NO121788B - - Google Patents

Description

Analogy method for the preparation of therapeutically effective DL-, D- or L-S-phenylalanine derivatives.

The present invention relates to an analogous method for

production of new p-phenylalanine derivatives with prolonged hypotensive effect.

p-phenylalanine derivatives with hypotensive action are known from French medical patent No. 901 M. These known p-phenylala-

nin derivatives can be denoted by the following general formula:

where denotes a lower alkyl radical, hydrogen or an alkyl radical, hydrogen or a lower alkanoyl radical, X denotes hydrogen or a halogen atom or trifluoromethyl radical, and n is 1, 2 or 3, X is in p-position in relation to the amino acid side chain. Among these p-phenylalanine derivatives, α-methyl-dopa or α-methyl-p-(3,4-dihydroxyphenyl)-alanine is a well-known hypotensive agent.

It has now been found that new similar but chemically different p-phenylalanine derivatives also have a hypotensive effect, but that this effect is surprisingly longer than that of the known p-phenylalanine derivatives, especially a-methyl-dopa, which is described in the aforementioned French medical patent.

The new p-phenylalanine derivatives produced according to the present invention can be denoted by the following general formula I,

where R^ and R^ are identical or different and denote methyl or ethyl, and one of them is optionally hydrogen or an acyl radical with 1-30 carbon atoms, R^ denotes either hydrogen, or a pharmaceutically acceptable, non-toxic alkali imed all- , ammonium or substituted ammonium ion or denotes an alkyl or alkenyl radical with 1-30 carbon atoms with a straight or branched chain, X denotes chlorine, bromine, iodine or fluorine, and Z denotes hydrogen or an acyl radical with 1-30 carbon atoms,

or a non-toxic acid addition salt thereof.

The compounds of the general formula I exhibit prolonged hypotensive activity and are therefore useful for lowering blood pressure. Preferred compounds such as 3-methoxy-4-hydroxy-5-chloro-phenylalanine (hydrochloride), 3-methoxy-4-hydroxy-5-bromo-phenylalanine (hydrochloride) and 3-hydroxy-4-methoxy-5-bromo-phenyl -alanine (hydrochloride) has been found to lower blood pressure in hypertensive rats when administered orally or subcutaneously at doses of from 30 to 100 mg/kg by the method described by M. GEROLD, A. HURLIMANN and C von PLANTA in Heiv. Physiol.

Acta 24, 58 (1966).

In the following, results from carried out comparison tests between α-methyl-dopa according to French medical patent no.

901 M and two compounds produced according to the present invention:

A. Antihypertensive effect.

In a comparative study carried out on laboratory animals (rats) made hypertensive according to the method of A. Grollmann (Proe. Soc. Exp. Biol. Med. 5^7, 102 (1944) with a-methyl-dopa, and two compounds prepared according to the present invention, namely 3-methoxy-4-hydroxy-5-bromo-phenylalanine (hydrochloride) and 3-methoxy-4-hydroxy-5-chloro-phenylalanine (hydrochloride) hereinafter referred to as RIT 1412/HC1 and RIT 1456 /HC1, the following results were obtained after subcutaneous injection of the various compounds with the indicated doses, and the compounds are administered in the form of a solution in physiological salt solution.

The results clearly demonstrate the special, long-lasting hypotensive effect of RIT 1412 and RIT 1456, an effect that α-methyl-dopa lacks.

B. Toxicity studies.

I. Acute toxicity (on 10 mice)/lethal dose 50% (LD5o).

The products are administered in solution in normal saline (NaCl 8 o/oo), adjusted to pH 7.4 with NaOH (for the hydrochloride).

II- Subacute toxicity (on rats)

a) RIT 1412

A subacute toxicity test has been carried out on 3 groups of

at least 15 rats, one group as a reference (untreated) and each of the other two groups receive 25 intraperitoneal injections of 100 and 500 mg/kg RIT 1412 between the 12th and 44th day. The animals were killed after the 47th day.

Tissue examination (liver, kidney, spleen) showed no toxicity.

The growth curve was normal and the blood composition was not affected,

b) RIT 1456 HC1

A subacute toxicity test as described for RIT 1412 (but with 40 intraperitoneal injections between days 10 and 80, when the animals were killed) was performed with RIT 1456 HCl with the same result.

The toxicity test clearly shows that the new |3-phenylalanine derivatives of formula I have a low toxicity, and the lethal doses are far above the normal therapeutically active doses.

The compounds of formula I can be administered orally, intramuscularly, intravenously or subcutaneously.

The compounds of the general formula I with a free amino group are preferably administered in the form of a non-toxic addition salt thereof, and the acid is an inorganic acid, such as hydrochloric acid, hydrobromic acid, phosphoric acid or sulfuric acid. When R^ is alkyl, other possible acid addition salts are those with organic acids, such as acetic acid, succinic acid, maleic acid, fumaric acid, tartaric acid, citric acid, palmitic acid, methanesulfonic acid, ethanesulfonic acid, etc., and production of the acid addition salts also falls within the scope of the present invention.

The new (3-phenylalanine derivatives can be processed into and formulated into pharmaceutical preparations for oral or parenteral administration with pharmaceutically acceptable carriers. The preparations can be in the form of tablets, powders, granules, capsules, suspensions, solutions, emulsions, injectable solutions and suspensions and the like.Such preparations also fall within the scope of the invention.

The method for producing the p-phenylalanine derivatives according to the present invention is characterized by

a) a suitable substituted 2-benzyl-2-amino-malonic acid lower (1 -

4 C) alkyl esters of the general formula III,

where Alk1 denotes an alkyl radical with 1-4 carbon atoms, Y denotes a formyl, acetyl, benzoyl, phthaloyl or benzyl oxycarbonyl radical and R^, R2 and X are as defined above, hydrolyzed and decarboxylated, the reaction being carried out in a solvent1 under the influence of heat in an acidic medium, and preferably in the presence of a reducing agent, or b) a suitable substituted phenylpyruvic acid of the general formula IV,

where R^, R ? and X is as defined above and M denotes hydrogen or a non-toxic monovalent cation, is reduced under mild conditions in ammonium hydroxide solution,

after which the desired salt, ester, acyl derivative and/or optical isomer is optionally obtained from the reaction product using methods known per se.

The N-substituted aminomalonic acid lower alkyl (1 - 4 carbon atoms) ester derivatives and phenylpyruvic acid derivatives used in the synthesis and the 5-halobenzaldehydes used in the preparation of the phenylpyruvic acid derivatives are new compounds and are represented by the above general formulas III and IV and formula II below,

In the general formula II, R1 > R1, and X are as defined above.

According to the particular nature and position of R-^ and R2, the 3,4-disubstituted-5-halo-benzaldehydes of formula II and the N-substituted aminomalonic acid ester derivatives of general formula III can be obtained in different ways, some of which in what follows is described under the headings A to C.

A. When R1 is methyl or ethyl and R> is hydrogen, the intermediate N-substituted aminomalonic acid ester derivative is obtained from the corresponding 3,4-disubstituted benzaldehyde. Therefore, the 3,4-disubstituted benzaldehyde is first halogenated to the corresponding 5-halobenzaldehyde, and the reaction is preferably carried out at room temperature in a suitable solvent such as e.g. acetic acid. When X is fluorine, the 3,4-disubstituted 5-fluorobenzaldehyde is preferably prepared from the corresponding 5-bromobenzaldehyde by halogen replacement.

The 5-halobenzaldehyde obtained is then reduced under mild conditions to the corresponding alcohol, and alkali borohydride is used, e.g. to avoid hydrogenolysis of the halogen bond in the 5-position of the phenyl group.

By reaction with a mineral acid, e.g. hydrochloric acid, in an anhydrous medium, the alcohol is converted into the corresponding halo derivative. This is allowed to react with an alkali (preferably sodium) di-lower (1 to 4 carbon atoms) alkyl N-substituted aminomalonate (preferably the dimethyl or diethyl ester) and gives the N-substituted aminomalonic acid ester derivative of formula IIIa. This step is carried out in a suitable solvent, preferably at the reflux temperature. Examples of suitable solvents are anhydrous ethanol, benzene, dimethylformamide and toluene.

This procedure can be indicated by the following reaction scheme 1:

where Alk denotes methyl or ethyl, Alk<1> denotes a lower alkyl radical with from 1 to 4 carbon atoms, preferably methyl or .ethyl, X and X' - which may be identical or different - denotes halogen, X is preferably chlorine or bromine and X' is preferably chlorine, denotes an alkali metal ion, preferably sodium ion and Y is as defined above.

B. When in general formula I denotes hydrogen and R 2 denotes methyl or ethyl, the intermediate N-substituted aminomalonic acid ester derivative is obtained from a 3-alkoxy-substituted benzaldehyde, and the alkoxy group contains from 1 to 4 carbon atoms. 3-Alkoxy-substituted-benzaldehyde is therefore first halogenated to the corresponding 5-halo-benzaldehyde which is dealkylated to 5-halo-protocatechualdehyde, and this is then selectively alkylated in position 4.

The dealkylation is carried out using methods known in the field for such reactions, e.g. with anhydrous aluminum chloride and pyridine in methylene chloride, under the action of heat.

The O-alkylation, which is selective for position 4, is carried out in an inert solvent using known alkylation methods, provided that the molar ratio between alkylating agent and aldehyde is lower than two. Acetone + methyl iodide and dioxane + diazomethane are examples of solvent/alkylating agent systems.

The 3-hydroxy-4-alkoxy-aldehyde is then successively reduced with mineral acid and then with the alkali-dilute-alkyl-N-substituted-aminomalonate as described under A.

The following form 2 describes the special features of this method compared to the method according to form 1.

where R^ denotes alkyl with 1-4 carbon atoms and the other symbols are as defined above.

Optionally, the intermediate N-substituted aminomalonic acid ester derivative is also obtained from a 3-alkoxy-substituted benzaldehyde, where the alkoxy group has more than two carbon atoms, e.g. 3-iso-propoxy-4-hydroxy-benzaldehyde.

This starting material is therefore first halogenated to the corresponding 5-halobenzaldehyde, which is then alkylated, e.g. with dimethyl or diethyl sulfate to the corresponding 3-isopropoxy-4-alkoxy-5-halo-benzaldehyde. This product is then deisopropylated, e.g.

by refluxing for a short time (from one to ten minutes) a solution of this in aqueous hydrobromic acid (48%). The de-isopropylated compound is then successively reduced, reacted with mineral acid and then with alkali dilute alkyl N-substituted amino malonate as described under A.

The following form 3 reproduces the special features of this method in relation to the method according to form 1.

where the symbols are as defined above.

C. When in general formula I both R i and R 2 denote methyl and/or ethyl, the intermediate product N-substituted aminomalonic acid ester derivative is obtained according to the method described under A in scheme 1, and the substituted 4-hydroxybenzaldehyde is converted to the corresponding 4-alkoxy compound for reduction of the aldehyde group to alcohol.

This alkylation step is optionally carried out with methyl or ethyl sulphate in aqueous sodium hydroxide.

The following form 4 describes the special features of this method in relation to form 1.

where Alk and Alk" are identical or different and denote methyl or ethyl, and the other symbols are as defined above.

The compounds of general formula I are then prepared from compounds of general formula II using various methods, among which the preferred ones are those described below under the headings Method I and Method II.

Method I.

According to this method, the derivatives of general formula I are prepared as described in the following scheme 5 by hydrolysis and decarboxylation of suitable substituted 2-benzyl-2-aminomalonic acid esters of general formula III, and the obtained amino acid is then converted into the desired salt, ester and /or acylated compound according to methods known in the field. In this scheme 5, R.sub.2 and X are as defined above, Alk' denotes a straight or branched chain lower alkyl radical with from 1 to 4 carbon atoms, preferably methyl or ethyl, and Y denotes a formyl, acetyl, benzoyl , phthaloyl or benzyl oxycarbonyl radical.

In order to avoid dealkylation of the alkoxy substituent or substituents in the phenyl ring, the reaction is carried out under mild conditions characterized by a reaction period of between 9 and 10 hours at a temperature between 95° and 105°C (reflux temperature) for a 40/60 ( v/v) mixture of hydrochloric acid and glacial acetic acid. It is clear that the said mild conditions are not limited to the preferred ones, but they can be from 3 to 20 hours at a temperature between 90° and 110°C for either mineral acid/glacial vinegar mixtures (containing at least 10% mineral acid) or for hydrochloric acid alone, and it should be understood that these working conditions are mutually dependent on each other, as is clear to the person skilled in the art.

To avoid possible oxidation of the reaction products, a reducing agent is preferably added to the medium.

Suitable reducing agents are thus either sulfur dioxide which is bubbled through the medium for heating, or sodium bisulphite or sodium dithionite.

Method II.

According to this method, the derivatives of general formula I are prepared as described below in scheme 6. A suitable substituted benzaldehyde of general formula II is therefore reacted with a stoichiometric amount of acetylglycine in the presence of an excess of acetic anhydride. The reaction is carried out in a suitable solvent (such as an alcohol/water mixture) under the influence of heat (reflux) preferably in the presence of sodium acetate to give the azlactone.

The new azlactone is then converted to the corresponding phenylpyruvic acid derivative with either strong alkalis or strong acids. with alkalis being preferred, and the reaction being carried out under the influence of heat in an inert solvent, such as e.g. water or water-alcohol mixture, and concentration in alkali is at least 10%.

Optionally, by using mild alkaline conditions (alkali concentration below 10%), an intermediate product 2-acetamido-3-substituted phenylpropenoic acid is obtained, which is then further converted to the corresponding substituted phenylpyruvic acid with strong mineral acids or alkalis.

The following scheme 6 illustrates the process starting from a 3-alkoxy-4-hydroxy-5-halo-benzaldehyde (formula Ila).

Because the compounds of general formula II exhibit an asymmetric carbon atom, they can exist as 'D' and 'L' isomers as well as in the optically inactive 'DL' form. At the end of the aforementioned reaction core, the 'DL' form is achieved. The 'D' and 'L' isomers are obtained from this by optical resolution using methods well known in the art, e.g. by salt formation with an optically active base or by chromatography on cellulose (e.g. Whatman CF 11 or CC 31) and elution with a polar solvent (e.g. n.butanol saturated with hydrochloric acid 3n). Preparation of each isomer as well as the optical resolution step falls within the scope of the present invention.

The invention is illustrated by the following examples.

Example 1

a) Preparation of diethylacetamido-(3-methoxy-4-hydroxy-5-chloro-benzy])-malonate (formula III).

Vanillin (51 g) is dissolved in 600 ml of glacial acetic acid, and a stream of chlorine is allowed to pass through the solution, until formation of hydrochloric acid is complete. The reaction medium is then kept overnight at 4°C and the precipitate obtained is filtered, washed with water and dried over phosphorus pentoxide under reduced pressure to give 5-chlorovanillin, m.p. 164 - 165°C.

A 40 g aliquot of the obtained 5-chlorovanillin is treated with 40 ml of a 30% aqueous sodium hydroxide solution and 210 ml of water.

6.4 g of sodium borohydride are added and the reaction medium is stirred for 15 hours and then acidified with a 50% aqueous hydrochloric acid solution.

The obtained precipitate is filtered, washed with water and dried over phosphorus pentoxide at 40°C under reduced pressure to give 5-chloro-vanillin alcohol, m.p. 111.2 - 112.6°C after recrystallization from water.

A 20 g aliquot of this substituted vanillin alcohol is suspended in 100 ml of anhydrous benzene, and a stream of dry hydrochloric acid is allowed to pass through the medium until dissolution is complete. The solvent is then evaporated under reduced pressure and the residue is treated twice with 150 ml of anhydrous benzene, which is then evaporated to eliminate the remaining hydrochloric acid. The residue is dried under reduced pressure at 40°C. In this way, 3-methoxy-4-hydroxy-5-chloro-benzyl chloride is obtained, m.p. 64.6 - 66.6°C.

Diethyl acetamidomalonate (32.2 g) is suspended in 50 ml of anhydrous ethanol and an ethanolic solution of sodium ethoxide (2.1 g of sodium in 100 ml of ethanol) is added. The medium is stirred for 1/2 hour at 70°C.

A solution of 16 g of the previously obtained 3-methoxy-4-hydroxy-5-chloro-benzyl chloride in 45 ml of anhydrous ethanol is then added, and the medium is refluxed for 17 hours.

The medium is concentrated to half its original volume

and the reaction product is precipitated by pouring the medium into water. The precipitate is filtered, washed with water and dried over phosphorus pentoxide at 40°C under reduced pressure to give diethylacetamido-(3-methoxy-4-hydroxy-5-chlorobenzyl)malbnate, m.p. 154.2 - 155.6°C after recrystallization from benzene. b) Preparation of DL-3-methoxy-4-hydroxy-5-chloro-phenylalanine HC1 (formula I).

Diethylacetamido-(3-methoxy-4-hydroxy-5-chlorobenzyl) malonate (8 g) is dissolved in 20 ml of glacial acetic acid at 60 - 70°C. Sulfur dioxide is bubbled through the solution and 32 ml of concentrated hydrochloric acid is added.

The medium is heated for 9 hours at 95°C, and the solvent is then evaporated. The residue is taken up with 4 parts water and evaporated to eliminate hydrochloric acid and decolorized with charcoal in water.

The solution is filtered, the solvent is evaporated, and the residue is taken up in a small amount of butanol.

The solvent is evaporated, and the residue is dissolved in hot butanol, from which it is precipitated by the addition of anhydrous ether. The precipitate is filtered and dried under reduced pressure at 40°C to give DL-3-methoxy-4-hydroxy-5-chloro-phenylalanine hydrochloride, m.p.

218 - 220°C (decomposition), soluble in water and in ethanol.

Example 2.

a) Preparation of diethyl acetamido-(3-methoxy-4-hydroxy-5-bromobenzyl)-malonate (formula III).

Vanillin (15.2 g) is dissolved in 100 ml of glacial acetic acid, and a solution of 16 g of bromine in 100 ml of glacial acetic acid is added dropwise. The precipitate is filtered, washed with water and dried over phosphorus pentoxide under reduced pressure to give 5-bromovanillin, m.p. 162 - 164°C.

A 23.1 g aliquot of 5-bromovanillin is suspended in 150 ml

water and dissolve in this by adding 45 ml of aqueous sodium hydroxide (10%). An aqueous solution of 2.08 g of sodium borohydride is added with stirring over a period of 15 minutes. The yellow color of the solution slowly disappears and stirring is maintained for 15 hours at room temperature. By adding aqueous hydrochloric acid (6n) until pH 5 is achieved, a precipitate is obtained which is filtered, washed with water until neutral pH for the washings and dried over phosphorus pentoxide under reduced pressure to give 5-bromo-vanillin alcohol, m.p. 133 - 134°C.

A 21 g aliquot of 5-bromo-vanillin alcohol is suspended in 150 ml of anhydrous benzene and a stream of dry hydrochloric acid is passed through the medium which is kept at a temperature of 7-8°C. The hydrochloric acid stream is still maintained 15 minutes after complete dissolution of the reaction component. The medium is then dried over anhydrous sodium sulphate and filtered on sintered glass. The filtrate is evaporated to dryness and the residue is treated with two parts of 150 ml of anhydrous benzene, which is evaporated to eliminate residual hydrochloric acid. The final residue is dissolved again in a 150 ml portion of anhydrous benzene, and the solution is poured into 1.5 l of hexane previously dried over calcium chloride. The precipitate is filtered and dried to give 3-methoxy-4-hydroxy-5-bromobenzyl chloride, m.p. 84 - 86°C.

Diethylacetamidomalonate (6.95 g) is suspended in 12 ml anhydrous. ethanol, and an ethanolic solution of sodium ethoxide (0.735 g sodium in 24 ml ethanol) is added with stirring. In this way, a yellowish solution is obtained which is stirred for 30 minutes at 65°C.

A solution of 4 g of the previously obtained 3-methoxy-4-hydroxy-5-bromobenzyl chloride in 15 ml of anhydrous ethanol is then added. A precipitate of sodium chloride immediately appears, and the medium is refluxed for 3 1/2 hours and then evaporated to dryness. The rest is then taken up with 500 ml of water. After vigorous stirring, the white precipitate obtained is filtered on sintered glass, washed with water and dried over phosphorus pentoxide at 40°C under reduced pressure to give diethyl acetamido-(3-methoxy-4-hydroxy-5-bromobenzyl)-malonate, m.p. 161 - 162°C, purity by phenol group titration: 96.5%. b) Preparation of DL-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride (formula I).

Diethyl acetamido-(3-methoxy-4-hydroxy-5-bromobenzyl) malonate

(5 g) is dissolved in a mixture of 12 ml of glacial acetic acid and 20 ml of concentrated hydrochloric acid at 70°c, and the solution is saturated with sulfur dioxide.

The medium is then heated for 6 hours at 95°C (reflux).

After this reaction time, the solvent evaporates.

The residue is taken up with anhydrous ether.

After filtration, the precipitate is dried at 40°C under reduced pressure and gives DL-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride,

s.p. 220 - 223°C (decomposition). Rf = 0.65 (+ 0.05) and 0.77 (+ 0.05) by ascending paper chromatography on Whatman No. 1, elution with n-butanol saturated with hydrochloric acid 3n.

Example 3.

Preparation of DL-3-methoxy-4-hydroxy-5-bromophenylalanine (formula I) from its hydrochloride.

A solution of 1 g of D1-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride as prepared in Example 2 in 50 ml of water is batch-treated with 2.5 ml of anionic-ion exchanger "Amberlite LA2" in 60 ml of benzene.

The medium is stirred for 24 hours. The aqueous layer is then washed twice with benzene and the organic layer is washed twice with water.

The aqueous portions are collected and the solvent is evaporated to give DL-3-methoxy-4-hydroxy-5-bromophenylalanine, free base, purity by acid/base titration: 96.4%. S. p. 177°C (decomposition).

Example 4.

Preparation of DL-3-methoxy-4-hydroxy-5-bromophenylalanine from its hydrochloride. DL-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride as prepared in example 2 (16.33 g) is dissolved in 50 ml of water. By adding triethylamine in alcohol, the pH value of the solution is brought to 5.1. The solution is filtered and the filtrate is evaporated to dryness. The remainder is treated with two parts ethanol which is evaporated.

The residue is triturated first with two parts chloroform to eliminate the triethylamine hydrochloride and then with acetone. The solution is filtered and the filtrate is evaporated to dryness.

The residue is crystallized from hot water to give DL-3-methoxy-4-hydroxy-5-bromophenylalanine, free base, purity by acid/base titration: 95.2%, water content: 2.4%, m.p. 177°C (decomposition).

Example 5.

Preparation of DL-3-methoxy-4-hydroxy-5-bromophenylalanine-(hydrochloride) ethyl ester (formula I).

A solution of 1 g of DL-3-methoxy-4-hydroxy-5-bromophenylalanine (hydrochloride) as prepared in Example 2 in 25 ml of anhydrous ethanol is saturated at 0°C with gaseous hydrochloric acid. The solution is then heated for 1 hour at 80°C. The solvent is evaporated and the residue is taken up with two parts of anhydrous ethanol and precipitated by pouring the solution into anhydrous ether to give DL-3-methoxy-4-hydroxy-5-bromophenylalanine (hydrochloride) ethyl ester, m.p. 194 - 197°C, purity by acid/base titration: 100%.

Example 6.

Preparation of DL-3-methoxy-4-acetoxy-5-bromo-N-acetyl-phenyl-alanine.

To a solution of 1 g of DL-3-methoxy-4-hydroxy-5-bromophenylalanine (hydrochloride) as prepared in example 2 in 33.6 ml of aqueous sodium hydroxide (N), 2.4 ml of acetic anhydride is added dropwise with stirring. The reaction is exothermic and the color of the medium changes from orange to yellow.

The medium is kept under stirring at room temperature for 17 hours and then filtered. The pH value of the filtrate is brought to 2.3 with hydrochloric acid and the solvent is then evaporated by azeotropic distillation. The remainder is taken up with methylene chloride. After filtration, the solution is treated with charcoal, filtered, concentrated to a small volume, and hexane is added to give a precipitate which is filtered and dried under reduced pressure. In this way, DL-3-methoxy-4-acetoxy-5-bromo-N-acetyl-phenylalanine is obtained.

When this product is examined by thin-layer chromatography on "Kie-sel-gel G" (a product of E. Merck, Dramstadt, Germany) in the system propanol/water : 75/25 followed by exposure to bromcreson blue, one only spot, and reaction to ninhydrin and ferric chloride is negative.

Example 7.

Preparation of DL-3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine.

To a solution of 50 g of DL-3-methoxy-4-hydroxy-5-bromo-phenyl-alanine (hydrochloride) as prepared in example 2 in 500 ml of aqueous sodium hydroxide (N), 0.5 g of sodium hydrosulphite is added, and slowly acetic anhydride until the pH is 7. The addition of acetic anhydride is then continued while the pH value is kept at approx. 8 with aqueous sodium hydroxide (N).

After complete addition of the acetic anhydride reaction component (36.25 ml), the pH is brought to 10.8 with aqueous sodium hydroxide (total amount used of this is 602.5 ml). The temperature is kept between 30 and 40°C during the entire reaction time.

The medium is kept for 4 hours at room temperature and then acidified with hydrochloric acid (6n). Crystallization of the N-acylated compound begins at a pH value of approx. 4, but acidification is continued until the pH is 1.4, and crystallization is allowed to take place at this pH for 15 hours at 4°C.

The resulting precipitate is then filtered, washed with cold water and dried over phosphorus pentoxide under reduced pressure at 50°C to give DL-3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine, m.p. 222 - 223°C (decomposition).

When this product is examined by thin-layer chromatography on "Kie-sel-gel G" (a product of E. Merck, Darmstadt, Germany) in the system propanol/water : 75/25 followed by detection with either bromo-cresone blueligrod or ferric chloride, a single spot is obtained, and the reaction to ninhydrin is negative.

Example 8.

a) Preparation of L(-)-ephedrine salt from (-)-3-methoxy-4-hydroxy

-5-bromo-N-acetyl-phenylalanine.

To 31.6 ml of an ethanolic solution (4.3 M) of L(-) ephedrine diluted with 84.5 ml of acetone, 45 g of DL-3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine are obtained , as shown in example 7.

After further addition of 90 ml of acetone, a solution is obtained by heating with stirring. The solution is kept for 5 days at room temperature.

The crystals obtained are then filtered, washed with acetone, dried, pulverized and taken up with 400 ml of acetone. The suspension is stirred for 1 hour and then filtered.

The collected crystals are dissolved with stirring in 80 ml of hot, anhydrous ethanol. By slowly adding 360 ml of ether while stirring and with cooling, a precipitate is obtained which is allowed to stand for 4 hours at room temperature before it is filtered, washed with ether and dried under reduced pressure.

In this way the L(-) ephedrine salt of (-)3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine is obtained, («)q<5> = -66° (c = 1 in ethanol), m.p. 128 - 131°C. b) Preparation of (-)-3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine (formula I).

In 1075 ml of a water/ethanol 25/75 mixture, 21.5 g of L(-)-ephedrine salt of (-)3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine, as prepared in paragraph a) in the present example.

The solution is poured onto a column, 5 cm in diameter, of "Amberlite IR 124 (a product of Rohm & Haas, Philadelphia, Pa., USA) under H + form, and the flow rate is adjusted to 5 ml/minute.

Elution is performed with the same solvent mixture.

The eluate is concentrated to a small volume which is taken up with ethanol, treated with charcoal and filtered.

The solvent is evaporated under reduced pressure at 40°C and gives (-)3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine, (a)c 25 = -40<o >(c = in ethanol). S. p. 127°C (decomposition).

Example 9.

Preparation of (+)3-methoxy-4-hydroxy-5-bromo-phenylalanine (formula I).

A suspension of 11.5 g of (-)3-methoxy-4-hydroxy-5-bromo-N-acetyl-phenylalanine as prepared in section b) of Example 8 in 230 ml of hydrochloric acid (1,2n) is saturated with sulfur dioxide. A solution is obtained after 30 minutes of heating with stirring at 110°C (bath temperature), but heating and stirring are maintained for an additional 3 1/2 hours to effect complete hydrolysis.

After this reaction time, the solution is decolored with charcoal and filtered. The solution is concentrated to a small volume, taken up with water and evaporated to dryness by azeotropic distillation. The residue is taken up with anhydrous ether. After filtration and drying under reduced pressure at 40°C (+)3-methoxy-4-hydroxy-5-bromo-phenylalanine (hydrochloride) (a)p^ = +10° (c = 1 in water) is obtained. S. p. 207 - 210°C.

Example 10.

Preparation of DL-3-methoxy-4-hydroxy-5-bromo-N-palmitoyl-phenyl-alanine (formula I). DL-3-methoxy-4-hydroxy-5-bromo-phenylalanine hydrochloride (15 g) as obtained at the end of Example 2, is dissolved in 100 ml of aqueous sodium hydroxide (N).

15 ml palmitoyl chloride dissolved in 30 ml freshly distilled tetrahydrofuran is added to this dropwise and with stirring, and the pH of the medium is adjusted between 6.5 and 7.5 with aqueous sodium hydroxide (N) during the addition. When the addition is complete, the pH is brought to 8. During the next 5 hour period, the agitation is maintained, and the pH value of the medium is slowly brought to 9 by the addition of aqueous sodium hydroxide (N), and the medium is then allowed to stand overnight.

The solution is concentrated under reduced pressure in the presence of a small amount of sodium dithionite up to 1/3 of its original volume and extracted with two parts of ether, and the pH value is brought to 2 by the addition of hydrochloric acid (n).

The organic layers are collected, decolorized with charcoal, filtered, dried over anhydrous sodium sulfate and concentrated under reduced pressure. On addition of hexane, a precipitate is obtained which is filtered on sintered glass and dried under reduced pressure at 40°C and gives 3-methoxy-4-hydroxy-5-bromo-N-palmitoyl-phenylalanine, m.p. 104 - 107°C.

Example 11.

a) Preparation of diethyl acetamido-(3,4-dimethoxy-5-bromo-benzyl) malonate (formula III).

Diethyl acetamidomalonate (38.43 g) is dissolved in 300 ml of freshly distilled dimethylformamide and 8.17 g of 50% sodium hydride in oil is added.

The medium is stirred for 1 hour at 25°C and 39.43 g of 3,4-dimethoxy-5-bromobenzyl chloride (PSCHORR, Liebig's Annalen 391, 29 - 33, 1912) dissolved in 200 ml of dimethylformamide is then added. After heating for 4 hours at 105°C, the yellowish solution is poured into 3 liters of water. The precipitate obtained is filtered, washed with water and dried over phosphorus pentoxide at 70°C to give diethyl acetamido-(3,4-dimethoxy-5-bromo-benzyl) malonate, m.p. 118 - 119.5°C. b) Preparation of DL-3,4-dimethoxy-5-bromo-phenylalanine hydrochloride (formula I).

Diethyl acetamido-(3,4-dimethoxy-5-bromobenzyl) malonate (10 g) as prepared in section a) in the present example is dissolved in a mixture of 60 ml of glacial acetic acid and 60 ml of concentrated sulfuric acid, and the solution is saturated with sulfur dioxide.

The medium is then heated for 20 hours at 95°C (reflux).

After the reaction time is over, the solvent is evaporated and the residue is taken up with 100 ml of water and decolorized with charcoal. The pH of the solution is brought to 11.5 by addition of aqueous sodium hydroxide (20%) to precipitate DL-3,4-dimethoxy-5-bromo-phenyl-alanine, which is filtered, washed with water and taken up with hot hydrochloric acid ( 6n).

The precipitate obtained is filtered, washed with ice water and dried under reduced pressure to give DL-3,4-dimethoxy-5-bromo-phenylalanine (hydrochloride), purity 99% (by titration of the amino group), Rf = 0.53 (+ 0 .05) by thin-layer chromatography on 'silica gel G' (a product of E. Merck, Darmstadt, Germany), elution with ethanol/ammonium hydroxide (25%): 80/20. M.p. 235°C (dec.).

Example 12.

a) Preparation of 3-methoxy-4-hydroxy-5-bromophenyl-pyruvic acid (formula IV).

A mixture of 5-bromovanillin (115 g), acetylglycine (58.5 g), sodium acetate (82 g) and acetic anhydride (150 ml) is heated to 110°C for 2 hours.

Then 1.25 1 of a 1/1 mixture of ethanol/water is added,

and the reaction medium is stirred for 30 minutes, filtered, washed with a further 500 ml portion of the ethanol/water mixture and. dried at 40°C under reduced pressure and gives 130 g of azlactone.

A 50 g aliquot of the azlactone obtained is dissolved in 500 ml of aqueous sodium hydroxide (2N) and the solution is heated for 2 hours at 60 - 70°C. The pH of the solution is then brought to 5.5 with hydrochloric acid (6n) and the solution is decoloured with charcoal. After filtration, the pH of the solution is brought to 2 with hydrochloric acid (6n).

The crystals obtained are filtered, washed with water and dried under reduced pressure to give 49 g of 2-acetylamino-3(3'-methoxy-4'-hydroxy-51-bromo-phenyl)-propenoic acid.

A 25 g aliquot of this substituted propenoic acid is suspended in 200 ml of a glacial acetic acid/hydrochloric (12n) mixture (30/70) and heated for 6 hours at the reflux temperature with vigorous stirring. The medium is then dressed and poured into 2 liters of water while stirring.

The crystals obtained are filtered, washed with water and dried under reduced pressure at 40°C to give 17.9 g of 3-methoxy-4-hydroxy-5-bromophenylpyruvic acid, m.p. 238 - 240°C (decomposition), Rf =

0.25 (+ 0.05) by thin-layer chromatograph on ..Silica gel G,' elution with benzene/methanol/acetic acid: 45/8/4 followed by detection with ferric chloride. b) Preparation of DL-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride (formula I).

A 10 g aliquot of the acid obtained is dissolved in 100 ml of concentrated ammonium hydroxide, and a solution of 350 mg of sodium borohydride in 10 ml of water is added while stirring. Stirring is maintained for 2 hours. After this reaction time, excess ammonium hydroxide is eliminated by evaporation of the solvent under reduced pressure.

The rest is taken up with water which then evaporates, and the rest is taken up again with water.

The obtained solution is acidified with concentrated hydrochloric acid until pH 1.5.

The solution is stirred for 1 hour, and the solvent is then evaporated, and the residue is taken up by two successive parts of water and then

of n.butanol and the solvent is evaporated. The rest is taken up with ethanol. The insoluble fraction (mineral salts) is eliminated by filtration and the filtrate is concentrated until a sir-up is obtained. On addition of ether, DL-3-methoxy-4-hydroxy-5-bromophenylalanine hydrochloride is obtained with the same characteristics as those of the product obtained at the end of Example 2.

Example 13.

a) Preparation of diethylacetamido-3,4-dihydroxy-5-chlorobenzyl malonate (formula III).

A 10 g aliquot of diethyl acetamido-(3-methoxy-4-hydroxy-5-chloro-benzyl) malonate obtained as described in section a) in example 1 is dissolved in 150 ml of methylene chloride and allowed to react with 180 ml of pyridine and 7 .8 g aluminum chloride.

Demethylation is completed after 6 hours at 60°C. The aluminum complex obtained is cleaved with hydrochloric acid (6n) and diethyl-acetamido-(3,4-dihydroxy-5-chloro-benzyl) malonate is extracted with two parts of ethyl ether.

The extract is washed with water, dried over sodium sulfate and filtered, and the solvent is evaporated.

The residue is taken up with a minimum of methanol and precipitated by pouring the methanol solution into water.

After filtration, acetamido-3,4-hydroxy-5-chloro-benzyl-malonic acid-diethyl ester is obtained (m.p. 207.4 - 208.2°C). b) Preparation of DL-3,4-dihydroxy-5-chlorophenylalanine hydrochloride (formula I).

This product is dissolved in a mixture of 75 ml acetic acid and 65 ml hydrochloric acid (12n).

The solution is saturated with sulfur dioxide and heated for 20 hours at 95°C. The solvent is then evaporated and the residue is taken up with three successive parts of water, and the solvent is evaporated under reduced pressure. The residue is taken up with methanol and the solution is decolorized with charcoal. The solvent is evaporated to give DL-3,4-dihydroxy-5-chloro-phenylalanine, hydrochloride (purity 97.5% by titration analysis of the amino group). S. p. 157°C (decomposition).

Example 14.

a) Preparation of diethylacetamido-(3-ethoxy-4-hydroxy-5-bromo-benzyl)-malonate (formula III).

A solution of 48 g of bromine in 300 ml of glacial acetic acid is added dropwise to a mixture of 3-ethoxy-4-hydroxy-benzaldehyde (49.86 g) and sodium acetate (24.6 g) in 300 ml of glacial acetic acid. The medium is stirred in 4 hours at room temperature and then poured into water saturated with sulfur dioxide. The precipitate is washed with water and dried under reduced pressure to give 3-ethoxy-4-hydroxy-5-bromobenzaldehyde (m.p. 142°C).

A 65 g aliquot of the substituted benzaldehyde obtained is poured

in 500 ml of water and dissolve in this by adding 273 ml of aqueous, normal sodium hydroxide.

Sodium borohydride (6 g) is added with stirring over the course of 15

minutes and stirring is maintained for 48 hours at room temperature. By adding aqueous hydrochloric acid (6n) up to pH 2.5, a precipitate is obtained which is filtered, washed with water until the pH of the washings is neutral and dried at 40°C under reduced pressure and gives 3-ethoxy-4-hydroxy 5-bromobenzyl alcohol, m.p. 130 - 131°C.

A 20 g aliquot of this alcohol is suspended in 300 ml of anhydrous benzene and a stream of dry hydrochloric acid is allowed to pass through the medium for 3 hours.

The medium is then filtered on sintered glass and the filtrate is evaporated to dryness and gives 3-ethoxy-4-hydroxy-5-bromobenzyl chloride.

Diethyl acetamidomalonate (17.5 g) is suspended in 100 ml of dimethylformamide, and 4.1 g of a 50% (w/w) sodium hydride in oil is added with stirring. In this way, a solution is obtained which is stirred for 30 minutes, and the temperature then reaches 90°C.

A solution of 19.5 g of the previously obtained 3-ethoxy-4-hydroxy-5-bromobenzyl chloride in 150 ml of dimethylformamide is then added, and the temperature of the medium is maintained at 100°C for 5 hours. The reaction medium is then poured into water and gives a precipitate which is filtered on sintered glass, washed with water and dried over phosphorus pentoxide at 40°C under reduced pressure and gives diethyl acetamido-(3-ethoxy-4-hydroxy-5-bromobenzyl) malonate, s.p. 154 - 156°C, purity by phenol group titration: 99%. b) Preparation of DL-3-ethoxy-4-hydroxy-5-bromophenylalanine hydrochloride (formula I).

The obtained diethyl acetamido (3-ethoxy-4-hydroxy-5-bromobenzyl) malonate is then poured into a mixture of 200 ml of glacial acetic acid and 200 ml of hydrochloric acid (6n), and the medium is heated for 6 hours at 95°C (reflux) .

After this reaction time, the solvent evaporates.

The rest is taken up with water, and the solution is de-coloured with charcoal

and filtered. The obtained yellow solution is evaporated to dryness, and the residue is dried at 40°C under reduced pressure to give DL-3-ethoxy-4-hydroxy-5-bromo-phenylalanine hydrochloride, (purity 99% by titration analysis of the amino group). S. p. 192°C (decomposition).

Example 15.

a) Preparation of 3-methoxy-4-hydroxy-5-iodo-phenylpyruvic acid (formula IV).

A solution of vanillin (500 g), sodium bicarbonate (250 g) and potassium iodide (747 g) in 10 1 of water is treated with 834 g of iodine. The medium is stirred for 4 hours and kept overnight. The crystals obtained are treated with an aqueous solution (10%) of sodium thiosulphate, filtered, washed with water and dried under reduced pressure to give 5-iodovanillin.

A 27.8 g aliquot of the previously obtained 5-iodovanillin, 11.7 g acetylglycine, 8.2 g sodium acetate and 30.6 g acetic anhydride is heated to 105° C. for 4 hours. The reaction medium is taken up with 125 ml of a 1/1 mixture of ethanol and water, and the crystals are filtered and dried under reduced pressure.

The azlactone obtained is recrystallized from acetic acid (m.p. 194 - 195°C) and dissolved in 300 ml of aqueous sodium hydroxide (stirring for 1 hour at 55°C).

The solution is acidified to pH 5.3 with hydrochloric acid (6n), decolorized with charcoal, filtered and the pH is brought to 1.5 with a further amount of hydrochloric acid (6n). The solution is then heated with stirring at 55°C until crystallization occurs.

The crystals are filtered, washed with water and dried under reduced pressure to give 2-acetamido-3-(3'-methoxy-4'-hydroxy-51-iodo-phenyl)-propenoic acid, m.p. 218.5 - 220°C.

This acid is suspended in 100 ml of an acetic acid/hydrochloric (12n) mixture (30/70), and the medium is heated for 3 hours at 90°C with stirring.

After this reaction time, the precipitate is filtered, washed with water and dried under reduced pressure to give 3-methoxy-4-hydroxy-5-iodo-phenylpyruvic acid, m.p. 226 - 229°C, Rf = 0.22 (+ 0.05) by thin-layer chromatography on "Silicagel G" in the system benzene/methanol/acetic acid: 45/8/4. b) Preparation of DL-3-methoxy-4-hydroxy-5-iodo-phenylalanine hydrochloride (formula I).

This acid is dissolved in 50 ml of concentrated ammonium hydroxide, and the solution is stirred for 15 minutes. Then 0.250 g of sodium norhydride is added, and the medium is stirred for 2 hours.

After this reaction time, the pH of the solution is brought to 1.2 with hydrochloric acid (6n), and the solvent is evaporated under reduced pressure. The residue is taken up with three successive parts of water to eliminate the free hydrochloric acid.

This residue is then taken up with n-butanol, the solvent is evaporated, and the residue is taken up with a minimum of hot n-butanol and treated with anhydrous ether.

The crystals are filtered, washed with anhydrous ether and dried under reduced pressure to give DL-3-methoxy-4-hydroxy-5-iodo-phenylalanine (hydrochloride), m.p. 187 - 190°C, Rf = 0.35 (+ 0.05) by thin-layer chromatography in the system methanol/chloroform/ammonium hydroxide: 20/20/5.

Example 16.

a) Preparation of 3-hydroxy-4-methoxy-5-bromo-phenyl-pyruvic acid (formula IV).

5-Bromovanillin (231 g) and anhydrous aluminum chloride (146.7 g) are suspended in 1 liter of methylene chloride and anhydrous pyridine (348 g) is added dropwise. The medium is heated for 24 hours at 45°C and then poured into 2 liters of hydrochloric acid (4n) at 0°C. The precipitate is filtered, washed with water and dried under reduced pressure to give 5-bromo-protocatechualdehyde (m.p. 228 - 229°C after recrystallization from ethanol).

A 108.5 g aliquot of 5-bromo-protocatechualdehyde, 43.3 g sodium bicarbonate, 100 ml methyl iodide and 700 ml acetone (dried over potassium carbonate) is refluxed for 20 hours.

The solution is then evaporated to dryness, and the residue taken up in chloroform. The solution obtained is treated with dry hydrochloric acid. The medium is filtered, and the solution is poured onto 200 g "Silicagel Merck 7729", decolorized on charcoal and concentrated until crystallization occurs. After filtration, 5-bromo-isovanillin is obtained (m.p. 116.5 - 117.5°C).

A 32.4 g aliquot of 5-bromo-isovanillin, 16.4 g acetylglycine, 22.9 g sodium acetate and 27 ml acetic anhydride is treated for 2 hours at 110°C. The reaction medium is poured into 800 ml of water. The precipitate obtained is filtered, washed with water and dried under reduced pressure at 40°C over phosphorus pentoxide.

After recrystallization from glacial acetic acid, filtration, washing with ethyl ether and drying, the azlactone is obtained m.p. 210 - 211°C, Rf = 0.66 (+ 0.05) by thin-layer chromatography on "Silicagel G" in the system benzene/dioxane/acetic acid: 90/25/4.

A 20 g aliquot of the azlactone obtained is dissolved in 250 ml of aqueous sodium hydroxide (2N), and the solution is heated for 1 hour at 70°C with stirring.

The pH of the solution is then brought to 1.5 with hydrochloric acid (6n), and the reaction medium is heated for 1 hour at 70°C. The crystals obtained are filtered, washed with water and dried at 40°C under reduced pressure to give 2-acetamido-3(3'-hydroxy-4'-methoxy-5'-bromophenyl)-propenoic acid, m.p. 218 - 219°C, Rf = 0.25 (+ 0.05) by thin-layer chromatography on "Silicagel G" in the system benzene/methanol/acetic acid: 45/8/4 followed by detection with ferric chloride.

A 12 g aliquot of the obtained 2-acetamido-3-(3<1->hydroxy-41-methoxy-5'-bromo-phenyl)-propenoic acid in a mixture of 30 ml of acetic acid and 70 ml of hydrochloric acid (12n) is heated for 5 hours at 95°C.

The hot medium is then filtered on charcoal and crystallization occurs when the solution is cooled.

After filtration, the crystals are washed with water and dried at 40°C under reduced pressure to give 3-hydroxy-4-methoxy-5-bromo-phenylpyruvic acid, m.p. 203 - 205°C, Rf = 0.23 (+ 0.05) by thin-layer chromatography in the system benzene/methanol/acetic acid: 45/8/4 followed by detection with ferric chloride. b) Preparation of DL-3-hydroxy-4-methoxy-5-bromophenylalanine hydrochloride (formula I).

A 5 g aliquot of the obtained substituted phenylpyruvic acid is dissolved in 50 ml of concentrated ammonium hydroxide, and the solution is stirred for 1/4 hour. 0.5 g of sodium borohydride is then added, and the medium is stirred for 4 hours.

The pH of the solution is then brought to 1.5 with hydrochloric acid (6n) and the solvent is evaporated. The rest is taken up with several parts of water followed by evaporation until elimination of free hydrochloric acid.

o

The remainder is taken up by two parts of butanol, which is then evaporated and then with a minimum of hot butanol from "which crystallization occurs on cooling.

After filtration, washing with ether and drying under reduced pressure, DL-3-hydroxy-4-methoxy-5-bromo-phenylalanine (hydrochloride) is obtained, m.p. 151 - 153°C, Rf = 0.53 (+ 0.05) by thin-layer chromatography on "Silica gel G" in the system methanol/chloroform/ammonium hydroxide: 20/20/5 followed by detection with ferric chloride.

Example 17.

Preparation of D(+)3-methoxy-4-hydroxy-5-chlorophenylalanine hydrochloride (formula I). DL-3-methoxy-4-hydroxy-5-chloro-phenylalanine hydrochloride (4.5 g) as obtained in Example 1 is suspended in 150 ml of water and treated with 400 ml of buffer solution at pH 7.4 (a solution of 23.9 g disodium phosphate (12 aq) in 1 liter of water adjusted to pH 7.4 by adding monopotassium phosphate).

The pH of the solution (6.5) is adjusted to 7.4 by adding disodium phosphate, and after filtration, 100 ml of the above buffer solution and 0.15 g of "L-amino acid oxidase" are added. The medium is kept under stirring at 37°C for 43 hours.

After this reaction time, the pH of the medium is brought to 1.65 by adding hydrochloric acid (6n), decolorizing charcoal is added, and the medium is heated to 50°C for 1/2 hour and then filtered. The filtrate is treated with "Amberlite LA-2" diluted with benzene.

The aqueous layer is separated, washed with benzene, acidified with hydrochloric acid (6n) and the solvent is evaporated. The residue is dissolved in hot ethanol, the solution (after filtration) is concentrated by evaporation, treated with water until the ethanol is eliminated, extracted with ethyl ether and decolorized with charcoal.

After filtration, the solution is alkalized and the solvent is evaporated.

The rest is taken up in methanol. After filtration, the solvent is evaporated

the agent and the residue are suspended in ethanol, filtered, washed with eta-

nol and with ether, suspend in a minimum of water and treat with 20 ml of hydrochloric acid (n).

The obtained solution is decoloured, the solvent is evaporated, and

the residue is taken up in a minimum of ethanol, diluted with ether, and

the solution is poured into anhydrous ethyl ether and gives a precipitate which is washed with anhydrous ether and dried under reduced pressure at 50°C and gives D(+)3-methoxy-4-hydroxy-5-chloro-phenylalanine (hydrochloride). After

25 o

recrystallization from n.propanol, (tf)D = between + 8.6 and + 9.25

(c = 1 in water), Rf = 0.42 (+ 0.05) by thin-layer chromatography on

Whatman cellulose, Chromedia CC 31 in n.butanol saturated with salt-

acid (3n) followed by detection with ninhydrin. S. p. 203°C (decomposition).

Claims (1)

Analogous process for the preparation of therapeutically active DL-, D- or L-S-phenylalanine derivatives of the general formula I where R^ and R2 are identical or different and denote methyl or ethyl, and one of them is optionally hydrogen or an acyl radical with 1-30 carbon atoms, R^ denotes either hydrogen, or a pharmaceutically acceptable, non-toxic alkali metal-, ammonium or substituted ammonium ion or denotes an alkyl or alkenyl radical with 1-30 carbon atoms directly or branched chain, X denotes chlorine, bromine, iodine or fluorine, and Z denotes hydrogen or an acyl radical with 1-30 carbon atoms, or a non-toxic acid addition salt thereof, characterized in that a) a suitable substituted 2-benzyl-2- aminomalonic acid lower (1-4 C) alkyl ester of the general formula III where Alk' denotes an alkyl radical with 1-4 carbon atoms, Y denotes a formyl, acetyl, benzoyl, phthaloyl or benzyl oxycarbonyl radical and , R^ and X are as defined above, hydrolyzed and decarboxylated, the reaction being carried out in a solvent under the influence of heat in an acidic medium and preferably in the presence of a reducing agent, or b) a suitable substituted phenylpyruvic acid with the general formula TV where R 1 , R 2 and X are as defined above and M denotes hydrogen or a non-toxic monovalent cation, is reduced under mild conditions in ammonium hydroxide solution, after which the desired salt, ester, acyl derivative and/or optical isomer is optionally obtained from the reaction product using methods known per se.