogen atom, a hydroxyl group or a lower alkylcarbonyloxy group, and R ₂ is a lower alkyl group.) 2-acetoxy-4-aryl-3-oxobutanoic acid derivatives. 2 General formula (In the formula, R ₁ is a hydrogen atom, a hydroxyl group, or a lower alkylcarbonyloxy group, and R ₂ is a lower alkyl group.) A derivative of 4-aryl-3-oxobutanoic acid represented by the formula is used as an acetoxylation reagent. The active methylene group at the α-position is acetoxylated by reacting with acetic acid metal salt. formula A method for producing a 2-acetoxy-5-aryl-3-oxobutanoic acid derivative represented by the formula (wherein R ₁ and R ₂ have the same meanings as above).