CH624931A5 - - Google Patents

Description

The subject of the present invention is a process for the preparation of new proline derivatives and related compounds of general formula I: p

R —S 8

I4 I1

<ÇH) - ÇH-CO

H2C

I ï

NOT

wherein R is a hydroxyl or lower alkoxy group; Ri is a hydrogen atom or a lower alkyl group; Rg is a benzoyl or lower alkanoyl group; and n = 0, 1 or 2. In the group of compounds represented by formula II, the following subgroups are preferred in order (a to j) preferably increasing for those compounds which are embodiments favorite:

a) R is a hydroxyl group;

b) n = 1;

C) Rs is a lower alkanoyl group;

d) Rs is an acetyl group;

e) Ri is a hydrogen atom or a lower alkyl group;

f) Ri is a hydrogen atom or a methyl group;

g) R is a hydroxyl group, R 1 is a hydrogen atom or 40 a methyl group;

h) R is a hydroxyl group, Ri is a hydrogen atom or a methyl group, Rg is an acetyl group and n = 0, 1 or 2;

i) R is a hydroxyl group, Ri is a hydrogen atom, Rs is an acetyl group and n = 1;

J) R is a hydroxyl group, Ri is a methyl group, Rs is an acetyl group and n = 1.

It will be understood that combinations of the foregoing, where applicable, are among the preferred groups.

Particularly preferred are stereoisomers in which the remainder of proline is in the L- form.

The lower alkyl groups represented by one or the other of the variants include straight or branched chain hydrocarbon groups ranging from methyl to heptyl, for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, 55 pentyle, isopentyle, etc. The lower alkoxy groups are of the same kind having from 1 to 7 carbon atoms linked to oxygen, for example methoxy, ethoxy, propoxy, isopropoxy, butoxy, iso-butoxy, etc. Preferred are those in C1-C4, especially Ci and C2 of the two types. The phenylmethyl group is the preferred lower phenylalkyl group.

The lower alkanoyl groups are those having the acyl groups of the C2-C7 lower fatty acids, for example acetyl, propionyl, butyryl, isobutyryl, etc. Likewise, lower alkanoyl groups having up to 4 carbon atoms and in particular the acetyl group are preferred.

The four common halogens are included by the term halogen, but chlorine and bromine are preferred. The substituted phenyl -CH-COR groups preferably carry the substituent in position 4- of the

(£ H) m * m

3

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core. The hydroxy-lower alkyl groups have a hydroxyl group on an alkyl chain such as those described above, in particular on the terminal carbon atom, for example hydroxymethyl, 2-hydroxyethyl, etc. The aminocarboxy-lower alkyl groups have an amino group and a carboxy group on a lower alkyl group such as those described above and preferably both on a carbon atom, for example on the terminal carbon atom as in the preferred 2-amino-2-carboxyethyl group.

The products of formula I and the preferred subgroups can be prepared by various synthetic methods.

The products obtained by the present process are prepared by acylation of a compound of formula III:

H2?

HN

with an acid of formula IV: R.

<CHL I

CH - COR Ri r s - (CH) CH— COOH

8 n or a functional derivative of this acid.

The acylation can be carried out with a mercapto-alca-noic acid of formula IX:

r

S - (CH)

laughed

I1

CH —COR

in which Y is a protecting group such as: (a) CH30- (Ö) _CH2-, (b) ÇX '

R1 R4

(c) CH-CONHCH-, (d) R-O-C-èH- (éH) -S-j £, n or another sulfur protecting group. "Deprotection" can be carried out by known means such as treatment with hot trifluoroacetic acid, cold trifluoromethane sulfonic acid, mercuric acetate, sodium in liquid ammonia, zinc and hydrochloric acid, etc. For a review of these methods, [see “Methoden der Organischen Chemie” (Houben-Weyl), Vol. XV, part. I, p. 736 and seq. (1974)].

When the acid of formula IV is used as the acylating agent, the acylation can be carried out in the presence of a coupling agent such as dicyclohexylcarbodiimide, etc., or the acid can be activated by the formation of its mixed anhydride, symmetrical anhydride, acid chloride, acid ester or using the reagent of Woodward K, N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquino-leine, etc. For an account of acylation processes, [see “Methoden der Organischen Chemie” (Houben-Weyl), Vol. XV, part. II, p. 1 and seq. (1974)].

Compounds of formula III include for example proline, hydroxyproline, 4-methylproline, pipecolic acid, 5-hydroxypipecolic acid, azetidine-2-carboxylic acid, their lower alkyl esters, etc. The acylation of such compounds is described in more detail below.

When Rs is the R5CO group, we can then convert the product obtained into product XII:

f 4? 1

H ^ C (CH)

; 3 - (CH) - CH CO - Ü

n m

i

CH-COR

by ammonolysis, for example by means of an alcoholic solution of ammonia or concentrated ammonium hydroxide or by alkaline hydrolysis, for example with an aqueous hydroxide of a metal. When Rs is another protective group, the compound of formula XII can then be obtained by deprotection as described above. When R is an ester group (i.e. R is a lower alkoxy group), the ester group can be removed for example when R is a t-butoxy or t-amyloxy group by treating the ester of formula XI or XII with trifluoroacetic acid and anisole to obtain the corresponding free acid. When other alkoxy groups are present, the hydrolysis alka-

20 line gives the corresponding acid.

According to a variant of this process, an acrylic acid of formula VI: RR is used

l4 I1

21 CH = C-COOH

We can first react the acrylic acid of formula VI with the thio-acid of formula VII to obtain a product of formula XV:

f4 fi

I I

R -S-CH-CH-COOH 8

which is converted to its acid halide, for example with thionyl chloride, then it is coupled to the compound of formula III and the same sequence is then carried out as above.

The acid or ester of formula III can also be acylated with a protected form of a co-mercapto-alkanoic acid of formula XVI: u

, 4

R -S- (CH) -CH-COOH 8 n in which Rs is the protecting group. Such protecting groups can have the form described above.

After the acylation, the product can be deprotected by one of the known methods mentioned above.

Further details of the preferred modes of preparation of the present compounds will be found in the following and in the examples. When an acid of formula III is used as a starting material, the final product obtained as free carboxylic acid can then be converted into its ester, for example by esterification with a diazo-alkane such as diazomethane, an l-alkyl- 3-p-tolyl-triazene such as ln-butyl-3-p-tolyltriazene, etc. The treatment of an ester, preferably the methyl ester, with an alcoholic solution of ammonia, converts the free acid to the amide, that is to say R is NH2.

According to another variant, an ester, preferably the t-butylester of formula III, is treated in an anhydrous medium such as dichloromethane, tetrahydrofuran, dioxane, etc., with a thio-alkanoic acid of formula XVIII:

Ri

"VS- (CH2'n-

CH

-COOH

in the presence of dicyclohexylcarbodi-imide, N, N'-carbonyl-bis-imidazole, ethoxyacetylene, diphenylphosphoryl azide or

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similar coupling agents at a temperature between about 0 and 10 ° C. The ester group R can then be removed, for example by treatment with trifluoroacetic acid and anisole at approximately ordinary temperature.

The products of formula I have one or more asymmetric carbon atoms. When Ri, R3 or R4 is other than hydrogen, the carbon atom to which it is attached is asymmetric. These carbon atoms are indicated by an asterisk in formula I. Thus the compounds exist in stereoisomeric forms or in their racemic mixtures. All of these are within the scope of the invention. The synthesis described above can use the racemate or one of the enantiomers as starting material. When the racemic product is used as a starting material for the synthesis process, the stereoisomers obtained in the product can be separated by conventional methods of chromatography or fractional crystallization. In general, the L- isomer, relative to the carbon atom of the amino acid, represents the preferred isomer form. The D-isomer is also preferred with respect to the carbon atom a in the acyl side chain (that is to say the carbon atom carrying Ri) -

The present compounds form basic salts with various inorganic and organic bases which are also within the scope of the invention. These salts include ammonium salts, alkali metal salts such as the preferred sodium and potassium salts, alkaline earth metal salts such as calcium and magnesium salts, salts with bases organic, for example the dicyclohexylamine salt, the benzathine, N-methyl-D-glucamine, hydrabamine salts, salts with amino acids such as arginine, lysine, etc. Physiologically acceptable non-toxic salts are preferred, although other salts are also useful, for example to isolate or purify the product as illustrated in the examples in the case of the dicyclohexylamine salt.

The salts are formed in known manner by reacting the product in the form of free acid with one or more equivalents of the appropriate base providing the desired cation in a solvent or a medium in which the salt is insoluble or in water, then by separating the water by lyophilization. By neutralizing the salt with an insoluble acid such as a cation exchange resin in hydrogen form (for example, a polystyrene-sulfonic acid resin such as Dowex 50) or with an aqueous acid, then extraction with an organic solvent, for example ethyl acetate, dichloromethane, etc., the product can be obtained in the form of free acid and, if desired, form another salt.

Further experimental details are found in the examples which are preferred embodiments and which also serve as a model for the preparation of other group members.

The compounds of formula I, in their deprotected form, that is to say in which the protective group Rs has been replaced by a hydrogen atom, inhibit the conversion of the decapeptide which is angiotensin I into angiotensin II, and they are therefore useful for reducing or relieving hypertension in relation to angiotensin.

The following examples illustrate the invention. All temperatures are in degrees centigrade.

Example 1:

tert-Butylester of L-proline (starting material)

230 g of L-proline are dissolved in a mixture of 11 of water and 400 ml of 5N sodium hydroxide. The solution is refrigerated in an ice bath and then, with vigorous stirring, 460 ml of 5N sodium hydroxide and 340 ml of benzyloxycarbonyl chloride are added in five aliquots in the course of 1 h. After stirring for 1 hour at room temperature, the mixture is extracted twice with ether and acidified with hydrochloric acid. concentrated drique. The precipitate is filtered and dried. 442 g are obtained, which melts at 78-80 ° C.

The 180 g of the benzyloxycarbonyl-L-proline thus obtained are dissolved in a mixture of 300 ml of dichloromethane, 800 ml of liquid isobutylene and 7.2 ml of concentrated sulfuric acid. The solution is stirred in a pressure bottle for 72 h. The pressure is released, the isobutylene is allowed to evaporate and the solution is washed with 5% sodium carbonate, water, dried over magnesium sul-sate and concentrated to dryness under vacuum to obtain 205 g of benzyloxy-carbonyl-L-proline t-butyl ester.

205 g of benzyloxycarbonyl-L-proline t-butyl ester are dissolved in 1.21 of absolute ethanol and hydrogenated at normal pressure with 10 g of 10% palladium on carbon until only 10 is observed. a trace of carbon dioxide in hydrogen which is the outlet gas (24 h). The catalyst is filtered off and the filtrate is concentrated in vacuo to 30 mm Hg. The residue is distilled in vacuo to obtain the L-proline t-butyl ester which boils at 50-51 ° C / l mm.

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Example 2:

1- (3-acetylthiopropanoyl) -L-proline tert-butylester

5.13 g of L-proline t-butylester are dissolved in 40 ml of dichloromethane and the solution is refrigerated in an ice-water bath. A solution of 6.18 g of dicyclohexylcarbodi-imide in 20 ml of dichloromethane is added and then immediately 4.45 g of 3-acetylthiopropionic acid is added. After 15 minutes of stirring in the ice-water bath and 16 hours at ordinary temperature, the precipitate is separated by filtration and the filtrate is concentrated to dryness under vacuum. The residue is dissolved in ethyl acetate and washed until neutral. The organic layer is dried over magnesium sulfate and concentrated to dryness in vacuo to obtain 9.8 g of 1- (3-acetylthiopropanoyl) -L-proline t-butylester.

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Example 3:

t- (3-acetylthiopropanoyl) -L-azetidine-2- acid t-butylester

carboxylic

By substituting the t-butyl ester of L-azetidine-2-carboxy-lic acid (prepared by substitution of L-azetidine-2-carboxy-lic acid for proline in Example 1) for the t-butyl ester of L-proline in the process of Example 2, the t- butyl ester of l- (3-acetylthiopropanoyl) -L-azetidine-2-carboxylic acid is obtained.

40 Example 4:

t-Buty lester of l- (3-acetylthiopropanoyl) -L-pipecolic acid

Substituting L-pipecolic acid t-butylester (prepared by substituting L-pipecolic acid for L-proline in Example 1) for L-proline t-butylester in the process of Example 2 , the t- butyl ester of l- (3-acetylthiopro-panoyl) -L-pipecolic acid is obtained.

Example 5:

50 1- (3-A cetylthiopropanoyl) -4-methyl-L-proline

By substituting 4-methyl-L-proline for L-proline in the method of Example 1 and then treating the product by the method of Example 2, we obtain l- (3-acetylthiopropanoyl) -4- methyl-L-proline.

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Example 6:

1- (3-acetylthiopropanoyl) -5-hydroxy-L-pipecolic acid

By substituting 5-hydroxy-L-pipecolic acid for L-proline in the method of Example 1, then by treating the product by the method of Example 2, we obtain the acid l- (3- acetylthiopropa-nucleus) -5-hydroxy-L-pipecolic.

Example 7;

65 l- (3-A cetylthiopropanoyl) -D-proline

By substituting D-proline for L-proline in the method of Example 1, then treating the product by the method of Example 2, we obtain l- (3-acetylthiopropanoyl) -D-proline.

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Example 8:

3-acetylthio-2-methylpropanoic acid (starting material)

Heated in a water bath for 1 h a mixture of 50 g of thio-acetic acid and 40.7 g of methacrylic acid and then kept at room temperature for 18 h. After confirming by NMR spectroscopy that the complete reaction of methacrylic acid has taken place, the reaction mixture is distilled under vacuum and the desired 3-acetylthio-2-methylpropanoic acid is separated in the boiling fraction at 128.5-131 ° C / 2.6 mm Hg; the yield is 64 g.

Example 9:

3-Benzoylthio-2-methylpropanoic acid (starting material)

By substituting thiobenzoic acid for thioacetic acid in the process of Example 8, 3-benzoylthio-2-methylpropanoic acid is obtained.

Example 10:

3-Phenylacetylthio-2-methylpropanoic acid (starting material)

By substituting thiophenylacetic acid for thio-acetic acid in the process of Example 8, 3-phenyla-cetylthio-2-methylpropanoic acid is obtained.

Example 11:

1- (3-acetylthio-2-methylpropanoyl) -L-proline tert-butylester

5.1 g of L-proline t-butyl ester are dissolved in 40 ml of dichloromethane and the solution is stirred and refrigerated in an ice bath. 6.2 g of dicyclohexylcarbodi-imide dissolved in 15 ml of dichloromethane are added, then a solution of 4.9 g of 3-acetylthio-2-methylpropanoic acid in 5 ml of dichloromethane is immediately added. After shaking for

15 min in the ice bath and 16 h at room temperature, the precipitate is separated by filtration and the filtrate is concentrated to dryness under vacuum. The residue is dissolved in ethyl acetate and washed until neutral. The organic phase is dried over magnesium sulfate and concentrated to dryness under vacuum. The residue, i.e. the 1- (3-acetylthio-2-methylpropanoyl) -L-proline t-butyl ester, is purified by column chromatography (silica gel-chloroform) and 7.9 g are obtained. .

Example 12:

1- (3-Acetylthio-2-methylpropanoyl) -L-proline

8.1 g of 3-acetylthio-2-methylpropanoic acid and 7 g of thionyl chloride are mixed and the suspension is stirred for

4 p.m. at room temperature. The reaction mixture is concentrated to dryness and distilled under vacuum (m.p. = 80 ° C). The 5.4 g of this 3-acetylthio-2-methylpropanoic acid chloride and 15 ml of 2N sodium hydroxide are added to a solution of 3.45 g of L-proline in 30 ml of normal sodium hydroxide refrigerated in an ice water bath. After stirring for 3 h at room temperature, the mixture is extracted with ether, the aqueous phase is acidified and extracted with ethyl acetate. The organic phase is dried over magnesium sulfate and concentrated to dryness to obtain l- (3-acetylthio-2-DL-methylpropanoyl) -L-proline.

Example 13:

1- (3-Benzoylthio-2-methylpropanoyl) -L-proline tert-butylester

By substituting 3-benzoylthio-2-methylpropanoic acid for 3-acetylthio-2-methylpropanoic acid in the process of Example 11, the t- (3-benzoylthio-2-methylpropanoyl) t-butylester is obtained -L-proline.

Example 14:

1- (3-Phenylacetylthio-2-methylpropanoyl) -L-prolirte tert-Butylester

By substituting 3-phenylacetylthio-2-methylpropanoic acid for 3-acetylthio-2-methylpropanoic acid in the process of Example 11, the t- (3-phenylaceous-tylthio-) t-butylester is obtained. 2-methylpropanoyl) -L-proline.

Example 15:

3-acetylthio-2-benzylpropanoic acid (starting material) By substituting 2-benzylacrylic acid for methacrylic acid in the process of Example 9, 3-acetyl-thio-2-benzylpropanoic acid is obtained.

Example 16:

1- (3-acetylthio-2-benzylpropanoylj -L-proline tert-butylester By substituting 3-acetylthio-2-benzylpropanoic acid for 3-acetylthio-2-methylpropanoic acid in the process of Example 5, 1- (3-acetylthio-2-benzyl-propanoyl) -L-proline t-butyl ester is obtained.

Example 17:

t- (3-acetylthio-2-methylpropanoyl) -L-azetidine-2-carboxylic acid t-butylester

By substituting the t-butyl ester of L-azetidine-2-carboxy-lic in the process of Example 11, the t-butyl ester of 1- (3-acetylthio-2-methylpropanoyl) -L- is obtained. azetidine-2-carboxy-lique.

Example 18:

t- (3-Acethylthio-2-methylpropanoyl) -L-pipecolic acid t-Butylester

By substituting L-pipecolic acid in the process of Example 11, there is obtained t- (3-acetylthio-2-methylpropanoyl) -L-pipecolic acid t-butyl ester.

Example 19:

1- (3-acetylthiobutanoyl) -L-proline tert-butylester

6.2 g of dicyclohexylcarbodi-imide and 4.86 g of 3-acetylthiobutyric acid are added to a solution of 5.1 g of L-proline t-butyl ester in 60 ml of dichloromethane stirred in an ice bath. After 15 min, the ice bath is removed and the mixture is stirred at room temperature for 16 h. The precipitate is filtered, the filtrate is concentrated to dryness and the residue is chromatographed on a silica gel column with chloroform to give 5.2 g of 1- (3-acetylthiobutanoyl) -L-proline t-butyl ester.

Example 20:

l- (3-Methylthiopropanoyl) -L-proline

51 g of methyl 3-methylthiopropionate are saponified with 150 ml of a 10% sodium hydroxide solution for 30 min at 100 ° C. The cooled solution is extracted with ether and then acidified. The crude acid thus obtained is distilled and converted to acid chloride with thionyl chloride.

A solution of 11.5 g of L-proline in 100 ml of sodium hydroxide N is refrigerated in an ice bath and 6.9 g of 3-methylthiopropanoic acid chloride are added dropwise with vigorous stirring during 10 mins. After 5 h, the reaction mixture is acidified and extracted with ethyl ether to obtain l- (3-methylthiopropanoyl) -L-proline. The dicy-clohexylammonium salt is prepared by adding dicyclohexylamine to a solution of the free acid in ethyl acetate; it melts at 169-171 ° C.

Example 21:

1 - (Methylthio-acetyD-Lrproline

By substituting methyl methyl thio-acetate for 3-methyl-

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methyl thiopropionate in the process of example 20, one obtains l- (methylthio-acetyl) -L-proline which melts at 123-124 ° C.

Example 22:

1- (Benzylthio-acetyl) -L-proline

By substituting benzylthio-acetyl chloride for 3-methylthiopropanoyl chloride in the process of Example 20, one obtains l- (benzylthio-acetyl) -L-proline which melts at 86-88 ° C.

Example 23:

A 1- (3-methylthiopropanoyl) -L-azetidine-2-carboxylic acid By substituting L-azetidine-2-carboxylic acid for L-pro-line in the process of Example 20, the acid is obtained 1- (3-methylthiopropanoyl) -L-azetidine-2-carboxylic.

Example 24:

A 1- (3-methylthiopropanoyl) -L-pipecolic acid By substituting L-pipecolic acid for L-proline in the process of Example 20, we obtain l- (3-methylthiopropa-nucleus) acid - L-pipecolic.

Example 25:

A 3-acetylthio-2-phenylpropanoic acid

By substituting 2-phenylacrylic acid for methacrylic acid in the process of Example 8, 3-acetyl-thio-2-phenylpropanic acid is obtained.

1- (3-acetylthio-2-phenylpropanoyl) -L-proline tert-butylester By substituting 3-acetylthio-2-phenylpropanoic acid for 3-acetylthio-2-methylpropanoic acid in the process of Example 11 , the t- butyl ester of l- (3-acetylthio-2-phe-nylpropanoyl) -L-proline is obtained.

Example 26:

With 1- [3- (acetylthio) -DL-propanoyl] pipecolic acid 6.5 g of pipecolic acid is suspended in 200 ml of dimethylacetamide. 8.3 g of 3-acetylthiopropanoyl chloride at 23 ° C are added dropwise to the suspension. A clear solution is formed and the temperature rises to 28 ° C. Add to. this clear solution 10.1 g of N-methylmorpholine. A precipitate is immediately formed and the temperature rises to 34 ° C. The mixture is heated in a water bath for 1 h and then a clear solution is formed. During cooling, the precipitated solid is filtered to obtain 5.1 g of 1- [3- (acetylthio) -DL-propanoyl] pipecolic acid which melts at 190-200 ° C. The solvent is separated and the triturated viscous residue with isopropyl ether to obtain 7.8 g of product which melts at 98-101 ° C. Recrystallization from acetone-hexane gives a solid substance with constant melting point which melts at 102-104 ° C, has a value Rf = 0.72 (silica gel, 7: 2 mixture of benzene: acetic acid).

Example 27:

Acid] - (3-acetylthiopropanoyl) -L-pipecolic

By substituting L-pipecolic acid for DL-pipecolic acid in the process of Example 26, l- [3- (acetyl-thio) propanoyl] -L-pipecolic acid is obtained.

Example 28:

A cide 1- [3- (acetylthio) -2-methylpropanoyl] -DL-pipecolic 6.5 g (0.05 mol) of pipecolic acid is suspended in 200 mg of dimethylacetamide, and dropwise added 9 0.0 g (0.05 mol) 3-acetylthio-2-methylpropanoyl chloride. The temperature rises to 29 ° C and a clear solution is formed. 10.1 g of N-methylmorpholine are then added at once and the temperature rises to 34 ° C. The mixture is heated in a water bath for 1 h, then a clear solution is formed. It is left to stand at room temperature overnight and the solid which precipitates is filtered off to obtain 0.1 g which melts at 203-204 ° C. The solvent is separated off and the viscous residue is triturated with water and 20% HCl. The yellow oil is extracted with three times 150 ml of ethyl acetate. The ethyl acetate extracts are dried over magnesium sulfate and separated to obtain 14 g of l- [3- (acetylthio) -2-methylpropa-noyl] -DL-pipecolic acid as a viscous oil.

Example 29:

3- [(4-methoxyphenyl) methylthio] -2-methylpropanoic acid

(starting material)

15.4 g (0.1 mol) of p-methoxy-a-toluenethiol are added to a solution of 8.6 g (0.1 mol) of methacrylic acid in 50 ml of 2N sodium hydroxide. The mixture is heated in a water bath for 3 h, then it is refluxed for 2 h and cooled. The mixture is extracted with ether then the aqueous layer is acidified with concentrated HCl and extracted with dichloromethane. The acid extracts are washed with brine, dried over MgSO4 and evaporated in vacuo. The semi-solid substance obtained is taken up in 50 ml of dichloromethane, diluted with 50 ml of hexane and refrigerated. 3 - [(4-methoxyphé-nyl) methylthio] -2-methylpropanoic acid is isolated in the form of a crystalline solid which melts at 74-82 ° C (5.5 g).

Example 30:

1- [3- (4-methoxyphenyl) methylthio] -2- tert-Butylester -2-

methylpropanoyl-L-proline

3.6 g (0.015 mol) of 3 - [(4-methoxyphenyl) methylthio] -2-methylpropanoic acid, 2.6 g (0.015 mol) of L-proline t-butylester and 3.1 are dissolved. g (0.015 mol) of dicyclohexyl-carbodi-imide in 50 ml of dichloromethane and the mixture is stirred for 30 min at 0 ° C. The cooling bath is removed and the mixture is stirred overnight (16 h). The suspension obtained is filtered and the filtrate is washed with 5% potassium bisulfate, saturated sodium bicarbonate and brine, then dried over MgSO4 and evaporated in vacuo. The clear oil obtained is applied to a 250 ml silica gel column and chromatographed using 20% ethyl acetate / hexane as the eluent. The main fraction is evaporated (Rf = 0.70, silica gel, ethyl acetate) until 5.5 g (93%) of 1- [3- (4-methoxyphet) t-butylester are obtained. nyl) methylthio] -2-methylpropanoyl-L-proline in the form of a clear oil. Rf = 0.70 (silica gel, ethyl acetate); Rf = 0.60 (silica gel, ether).

Example 31:

l- (3-Mercapto-2-methylpropanoyl) -L-proline

1.2 g (0.003 mol) of the ester of Example 30, 5 ml of anisole and 0.5 ml of trifluoromethane sulfonic acid are dissolved in 20 ml of trifluoroacetic acid under nitrogen and the red solution obtained is left to stand for 1 h at ordinary temperature. The solution is evaporated in vacuo until a red residue is obtained which is taken up in ethyl acetate and washed with water, in brine, then dried over MgSO 4 and qu 'we evaporate. The residue is triturated several times with hexane and the residual hexane is evaporated; the oily residue represents 0.4 g. Part of this material (180 mg) is subjected to preparative thin layer chromatography on 2 mm silica gel plates using a 75:25 mixture of benzene: acetic acid as eluent. The main band positive for nitroprus-siate (nitroprusside) is isolated (Rf = 0.40) to obtain 135 mg of l- (3-mer-capto-2-methylpropanoyl) -L-proline in the form of an oil. Thin layer chromatography using a 75:25 mixture of benzene: acetic acid (Rf = 0.40) and a 50:40:10 mixture of chloroform: methanol: acetic acid (Rf = 0.62).

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Example 32:

l- [3-Tosyloxy-2-methylpropanoyl] -L-proline By substituting 3-tosyloxy-2-methylpropanoic acid chloride for 3-acetylthio-2-methylpropanoic acid chloride in the process of the example 12, we obtain l- [3-tosyloxy-2-methylpropanoyl] -L-proline.

Example 33:

3-Benzylthio-2-methylpropanoic acid (starting material)

By substituting a-toluenethiol for p-methoxy-a-toluenethiol in the process of Example 29, 3-benzylthio-2-methylpropanoic acid is obtained.

Example 34:

1- [3- (Benzylthio) -2-methylpropanoyl] -L-proline t-Butylester

By substituting 3-benzylthio-2-methylpropanoic acid for 3 - [(4-methoxyphenyl) methylthio] -2-methylpropanoic acid in the process of Example 30, the 1- [3-t-butylester is obtained - (benzylthio) -2-methylpropanoyl] -L-proline.

Example 35:

3-triphenylmethylthio-2-methylpropanoic acid (starting material)

A solution of 1.2 g of 3-mercapto-2-methyl-propanoic acid and 2.9 g of trityl chloride in 50 ml of methylene chloride is kept at ordinary temperature for 2 h. The mixture is heated in a water bath for 20 min then evaporated to dryness under vacuum and the residue is dissolved in saturated aqueous sodium bicarbonate and the solution is washed with ethyl acetate. The aqueous phase is acidified to pH = 3 and extracted with ethyl acetate. The organic layer is dried and concentrated to dryness to obtain 3-triphenylmethylthio-2-methylpropanoic acid. Rf = 0.8 (silica gel, 3: 1 mixture of benzene: acetic acid).

Example 36:

1- [3- (triphenylmethylthio) -2-methylpropa-noyl] -L-proline tert-butylester

By substituting 3-triphenylmethylthio-2-methy] propa-noic acid for 3 - [(4-methoxyphenyl) methylthio] -2-methylpropa-noic acid in the process of Example 30, the t- 1 - [3- (triphenylmethylthio) -2-methylpropanoyl] -L-proline butylester.

Example 37:

l- [3- (Triphenylmethylthio) -2-methylpropanoyl] -L-proline

1.8 g of 3-triphenylmethylthio-2-methylpropanoic acid and 0.8 g of N, N'-carbonyldi-imidazole are dissolved in 10 ml of tetrahydrofuran with stirring at room temperature. After 20 min, the solution is added to a mixture of 0.6 g of L-proline and 1 g of N-methylmorpholine in 20 ml of dimethylacetamide. The mixture obtained is stirred overnight at room temperature, concentrated to dryness and the residue is dissolved in a mixture of ethyl acetate and 10% aqueous potassium bisulfate. The organic layer is separated, dried and concentrated to dryness under vacuum to obtain l- [3- (triphenylmethylthio) -2-methylpropa-noyl] -L-proline. Rf = 0.4 (silica gel, 3: 1 mixture of benzene: acetic acid), Rf = 1.0 (silica gel, 14: 1: 2: 1 mixture of methyl ethyl ketone: acetic acid: pyridine: water).

Example 38:

3- (Tetrahydropyran-2-ylthio) -2-methylpropanoic (starting material)

To a solution of 2.4 g of 3-mercapto-2-methyl-propanoic acid and 1.9 g of freshly distilled 2,3-dihydro-4H-pyran in 60 ml of-benzene, 2.8 g are added boron trifluoride etherate. After 2 h, 4 g of potassium carbonate are added, the mixture is stirred and filtered. The filtrate is concentrated to dryness to obtain 3- (tetrahydropyran-2-ylthio) -2-methylpropanoic acid.

Example 39:

l- [3- (Tetrahydropyran-2-ylthio) -2-methylpropanoyl] -L-proline

By substituting 3- (tetrahydropyran-2-ylthio) -2-methyl-propanoic acid for 3-triphenylmethylthio-2-methylpropanoic acid in the process of Example 37, the 1- [3- (tetra-hydropyran-2-ylthio) -2-methylpropanoyl] -L-proline. Rf = 0.8 (silica gel, 3: 1 mixture of benzene: acetic acid), Rf = 0.75 (silica gel, 14: 1: 2: 1 mixture of methyl ethyl ketone: acetic acid: pyridine: water.

Example 40:

3-acetamidomethylthio-2-methylpropanoic acid (starting material)

2.4 g of 3-mercapto-2-methylpropanoic acid and 1.8 g of N-hydroxymethylacetamide are dissolved in trifluoroacetic acid and the solution is kept at ordinary temperature for 1 h. The trifluoroacetic acid is separated in vacuo and the residue is dried in vacuo over potassium hydroxide to obtain 3-acetamidomethylthio-2-methylpropanoic acid.

Example 41:

l- [3- (Acetamidomethylthio) -2-methylpropanoyl] -L-proline

By substituting 3-acetamidomethylthio-2-methylpropa-noic acid for 3- (tetrahydropyran-2-ylthio) -2-methylpropa-noic acid in the process of Example 39, the l- [3- (aceta-midomethylthio) -2-methylpropanoyl] -L-proline. Rf = 0.2 (silica gel, 3: 1 mixture of benzene: acetic acid), Rf = 0.3 (silica gel, 14: 1: 2: 1 mixture of methyl ethyl ketone: acetic acid Pyridine: water).

Example 42:

l- (3-Mercapto-2-methylpropanoyl) -L-proline 1.4 g of l- [3- (acetamidomethylthio) -2-methylpro-panoyl] -L-proline and 1.93 g of mercuric acetate are dissolved in a mixture of 25 ml of acetic acid and 25 ml of water. After 1 hour of stirring in a water bath, hydrogen sulfide is bubbled through until no more precipitation of mercuric sulfide is observed. The mixture is filtered, the precipitate is washed with ethanol and the filtrate is concentrated to dryness under vacuum to obtain l- (3-mercapto-2-methylpro-panoyl) -L-proline. Rf = 0.35 (silica gel, 3: 1 benzene mixture: acetic acid). Rf = 0.5 (silica gel, 14: 1: 2: 1 mixture of methyl ethyl ketone: acetic acid: pyridine: water).

The racemic form of the final product of any of the preceding examples is prepared using the starting amino acid of the DL- form instead of that of the L- form.

Likewise, form D- of the end products of any of the preceding examples is prepared using the starting amino acid of form D- instead of that of form L-.

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Claims (7)

624,931 *) CLAIMS 1. Process for the preparation of a new compound of formula: I I Ri h2C r8-S (CH) —CH— coli i T " N— CH-COR (I) wherein R is a hydroxyl group, NH2 or lower alkoxy; R1 and R4 are each a hydrogen atom, a lower alkyl, phenyl or lower phenylalkyl group; Rs is a protecting group; R3 is a hydrogen atom, a hydroxyl group or a lower alkyl group; m is 1, 2 or 3; n is 0.1 or 2; as well as their basic salts, characterized in that a compound of formula is acylated; wherein R is a hydroxyl group, NH2 or lower alkoxy; R1 and R4 are each a hydrogen atom, a lower alkyl, phenyl or phenyl-lower alkyl group; R3 is a hydrogen atom, a hydroxyl or lower alkyl group; Rs is a protective group, for example O, R5 being a Combines lower alkyl, phenyl or phenyl-lower alkyl; m = 1 to 3; n is 0, 1 or 2. m Asterisks indicate asymmetric carbon atoms. Each of the carbon atoms carrying a substituent Ri, R3 and R4 is asymmetric when this substituent is other than hydrogen. In general, preferred are the compounds of formula I wherein R is a hydroxyl or lower alkoxy group; Ri is a hydrogen atom or a lower alkyl group; R3 and R4 are each a hydrogen atom; m = 2, n = 0, 1 or 2 and especially 1. Particularly preferred are the compounds of formula II: h2c (CH) m di ') S - (CH,) - CH — CO — N KN with an acid of formula: CH ' HORN 2. Method according to claim 1, characterized in that said acylation is carried out in the presence of a coupling agent. 2 n HORN 3. Method according to claim 1 or 2, characterized in that the acid is in activated form. 4. Method according to claim 1, characterized in that R is a hydroxyl or lower alkoxy group, Ri is hydrogen or a lower alkyl group, R3 and R4 are each hydrogen and m is 2. 4 r Rg — s (CH) CH COOH (III ') or a functional derivative of this acid. 5. Method according to claim 1, characterized in that the product has the formula: î1 R— S- (CHj) - CH wherein R is a hydroxyl group, Ri is a hydrogen atom or a lower alkyl group, and Rs is a benzoyl or lower alkanoyl group. 6. Method according to claim 1, characterized in that the product is l- (3-mercapto-2-d-methyl-propanoyl) -L-proline in which the mercapto group is protected. 7. Use of a compound of formula I in which Rs is a thioether or disulfide residue to prepare a compound of the same formula in which Rs is replaced by a hydrogen atom. O —CO — N L HORN