Introduction of a methyl group in α- or β-position of 1-heteroarylethyl-4-phenyl-piperazines affects their dopaminergic/serotonergic properties

Article abstract of DOI:10.1002/1521-4184(200112)334:12<375::AID-ARDP375>3.0.CO;2-P

1-(2-Heteroarylalkyl)-4-phenylpiperazines containing methyl group in either the α- or the β-position of the side alkyl chain were synthesized as racemic mixtures. They were evaluated for in vitro binding affinity at the D₁ and D₂ dop

Full text of DOI:10.1002/1521-4184(200112)334:12<375::AID-ARDP375>3.0.CO;2-P

Full Papers
Goran Roglica), Deana Andrica)b)
Sladjana Kostic-Rajacicb),
Sladjana Dukicc), and
,
Introduction of a methyl group in α- or
β-position of 1-heteroarylethyl-4-phenyl-
piperazines affects their
Vukic Šoškica)b)c)
a)
Faculty of Chemistry, University of
dopaminergic/serotonergic properties
Belgrade, 11000 Belgrade, Studentski
b)
trg 12–16;
Institute for Chemistry,
Technology and Metallurgy. 11 000
Belgrade, Njegoeva 12; c) Institute for
Biological Research, 11060 Belgrade,
29 Novembra 142, Yugoslavia
1-(2-Heteroarylalkyl)-4-phenylpiperazines containing methyl group in either the α- or the
β-position of the side alkyl chain were synthesized as racemic mixtures. They were
evaluated for in vitro binding affinity at the D1 and D2 dopamine and 5-HT1A serotonin
receptors using synaptosomal membranes of the bovine caudate nucleus and hippo-
campus, respectively, as a source of the corresponding receptors. Tritiated SCH 23390
(D1 receptor-selective), spiperone (D2 receptor-selective), and 8-OH-DPAT (5-HT1A
receptor-selective) were employed as the radioligands. None of the new compounds
expressed significant affinity for the D1 receptor. Introduction of the methyl group into
the β-position of the parent molecules increased the affinity for the D2 receptor (10b–
13b), and decreased the affinity for the 5-HT1A receptor with the exception of imidazole
(11b) which was a rather efficient displacer of 8-OH-DPAT. Most potent of the newly
synthesized compounds in [3H]spiperone assay were compounds (±)6-[1-methyl-2-(4-
phenylpiperazin-1-yl)-ethyl]-1,4-dihydroquinoxaline-2,3-dione (10b), Kd = 6.0 nM and
(±)5-[1-methyl-2-(4-phenylpiperazin-1-yl)-ethyl]-1,3-dihydrobenzoimidazol-2-thione
(13b), Kd = 5.3 nM. However, compounds containing methyl group in α-position (10a–
13a) of the parent molecules expressed a decreased affinity for the D2 receptor, while
the affinity for the 5-HT1A receptor remained in the same range of concentrations as that
of closely related achiral parent compounds (14–17) run in the same binding assays as
references.
Key Words: α-Methyl-heteroaryl-ethyl-aryl-piperazines; β-Methyl-heteroaryl-ethyl-aryl-
piperazines; Dopaminergic; Serotonergic; D1; D2; 5-HT1A
Received: March 8, 2001 [FP553]
molecule conformation achieved by introduction of a methyl
Introduction
group into the α- or the β-position of the alkyl bridge
Numerous dopaminergic[1] and serotonergic[2] compounds
are useful therapeutics in the treatment of a number of
psychiatric and neurological disorders. However, classical
neuroleptics such as haloperidol express undesirable side
effects including extrapyramidal symptoms, tardive dys-
kinesia, and increased prolactin levels[3]. Because of that,
the search for new dopaminergic/serotonergic compounds
as potential pharmaceuticals is continually intensifying.
Besides, such compounds represent useful tools for funda-
mental research, especially with regard to topology of the
receptor molecule(s) and specific ligand/receptor interac-
tions.
connecting the heteroaryl- and the N-arylpiperazine part of
the molecule, on the binding affinity of the ligands at the
dopamine (D1 and D2) and serotonin (5-HT1A) receptors of
the specific mammalian brain structures.
Chemistry
Structures of the compounds synthesized throughout the
present work and the corresponding synthetic pathways
are presented in Schemes 1 and 2. Synthesis of the parent
compounds of α-methyl and β-methyl ligands is presented
in Scheme 1 (Panel A and B, respectively). The commer-
cially available acid 1 was first transformed into chloride
and further into amide (2) by the acylation of N-phenyl-
piperazine. The resulting amide 2 was reduced with dibo-
rane to afford 1-[2-(4-nitrophenyl)propyl]-4-phenyl-
piperazine (3). Scheme 1 (B) shows that reductive amina-
tion of the ketone 4 resulted in production of (±)1-[1-methyl-
2-(4-nitrophenyl)ethyl]-4-phenylpiperazine (5), a starting
compound for the synthesis of the β-series of compounds
described in the present study. The general procedure for
the synthesis of diamines 9a and 9b used as a starting
We have demonstrated previously that N-benzimidazolyl-
ethyl-1-arylpiperazines express mixed dopaminergic/sero-
tonergic activity[4]. The effects of N-aryl substituent and
substitutions in the imidazole ring on the activity of this
compounds were also examined[5,6]. The aim of the present
study was to examine the influence of the changed ligand
———
Correspondence: Prof. G. Roglic, Faculty of Chemistry,
University of Belgrade, 11000 Belgrade, Studentski trg 12–16,
Yugoslavia.
© WILEY-VCH Verlag GmbH, D-69451 Weinheim, 2001
0365-6233/01/1212/0375 $17.50 +.50/0

376 Dopaminergic/serotonergic properties
Arch. Pharm. Pharm. Med. Chem. 2001, 334, 375–380
Scheme 1
material to produce compounds 10a,b–13a,b is presented
in Scheme 2. As seen, the synthesis started with reduction
of nitro compounds 3 and 5 with Ra-Ni, followed by acety-
lation of the resulting amines 6a and 6b. Nitration of
acetamides 6a and 6b afforded o-nitroacetanilides 7a and
7b. Hydrolysis of 7a and 7b with HCl gave o-nitroanilines
8a and 8b, which were reduced with Ra-Ni to produce
diamines 9a and 9b. Novel ligands 10a,b–13a,b synthe-
sized according to general procedures already described[7–
9]are shown in Scheme 2.
A
OH
a
N
b
N Ph
O
O
O2N
O2N
2
1
N
N
N Ph
Results and Discussion
O2N
3
The final products, racemic mixtures 10a,b–13a,b, were
evaluated for the binding affinity at the D1 and D2 dopamine
and 5-HT1A serotonin receptors by in vitro displacement of
the specific radioligands from synaptosomal membranes
prepared from fresh bovine caudatenucleiandhippocampi,
respectively[4]. The Ki values for individual compounds
calculated from the displacement curves are listed in Ta-
ble 1, since Hill coefficients of the competition curves were
in the range 0.91–1.05 (data not shown). Structurally close
compounds 14–17[4] were run simultaneously in the same
test system as references. Obtained Hill coefficient values
B
N Ph
c
O
O2N
O2N
5
4
A a) 1. SOCl2, 2. N-phenylpiperazine, Et3N, CH2Cl2, 60 °C, 12 h;
b) 1. B2H6, diglyme, 80–90 °C, 1 h; 2. HCl, reflux; 3. NaOH;
B c) N-phenylpiperazine, NaBH3CN, ZnCl2, MeOH, rt, 2 h.
Scheme 2
1
1
R
R
b
a
N
N Ph
N
N Ph
2
2
R
R
O2N
AcHN
3,5
6a,b
1
1
R
R
N
N Ph
N
N Ph
c
2
2
R
R
AcHN
H2N
8a,b
NO2
NO2
7a,b
1
R
N
N Ph
10a,b
2
e
f
R
HN
NH
O
d
1
O
R
N
N Ph
1
R
2
R
11a,b
N
N Ph
N
2
NH
R
H2N
NH2
9a,b
1
R
N
N Ph
g
2
R
12a,b
N
N
NH
1
R
N
N Ph
h
2
R
13a,b
HN
S
6a - 13a R1 = CH3 , R2 = H
6b - 13b R1 = H , R2 = CH3
NH
a) 1. Ra-Ni, N2H4, (CH2Cl)2, EtOH; 2. Ac2O, Et3N; b) Ac2O, H2SO4, HNO3; c) HCl 4N,
reflux; d) Ra-Ni, N2H4, (CH2Cl)2, EtOH; e) (COOH)2, HCl, reflux; f) HCOOH, 100 °C;
g) NaNO2, AcOH; h) CS2, KOH, EtOH, reflux

Arch. Pharm. Pharm. Med. Chem. 2001, 334, 375–380
Dopaminergic/serotonergic properties 377
Table 1. Affinity and selectivity of the new ligands for the binding
at the D2 dopamine and 5-HT1A serotonin receptor
zines serving as lipophilic groups were attached to the
heterocyclic dopaminergic pharmacophores[5,6]. These in-
vestigations showed that D2 receptor molecule can accom-
modate rather voluminous groups introduced as
substituents into the heteroaryl-piperazine part of the mole-
cule. In the present study, our intention was to enrich our
knowledge on the influence of position of methyl group (α-
or β-) attached to the alkyl chain of 1-(2-heteroaryl-alkyl)-
4-phenyl-piperazines on the affinity of these ligands for the
dopamine and serotonin receptors. None of the new com-
pounds acted as efficient displacers of [3H]SCH 23390,
which is characteristic for all ligands of this class, tested so
far[4]. Introduction of the methyl group into the α-position of
the alkyl chain led to a decreased affinity for the D2 receptor,
probably due to the prevention of N-phenyl group from
reaching the accessory binding pocket of the receptor. In
the β-series (compounds 10b–13b), introduction of the
methyl group in the β-position led to a pronounced selec-
tivity of the binding at the D2 receptor. This selectivity was
especially expressed in the case of 10b and 13b. In our
opinion, these two ligands, and especially the enantiomers
they consist of, deserve further trials as potential pharma-
cological agents with mixed dopaminergic/serotonergic ac-
tivity.
————————————————————————————–
No
X
R1
R2
Ki + S.E.M (nM)
5-HT1A
————————————————————————————–
D2
14
CH
CH
CH
C=S
C=S
C=S
N
H
H
138 + 23
20 + 5
197 + 52
130 + 22
300+ 28
13.4 + 2.8
170 + 31
36 + 7
11b
11a
15
H
CH3
H
CH3
H
>1000
H
15.7 + 2.0
5.3 + 1.7
304 + 52
ND
13b
13a
16
H
CH3
H
CH3
H
H
ND
12b
12a
17
N
H
CH3
H
15.2 + 2.1
>1000
548 + 102
300 + 71
25.4 + 3.8
103 + 18
58 + 14
ND
N
CH3
CO-CO H
CO-CO H
CO-CO CH3
H
23.3 + 4.2
6.0 + 2.2
540 + 178
>1000
10b
10a
CH3
H
Acknowledgement
SCH 23390
This work was partially supported by the Ministry for Science
and Technology of Serbia.
Haloperidol
12.3 + 2.3
>1000
>1000
5-Hydoxytryptamine
5.2 + 1.6
————————————————————————————–
Experimental
Values are the means of three independent experiments done in
triplicate performed at eight competing ligand concentrations (10–
4–10–11 M) and [3H]spiperone or 0.6 nM of [3H]-8-OH-DPAT.
Results ofexperiments using synaptosomal membranes of the
bovine caudate nucleus and 0.2 nM of [3H]SCH 23390 are not
showed since in tested ligands concentration range there were no
significant competition detected. Ki values are caculated using
Cheng-Prussoffequation[11] since Hill coefficient ofthe competition
curves ware in the range 0.91–1.05 (data are not shown).
General
Melting points were determined on a Boetius PHMK apparatus
(WEB Analytic, Dresden, Germany) and are uncorrected. The
results of microanalyses were within 0.4% of the calculated
values. 1H-NMR spectra were recorded on a Gemini 2000
spectrometer (Varian, Palo Alto, CA, USA) with CDCl3 as a
solvent unless otherwise stated and are reported in ppm (δ)
downfield from the internal standard tetramethylsilane. The IR
spectra were run on a Perkin Elmer 457 Grating Infrared Spec-
trophotometer (Perkin Elmer Beaconsfield, England). The mass
spectra were determined on a Bruker Biflex MALDI time-of-
flight mass spectrometer (Bruker, Bremen, Germany). Analyti-
cal TLC was performed using F-254 plastic-backed thin-layer
silica gel plates E. Merck (Darmstadt, Germany). Chroma-
tographic purifications were accomplished on Merck-60 silica
gel columns, 230–400 mesh ASTM, under medium pressure
(MPLC).
probably mean that this group of compounds behave as
antagonists but further functional studies have not been not
performed.
None of the ligands expressed significant affinity for the D1
dopamine receptor. Compounds 11a and 12a were inactive
in [3H]spiperone assay. All other novel compounds acted
as efficient competitors of both [3H]spiperone and [3H]-8-
OH-DPAT expressing the binding affinity at the correspond-
ing receptors in a nanomolar range of concentrations.
Compounds 10b and 13b with Ki values of 6.0 nM and
5.3 nM, respectively, were the most potent displacers of
[3H]spiperone from the D2 receptor. The affinity for the
5-HT1A serotonin receptor of the α-series (R1 = CH3, R2 =
H) of ligands (10a–13a) remained in the same range of
concentrations as that of reference compounds (14–17).
The β-series of ligands (R1 = H, R2 = CH3), with the
exception of 11b, displayed a decreased affinity for the
5-HT1A serotonin receptor compared to that of reference
compounds (14–17). A part of our previous studies was
focused on the synthesis of ligands in which 1-aryl-pipera-
Chemistry
Synthesis of 2-(4-nitrophenyl)-1-(4-phenylpiperazin-1-yl)-
propan-1-one (2)
Thionyl chloride (8.5 g, 5.2 ml, 72 mmol) and 2-(4-nitro-
phenyl)propanoic acid (11.7 g, 60 mmol) were introduced into
a 100 ml flask equipped with a magnetic stirrer bar and a
condenser protected with a drying tube. The reaction mixture
was stirred and heated in an oil bath (60 °C, 12 h). After that,
the excess of thionyl chloride was evaporated under reduced
pressure. The chloride was dissolved in of dry CH2Cl2 (40 ml),
transferred to the dropping funnel, and added dropwise to a
pre-cooled solution (0 °C) of N-phenylpiperazine (9.72 g,

378 Dopaminergic/serotonergic properties
Arch. Pharm. Pharm. Med. Chem. 2001, 334, 375–380
60 mmol) and triethylamine (6.1 g, 60 mmol) in of CH2Cl2
(150 ml). The mixture was stirred overnight. The organic phase
was washed with dil. HCl and 10% NaHCO3 solution. After
evaporation, the crude product was crystallized from toluene to
yield 17.9 g (88%) of 2 (mp 125°C).– IR (KBr): (cm–1) 2925,
1638, 1600, 1509, 1344.– 1H-NMR: δ 1.51 (d, 3H, J = 6.8 Hz,
methyl); 2.71 (m, 1H, piperazine); 3.00–3.20 (m, 3H,
piperazine); 3.48–3.77 (m, 3H, piperazine); 3.89 (m, 1H,
piperazine); 4.03 (q, 1H, J = 6.8 Hz, benzyl); 6.84 (m, 1H,
phenylpiperazine); 6.90 (m, 2H, J = 8 Hz, phenylpiperazine);
7.26 (m, 2H, phenylpiperazine); 7.45 (m, 2H, nitro-phenyl); 8.20
(m, 2H,nitrophenyl).– Anal. (C19H21N3O3), C, H, N.
pleted, the mixture was heated in a water bath (50 °C, 60 min)
and filtered through celite. The filtrate was evaporated in vacuo
and the crude products used for further synthesis. The amine
was dissolved in 90 ml CH2Cl2 and 1.7 g (1.8 ml, 22 mmol) of
pyridine was added. The solution was cooled to 0 °C and
2.25 ml (22 mmol) of acetanhydride was introduced dropwise.
After stirring (24 h, room temperature), 120 ml of 10% Na2CO3
was added. The layers were separated and after drying with
Na2SO4 organic layer was evaporated.
6a Yield 6.91 g (83%); mp 118 °C.– IR (KBr): (cm–1) 3340, 2966,
1665, 1527, 1504.– 1H-NMR: δ 1.26 (d, 3H, J = 7 Hz, methyl);
2.15 (s, 3H, acetyl); 2.47–2.67 (m, 6H, piperazine); 2.95 (m, 1H,
CH); 3.15 (m, 4H, piperazine); 6.83 (t, 1H, J = 7 Hz,
phenylpiperazine); 6.90 (d, 2H, J = 8 Hz, phenylpiperazine);
7.14–7.29 (m, 4H, phenylpiperazine, acetanylido), 7.42 (d, 2H,
J = 8.8 Hz, acetanylido).– Anal. (C20H27N3O), C,H,N.
Synthesis of 1-[2-(4-nitrophenyl)-propyl]-4-phenyl-
piperazine (3)
A 500 ml round-bottom flask fitted with a thermometer, pressure
equalizing dropping funnel, reflux condenser, and an oil bubbler
was purged with Ar, and charged with diglyme (120 ml), NaBH4
(5 g, 0.1 mol) and 15.25 g (45 mmol) of 2-(4-nitrophenyl)-1-(4-
phenylpiperazin-1-yl)-propan-1-one (2). The mixture was
cooled to –5 °C (ice-salt bath) and pure BF3• Et2O complex
17.55 g (20.25 ml, 124 mmol) was added dropwise. After stirring
(0–5 °C, 1 h), the mixture was heated at 80–90 °C for 1 h, then
cooled to room temperature and treated slowly with water
(40 ml) followed by conc. HCl (80 ml). It was further stirred and
heated in a boiling water bath for 3 h, cooled to room tempera-
ture, and evaporated to dryness at reduced pressure. The solid
residue was made alkaline (10% NaOH, pH>11), extracted with
CH2Cl2 (2×150 ml), dried (anh. K2CO3), and evaporated to yield
10.9 g (75%) of 3 (mp 97 °C).– IR (KBr): (cm–1) 2931, 1600,
1516, 1349.– 1H-NMR: δ 1.31 (d, 3H, J = 6.6 Hz, methyl); 2.57
(m, 6H, pyperazine, CH2); 3.13 (m, 5H, pyperazine, benzyl);
6.84 (m, 1H, phenylpiperazine); 6.90 (m, 2H, phenylpiper-
azine); 7.26 (m, 2H, phenylpiperazine); 7.38 (m, 2H, nitro-
phenyl); 8.16 (m, 2H, nitrophenyl).– Anal. (C19H23N3O2), C, H,
N.
6b Yield 6.52 g (79%); mp 149 °C.– IR (KBr): (cm–1) 3284, 2965,
1660, 1603, 1509.– 1H-NMR: δ 0.98 (d, 3H, J = 6 Hz, methyl);
2.15 (s, 3H, acetyl); 2.41 (dd, 1H, J = 9.4 Hz, J = 12.8 Hz,
benzyl); 2.77 (m, 5H, piperazine); 2.99 (dd, 1H, J = 4 Hz, J =
8.6 Hz, benzyl); 3.21 (m, 4H, piperazine); 6.85 (m, 1H,
phenylpiperazine); 6.91 (m, 2H, phenylpiperazine); 7.13 (m,
2H, acetanylido); 7.26 (m, 2H, phenylpiperazine); 7.42 (m, 2H,
acetanylido).– Anal. (C20H27N3O), C,H,N.
Synthesis of (±)1-[2-methyl-2-(3-nitro-4-acetanylido)-
ethyl]-4-phenylpiperazine (7a) and (±)1-[1-methyl-2-(3-ni-
tro-4-acetanylido)-ethyl]-4-phenylpiperazine (7b)
To cooled solution (0 °C) of 15 mmol of either acetanilide (6a
or 6b) in 25 ml of acetanhydride 0.6 ml of conc. H2SO4 was
added. Upon cooling to –5 °C, 1.06 g (0.7 ml, 13 mmol) of 100%
nitric acid was introduced in small portions. After reaching room
temperature, the mixture was stirred for 3 h, 80 g of crushed ice
was added, and the mixture made alkaline with 10% NaOH.
Then it was extracted with CH2Cl2. After drying and evapora-
tion, crude products were purified by chromatography.
Synthesis of (±)1-[1-methyl-2-(4-nitrophenyl)-ethyl]-4-
phenylpiperazine (5)
7a Yield 4.62 g (80%); mp 138 °C.– IR (KBr): (cm–1) 2938, 1705,
1578, 1508, 1338.– 1H-NMR: δ 1.29 (d, 3H, J = 6.6 Hz, methyl);
2.28 (s, 3H, acetyl); 2.51 (d, 2H, J = 7.2 Hz, CH2); 2.58 (m, 4H,
piperazine); 3.04 (m, 1H, benzyl); 3.14 (m, 4H, piperazine); 6.84
(m, 1H, phenylpiperazine); 6.90 (m, 2H, phenylpiperazine);
7.26 (m, 2H, phenylpiperazine); 7.52 (m, 1H, 3-nitro-4-
acetanylido); 8.07 (m, 1H, 3-nitro-4-acetanylido); 8.66 (m, 1H,
3-nitro-4-acetanylido) 10.25 (NH).– Anal. (C20H25N4O3), C,H,N.
To a stirred solution of ketone 4 (7.1 g, 40 mmol) and N-
phenylpiperazine (8.1 g, 50 mmol) in methanol (100 ml), a
mixture of sodium cyanoborohydride (2.5 g, 40 mmol) and
ZnCl2 (2.8 g, 20 mmol) in methanol (50 ml) was added at room
temperature. The resulting solution was stirred at room tem-
perature for 2 h and transferred into 0.1 M NaOH (200 ml). After
most of methanol was evaporated under reduced pressure, the
7b Yield 4.75 g (83%); mp 156 °C.– IR (KBr): (cm–1) 3355, 2973,
1703, 1586, 1525, 1337.– 1H-NMR: δ 1.01 (d, 3H, J = 6.4 Hz,
methyl); 2.28 (s, 3H, acetyl); 2.53 (dd, 1H, J = 7 Hz, J = 12.6 Hz,
CH); 2.67–3.02 (m, 6H, piperazine); 3.19 (m, 4H, piperazine);
6.85 (m, 1H,phenylpiperazine); 6.93 (m, 2H, phenylpiperazine);
7.26 (m, 2H, phenylpiperazine); 7.49 (m, 1H, 3-nitro-4-
acetanylido); 8.07(m, 1H, 3-nitro-4-acetanylido); 8.65 (m, 1H,
3-nitro-4-acetanylido); 10.25 (NH).– Anal. (C20H25N4O3),
C,H,N.
aqueous phase was extracted with ethyl acetate (3
×
150 ml).The combined extracts were washed with water and
brine, dried over MgSO4, and evaporated under reduced pres-
sure. The residue purified by dry flash column chromatography
yielded 8.45 g (65%) of 5 (mp 98 °C).– IR (KBr): (cm–1) 2966,
1598, 1515, 1343. – 1H-NMR: δ 1.03 (d, 3H, J = 6.4 Hz, methyl);
2.60 (dd, 1H, J = 8 Hz, J = 12.8 Hz, benzyl); 2.76 (m, 4H,
piperazine); 2.89 (m, 1H, benzyl); 3.05 (dd, 1H, J = 6 Hz, J =
12.8 Hz, CH); 3.20 (m, 4H, piperazine); 6.86 (t, 1H, J = 7.2 Hz,
phenylpiperazine); 6.94 (d, 2H, J = 8 Hz, phenylpiperazine);
7.27 (m, 2H, phenylpiperazine); 7.35 (d, 2H, J = 8 Hz, ni-
trophenyl); 8.15 (d, 2H, J = 8 Hz, nitrophenyl).– Anal.
(C19H23N3O2), C, H, N.
Synthesis of (±)1-[2-methyl-2-(3-nitro-4-aminophenyl)-
ethyl]-4-phenylpiperazine (8a) and (±)1-[1-methyl-2-(3-ni-
tro-4-aminophenyl)-ethyl]-4-phenylpiperazine (8b)
Synthesis of (±)1-[2-methyl-2-(4-acetanylido)-ethyl]-
4-phenylpiperazine (6a) and (±)1-[1-methyl-
2-(4-acetanylido)-ethyl]-4-phenylpiperazine (6b)
3.85 g (10 mmol) of either o-nitroacetanilide (7a or 7b) was
resuspended in 50 ml of 6N HCl and refluxed for 4 h. The solution
was cooled to room temperature and diluted with 150 ml of
ice-water mixture. The excess acid was neutralized with 10%
NaOH keeping temperature below 30 °C and the product extracted
with CH2Cl2. After drying and evaporation in vacuo crude products
were recrystallized from i-PrOH.
Ra-Ni (0.4–0.5 g) was added in small portions to a stirred
solution (8.12 g, 25 mmol) of either nitro compound (3 or 5) in
40 ml EtOH, 40 ml 1,2-dichloroethane and 7 ml (70 mmol)
hydrazine hydrate at 30 °C. After addition of Ra-Ni was com-

Arch. Pharm. Pharm. Med. Chem. 2001, 334, 375–380
Dopaminergic/serotonergic properties 379
8a Yield 2.7 g (80%); mp 101 °C.– IR (KBr): (cm–1) 3366, 2947,
1637, 1516, 1245.– 1H-NMR: δ 1.26 (d, 3H, J = 7 Hz, methyl);
2.47 (d, 2H, J = 7.5 Hz, CH2); 2.58 (m, 4H, piperazine); 2.92
(m, 1H, benzyl); 3.15 (m, 4H, piperazine); 5.97 (NH2); 6.73–
6.93 (m, 4H, phenylpiperazine); 7.25 (m, 3H, phenylpiperazine,
3-nitro-4-aminophenyl); 7.97 (m, 1H, 3-nitro-4-aminophenyl).–
Anal. (C18H24N4O2), C,H,N.
8b Yield 2.86 g (85%); mp 108 °C.– IR (KBr): (cm–1) 3369, 2981,
1636, 1600, 1518, 1240.– 1H-NMR: δ 1.01 (d, 3H, J = 6.8 Hz,
methyl); 2.41 (dd, 1H, J = 7.8 Hz, J = 12.4 Hz, CH); 2.66–2.94
(m, 6H, piperazine, benzyl); 3.20 (m, 4H, piperazine); 5.97
(NH2); 6.73 (m, 1H, phenylpiperazine); 6.82 (m, 1H, phenyl-
piperazine); 6.94 (m, 2H,phenylpiperazine); 7.25 (m, 3H,
phenylpiperazine, 3-nitro-4-aminophenyl); 7.95 (s, 1H, 3-nitro-
4-aminophenyl).– Anal. (C18H24N4O2), C,H,N.
11a Yield 384 mg (60%); mp 74 °C.– IR (KBr): (cm–1) 3030,
2960, 1598, 1499, 1451.– 1H-NMR: δ 1.34 (d, 3H, J = 6.8 Hz,
methyl), 2.64 (m, 6H, piperazine, CH2); 3.15 (m, 5H, piperazine,
benzyl); 6.84 (m, 1H, phenylpiperazine); 6.89 (m, 2H, phenyl-
piperazine); 7.17 (m, 3H, phenylpiperazine, benzimidazole);
7.45 (s,1H, benzimidazole); 7.54(m, 1H, benzimidazole); 7.94
(s,1H, H-1 benzimidazole).– MS (MALDI TOF); m/z =320.199
(C20H24N4, calc. MW 320.200).
11b Yield 350 mg (55%); mp 99 °C.– IR (KBr): (cm–1) 3031,
2969, 1599, 1499, 1451.– 1H-NMR: δ 1.01 (d, 3H, J = 6.6 Hz,
methyl); 2.57 (dd, 2H, J = 9 Hz, J = 12.8 Hz, benzyl); 2.81 (m,
4H, piperazine), 2.94 (m, 1H, CH); 3.20 (m, 4H, piperazine);
6.87 (m, 1H, phenylpiperazine); 6.95 (m, 2H, phenyl-
piperazine); 7.14 (m, 1H, benzimidazole); 7.25 (m, 2H, phenyl-
piperazine); 7.46 (s, 1H, benzimidazole); 7.58 (m, 1H, benz-
imidazole); 8.04 (s, 1H, H-1 benzimidazole).– MS (MALDI
TOF); m/z =320.1992 (C20H24N4, calc. MW 320.200).
Synthesis of (±)1-[2-methyl-2-(3,4-diaminophenyl)-ethyl]-
4-phenylpiperazine (9a) and (±)1-[1-methyl-2-(3,4-diami-
nophenyl)-ethyl]-4-phenylpiperazine (9b)
Synthesis of (±)5-[2-methyl-2-(4-phenylpiperazin-1-yl)-
ethyl]-1H-benzotriazole (12a) and (±)5-[1-methyl-2-(4-
phenylpiperazin-1-yl)-ethyl]-1H-benzotriazole (12b)
Ra-Ni (0.4–0.5 g) was added in small portions to a stirring
solution (6.5 g, 20 mmol) of either nitro compound (8a or 8b) in
40 ml EtOH, 40 ml 1,2-dichloroethane and 7 ml (70 mmol)
hydrazine hydrate at 30 °C. After addition of Ra-Ni was com-
pleted, the mixture was heated in a water bath (50 °C, 60 min)
and filtered through celite. The filtrate was evaporated in vacuo
and crude products 9a and 9b were used for further syntheses.
2 mmol of either diamine 9a or 9b was dissolved in a mixture
of 0.5 ml of acetic acid and 0.9 ml of water. After that, 0.16 g
(2.35 mmol) of NaNO2 dissolved in 0.25 ml of water was added
at 0 °C. The solution was heated (water bath, 70 °C, 10 min)
and after cooling to room temperature the solvent was removed
in vacuo. The residue was resuspended in 10 ml of 5% Na-
HCO3, extracted with CH2Cl2, concentrated in vacuo and puri-
fied by column chromatography.
Synthesis of (±)6-[2-methyl-2-(4-phenylpiperazin-1-yl)-
ethyl]-1,4-dihydroquinoxaline-2,3-dione (10a) and
(±)6-[1-methyl-2-(4-phenylpiperazin-1-yl)-ethyl]-1,4-di-
hydroquinoxaline-2,3-dione (10b)
12a Yield 300 mg (47%); mp 88 °C.– IR (KBr): (cm–1) 3057,
2960, 1598, 1499, 1452.– 1H-NMR: δ 1.32 (d, 3H, J = 6.8 Hz,
methyl); 2.60-2.97 (m, 6H, piperazine, CH2); 3.20 (m, 5H,
piperazine, benzyl); 6.86 (m, 3H, phenylpiperazine); 7.19 (m,
4H, phenylpiperazine, benzotriazole); 7.61 (s, 1H, benzotria-
zole).– MS (MALDI TOF); m/z = 321.196 (C19H23N5, calc. MW
321.195).
2 mmol of either diamine 9a or 9b, 0.55 g (4.4 mmol) of oxalic
acid, and 2.5 ml of 4N HCl were refluxed for 30 min. Upon
cooling to ambient temperature the solvent was removed in
vacuo. The residue was suspended in 20 ml of 10% NaHCO3,
extracted with CH2Cl2, concentrated in vacuo and chromatogra-
phed on silica gel.
12b Yield 327 mg (51%); mp 93 °C.– IR (KBr): (cm–1) 3032,
2959, 1598, 1499, 1453.– 1H-NMR: δ 1.04 (d, 3H, J = 6.4 Hz,
methyl); 2.66 (dd, 2H, J = 9 Hz, J = 12.8 Hz, benzyl); 2.88 (m,
4H, piperazine); 3.04 (m, 1H, CH); 3.26 (m, 4H, piperazine,
CH2); 6.88 (t, 1H, J = 7.4 Hz, phenylpiperazine); 6.95 (d, 2H, J
= 8 Hz, phenylpiperazine); 7.28 (m, 3H, phenylpiperazine,
benzotriazole); 7.66 (s, 1H, benzotriazole); 7.81 (d, 1H,
8.4 Hz).– MS (MALDI TOF); m/z =321.196 (C19H23N5,
321.195).
10a Yield 225 mg (31%); mp 247 °C.– IR (KBr): (cm–1) 3196,
2926, 1688, 1600, 1391.– 1H-NMR (d6DMSO) δ 1.19 (d, 3H, J
= 6.8 Hz, methyl); 2.39 (d, 2H, J = 7.6 Hz, CH2); 2.51 (m, 4H,
piperazine); 3.06 (m, 5H, piperazine, benzyl); 6.76 (m, 1H,
dihydroquinoxaline-2,3-dione); 6.95 (m, 2H, phenylpiperazine,
dihydroquinoxaline-2,3-dione); 7.05 (m, 3H, phenylpiperazine,
dihydroquinoxaline-2,3-dione); 7.19 (m, 2H, dihydroquinox-
aline-2,3-dione),11.85 (NH, 2H).– MS (MALDI TOF); m/z =
364.189 (C21H24N4O2, calc. MW 364.190).
Synthesis of (±)5-[2-methyl-2-(4-phenylpiperazin-1-yl)-
ethyl]-1,3-dihydrobenzoimidazol-2-thione (13a) and
(±)5-[1-methyl-2-(4-phenylpiperazin-1-yl)-ethyl]-1,3-di-
hydrobenzoimidazol-2-thione (13b)
10b Yield 247 mg (34%); mp 196 °C.– IR (KBr): (cm–1) 3177,
2939, 1693, 1600, 1396; – 1H-NMR (d6DMSO) δ 1.05 (d, 3H, J
= 7 Hz, methyl), 2.52 (m, 6H, piperazine, benzyl), 3.09 (m, 5H,
piperazine, CH); 6.84 (m, 1H, dihydroquinoxaline-2,3-dione);
7.01 (m, 5H, phenylpiperazine, dihydroquinoxaline-2,3-dione);
7.22 (m, 2H, dihydroquinoxaline-2,3-dione); 11.93 (NH, 2H).–
MS (MALDI TOF); m/z = 364.189 (C21H24N4O2, calc. MW
364.190).
Carbon disulfide (0.24 ml, 4 mmol) and KOH solution (0.25 g in
0.6 ml water) were added to 2 mmol of either diamine 9a or 9b
in 5 ml EtOH. After refluxing for 3 h, activated charcoal was
added and the suspension filtered through celite. The solvent
was removed in vacuo and the residue resuspended in 10 ml
of 10% NaHCO3, extracted with CH2Cl2 and concentrated in
vacuo. The resulting benzimidazole-thiones 13a and 13b were
recrystallized from hot EtOH.
Synthesis of (±)5-[2-methyl-2-(4-phenylpiperazin-1-yl)-
ethyl]-1H-benzoimidazole (11a) and (±)5-[1-methyl-2-(4-
phenylpiperazin-1-yl)-ethyl]-1H-benzoimidazole (11b)
13a Yield 429 mg (61%); mp 265 °C.– IR (KBr): (cm–1) 3063, 2957,
1597, 1498, 1459.– 1H-NMR (d6DMSO): δ 1.28 (d, 3H, J = 6.8 Hz,
methyl); 3.0–3.45 (m, 11H, benzyl, piperazine, CH2); 6.84 (m, 4H);
7.20 (m, 3H, phenylpiperazine, 1,3-dihydrobenzoimidazol-2-
thione), 7.45 (s, 1H, 1,3-dihydrobenzoimidazol-2-thione),12.2
(NH).– MS (MALDI TOF); m/z = 352.171 (C20H24N4S, calc. MW
352.172).
2 mmol of either diamine 9a or 9b and 0.44 ml (7.3 mmol) of
98% formic acid were heated in an oil bath at 100 °C for 2 h.
After cooling to ambient temperature, 15 ml of 10% NaHCO3
was added and the product extracted with CH2Cl2. The solvent
was removed in vacuo. Oily residue was purified by chromatog-
raphy.

380 Dopaminergic/serotonergic properties
Arch. Pharm. Pharm. Med. Chem. 2001, 334, 375–380
13b Yield 373 mg (53%); mp 239 °C.– IR (KBr): (cm–1) 3031,
2974, 1599, 1488, 1455.– 1H-NMR (d6DMSO): δ 0.91 (d, 3H, J
= 6.4 Hz, methyl); 2.69 (m, 4H, piperazine); 2.71 (m, 3H); 3.11
(m, 4H, piperazine); 6.79 (t, 1H J = 7 Hz, phenylpiperazine);
6.99 (m, 5H, phenylpiperazine); 7.20 (m, 2H, 1,3-dihydroben-
zoimidazol-2-thione); 12.1 (NH).– MS (MALDI TOF); m/z =
352.173 (C20H24N4S, calc. MW 352.172).
[2] C .L. E. Broekkamp, D. Leysen, B. W. M. Peeters, R. M.
Pinder, J. Med. Chem. 1995, 38, 4615–4634.
[3] G. P. Reynolds, Trends Pharmacol. Sci. 1992, 13, 116–121.
[4] V. Šoškic, J. Joksimovic, Curr .Med. Chem. 1998, 5, 493–512.
[5] S. Dukic, M. Vujovic, V. Šoškic, J. Joksimovic, Arzneim.-
Forsch. 1997, 47, 239–243.
Membrane preparation, radioligand binding assays, and
data analysis
[6] S. Dukic, S. Kostic-Rajacic, D. Dragovic, V. Šoškic, J. Joksi-
movic, J. Pharm. Pharmacol.1997, 49, 1036–1041.
Experiment were performed exactly as previously de-
scribed[8,9]
.
3[H]SCH 23390 (spec. act. 80 Ci mmol–1),
[7] S. Kostic, V. Šoškic, J. Joksimovic, Bioorg .Med. Chem. Lett.
3[H]spiperone (spec. act. 70 Ci mmol–1) and 3[H]-8-OH-DPAT
(spec. act. 223 Ci mmol–1) used to label D1, D2, and 5-HT1A
receptors, respectively, were purchased from Amersham
Buchler GmbH (Braunschweig, Germany). Competition binding
data were analyzed by the iterative non-linear least-squares
1991, 8, 403–406.
[8] D. Dragovcæ, S. Kostic-Rajacic, V. Šoškic, J. Joksimovic,
Pharmazie 1996, 51, 694–697.
curve-fitting program LIGAND [10]
.
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