CS277132B6 - Process for preparing cyclo (L-alanyl-1-amino-1-cyclopentanecarbonyl) - Google Patents

Abstract

A method for producing cyclo(L-alanyl-1-amino-1- -cyclopentanecarbonyl) of formula I from benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentanecarboxylic acid ester of general formula II, where R represents methyl or ethyl, by catalytic hydrogenolytic cleavage of the benzyloxycarbonyl group and subsequent cyclization. The process is characterized primarily by the use of pressure catalytic hydrogenolysis with optimal hydrogen pressures of up to 2 MPa using a Pd-on-carbon catalyst, when a high concentration of the starting raw material II is used in an organic solvent, preferably methanol, in the form of an evaporating residue dissolved to a concentration of up to 60% by weight. After removal of the catalyst, cyclization is carried out at laboratory or elevated temperatures for several hours to days.

Description

The invention relates to a process for the preparation of cyclo (L-alanyl-1-amino-1-cyclopentanecarbonyl) of formula I

^ch ₃ known substances, another name is 8 (S) -methyl-6,9-diazaspiro [4,5] decane-7,10-dione or Alaptide. The substance and its therapeutic use is protected in the Czechoslovak Socialist Republic and abroad (ČS 231 227; 231 231; 260 899; EP 268 868-A ;, ČS 276 270).

Alaptide significantly stimulates the growth of healthy human diploid cells. This property can be successfully used wherever the regeneration of damaged cells and tissues is involved, ie as a remedy for burns, skin lesions, gastrointestinal diseases, memory disorders, etc.

The compound of formula I is available by generally known methods for the preparation of cyclic dipeptides, 2,5-piperazinedione derivatives. In the final steps of the synthesis, a mixed anhydride is prepared from benzyloxycarbonyl-L-alanine and an alkyl ester, preferably methyl or ethyl chloroformate in the presence of a base such as N-ethylpiperidine, which is further reacted with 1-amino-1-cyclopentanecarboxylic acid methyl or ethyl ester. . Work-up of the reaction mixture gives benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentanecarboxylic acid ester of formula II

ch ₂ -o-co-nh-ch-co-nh- c -co-or ch ₃

(II) (R denotes methyl or ethyl), which is neither isolated nor characterized and which is further worked up in the form of a residue of the reaction mixture. Prior to the final step, i.e. cyclization, the benzyloxycarbonyl protecting group is removed and the product obtained, again in the form of an unpurified and uncharacterized residue, is cyclized under acid-base catalysis at elevated temperature, usually at the boiling point of the reaction mixture, in an inert solvent. toluene. Only the final product, the compound of formula I, is purified by crystallization and characterized by physical constants.

Experience has shown that the problematic step in concluding the synthesis of a compound of formula I is the removal of the benzyloxycarbonyl protecting group (hereinafter referred to as the Z-group). Removal is accomplished by several known methods, such as acidolysis or reduction, for example, sodium in liquid ammonia. In the synthesis of the compound of formula I, in particular acidolysis with hydrogen bromide in octo acid was used to give the dipeptide ester of formula II in the form of a salt.

The ester cyclized after deionization. The described method was time and material consuming, inefficient and unsuitable for large scale production.

More preferred methods for removing the Z-group are hydrogenolytic methods (Ber. 65, 1192, (1932), Chemistry of Amino Acids Vol. 2, J. Wiley 1961). Under palladium catalysis, the Z-group is cleaved off under the action of hydrogen in the form of toluene and carbon dioxide. The method of pressureless hydrogenolysis, in which hydrogen is bubbled through the reactor and carbon dioxide is removed in the off-gas, has been used many times in peptide chemistry (Houben-Weyl, Methoden der org. Chem. 15/1, 51 (1974); EP 27 319).

The use of pressureless hydrogenolysis to remove the Z-group from the compound of formula II is possible, but the initial concentration of this compound must be low and the reaction times are long. Under these conditions, however, cyclization to the compound of formula I is already taking place, which, however, is very slightly soluble in the reaction mixture, is precipitated and must be laboriously removed from the catalyst during isolation. Other disadvantages of pressureless hydrogenolysis are the difficult indication of reaction termination and problems with the operation and design of flow reactors.

More recently, hydrogenolytic methods using hydrogen transfer from excipients have been published for other types of peptides. Using palladium catalysts, hydrogen is obtained in situ from these substances, for example from cyclohexene, cyclohexadiene, formic acid, hydrazine, ammonium formate, etc. (J. Chem. Soc. Perk. I, 490 (1977)); J. Org. Chem. 433 4149, (1978), 44 3442 (1979); Synthesis 1978, 751, 1980, 929). However, these methods again have some disadvantages: the use of excipients and their removal from the reaction mixtures, large amounts of catalyst, low concentrations of starting materials (less than 10% by weight), difficult monitoring of the reaction (for example by chromatography).

In general, cobalt-based catalysts (DD 157 094) or cellulose-supported palladium (DD-209 196) have been used for hydrogen transfer hydrogenolysis or for pressureless Z-group reaction.

The use of higher than atmospheric hydrogen pressure, but still relatively low (up to 0.35 MPa), low starting material concentration and long reaction time, has also recently been described in the synthesis of other types of peptides (USA 4,454,065; EP 27,260).

Hydrogenolysis of N-carbobenzoxyprolyl-arginine on a palladium catalyst was monitored at hydrogen pressures of 1 MPa, at temperatures of 55 to 75 ° C and concentrations of only up to 14 mmol per liter. Reaction trvě · ¹ 'for more than 9 hours, the yield does not exceed 69%. When absolute ethanol was used as the solvent, reductive alkylation also occurred to give the N-ethyl product (Izv. Akad. Nauk Latv. SSR 1984 (2), 244).

These difficulties and disadvantages have prompted in particular the study of an unreliable method for removing the Z-group from a compound of formula II by hydrogenolysis. At the same time, the parameters of the final cyclization to the product of formula I were investigated. The findings obtained by this study made it possible to develop a substantially simplified and improved process for the preparation of Alaptide, the compound of formula I according to the invention. of a mixed anhydride formed from ZL-alanine and an alkyl ester, for example methyl or ethyl chloroformate, with methyl or ethyl 1-amino-1-cyclopentanecarboxylate, in the form of a residue containing ZL-alanyl-1-amino-1-cyclopentanecarboxylic acid ester of general formula II, dissolved in an inert organic solvent, for example methanol or ethanol, to a solution with a concentration of 10 to 60% by weight, preferably 20 to 40% by weight, which is hydrogenolyzed under a hydrogen pressure of 0.1 to 10 MPa, with preferably 0.2 to 1.5 MPa, at a temperature of 0 to 80 ° C, preferably 10 to 30 ° C, in the presence of a catalyst, for example palladium on carbon, after completion of the hydrogenolysis and removal of the catalyst The mixture is cyclized at 0 DEG to 70 DEG C. for 2 hours to 20 days, then the precipitated substance of the formula I is isolated.

In some cases, it is expedient if the reactor is degassed at least once during the hydrogenolysis and, after filling with hydrogen to the original pressure, the hydrogenolysis is continued until completion.

The process according to the invention makes it possible to work with high concentrations of the starting material of the formula II by maintaining in the reactor the predominance of the partial pressure of hydrogen over the partial pressure of the carbon dioxide formed. It can therefore be hydrogenated at high hydrogen pressures (above 2 MPa); if a suitable autoclave is not available, it is possible to operate at low pressures up to 0.6 MPa, the device being degassed at least once during the hydrogenolysis and then refilled with hydrogen. By degassing, the reaction mixture is freed of carbon dioxide. In discontinuous mode, the pressure conditions can also be controlled by the degree of autoclave filling. '

At a sufficient rate of hydrogenolysis, although a high concentration of the starting material of formula II is used, no significant cyclization to the compound of formula I occurs during the reaction, which previously greatly complicated the work before the final step. The catalyst can be easily filtered off and the hydrogenolysis product processed smoothly under the selected cyclization conditions to Alaptide. AND

The process according to the invention furthermore makes it possible to make efficient use of other suitable known conditions which relate to hydrogenolysis or hydrogenation. It is possible to start from raw materials of various qualities, of course pure raw materials are preferred, catalyst deactivation is then low. Cooling is provided for the exothermic process, it is also possible to react in a non-isothermal mode, preferably at temperatures up to 30 ° C. The amount and activity of the catalyst (in addition to temperature and pressure and other conditions) determines the reaction rate. Most preferred is palladium on carbon, in an amount of 1 to 100% by weight, based on the weight of the starting material, usually 1 to 10% by weight; for example at a palladium content of 1 to 10% by weight, on a support. The catalyst can also be formed in situ in a reaction mixture of activated carbon and palladium chloride. The catalyst can be reused, which is another economic advantage of the process according to the invention. Depending on the technological conditions, the duration of the hydrogenolysis can be selected from 10 minutes to 3 hours. Sufficient stirring ensures that the reaction rate is not limited by mass transfer and takes place in a kinetic reaction mode. The course of hydrogenolysis can be monitored manometrically. In the process according to the invention, customary solvents, such as alcohols, hydrocarbons, dimethylformamide, or mixtures thereof, can be used for the hydrogenolysis. Solvents in which the hydrogenolysis product is readily soluble are useful.

In studying the optimal conditions for the cyclization of the hydrogenolysis product to the compound of formula I, it has surprisingly been found that, unlike other known dipeptide cyclization processes where higher temperatures (100 ° C) and acid-base catalysis are required, relatively high spontaneous cyclization rates can be used in the laboratory. temperature, usually at 15 to 30 ° C. This is greatly facilitated by the high concentration of product in the solution after hydrogenolysis. The fact that Alaptide crystallizes in high purity and is sparingly soluble, while the impurities are readily soluble and remain in the mother liquor, also has a positive effect.

It has been found that, while maintaining the concentrations recommended for hydrogenolysis, spontaneous cyclization at room temperature after 1 day gives a yield of about 50% of theory, after 2 days about 75% of theory, after 4 days about 90% and after 20 days the yield is almost quantitative. The advantage of this embodiment of cyclization is simplicity, low labor, no additional raw materials, energy and equipment are needed as in acid-base cyclization at elevated temperature.

The catalyst-free reaction mixture after hydrogenolysis is collected in a tank where spontaneous cyclization and crystallization take place. After the selected time, Alaptide is isolated, depending on the density of the suspension, several times, and a solvent for reuse is obtained from the mother liquors by distillation, depending on the operating possibilities. The residue is processed to the second fraction of the product.

The cyclization and crystallization of the product in the tank, with a suitable arrangement, does not slow down the periodic production, because in the final stages of the synthesis the performance of the reactors for the condensation of amino acids and in particular for hydrogenolysis can be a limiting factor. When Alaptid is isolated after a relatively short residence time, no product losses occur. In the first phase, less product is obtained and in the second phase, more is obtained in the processing of mother liquors from which solvents can be recovered.

Termination of the synthesis by thermal cyclization is also possible, the speed of the process is increased, and finally distillation of methanol is also suitable. For example, cyclization is practically quantitative when the solution is stirred at 65 ° C after hydrogenolysis for 2 h and methanol is distilled off.

A combination of the two extreme methods described above can be advantageously used in the production process. For example, the filtrate after hydrogenolysis is heated, after a few hours the first portion of the product is isolated according to the consistency of the suspension, the mother liquors are returned to the reactor and heating is combined with distilling off methanol (e.g. under vacuum), the precipitated product is isolated again, etc.

If necessary, the products obtained can be purified by known methods, for example by crystallization with 50% aqueous ethanol.

A prerequisite for the industrial production of Alaptide is, in particular, the hydrogenolysis according to the invention, this step being followed by an improved cyclization process. The process is reflected in a reduction in labor, consumption of raw materials and energy, increased productivity without investment requirements and improved working conditions and environment. There is no deionization, difficult substances (hydrogen bromide, chloroform, ammonia) are eliminated, there is no environmentally harmful waste. Yields of more than 70% of theory (based on the starting Z-Alanine) are obtained, compared with at most 40% of the theory obtained by acidolytic cleavage of the Z-group.

In the process according to the invention, the three final steps in the synthesis of the compound of the formula I form one technological unit, since it is isolated and characterized by physical constants until the final cyclization product.

Further details of the process according to the invention follow from the following examples, which merely illustrate the process but do not limit it in any way.

Example 1

To a solution of 100.5 g (0.45 mol) of benzyloxycarbonyl-L-alanine and 63 ml of N-ethylpiperidine in 1 liter of methylene chloride, cooled to -30 DEG C., was added with stirring 45 ml of ethyl chloroformate and after 15 minutes. A solution of 1-amino-1-cyclopentanecarboxylic acid methyl ester, liberated from 81 g (0.45 mol) of the corresponding hydrochloride by adding 63 ml of N-ethylpiperidine in 700 ml of methylene chloride was added to stirring at -10 DEG C.. After mixing the two solutions, the reaction mixture was stirred for 30 min. at -10 ° C and 2 h at room temperature, then shaken with 1 M hydrochloric acid, water, 5% sodium bicarbonate solution and water and evaporated in vacuo. The non-crystalline residue was redissolved in 220 ml of methanol and 50 ml of toluene and evaporated again.

The residue obtained (about 150 g), i.e. the crude compound of formula II, was dissolved in 400 ml of methanol and the solution was divided into 4 portions.

The first portion was charged to an autoclave, 3 g of 5% Pd / C catalyst were added as a suspension in 30 ml of toluene, and after purging the autoclave with nitrogen and hydrogen, hydrogenolysis was started at an initial hydrogen pressure of 1 MPa. When the pressure dropped to 0.3 MPa, the autoclave was degassed and again pressurized with hydrogen to 1 MPa. This intervention was repeated once more. Hydrogenolysis lasted 50 minutes.

The catalyst was filtered off and used to treat the remaining portions of the stock solution of the compound of formula II, under the same conditions as described above, except for the fourth portion.

This was treated similarly, except that the hydrogenolysis was carried out at pressures of 0.4 to 0.15 MPa, while the degassing of the autoclave and the filling with hydrogen to the initial pressure of 0.4 MPa were repeated 5 times.

The combined filtrates after hydrogenolysis were stirred for 2 h at 60 ⁴ C, the methanol was evaporated at 55 ° C under a slight vacuum. The residue was suspended in 150 ml of methanol and the crystalline product was filtered off. The yield was 53 g (65% of theory, based on Z-Alanine) of the compound of formula I, mp 289-291 ° C, alpha ²⁰ = -21 ° (c 0.2; methanol). ^D

Example 2

The crude benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentacarboxylic acid methyl ester (Formula II, R = methyl), obtained according to Example 1 in the form of a residue, was dissolved in an amount of 50 g with methanol to a volume of 68 ml of solution.

After the addition of 2 g of 5% Pd / C catalyst, 20 ml of methanol and 20 ml of toluene, it was hydrogenolyzed at 50 ° C, under an initial hydrogen pressure of 2 MPa. After the pressure dropped to 1 MPa, the autoclave was degassed and, after pressurizing to 2 MPa with hydrogen, the hydrogenolysis was continued for a total of 15 minutes.

After filtering off the catalyst, the filtrate was spontaneously cyclized at room temperature for 2 days. After filtration, washing with methanol and drying, 14.2 g of Alaptide with the same properties as in Example 1 were obtained.

Example 3

The procedure of Example 1 was based on 1.5 kg of Z-Alanine and equivalent amounts of other components. 2.45 kg were obtained. of benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentanecarboxylic acid methyl ester residue, which was dissolved in methanol to a volume of 3.4 liters and the solution was divided into 5 portions.

A first portion of this solution was charged to a 3 liter autoclave, 50 g of 5% Pd / C catalyst, 200 ml of methanol and 300 ml of toluene were added and hydrogenolyzed at 18-22 ° C for 1 h. The initial hydrogen pressure was 2 MPa, after decreasing to 1 MPa, the autoclave was degassed and again pressurized with hydrogen to 2 MPa. After filtration, the catalyst was used for 4 further hydrogenolyses under the same conditions.

Solution after filtration of the catalyst were collected in a container, where took 8 days at room temperature, a spontaneous cyclization and crystallisation After filtered off, washed with methanol and dried to afford 890 g (73%) Alaptidu, mp was 289-291 ° C, alpha ² ^ = -21.2 (c 0.2, methanol).

The solvents were recovered from the mother liquor by distillation and II was obtained. Alaptide content in a yield of 90 g, alpha ²⁰ = -20.0 (c 0.2, methanol).

Claims (2)

PATENT CLAIMS ch ₃ from benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentanecarboxylic acid ester of formula II ch ₂ -o-co-nh-ch-co-nh- c -co-or ch ₃ (II) in which R is methyl or ethyl by removal of the benzyloxycarbonyl protecting group and subsequent cyclization, characterized in that the starting material used is the reaction product of a mixed anhydride formed from benzyloxycarbonyl-L-alanine and an alkyl ester, for example methyl or ethyl ester chloroformate with 1-amino-1-cyclopentanecarboxylic acid methyl or ethyl ester, in the form of a residue containing benzyloxycarbonyl-L-alanyl-1-amino-1-cyclopentanecarboxylic acid ester of formula II, dissolved in an inert organic solvent, for example methanol or of ethanol to a solution with a concentration of 10 to 60% by weight, preferably 20 to 40% by weight, which is hydrogenolyzed under a hydrogen pressure of 0.1 to 10 MPa, preferably 0.2 to 1.5 MPa, at a temperature of 0 to 80 ° C, preferably 10 to 30 ° C, in the presence of a catalyst, for example palladium on carbon, after completion of the hydrogenolysis and removal of the catalyst, cyclization is carried out at 0 to 70 ° C for 2 h to 20 days, then the precipitated substance formula I isolates. 2. The process according to item 1, characterized in that the reactor is degassed at least once during the hydrogenolysis and, after pressurizing with hydrogen to the original pressure, the hydrogenolysis is continued until completion. End of document