N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide: A potent and selective dopamine D4 ligand

Article abstract of DOI:10.1021/jm981041x

A series of new 1-aryl-4-alkylpiperazines containing a terminal benzamide fragment or a tetralin-1-yl nucleus on the alkyl chain were synthesized and tested for binding at cloned human dopamine D₄ and D₂ receptor subtypes. A SAFIR (s

Full text of DOI:10.1021/jm981041x

J . Med. Chem. 1998, 41, 4903-4909
4903
Notes
N-[2-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]eth yl]-3-m eth oxyben za m id e: A P oten t
a n d Selective Dop a m in e D4 Liga n d
Roberto Perrone,* Francesco Berardi, Nicola A. Colabufo, Marcello Leopoldo, and Vincenzo Tortorella
Dipartimento Farmaco-Chimico, Universita´ di Bari, via Orabona, 4, 70126 Bari, Italy
Received May 29, 1998
A series of new 1-aryl-4-alkylpiperazines containing a terminal benzamide fragment or a
tetralin-1-yl nucleus on the alkyl chain were synthesized and tested for binding at cloned human
dopamine D4 and D2 receptor subtypes. A SAFIR (structure-affinity relationship) study on
this series is herein discussed. The most relevant D4 receptor affinities were displayed by
N-[ω-[4-arylpiperazin-1-yl]alkyl]-methoxybenzamides (compounds 5, 16-20), their IC50 values
ranging between 0.057 and 7.8 nM. Among these, N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-
3-methoxybenzamide (17) emerged since it exhibited very high affinity for dopamine D4 receptor
(IC50 ) 0.057 nM) with selectivity of >10 000 for the D4 versus the D2 receptor; compound 17
was also selective versus serotonin 5-HT1A and adrenergic R1 receptors.
From a survey of the recent literature, it is clear that
the discovery of ligands for dopamine D4 receptor is a
priority for many research laboratories.1 Interest in this
area is due to the speculation about the possible
involvement in schizophrenia of D4 receptors.2-5 In the
early 1990s molecular biology techniques showed that
the D2-like receptors are subdivided into D2, D3, and D4
subtypes.6-8 This latter receptor subtype is located in
cortical and other areas of the brain believed to control
emotional and cognitive functions.9,10 Most clinically
effective classical antipsychotic drugs bind at dopamine
D2-like receptors, including the D4 subtype, at thera-
peutically relevant concentration.11 It is known that the
unwanted extrapyramidal motor side effects (EPS) and
hormonal side effects such as hyperprolactinemia, in-
duced during the classical antipsychotic drugs therapy,
are due to the block of D2 receptors concentrated
primarily in the nigrostriatal and tubero-infundibular
systems of the central nervous system. On the other
hand, unlike classical neuroleptics, the atypical anti-
psychotic clozapine not only causes fewer EPS but also
displays high affinity for a variety of other receptors and
produces fatal agranulocytosis which occurs in ap-
proximately 2% of patients.12 Therefore, at the moment,
new and selective D4 ligands are needed to evaluate
them as potential antipsychotic agents devoid of un-
wanted EPS and hormonal side effects. Recent reports
of D4 selective ligands highlight that several chemical
classes of compounds bind at D4 receptor and among
these several arylpiperazine derivatives (compounds
1-4) can be found (Table 1).13-16 In a preliminary
appears to be effective in many schizophrenic patients
who are refractory to treatment with traditional neu-
roleptics. These beneficial effects of clozapine have been
assigned to its approximately 10-fold higher affinity for
D4 receptor than D2 receptor. Unfortunately, clozapine
letter17 we reported the high affinity at D4 receptor of
some N-1-(2-methoxyphenyl)piperazine derivatives bear-
ing different substituents in the ω-position of the N-4
alkyl chain (compounds 5 and 6). In the present study
we report a development of the compounds previously
* To whom correspondence should be addressed.
10.1021/jm981041x CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/04/1998

4904 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Notes
chloroformate.18 The other benzamides 21 and 22 were
prepared as follows: 3-methoxybenzoic acid (8a ) was
transformed in its acyl chloride by means of SOCl2 and
then was reacted with 2-chloroethylamine to give
benzamide 9.19 This compound was derivatized with
1-(2-methoxybenzyl)piperazine20 and 1-(4-chlorobenzyl)-
piperazine21 to give final compounds 21 and 22, respec-
tively. The synthesis of the remaining compounds is
reported in Scheme 2. The synthesis of thiazole deriva-
tives 23 and 24 required the key amides 12a ,b which
were obtained by alkylating 1-(2-methoxyphenyl)pip-
erazine (10) with 2-chloroacetamide and by hydrolyzing
nitrile derivative 11, respectively. Amides 12a ,b were
thionated with Lawesson’s reagent to give the corre-
sponding thioamides 13a ,b which were condensed with
2-bromo-3′-methoxyacetophenone to give thiazoles 23
and 24.22 Tetrahydronaphthalenamine derivatives were
prepared starting from the appropriate amines 14a ,b
which were acylated with bromoacetyl chloride or
3-chloropropionyl chloride to give the intermediates
15a -c. The reaction of these haloderivatives with 1-(2-
methoxyphenyl)piperazine (10) provided the target
amides 28-30.23
Ta ble 1. Affinities of 1-Arylpiperazine Derivatives 1-4 at
Cloned Human Dopamine Receptors
Ki, nM
compd
D4
D2
selectivity
1 (L-745870)a
0.43
8
0.7
3
920
2519
1.3
280
2140
315
2
2b
3c
4d
93
a
b
d
See ref 13. See ref 14. c See ref 15. See ref 16.
Sch em e 1a
P h a r m a cology
All final compounds (Table 2 and Table 3) were tested
for their in vitro binding affinities for human cloned
dopamine D4.2 and D2S receptors both in Sf9 cells
baculovirus expression. The following specific radioli-
gands were used: (a) dopamine D4.2 receptors-[3H]YM
09151-2; (b) dopamine D2S receptorss[3H]spiroperidol.
Compounds 5, 16, and 17 were also evaluated for in
vitro affinity on serotonin 5-HT1A and adrenergic R1
receptor binding. The following specific radioligands
and tissue sources were used: (a) serotonin 5-HT1A
receptorss[3H]-8-OH-DPAT, rat hippocampal mem-
branes; (b) R1 adrenergic receptorss[3H]prazosin, rat
brain cortex membranes. Concentrations required to
inhibit 50% of radioligand specific binding (IC50) were
determined by using eight to nine different concentra-
tions of the drug studied. Specific binding was defined
as described in the Experimental Section under Phar-
macological Methods; in all binding assays, it represents
more than 80% of total binding. The results were
analyzed by using the LIGAND program to determine
IC50 values.
a
Reagents: (A) methyl chloroformate, triethylamine; (B) SOCl2;
(C) 2-chloroethylamine; (D) 1-(2-methoxybenzyl)piperazine or 1-(4-
chlorobenzyl)piperazine.
studied in order to establish the structure-affinity
relationship (SAFIR) of this type of compounds toward
D4 receptor and D4/D2 selectivity. In particular, con-
sidering derivative 5, the ω-position substituted with a
benzamide moiety on the N-4 alkyl chain, the following
modifications were effected: (a) substitution of the
2-methoxyphenyl group on the piperazine ring with
other groups (compounds 16, 21, and 22) and also with
the 4-chlorophenyl group (compound 17) which is present
in compounds 1 and 2, two of the most potent D4 ligands
reported in the literature;13,14 (b) elongation of the alkyl
chain (compound 18); (c) suitable substitution of the
benzamide moiety to favor the formation of an intra-
molecular hydrogen bond between the amidic hydrogen
atom and the oxygen atom of the methoxy group
(compounds 19 and 20); (d) isosteric replacement of the
amide group with a thiazole ring (compounds 23 and
24). Furthermore, considering derivative 5, the ω-posi-
tion substituted with a 1-tetralinyl group on the N-4
alkyl chain, the effect on D4 affinity of the substitution
pattern of the tetralin nucleus and of the intermediate
alkyl chain length (compounds 25-30) was studied.
Resu lts a n d Discu ssion
Considering the binding affinity values for D4 receptor
(Table 2), it can be noted that benzamides 5, 16, and
17 display the highest IC50 values, ranging between
0.057 and 1.0 nM. Elongation of the alkyl chain of
derivative 5 yielded benzamide 18 with no significant
changes in affinity. The same trend was shown by
changing the position of the methoxy group on the
benzamide moiety: compounds 19 and 20 displayed
binding affinities comparable to that of the reference
compound 5. Among these derivatives it can be noted
that a marked increase in affinity and selectivity was
shown by compound 17; it bound at D4 receptor with
an affinity superior by 10000-fold to that for the
dopamine D2 receptor. Compounds 5, 16, and 17, which
displayed D4 affinity values of e1 nM and a D4/D2 IC50
ratio of >500-fold, were also evaluated for their affinities
Ch em istr y
Several synthetic routes were followed to obtain the
final compounds. The synthesis of final benzamides is
reported in Scheme 1. Compounds 16-20 were ob-
tained by condensing the amines 7a -d with the ap-
propriate benzoic acids 8a -c in the presence of methyl

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4905
Sch em e 2a
a
Reagents: (A) 2-chloroacetamide; (B) conc H2SO4; (C) Lawesson’s reagent; (D) 2-bromo-3′-methoxyacetophenone; (E) bromoacetyl
chloride or 3-chloropropionyl chloride, 1.2% NaOH.
Ta ble 2. Physical Properties and Binding Affinities of Derivatives 5, 6, 16-24
IC50, nMa
cpd
R1
R2
Xb
n
R3
formulac
mp, °C
recryst solv
D4
D2
700
13e
>1000 (18%)f 30
5-HT1A R1
5d
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
OCH3
A
B
A
A
A
A
A
A
A
C
C
2
2
2
2
3
2
2
2
2
1
2
2-CH3O-Ph
2-CH3O-Ph
2-Py
4-Cl-Ph
2-CH3O-Ph C22H29N3O3
2-CH3O-Ph C22H29N3O4‚(COOH)2
2-CH3O-Ph C21H27N3O3‚(COOH)2
2-CH3O-Bz C22H29N3O3‚2HCl‚H2O
4-Cl-Bz
2-CH3O-Ph C22H25N3O2S‚3HCl‚1/3H2O 181-183 CH2Cl2/Et2O
2-CH3O-Ph C23H27N3O2S‚HCl 177-178 CHCl3/Et2O
1.0
3.1e
1.0
0.09 360
6d
16
17
18
C19H24N4O2
C20H24ClN3O2
111
152
CHCl3/n-hexane
CHCl3/n-hexane
340
270
0.057 >1000 (42%) 220
102-104 Et2O/n-hexane
150-151 MeOH/Et2O
152-153 MeOH/Et2O
230-233 MeOH/Et2O
2.8
7.8
4.0
>1000 (33%)
19 OCH3 OCH3
20 OCH3
21
22
23
24
250
810
H
H
H
H
H
OCH3
OCH3
OCH3
OCH3
30
>1000 (13%)
>1000 (12%)
>1000 (22%)
870
C21H26ClN3O2‚2HCl‚3/2H2O 223-225 MeOH/Et2O
70
740
110
23
clozapine
230
haloperidol
1.3
4.1
a
b
Data are the mean of three independent determinations (samples in triplicate) each with SEM < 10%. Structures for X:
d
c Analyses for C, H, N; results were within (0.4% of the theoretical values for the formulas given. Formerly published compounds.17
e Formerly published data.17 f Full IC50 not obtained, percentage inhibition at the concentration shown given in parentheses. Values
taken from only one experiment.
to both 5-HT1A and R1 receptors because it is well known
that 1-arylpiperazines represent a class of serotonin
5-HT1A ligands and bind with somewhat affinity at
adrenergic R1 receptor. It can be noted that compound
17 was also highly selective versus 5-HT1A receptors
(IC50 ratio 5-HT1A/D4 ) 3860) and R1 receptor (IC50 ratio
R1/D4 ) 4700). Variation of the N-1-substituent of
piperazine ring from an aryl to a benzyl group (com-
pounds 21 and 22) resulted in decreasing the D4 affinity.
A drop in D4 affinity was observed when the amide
group was replaced by a thiazole ring (compounds 23
and 24).
Considering 1-tetralinyl derivatives 25-30 (Table 3),
the modification effected (variation of the substitution

4906 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Notes
Ta ble 3. Physical Properties and Binding Affinities of 1-Tetralinyl Derivatives 25-30
IC50, nMa
D2
20d
cpd
R1
R2
X
n
formulab
mp, °C
recryst solv
D4
25c
26c
27e
28
29
30
H
OCH3
H
OCH3
H
OCH3
H
CH2
CH2
NHCO
NHCO
NHCO
NHCO
2
2
2
2
1
1
60d
OCH3
H
OCH3
H
280
150
120d
30
761d
650
C25H33N3O3‚2HCl
C24H31N3O3‚2HCl
C24H31N3O3‚2HCl
186-187
197-203
208-214
MeOH/Et2O
EtOH/Et2O
EtOH/Et2O
850
470
>1000 (21%)f
>1000 (13%)
OCH3
a
b
Data are the mean of three independent determinations (samples in triplicate) each with SEM < 10%. Analyses for C, H, N; results
were within (0.4% of the theoretical values for the formulas given. c Formerly published compound.24 Formerly published data.17
d
e Formerly published compound.23 f Full IC50 not obtained, percentage inhibition at the concentration shown given in parentheses. Values
taken from only one experiment.
was dropped into the mixture, and the resulting mixture was
kept at -10 to - 5 °C for 1 h. After being stirred overnight at
room temperature, the reaction mixture was washed with 5%
aqueous NaOH and with water and dried over Na2SO4.
Evaporation of the solvent in vacuo afforded a crude product.
Final compounds were purified by column chromatography
(eluent CH2Cl2/MeOH, 19:1, unless otherwise indicated) to give
benzamides 16-20.
pattern of the tetralin nucleus and of the intermediate
alkyl chain length) did not lead to any remarkable D4
receptor affinity value, IC50 ranging between 30 and 850
nM, and for derivatives 25-27, the affinity at 5-HT1A
receptor was predominant (see references cited in Table
3). Any SAFIR can be drawn for these derivatives, as
regards D4 affinity.
N -[2-[4-(2-P yr id yl)p ip e r a zin -1-yl]e t h yl]-3-m e t h oxy-
ben za m id e (16). Starting from 3-methoxybenzoic acid (8a )
and 4-(2-pyridyl)-1-piperazineethanamine (7a ),23 the title com-
pound was obtained in 48% yield: 1H NMR 2.68-2.74 (m, 6H,
CH2N(CH2)2), 3.59-3.64 (m, 6H, (CH2)2NAr, NHCH2), 3.83 (s,
3H, CH3), 6.61-7.50 (m, 8H, aromatic, NH, 1H D2O ex-
changed), 8.16-8.18 (m, 1H, aromatic NdCH); GC/MS m/z 341
(M+ + 1, 2), 340 (M+, 8), 246 (73), 221 (34), 176 (100), 147
(60), 121 (92), 107 (86).
N-[2-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]eth yl]-3-m eth -
oxyben za m id e (17). Starting from acid 8a and 4-(4-chlo-
rophenyl)-1-piperazineethanamine (7b),25 the title compound
was obtained in 76% yield: 1H NMR 2.71-2.73 (m, 6H,
CH2N(CH2)2), 3.21 (br t, 4H, (CH2)2NAr), 3.60 (q, 2H, J ) 5.5
Hz, NHCH2), 3.83 (s, 3H, CH3), 6.80-7.38 (m, 9H, aromatic,
NH, 1H D2O exchanged); GC/MS m/z 376 (M+ + 3, 1), 375 (M+
+ 2, 6), 374 (M+ + 1, 4), 373 (M+, 16), 211 (33), 209 (100), 166
(26).
In conclusion, the main information obtained from
this study was that, considering the N-[2-[4-(2-methoxy-
phenyl)piperazin-1-yl]ethyl]methoxybenzamides, the sub-
stitution pattern on the benzamide moiety does not have
great relevance for binding affinity at D4 receptor and
the replacement of the 2-methoxyphenyl group in
compound 5 with a 4-chlorophenyl group (compound 17)
greatly increased the affinity and selectivity for dopa-
mine D4 vs D2. It can be noted that a similar trend was
shown by the analogues of compound 2.14 Studies are
in progress to better define the structural requirements
for an optimal affinity at the dopamine D4 receptor of
this class of compounds.
Exp er im en ta l Section
Ch em istr y. Column chromatography was performed with
1:30 ICN silica gel 60 Å (63-200 µm) as the stationary phase.
Melting points were determined in open capillaries on a
Gallenkamp electrothermal apparatus. Elemental analyses
(C, H, N) were performed on a Carlo Erba model 1106
analyzer; the analytical results were within (0.4% of the
theoretical values for the formula given. 1H NMR spectra were
recorded either on a Varian EM-390 where indicated 90 MHz
(TMS as internal standard) or on a Bruker AM 300 WB
instrument, with CDCl3 as solvent; all values are reported in
ppm (δ). Recording of mass spectra was done on a HP 5995C
gas chromatograph/mass spectrometer, electron impact 70 eV,
equipped with HP59970A workstation; only significant m/z
peaks, with their % relative intensity in parentheses, are
herein reported. All spectra were in accordance with the
assigned structures. When necessary, final compounds were
transformed into their hydrochloride or hydrogen oxalate salts
in the usual manner. Preparation and spectral properties of
compound 26 have been already reported.24
N-[3-[4-(2-Meth oxyp h en yl)p ip er a zin -1-yl]-n -p r op yl]-3-
m eth oxyben za m id e (18). This compound was prepared in
51% yield starting from acid 8a and 4-(2-methoxyphenyl)-1-
piperazinepropanamine (7d ):26 1H NMR 1.79-1.87 (m, 2H,
CH2CH2CH2), 2.64 (br t, 2H, CH2N(CH2)2), 2.68 (br s, 4H,
CH2N(CH2)2), 3.10 (br s, 4H, (CH2)2NAr), 3.58 (q, 2H, J ) 5.5
Hz, NHCH2), 3.77 and 3.84 (2 s, 6H, 2 CH3), 6.83-7.44 (m,
8H, aromatic), 8.39 (br s, 1H, NH, D2O exchanged); GC/MS
m/z 385 (M+ + 2, 3), 384 (M+ + 1, 22), 383 (M+, 89), 368 (100),
221 (57), 205 (85), 192 (56), 135 (99).
N-[2-[4-(2-Met h oxyp h en yl)p ip er a zin -1-yl]et h yl]-2,5-
d im eth oxyben za m id e (19). Starting from 2,5-dimethoxy-
benzoic acid (8b) and 4-(2-methoxyphenyl)-1-piperazineetha-
namine (7c),26 the title compound was obtained in 72% yield:
1H NMR 2.66-2.75 (m, 6H, CH2N(CH2)2), 3.13 (br s, 4H,
(CH2)2NAr), 3.62 (q, 2H, J ) 5.7 Hz, NHCH2), 3.80, 3.85, and
3.91 (3 s, 9H, 3 CH3), 6.84-7.02 and 7.76-7.77 (m, 7H,
aromatic), 8.54 (br s, 1H, NH, D2O exchanged); GC/MS m/z
400 (M+ + 1, 3), 399 (M+, 11), 218 (22), 205 (100), 190 (27).
Gen er a l P r oced u r e for P r ep a r a tion of th e Ben za -
m id es 16-20. A mixture of substituted benzoic acid 8a -c
(3.5 mmol) in CHCl3 (20 mL) and triethylamine (4.0 mmol)
was stirred at room temperature for 15 min. After the mixture
cooled at -10 °C, methyl chloroformate (4.0 mmol) was added
and the mixture reacted at the same temperature for 1 h. Then
a solution of appropriate amine 7a -d (3.8 mmol) in CHCl3
N-[2-[4-(2-Meth oxyph en yl)piper azin -1-yl]eth yl]-2-m eth -
oxyben za m id e (20). Starting from 2-methoxybenzoic acid
(8c) and amine 7c, the title compound was obtained in 56%
yield after purification by column chromatography with CH2-
Cl2/ethyl acetate, 1:1, as eluent: 1H NMR 2.64-2.73 (m, 6H,
CH2N(CH2)2), 3.12 (br s, 4H, (CH2)2NAr), 3.61 (q, 2H, J ) 5.9

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4907
Hz, NHCH2), 3.85 and 3.96 (2 s, 6H, 2 CH3), 6.84-8.22 (m,
8H, aromatic), 8.42 (br s, 1H, NH); GC/MS m/z 368 (M+ + 1,
1), 367 (M+, 2), 218 (21), 205 (100), 190 (31), 135 (30).
tate was filtered and the filtrate was evaporated to dryness.
The residual oil was taken up with 3 N HCl and the aqueous
phase was washed with CH2Cl2, alkalinized with Na2CO3, and
extracted with CHCl3. The organic phase was dried (Na2SO4)
and the solvent removed to give an oil which was chromato-
graphed with CHCl3/MeOH, 9:1, as eluent. The thioamide 13a
was obtained as a yellow solid (3.19 g, 86% yield): mp 130-
132 °C (from CH2Cl2/petroleum ether); 1H NMR (90 MHz)
2.75-3.00 (m, 4H, CH2N(CH2)2), 3.10-3.30 (m, 4H, (CH2)2-
NAr), 3.60 (s, 2H, CH2N(CH2)2), 3.85 (s, 3H, CH3), 7.00-7.05
(m, 4H, aromatic), 8.25 and 8.95 (2 br s, 2H, NH2, D2O
exchanged); GC/MS m/z 267 (M+ + 2, 3), 266 (M+ + 1, 7), 265
(M+, 43), 205 (100), 191 (28), 190 (90), 162 (25), 135 (39), 134
(29), 120 (40).
4-(2-Meth oxyp h en yl)-1-p ip er a zin ep r op a n eth ioa m id e
(13b). Lawesson’s reagent (4.61 g, 11.4 mmol) was added
portionwise to a stirred solution of the amide 12b (3.00 g, 11.4
mmol) in anhydrous toluene (30 mL). The suspension was
refluxed for 1 h under nitrogen, until it became a yellow
solution. The reaction mixture was worked up as for deriva-
tive 13a . Thioamide 13b was obtained as a yellow solid (0.90
g, 28% yield): mp 139-141 °C (from CH2Cl2/petroleum ether);
1H NMR (90 MHz) 2.60-3.20 (m, 12H, 3CH2CH2), 3.85 (s, 3H,
CH3), 6.95-7.00 (m, 4H, aromatic), 7.90 and 10.30 (2 br s, 2H,
NH2, D2O exchanged); GC-MS m/z 245 (100), 205 (65), 190 (41),
177 (42), 136 (47), 135 (42), 134 (29), 120 (62).
2-[[4-(2-Met h oxyp h en yl)p ip er a zin -1-yl]m et h yl]-4-(3-
m eth oxyp h en yl)th ia zole (23). A solution of the thioamide
13a (1.20 g, 4.5 mmol) and 2-bromo-3′-methoxyacetophenone
(2.06 g, 9.0 mmol) in anhydrous EtOH was refluxed for 6 h
under nitrogen. Evaporation of the solvent afforded an oil
which was chromatographed (CH2Cl2/MeOH, 49:1, as eluent)
to give 1.30 g (73% yield) of pure 23 as a pale yellow oil: 1H
NMR 2.95 (br s, 4H, CH2N(CH2)2), 3.20 (br s, 4H, (CH2)2NAr),
3.84 and 3.86 (2 s, 6H, CH3), 4.08 (br s, 2H, CH2N(CH2)2),
6.84-7.46 (m, 9H, aromatic); GC/MS m/z 397 (M+ + 2, 4), 396
(M+ + 1, 12), 395 (M+, 46), 326 (29), 246 (32), 205 (100), 204
(55), 191 (64), 176 (50), 175 (55), 162 (55).
2-[2-[4-(2-Met h oxyp h en yl)p ip er a zin -1-yl]et h yl]-4-(3-
m eth oxyp h en yl)th ia zole (24). As above, starting from the
thioamide 13b (0.90 g, 3.2 mmol) and 2-bromo-3′-methoxy-
acetophenone (1.47 g, 6.4 mmol), the title compound was
obtained as a pale yellow oil (0.72 g, 56% yield): 1H NMR 2.85
and 2.98 (2 br s, 6H, CH2CH2N(CH2)2), 3.18 (br s, 4H, (CH2)2-
NAr), 3.34 (br s, 2H, CH2CH2N(CH2)2), 3.85 and 3.86 (2 s, 6H,
CH3), 6.84-7.45 (m, 9H, aromatic); GC/MS 410 (M+ + 1, 1),
409 (M+, 5), 260 (25), 247 (57), 205 (100), 204 (60), 203 (22),
191 (28), 190 (37).
N-(2-Ch lor oeth yl)-3-m eth oxyben zam ide (9). To a cooled
mixture containing 2-chloroethylamine hydrochloride (2.04 g,
17.6 mmol) in 1.2% aqueous NaOH (120 mL) was added
dropwise under vigorous stirring a CH2Cl2 solution (50 mL)
of 3-methoxybenzoyl chloride, prepared from the acid 8a (2.43
g, 16.0 mmol) and SOCl2 (5 mL). Then, the aqueous layer was
separated and extracted with CH2Cl2. The combined organic
layers were dried over Na2SO4 and evaporated to dryness
under reduced pressure to give nearly pure benzamide 9 as a
colorless oil (3.27 g, 96% yield): 1H NMR (90 MHz) 3.55-3.85
(m + s, 7H, CH2CH2, CH3), 6.65-7.45 (m, 5H, aromatic, NH,
1H D2O exchanged); GC/MS m/z 215 (M+ + 2, 1), 213 (M+, 5),
177 (81), 176 (36), 147 (100).
N-[2-[4-(2-Meth oxyben zyl)piper azin -1-yl]eth yl]-3-m eth -
oxyb en za m id e (21). A stirred solution of 1-(2-methoxy-
benzyl)piperazine (1.73 g, 8.4 mmol), benzamide 9 (1.50 g, 7.0
mmol), and triethylamine (4 mL) in toluene (50 mL) was
refluxed for 20 h. Then the solvent was evaporated under
reduced pressure and the residue taken up with a 20% aqueous
Na2CO3 and extracted with ethyl acetate. The organic layer
was dried (Na2SO4) and evaporated to dryness. The crude
residue was eluted with CHCl3/MeOH, 19:1, to give 0.45 g of
benzamide 21 (17% yield) as a pale yellow oil: 1H NMR 2.59-
2.64 (m, 10H, NHCH2CH2, piperazine), 3.53 (q, 2H, J ) 5.5
Hz, NHCH2CH2), 3.60 (s, 2H, benzyl CH2), 3.80 and 3.83 (2 s,
6H, 2 CH3), 6.84-7.38 (m, 9H, aromatic, NH); GC/MS m/z 384
(M+ + 1, 2), 383 (M+, 8), 219 (100), 121 (53).
N-[2-[4-(4-Ch lor oben zyl)p ip er a zin -1-yl]eth yl]-3-m eth -
oxyb en za m id e (22). As above, starting from 1-(4-chloro-
benzyl)piperazine (1.77 g, 9.0 mmol) and the benzamide 9 (1.60
g, 7.5 mmol), the title compound was obtained in 36% yield:
1H NMR 2.51-2.66 (m, 10H, NHCH2CH2, piperazine), 3.47 (s,
2H, benzyl CH2), 3.51-3.70 (m, 2H, NHCH2CH2), 3.84 (s, 3H,
CH3), 6.97-7.38 (m, 9H, aromatic, NH); GC/MS m/z 389 (M+
+ 2, 1), 388 (M+ + 1, 1), 387 (M+, 4), 225 (33), 223 (100), 125
(44).
4-(2-Meth oxyp h en yl)-1-p ip er a zin ea ceta m id e (12a ). A
mixture of the piperazine 10 (3.25 g, 17.0 mmol) and 2-chlo-
roacetamide (3.18 g, 34.0 mmol) in toluene (30 mL) was
refluxed overnight in the presence of a slight excess of K2CO3.
After the mixture cooled, the solvent was removed under
reduced pressure. The residue was taken up in H2O and
extracted with CH2Cl2. The organic phase was dried (Na2SO4)
and the solvent removed, affording the amide 12a as a white
solid (3.19 g, 75% yield): mp 154-156 °C (from CH2Cl2/
petroleum ether); 1H NMR (90 MHz) 2.65-2.85 (m, 4H, CH2N-
(CH2)2), 3.00-3.25 (m, 6H, (CH2)2NAr, CH2N(CH2)2), 3.85 (s,
3H, CH3), 6.30 (br s, 2H, NH2), 6.80-7.10 (m, 4H, aromatic);
GC/MS m/z 251 (M+ + 2, 1), 250 (M+ + 1, 9), 249 (M+, 62),
205 (100), 190 (60), 162 (26), 134 (23), 120 (36).
N-(7-Meth oxy-1,2,3,4-tetr a h yd r on a p h th a len -1-yl)br o-
m oa ceta m id e (15a ). Following the procedure reported for
the synthesis of the amide 9, the title compound was obtained
from 7-methoxy-1,2,3,4-tetrahydro-1-naphthalenamine (14a )27
(1.35 g, 9.9 mmol) and bromoacetyl chloride (0.7 mL, 9.5 mmol)
in nearly quantitative yield, as a white solid: mp 101-103 °C
(from CHCl3/n-hexane); 1H NMR (90 MHz) 1.65-2.15 (m, 4H,
endo CH2CH2), 2.75 (br t, 2H, benzyl CH2), 3.75 (s, 3H, CH3),
3.85 (s, 2H, CH2Br), 4.95-5.25 (m, 1H, CHNH), 6.60-7.10 (m,
4H, aromatic, NH); GC/MS m/z 299 (M+ + 2, 2), 297 (M+, 2),
160 (100), 159 (26).
4-(2-Meth oxyp h en yl)-1-p ip er a zin ep r op a n a m id e (12b).
4-(2-Methoxyphenyl)-1-piperazinepropanenitrile26 (11) (3.20 g,
13.0 mmol) was slowly added under vigorous stirring to
concentrated H2SO4 (10 mL), at room temperature. The
mixture was heated for 1 h at 70-80 °C, then poured on ice
and subsequently alkalinized with Na2CO3 and extracted with
CH2Cl2; the separated organic layer was dried (Na2SO4) and
evaporated under reduced pressure to give amide 12b (2.74
g, 80% yield) as a white powder: mp 147-148 °C (from CH2-
Cl2/petroleum ether); 1H NMR (90 MHz) 2.35-2.95 (m, 8H,
CH2CH2N(CH2)2), 3.05-3.30 (m, 4H, (CH2)2NAr), 3.90 (s, 3H,
CH3), 5.83 and 8.15 (2 br s, 2H, NH2, D2O exchanged), 6.90-
7.05 (m, 4H, aromatic); GC/MS m/z 265 (M+ + 2, 2), 264 (M+
+ 1, 17), 263 (M+, 100), 205 (52), 190 (36), 162 (28), 150 (25),
136 (71), 135 (38), 134 (38), 121 (25), 120 (67).
N-(7-Meth oxy-1,2,3,4-tetr ah ydr on aph th alen -1-yl)-3-ch lo-
r op r op a n a m id e (15c). In the same manner as above, this
compound was obtained from the amine 14a (1.24 g, 7.0 mmol)
and 3-chloropropionyl chloride (0.6 mL, 9.1 mmol) in nearly
quantitative yield as a white solid: mp 126-127 °C (from CH2-
Cl2/n-hexane); 1H NMR (90 MHz) 1.66-2.10 (m, 4H, endo CH2-
CH2), 2.45-2.80 (m, 4H, benzyl CH2, COCH2), 3.70-3.90 (m
+ s, 5H, CH3, CH2Cl), 5.00-5.30 (m, 1H, CHNH), 6.20 (br d,
1H, NH), 6.65-7.00 (m, 3H, aromatic); GC/MS m/z 269 (M+
2, 1), 268 (M+ + 1, 1), 267 (M+, 4), 160 (100), 159 (25).
+
4-(2-Meth oxyph en yl)-1-p ip er a zin eth ioa ceta m id e (13a ).
Lawesson’s reagent (5.66 g, 14.0 mmol) was added portionwise
to a stirred solution of the amide 12a (3.49 g, 14.0 mmol) in
anhydrous THF (30 mL). The suspension was refluxed for 1
h under nitrogen, until it became a yellow solution. After the
solution was cooled at room temperature, the formed precipi-
N-(7-Meth oxy-1,2,3,4-tetr a h yd r on a p h th a len -1-yl)-4-(2-
m et h oxyp h en yl)-1-p ip er a zin ep r op a n a m id e (28). The
amide 15c (1.05 g, 3.9 mmol) was refluxed overnight with the
piperazine 10 (1.39 g, 7.8 mmol) and a slight excess of NaHCO3
in acetonitrile. After cooling, the mixture was concentrated

4908 J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24
Notes
under reduced pressure, and the residue was taken up with
water and extracted with CHCl3. The chloroform phase was
dried over Na2SO4, the solvent was evaporated, and the crude
residue was chromatographed (CHCl3/MeOH, 19:1 as eluent)
to give 28 as a pale yellow semisolid (1.23 g, 78% yield): 1H
NMR 1.74-2.01 (m, 4H, endo CH2CH2), 2.45-3.03 (m, 14H),
3.71 and 3.82 (2 s, 6H, 2 CH3), 5.05-5.09 (m, 1H, CHNH),
6.69-7.02 (m, 7H, aromatic), 8.66 (br s, 1H, NH); GC/MS m/z
425 (M+ + 2, 2), 424 (M+ + 1, 13), 423 (M+, 50), 409 (27), 408
(100), 205 (26), 161 (60), 160 (32).
N-(5-Meth oxy-1,2,3,4-tetr a h yd r on a p h th a len -1-yl)-4-(2-
m eth oxyp h en yl)-1-p ip er a zin ea ceta m id e (29). Starting
from N-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)bro-
moacetamide23 (15b) and 1-(2-methoxyphenyl)piperazine (10),
the title compound was prepared as above in the same yield:
1H NMR 1.72-1.84 and 1.97-2.04 (mm, 4H, endo CH2CH2),
2.57-2.73 (m, 6H, benzyl CH2, CH2N(CH2)2), 3.03 (br s, 4H,
(CH2)2NAr), 3.13 (br s, 2H, CH2N(CH2)2), 3.80 and 3.83 (2 s,
6H, 2 CH3), 5.13-5.22 (m, 1H, CHNH), 6.71-7.16 (m, 7H,
aromatic), 7.42 (br s, 1H, NH, D2O exchanged); GC/MS m/z
411 (M+ + 2, 1), 410 (M+ + 1, 5), 409 (M+, 29), 205 (100), 190
(27).
N-(7-Meth oxy-1,2,3,4-tetr a h yd r on a p h th a len -1-yl)-4-(2-
m eth oxyp h en yl)-1-p ip er a zin ea ceta m id e (30). As above
and in the same yield, the title compound was prepared
starting from compound 15a and 1-(2-methoxyphenyl)pipera-
zine (10): 1H NMR 1.67-1.85 and 2.00-2.10 (mm, 4H, endo
CH2CH2), 2.63-2.80 (mm, 6H, benzyl CH2, CH2N(CH2)2), 3.02
(br s, 4H, (CH2)2NAr), 3.12 (d, 2H, J ) 5.4 Hz, CH2N(CH2)2),
3.73 and 3.83 (2 s, 6H, 2 CH3), 5.14-5.20 (m, 1H, CHNH),
6.73-7.02 (m, 7H, aromatic), 7.43 (br d, 1H, NH); GC/MS m/z
411 (M+ + 2, 1), 410 (M+ + 1, 9), 409 (M+, 38), 205 (100), 190
(27).
P h a r m a cologica l Meth od s. D4.2 Dop a m in er gic Bin d -
in g Assa y. Binding of [3H]YM-09151-2 for human cloned D4.2
dopamine receptor produced in Sf9 cells baculovirus expression
(NEN Life Science) was performed according to Hadley et al.28
with minor modifications. The reaction buffer consisted of 50
mM Tris‚HCl, 5 mM MgCl2, 5 mM EDTA, 5 mM KCl, 1.5 mM
CaCl2 (pH 7.4), including 500 µL of dopamine D4.2 diluted
membranes, 0.06 nM of [3H]YM-09151-2 (Kd) 0.06 nM), and
100 µL of various concentrations (10-6-10-11 M) of drugs to
reach a total volume of 1 mL. After a 60 min incubation at
25 °C, the incubations were terminated by rapid filtration
through Whatman GF/C glass fiber filters (presoaked in 0.3%
polyethylenimine) with two washes of 1 mL of ice cold buffer
(50 mM Tris‚HCl, pH 7.4). Nonspecific binding was defined
in the presence of haloperidol (1 µM).
D2S Dop a m in er gic Bin d in g Assa y. Binding of [3H]-
spiperone for human cloned D2S dopamine receptor produced
in Sf9 cells baculovirus expression (NEN Life Science) was
performed according to Hadley et al.28 with minor modifica-
tions. The reaction buffer consisted of 50 mM Tris‚HCl, 10
mM MgCl2, 1 mM EDTA (pH 7.4), including 500 µL of
dopamine D2S diluted membranes, 0.2 nM of [3H]spiperone (Kd
) 0.17 nM), and 100 µL of various concentration (10-6-10-11
M) of drugs to reach a total volume of 1 mL. After a 60 min
incubation at 27 °C, the incubations were terminated by rapid
filtration through Whatman GF/C glass fiber filters (presoaked
in 0.3% polyethylenimine) with two washes of 1 mL of ice cold
buffer (50 mM Tris‚HCl, pH 7.4). Nonspecific binding was
defined in the presence of haloperidol (1 µM).
5-HT1A Ser oton er gic Bin d in g Assa y. Standard receptor
binding methods were used to label 5-HT1A receptors using
[3H]-8-OH-DPAT as previously decribed.29
r1 Ad r en er gic Bin d in g Assa y. Standard receptor binding
methods were used to label R1 receptors using [3H]prazosin
as previously decribed.29
and biological evaluation of new drugs: SAR studies on
serotonergic agents with arylpiperazine structure”.
Refer en ces
(1) Lie´geois, J .-F.; Eyrolles, L.; Bruhwyler, J .; Delarge, J . Dopamine
D4 receptors: a new opportunity for research on schizophrenia.
Curr. Med. Chem. 1998, 5, 77-100.
(2) Seeman, P.; Guan, H. C.; Van Tol, H. H. Dopamine D4 receptors
elevated in schizophrenia. Nature 1993, 365, 441-445.
(3) Reynolds, G. P.; Mason, S. L. Absence of detectable striatal
dopamine D4 receptors in drug-treated schizophrenia. Eur. J .
Pharmacol. 1995, 281, R5-R-6.
(4) Seeman, P.; Guan, H. C.; Van Tol, H. H. Schizophrenia:
elevation of dopamine D4-like sites, using [3H]nemonapride and
[
125I]epidepride. Eur. J . Pharmacol. 1995, 286, R3-R-5.
(5) Sumiyoshi, T.; Stockmeier, C. A.; Overholser, J . C.; Thompson,
P. A.; Meltzer, H. Y. Dopamine D4 receptors and effects of
guanine nucleotides on [3H]raclopride binding in postmortem
caudate nucleus of subjects with schizophrenia or major depres-
sion. Brain Res. 1995, 681, 109-116.
(6) Grandy, D. K.; Marchionni, M. A.; Makam, H.; Stofko, R. E.;
Alfano, M.; Frothingham, L.; Fisher, J . B.; Burke-Howie, K. J .;
Bunzow, J . R.; Server, A. C.; Civelli, O. Cloning of the cDNA
and gene for a human D2 dopamine receptor. Proc. Natl. Acad.
Sci. U.S.A. 1989, 86, 9762-9766.
(7) Sokoloff, P.; Giros, B.; Martres, M. P.; Bouthenet, M. L.; Schwarz,
J . C. Molecular cloning and characterization of a novel dopamine
receptor (D3) as a target of neuroleptics. Nature 1991, 347, 72-
76.
(8) Van Tol, H. H.; Bunzow, J . R.; Guan, H. C.; Sunahara, R. K.;
Seeman, P.; Niznik, H. B.; Civelli, O. Cloning of the gene for a
human dopamine D4 receptor with high affinity for the anti-
psychotic clozapine. Nature 1991, 350, 610-614.
(9) Matsumoto, M.; Hidaka, K.; Tada, S.; Tasaki, Y.; Yamaguchi,
T. Full-length cDNA cloning and distribution of human dopam-
ine D4 receptor. Brain Res. Mol. Brain Res. 1995, 29, 157-162.
(10) Seeman, P. Dopamine receptors and the dopamine hypothesis
of schizophrenia. Synapse 1987, 1, 133-152.
(11) Fitton, A.; Heel, R. C. Clozapine. A review of its pharmacological
properties, and therapeutic use in schizophrenia. Drugs 1990,
40, 722-747.
(12) Krupp, P.; Barnes, P. Clozapine-associated agranulocytosis: risk
and aetiology. Br. J . Psychiatry 1992, 160 (suppl. 17), 38-40.
(13) Kulagowski, J . J .; Broughton, H. B.; Curtis, N. R.; Mawer, I.
M.; Ridgill, M. P.; Baker, R.; Emms, F.; Freedman, S. B.;
Marwood, R.; Patel, S.; Patel, S.; Ragan, C. I.; Leeson, P. D.
3-[[4-(4-Chlorophenyl)piperazin-1-yl]methyl]-1H-pyrrolo[2,3-b]-
pyridine: an antagonist with high affinity and selectivity for
the human dopamine D4 receptor. J . Med. Chem. 1996, 39,
1941-1942.
(14) Boyfield, I.; Coldwell, M. C.; Hadley, M. S.; Healy, M. A. M.;
J ohns, A.; Nash, D. J .; Riley, G. J .; Scott, E. E.; Smith, S. A.;
Stemp, G.; Wilson, K. N-(Substituted-phenyl)piperazines: an-
tagonists with high binding and functional selectivity for dopam-
ine D4 receptors. Bioorg. Med. Chem. Lett. 1996, 6, 1227-1232.
(15) Thurkauf, A.; Yuan, J .; Chen, X.; Wasley, J . W. F.; Meade, R.;
Woodruff, K. H.; Huston, K.; Ross, P. C. 1-Phenyl-3-(amino-
methyl)pyrroles as potential antipsychotic agents. Synthesis and
dopamine receptor binding. J . Med. Chem. 1995, 38, 4950-4952.
(16) He, X. S.; Woodruff, K.; Brodbeck, R. A new series of selective
dopamine D4 ligands: 3-([4-arylpiperazin-1-yl]alkylamino)-2H-
1,4-benzoxazines. Bioorg. Med. Chem. Lett. 1997, 7, 2399-2402.
(17) Perrone, R.; Berardi, F.; Colabufo, N. A.; Leopoldo, M.; Tortorella,
V. 1-(2-Methoxyphenyl)-4-alkylpiperazines: effect of the N-4
substituent on the affinity and selectivity for dopamine D4
receptor. Bioorg. Med. Chem. Lett. 1997, 7, 1327-1330.
(18) Kato, S.; Morie, T.; Hino, K.; Kon, T.; Naruto, S.; Yoshida, N.;
Karasawa, T.; Matsumoto, J . Novel benzamides as selective and
potent gastric prokinetic agents. 1. Synthesis and structure-
activity relationships of N-[(2-morpholinyl)alkyl]benzamides. J .
Med. Chem. 1990, 33, 1406-1413.
(19) Perrone, R.; Berardi, F.; Leopoldo, M.; Tortorella, V.; Lograno,
M. D.; Daniele, E.; Govoni, S. 5-HT and DA receptor affinity of
arylpiperazine derivatives with terminal benzamide fragment.
Farmaco 1994, 49, 567-572.
(20) Ohtaka, H.; Fujimoto, Y.; Yoshida, K.; Kanazawa, T.; Ito, K.;
Tsukamoto, G. Benzylpiperazine derivatives. II. Syntheses and
cerebral vasodilating activities of 1-[(3-alkyl-3-hydroxy-3-
phenyl)propyl]-4-benzylpiperazine derivatives. Chem. Pharm.
Bull. 1987, 35, 2782-2791.
Ack n ow led gm en t. This study was supported by
research Grant 9703028183-022 from “Universita` degli
Studi di Bari” and M.U.R.S.T. (Italy) for the scientific
program in CO7X field - 1998-2000: “Design, synthesis
(21) Baltzly, R.; Buck, J . S.; Lorz, E.; Scho¨n, W. The preparation of
N-mono-substituted and unsymmetrically disubstituted pipera-
zines. J . Am. Chem. Soc. 1944, 66, 263-266.

Notes
J ournal of Medicinal Chemistry, 1998, Vol. 41, No. 24 4909
(22) Perrone, R.; Berardi, F.; Colabufo, N. A.; Tortorella, V.; Forna-
retto, M. G.; Caccia, C.; McArthur, R. Synthesis of arylpipera-
zines with a terminal naphthothiazole group and their evalua-
tion on 5-HT, DA and R receptors. Eur. J . Med. Chem. 1997,
32, 739-746.
(23) Perrone, R.; Berardi, F.; Leopoldo, M.; Tortorella, V.; Fornaretto,
M. G.; Caccia, C.; McArthur, R. 1-Aryl-4-[(1-tetralinyl)alkyl]-
piperazines: alkylamido and alkylamino derivatives. Synthesis,
5-HT1A receptor affinity, and selectivity. 3. J . Med. Chem. 1996,
39, 3195-3202.
M. D.; Daniele, E.; Govoni, S. 5-HT1A and D-2 receptor affinity
of o-methoxyphenylpiperazine derivatives with terminal benz-
amide fragment on N-4 alkyl chain. 2. Farmaco 1995, 50, 505-
510.
(27) Vaccaro, W.; Amore, C.; Berger, J .; Burrier, R.; Clader, J .; Davis,
H.; Domalski, M.; Fevig, T.; Salisbury, B.; Sher, R. Inhibitors of
acyl CoA:cholesterol acyltransferase. J . Med. Chem. 1996, 39,
1704-1719.
(28) Boyfield, I.; Brown, T. H.; Coldwell, M. C.; Cooper, D. G.; Hadley,
M. S.; Hagan, J . J .; Healy, M. A.; J ones, A.; King, R. J .;
Middlemiss, D. N.; Nash, D. J .; Riley, G. J .; Scott, E. E.; Smith,
S. A.; Stemp, G. Design and synthesis of 2-naphthoate esters as
selective dopamine D4 antagonists. J . Med. Chem. 1996, 39,
1946-1948.
(29) Perrone, R.; Berardi, F.; Colabufo, N. A.; Leopoldo, M.; Lograno,
M.; Tortorella, V. 4-[ω-(Tetralin-1-yl)alkyl]-1-benzylpiperazines
and related compounds as 5-HT1A/D-2 ligands. Med. Chem. Res.
1997, 7, 76-86.
(24) Perrone, R.; Berardi, F.; Colabufo, N. A.; Leopoldo, M.; Tortorella,
V.; Fiorentini, F.; Olgiati, V.; Ghiglieri, A.; Govoni, S. High
affinity and selectivity on 5-HT1A receptor of 1-aryl-4-[(1-
tetralin)alkyl]piperazines. 2. J . Med. Chem. 1995, 38, 942-949.
(25) Mull, R. P.; Mizzoni, R. H.; Dapero, M. R.; Egbert, M. E.
Guanidines with antihypertensive activity. II. J . Med. Pharm.
Chem. 1962, 5, 944-949.
(26) Perrone, R.; Berardi, F.; Leopoldo, M.; Tortorella, V.; Lograno,
J M981041X