NO145690B - ANALOGY PROCEDURE FOR THE PREPARATION OF THERAPEUTIC ACTIVE DERIVATIVES OF ALFA-METHYL-3,4-DIHYDROXYPHENYLALANINE. - Google Patents

Description

The present invention relates to an analog method

in the preparation of a new and useful group of therapeutically active compounds which are derivatives of α-methyl-3,4-dihydroxyphenyl-

alanine.

It has been suggested in the art that various alanine compounds may be useful in the treatment of hypertension (see US patent 2,868-818). It is further known in the art that hypertension is preferably treated with L-α-methyl-3,4-dihydroxyphenylalanine as the D form of the compound is therapeutically inert and only the L form is therapeutically active. The removal of the D-form thereby reduces toxicity and increases effectiveness (see US patent 3-344-023 and British patent 936,074) • The L-isomer of α-methyl-3,4-dihydroxyphenylalanine is usually referred to as L-α-methyldopa or methyldopa. It is further known in the art that the alkyl esters of L- or DL-α-methyl-3,4-dihydroxyphenylalanine are useful in the emergency treatment of hypertension by parenteral administration (see US patent 3,230,143). It has now been shown that other esters and derivatives of DL- or L-α-methyl-3,4-dihydroxyphenylalanine with specific structures are also effective in the treatment of hypertension, whereby alternative compounds are obtained for such treatment. It has also been shown that some of the new compounds have a much higher activity and thus require a lower dosage than the known compounds.

It is therefore an aim of the present invention to provide a new and useful group of compounds which are more active in the treatment of hypertension than previously known compounds.

others.

The present invention thus relates to an analog

procedure for the production of therapeutically active compounds as stated in the preamble to claim 1,

The alternative methods of analogy appear from the characteristics of claim 1.

In a preferred embodiment of the present invention, n and m are O or 1, A1 and A2 are hydrogen, R1 and R2 are hydrogen or methyl, and R^ is the heterocyclic ring:

which may be substituted with lower alkyl groups with 1-3 carbon atoms, or R^ is -X-R^ where X is -O- or -NH-, and R^ is an acyl group of an alkanoic acid with 2-5 carbon atoms.

In the present method, further esters of the L-isomer of an amino acid, essentially free of the D-isomer, are obtained with the formula:

or pharmaceutically acceptable acid addition salts thereof, where n, m, R^, R^ and Rg are as above. With regard to the L-isomer, it should be noted that the asymmetric carbon atom is the one that carries the amino and methyl groups in the acid part of the molecule. It is this part of the molecule that is designated as being in the L configuration. Note that the L configuration refers to the space configuration and not to the optical rotation, although in this case the L space configuration is the 1 or levo form of the optical isomer.

However, it should be noted that in some cases when R 1 and R 2 are different groups, the carbon atom to which they are attached is also an asymmetric carbon atom, and can thus be in either the L or D configuration. As will be pointed out below, both isomers of this part of the compound are active. As further pointed out, these stereoisomers have been separated, but their stereoconfiguration has not been determined so that they are only referred to as the α and β isomers. in any case, both the α- and β-isomers are active regardless of their spatial configuration.

In the treatment of hypertension, the process compounds are generally administered in amounts from 0.005 to 300 mg/kg body weight of the animal, and preferably from 0.05 to 100 mg/kg. In an even more preferred embodiment, the compounds are administered in amounts from 0.1 to 25 mg/kg body weight of the animal. In this connection, it should be noted that the dose must be adjusted depending on the activity of the compound, the desired response in reducing blood pressure, and also the weight of the animal. In the areas indicated above, the more active compounds would be given in the lower doses, and the less active compounds in the higher doses.

When the L-isomer of one of the process compounds is given in

in the substantial absence of the D-isomer, the required dose of the L-isomer is approx. half that of the racemate, as the D-isomer is therapeutically inactive. However, the process compounds vary with regard to activity to some extent, and thus the racemate of a less active process compound may require several times the dose of a more active compound. In general, however, the compounds will be administered within the dosages indicated above.

In a single dose form of preparations of the process compounds, the active compound is generally present in the preparation in amounts from 1 mg to 2000 mg, and more preferably 5 mg to 1000 mg. In an even more preferred embodiment, the active compound is present in amounts from 10 mg to 500 mg. The single dose form of the compound can be administered in a single slow-acting dose or it can be administered in several small doses

doses during the day, generally 2 to 8 individual doses.

Reduced doses of the L-isomer substantially free of the D-isomer are required compared to the racemate. However, the difference in activity of different compounds necessitates the use of different doses. In some cases, the compounds are many times more active than others, and thus the racemate of one may require an even smaller dose than that of the L-isomer of another. In general, however, the doses will lie within the ranges indicated above.

In a preferred embodiment of the invention, the method is carried out with an amino acid part of the molecule which is in the L space configuration.

In a preferred embodiment of the invention, the method is carried out with an amino acid part of the molecule which is in the L-space configuration.

The terms <M>(-CH2)n" and "(-CH2)m" also include the branched alkylene groups which

Preferably n and m are 0 or 1.

in

The expression "a monocyclic or bicyclic ..... 5 to 6 membered" means that the compounds contain one or two ring nitrogen atoms with optionally a ring sulfur atom and from 3 to 12 ring carbon atoms. The compounds also contain 1 or 2 rings with 5 or 6 members

in each ring, and the rings may be substituted with such groups as halogen, hydroxyl, amino or other such groups.

The phrase "the L-isomer of an amino acid, substantially free of the D-isomer" means that the D-isomer is present in amounts not exceeding 10%. However, it is desirable that the D-isomer is essentially absent from the preparation. In the examples that follow, when the L isomer is indicated, substantially 100% (ie, well over 99%) is in the L configuration.

The term "blocking group" denotes any group that will protect the amino or hydroxyl groups during the reaction. Among suitable blocking groups for the nitrogen atom are carbobenzyloxy, p-methoxy-carbobenzyloxy, trifluoroacety1, HCl and the like. Suitable blocking groups for the hydroxyl group are diphenyl ketal for both hydroxyl groups and acetyl and carbobenzyloxy for the individual hydroxyl groups as well as other such groups. The substituent in the "substituted -SO^ group" can be basically any group as these groups are easily split off during the esterification reaction and the nature of the group is not at all critical.

When racemic mixtures are formed by the present process, it is sometimes desirable to separate the mixtures into their L-

and D isomers. The isomers can be separated at any point in the synthesis, and in most cases it is desirable to separate them before the formation of the final product. In the second case (when R^ and are different groups, and the acid part is in the L configuration), a mixture of diastereomers is formed as the final product, and these can be separated directly by crystallization or the formation of simple derivatives with crystallization. However, it is far preferred to proceed from the desired isomer (ie the L-isomer) when a single isomer is desired. It is also possible to form a diastereomer of the racemic mixture prepared according to the invention to effect separation.

In such cases, an optically active acid such as tartaric acid, 10-camphor sulphonic acid, malic acid, pyroglutamic acid, menthoxyacetic acid and the like can be used. The choice of the particular acid can be as desired and will be obvious to a person skilled in the art.

The process compounds can be used in the form of preparations which are preferably administered in unit dose forms such as tablets, pills, capsules, powders, granules, sterile parenteral solutions or suspensions, oral solutions or suspensions and the like. Such preparations are produced in a conventional manner. The tablets or pills of the method compounds may be laminated or otherwise composed to provide a dose which provides the benefit of prolonged or delayed action or predetermined successive action of the contained drug. For example, the tablets or pill may comprise an inner dose and an outer dose component, the latter being in the form of a shelf above the former.

The following examples are given to illustrate the invention.

All parts are stated in parts by weight unless otherwise expressly stated. The term "reduced pressure" used in the following examples is 15 to 25 mm Hg at 25 - 35°C (where not otherwise stated). When reduced pressure is used to remove a solvent, the product obtained is often a solvate and thus the examples refer to the formation of a "concentrated" product, although all solvent has been removed except that which is bound in the product.

Example 1

A. Preparation of L-3-(3>4-diphenylmethylenedioxyphenyl)-2-methyl-alanine hydrochloride

A mixture of 19.3 g (0.0777 mol) of L-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride [L-α-methyldopa hydrochloride] and 37 g.

(0.156 mol) of dichlorodiphenylmethane is immersed under slow stirring

in a preheated oil bath at 190°C. After the reaction has begun, as evidenced by strong gas evolution, the reaction mixture is stirred rapidly for 6 minutes at 190°C, removed from the hot oil bath and allowed to cool to 25 - 30°C. The crude product from 12 experiments is combined, slurried with 3 1 diethyl ether, filtered, washed with a further 2 1 diethyl ether and dried at 30°C under 50 mm pressure.

Recrystallization is performed by dissolving the product in ethanol and adding ethyl acetate to precipitate the product. The process yields 255 g (66.4%) of L-3-(3,4-diphenylimethylenedioxyphenyl)-2-methylalanine hydrochloride, m.p. 267 - 268°C (splitn.y

Anal. calculate, for C^H^NO^HCL: C 67.07; H 5.39; N 3.40

Found: C 66.91; H 5.29; N 3.34

B. Preparation of L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxy-phenyl1)-2-methylalanine

A mixture of 175 g (0.425 mol) L-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalanine hydrochloride, 1750 ml of acetone and 1750 ml of water is stirred under nitrogen at a temperature below 10 C while the pH is adjusted to 12.0 by slow addition of a 10% sodium hydroxide solution. 93 9 (0.545 mol) carbobenzyloxychloride is added dropwise over 5 - 7 minutes to the reaction mixture at 20 - 30°C while simultaneously adding a 10% sodium hydroxide solution to maintain a pH of 12.0 - 12.2. After the addition of the carbobenzyloxychloride has been completed, the reaction mixture is stirred at 25 - 30°C for 3 hours. Most of the acetone is then removed under reduced pressure at 25-35°C to precipitate the sodium salt of the desired N-carbobenzyloxy derivative. The sodium salt is extracted in 1.5 1 ethyl acetate, washed with 200 ml of 5% sodium hydroxide solution and 200 ml of a saturated sodium chloride solution and then dried over magnesium sulphate. After adding 17.5 g of decolorizing carbon and filtering through a magnesium sulfate plate, the solvents are removed under reduced pressure at 25 - 35°C. The residue is slurried twice with 1 1 of a 20% by volume ethyl ether-80% by volume hexane solution and filtered, whereby the sodium salt of the desired N-carbobenzyloxy derivative is obtained. This sodium salt is dissolved in 1.5 1 ethyl acetate, cooled to 10°C and acidified to pH 2 with 6 N hydrochloric acid. The ethyl acetate extract is washed with 200 ml of a saturated sodium chloride solution, dried over magnesium sulphate, filtered and evaporated under reduced pressure at 25 - 35°C. The N-carbobenzyloxy derivative is further dried at 25 - 30°C and 0.2 - 0.3 mm Hg, whereby 169 g (78.0%) of L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2 are obtained -methylalanine.

C> Preparation of succinimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2- methylalaninate

A solution of 13.5 g (0.0265 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.7 g (0.027 mol) triethylamine and 5.19 9 (0.029 mol) N -bromomethylsuccinimide in 35 ml of dry dimethylformamide is stirred at 25 - 30°C for 16 hours. The reaction mixture is poured into 400 ml of ice water, and the product is extracted into 200 ml of a 50% by volume chloroform-50% by volume diethyl ether mixture.

The organic extract is washed with 50 ml of diluted (5% strength) sodium carbonate solution and 50 ml of saturated sodium chloride solution and dried over anhydrous magnesium sulfate to remove water. After filtration and evaporation under reduced pressure, the residue is recrystallized. Recrystallization is performed by dissolving the product in ethanol and adding hexane to precipitate the product. The process yields 12.1 g (73.6) of succinimidomethyl-L-N-carbobenzyloxy-3-(3,4~di-phenylmethylenedioxy-phenyl)-2-methylalaninate, m.p. 143.0 - 145.0 C.

Anal. calculate, for C^ H^ N^^ : C 69.66; H 5.20; N 4.51

Found: C 69.83; H 5.14" N 4.52

D. Preparation of succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A suspension of 6.6 g (0.0106 mol) of succinimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 180 ml of absolute ethanol and 9 ml of 9.6 N ethanolic-anhydrous hydrogen chloride solution is hydrogenated with 3.3 9 of a 10% palladium-on-carbon catalyst at an initial thrust of o 2.1 kg/cm 2 until hydrogen uptake is complete. After removal of the catalyst by filtration, the filtrate is evaporated under reduced pressure. The residue is extracted with 50 ml of benzene and then with 50 ml of ethyl acetate. The insoluble solid is then shaken with 50 ml of a 10% by volume ethanol-90% by volume ethyl acetate mixture and 10 ml of saturated sodium carbonate solution. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure. The residue is dissolved in 25 ml absolute ethanol, treated with 5 ml 9.6 N ethanolic-anhydrous hydrogen chloride solution and evaporated under reduced pressure, whereby 2.5 9 (62.7%) succinimidomethyl-L-3-(3,4- dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate, homogeneous by thin layer chromatography (fluorescent silica gel plate, 30 vol% methanol-70 vol% benzene solvent) with an observed Rf = 0.5.

Anal. calculate, for ^ 1^ 1^ 206'HC1-H20: C ^7'ol> H 5.62-, N 7.44 Found: C 48.09; H 5.74; N 7.42

Example 2

A. Preparation of N-(1-chloroethyl)-succinimide

50.0 g (0.40 mol) of N-vinylsuccinimide is dissolved in 1000 ml of carbon tetrachloride, 5.20 g (0.020 mol) of stannous chloride is added, and the mixture is stirred while being saturated with hydrogen chloride for 6 hours at 20 - 30°C. After 24 hours, the mixture is saturated again with hydrogen chloride for 1.5 hours. At the end of 48 hours, the solution is decanted, and the gummy residue is washed with 10 x 100 ml of carbon tetrachloride.

The combined extracts are slurried with 10 g of diatomaceous earth, filtered, and the filtrate is evaporated under reduced pressure to approx. 400 ml. The N-(1-chloroethyl)-succinimide is filtered off and dried at 20 - 30°C under reduced pressure, whereby 38.4 g (59%) of a white solid is obtained which melts at 83.5 - 84.5°C .

B. Preparation of α-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4~

diphenylmethylenedioxyphenyl)- 2- methylalaninate

A mixture of 30.66 g (0.060 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 9.70 g (0.060 mol) N-(1-chloroethyl) -succinimide, 6.07 g (0.060 mol) of triethylamine and 75 ml of dry dimethylformamide are stirred at 95°C for 19 hours. The reaction mixture is poured into 750 ml of water, and the product is extracted into 3 x 500 ml of ethyl acetate. The combined organic extracts are washed with 3 x 300 ml of 5% sodium hydroxide solution, then with 3 x 300 ml of saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtration, the solution is treated with 5 g of charcoal, filtered, and the solvent is evaporated under reduced pressure, whereby 37.90 g (99%) of α-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2 is obtained -methylalaninate as a mixture of diastereomeric isomers (a and (3) .

C Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A suspension of 20.18 9 (0.032 mol) α-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 275 ml of 25% by volume absolute ethanol-75% by volume ethyl acetate solution is hydrogenated with 8 .5 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.8 kg/cm and room temperature for 23 hours. The catalyst is filtered off, and the filtrate is evaporated under reduced pressure at 30 - 40°C. The residue is dissolved in 250 ml of 10% by volume ethanol-90% by volume ethyl acetate solution and stirred with 20 ml of saturated sodium carbonate solution and approx. 30 g. anhydrous sodium carbonate i

10 minutes. After filtration, the filtrate is dried over anhydrous magnesium sulphate, filtered and evaporated to dryness under reduced pressure. The residue is dissolved in 130 ml of dry chloroform, the solution is cooled in an ice bath and saturated with hydrogen chloride for 15 minutes. The solid is collected, washed by suspending it in 100 ml of anhydrous ether three times and then slurried in 300 ml of ethyl acetate under nitrogen in a stoppered flask at room temperature overnight. The α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is collected, stirred in 300 ml of hexane for 2 hours and dried in a vacuum desiccator over calcium chloride, thereby obtaining 8.32 g (62%)

of the hydrochloride of a mixture of α- and β-isomers, observed Rf =0.7 by thin-layer chromatography (fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent).

Anal. calculate, for <C>1<6H>20N206.HC1.1/2 CH3C02C2H^: C 51.86; H 6.05;

N 6.7 Found: C 51.98; H 5.87;

N 6.65

Example 3

A. Separation of α-succinimidoethyl-L-N-carbobenzyloxy-3-(3>4-dihydroxyphenylmethylenedioxyphenyl)-2- methylalaninate isomers

A mixture of 150.5 g of the diastereomeric isomers from example 2 is dissolved in a boiling mixture of 1200 ml of benzene and 100 ml of absolute methanol, filtered, and the filtrate is evaporated to a volume of approx. 700 ml. 100 ml of absolute methanol is added to the solution which is then diluted to pale with 1000 ml of hexane, seeded and scraped to effect crystallization. The mixture is cooled at 5°C for approx. 16 hours, and the crude crystalline α-isomer is then collected, washed by suspension in 200 ml of a 50:50 mixture (volume) of benzene and hexane and dried at 70°C. The product weighs 68.1 g and melts at 185.5 - 191°C. An analytical sample melts at 199.5 - 201.5°C after two further recrystallizations.

Anal. calculated for C^H^I^Og: C 70.02; H 5.40; N 4.4l

Found: C 70.22; H 5.52; N 4.29

The combined mother liquors and washings from the a-isomer are evaporated to dryness under reduced pressure at 6o°C, whereby 79.3 g of the (3-isomer) are obtained as a very viscous oil.

B. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methyl lananinate - hydrochloride id- dihydrate ((3-isomer)

A solution of 10.0 g (0.016 mol) of α-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate ((3-isomer) in 140 ml of 25 vol% absolute ethanol-75 vol% ethyl acetate solution is hydrogenated with 4.2 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.8 kg/cm<2> and room temperature for 20 hours until hydrogen absorption is complete. The catalyst is filtered off under nitrogen, the filtrate is acidified with 2 .0 ml of 9.4 N ethanolic hydrogen chloride and evaporated to dryness under reduced pressure at 30 - 40° C. The amorphous, solid residue is dissolved in 50 ml of hot 95% ethanol (5% water), filtered, and the filtrate is diluted to initial bleaching with 68 mL of anhydrous ether, seeded and scraped to effect crystallization. The product is collected and stirred in 300 mL of anhydrous ether to remove any diphenylmethane. After 1 hour, the solid is collected and dried at 70°C overnight to give 3.7 g of material melting at 123 - 126°c (dec.).Recrystallization n from 20 ml of 95% ethanol gives 3.36 g (51%) α-succin-imidoethyl -L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate (|3-isomer) as dihydrate which melts at 129 - 131 C (dec.)

(dried at 70°C overnight), which is homogeneous by thin-layer chromatography (fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent), Rf = 0.7-

Anal. calculate, for C^H^r^Og .HCl.2H20: C 47.00; H 6,16; N 6.85 Found: C 46.85, 47.09; H 6.12, 6.16;

N 6.76, 6.61

[a]2/* = + 33.46° (C = 1.5 CH 3 OH)

Example 4

A. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate - hydrochloride fg-isomer)

A solution of 10.0 g (0.016 mol) α-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate (α-isomer) in 140 mL 25% absolute ethanol-75% ethyl acetate by volume solution is hydrogenated with 4.2 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.8 kg/cm 2 and room temperature for 27.5 hours until hydrogen uptake is complete. 2 ml of a 9.4 N ethanolic solution of anhydrous hydrogen chloride is added,

and the catalyst is removed by filtration through a pad of diatomaceous earth. After evaporation under reduced pressure, the residue is extracted by shaking with 200 ml of diethyl ether, twice with 200 ml of benzene and finally with 200 ml of diethyl ether. The material remaining after these extractions is the desired α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride diethylether solvate (α-isomer), Rf = 0.7 (thin layer chromatography , fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent) contaminated with 12% diphenylmethane.

[α] 24 = -18.75 (C = 1.68, CH 2 OH).

Example 5

A. Preparation of 2-trifluoroacetamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 5.09 g (0.010 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 1.01 g (0.010 mol) triethylamine, and 1.7 g (0.010 mol ) N-(2-chloroethyl)-2,2,2-trifluoroacetamide in 20 ml of dry dimethylformamide is stirred at 110°C for 20 hours under nitrogen. The cooled reaction mixture is poured into 500 ml of ice water,

and the product is extracted in 3 x 500 ml of ethyl acetate. The combined extracts are washed with 200 ml of water, dried over magnesium sulphate, filtered and evaporated to an oil under reduced pressure. The remaining oil is dissolved in 100 ml of ethyl acetate, extracted with 2 x 50 ml of 5% sodium hydroxide solution, washed with 50 ml of water and dried over magnesium sulphate. Filtration and evaporation under reduced pressure gives 4.92 g of an oil. Chromatography of this oil on 200 g of silica gel and elution with a 5% solution of methanol in chloroform gives 4.11 g (63.4%) of 2-trifluoroacetamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-1-). .methylenedioxyphenyl)-2-methylalaninate as an oil, homogeneous by thin-layer chromatography (fluorescent silica gel plate developed with 5 vol% methanol-95 vol% chloroform) Rf = 0.8-

B. Preparation of 2-trifluoroacetamidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 2.0 g (0.0031 mol) of 2-trifluoroacetamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 125 ml of absolute ethanol and 1.0 g of 10% palladium- on-carbon catalyst is hydrogenated at room temperature and an initial pressure of 2.5 kg/cm for 5 hours and 40 minutes until hydrogen absorption is complete. The catalyst is removed by filtration under nitrogen through a diatomaceous earth filter plate, and the filtrate is evaporated under reduced pressure at a temperature of 20 - 30°C. The residue is dissolved in 25 ml of absolute ethanol, transferred to the hydrochloride by adding 2 ml of 7.6 N ethanolic anhydrous hydrogen chloride solution and then evaporated under reduced pressure. The residue is precipitated twice by dissolving in ethanol and adding sufficient ethyl ether to precipitate the product, whereby 800 mg (66.6%) of 2-trifluoroacetamidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is obtained as an ethanol solvate, homogeneous by thin-layer chromatography (fluorescent silica gel developed with 50 vol% methanol-50 vol% chloroform) Rf = 0.8-

Anal. calculate, for C^H-^F^C^.HCl .C^OH: C 44.40; H 5.59; N 6.47 Found: C 44.55; H 5.29; N 6.72

Example 6

A. Preparation of 2-nicotinamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 5.84 g (0.015 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 1.52 g (0.015 mol) triethylamine and 2.77 9 (0.015 mol) N-( 2-chloroethyl)-nicotinamide in 20 ml of dry dimethylformamide is stirred under nitrogen at 95°C for 20 hours.

The cooled reaction mixture is poured into 200 ml of ice water, and the product is extracted into 3 x 175 ml of ethyl acetate. The combined extracts are washed with 100 ml saturated sodium bicarbonate solution, 100 ml water and dried over magnesium sulphate. After filtration, the solvents are removed under reduced pressure, whereby 6.28 9 (85%) of 2-nicotinamido-ethyl-L-N -carbobenzyloxy -3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate is obtained, homogeneous by thin-layer chromatography (fluorescent silica gel plate developed with a 20% by volume methanol-80% by volume benzene solution) observed Rf = 0.45.

B. Preparation of 2-nicotinamiiroethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrobromide

A mixture of 1.0 g (2.0 mmol) 2-nicotinamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate and 10 ml of a 30 - 32% solution of anhydrous hydrogen bromide in acetic acid is prepared at 20 - 25°C for 30 minutes until gas evolution has ended. The homogeneous solution is evaporated under reduced pressure at 20 - 25°C,

and the residue is stirred with 50 ml of diethyl ether for 3 days. The almost white solid is collected, washed with 50 ml of anhydrous ethyl ether and dried under high vacuum (0.1 - 0.3 mm Hg) at 20 - 25°C, thereby obtaining 800 mg (77%) of 2-nicotinamidoethyl-L -3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrobromide, observed Rf = 0.5 by thin-layer chromatography (fluorescent silica gel plate developed with a solution containing equal parts by volume of n-butanol, acetic acid, 1% aqueous sodium bisulphite, benzene and acetone).

Anal. calculate, for C^H^N^. 2HBr. 2H 2 O: C 38.79; H 4.88; N 7.54 Found: C 38.79; H 4.56; n 7.37 Example 7

A. Preparation of g-chloroethyl pivalate

400 mg of zinc chloride is melted at 0.2 - 0.5 mm pressure and cooled

to 25 - 30°C under nitrogen. 48 g (0.40 mol) of pivaloyl chloride is added to the molten zinc chloride followed by 19.2 g (0.44 mol) of acetaldehyde. During the addition of the acetaldehyde which occurs as quickly as possible, the reaction mixture is stirred and cooled to prevent loss of acetaldehyde due to the exothermic nature of the reaction. After heating under reflux for 1 hour, distillation gives 3° 9 (55%) a-chloroethylpivalate, b.p. 32 - 34°C at 4 mm.

B. Preparation of α-pivaloyloxyethyl-L-N-carbobenzyloxy-3-(3,4~

diphenylmethylenedioxyphenyl)- 2- methylalaninate

To a stirred solution of 9.0 g (0.018 mol) of L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine in 25 ml of dry dimethylformamide is added 1.80 g (0.018 mol) of triethylamine followed by 2.96 g (0.018 mol) α-chloroethyl pivalate. After stirring at 90 - 95°C

for 20 hours, the reaction mixture is poured into 350 ml of water, and the product is extracted with 3 x 100 ml of ethyl ether. The ether extracts are combined,

washed with 50 ml of 5% sodium hydroxide solution, 50 ml of water and dried over anhydrous magnesium sulphate. After filtration, the solvents are removed under reduced pressure, whereby 7.9 9 is obtained

(68.9%) crude α-pivaloyloxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalaninate.

C. Preparation of α-pivaloyloxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 7.8 g of α-pivaloyloxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 140 ml of absolute ethanol and 11 ml of 8 N ethanolic anhydrous hydrogen chloride solution is hydrogenated with 3.7 9 10%- ig palladium-on-carbon catalyst at 20 - 25°C and an initial pressure of 2.46 kg/cm<2> for 19 hours until hydrogen uptake ceases. After removal of the catalyst by filter-

ing the ethanol is removed under reduced pressure. The residue is stirred overnight with 80 ml of benzene. The benzene is removed by decantation, replaced with 80 ml of hexane, stirred and the hexane decanted off. The residue up-

dissolve in 30O ml of ethyl acetate, stir briefly with a mixture of 5 g of solid sodium carbonate and 5 ml of saturated sodium carbonate solution, and dry over anhydrous magnesium sulfate. After filtration, 3 ml of 9.6 N ethanolic anhydrous hydrogen chloride are added, and the solution is evaporated under reduced pressure to dryness. Further drying at 65°C and 0.2 mm pressure gives 2.16 g (47.2%) of the α-pivaloyloxyethyl ester hydrochloride.

Anal. calculate, for C1?H25N06.HC1: C 54.32; H 6.97; N 3.73

Found: C 54.47; H 7.36; n 3.39

Example 8

A. Preparation of L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine

To a stirred solution of 3.0 g (0.0126 mol) L-3-(3,4-di-hydroxyphenyl)-2-methylalanine sesquihydrate in 20 ml of 2 N sodium hydroxide solution kept at 0°C under a nitrogen atmosphere, a solution of 3 ml of carbobenzyloxychloride in 10 ml of diethyl ether is added. After stirring at 0°C for 1 hour, followed by 1 hour at 25°C, the reaction mixture is extracted with 50 ml of diethyl ether. The aqueous part is acidified to pH 3 - 4 with 6 N hydrochloric acid solution, and the impure product is extracted in 100 ml of ethyl acetate and washed three times with 25 ml of water.

After drying over anhydrous magnesium sulfate and filtration, the solvent is removed under reduced pressure, whereby 1.5 g (34.5%) of L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine is obtained as a viscous oil.

B. Preparation of pivaloyloxymethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A mixture of 2.1 g (6.1 mmol) L-N-carbobenzyloxy-3~(3,4-dihydroxyphenyl)-2-methylalanine, 0.93 g (6.2 mmol) chloromethylpivalate, 0.63 g (6 .3 mmol) of potassium bicarbonate and 0.15 g of potassium iodide in 60 ml of acetone and 4 ml of water are stirred at reflux under nitrogen for 18 hours. After evaporation under reduced pressure, 50 ml of water is added, and the N-carbobenzyloxy derivative of the desired ester is extracted with 3 x 50 ml of diethyl ether. The ether extract is washed with 50 ml of water, dried over anhydrous magnesium sulfate and evaporated under reduced pressure. The oily residue is dissolved in 100 ml of absolute ethanol and 4 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution and hydrogenated with 1 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.74 kg/cm for 24 hours. After removal of the catalyst by filtration, the filtrate is evaporated under reduced pressure. The residue is dissolved in 5 ml of water, made basic to pH 8 with a standard sodium carbonate solution, and the insoluble product is extracted into 25 ml of ethyl acetate. After drying over anhydrous magnesium sulfate and filtration, 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution is added, and the solution is evaporated under reduced pressure, whereby 0.50 g (22.6%) of the hydrochloride of pivaloyloxymethyl-L-3-(3, 4-dihydroxy-phenyl)-2-methylalaninate hydrochloride, Rf = 0.86 by thin layer chromatography (fluorescent silica gel plate developed with a 5:2:3 by volume mixture of n-butanol:acetic acid:water).

Anal. calculate, for C-^H^NOg.HCl: C 53.11; H 6.69; N 3.87

Found: C 53.76; H 6.64; N 3.69

Example 9

A. Preparation of 1,2-ethylene-bis-L-N-carbobenzyloxy-3-(3,4-di-hydroxyphenyl)-2-methylalaninate

A solution of 7.8 g (0.023 mol) L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 1.88 g (0.01 mol) 1,2-dibromoethane and 2.1 g (0.021 mol) of triethylamine in 20 ml of dimethylformamide is heated at 85 - 90°C for 10 hours and then poured into 200 ml of water. The blocked bis-ester is extracted with 3 x 100 ml of ethyl acetate and washed with 100 ml of saturated sodium bicarbonate solution and 100 ml of saturated sodium chloride solution. After drying over anhydrous magnesium sulfate and evaporation under reduced pressure at 30 - 40°C, 5.3 9 (74%) of 1,2-ethylene-bis-L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate are obtained .

B. Preparation of 1,2-ethylene-bis-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride

A solution of 5.0 g (6.98 mmol) of 1,2-ethylene-bis-L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate in 120 ml of a 25% by volume methanol-75% by volume % ethyl acetate mixture is hydrogenated at an initial thrust of o 2.46 kg/cm 2 with 2 g of 10% palladium on o carbon catalyst until hydrogen absorption is complete. After filtration to remove the catalyst, the solvents are removed under reduced pressure. The residue is dissolved in a 1% by volume ethanol-90% by volume ethyl acetate mixture, stirred with 5 ml of saturated sodium carbonate solution and 5 g of solid sodium carbonate. Anhydrous magnesium sulfate is added, the mixture is filtered, and the filtrate is acidified with 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution. The solvents are removed under reduced pressure at a temperature of 20 - 30°C, whereby 1,2-ethylene-bis-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride is obtained as the ethyl acetate solvate.

Anal. calculate, for C^H^N^g . 2HC1. 2C₂HgO₂ : C 51.65; H 6.65 > N 4.07 Found: C 50.91; H 6.69; N 4.27

Example IO

A. Preparation of 1,3-propylene-bis-L-N-carbobenzyloxy-3-(3,4-di-hydroxyphenyl)-2-methylalaninate

A solution of 7.8 g (0.023 mol) of L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate, 2.1 g (0.020 mol) of triethylamine and 2.02 g (0.010 mol) of 1, 3-dibromopropane in 20 ml of dimethylformamide is heated under nitrogen for 15 hours at 95°C and then poured into 200 ml of water. The product is extracted with 3 x 100 ml of ethyl acetate and washed with 50 ml of diluted (5%) sodium bicarbonate solution, 50 ml of water and finally 50 ml of saturated sodium chloride solution. After drying over anhydrous magnesium sulfate and evaporation under reduced pressure, 5.4 9 (73.8%) of 1,3-propylene-bis-L-N-carbobenzyloxy-3-(3,4-dihydroxy-phenyl)-2-methylalaninate are obtained.

B. Preparation of 1,3-propylene-bis-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate dihydrochloride

A solution of 5,4 9 (7.39 mmol) 1,3-propylene-bis-L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalaninate in 100 mL of 25% v/v ethanol-75% v/v ethyl acetate hydrogenated at an initial pressure of 2.46 kg/cm with 255 g of 10% palladium-on-carbon catalyst at 25°C until hydrogen absorption ceased. After removal of the catalyst by filtration, the solvents are removed under reduced pressure. The residue is dissolved in 10% by volume methanol-90% by volume ethyl acetate, stirred with 5 ml of saturated sodium carbonate solution and 5 g of solid sodium carbonate. 5 9 anhydrous magnesium sulfate is added, the mixture is filtered, and the filtrate is acidified with 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution. The solution is evaporated under reduced pressure to approx. 50 - 6o ml volume and decanted from an insoluble gum. The gum is stirred with 25 ml of ethyl acetate, filtered and dried, whereby 1.74 g (33%) of 1,3-propylene-bis-L-3-(3,4-dihydroxy-phenyl)-2-methylalaninate dihydrochloride is obtained as ethyl acetate solvate,

Rf = 0.56, thin layer chromatography (fluorescent silica gel plate developed with a solution containing equal parts by volume of n-butanol, acetone, acetic acid, water and benzene).

Example 11

A. Preparation of 1-chloro-1-succinimidopropane

Anhydrous hydrogen chloride is bubbled through a mixture of 1 g (0.072 mol) N-propenyl succinimide and 1.04 g of stannous chloride for 6 hours. The solution is left at room temperature for 10 days, the solution being saturated again with hydrogen chloride gas after 3 and 4 days. The solvents are removed under reduced pressure at 30 - 40°C, whereby 1-chloro-1-succinimidopropane is obtained as a. yellow oil.

B. Preparation of α-succinimidopropyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g (0.020 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-3-methylalanine, 2.1 g (0.021 mol) triethylamine and 3.51 g (0.020 mol) 1-chloro -1-succinimidopropane in 20 ml of dimethylformamide is heated at 90°C for 10 hours and then poured into 200 ml of water. The product is extracted with 3 x 100 ml of ethyl ether and washed with 50 ml of 5% sodium hydroxide, 50 ml of water and 50 ml of a saturated solution of sodium chloride. After drying over anhydrous magnesium sulfate and filtration, the solvents are removed under reduced pressure, whereby 8.6 g (68%) of a-succinimidopropyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate are obtained, Rf =0 ,2, thin-layer chromatography (fluorescent silica gel plate developed with chloroform). •

C. Preparation of α-succinimidopropyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 8.6 g (0.014 mol) of α-succinimidopropyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 120 ml of 25% by volume ethanol-75% by volume ethyl acetate solution is hydrogenated with 4 g 10% palladium-on-carbon catalyst at an initial pressure of o 2.81 kg/cm 2 for 18 hours until hydrogen absorption ceases. After removal of the catalyst by filtration, the solvents are removed under reduced pressure at 30 - 4o°C. The residue is dissolved in 10 vol% ethanol-90 vol% ethyl acetate and stirred with 5 ml saturated sodium carbonate solution and excess solid sodium carbonate in

2 minutes. 10 g of anhydrous magnesium sulfate are added, the mixture is filtered, and the filtrate is made acidic with 2 ml of 9.6 N ethanolic hydrogen chloride solution. The solution is evaporated to dryness under reduced pressure, 100 ml ethyl acetate is added, and the mixture is evaporated again to dryness under reduced pressure. 100 ml of ethyl acetate are added, and after stirring at 25°C for 1 hour, the product is removed by filtration and dried under reduced pressure, whereby 3.0 g (51.0%) of a-succin-imidopropyl-L-3-(3 ,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the ethanol solvate, Rf =0.63, thin layer chromatography (fluorescent silica gel plate developed with 30 vol% methanol-70 vol% benzene) Anal. calculate, for C-^H^N.^ .HCl .C^OH: C 52.71; H 6.75-, N 6.47 Found: C 53.62; H 6.51* N 6.32

Example 12

A. Preparation of N-chloromethylglutarimide

8.35 9 (0.070 mol) of thionyl chloride is added slowly to a solution of 9.0 g (0.063 mol) of N-hydroxymethylglutarimide in 50 ml of benzene at 4o°C. After the addition is finished, the solution is stirred under reflux for 1.5 hours and then at room temperature for a further 1.5 hours. The benzene is removed under reduced pressure at 30 - 40°C, and the residue is distilled, whereby 5.4 9 (53%) N-chloromethylglutarimide is obtained, b.p. 97 - 100°C at 0.1 mm.

B. Preparation of glutarimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g (0.020 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.02 g (0.020 mol) triethylamine and 3.23 g (0.020 mol) N-chloromethylglutarimide in 20 ml of dimethylformamide is stirred at 70°C for 5 hours, then at 20 - 30°C for 5 hours, and finally the mixture is poured into 200 ml of water. The product is extracted with 3 x 100 ml ethyl acetate, washed with 50 ml 5% sodium hydroxide solution, 50 ml water and 50 ml saturated sodium chloride solution and dried over anhydrous magnesium sulfate. After filtration, the solvents are removed under reduced pressure, whereby 12.1 g (95%) of glutarimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalaninate is obtained, Rf = 0.14 by thin-layer chromatography (fluorescent silica gel plate developed with chloroform).

C. Preparation of glutarimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 12 g (0.0189 mol) glutarimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 130 ml of 25% by volume absolute ethanol-75% by volume ethyl acetate is hydrogenated with 5 g of 10%- ig palladium-on-carbon catalyst at 20 - 25°C and an initial pressure of 2.81 kg/cm for 18 hours until hydrogen uptake ceases. After removal of the catalyst by filtration and evaporation to dryness under reduced pressure, the residue is dissolved in 200 ml of 10 vol% absolute ethanol-90 vol% ethyl acetate solution and stirred with 5 ml of a saturated sodium carbonate solution and excess

of solid carbonate for 2 minutes. Add anhydrous magnesium sulfate and remove after a few minutes by filtration. The solvents are removed under reduced pressure, the residue is washed with 25 ml of hexane and then with 25 ml of ethyl acetate and dried under reduced pressure. The residue is again treated with sodium carbonate as above to remove them

last trace of α-methyl-3,4-dihydroxyphenylalanine and transferred to the hydrochloride salt with 3 ml of 9.6 N ethanolic anhydrous hydrogen chloride, thereby obtaining 3.0 g (36%) glutarimidomethyl-L-3"(3,4-dihydroxy -phenyl)-2-methylalaninate hydrochloride as the ethyl acetate solvate, homogeneous by thin layer chromatography (fluorescent silica gel plate developed with 30 vol% methanol-70 vol% benzene), Rf = 0.56.

Anal. calculate, for Cl6H2oN206.HCl. 3/4 C₂H₂: C 51.99; H 6.20; N 6.38 Found: C 52.15; H 6.45; N 6.53

Example 13

A. Preparation of 2-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxyd

A solution of 7.65 g (0.015 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 1.5 g (0.015 mol) triethylamine and 3.0 g (0.015 mol) N-chloromethylsaccharin in 15 ml of dimethylformamide is heated at 75 - 80°C for 17 hours and then poured into 150 ml of water. The product is extracted with 3 x 100 ethyl acetate, washed with 50 ml saturated sodium bicarbonate solution, 50 ml water and 50 ml saturated sodium chloride solution and dried over anhydrous magnesium sulphate.

After filtration, the solvents are removed under reduced pressure,

thereby obtaining 9.3 g (100%) of 2-[L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)-one-1, 1-dioxide, Rf = 0.32, thin-layer chromatography (fluorescence

end silica gel plate developed with chloroform).

B. Preparation of 2-[L-3-(3,4-dihydroxyphenyl)-2-methylalanyloxy-methyl]-1,2-benzisothiazol-3(2H)-one-1,1-dioxyd-hydrochloride

A solution of 3.0 g (0.0043 mol) of 2-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-1,2-benz-isothiazol-3(2H)-one- 1,1-dioxide in 100 ml of absolute ethanol and 5 ml of 8 N ethanolic anhydrous hydrochloride solution is hydrogenated with 1.5 g of 10% palladium-on-carbon catalyst at 20 - 25°C and an initial pressure of o 2.46 kg/cm 2 for 20 hours until hydrogen absorption ceases. After removal of the catalyst by filtration and evaporation to dryness under reduced pressure, the residue is stirred with 50 ml of ethyl acetate

for 1 hour, and the ethyl acetate is decanted off. The residue is dissolved in 200 ml of 20% by volume ethanol-80% by volume ethyl acetate and stirred with 10 ml of saturated sodium carbonate solution and excess solid sodium carbonate.

10 g of anhydrous magnesium sulphate is added and removed after a few minutes by filtration, and the filtrate is acidified with 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution. The solvents are removed under reduced pressure, whereby 0.2 g (10.0%) of 2-[L-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-1,2-benzisothiazol-3(2H)- one-1,1-dioxyd-hydrochloride as the ethyl acetate solvate, Rf = 0.74, thin-layer chromatography (fluorescent silica gel plate developed with a solvent consisting of equal parts benzene, water, acetic acid, n-butanol and acetone).

Anal. calculate, for C^H^N^yS .HC1. 1/4c^HgO 2 : C 49.08; H 4.55; N 6.03 Found: C 49.27; H 4.76; N 5.65

Example 14

A. Preparation of 1-methyl-2-[L-N-carbobenzyloxy-3-(3,4-dihydroxy -

phenyl)- 2- methylalanyloxymethyl]- imidazole

A solution of 7.8 9 (0.0226 mol) L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 4.2 g (0.042 mol) triethylamine and 3.34 g (0.0256 mol) of 1-methyl-2-chloromethylimidazole in 20 ml of dimethylformamide is heated at 70 - 75°C for 10 hours and then poured into 200 ml of water. The product is extracted with 3 x 100 ml of ethyl acetate, washed with 50 ml of saturated sodium bicarbonate solution, 50 ml of saturated sodium chloride solution and evaporated under reduced pressure, whereby 2.2 g (22%) of l-methyl-2-[L-N-carbobenzyloxy- 3-(3,4-dihydroxyphenyl)-2-methyl-alanyloxymethyl]-imidazole, homogeneous by thin-layer chromatography (fluorescent silica gel plate developed with 15 vol% methanol-

85% by volume chloroform), Rf = 0.66.

B. Preparation of L-1-methyl-2-[2-(3,4-dihydroxybenzyl)-alanyloxy-methyl-1-imidazole-dihydrochloride-dxhydrate

A solution of 2.1 g (4.78 mmol) of 1-methyl-2-[L-N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanyloxymethyl]-imidazole in 100 ml of absolute ethanol is hydrogenated with 1 g of 10 % palladium-on-carbon catalyst at an initial pressure of 2.46 kg/cm for 4 hours. After removal of the catalyst by filtration and evaporation to 50 ml under reduced pressure, 2 ml of 9.6 N ethanolic anhydrous hydrogen chloride are added, and the remaining solvents are removed under reduced pressure. The residue is stirred with 200 ml of 20% by volume ethanol-80% by volume ethyl acetate, 10 ml of saturated sodium carbonate solution and excess solid sodium carbonate. 10 g of anhydrous magnesium sulfate is added and removed after a few minutes by filtration. The filtrate is acidified with 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution The solvents are removed under reduced pressure to give 0.2 g (8.5%) of L-1-methyl-2-[2-(3,4-dihydroxybenzy1)-alanyloxymethyl] -imidazole dihydrochloride dihydrate as the ethyl acetate solvate, Rf = 0.3 at thins liquid chromatography (fluorescent silica gel plate developed with a solution consisting of equal parts by volume of n-butanol, acetic acid, water, benzene and acetone)

Anal. calculate, for C^H-^N.^. 2HC1. 2H20. 1/2C₂HgO 2 : C 44.55; H 6.34;

N 9.17 Found: C 44.62; H 6.84;

N 8.95

Example 15

A. Preparation of l-methyl-3-chloromethylhydantoin

30 ml of thionyl chloride are added slowly over 20 minutes to a well-stirred mixture of 25 g (0.173 mol) of 1-methyl-3-hydroxy-methylhydantoin and 160 ml of benzene under reflux. After stirring under reflux for 2 hours, the reaction mixture is evaporated to dryness under reduced pressure, 70 ml of benzene is added, and the solution is evaporated again to dryness. After repeating this procedure once more with 70 ml of benzene, the residue is extracted with 3 x 100 ml of carbon tetrachloride. Removal of solvents under reduced pressure gives 15.7% (55.7%) 1-methyl-3-chloromethylhydantoin.

B. Preparation of l-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalanyloxymethyl]- hydantoin

A solution of 10.2 g (0.020 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.1 g (0.021 mol) triethylamine and 3.25 g (0.020 mol) l-methyl -3-Chloromethylhydantoin in 23 ml of dimethylformamide is heated at 70°C for 18 hours and then poured into 230 ml of water. The product is extracted with 3 x 100 ml of ethyl acetate, washed with 50 ml of dilute (5%) sodium hydroxide solution, 50 ml of water and 50 ml of saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtration, the solvents are removed under reduced pressure, whereby 11.7 9 (92%) of 1-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-hydantoin is obtained.

C Preparation of L-1-methyl-3-[2-(3,4-dihydroxybenzyl)-alanyloxy-methyl]- hydantoin - hydrochloride - hyarate

A solution of 4.0 g (6.3 mmol) of 1-methyl-3-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanyloxymethyl]-hydantoin in 140 ml of absolute ethanol and 2 g of 10% -ig palladium-on-carbon catalyst is hydrogenated at an initial pressure of 2.53 kg/cm<2> in

20 hours. After removal of the catalyst by filtration and evaporation to dryness under reduced pressure, the residue is washed with 100 ml of hexane. The hexane-insoluble material is dissolved in 150 ml of 10 vol.% methanol-90 vol.% ethyl acetate, stirred with 5 ml of saturated sodium carbonate solution and excess sodium carbonate and dried over anhydrous magnesium sulfate. After filtration, the filtrate is acidified with 2 ml of 9.6 N ethanolic anhydrous hydrogen chloride and evaporated to dryness under reduced pressure. The residue is stirred with 80 ml of ethyl acetate for 3 hours, filtered and dried under reduced pressure, whereby 0.50 g (18%) of L-1-methyl-3-[2-(3,4-dihydroxybenzyl)-alanyl-oxymethyl]- hydantoin hydrochloride hydrate as the ethyl acetate solvate. Anal. calculate, for C^H^N^Og .HCl .H 2 O.1/2C^HgO 2 : c 46.84; h 6,00; n 9.64

Found: C 46.28; H 6.09; N 9.06

Example 16

A. Preparation of 2-phenoxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalaninate

A solution of 4.5 g (0.0088 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 0.90 g (0.009 mol) triethylamine and 1.81 g (0.009 mol ) 2-bromomethylphenyl ether in 15 ml of dimethylformamide is heated at JO - 75°C for 24 hours, then cooled and poured into 150 ml of water. The product is extracted with 3 x 100 ml portions of ethyl ether, washed with 50 ml of 5% sodium hydroxide solution, 50 ml of water and 50 ml of saturated sodium chloride solution and dried over anhydrous magnesium sulfate. After filtration, the solvents are removed under reduced pressure, whereby 4.8 g (86.5) of 2-phenoxy-ethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate are obtained, homogeneous by thin-layer chromatography ( fluorescent silica gel plate developed with chloroform) Rf = o.91.

B. Preparation of 2-phenoxyethyl-L-3-(3,4-dihydroxybenzyl)-alaninate hydrochloride hemihydrate

A solution of 4.7 g (7.5 mmol) of 2-phenoxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in

120 ml of absolute ethanol is hydrogenated at 1.7 Q of 10% palladium-on-carbon catalyst at an initial pressure of 1.4 l kg/cm<2> for 20 hours. After filtering off the catalyst, the solvents are removed under reduced pressure, and the residue is chromatographed on a column of 75 g silica gel. Elution with 400 ml of a 5 vol% methanol-95 vol% benzene mixture gives 1.42 g (58%) of ester base, m.p. 35 - 42°C homo-

gent by thin-layer chromatography (fluorescent silica gel plate developed with 30% by volume methanol-70% by volume benzene) Rf = 0.52. The base is transferred to the hydrochloride salt by dissolving in 25 ml of a 50% by volume chloroform-50% by volume methanol mixture and acidifying with 2 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution. Solvents are removed under reduced pressure, whereby 2-phenoxyethyl-L-3-(3,4-dihydroxybenzyl)-alaninate hydrochloride hemihydrate is obtained.

Anal. calculate, for C^H^NO^ .HCl.1/2H2O: C 57.37; H 6.15; N 3.72 Found: C 57.17; H 6.16; N 3.41

Example 17

A. Preparation of 2-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate"

A solution of 4.5 g (8.8 mmol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 0.90 g (9 mmol) triethylamine and 1.85 g (9, 3 mmol) of N-(2-bromomethyl)-succinimide in 15 ml of dimethylformamide is heated at 95° C. for 19 hours, then cooled and poured into 150 ml of water. The product is extracted with 3 x 100 ml ethyl ether, washed with 50 ml 5% sodium hydroxide solution, 50 ml water and 50 ml saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtration, the solvents are removed under reduced pressure, thereby obtaining 3.8 9 (86%) 2-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate, homogeneous by thin-layer chromatography (fluorescent silica gel plate developed with chloroform ) Rf = 0.27.

B. Preparation of 2-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hemihydrate

A suspension of 2.5 g (3.94 mmol) of 2-succinimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 75 ml of methanol, 75 ml of ethanol and 3 ml of 7.6 N ethanolic anhydrous hydrogen chloride solution is hydrogenated with 1.2 g of 10% palladium-on-carbon catalyst at an initial pressure of 1.4 l kg/cm for 20 hours. After removal of the catalyst by filtration, the solvents are removed under reduced pressure, and the residue is stirred with 25 ml of benzene and then 25 ml of ethyl acetate. The insoluble material is treated with 100 ml of 10 vol% ethanol-90 vol% ethyl acetate, 5 ml of saturated sodium carbonate solution and 5 g of solid sodium carbonate. The organic extract is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure. 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution is added. Removal of. all solvents under reduced pressure yield 0.5 g (33%) 2-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hemihydrate, homogeneous by thin-layer chromatography (fluorescent silica gel plate developed with 30 vol% methanol -70 vol% benzene), Rf = 0.4-

Anal. calculate, for Cl6H2Q<N>2<0>6.HC1.1/2H2O: C 50.33; H 5.54; N 7.34 Found: C 50.89; H 5.65; N 7.22

Example 18

A. Preparation of 1,2-ethylene-bis-[L-N-carbobenzyloxy-3-(3,4~di-phenylmethylenedioxyphenyl)-2-methylalaninate]

A solution of 10.18 9 (0.020 mol) of L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.12 g (0.021 mol) of triethylamine and 0.99 g (0.010 mol) of 1, 2-dichloroethane in 35 ml of dimethylformamide is stirred under nitrogen at 105 - HO°C for 28 hours and then poured into 400 ml of ice water. The product is extracted in 800 ml ethyl ether, washed with 100 ml 5% sodium hydroxide solution, 100 ml water, dried over anhydrous magnesium sulphate, filtered and evaporated under reduced pressure. The residue is chromatographed on 800 g of silica gel, 2.25 9 (21.5%) of 1,2-ethylene-bis-[L-N-carbobenzyloxy-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalaninate is eluted with chloroform.

Preparation of L,L-2-[2-(3,4-diphenylmethylenedioxybenzyl)-alanyloxy]-ethyl-2-(3,4-dihydroxybenzyl)-alaninate-bishydrogen-oxalate

A solution of 2.25 g (2.2 mmol) of 1,2-ethylene-bis-[L-N-carbo~ benzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate] in 100 ml of absolute ethanol is hydrogenated with 1 .2 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.11 kg/cm for 28 hours until the hydrogen uptake has ended. After removing the catalyst by filtration, the solvents are removed under reduced pressure. The residue is stirred with 100 ml of 10% by volume ethanol-90% by volume ethyl acetate, 2 ml of saturated sodium carbonate solution and 3 g of solid sodium carbonate for 15 minutes and then filtered. The filtrate is dried over anhydrous magnesium sulphate, filtered and evaporated under reduced pressure. The residue is chromatographed over silica gel and eluted with 30% by volume methanol-70% by volume benzene, which gives 220 mg of product. This product is transferred to the oxalate salt with 500 mg of oxalic acid in 10 ml of ethanol by filtering with sufficient ethyl ether. After another filtration from 10 ml of ethanol with the addition of sufficient ethyl ether, 246 mg (14%) of L,L-2-[2-(3,4-diphenyImethylenedioxybenzyl)-alanyloxy]-ethyl-2 are obtained -

(3,4-dihydroxybenzyl)-alanine bishydrogen oxalate.

Anal. calculate, for C^H^N^g.20^O^: C 59.08; H 5.08; N 3.53 Found: c 59.15; H 5.18; N 3.55

Example 19

A. Preparation of 2-phthalimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.18 9 (0.020 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate, 2.12 g (0.021 mol) triethylamine and 5.08 9 (0.020 mol) N-( 2-bromomethyl)-phthalimide in 30 ml of dimethylformamide is stirred under nitrogen at 105 - 110 C overnight and then poured into 600 ml of ice water. The product is extracted with 3 x 100 ml of ethyl ether and washed with 50 ml of water. The ether extract is dried over anhydrous magnesium sulphate, filtered and evaporated under reduced pressure, whereby a gummy solid is obtained. Chromatography over silica gel and elution with chloroform gives 10.88 9 (80%) 2-phthalimido-ethyl-L-N-carbobenzyloxy ~3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate, Rf = 0.53, thin-layer chromatography (fluorescent silica gel plate developed with chloroform).

B. Preparation of 2-hydroxyimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-

methylalaninate hydrochloride

A solution of 10.88 g (0.0159 mol) of 2-phthalimidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 125 ml of ethyl acetate is hydrogenated with 6 g of 10% palladium-on- carbon catalyst at an initial pressure of 2.18 kg/cm for 5 hours until hydrogen absorption ceases. After removal of the catalyst by filtration and removal of solvents under reduced pressure, the residue is dissolved in 150 ml absolute ethanol containing 4 ml 5.15 N ethanolic anhydrous hydrogen chloride solution and hydrogenated with 4.3 9 palladium-on-carbon catalyst at 1.90 - 2, 67 kg/cm <2> for 5 days. A further 4.3 9 amounts of 10% palladium-on-carbon catalyst are added during this time. After removal of the catalyst by filtration and evaporation under reduced pressure, the residue is washed with 100 ml of petroleum ether and dissolved in ethanol. It is precipitated three times from ethanol by adding sufficient ethyl ether to precipitate the product. The product is dried under reduced pressure, whereby 2.80 g (41.8%) of 2-phthalimidoethyl-L-3-(3,4-dihydroxy-phenyl)-2-methylalaninate hydrochloride is obtained, m.p. 138.0 - 140.0°C during decomposition, homogeneous by thin layer chromatography (fluorescent silica gel plate developed with 50% by volume methanol-50% by volume benzene), Rf = 0.6l.

Anal. calculate, for C20H20<N>2<0>6.<H>Cl: C 57.07; H 5.03; N 6.65; Cl 8,<42 >Found: c 56.31; H 5.62; N 6.48; Cl 8.75

Example 20

A. Preparation of 2-acetoxyethyl -L-N-carbobenzyloxy-3-(3,4-diphenyl-

methylenedioxyphenyl) - 2- methylalaninate

A solution of 10.0 g (0.0196 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.39 g (0.0235 mol), triethylamine and 2.40 g (0 .0196 mol) of 2-chloroethyl acetate in 30 ml of dimethylformamide is stirred under nitrogen at 110°C for 20 hours and then poured into 500 ml of ice water. The product is extracted in 4 x 200 ml ethyl ether which is combined and washed with 200 ml water, 200 ml 5% sodium hydroxide solution and then with 200 ml water. After drying over anhydrous magnesium sulfate and filtration, the solvents are removed under reduced pressure. The residue is chromatographed on 700 g of silica gel. Elution with 5% by volume methanol-95% by volume chloroform gives 5.60 g (48%) of 2-acetoxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate.

B. Preparation of 2-acetoxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A solution of 5.60 g (0.0094 mol) of 2-acetoxyethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 100 ml of absolute ethanol is hydrogenated with 2.8 g of 10% palladium -on-carbon catalyst at an initial pressure of 2.6o kg/cm p for 24 hours until the hydrogen uptake has ended. After removal of the catalyst by filtration and removal of solvents under reduced pressure, the residue is washed with 100 ml of petroleum ether and dissolved in 124 ml of 10% by volume ethanol-90% by volume ethyl acetate. 6.2 g of sodium carbonate and 4 ml of saturated sodium carbonate solution are added and stirred for 20 minutes. The mixture is filtered, dried over anhydrous magnesium sulfate, filtered again and evaporated under reduced pressure. The residue is chromatographed on silica gel and eluted with 20 vol% methanol-80 vol% benzene. Recrystallization is carried out by dissolving it in ethyl acetate and adding sufficient cyclohexane to precipitate it, yielding 1.01 g (36%) of 2-acetoxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate,

m.p. 114 - 118°C, split.

Anal. calculate, for C^H^NOg.- C 56.55; H 6.44; N 4.71

Found; C 56.64; H 6.63; N 4.33

kkseropel 21

A. Preparation of 2-benzamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.0 g (0.0196 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.11 g (0.021 mol) triethylamine and 3.64 9 (0.0196 mol ) N-(2-chloroethyl)-benzamide in 20 ml of dimethylformamide is stirred under nitrogen at 110°C for 20 hours and then poured into 400 ml of ice water. The precipitate is removed by filtration, washed with 100 ml of water and dissolved in 200 ml of ethyl ether. The ether solution is washed with 50 ml of 5% sodium hydroxide solution, 50 ml of water and dried over anhydrous magnesium sulphate. The drying agent is filtered off, and the filtrate is evaporated under reduced pressure, thereby obtaining 11.21 g (87%) of 2-benzamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalaninate, Rf = 0, 7, thin layer chromatography (fluorescent silica gel plate developed with 5 vol% methanol-95 vol% chloroform).

B. Preparation of 2-benzamidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate oxalate hemihydrate

A solution of 11.21 g (0.017 mol) of 2-benzamidoethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 100 absolute ethanol is hydrogenated with 5.5 g of 10% palladium-on- carbon catalyst at an initial pressure of 2.11 kg/cm for 7 hours. After removal of the catalyst by filtration and removal of solvents under reduced pressure, the residue is stirred with 100 ml of petroleum ether overnight. The insoluble material is dissolved in 250 ml of 10% by volume ethanol-90% by volume ethyl acetate, shaken for 10 minutes with 12 ml of saturated sodium carbonate solution and 12 g of sodium carbonate and filtered. The filtrate is dried over anhydrous magnesium sulphate, filtered and evaporated under reduced pressure. The residue is treated with 1.3 g of oxalic acid dissolved in 25 ml of absolute ethanol, and the oxalate salt is precipitated by adding sufficient ethyl ether. Two further precipitations are carried out by dissolving the product in ethanol and adding sufficient ethyl ether to precipitate the product, whereby 1.60 g (23%) of 2-benz-amidoethyl-L-3-(3,4-dihydroxyphenyl)- 2-methylalaninate oxalate hemihydrate, homogeneous by thin layer chromatography (fluorescent silica gel plate developed with 50 vol% methanol-50 vol% chloroform) Rf = 0.44.

Anal. calculate, for ClgH22N205.1/20^0^. 1/2H 2 O: C 58.24; H 5.86; n"6.79 Found: c 58.39; h 5.73; n 6.37

Example 22

A. Preparation of naphthalimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 10.2 g (0.020 mol) L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.02 g (0.020 mol) triethylamine and 4.9 9 (0.020 mol) N-chloromethylnaphthalimide in 50 ml of dimethylformamide is stirred at 90°C for 20 hours and then poured into 500 ml of ice water. The product is extracted with 200 ml ethyl acetate, washed with 50 ml 5% sodium hydroxide solution, 50 ml water and 50 ml saturated sodium chloride solution and dried over anhydrous magnesium sulphate. After filtration, solvents are removed under reduced pressure, whereby 13.1 g (91%) of naphthalimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate are obtained.

B. Preparation of naphthalimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 13 g (0.0181 mol) of naphthalimidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 150 ml of 25 vol% absolute ethanol-75 vol% ethyl acetate is hydrogenated with 5 g of 10%- ig palladium-on-carbon catalyst at 25°C and an initial pressure of o 2.81 kg/cm 2 for 24 hours until the hydrogen uptake has ended. After removal of the catalyst by filtration and evaporation of the filtrate under reduced pressure, the residue is dissolved in 200 ml of 10 vol% absolute ethanol-90 vol% ethyl acetate and stirred with 5 ml of saturated sodium carbonate solution and 5 g of solid sodium carbonate for 10 minutes. The mixture is filtered, the filtrate is dried over anhydrous magnesium sulphate, filtered again and evaporated under reduced pressure. The residue is washed with 100 ml of hexane to remove diphenylmethane, dissolved in 25 ml of absolute ethanol and made sut with 5 ml of 8 N ethanolic anhydrous hydrogen chloride solution. Addition of ethyl ether precipitates the hydrochloride salt of naphthaiimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate.

Example 23

A. Preparation of racemic N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-

2- methylalanine

A solution of 9 ml of carbobenzyloxychloride in 25 ml of diethyl ether. After stirring at 0°C for 1 hour followed by 1 hour at 25°C, the reaction mixture is extracted with 50 ml of diethyl ether. The aqueous part is acidified to pH 3 with 6 N hydrochloric acid, and the crude product is extracted in 100 ml of ethyl acetate and washed three times with 35 ml of water. After drying over anhydrous magnesium sulfate and filtration, the solvent is removed under reduced pressure, whereby 4.5 g (34%) of racemic N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine are obtained as a viscous oil.

B. Preparation of racemic pivaloyloxymethyl-3-(3,4-dihydroxy-phenyl)-2-methylalaninate hydrochloride

A solution of 4.2 g (0.012 mol) of racemic N-carbobenzyloxy-3-(3,4-dihydroxyphenyl)-2-methylalanine, 1.3 g (0.013 mol) of triethylamine and 1.26 g (0.013 mol) of chloromethylpivalate in 20 ml of dimethylformamide is stirred at 90°C for 20 hours and then poured into 200 ml of water. The product is extracted in 100 ml of ethyl acetate and washed with 25 ml of saturated sodium bicarbonate solution and 25 ml of water. After drying over anhydrous magnesium sulfate and filtering, the filtrate is evaporated under reduced pressure, whereby the N-carbobenzyloxy derivative of the desired ester is obtained. This material is dissolved in 100 ml of absolute ethanol containing 10 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution and hydrogenated with 3 g of 10% palladium-on-carbon catalyst at an initial pressure of o 2.46 kg/cm 2 for 24 hours. After removing the catalyst by filtration, the filtrate is evaporated under reduced pressure. The residue is dissolved in 25 ml of water, made alkaline with a saturated sodium carbonate solution to pH 8, and the insoluble product is extracted with 100 ml of ethyl acetate. After drying over anhydrous magnesium sulfate and filtering, 5 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution is added, and the solution is evaporated under reduced pressure, whereby 1.5 g (22.6%) of the hydrochloride of the racemic pivaloyloxymethyl-3-(3 ,4-dihydroxyphenyl)-2-methylalaninate, homogeneous by thin layer chromatography (fluorescent silica gel plate developed with a 5 volume:2 volume:3 volume mixture of n-butanol:acetic acid:water) Rf = 0.86.

Example 24

Preparation of 2-acetamidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate - hydrochloride

A suspension of 88.3 g (0.30 mol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride ethanol solvate (by evaporation of an ethanolic solution of the hydrochloride under reduced pressure) and 146.4 g (1.42 mol) of N-acetylethanolamine, under nitrogen, is heated to 104 - 108 C. 84.8 g (0.713 mol) of thionyl chloride are added during 15 minutes with stirring. The reaction mixture foams vigorously during the addition. After the addition has ended, the reaction mixture is stirred at 104 - 108°C for 18 hours. A further 42.4 g (0.357 mol) of thionyl chloride is added over 7 minutes. The reaction mixture is stirred at 104 - 108°C for a further 3.5 hours, then cooled to 30°C and evaporated under reduced pressure, whereby a viscous oil is obtained. This oil is slurried with 100 ml of chloroform, and the chloroform is removed under reduced pressure. This is repeated a further three times, and then the oil is washed with 100 ml of benzene which is decanted. The residue is dissolved in 700 ml isopropanol and added to 6 1 ethyl ether. The precipitate that forms is washed with 500 ml of ethyl ether and shaken with 6 1 10% by volume ethanol-90% by volume ethyl acetate, 150 ml of saturated sodium carbonate solution and 100 g of sodium carbonate. The organic extract is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure, whereby the free base of the acetamidoethyl ester is obtained. This base is treated with 15 g of fumaric acid in 300 ml of isopropanol, and the fumarate salt is precipitated by adding sufficient ethyl ether. The fumarate salt is separated once again from isopropanol by adding sufficient ethyl ether and then transferred to the free base as before by shaking with 200 ml of 10% by volume ethanol-90% by volume ethyl acetate, 20 ml of saturated sodium carbonate solution and 20 g of solid sodium carbonate. The free base is transferred to the hydrochloride salt by dissolving in 100 ml of absolute ethanol, adding 10 ml of 9.6 N hydrochloric acid and refining by adding 1 1 of ethyl ether. After three precipitations from ethanol-ethyl ether carried out as above, 15.1 g (15%) of the hydrochloride salt of 2-acetamidoethyl-L-3-(3,4-dihydroxy-phenyl)-2-methylalaninate hydrochloride are obtained, Rf =0 ,57, thin layer chromatography (fluorescent silica gel plate developed with 50 vol% methanol-50 vol% benzene).

Anal. be<r>e<g>n, for C^H^N^ .HCl: C 50.52; H 6.36; N 8.4l

Found: C 50 , 49; H 6.69; N 8.49

Example 25

Preparation of 3-acetamidopropyl-L-3-(3,4-dihydroxyphenyl)-2-methyl-alaninate hydrogen oxalate hydrate

275 ml of thionyl chloride are added to 250 g of L-3-(3,4-dihydroxy-phenyl)-2-methylalaninate sesquihydrate at 25°C, and the mixture is heated on a steam bath. After heating for 2 hours, the thick reaction mixture is diluted with 7.5 ml of dimethylformamide dissolved in 25 ml of benzene

and stirred on a steam bath until gas evolution ceases. 100 ml of benzene is added, and the crude sulfuric acid ester is removed by filtration, washed with 100 ml of benzene, 100 ml of chloroform and 100 ml of ether,

and dried under reduced pressure, whereby 280 g of the sulfuric acid ester intermediate is obtained, m.p. 199°C during decomposition.

A mixture of 13.7 g of the crude sulfuric ester intermediate, 24.98 g (0.212 mol) of N-acetylpropanolamine and 2 g of anhydrous dimethylformamide is stirred on a steam bath for 20 hours and cooled. The reaction mixture is washed with 6 x 200 ml ethyl ether, 4 x 200 ml methylene chloride and dried under reduced pressure. The semi-solid material that remains is stirred with 200 ml of 20 vol% ethanol-80 vol% ethyl acetate, 20 ml of saturated sodium carbonate solution and 20 g of solid sodium carbonate. The organic extract is dried over anhydrous magnesium sulphate, filtered and the filtrate is added to a solution of 3.2 g of oxalic acid in 50 ml of ethanol. Solvents are removed under reduced pressure, and the product is precipitated by dissolving it in 50 ml of ethanol and adding 500 ml of ethyl ether. The product is separated again by dissolving in 50 ml of ethanol and adding 500 ml of ethyl acetate, whereby 3-acetamidopropyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate is obtained, Rf = 0.45 , thin-layer chromatography (fluorescent silica gel plate developed with 25 vol% methanol-75 vol% chloroform) .

Anal. calculate for C-^H^I^O^ .C 2 H 2 O^ -H 2 O : C 48.80; H 6.26; N 6.69 Found: C 48.73; H 6.85; N 6.68

Example 26

Preparation of 2-methylthioethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate

275 ml of thionyl chloride are added to 250 g of L-3-(3-,4~dihydroxy-phenyl)-2-methylalaninate sesquihydrate at 25°C, and the mixture is heated on a steam bath. After heating for 2 hours, the thick reaction mixture is diluted with 7.5 ml of dimethylformamide in 25 ml of benzene and stirred on a steam bath until gas evolution ceases. 100 ml of benzene is added, and the crude sulfuric acid ester is removed by filtration, washed with 100 ml of benzene, 100 ml of chloroform and 100 ml of ether, and dried under reduced pressure, whereby 280 g of the intermediate sulfur acid ester product, mp 199°C with decomposition, is obtained.

A mixture of 30 g of the crude sulfuric acid ester, 34.6 g

(0.375 mol) of 2-hydroxyethylmethylsulphide and 6 g of anhydrous dimethylformamide are stirred on a steam bath for 28 hours and cooled. reaction

the mixture is washed with 4 x 100 ml ethyl ether and 3 x 100 methylene chloride. The remaining material is stirred with 250 ml of 20 vol% ethanol-80 vol% ethyl acetate, 30 ml of saturated sodium carbonate solution and 60 ml of solid sodium carbonate and then filtered. The insoluble material is washed with 3 x 250 ml 20% by volume ethanol-80% by volume ethyl acetate, combined with the first ethanol-ethyl acetate extract and dried over anhydrous magnesium sulfate. After filtration, solvents are removed under reduced pressure, and the residue is chromatographed over silica gel. A total of 2.3 g of product is eluted with a 25% by volume methanol-75% by volume chloroform mixture. This product is transferred to the oxalate salt by adding it to a solution of 1.39 oxalic acid in 125 ml of ethanol followed by filtration with sufficient ethyl ether.

After three additional precipitations using ethanol to dissolve the product and ethyl ether to precipitate it, 300 mg of 2-methylthioethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate is obtained, homogeneous by thin-layer chromatography ( fluorescent silica gel plate developed with 25 vol% methanol-75 vol% chloroform)

Rf =0.83, m.p. 85 - 90°C during decomposition.

Anal. calculate, for C-^H^NO^S .C^O^: C 47.99; H 5.64; N 3.73

Found: C 48.00; H 6.10; N 4.07

Example 27

A. Preparation of D,L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methyl-alanine hydrochloride

A mixture of 38.6 g (0.155 mol) of racemic 3-(3,4-dihydroxy-phenyl)-2-methylalanine hydrochloride and 74 g (0.312 mol) of dichlorodiphenylmethane is immersed with slow stirring in a preheated oil bath at 190°C . After the reaction has started, the reaction mixture is stirred rapidly for 6 minutes at 190°C, removed from the hot oil bath and allowed to cool to 25 - 30°C. The crude product from 6 such experiments is combined, slurried with 2 1 diethyl ether, filtered, washed with a further 2 1 diethyl ether and dried at 30°C under 50 mm pressure. The solid is recrystallized by dissolving the product in ethanol and adding ethyl acetate to precipitate D,L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine hydrochloride.

B. Preparation of D,L-N-carbobenzyloxy-3-(3,4-diphenylimethylenedioxy-phenyl)-2-methylalanine

A mixture of 175 g (0.425 mol) of racemic 3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalanine hydrochloride, 1750 ml of acetone and 1750 ml of water is stirred under nitrogen at a temperature below 10°C, while the pH is set to 12.0 by slow addition of a 10% sodium hydroxide solution. 93 g (0.545 mol) carbobenzyloxychloride is added dropwise over 5 - 7 minutes to the reaction mixture at 20 - 30°C while simultaneously adding a 10% sodium hydroxide solution to keep the pH at 12.0 - 12.2. After the addition of the carbobenzyloxychloride is finished, the reaction mixture is stirred at 25 - 30°C for 3 hours. Most of the acetone is then removed under reduced pressure at 25-35°C to precipitate the sodium salt of the desired N-carbobenzyloxy derivative. The sodium salt is extracted in 1.5 1 ethyl acetate, washed with 200 ml of 5% sodium hydroxide solution and 200 ml of saturated sodium chloride solution, and then dried over magnesium sulphate. After adding 17.5 g of decolorizing charcoal and filtering through a magnesium sulfate plate, solvents are removed under reduced pressure at 25 - 35°C. The residue is slurried twice with 1 1 20% by volume ethyl ether-80% by volume hexane solution and filtered, which gives the sodium salt of the desired N-carbobenzyloxy derivative. This sodium salt is dissolved in 1.5 1 ethyl acetate, cooled to 10°C and acidified to pH 2 with 6 N hydrochloric acid. The ethyl acetate extract is washed with 200 ml saturated sodium chloride solution, dried over magnesium sulphate, filtered and evaporated under reduced pressure at 25 - 35°C. The N-carbobenzyloxy derivative is further dried at 25 - 30°C and 0.2 - 0.3 mm Hg, whereby D,L-N-carbobenzyloxy -3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine is obtained.

C. Preparation of D,L-succinimidomethyl-N-carbobenzyloxy~3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate

A solution of 13.5 g (0.0265 mol) D,L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.7 g (0.027 mol) triethylamine and 5.19 g (0.029 mol ) N-bromomethylsuccinimide in 35 ml of dry dimethylformamide is stirred at 25 - 30°C for 16 hours. The reaction mixture is poured into 400 ml of ice water, and the product is extracted into 200 ml of a 50% by volume chloroform-50% by volume diethyl ether mixture. The organic extract is washed with 50 ml of 5% sodium carbonate solution and 50 ml of saturated sodium chloride solution and then dried over anhydrous magnesium sulphate. After filtration and evaporation under reduced pressure, the residue is recrystallized. Recrystallization was performed by dissolving the product in ethanol and adding hexane to precipitate D,L-succinimidomethyl-N-carbobenzyloxy-3-(3,4-diphen<y>lmeth<y>phen ndioxyphenyl)-2-methylalaninate.

D. Preparation of D,L-succinimidomethyl-3-(3,4-dihydroxyphenyl)-2- methylalaninate - hydrochloride - hydrate

A suspension of 6.6 g (0.0106 mol) of racemic succinimido-methyl-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 180 ml of absolute ethanol and 9 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution hydrogenated with 3.3 9 10% palladium-on-carbon catalyst at an initial pressure of 2.11 kg/cm <2> until hydrogen absorption was complete. After removing the catalyst by filtration, the filtrate is concentrated under reduced pressure. The residue is extracted with 50 ml of benzene and then 50 ml of ethyl acetate. The insoluble solid was then shaken with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate mixture and 10 ml of saturated sodium carbonate solution. After filtration, the filtrate was dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure, whereby D,L-succinimidomethyl-3-(3,4-dihydroxyphenyl)-2-methylalaninate was obtained as the base.

E. Preparation of succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate via recrystallization of diastereomeric salts

A solution of 0.47 9 (3.1 mmol) (-)-tartaric acid in 10 ml 50

50 vol% absolute ethanol-50 vol% ethyl acetate solution was added under nitrogen at 20 - 25°C to a solution of 1.0 g (3.1 mmol) D,L-succinimidomethyl-3-(3,4-dihydroxyphenyl)- 2-methylalaninate in 10 ml absolute ethanol. After heating the solution to 40 - 60°C, ethyl acetate was added to start bleaching and then cooled slowly to 25°C and finally stored at 5 - 10°C for 12 hours. The insoluble crude tartaric salt was removed by filtration and dried at 20-25°C and 0.2-0.5 mm pressure.

This recrystallization treatment was repeated until the melting point and optical rotation of the tartaric salt were substantially constant.

The mother liquor from the first crystallization was evaporated with wood

15 - 20 mm and 4o - 50°C. The residue was shaken with 25 ml of 10% by volume ethanol-90% by volume ethyl acetate mixture and 10 ml of saturated sodium carbonate solution. After filtration, the filtrate was dried over anhydrous magnesium sulfate, filtered and evaporated at 15-20 mm and 40°C to a gum. The residue was dissolved in 5 ml of absolute ethanol and under nitrogen added to a solution of 0.3 of (+)-tartaric acid in 10 ml of 50% by volume absolute ethanol-50% by volume ethyl acetate solution. After heating the solution to 40 - 6o°C, ethyl acetate was added to begin to pale and then cooled slowly to 25°C and then

stored at 5 - 10°C for 14 hours. The insoluble crude tartaric salt was removed by filtration. Repetition of this recrystallization treatment gives the second optical antipode of succinimidomethyl-3-(3,4-dihydroxyphenyl)-2-methylalaninate as the tartaric acid salt. The optically active tartaric acid salts were converted to the optically active hydrochloride salts by the following method. The tartaric acid salt of succinimido-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate is shaken with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate mixture and 10 ml of saturated sodium carbonate solution. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure. The residue is dissolved in 25 ml of absolute ethanol, treated with 5 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution and evaporated under reduced pressure, whereby succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate is obtained, homogeneous by thin layer chromatography (fluorescent silica gel plate, 30 vol% methanol-70 vol% benzene solvent) with an observed Rf = 0.5.

Example 28

Cleavage of racemic pivaloyloxymethyl-3-(3,4-dihydroxyphenyl)-2-methylalaninate by direct recrystallization

Racemic pivaloyloxymethy1-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride was prepared as in Example 23. 30 g of racemic pivaloyloxymethy1-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride were slurried at 35° C in lOO ml of 1.0 N hydrochloric acid. Excess solids were filtered off. The saturated solution was then seeded at 35°C with pivaloyloxymethyl-D-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate. The mixture was cooled to 20°C over 30 minutes and left at 20°C for 0.5 hours. The precipitated material was isolated by filtration, washed twice with 5 ml of cold water and dried at 0.1 - 0.5 mm and 20 - 25°C for 20 hours to give pivaloyloxymethyl-D-3-(3,4 -dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate.

The mother liquor from the above step was heated to 35°C and seeded at 35°C with pivaloyloxymethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride. The mixture was then cooled to 20°C over 30 minutes and left at 20°C for 0.5 hours. The precipitated material was isolated by filtration, washed twice with .5 ml of cold water and dried at 0.1 - 0.5 mm and 20 - 25°C for 20 hours to give pivaloyloxymethyl-L-3-(3, 4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate.

Example 29

A. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride dihydrate ((3-isomer) by fractional crystallization

10 g of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride (α- and (3-isomer mixture) from example 2 was dissolved in 50 ml of hot 95% ethanol (5% water ), diluted to incipient paleness with anhydrous ether, seeded and scraped to effect crystallization. After cooling at 5 - 10°C for 12 hours, the precipitated solid was collected and dried at 70°C. Additional similar recrystallizations from 95 vol% ethanol-5 vol% water-ethyl ether gave material melting at 123 - 126°C (dec.) A final recrystallization from 95% ethanol gave α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2- methylalaninate hydrochloride dihydrate (P-isomer) as the dihydrate which melted at 129 - 131°C (decomposition)

(dried at 70°C overnight, homogeneous by thin-layer chromatography (fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent), Rf =0.7-

B. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate (α-isomer)

The mother liquor from the first crystallization of the β-isomer of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate rich in the corresponding α-isomer was evaporated at 15-20 mm and 40 - 45°C. The residue was dissolved in 20 mL of hot 95% ethanol (5% water), diluted to incipient paleness with ethyl acetate, seeded and scraped to precipitate the enriched α-isomer of α-succinimidoethyl-L-3-(3,4- dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate. Further precipitation from 95% ethanol (5% water) and ethyl acetate gives the α-isomer as the ethyl acetate solvate, Rf = o.7

(thin layer chromatography, fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent).

Example 30

Preparation of pivaloyloxymethyl-L-3-(3,4-dihydroxyphenyl)-2-methyl-alanine hydrochloride

A solution of 0.95 g (4.0 mmol) of L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.6 l g (4.06 mmol) of pivaloyloxymethyl chloride in 5 ml of dimethylsulfoxide is stirred at 20 - 25°C for 23 hours.

The solution is diluted with 10 ml of distilled water and passed through

a column containing 5 g of weakly basic anion exchange resin in the base form. After elution with water fractions, the fractions which give a positive ferric chloride test are combined and added to a column of 3 g of weakly acidic cation exchange resin in the acid form. Unreacted L-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled water until a negative ferric chloride test is obtained, the ester is then eluted with 1 N acetic acid. The ester fraction, 50 ml (pH 3.2), is acidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at 0.1 - 0.3 mm for 20 hours, whereby pivaloyl-oxymethyl-L-3-( 3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the acetic acid solvate.

Anal. calculate, for C^H^NOg.HCl.1/3HC2H^O2: C 52.11; H 6.69; N 3.58 Found: C 52.11; H 6.49; N 3.73

Example 31

Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g (4.0 mmol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.65 g (4.0 mmol) N-(α-chloroethyl)-succinimide in 5 ml of dimethylsulfoxide is stirred at 20 - 25°C for 23 hours. The solution is diluted with 10 ml of distilled water and passed through a column containing 5 g of weakly basic anion exchange resin in the basic form. After elution with water fractions, the fractions which give a positive ferric chloride test are combined and added to a column of 3 g of weakly acidic cation exchange resin in the acidic form. Unreacted L-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled water until a negative ferric chloride test is obtained, and the ester is then eluted with 1 N acetic acid. The ester fraction, 55 ml (pH 3.2), is treated with 1 N hydrochloric acid to pH 2.0 and lyophilized at 0.1 - 0.3 mm for 20 hours, whereby α-succinimidoethyl-L-3-(3, 4-dihydroxyphenyl)-2-methylalaninate hydrochloride-acetic acid solvate.

Anal. calculate, for C^H^gOg .HCl.1/3C2H^O2: C 50.96; H 5.73; N 7.13 Found: c 50.48; H 6.13; H 6.77 Example 32

Preparation of 3-acetamidopropyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate

275 ml of thionyl chloride are added to 250 g of L-3-(3,4-dihydroxy-phenyl)-2-methylalaninate sesquihydrate at 25°C, and the mixture is heated on a steam bath. After heating for 2 hours, the thick mixture is diluted

reaction mixture with 7.5 ml of dimethylformamide dissolved in 25 ml of benzene and stirred on a steam bath until gas evolution ceases. 100 ml of benzene is added, and the crude sulfuric acid ester is removed by filtration, washed with 100 ml of benzene, 100 ml of chloroform and 100 ml of ether and dried under reduced pressure, thereby obtaining 280 g of the intermediate sulfuric acid ester, m.p. 199°C during decomposition.

A mixture of 13.7 g of the crude sulfuric ester intermediate, 24.98 g (0.212 mol) of N-acetylpropanolamine and 2 g of anhydrous dimethylformamide is stirred on a steam bath for 20 hours and cooled. The reaction mixture is washed with 6 x 200 ml ethyl ether, 4 x 200 ml methylene chloride and dried under reduced pressure. The semi-solid material that remains is stirred with 200 ml of 20 vol% ethanol-80 vol% ethyl acetate, 20 ml of saturated sodium carbonate solution and 20 g of solid sodium carbonate. The organic extract is dried over anhydrous magnesium sulfate, filtered, and the filtrate is added to a solution of 3.2 g of oxalic acid in 50 ml of ethanol. Solvents are removed under reduced pressure, and the product is precipitated by dissolving it in 50 ml of ethanol and adding 500 ml of ethyl ether. The product is separated again by dissolving in 50 ml of ethanol and adding 500 ml of ethyl acetate, which gives 3-acetamidopropyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrogen oxalate hydrate, Rf = 0.45, thin layer chromatography (fluorescent silica gel plate developed with 25 vol% methanol-

75 vol% chloroform).

Anal. calculate, for ^- L^ 22^ 2°5' C2H2°4' H2°: C Zf8'80; H 6'26' N °>69 Found: C 48.73; H 6.85; N 6.68

Example 33

Preparation of 2-acetamidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A slurry of 88.3 g (0.30 mol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride ethanol solvate (by concentration of an ethanolic solution of the hydrochloride under reduced pressure) and 146.5 g (1.42 mol) of N-acetylethanolamine, under nitrogen, is heated to 104 - 108°C. 84.8 g (0.713 mol) of thionyl chloride are added during 15 minutes with stirring. The reaction mixture foams vigorously during the addition. After the addition has ended, the reaction mixture is stirred at 104 - 108°C for 18 hours. A further 42.4 g (0.357 mol) of thionyl chloride is added over 7 minutes. The reaction mixture is stirred at 104 - 108°C for a further 3.5 hours, then cooled to 30°C and evaporated under reduced pressure, whereby a viscous oil is obtained. This oil is slurried with 100 ml of chloroform, and the chloroform is removed under reduced pressure. This is repeated a further three times, and then the oil is washed with 100 ml of benzene which is decanted. The residue is dissolved in 700 ml isopropanol and added to 6 1 ethyl ether. The precipitate that forms is washed with 500 ml of ethyl ether and shaken with 6 1 10 volume% ethanol-90 volume% ethyl acetate, 150 ml of saturated sodium carbonate solution and 100 g of sodium carbonate. The organic extract is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure, whereby the free base of the acetamidoethyl ester is obtained. This base is treated with 15 g of fumaric acid in 300 ml of isopropanol, and the fumarate salt is precipitated by adding sufficient ethyl ether. The fumarate salt is separated once again from isopropanol by adding sufficient ethyl ether and then transferred back to the free base as before by shaking with 200 ml of 10% ethanol-90% by volume ethyl acetate, 20 ml of saturated sodium carbonate solution and 20 g of solid sodium carbonate. The free base is transferred to the hydrochloride salt by dissolving in 100 ml of absolute ethanol, adding 10 ml of 9.6 N hydrochloric acid and refining by adding 1 1 of ethyl ether. After three precipitations from ethanol-ethyl ether as carried out above, 2-acet-amidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrochloride, Rf = 0.57, thin-layer chromatography (fluorescent silica gel plate developed with 50 vol% methanol-50 vol% benzene).

Anal. calculate, for C^H^NgO^ .HCl: C 50.52; H 6.36; N 8.4l

Found: C 50.49; H 6.69; N 8.49

Example 34

A. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride

To a mixture of 320 ml of glacial acetic acid and 24 ml of acetyl chloride, 69.4 g (0.291 mol) of L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate is added in one portion. The temperature of the reaction mixture rises to approx. 50°C, and a clear solution is formed. At this temperature, a further 85 ml of acetyl chloride are added over the course of 10 minutes. The clear, pale yellow solution obtained is allowed to stand at 20 - 25°C for 14 hours. 400 ml of anhydrous ethyl ether are added over 15 minutes. When the addition is nearly complete, a white solid begins to precipitate. The mixture is stirred at 20 - 25°C for 30 minutes, at 5 - 10°C for 1 hour and then cooled to -10°C for 2 hours.

The solid is removed by filtration, suspended in 150 ml of 30% by volume acetic acid-70% by volume ethyl ether, filtered and washed with 500 ml of ethyl ether. After drying at 70 C for 2 hours, 83.7 g (88%) of L-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride are obtained, m.p. 196.0 - 197.0°C.

B. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloride hydrochloride

A mixture of 6.60 g (0.020 mol) L-3~(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride and 40 ml of thionyl chloride is stirred at 60°C for 2 hours until dissolution is complete. Excess thionyl chloride is removed at 15 - 20 mm and 40 - 50°C. 50 ml of methylene chloride are added, and the mixture is concentrated again at 15 - 20 mm and 40 - 50°C. This is repeated once more with another 50 ml of methylene chloride. After drying at 0.2 - 0.5 mm and 40°C for 30 minutes, L-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloride is obtained.

C. Preparation of succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A solution of 3.50 g (10 mmol) of L-3-(3,4-diacetoxyphenyl)-2-methylalanyl chloride hydrochloride in 20 ml of chloroform is added to a solution of 3.87 g (30 mmol) of N-hydroxymethylsuccinimide in 20 ml of chloroform at 25°C. After stirring under reflux for 20 hours, the chloroform is removed at 15 - 20 mm and 30 - 40°C. The residue is diluted with 10 ml of 1 N hydrochloric acid and extracted with 2 x 20 ml of ethyl ether.

The aqueous extract is stirred under nitrogen at 20 - 25°C for 5 hours. After lyophilization at 0.1 - 0.3 mm for 20 hours, the residue is treated with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate solution, 5 ml

saturated sodium carbonate solution and 5 g of solid sodium carbonate. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated at 15 - 20 mm and 30 - 40°C. The residue is dissolved in 25 ml of absolute ethanol, treated with 5 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution and evaporated under reduced pressure, whereby succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is obtained hydrate, homogeneous by thin-layer chromatography (fluorescent silica gel plate, 30% by volume methanol-70% by volume benzene solvent) with an observed Rf = 0.5.

Example 35'

A. Preparation of the N-carboxyanhydride of L-3-(3,4-dihydroxyphenyl)-

2- methylalanine

Phosgene gas is bubbled through a mixture of 9.0 g (0.038 mol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate in 500 ml tetrahydrofuran for 25 minutes until the solution is saturated. During the addition, the temperature of the reaction mixture rises to 45°C. The solution is stirred under nitrogen gas bubbling for a further 50 minutes. Insoluble material is removed by filtration through a diatomaceous earth plate, and the filtrate is evaporated to an oil at 15 -

20 mm pressure and 30 - 35°C. The residue is dissolved in 75 ml of ethyl acetate,

and hexane is added to the boiling point. After cooling for several days at 0 - 5°C, the precipitated solid substance is removed by filtration and dried at 0.1 - 0.3 mm pressure and 25°C, whereby the N-carboxyanhydride of L-3-(3, 4-dihydroxyphenyl)-2-methylalanine.

B. Preparation of succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A solution of 2.37 g (10 mmol) of the N-carboxyanhydride of L-3-(3,4-dihydroxyphenyl)-2-methylalanine and 1.29 g (10 mmol) of N-hydroxymethylsuccinimide is heated under reflux until all the N- carboxy anhydride has reacted. After evaporation at 15 - 20 mm pressure and 30 - 40°C, the residue is extracted with 50 ml of benzene and then with 50 ml of ethyl acetate. The insoluble solid is then shaken with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate mixture and 10 ml of saturated sodium carbonate solution. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated under reduced pressure. The residue is dissolved in 25 ml of absolute ethanol, treated with 5 ml of 9.6 N ethanolic anhydrous hydrogen chloride solution and evaporated under reduced pressure, whereby succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate is obtained, homogeneous by thin-layer chromatography (fluorescent silica gel plate, 30 vol% methanol-70 vol% benzene solution) with an observed Rf =0.5.

Example 36

A. Preparation of L-3"(3,4-diphenylmethylenedioxyphenyl)-2-methyl-a lanine - hydrochloride

A mixture of 19.3 g (0.0777 mol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine hydrochloride and 37 g (0.156 mol) dichlorodiphenylmethane is immersed with slow stirring in a preheated oil bath at 190°C After the reaction has started, as evidenced by strong gas evolution, the reaction mixture is stirred rapidly for 6 minutes at 190°C, removed from the hot oil bath and allowed to cool to 25 - 30°C. The crude product from 12 experiments is combined, slurried with 3 1 diethyl ether, filtered, washed with a further 2 1 diethyl ether and dried at 30°C under 50 mm pressure. The product is recrystallized by dissolving it in ethanol and adding ethyl acetate to precipitate the product. 255 g (66.4%) of L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methyl-alanine hydrochloride are obtained, m.p. 267 - 268°C during decomposition.

B. Preparation of α-succinimidoethyl-L-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalaninate

A solution of 1.4 g (4.0 mmol) of L-3-(3,4-diphenylmethylene-dioxyphenyl)-2-methylalanine and 0.65 g (4.0 mmol) of N-(α-chloroethyl)- succinimide in 5 ml of dimethylsulfoxide is stirred at 20 - 25°C for 23 hours. 150 ml of water is added followed by a saturated sodium carbonate solution until a pH of 8 is obtained. The product is extracted in 500 ml of ethyl ether, which is then washed with 4 x 25 ml of water, dried over anhydrous magnesium sulphate and filtered. Evaporation at 15 - 20 mm and 35 - 40°C gives crude α-succinimidoethyl-L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate of sufficient purity for use in the next step.

C. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate - hydrochloride

A suspension of 1.0 g (2.0 mmol) of α-succinimidoethyl-L-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalaninate in 25 ml of 25% by volume absolute ethanol-75% by volume ethyl acetate solution is hydrogenated with 1 .0 g of 10% palladium-on-carbon catalyst at an initial pressure of 2.81 kg/cm and room temperature for 23 hours. The catalyst is filtered off, and the filtrate is evaporated under reduced pressure at 30 - 4o°C. The residue is dissolved in 50 ml of 10% by volume ethanol-90% by volume ethyl acetate solution and stirred with 5 ml of saturated sodium carbonate solution and approx. 5 g anhydrous sodium carbonate for lo minutes. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated to dryness under reduced pressure. The residue is dissolved in 20 ml of dry chloroform, the solution is cooled in an ice bath and saturated with hydrogen chloride gas for 15 minutes. The solid is collected, washed by suspension in 25 ml of anhydrous ether three times, and then suspended in 25 ml of ethyl acetate under nitrogen in a corked flask at room temperature overnight. The insoluble solid is removed by filtration, stirred with 30 ml of hexane for 2 hours and dried in a vacuum desiccator over calcium chloride, whereby |3-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is obtained as a mixture of α- and β-isomers, observed Rf = 0.7 by thin-layer chromatography (fluorescent silica gel plate, 50 vol% methanol-50 vol% benzene solvent).

Example 37

A. Preparation of L-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride

To a mixture of 320 ml of glacial acetic acid and 24 ml of acetyl chloride, 69.4 g (0.291 mol) of L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate are added in one portion. The temperature of the reaction mixture rises to approx. 50°C and a clear solution is obtained. At this temperature, a further 85 ml of acetyl chloride are added over the course of 10 minutes. The clear, pale yellow solution obtained is allowed to stand at 20 - 25°C for 14 hours. 400 ml of anhydrous ethyl ether are added over 15 minutes. When the addition is almost complete, a white solid begins to precipitate. The mixture is stirred at 20 - 25°C for 30 minutes, at 5 - 10°C for 1 hour and then cooled at -10°C for 2 hours. The solid is removed by filtration, suspended in 150 ml of 30% by volume acetic acid-70% by volume ethyl ether, filtered and washed with 500 ml of ethyl ether. After drying at 70°C for 2 hours, 83.7 g (88%) of L-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride are obtained, m.p. 196.0 - 197.0°C.

B. Preparation of α-succinimidoethyl-L-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.66 g (5 mmol) L-3-(3,4-diacetoxyphenyl)-2-methylalanine hydrochloride, 0.51 g (5 mmol) triethylamine and 0.81 g (5 mmol) N-( (α-chloroethyl)-succinimide in 5 ml of dimethylsulfoxide is stirred at 20 - 25°C for 20 - 24 hours. The dimethylsulfoxide is removed by stirring with 20 ml of ethyl ether for several minutes and then the ethyl ether is decanted off. This extraction process is performed three times. The residue is dissolved in 10 ml of absolute ethanol, and the product is precipitated by adding an excess of ethyl ether. This folding process is repeated two more times, whereby pure α-succinimidoethyl-L-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride is obtained.

Example 38

Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.8 g (3.94 mmol) of α-succinimidoethyl-L-3-(3,4-diacetoxyphenyl)-2-methylalaninate hydrochloride (from Example 37) in 10 ml of 1 N hydrochloric acid is stirred under nitrogen at 20 - 25°C for 5 hours. After lyophilization at 0.1 - 0.3 mm for 20 hours, the residue is treated with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate solution, 5 ml

saturated sodium carbonate solution and 5 g of solid sodium carbonate. After

filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated to dryness under reduced pressure. The residue is dissolved in 20 ml of dry chloroform, the solution is cooled in an ice bath and saturated with hydrogen chloride gas for 15 minutes. The solid is collected, washed by suspension in 25 ml of anhydrous ethyl ether three times and then suspended in 25 ml of ethyl acetate under nitrogen in a corked flask at room temperature overnight. The α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is collected and dried in a vacuum desiccator over calcium chloride, whereby the hydrochloride is obtained from a mixture of α- and β-isomers, observing Rf =0 .7 by thin-layer chromatography (fluorescent silica gel plate, 50% by volume methanol-50% by volume benzene solvent).

Example 39

A. Preparation of N-(1-chloroethyl)-maleimide

5.20 g (0.020 mol) stannous chloride is added to a solution

of 49.2 g (0.40 mol) of n-vinylmaleimide in carbon tetrachloride, and the mixture is stirred while being saturated with hydrogen chloride for 6 hours at 20 - 30°C. After 24 hours, the mixture is again saturated with hydrogen chloride for 1.5 hours. At the end of 48 hours, the solution is decanted, and the gummy residue is washed with 10 x 100 ml of carbon tetrachloride. The combined extracts are slurried with 10 g of diatomaceous earth, filtered, and the filtrate is evaporated under reduced pressure to approx. 4O0 ml. The N-(1-chloroethyl)-maleimide is filtered off and dried at 20 - 30°C

B. Preparation of α-maleimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g (4.0 mmol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.64 g (4.0 mmol) N-(α-chloroethyl)-maleimide in 5 ml of dimethylsulfoxide is stirred at 20 - 25°C for 23 hours. The solution is diluted with 10 ml of distilled water and passed through a column containing 5 g of weakly basic anion exchange resin in the basic form. After elution with water fractions, the fractions giving a positive ferric chloride test are combined and added to a column of 3 g of a weakly acidic cation exchange resin in the acid form. Unreacted L-3-(3,4-di-hydroxyphenyl)-2-methylalanine is eluted with distilled water until a negative ferric chloride test is obtained, and the ester is then eluted with 1 N acetic acid. The ester fraction, 55 ml (pH 3.2), is treated with 1 N hydrochloric acid to a pH of 2.0 and lyophilized at 0.1 - 0.3 mm for 20 hours, whereby α-maleimidoethyl-L-3-( 3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride.

C. Preparation of α-succinimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.0 g (2.7 mmol) of α-maleimidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride in 25 ml of absolute ethanol is hydrogenated with 1.0 g of 10% palladium-on-carbon catalyst at atmospheric pressure and 25°C until 1 equivalent of hydrogen is occupied. The catalyst is filtered off, and the filtrate is evaporated under reduced pressure at 30 - 40°C. The residue is dissolved in 50 ml of 10% by volume ethanol-90% by volume ethyl acetate solution and stirred with 5 ml of saturated sodium carbonate solution and approx. 5 g anhydrous sodium carbonate for 10 minutes. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated to dryness under reduced pressure. The residue is dissolved in 20 ml of dry chloroform, the solution is cooled in an ice bath and saturated with hydrogen chloride for 15 minutes. The solid is collected, washed by suspending in 25 ml of anhydrous ether three times, and then suspended in 25 ml of ethyl acetate under nitrogen in a corked flask at 20 - 25°C overnight. The insoluble solid is removed by filtration, stirred with 30 ml of hexane for 2 hours and dried in a vacuum desiccator over calcium chloride, whereby a-succin-imidoethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride is obtained as a mixture of α- and β-isomers, observed Rf = 0.7 by thin-layer chromatography (fluorescent silica gel plate, 50 vol% methanol

50 vol% benzene solvent).

Example 40

A. Preparation of g-chloroethyl-3-chloro-2,2-dimethylpropionate

400 mg of zinc chloride is melted at 0.2 - 0.5 mm pressure and cooled to 25 - 30°C under nitrogen. 62 g (0.40 mol) of 3-chloro-2,2-dimethyl-propionyl chloride is added to the molten zinc chloride followed by 19.2 g (0.44 mol) of acetaldehyde. During the addition of the acetaldehyde, which is done as quickly as possible, the reaction mixture is stirred and cooled to prevent loss of acetaldehyde due to the exothermic nature of the reaction. After heating under reflux for 1 hour, distillation gives α-chloroethyl-3-chloro-2,2-dimethylpropionate.

B. Preparation of α-(3-chloro-2,2-dimethylpropionyloxy)-ethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g (4.0 mmol) L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.81 g (4.06 mmol) α-chloroethyl-3-chloro-2 ,2-dimethylpropionate in 5 ml of dimethylsulfoxide is stirred at 20 - 25 C for 24 hours. The solution is diluted with 10 ml of distilled water and passed through a column containing 5 g of weakly basic anion exchange resin in the base form. After elution with water fractions, the fractions which give a positive ferric chloride test are combined and added to a column of 3 g of weakly acidic cation exchange resin in the acid form.

Unreacted L-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled water until a negative ferric chloride test is obtained, the ester is then eluted with 1 N acetic acid. The ester fraction, 50 ml (pH 3.2), is acidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at 0.1 - 0.3 mm for 20 hours, whereby α-(3-chloro-2,2- dimethylpropionyloxy)-ethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride as the acetic acid solvate.

C. Preparation of α-pivaloyloxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 1.5 g (3.66 mmol) of α-(3~chloro-2,2-dimethyl-propionyloxy)-ethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride in 20 ml of absolute ethanol is hydrogenated with 1.0 g of 10% palladium-on-carbon catalyst at 20 - 25°C and atmospheric pressure until 1 equivalent of hydrogen has been taken up. After removing the catalyst by filtration, the ethanol is removed at 15 - 20 mm and 30 -

35°C. The residue is dissolved in 40 ml of ethyl acetate, stirred briefly with a mixture of 2 g of solid sodium carbonate and 2 ml of saturated sodium carbonate solution and dried over anhydrous magnesium sulfate. After filtration, 1 ml of 9.6 N ethanolic anhydrous hydrogen chloride is added, and the solution is evaporated under reduced pressure to dryness. Further drying at 65°C and 0.2 mm pressure gives the α-pivaloyloxyethyl ester hydrochloride.

Example 41

A. Preparation of Benzyl Succinamate

A mixture of 23.4 g (0.20 mol) succinic acid, 25.4 g (0.20 mol) benzyl chloride, 20.2 g (0.20 mol) triethylamine and 250 ml dimethylformamide is stirred at 95 C for 20 hours. The reaction mixture is diluted with 500 ml of water, and the product is extracted into 2 x 200 ml of ethyl ether. The combined ether extracts are washed with 2 x 50 ml saturated sodium bicarbonate solution, then with 2 x 50 ml water and dried over anhydrous magnesium sulfate. After filtration, the solution is evaporated at 15 - 20 mm and 4o°C, whereby benzyl succinamate is obtained.

B. Preparation of benzyl-N-hydroxymethylsuccinamate

To a stirred solution of 20.7 g (0.10 mol) of benzyl succinamate in 150 ml of ethyl acetate at 25°C, 3.0 g of paraformaldehyde and 1 ml of 20% by weight ethanolic potassium hydroxide are added. After stirring at 25°C for 20 hours, hexane is added to the boiling point, and the mixture is cooled at 5°C for 24 hours. The solvents are decanted off, and the residue is washed with 25 ml of hexane, whereby benzyl-N-hydroxymethylsuccinamate is obtained.

C. Preparation of benzyl-N-chloromethylsuccinamate

A solution of 24.2 g (0.10 mol) of benzyl-N-hydroxymethylsuccinamate and 28.9 g (0.11 mol) of triphenylphosphine in 500 ml of carbon tetrachloride is stirred under reflux for 12 hours. After filtering and washing the precipitate with benzene, the organic solvents are removed at 5l5 - 20 mm and 30 - 4o°C, thereby obtaining benzyl-N-chloromethylsuccinamate of sufficient purity for use in the next step.

D. Preparation of benzylsuccinamidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine

A solution of 10.2 g (0.020 mol) L-N-carbobenzyloxy-3~(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine, 2.02 g (0.020 mol) triethylamine and 5.12 g (0.020 mol) benzyl-N -chloromethylsuccinamate in 20 ml of dimethylformamide is stirred at 70°C for 5 hours, then at 20 - 30°C for 5 hours and finally poured into 200 ml of water. The product is extracted with 3 x 100 ml ethyl acetate, washed with 50 ml 5% sodium hydroxide solution, 50 ml water and 50 ml saturated sodium chloride solution, and dried over anhydrous magnesium sulfate. After filtration, the solvents are removed at 15 - 20 mm and 30 - 40°C, whereby benzylsuccinamidomethyl-L-N-carbobenzyloxy-3-(3,4-diphenyl-methylenedioxyphenyl)-2-methylalanine is obtained.

E. Preparation of succinamidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 13.8 9 (0.0189 mol) benzylsuccinamidomethyl-L-N -carbobenzyloxy-3-(3,4-diphenylmethylenedioxyphenyl)-2-methylalanine in 130 ml of 25 vol% absolute ethanol-75 vol% ethyl acetate is hydrogenated with 5 g 10 % palladium-on-carbon catalyst at 20 - 25°C and an initial pressure of 2.81 kg/cm for 18 hours until hydrogen uptake ceases. After removal of the catalyst by filtration and evaporation to dryness under reduced pressure, the residue is dissolved in 200 ml of 10% by volume absolute ethanol-90% by volume ethyl acetate solution and stirred with 5 ml of saturated sodium carbonate solution and excess of solid sodium carbonate for 2 minutes. 10 g of anhydrous magnesium sulphate is added, and after a few minutes it is removed by filtration. Solvents are removed under reduced pressure, the residue is washed with 25 ml of hexane and then with 25 ml of ethyl acetate and dried under reduced pressure. The residue is again treated with sodium carbonate as before to remove the last traces of α-methyl-3,4-dihydroxyphenylalanine and transferred to the hydrochloride salt with 3 ml of 9.6 N ethanolic anhydrous hydrogen chloride, whereby succinamidomethyl-L-3-( 3,4-dihydroxy-phenyl)-2-methylalaninate hydrochloride.

F. Preparation of succinimidomethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride hydrate

A mixture of 3.95 g (10 mmol) of succinamidomethyl-L-3-(3,4-dihydroxyphenyl-2-methylalaninate hydrochloride and 100 ml of acetyl chloride is stirred at 25°C for 6 hours. After evaporation at 15 - 20 mm and 35 ° C, the residue is dissolved in 25 ml of 1 N hydrochloric acid and stirred under nitrogen at 20 - 25 ° C for 5 hours. After lyophilization at 0.1 - 0.3 mm for 20 hours, the residue is treated with 50 ml of 10 vol% ethanol -90% by volume ethyl acetate solution, 5 ml saturated sodium carbonate solution and 5 g solid sodium carbonate. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated at 15 - 20 and 30 - 4o°C. The residue is dissolved in 25 ml absolute ethanol, treated with 5 ml 9.6 N ethanolic anhydrous hydrogen chloride solution and evaporated under reduced pressure, thereby obtaining succinimidomethyl-L-3-(3,4-di-hydroxyphenyl)-2-methylalaninate hydrochloride hydrate, homogeneous by thin-layer chromatography (fluorescent silica gel plate, 30 volume % methanol-70 vol% benzene solvent) with an observed Rf = 0.5-Example 4 2

A. Preparation of 2-hydroxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride

A solution of 0.95 g (4.0 mmol) of L-3-(3,4-dihydroxyphenyl)-2-methylalanine sesquihydrate and 0.51 g (4.06 mmol) of 2-bromoethanol in 5 ml of dimethyl sulfoxide is stirred at 6o°C for 5 hours and then allowed to cool to 20 - 25°C over 23 hours. The solution is diluted with 10 ml of distilled water and passed through a column containing 5 9 weakly basic anion exchange resin in the base form. After elution with water fractions, the fractions which give a positive ferric chloride test are combined and added to a column of 3 g of weakly acidic cation exchange resin in the acid form. Unreacted L-3-(3,4-dihydroxyphenyl)-2-methylalanine is eluted with distilled water until a negative ferric chloride test is obtained, and the ester is then eluted with 1 N acetic acid. The ester fraction, 50 ml (pH 3.2), is acidified to pH 2.0 with 1 N hydrochloric acid and lyophilized at 0.1 - 0.3 mm for 20 hours, whereby 2-hydroxyethyl-L-3"(3, 4-dihydroxyphenyl)-2-methylalaninate hydrochloride.

B. Preparation of 2-acetoxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A mixture of 1.0 g (3.4 mmol) 2-hydroxyethyl-L-3"(3,4~ dihydroxyphenyl)-2-methylalaninate hydrochloride and 50 ml acetyl chloride is stirred at 25°C for 6 hours. After evaporation at 15 - 20 mm and 35 ° C, the residue is dissolved in 25 ml of 1 N hydrochloric acid and stirred under nitrogen at 20 - 25 ° C for 5 hours. After lyophilization at 0.1 - 0.3 mm for 20 hours, the residue is treated with 50 ml 10 vol% ethanol-90 vol% ethyl acetate solution, 5 ml saturated sodium carbonate solution and 5 g solid sodium carbonate After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated at 15 - 20 mm and 30 - 4o°c.

The residue is chromatographed on silica gel and eluted with 20 vol% methanol-80 vol% benzene. Recrystallization takes place by dissolving the ester in hot ethyl acetate and adding sufficient cyclohexari to precipitate the desired 2-acetoxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate, m.p. 114 - H8°C (dec.).

Example 43

Preparation of 2-acetoxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate

A mixture of 1.0 g (3.4 mmol) of 2-hydroxyethyl-L-3-(3,4-dihydroxyphenyl)-2-methylalaninate hydrochloride and 50 ml of methanesulfonyl chloride is stirred at 25°C for 6 hours. Evaporation at 15 - 20 mm and 35°C followed by drying at 0.1 - 0.5 mm and 4o°C gives the crude methane-sulfonyl derivative. To this is added 10 ml of dimethylsulfoxide and 6.6 g (10 mmol) lithium acetate, and the mixture is stirred at 6o°C for 6 hours. After adding an excess of ethanolic anhydrous hydrogen chloride solution, the dimethylsulfoxide is removed by stirring three times with 50 ml of ethyl ether and decanting off the ethyl ether. The residue is dissolved in 25 ml of 1 N hydrochloric acid and stirred under nitrogen at 20 - 25°C for 1 hour. After lyophilization at 0.1 - 0.3 mm for 20 hours, the residue is treated with 50 ml of 10% by volume ethanol-90% by volume ethyl acetate solution, 5 ml of saturated sodium carbonate solution and 5 g of solid sodium carbonate. After filtration, the filtrate is dried over anhydrous magnesium sulfate, filtered and evaporated at 15 - 20 mm and 30 - 40°C.

The residue is chromatographed on silica gel and eluted with 20 vol% methanol and 0 vol% benzene. Recrystallization of the ester occurs by dissolving in ethyl acetate and adding sufficient cyclohexane to precipitate the desired 2-acetoxyethyl-L-3"(3,4-dihydroxypheny1)-2-methylalaninate, m.p. 114 - H8°C during cleavage.

Example 44

Anti-hypertensive activity

The method for assessing the anti-hypertensive activity of the active compounds comprises administering the compound either orally or intraperitoneally to spontaneously hypertensive rats of the Wistar-Okamoto strain. Arterial pressure is recorded continuously in these animals through an indwelling aortic catheter inserted through the caudal artery. The animals are allowed free movement in the metabolism cage during the measurements.

When the compounds produced according to the invention are tried, say orally, clear anti-hypertensive activity is noted. The compounds also show anti-hypertensive activity when tested intraperitoneally. In some cases, the compounds show considerably more activity than L-α-methyldopa.

The table below shows the relative antihypertensive activities in spontaneously hypertensive rats of some of the process compounds compared to L-methyldopa.

Antihypertensive activity of compounds with the formula

Claims (4)

1. Analogy method in the preparation of therapeutically active compounds with the formula: where n is 0, 1, 2 or 3; m is 0, 1, 2 or 3; A 1 and A 2 are each hydrogen or lower alkanoyl; R 10 and R 2 are each nitrogen or alkyl of 1-3 carbon atoms; and R 3 is: (A) a monocyclic or bicyclic heterocyclic group having 3-12 core carbon atoms and 1 or 2 core heteroatoms which are nitrogen and/or sulfur, at least one being nitrogen, and wherein each ring in the heterocyclic group has 5 or 6 members, or (B) the group X-R^, where X is -O-, -S- or -NH-, and R^ has up to 21 carbon atoms and is (1) a hydrocarbon group, or (2) an acyl group of an organic acyclic or monocyclic carboxylic acid having no more than one heteroatom in the ring, or an acid addition ion salt thereof," characterized in that (a) an acid derivative with the formula: or an acid addition salt thereof, where n, m, R^ , R 2 and R^ are as above, and R^, R^ and R^ are hydrogen or a blocking group, at least one being a blocking group, is hydrolyzed or reduced, or (b) an acid derivative of the formula: or an acid derivative thereof, where A-j^ and A^ are as indicated above, and Y is -COOH, -COhalogen or -carboxylic acid salt, is esterified with a compound of the formula: where n, m, R^ , R^ and R^ are as above, and X is hydroxyl, alkali metal -O-, halogen or a substituted -SO^ group; or (c) a compound of the formula: where n, m, A1, A^, R^ and R^ are as above, and Z is hydroxy, mercapto, halogen, substituted -SO^ group or amino, is reacted with an acylating agent; R„-H or R„-3 3 alkali metal where R is as indicated above, and, if desired, the stereoisomers are separated by (1) fractional crystallization of one stereoisomer from solution, or (2) diastereomers are formed with an optically active acid and one of the diastereomers is crystallized from solution. 2. Process according to claim 1 for the production of 2-methyl-3-(3<1>,4<1->dihydroxyphenyl)-alanine-(succinimido-ethyl-ester), characterized in that starting materials are used where m and n is zero, R, is methyl, is hydrogen, and R, is succinimido, and R,, and R^, if necessary, are transferred to hydrogen. 3. Method according to claim 1 for the production of 2-methyl-3-(3<1>,4'-dihydroxyphenyl)-alanine-(succinimido-methyl-ester), characterized in that starting materials are used where m and n are zero, R 1 and R 2 are hydrogen, and R 5 and R 8 , if necessary, are transferred to hydrogen. 4. Method according to claim 2 or 3, characterized in that an acid derivative is used where the acid is in L-configuration.