Synthesis, 5-HT(1A) and 5-HT(2A) receptor affinity of new 1-phenylpiperazinylpropyl derivatives of purine-2,6- and pyrrolidine-2,5-diones

Article abstract of DOI:10.1016/S0014-827X(00)00069-0

Two series of 1-phenylpiperazinylpropyl derivatives 10, 11, 16, 17 and 19-24, structurally related to previously described 5-HT(1A) or 5-HT(2A) ligands 4 and 1, respectively, were synthesized and their binding properties were determined. Structural modifi

Full text of DOI:10.1016/S0014-827X(00)00069-0

www.elsevier.nl/locate/farmac
Il Farmaco 55 (2000) 461–468
Synthesis, 5-HT and 5-HT receptor affinity of new
1
A
2A
1
-phenylpiperazinylpropyl derivatives of purine-2,6- and
pyrrolidine-2,5-diones
a,
a
a
a
Maciej Paw *l owski *, Graz
;
yna Ch *l o n´ , Jolanta Obniska , Alfred Zejc ,
b
b
Sijka Charakchieva-Minol , Maria J. Mokrosz
a
Department of Pharmaceutical Chemistry, Collegium Medicum of Jagiellonian Uni6ersity, Medyczna 9, 30-688 Krakow, Poland
b
Institute of Pharmacology, Polish Academy of Sciences, Sm e˛ tna 12, 31-343 Krakow, Poland
Received 4 November 1999; accepted 12 June 2000
Abstract
Two series of 1-phenylpiperazinylpropyl derivatives 10, 11, 16, 17 and 19–24, structurally related to previously described
-HT1A or 5-HT2A ligands 4 and 1, respectively, were synthesized and their binding properties were determined. Structural
5
modifications which involved 1,3-diazepine ring opening in 4 (compounds 10, 11, 15, 16) and replacement of spiroalkyl moiety in
by aryl substituent (19–24) did not improve binding affinity and selectivity of the tested compounds. The results showed,
1
however, that the diazepine ring present in 4 or spiroalkyl ring in 1 are important for high 5-HT1A or 5-HT2A binding affinity and
selectivity of these compounds. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: 1-Phenylpiperazinylpropylpurine-2,6-diones; 1-Phenylpiperazinylpropyl-pyrrolidine-2,5-diones; 5-HT1A and 5-HT2A receptor affinity
1
. Introduction
local dipole–dipole interaction. Also, the results ob-
tained by Mokrosz et al. [8] showed that the basic
nitrogen atom and terminal, bulky cycloimide moiety,
but not the 2-pyrimidinyl group of buspirone, are di-
rectly involved in the formation of the bioactive com-
plex with 5-HT1A receptors.
Serotonin (5-hydroxytryptamine, 5-HT) is involved
in many physiological and pathophysiological processes
in the brain which are mediated by the specific interac-
tion of 5-HT with seven major receptor classes [1]. The
5
-HT1A receptors are to date one of the best character-
In previous studies [9] we showed that 3-(v-
aminoalkyl)-5,5-dialkyl (or spirocycloalkyl-1%,5-)hydan-
toins containing 1-phenylpiperazine or 1-(o-methoxy-
phenyl)-piperazine fragments are recognized by 5-HT1A
and 5-HT2A receptors due to the presence of the 1-
arylpiperazine fragment; however, the terminal hydan-
toin moiety plays an important role in the stabilization
of the receptor–ligand complex. It has also been found
that two selected compounds, 5-cyclopentanespiro-3-[3-
(4 - phenyl - 1 - piperazinyl) - propyl] - imidazolidine - 2,4-
ized subtypes and it is generally accepted that they are
involved in psychiatric disorders such as depression and
anxiety [2]. Several compounds from different chemical
classes possess high affinity for 5-HT1A receptors.
Among them, some 1-arylpiperazines linked with a
terminal cyclic amide fragment via a long-chain, e.g.
buspirone or ipsapirone (Fig. 1), are effective antianxi-
ety and antidepressant drugs [3]. Many studies on the
structure–affinity relationship of the 1-arylpiperazine
class of 5-HT1A receptor ligands have been reported
dione (1) and its 5-cyclohexanespiro analog (2) (K =34
i
[
4–6]. Misztal et al. [7] assumed that the terminal amide
and 37 nM, respectively) are new selective 5-HT1A re-
ceptor ligands, whereas the 5-cyclohexanespiro-3-[3-(4-
o-methoxyphenyl-1-piperazinyl)-butyl]-imidazolidine-
fragment in buspirone-like ligands stabilized the 5-
HT1A receptor-ligand complex by either p-electron or
2
,4-dione (3) is a new, highly potent 5-HT1A receptor
ligand (K =0.51 nM) with a moderate affinity for
*
Corresponding author. Tel.: +48-12-657 0560; fax: +48-12-657
i
0
0
262.
5-HT2A receptors (K =213 nM) [9] (Fig. 1). In addi-
i
014-827X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(00)00069-0

4
62
M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
tion, 5-HT1A and 5-HT2A receptor affinities of several
v-alkyl-1-arylpiperazines containing a terminal pyrimi-
dopurine or 1,3-diazepinopurine ring system have been
reported [10]. Several behavioral models demonstrated
2. Chemistry
The 4-(3-aminopropyl)-l-phenylpiperazine 7 was syn-
thesized based on the described method [11]. The 1,3-
dimethyl-7-alkyl-8-bromo-purine-2,6-diones 8 and 9
were prepared according to the published procedures
[12]. The 1,3-dimethyl-7-alkyl-8-[3-(4-phenyl-1-piper-
azinyl)-propylamino]-purine-2,6-diones 10 and 11 were
obtained by reaction of the appropriate 1,3-dimethyl-7-
alkyl-8-bromo-purine-2,6-diones 8 or 9 with 7 in the
presence of anhydrous K CO (Scheme 1).
The previously reported ethyl esters of 1,3-dimethyl-
8-bromo-purine-2,6-dione-7-acetic acid 12 [13] and 1,3-
dimethyl-8-bromo-purine-2,6-dione-7-butyric acid 13
[14] were heated with 7 in the presence of K CO in
that
1,3-dimethyl-10-[3-(4-phenyl-1-piperazinyl)-pro-
pyl]-2,4-dioxo-1,3,6,7,8,9-hexahydro-10H-1,3-diaze-
pino-[2,1-f ]-purine (4) and its analog (5) may be
classified as 5-HT1A postsynaptic antagonists, whereas
1,3-dimethyl-9-[3-(4-phenyl-1-piperazinyl)-butyl]-2,4-
dioxo-1,3,6,7,8,9-hexahydropyrimido-[2,1-f ]-purine (6)
is a partial agonist of 5-HT1A receptors [10] (Fig. 1).
Although the terminal amide fragment significantly
affects binding of 1-arylpiperazine derivatives to sero-
tonin receptors, its role is not clear yet. To evaluate the
influence of the 1,3-diazepine ring in 4 and of the
spiroalkyl ring in 1 on their binding affinity and selec-
tivity, two series of compounds, i.e. 10, 11, 16 and 17
related to 4 and 19–24 related to 1, were synthesized
and their 5HT1A and 5-HT2A binding constants were
determined.
2
3
2
3
n-butanol. In these reactions, the nucleophilic substitu-
tion in the 8 position took place and the esters were
transformed into the appropriate potassium salts. After
treating with HCl solution, the free acids 14 and 15
were isolated. For the synthesis of the esters 16 and 17
Fig. 1.
Scheme 1.

M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
463
Scheme 2.
Scheme 3.
compounds 14 and 15 were O-alkylated by ethyl bro-
mide in DMF, in the presence of 1,8-diazabicyclo-
derivatives with ammonia [15,16]. The reaction of 3-
aryl-pyrrolidine-2,5-diones with 18 finally led to N-[(4-
phenyl-1-piperazinyl)-propyl]-3-aryl-pyrrolidine-2,5-
diones 19–23 which were isolated as hydrochlorides
(Scheme 3).
[
5,4,0]-undec-7-ene (DBU) (Scheme 2).
The phenylpropylpiperazine derivatives of 3-aryl-
pyrrolidine-2,5-diones 19–23 were obtained by several
condensation steps. For the synthesis of 1-(3-chloro-
propyl)-4-phenylpiperazine 18 the reaction of 1-
phenylpiperazine with 1-bromo-3-chloropropane was
developed [6].
Compound 24 was prepared by cyclocondensation of
2,2-diphenylsuccinic acid [15,16] with 7 (Scheme 4).
The structures of 10, 11, 16, 17 and 19–24 were
1
confirmed by examination of their H NMR and MS
The N-unsubstituted pyrrolidine-2,5-diones with aryl
substituent in 3-position were obtained by intramolecu-
lar cyclocondensation of appropriate succinic acid
spectra as well as by elemental analyses. For binding
studies free bases of 10, 11, 16 and 17 were converted
into hydrochloride salts.

4
64
M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
3. Experimental
HCl salt 10. M.p. 254–257°C (ethanol). Anal.
C H N O xHCl) C, H, N.
(
21
29
7
2
3.1. Chemistry
3.2.3. 1,3-Dimethyl-7-n-butyl-8-[3-(4-phenyl-1-
Analytical results for C, H, N of compounds 10, 11,
6, 17 and 19–24 were within 90.4% of their theoreti-
piperazinyl)-propylamino]-purine-2,6-dione
hydrochloride (11)
1
cal values. Melting points are uncorrected. UV spectra
Free base of 11 from 9. Yield 1.4 g (31%); m.p.
135–136°C (i-propanol). Anal. (C H N O ) C, H, N.
were recorded on a Perkin–Elmer Lambda 12 UV–Vis
2
4
35
7
2
−
5
spectrometer in 5×10
mol/l methanolic solutions.
TLC: R =0.90 (A), R =0.67 (B). UV (methanol): u
f f max
1
1
H NMR spectra (Varian BB 200 MHz NMR spec-
trometer) were determined in CDCl3 solution, with
TMS as internal standard. All chemical shifts are
quoted in l values. MS spectra were obtained with an
AMD-604 spectrometer (70 eV). The chromatography
was performed with Merck silica gel GF254 precoated
TLC sheets using the following developing systems: A,
(log m)=295 nm (4.032); H NMR: l=0.85 (t, J=7.2
Hz, 3H, CH CH ), 1.22–1.33 (m, 2H, CH CH ), 1.65–
2
3
2
3
1.73 (m, 2H, CH CH CH ), 1.85–1.94 (m, 2H,
2
2
3
CH CH CH ), 2.60–2.72 (m, 6H, CH N(CH ) ), 3.21–
2
2
2
2
2 2
3.26 (m, 4H, (CH ) N–Ph), 3.37 (s, 3H, N1–CH ); 3.52
2
2
3
(s, 3H, N3–CH ), 3.55–3.63 (m, 2H, NHCH CH ),
3
2
2
3.98 (t, J=7.2 Hz, 2H, N–7CH ), 6.32 (t, J=4.4 Hz,
2
1
:1:1 benzene–acetone–methanol; B, 60:10:5 chloro-
1H, NHCH ), 6.89–6.95 (m, 3H aromatic, Ph), 7.24–
7.32 (m, 2H, aromatic Ph); MS m/z (%): 453 (44) [M ],
438 (42), 321 (100), 292 (17), 278 (48), 264 (4), 250 (2),
208 (7), 203 (6), 195 (5), 194 (2), 189 (3), 175 (23), 161
(59), 132 (19), 77 (7), 57 (5), 43 (3).
2
+
form–methanol–acetic acid; C, 9:11:2 chloroform–iso-
propanol–NH3 aq. Spots were detected by their
absorption under UV light and visualization with 0.05
mol J2 in 10% HCl. Some starting materials were
commercial products (Aldrich or Fluka).
HCl salt of 11 was prepared according to the proce-
dure of HCl salt of 10. M.p. 210–212°C (ethanol).
Anal. (C H N O xHCl) C, H, N.
24
35
7
2
3.2. Chemical procedures
3
.2.4. General procedure for the synthesis of acids 14
and 15
A mixture of the appropriate ester (12 or 13) (0.01
mol), amine 7 (2.19 g, 0.01 mol), anhydrous K CO
3
1
.2.1. General procedure for the preparation of the
,3-dimethyl-7-alkyl-8-[3-(4-phenyl-1-piperazinyl)-
propylamino]-purine-2,6-diones (10 and 11)
2
3
A mixture of the appropriate 1,3-dimethyl-7-alkyl-8-
(
4.14 g, 0.03 mol) and n-butanol (30 ml) was refluxed
bromo-purine-2,6-diones 8 or 9 (0.01 mol), amine 7
for 5 h. After cooling the precipitated potassium salt
was filtered off, dissolved in water (50 ml) and the
solution was acidified to pH 2–3 by the addition of 5%
HCl. The precipitated acid 14 or 15 was collected,
(
2.19 g, 0.01 mol), anhydrous K CO (2.76 g, 0.02 mol),
2 3
and n-butanol (20 ml) was refluxed for 12 h. Then the
reaction mixture was cooled and refrigerated overnight.
The precipitated solid product was filtered off, washed
washed with H O and cold methanol.
2
with H O and then purified by crystallization from 50°
2
ethanol or i-propanol.
3.2.5. 1,3-Dimethyl-8-[3-(4-phenyl-1-piperazinyl)-
propylamino]-purine-2,6-dione-7-acetic acid (14)
From 12. Yield 2.89 g (60%); m.p. 242–244°C (etha-
nol); Anal. (C H N O ) C, H, N; TLC: R =0.16 (A);
3
.2.2. 1,3,7-Trimethyl-8-[3-(4-phenyl-1-piperazinyl)-
propylamino]-purine-2,6-dione hydrochloride (10)
Free base of 10 from 8. Yield 1.64 g (40%); m.p.
1
22
29
7
4
f
1
H NMR: l=1.90–1.96 (m, 2H, CH CH CH ), 2.62–
2
2
2
90–192°C (i-propanol). Anal. (C H N O ) C, H, N.
21 29 7 2
2
.77 (m, 6H, CH N(CH ) ), 2.81–2.90 (m, 4H,
2 2 2
TLC: R =0.83 (A), R =0.42 (B); UV (methanol): u
f
f
max
1
(CH ) N–Ph), 3.21 (s, 3H, N1–CH ), 3.36 (s, 3H,
2
2
3
(
log m)=294 nm (4.104); H NMR: l=1.85–1.94 (m,
N3ꢀCH ) 3.42–3.46 (m, 2H, NHCH ), 4.62 (s, 2H,
3
2
2H, CH CH CH ), 2.62–2.72 (m, 6H, CH N(CH ) ),
2 2 2 2 2 2
N7ꢀCH CO), 6.89–6.95 (m, 3H aromatic, Ph), 7.25–
2
3
.20–3.25 (m, 4H, (CH ) N–Ph), 3.36 (s, 3H, N1–
2
2
7
.33 (m, 2H aromatic, Ph), 8.43 (t, J=4.4 Hz, 1H,
CH ), 3.51 (s, 3H, N3–CH ), 3.55–3.58 (m, 2H,
NHCH ), 3.61 (s, 3H, N7–CH ); 6.67 (t, J=4.3 Hz,
3
3
+
+
NHCH ); MS m/z (%): 455 (2) [M ], 437 (59) [M −
2
2
3
H O], 422 (60), 396(4), 305(100), 276(15), 262(6),
2
1
7
3
H, NHCH ), 6.85–6.95 (m, 3H aromatic, Ph); 7.24–
2
+
248(11), 189(6), 175(64), 161(18), 132(50), 77(4).
.32 (m, 2H aromatic, Ph); MS m/z (%): 411 (54) [M ],
+
96 (56) [M −CH ], 305 (34), 279 (100), 250 (38), 236
3
(
1
78), 222 (14), 208 (5), 203 (8), 195 (5), 194 (4), 188 (3),
75 (27), 161 (73), 132 (26), 77 (6).
Free base of 10 was converted into HCl salt in
3.2.6. 1,3-Dimethyl-8-[3-(4-phenyl-1-piperazinyl)-
propylamino]-purine-2,6-dione-7-butyric acid (15)
From 13. Yield 2.17 g (45%); m.p. 209–211°C (etha-
nol); Anal. (C H N O ) C, H, N; TLC; R =0.28 (A);
anhydrous ethanol saturated with HCl gas. The ob-
tained precipitate was crystallized from ethanol.
24
33
7
4
f
1
H NMR: l=2.05–2.1 (m, 4H, CH CH CH and
2
2
2

M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
465
Scheme 4.
1
CH CH CO), 2.20–2.23 (m, 2H, CH CH CO), 2.90–
UV: umax (log m)=295 nm (4.381); H NMR: l=1.21–
1.28 (t, J=7.1 Hz, 3H, CH CH ), 1.86–1.96 (m, 2H,
2
2
2
2
3
3
2
6
7
.3 7 (m, 10H, CH N(CH ) and (CH ) NꢀPh), 3.37 (s,
2
2 2
2 2
2
3
H, N1ꢀCH ), 3.51 (s, 3H, N3ꢀCH ), 3.55–3.57 (m,
CH CH CH ), 2.00–2.03 (m, 2H, N7ꢀCH CH CH ),
3
3
2
2
2
2
2
2
H, NHCH ), 4.16 (t, J=6 Hz, 2H, N7ꢀCH CH ),
2.31–2.38 (t, J=6.6 Hz, 2H, CH CH CO), 2.54–2.68
2
2
2
2 2
.43 (t, 1H, NHCH ), 6.89–6.96 (m, 3H aromatic, Ph),
(m, 6H, CH N(CH ) ), 3.20–3.25 (m, 4H, CH ) NꢀPh,
2
2
2 2
2 2
.25–7.33 (m, 2H aromatic, Ph); MS m/z (%): 483(56)
3.31 (s, 3H, N1ꢀCH ), 3.52 (s, 3H, N3ꢀCH ), 3.56–3.62
3
3
+
[
M ], 468(71), 466(5), 450(24), 351(100), 322(13),
(m, 2H, NHCH ), 4.04–4.17 (m, 4H, OCH CH and
2 2 3
3
1
08(56), 208(8), 195(8), 194(4), 189(6), 175(75), 161(84),
32(14), 87(2), 77(10).
N7ꢀCH ), 6.25 (t, J=5 Hz, 1H, NHCH ), 6.86–6.95
2
2
(m, 3H aromatic, Ph), 7.23–7.31 (m, 2H aromatic, Ph);
+
MS m/z (%): 511 (51) [M ], 496(65), 466(24), 450(3),
3
.2.7. General method for the preparation of esters 16
379(100), 350(10), 336(62), 322(2), 208(4), 203(8),
194(3), 189(3), 175(34), 161 (82), 132(21), 115(27).
and 17
To a solution of the suitable acid (14 or 15) (0.005
mol) in DMF (20 ml), DBU (0.75 ml, 0.005 mol) was
added, followed by ethyl bromide (1.12 ml, 0.015 mol).
The mixture was stirred at room temperature (r.t.) for 3
h. Then water (150 ml) was added, and the precipitated
product (16 or 17) was filtered off, washed with water
and purified by crystallization from 96% ethanol.
3.2.10. 1-(3-Chloropropyl)-4-phenylpiperazine (18)
A mixture of 1-phenylpiperazine (4.99 g, 0.03 mol),
1-bromo-3-chloropropane (6.3 g, 0.04 mol) and anhy-
drous K CO (1.2 g, 0.009 mol) in acetone (20 ml) was
stirred for 24 h at r.t. Then the inorganic salt was
filtered off and acetone was evaporated to dryness. The
residue was dissolved in n-hexane, filtered off again and
the solvent was evaporated. The crude product of 18
was purified using a silica gel column chromatography
eluting system 1:1 chloroform–ethyl acetate.
2
3
3.2.8. Ethyl ester of 1,3-dimethyl-8-[3-(4-phenyl-1-
piperazinyl)-propylamino]-purine-2,6-dione-7-acetic acid
hydrochloride (16)
Free base of 16 from 14. Yield 1.52 g (63%); m.p.
1
56–158°C (ethanol); Anal. (C H N O ) C, H, N;
3.2.11. General method for the synthesis of imides 19–24
To the sodium butoxide solution, prepared from
sodium (0.23 g, 0.01 mol) and n-butanol (50 ml), ap-
propriate 3-substituted succinimide (0.01 mol), and 18
(2.83 g, 0.001 mol) were added. The reaction mixture
was refluxed for 1 h and left overnight at r.t. Then the
solvent was evaporated and the residue was treated
with benzene (100 ml) and 20% K CO (10 ml). The
2
4
34
7
4
TLC: R =0.82 (A); UV: (methanol): u
nm (4.372); H NMR: l=1.20 (t, J=7.1 Hz, 3H,
CH CH ), 2.03–2.10 (m, 2H, CH CH CH ), 3.04–3.20
(log m)=296
f
max
1
2
3
2
2
2
(
3
m, 6H, CH N(CH ) ), 3.14 (s, 3H, N1ꢀCH ), 3.36 (s,
2
2 2
3
H, N3ꢀCH ), 3.52–3.94 (m, 4H, (CH ) NꢀPh), 4.12–
3
2 2
4
.19 (m, 4H, NHCH CH and CH CH ) 4.96 (s, 2H,
2
2
2
3
N7ꢀCH CO), 6.86 (t, J=7.1 Hz, 1H, NHCH ), 6.98–
7
Ph); MS m/z (%): 483(47) [M ], 468(53), 422(55),
2
2
2
3
.02 (m, 5H aromatic, Ph), 7.22–7.66 (m, 2H aromatic,
organic layer was separated, washed with water, dried
+
over anhydrous KCO and filtered off. The solvent was
3
3
1
96(4), 351(62), 308(56), 294(4), 208(8), 203(8), 194(3),
89(9), 175(83), 161(53), 132(68), 77(16), 70(100).
HCl salt of 16 was prepared according to the proce-
evaporated. The resulting free base was dissolved in
ethanol, treated with an excess of ethanol saturated
with dry HCl gas and kept in a refrigerator to obtain
crystalline products.
dure for the HCl salt of 10. M.p. 218–220°C (ethanol);
Anal. (C H N O ×HCl) C, H, N.
2
4
34
7
4
3.2.12. N-[(4-Phenyl-1-piperazinyl)-propyl]-3-phenyl-
3.2.9. Ethyl ester of 1,3-dimethyl-8-[3-(4-phenyl-1-
pyrrolidine-2,5-dione dihydrochloride (19)
piperazinyl)-propylamino]-purine-2,6-dione-7-butyric
acid (17)
Yield 2.61 g (58%); m.p. 191–194°C (ethanol); Anal.
(C H N O Cl ) C, H, N; TLC: R =0.79 (B), R =
2
3
29
3
2
2
f
f
1
From 15. Yield 1.35 g (53%); m.p. 128–130°C (etha-
nol); Anal. (C H N O ) C, H, N; TLC: R =0.92 (A);
0.83 (C); UV: umax (log m)=205 nm (3.502). H NMR:
l=2.06 (t, J=7.6 Hz, 2H, CH CH CH ), 2.70–2.82
2
6
37
7
4
f
2
2
2

4
66
M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
(
(
3
dd, J=5.3 Hz, 1H, H-imide), 3.15–3.19 (m, 4H,
CH ) NꢀPh), 3.24–3.37 (q, J=9.4 Hz, 1H, H-imide),
gradually added. The mixture was then heated on an oil
bath with simultaneous distillation of water. After com-
plete removal of water the reaction temperature was
raised to 200°C and heating was maintained for 2 h.
The crude product, isolated as hydrochloride salt, was
purified by recrystallization from ethanol.
2
2
.40–3.43 (d, J=6.9 Hz, 2H, CH N), 3.49–3.55 (t,
2
J=6.5 Hz, 4H, N(CH ) ), 3.76–3.81 (d, J=9.9 Hz,
2
7
2
2
H, NCH ), 4,19 (q, J=5.2 Hz, 1H, CH-imide), 6.82–
2
.36 (m, 10H, aromatic Ph).
Yield 5.15 g (49%); m.p. 202–204°C (ethanol); Anal.
(C H N O Cl ) C, H, N; TLC: R =0.89 (B), R =
3
.2.13. N-[(4-phenyl-1-piperazinyl)-propyl]-3-(3-bromo-
29
33
3
2
1
2
f
f
phenyl)-pyrrolidine-2,5-dione dihydrochloride (20)
Yield 3.3 g (63%); m.p. 220–223°C (ethanol); Anal.
0.64 (C); H NMR: l=2.02 (t, J=7.5 Hz, 2H,
CH CH CH ), 3.06–3.26 (m, 6H, (CH ) NꢀPh,CH N),
2
2
2
2 2
2
(
C H N O BrCl ) C, H, N; TLC: R =0.74 (B), R =
3.37 (s, 2H, CH -imide), 3.52–3.59 (t, J=6.9 Hz, 4H,
2
3
28
3
2
2
f
f
2
0
.81 (C); UV: umax (log m)=207 nm (3.590); u
NCH ) , 3.75–3.82 (d, J=9.8 Hz, 2H, NCH ), 6.82–
7.43 (m, 15H, aromatic, Ph).
max
2 2
2
1
(
log m)=250 nm (3.145); H NMR: l=2.04 (t, J=7.5
Hz, 2H, CH CH CH ), 2.76–2.86 (dd, J=5.6 Hz, 1H,
2
2
2
H-imide), 3.12–3.26 (m, 7H, (CH ) NꢀPh, H-imide,
3.3. Pharmacology: binding experiments
2
2
CH N), 3.50–3.53 (t, J=6.6 Hz, 4H, N(CH ) ), 3.76–
2
2 2
3
1
.82 (d, J=10.2 Hz, 2H, NCH ), 4.25 (q, J=5.7 Hz,
H, H-imide), 6.83–7.62 (m, 9H, aromatic Ph).
Radioligand binding studies were carried out in the
rat brain using the hippocampus (5-HT ) and cortex
2
1A
(
5-HT ) according to published procedures [17]. Radi-
2A
3
3.2.14. N-[(4-phenyl-1-piperazinyl)-propyl]-3-(3-chloro-
oligands used were [ H]-8-OH-DPAT (190 Ci/mmol,
Amersham) and [ H]-ketanserin (60 Ci/mmol, NEN
3
phenyl)-pyrrolidine-2,5-dione dihydrochloride (21)
Yield 2.8 g (58%); m.p. 204–206°C (ethanol); Anal.
Chemicals) for 5-HT1A and 5-HT2A receptors,
respectively.
K values were determined on the basis of at least
i
(
C H N O Cl ) C, H, N; TLC: R =0.83 (B), R =
23 28 3 2 3 f f
1
0.92 (C); H NMR: l=2.03 (t, J=7.6 Hz, 2H,
CH CH CH ), 2.78–2.88 (dd, J=5.7 Hz, 1H, H-
three competition binding experiments in which 10–14
2
2
2
−
10
−3
imide), 3.12–3.26 (m, 7H, (CH ) NꢀPh, H-imide,
drug concentrations (10
–10
M), run in triplicate,
2
2
CH N), 3.47–3.53 (t, J=6.7 Hz, 4H, N(CH ) ), 3.76–
were used. K values were calculated using an ACCUFIT
2
2 2
i
3
1
.82 (d, J=10.6 Hz, 2H, NCH ), 4.26 (q, J=5.7 Hz,
H, H-imide); 6.83–7.49 (m, 9H, aromatic, Ph).
(Lundon Software) program.
2
3.2.15. N-[(4-Phenyl-1-piperazinyl)-propyl]-3-(4-fluoro-
4. Results and discussion
phenyl)-pyrrolidine-2,5-dione dihydrochloride (22)
Yield 2.57 g (55%); m.p. 212–214°C (ethanol); Anal.
The hydrochlorides 10, 11, 16, 17 and 19–24 were
(
0
C H N O FCl ) C, H, N; TLC: R =0.75 (B), R =
.80 (C); H NMR: l=2.05 (t, J=7.5 Hz, 2H,
evaluated for their affinities for 5-HT1A and 5-HT
2
3
28
3
2
1
2
f
f
2A
3
receptors by determining their ability to displace [ H]-8-
3
CH CH CH ), 2.72–2,81 (dd, J=5.5 Hz, 1H, H-
OH-DPAT in the hippocampus and [ H]-ketanserin in
2
2
2
imide), 3.13–3.26 (m, 7H, (CH ) NꢀPh, H-imide,
the cortex of rat brain, respectively. The obtained re-
sults are summarized in Table 1.
2
2
CH ꢀN), 3.47–3.53 (t, J=6.7 Hz, 4H, N(CH ) ), 3.76–
2
2 2
3
1
.81 (d, J=10.9 Hz, 2H, NCH ), 4.24 (q, J=5.5 Hz,
H, H-imide); 6.83–7.43 (m, 9H, aromatic, Ph).
All the evaluated compounds 10, 11, 16, 17 and
19–24 showed similar, moderate 5-HT and 5-HT2A
2
1A
−
7
−6
receptor affinity (K within 10 –10
M) and rather
i
3.2.16. N-[(4-Phenyl-1-piperazinyl)-propyl-3-(4-bromo-
low 5-HT /5-HT selectivity. Removal of the 1,3-di-
2A
1A
phenyl)-pyrrolidine-2,5-dione dihydrochloride (23)
Yield 2.7 g (51%); m.p. 210–212°C (ethanol); Anal.
azepine ring in 4 resulted in a 12-fold decrease in
5-HT1A affinity of 10. Its n-butyl analog 11, structurally
similar to 4, showed 5-HT1A binding constant three
times lower than the parent compound. Increasing the
lipophilicity of the 7-substituent also did not improve
binding properties of 16 and 17 (Table 1). In the second
series replacement of spiroalkyl fragment of 1 with a
3-phenyl substituent produced 19, which demonstrated
the same weak 5-HT1A affinity as 1, but seven times
lower 5-HT2A binding constant. Introduction of a halo-
gen atom on the 3-phenyl ring in 19 enhanced the
5-HT1A affinity of compounds 20–23, but their 5-HT2A
properties remained on the comparable moderate level
as for 19 (Table 1). This suggests that the 3-aryl sub
(
0
C H N O BrCl ) C, H, N; TLC: R =0.69 (B), R =
.78 (C); H NMR: l=2.03 (t, J=7.4 Hz, 2H,
23 28 3 2 2 f f
1
CH CH CH ), 2.73–2.82 (dd, J=5.5 Hz, 1H, H-
2
2
2
imide), 3.13–3.27 (m, 7H, (CH ) NꢀPh, H-imide,
2
2
CH ꢀN), 3.46–3.53 (t, J=6.3 Hz, 4H, N(CH ) ), 3.76–
2
2 2
3
1
.81 (d, J=10.8 Hz, 2H, NCH ), 4.22 (q, J=5.5 Hz,
H, H-imide); 6.83–7.57 (m, 9H, aromatic, Ph).
2
3.2.17. N-[(4-Phenyl-1-piperazinyl)-propyl]-3,3-
diphenyl-pyrrolidine-2,5-dione dihydrochloride (24)
To a mixture of amine 7 (4.38 g, 0.02 mol) in water
(
50 ml), 3,3-diphenylsuccinic acid (5.4 g, 0.02 mol) was

M. Paw *l owski et al. / Il Farmaco 55 (2000) 461–468
467
Table 1
5
-HT1A and 5-HT2A receptor affinities (K ) and selectivity ratios (S2,1) of compounds 1–3, 4–6, 10, 11, 16, 17 and 19–24
i
a
Comp.
K 9SEM (nM)
i
Selectivity ratio S2.1=K (5-HT )/K (5-HT1A)
i 2A i
5-HT1A
5-HT2A
b
1
2
3
4
5
6
1
1
1
1
1
2
2
2
2
2
8
1185945
830960
0.5190.06
3192
1692
2.190.2
38595
10091
592972
45794
1069950
177910
258927
22399
510914
444930
1.4390.21
3496
3793
0.029
0.045
b
b
21394
258914
422951
243946
19796
614910
17995
1010914
26894
329921
388914
43698
43697
842911
418
8.3
26
116
0.51
6.14
0.30
2.21
0.25
1.85
1.50
1.95
0.85
1.89
c
c
c
0
1
6
7
9
0
1
2
3
4
b
-OH-DPAT
Ritanserin
b
1.1490.13
a
The mean value from at least three independent experiments; Hill slopes n =0.84–1.08.
Data taken from Ref. [9].
Data taken from Ref. [10].
H
b
c
[
4] R. Perrone, F. Berardi, M. Leopoldo, V. Tortorella, M.G.
Fornaretto, C. Caccia, R.A. McArthur, 1-Aryl-4-[(1-te-
tralinyl)alkyl]piperazines: alkylamido and alkyamino derivatives.
synthesis, 5-HT1A receptor affinity and selectivity, J. Med.
Chem. 39 (1996) 3195–3202.
stituent in pyrrolidine-2,5-dione is tolerated better than
the spiroalkyl fragment at 5-HT1A receptors, but is
apparently less favoured at 5-HT2A binding sites.
In conclusion, the present results show that structural
modifications in both series of compounds do not im-
prove binding affinity and selectivity in comparison to
the parent compounds. They demonstrate, however,
that other elements, i.e. 1,3-diazepine ring in 4 or
spiroalkyl ring in 1 are important for high 5-HT1A or
[5] B.J. van Steen, I. van Wijngaarden, M.T.M. Tulp, W. Soudijn,
Structure–affinity relationship studies on 5-HT1A receptor lig-
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stituents, J. Med. Chem. 36 (1993) 2751–2760.
[
[
[
[
6] J.L. Mokrosz, M.H. Paluchowska, E. Chojnacka-Wojcik, M.
Filip, S. Charakchieva-Minol, A. Dere n´ -Wesotek, M.J.
Mokrosz, Structure–activity relationship studies of central ner-
vous system agents 13. 4-[3-(Benzotriazol-1-yl)propyl]-1-(2-
methoxyphenyl) piperazine, a new putative 5-HT1A receptor
antagonist, and its analogs, J. Med. Chem. 37 (1994) 2754–2760.
7] S. Misztal, A. Bojarski, M. Ma c´ kowiak, J. Boksa, Z. Bielecka,
J.L. Mokrosz, Structure–activity relationship studies of CNS
agents 6. Effect of terminal amide fragment on 5-HT1A and
5-HT2A receptor affinity for N-[3-(4-aryl-1-piperazinyl)-
propyl]derivatives of 3,4-dihydroquinolin-2-(1H)-one and its iso-
meric isoquinolinones, Med. Chem. Res. 2 (1992) 82–87.
5-HT2A binding affinity and selectivity of these
compounds.
Acknowledgements
This study was partly supported by the Polish State
Committee for Scientific Research. grant no. 6-P206-
008-07, 1994–1996, M.P.
8] J.L. Mokrosz, A. Dere n´ -Wesotek, E. Tatarczyfiska, B.
Duszyfiska, A.J. Bojarski, M.J. Mokrosz, E. Chojnacka-W o´ jcik,
8
-[4-[2-(1,2,3,4-Tetrahydroisoquinolinyl)]butyl]-8-azaspiro[4,5]-
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