Synthesis, antiarrhythmic, and antihypertensive effects of novel 1-substituted pyrrolidin-2-one and pyrrolidine derivatives with adrenolytic activity

Article abstract of DOI:10.1016/S0223-5234(01)01321-6

A series of 1-substituted pyrrolidin-2-one and pyrrolidine derivatives were synthesised and tested for electrocardiographic, antiarrhythmic, and antihypertensive activity as well as for α₁- and α₂-adrenoceptors binding affinities. Among the newly synthesised derivatives several compounds with 3-(4-arylpiperazin-1-yl)propyl moiety displayed strong antiarrhythmic (7a-12a) and antihypertensive (7a-11a) activities. Compound 11a, 1-[2-acetoxy-3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-one, was the most potent in this series. The pharmacological results and binding studies suggest that their antiarrhythmic and hypotensive effects may be related to their α-adrenolytic properties, and that those properties depend on the presence of the 1-phenylpiperazine moiety with a methoxy- or chloro- substituent in the ortho position in the phenyl ring.

Full text of DOI:10.1016/S0223-5234(01)01321-6

European Journal of Medicinal Chemistry 37 (2002) 183–195
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Original article
Synthesis, antiarrhythmic, and antihypertensive effects of novel
1-substituted pyrrolidin-2-one and pyrrolidine derivatives with
adrenolytic activity
Barbara Malawska a,*, Katarzyna Kulig a, Barbara Filipek b, Jacek Sapa b,
Dorota Macia˛g b, Małgorzata Zygmunt b, Lucyna Antkiewicz-Michaluk c
a Department of Pharmaceutical Chemistry, Collegium Medicum of Jagiellonian Uni6ersity, 9 Medyczna St., 30-688 Krako´w, Poland
b Laboratory of Pharmacological Screening, Collegium Medicum of Jagiellonian Uni6ersity, 9 Medyczna St., 30-688 Krako´w, Poland
c Institute of Pharmacology Polish Academy of Sciences, 12 Sme˛tna St., 31-343 Krako´w, Poland
Received 26 January 2001; received in revised form 13 June 2001; accepted 7 November 2001
Abstract
A series of 1-substituted pyrrolidin-2-one and pyrrolidine derivatives were synthesised and tested for electrocardiographic,
antiarrhythmic, and antihypertensive activity as well as for a1- and a2-adrenoceptors binding affinities. Among the newly
synthesised derivatives several compounds with 3-(4-arylpiperazin-1-yl)propyl moiety displayed strong antiarrhythmic (7a–12a)
and antihypertensive (7a–11a) activities. Compound 11a, 1-[2-acetoxy-3-[4-(2-methoxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-
one, was the most potent in this series. The pharmacological results and binding studies suggest that their antiarrhythmic and
hypotensive effects may be related to their a-adrenolytic properties, and that those properties depend on the presence of the
´
1-phenylpiperazine moiety with a methoxy- or chloro- substituent in the ortho position in the phenyl ring. © 2002 Editions
scientifiques et me´dicales Elsevier SAS. All rights reserved.
Keywords: N-(4-Arylpiperazin-1-yl)propylpyrrolidin-2-one and pyrrolidine derivatives; Antiarrhythmic; Antihypertensive; a-Adrenoceptors block-
ing activity
coronary artery occlusion and reperfusion in the iso-
lated rat’s hearts, demonstrated potent local anaesthetic
properties and depressed the depolarisation phase of
the action potential of cardiac cells [2]. According to
Vaughan Williams classification [4], MG-1 could be
considered as a class Ia antiarrhythmic drug. Moreover,
MG-1 showed strong hypotensive/antihypertensive ef-
fect and affinity for a1- and a2-adrenoceptors [5].
Previously, we have described the synthesis and the
antiarrhythmic and antihypertensive activities of a se-
ries of 1-substituted pyrrolidin-2-one and pyrrolidine
derivatives [5]. Some of them slightly decreased the
heart rate, prolonged P–Q, Q–T intervals and QRS
complex. Compound 1-[2-hydroxy-3-(4-phenylpipe-
razin-1-yl)propyl]pyrrolidine possessed potent an-
tiarrhythmic activity, slight hypotensive properties and
affinity for a1- and a2-adrenoceptors. Our earlier inves-
tigations suggested that the antiarrhythmic effect of
MG-1 may be related to their a-adrenolytic properties.
1. Introduction
In the search for new antiarrhythmics among deriva-
tives of pyrrolidin-2-one, we obtained MG-1, 1-[2-hy-
droxy-3-(4-phenylpiperazin-1-yl)propyl]pyrrolidin-2-one
[1–3] (Fig. 1) which became a lead structure for further
investigations. MG-1 attenuated or prevented the
adrenaline- and barium chloride-induced arrhythmia,
statistically diminished arrhythmias associated with
Fig. 1. Chemical structure of MG-1.
* Correspondence and reprints.
E-mail address: mfmalaws@cyf-kr.edu.pl (B. Malawska).
´
0223-5234/02/$ - see front matter © 2002 Editions scientifiques et me´dicales Elsevier SAS. All rights reserved.
PII: S0223-5234(01)01321-6

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B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
It has been known that non-selective a-blocking
pounds 7 and 8 enabled to obtain appropriate acetoxy
derivatives such as 1-[2-acetoxy-3-[4-(2-methoxy-
phenyl)- or 2-acetoxy-3-[4-(2-chlorophenyl)piperazin-1-
yl]propyl]pyrrolidin-2-one. The above compounds were
isolated as a water soluble hydrochloride salt (10a,
11a). Reduction of 7 with lithium aluminium hydride
(LAH) led to 1-[2-hydroxy-3-[4-(2-methoxyphenyl)-
piperazin-1-yl]propyl]pyrrolidine (12), which was iso-
lated as a maleic acid salt (12a). The course of reaction
is presented in Fig. 3. The structures of these new
compounds were established by elemental analysis and
spectral data [15].
agents (phentolamine, prazosine) in relatively high
doses diminished or prevented reperfusion arrhythmias
and cardiac arrhythmias caused by adrenaline intoxica-
tion [6–9]. On the other hand, blocking the action of
adrenergic neurotransmitters on the a1-adrenoceptor is
a well-known approach for the clinical treatment of
hypertension [10,11]. It was also recently reported that
a1-adrenergic receptors mediate both vascular and
lower urinary tract tone. Several non-subtype selective
a1-adrenergic receptors antagonists, such as prazosin
and terazosin, are used to treat both hypertension and
benign prostatic hyperplasia (BPH) [12–14].
Taking into consideration the pharmacologically in-
teresting properties shown by 1-substituted pyrrolidin-
2-one derivatives, we decided to continue our studies
directed toward the synthesis of the products with
potential a-adrenolytic activity.
3. Pharmacology
In the present study, several pharmacological tests
were carried out to assess the effect on normal electro-
cardiogram (ECG), antiarrhythmic, hypotensive and
a-adrenergic blocking activities of novel pyrrolidin-2-
one and pyrrolidine derivatives.
In this paper, we report the synthesis and pharmaco-
logical results of a new series of MG-1 derivatives.
Thus, the 1-phenylpiperazine moiety was replaced by
an arylalkylamine group such as benzylamine or 2-
chloro, 4-methoxy, 3,4-dimethoxy substituted benzy-
lamine; the phenyl ring of MG-1 was replaced by
pyrimidine, diphenylmethyl group or 2-chloro-, 4-
chloro-, 2-methoxyphenyl. Using previously structure–
activity relationships as a guide, we have chosen novel
derivatives of lead structure for further modifications
within hydroxy group and pyrrolidin-2-one ring. The
newly synthesised compounds (in form of salts) were
tested for antiarrhythmic, and antihypertensive activity
as well as for a1- and a2-adrenoceptors binding
affinities.
The effect on ECG intervals and the heart rate (the
number of cardiac beats per minute) was determined
for all compounds in a dose of 1/10 and 1/5 LD50. The
novel pyrrolidin-2-one derivatives (1a–5a and 12a) in
these two doses, and compounds 6a, 8a and 10a in the
dose of 1/10 LD50 did not significantly affect the nor-
mal ECG (not included in Table 1). Electrocardio-
graphic experiments showed that compounds 7a, 9a
and 11a affected the normal ECG in a dose of 1/10
LD50, i.e. significantly decreased the number of cardiac
beats per minute (7a, 9a), prolonged P–Q intervals
(11a) and QRS complex (9a), (Table 1). On the other
hand compounds 7a and 11a administered in a dose of
1/5 LD50 induced disturbances of cardiac rhythm.
Compounds 6a, 8a–10a changed the ECG pattern in a
dose of 1/5 LD50 significantly decreased the number of
cardiac beats per minute (9a), prolonged P–Q (6a) and
QT (6a, 8a, 9a and 10a) intervals and QRS complex
(6a). The electrocardiographic changes observed after
administration of these compounds were similar to
those seen after administration of MG-1 and quinidine
[5].
All compounds were tested in two arrhythmia’s mo-
dels (prophylactic and therapeutic) using adrenaline-
and barium chloride-induced arrhythmia [16]. The ED50
values and therapeutic index of prophylactic an-
tiarrhythmic activity are presented in Table 2. Among
the studied compounds, only compounds 7a–12a inhi-
bited adrenaline-induced arrhythmia in the anaes-
thetised rat by more than 50% after intravenous dosing.
These compounds also significantly reduced mortality.
Compounds 7a, 8a and 11a, given orally 60 min before
adrenaline, also diminished the number of extrasystoles
by 50% or more in rats and decreased or prevented
mortality of these animals. The data reported in Table
2. Chemistry
1-(2,3-Epoxypropyl)pyrrolidin-2-one was used as a
starting material for synthesis of new 1-substituted
pyrrolidin-2-one or pyrrolidine derivatives. The aminol-
ysis of 1-(2,3-epoxypropyl)pyrrolidin-2-one with benzyl
or substituted benzylamines such as: 2-chloro-, 3-
methoxy- or 3,4-dimethoxybenzylamine gave relevant
1-[(3-benzylamino)-2-hydroxypropyl]pyrrolidin-2-one
derivatives (1–4). However, the similar reaction with
N-substituted
methoxyphenyl-; pyrimidine or diphenylmethyl) led to
obtain relative 1-[2-hydroxy-3-(4-arylpiperazin-1-
piperazine
(2-chlorophenyl-,
2-
yl)propyl]pyrrolidin-2-one (5–9). The yields of that re-
actions were in range from 59 to 76%. Compounds
were isolated as a free bases and a water soluble
hydrochloric salt. The course of reactions is presented
at Fig. 2. Compounds 7 and 8 were chosen for farther
synthesis as they are the most active derivatives in
pharmacological investigations. Acetylation of com-

B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
185
Fig. 2. Reagents and conditions: (i) n-propanol, reflux, 12 h; (ii) HCl, anhydrous ethanol.
Fig. 3. Reagents and conditions: (i) (CH3CO)2O, pyridine, 50 °C, 5 h; (ii) ethanol solution HCl gas; (iii) LAH, THF, room temperature; (iv)
ethanol solution (HCCOOH)2.
2 suggest that special attention should be paid to
compound 11a, which showed more profitable thera-
peutic index than MG-1. The other compounds pos-
sessed therapeutic index a little more profitable (8a) or
worse (7a, 9a, 10a, 12a) than that of reference com-
pound. Compounds 7a, 8a and 11a possessed prophy-

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B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
lactic antiarrhythmic properties also after oral applica-
tion, but this effect was weaker than that given in the
reference compound MG-1. These compounds adminis-
tered 15 min before barium chloride reduced the num-
ber of premature ventricular beats, prevented in a
statistically significant manner occurrence of ventricular
fibrillation and protected the rats against fatal conse-
quence of barium chloride administration. The ED50 (a
dose producing a 50% inhibition of premature ventricu-
lar beats) and LD50/ED50 are presented in Table 2. The
ED50 values after intravenous administration were simi-
lar (7a), about 1.6 times lower (8a), or about 1.5 times
higher (11a) than that of MG-1. Compounds 9a, 10a
and 12a did not change the occurrence of disturbances
in this barium chloride-induced model of arrhythmia.
Compounds 7a–12a were evaluated for therapeutic
antiarrhythmic activity. Compounds 7a, 8a and 12a,
administered intravenously at the peak of adrenalinein-
duced arrhythmia converted the cardiac arrhythmias
into regular sinus rhythms in more than 50% animals.
The therapeutic antiarrhythmic activity data are shown
in Table 3. From the data presented it follows that
compounds 7a, 8a and 12a were about 2–4 times less
effective than that of reference compound. Similarly to
MG-1, these compounds did not abolish cardiac
arrhythmias caused by barium chloride intoxication.
Hypotensive activity of compounds 1a–12a was de-
termined after iv administration to normotensive anaes-
thetised rats. The results are presented in Fig. 4. The
studied compounds injected intravenously in doses cor-
Table 1
Effects of an intravenous injection of the investigated compounds on heart rate and ECG intervals in anaesthetised male Wistar rats (60 mg
thiopental kg−1 intraperitoneally)
Compound
Dose (mg kg−1
)
Parameters
Time of observation (min)
0
1
5
15
6a
14
beats per minute
P–Q (ms)
QRS (ms)
364.5910.5
52.592.5
17.090.9
70.094.1
320.2922
55.092.9
19.090.6 *
88.094.8 ***
333.2929.5
55.092.9
18.590.5
325.2923.5
65.092.9 ***
19.090.6 *
1/5 LD50
Q–T (ms)
85.092.9 **
88.092.5 ***
7a
8a
9a
14.5
beats per minute
P–Q (ms)
QRS (ms)
401.3913
53.393.3
20.790.7
76.793.4
347914
63.393.3
20.790.7
83.393.0
336921.7
56.793.4
20.790.7
86.793.3
327929.9 *
63.393.3
20.790.8
83.393.3
1/10 LD50
Q–T (ms)
16
beats per minute
P–Q (ms)
QRS (ms)
378919.7
62.592.5
19.590.5
75.092.9
343.5910.5
65.092.9
20.590.5
82.592.5
378919.7
62.592.5
20.590.5
85.092.9 *
359.2927.8
67.594.8
20.590.5
1/5 LD50
Q–T (ms)
85.092.9 *
10
beats per minute
P–Q (ms)
QRS (ms)
402915.6
55.092.9
18.590.5
77.592.5
384.2920.3
55.092.9
18.590.5
83.092.4
360.2916.5
55.793.3
19.790.6
77.592.5
345.7918 *
61.291.2
20.290.2 *
82.792.4
1/10 LD50
Q–T (ms)
20
beats per minute
P–Q (ms)
QRS (ms)
388.8913.5
50.094.1
17.590.9
75.092.9
353.598.6 *
55.092.9
24.093.5
354912.1 *
57.597.5
24.093.5
324.595 ****
62.592.5
24.093.5
1/5 LD50
Q–T (ms)
88.092.5 ***
9090.2 ****
8892.5 ***
10a
11a
24
beats per minute
P–Q (ms)
QRS (ms)
378920.1
55.093.0
18.290.6
76.093.0
343911
350919.6
56.093.2
19.690.7
87.092.2 *
351926.7
58.093.6
19.690.9
87.092.2 *
55.093.0
18.590.5
86.092.1 *
1/5 LD50
Q–T (ms)
35
beats per minute
P–Q (ms)
QRS (ms)
364.5910.5
50.292.5
19.090.6
80.290.2
335.2915.4
5892.5 ***
20.590.5
367.5922.8
6090.2 ****
20.590.5
335.2915.4
6090.2 ****
20.590.5
1/10 LD50
Q–T (ms)
82.592.5
82.592.5
85.092.9
The data are the means of six experiments9S.E.M. Statistical analyses were performed using a one-way ANOVA test.
* PB0.05;
** PB0.02;
*** PB0.01;
**** PB0.001.

B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
187
Table 2
Prophylactic antiarrhythmic activity in anaesthetised rats
Compound
Route
Adrenaline-induced arrhythmia
Barium chloride-induced arrhythmia
ED50 (mg kg−1
)
LD50/ED50
ED50 (mg kg−1
)
LD50/ED50
7a
iv
po
12 (9.7–14.8)
151 (75.9–300.5)
12.1
5.3
11 (7.9–15.3)
–
13.2
–
8a
iv
po
2.7 (1.95–3.7)
65.5 (32.5–132)
29.6
5.3
7.1 (4.7–10.6)
11.3
–
–
9a
iv
po
13.5 (7.9–22.9)
7.4
–
–
–
–
–
–
10a
iv
po
8.8 (4.9–15.9)
13.6
–
–
–
–
–
–
11a
iv
po
4.9 (2.5–6.9)
110 (68.3–177)
83.3
6.7
17.5 (10.3–29.7)
–
20
–
12a
iv
po
12 (9.1–24.7)
12.1
–
–
–
–
–
MG-1
Propranolol
Quinidine
iv
po
7.6 (6.9–8.4)
29.0 (21.3–39.4)
21
10
11.3 (6.45–19.2)
31.0 (18.8–51.1)
14
9
iv
po
1.05 (0.64–1.73)
19.5 (14.5–26.1)
37
24
–
–
–
–
iv
po
8.7 (8.0–9.4)
38.0 (33.6–42.9)
6
15.6
–
–
–
–
Each value was obtained from three experimental groups. Each group consisted of six animals. The ED50 values and their confidence limits were
calculated according to the method of Litchfield and Wilcoxon [17].
Table 3
Therapeutic antiarrhythmic activity in anaesthetised rats
Compound
Route of administration
Suppression of arrhythmia induced by adrenaline ED50 (mg kg−1
)
Ratio LD50/ED50
7a
8a
iv
iv
iv
iv
iv
9.5 (6.3–14.2)
10.5 (8.27–13.3)
21.0 (15.7–28.1)
5.2 (3.1–8.0)
15.3
7.6
6.9
31
12a
MG-1
Quinidine
3.2 (1.7–6.0)
17
Each value was obtained from three experimental groups. Each group consisted of six animals. The ED50 values and their confidence limits were
calculated according to the method of Litchfield and Wilcoxon [17].
pounds 6a–12a, given intravenously in doses of 1/40–
1/10 LD50, significantly antagonised the pressor
response elicited by epinephrine. As shown in Figs. 6
and 10, the most active compounds were 7a and 11a
which blocked the pressor response up to dose 1/40
LD50. Compounds 7a (Fig. 6), 10a (Fig. 9) (1/10 LD50),
and 11a (Fig. 10) (1/40 LD50) also statistically signifi-
cant antagonised the pressor response to nore-
pinephrine. Compounds 7a, 8a, 10a, 11a significantly
reduced the pressor responses to methoxamine, tyra-
mine and DMPP. Compound 6a in a dose of 1/10 LD50
significantly increased the pressor response after
methoxamine.
responding to 1/40–1/10 LD50 had no effect on the
blood pressure (systolic and diastolic) (1a–6a and 12a)
or evoked directly after administration 44–15.6 (sys-
tolic) and 51–20.9% (diastolic) decreased in blood pres-
sure, which persisted for ca. 10–60 min or more (7a).
Their hypotensive effects were comparable to MG-1 [5].
Compounds with a significant hypotensive effect after
iv administration were also tested for hypotensive acti-
vity after intragastrically administration (7a–11a). Only
compounds 7a, 8a, 9a and 11a given in a dose of 1/10
LD50, significantly decreased the systolic (7a, 8a, 9a)
and/or diastolic pressure (7a, 8a, 9a, 11a) (Table 4).
To examine the mechanism of the hypotensive effects
of these compounds, we studied their influence on the
pressor responses to epinephrine, norepinephrine,
methoxamine, tyramine and DMPP (Figs. 5–11). Com-
Binding studies presented in Table 5. Compounds
6a–12a displaced [3H]prazosin from cortical binding
sites in low concentration range (Ki=0.27–2.9 mM).

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B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
derivatives of 3-[(4-arylpiperazin-1-yl)-propyl]pyrro-
lidin-2-one which contain ortho-chloro, ortho-methoxy
or para-chloro substituent in the phenyl ring (7a–11a),
similarly to MG-1 displayed strong antiarrhythmic and
antihypertensive activity. The replacement of the
arylpiperazine ring with the benzylamine, substituted
benzylamine group (1a–4a) or the phenylpiperazine
ring with pirimidinepiperazine (5a) or diphenyl-
methylpiperazine (6a) group led to the lack of activity.
Compound 12a, obtained by reduction of 7 exhibited
prophylactic and therapeutic antiarrhythmic activity in
the adrenaline induced model of arrhythmia. The
pyrrolidine derivative 12a had no effect on the blood
pressure. In order to further exploration structure–ac-
tivity relationship, acylation of the hydroxy group in
compounds 7 and 8 was effected to gave compounds
10a and 11a. These acylated derivatives showed both
antiarrhythmic and hypotensive effects. Compound 11a
showed enhanced activity (about seven times higher) in
comparison to the parent compounds when tested in
the prophylactic antiarrhythmic activity. Among the
hypotensive active derivatives of pyrrolidin-2-one 7a–
11a, compounds 7a and 11a with ortho-methoxy-
phenylpiperazine substituent were the most potent.
It is generally accepted that a1-antagonist reversed
the pressor response to epinephrine, depressed the pres-
sor effect of methoxamine, tyramine and DMPP and
potentiated the pressor response to norepinephrine,
while a2-antagonists antagonised the hypertensive effect
of norepinephrine, reversed the hypertension induced
by epinephrine, no changed or potentiated the pressor
response to tyramine or DMPP [18–20]. Some of inves-
tigated compounds significantly antagonised the pressor
response to epinephrine (6a–12a), norepinephrine (7a,
10a, 11a), methoxamine (7a–11a), tyramine and DMPP
(7a–11a) or no changed the pressor responses to
norepinephrine.
These in vivo experiments with a non-selective ago-
nist of a1 and a2 such as epinephrine or norepinephrine
and a selective agonist of a1-adrenoceptor such as
methoxamine suggest in agreement with previous re-
sults that hypotensive effects of the compounds 7a–11a
were related to their adrenolytic properties.
Compounds 6a–12a were identified as ligands for the
a1-adrenoceptors. When the ortho-chloro or ortho-
methoxy group was introduced into the phenyl ring of
MG-1, the affinity increased, in agreement with reports
showing that the introduction of these two substituents
to the ortho position of the phenyl ring of the
phenylpiperazine may produce potent a1-adrenoceptor
antagonists [21,22]. Compound 10a was the most po-
tent and selective compound in this series with 12-fold
greater affinity than MG-1. Investigated compounds
displayed lower affinity for a2-adrenoceptors than for
a1-adrenoceptors. The a2/a1-selectivity ratio of com-
pounds 7a, 8a, 10a and 11a were higher than that of
Fig. 4. Hypotensive activity of tested compounds in anesthezised
normotensive rats.
The shape of the curves suggested competitive binding.
Compounds 6a–8a and 10a–12a also displaced
[3H]clonidine from its binding sites in mM concentra-
tions (Ki=5.3–80). Only compound 8a weakly dis-
placed [3H]-CGP12177 from cortical binding sites.
The acute toxicity of the investigated compounds
1a–12a was determined in mice after intravenous or
intragastrically administration according to Litchfield
and Wilcoxon [17], the LD50 values are presented in
Table 6.
4. Discussion
In previous studies, we have demonstrated that the
compound MG-1 reduced significantly the blood pres-
sure in normotensive and hypertensive anaesthetised
rats, and reversed the pressor response to adrenaline.
Preliminary pharmacological assessment revealed that

B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
189
Table 4
Hypotensive activity of tested compounds in anaesthetised normotensive rats after orally administration in the dose corresponding
Compound
Dose (mg kg−1
)
Blood pressure
(mmHg9S.E.M)
Before
Time of observation (min)
10
30
97.0912.1 **
60
7a
80.0 po
34.8 po
59.5 po
40.0 po
73.3 po
systolic
diastolic
147.399.1
123.3913.6
96.799.2 **
64.793.2 ***
118.8917.0
90.3918.3
73.7915.5 **
8a
systolic
diastolic
132.493.3
111.094.5
119.893.1 *
97.092.2 *
124.092.8
99.294.0
126.593.5
103.294.3
9a
systolic
diastolic
136.292.0
106.694.6
127.495.7
95.095.3 **
19.894.0 **
91.692.2 ***
127.695.5
93.693.6 *
10a
11a
systolic
diastolic
14391.4
11598.2
14094.2
11294.2
13492.8
10898.3
129.098.6
115.094.2
systolic
diastolic
150.091.2
134.793.3
128.0912.0
115.399.9
108.3913.1
93.7912.4 *
117.7910.3
97.0912.3 *
The data were the means of 5–6 experiments9S.E.M. Statistical analyses were performed using a one-way ANOVA test.
* PB0.05;
** PB0.02;
*** PB0.01.
MG-1. These investigations demonstrated that new
derivatives of 1-[3-(4-phenylpiperazin-1-yl)propyl]-
pyrrolin-2-one with ortho-substituent in the phenyl ring
displayed higher affinity than MG-1 for a1-adrenocep-
tors.
their adrenolytic properties, and those properties were
due to the presence of the 1-phenylpiperazine moiety
with a methoxy- or chloro- substituent in the ortho
position in the phenyl ring. The mode of action and
activity of compounds 7a–11a were promising enough
to continue further experiments.
5. Conclusions
6. Experimental
In summary, we have synthesised several new ana-
logues of MG-1 with potent antiarrhythmic activity on
adrenaline-induced arrhythmia (7a–12a) and hypoten-
sive activity (7a–11a). Compound 11a was the most
potent in this series. The pharmacological results and
binding studies suggested that the antiarrhythmic and
hypotensive effects of these compounds were related to
6.1. Chemistry
M.p. were determined in open glass capillaries on a
Bu¨chi 353 m.p. apparatus and are uncorrected. Elemen-
tal analyses (C, H, N) were determined within 0.4% of
Fig. 5. The effect of 6a on the blood pressure response to epinephrine,
norepinephrine, methoxyamine, tyramine and DMPP. All values
represent the mean9S.E.M. from six rats.
Fig. 6. The effect of 7a on the blood pressure response to epinephrine,
norepinephrine, methoxyamine, tyramine and DMPP. All values
represent the mean9S.E.M. from six rats.

190
B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
mm) silica gel 60 F254 plates, using: S1-CHCl3–C3H6O
(1:1); S2-CHCl3–MeOH–AcOH (60:10:5); S3-n-
C6H14:anhydrous EtOH:Et3N (7:2:1) or S4-MeOH–25%
NH3 (98:2) as developing system. The plates were visu-
alised with UV light or iodine solution (0.05 M in 10%
HCl). Column chromatography was performed on silica
gel 60 (70–230 mesh ASTM) using S3 or S4 as eluent.
6.1.1. General procedure for the synthesis of
1-(2-hydroxy-3-substituted aminopropyl)pyrrolidin-2-
one (1a–9a)
A
solution of 1.4
g
(10 mmol) of 1-(2,3-
Fig. 7. The effect of 8a on the blood pressure response to epinephrine,
norepinephrine, methoxyamine, tyramine and DMPP. All values
represent the mean9S.E.M. from six rats.
epoxypropyl)pyrrolidin-2-one and 10 mmol of the cor-
responding amine in n-propanol (40 mL) was heated
under reflux for 12 h. After evaporating the solvent, the
residue was dissolved in EtOAc and cooled down. In
the case of compounds 5, 7, 9 which crystallised in this
condition, the further purification was done by crys-
tallisation from a mixture of n-C6H14:acetyl acetate
(1:5) (compound 7) or by column chromatography
using S3 (5, 9) as a solvent. The other compounds were
purified by column chromatography using S3 or S4 as a
Fig. 8. The effect of 9a on the blood pressure response to epinephrine,
norepinephrine, methoxyamine, tyramine and DMPP. All values
represent the mean9S.E.M. from six rats.
Fig. 10. The effect of 11a on the blood pressure response to
epinephrine, norepinephrine, methoxyamine, tyramine and DMPP.
All values represent the mean9S.E.M. from six rats.
Fig. 9. The effect of 10a on the blood pressure response to
epinephrine, norepinephrine, methoxyamine, tyramine and DMPP.
All values represent the mean9S.E.M. from six rats.
1
theoretical values. H-NMR spectra were recorded on a
Bruker spectrometer at 300 MHz in CDCl3 or in [d6]-
DMSO with tetramethylsilane (TMS) as an internal
standard. The mass spectra were taken at 70 eV with an
LKB 2091 GCMS spectrometer. Thin-layer chromato-
graphy (TLC) was performed on Merck precoated (0.20
Fig. 11. The effect of 12a on the blood pressure response to
epinephrine, norepinephrine, methoxyamine, tyramine and DMPP.
All values represent the mean9S.E.M. from six rats.

B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
191
Table 5
Affinity towards different a-adrenoceptor subtypes in rat cerebral cortex
Compound [3H]Prazosin (a1 rec.) Ki (mM) [3H]Clonidine (a2 rec.) Ki (mM)
[3H]-CGP12177 (b rec.) Ki (mM)
Ratio a2/a1
5a
6a
7a
8a
\100
0.27
\100
5.3
40.5
16.2
\100
\100
ND
\100
54
\100
ND
\100
\100
\100
–
20
31
60
–
70
62
6
1.3
0.27
2.6
0.16
1.3
2.9
9a
10a
11a
12a
MG-1
11.2
80
16.9
29
1.9
15
ND, not determined; each Ki value was obtained from three experiments.
solvent. The obtained oils were dissolved in anhydrous
EtOH and then EtOH saturated with HCl gas was
added until the mixture become acidic.
2H), 3.23–3.26 (d, CHCH2NH, 2H), 3.40–3.57 (m,
CH2CH2N, CH, 3H), 3.73 (s, OH, 1H), 4.11 (s, OCH3,
3H), 5.65 (s, NH, 1H), 6.87–6.93 (t, arom., 2H), 7.51–
7.57 (t, arom., 2H).
6.1.1.1. 1-[3-(Benzylamino)-2-hydroxypropyl]pyrrolidin-
2-one hydrochloride (1a). Yield: 60.25%. Anal. Calc. for
C14H20N2O2·HCl; Mr 283.83; m.p. 247–248 °C; TLC:
0.08 (S1), 0.24 (S2), 0.10 (S4); MS (70 eV), m/z (70 eV)
248 [M+] (0.34), 230 (0.53), 167 (0.18), 106 (0.50), 101
(24.71), 86 (100), 72 (4.07), 58 (35.31), 56 (4.59), 44
6.1.1.4. 1-[2-Hydroxy-3-(3,4-dimethoxybenzylamino)-
propyl]pyrrolidin-2-one hydrochloride (4a). Yield:
67.85%. Anal. Calc. for C16H24N2O4·HCl; Mr 344.84;
m.p. 150–153 °C; TLC: 0.24 (S2), 0.10 (S3); MS (70
eV), m/z (%): 308 (2.39) [M+], 209 (2.31) [M+−H2O],
192 (8.48), 166 (37.80), 151 (100), 139 (21.93), 136
(25.97), 128 (7.71), 124 (7.13), 107 (8.89), 98 (4.29), 86
(5.70), 77 (4.35), 36 (10.68); 1H-NMR ([d6]-DMSO):
1
(10.85), 42 (7.46), 38 (6.42), 36 (19.10); H-NMR ([d6]-
DMSO): l=1.99–2.14 (m, CH2CH2CH2, 2H), 2.32–
2.40 (m, CH2CO, NCH2CH, 4H), 3.16–3.24 (m,
CHCH2NH, CH2 benzyl, 4H), 3.51–3.58 (m,
CH2CH2N, CH, 3H), 3.91 (s, OH, 1H), 5.28 (s, NH,
1H), 7.06–7.34 (m, arom., 5H).
Table 6
Acute toxicity of the investigated compounds, according to Litchfield
and Wilcoxon [17] in mice
Compound
Route
LD50 mg kg−1
6.1.1.2. 1-[3-(2-Chlorobenzylamino)-2-hydroxypropyl]-
pyrrolidin-2-one hydrochloride (2a). Yield: 68.32%.
Anal. Calc. for C14H19ClN2O2·HCl; Mr 319.23; m.p.
141.7–142.8 °C; TLC: 0.26 (S1), 0.31 (S2); MS (70 eV),
m/z (%): 285 (0.3) [M++2], 283 (0.6) [M+], 264 (1.75),
216 (0.84), 203 (3.10), 184 (4.04), 180 (10.12), 154
(50.04), 139 (95.30), 125 (100), 98 (16.01), 86 (21.83), 77
(3.63), 70 (5.90), 36 (17.24); 1H-NMR ([d6]-DMSO):
l=1.95–2.09 (m, CH2CH2CH2, 2H), 2.32–2.40 (m,
CH2CO, NCH2CH, 4H), 3.04–3.09 (d, CHCH2NH,
2H), 3.26–3.32 (d, CH2 benzyl, 2H), 3.51–3.58 (m,
CH2CH2N, CH, 3H), 4.11 (s, OH, 1H) 5.36 (s, NH,
1H), 7.26–7.91 (m, arom., 4H).
1a
2a
3a
4a
5a
6a
7a
iv
iv
iv
iv
iv
iv
iv
po
iv
po
iv
po
iv
po
iv
po
iv
po
iv
po
iv
po
iv
po
340 (315–367)
175 (160.6–190.7)
124 (96.8–158.7)
150 (133–169)
310 (269.5–356.5)
71 (60.7–83.1)
145 (118.8–176.9)
800 (710–920)
80 (61.5–104)
348 (274–442)
100 (76–132)
595 (476–743.7)
120 (100.2–137.4)
400 (312–476)
350 (324–384)
733 (632–850)
145 (126–187.2)
700 (610–897)
132 (102.3–170.3)
290 (238.9–368.0)
22
8a
9a
10a
11a
6.1.1.3.
1-[2-Hydroxy-3-(4-methoxybenzylamino)-
12a
propyl]pyrrolidin-2-one hydrochloride (3a). Yield:
59.23%. Anal. Calc. for C15H22N2O3·HCl; Mr 314.81;
m.p. 159.1–160.6 °C; TLC: 0.38 (S1), 0.35 (S2); MS (70
eV), m/z (%): 278 (0.44) [M+], 260 (1.92), 162 (6.04),
157 (2.77), 150 (5.35), 139 (24.03), 136 (28.54), 128
(9.20), 121 (100), 98 (5.03), 91 (2.98), 86 (4.35), 77
MG-1
Propranolol
Quinidine
471 (448–503)
66.9 (63.6–70.3)
594.0 (511–677)
1
(4.10), 70 (2.83), 36 (5.47); H-NMR ([d6]-DMSO: l=
1.93–2.08 (qw, CH2CH2CH2, 2H), 2.33–2.40 (m,
CH2CO, NCH2CH, 4H), 3.19–3.22 (d, CH2 benzyl,
The data are median lethal doses with 5% confidence limits in
parentheses.

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B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
l=1.98–2.09 (qw, CH2CH2CH2, 2H), 2.32–2.40 (m,
CH2CO, NCH2CH, 4H), 3.23–3.26 (m, CHCH2NH,
CH2 benzyl, 4H), 3.50–3.53 (m, CH2CH2N, CH, 3H),
3.81 (s, OH, 1H), 3.86 (s, OCH3, 3H), 3.94 (s, OCH3,
3H), 5.58 (s, NH, 1H), 6.81–6.85 (d, arom., JHꢀH=8.18
Hz, 1H), 7.04–7.08 (d, arom., JHꢀH arom. =8.18 Hz,
1H), 7.35 (s, 1H, arom.).
4H), 2.61–2.66 (m, CH2 piper., 4H), 2.78–2.88 (m, CH2
piper., 4H), 3.08 (s, OCH3, 3H), 3.15–3.26 (dd,
CHCH2N, 2H), 3.44–3.45 (d, OH, 1H), 3.51–3.63 (m,
CH2CH2N, CH, 3H), 6.84–7.00 (m, arom., 4H); 13C-
NMR (CDCl3): l=18.14, 30.78, 49.29 (CH2 pyrrol.),
46.98 (NCH2CH), 50.63 (CHOHCH2N), 66.05
(CH2CHOHCH2), 53.35 (CH2 piper.), 55.35 (CH2
piper.), 61 (OCH3), 111.18, 118.09, 120.88, 141.03,
152.18 (arom.), 175.76 (carbonyl).
6.1.1.5. 1-[2-Hydroxy-3-[4-(2-pyrimidinyl)piperazin-1-
yl]propyl]pyrrolidin-2-one (5). Yield: 78.36%. Anal.
Calc. for C15H23N5O2; Mr 305.38; m.p. 93.0–94.7 °C;
TLC: 0.20 (S2), 0.63 (S4); MS (70 eV), m/z (%): 276
(2.61), 258 (0.81), 237 (0.73), 208 (0.72), 177 (100), 150
(0.63), 147 (29.39), 137 (1.39), 133 (4.84), 122 (33.22),
120 (7.39), 108 (6.85), 106 (2.39), 94 (1.06), 79 (5.83);
1H-NMR (CDCl3): l=1.93–2.06 (qw, CH2CH2CH2,
2H), 2.17–2.25 (m, CH2CO, NCH2CH, 4H), 3.17–3.20
(m, CHCH2NH, CH2 piper., 6H), 3.40–3.58 (m,
CH2CH2N, CH, CH2 piper., 7H), 3.79 (s, OH, 1H),
6.04–7.27 (m, arom., 3H); 13C-NMR (CDCl3): l=
40.83, 52.64, 54.19 (CH2 pyrrol.); 56.64, 69.53, 62.36
(propyl), 54.21, 62.36 (piper.), 111.53, 121.99, 129.23
(pyrimid.), 157.90 (carbonyl).
6.1.1.9. 1-[2-Hydroxy-3-[4-(2-methoxyphenyl)piperazin-
1-yl]propyl]pyrrolidin-2-one hydrochloride (7a). Yield:
76.26%. Anal. Calc. for C18H27N3O3·2HCl; Mr 405.99;
m.p. 208–209 °C.
6.1.1.10. 1-[3-[4-(2-Chlorophenyl)piperazin-1-yl]-2-hy-
droxypropyl]pyrrolidin-2-one hydrochloride (8a). Yield:
76.32%. Anal. Calc. for C17H24N3O2Cl; Mr 374.31; m.p.
202.5–203.9 °C; TLC: 0.46 (S2), 0.77 (S3); MS (70 eV),
m/z (%): 339 (0.47) [M++2], 337 (1.32) [M+], 319
(6.24), 221 (1.41), 211 (31.37), 209 (100), 194 (8.10), 181
(0.92), 171 (6.36), 166 (15.75), 138 (5.46), 128 (2.39),
1
111 (1.54), 98 (4.71), 70 (32.12), 36 (6.00); H-NMR
([d6]-DMSO): l=1.89–2.19 (qw, CH2CH2CH2, 2H),
2.23–2.50 (m, CH2CO, NCH2CH, 4H), 2.51 (m, CH2
piper., 4H), 3.07–3.47 (m, CH2, piper., CHCH2N, OH,
7H), 3.57–3.70 (m, CH2N, CH, 3H), 7.00–7.40 (m,
arom., 4H); 13C-NMR ([d6]-DMSO): l=17.69, 25.47,
40.33 (CH2 pyrrol.), 38.24 (NCH2CH), 47.54
(CHOHCH2N), 63.30 (CH2CHOHCH2), 51.33 (CH2
piper.), 54.06 (CH2 piper.), 120.95, 124.76, 127.51,
128.25, 130.45, 147.43 (arom.), 174.58 (carbonyl).
6.1.1.6. 1-[2-Hydroxy-3-[4-(2-pyrimidinyl)piperazin-1-
yl]propyl]pyrrolidin-2-one hydrochloride (5a). Anal.
Calc. for C15H23N5O2·2HCl; Mr 378.38; m.p. 150.9–
152.6 °C.
6.1.1.7. 1-[2-Hydroxy-3-[4-(diphenylmethyl)piperazin-1-
yl]propyl]pyrrolidin-2-one hydrochloride (6a). Yield:
64.24%. Anal. Calc. for C24H31N3O2·2HCl; Mr 466.45;
m.p. 238.1–239.6 °C; TLC: 0.11 (S2), 0.57 (S3); MS (70
eV), m/z (%): 393 (5.35) [M+], 251 (1.21), 226 (0.67),
208 (12.78), 194 (4.56), 167 (100), 152 (7.22), 142 (3.59),
128 (1.89), 98 (6.39), 77 (0.73), 70 (2.98), 36 (52.18);
1H-NMR ([d6]-DMSO): l=1.86–1.93 (qw, CH2CH2-
CH2, 2H), 2.17–2.25 (m, CH2CO, NCH2CH, 4H),
2.45–2.58 (m, CH2 piper., 4H), 3.19–3.22 (m,
CHCH2NH, CH2 piper., 6H), 3.38–3.45 (m, CH2CH2-
N, CH, 3H), 3.78 (s, OH, 1H), 4.21 (s, CH, 1H),
7.29–7.94 (m, arom., 10H); 13C-NMR ([d6]-DMSO):
l=17.71, 25.51, 38.25 (CH2 pyrrol.), 30.31
(NCH2CH), 39.34 (CHOHCH2N), 39.91 (CH2-
CHOHCH2), 40.75 (CH2 piper.), 47.84 (CH2 piper.),
63.55 (CH), 128.33, 128.82, 192.32, 136.15 (arom.),
174.79 (carbonyl).
6.1.1.11.
1-[3-[4-(Chlorophenyl)piperazin-1-yl]-2-hy-
droxypropyl]pyrrolidin-2-one hydrochloride (9). Yield:
60.53%. Anal. Calc. for C17H24N3O2Cl; Mr 337.85; m.p.
106.8–108.0 °C; TLC: 0.50 (S2), 0.41 (S3); MS (70 eV),
m/z (%): 339 (2.95) [M++2], 337 (8.70) [M+], 319
(6.14), 221 (1.80), 211 (32.51), 209 (100), 194 (7.75), 171
(20.42), 168 (10.16), 166 (23.07), 142 (2.81), 138 (10.98),
128 (5.49), 125 (2.89), 111 (4.63), 98 (7.68), 70 (54.37),
1
56 (6.84), 42 (7.05); H-NMR (CDCl3): l=2.00–2.11
(qw, CH2CH2CH2, 2H), 2.31–2.44 (m, CH2CO,
NCH2CH, 4H), 2.43–2.61 (m, CH2 piper., 4H), 2.73–
2.83 (m, CH2 piper., 4H), 3.22–3.44 (dd, CHCH2N,
2H), 3.44–3.48 (d, OH, 1H), 3.51–3.64 (m, CH2N, CH,
3H), 6.78–7.27 (m, arom., 4H); 13C-NMR (CDCl3):
l=18.15, 30.77, 49.13 (CH2 pyrrol.), 46.93
(NCH2CH), 49.33 (CHOHCH2N), 66.20 (CH2CHO
HCH2), 52.98 (CH2 piper.), 61.13 (CH2 piper.), 117.15,
124.50, 128.83, 149.66 (arom.), 175.73 (carbonyl).
6.1.1.8. 1-[2-Hydroxy-3-[4-(2-methoxyphenyl)piperazin-
1-yl]propyl]pyrrolidin-2-one (7). Yield: 76.26%. Anal.
Calc. for C18H27N3O3; Mr 333.43; m.p. 97.7–95.6 °C;
TLC: 0.37 (S2), 0.32 (S3); MS (70 eV), m/z (%): 333
(6.88) [M+], 315 (10.17), 206 (21.16), 205 (100), 190
(25.14), 162 (9.15), 133 (4.09), 120 (4.87), 98 (3.49), 69
(19.93); 1H-NMR (CDCl3): l=1.99–2.11 (qw,
CH2CH2CH2, 2H), 2.36–2.46 (m, CH2CO, NCH2CH,
6.1.1.12.
1-[3-[4-(Chlorophenyl)piperazin-1-yl]-2-hy-
droxypropyl]pyrrolidin-2-one hydrochloride (9a). Anal.
Calc. for C17H24N3O2Cl·2HCl; Mr 410.85; m.p. 227.9–
229.1 °C.

B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
193
6.1.2. Synthesis of 1-[2-acetoxy-3-
(4-arylpiperazin-1-yl)propyl]pyrrolidin-2-one 10, 11
residue was purified by column chromatography using
S3 as a solvent. Free base was dissolved in anhydrous
EtOH, and a solution of maleic acid in EtOH was
added until the mixture become acidic.
6.1.2.1. General procedure. Five millimol of compound
7 or 8 was added to mixture of 10 mL Ac2O and 1 mL
of (10 mmol) Py. The mixture was heated under reflux
at 50 °C for 5 h and then the solvents were evaporated
under vacuum. The crude product was purified by
column chromatography using S4 as a solvent. The
obtained oil was dissolved in anhydrous EtOH and
then EtOH saturated with HCl gas was added until the
mixture become acidic.
Yield: 52.01%. Anal. Calc. for C18H29N3O2; Mr
435.45; m.p. 246–247 °C; TLC: 0.62 (S4); MS (70 eV),
m/z (%): 319 (7.71) [M+], 239 (4.41), 212 (4.14), 209
(100), 196 (3.01), 194 (7.40), 168 (5.46), 166 (15.37), 138
(6.42), 98 (6.31), 79 (27.85), 72 (9.75), 70 (24.58), 52
(16.52); 1H-NMR ([d6]-DMSO): l=1.96–2.03 (qw,
CH2CH2, 4H), 2.41–2.75 (t, CH2N, CH2N, 4H), 2.97–
3.33 (m, CH, OCH3, NCH2CH, CH2 piper., 14H) 3.78–
3.85 (d, CHCH2N, 2H), 4.30 (s, OH, 1H) 6.83–7.28 (m,
arom., 4H); 13C-NMR ([d6]-DMSO): l=22.49, 47.41
(pyrrol.); 38.25 (NCH2CH), 46.16 (CHOHCH2N),
61.62 (CH2CHOHCH2), 52.07 (CH2 piper.), 53.82
(CH2 piper.), 59.14 (OCH3); 111.96, 115.73, 118.21,
119.63, 120.87, 129.08 (arom.).
6.1.2.2. 1-[2-Acetoxy-3-[4-(2-chlorophenyl)piperazin-1-
yl]propy]pyrrolidin-2-one hydrochloride (10a). Yield:
76.32%. Anal. Calc. for C19H26N3O3Cl·2HCl; Mr 452;
m.p. 202.5–203.948 °C; TLC: 0.37 (S2), 0.73 (S3); MS
(70 eV), m/z (%): 381 (0.31) [M++2], 379 (0.31) [M+],
363 (2.27), 319 (12.43), 239 (4.82), 211 (31.97), 209
(100), 194 (8.16), 184 (3.76), 171 (4.23), 168 (5.50), 166
(14.92), 154 (2.13), 138 (5.53), 124 (3.23), 111 (1.38), 98
6.2. Pharmacology
1
(4.27), 77 (1.24), 70 (18.62), 56 (2.55), 36 (3.76); H-
6.2.1. Materials and methods
NMR (CDCl3): l=2.00–2.11 (qw, CH2CH2CH2, 2H),
2.18 (s, CH3, 3H), 2.34–2.42 (m, CH2CO, NCH2CH,
4H), 2.94–3.64 (m, CH, CH2CH2N, CH2 piper., 11H),
3.69–3.80 (m, CHCH2N, 2H), 7.02–7.36 (m, arom.,
4H).
6.2.1.1. Compounds. Barium chloride (POCh, Poland),
[3H]Clonidine (Amersham), DMPP (dimethylphenyl-
piperazine, Sigma, Aldrich Chemie Gmbh), epinephrine
(Adrenalinum hydrochloricum, Polfa), [3H]CGP12177
(NEN), norepinephrine (Levonor, Polfa), methoxamine
(Sigma, Aldrich Chemie Gmbh), [3H]Prazosin (Amer-
sham), tyramine (Sigma, Aldrich Chemie Gmbh),
sodium heparin (Polfa), thiopental sodium (Biochemie
Gmbh, Vienna).
6.1.2.3. 1-[2-Acetoxy-3-[4-(2-methoxyphenyl)piperazin-
1-yl]propyl]pyrrolidin-2-one hydrochloride (11a). Yield:
76.32%. Anal. Calc. for C20H29N3O4·2HCl; Mr 429.94;
m.p. 176.6–178.2 °C; TLC: 0.52 (S1), 0.67 (S2), 0.75
(S3); MS (70 eV), m/z (%): 375 [M+] (9.48), 316 (4.78),
315 (20.58), 217 (4.66) 205 (100), 190 (25.74), 162
(16.75), 134 (6.28), 124 (5.75), 120 (7.37), 98 (4.78), 70
(21.93), 56 (5.66); 1H-NMR (CDCl3): l=1.86–2.18
(qw, CH2CH2CH2, 2H), 2.18 (s, CH3CO, 3H), 2.22–
2.26 (m, CH2CO, NCH2CH, 4H), 3.05–3.59 (m, CH,
CH2CH2N, CH2 piper., 11H), 3.67–3.79 (m, CHCH2N,
2H), 3.79 (s, OCH3, 3H), 6.86–7.10 (m, arom., 4H);
13C-NMR (CDCl3): l=17.75, 30.32, 47.76 (CH2
pyrrol.), 38.26 (NCH2CH), 46.30 (CHOHCH2N), 63.43
(CH2CHOHCH2), 51.18 (CH2 piper.), 52.14 (CH2
piper.), 55.54 (COCH3), 59.16 (OCH3), 112.25, 118.72,
120.93, 124.30, 138.34 (arom.), 151.90 (carbonyl ester)
174.20 (carbonyl).
6.2.1.2. Animals. The experiments were carried out on
male albino Swiss mice (18–25 g) and male Wistar rats
(180–250 g). Animals were housed in wire mesh cages
in room at 2092 °C with natural light–dark cycles.
The animals had free access to standard pellet diet and
water, and were used after a minimum of 3 days
acclimatisation to the housing conditions. Control and
experimental groups consisted of 8–10 animals each.
6.2.1.3. Reference compound. MG-1 was used as a refer-
ence compound.
6.2.1.4. Statistical analysis. The data are expressed as
mean9S.E.M. The statistical significance was calcu-
lated using a one-way ANOVA. Differences were con-
sidered significant when PB0.05.
6.1.3. Synthesis of 1-[2-hydroxy-3-[4-(2-methoxy-
phenyl)piperazin-1-yl]propyl]pyrrolidine (12a)
A suspension of 0.57 g (15 mmol) of LAH in dry
THF (40 mL) was stirred at room temperature for 10
min. Then a solution of 1.16 g (5 mmol) of 7 in THF
was added dropwise. The mixture was stirred overnight.
The reaction was quenched by adding EtOAc and
water. The organic phases were collected, dried with
Na2SO4 and evaporated under vacuum. The obtained
6.2.2. The effect on normal electrocardiogram
Electrocardiographic investigations were carried out
using Multicard 30 apparatus, standard lead II and
paper speed of 50 mm s−1. The tested compounds were
administered intraperitoneally or intravenously in the

194
B. Malawska et al. / European Journal of Medicinal Chemistry 37 (2002) 183–195
dose corresponding to 1/10–1/5 LD50 iv. The ECG
record was made just before and 1.5 and 15 min after
administration of compounds.
Briefly, rats’ brains were homogenised at 0 °C in 20
vols. of 50 mM Tris–HCl buffer (pH 7.6). The ho-
mogenate was centrifuged at 1000×g (0 °C) for 10
min using a Polytron. The membranes were collected by
centrifuration at 25,000×g for 30 min, resuspended in
Tris–HCl buffer and centrifuged again. A 450 mL sam-
ple of the latter membrane suspension was incubated at
37 °C for 30 min with 50 mL of the buffer solution of
the investigated compound (1 nM–100 mM) and 50 mL
of a [3H]prazosin (0.6 nM) or 50 mL of a [3H]clonidine
(2 nM) solution. The incubation was followed by a
rapid vacuum filtration through Whatman GB/C glass
filters, and then was washed two times with 5 mL of a
cold buffer (50 mM Tris–HCl, pH 7.6) dried, immersed
in 3 mL of a scintillation liquid. Radioactivity was
measured in a Beckmann LS 3801 b-scintillation coun-
ter. For measuring unspecific binding, phentolamine (in
the case of [3H]prazosin) and clonidine (in the case of
[3H]clonidine) in a final concentration 10 mM were
present.
6.2.3. Antiarrhythmic acti6ity
6.2.3.1. Prophylactic effect
Adrenaline-induced arrhythmia according to Szekeres
[16]. The arrhythmia was evoked in rats anaesthetised
with thiopental (60 mg kg−1, ip) by iv injection of
adrenaline (20 mg kg−1). The tested compounds were
administered intravenously 15 min or orally 1 h before
adrenaline. The criterion of antiarrhythmic activity was
the lack of premature beats and inhibition of cardiac
arrhythmia in comparison with the control group.
Barium chloride-induced arrhythmia according to
Szekeres [16]. Barium chloride solution was injected
into the caudal vein of rats (32 mg kg−1, in a volume
of 1 mL kg−1). The tested compounds were given iv 15
min or po 1 h before arrhythmogen. The criterion of
antiarrhythmic activity was a gradual disappearance of
the arrhythmia and restoration of the sinus rhythm.
6.2.6. Acute toxicity according to Litchfield and
Wilcoxon [17]
6.2.3.2. Therapeutic effect. The tested compound was
administered intravenously at the peak of arrhythmia,
immediately after administration of adrenaline or bar-
ium chloride.
The compounds, dissolved in 0.9% saline, were in-
jected into the caudal vein (10 mL kg−1) or adminis-
tered intragastrically. Each dose was given to six
animals. The LD50 values were calculated according to
the method of Litchfield and Wilcoxon [17] after a 24 h
observation period.
6.2.4. Influence on the blood pressure
Male Wistar normotensive rats were anaesthetised
with thiopental (50–75 mg kg−1) by intraperitoneally
injection. The right carotid artery was cannulated with
polyethylene tub filled with heparin in saline to facili-
tate pressure measurements using a Datamax apparatus
(Columbus Instruments). The studied compounds were
injected in doses corresponding to 1/40–1/10 LD50 iv
into the cadual vein, after a 5 min stabilisation period,
Acknowledgements
The study was supported by the Polish State Com-
mittee for Scientific Research (KBN), grant no. P-05F
02210 and 4P05F00514.
in a volume equivalent to 1 mL kg−1
.
In separate series of experiments on anesthetised
normotensive rats, the effect of studied compounds
(1/40–1/10 LD50) on the pressor response to
epinephrine (2 mg kg−1), norepinephrine (2 mg kg−1),
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