A structure-affinity relationship study on derivatives of N-[2-[4-(4- chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide, a high-affinity and selective D4 receptor ligand

Article abstract of DOI:10.1021/jm991138z

N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (1), a high-affinity and selective dopamine D₄ receptor ligand, was chosen as a lead, and structural modifications were done on its amide bond and on its alkyl chain linking the b

Full text of DOI:10.1021/jm991138z

270
J . Med. Chem. 2000, 43, 270-277
A Str u ctu r e-Affin ity Rela tion sh ip Stu d y on Der iva tives of
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
High -Affin ity a n d Selective D4 Recep tor 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 August 2, 1999
N-[2-[4-(4-Chlorophenyl)piperazin-1-yl]ethyl]-3-methoxybenzamide (1), a high-affinity and
selective dopamine D4 receptor ligand, was chosen as a lead, and structural modifications were
done on its amide bond and on its alkyl chain linking the benzamide moiety to the piperazine
ring and by preparing some semirigid analogues. The binding profile at dopamine D4 and
dopamine D2, serotonin 5-HT1A, and adrenergic R1 receptors of 16 new compounds was
determined. From the results emerged that the modification of the amide bond and the
elongation of the intermediate alkyl chain caused a decrease in dopamine D4 receptor affinity.
All prepared semirigid analogues displayed D4 receptor affinity values in the same range of
the opened counterparts.
Currently, much research effort is being focused on
the discovery of highly selective dopamine D4 receptor
ligands.1 The reason for the interest in this area derives
from the possible involvement of D4 receptor in schizo-
phrenia.2-5 Recent advances in molecular biology have
identified five cloned human subtypes of dopamine
receptor, divided pharmacologically into two classes: D1-
like (D1 and D5)6,7 and D2-like (D2, D3, and D4).8-10
Classical antipsychotic drugs are presumed to act by an
unselective blockade of D2-like dopamine receptors.11
These drugs are useful for the treatment of positive
symptoms of schizophrenia, and their use is limited by
disabling side effects such as the unwanted extrapyra-
midal syndrome (EPS), tardive dyskinesia, and hor-
monal side effects such as hyperprolactinemia.12 On the
other hand, unlike classical neuroleptics, the atypical
antipsychotic clozapine can be used to treat both positive
and negative symptoms of schizophrenia and it causes
fewer cases of EPS.13 These beneficial effects of cloza-
pine have been assigned to its approximately 10-fold
higher affinity for D4 receptor than D2 receptor. Unfor-
tunately, clozapine displays high affinity for a variety
of other receptors and produces fatal agranulocytosis
in approximately 2% of patients.14 In the last five years,
several research groups have communicated on a num-
ber of series of D4 receptor ligands. Some of them
underwent clinical trials giving somewhat different
results. For example, L-745,870 was found to be inef-
fective as an antipsychotic in humans;15 on the contrary,
CP-293,019 was claimed to display an excellent activity
in an in vivo model responsive to antipsychotic drugs,
yet lacked the property to produce APO-induced ste-
reotypy and to induce catalepsy.16 Therefore, to date,
new potent and selective D4 receptor ligands are needed
to clarify the role of the D4 receptors in the etiology of
schizophrenia and related disorders. Our research group
initiated a research program aimed to discover new D4
receptor ligands with 1-arylpiperazine structure17 which
led to N-[2-[4-(4-chlorophenyl)piperazin-1-yl]ethyl]-3-
methoxybenzamide (1).18 This derivative exhibited very
high affinity toward dopamine D4 receptor (Ki ) 0.04
nM) with a >10000-fold selectivity versus the D2 recep-
tor. In the present paper we studied some structural
modifications with the aim to put in evidence the
fundamental structural requirement for the high affin-
ity and selectivity of compound 1 at D4 receptor. We first
studied the importance of the amide function in com-
pound 1 through the substitution of the amido group
with a keto group (compound 28), the replacing of the
amide function with two methylene groups (compound
29), and the reduction of the amide function (compound
30). Furthermore, we provided for the synthesis of the
corresponding retro amide 31 and the methylation of
the nitrogen of the amide function (compound 32).
Subsequently, we studied the effect on D4 receptor
binding affinity of the alkyl chain length for the most
high affinity compounds (derivatives 1 and 28) by
preparing compounds 33-37. Finally, as we noted that
the optimal chain length was of two methylene groups
* To whom correspondence should be addressed. Phone: +39 080
54 42 752. Fax: +39 080 54 42 724. E-mail: perrone@farmchim.uniba.it.
10.1021/jm991138z CCC: $19.00 © 2000 American Chemical Society
Published on Web 12/28/1999

SAR of a Selective D4 Receptor Ligand
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2 271
Sch em e 1a
a
Reagents: (A) (CH3)3SiCN, ZnI2; (B) (i) LDA, Br(CH2)3Cl, (ii) 2 N HCl; (C) BrMg(CH2)4Cl or BrMg(CH2)5Cl; (D) J ones’ reagent; (E)
(CH3)3CNH2‚BH3, AlCl3; (F) Cl(CH2)2COCl; (G) 1-(4-chlorophenyl)piperazine (14).
(n ) 2), some semirigid congeners of compounds 1, 29,
and 30 were prepared and tested. In particular, com-
pounds 38 and 39, 40 and 41, 42 and 43 can be
considered structurally related with compounds 1, 29,
and 30, respectively.
The intermediate anilide 13 was prepared by acyla-
tion of 3-methoxyaniline (11) with 3-chloropropionyl
chloride.
The synthesis of compounds 33-35 (Scheme 2) re-
quired amines 17-19 as the key intermediates. The
amines 17 and 18 were prepared as described in the
literature.23 The amine 19 was prepared by alkylating
1-(4-chlorophenyl)piperazine (14) with 4-chloropentane-
nitrile to give compound 15; reduction of the latter with
borane methyl sulfide complex24 yielded amine 19.
Finally, benzamides 33-35 were obtained by condens-
ing 3-methoxybenzoyl chloride with the amines 17-19.
Tetrahydronaphthalenamine derivatives 42 and 43
were prepared by condensing methoxy-1-tetralones 20
and 21 with the amine 1623 and then reducing the
intermediate imines with NaBH4.
Ch em istr y
The final step for the preparation of compounds 28,
29, 31, 36, 37, 40, and 41 was the alkylation of 1-(4-
chlorophenyl)piperazine (14) with the appropriate alkyl
halides (Scheme 1). Among the latter compounds,
derivatives 9 and 10 were prepared according to the
reported procedure,19 and the remaining were obtained
as described below.
Ketone 6 was prepared as follows: 3-methoxybenzal-
dehyde (2) was reacted with trimethylsilyl cyanide to
give the trimethylsilyl cyanohydrin derivative 3;20 the
latter was transformed into its anion with lithium
diisopropylamide (LDA) and then it was alkylated with
1-bromo-3-chloropropane.21 The protected cyanohydrin
so obtained gave the intermediate ketone 6 by subse-
quent treatment with dilute hydrochloric acid.
The ketones 7 and 8 were obtained from 3-methoxy-
benzaldehyde (2) which was reacted with the appropri-
ate Grignard reagent to give the secondary alcohols 4
and 5; oxidation of the latter compounds with J ones’
reagent gave the key intermediates 7 and 8.
Chlorobutyl derivative 12 was obtained from ketone
6 by reduction of the carbonyl function with tert-
butylamino borane complex in the presence of AlCl3.22
The amine 30 was prepared by reducing benzamide
1 with borane methyl sulfide complex.24
N-Methylated benzamide 32 and cyclic amides 38 and
39 were prepared (Scheme 2) by reacting, under phase-
transfer catalysis,25 4-(2-chloroethyl)-1-(4-chlorophenyl)-
piperazine26 (22) with the N-methyl-3-methoxybenza-
mide27 (23) or intermediate amides 26 and 27, respec-
tively. Isoquinolinone 26 was prepared, following the
same synthetic procedure reported for its isomer 27,28
starting from 2-methoxyphenethylamine (24) which was
reacted with methyl chloroformate to give the carbam-
ate 25; cyclization of the latter with polyphosphoric acid
afforded isoquinolinone 26.

272 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2
Perrone et al.
Sch em e 2a
a
Reagents: (A) Cl(CH2)4CN; (B) (CH3)2S‚BH3; (C) 3-methoxybenzoyl chloride; (D) (i) p-toluenesulfonic acid, (ii) NaBH4; (E) Br(CH2)2Cl;
(F) ClCOOCH3, triethylamine; (G) polyphosphoric acid; (H) tetrabutylammonium bromide, KOH.
Ta ble 1. Physical Properties and Binding Affinities of Derivatives 28-37
Ki ( SEM, nMa
cpd
X
n
formulab
C21H25ClN2O2
mp, °C
recryst solv
D4.4
D2L
5-HT1A
R1
1c
CONH
2
2
2
2
2
2
3
4
5
3
4
0.040 ( 0.002 1900 ( 250
147 ( 14
183 ( 11
514 ( 29
245 ( 30
908 ( 37
28
29
30
31
32
33
34
35
36
37
COCH2
CH2CH2
CH2NH
NHCO
CON(CH3)
CONH
CONH
CONH
COCH2
COCH2
96-97
CHCl3/n-hexane
MeOH/Et2O
MeOH/Et2O
MeOH/Et2O
4.0 ( 0.8
204 ( 19
23 ( 9
2550 ( 140
2740 ( 200
C21H27ClN2O‚2HCl‚1/2H2O 161
>850 (25%)d
C20H26ClN3O‚2HCl
20H24ClN3O2‚2HCl
C21H26ClN3O2‚HCl
235
254 dec
237-239 MeOH
121-123 CHCl3/n-hexane
5000 ( 210 >850 (16%) >850 (12%)
C
42 ( 8
282 ( 21
859 ( 93
303 ( 28
180 ( 12
5.4 ( 0.7
25 ( 2
>850 (10%) >850 (18%) >850 (22%)
C
C
C
21H26ClN3O2
3950 ( 150 >850 (41%)
2350 ( 270 397 ( 32
>850 (22%) >850 (44%)
437 ( 31
406 ( 40
470 ( 25
146 ( 12
678 ( 35
56 ( 8
22H28ClN3O2‚HCl‚5/4H2O 191-193 MeOH/Et2O
23H30ClN3O2‚HCl
189-190 MeOH/Et2O
241 ( 35
21 ( 8
280 ( 21
30.0 ( 0.3
1.0 ( 0.1
C22H27ClN2O2‚HCl‚3/2H2O 179-180 MeOH/Et2O
>850 (20%)
>850 (15%)
876 ( 72
37 ( 6
45 ( 8
443 ( 13
2390 ( 320
C23H29ClN2O2
75-77
CHCl3/n-hexane
clozapine
haloperidol
5.6 ( 0.3
146 ( 18
a
b
Data are the mean of three independent determinations (samples in triplicate). Analyses for C, H, N; results were within (0.4% of
the theoretical values for the formulas given. c See ref 18. Full Ki not obtained, percentage inhibition at the concentration shown given
d
in parentheses. Values taken from only one experiment.
P h a r m a cology
were used: (a) dopamine D4.4 receptorss[3H]YM
09151-2, human cloned in Sf9 baculovirus expression;
(b) dopamine D2L receptorss[3H]spiroperidol, human
cloned in Sf9 baculovirus expression; (c) serotonin
5-HT1A receptorss[3H]-8-OH-DPAT, rat hippocampal
All final compounds (Tables 1 and 2) were tested for
their in vitro binding affinities toward dopamine D4.4
and D2L, serotonin 5-HT1A, and R1 adrenergic receptors.
The following specific radioligands and tissue sources

SAR of a Selective D4 Receptor Ligand
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2 273
Ta ble 2. Physical Properties and Binding Affinities of Derivatives 38-43
Ki ( SEM, nMa
cpd type
R1
R2
X
formulab
mp, °C
recryst solv
MeOH/Et2O
D4
D2
5-HT1A
R1
38
39
40
41
42
43
A
A
B
B
B
B
H
OCH3
H
C22H26ClN3O2‚2HCl‚3/2H2O 234
C22H26ClN3O2
42 ( 8
3170 ( 120
451 ( 78
11 ( 1
105 ( 15
708 ( 19
821 ( 29
631 ( 27
>850 (33%)c
>850 (34%)
>850 (19%)
>850 (27%)
OCH3
H
OCH3
H
120-122 CHCl3/n-hexane 141 ( 15 3960 ( 210
OCH3 CH2 C24H31ClN2O‚2HCl
CH2 C24H31ClN2O‚2HCl
OCH3 NH C23H30ClN3O‚2HCl
230-231 MeOH/Et2O
196-198 MeOH
256-258 MeOH
416 ( 24 3400 ( 140
H
391 ( 25
32 ( 6
46 ( 9
980 ( 62
3180 ( 170
262 ( 12
OCH3
H
NH C23H30ClN3O‚2HCl‚1/2H2O 235 dec
MeOH/Et2O
>850 (37%) >850 (37%)
a
b
Data are the mean of three independent determinations (samples in triplicate). Analyses for C, H, N; results were within (0.4% of
the theoretical values for the formulas given. c Full Ki not obtained, percentage inhibition at the concentration shown given in parentheses.
Values taken from only one experiment.
membranes; (d) 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 which were used to calculate the inhibition
constants (Ki) using the Cheng-Prusoff equation.29
benzophenone derivatives exhibited similar trends: re-
ceptor binding affinities for dopamine D4 declined with
the increasing of the number of atoms in the chain. With
regard to D2 receptor affinity, it can be noted that
compounds 33-37 displayed poor affinity values, having
Ki values always over 850 nM. On the other hand,
considering 5-HT1A and R1 receptor affinities, they were
low with the exception of benzophenones 36 and 37
which displayed moderate 5-HT1A receptor affinity (Ki
) 37 and 45 nM, respectively). These results indicated
that in both class of compounds a four-atom linker
(derivative 1 and 28) provided optimal D4 receptor
affinity. Furthermore, in benzophenone derivatives the
elongation of the linker shifted the affinity from D4 to
5-HT1A receptor. Finally, regarding the semirigid con-
geners, compounds 38 and 39 can be considered as
derived from two possible rotamers of compound 1.
Comparing their D4 receptor affinity with that of the
reference compound 1, a dramatic loss in D4 receptor
affinity was observed. More correctly, one should com-
pare isoquinolinones 38 and 39 with derivative 32 which
is devoid of the hydrogen atom on the amide function.
In this way, a great difference in D4 receptor affinity
can not be found. The same behavior was observed when
comparing compound 29 (Ki ) 204 nM) with tetralin
derivatives 40 and 41 (Ki ) 416 and 391 nM, respec-
tively) and compound 30 (Ki ) 23 nM) with compounds
42 and 43 (Ki ) 32 and 46 nM, respectively). The only
interesting data from these semirigid congeners derived
from compounds 38 and 39: the 5-HT1A receptor affinity
of the latter compound is higher than that of its isomer
38. Consequently, the compound 38 showed higher D4
receptor affinity and selectivity than compound 39. In
the other cases of semirigid congeners, both the pair 40,
41 and 42, 43, corresponding to the possible rotamers
of 29 and 30, respectively, displayed D4 receptor affinity
and selectivity values in the same range.
Resu lts a n d Discu ssion
The results of the in vitro binding experiments on the
target compounds 28-43 are summarized in Tables 1
and 2. Considering the first group of compounds (de-
rivatives 28-32), where the amide function of compound
1 has been changed, it can be noted that none of these
compounds displayed better D4 receptor affinity than
the reference compound 1. Only compound 28, where
the benzamide moiety was replaced by a benzophenone
one, retained a D4 receptor affinity in the nanomolar
range (Ki ) 4 nM). The reduced analogue 30 of the lead
benzamide 1 and the retro amide 31 still retained D4
receptor affinity (Ki ) 23 and 42 nM, respectively). A
dramatic loss in D4 receptor affinity was observed when
the amide function was replaced by two methylene
groups (compound 29) or in the case that the amide
group was N-methylated (compound 32), being Ki ) 204
and 180 nM, respectively. These data indicated the
importance of the secondary benzamide moiety for
binding with a possible H-bond at D4 receptor in this
series of compounds. Considering the D2 receptor it can
be noted that compounds 28-32 displayed poor receptor
affinities. As far as 5-HT1A and R1 receptor affinities
were considered, compounds 28-32 displayed Ki values
lower than those displayed by the reference compound
1.
In conclusion, it can be affirmed that the optimal
structural conditions for D4 receptor affinity in this
series of compounds are achieved for opened derivatives
with a secondary 3-OCH3-benzamide moiety (com-
pounds 1 and 33) or a 3-OCH3-benzophenone group
(compounds 28 and 36) joined to the piperazine ring by
two or three methylene groups.
Starting from these results, we prepared the com-
pounds 33-37 in order to investigate the effect of the
elongation of the alkyl chain on D4 receptor binding
affinity; such a study was limited only to compounds
showing the highest D4 receptor affinity (derivative 1
and 28). As additional methylene groups were added to
extend the length of the spacer, both the benzamide and

274 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2
Perrone et al.
tion with Et2O and evaporation of the dried (Na2SO4) organic
layer gave a crude residue which was chromatographed (CH2-
Cl2/AcOEt, 7:3 as eluent) to give alcohol 4 as a colorless liquid
(3.20 g, 64% yield). 1H NMR (90 MHz): 1.15-2.13 [m, 7H,
(CH2)3CH2Cl, OH, 1H D2O exchanged], 3.50 (br t, 2H, CH2-
Cl), 3.80 (s, 3H, CH3), 4.53-4.75 (m, 1H, CHOH), 6.73-7.30
(m, 4H, aromatic). GC/MS: m/z 230 (M+ + 2, 4), 229 (M+ + 1,
2), 228 (M+, 12), 137 (99), 109 (100).
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
1
values for the formula given. H NMR spectra were recorded
6-Ch lor o-1-(3-m eth oxyp h en yl)-1-h exa n ol (5). The title
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 (unless otherwise indicated); all chemi-
cal shift values are reported in ppm (δ). Recording of mass
spectra was done on a HP6890-5973 MSD gas chromatograph/
mass spectrometer; only significant m/z peaks, with their
percent 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 salt by adding an HCl ethereal solution to a
methanolic solution of the amine; the salts were recrystallized
as detailed in Tables 1 and 2.
The following compounds were synthesized by published
procedures: 1-(3-bromopropyl)-5-methoxy-1,2,3,4-tetrahydro-
naphthalene (9),19 1-(3-bromopropyl)-7-methoxy-1,2,3,4-tetra-
hydronaphthalene (10),19 4-(4-chlorophenyl)-1-piperazineethan-
amine (16),23 4-(4-chlorophenyl)piperazinepropanamine (17),23
4-(4-chlorophenyl)-1-piperazinebutanamine (18),23 4-(2-chlo-
roethyl)-1-(4-chlorophenyl)piperazine (22),26 N-methyl-3-meth-
oxybenzamide (23),27 and 7-methoxy-3,4-dihydroisoquinolin-
1-one (27).28
3-Me t h o x y -r-[(t r im e t h y ls ily l)o x y ]b e n ze n e a c e t o -
n itr ile (3). 3-Methoxybenzaldehyde (2) (2.7 mL, 22.2 mmol)
was added to a cooled mixture of trimethylsilyl cyanide (3.2
mL, 24.2 mmol) and a catalytic amount of ZnI2, under stirring.
The mixture was heated at 80 °C for 8 h, then cooled and
diluted with CH2Cl2. The organic phase was washed with 20%
aqueous Na2CO3 and dried over Na2SO4. Evaporation of the
solvent under reduced pressure gave the crude trimethylsilyl
cyanohydrin that was chromatographed (petroleum ether/
AcOEt, 4:1 as eluent) to give compound 3 as a pale yellow oil
(3.60 g, 69% yield). 1H NMR (90 MHz, TMS was not used):
0.10 [s, 9H, Si(CH3)3], 3.75 (s, 3H, OCH3), 5.33 (s, 1H, CH),
6.65-7.30 (m, 4H, aromatic). GC/MS: m/z 237 (M+ + 2, 2),
236 (M+ + 1, 8), 235 (M+, 39), 221 (28), 220 (100), 146 (28).
4-Ch lor o-1-(3-m eth oxyp h en yl)-1-bu ta n on e (6). Freshly
distilled diisopropylamine (5 mL) was mixed with anhydrous
THF (10 mL) under N2. The solution was cooled at 0 °C and
n-butyllithium (2.336 M solution in n-hexane, 7.7 mL, 18.0
mmol) was added. After 15 min the mixture was cooled at -70
°C, and the trimethysilyl cyanohydrin 3 (3.86 g, 16.4 mmol)
in anhydrous THF was added dropwise. The mixture was kept
at -70 °C for 30 min, and then 1-bromo-3-chloropropane (1.8
mL, 18.0 mmol) in THF was added. The stirred reaction
mixture was allowed to warm at room temperature and so was
kept for 2 h; then it was treated with 2 N HCl (20 mL) and
MeOH (10 mL) and was stirred overnight at room tempera-
ture. Finally, the reaction mixture was diluted with H2O and
extracted with Et2O. The separated organic layer was washed
with 1 N NaOH, then with H2O, and dried (Na2SO4). The
solvent was evaporated under reduced pressure, and the crude
residue was chromatographed (petroleum ether/AcOEt, 2:1 as
eluent) to give ketone 6 as a colorless oil (2.13 g, 61% yield).
1H NMR (90 MHz): 2.03-2.40 [m, 2H, COCH2CH2], 3.16 (t,
2H, J ) 6.0 Hz, COCH2), 3.67 (t, 2H, J ) 6.0 Hz, CH2Cl), 3.85
(s, 3H, CH3), 7.05-7.70 (m, 4H, aromatic). GC/MS: m/z 214
(M+ + 2, 9), 213 (M+ + 1, 3), 212 (M+, 25), 150 (30), 135 (100),
107 (33).
compound was prepared from bromo(5-chloropentyl)magne-
sium and aldehyde 2 in the same manner as above. H NMR
1
(90 MHz): 1.05-1.95 [m, 8H, (CH2)4CH2Cl], 2.13 (s, 1H, OH,
D2O exchanged), 3.45 (t, 2H, J ) 6.0 Hz, CH2Cl), 3.78 (s, 3H,
CH3), 4.50-4.73 (m, 1H, CHOH), 6.73-7.40 (m, 4H, aromatic).
GC/MS: m/z 244 (M+ + 2, 11), 243 (M+ + 1, 5), 242 (M+, 30),
138 (21), 137 (100), 109 (80).
5-Ch lor o-1-(3-m eth oxyp h en yl)-1-p en ta n on e (7). J ones’
reagent (2.5 mL, prepared by dissolving 40 g of CrO3 in 80
mL of H2O and 20 mL of concentrated H2SO4) was added
dropwise to a cooled solution of the compound 4 (1.01 g, 4.4
mmol) in acetone (50 mL, distilled over KMnO4) and kept at
0 °C. When the addition was over, the reaction mixture was
stirred for 6 h at room temperature and then diluted with H2O.
The aqueous phase was extracted with AcOEt (3 × 50 mL),
and the collected organic layers were washed with 5% aqueous
NaHCO3 and dried (Na2SO4). Evaporation of the solvent gave
a crude residue which was chromatographed (petroleum ether/
CH2Cl2, 4:1 as eluent) to give ketone 7 as a colorless oil (0.89
1
g, 89% yield). H NMR (90 MHz): 1.75-1.97 [m, 4H, (CH2)2-
CH2Cl], 2.95 (br t, 2H, COCH2), 3.55 (br t, 2H, CH2Cl), 3.80
(s, 3H, CH3), 6.98-7.60 (m, 4H, aromatic). GC/MS: m/z 228
(M+ + 2, 4), 227 (M+ + 1, 2), 226 (M+, 13), 135 (100), 107 (30).
6-Ch lor o-1-(3-m eth oxyph en yl)-1-h exan on e (8). As above,
1
the title compound was obtained from alcohol 5. H NMR (90
MHz): 1.33-2.03 [m, 6H, (CH2)3CH2Cl], 2.98 (t, 2H, J ) 6.0
Hz, COCH2), 3.55 (t, 2H, J ) 6.0 Hz, CH2Cl), 3.85 (s, 3H, CH3),
7.03-7.66 (m, 4H, aromatic). GC/MS: m/z 242 (M+ + 2, 6),
241 (M+ + 1, 3), 240 (M+, 18), 150 (78), 135 (100), 107 (39).
3-(4-Ch lor obu tyl)m eth oxyben zen e (12). To a cooled (0
°C), stirred suspension of AlCl3 (1.56 g, 11.7 mmol) in CH2Cl2
(30 mL) was added tert-butylamine-borane (2.04 g, 23.4 mmol).
The mixture was stirred at 0 °C for 10 min. A clear solution
resulted. A solution of ketone 6 (0.83 g, 3.9 mmol) in CH2Cl2
(30 mL) was added. The resulting mixture was stirred at 0 °C
for 2 h. Then cold 1 N HCl (30 mL) was added dropwise to the
reaction mixture. The separated organic phase was dried (Na2-
SO4), and the solvent evaporated under reduced pressure. The
crude residue was chromatographed (petroleum ether/CH2Cl2,
4:1 as eluent) to give chloro derivative 12 as a colorless oil
(0.41 g, 53% yield). 1H NMR (90 MHz): 1.66-1.95 [m, 4H,
(CH2)2CH2Cl], 2.60 (br t, 2H, ArCH2), 3.53 (br t, 2H, CH2Cl),
3.80 (s, 3H, CH3), 6.70-7.36 (m, 4H, aromatic). GC/MS: m/z
200 (M+ + 2, 18), 199 (M+ + 1, 7), 198 (M+, 50), 163 (33), 122
(66), 121 (100), 91(29).
3-Ch lor o-N-(3-m eth oxyph en yl)pr opan am ide (13). 3-Chlo-
ropropionyl chloride (1.4 mL, 14.8 mmol) in CH2Cl2 was added
dropwise to a cooled suspension of 3-methoxyaniline (11) (1.82
g, 14.8 mmol) and a slight excess of K2CO3 in CH2Cl2. The
resulting mixture was stirred at room temperature for 30 min,
and then H2O was added. The separated organic layer was
washed with dilute HCl, dried over Na2SO4, and evaporated
under reduced pressure. The crude residue was chromato-
graphed (CH2Cl2/AcOEt, 1:1 as eluent) to obtain anilide 13
(2.31 g, 73% yield) as a white solid, mp 90-92 °C (from Et2O/
petroleum ether) [lit.30 95 °C (from aqueous ethanol)]. 1H NMR
(90 MHz): 2.75 (t, 2H, J ) 7.0 Hz, COCH2), 3.70 (s, 3H, CH3),
3.80 (t, 2H, J ) 7.0 Hz, CH2Cl), 6.53-7.30 (m, 4H, aromatic),
8.15 (br s, 1H, NH, D2O exchanged). GC/MS: m/z 215 (M++
2, 8), 214 (M+ + 1, 3), 213 (M+, 23), 123 (100), 94 (30).
5-Ch lor o-1-(3-m et h oxyp h en yl)-1-p en t a n ol (4). To a
stirred solution of Grignard reagent, prepared from Mg turn-
ings (0.75 g, 30.7 mmol) and 1-bromo-4-chlorobutane (3.0 mL,
26.4 mmol) in anhydrous THF (20 mL), was added dropwise
3-methoxybenzaldehyde (2) (3.00 g, 22.0 mmol) in the same
solvent (20 mL). After the mixture was refluxed for 3 h and
cooled at room temperature, a cooled saturated solution of NH4-
Cl (40 mL) was added to the cooled reaction mixture. Extrac-
Gen er a l P r oced u r e for th e Syn th esis of Com p ou n d s
28, 29, 31, 36, 37, 40, a n d 41. A stirred suspension of the
appropriate alkyl halide (2.0 mmol), piperazine 14 (4.0 mmol),
and a slight excess of K2CO3 (this reagent was omitted in the
case of compounds 28, 36, and 37) in acetonitrile was refluxed

SAR of a Selective D4 Receptor Ligand
J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2 275
overnight. After cooling, the mixture was evaporated to
dryness, and 20% aqueous Na2CO3 was added to the residue.
The aqueous phase was extracted two times with CH2Cl2, and
the collected organic layers were dried over Na2SO4 and were
evaporated under reduced pressure. The crude residue was
chromatographed as indicated below to give title compounds.
4-[4-(4-Ch lor oph en yl)-piper azin -1-yl]-1-(3-m eth oxyph en -
yl)-1-bu ta n on e (28). Eluted with CHCl3/AcOEt, 7:3; 40%
mL), under stirring. After being refluxed for 1 h, the reaction
mixture was cooled at -10 °C and MeOH was added very
carefully dropwise until gas evolution ceased. The mixture was
treated with 3 N HCl (5 mL) and was refluxed for 1 h. After
cooling, the mixture was alkalized with 3 N NaOH and
extracted with CH2Cl2 (2 × 50 mL). The collected organic
layers were dried over Na2SO4, and the solvent was evaporated
under reduced pressure to give the amine 19 as a white
semisolid in nearly quantitative yield. 1H NMR (90 MHz):
1.25-1.75 [m, 6H, (CH2)3CH2NH2], 2.00 (br s, 2H, NH2, D2O
exchanged), 2.25-2.90 [m, 8H, CH2N(CH2)2, CH2NH2], 3.05-
3.33 [m, 4H, ArN(CH2)2], 6.75-7.35 (m, 4H, aromatic). GC/
MS: m/z 283 (M+ + 2, 2), 282 (M+ + 1, 3), 281 (M+, 6), 268
(20), 266 (58), 211 (34), 209 (100), 195 (28), 166 (45), 141 (71),
98 (71).
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 33-35. To a cooled mixture containing amines 17-19
(5.0 mmol) and a slight excess of NaHCO3 was added dropwise
a solution of 3-methoxybenzoyl chloride, prepared from 3-meth-
oxybenzoic acid (2.00 g, 11 mmol) in SOCl2 (5 mL), in CH2Cl2
(50 mL) under vigorous stirring. Then the aqueous layer was
separated and extracted with CH2Cl2. The organic layer was
dried over Na2SO4 and evaporated to dryness under reduced
pressure. Final compounds were purified by column chroma-
tography (CHCl3/MeOH, 19:1 as eluent) to give benzamides
33-35 in 90-95% yield.
N-[3-[4-(4-Ch lor oph en yl)piper azin -1-yl]pr opyl]-3-m eth -
oxyben za m id e (33). 1H NMR: 1.75-1.85 (m, 2H, CH2CH2-
CH2), 2.59-2.66 [m, 6H, CH2N(CH2)2], 3.14 [br t, 4H, (CH2)2-
NAr], 3.56 (q, 2H, J ) 5.5 Hz, NHCH2), 3.72 (s, 3H, CH3),
6.77-7.44 (m, 8H, aromatic), 8.11 (br s, 1H, NH, D2O ex-
changed). GC/MS: m/z 389 (M+ + 2, 7), 388 (M+ + 1, 5), 387
(M+, 20), 372 (34), 221 (100), 209 (54), 192 (56), 135 (56).
N-[4-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]bu tyl]-3-m eth -
oxyben za m id e (34). 1H NMR: 1.70-1.75 [m, 4H, CH2(CH2)2-
CH2], 2.57 [br s, 2H, CH2N(CH2)2], 2.72 [br t, 4H, CH2N(CH2)2],
3.21 [br t, 4H, (CH2)2NAr], 3.44-3.49 (m, 2H, NHCH2), 3.81
(s, 3H, CH3), 6.77-7.34 (m, 9H, aromatic, NH). GC/MS: m/z
403 (M+ + 2, 4), 402 (M+ + 1, 4), 401 (M+, 11), 386 (20), 235
(100), 209 (57), 135 (51).
1
yield. H NMR: 1.92-2.02 (m, 2H, CH2CH2CH2), 2.46 [t, 2H,
J ) 7.1, CH2N(CH2)2], 2.58 [br t, 4H, CH2N(CH2)2], 3.00 (t,
2H, J ) 7.0 Hz, COCH2), 3.10 [br t, 4H, (CH2)2NAr], 3.82 (s,
3H, CH3), 6.77-7.55 (m, 8H, aromatic). GC/MS: m/z 374 (M+
+ 2, 14), 373 (M+ + 1, 10), 372 (M+, 39), 224 (36), 222 (100),
211 (30), 209 (91), 177 (31), 166 (56), 135 (32).
1-(4-Ch lor op h en yl)-4-[4-(3-m eth oxyp h en yl)bu tyl]p ip -
er a zin e (29). Eluted with CHCl3/AcOEt, 7:3; 36% yield. 1H
NMR: 1.50-1.70 [m, 4H, CH2(CH2)2CH2], 2.40 [t, 2H, J ) 7.4
Hz, CH2N(CH2)2], 2.55-2.63 [m, 6H, ArCH2, CH2N(CH2)2], 3.15
[br s, 4H, (CH2)2NAr], 3.78 (s, 3H, CH3), 6.69-7.24 (m, 8H,
aromatic). GC/MS: m/z 360 (M+ + 2, 17), 359 (M+ + 1, 12),
358 (M+, 47), 211 (35), 209 (100).
3-(4-Ch lor op h en yl)-N-(3-m et h oxyp h en yl)-1-p ip er a zi-
n op r op a n a m id e (31). Eluted with CHCl3/AcOEt, 1:1; 75%
yield. 1H NMR: 2.53-2.57 [m, 2H, CH2N(CH2)2], 2.73-2.79 [m,
6H, CH2CH2N(CH2)2], 3.25 [br t, 4H, (CH2)2NAr], 3.76 (s, 3H,
CH3), 6.58-7.35 (m, 8H, aromatic), 10.72 (br s, 1H, NH, D2O
exchanged). GC/MS: m/z 196 (31), 177 (38), 156 (28), 154 (100),
123 (41).
5-[4-(4-Ch lor oph en yl)-piper azin -1-yl]-1-(3-m eth oxyph en -
yl)-1-p en ta n on e (36). Eluted with CHCl3/AcOEt, 7:3; 56%
1
yield. H NMR: 1.56-1.66 (m, 2H, CH2CH2N), 1.72-1.82 (m,
2H, COCH2CH2), 2.43 [br t, 2H, CH2N(CH2)2], 2.59 [br t, 4H,
CH2N(CH2)2], 2.98 (t, 2H, J ) 7.2 Hz, COCH2), 3.15 [br t, 4H,
(CH2)2NAr], 3.83 (s, 3H, CH3), 6.79-7.54 (m, 8H, aromatic).
GC/MS: m/z 388 (M+ + 2, 13), 387 (M+ + 1, 10), 386 (M+, 38),
211 (34), 209 (100).
6-[4-(4-Ch lor oph en yl)-piper azin -1-yl]-1-(3-m eth oxyph en -
yl)-1-h exa n on e (37). Eluted with CH2Cl2/AcOEt, 7:3; 23%
1
yield. H NMR: 1.37-1.45 [m, 2H, CH2(CH2)2], 1.53-1.63 (m,
2H, CH2CH2N), 1.70-1.80 (m, 2H, COCH2CH2), 2.40 [br t, 2H,
CH2N(CH2)2], 2.59 [br t, 4H, CH2N(CH2)2], 2.95 (t, 2H, J )
7.3 Hz, COCH2), 3.16 [br t, 4H, (CH2)2NAr], 3.83 (s, 3H, CH3),
6.79-7.53 (m, 8H, aromatic). GC/MS: m/z 402 (M+ + 2, 12),
401 (M+ + 1, 10), 400 (M+, 35), 211 (35), 209 (100), 177 (31),
166 (56), 135 (32).
N-[5-[4-(4-Ch lor oph en yl)piper azin -1-yl]pen tyl]-3-m eth -
oxyben za m id e (35). 1H NMR: 1.38-1.46 [m, 2H, (CH2)2CH2-
(CH2)2] 1.54-1.68 (m, 4H, CH2CH2CH2CH2CH2), 2.43 [br t, 2H,
CH2N(CH2)2], 2.61 [br t, 4H, CH2N(CH2)2], 3.16 [br t, 4H,
(CH2)2NAr], 3.43 (q, 2H, J ) 5.0, NHCH2), 3.81 (s, 3H, CH3),
6.21 (br s, 1H, NH, D2O exchanged), 6.78-7.34 (m, 8H,
aromatic). GC/MS: m/z 417 (M+ + 2, 5), 416 (M+ + 1, 4), 415
(M+, 14), 400 (20), 249 (100), 211 (26), 209 (77), 135 (44).
1-(4-Ch lor op h en yl)-4-[3-(1,2,3,4-tetr a h yd r o-5-m eth oxy-
1-n aph th alen yl)pr opyl]piper azin e (40). Eluted with CHCl3/
AcOEt, 1:1; 81% yield. 1H NMR: 1.54-1.84 [m, 8H, CH-
(CH2CH2)2], 2.40 [br t, 2H, CH2N(CH2)2], 2.52-2.77 [m, 7H,
benzylic CH2 and CH, CH2N(CH2)2], 3.16 (br t, 4H, (CH2)2NAr],
3.79 (s, 3H, CH3), 6.63-7.24 (m, 7H, aromatic). GC/MS: m/z
400 (M+ + 2, 27), 399 (M+ + 1, 22), 398 (M+, 77), 210 (36), 209
(100), 196 (40).
4-(4-Ch lor op h en yl)-N-[(3-m et h oxyp h en yl)m et h yl]-1-
p ip er a zin eeth a n a m in e (30). This compound was obtained
in nearly quantitative yield from the reduction of benzamide
1 with borane methyl sulfide complex, following the procedure
1
reported for the compound 19. H NMR: 2.06 (br s, 1H, NH,
1-(4-Ch lor op h en yl)-4-[3-(1,2,3,4-tetr a h yd r o-7-m eth oxy-
1-n a p h th a len yl)p r op yl]p ip er a zin e (41). Eluted with CH2-
Cl2/AcOEt, 4:1; 95% yield. 1H NMR: 1.57-1.88 [m, 8H,
CH(CH2CH2)2], 2.41 [br t, 2H, CH2N(CH2)2], 2.59-2.74 [m, 7H,
benzylic CH2 and CH, CH2N(CH2)2], 3.16 (br t, 4H, (CH2)2NAr],
3.76 (s, 3H, CH3), 6.63-7.24 (m, 7H, aromatic). GC/MS: m/z
400 (M+ + 2, 11), 399 (M+ + 1, 9), 398 (M+, 33), 211 (33), 209
(100), 196 (37).
4-(4-Ch lor oph en yl)-1-piper azin open tan en itr ile (15). The
title compounds was prepared in 83% yield from the piperazine
14 and 4-chloropentanenitrile following the procedure de-
scribed for the synthesis of the above compounds. 1H NMR
(90 MHz): 1.50-1.85 [m, 4H, (CH2)2CH2CN], 2.20-2.70 [m,
8H, (CH2)2NCH2, CH2CN], 3.00-3.30 [m, 4H, ArN(CH2)2],
6.75-7.35 (m, 4H, aromatic). GC/MS: m/z 279 (M+ + 2, 24),
278 (M+ + 1, 14), 277 (M+, 68), 211 (37), 209 (100), 166 (22),
139 (30), 138 (25).
D2O exchanged), 2.52-2.56 (m, 6H, CH2CH2N(CH2)2], 2.72 [t,
2H, J ) 6.0, CH2N(CH2)2], 3.11 [br t, 4H, (CH2)2NAr], 3.79 (s,
5H, ArCH2, CH3), 6.76-7.25 (m, 8H, aromatic). GC/MS: m/z
361 (M+ + 2, 1), 360 (M+ + 1, 1), 359 (M+, 3), 211 (24), 210
(21), 209 (77), 179 (21), 166 (30), 138 (23), 121 (70), 70 (100).
N -(Me t h o x y c a r b o n y l)-2-(2-m e t h o x y p h e n y l)e t h y l-
a m in e (25). To a solution of 2-methoxyphenetylamine (24)
(5.00 g, 33.1 mmol) and triethylamine (5.5 mL, 39.5 mmol) in
anhydrous THF (50 mL) at 0 °C was carefully added methyl
chloroformate (13.1 mL, 169 mmol). The reaction mixture was
stirred at room temperature for 24 h. H2O was added, the
aqueous and organic layers were separated, and the former
was extracted with Et2O (3 × 20 mL). The combined organic
fractions were washed with 1 N HCl (2 × 50 mL), H2O (50
mL), and brine (50 mL) and dried over Na2SO4. Evaporation
of the solvent in vacuo gave compound 25 in nearly quantita-
1
tive yield. H NMR (90 MHz): 2.80 (t, 2H, J ) 6.0 Hz, CH2-
4-(4-Ch lor op h en yl)-1-p ip er a zin ep en ta n a m in e (19). Bo-
rane-methyl sulfide complex, as 10.0 M BH3 in excess methyl
sulfide (2.0 mL, 20.0 mmol), was dropped into an ice-cooled
solution of nitrile 15 (1.16 g, 4.2 mmol) in anhydrous THF (10
NH), 3.25-3.55 (m, 2H, ArCH2), 3.73 and 3.83 (2 s, 6H, 2 CH3),
4.87 (br s, 1H, NH), 6.75-7.35 (m, 4H, aromatic). GC/MS: m/z
211 (M+ + 2, 1), 210 (M+ + 1, 6), 209 (M+, 40), 134 (100), 122
(26), 121 (52), 119 (37), 91 (80).

276 J ournal of Medicinal Chemistry, 2000, Vol. 43, No. 2
Perrone et al.
5-Meth oxy-3,4-d ih yd r oisoqu in olin -1-on e (26). Carbam-
ate 25 (6.85 g, 32.7 mmol) was added to polyphosphoric acid
(40 g) heated at 145 °C, and the mixture was stirred for 10
min. Then the cooled reaction mixture was poured onto ice,
and the aqueous phase was extracted with CH2Cl2 (3 × 50 mL).
The combined organic layers were dried over Na2SO4 and
concentrated in vacuo to give a crude residue which was
chromatographed (CHCl3/AcOEt, 1:1 as eluent) to afford
compound 26 as a pale yellow semisolid (1.29 g, 22% yield).
Spectral properties of the obtained compound were fully
consistent with those reported.31
aromatic). GC/MS: m/z 401 (M+ + 2, 1), 400 (M+ + 1, 1), 399
(M+, 2), 210 (26), 209 (35), 161 (100).
P h a r m a cologica l Meth od s. D4.4 Dop a m in er gic Bin d in g
Assa y. Binding of [3H]YM-09151-2 for human cloned D4.4
dopamine receptor produced in Sf9 cells baculovirus expression
(NEN Life Science) was performed according to Hadley et al.33
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 D4.4 diluted
membranes, 0.15 nM of [3H]YM-09151-2 (Kd ) 0.17 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/A glass fiber filters (presoaked in 0.3% polyeth-
ylenimine) 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 10 µM clozapine.
N-[2-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]eth yl]-N-m eth -
yl-3-m eth oxyben za m id e (32). A mixture of benzamide 23
(0.88 g, 5.3 mmol), KOH (1.20 g, 21.4 mmol), tetrabutylam-
monium bromide (0.051 g, 0.16 mmol), and compound 22 (0.70
g, 2.7 mmol) in DMF was heated at 80 °C for 4 h. After cooling,
the solvent was removed under reduced pressure and the crude
residue was taken up with H2O. The aqueous phase was
extracted with CH2Cl2, and the separated organic layer was
dried over Na2SO4 and concentrated under reduced pressure.
The crude residue was chromatographed (CHCl3/AcOEt, 1:1
as eluent) to give compound 32 as a semisolid (0.51 g, 48%
yield). 1H NMR (DMSO-d6):32 2.32 and 2.58 [2 br s, 6H, CH2N-
(CH2)2], 2.89, 2.96, 3.02, 3.10 [4 br s, 7H, NCH3, (CH2)2NAr],
3.31, 3.57 (2 br s, 2H, CH3NCH2), 3.75 (s, 3H, OCH3), 6.89-
7.34 (m, 8H, aromatic). GC/MS: m/z 389 (M+ + 2, 2), 388 (M+
+ 1, 1), 387 (M+, 5), 222 (23), 211 (34), 209 (100), 166 (21).
N-[2-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]eth yl]-5-m eth -
oxy-3,4-d ih yd r oisoqu in olin -1-on e (38). Title compound was
obtained from the amide 26 and the compound 22, following
the above-reported procedure. 1H NMR: 2.70 [br s, 6H, CH2N-
(CH2)2], 2.93 (t, 2H, J ) 6.7 Hz, ArCH2), 3.14 [br t, 4H, (CH2)2-
NAr], 3.58 (t, 2H, J ) 6.7 Hz, endo CONCH2), 3.72 (t, 2H, J )
6.7 Hz, exo CONCH2), 3.83 (s, 3H, CH3), 6.79-7.68 (m, 7H,
aromatic). GC/MS: m/z 401 (M+ + 2, 1), 400 (M+ + 1, 1), 399
(M+, 4), 233 (24), 222 (35), 211 (33), 209 (100), 166 (31).
D2L Dop a m in er gic Bin d in g Assa y. Binding of [3H]spiro-
peridol for human cloned D2L dopamine receptor produced in
Sf9 cells baculovirus expression (NEN Life Science) was
performed according to Hadley et al.33 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
D
2L diluted membranes, 0.2 nM [3H]spiperone (Kd ) 0.20 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
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 10 µM haloperidol.
5-HT1A Ser oton er gic Bin d in g Assa y. Binding experi-
ments were performed according to Borsini et al.34 with minor
modifications. Each tube received 50 mM Tris‚HCl (pH 7.6)
hippocampus membranes suspension and 1 nM [3H]-8-OH-
DPAT in a final volume of 1 mL. For competitive inhibition
experiments, various concentrations (10-5-10-11 M) of drugs
studied were incubated. Nonspecific binding was defined using
1 µM 8-OH-DPAT. Samples were incubated at 37 °C for 20
min and then filtered on Whatman GF/B glass microfiber
filters. The Kd value determined for 8-OH-DPAT was 8.8 nM.
r1 Ad r en er gic Bin d in g Assa y. Binding experiments were
performed according to Glossman and Hornung35 with minor
modifications. Each tube received 50 mM Tris‚HCl (pH 7.4)
rat cerebral cortical membranes suspension and 1 nM [3H]-
prazosin in a final volume of 1 mL. For competitive inhibition
experiments, various concentrations (10-5-10-11 M) of drugs
studied were incubated. Nonspecific binding was defined using
1 µM prazosin. Samples were incubated at 25 °C for 50 min
and then filtered on Whatman GF/B glass microfiber filters.
The filters were presoaked for 50 min in Tris‚HCl-polyeth-
ylenimine 0.5%. The Kd value determined for prazosin was 0.5
nM.
N-[2-[4-(4-Ch lor op h en yl)p ip er a zin -1-yl]eth yl]-7-m eth -
oxy-3,4-d ih yd r oisoqu in olin -1-on e (39). As for compound 38,
the title compound was obtained from the amide 27 and the
derivative 22. 1H NMR: 2.66-2.71 [m, 6H, CH2N(CH2)2], 2.91
(t, 2H, J ) 6.7 Hz, ArCH2), 3.14 [br t, 4H, (CH2)2NAr], 3.59 (t,
2H, J ) 6.7 Hz, endo CONCH2), 3.73 (t, 2H, J ) 6.7 Hz, exo
CONCH2), 3.82 (s, 3H, CH3), 6.79-7.58 (m, 7H, aromatic). GC/
MS: m/z 401 (M+ + 2, 2), 400 (M+ + 1, 1), 399 (M+, 4), 233
(21), 211 (33), 222 (29), 209 (100), 166 (28).
4-(4-Ch lor oph en yl)-N-[3-(1,2,3,4-tetr ah ydr o-5-m eth oxy-
1-n a p h th a len yl)p r op yl]-1-p ip er a zin eeth a n a m in e (42). A
mixture of 5-methoxy-1-tetralone (20) (1.38 g, 7.8 mmol) and
4-(4-chlorophenyl)-1-piperazinoethanamine (16) (1.01 g, 4.2
mmol) in anhydrous toluene (100 mL) was refluxed in the
presence of a catalytic amount of p-toluenesulfonic acid, and
the formed H2O was azeotropically distilled off and collected
with a Dean-Stark trap for 1 h. After cooling, the solvent was
evaporated, and the crude intermediate Schiff’s base was
solubilized in absolute ethanol (50 mL) and treated with
NaBH4 (0.38 g, 8.7 mmol) for 2 h at room temperature, under
N2. Then the solvent was removed under reduced pressure,
and the residue was partitioned between H2O and CH2Cl2. The
separated organic layer was dried (Na2SO4) and concentrated
in vacuo to give a crude residue which was chromatographed
(CH2Cl2/MeOH, 95:5 as eluent) to afford amine 42 (1.28 g, 76%
yield). 1H NMR: 1.66-2.00 (m, 5H, endo CH2CH2, NH, 1H D2O
exchanged), 2.48-2.88 [m, 10H, benzylic CH2, CH2CH2N-
(CH2)2], 3.13 [br t, 4H, (CH2)2NAr], 3.75-3.79 (t+s, 4H, CHN,
CH3), 6.68-7.24 (m, 7H, aromatic). GC/MS: m/z 210 (32), 209
(33), 161 (100).
Ack n ow led gm en t. This study was supported by
research grant no. 9703028183-022 from Universita`
degli Studi di Bari and MURST (Italy) for the scientific
program in CO7X field - 1998-2000: “Design, synthe-
sis and biological evaluation of new drugs: SAR studies
on serotonergic agents with arylpiperazine structure”.
Su p p or tin g In for m a tion Ava ila ble: Elemental analyses.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Refer en ces
4-(4-Ch lor oph en yl)-N-[3-(1,2,3,4-tetr ah ydr o-7-m eth oxy-
1-n a p h th a len yl)p r op yl]-1-p ip er a zin eeth a n a m in e (43). As
above, the title compound was obtained from amine 16 and
7-methoxy-1-tetralone (21). 1H NMR: 1.67-1.99 (m, 4H, endo
CH2CH2), 2.09 (br s, 1H, NH, D2O exchanged), 2.52-2.87 [m,
10H, benzylic CH2, CH2CH2N(CH2)2], 3.13 [br t, 4H, (CH2)2-
NAr], 3.74-3.81 (t+s, 4H, CHN, CH3), 6.69-7.24 (m, 7H,
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