GB2039906A - Dehydroproline derivative - Google Patents

Abstract

1-[(S)-3-Mercapto-2- methylpropanoyl]-L-3,4-dehydroproline and salts thereof with a base, preferably physiologically acceptable salts, possess valuable anti-hypertensive properties and, thus, can be used for the treatment of hypertension, e.g. as pharmaceutical compositions. They can be prepared from corresponding novel S- acyl derivatives.

Description

SPECIFICATION Dehydroproline derivative The present invention relates to 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4dehydroproline of the formula

and salts thereof with a base.

According to the present invention, 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and its salts with a base are manufactured by a process which comprises a) splitting-off the acyl group R1-CO- in a compound of the general formula

wherein R1 represents lower alkyl, phenyl or phenyl-lower-alkyl,or b) converting a compound of the general formula

wherein R represents lower alkyl, to the corresponding free acid, and if desired, converting the 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline obtained into a salt thereof with a base.

The splitting-off of the acyl group R1-CO- in a compound of the formula II above is performed according to methods known per se, expediently by ammonolysis or alkaline hydrolysis. Preferabiy, a compound of the formula 11 above is treated with alcoholic or aqueous ammonia, preferably with an alcoholic ammonia or concentrated ammonium hydroxide solution, conveniently at about room temperature.

The conversion of a compound of the formula Ill above into the corresponding free acid is also performed according to methods known per se. Preferably, a compound of the formula Ill above wherein R represents tert.butyl or tert.amyl is treated with trifluoroacetic acid and anisole at about room temperature. In case R in formula Ill represents an other alkyl group, then the conversion into the free acid will be performed by alkaline hydrolysis, suitably with an alkali metal hydroxide, preferably sodium hydroxide. When the conversion of a compound of formula Ill above into the free acid is performed by alkaline hydrolysis, racemisation in the 3,4-dehydroproline moiety can occur.

The compounds of the formula II and Ill form also part of the present invention. The compounds of the formula II can be prepared, for example, by reacting a L-3,4-dehydroproline derivative of the general formula

wherein R" represents hydrogen or lower alkyl, with a haloalkanoic acid otthe general tormula

wherein X represents halogen, preferably chlorine or bromine, according to known procedures in which the acid of formula V is activated, either prior to reaction with the compound of formula IV, involving formation of a mixed anhydride, symetrical anhydride, acid chloride, active ester, or by use of Woodward reagent K, EEDQ(N-ethoxycarbonyl-2-ethoxy-1 ,2-dihydroquinoline), dicyclohexylcarbodiimide, and the like yielding a compound of the general formula

wherein X and R2 have the meaning indicated above, which in turn is subjected to a displacement reaction with the anion of a thioacid of the general formula

wherein R1 has the meaninq indicated above, yielding a compound of the general formula

wherein R' and R2 have the meaning indicated above.

Alternatively, the compounds of the formula VIII above can also be prepared by reacting athioacid of the formula VI above with methacrylic acid of the formula

yielding an acylthioalkanoic acid of the general formula

wherein R1 has the meaning indicated above, which in turn is reacted with a L-3,4-dehydroproline derivative of the formula IV above to yield the desired compound of formula VIII.

According to a further process embodiment, the methacrylic acid is first made to react with a L-3,4-dehydroproline derivative of the formula IV above to obtain a compound of the general formula

wherein R2 has the meaning indicated above, which in turn is then made to react with a thioacid of the formula VI above to yield the desired compound of formula Vill.

In a still further process embodiment, a L-3,4-dehydroproline derivative of the formula IV above is made to react with a haloalkanoyl halide of the general formula

wherein X and X' are same or different and represent halogen, preferably chlorine or bromine.

This reaction is effected in an alkaline medium, e.g., in a dilute alkali metal hydroxide, an alkali metal bicarbonate or an alkali metal carbonate solution at a reduced temperature, conveniently at about 0 to 15"C.

The reaction product is then treated with the anion of a thioacid of formula VI above in an alkaline medium, preferably in an alkali metal carbonate solution, and then working up in a conventional manner to yield the desired compound of formula VIII.

In a still alternate process embodiment, a L-3,4-dehydroproline derivative of the formula IV above wherein R2 represents lower alkyl, preferably tert.butyl, can be made to react with a-methyl-p-prnpiothiolactone in an anhydrous solvent such as tetrahydrofuran, dioxane, methylene chloride, and the like at about 0 C to about room temperatue yielding the desired compound of formula VIII wherein R2 represents lower alkyl.

The compounds of formula VIII wherein R2 represents lower alkyl can be converted into the corresponding free acids according to methods known per se and in the same manner as described above for the conversion of a compound of formula III into 1 -[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline of formula I above.

The above described process embodiments for the synthesis of a compound of formula VEIL, except those using methacrylic acid, can utilize the racemate or the required enantiomer as starting material. When a racemic starting material is used in the synthetic procedures described above, the mixture of the two epimers obtained have to be separated at a suitable stage of the procedure by conventional chromatographic or fractional crystallization methods. Conveniently, a compound of the formula Vlil wherein R2 represents hydrogen is treated with a suitable base, preferably dicyclohexylamine, and the salt thus obtained is separated by fractional crystallization.

It is evident that the compounds of the formula Il are embraced by the above formula VIII.

The compounds of the formula Ill can be prepared in an analogous manner as described for the preparation of the compounds of formula II. It is appreciated that the synthetic procedure starts with a L-3,4-dehydroproline derivative of the formula IV wherein R2 represents lower alkyl and that in the last step of the synthesis the acyl group R'-CO- is splitted off. This splitting-off can be performed in the same manner as described above for the conversion of a compound of formula Il into the desired end product of formula 1-[(S)-3-mercapto-2-methyipropanoyl]-L-3,4-dehydroproiine of formula I forms salts with various inorganic and organic bases which salts are also within the scope of this invention.Such salts include ammonium and alkali metal salts such as the sodium and potassium salts (which are preferred), alkaline earth metal salts such as the calcium and magnesium salts, salts wich organic basis, e.g., dicyclohexylamine, benzothine, N-methyl-D-glucamine, hydrabamine, salts with amino acids such as arginine, lysine, and the like. The non-toxic, physiologically acceptable salts are preferred, although other salts are also useful, e.g., in isolating or purifying the product.

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

Additional experimental details are found in the examples which are preferred embodiments of the invention.

The term "lower alkyl" denotes straight and branched chain saturated hydrocarbon radicals containing 1 to 7 carbon atom, for example, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert.butyl, pentyl, isopentyl and the like. The membres with 1 to 4 carbon atoms, especially methyl and ethyl, are preferred.

Phenylmethyl is the preferred phenyl-lower alkyl group. The term "halogen" denotes fluorine, chlorine, bromine and iodine, with chlorine and bromine being preferred.

1 -[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and its salts inhibit the conversion of the decapetide angiotensin I to angiotensin II, and therefore are useful in reducing or relieving angiotensinrelated hypertension. The action of the enzyme renin on angiotensinogen, pseudoglobulin in blood plasma, produces angiotensin I. Angiotensin I is converted by angiotensin-converting enzyme (ACE) to angiotensin 11.

The latter is present as an active pressor substance which has been implicated as a causative agent in various forms of hypertension in various mammalian species, for example, rats and dogs. 1-[(S)-3-mercapto 2-methylpropanoyl]-L-3,4-dehydroproline and its salts intervene in the renin oangiotensin I iotensin eangiotensin Il sequence, by inhibiting angiotensin-converting enzyme and reducing or eliminating the formation of the pressor substance, angiotensin II. Thus, by the administration of a composition containing 1 -[(S)-3 mercapto-2-methylpropanoyl]-L-3,4-dehydroproline or a physiologically acceptable salt thereof, angiotensin-dependent hypertension in the species of mammals suffering therefrom is alleviated.A single dose, or preferably 2-4 divided daily dose, provided on a basis of about 0.02-100 mg/kg. 1-[(S)-3-mercapto-2- methylpropanoyl]-L-3,4-dehydroproline and its salts are preferably administered orally, but parenteral routes, such as subcutaneously, intramuscularly, intravenously or intraperitoneally can also be employed.

1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and its salts can be utilized to achieve the reduction of blood pressure by formulation in compositions such as tablets, capsules or elixirs for oral administration or in sterile solutions or suspensions for parenteral administration. About 1 to 500 mg of 1 -[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline or of a physiologically acceptable salt thereof are compounded with a physiologically acceptable vehicle, carrier excipient, binder, preservative, stabilizer, flavor, etc., in a unit dosage form as called for by accepted pharmaceutical practice. The amount of active substance in these compositions or preparations is such that a suitable dosage in the range indicated is obtained.

Illustrative of the adjuvants, which may be incorporated in tablets, capsules and the like are the following: a binder such as gum tragacanth, acacia, corn starch or gelatin; an excipient such as dicalciumphosphate; a disintegrating agent such as corn starch, potato starch, alginic acid and the like; a lubricant such as magnesium stearatae, a sweetening agent such as sucrose, lactose or saccharin; a flavoring agent such as peppermint, oil of wintergreen or cherry. When the dosage unit form is a capsule, it may contain, in addition to materials of the above type, a liquid carrier such as a fatty oil. Various other materials may be present as coatings orto otherwise modify the physical form of the dosage unit. For instance, tablets may be coated with shellac, sugar or both.A syrup or elixir may contain the active compound, sucrose as a sweetening agent, methyl and propyl parabens as preservative, a dye and a flavouring such as cherry or orange flavor.

Sterile compositions for injection can be formulated according to conventional pharmaceutical practice by dissolving or suspending the active substance in a vehicle such as water for injection, a naturally occuring vegetable oil such as sesame oil, coconut oil, peanut oil, cottonseed oil, etc., or a synthetic fatty vehicle such as ethyl oleat and the like. Buffers, preservatives, antioxidants and the like can be incorporated as required.

The following examples illustrate the present invention. All temperatures are given in degrees Centigrade.

They describe the synthesis of 1 -[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline according to the following procedure: thioacetic acetic acid and methacrylic acid were reacted at 1000 to provide (RS)-3-acetylthio-2-methylpropionic acid. L-3,4-Dehydroproline was converted to the tert.butyl ester by the procedure of Roeske, J. Org. Chem., 28, (1963). Coupling of the above compounds by the dicyclohexylcarbodiimide procedure provided the 1-[(RS)-3-acethylthio-2-methylpropanoyl]-L-3,4- dehydroproline tert.butyl ester in excellent yield. The tert.butyl ester group was removed selectively by trifluoroacetic acid. Conversion to the dicyclohexylammonium salt was followed by the resolution of the epimers.The 1 -[(S)-3-acetylthio-2-methylpropanoyl]-L-3,4-dehydroproline dicyclohexylammonium salt was crystallized to constant rotation, converted to the free acid, and deprotected with ammonia in methanol. The final product was purified by ion exchange chromatography. The absolute configuration was confirmed by x-ray crystal structure analysis.

EXAMPLE 1 Preparation of (RS)-3-acetylthio-2-meth ylpropionic acid A mixture of 32.5 g (0.378 mol) of methacrylic acid and 25 g (0.325 mol) thioacetic acid was refluxed on a steam bath for 2 hours. Unreacted reagents were removed by distillation (water aspirator) and the residual oil was crystallized from petroleum ether. Recrystallization from petroleum ether yielded 34.7 g (65.8%) of (RS)-3-acetylthio-2-methylpropionic acid as white crystalline product, m.p. 34-37".

EXAMPLE 2 Preparation ofL-3,4-dehydroproline tert butyl ester Into each of five pressure bottles was placed a mixture of 2.83 g (0.025 mol) of L-3,4-dehydroproline and 50 ml of dioxane. 5.0 ml of conc. sulfuric acid were added portionwise with stirring followed by the addition of 30 ml of isobutylene. Stirring proceeded at 25 for 16 hours. The reaction mixtures were added to a chilled solution of 800 ml of 1 N sodium hydroxide solution. The reaction mixture was extracted with ether (3 x '100 ml), and the organic layer was washed with water (3 x 50 ml), dried over magnesium sulfate and evaporated.

The residue was distilled under reduced pressure until all the volatile material was removed. 9.77 g (46.2%) of a viscous residual colorless oil consisting of L-3,4-dehydroproline tert.butyl ester was obtained.

L-3,4-dehydroproline tert.butyl ester was converted to the hydrochloride by treatment with hydrogen chloride in ether and crystallized from isopropanol/etheryielding a white crystalline product, m.p. 122-128" (dec.), iaI25- 187.00 (c,2%, ethanol).

EXAMPLE 3 Preparation of l-[(RS)-3-acetylthio-2-meth ylpropan 0 ylJ-L-3,4-deh ydroprollne tert. butyl ester A mixture of 9.77 g (0.0577 mol) of L-3,4-dehydroproline tert.butyl ester and 10.3 g (0.0635 mol) of (RS)-3-acetylthio-2-methylpropionic acid in 80 ml of methylene chloride was cooled to 0" and coupled with 13.1 g (0.0635 mol) of dicyclohexylcarbodiimide. Stirring proceeded at 0" four 1 hour and at 25" for 3 hours.

The reaction mixture was filtered and the filtrate extracted with 1 M citric acid (3 x 50 ml), saturated sodium chloride solution (3 x 50 ml), 10% sodium bicarbonate solution (3 x 50 ml), dried over magnesium sulfate and evaporated yielding 16.8 g (92.9%) of a viscous residual oil, [a]25 - 94.20 (c, 1,3%, ethanol).

EXAMPLE 4 Preparation of l-(S)-3-acetylthio-2-methylpropanoylj-L-3,4-dehydroprollne dicyclohexylammonium salt 16.8 g (0.0536 mol) of 1 -[(RS)-3-acetylthio-2-methylpropanoyi]-L-3,4-dehydroproline tert.butyl ester were treated with a mixture of trifluoroacetic acid/anisole/mercaptoethanol (200 ml:100 ml:0.5 ml) under nitrogen at 25 for 1 hour. The reaction mixture was evaporated to dryness, taken up in ethyl acetate and extracted with 10% sodium bicarbonate solution (3 times). The aqueous layer was acidified with 6 M hydrochloric acid and extracted with ethyl acetate (3 times), dried over magnesium and evaporated under reduced pressure.

The residual yellow oil (11.85 g, 44.9 mmol) was taken up in 75 ml of ethyl acetate and 8.8 ml (44.9 mmol) of dicyclohexyiamine were added. After standing at 0 for 18 hours, a white crystalline product was obtained.

Crystallization from acetonitrile yielded 4.91 g of 1-[(S)-3-acetylthio-2-methylpropanoyl]-L-3,4- dehydroproline dicyclohexylammonium salt as a white crystalline product, m.p. 185-186.5' (dec.), [a]D5 -208.7" (c, 1.4%, ethanol). The melting point and the rotation were unchanged on further crystallization.

EXAMPLE 5 Preparation of l-f(S)-3-acetylthio-2-meth ylpropanoylj-L-3, 4-deh ydroproline 4.49 g (10.2 mmol) of 1-[(S)-3-acetylthio-2-methylpropanoyi]-L-3,4-dehydroproline dicyclohexylammonium salt were taken up in 50 ml of 5% potassium bisuifate solution and extracted with ethyl acetate (3 x 30 ml). The organic layer was backextracted with 5% potassium bisulfate solution and water and dried over magnesium sulfate and evaporated under reduced pressure yielding 2.03 g (77.4%) of a viscous colorless oil, [a]f7;5-297.3 (c, 1%, ethanol).

EXAMPLE 6 Preparation of 1-[rS)-3-mercapto-2-methylpropanoyll-L-3,4dehydroproline 1.71 g (6.65 mmol) of 1-[(S)-3-acetylthio-2-methylpropanoyl]-L-3,4-dehydroproline were dissolved in 14.5 ml (89.9 mmol) of freshly prepared 6.2 M ammonia in methanol and stirred at 25 for 2 hours. The reaction mixture was evaporated under reduced pressure and the residue passed through a column (1.5 x 17.5 cm) of Dowex 50WX2 (H+ form) and eluted with water (0.01 M in mercaptoethanol, 50 drops per fraction).Fractions 7-25 were pooled, lyophilized, triturated with water (0.01 M in mercaptoethanol) and crystallized from ethyl acetate/petroleum ether yielding 0.72 g (50.2%) of 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4- dehydroproline, m.p. 122-124', [aj25 -340.9" (c, 1.76%, ethanol). The infrared and nmr spectra were in agreement with the proposed structure. X-ray analysis confirmed the absolute stereochemistry as (S)-(L).

Example A Tablet formulations containing: mg/tablet 1 -[(S)-3-Mercapto-2-methyl propanoyl]-L-3,4-dehydro- proline 1 5 10 25 Lactose 221 217 212 181 Microcrystalline Cellulose 45 45 45 55 Direct Compression Starch 30 30 30 35 Magnesium Stearate 3 3 3 4 Tablet weight 300 mg 300 mg 300 mg 300 mg can be prepared as follows.

Mix the active ingredient with an equal amount of lactose and mix well. Mix with the microcrystalline cellulose, the direct compression starch and the remaining amount of the lactose and mix well. Add the magnesium stearate and mix for 3 minutes and compress on a suitable table press.

Example B Tablet formulations containing: mg/tablet 1 [(S)-3-Mercapto-2-methylpropanoyl]-L-3,4-dehydroproline 15 30 60 Lactose 207 192 162 Microcrystalline Cellulose 45 45 45 Direct Compression Starch 30 30 30 Magnesium Stearate 3 3 3 Tablet weight 300 mg 300 mg 300 mg can be prepared as follows: Mix the active ingredient with an equal amount of lactose and mix well. Mix with the microcrystalline cellulose, the direct compression starch and the remaining amount of the lactose and mix well. Add the magnesium stearate and mix for 3 minutes and compress on a suitable tablet press.

Example C Tablet formulations containing: mg/tablet 1-[(S)-3-Mercapto-2-methyl- propanoyl]-L-3,4-dehydro- proline 100 250 500 Lactose 147.5 100 97.5 Pregelatinized Starch , 25 30 60 Modified Starch 25 50 60 Cornstarch 25 50 60 Magnesium Stearate 2.5 5 7.5 Tablet weight 325 mg 485 mh 785 mg can be prepared as follows: Mix the first five ingredients in a suitable mixer. Granulate with water, dry overnight in a suitable oven and mill through a suitable mill. Mix with the magnesium stearate and compress on a suitable tablet press.

Example Tablet formulations containing: mg/tablet 1 -[(S)-3-Mercapto-2-methyl- propanoyl]-L-3,4-dehydro proline 1 5 15 30 60 Lactose 202 198 188 173 188 Modified Starch 25 25 25 25 30 Pregelatinized Starch 20 20 20 20 20 Distilled Water q.s. q.s. q.s. q.s. q.s.

Magnesium Stearate 2 2 2 2 2 Tablet weight 250 mg 250 mg' 250 mg 250 mg 300 mg can be prepared as follows: Mix the first four ingredients in a suitable mixer. Granulate with sufficient distilled water to proper consistency and mill and dry in a suitable oven. Add the magnesium stearate and mix for 3 minutes and compress on a suitable tablet press.

Example E Capsule formulations containing: mg/capsule 1 -[(S)-3-Mercapto-2-methyl propanoyl]-L-3,4-dehydro- proline 1 5 15 30 60 Lactose 203 199 239 224 194 Starch 30 30 30 30 30 Talc 15 15 15 15 15 Magnesium Stearate 1 1 1 1 1 Capsule fill weight 250 mg 250 mg 300 mg 300 mg 300 mg can be prepared as follows: The first three ingredients are blended in a suitable mixer and thereafter the talc and the magnesium stearate are added and mixed for a short period of time. The mixture is filled on an appropriate capsule machine.

Example F Capsule formulations containing: mg/capsule l-[(S)-3-Mercapto-2-methyl- propanoyl]-L-3,4-dehydroproline 100 250 500 Lactose 99 148 Cornstarch 20 30 57 Talc 5 10 15 Magnesium Stearate 1 2 3 Capsule fill weight 225 mg 440 mg 575 mg can be prepared as follows: The first three ingredients are blended in a suitable mixer and milled through a suitable mill. Add the talc and the magnesium stearate and mix. The mixture is filled on a suitable capsule machine.

Claims (10)

1. 1 -[(S)-3-Mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and salts thereof with a base.

2. A compound of the general formula

wherein R3 represents hydrogen and R4 represents the group R1-CO- wherein R1 represents lower alkyl, phenyl or phenyl-lower alkyl, or R3 represents lower alkyl and R4 represents hydrogen.

3. 1-[(S)-3-Mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and physiologically acceptable salts thereof with a base as pharmaceutically active substances.

4. 1-[(S)-3-Mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and physiologically acceptable salts thereof with a base as anti-hypertensive agents.

5. A process for the preparation of 1 -[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline and salts thereof with a base, which process comprises a) splitting-off the acyl group R1-CO- in a compound of the general formula

wherein R1 represents lower alkyl, phenyl or phenyl-lower alkyl, or b) converting a compound of the general formula

wherein R represents lower alkyl, to the corresponding free acid, and if desired, converting the 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline obtained into a salt thereof with a base.

6. A medicament containing 1-[(S)-3-mercapto-2-methy-propanoyl]-L-3,4-dehydroproline or a physiolo gically acceptable salt thereof with a base.

7. An anti-hypertensive agent containing 1 -[(S)-3-mernapto-2-methylprnpanoylj-L-3A-dehydrnprnline or a physiologically acceptable salt thereof with a base.

8. The use of 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline or a physiologically acceptable salt thereof with a base in the control or prevention of illnesses.

9. The use of 1-[(S)-3-mercapto-2-methylpropanoyl]-L-3,4-dehydroproline or a physiologically acceptable salt thereof with a base in the treatment of hypertension.

10. The invention as hereinbefore described.