Bicyclic .alpha.-iminocarboxylic acid compounds having hypotensive activity

What are disclosed are indole, quinoline and isoquinoline compounds of the formula ##STR1## in which n denotes 0 or 1, m denotes 1 or 2, but (n+m).ltoreq.2, A together with the bridgehead carbon atoms denotes a benzene or a cyclohexane ring, Y.sub.1 denotes hydrogen, lower alkanoyl or lower cycloalkanoyl, benzoyl nicotinoyl or a radical of the formula II, and Y.sub.2 denotes methyl, amino, lower alkanoylamino, lower cycloalkanoylamino, benzoylamino or nicotinoylamino, and salts thereof, useful as hypotensive agents, and methods for making the same.

The invention relates to compounds of the formula I 
##STR2## 
in which 
n denotes 0 or 1, m denotes 1 or 2, but (n+m).ltoreq.2, 
A together with the bridgehead carbon atoms denotes a benzene or a 
cyclohexane ring, 
Y.sub.1 denotes hydrogen, lower alkanoyl or lower cycloalkanoyl, benzoyl or 
a radical of the formula II, m and n each preferably having the same 
meaning in both halves of the molecule 
##STR3## 
or, if 
A is part of a benzene ring then Y.sub.1 is as defined above or denotes 
nicotinoyl, and 
Y.sub.2 denotes methyl, amino, lower alkanoylamino, lower 
cycloalkanoylamino or benzoylamino, 
or, if A is part of a benzene ring then Y.sub.2 is as defined above or 
denotes nicotinoylamino, 
or the salts thereof. 
Lower alkanoyl as defined above denotes, in particular, alkanoyl having 1 
to 6 C atoms or lower cycloalkanoyl, particularly cycloalkanoyl having 5 
to 8 C atoms. 
Similar to many other derivatives of indoline and 
1,2,3,4-tetrahydroquinoline, the compounds according to the invention have 
valuable pharmacological properties. 
The invention also relates to a process for the preparation of these 
compounds. This process comprises reacting a lower alkyl ester of an 
iminoacid of the formula III 
##STR4## 
or a salt of such iminoacid with a strong, non-volatile base, with an 
activated derivative of a carboxylic acid of the formula IV 
##STR5## 
in which Y.sub.1 is not H, splitting off the base or the ester group, 
respectively, from the resulting product, if appropriate splitting off an 
acid radical in the position Y.sub.1 or replacing it by another acid 
radical, and, if the compound has a free SH group, oxidizing the product, 
if desired, to give the disulfide compound. 
The synthesis of the compounds of the invention is simple. The 
indoline-2-carboxylic acid suitable as starting compound is known from 
Aust. J. Chem. 20, page 1935 (1967) and 
1,2,3,4-tetrahydroquinoline-2-carboxylic acid is known from Chem. Ber. 61, 
page 2377 (1928). 
1,2,3,4-Tetrahydroisoquinoline-3-carboxylic acid used as starting material 
is easily accessible by reaction of phenyl aniline with formaldehyde as 
described in J. Amer. Chem. Soc. 70, page 182 (1948). 
The starting compounds wherein A is part of a cyclohexane ring can be 
synthesized by subjecting the known compounds indole-2-carboxylic acid, 
quinoline-2-carboxylic acid or 
1,2,3,4-tetrahydro-isoquinoline-3-carboxylic acid to catalytic 
hydrogenation. Preferred catalysts are platinum and rhodium, and these are 
used at temperatures of up to about 100.degree. C. and under pressures of 
up to about 150 bar. 
Carboxylic acids of the formula IV, especially 
##STR6## 
are described, inter alia in DE-OS No. 2,752,720 as well as its English 
language equivalent U.S. Pat. No. 4,116,962 or they can be prepared in 
analogous manner. 
The compound of the formula IV in which Y.sub.2 denotes nicotinoylamino is 
prepared from thionicotinic acid and methacrylic acid in a manner similar 
to that described in DE-OS No. 2,845,499. 
Suitable derivatives of cysteine are known from the literature. 
The acid amides are prepared according to conventional methods, preferably 
those of peptide chemistry, for example as described in detail in 
Houben-Weyl, Methoden der Organischen Chemie ("Methods of Organic 
Chemistry"), Volume 15. 
Examples of suitable activated derivatives of a carboxylic acid of the 
formula IV are the acid chlorides, active esters, mixed anhydrides with 
any desired other carboxylic acids or carbonic acid half-esters. They can 
be reacted directly with iminoacids of the formula III or salts thereof as 
discussed previously. Bases are understood as meaning primarily alkali 
metal hydroxides or alkaline earth metal hydroxides. In addition, examples 
of suitable strong, non-volatile organic bases in the sense of the 
invention are tetraalkylammonium or tetraaralkylammonium hydroxides or 
tetra-alkylated guanidines, such as tetramethylguanidine. 
Activated esters can be prepared, for example, from the corresponding acid 
and N-hydroxysuccinimide, 2,4,5-trichlorophenol or 1-hydroxybenzotriazole 
in a known manner by means of dicyclohexylcarbodiimide, and, after 
removing the dicyclohexylurea formed in their preparation, are used at 
once in solution. Preferred solvents are dimethylformamide, 
dimethylacetamide, N-methylpyrrolidone, phosphoric acid tris-dimethylamide 
or methylene chloride. The same solvents are used to dissolve the salts, 
according to the invention, of the iminoacids of the formula III, which 
have previously been obtained from the components in equimolar quantities, 
for example in an alcoholic or aqueous-alcoholic solution, and have been 
freed from the solvent, for example by distilling off the latter in vacuo. 
Compounds in which Y.sub.1 denotes hydrogen can be obtained by treating the 
corresponding S-acyl derivatives with ammonia or alkali metal or alkaline 
earth metal hydroxides. The latter substances may simultaneously serve to 
saponify methyl or ethyl ester groups possibly being present. 
The reaction can be carried out at room temperature and is complete after 
about 30 minutes when using the acid chlorides or after 14 hours at the 
most when using active esters. The solvent is then removed, for example by 
distillation in vacuo, and the crude product is purified, for example by 
liquid chromatography over silica gel, in which respect solvent systems 
containing chloroform, methanol and acetic acid have proved suitable. 
However, it is also possible, as in the process which is preferred in 
peptide chemistry, the subject the carboxylic acids IV to a condensation 
reaction with alkyl esters of the iminoacids of the formula III and then 
to split or saponify the esters, the S-acyl linkage being split by alkali 
at the same time. The preferred condensation agent is 
dicyclohexylcarbodiimide, if appropriate with the addition of 
N-hydroxysuccinimide or 1-hydroxy-benzotriazole. The preferred solvents 
are those mentioned above. 
Compounds of the formula V 
##STR7## 
in which Y.sub.1 denotes lower alkanoyl or lower cycloalkanoyl, benzoyl or 
nicotinoyl and Y.sub.2 is methyl, lower alkanoylamino, lower 
cycloalkanoylamino, benzoylamino or nicotinoylamino can be obtained, for 
example, by reacting an ester of the formula VI 
##STR8## 
in which R denotes the radical of an alcohol capable of being split off 
under acid conditions, for example the tert. butoxy radical, with a 
carboxylic acid of the formula IV. After acid splitting of the ester 
grouping --CO--R by reacting with ammonia, a primary or secondary amine or 
an alkali metal hydroxide and treatment of the salt with acid or a 
strongly acid ion exchanger, the radical Y.sub.1 in the compounds thus 
obtained can then be replaced by hydrogen. 
It is also possible to condense other alkyl esters, preferably the methyl 
or ethyl esters of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid with a 
carboxylic acid of the formula IV and to treat the reaction product with 
an alkali metal or alkaline earth metal hydroxide in order to split off 
the methyl or ethyl ester and the S-acyl group. 
Another way of prepare compounds of the formula V in which Y.sub.1 is 
hydrogen and Y.sub.2 is amino is the condensation of a compound of the 
formula VI with N,S-di-tert.butyloxycarbonyl cysteine with splitting off 
of the protective groups by a treatment with a strong acid, preferably in 
the presence of a cation acceptor carrying SH groups such as thiophenol, 
ethylmercaptan or dithioglycol. 
Alternatively, a tetraalkylguanidinium, trialkylbenzyl, or tetraalkyl 
ammonium salt of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid can be 
reacted with an activated derivative of a carboxylic acid IV and the salt 
obtained can be decomposed with an acid or a strongly acid ion exchanger. 
If desired, the products obtained can be further modified by splitting off 
the acyl group such as acetyl or benzoyl in position Y.sub.1, for example 
by a treatment with ammonia, an alkali metal or alkaline earth metal 
hydroxide and, if appropriate, by a treatment with a mild oxidant such as 
air, iodine or potassium hexacyanoferrate(III) in order to introduce a 
radical of the formula II. 
For example, it is also possible to react, with a carboxylic acid of the 
formula IV, an ester of the formula VII 
##STR9## 
in which R represents the radical of an alcohol which can be split off 
under acid conditions, for example tert.-butoxy. After splitting the ester 
under acid conditions, the radical Y.sub.1 in the compounds thus obtained 
can be replaced by hydrogen by treating the product with ammonia, a 
primary or secondary amine or alkali metal hydroxide or alkaline earth 
metal hydroxide. The compound of the formula I in which Y.sub.1 .dbd.H is 
liberated by further treatment with acid or with a strongly acid ion 
exchanger. 
It is also possible to subject other alkyl esters, preferably methyl or 
ethyl esters, of decahydroisoquinoline-3-carboxylic acid to a condensation 
reaction with a carboxylic acid of the formula IV and to treat the 
reaction product with an alkali metal hydroxide or alkaline earth metal 
hydroxide in order to split off the ester group and the S-acyl group. 
Compounds of the formula I in which Y.sub.1 represents a radical of the 
formula II can also be prepared, for example, by reacting a compound of 
the formula III or salts or esters thereof, with a compound of the formula 
VIII 
##STR10## 
and, if desired, splitting off protective groups which may be present. 
Compounds of the formula I in which Y.sub.1 denotes nicotionyl can also be 
obtained by reacting a corresponding compound of the formula III with an 
activated derivative of nicotinic acid. 
Depending on the character of the starting materials, particularly on the 
meaning of the substituents Y.sub.1 and Y.sub.2, one or other of the 
processes described can, in individual cases, yield a desired individual 
compound only in poor yields or can be unsuitable for synthesizing it. In 
such cases, which occur relatively seldom, those skilled in the art 
experience no difficulties in synthesizing the desired product by another 
of the process routes described. 
The compounds of the invention have 2 or more chiral centers. They are 
obtained in the form of resins and some of them can be converted to the 
solid state by a prolonged treatment with petroleum ether. They mostly 
melt with decomposition and they do not have a sharp melting point, which, 
besides, is strongly dependent on the time of heating. Their identity has 
been verified by elemental analysis, UV, IR and NMR spetroscopy. 
By countercurrent distribution of their salts with optically active bases, 
stereochemically more uniform compounds can be obtained having a higher 
biological activity and a still unknown absolute configuration. In 
practice the more active compounds with prolonged activity can also be 
used in the form of the stereoisomeric mixture. 
With peroral administration of 1 to 20 mg per kilogram and day, the 
indoline, 1,2,3,4-tetrahydroquinoline and 1,2,3,4-tetrahydroisoquinoline 
compounds according to the invention reduce blood pressure in the 
hypertonic rat and in dogs and they are effective in the same dosage range 
in human beings as well. 
Octahydroindole, decahydroquinoline and decahydroisoquinoline compounds 
according to the invention are 2-4 times as effective as the 
corresponding benzenoid compounds with indoline-2-carboxylic acid, 
1,2,3,4-tetrahydroquinoline-2-carboxylic acid or 
1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid and compounds in which 
the carboxylic acid of the formula IV is linked with proline in the manner 
of an acid amide. 
When administered perorally at 0.5 to 20 mg per kg and per day to 
hypertensive rats and dogs, the perhydrocompounds according to the 
invention lower the blood pressure, and are also effective on humans 
within the same dosage range. 
In animal experiments it was possible to increase the dose of all compounds 
tested without harmful effects. 
The novel compounds can be used to combat hypertension of various geneses. 
They can be used either along or in combination with other blood pressure 
reducing, vasodilatory or diuretically active compounds. 
Typical representatives of this class of active compounds are described, 
for example, in Erhardt-Ruschig, Arzneimittel ("Drugs") 2nd Edition, 
Weinheim 1972. 
The invention is illustrated in greater detail by means of the following 
examples:

EXAMPLE 1 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3-c 
arboxylic acid 
(A) N-benzyloxycarbonyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid 
35 g of L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, prepared from 
L-phenylalanine by condensation with formaldehyde according to J. Amer. 
Chem. Soc. 70, page 182 (1948), are suspended in 200 ml of 1N NaOH. While 
vigorously stirring, 30.2 ml of benzyloxycarbonyl chloride and 232 ml of 
1N NaOH are simultaneously added slowly at 0.degree. to 5.degree. C. and 
stirring of the mixture is continued for 2 hours. The mixture is then 
extracted twice with ether, the aqueous solution is acidified with 
concentrated hydrochloric acid and shaken with ethyl acetate. The ethyl 
acetate phase is washed with water and dried over Na.sub.2 SO.sub.4. After 
distillation of the solvent in vacuo, a resin is obtained which is 
dissolved in hot diisopropyl ether. The product crystallizes on cooling 
and after trituration. Yield 50.4 g, melting point 139.degree. to 
140.degree. C. 
[.alpha.].sub.D : +23.9.degree. (c=1 in methanol). 
(B) N-Benzyloxycarbonyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid 
tert. butyl ester 
31.1 g of the compound obtained according to (A) are dissolved in 250 ml of 
methylene chloride. 38.5 g of tert. butanol and 1 g of 
4-dimethylaminopyridine are added, and while stirring at 0.degree. C., a 
solution of 22 g of dicyclohexyl carbodiimide in 60 ml of methylene 
chloride is added drop by drop. The mixture is stirred for 15 minutes at 
0.degree. C. and then for 5 hours at room temperature, filtered, and the 
filtrate is evaporated to dryness in vacuo. The residue is taken up in 
methylene chloride. The solution is successively shaken with sodium 
bicarbonate solution and potassium hydrogen sulfate/potassium sulfate 
solution, washed neutral with water and dried over Na.sub.2 SO.sub.4. 
After concentration by evaporation, an oily residue is obtained. Yield 
32.6 g. 
(C) L-1,2,3,4-Tetrahydrosioquinoline-3-carboxylic acid tert. butyl ester 
toluene sulfonate 
30.5 g of the compound prepared according to (B) are dissolved in 300 ml of 
methanol and catalytically hydrogenated on palladium black while 
maintaining a pH of 5 on an autotitrator by adding 1N toluene-sulfonic 
acid. When the reaction is terminated, the catalyst is filtered off and 
the solvent is distilled off. The resinous residue becomes solid after 
trituration with ether. Yield 31.4 g. The compound is chromatographically 
almost pure and differs from the starting compound by a lower R.sub.f 
value in a thin layer chromatogram. 
(D) 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3- 
carboxylic acid tert. butyl ester 
20.3 g of the tert. butyl ester tosylate prepared according to (C) are 
dissolved in 200 ml of methylene chloride, 8.3 g of 
2-methyl-3-acetylmercaptopropionic acid, 6.4 ml of N-ethylmorpholine and, 
while cooling, 11 g of dicyclohexyl carbodiimide dissolved in 60 ml of 
methylene chloride are added. The mixture is stirred at room temperature 
over night, filtered, the solvent is distilled off in vacuo and the 
residue is taken up in ethyl acetate. The solution is successively washed 
with NaHCO.sub.3 solution, KHSO.sub.4 /K.sub.2 SO.sub.4 solution and 
water, dried over Na.sub.2 SO.sub.4 and evaporated in vacuo. 16.3 g of oil 
are obtained. 
(E) 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3- 
carboxylic acid 
13 g of the compound obtained according to (D) are dissolved in 70 ml of 
trifluoroacetic acid which is distilled off in vacuo after 45 minutes. The 
residue is distributed between 180 ml of ethyl ether and 90 ml of 
saturated NaHCO.sub.3 solution. The ether phase is rejected. The aqueous 
phase is acidified with concentrated hydrochloric acid and extracted three 
times with ethyl acetate. The combined ethyl acetate solutions are washed 
with water and dried over Na.sub.2 SO.sub.4. The solvent is distilled off. 
The residue is taken up in ether and cyclohexylamine is added while 
stirring until moist pH paper indicates a value of 8. After cooling the 
suspension obtained, the cyclohexyl ammonium salt is filtered off and 
washed with ether. After drying the salt is recrystallized from 
isopropanol and acetonitrile. Melting point 159.degree. to 161.degree. C., 
[.alpha.].sub.D : -11.5.degree. (c=0.5 in methanol). Yield 4.8 g. In order 
to obtain the free acid, the salt is suspended between water and ethyl 
acetate/ether. After addition of KHSO.sub.4 solution to pH 2, all is 
dissolved. The phases are separated. The aqueous solution is washed with a 
small amount of ethyl acetate and the combined organic phases are washed 
with a small amount of water, dried over Na.sub.2 SO.sub.4 and the solvent 
distilled off in vacuo. The resinous residue becomes solid on rubbing with 
ether. Yield 3.0 g. Elemental analysis correct. 
EXAMPLE 2 
N-(2-Methyl-3-mercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3-carboxy 
lic acid 
1.3 g of the compound prepared according to Example 1(E) in 8 ml of 5N 
ammonia are kept for 2 hours under nitrogen. Next, the solution is 
evaporated to dryness in vacuo and the solid residue is dissolved in 10 ml 
of 50% aqueous methanol. The solution is filtered over a small column of 
the strongly acid ion exchanger "Lewatit S 100" and the eluate is 
evaporated to dryness in vacuo. The resinous residue is digested in 
petroleum ether, whereupon it becomes solid. After drying in vacuo, the 
title compound is obtained in a yield of 0.85 g. The elemental analysis is 
correct. 
EXAMPLE 3 
N-D-Cysteinyl-L-1,2,3,4-tetrahydroisoquinolin-3-carboxylic acid 
(A) N-S-Di-Boc-D-cysteinyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic 
acid tert. butyl ester 
4.36 g of N-S-di-Boc-D-cystein-N-hydroxysuccinimide ester, prepared by the 
method described in Liebig's Ann. Chem. 743, page 57 (1971) and 4.05 g of 
L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid tert. butyl ester 
tosylate, prepared according to Example 1, are dissolved in 60 ml of 
dimethyl formamide. 1.28 ml of N-ethylmorpholine are added and the mixture 
is stirred over night at room temperature. Next, the solvent is distilled 
off in vacuo, the resinous residue is digested in water and dried in 
vacuo. Yield 4.49 g (81%) of a solid mass without sharp melting point. 
(B) D-Cysteinyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid 
4.4 g of the compound prepared according to (A) are kept for 15 to 20 
minutes at room temperature in 0.2N HCl in formic acid containing 5% of 
dithioglycol. The mixture is evaporated to dryness in vacuo and the 
residue is digested in ether. The solid product obtained is a little 
hygroscopic. Yield 1.44 g (56%). An elemental analysis, taking 3 to 5% 
water into consideration, was correct. 
EXAMPLE 4 
N-Acetyl-S-benzoyl-D-cysteinyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxyli 
c acid 
3.9 g of N-acetyl-S-benzoyl-D-cysteine-4-nitrophenyl ester, obtained by the 
method described in J. Org. Chem. 27, page 3329 (1962), are reacted 
according to Example 3(A) with 4.1 g of 
L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid tert. butyl ester 
tosylate and 1.28 ml of N-ethylmorpholine. The crude product is purified 
by filtration of its chloroformic solution over silica gel. Yield 3.65 g 
(73%) of a semi-solid mass which is uniform in a thin layer chromatogram 
and the elemental analysis of which is satisfactory. 
To split off the tert. butyl alcohol from the ester group, the compound is 
kept for 40 minutes in trifluoroacetic acid, which is then distilled off 
in vacuo. The residue is dissolved in aqueous 50% methanol and treated 
with a weakly basic ion exchanger in acetate form until the pH is shifted 
from about 2 to about 3 to 4. The exchanger is filtered off. After 
distillation of the solvent in vacuo and drying over P.sub.2 O.sub.5, a 
hard pulverizable mass is obtained. Yield 2.5 g (81%). For analysis the 
cyclohexyl ammonium or dicyclohexyl ammonium salt is recrystallized from 
isopropanol. Elemental analysis of the salts is correct. 
EXAMPLE 5 
N-Acetyl-D-cysteinyl-L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid 
1 g of the compound obtained according to Example 4 is dissolved in 4N 
methanolic ammonia and kept for 2 hours under nitrogen. The reaction 
product is further treated as described in Example 2. Yield 0.54 g (71%). 
EXAMPLE 6 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3-c 
arboxylic acid 
(A) 2-Methyl-3-acetylmercaptopropionic acid-2,4,5-trichlorophenyl ester 
The trichlorophenyl ester is prepared in a known manner from 16.2 g of the 
acid, 19.7 g of 2,4,5-trichlorophenol and 22 g of dicyclohexyl 
carbodiimide in tetrahydrofurane. After filtration, the compound is 
purified by chromatography on silica gel using tetrahydrofuran as an 
eluant. Yield 29.8 g (79%), melting point 40.degree.-41.degree. C. 
(B) 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3- 
carboxylic acid 
A salt is prepared from 1.77 g of 
1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid and 1.05 g of tetramethyl 
guanidine in 10 ml of methanol and under nitrogen. The methanol is 
distilled off in vacuo and the residue is dissolved under nitrogen in 10 
ml of dimethyl formamide. 3.4 g of 2-methyl-3-acetylmercaptopropionic acid 
active ester prepared according to (A) and 0.1 g of 1-hydroxybenzotriazole 
in 10 ml of dimethyl formamide are added to the solution obtained and the 
whole is kept over night at room temperature. After distillation of the 
solvent, the product is purified as described in Example 1(E), whereupon 
1.0 g of title compound is obtained, which is identical with the compound 
obtained according to Example 1(E). 
EXAMPLE 7 
N-(2-Methyl-3-nicotinoylmercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline 
-3-carboxylic acid 
(A) Nicotinic acid N-hydroxysuccinimide ester 
The title compound is prepared in known a manner from 30.8 g of nicotinic 
acid, 34.5 g of N-hydroxysuccinimide and 55 g of dicyclohexyl carbodiimide 
in 800 ml of dimethyl formamide. When the reaction is terminated, the 
mixture is concentrated in vacuo to one third of its volume, cooled to 
0.degree. C., filtered and the filtrate is evaporated to dryness in vacuo. 
The residue is recrystallized from 200 ml of isopropanol. Yield 49.0 g, 
melting point 137.degree. to 138.degree. C. 
(B) 
N-(2-Methyl-3-nicotinoylmercaptopropionyl)-L-1,2,3,4-tetrahydrosioquinolin 
e-3-carboxylic acid 
3.3 g of active ester obtained according to (A) are reacted with 2.8 g of 
N-(2-methyl-3-mercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3-carbox 
ylic acid and 1.28 ml of N-ethylmorpholine in 50 ml of dimethyl formamide. 
The mixture is left to stand over night, the solvent is distilled off, the 
residue is digested in dilute acetic acid and water, dried in vacuo and 
taken up in a small amount of isopropanol. The cyclohexylammonium salt is 
prepared by adding cyclohexylamine and for purification the salt is 
recrystallized from isopropanol. The free compound is obtained by 
filtration of the solution of the salt in aqueous 50% methanol over a 
weakly acid ion exchanger. The solvent is distilled off in vacuo. After 
drying of the residue, a pulverizable resin is obtained. UV extinction 
curve and elemental analysis confirm the correct structure of the 
compound. 
EXAMPLE 8 
N-(2-Methyl-3-mercaptopropionyl)-L-1,2,3,4-tetrahydroisoquinoline-3-carboxy 
lic acid 
17.7 g of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid are converted 
into the methyl ester hydrochloride using hydrochloric acid or thionyl 
chloride in methanol in known manner. After distillation of the solvent 
the compound is isolated by digestion with ether. 
The dry residue is reacted as described in Example 1(D) with 16.2 g of 
2-methyl-3-acetylmercaptopropionic acid, 12.8 ml of N-ethylmorpholine and 
22 g of dicyclohexyl carbodiimide in methylene chloride. The reaction 
mixture is worked up as described in Example 1(D). 
The oily residue is dissolved in 150 ml of dioxane/methanol 1:1. 2N NaOH is 
added drop by drop while stirring under nitrogen in order to maintain a pH 
of 12.5 to 13. When no more sodium hydroxide is consumed, the solution is 
treated with aqueous 50% methanol and the combined solutions are 
concentrated by evaporation in vacuo. The residue is digested with 
petroleum ether and dried in vacuo. Yield 7.8 g. According to thin layer 
chromatography the compound is identical with that of Example 2. 
EXAMPLE 9 
.beta.,.beta.-Dithiodiisobutyryl-bis-L-1,2,3,4-tetrahydroisoquinoline-3-car 
boxylic acid 
(A) 4 g of L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid tert. butyl 
ester tosylate are reacted, in the presence of 1.28 ml of 
N-ethylmorpholine, with 1.2 g of .beta.,.beta.-dithiodiisobutyric acid, 
prepared as described in Svensk kem. Tidskr. 55, page 170 (1943), and 1.1 
g of dicyclohexyl carbodiimide in 50 ml of dimethyl formamide. After 
filtration, the reaction product is precipitated with water and dried. For 
splitting the tert. butyl ester, the product is treated for 45 minutes 
with trifluoroacetic acid which is then distilled off in vacuo. The 
residue is dissolved in 80 ml of methanol. The solution is stirred in a 
small amount of weakly basic ion exchanger in acetate form and, after 
filtration, the reaction product is evaporated to dryness in vacuo. A 
resinous mass is obtained, which solidifies on prolonged standing under 
ether/petroleum ether and can then be triturated. It is preferably 
converted into its alkali metal or ammonium salt in which form it is 
easier to handle. 
(B) 2 g of the compound prepared as described in A are dissolved in a 
mixture of ethanol and sodium phosphate buffer of pH 6. Iodine is added 
drop by drop and while stirring until the yellow coloration remains 
constant. The mixture is decolorized with thiosulfate and the ethanol is 
distilled off in vacuo. Next, the mixture is cautiously acidified with 4N 
hydrochloric acid to pH 1.5 to 2 and the title compound is shaken with 
ethyl acetate. The ethyl acetate solution is washed with a small amount of 
water, dried over Na.sub.2 SO.sub.4 and concentrated in vacuo. Yield 1.77 
g. For analysis the cyclohexyl amine salt is prepared in acetonitrile. 
Melting point 186.degree. to 190.degree. C. Elemental analysis correct. 
EXAMPLE 10 
3-Mercapto-2-methylpropionyl-1,2,3,4-tetrahydroquinoline-2-carboxylic acid 
1.63 g of 2-methyl-3-acetylmercaptopropionic acid and 2.3 g of 
1,2,3,4-tetrahydroquinoline-2-carboxylic acid methyl ester hydrochloride, 
prepared as described in Chem. Ber. 61, page 2377 (1928), are dissolved 
under nitrogen in 20 ml of dimethyl acetamide. 1.35 g of 
1-hydroxy-benzotriazole, 1.28 ml of N-ethylmorpholine and 2.2 g of 
dicyclohexyl carbodiimide are successively added and the whole is stirred 
for 4 hours at room temperature. The reaction mixture is then filtered and 
the solvent is distilled off from the filtrate in vacuo. The residue is 
dissolved in 30 ml of methanol. The solution is stirred and 10 ml of 4N 
NaOH are added drop by drop and under nitrogen. 10 minutes after 
termination of the addition, 10 ml of 4N HCl are added, whereupon the 
mixture is evaporated to dryness in vacuo. After distillation of the 
solvent, the reaction product is purified by chromatography on 130 g of 
SiO.sub.2 in a system of chloroform/isopropanol/acetic acid (50:10:3). 
Yield 2.3 g. Elemental analysis and NMR spectrum correct. 
EXAMPLE 11 
N-(2-Methyl-3-nicotinoylmercaptopropionyl)-1,2,3,4-tetrahydroquinoline-2-ca 
rboxylic acid 
1.4 g of the compound obtained as described in Example 10 are dissolved in 
10 ml of dimethyl formamide and reacted under nitrogen with 1.1 g of 
nicotinic acid N-hydroxysuccinimide ester, prepared in usual manner form 
nicotinic acid, N-hydroxy-succinimide and dicyclohexylcarbodiimide, 
melting point 137.degree. to 138.degree. C. The solvent is distilled off 
after 3 hours and the residue is chromatographed as described in Example 
10. Yield 0.7 g. UV and NMR spectra confirm that the product is the 
desired compound. 
EXAMPLE 12 
N-(2-Methyl-3-acetylmercaptopropionyl)-indoline-2-carboxylic acid 
The acid chloride is prepared from 2-methyl-3-acetylmercaptopropionic acid 
with a 10% excess of thionyl chloride in methylene chloride by heating for 
3 hours. The acid chloride is obtained in pure form by distillation under 
1 mm Hg. 
1.9 g of the acid chloride are reacted under nitrogen with the 
tetramethylguanidinium salt of 1.63 g of indoline-2-carboxylic acid in 
dimethyl acetamide. After working up and purification as described in 
Example 10, 2.9 g of pure title compound are obtained with correct 
elemental analysis. 
EXAMPLE 13 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-decahydroisoquinoline-3-carboxylic 
acid 
A. N-Benzyloxycarbonyl-L-decahydroisoquinoline-3-carboxylic acid 
36 g of L-decahydroisoquinoline-3-carboxylic acid, prepared from the 
1,2,3,4-tetrahydro compound by catalytic hydrogenation over 5% 
rhodium-on-charcoal at 60.degree.-90.degree. C. and 80-150 bars H.sub.2 
pressure in 90% strength acetic acid, are suspended in 200 ml of 1N NaOH. 
30.2 ml of benzyloxycarbonyl chloride are added at 0.degree.-5.degree. C., 
while stirring vigorously, and 232 ml of 1N NaOH are added slowly at the 
same time and the mixture is stirred for a further 2 hours. It is then 
extracted twice with ether, disregarding a precipitate, and the aqueous 
solution is acidified with concentrated hydrochloric acid and is extracted 
by shaking with ethyl acetate. The ethyl acetate phase is washed with 
water and dried over Na.sub.2 SO.sub.4. A resin is left as residue after 
removing the solvent by distillation in vacuo. This solid is dissolved in 
hot diisopropyl ether. After adding dicyclohexylamine, the salt is 
precipitated on cooling. Yield 49.1 g. The acid is liberated in the 
customary manner by means of potassium bisulfate/ethyl acetate. 
B. N-Benzyloxycarbonyl-L-decyhydroisoquinoline-3-carboxylic acid 
tert.-butyl ester 
32 g of the compound obtained in (A) are dissolved in 250 ml of methylene 
chloride. 38.5 ml of tert.-butanol and 1 g of 4-dimethylaminopyridine are 
added and the solution of 22 g of dicyclohexylcarbodiimide in 60 ml of 
methylene chloride is added dropwise at 0.degree. C., while stirring. The 
mixture is then stirred for 15 minutes at 0.degree. C. and for 5 hours at 
room temperature, and is filtered and the filtrate is evaporated to 
dryness in vacuo. The residue is redissolved in methylene chloride and the 
solution is extracted by shaking successively with saturated sodium 
dicarbonate solution and potassium bisulfate/potassium sulfate solution, 
washed with water until it is neutral and dried over Na.sub.2 SO.sub.4. 
Evaporation leaves an oily residue. Yield 32.0 g. 
C. L-Decahydroisoquinoline-3-carboxylic acid tert.-butyl 
ester-toluenesulfonate 
30.5 g of the compound obtained in (B) are dissolved in 300 ml of methanol 
and hydrogenated catalytically over palladium black, the pH value being 
kept at 5 by adding 1N toluenesulfonic acid in methanol by means of an 
autotitrator. When the reaction is complete, the catalyst is filtered off 
and the solvent is removed by distillation. The resinous residue 
solidifies on being triturated with ether and water. Yield 31.4 g. The 
compound is virtually pure according to chromatography and is 
distinguished from the starting material by a lower R.sub.f value in the 
thin layer chromatogram (silica gel). 
D. 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-decahydroisoquinoline-3-carboxyli 
c acid tert.-butyl ester 
20.5 g of the tert.-butyl ester-tosylate obtained in (C) are dissolved in 
200 ml of methylene chloride and 8.3 g of 
2-methyl-3-acetylmercaptopropionic acid and 6.4 ml of N-ethylmorpholine 
are added, followed, while cooling with ice, by 11 g of 
dicyclohexylcarbodiimide, dissolved in 60 ml of methylene chloride. The 
mixture is stirred overnight at room temperature and filtered, the solvent 
is removed by distillation in vacuo and the residue is taken up in ethyl 
acetate. The solution is washed successively with NaHCO.sub.3 solution, 
KHSO.sub.4 /K.sub.2 SO.sub.4 solution and water, is dried over Na.sub.2 
SO.sub.4 and is evaporated in vacuo. This gives 15.9 g of an oil. 
NMR (CDCl.sub.3):1.20 (d, 3H); 1.40 (s, 9H); 2.13 (s, 3H); 1.1-5.1 (m, 
18H). 
E. 
N-(2-Methyl-3-acetylmercaptopropionyl)-L-decahydroisoquinoline-3-carboxyli 
c acid 
13 g of the compound obtained in (D) are dissolved in 70 ml of 
trifluoroacetic acid, which is distilled off in vacuo after 45 minutes. 
The residue is partitioned between 180 ml of ethyl ether and 90 ml of 
saturated NaHCO.sub.3 solution. The ether phase is discarded and the 
aqueous phase is acidified with concentrated hydrochloric acid and 
extracted three times with ethyl acetate. The combined ethyl acetate 
solutions are washed with water and dried over Na.sub.2 SO.sub.4. The 
solvent is removed by distillation, the residue is taken up in ether and 
cyclohexylamine is added, while stirring, until the moist pH paper 
indicates a value of 8. After cooling the resulting suspension, the 
cyclohexylammonium salt ist filtered off and is washed with ether. After 
drying, it is recrystallised from isopropanol and acetonitrile. Yield 4.6 
g. The free acid is obtained by suspending the salt between water and 
ethyl acetate/ether. The addition of KHSO.sub.4 solution until pH 2 is 
reached produces complete solution. The phases are separated, the aqueous 
solution is washed with a little ethyl acetate and the combined organic 
phases are washed with a little water and dried over Na.sub.2 SO.sub.4 and 
the solvent is removed by distillation in vacuo. The resinuous residue 
solidifies on being triturated with ether. Yield 3.0 g. Elementary 
analysis correct. 
NMR (DMSO-d.sub.6): 1.22 (d, 3H); 2.15 (s, 3H), 1.1-5.1 (m, 18H). 
EXAMPLE 14 
N-(2-Methyl-3-mercaptopropionyl)-L-decahydroisoquinoline-3-carboxylic acid 
1.5 g of the compound prepared in Example 13(E) are kept in 8 ml of 5N 
ammonia in methanol for 2 hours under nitrogen. The solution is then 
evaporated to dryness in vacuo. The solid residue is dissolved in 10 ml of 
50% strength aqueous methanol. The solution is filtered through a small 
column containing the strongly acid ion exchanger "Lewatit S 100" and the 
eluate is evaporated to dryness in vacuo. The resinuous residue is 
digested with petroleum ether, whereupon it solidifies. Drying in vacuo 
gives the title compound in a yield of 0.81 g. Elementary analysis 
correct. 
NMR (CF.sub.3 COOH): 1.20 (d, 3H); 1.2-5.2 (m, 19H). 
EXAMPLE 15 
N-D-Cysteinyl-L-decahydroisoquinoline-3-carboxylic acid 
A. N-S-Di-Boc-D-cysteinyl-L-decahydroisoquinoline-3-carboxylic acid 
tert.-butyl ester 
4.36 g of N-S-Di-Boc-D-cysteine-N-hydroxysuccinimide ester, prepared 
analogously to Liebig's Ann. Chem. 743 (1971), page 57 and 4.1 g of 
L-decahydroisoquinoline-3-carboxylic acid tert.-butyl ester-tosylate, 
prepared in accordance with Example 13, are dissolved in 60 ml of 
dimethylformamide. 1.28 ml of N-ethylmorpholine are added and the mixture 
is stirred overnight at room temperature. The solvent is then removed by 
distillation in vacuo and the resinous residue is digested with water and 
dried in vacuo. Yield 4.38 g of a solid mass having an unsharp melting 
point. 
B. D-Cysteinyl-L-decahydroisoquinoline-3-carboxylic acid 
4.4 g of the compound obtained in (A) are kept in 0.2N HCl in formic acid, 
containing 10% of ethyl mercaptan, for 15-20 minutes at room temperature. 
The mixture is evaporated to dryness in vacuo and the residue is digested 
with ether. The solid product obtained is somewhat hygroscopic. Yield 1.44 
g (56%). After allowing for 3-5% of water, the elementary analysis is 
correct. 
EXAMPLE 16 
N-Acetyl-S-benzoyl-D-cysteinyl-L-decahydroisoquinoline-3-carboxylic acid 
3.9 g of N-acetyl-S-benzoyl-D-cysteine 4-nitrophenyl ester, obtained 
analogously to J. Org. Chem. 27 (1962), page 3329, are reacted in 
accordance with Example 15(A) with 4.2 g of 
L-decahydroisoquinoline-3-carboxylic acid tert.-butyl ester-tosylate and 
128 ml of N-ethylmorpholine. The crude product is purified by filtration 
in solution in chloroform over silica gel. Yield 3.52 g of a semi-solid 
mass which has a single-substance thin layer chromatogram and exhibits a 
satisfactory elementary analysis. The tert.butyl alcohol is split off from 
the ester group by keeping the compound for 40 minutes in trifluoroacetic 
acid, which is then removed by distillation in vacuo. The residue is 
dissolved in 50% strength aqueous methanol and is treated with a weakly 
basic ion exchanger in the acetate form until the pH value has fallen back 
from about 2 to about 3-4. The exchanger is then filtered off. Distilling 
off the solvent in vacuo and drying the residue over P.sub.2 O.sub.5 gives 
a hard, powderable mass. Yield 2.1 g. For analysis, the cyclohexylammonium 
or diyclohexylammonium salt is recrystallized from isopropanol. The salts 
have a correct elementary analysis. 
EXAMPLE 17 
N-Acetyl-D-cysteinyl-L-decahydroisoquinoline-3-carboxylic acid 
1 g of the compound obtained in Example 16 is dissolved in 4N methanolic 
ammonia and is kept under nitrogen for 2 hours. The mixture is worked up 
as in Example 14. Yield 0.50 g. 
NMR (CF.sub.3 COOH): 2.1 (s, 3H); 1.1-5.2 (20H). 
EXAMPLE 18 
2-Methyl-3-acetylmercaptopropionyl-L-decahydroisoquinoline-3-carboxylic 
acid 
A. 2-Methyl-3-acetylmercaptopropionic acid 2,4,5-trichlorophenylester 
The trichlorophenyl ester is prepared in a known manner from 16.2 g of the 
acid, 19.7 g of 2,4,5-trichlorophenol and 22 g of dicyclohexylcarbodiimide 
in tetrahydrofuran. After filtration, the compound is purified by 
chromatography over silica gel using tetrahydrofuran as the migrating 
agent. Yield 29.8 g (79%). Melting point 40.degree.-41.degree.. 
B. 2-Methyl-3-acetylmercaptopropioyl-L-decahydroisoquinoline-3-carboxylic 
acid 
The corresponding salt is prepared from 1.8 g of 
decahydroisoquinoline-3-carboxylic acid and 1.05 g of tetramethylguanidine 
in 10 ml of methanol, under nitrogen, the methanol is removed by 
distillation in vacuo and the residue is dissolved in 10 ml of 
dimethylformamide under nitrogen. 3.4 g of the 
2-methyl-3-acetylmercaptopropionic acid active ester obtained in (A) and 
0.1 g of 1-hydroxybenzotriazole in 10 ml of dimethylformamide are added to 
this solution and the whole mixture is kept overnight at room temperature. 
After removing the solvent by distillation, the product is purified as 
described in Example 13(E) to give 0.95 g of the tilte compound, which is 
identical with the compound obtained in Example 13(E). 
EXAMPLE 19 
N-(2-Methyl-3-mercaptopropionyl)-L-decahydroisoquinoline-3-carboxylic acid 
17.9 g of decahydroisoquinoline-3-carboxylic acid are converted into the 
methyl ester-hydrochloride in a known manner by means of hydrochloric acid 
or thionyl chloride in methanol. After distilling off the solvent, the 
compound is isolated by digesting the residue with ether. 
The dry residue is reacted in accordance with Example 13(D) with 16.2 g of 
2-methyl-3-acetylmercaptopropionic acid, 12.8 ml of N-ethylmorpholine and 
22 g of dicyclohexylcarbodiimide in methylene chloride. The mixture is 
worked up analogously to Example 13(D). 
The oily residue is dissolved in 150 ml of 1:1 dioxane-methanol. 2N NaOH is 
added dropwise, while stirring and under nitrogen, and the pH value is 
kept at 12.5-13. When no further sodium hydroxide solution is consumed, 
the solution is treated with a strongly acid ion exchanger in 50% strength 
aqueous methanol and the combined solutions are concentrated in vacuo. The 
residue is digested with petroleum ether and dried in vacuo. Yield 7.8 g. 
The compound is identical, in terms of thin layer chromatography, with the 
compound obtained in Example 14. 
EXAMPLE 20 
.beta.,.beta.-Dithiodiisobutyryl-bis-L-decahydroisoquinoline-3-carboxylic 
acid 
A. 4.2 g of L-decahydroisoquinoline-3-carboxylic acid tert.-butyl 
ester-tosylate are reacted with 1.2 g of .beta.,.beta.-dithiodiisobutyric 
acid, prepared as in Svensk kem. Tidskr. 55 (1943), page 170, and 1.1 g of 
dicyclohexylcarbodiimide in 50 ml of dimethylformamide in the presence of 
1.28 ml of N-ethylmorpholine. After filtering the mixture, the reaction 
product is precipitated with water and is dried. The tert.-butyl ester is 
split by treating the product for 45 minutes with trifluoroacetic acid, 
which is then removed by distillation in vacuo. The residue is dissolved 
in 80 ml of methanol and the solution is stirred with a little of a weakly 
basic ion exchanger in the acetate form and, after filtration, is 
evaporated to dryness in vacuo. A resinous mass is formed, which 
solidifies and can be triturated after standing for a fairly long period 
under ether/petroleum ether. It is advantageously converted into an alkali 
metal salt or ammonium salt and is then easier to handle. 
B. 2 g of the compound prepared in example 14 are dissolved in a mixture of 
ethanol and a sodium phosphate buffer of pH 6. Iodine is added dropwise, 
while stirring, until a constant yellow coloration is obtained, the 
mixture is decolorized with thiosulfate and the ethanol is removed by 
distillation in vacuo. The mixture is then acidified cautiously to pH 
1.5-2 with 4N hydrochloric acid and the title compound is extracted by 
shaking with ethyl acetate. The ethyl acetate solution is washed with a 
little water, dried over Na.sub.2 SO.sub.4 and concentrated in vacuo. 
Yield 1.77 g. For analysis, the cyclohexylamine salt is prepared in 
acetonitrile. Elementary analysis correct. 
EXAMPLE 21 
3-Mercapto-2-methylpropanoyldecyhydroquinoline-2-carboxylic acid 
1.63 g of 2-methyl-3-acetylmercaptopropionic acid and 2.4 g of 
decahydroquinoline-2-carboxylic acid methyl esterhydrochloride are 
dissolved in 20 ml of dimethylacetamide under nitrogen. 1.35 g of 
1-hydroxybenzotriazole, 1.28 ml of N-ethylmorpholine and 2.2 g of 
dicyclohexylcarbodiimide are also added successively and the mixture is 
stirred for 4 hours at room temperature. It is then filtered and the 
solvent is removed from the filtrate by distillation in vacuo. The residue 
is dissolved in 30 ml of methanol. The solution is stirred and 10 ml of 4N 
NaOH are added dropwise, under nitrogen, and, 10 minutes after the 
addition has been completed, 10 ml of 4N HCl are added. The mixture is 
then evaporated to dryness in vacuo. After removing the solvent by 
distillation, the residue is purified by chromatography over 130 g of 
SiO.sub.2 using the system 50:10:3 chloroform/isopropanol/acetic acid. 
Yield 2.2 g. Elementary analysis correct. 
NMR (CF.sub.3 COOH): 1.21 (d, 3H); 1.2-3.8 (m, 12H); 4.96 (m, 1H). 
EXAMPLE 22 
2-Methyl-3-acetylmercaptopropionyloctahydroindole-2-carboxylic acid 
The acid chloride is prepared from 2-methyl-3-acetylmercaptopropionic acid 
by warming for 3 hours with a 10% excess of thionyl chloride in methylene 
chloride, and the product is obtained in a pure state by distillation 
under a pressure of 1 mm Hg. 1.9 g of the acid chloride are reacted with 
the tetramethylguanidinium salt of 1.63 g of 
octahydroindoline-2-carboxylic acid in dimethylacetamide under nitrogen. 
Working up and purifying analogously to Examle 22 gives 2.9 g of the pure 
title compound having a correct elementary analysis. 
EXAMPLE 23 
2-Methyl-3-mercaptopropionyloctahydroindole-2-carboxylic acid 
The acetyl group is split off analogously to Example 14 from the compound 
prepared in Example 22 and the product is worked up as described in 
Example 14. A resin, having a correct elementary analysis is obtained.