GB2072671A

GB2072671A - Alkylthio-acylamino acids and pharmaceutical compositions thereof

Info

Publication number: GB2072671A
Application number: GB8108836A
Authority: GB
Original assignee: Boehringer Ingelheim International GmbH
Current assignee: Boehringer Ingelheim International GmbH
Priority date: 1980-03-22
Filing date: 1981-03-20
Publication date: 1981-10-07
Also published as: ES8400104A1; ZA811866B; NO810941L; DK127281A; FI810866L; ES8306138A1; ES509618A0; EP0036572A1; DE3011239A1; ES8400105A1; AU6858881A; IL62445A0; ES500553A0; JPS56150059A; ES509619A0

Description

SPECIFICATION Alkylthio-acylamino acids, processes for their preparation and pharmaceutical compositions thereof The present invention relates to alkylthio-acylamino acids, to processes for their preparation and to pharmaceutical compositions containing them. It has been found that certain alkylthio-acylamino acids have interesting pharmacological properties, in particular blood-pressure reducing properties. According to one aspect of the present invention we provide compounds of formula I

(wherein: R1 represents a nitro, cyano or pyridyl group or a group of formula - COR', -COOR' - PO(OR')2 or

R2 represents a hydrogen atom, a methyl, ethyl or -S02CH3 group, or a group offormula -COOR' or -COR'; R3 represents a hydrogen atom, a C1 to C3 alkoxy group, a phenyl group or a thienyl group; R4 represents a hydrogen atom or a methyl group; X represents a divalent group of formula

R' represents a methyl or ethyl group) and salts thereof. In compounds of formula I and salts thereof wherein substituent R1 represents a pyridyl group, this pyridyl group may be bonded via the 2-, 3- or 4- position, preferably via the 4-position. The compounds and salts of formula I possess at least one centre of asymmetry, for example the carbon atom to which the carboxylic acid group is bonded. The compounds therefore occur as diastereoisomers or as racemates or racemic mixtures thereof all of which are deemed to fall within the scope of the present invention. However, those enantiomers in which the asymmetric carbon atom of the amino acid is present in the L-configuration are preferred. The compounds of formula I of the present invention form salts with inorganic or organic bases. As basic salts of compounds of formula I, physiologically acceptable salts of course are preferred. However, other salts may be useful in the preparation of physiologically acceptable basic salts. Suitable inorganic bases include ammonia, alkali metal hydroxides (such as sodium or potassium hydroxide and alkaline earth metal hydroxides (such as calcium or magnesium hydroxide); and suitable organic bases include dicyclohexylamine, N,N'-dibenzyl-ethylenediamine, N,N'-bis-(dehydroabietyl)-ethylenediamine, N-methyl-D-glycamine, arginine and lysine. Preferred compounds, according to the present invention include compounds of formula I wherein R1 represents a hydrogen atom or an acetyl or methoxycarbonyl group, R2 represents a nitro, acetyl or methoxycarbonyl group, R3 represents a phenyl, thienyl or methoxy group, R4 represents a methyl group and X represents a divalent group of formula-(-CH2-)3 or -CH2-S-CH2-, and salts thereof. Especially preferred compounds according to the invention include: (a) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof; (b) 1-[3-(1-thienyl(2)-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof;

thereof; (d) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D,L-methyl-propanoyl]-L-proline and salts thereof; and (e) 1-[3-(1-phenyl-2,2-diacetyl-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof. Particularly preferred compounds of the present invention are those in which the 3-mercapto-2-methylpropionic acid skeletal moiety on which those compounds of formula I are based is in the L-configuration. According to a further aspect of the present invention we provide a process forthe preparation of compounds of formula I and salts thereof which process comprises at least one of the following steps: (a) the addition of the free mercapto group of a compound of formula II

(wherein R4 and X are as herein before defined and R5 represents a hydrogen atom or a C1 to C3 alkyl group) at the double bond of an olefin offormula III

(wherein R1, R2, and R3 are as hereinbefore defined) activated by at least one electron-attracting group and, where R5 represents other than a hydrogen atom, the subsequent acid or alkaline hydrolysis of the ester group -COOR5;(b) the reaction of a substituted alkylthiocarboxylic acid of formula IV

(wherein R1, R2, R3 and R4 are as hereinbefore defined) with an amino acid of formula V

(wherein R5 represents a hydrogen atom or a C1 to C3 alkyl group) and, where R5 represents other than a hydrogen atom, the subsequent acid or alkaline hydrolyis of the ester group -COOR5; (c) (for the preparation of dimeric- compounds of formula I and salts thereof wherein R, represents a group of formula

[in which R2, R3, R4 and X are as hereinbefore defined]) the reaction of a compound of formula II with divinylsulfone in a mole ratio of about 2:1 and, where R5 represents other than a hydrogen atom, the subsquent acid or alkaline hydrolysis of the ester group -COOR5;(d) the conversion of a compound of formula I into a salt thereof or a salt of an acid of formula I into the free acid; and (e) the separation of a racemic mixture of a compound of formula I or a salt thereof into its enantiomers, for example by conventional racemate resolving techniques such as fractional crystalization. The addition reaction of process step (a) above may be carried out in the presence or absence of solvents. Suitable solvents include water, alcohol, ether, tetrahydrofuran, dioxane, halogenated hydrocarbons (such as dichloromethane), benzene, toluene, ethyl acetate, acetone, dimethylsulfoxide, dimethylformamide and pyridine. The activated olefin of formula III, if it is liquid, aiso may serve as a solvent. Preferred solvents include water and ethanol. The additional reaction of process step (a) above may be a radical or an ionic reaction. If the reaction to be affected is an ionic reaction, it is suitably carried out at a pH in the range of 6 to 14, preferably at a pH between 7 and 10. In such reactions the addition of one or more basic substances (such as for example ammonia, triethylamine, trimethylamine, dicyclohexylamine, N-methyl-morpholine, piperidine, pyridine, trimethylbenzyl-ammonium hydroxide, alkali metal hydroxides, alkali metal - carbonates and alkali metal alcoholates) has been found to be advantageous. Preferred bases include ammonia, treiethylamine, dicyclohexylamine and N-methyl-morpholine. Where process step (a) is an ionic addition reaction, the reaction temperature may vary over a wide range according to the starting materials used, e.g. between -80[deg]C and +150[deg]C; reaction temperatures of between 0 and 50[deg]C are preferred. In general the reaction of process step (a) is carried out under normal pressure and under a nitrogen atmosphere; however, in some cases the use of elevated pressure can be advantage. When the addition reaction is a radical addition reaction, a radical former should be used (such as for example, benzoylperoxide, di-tert. butylperoxide, ascaridole, azobis-(isobutyronitrile) and potassium persulfate). The radical reaction may be effected under the conditions mentioned above for the ionic addition reaction. The starting compounds of formulae IV and V used in reaction step (b) above may be linked by means of a coupling reaction, such as is usually applied in peptide chemistry, using an activated alkylthiocarboxylic acid offormula IV. Suitable carboxyl activating groups include acid chlorides, azides, anhydrides, p-nitrophenylesters, trichlorophenylesters, thiophenylesters and o-cyanomethylesters. Suitable coupling agents include carbonyl-diimidazole, dicyclohexylcarbodiimide and alkyl chloroformate (vide Houben-Weyl, "Methoden der organischen Chemie", Volume XV, part 11,1974). The reaction conditions suitable for process step (c) above are substantially similar to those described above for reaction steps (a) and (b). In the processes described above, the starting compounds may be in the form of racemic mixtures or individual diastereoisomers. If they are present as racemic mixtures, the reaction products obtained may be resolved into the individual enantiomers by conventional processes, such as for example, fractional crystallization or by conventional chromatographic processes. The following are examples of compounds of formula I which may be prepared in line with the processes herein-before described: (a) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline; (b) 1-[3-(1-thienyl(2)-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline; (c) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D,L-methyl-propanoyl]-L-thiazolidine-4-carboxylic acid; (d) 1-[3-(1-thienyl-(3)-2-nitro-ethylthio)-propanoyl]-L-proline; (e) 1-[3-(1-phenyl-2,2-diacetyl-ethylthio]-2-D-methyl-propanoyl]-L-proline; (f) 1-[3-(2-methyl-2-cyano-ethylthio)-2-D-methyl-propanoyl]-L-proline; (g) 1-[3-(2-pyridyl(4)-ethylthio)-2-D-methyl-propanoyl]-L-proline: (h) 1-[3-(1-phenyl-2,2-bis-[ethoxycarbonyl]-ethylthio)-propanoyl]-L-proline; (i) 1-[3-(3-oxo-n-butylthiol-2-D-methyl-propanoyl]-L-proline ;

(k) 1-[3-(1-[p-tolyl]-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline; (I) 1-[3-(1-thienyl(3)-2-nitro-ethylthio)-propanoyl]-L-proline; (m) 1 -[3-(1 -phenyl-2,2-diacetyl-ethylthio)-2-D-methyl-propanoyl]-L-proline; (n) 1-[3-(1-phenyl-2,2-bis-[ethoxycarbonyl]-ethylthio)-2-D-methyl-propanoyl]-L-proline; (o) 1-[3-(1-methoxy-2,2-bis-[methoxycarbonyl]-ethylthio)-2-D-methyl-propanoyl]-L-proline; (y) 1-[3-(2-[O,O-diethylphosphonyl]-ethylthio)-2-D-methyl-propanoyl]-L-proline; (q) 1-[3-(1-phenyl-2-methylsulfonyl-ethylthio)-2-D-methyl-propanoyl]-L-proline;(r) 1-[3-(1-methoxy-2,2-bis-[methoxycarbonyl]-ethylthio)-2-D-methyl-propanoyl]-L-proline;

(t) sulfonyl-bis[(ethylthio-2-D-methyl-propanoyl)-L-proline], i.e. the compound of formula

(u) sulfonyl-bis-[(ethylthio-propanoyl)-L-proline]; and (v) 1-[3-(1-phenyl-2-methylsulfonyl-ethylthio)-2-D-methyl-propanoyl]-L-proline. The starting compounds of formulae II, III and V are known from the literature. The compounds of formula IV are novel and may be obtained for example by addition of the free SH-group of a mercapto-alkyl carboxylic acid at the double bond of an olefin substituted by one or several electronegative groups. The substituted alkylthioacylamino acids of formula I and basic salts thereof which have been tested exhibit a strong long-lasting, blood-pressure decreasing activity. This appears to result from an inhibition of the angiotensin 1-converting enzyme and, thus, to a blocking of the formation of the vasoconstrictor angiotensin II from angiotensin I. Moreover, the novel compounds of the invention which have been tested exhibit an inhibiting effect upon the enzyme kininase II, which is responsible for the bradykinin degradation and which is considered to be identical to the above-mentioned angiotensin I - converting enzyme. As bradykinin has a vasodilating effect, the blood-pressure decreasing effect is intensified by this additional activity. The blood pressure decrease in normal rats caused by bradykinin is intensified by the novel compounds.This additional activity may also be responsible for the blood-pressure decreasing effect which is observed in untreated genetically high blood-pressure rats.

hereinafter) causes a blood pressure decrease of 19% on administration p.o. of a dose of 30 mg/kg to genetically high blood-pressure rats. The blood pressure decrease caused in rats by i.v. injection of 3.0 g/kg of bradykinin is intensified by 142% on administering 1.38 Micromol/kg i.v. of 1-[3-(1-phenyl-2-nitro-ethylthio)-2methyl-propanoyl]-L-proline.

D-methylpropanoyl]-L-proline (the final products of Examples 1 and 3 hereinafter) show inhibiting activities towards angiotensin-I- converting enzyme in vitro (IC50) of 1 .10-8 and 1.8 . 10-9 M/I respectively. IC50 is used herein to designate the concentration of inhibiting substance by which the angiotensin-I-converting-enzyme is inhibited by 50% (see H.S. Cheung, D.W. Cushman, Biochem. Biophys. Acta 293, 451 (1973)). In the compounds according to the invention there is no SH-group, which is responsible to a large degree for the side effects resulting from the use of substances of similar structure, for example of Captopril. Therefore, it may be expected that the novel compounds will be better tolerated. According to a further aspect of the present invention we provide pharmaceutical compositions comprising at least one compound of formula I (as hereinbefore defined) or physiologically acceptable salt thereof together with a pharmaceutical carrier and/or excipient. The pharmaceutical compositions of the present invention preferably are in forms suitable for oral, rectal or partenteral administration, and are advantageously in dosage unit form. According to a still further aspect of the present invention we provide a method of treatment of the human or animal body to counteract elevated blood pressure thereof, which method comprises administering to the said body an effective amount of at least one compound of formula I or physiologically acceptable salt thereof, preferably in the form of a pharmaceutical composition according to the present invention. The compounds of formula I and physiologically acceptable salts are conveniently administered in daily doses of 50 - 1000 mg, preferably 100 - 600 mg, and may be taken in one or more, advantageously 1 to 4, individual doses. The pharmaceutical compositions of the invention may include conventional pharmaceutical excipients or carriers, disintegrants, binders, lubricants, thickeners or diluents. The pharmaceutical compositions of the present invention are conveniently in such forms as, for example, tablets, capsules, suppositories, solutions, syrups, emulsions or dispersible powders, and, if desired, may contain further known active ingredients for example, saluretics, diuretics and/or antihypertensive agents. Pharmaceutical compositions of the invention in the form of tablets can be producted, for example, by admixing the active ingredient(s) with known excipients, for example inert diluents (e.g. calcium carbonate, calcium phosphate and lactose), disintegrants (e.g. corn starch and alginic acid), binders (e.g. starch and gelatin), lubricants (e.g. magnesium stearate and talc) and agents for obtaining sustained release (e.g. carboxypolymethylene, carboxymethyl cellulose, cellulose acetate phthalate and polyvinylacetate). Such tablets, if desired may consist of several layers. Pharmaceutical compositions of the invention in the form of coated tablets may be produced, for example by coating cores produced analogously to the tablets with agents such as are conventionally used in tablet, coating (e.g. polyvinyl-pyrrolidone or shellac, gum arabic, talc, titanium dioxide and sugar). In order to obtain sustained release or to avoid incompatibilities, the core and/or the tablet coating may consist of several layers in the preparation of which excipients such as are mentioned above for the tablets may be used. Pharmaceutical compositions of the invention in syrup form may contain additives such as sweeteners (e.g. saccharin, cyclamate, glycerin and sugar) taste improving agents (e.g. flavouring agents such as vanilla or orange extract), suspension agents, thickeners (e.g. sodium carboxymethyl cellulose), wetting agents (e.g. condensation products of fatty alcohols with ethylene oxide) and preservatives (e.g. phydroxybenzoates). Pharmaceutical compositions of the present invention in the form of injection solutions may be produced in a conventional way, for example with the addition of preservatives (e.g. p-hydroxybenzoates), stabilizers, (e.g. alkali metal salts of ethyl enedia mi ne-tetraacetic acid) or solubilizers and may than be filled into injection vials or ampoules. Pharmaceutical compositions of the present invention in the form of capsules may be produced, for example, by admixing the active substance(s) with inert carriers (e.g. lactose or sorbitol) and filling the mixture into gelatin capsules. The following Examples are provided to illustrate the invention without restricting the scope of protection sought therefor:- EXAMPLE 1

2.7 g of the t.butyl ester of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline and 1.5 g of -nitrostyrene are dissolved in 20 ml of anhydrous ethanol and admixed under nitrogen with 1 ml of N-methyl-morpholine at ambient temperature. After being allowed to stand for 2 hours at ambient temperature, the solvent is evaporated under reduced pressure and the residue is taken up in ethyl acetate. The ethyl acetate phase is shaken twice with KHS04-solution and once with NaCI-solution, dried with MgS04 and evaporated in vacuo.The oily product which is obtained is treated with approximately 30 ml of 1 N HCI at ambient temperature for more than 1 hour, the solvent is evaporated off using a rotating evaporator and the residue is admixed with ether several times and the solvent subsequently is evaporated off. 2g (56% of theory) of the title compound are obtained as a colourless oily material. Elemental analysis: Calculated: Found:

EXAMPLE 2

8.5 g of the t.butyl ester of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline are dissolved in 30 g of 5 ethyl-acrylate, admixed with 2.6 g of piperidine and 10 drops of Triton B and refluxed for 5 hours. After having distilled off the excess ethyl acrylate using a rotating evaporator, the residue is purified chromatographically on a silica gel column using CH2CI2/methanol (19:1) as eluting agent. Overthe oil product which is obtained are poured approximately 100 ml of 1 N HCI in glacial acetic acid and the mixture is stirred for 1 hour at 20[deg]C. After concentration and evaporation with ether of the residue, 3.2 g of the title ) compound are obtained as an oily material which then is dissolved in a little ether, admixed with the equivalent quantity of dicyclohexylamine and allowed to stand in a refrigeratorfor several days.The crystals which separate are suction filtered, washed with ether and dried in a desiccator. 3.5 g (23% of theory) of the dicyclohexylammonium salt of the title compound are isolated and have a pasty consistency. Elemental analysis: Calculated: Found: EXAMPLE 3

0.35 g of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline and 0.25 g of w-nitro-2-vinyl-thiophene are dissolved in anhydrous ethanol, admixed under nitrogen with 0.16 ml of N-methyl-morpholine and the mixture is stirred over-night at ambient temperature. After evaporating off the solvent and acidifying the reaction mixture with 2 N HCI, the product is extracted with ethyl acetate, the ethyl acetate extract being shaken after acidifying with 2 N HCI with NaHC03-solution, and the product again is extracted with ethyl acetate. The organic'phase thus obtained is dried over MgS04 and the solvent is evaporated off. The oily substance which remains is admixed with the equivalent quantity of a dicyclohexylamine and triturated with petroleum ether. 0.3 g (34% of theory) of the dicyclohexylammonium salt of the 1-[3-(1-thienyl(2)-2-nitro-ethylthio)2-Dmethyl-propanoyl]-L-proline in crystalline form, are obtained in this manner, m.p.: 61[deg]C. Elemental analysis: Calculated: Found:

EXAMPLES

2 g of w-nitro-2-vinyl-thiophene and 1.55 g of 3-mercapto-2-D-methyl-propionic acid are dissolved in anhydrous ethanol, admixed under nitrogen with 1.3 ml of N-methyl-morpholine and the mixture is stirred overnight at ambient temperature. After evaporation of the solvent the residue is taken up in dilute hydrochloric acid, the aqueous phase is extracted with ethyl acetate, the ethyl acetate extract is shaken with NaHC03 solution and, after acidifying with 2N HCI, this solution is extracted again with ethyl acetate. After having dried the solution over MgS04 and evaporated off the solvent, 2.5 g of 3-(1-thienyl(2)-2-nitroethylthio)-2-D-methyl-propionic acid are obtained as an oily substance.This oily substance is dissolved in anhydrous methylene chloride, admixed with 0.9 ml N-methyl-morpholine, cooled to -15[deg]C with the exclusion of moisture and admixed with 1.2 g of isobutyl chloroformate. After 8 minutes, a solution of 1.4 g of the t.butyl ester of L-proline in anhydrous methylene chloride is added. The mixture is allowed to warm up to ambient temperature and is stirred overnight. The solution subsequently is shaken with NaHC03 solution three times, with saturated KHS04 solution and once with distilled water, and is then dried and the solvent evaporated leaving an oily residue. The oily residue is treated with 1 N HCI in glacial acetic acid for 1 hour at ambient temperature. Thereafter the mixture is allowed to evaporate, ether is poured over the residue several times and the solvent subsequently is evaporated.The oily substance which remains is admixed with the equivalent quantity of dicyclohexylamine and triturated with ether. 2.8 g (42% of the theoretical total yield) of 1-[3-(1-thienyl(2)-2-nitroethylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt are obtained in the form of white crystals of m.p.: 61[deg]C. EXAMPLE 5

0.85 g of 3-(3-mercapto-2-methyl-propanoyl)-L-thiazolidine-4-carboxylic acid are reacted with 0.5 g of w-nitrostyrene. 300 mg of 3-[3-(1-phenyl-2-nitro-ethylthio)-2-D,L-methyl-propanoyl]-L-thiazolidine-4carboxylic acid-dicylohexyl ammonium salt of m.p.: 190[deg]C (decomp.) are obtained. Elemental analysis: Calculated: Found:

EXAMPLE 6 1-[3-(2-Cyano-propylthio)-2-D-methyl-propanoyl]-L-proline 0.35 g of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline are dissolved in water, the solution is adjusted to pH 8.1 with dilute ammonia and admixed under nitrogen with 0.2 g of methacrylonitrile. The reaction mixture is stirred overnight, the water is distilled off under reduced pressure, the oily residue is admixed with an equivalent quantity of dicyclohexylamine and triturated with ether. 0.4 g (53% of theory) of white crystals of the dicyclohexyl ammonium salt of the title compound are obtained. m.p.: 125[deg]C. Elemental analysis: Calculated: Found:

EXAMPLE

0.35 g of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline are dissolved in water, adjusted to pH 7 with triethylamine and admixed under nitrogen with 0.2 g of 4-vinylpyridine. The mixture is stirred overnight and extracted three times with ethyl acetate to separate excess vinyl pyridine. The aqueous phase is allowed to evaporate, the residue is admixed with an equivalent quantity of dicyclohexylamine and trituratedwith petroleum ether (Bp. 40 - 60[deg]C). 0.4 g (50% of theory) of 1-[3-(2-pyridyl(4)-ethylthio)-2-D-methyl-propanoyl]-Lproline-dicyclohexyl ammonium salt of m.p. 121[deg]C are obtained. Elemental analysis: Calculated: Found:

EXAMPLE

3 g of 1-(3-mercapto-2-D-methyl-propanoyl)-L-proline and 1.3 g of p-cyano-Q-nitrostyrene are dissolved in ethanol and admixed under nitrogen with 0.75 g of N-methyl-morpholine. The mixture is stirred overnight at ambient- temperature, the ethanol is distilled off and the residue is taken up in saturated KHS04 solution. The emulsion which is obtained is extracted three times with ethyl acetate and the combined ethyl acetate phases are shaken with a 10% KHC03 solution three times. The combined KHC03 phases are cooled, acidified with concentrated hydrochloric acid and extracted again with ethyl acetate three times. The combined ethyl acetate phases are washed with saturated sodium chloride solution, dried with MgS04 and the solvent is evaporated off. The residue is taken up in isopropanol and admixed with ether.The crystals which precipitate are taken up in methanol and the solvent is distilled off. The residue is dissolved in ethyl acetate and added dropwise to an ether/petroleum ether mixture (40 - 60[deg]C; 1: 1). The title compound is obtained in crystalline form. Yield:2.1 g (72% oftheory); m.p.78-80[deg]C. Elemental analysis: Calculated: Found:

The following compounds of the present invention were obtained in a manner analogous to Example 6 above: (a) 1-[3-(1-thienyl(3)-2-nitro-ethylthio)-propanoyl]-L-proline-dicyclohexyl ammonium salt. (hygroscopic)' Elemental analysis: C26H4, N3O5S2 Calculated: Found:

(b) 1-[3-(1-phenyl-2,2-diacetyl-ethylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt. m.p.: 144 -145[deg]C. Elemental analysis: Calculated: Found:

(c) 1-[3-(1-phenyl-2,2-bis{ethoxycarbonyl}-ethylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt m.p.. 76[deg]C Elemental analysis: Calculated: Found:

(d) 1-[3-(1-methoxy-2,2-bis-{methoxycarbonyl}-ethylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt. m.p.: 103[deg]C Elemental analysis: Calculated: Found:

salt. m.p.: 117[deg]C Elemental analysis: Calculated: Found:

(f) Sulfonyl-bis-[(ethylthio-2-D-methylpropanoyl)-L-proline]-bis-dicyclohexyl ammonium salt. m.p.: 127[deg]C Elemental analysis: Calculated: Found:

(g) 1-[3-(1-phenyl-2-methylsulfonyl-ethylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt. m.p..,168[deg]C(decomp.) Elemental analysis: Calculated: Found:

(h) 1-[3-(3-oxo-n-butylthio)-2-D-methyl-propanoyl]-L-proline-dicyclohexyl ammonium salt. m.p.: 125[deg]C Elemental analysis: Calculated: Found:

) (i) 1-[3-(1-p-tolyl-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline. m.p.: 58[deg]C. Elemental analysis: Calculated: Found:

The following are examples of pharmaceutical compositions according to the invention:

EXAMPLE I:

A mixture of the active ingredient with lactose and corn starch is granulated with a 10% aqueous gelatin solution through a screen of 1 mm mesh-size, dried at 40[deg]C and triturated through a screen once more. The granulated product thus obtained is admixed with magnesium stearate and pressed. The cores thus obtained are coated in the conventional way, the coating being applied with an aqueous suspension of sugar, titanium dioxide, talc and gum arabic. The finished coated tablets are polished with beeswax.

EXAMPLE II

Active ingredient and magnesium stearate are granulated with an aqueous solution of the soluble starch. The granulate is dried and admixed thoroughly with lactose and corn starch. Then the mixture is pressed to tablets of 230 mg weight, each tablet containing 100 mg of active ingredient.

EXAMPLE III:

Active ingredients and excipients are dissolved in a sufficient quantity of distilled water and brought to the desired concentration with the required quantity of water. The solution is filtered and filled into 2 ml ampoules under aseptic conditions. The ampoules are sterilized and sealed. Each ampoule contains 50 mg of active ingredient.

EXAMPLE IV:

Active ingredient, lactose and corn starch are admixed initially in a mixer and subsequently in a mill. Thereafter the mixture once more is introduced into the mixer, admixed thoroughly with talc and filled mechanically into hard gelatin capsules.

EXAMPLE V:

Cocoa butter and carnauba wax are melted, admixed thoroughly and cooled to 45[deg]C. The finely pulverized active ingredient is stirred into this mass. Subsequently the mixture is poured into slightly precooled suppository moulds of suitable size and allowed to cool.

Claims

1. Compounds of formula I

(wherein: R1 represents a nitro, cyano or pyridyl group or a group of formula -COR', -COOR', -PO(OR')2 or

R2 represents a hydrogen atom; a methyl, ethyl or -S02CH3 group, or a group of formula -COOR' or-COR'; R3 represents a hydrogen atom, a C1 to C3 alkoxy group, a phenyl group or a thienyl group; X represents a divalent group of formula -CH2 - CH2 - CH2 - or -CH2 - S - CH2 -; and R' represents a methyl or ethyl group) and salts thereof.

2. Compounds of formula I as claimed in claim 1 wherein R1 represents a hydrogen atom or a acetyl or methoxycarbonyl group; R2 represents a nitro, acetyl or methoxycarbonyl group; R3 represents a phenyl, thienyl or methoxy group; R4 represents a methyl, group; and X represents a divalent group of formula

and salts thereof.

3. Compounds offormula I as claimed in claim 1 and salts thereof wherein R4 represents a methyl group and wherein the 3-mercapto-2-methyl-propionic acid skeletal moiety is in the L-configuration.

4. Compounds as claimed in claim 1 selected from the following: (a) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof; (b) 1-[3-(1-thienyl(2)-2-nitro-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof; (c) 1-[3-(1-phenyl-2-nitro-ethylthio)-2-D,L-methyl-propanoyl]-L-thiazolidine-4-carboxylic acid and salts thereof; (d) 1-[3-(1-methoxy-2,2-bis-{methoxycarbonyl}-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof; and (e) 1-[3-(2-pyridyl(4)-ethylthio)-2-D-methyl-propanoyl]-L-proline and salts thereof.

5. Compounds as claimed in any one of claims 1 to 3 as herein specifically disclosed with the exclusion of compounds as claimed in claim 4.

6. A process forthe preparation of compounds of formula I (as defined in claim 1) and salts thereof which process comprises at least one of the following steps: (a) the addition of the free mercapto group of a compound of formula II

(wherein R4 and X are as defined in claim 1 and R5 represents a hydrogen atom or a Ci to C3 alkyl group at the double bond of an olefin of formula III

(wherein R1, R2 and R3 are as defined in claim 1) activated by at least one electron-attracting group and, where R5 represents other than a hydrogen atom, the subsequent acid or alkaline hydrolysis of the ester , group -COORs; (b) the reaction of a substituted alkylthio-carboxylic acid of formula IV

(wherein R1, R2, R3 and R4 are as defined in claim 1) with an amino acid of formula V

(wherein R5 represents a hydrogen atom or a C1 to C3 alkyl group) and, where R5 represents other than a hydrogen atom, the subsequent acid or alkaline hydrolysis of the ester group -COOR5; (c) (for the preparation of dimeric compounds of formula I and salts thereof, where R, represents a group offormula

[in which R2, R3, R4 and X are as defined in claim 1]) the reaction of a compound of formula II (as defined above) with divinylsulfone in a mole ratio of about 2:1 and, where R5 represents otherthan a hydrogen atom, the subsequent acid or alkaline hydrolysis of the ester group -COORs; (d) the conversion of a compound of formula I (as defined in claim 1) into a salt thereof or a salt of an acid of formula I into the free acid; and (e) the separation of a racemic mixture of a compound of formula I (as defined in claim 1) or a salt thereof into its enantiomers.

7. A process as claimed in claim 6 substantially as herein described in any one of Examples 1 to 8.

8. Pharmaceutical compositions comprising at least one compound offormula I (as defined in claim 1) or physiologically acceptable salt thereof togetherwith a pharmaceutical carrier and/or excipient.

9. Pharmaceutical compositions as claimed in claim 8 further containing as an active ingredient one or more saluretic, diuretic and/or antihypertensive agents.

10. Pharmaceutical compositions as claimed in claim 8 substantially as herein described in any one of Examples I to V.

11. A method of treatment of the human or animal body to counteract elevated blood pressure thereof which method comprises administering to the said body an effective amount of at least one compound of formula I or physiologically acceptable salt thereof.

12. Compounds offormula IV

(wherein R1, R2, R3, and R4 are as defined in claim 1) and salts thereof

13. A process for the preparation of compounds of formula IV (as defined in claim 12) which process comprises the addition of the mercapto group of a compound offormula VI

(wherein R4 is as defined in claim 1 and Rs represents a hydrogen atom or a C1 or C3 alkyl group) at the double bond of an olefin of formula III (as defined in claim 6) activated by at least one electron attacting group and, where R5 represents other than a hydrogen atom, the subsequent acid or alkaline hydrolysis of the ester group -COOR5. New claims or amendments to claims filed on 1.6.81 Superseded claims 1 New or amended claims:- 1. Compounds of formula I

(wherein R1 represents a nitro, cyano or pyridyl group or a group of formula -COR', -COOR', -PO(OR')2 or

R2 represents a hydrogen atom; a methyl, ethyl or -S02CH3 group, or a group of formula -COOR' or -COR'; R3 represents a hydrogen atom, a C1 to C3 alkoxy group, a phenyl group or a thienyl group; R4 represents a hydrogen atom or a methyl group; X represents a divalent group of formula -CH2 - CH2 - CH2 - or - CH2 - S - CH2 -; and R' represents a methyl or ethyl group) and salts thereof.