N-Acyl-3-[4-(benzoylalkyl)piperazin-1-yl]-sydnonimine compound, process for prodction thereof, and use thereof

An N-acyl-3-[4-(benzoylalkyl)piperazin-1-yl]-sydnonimine compound represented by the following formula ##STR1## wherein R.sup.1 represents a hydrogen atom or an alkyl group having 1 to 8 carbon atoms, PA1 R.sup.2 represents a lower alkyl group, PA1 a lower alkoxy group or a phenyl group, and PA1 n represents zero or an integer of 1 to 10, and its acid addition salt. The above sydnonimine compounds are useful for the treatment of troubles of the circulatory system and can be produced by contacting a 3-[4-(benzoylalkyl)-piperazin-1-yl]sydnonimine compound represented by the following formula ##STR2## wherein R.sup.1 and n are as defined, with a carboxylic acid represented by the following formula EQU R.sup.2 COOH wherein R.sup.2 is as defined.

This invention relates to a novel sydnonimine derivative useful for the 
treatment of troubles of the circulatory system, a process for its 
production, and a pharmaceutical composition for the treatment of the 
aforesaid troubles. 
More specifically, this invention relates to 
N-acyl-3-[4-(benzoylalkyl)piperazin-1-yl]sydnonimine compounds of the 
following general formula (1) 
##STR3## 
wherein R.sup.1 represents a hydrogen atom or an alkyl group having 1 to 8 
carbon atoms, 
R.sup.2 represents a lower-alkyl group, a lower alkoxy group or a phenyl 
group, and 
n represents 0 or an integer of from 1 to 10, 
and their acid addition salts. This invention also pertains to a process 
for the production of the compounds of formula (1) and their acid addition 
salts, and to a pharmaceutical composition comprising an amount, effective 
for the treatment of troubles of the circulatory system, of a compound of 
formula (1) or its acid addition salt and a pharmaceutically acceptable 
diluent or carrier. 
Known derivatives of N-acyl-3-(piperazin-1-yl)-sydnonimines are those in 
which a lower alkyl, arylalkyl or aryl group is bonded to nitrogen at the 
4-position of piperazine ring, and it is also known that these compounds 
are useful as medicines having unique pharmacological activities on the 
circulatory system and the central nervous system (Japanese Patent 
Publication No. 6265/1970). 
We have been engaged in developing new piperazinosydnonimine derivatives, 
and finally succeeded in synthesizing the N-acyl-piperazinosydnonimine 
compounds having a benzoylalkyl group as represented by the above formula 
(1) and their acid addition salts which have not been described previously 
in the literature. We have also found that the compounds of formula (1) 
and their acid addition salts have coronary blood flow increasing 
activity, peripheral blood flow increasing activity, and platelet 
aggregation inhibiting activity, and are useful for the prevention and 
treatment of troubles of the circulatory system as peripheral circulation 
improvers, coronary artery dilators, cerebral thrombosis treating agents, 
etc. 
It is an object of this invention therefore to provide novel 
N-acyl-piperazinosydnonimine compounds of formula (1) and their acid 
addition salts. 
Another object of this invention is to provide a process for the production 
of the compounds of formula (1) and their acid addition salts. 
Still another object of this invention is to provide a pharmaceutical 
composition comprising a compound of formula (1) or its pharmaceutically 
acceptable acid addition salt as an active ingredient. 
The above and other objects and advantages of this invention will become 
more apparent from the following description. 
In the compounds of this invention represented by formula (1), the C.sub.1 
-C.sub.8 alkyl group for R.sup.1 may be a linear or branched alkyl group 
such as methyl, ethyl, propyl, isopropyl, butyl, sec-butyl, tert-butyl and 
pentyl. The lower alkyl group, preferably a C.sub.1 -C.sub.4 alkyl group, 
for R.sup.2 in formula (1), may be a linear or branched lower alkyl group 
such as methyl, ethyl, propyl, isopropyl and butyl, and the lower alkoxy 
group, preferably a C.sub.1 -C.sub.4 alkoxy group, for R.sup.2 may be a 
linear or branched lower alkoxy group such as methoxy, ethoxy, propoxy, 
isopropoxy, and tert-butoxy. In formula (1), n represents zero or an 
integer of from 1 to 10, preferably zero or an integer of from 1 to 7. 
The acid addition salts of the compounds of formula (1) are preferably 
pharmaceutically acceptable acid addition salts. For example, they are 
salts with inorganic acids such as hydrochloric acid, nitric acid, 
sulfuric acid and phosphoric acid, and salts with organic acids such as 
formic acid, acetic acid, propionic acid, alkylsulfonic acids (e.g., 
methanesulfonic acid, ethanesulfonic acid and isothionic acid), 
arylsulfonic acids (e.g., benzenesulfonic acid and p-toluenesulfonic 
acids), oxalic acid, maleic acid and malic acid. 
Examples of preferred compounds of formula (1) and their acid addition 
salts are as follows: 
N-ethoxycarbonyl-3-[4-(4-benzoylbutyl)piperazin-1-yl)sydnonimine and its 
acid addition salts; 
N-acetyl-3-[4-(benzoylmethyl)piperazin-1-yl]-sydnonimine and its acid 
addition salts; 
N-benzoyl-3-[4-(benzoylmethyl)piperazin-1-yl]-sydnonimine and its acid 
addition salts; 
N-ethoxycarbonyl-3-[4-(8-benzoyloctyl)piperazin-1-yl)sydnonimine and its 
acid addition salts; 
N-benzoyl-3-[4-(4-benzoyl-6-methylheptyl)-piperazin-1-yl]sydnonimine and 
its acid addition salts; and 
N-ethoxycarbonyl-3-[4-(benzoylmethyl)piperazin-1-yl]sydnonimine and its 
acid addition salts. 
The compounds of formula (1) and their acid addition salts can be produced 
easily by contacting a 3-[4-(benzoylalkyl)piperazin-1-yl]sydnonimine 
compound represented by the following formula (2) 
##STR4## 
wherein R.sup.1 represents a hydrogen atom or an alkyl group having 1 to 8 
carbon atoms, 
and n represents zero or an integer of 1 to 10, 
with a carboxylic acid represented by the following formula (3) 
EQU R.sup.2 COOH (3) 
wherein R.sup.2 represents a lower alkyl group, 
a lower alkoxy group or a phenyl group, 
or a reactive derivative thereof. 
Examples of the reactive derivative of the carboxylic acid of formula (3) 
include halides, anhydrides and active esters of the carboxylic acids of 
formula (3). Illustrative of these reactive derivatives are anhydrides of 
the carboxylic acids of formula (3), halides, such as chlorides and 
bromides, of the carboxylic acids of formula (3), and active esters, such 
as 2,4-dinitrophenyl esters and phenyl thioesters, of the carboxylic acids 
of formula (3). When the carboxylic acid of formula (3) itself is used, it 
is preferred to carry out the reaction in the presence of a 
dehydrocondensing agent such as dicyclohexylcarbodiimide. 
Since the condensing reaction between the compound of formula (2) and the 
compound of formula (3) is promoted in the presence of a tertiary amine, 
it is preferred to carry it out in pyridine or the like as a solvent. 
Other tertiary amines such as picoline, lutidine and triethylamine may 
also be used as the reaction solvent instead of pyridine. Or the reaction 
may be carried out in the presence of a catalytic amount of a tertiary 
amine in an aprotic solvent such as ether, dioxane, tetrahydrofuran and 
dimethylformamide. 
The reaction temperature may be properly selected, and for example, 
temperatures of from about -20.degree. C. to about 60.degree. C. are 
preferred. Usually, the reaction can be carried out at room temperature. 
The reaction time may also be properly selected. It may vary depending 
upon the reaction temperature, and is, for example, up to about 24 hours. 
The desired compound of formula (1) may be obtained from the reaction 
mixture by, for example, diluting the reaction mixture with water and 
separating the precipitated compound of formula (1); or by evaporating the 
reaction solvent from the reaction mixture and extracting the residue with 
a solvent. The desired compound of formula (1) may be purified by known 
purifying means such as recrystallization and column chromatography. 
An acid addition salt of the compound of formula (1) of this invention may 
be prepared by, for example, dissolving the compound of formula (1) in an 
alcoholic solvent, and adding about one equivalent of an acid. In this 
case, the acid addition salt is generally isolated as crystals. 
The starting compound of formula (2) used in the process of this invention 
is also a novel compound not described in the literature, and can be 
produced, for example, by contacting a 
4-(benzoylalkyl)-1-(N-nitrosocyanomethylamino)piperazine represented by 
the following formula (4) 
##STR5## 
wherein R.sup.1 and n are as defined, with an acid to induce cyclization 
reaction. 
The compound of formula (4) can be easily produced, for example, by 
introducing a nitroso group into a 
4-(benzoylalkyl)-1-(cyanomethylamino)piperazine of the following formula 
(5) 
##STR6## 
wherein R.sup.1 and n are as defined with regard to formula (1). 
The compound of formula (5) can be produced easily from a benzoylalkyl 
halide, for example. The synthetic route of the compound of formula (2) 
including steps of forming the staring compounds can be schematically 
shown as follows: 
##STR7## 
In the above formulae, X represents a halogen atom such as chlorine or 
bromine, and R.sup.1 and n are as defined with regard to formula (1). 
The compound of formula (5) can be produced, for example, by the following 
method. 
A benzoylalkyl halide is reacted with 1-(ethoxycarbonylamino)piperazine in 
the presence of an excessive amount of an alkali bicarbonate to give a 
4-(benzoylalkyl)-1-(ethoxycarbonylamino)piperazine. This reaction is 
carried out under heat in an alcohol solvent such as methanol, ethanol, 
isopropanol or butanol. The reaction product is isolated by solvent 
extraction. If desired, it may be purified by recrystallization. The 
resulting 4-(benzoylalkyl)-1-(ethoxycarbonylamino)piperazine is heated 
together with an alkali such as potassium hydroxide or sodium hydroxide, 
whereby hydrolysis and subsequently decarboxylation take place to yield a 
4-(benzoylalkyl)-aminopiperazine. This hydrolysis and decarboxylation 
reaction is carried out in an alcohol solvent such as ethanol or methanol 
or a hydrous alcohol solvent such as hydrous ethanol or methanol at the 
boiling point of the solvent. The resulting 
4-substituted-1-aminopiperazine can be isolated by solvent extraction. 
Usually, it is advantageous to use the reaction mixture directly in the 
subsequent step. The resulting 4-substituted-1-aminopiperazine solution is 
then neutralized by adding one equivalent of hydrochloric acid, and 
reacted first with formaldehyde sodium bisulfite hydrate and then with 
potassium cyanide to produce a cyanomethylaminopiperazine derivative. This 
cyanomethylation reaction may be carried out at a temperature of 
50.degree. to 70.degree. C. The cyanomethylation product is isolated by 
extraction with an organic solvent, and if required, purified by 
recrystallization. The cyanomethylated derivative may be converted to its 
dihydrochloride by introducing hydrogen chloride into an ethanolic 
solution of it. 
From the compound of formula (5) which can be obtained as above, the 
compound of formula (4) may be produced by introducing a nitroso group 
into the compound of formula (5) which can be obtained as shown above. 
This reaction can be carried out by utilizing known methods of 
nitrosozation. For example, it can be effected by reacting the 
dihydrochloride of the compound of formula (5) with an alkali nitrite such 
as sodium nitrite or potassium nitrite at a relatively low temperature. 
The reaction can be performed by contacting the dihydrochloride of the 
compound of formula (5) with the alkali nitrite in an aqueous medium at a 
relatively low temperature of, for example, about -5.degree. C. to about 
10.degree. C. The reaction proceeds rapidly, and ends in 0.5 to 5 hours. 
The reaction product is isolated from the reaction mixture by solvent 
extraction. Without particularly purifying it, the product is used in the 
subsequent cyclization step. As required, however, it may be purified by 
recrystallization, etc. 
By contacting the compound of formula (4) with an acid in the presence of a 
solvent, the compound of formula (2) is obtained in the form of its acid 
addition salt. Any inorganic or organic acid can be used in this 
cyclization reaction. Preferably, acids capable of forming 
pharmaceutically acceptable acid addition salts are used. Examples of 
preferred acids include such inorganic acids as hydrochloric acid, nitric 
acid, sulfuric acid and phosphoric acid and such organic acids as formic 
acid, acetic acid, propionic acid, alkylsulfonic acids (e.g., 
methanesulfonic acid, ethanesulfonic acid and isothionic acid), 
arylsulfonic acids (e.g., benzenesulfonic acid and p-toluenesulfonic 
acid), oxalic acid, maleic acid and malic acid. 
Alcohols are preferred as the solvent used for the cyclization reaction, 
and lower alcohols such as methanol and ethanol may be cited as typical 
examples. The reaction is carried out preferably at relatively low 
temperature, for example about 0.degree. C. to room temperature. Too high 
temperatures may result in undesirable side-reactions. The reaction time 
can be properly chosen, and may, for example, be about 5 to about 24 
hours. The resulting acid addition salt may be isolated from the reaction 
mixture as a solid, and purified by recrystallization. 
When the compound of formula (2) which can be obtained as above is used as 
a starting material for the compound of formula (1) of this invention, it 
may be used in the form of its acid addition salt. 
The compounds of formula (1) of this invention show coronary blood flow 
increasing activity, but in an in vitro test, they do not show a relaxing 
activity on an extracted arterial vessel and an inhibitory activity on 
platelet aggregation. However, they do show an activity of increasing 
cerebral local blood flows in an in vivo test, and platelet aggregation 
inhibiting activity in an ex vivo test. The foregoing fact shows that the 
compounds of formula (1) are prodrugs which are activated upon undergoing 
metabolism in vivo. Furthermore, the compounds of formula (2) show a 
strong arterial vessel relaxing activity and a strong platelet aggregation 
inhibiting activity in in vitro tests. It is presumed from this fact that 
the active metabolite of the compound of formula (1) of this invention 
will be the 3-[4-(benzoylalkyl)piperazin-1-yl]sydnonimine of formula (2). 
Table 1 summarizes the results of in vitro tests in which the human 
platelet aggregation inyibitory activity of the 
3-[4-(benzoylalkyl)piperazin-1-yl]sydnonimines of formula (2) and their 
relaxing activity on the extracted mesenteric artery of a rabbit were 
examined. 
The mesenteric artery relaxing activity is shown by the conversion (.mu.M) 
of a drug required to induce 50% of the maximum relaxation, and the 
platelet aggregation inhibiting activity, by the concentration (.mu.M) of 
a drug required to inhibit collagen-induced platelet aggregation to an 
extent of 50%. 
TABLE 1 
______________________________________ 
##STR8## 
Mesenteric artery 
Platelet aggre- 
relaxing activity 
gation inhibiting 
R n (.mu.M) activity (.mu.M) 
______________________________________ 
H 0 0.16 0.14 
H 2 2.3 5.4 
H 3 0.2 3.4 
H 4 3.0 6.3 
H 5 0.12 0.94 
H 7 0.058 0.028 
iso-C.sub.4 H.sub.9 
3 1.3 11.0 
______________________________________ 
For example, in a test for inhibition of platelet aggregation using a 
rabbit, the activity of the compound of formula (1) lasts longer than the 
activity of the compound of formula (2), and this shows the compound of 
formula (1) to have an excellent property as a medicine. 
Pharmacological tests on 
N-carboethoxy-3-[4-(4-benzoylbutyl)piperazin-1-yl]sydnonimine (compound 
A), a typical example of the compound of formula (1) of this invention, 
are shown below. 
Pharmacological tests 
(1) Activity on the extracted heart 
The increase or decrease of the coronary blood flow was examined by the 
Langendorf's method using the extracted heart of a guinea pig. When 0.1 ml 
of the compound A (10.sup.-4 g/ml solution) was injected, a 14% increase 
was observed in the coronary blood flow. On the other hand, when 0.1 ml of 
morsydmine (10.sup.-4 g/ml solution) was injected, no increase in the 
coronary blood flow was observed. 
(2) Activity on the local cerebral blood flow 
(a) Activity on the hippocampus and amygdaloid nucleus (by the hydrogen gas 
clearance method) Rabbits having a body weight of about 3 kg, five per 
group, were used. A tracheal cannula was inserted into each rabbit under 
sodium pentobarbital anesthesia, and under artificial respiration, 
gallamine triethiodide was intravenously administered in a dose of 2 mg/kg 
to immobilize it. The animal was then fixed to a brain stereotaxic 
apparatus (Todai Noken type). Gallamine triethiodide was also 
intramuscularly administered in a dose of 3 mg/kg every one hour. 
The local cerebral blood flow was measured by the hydrogen gas clearance 
method (UH meter, PHG-201, manufactured by Unique Medical Co., Ltd.). 
Platinum electrodes having a diameter of 300 .mu.m and coated with an 
epoxy resin were inserted in the hippocampus (P:4, L:5, H:+5) and the 
amygdaloid nucleus (A:2, L:6, H:-6) in accordance with the brain atlas of 
Sawyer et al. An indifferent electrode was placed under the skin of the 
head and fixed there. After a waiting time of more than 30 minutes until 
the blood flow was stabilized, about 8% hydrogen gas was caused to be 
inhaled for three minutes through a side tube of the tracheal cannula, and 
a clearance curve was drawn. The resulting curve was plotted 
semilogarithmically, and the half-time period (T 1/2) was determined by 
the initial slope method. The blood flow was calculated from the following 
equation. 
EQU Blood flow F=69.3/T 1/2(ml/min./100 g) 
The blood flow was measured every thirty minutes. When the blood flow 
became constant, the test drug or the control drug was intravenously 
administered, and the measurement was made until 1 hour after the 
administration. The change in the blood flow was expressed by the percent 
change based on the blood flow before the administration of the drug. When 
the compound A (0.5 mg/kg) was administered as the test drug, an increase 
of 5 to 15% was observed at the hippocampus and an increase of about 10%, 
at the amygdaloid nucleus. When the morsydmine (0.5 mg/kg) as a control 
drug was administered, an increase of 10 to 20% was observed at the 
hippocampus and an increase of about 15%, at the amygdaloid nucleus. Thus, 
the compound A has as strong an activity on the blood flow of the 
hippocampus and the amigdaloid nucleus as the morsydmine. 
(b) Activity on the cerebral cortex (a cross thermocouple method) 
Male rabbits having a body weight of about 3 kg, five per group, were used. 
Under sodium pentobarbital anesthesia, a tracheal cannula was inserted 
into each rabbits, and under artificial respiration, 2 mg of gallamine 
triethiodide was intravenously injected to immobilize the animals. The 
animals were each fixed to a brain stereotaxic apparatus (Todai Noken 
type). An element of the double needle type (WN-301, manufactured by 
Unique Medical Co.) was inserted into the frontal contex through a hole 
provided by a dental drill, and variations in potential were recorded. 
After the blood flow was stabilized, the test drug and a control drug were 
each administered through a cannula inserted into the retroauricular vein 
of the right ear. The percent increase in the blood flow was calculated by 
taking the blood flow at death as 0 and the blood flow before drug 
administration as 100%. When the compound A (0.5 mg/kg) was administered 
as the test drug, the blood flow increased by 10 to 20%. But when the 
control drug, morsydmine, (0.5 mg/kg) was administered, no increase in the 
blood flow was noted. 
(3) Platelet aggregation inhibiting action 
Rabbits having a body weight of about 3 kg, three per group, were used. In 
a group, the compound A was administered intravenously in a dose of 5 
mg/kg to one rabbit; 3-[4-(4-benzoylbutyl)piperazin-1-yl]sydnonimine 
dihydrochloride (compound A') was administered to another rabbit 
intravenously in a dose of 5 mg/kg; and the remaining one rabbit was used 
as a control. The blood was drawn from each of the rabbits periodically. 
Citric acid was added to each of the blood samples, and the mixture was 
centrifuged to separate the plasma. 
A solution containing 10 .mu.M of ADP (adenosine diphosphate) was added to 
0.4 ml of each of the plasma samples, and the induced platelet aggregation 
was measured by using an aggregometer. By a similar method, platelet 
aggregation induced by collagen (an extract of the bovine tendon) was 
measured. 
The results of the test were expressed by the percent inhibition of 
platelet aggregation determined by taking the percent inhibition for the 
control animal as 0. 
TABLE 2 
______________________________________ 
Percent inhibition of platelet aggregation 
Platelet 
aggregation 
Time after administration 
inhibiting 
(minutes) 
Compound agent 5 30 60 180 300 
______________________________________ 
Compound A 
ADP 16 99 96 87 37 
Collagen 29 98 100 91 61 
Compound A' 
ADP 97 100 33 9 0 
Collagen 95 99 59 5 0 
______________________________________ 
Thus, according to this invention, there can be provided a pharmaceutical 
composition comprising an amount, effective for treating troubles of the 
circulatory system, of an 
N-acyl-3-[4-(benzoylalkyl)piperazin-1-yl]sydnonimine compound of the 
following formula (1) 
##STR9## 
wherein R.sup.1 represents a hydrogen atom or an alkyl group having 1 to 8 
carbon atoms, 
R.sup.2 represents a lower alkyl group, a lower alkoxy group or a phenyl 
group and 
n represents zero or an integer of from 1 to 10, 
or its pharmaceutically acceptable acid addition salt, as a prodrug, and a 
pharmaceutically acceptable diluent or carrier. 
The pharmaceutical composition of this invention may be in various forms 
prepared by methods known in the pharmaceutical field. For example, it may 
be in the form of powders, granules, tablets, injections, capsules, etc. 
The pharmaceutically acceptable diluent or carrier used in the 
pharmaceutical composition of this invention may be any liquid or solid 
diluent or carrier known in pharmaceutical fields. Examples of such a 
liquid or solid diluent or carrier include distilled water, ethanol, 
isopropanol, propylene glycol, glycerol, lactose, corn starch, crystalline 
cellulose, talc, stearic acid, magnesium stearate, carboxymethyl 
cellulose, hydroxypropyl cellulose, gum arabic and beeswax. 
The pharmaceutical composition of this invention may contain the compound 
of formula (1) in any amount which is effective for the treatment of 
troubles of the circulatory system. For example, its amount is 0.01 to 99% 
by weight based on the weight of the pharmaceutical composition. The dose 
of the compound of formula (1) in accordance with this invention may, for 
example, be about 0.1 to about 100 mg/body/day, preferably about 0.3 to 
about 30 mg/body/day. The toxicity of the compounds (1) of this invention 
is extremely low as shown by the results of a test described hereinbelow. 
Preferred examples of the compounds of formula (1) are those in which 
R.sup.1 is a hydrogen atom or an isobutyl group, and their acid addition 
salts. Compounds of formula (1) in which n is 0, 2, 3, 4, 5 or 7 and their 
acid addition salts are also preferred. The especially preferred compound 
is N-carboethoxy-3-[4-(4-benzoylbutyl)piperazin-1-yl]sydnonimine. 
The acute toxicity of the in vivo active type of this typical compound as a 
prodrug was tested by using male dd-strain mice (body weight 16 to 20 g). 
It was found that the LD.sub.50 of the present compound A was 91 mg/kg in 
intravenous administration, 350 mg/kg in subcutaneous administration, and 
750 mg/kg in oral administration.