Synthesis and dopamine D2-like receptor binding affinity of substituted 5-phenyl-pyrrole-3-carboxamides.

Article abstract of DOI:10.1016/S0014-827X(99)00061-0

A series of 5-p-substituted phenyl-pyrrole-3-carboxamide derivatives was designed as hybrid analogs of the dopamine D2-like 5-phenyl-pyrrole and heterocyclic carboxamide antipsychotics. The title compounds were synthesized and evaluated for dopamine D2-like receptor by means of [3H]YM-09151-2 receptor binding assay. The compound bearing a 1-ethyl-2-methyl-pyrrolidine moiety as the basic part of 5-phenyl-pyrrole-3-carboxamide derivative 1a together with its 2-chloro analog 1f were found to possess affinity in the low micromolar range. Substituted phenyl-pyrrolecarboxamides containing groups such as F, Cl, NO2, CH3, at the 4-position of the phenyl ring, gave ligands with lower D2-like affinity.

Full text of DOI:10.1016/S0014-827X(99)00061-0

www.elsevier.nl/locate/farmac
Il Farmaco 54 (1999) 542–550
Synthesis and dopamine D2-like receptor binding affinity of
substituted 5-phenyl-pyrrole-3-carboxamides
Ge´rard A. Pinna a,*, Maria M. Curzu a, Mario Sechi a, Giorgio Chelucci b,
Elisabetta Maciocco c
a Istituto di Chimica Farmaceutica e Tossicologica, Uni6ersita` di Sassari, Via Muroni 23, 07100 Sassari, Italy
b Dipartimento di Chimica, Uni6ersita` di Sassari, Via Vienna 2, 07100 Sassari, Italy
c Dipartimento di Biologia Sperimentale, Uni6ersita` di Cagliari, Via Palabanda 12, 09123 Cagliari, Italy
Received 13 October 1998; accepted 10 May 1999
Abstract
A series of 5-p-substituted phenyl-pyrrole-3-carboxamide derivatives was designed as hybrid analogs of the dopamine D2-like
5-phenyl-pyrrole and heterocyclic carboxamide antipsychotics. The title compounds were synthesized and evaluated for dopamine
D2-like receptor by means of [3H]YM-09151-2 receptor binding assay. The compound bearing a 1-ethyl-2-methyl-pyrrolidine
moiety as the basic part of 5-phenyl-pyrrole-3-carboxamide derivative 1a together with its 2-chloro analog 1f were found to
possess affinity in the low micromolar range. Substituted phenyl-pyrrolecarboxamides containing groups such as F, Cl, NO2, CH3,
at the 4-position of the phenyl ring, gave ligands with lower D2-like affinity. © 1999 Elsevier Science S.A. All rights reserved.
Keywords: D2-like receptor binding; Substituted 5-phenyl-pyrrole-3-carboxamides; Structure–activity relationship
extrapyramidal syndrome (EPS) and irreversible tardive
dyskinesia.
1. Introduction
The therapeutic benefit of D2 antagonists in treating
psychotic disorders has been fully accepted with the
discovery of more effective antipsychotic drugs charac-
terized by minimal induction of extrapyramidal effects
(atypical antipsychotic) [3].
Dopamine receptors can be divided into two major
families: the D1-like and D2-like receptors based on
their pharmacological profiles and coupling with the
enzyme adenylate cyclase [1]. Molecular cloning tech-
niques have shown that the D1-like family is further
divided into the D1 and D5 receptors, both of which
activate adenylate cyclase, while the D2-like family is
divided into the D2, D3, and D4 receptors, which either
inhibit cyclic adenosine monophosphate (cAMP) pro-
duction or are not coupled to adenylate cyclase [2].
Psychotic disorders such as schizophrenia seem to be
characterized by an overreactivity of dopamine-secret-
ing neurons in the ‘limbic’ brain, rich in D2 receptors
[3]. From a pharmacological point of view, D2 receptor
antagonists have been shown to treat these diseases
effectively; however, a long-term treatment is associated
with the induction of disabling side effects such as
Therefore, the synthesis of novel antipsychotics with
a better pharmacological profile still remains a primary
goal in the search for the therapy of psychoses [3].
Thus, we have undertaken a research program aimed at
the discovery of potential antipsychotic agents, taking
as lead compounds the known aryl-pyrroles (I) and
related heterocycles displaying high affinity for D2 re-
ceptors [4a–e]. Recent reports [5a,b] about heterocyclic
carboxamides (II) exhibiting interesting binding affinity
towards both D2 and 5-HT1a receptors induced us to
design a new series of 5-phenyl-pyrrole-3-carboxamides
of general formula 1 (Scheme 1), whose 3-amidic side-
chain was selected taking as reference known D2
blockers.
In this article, we report on the synthesis of substi-
tuted 5-phenyl-pyrrole-3-carboxamides (1) and the re-
sults of the binding affinities for the D2-like receptors.
* Corresponding author. Tel.: +39-079-228 719; fax: +39-079-
228 720.
E-mail address: pinger@ssmain.uniss.it (G.A. Pinna)
0014-827X/99/$ - see front matter © 1999 Elsevier Science S.A. All rights reserved.
PII: S0014-827X(99)00061-0

G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
543
Scheme 1. Design of 5-phenyl-pyrrole-3-carboxamides.
2. Chemistry
D2-like receptors. Affinities for the dopamine sites were
determined via standard competitive displacement as-
says using D2-like receptors isolated from caudate nu-
cleus of male Sprague–Dowley rats with [3H]YM-
09151-2 (nemonapride) as a specific ligand [10] and
(−)-sulpiride as a specific displacer [11].
Preparation of the substituted 5-aryl-3-carboxamides
(1a–l) is outlined in Scheme 2. Alkylation of the
sodium salt of the ethyl cyanoacetate [6] with suitable
a-haloacetophenones (2–6) [7,8], afforded mixtures of
monoalkyl (7–11) [6] and dialkyl (12–15) derivatives,
with the exception of 5 that gave only the monoalky-
lated product 10.
The desired cyanoketoesters 7–11 were separated
either by trituration with ether of the crude alkylation
mixtures or by flash chromatography in 50–82% yields.
The structures assigned to 7–11 and 12–15 were sup-
ported by 1H and 13C NMR analyses. Esters of 5-
phenyl-pyrrole (16–20) were obtained in satisfactory
yield treating ethereal solution of 7–11 with gaseous
HCl at room temperature (r.t.) for 18–24 h.
The formation of the pyrroles 16–20 most likely
involved a Pynner-type cyclization as reported by Foley
[9]. Compounds 21–23 were obtained in nearly quanti-
tative yields by catalytic (10% Pd–C) hydrogenolysis of
the 2-Cl substituted 16–18. Saponification of 16–23
with hydroalcoholic NaOH provided carboxylic acids
24–31 which were condensed, as mixed anhydrides
(Method A) or acid chlorides (Method B), with appro-
priate amines to give 1a–l.
4. Results and discussion
The D2-like receptor binding affinity data for substi-
tuted phenyl-pyrrolecarboxamides 1 are presented in
Table 1.
Compounds 1a–l showed a marked decrease in D2-
like binding affinity with respect to the reference drug
raclopride. However, it is worth noting that the pres-
ence of a 2-chloro substituent on the pyrrole moiety
kept the affinity in the low micromolar range of the
ground term (1f versus 1a), while it significantly im-
proved affinity of the p-phenyl substituted derivatives
(1j versus 1g, 1i versus 1h).
5. Chemical experimental
Unless otherwise noted, all materials were obtained
from commercial suppliers and used without purifica-
tion. Anhydrous solvent such as ethanol (EtOH) tetra-
hydrofuran (THF) and dimethylformamide (DMF)
were obtained from Aldrich in sure-seal bottles.
All reactions involving air- or moisture-sensitive
compounds were performed under an argon ‘S’ atmo-
sphere. Flash chromatography was performed using
Merck Silica gel 60 (230–400 mesh ASTM).
3. Pharmacology
3.1. Receptor binding
The target aryl-pyrrolecarboxamides 1a–l were ex-
amined in vitro for their binding affinities to dopamine

544
G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
Scheme 2.
Thin layer chromatography (TLC) was performed
were performed at Laboratorio di Microanalisi, Dipar-
timento di Scienze Farmaceutiche, Universita` di
Padova (Italy), and are within 90.4% of the calculated
values. For the binding studies [3H] YM-09151-2 was
purchased from NEN-DuPont (Boston, MA, USA).
with Polygram® SIL N-HR-/HV254 precoated plastic
1
sheet (0.2 mm). H and 13C NMR spectra were deter-
mined in CDCl3 with superconducting FT-NMR using
a XL-200 Varian apparatus at 200 MHz.
Chemical shifts are expressed in l (ppm) downfield
from internal TMS and coupling constants in Hz. Sig-
1
nificant H NMR data are reported in the following
5.1. General cyan(ethoxycarbonyl)methyl-alkylation
procedure for compounds 7–15
order: multiplicity (s, singlet; d, doublet; t, triplet; q,
quartet; m, multiplet), number of protons, and coupling
constants in Hz. IR spectra were recorded as thin films
or Nujol mulls on NaCl plates with a Perkin–Elmer
781 IR spectrophotometer and are expressed in w
(cm−1). UV–Vis spectra were recorded as ethanolic
solutions with a Perkin–Elmer Lambda 5 spectropho-
tometer and the absorption wavelengths are expressed
in nm followed by (log m). Melting points were deter-
mined on a Thomas Hoover capillary melting point
apparatus and are uncorrected. Elemental analyses
To a suspension of Na (16 mmol) in 4 ml of dry
ethanol was added dropwise ethyl cyanoacetate (16
mmol) at 0–5°C. The reaction mixture was stirred until
sodium dissolution was complete and then was evapo-
rated in vacuo to give a solid residue, which was added
portionwise to a solution of appropriate haloacetophe-
none (2–6) (16 mmol) in 10 ml of THF. The resulting
suspension was stirred at r.t. (0.5–1 h) then concen-
trated in vacuo and the residue suspended in water. The

G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
545
Table 1
2H, J=7.2, CH2), 7.30 and 7.86 (2d, 4H, J=8.4,
Ar-H). Anal. C14H15NO3 (C, H, N).
D2-like receptor binding affinity a of compounds 1a–l
5.1.3. Ethyl 2-cyano-4-(4-fluorophenyl)-4-oxobutanoate
(9)
55% Yield; Rf 0.42 (AcOEt/light petroleum, 2:8); b.p.
140°C/0.05 mmHg; IR: 2260 (CN), 1750 (CO), 1690
1
(CO); UV: 227.8 (3.93), 194.8 (3.80); H NMR: 1.35 (t,
3H, J=7.2, CH3), 3.48–4.18 (ABXm, 3H, J=5.4, 6.8
and 18.0, CH2CH), 4.13 (q, 2H, J=7.2, CH2), 7.13 and
8.04 (m, 4H, Ar-H). Anal. C13H12FNO3 (C, H, F, N).
5.1.4. Ethyl 4-(4-chlorophenyl)-2-cyano-4-oxobutanoate
(10)
82% Yield; Rf 0.42 (AcOEt/light petroleum, 2:8); bp
138–140°C/0.05 mmHg; IR: 2260 (CN), 1750 (CO),
1
1690 (CO); UV: 240.8 (3.97), 209.2 (3.84); H NMR:
1.35 (t, 3H, J=7.2, CH3), 3.47–4.17 (m, 3H, J=5.6,
6.8 and 18.2, CH2CH), 4.32 (q, 2H, J=7.2, CH2), 7.47
and 7.90 (2d, 4H, Ar-H). Anal. C13H12ClNO3 (C, H, Cl,
N).
5.1.5. Ethyl 2-cyano-4-(4-nitrophenyl)-4-oxobutanoate
(11)
25% Yield; Rf 0.39 (AcOEt/light petroleum, 3:7);
m.p. 81–83°C (EtOH); IR: 2250 (CN), 1740 (CO), 1690
1
(CO); UV: 262.3 (4.00), 205.1 (3.97); H NMR: 1.36 (t,
3H, J=7.2, CH3), 3.55–3.90 (m, 3H, J=5.6, 6.8 and
18.2, CH2CH), 4.32 (q, 2H, J=7.2, CH2), 8.14 and
8.36 (2d, 4H, J=7.0, Ar-H). Anal. C13H12N2O5 (C, H,,
N).
5.1.6. Ethyl 2-cyano-4-oxo-2-(2-oxo-2-phenylethyl)-4-
phenylbutanoate (12)
aqueous mixture was extracted twice with CH2Cl2, and
the combined extracts were washed with brine, dried
(Na2SO4), and concentrated. The crude product was
triturated with ether isolating the dialkylated deriva-
tives (12–15) by filtration and the monoalkylated com-
pounds (7–11) by evaporation of the solvent.
46% Yield; Rf 0.34 (AcOEt/light petroleum, 3:7);
m.p. 130°C (triturated with ether); IR: 2260 (CN), 1730
(CO), 1690 (CO); UV: 247.3 (4.34), 208.3 (4.25); 1H
NMR: 1.33 (t, 3H, J=7.2, CH3), 3.82–4.02 (m, 4H,
2×CH2), 4.32 (q, 2H, J=7.2, CH2), 7.43–7.96 (m,
10H, Ar-H). Anal. C21H19NO4 (C, H, N).
5.1.1. Ethyl 2-cyano-4-oxo-4-phenylbutanoate (7) [6]
50.3% Yield; Rf 0.48 (AcOEt/light petroleum, 3:7);
m.p. 53–55°C (EtOH); IR: 2260 (CN), 1740 (CO), 1690
5.1.7. Ethyl 2-cyano-4-(4-methylphenyl-2-[2-(4-methyl-
phenyl)-2-oxoethyl])-4-oxobutanoate (13)
1
48% Yield; Rf 0.36 (AcOEt/light petroleum, 3:7);
m.p. 148°C (triturated with ether); IR: 2260 (CN), 1740
(CO), 1680 (CO); UV: 247.0 (4.24), 207.7 (4.21); 1H
NMR: 1.25 (t, 3H, J=8.0, CH3), 2.41 (s, 6H, 2×CH3),
3.78–4.03 (m, 4H, 2×CH2), 4.22 (q, 2H, J=8.0, CH2),
7.34 and 7.88 (2d, 8H, J=8.0, Ar-H). Anal. C23H23NO4
(C, H, N).
(CO); UV: 238.7 (3.96), 208.7 (3.80); H NMR: 1.39 (t,
3H, J=7.2, CH3), 3.51–4.20 (ABXm, 3H, J=5.4, 6.8
and 18.2, CH2CH), 4.30 (q, 2H, J=7.2, CH2), 7.46–
7.99 (m, 5H, Ar-H). Anal. C13H13NO3 (C, H, N).
5.1.2. Ethyl 2-cyano-4-(4-methylphenyl)-4-
oxobutanoate (8)
51% Yield; Rf 0.46 (AcOEt/light petroleum, 3:7);
m.p. 53–55°C (MeOH); IR: 2260 (CN), 1750 (CO),
1690 (CO); UV: 252.0 (3.88), 212.7 (3.80); H NMR:
5.1.8. Ethyl 2-cyano-4-(4-fluorophenyl-2-[2-(4-fluoro-
phenyl)-2-oxoethyl])-4-oxobutanoate (14)
1
1.34 (t, 3H, J=7.2, CH3), 2.34 (s, 3H, CH3), 3.48–4.18
(ABXm, 3H, J=5.6, 6.8 and 18.0, CH2CH), 4.30 (q,
43% Yield; Rf 0.36 (AcOEt/light petroleum, 2:8);
m.p. 138°C (triturated with ether); IR: 2260 (CN), 1740

546
G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
(CO), 1680 (CO); UV: 247.0 (4.39), 208.5 (4.29); 1H
NMR: 1.26 (t, 3H, J=8.0, CH3), 3.88–4.10 (m, 4H,
2×CH2), 4.20–4.32 (q, 2H, J=8.0, CH2), 7.28 and
8.13 (m, 8H, Ar-H). Anal. C21H17F2NO4 (C, H, F, N).
J=7.2, CH3), 4.33 (q, 2H, J=7.2, CH2), 6.79 (d, 1H,
J=3.0, C4H), 7.04–7.46 (m, 4H, Ar-H), 8.93 (br s, 1H,
NH exch. with D2O). Anal. C13H11ClFNO2 (C, H, Cl,
F, N).
5.2.4. Ethyl-2-chloro-5-(4-chlorophenyl)-1H-3-pyrrole-
carboxylate (19)
82% Yield; Rf 0.50 (AcOEt/light petroleum, 2:8);
5.1.9. Ethyl 2-cyano-4-(4-nitrophenyl-2-[2-(4-nitro-
phenyl)-2-oxoethyl])-4-oxobutanoate (15)
25% Yield; Rf 0.24 (AcOEt/light petroleum, 3:7);
m.p. 164–167°C (triturated with ether); IR: 2240 (CN),
1745 (CO), 1700 (CO); UV: 262.9 (4.17), 210.2 (3.62);
1H NMR: 1.36 (t, 3H, J=7.2, CH3), 3.88–4.18 (m, 4H,
2×CH2), 4.34 (q, 2H, J=7.2, CH2), 8.20 and 8.36 (2d,
8H, J=8.8, Ar-H). Anal. C21H17N3O8 (C, H, N).
m.p. 178–179°C (MeOH); IR: 3300 (NH), 1690 (CO);
1
UV: 259.0 (4.10), 209.1 (4.06); H NMR: 1.37 (t, 3H,
J=7.6, CH3), 4.30 (q, 2H, J=7.6, CH2), 6.83 (d, 1H,
J=2.6, C4H), 7.30 and 7.53 (2d, 4H, J=7.4, Ar-H),
11.84 (br s, 1H, NH exch. with D2O). Anal.
C13H11Cl2NO2 (C, H, Cl, N).
5.2. General ring closure procedure for compounds 16–20
5.2.5. Ethyl-2-chloro-5-(4-nitrophenyl)-1H-3-pyrrole-
carboxylate (20)
A solution of the appropriate cyanoketoester 7–11
(4.3 mmol) in diethyl ether (30 ml) at 0–5°C was
bubbled with an excess of gaseous HCl. After the HCl
addition was completed the cooling bath was removed
and the stirring continued at r.t. for 18–24 h and the
progress of the reaction was monitored by TLC. Argon
was then bubbled through the solution and the reaction
mixture was concentrated to leave a solid which was
purified by flash-chromatography eluting with ethylac-
etate/light petroleum to give phenyl-pyrroles 16–20.
72% Yield; Rf 0.66 (AcOEt/light petroleum, 2:8);
m.p. 249–252°C (MeOH); IR: 3250 (NH), 1690 (CO);
1
UV: 369.3 (4.16), 264.4 (4.38), 199.9 (4.62); H NMR:
1.38 (t, 3H, J=7.2, CH3), 4.30 (q, 2H, J=7.2, CH2),
7.07 (d, 1H, J=2.2, C4H), 7.80 and 8.20 (2d, 4H,
J=8.80, Ar-H), 12.22 (br s, 1H, NH exch. with D2O).
Anal. C13H11ClN2O2 (C, H, Cl, N).
5.3. General dechlorination procedure for compounds
21–23
5.2.1. Ethyl-2-chloro-5-phenyl-1H-3-pyrrolecarboxylate
(16) [9]
80% Yield; Rf 0.46 (AcOEt/light petroleum, 2:8):
A solution of the appropriate ethyl-2-chloro-5-
phenyl-3-pyrrolecarboxylate (4.7 mmol) (16–18) in 60
ml of ethanol was hydrogenated over 10% Pd–C at 4
atm pressure and at r.t. After the theoretical amount of
hydrogen had been adsorbed (ca. 2–6 h) the catalyst
was removed by filtration through a bed of Celite and
the filtrate concentrated in vacuo to give the title com-
pound 21–23 as a solid product.
m.p. 118–120°C (MeOH/H2O); IR: 3300 (NH), 1700
1
(CO); UV: 252.4 (3.99), 213.1 (3.97); H NMR: 1.37 (t,
3H, J=7.0, CH3), 4.33 (q, 2H, J=7.0, CH2), 6.87 (d,
1H, J=3.2, C4H), 7.24–7.49 (m, 5H, Ar), 8.99 (br s,
1H, NH exch. with D2O). 13C NMR 14.30 (CH3), 60.32
(CH2), 107.51 (C-4), 112.73 (C-3), 121.01 (C-2), 123.91
(C-3% and C-5%), 127.13 (C-4%), 128.86 (C-2% and C-6%),
130.85 (C-5), 131.12 (C-1%), 164.08 (CꢀO). Anal.
C13H12ClNO2 (C, H, Cl, N).
5.3.1. Ethyl 5-phenyl-1H-3-pyrrolecarboxylate (21)
98% Yield; Rf 0.34 (AcOEt/light petroleum, 2:8);
m.p. 152°C (MeOH); IR: 3300 (NH), 1690 (CO); UV:
1
277.9 (4.29), 220.0 (4.39), 204.0 (4.35); H NMR: 1.36
5.2.2. Ethyl-2-chloro-5-(4-methylphenyl)-1H-3-pyrrole-
carboxylate (17)
83% Yield; Rf 0.60 (AcOEt/light petroleum, 2:8):
(t, 3H, J=7.2, CH3), 4.31 (q, 2H, J=7.2, CH2), 6.90–
6.93 (m, 1H, C4H), 7.25–7.60 (m, 6H, Ar-H and C2H),
9.15 (br s, 1H, NH exch. with D2O); 13C NMR: 14.42
(CH3), 59.98 (CH2), 106.45 (C-4), 117.65 (C-3), 124.04
(C-3% and C-5%), 124.36 (C-2), 126.90 (C-4%), 128.90 (C-2%
and C-6%), 131.69 (C-5), 133.08 (C-1%), 165.38 (CꢀO).
Anal. C13H13O2 (C, H, N).
m.p. 130–133°C (MeOH); IR: 3260 (NH), 1670 (CO);
1
UV: 252.7 (4.10), 210.9 (4.07); H NMR: 1.37 (t, 3H,
J=7.0, CH3), 2.35 (s, 1H, CH3), 4.32 (q, 2H, J=7.0,
CH2), 6.81 (d, 1H, J=3.2, C4H), 7.17 and 7.36 (2d, 4H,
J=8.0, Ar-H), 9.09 (br s, 1H, NH exch. with D2O).
Anal. C14H14ClNO2 (C, H, Cl, N).
This compound could also be obtained in quantita-
tive yield by hydrogenation of 19.
5.2.3. Ethyl-2-chloro-5-(4-fluorophenyl)-1H-3-pyrrole-
carboxylate (18)
5.3.2. Ethyl 5-(4-methylphenyl)-1H-3-pyrrolecarboxy-
late (22)
87% Yield; Rf 0.49 (AcOEt/light petroleum, 2:8);
100% Yield; Rf 0.30 (AcOEt/light petroleum, 2:8);
m.p. 159–161°C (MeOH), IR 3290 (NH), 1680 (CO);
UV: 255.7 (4.01), 210.4 (4.06); H NMR: 1.37 (t, 3H,
m.p. 160–163°C (MeOH/H2O); IR: 3290 (NH), 1670
(CO); UV: 253.6 (4.02), 211.4 (4.01); H NMR: 1.35 (t,
1
1

G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
547
3H, J=7.0, CH3), 2.34 (s, 3H, CH3), 4.28 (q, 2H,
J=7.0, CH2), 6.80–6.90 (m, 1H, C4H), 7.17 and 7.48
(2d, 4H, J=8.0, Ar-H), 7.39–7.45 (m, 1H, C2H), 10.73
(br s, 1H, NH exch. with D2O). Anal. C14H15NO2 (C,
H, N).
7.01–7.62 (m, 5H, Ar-H and C2H), 11.36 (br s, 1H, NH
exch. with D2O). Anal. C11H8FNO2 (C, H, F, N).
5.4.4. 2-Chloro-5-phenyl-1H-3-pyrrolecarboxylic acid
(27)
78.3% Yield; Rf 0.45 (CHCl3/MeOH, 9:1): m.p. 193–
195°C; IR: 3290 (NH), 1650 (CO); UV: 251.5 (3.96),
210.5 (3.92); 1H NMR: 6.88 (d, 1H, J=3.0, C4H),
7.20–7.69 (m, 5H, Ar-H), 9.80–10.60 (br s, 1H, COOH
exch. with D2O), 11.40 (br s, 1H, NH exch. with D2O).
Anal. C11H8ClNO2 (C, H, Cl, N).
5.3.3. Ethyl 5-(4-fluorophenyl)-1H-3-pyrrolecarboxylate
(23)
67.5% Yield; Rf 0.42 (AcOEt/light petroleum 2:8);
m.p. 162–164°C (MeOH); IR: 3300 (NH), 1680 (CO);
1
UV: 246.0 (4.01), 212.6 (3.99); H NMR: 1.36 (t, 3H,
J=7.0, CH3), 4.29 (q, 2H, J=7.0, CH2), 6.81–6.83 (m,
1H, C4H), 7.01–7.10 (m, 2H, Ar-H), 7.42–7.44 (m, 1H,
C2H), 7.51–7.56 (m, 2H, Ar-H), 10.65 (br s, 1H, NH
exch. with D2O). Anal. C13H12FNO2 (C, H, F, N).
5.4.5. 2-Chloro-5-(4-methylphenyl)-1H-3-pyrrolecar-
boxylic acid (28)
54% Yield; Rf 0.60 (CHCl3/MeOH, 8:2); m.p. 198–
201°C (benzene); IR: 3300 (NH), 1680 (CO); UV: 253.2
1
(4.01), 211.0 (3.98); H NMR: 2.34 (s, 3H, CH3), 2.36–
5.4. General ester hydrolysis procedures for compounds
24–31
3.40 (br s, 1H, COOH exch. with D2O), 6.80 (d, 1H,
J=3.0, C4H), 7.32 (ABq, 4H, Ar-H), 10.60 11.63 (br s,
1H, NH exch. with D2O). Anal. C12H10ClNO2 (C, H,
Cl, N).
A mixture of appropriate ester (16, 17, 20 and 21–
23) (4.65 mmol) in 48 ml of hydroalcoholic solution
(1:2) of 10% NaOH was refluxed for 12 h and then
poured into ice-water. The basic solution was acidified
with conc. HCl and the solid precipitated was filtered
off. The crude product was dissolved in 5% aqueous
NaHCO3 and the resulting mixture filtered. Concen-
trated HCl was added dropwise to the filtrate and the
solid precipitated was filtered off to give the desired
acid (24–28, 31) which was used without further
purification.
5.4.6. 2-Chloro-5-(4-nitrophenyl)-1H-3-pyrrolecar-
boxylic acid (31)
57.6% Yield; Rf 0.78 (CHCl3/MeOH, 8:2); m.p. 278–
279°C; IR: 3280 (NH), 1775 (CO); UV: 367.9 (4.06),
1
217.6 (4.11); H NMR: 3.02–4.10 (br s, 1H, COOH
exch. with D2O), 7.10 (d, 1H, J=2.8, C4H), 7.88 and
8.20 (2d, 4H, J=8.80, Ar-H), 12.72 (br s, 1H, NH
exch. with D2O). Anal. C11H7ClN2O4 (C, H, Cl, N).
5.4.7. 2-Chloro-5-(4-fluorophenyl)-1H-3-pyrrolecar-
boxylic acid (29)
5.4.1. 5-Phenyl-1H-3-pyrrolecarboxylic acid (24)
85% Yield; Rf 0.41 (CHCl3/MeOH, 9:1): m.p. 176–
178°C; IR: 3400 (NH), 1650 (CO); UV: 244.8 (3.89),
A solution of ethyl-2-chloro-5-(4-fluorophenyl)-1H-
3-pyrrolecarboxylate (18) (7.5 mmol) in 7.5 ml of EtOH
and 75 ml of 20% aqueous NaOH was refluxed for 5 h
and then poured into ice-water. The mixture was aci-
dified with conc. HCl and extracted with CHCl3. The
organic layers were combined, dried (Na2SO4), filtered
and concentrated in vacuo to give a brown solid, which
was dissolved in 5% NaHCO3 solution. The basic mix-
ture was extracted with Et2O, acidified with conc. HCl
and extracted with CHCl3 which was dried (Na2SO4)
and evaporated in vacuo to give compound 29.
84% Yield; Rf 0.42 (CHCl3/MeOH, 9:1); m.p. 125–
127°C; IR: 3300 (NH), 1690 (CO); UV: 248.0 (4.01),
1
214.7 (3.88); H NMR: 3.05–5.00 (br s, 1H, COOH
exch. with D2O), 6.82–6.90 (m, 1H, C4H), 7.16–7.80
(m, 6H, Ar-H and C2H), 11.55 (br s, 1H, NH exch.
with D2O). Anal. C11H9NO2 (C, H, N).
5.4.2. 5-(4-Methylphenyl)-1H-3-pyrrolecarboxylic acid
(25)
78% Yield; Rf 0.59 (CHCl3/MeOH, 8:2); m.p. 197–
200°C; IR: 3420 (NH), 1680 (CO); UV: 246.7 (3.98),
213.7 (3.96); 1H NMR: 2.34 (s, 3H, CH3), 5.20–6.10 (br
s, 1H, COOH exch. with D2O), 6.80–6.84 (m, 1H,
C4H), 7.17 and 7.48 (2d, 4H, J=8.0, Ar-H), 7.40–7.46
(m, 1H, C2H), 11.07 (br s, 1H, NH exch. with D2O).
Anal. C12H11NO2 (C, H, N).
1
211.6 (3.98); H NMR: 3.83 (br s, 1H, COOH exch.
with D2O), 6.76 (d, 1H, J=2.5, C4H), 7.01–7.61 (m,
4H, Ar-H), 11.88 (br s, 1H, NH exch. with D2O). Anal.
C11H7ClFNO4 (C, H, Cl, F, N).
5.4.3. 5-(4-Fluorophenyl)-1H-3-pyrrolecarboxylic acid
(26)
94.5% Yield; Rf 0.62 (CHCl3/MeOH, 8:2); m.p.
190°C (dec.); IR: 3330 (NH), 1660 (CO); UV: 249.8
(3.93), 211.0 (3.91); 1H NMR: 2.66–4.20 (br s, 1H,
COOH exch. with D2O), 6.79–6.90 (m, 1H, C4H),
5.4.8. 2-Chloro-5-(4-chlorophenyl)-1H-3-pyrrolecar-
boxylic acid (30)
A solution of ethyl-2-chloro-5-(4-chlorophenyl)-1H-
3-pyrrolecarboxylate (19) (1.76 mmol) and KOH (9.5
mmol) in 10.6 ml of CH3OH and 0.35 ml of H2O was

548
G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
heated at 75°C for 12 h, then concentrated in vacuo.
Water was added to the residue and the suspension was
acidified with concentrated HCl and filtered to give the
title compound.
D2O), 6.71–6.72 (m, 1H, C4H), 7.16–7.56 (m, 6H,
Ar-H and C2H), 10.64 (br s, 1H, NH exch. with D2O);
13C NMR: 10.96 (2×CH3), 36.50 (CH2), 46.68 (2×
CH2), 51.73 (CH2), 103.79 (C-4), 120.35 (C-3), 122.32
(C-2), 124.02 (C-3% and C-5%), 126.36 (C-4%), 128.64 (C-2%
and C-6%), 132.06 (C-5), 133.09 (C-1%), 165.66 (CꢀO).
Anal. C17H23N3O (C, H, N).
100% Yield; Rf 0.40 (AcOEt/light petroleum, 4:6):
m.p. 185–187°C; IR: 3300 (NH), 1680 (CO); UV: 250.0
1
(4.06), 209.1 (4.03); H NMR: 5.80 (br s, 1H, COOH
exch. with D2O), 6.86 (d, 1H, J=3.0 C4H), 7.31. and
7.53 (2d, 4H, J=8.6, Ar-H), 11.55 (br s, 1H, NH exch.
with D2O). Anal. C11H7Cl2NO2 (C, H, Cl, N).
5.5.3. (4-Ethylpiperazino)(5-phenyl-1H-3-pyrrolyl)-
methanone (1c)
72.3% Yield; Rf 0.70 (CHCl3/MeOH, 8:2); m.p. 176–
178°C (triturated with Et2O); IR: 3200 (NH), 1660
(CO); UV: 282.3 (4.35), 218.5 4.44), 203.8 (4.49); H
5.5. General acid amination procedures for compounds
1a–l
1
NMR: 1.07 (t, 3H, J=6.8, CH3), 2.34–2.50 (m, 6H,
3×CH2), 3.70–3.90 (m, 4H, 2×CH2), 6.52–6.62 (m,
1H, C4H), 6.88–6.98 (m, 1H, C2H), 7.15–7.60 (m, 5H,
Ar-H), 10.86 (br s, 1H, NH exch. with D2O); 13C
NMR: 11.75 (CH3), 52.11 (3×CH2), 52.70 (2×CH2),
105.51 (C-4), 118.70 (C-3), 122.38 (C-2), 124.07 (C-3%
and C-5%), 126.35 (C-4%), 128.64 (C-2% and C-6%), 132.04
(C-5), 132.36 (C-1%), 166.98 (CꢀO). Anal. C17H21N3O
(C, H, N).
5.5.1. Method A: for amides 1a–d, g–l
A heterogeneous mixture of appropriate acid (2.67
mmol) (24–26, 28–31), the requisite amine (2.94 mmol)
and hydrate 1-hydroxybenzotriazole (BTOH, 2.94
mmol) in 15 ml of THF was cooled to 0°C and then
dicyclohexylcarbodiimide (DCC, 2.94 mmol) in 3 ml of
THF was added. The reaction was warmed to r.t. and
stirred for 15 h. The solid was removed by filtration
and rinsed with THF. The filtrate was concentrated
under reduced pressure, and the oily residue was dis-
solved in CH2Cl2 and washed with 5% aqueous
NaHCO3 and then extracted with 2 M H3PO4. The
acidic aqueous layer was made basic with 2 M NaOH
and extracted with CH2Cl2, which was dried (Na2SO4)
and concentrated in vacuo to afford a residue. The
residue was dried under vacuum (60°C, 0.5 mmHg) or
triturated with ether or acetone to give the title com-
pound 1a, 1i, 1h, 1k as amorphous or 1g, 1j, 1b, 1c, 1d
and 1l) as powder solids.
5.5.4. [4-(2-Methoxyphenyl)piperazino](5-phenyl-1H-3-
pyrrolyl)methanone (1d)
45% Yield; Rf 0.53 (CHCl3/MeOH, 9:1); m.p. 193–
196°C (triturated with acetone); IR: 3310 (NH), 1630
1
(CO); UV: 281.0 (4.14), 207.5 (4.40); H NMR: 3.01–
3.20 (m, 4H, 2×CH2), 3.89 (s, 3H, OCH3), 3.97–4.10
(m, 4H, CH22x), 6.66–6.75 (m, 1H, C4H), 6.91–7.70
(m, 10H, Ar-H and C2H), 11.83 (br s, 1H, NH exch.
with D2O). Anal. C22H23N3O2 (C, H, N).
5.5.5. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
5-(4-fluorophenyl)-1H-3-pyrrolecarboxamide (1g)
62% Yield; Rf 0.30 (CHCl3/MeOH, 8:2); m.p. 104–
107°C (triturated with EtOH); IR: 3220 (NH), 1630
5.5.1.1. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
5-phenyl-1H-3-pyrrolecarboxamide (1a). 77.2% Yield;
Rf 0.22 (CHCl3/MeOH, 8:2); m.p. 72–75°C (amor-
phous); IR: 3230 (NH), 1710 (CO); UV: 282.6 (4.15),
1
(CO); UV: 274.8 (4.17), 219.2 (4.48), 208.0 (4.22); H
NMR: 1.17 (t, 3H, J=7.0, CH3), 1.63–1.91 (m, 4H,
2×CH2), 2.16–2.40 (m, 2H, CH2), 2.78–2.97 (m, 2H,
CH2), 3.23–3.40 (m, 2H, CH2), 3.64–3.80 (m, 1H, CH),
6.68 (br s, 1H, C4H), 6.96–7.56 (m, 5H, Ar-H and
C2H), 10.41 (br s, 1H, NH exch. with D2O). Anal.
C18H22FN3O (C, H, F, N).
1
217.5 (4.32), 200.9 (4.44); H NMR: 1.14 (t, 3H, J=
7.0, CH3), 1.60–1.90 (m, 4H, 2×CH2), 2.20–2.31 (m,
2H, CH2), 2.84 (m, 2H, CH2), 3.21–3.90 (m, 2H, CH2),
3.60–3.79 (m, 1H, CH), 6.71–6.73 (m, 1H, C4H), 7.20–
7.60 (m, 6H, Ar-H and C2H), 10.25 (br s, 1H, NH exch.
with D2O); 13C NMR: 13.82 (CH3), 22.78, 27.92, 40.48,
48.20 and 53.49 (5×CH2), 62.67 (CH), 120.52 (C-3),
122.18 (C-2), 124.09 (C-3% and C-5%), 126.33 (C-4%),
126.61 (C-2% and C-6%), 132.11 (C-5), 133.12 (C-1%),
165.78 (CꢀO). Anal. C18H23N3O (C, H, N).
5.5.5.1. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
5-(4-methylphenyl)-1H-3-pyrrolecarboxamide (1h).
67.53% Yield; Rf 0.40 (CHCl3/MeOH, 8:2); m.p. 130–
134°C (as hydrochloride triturated with Et2O); IR: 3280
1
(NH), 1630 (CO); UV: 281.8 (4.12). 218.8 (4.37); H
5.5.2. N3-[(2-(Diethylamino)ethyl]-5-phenyl-1H-3-
pyrrolecarboxamide (1b)
73.7% Yield; Rf 0.22 (CHCl3/MeOH, 8:2); m.p. 60–
NMR: 1.13 (t, 3H, J=7.2, CH3), 1.60–1.88 (m, 4H,
2×CH2), 2.32 (s, 3H, CH3), 2.38–2.59 (m, 2H, CH2),
2.75–2.92 (m, 2H, CH2), 3.60–3.71 (m, 1H, CH), 6.65–
6.71 (br s, 1H, C4H), 6.86 (br s, 1H, NH exch. with
D2O), 7.13 and 7.44 (2d, 4H, J=8.2, Ar-H), 7.39 (br s,
1H, C2H), 10.19 (br s, 1H, NH exch. with D2O). Anal.
C19H25N3O (C, H, N).
62°C (triturated with Et2O); IR: 3260 (NH), 1730 (CO);
1
UV: 282.2 (4.26), 218.5 (4.39), 202.2 (4.46); H NMR:
1.01 (t, 6H, J=7.4, 2×CH3), 2.50–2.82 (m, 6H, 3×
CH2), 3.49 (m, 2H, CH2), 3.68 (br s, 1H, NH exch. with

G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
549
5.5.5.2. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
2-chloro-5-(4-methylphenyl)-1H-3-pyrrolecarboxamide
(1i). 58.4% Yield; Rf 0.39 (CHCl3/MeOH, 8:2); m.p.
115–120°C (as hydrochloride, triturated with Et2O);
IR: 3240 (NH), 1630 (CO); UV: 281.8 (4.18), 218.8
UV:370.0(4.03),226.0(4.02);1HNMR:1.23(t,3H,J=6.4,
CH3), 1.98–2.20 (m, 4H, 2×CH2), 2.80–3.10 (m, 2H,
CH2), 3.22–3.42 (m, 2H, CH2), 3.58–3.72 (m, 2H, CH2),
3.82–4.01 (m, 1H, CH), 7.24 (s, 1H, C4H), 7.68 and 8.13
(2d, 4H, J=8.0 Ar-H), 8.60 (br s, 1H, NH exch. with
D2O), 12.43 (br s, 1H, NH exch. with D2O). Anal.
C18H21ClN4O3 (C, H, Cl, N).
1
(4.19); H NMR: 1.12 (t, 3H, J=7.0, CH3), 1.78–1.92
(m, 4H, 2×CH2), 2.10–2.28 (m, 2H, CH2), 2.63 (s, 3H,
CH3), 2.65–2.98 (m, 2H, CH2), 3.10–3.22 (m, 2H,
CH2), 3.52–3.75 (m, 1H, CH), 6.79 (s, 1H, C4H), 7.15
and 7.49 (2d, 4H, J=8.0, Ar-H), 7.18 (br s, 1H, NH
exch. with D2O), 11.80 (br s, 1H, NH exch. with D2O);
13C NMR: 13.15 (CH3), 20.13 (CH2), 21.93 (CH2),
27.50 (CH3), 40.07 (CH2), 47.05 (CH2), 52.57 (CH2),
61.45 (CH), 105.03 (C-4), 114.09 (C-3), 115.01 (C-2),
123.40 (C-3% and C-5%), 127.91 (C-4%), 128.48 (C-2% and
C-6%), 130.35 (C-5), 135.30 (C-1%), 162.54 (CꢀO). Anal.
C19H24ClN3O (C, H, Cl, N).
5.5.9. Method B: for amides 1e,f
To a solution of appropriate acid (0.534 mmol) (24, 27)
in 5 ml of CH2Cl2 at 0–5°C was added oxalyl chloride
(1.34 mmol) followed by DMF (7.3 ml, 20 mol%). The
reaction mixture was warmed to r.t. and stirred for 30
min, concentrated in vacuo. The corresponding acid
chloride residue was dissolved in 5 ml of CH2Cl2 and
added of the requisite amine (0.801 mmol). The solution
was stirred at r.t. for 20 min, then concentrated in vacuo
to give a crude residue which was triturated with acetone
to afford title compound as a powder (1e, f).
5.5.6. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
2-chloro-5-(4-fluorophenyl)-1H-3-pyrrolecarboxamide
(1j)
5.5.10. (4-Hydroxy-4-chlorophenylpiperidino)(5-phenyl-
1H-3-pyrrolyl)methanone (1e)
75% Yield; Rf 0.46 (CHCl3/MeOH, 8:2); m.p. 230–
67.5% Yield; Rf 0.40 (CHCl3/MeOH, 8:2); m.p. 188–
189°C (triturated with Et2O); IR: 3360 (NH), 1630 (CO);
UV: 277.3 (4.29), 216.5 (4.31), 207.5 (4.35); 1H NMR: 1.12
(t, 3H, J=7.4, CH3), 1.67–1.91 (m, 4H, 2×CH2),
2.16–2.30 (m, 2H, CH2), 2.81–2.94 (m, 2H, CH2),
3.20–3.27 (m, 2H, CH2), 3.64–3.80 (m, 1H, CH), 6.80,
(s, 1H, C4H), 6.70–7.61 (m, 4H, Ar-H), 11.80 (br s, 1H,
NHexch. withD2O);13CNMR:13.62(CH3), 22.37(CH2),
27.87 (CH2), 40.35 (CH2), 47.44 (CH2), 53.01 (CH2), 61.78
(CH), 106.04 (C-4), 114.83 and 115.26 (C-3% and C-5%),
115.61 (C-3), 125.27 and 125.43 (C-2% and C-6%), 127.48
(C-2), 129.87 (C-5), 158.63 (C-1%), 163.03 (C-4%), 163.52
(CꢀO). Anal. C18H21ClFN3O (C, H, Cl, F, N).
231°C(trituratedwithacetone);IR:3305(NH),1630(CO);
1
UV: 281.80 (3.90), 220.0 (4.11), 204.8 (4.16); H NMR:
1.04–2.01 (m, 8H, 4×CH2), 4.20–4.50 (m, 1H, OH exch.
with D2O), 6.71 (br s, 1H, C4H), 7.19 (br s, 1H, C2H),
7.19–7.68 (m, 9H, Ar-H), 11.63 (br s, 1H, NH exch. with
D2O); 13C NMR: 22.64 (CH2), 23.49 (CH2), 31.53 (CH2),
45.70 (CH2), 68.29 (CꢁOH), 104.10 (C-4), 117.60 (C-3),
119.84(C-2), 121.85(2×C), 124.10(C-4%), 124.86(2×C),
125.85(2×C), 126.93(2×C), 129.28(C-1%), 129.37(C-5),
146.47 (C-1%%%), 154.89 (C-4%%%), 163.49 (CꢀO). Anal.
C22H21ClN2O2 (C, H, Cl, N).
5.5.7. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
2-chloro-5-(4-chlorophenyl)-1H-3-pyrrolecarboxamide
(1k)
5.5.11. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
2-chloro-5-phenyl-1H-3-pyrrolecarboxamide (1f)
43%Yield;Rf0.32(CHCl3/MeOH,8:2);m.p.100–102°C
(amorphous);IR:3360(NH),1630(CO);UV:291.9(3.26),
221.3 (3.34), 216.0 (3.49); 1H NMR: 1.26 (t, 3H, J=6.8,
CH3), 1.82–2.15 (m, 4H, 2×CH2), 2.84–2.94 (m, 2H,
CH2), 3.24–3.49 (m, 2H, CH2), 3.61–3.71 (m, 2H, CH2),
3.74–3.83 (m, 1H, CH), 6.88–6.94 (m, 1H, C4H), 7.27
and 7.47 (2d, 4H, J=8.2, Ar-H), 8.45 (br s, 1H, NH exch.
withD2O),11.90(brs,1H,NHexch.withD2O);13CNMR:
12.40 (CH3), 22.37 (CH2), 27.62 (CH2), 39.98 (CH2), 48.30
(CH2),53.02(CH2),63.18(CH),106.13(C-4),122.85(C-3),
123.30(C-2),124.76(C-3%andC-5%),128.15(C-2%andC-6%),
129.49 (C-5), 129.57 (C-1%), 131.31 (C-4%), 163.12 (CꢀO).
Anal. C18H21Cl2N3O (C, H, Cl, N).
56% Yield; Rf 0.34 (CHCl3/MeOH, 8:2); m.p. 175–
177°C (triturated with acetone); IR: 3360 (NH), 1630
1
(CO); UV: 282.0 (4.20), 218.5 (4.33), 200.6 (4.45); H
NMR: 1.07 (t, 3H, J=7.2, CH3), 1.58–1.90 (m, 4H,
CH2x2), 2.11–2.29 (m, 2H, CH2), 2.50–2.83 (m, 2H,
CH2), 3.08–3.32 (m, 2H, CH2), 3.66–3.69 (m,1H, CH),
6.89 (s,1H, C4H), 7.15–7.55 (m, 5H, Ar-H), 11.07 (br s,
1H, NH exch. with D2O). Anal. C18H22ClN3O (C, H, Cl,
N).
6. Pharmacological experimental
6.1. In 6itro pharmacology
5.5.8. N3-[(1-Ethyltetrahydro-1H-2-pyrrolyl)methyl]-
2-chloro-5-(4-nitrophenyl)-1H-3-pyrrolecarboxamide
(1l)
6.1.1. Membrane preparation
22%Yield;Rf0.33(CHCl3/MeOH,8:2);m.p.170–175°C
(dec.) (triturated with Et2O); IR: 3350 (NH), 1620 (CO);
Membranes for D2-like receptor binding assays were
prepared from caudate nucleus of Sprague–Dowley rats.

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G.A. Pinna et al. / Il Farmaco 54 (1999) 542–550
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Tissue was homogenized in 200 volumes of ice-cold 50
mmol Tris–HCl buffer pH 7.7 (buffer A) and cen-
trifuged at 50000 g at 4°C for 25 min. The pellet was
resuspended in 50 mmol Tris–HCl buffer pH 7.7 con-
taining 120 mM NaCl, 5 mM KCl, 2 mM CaCl2, 1 mM
EDTA and 5.7 mmol ascorbic acid (buffer B).
6.1.2. Binding assay
[3H]YM-09151-2 was used as a specific ligand for
D2-like receptors [10] and 50 mM (−)-sulpiride as a
specific displacer [11]. [3H]YM-09151-2 binding was
determined in a final volume of 1000 ml, consisting of
400 ml tissue homogenate, 100 ml 0.4 nM [3HY]YM-
09151-2, 100 ml drugs (dissolved in dimethylsulfoxide
and serial dilutions made up in buffer) or incubation
buffer (total and non specific samples). The incubation
(at 25°C, in the dark) was started by the addition of
tissue homogenate and was terminated 60 min later by
rapid filtration through glass-fiber filter strips (What-
man GF/B) with a filtration manifold (Model M-24,
Brandel). The filters were rinsed three times with 4 ml
of ice-cold Tris buffer B.
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Acknowledgements
The authors acknowledge Professor G. Cignarella for
his insightful comment on this work.
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