WO1993012091A1

WO1993012091A1 - D- and l-1,2,3,4-tetrahydro-isoquinoline-1-carboxylic acids and their derivatives containing urethane-type n-protecting groups as well as a process for preparing them and the corresponding racemates

Info

Publication number: WO1993012091A1
Application number: PCT/HU1992/000056
Authority: WO
Inventors: Sándor BAJUSZ; Lászlóné MOHAI; András FEHÉR; Jánosné LÁVICH; Györgyné SZÉLL; Béláné VÉGHELYI
Original assignee: Gyógyszerkutató Intézet Kft.
Priority date: 1991-12-19
Filing date: 1992-12-18
Publication date: 1993-06-24
Also published as: HUT63388A; HU914020D0; AU3265193A; HU212427B

Abstract

The invention relates to new L- and D-1,2,3,4-tetrahydro-isoquinoline-1-carboxylic acids and their derivatives containing urethane-type N-protecting groups of the formula: R-O-CO, wherein R represents a linear or branched C1-6 alkyl group; a benzyl group optionally substituted with one or more halogen atoms, nitro, methyl or methoxy groups; a picolyl group or a 9-fluorenylmethyl group, and their salts, furthermore to a process for preparing these compounds and the corresponding racemates, which comprises condensing glyoxylic acid hydrate and 2-phenethylamine with an N-protecting group of the general formula: R'-O-CO, wherein R' represents a linear or branched C1-3 alkyl group; a benzyl group optionally substituted with one or more halogen atoms or nitro groups; a picolyl group or a 9-fluorenylmethyl group in trifluoroacetic acid or in a halogenated hydrocarbon containing trifluoroacetic acid.

Description

D- AND L-l,2,3,4-TETRAHYDRO-ISOQUINOLINE-l-CARBOXYLIC ACIDS AND THEIR DERIVATIVES CONTAINING URETHANE-TYPE N-PROTECTING GROUPS AS WELL AS A PROCESS FOR PREPARING THEM AND THE CORRESPONDING RACEMATES

This invention relates to new L- and D- -1,2,3,4-tetrahydro-isoquinoline-l-carboxylic acids and their derivatives containing urethane-type N-protecting groups of the formula R-O-CO, wherein R represents a linear or branched C^_g alkyl group; a benzyl group optionally substituted with one or more halogen atoms, nitro, methyl or methoxy groups; a picolyl group or a

9-fluorenylmethyl group, and the salts thereof.

Furthermore, the invention relates to a process for preparing these compounds and the corresponding racemates.

In the course of the synthesis of peptides with biological activity it was observed that the introduction of structural modification leading to restriction of flexibility of molecules often gives analogues with enhanced biological activity and/or metabolic stability [V. J. Hruby: Life Sci. 31, 189-199 (1982)]. The structural elements 1,2,3,4-tetrahydro- -beta-carboline-3-carboxylic acid, replacing tryptophan

SUBSTITUTESHEET [J. Singh and B. A. Morgan: US Patent Specification 4,839,465 (1989)], and 1,2,3,4-tetrahydro-isoquinoline- -3-carboxylic acid replacing phenylalanine [ . Kazimierski et al. : J. Med. Chem. 31, 2170-2177 (1988)] may be such a ino acid analogues containing an immobilized amino acid side-chain. In these compounds the original amino acid side-chain, the 3-indolylmethyl residue of tryptophan and the benzyl group of phenylalanine, are fixed by a ethylene bridge to the alpha-amino group. According to the literature D- or L- -1,2,3 ,4-tetrahydro-beta-carboline-3-carboxylic acid and D- or L-l,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid can be readily synthesized by reacting formaline with the corresponding enantiomer of tryptophan [K. P. Lipke et al. : J. Med. Chem. 26, 499-503 (1983); J. Singh and B. A. Morgan: US Patent Specification 4,839,465 15 (1989)] or phenylalanine [A. Pictet and T. Spengler: Ber. 44, 2030-2036 (1911); H. Shinkai et al: J. Med. Chem. 31, 2092-2097 (1988)]. Similarly, 1,2,3,4-tetrahydro-isoquinoline-l-

-carboxylic acid, the immobilized side-chain analogue of phenylglycine, related to phenylalanine, can be advantageously applied as a building block for the synthesis of peptides with biological activity (R.- T. Shu an et al. : "A series of highly selective thrombin inhibitors", lecture at the 12th American

SUBSTITUTESHEET Peptide Symposium, Boston, USA. June 16-21, 1991. Abstract No. 495).

In the literature a single process is described for the synthesis of DL-l,2,3,4-tetrahydro- -isoquinoline-1-carboxylic acid, namely the hydrogenation of isoquinoline-1-carboxylic acid in the presence of Adams' catalyst, giving a yield of about 65 % [ . Solomon: J. Chem. Soc. 129 (1947)]. However, no procedure is known for the resolution of the resulting DL-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid.

It is well known that 1,2,3,4-tetrahydro-iso- quinoline and its derivatives can be prepared with the Pictet-Spengler synthesis by condensing 2-phenyl-l- -aminoalkanes and aldehydes in hydrochloric acid, thus the reaction of 2-phenethylamine with formaldehyde gives 1,2,3,4-tetrahydro-isoquinoline in 36 % yield [(A. Pictet and T. Spengler: Ber. 44, 2030-2036 (1911)]. Suitable substituents at the phenyl group, e. g. 3-hydroxy or methoxy groups, improve the rate of the condensation [J. S. Buck: J. Am. Chem. Soc. 56, 1769-1771 (1934)], thus the reaction of 2-(3,4-di- hydroxypheny1)ethylamine with acetaldehyde gives l-methyl-6,7-dihydroxy-l,2 ,3,4-tetrahydro-isoquinoline in 83 % yield [C. Schβpf and H. Bayerle: Ann. 513, 190-202 (1934)] while the condensation of glyoxylic acid hydrate and 2-(3,4-dimethoxyphenyl)-ethylamine results

SUBSTITUTESHEET in 6,7-dimethoxy-l,2,3,4-tetrahydro-isoquinoline-l- carboxylic acid only in a yield of maximum 20 %. The analogue synthesis of 1,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid by the reaction of glyoxylic acid hydrate and 2-phenethylamine was not even attempted [(F. M. Hershenson: J. Org. Chem. 40, 740-743 (1975)].

It is the objective of the present invention to develop a simple, economic process for preparing DL-, D- and L-l,2,3,4-tetrahydro-isoquinoline-l- -carboxylic acids and their derivatives substituted by an R-O-CO group at the N atom, wherein R has the same meaning as above.

It was unexpectedly found that the condensa¬ tion of 2-phenethylamine and glyoxylic acid hydrate can be realized in high yields if the phenethylamine is reacted in the form of its acyl derivative formed with an urethane-type N-protecting group, e. g. benzyloxy- carbonyl or 9-fluorenylmethyloxycarbonyl group, and the reaction is performed in trifluoroacetic acid or in a chlorinated hydrocarbon such as methylenechloride, containing trifluoroacetic acid, possibly in the presence of trifluoroacetic anhydride, in the temperature range of 0 to 10°C. Thereafter the N-protecting group is removed from the resulting N-protected, e. g. N-benzyloxycarbonyl-DL-l,2,3,4-tetra- hydro-isoquinoline-1-carboxylic acid, by methods known

SUBSTITUTESHEET in the art, yielding the desired DL-1,2,3,4-tetrahydro- -isoquinoline-1-carboxylic acid.

Furthermore it was found that N-benzyloxy- carbonyl-DL-1,2 ,3,4-tetrahydro-isoquinoline-l- -carboxylic acid can be easily^' resolved with an

0.475-0.5 equivalent of D-threo-2-amino-l-(4-nitro- phenyl)-1,3-propanediol in benzene solution ([α]D²⁰= -28.8", c=5, 1 N HCl) . From the dia- stereomeric salt forming crystals in the solution the D- and from the mother liquor the L-enantiomer is separ¬ ated. Analogously, N-benzyloxycarbonyl-DL-1,2,3,4-tetra- hydro-isoquinoline-1-carboxylic acid can also be resolved with the antipode of the above base, namely with L-threo-2-amino-l-(4-nitrophenyl)-1,3-propanediol ([<*]D²⁰⁼ +30.1°, c=5, 1 N HCl), a by-product of chloramphenicol production. In this case the L-enantiomer is isolated from the diastereomeric salt crystals formed and the D-enantiomer from the mother liquor. The free L- and D-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acids are obtained from the N-protected compounds by known methods. They can be transformed into other N-protected derivatives, such as N-(t-butyloxycarbonyl)-L- and -D-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acids, too. These protecting groups can be cleaved by acidolysis, e. g. by 30-100 % trifluoroacetic acid.

SUBSTITUTESHEET Based on the above the present invention relates to a process for preparing the known DL- as well as the new L- and D-l,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acids and their derivatives containing urethane-type N-protecting groups of the formula

R-O-CO, wherein R represents a linear or branched C^.galkyl group; a benzyl group optionally substituted with one or more halogen atoms, nitro, methyl or methoxy groups; a picolyl group or a 9-fluorenylmethyl group, and their salts, which comprises condensing glyoxylic acid hydrate and 2-phenethylamine with an N-protecting group of the general formula

R'-O-CO, wherein R* represents a linear or branched Cι_₃ alkyl group; a benzyl group optionally substituted with one or more halogen atoms or nitro groups; a picolyl group or a 9-fluorenyl- methyl group, in trifluoroacetic acid or in a halogenated hydrocarbon containing trifluoroacetic acid, if desired, in the presence of trifluoroacetic anhydride, isolating the resulting N-(R^»-O-CO)-DL-1,2,3,4-tetrahydro-iso-

SUBSTITUTESHEET quinoline-1-carboxylic acid - wherein R¹ has the same and,/ meaning as above

desired, resolving it and/or removing the N-protecting group by a known method, then separating the L-, D- or DL-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid obtained, and, if desired, acylating its N-atom with a group of the general formula

R"-0-CO, wherein R" represents a C₄_g t-alkyl group or a benzyl group substituted with one or more methyl or methoxy groups, and isolating the resulting L-, D- or DL-1,2,3,4-tetra- hydro-isoquinoline-1-carboxylic acid containing an acid sensitive N-protecting group, if desired, in the form of a salt.

According to a preferred embodiment of the present invention N-benzyloxycarbonyl-2-phenethylamine, glyoxylic acid and trifluoroacetic anhydride are reacted in a molar ratio of 1:1:1 in trifluoroacetic acid, in a temperature range of 0 to 10°C, for 3 hours. The reaction mixture is diluted with water and extracted with benzene. The product is extracted from the benzene solution with 10 % ammonium hydroxide, the solution is acidified with potassium hydrogen sulfate and extracted with benzene. The benzene solution is washed with water,

SUBSTITUTESHEET dried over sodium sulfate and evaporated. The obtained N-benzyloxycarbonyl-DL-1,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid is isolated in the form of its cyclohexylam onium salt after crystallizing from diethyl ether. If desired, the^'N-benzyloxycarbonyl-DL- -1,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid is liberated from the salt obtained with 1 M potassium hydrogen sulfate and the protecting group is cleaved by catalytic hydrogenation, in the presence of a palladium catalyst, in 80 % aqueous acetic acid. The catalyst is filtered off, the filtrate is evaporated and the desired product, DL-1,2,3,4-tetrahydro-isoquinoline-l- carboxylic acid, is isolated after crystallizing from aqueous ethanol. According to an other embodiment of the present invention the N-benzyloxycarbonyl-DL- -1,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid, liberated from its cyclohexylammonium salt, is dissolved in a volume of 2 mL/mM of benzene, then 0.5 equivalent of D-threo-2-amino-l-(4-nitrophenyl)-1,3-propanediol is added and the mixture is left to stand for 5-10 hours. The crystalline diastereomeric salt is filtered, washed with benzene, the washings are combined with the benzene mother liquor, the mixture is washed with water, dried rapidly over sodium sulfate, evaporated at reduced pressure to about two thirds of its volume and left to stand at 5-10^βC for 5-10 hours. The N-benzyloxy-

SUBSΠTUTE SHEET carbonyl-L-1,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid crystals formed are separated. The diastereomeric salt is dissolved in ethyl acetate and 1 M potassium hydrogen sulfate, then the ethyl acetate layer is washed with water, dried over sodium sulfate and evaporated. The N-benzyloxycarbonyl-D-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid residue is isolated after recrystallizing from benzene. If desired, the protecting group of N-benzyloxycarbonyl-D- and/or -L-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid is removed by known methods, either by hydrogenation or acidolysis, then the D- or L-l,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid is isolated after recrystallizing from aqueous ethanol. According to an other preferred embodiment of the present invention the reaction of N-(9-fluorenyl- methyloxycarbonyl)-2-phenethylamine, glyoxylic acid hydrate and trifluoroacetic anhydride in a molar ratio of 1:1:1 is carried out in a volume of 2 mL/mM of trifluoroacetic acid, in a temperature range of 0 to

10°C, for 3 hours. The reaction mixture is diluted with water and extracted with benzene. The benzene solutions are combined, washed to neutrality with water, dried over sodium sulfate and evaporated. The obtained N-(9-fluorenyl ethyloxycarbonyl)-DL-1,2,3, -tetrahydro- -isoquinoline-1-carboxylic acid is isolated after

SUBSTITUTESHEET recrystallizing from diethyl ether.

According to a further preferred embodiment of the present invention the above-obtained DL-, D- and L-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid is reacted with di-t-butyl dicarbonate in aqueous t-butanol, in the presence of triethylamine. The resulting N-(t-butyloxycarbonyl)-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid of DL, D or L configuration is separated as a cyclohexylammonium salt after recrystallizing from diethyl ether.

The compounds applied as starting materials in the process of the present invention, the 2-phenethyl- amine derivatives with an N-protecting group of the general formula R'-O-CO, wherein R* has the same meaning as above, are new, and are prepared according to the subsequent examples.

The process of the invention provides a new, simple and economic method for preparing the known DL- and the new D- and L-l,2,3,4-tetrahydro-isoquinoline-l- -carboxylic acids and their new derivatives containing an urethane type N-protecting group of the general formula R-O-CO, wherein R has the same meaning as above, such as N-benzyloxycarbonyl, N-(9-fluorenylmethyloxy- carbonyl) and N-(t-butyloxycarbonyl) derivatives. The derivatives containing the N-protecting groups are suitable building blocks to introduce DL-, D- and

SUBSTITUTESHEET L-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid into oligopeptides by applying a combination of various protecting groups.

In the course of peptide syntheses three types of protecting groups are used: a) The side chains are blocked by groups derived from t-butanol, e. g. t-butyl ester, t-butyl ether or omega-N-(t-butyloxycarbonyl) groups, resp. ; the α-amino groups are protected by a group removable by hydrogenation, e. g. benzyloxycarbonyl group. In such cases the use of N-benzyloxycarbonyl-DL-, -D- or -L-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid is recommended. b) The side chains are protected as in a) while the α-amino groups are blocked by a protecting group removable under basic conditions, such as the 9-fluorenylmethyloxycarbonyl group. In such cases the use of N-(9-fluorenylmethyloxycarbonyl) - -DL-, -D- or -L-l,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid is advantageous. c) The side chains are blocked by groups derived from benzylalcohol, i. e. benzyl ester, benzyl ether or omega-N-benzyloxycarbonyl group, resp., while the α-amino groups are protected by residues of high acid sensitivity, e. g. t-butyloxycarbonyl group. In such cases N-(t-butyloxycarbonyl) -DL-, -D- or

SUBSTITUTESHEET -L-l,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid are the building blocks of choice.

The following examples are illustrating but not limiting the scope of the invention.

The Rf values recorded in the examples were determined by thin-layer chromatography, using silica gel as adsorbent (DC-Alufolien Kieselgel 60 F25 , Merck, Darmstadt) in the following developing solvents:

1. chloroform-methanol (98:2)

2. ethyl acetate-pyridine-acetic acid-water

(30:20:6:11) 3. ethyl acetate-pyridine-acetic acid-water

(480:20:6:11)

Example 1

N-Benzyloxycarbonyl-DL-1, 2 , 3 , 4-tetrahydro-isoquinoline- -1-carboxylic acid cyclohexylammonium salt

18.4 g (0.2 mole) of glyoxylic acid hydrate are dissolved under stirring in 100 mL of trifluoroacetic acid. The solution is cooled to 0-5 °C, 51.6 g (0.2 mole) of N-benzyloxycarbonyl-2-phenethylamine are added, then.

SUBSTITUTE SHEET after its dissolution, 27.8 mL (0.2 mole) of trifluoro¬ acetic anhydride. The reaction mixture is stirred for 30 minutes at 0-5*C, then for 3 hours at room temperature. Thereafter the reaction mixture is diluted with 150 mL of water and extracted with 3 x 50 mL of benzene. The benzene layers are combined, washed with 3 x 20 mL of water and extracted with 2 x 50 mL of 12 % (w/w) ammonium hydroxide. The ammonium hydroxide layers are combined, acidified to pH 3 with a saturated solution of potassium hydrogen sulfate and extracted with 3 x 30 mL of benzene. The benzene solutions are combined, washed to neutrality (3-4 x 20 mL) , dried over anhydrous sodium sulfate and evaporated from a water bath not warmer than 40^βC at 20-25 millibar. The residue is dissolved in 400 mL of diethyl ether, 23 mL (0.201 mole) of cyclohexylamine are added and the mixture is left to stand overnight. The precipitated crystals are filtered, washed with diethyl ether and dried at reduced pressure. Yield 66 g (80.5 %) . Rf(3) = 0.70-0.74 (and cyclohexylamine: 0.0). M.p.: 155-160^βC

Analysis for 24H₃₀N2O (410.60) Calculated: C% = 70.20; H% = 7.60; N% = 6.82; Found: C% = 70.0; H% = 7.4; N% = 6.6.

N-Benzyloxycarbonyl-2-phenethylamine, serving as starting material in Example 1 , is prepared as follows .

SUBSTITUTE SHEET 50.6 mL (0.4 mole) of 2-phenethylamine are dissolved in 1000 L of chloroform and 33.7 g (0.4 mole) of sodium hydrogen carbonate in 240 mL of water. The solutions are combined, cooled to about 5°C, and at this temperature, under vigorous stirring, 75 L (0.44 mole) of benzyloxycarbonyl chloride are added dropwise and 37.05 g (0.44 mole) of sodium hydrogen carbonate, dissolved in 300 L of water, at a rate ensuring that the pH of the mixture remains higher than 7. Stirring is continued for 30 minutes at about 5^βC, then for one hour at room temperature and the layers are separated. The aqueous layer is extracted with 30 ml of chloroform which is combined with the chloroform layer. The chloroform solution is first extracted with 40 mL of 1 M hydrochloric acid, washed to neutrality with water, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40°C. The residue is recrystallized from 200 mL of n-hexane, the crystals are filtered, washed with n-hexane and air-dried. Yield 86 g (84 %) R_f(3) = 0.88-0.92 M.p.: 60°C

Analysis for C₁₆ ^H17^N02 (255.30) Calculated: C% = 75.27; H% = 6.71; N% = 5.49 Found: C% = 75.4; H% = 6.7; N% = 5.3

SUBSTITUTESHEET Example 2

N-Benzyloxycarbonyl-DL-1,2,3,4-tetrahydro- -isoquinoline-1-carboxylic acid cyclohexylammonium salt

0.46 g (5 mmole) of glyoxylic acid hydrate is dissolved under stirring in 5 mL of methylene chloride containing 50 % (v/v) of trifluoroacetic acid. The solution is cooled to 0-5°C, then 1.26 g (5 mmole) of N-benzyloxy- carbonyl-2-phenethylamine are added and, after its dissolution, 0.69 mL (5 mmole) of trifluoroacetic anhydride. The reaction mixture is stirred for 30 minutes at 0-5 ' C then for 3 hours at room temperature. Thereafter the reaction mixture is diluted with 20 mL of water and extracted with 3 x 10 mL of methylene chloride. The methylene chloride solutions are combined, washed with 3 x 5 mL of water and extracted with 2 x 5 mL of 12 % (w/w) ammonium hydroxide. The ammonium hydroxide solutions are combined, acidified to pH 3 with a saturated potassium hydrogen sulfate solution and extracted with 3 x 5 mL of methylene chloride. The methylene chloride solutions are combined, washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40°C. The residue is dissolved in 20 mL of diethyl ether, 0.6 mL (5.4 mmole) of cyclo-

SUBSΠTUTE SHEET hexylamine is added and the mixture is left to stand overnight. The crystals formed are filtered, washed with diethyl ether and dried at reduced pressure. Yield: 1.63 g (80 %) . The quality of the product is identical to that of the product prepared in Example 1.

Example 3

N-Methyloxycarbonyl-DL-l,2,3,4-tβtrahydro-isoquinoline- -1-carboxylic acid cyclohexylamine salt

3.58 g (20 mmole) of N-methyloxycarbonyl-2-phenethyl- amine and 1.84 g (20 mmole) of glyoxylic acid hydrate are condensed according to the process described in Example 1 by using proportional amounts of reagents and solvents except that the cyclohexylammonium salt is crystallized from diisopropyl ether.

Yield: 5 g (75 %)

Rf(3) = 0.44-0.48 (and cyclohexylamine: 0.0) M.p.: 141-144^βC

Analysis for C₁₈H26N 0₄ (334.40)

Calculated: C% = 64.65; H% = 7.84; N% = 8.38;

Found: C% = 64.5; H% = 8.0; N% = 8.15;

N-Methyloxycarbonyl-2-phenethylamin, serving as starting material of Example 3 , is prepared as follows .

SUBSTITUTE SHEET aa 5.31 g (42 mmole) of 2-phenethylamine are dissolved in 100 mL of chloroform and 3.37 g (40 mmole) of sodium hydrogen carbonate in 24 mL of water. The solutions are combined, cooled to about 5°C, then at this temperature and under vigorous stirring 3.4 mL (44 mmole) of methyloxycarbonyl chloride are added dropwise and 3.7 g (44 mmole) of sodium hydrogen carbonate at a rate ensuring that the pH of the solution remains higher than 7. Stirring is continued for 30 minutes at about 5°C and for one hour at room temperature, then the phases are separated. The chloroform layer is extracted with 40 mL of 1 M hydrochloric acid, washed to neutrality with water, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40^βC. The residue is dissolved in 20 mL of benzene and the solution is evaporated. The oily residue is assumed to be N-methyloxycarbonyl-2- -phenethylamine, and is directly used in the above condensation reaction. Yield: 3.6 g (20 mmole) R_f(l) = 0.70-0.75; Rf(3) = 0.79-0.84

SUBSTITUTE SHEET Example 4

N-(9-Fluorenylmethyloxycarbonyl)-DL-1,2,3,4-tβtrahydro- -isoquinoline-l-carboxylic acid

1.29 g (14 mmole) of glyoxylic acid hydrate are dissolved under stirring in 7 mL of trifluoroacetic acid. The solution is cooled to 0-5^βC, then 4.81 g (14 mmole) of N-(9-fluorenylmethyloxycarbonyl)-2- -phenethylamine are added and, after its dissolution, 1.89 mL (14 mmole) of trifluoroacetic anhydride. The reaction mixture is stirred for 30 minutes at 0-5^*C and for 2 hours at room temperature. Thereafter the reaction mixture is diluted with 15 mL of water and extracted with 2 x 10 mL of benzene. The benzene solutions are combined, washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40°C. The residue is dissolved in 40 mL of diethyl ether and left to staΛd in the refrigerator for 1-2 days. The crystals formed are filtered, washed with 2 x 5 mL of diethyl ether and dried at reduced pressure. Yield: 3.93 g (70.4 %) R_f(3) = 0.72-0.75 M.p.: 156-158'C

Analysis for C₂5H₂ιN0₄ (399.43)

Calculated: C% = 75.17; H% = 5.30; N% = 3.51;

Found: C% = 75.2; H% = 5.4; N% = 3.5.

SUBSTITUTE SHEET N-(9-Fluorenylmethyloxycarbonyl)-2-phenethyl- a ine, serving as starting material in Example 4, is prepared as follows.

2.65 mL (21 mmole) of 2-phenethylamine are dissolved in 50 mL of chloroform, then 22 mL of 10 % (w/w) sodium carbonate solution are added. The biphasic mixture obtained is cooled to 0-5^βC and under vigorous stirring 5.17 g (20 mmole) of 9-fluorenyl- methyloxycarbonyl chloride are added. Stirring is continued for one hour at 0-5°C then for one hour at room temperature. The phases are separated, the chloroform layer is washed to neutrality with water, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40^βC. The residue is recrystallized from n-hexane, the crystals are filtered, washed with n-hexane and air-dried. Yield: 5.83 g (85 %) Rf(3) = 0.89-0.93 M.p.: 130-131*C

Analysis for C₂3H₂ιN0₂ (343.41) Calculated : C% = 80. 44 ; H% = 6. 16 ; N% = 4 . 08 ; Found: C% = 80 . 3 ; H% = 6. 2 ; N% = 4 . 1.

SUBSTITUTE SHEET Example 5

Diastereo eric salt of N-benzyloxycarbonyl-D-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid with D-threo-2-amino-l-(4-nitrophenyl)-l,3-propanediol and N-benzyloxycarbonyl-L-l,2,3,4-tetrahydro-isoquinoline-l- carboxylic acid

33 g (80 mmole) of N-benzyloxycarbonyl-DL-l,2,3,4-tetra- hydro-isoquinoline-1-carboxylic acid cyclohexylammonium salt (Examples 1 and 2) are dissolved in 85 mL of 1 M potassium hydrogen sulfate and 200 mL of benzene. The benzene solution is washed with water to neutrality, dried over anhydrous sodium sulfate and concentrated at 20-25 millibar from a water bath at a temperature not exceeding 40*C. To this benzene solution 8 g (37.7 mmole) of D-threo-2-amino-l-(4-nitrophenyl)-1,2- -propanediol base are added under stirring. Stirring is continued up to the dissolution of the base or to the precipitation of further crystals

(diastereomeric salt) . The crystal suspension is left in the refrigerator overnight, then it is filtered and washed with 4 x 30 mL of benzene. The washings are combined with the benzene mother liquor (processing of benzene solution see below) , and the crystals are dried under reduced pressure over paraffin shavings.

SUBSTITUTESHEET The crystalline product is the diastereomeric salt, Yield: 18.75 g (35.81 mmole, 95 %) M.p.: 166-172^βC

[α]_D ²⁰ = -24.9" (c=l, methanol) . Analysis for C27H₂9N₃0₈ (523.53) ^'

Calculated: C% = 61.94; H% = 5.58; N% = 8.03; Found: C% = 61.9; H% = 5.6; N% = 8.05

The above benzene solution (about 270 mL) is washed with 2 x 20 mL of 1 M potassium hydrogen sulfate, then with water to neutrality, dried over anhydrous sodium sulfate, evaporated at 20-25 millibar from a water bath at a temperature not exceeding 0"C to about 150 mL and left in the refrigerator overnight. The crystals formed are filtered, washed with 3 x 20 mL of benzene and dried under reduced pressure over paraffin shavings.

Yield: 9.05 g (29.1 mmole, 76.9 %) M.p.: 146-147.5°C [α]_D ²⁰ = +39.1° (c=l, methanol) Analysis for C₁₈Hi7N0₄ (311.32) Calculated: C% = 69.44; H% = 5.50; N% = 4.50; Found: C% = 69.8; H% = 5.5; N% = 4.6.

SUBSTITUTE SHEET Example 6

N-Benzyloxycarbonyl-D-1, 2 , 3 , 4-tetrahydro-isoquinoline- -1-carboxylic acid

15.2 g (29 mmole) of N-benzyloxycarbonyl-D-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid diastereomer salt with D-threo-2-amino-l-(4-nitrophenyl)-l,3-propane- diol (Example 5) are dissolved in 31 mL of 1 M potassium hydrogen sulfate and 100 mL of ethyl acetate. The ethyl acetate solution is washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated from a water bath at 20-25 millibar at a temperature not exceeding 40°C. Then 2 x 30 L of benzene are distilled from the residue. Thereafter 50 mL of benzene are added to the crystalline oily residue, the mixture is left at room temperature for 3-4 hours, filtered, washed with benzene and dried at reduced pressure over paraffin shavings. Yield: 8.6 g (95 %) M.p.: 147-148.5°C 0]D^{20 =} -40.1" (c=l, methanol) Analysis for C₁₈H₁₇N0₄ (311.32) Calculated: C% = 69.44; H% = 5.50; N% = 4.50; Found: C% = 69.7; H% = 5.6; N% = 5.4.

SUBSTITUTESHEET Example 7

Diastereomeric salt of N-Benzyloxycarbonyl-L-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid with L-threo-2-amino-l-(4-nitrophenyl)-l,3-propanediol and N-benzyloxycarbonyl-D-1,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid

17.5 g (42.5 mmole) of N-benzyloxycarbonyl-DL-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid cyclohexyl¬ ammonium salt (Examples 1 or 2) are processed - by using proportional amounts of reagents and solvents - according to Example 5, except that L-threo-2-amino-l- -(4-nitrophenyl)-1,3-propanediol is applied as base for forming the diastereomeric salt. Yield: 8.4 g (16 mmole, 80 %) M.p.: 168-172^βC [α]_D ²⁰ = 24.5° (c=l, methanol) Analysis for C₂7H₂₉N₃0₈ (523.53) Calculated: C% = 61.94; H% = 5.58; N% = 8.03; Found: C% = 61.9; H% - 5.6;1 N% = 8.05. (Processing of the diastereo er salt is described in Example 8) .

By processing the benzene solution N-benzyloxycarbonyl-D-1 ,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid is obtained.

SUBSTITUTESHEET Yield: 4.7 g (15 mmole, 75 ) M.p.: 146-147*C [α]_D ²⁰ = -40" (c=l, methanol) Analysis for C₁₈H₁₇N0₄ (311.32) Calculated: C% = 69.44; H% = 5.50; N% = 4.50; Found: C% = 69.8; H% = 5.5; N% = 4.6.

Example 8

N-Benzyloxyσarbonyl-L-1,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid

5.25 g (10 mmole) of the diastereomeric salt of

N-benzyloxycarbonyl-L-1,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid with L-threo-2-amino-l-(4-nitro- phenyl)-l,3-propanediol (Example 7) are transformed, by using proportional amounts of reagents and solvents, according to the process described in Example 6.

Yield: 3 g (95 %) M.p.: 146-147°C

[α]_D ²⁰ = +40.1" (c=l, methanol)

Analysis for C₁₈H₁₇N0₄ (311.32)

Calculated: C% = 69.44; H = 5.50; N% = 4.5;

Found: C% = 69.75; H% = 5.6; N% = 4.5.

SUBSTITUTE SHEET Example 9

DL-l,2,3,4-Tetrahydro-isoquinoline-l-carboxylic acid

10 g (24.34 mmole) of N-benzyloxycarbonyl-DL-1,2,3,4- -tetrahydro-isoquinoline-l-carboxylic acid cyclohexyl¬ ammonium salt (Examples 1 or 2) are dissolved in 30 mL of 1 M potassium hydrogen sulfate and 50 mL of benzene. The benzene solution is washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40°C. The residue is dissolved in 250 mL of 80 % acetic acid and the solution is hydrogenated in the presence of 0.3 g of 10 % Pd-C catalyst at room temperature. The progress of the reaction is monitored by thin-layer chromatography. After completed reaction the catalyst is filtered, washed with acetic acid and the solution is evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40"C. The residue is dissolved in 50 mL of a 1:2 mixture of ethanol and water and left in the refrigerator overnight. The crystals formed are filtered, washed with the above mixture of ethanol and water and dried at reduced pressure. Yield: 3.25 g (75 %) R_f(2) = 0.34-0.39

SUBSTITUTE SHEET M.p. : 243-248 'C

Analysis for C₁₀H₁₁NO₂ (177.20) Calculated: C% = 67.78; H% = 6.26; N% = 7.90; Found: C% = 67.7; H% = 6.2; N% = 7.7.

Example 10

DL-1,2,3,4-Tetrahydro-isoquinoline-l-carboxylic acid

1.67 g (5 mmole) of N-methyloxycarbonyl-DL-1,2,3,4-

-tetrahydro-isoquinoline-1-carboxylic acid cyclohexyl¬ ammonium salt (Example 3) are dissolved in 6 mL of 1 M potassium hydrogen sulfate and 10 mL of benzene. The benzene solution is washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40*C. Then 5 mL of glacial acetic acid, containing 32 % of hydrogen bromide, are added, the mixture is left to stand at room temperature for 3 hours, evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40"C and dried at reduced pressure over potassium hydroxide overnight. The dried residue is dissolved in a mixture of ethanol and water (1:2), the pH of the solution is adjusted with ammonium hydroxide to 5-6 and the mixture is left in the refrigerator overnight. The crystals formed are

SUBSTITUTESHEET filtered, washed with 3 x 1 mL of the above mixture of ethanol-water and dried at reduced pressure. Yield: 0.45 g (50 %) R_f(2) = 0.34-0.39 M.p.: 243-248"C

Example 11

L-l,2,3,4-Tetrahydro-isoquinoline-l-carboxylic acid

3.11 g (10 mmole) of N-benzyloxycarbonyl-L-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid (Example 5 or 8) are dissolved in 100 mL of 80 % acetic acid and the solution is hydrogenated in the presence of 0.3 g of a 10 % Pd-C catalyst at room temperature. The progress of hydrogenation is monitored by thin-layer chromatography. After completed reaction the catalyst is filtered, washed with acetic acid and the solution is evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40"C. The residue is dissolved in 50 L of ethanol-water (1:2) and left in the refrigerator overnight. The crystals formed are filtered, washed with the above mixture of ethanol- water and dried at reduced pressure. Yield: 1.35 g (76 %) R_f(2) = 0.34-0.39

SUBSTITUTE SHEET M.p. : 272 ' C

[α]_D ²⁰ = -22.7* (c=2, 1 N sodium hydroxide) Analysis for C₁₀H₁₁NO₂ (177.20) Calculated: C% = 67.78; H% = 6.26; N% = 7.90; Found: C% = 67.6; H% = 6.2,- N% = 7.6.

Example 12

D-1 ,2,3,4-Tetrahydro-isoquinoline-l-carboxylic acid

1 g (3.2 mmole) of N-benzyloxycarbonyl-D-l,2,3,4-tetra- hydro-isoquinoline-1-carboxylic acid (Example 6 or 7) is transformed, by using proportinal amounts of the catalyst and solvents, according to the process described in Example 11.

Yield: 0.35 g (75 %)

R_F(2) = 0.34-0.39

M.p.: 273'C

[α]_D ²⁰ = +22° (c=2, 1 N sodium hydroxide) Analysis for C₁₀H_ι:LNθ2 (177.20)

Calculated: C% = 67.78; H% = 6.26; N% = 7.9;

Found: C% = 67.8; H% = 6.2; N% = 7,8.

SUBSTITUTE SHEET Example 13

N-(t-Butyloxycarbonyl)-L-l,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid cyclohexylammonium salt

0.35 g (2 mmole) of L-l,2,3,4-tetrahydro-isoquinoline- -1-carboxylic acid (Example 11) and 0.56 mL (4 mmole) of triethylamine are dissolved in 1.5 mL of water. First 0.4 mL of t-butanol, then 0.48 mL (2.2 mmole) of di-t-butyl dicarbonate are added and the mixture is stirred for 15 hours. Thereafter the reaction mixture is diluted with 5 mL of water, extracted with 3 x 3 L of n-hexane, acidified with 1 M potassium hydrogen carbonate to pH 3 and extracted with 3 x 5 mL of ethyl acetate. The combined ethyl acetate layers are washed with water to neutrality, dried over anhydrous sodium sulfate and evaporated at 20-25 millibar from a water bath at a temperature not exceeding 40°C. The residue is dissolved in 5 mL of diethyl ether, 0.23 mL (2 mmole) of cyclohexylamine are added and the mixture is left to stand overnight at room temperature. The crystals formed are filtered, washed with diethyl ether and dried at reduced pressure. Yield: 0.65 g (85 %) Rf(3) = 0.74-0.78 (and cyclohexylamine: 0.0)

SUBSTITUTESHEET M.p.: 170-172.5*C [α]_D ²⁰ = +11.1" (c=l, methanol) Analysis for C₂ιH₃2N₂0₄ (376.48) Calculated: C% = 66.99; H% = 8.57; N% = 7.44; Found: C% = 65.9; H% = 8.6; N% = 7.1.

Example 14

N-(t-Butyloxycarbonyl)-D-1,2,3,4-tetrahydro-iso- quinoline-l-carboxylic acid cyclohexylammonium salt

0.35 g (2 mmole) of D-l,2,3,4-tetrahydro-isoquinoline-

-1-carboxylic acid (Example 12) is acylated, by using identical amounts of reagents and solvents, according to the process described in Example 13 and the product obtained is converted to a salt according to the method of Example 13.

Yield: 0.64 g (85 %)

Rf(3) = 0.74-0.78 (and cyclohexylamine: 0.0) M.p.: 170.5-173'C

[α]_D ²⁰ = -12.3* (c=l, methanol)

Analysis for C₂ιH32N₂0₄ (376.48)

Calculated: C% = 66.99; H% = 8.57; N% = 7.44;

Found: C% = 66.9; H% = 8.7; N% = 7.1.

SUBSTITUTE SHEET

Claims

What we claim is

1. New L- and D-1,2,3,4-tetrahydro-iso- quinoline-l-carboxylic acids and their derivatives containing urethane-type.N-protecting groups of the formula

R-O-CO, wherein RR represents a linear or branched C^g alkyl group; a benzyl group optionally substituted with one or more halogen atoms, nitro, methyl or methoxy groups; a picolyl group or a 9-fluorenylmethyl group and the salts thereof.

2. A compound as claimed in claim 1, selected from the group consisting of N-benzyloxycarbonyl-D- -1,2,3,4-tetrahydro-isoquinoline-l-carboxylic acid, N-benzyloxycarbonyl-L-l,2,3,4-tetrahydro-isoquinoline-l- -carboxylic acid, N-(t-butyloxycarbonyl)-D-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid, N-(t-butyl¬ oxycarbonyl)-L-l,2,3,4-tetrahydro-isoquinoline-l-

SUBSΠTUTE SHEET -carboxylic acid, D-l,2,3,4-tetrahydro-isoquinoline-l- -carboxylic acid, and L-l,2,3,4-tetrahydroisoquinoline- -1-carboxylic acid.

3. A process for preparing the known DL- as well as the new L- and D-l,2,3,4-tetrahydro-iso- quinoline~l-carboxylic acids and their derivatives containing urethane-type N-protecting groups of the formula R-O-CO, wherein R represents a linear or branched C^g alkyl group; a benzyl group optionally substituted with one or more halogen atoms, nitro, methyl or methoxy groups; a picolyl group or a

9-fluorenylmethyl group, and their salts, which comprises condensing glyoxylic acid hydrate and 2-phenethylamine having an N-protecting group of the general formula R'-O-CO, wherein R' represents a linear or branched C^_3 alkyl group; a benzyl group optionally substituted with one or more halogen atoms or nitro groups; a picolyl group or a 9-fluorenyl- ethyl group.

SUBSTITUTE SHEET in trifluoroacetic acid or in a halogenated hydrocarbon containing trifluoroacetic acid, if desired, in the presence of trifluoroacetic anhydride, separating the resulting N-(R'-O-CO)-DL-1,2,3,4-tetrahydro-iso- quinoline-1-carboxylic acid - wherein R¹ has the same meaning as above -, if desired, in the form of a salt, and, if desired, resolving same and/or removing the N-protecting group by a known method, then separating the L-, D- or DL-1,2,3,4-tetrahydro-isoquinoline-l- -carboxylic acid obtained and, if desired, acylating its N-atom with a group of the general formula

4. A process as claimed in claim 3 which comprises performing the condensation in a halogenated hydrocarbon containing 30-99 % (v/v) of trifluoroacetic acid, in the presence of not more than one equivalent of trifluoroacetic anhydride.

SUBSTITUTESHEET

5. A process as claimed in claim 3 or 4 which comprises resolving the N-protected DL-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid with D-threo-2-amino-l-(4-nitrophenyl)-1,3-propanediol.

6. A process as claimed in claim 3 or 4 which comprises resolving the N-protected D,L-1,2,3,4- -tetrahydro-isoquinoline-1-carboxylic acid with L-threo-2-amino-l-(4-nitrophenyl)-1,3-propanediol.

SUBSTITUTE SHEET