Solution-phase parallel synthesis and evaluation of anticonvulsant activity of N-substituted-3,4-dihydroisoquinoline-2(1H)-carboxamides

Article abstract of DOI:10.1016/j.ejmech.2008.02.025

In our previous studies we identified several isoquinoline derivatives displaying potent anticonvulsant effects in different animal models of epilepsy. With the aim to exploit the main structure-activity relationships (SAR) for this class of compounds we

Full text of DOI:10.1016/j.ejmech.2008.02.025

Available online at www.sciencedirect.com
European Journal of Medicinal Chemistry 44 (2009) 1349e1354
http://www.elsevier.com/locate/ejmech
Short communication
Solution-phase parallel synthesis and evaluation of anticonvulsant
activity of N-substituted-3,4-dihydroisoquinoline-2(1H )-carboxamides
a
b
b
Rosaria Gitto a, , Benedetta Pagano , Rita Citraro , Francesca Scicchitano ,
*
Giovanbattista De Sarro b, Alba Chimirri a
a Dipartimento Farmaco-Chimico, Universita` di Messina, Viale Annunziata, 98168 Messina, Italy
b Dipartimento di Medicina Sperimentale e Clinica, Universita` Magna Græcia, via T. Campanella, 88100 Catanzaro, Italy
Received 13 December 2007; received in revised form 17 January 2008; accepted 16 February 2008
Available online 7 March 2008
Abstract
In our previous studies we identified several isoquinoline derivatives displaying potent anticonvulsant effects in different animal models
of epilepsy. With the aim to exploit the main structureeactivity relationships (SAR) for this class of compounds we planned a solution-phase
parallel synthesis (SPPS) of new N-substituted-3,4-dihydroisoquinoline-2(1H )-carboxamides exploring the effect of introduction of different
(cyclo)alkyl groups at carboxamide moiety linked to N-2 atom of isoquinoline scaffold. The pharmacological effects were evaluated against
audiogenic seizures in DBA/2 mice and, even if some new derivatives were more active than valproate, the designed modifications did not
improve the anticonvulsant efficacy with respect to their precursors.
Ó 2008 Elsevier Masson SAS. All rights reserved.
Keywords: Anticonvulsant; Isoquinoline; DBA/2 mice; Solution-phase parallel synthesis (SPPS)
1. Introduction
the modulation of excitatory glutamatergic neurotransmission
[3]. With respect to this last pharmacological target, extensive
studies have demonstrated that competitive and non-competi-
tive antagonists of the ionotropic glutamate receptors (iGluRs)
show promise in terms of their therapeutic potential for the pre-
vention and treatment of the epilepsy [4].
In our previous works, a large series of isoquinolines were
found to have anticonvulsant activities in various seizure
models interacting with glutamate ionotropic AMPA receptor
(AMPAR) subtype in a selective and non-competitive fashion
[5e12]. The most active compound of the series was 2-acetyl-
1-(40-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquino-
line (1, Fig. 1) which showed the strongest activity with respect
to other known AMPAR antagonists (e.g. GYKI52466, Fig. 1)
when compared to both in vivo and in vitro tests [4,13e15].
Starting from this ‘‘lead compound’’ we explored the effect
of the modification of both acetyl moiety at N-2 position, and
the substituent on the C-1 phenyl group, as well as methoxy
groups on the benzene fused ring. Our computational studies
[5e7] suggested that the carbonyl moiety linked to the N-2
Epilepsy affects approximatily 1% of the world’s popula-
tion. Despite the introduction of many new antiepileptic drugs
(AEDs) and remarkable strides in this research field, more
than a third of patients with epilepsy remain refractory to avail-
able treatments and more effective therapies are needed.
Continued efforts are being made in the development of antiep-
ileptic drugs employing a range of strategies, including modifi-
cation of the structure of existing drugs, targeting novel
molecular substrates and non-mechanism-based drug screening
of compounds in traditional and newer animal models [1,2].
The mechanism of action of currently available effective an-
tiepileptics are: the induction of a prolonged inactivation of the
Naþ channel; the blockade of Ca2þ channel currents; the en-
hancement of the inhibitory GABAergic neurotransmission or
* Corresponding author. Tel.: þ39 0906766413; fax: þ39 090355613.
E-mail address: rgitto@pharma.unime.it (R. Gitto).
0223-5234/$ - see front matter Ó 2008 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2008.02.025

1350
R. Gitto et al. / European Journal of Medicinal Chemistry 44 (2009) 1349e1354
Me
MeO
MeO
MeO
MeO
MeO
O
N
N
N
Me
NHR2
N
O
MeO
N
N
O
O
O
Cl
R1
Br
H2N
GYKI 52466
1
2
3-30
Fig. 1.
position of tetrahydroisoquinoline system plays an important
role in the process of AMPAR recognition and we found that
the nature of fragment linked to carbonyl function significantly
influenced the pharmacological profile in terms of both pharma-
cokinetic and pharmacodynamic effects. Furthermore, the re-
sults of the pharmacological evaluation of some N-acetamide
derivatives [e.g. 2, 1-(40-bromophenyl)-6,7-dimethoxy-2-
(piperidin-1-yl-acetyl)-3,4-dihydroisoquinoline] demonstrated
that the substituent at 40-position of phenyl ring also modulated
the anticonvulsant potency and the halogens appeared to have
a better impact on anticonvulsant activity probably because of
their lipophilic effects [10].
On the basis of these findings and with the aim to gain more
insights into the structureeactivity relationships (SAR) we
herein describe a simple solution-phase parallel synthesis of
new N-(cyclo)alkyl-3,4-tetrahydroisoquinoline-2(1H )-carbox-
amide derivatives (3e30) in which we explored if the presence
of carboxamide frame could be a feature able to improve the
anticonvulsant efficacy against sound-induced seizures in
DBA/2 mice. Moreover we inserted on nitrogen atom of car-
boxamide moiety different (cyclo)alkyl fragments in an at-
tempt to decipher the impact of the bulkiness as well as the
lipophilicity on pharmacological properties. Finally, we inves-
tigated the influence of the nature of halogen substituent at
40-position of the C-1 aryl group and compared the activity
with that of the corresponding unsubstituted derivatives.
2. Results and discussion
As depicted in Scheme 1, a small library of N-substituted-1-
aryl-6,7-dimethoxy-3,4-dihydroisoquinoline-2(1H )-caboxamide
derivatives (3e30) was prepared starting from different 1-aryl-
6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines (31e34) [7] and
various alkylisocyanates. An efficient solution-phase parallel
synthesis was set up at room temperature employing a Buchi
Syncore reactor and the target compounds 3e30 were obtained
in good yields. The structures of the compounds obtained were
supportedbyelementalanalysesandspectroscopicmeasurements
(1H NMR).
The anticonvulsant effects of the synthesized N-substituted-
1-aryl-6,7-dimethoxy-3,4-dihydroisoquinoline-2(1H )-caboxa-
mide derivatives (3e30) were evaluated against audiogenic
seizures in DBA/2 mice, which is considered an excellent ani-
mal model for generalized epilepsy and for screening new anti-
convulsant drugs [16]. Table 1 reports the pharmacological
results compared with those of antiepileptic drugs such as gaba-
pentin and valproate as well as isoquinolines 1e2 and GYKI
52466 known as non-competitive AMPA receptor antagonists.
MeO
MeO
MeO
i
NH
NHR2
N
MeO
O
31-34
3-30
R1
R1
3-6, R2 = ethyl
7-10, R2 = n-propyl
11-14, R2 = i-propyl
15-18, R2 = n-butyl
19-22, R2 = t-butyl
23-26, R2 = cyclopentyl
27-30, R2 = cyclohexyl
R1
3, 7, 11, 15, 19, 23, 27, 31
H
4, 8, 12, 16, 20, 24, 28, 32 Br
5, 9, 13, 17, 21, 25, 29, 33 Cl
6, 10, 14, 18, 22, 26, 30, 34
F
Scheme 1. Reagents and conditions: (i) R2NCO, CH2Cl2, TEA, r.t., 90 min.

R. Gitto et al. / European Journal of Medicinal Chemistry 44 (2009) 1349e1354
1351
Table 1
Anticonvulsant activity against audiogenic seizures in DBA/2 mice
lengthening nor the bulkiness of the (cyclo)alkyl chain linked
to the carboxamide group. Considering the effect of the 40-sub-
stituent on the C-1 aryl group, we observed that the unsubsti-
tuted derivatives 3, 15, 19 and 27 are generally more active
than the halogen-substituted analogs. In an attempt to correlate
the rank order of potency with their lipophilic properties, we
also estimated [20] the log P values (Table 1) but no signifi-
cant correlation was observed.
In conclusion an efficientsolution-phase parallel synthesis for
the preparation of new N-substituted-1-aryl-6,7-dimethoxy-3,
4-dihydroisoquinoline-2(1H )-caboxamide derivatives (3e30)
as potential anticonvulsant agents was set up. Unfortunately,
even if some synthesized compounds showed anticonvulsant
activity comparable to other well-known anticonvulsants, the
planned modifications generally afforded molecules (3e30)
with lower activity than the previously reported isoquinoline de-
rivatives (e.g. 1 and 2). Considering the structureeactivity rela-
tionships so far obtained for this class of compounds and
analyzing the contribution of different groups at N-2 position
to the anticonvulsant efficacy we could speculate that both the
size and the nature of the substituents modulate the activity.
Compound
ED50 (mg/kg)a
log Pb
Clonus
Tonus
1
2.25 (1.70e2.97)
5.99 (2.87e12.4)
1.22 (0.90e1.56)
3.86 (1.90e7.86)
11.9 (8.77e16.1)
>35
3.40
4.93
3.41
4.18
4.00
3.46
3.94
4.71
4.53
3.99
3.75
4.53
4.35
3.81
4.47
5.24
5.06
4.52
4.10
4.88
4.70
4.16
4.37
5.14
4.97
4.42
4.94
5.71
5.53
4.99
e
2
3
32.5 (24.7e42.8)
>35
4
5
30.4 (22.3e41.5)
>35
14.2 (7.78e25.8)
>35
6
7
>35
>35
18.1 (12.6e26.1)
31.2 (19.8e54.0)
23.4 (16.9e32.3)
26.9 (15.4e47.2)
>35
8
9
10
>35
>35
11
12
>35
>35
23.6 (17.9e31.1)
26.1 (21.3e31.9)
17.3 (11.8e25.5)
11.0 (7.84e15.5)
15.5 (9.12e25.2)
16.5 (16.4e26.0)
13.7 (7.76e24.1)
13.9 (7.65e25.4
16.9 (9.30e30.8)
13.8 (8.60e23.6)
18.7 (14.1e24.7)
15.1 (9.84e23.2)
14.7 (11.0e19.6)
12.1 (7.91e18.7)
7.24 (4.42e11.8)
9.38 (6.46e13.6)
19.3 (10.2e36.4)
14.2 (9.67e20.8)
>35
13
14
>35
>35
15
16
31.7 (23.0e43.8)
>35
17
18
>35
>35
19
20
27.5 (22.2e34.0)
>35
21
22
30.6 (23.7e39.4)
>35
3. Experimental section
23
24
>35
>35
25
26
>35
3.1. Chemistry
27.7 (19.2e40.2)
26.9 (21.5e33.7)
>35
27
28
Melting points were determined on a Stuart SMP10 appara-
tus and are uncorrected. Elemental analyses (C, H, N) were
carried out on a Carlo Erba Model 1106 Elemental Analyzer
and the results are within ꢀ0.4% of the theoretical values.
Merck silica gel 60 F254 plates were used for analytical
TLC. 1H NMR spectra were measured in CDCl3 with a Varian
Gemini 300 spectrometer; chemical shifts are expressed in
d (ppm) relative to TMS as internal standard and coupling con-
stants (J ) in Hz.
29
30
>35
>35
GYKI 52466
Gabapentin
Valproate
a
10.5 (7.15e15.3)
20.3 (13.7e30.2)
>35
7.41 (4.69e11.7)
9.90 (7.81e12.6)
21.5 (16.1e28.7)
e
e
All data were calculated according to the method of Litchfield and Wil-
coxon. At least 32 animals were used to calculate each ED50. Confidence
limits (ꢀ95%) are given in parentheses.
b
log P data are predicted from a commercially available program (ACD/
Lab).
3.1.1. General procedure for the synthesis of N-(cyclo)alkyl-
1-aryl-6,7-dimethoxy-3,4-dihydroisoquinolin-2(1H )-
carboxamides (3e30)
The biological results presented in Table 1 show that these
compounds generally possess potency lower than other isoqui-
noline analogs 1e2 previously synthesized by us [7,10].
The analysis of reported ED50 values on clonic phase of the
test (see Table 1) shows that the most active derivatives of this
new series of compounds were 19, 26 and 27 in which the
anticonvulsant potency in the clonic phase of the test was
approximately 2.5 fold lower than GYKI 52466, the prototype
of non-competitive AMPAR antagonists showing anticonvul-
sant efficacy [13,14,17,18]. Nevertheless, their activity was
higher than that of valproate and comparable to that of gaba-
pentin two drugs largely used in antiepileptic therapy [19].
Moderate activity against sound-induced seizures charac-
terized compounds 3, 5, 15, 21 whereas the other studied com-
pounds were inactive at highest tested doses (i.e. clonic phase
ED50 > 35 mg/kg).
To a solution of the 1-aryl-6,7-dimethoxy-3,4-dihydroiso-
quinoline derivative (31e34) (0.001 mol) prepared as previ-
ously reported [7] in CH2Cl2 (5 ml) was added suitable
alkylisocyanate (0.0015 mol) and triethylamine (TEA)
(0.001 mol) in the Buchi Syncore reactor. The mixture was
stirred for 90 min at room temperature. After removal of the
solvent under reduced pressure, the residue was powdered
and then crystallized with diethyl ether to give target products
as white solid (3e30).
3.1.1.1. N-Ethyl-1-phenyl-6,7-dimethoxy-3,4-dihydroisoquino-
lin-2(1H )-carboxamide (3). Yield 90%. Mp. 158e160 ꢁC.
1H NMR (CDCl3): 1.13 (3H, t, J ¼ 7.0, CH3), 2.63e3.57
(4H, m, CH2CH2), 3.30 (2H, q, J ¼ 7.0, CH2), 3.78 (3H, s,
CH3O-6), 3.87 (3H, s, CH3O-7), 4.47 (1H, bs, NH), 6.34
(1H, s, H-1), 6.63 (1H, s, H-5), 6.66 (1H, s, H-8), 7.22e7.28
(5H, m, ArH). Anal. C20H24N2O3 (C, H, N).
The main structureeactivity relationship (SAR) consider-
ations suggest that the different degree of anticonvulsant
efficacies do not seem directly connected neither with the

1352
R. Gitto et al. / European Journal of Medicinal Chemistry 44 (2009) 1349e1354
3.1.1.2. 1-(40-Bromophenyl)-N-ethyl-6,7-dimethoxy-3,4-dihy-
3.20e3.28 (2H, m, CH2N), 3.79 (3H, s, CH3O-6), 3.88 (3H,
s, CH3O-7), 4.48 (1H, bs, NH), 6.38 (1H, s, H-1), 6.60 (1H,
s, H-5), 6.67 (1H, s, H-8), 6.93e7.23 (4H, m, ArH). Anal.
C21H25FN2O3 (C, H, N).
droisoquinolin-2(1H )-carboxamide (4). Yield 95%. Mp.
1
129e131 ꢁC. H NMR (CDCl3): 1.15 (3H, t, J ¼ 7.0, CH3),
2.63e3.52 (4H, m, CH2CH2), 3.30 (2H, q, J ¼ 7.0, CH2),
3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.46 (1H, bs,
NH), 6.38 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66 (1H, s, H-8),
7.11 (2H, d, J ¼ 8.5), 7.38 (2H, d, J ¼ 8.5). Anal.
C20H23BrN2O3 (C, H, N).
3.1.1.9. 6,7-Dimethoxy-N-isopropyl-1-phenyl-3,4-dihydroiso-
quinolin-2(1H )-carboxamide (11). Yield 79%. Mp. 141e
1
143 ꢁC. H NMR (CDCl3): 1.12 and 1.16 (6H, 2d, J ¼ 6.3,
CH3), 2.67e3.62 (4H, m, CH2CH2), 3.79 (3H, s, CH3O-6),
3.87 (3H, s, CH3O-7), 3.95e4.07 (1H, m, CH), 4.28 (1H, bs,
NH), 6.30 (1H, s, H-1), 6.62 (1H, s, H-5), 6.66 (1H, s, H-8),
7.22e7.29 (5H, m, ArH). Anal. C21H26N2O3 (C, H, N).
3.1.1.3. 1-(40-Chlorophenyl)-N-ethyl-6,7-dimethoxy-3,4-dihy-
droisoquinolin-2(1H )-carboxamide (5). Yield 96%. Mp.
1
144e146 ꢁC. H NMR (CDCl3): 1.14 (3H, t, J ¼ 7.0, CH3),
2.64e3.54 (4H, m, CH2CH2), 3.35 (2H, q, J ¼ 7.0, CH2),
3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.45 (1H, bs,
NH), 6.39 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66 (1H, s, H-8),
7.17 (2H, d, J ¼ 8.5), 7.24 (2H, d, J ¼ 8.5). Anal.
C20H23ClN2O3 (C, H, N).
3.1.1.10. 1-(40-Bromophenyl)-N-isopropyl-6,7-dimethoxy-3,4-
dihydroisoquinolin-2(1H )-carboxamide (12). Yield 84%.
1
Mp. 128e130 ꢁC. H NMR (CDCl3): 1.14 and 1.18 (6H, d,
J ¼ 6.6, CH3), 2.64e3.51 (4H, m, CH2CH2), 3.79 (3H, s,
CH3O-6), 3.88 (3H, s, CH3O-7), 3.99e4.05 (1H, m, CH),
4.27 (1H, bs, NH), 6.37 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66
(1H, s, H-8), 7.11 (2H, d, J ¼ 8.5), 7.39 (2H, d, J ¼ 8.5).
Anal. C21H25BrN2O3 (C, H, N).
3.1.1.4. 1-(40-Fluorophenyl)-N-ethyl-6,7-dimethoxy-3,4-dihy-
droisoquinolin-2(1H )-carboxamide (6). Yield 92%. Mp.
1
139e141 ꢁC. H NMR (CDCl3): 1.14 (3H, t, J ¼ 7.0, CH3),
2.65e3.54 (4H, m, CH2CH2), 3.33 (2H, q, J ¼ 7.0, CH2),
3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.45 (1H, bs,
NH), 6.39 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66 (1H, s, H-8),
6.92e7.22 (4H, m, ArH). Anal. C20H23FN2O3 (C, H, N).
3.1.1.11. 1-(40-Chlorophenyl)-N-isopropyl-6,7-dimethoxy-3,4-
dihydroisoquinolin-2(1H )-carboxamide (13). Yield 92%.
1
Mp. 133e135 ꢁC. H NMR (CDCl3): 1.14 and 1.18 (6H, d,
J ¼ 6.3, CH3), 2.63e3.51 (4H, m, CH2CH2), 3.80 (3H, s,
CH3O-6), 3.83 (3H, s, CH3O-7), 3.97e4.06 (1H, m, CH),
4.26 (1H, bs, NH), 6.38 (1H, s, H-1), 6.60 (1H, s, H-5), 6.67
(1H, s, H-8), 7.17 (2H, d, J ¼ 8.5), 7.24 (2H, d, J ¼ 8.5).
Anal. C21H25ClN2O3 (C, H, N).
3.1.1.5. 6,7-Dimethoxy-1-phenyl-N-propyl-3,4-dihydroisoqui-
nolin-2(1H )-carboxamide (7). Yield 90%. Mp. 141e143 ꢁC.
1H NMR (CDCl3): 0.88 (3H, t, J ¼ 7.4, CH3), 1.47e1.54
(2H, m, CH2), 2.68e3.63 (4H, m, CH2CH2), 3.19e3.27 (2H,
m, CH2N), 3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7),
4.49 (1H, bs, NH), 6.31 (1H, s, H-1), 6.63 (1H, s, H-5), 6.66
(1H, s, H-8), 7.23e7.28 (5H, m, ArH). Anal. C21H26N2O3
(C, H, N).
3.1.1.12. 1-(40-Fluorophenyl)-N-isopropyl-6,7-dimethoxy-3,4-
dihydroisoquinolin-2(1H )-carboxamide (14). Yield 93%.
1
Mp. 135e137 ꢁC. H NMR (CDCl3): 1.14 and 1.18 (6H, d,
J ¼ 6.3, CH3), 2.65e3.54 (4H, m, CH2CH2), 3.79 (3H, s,
CH3O-6), 3.88 (3H, s, CH3O-7), 3.99e4.06 (1H, m, CH),
4.27 (1H, bs, NH), 6.37 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66
(1H, s, H-8), 6.93e7.23 (4H, m, ArH). Anal. C21H25FN2O3
(C, H, N).
3.1.1.6. 1-(40-Bromophenyl)-6,7-dimethoxyeN-propyl-3,4-di-
hydroisoquinolin-2(1H )-carboxamide (8). Yield 91%. Mp.
1
135e137 ꢁC. H NMR (CDCl3): 0.91 (3H, t, J ¼ 7.4, CH3),
1.49e1.56 (2H, m, CH2), 2.65e3.54 (4H, m, CH2CH2),
3.18e3.26 (2H, m, CH2N), 3.80 (3H, s, CH3O-6), 3.88 (3H,
s, CH3O-7), 4.47e4.49 (1H, m, NH), 6.37 (1H, bs, H-1),
6.60 (1H, s, H-5), 6.66 (1H, s, H-8), 7.12 (2H, d, J ¼ 8.2),
7.39 (2H, d, J ¼ 8.2). Anal. C21H25BrN2O3 (C, H, N).
3.1.1.13. N-Butyl-6,7-dimethoxy-1-phenyl-3,4-dihydroisoqui-
noline-2(1H )-carboxamide (15). Yield 78%. Mp. 114e
1
116 ꢁC. H NMR (CDCl3): 0.90 (3H, t, J ¼ 7.1, CH3), 1.24e
3.1.1.7. 1-(40-Chlorophenyl)-6,7-dimethoxy-N-propyl-3,4-dihy-
3.31 (6H, m, CH2CH2CH2), 2.68e3.64 (4H, m, CH2CH2),
3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.48 (1H, bs,
NH), 6.31 (1H, s, H-1), 6.62 (1H, s, H-5), 6.66 (1H, s, H-8),
7.22e7.28 (5H, m, ArH). Anal. C22H28N2O3 (C, H, N).
droisoquinolin-2(1H )-carboxamide (9). Yield 88%. Mp.
1
127e129 ꢁC. H NMR (CDCl3): 0.91 (3H, t, J ¼ 7.1, CH3),
1.49e1.56 (2H, m, CH2), 2.65e3.55 (4H, m, CH2CH2),
3.23e3.26 (2H, m, CH2N), 3.79 (3H, s, CH3O-6), 3.88 (3H,
s, CH3O-7), 4.49 (1H, bs, NH), 6.39 (1H, s, H-1), 6.60 (1H,
s, H-5), 6.67 (1H, s, H-8), 7.17 (2H, d, J ¼ 8.2), 7.24 (2H, d,
J ¼ 8.2). Anal. C21H25ClN2O3 (C, H, N).
3.1.1.14. 1-(40-Bromophenyl)-N-butyl-6,7-dimethoxy-3,4-dihy-
droisoquinoline-2(1H )-carboxamide (16). Yield 77%. Mp.
1
132e134 ꢁC. H NMR (CDCl3): 0.92 (3H, t, J ¼ 7.1, CH3),
1.23e3.31 (6H, m, CH2CH2CH2), 2.63e3.52 (4H, m,
CH2CH2), 3.80 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.48
(1H, bs, NH), 6.37 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66 (1H,
s, H-8), 7.11 (2H, d, J ¼ 8.2), 7.39 (2H, d, J ¼ 8.2). Anal.
C22H27BrN2O3 (C, H, N).
3.1.1.8. 1-(40-Fluorophenyl)-6,7-dimethoxy-N-propyl-3,4-dihy-
droisoquinolin-2(1H )-carboxamide (10). Yield 80%. Mp.
1
121e123 ꢁC. H NMR (CDCl3): 0.91 (3H, t, J ¼ 7.4, CH3),
1.49e1.56 (2H, m, CH2), 2.66e3.55 (4H, m, CH2CH2),

R. Gitto et al. / European Journal of Medicinal Chemistry 44 (2009) 1349e1354
1353
3.1.1.15. 1-N-Butyl-(40-chlorophenyl)-6,7-dimethoxy-3,4-dihy-
3.1.1.22. 1-(40-Bromophenyl)-N-cyclopentyl-6,7-dimethoxy-3,
4-dihydroisoquinoline-2(1H )-carboxamide (24). Yield 79%.
Mp. 169e171 ꢁC. 1H NMR (CDCl3): 1.25e2.02 (8H, m,
cycloalkyl), 2.65e3.52 (4H, m, CH2CH2), 3.79 (3H, s,
CH3O-6), 3.88 (3H, s, CH3O-7), 3.95e4.16 (1H, m, CH),
4.41 (1H, bs, NH), 6.36 (1H, s, H-1), 6.59 (1H, s, H-5),
6.66 (1H, s, H-8), 7.11 (2H, d, J ¼ 8.2), 7.39 (2H, d,
J ¼ 8.5). Anal. C23H27BrN2O3 (C, H, N).
droisoquinoline-2(1H )-carboxamide (17). Yield 88%. Mp.
1
130e132 ꢁC. H NMR (CDCl3): 0.92 (3H, t, J ¼ 7.1, CH3),
1.27e3.31 (6H, m, CH2CH2CH2), 2.65e3.53 (4H, m,
CH2CH2), 3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.47
(1H, bs, NH), 6.38 (1H, s, H-1), 6.60 (1H, s, H-5), 6.66 (1H,
s, H-8), 7.17 (2H, d, J ¼ 8.5), 7.24 (2H, d, J ¼ 8.5). Anal.
C22H27ClN2O3 (C, H, N).
3.1.1.16. 1-N-Butyl-(40-fluorophenyl)-6,7-dimethoxy-3,4-dihy-
3.1.1.23. 1-(40-Chlorophenyl)-N-cyclopentyl-6,7-dimethoxy-3,
4-dihydroisoquinoline-2(1H )-carboxamide (25). Yield 94%.
Mp. 156e158 ꢁC. 1H NMR (CDCl3): 1.25e2.02 (8H, m,
cycloalkyl), 2.63e3.52 (4H, m, CH2CH2), 3.79 (3H, s,
CH3O-6), 3.88 (3H, s, CH3O-7), 3.93e4.18 (1H, m, CH),
4.40 (1H, bs, NH), 6.36 (1H, s, H-1), 6.59 (1H, s, H-5),
6.66 (1H, s, H-8), 7.17 (2H, d, J ¼ 8.5), 7.24 (2H, d,
J ¼ 8.5). Anal. C23H27ClN2O3 (C, H, N).
droisoquinoline-2(1H )-carboxamide (18). Yield 93%. Mp.
1
129e131 ꢁC. H NMR (CDCl3): 0.92 (3H, t, J ¼ 7.1, CH3),
1.29e3.29 (6H, m, CH2CH2CH2), 2.66e3.55 (4H, m,
CH2CH2), 3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.47
(1H, bs, NH), 6.38 (1H, s, H-1), 6.59 (1H, s, H-5), 6.66 (1H,
s, H-8), 6.93e7.23 (4H, m, ArH). Anal. C22H27FN2O3 (C,
H, N).
3.1.1.17. N-tert-butyl-6,7-dimethoxy-1-phenyl-3,4-dihydroiso-
quinoline-2(1H )-carboxamide (19). Yield 90%. Mp. 166e
168 ꢁC. 1H NMR (CDCl3): 1.33 (9H, s, CH3), 2.66e3.63
(4H, m, CH2CH2), 3.79 (3H, s, CH3O-6), 3.87 (3H, s,
CH3O-7), 4.38 (1H, bs, NH), 6.23 (1H, s, H-1), 6.62 (1H, s,
H-5), 6.66 (1H, s, H-8), 7.21e7.31 (5H, m, ArH). Anal.
C22H28N2O3 (C, H, N).
3.1.1.24. N-Cyclopentyl-6,7-dimethoxy-1-(40-fluorophenyl)-3,
4-dihydroisoquinoline-2(1H )-carboxamide (26). Yield 85%.
Mp. 141e143 ꢁC. 1H NMR (CDCl3): 1.25e2.03 (8H, m,
cycloalkyl), 2.66e3.55 (4H, m, CH2CH2), 3.79 (3H, s,
CH3O-6), 3.88 (3H, s, CH3O-7), 3.93e4.18 (1H, m, CH),
4.42 (1H, bs, NH), 6.35 (1H, s, H-1), 6.59 (1H, s, H-5),
6.66 (1H, s, H-8), 6.93e7.23 (4H, m, ArH). Anal.
C23H27FN2O3 (C, H, N).
3.1.1.18. 1-(40-Bromophenyl)-N-tert-butyl-6,7-dimethoxy-3,4-
dihydroisoquinoline-2(1H )-carboxamide (20). Yield 85%.
Mp. 188e190 ꢁC. 1H NMR (CDCl3): 1.36 (9H, s, CH3),
2.62e3.52 (4H, m, CH2CH2), 3.80 (3H, s, CH3O-6), 3.88
(3H, s, CH3O-7), 4.36 (1H, bs, NH), 6.32 (1H, s, H-1), 6.60
(1H, s, H-5), 6.66 (1H, s, H-8), 7.10 (2H, d, J ¼ 8.2), 7.39
(2H, d, J ¼ 8.5). Anal. C22H27BrN2O3 (C, H, N).
3.1.1.25. N-Cyclohexyl-6,7-dimethoxy-1-phenyl-3,4-dihydroi-
soquinoline-2(1H )-carboxamide (27). Yield 80%. Mp. 182e
1
184 ꢁC. H NMR (CDCl3): 1.01e1.95 (10H, m, cycloalkyl),
2.67e3.74 (5H, m, CH2CH2 and CH), 3.78 (3H, s, CH3O-6),
3.88 (3H, s, CH3O-7), 4.35 (1H, bs, NH), 6.29 (1H, s, H-1),
6.62 (1H, s, H-5), 6.66 (1H, s, H-8), 7.23e7.31 (5H, m,
ArH). Anal. C24H30N2O3 (C, H, N).
3.1.1.19. N-tert-Butyl-1-(40-chlorophenyl)-6,7-dimethoxy-3,4-
dihydroisoquinoline-2(1H )-carboxamide (21). Yield 73%.
Mp. 178e180 ꢁC. 1H NMR (CDCl3): 1.36 (9H, s, CH3),
2.62e3.52 (4H, m, CH2CH2), 3.80 (3H, s, CH3O-6), 3.88
(3H, s, CH3O-7), 4.36 (1H, bs, NH), 6.33 (1H, s, H-1), 6.60
(1H, s, H-5), 6.66 (1H, s, H-8), 7.16 (2H, d, J ¼ 8.5), 7.24
(2H, d, J ¼ 8.5). Anal. C22H27ClN2O3 (C, H, N).
3.1.1.26. 1-(40-Bromophenyl)-N-cyclohexyl-6,7-dimethoxy-3,4-
dihydroisoquinoline-2(1H )-carboxamide (28). Yield 75%.
Mp. 181e183 ꢁC. 1H NMR (CDCl3): 1.04e1.95 (10H, m, cy-
cloalkyl), 2.63e3.74 (4H, m, CH2CH2), 3.06e3.14 (1H, m,
CH), 3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.34 (1H,
bs, NH), 6.36 (1H, s, H-1), 6.59 (1H, s, H-5), 6.67 (1H, s,
H-8), 7.12 (2H, d, J ¼ 8.2), 7.39 (2H, d, J ¼ 8.2). Anal.
C24H29BrN2O3 (C, H, N).
3.1.1.20. N-tert-Butyl-1-(40-fluorophenyl)-6,7-dimethoxy-3,4-
dihydroisoquinoline-2(1H )-carboxamide (22). Yield 78%.
Mp. 150e152 ꢁC. 1H NMR (CDCl3): 1.35 (9H, s, CH3),
2.63e3.55 (4H, m, CH2CH2), 3.79 (3H, s, CH3O-6), 3.88
(3H, s, CH3O-7), 4.37 (1H, bs, NH), 6.32 (1H, s, H-1), 6.60
(1H, s, H-5), 6.67 (1H, s, H-8), 6.93e7.22 (4H, m, ArH).
Anal. C22H27FN2O3 (C, H, N).
3.1.1.27. 1-(40-Chlorophenyl)-N-cyclohexyl-6,7-dimethoxy-3,4-
dihydroisoquinoline-2(1H )-carboxamide (29). Yield 74%.
Mp. 176e178 ꢁC. 1H NMR (CDCl3): 1.04e1.95 (10H, m, cy-
cloalkyl), 2.65e3.74 (4H, m, CH2CH2), 3.05e3.13 (1H, m,
CH), 3.79 (3H, s, CH3O-6), 3.88 (3H, s, CH3O-7), 4.34 (1H,
bs, NH), 6.37 (1H, s, H-1), 6.60 (1H, s, H-5), 6.67 (1H, s,
H-8), 7.17 (2H, d, J ¼ 8.2), 7.24 (2H, d, J ¼ 8.2). Anal.
C24H29ClN2O3 (C, H, N).
3.1.1.21. N-Cyclopentyl-6,7-dimethoxy-1-phenyl-3,4-dihydroi-
soquinoline-2(1H )-carboxamide (23). Yield 93%. Mp. 157e
1
158 ꢁC. H NMR (CDCl3): 1.25e1.98 (8H, m, cycloalkyl),
2.69e3.64 (4H, m, CH2CH2), 3.78 (3H, s, CH3O-6), 3.87
(3H, s, CH3O-7), 4.11e4.18 (1H, m, CH), 4.41 (1H, bs,
NH), 6.27 (1H, s, H-1), 6.61 (1H, s, H-5), 6.66 (1H, s, H-8),
7.23e7.31 (5H, m, ArH). Anal. C23H28N2O3 (C, H, N).
3.1.1.28. N-Cyclohexyl-6,7-dimethoxy-1-(40-fluorophenyl)-3,4-
dihydroisoquinoline-2(1H )-carboxamide (30). Yield 94%.
Mp. 175e177 ꢁC. 1H NMR (CDCl3): 1.03e1.94 (10H, m, cy-
cloalkyl), 2.66e3.68 (5H, m, CH2CH2 and CH), 3.78 (3H, s,

1354
R. Gitto et al. / European Journal of Medicinal Chemistry 44 (2009) 1349e1354
[3] M.A. Rogawski, Diverse mechanisms of antiepileptic drugs in the devel-
opment pipeline, Epilepsy Res. 69 (2006) 273e294.
CH3O-6), 3.87 (3H, s, CH3O-7), 4.32 (1H, bs, NH), 6.36 (1H,
s, H-1), 6.59 (1H, s, H-5), 6.66 (1H, s, H-8), 6.92e7.25 (4H,
m, ArH). Anal. C24H29FN2O3 (C, H, N).
[4] G. De Sarro, R. Gitto, E. Russo, G.F. Ibbadu, M.L. Barreca, L. De Luca,
A. Chimirri, AMPA receptor antagonists as potential anticonvulsant
drugs, Curr. Top. Med. Chem. 5 (2005) 31e42.
3.2. Pharmacology
[5] M.L. Barreca, R. Gitto, S. Quartarone, L. De Luca, G. De Sarro,
A. Chimirri, Pharmacophore modeling as an efficient tool in the discov-
ery of novel noncompetitive AMPA receptor antagonists, J. Chem. Inf.
Comput. Sci. 43 (2003) 651e655.
3.2.1. Testing of anticonvulsant activity against audiogenic
seizures in DBA/2 mice
[6] L. De Luca, R. Gitto, M.L. Barreca, R. Caruso, S. Quartarone, R. Citraro,
G. De Sarro, A. Chimirri, 3D pharmacophore models for 1,2,3,4-tetrahy-
droisoquinoline derivatives acting as anticonvulsant agents, Arch. Pharm.
(Weinheim) 339 (2006) 388e400.
All experiments were performed with DBA/2 mice which
are genetically susceptible to sound-induced seizures. DBA/2
mice (8e12 g; 22e25-days-old) were purchased from Harlan
Italy (Corezzano, Italy). Groups of 10 mice of either sex
were exposed to auditory stimulation 30 min following admin-
istration of vehicle or each dose of drugs studied. The com-
pounds were given intraperitoneally (i.p.) (0.1 mL/10 g of
body weight of the mouse) as a freshly-prepared solution in
50% dimethylsulfoxide (DMSO) and 50% sterile saline
(0.9% NaCl). The mice were individually placed under a hemi-
spheric perspex dome (diameter 58 cm), and 60 s were al-
lowed for habituation and assessment of locomotor activity.
Auditory stimulation (12e16 kHz, 109 dB) was applied for
60 s or until tonic extension occurred, and induced a sequential
seizure response in control DBA/2 mice, consisting of an early
wild running phase, followed by generalized myoclonus and
tonic flexion and extension sometimes followed by respiratory
arrest. The control mice and drug-treated ones were scored for
latency to and incidence of the different phases of the seizures.
The experimental protocol and all the procedures involving
animals and their care were conducted in conformity with
the institutional guidelines and the European Council Direc-
tive of laws and policies.
[7] R. Gitto, M.L. Barreca, L. De Luca, G. De Sarro, G. Ferreri,
S. Quartarone, E. Russo, A. Constanti, A. Chimirri, Discovery of a novel
and highly potent noncompetitive AMPA receptor antagonist, J. Med.
Chem. 46 (2003) 197e200.
[8] R. Gitto, M.L. Barreca, E. Francica, R. Caruso, L. De Luca, E. Russo,
G. De Sarro, A. Chimirri, Synthesis and anticonvulsant properties of
1,2,3,4-tetrahydroisoquinolin-1-ones, Arkivoc (2004) 170e180.
[9] R. Gitto, R. Caruso, V. Orlando, S. Quartarone, M.L. Barreca, G. Ferreri,
E. Russo, G. De Sarro, A. Chimirri, Synthesis and anticonvulsant prop-
erties of tetrahydroisoquinoline derivatives, Farmaco 59 (2004) 7e12.
[10] R. Gitto, R. Caruso, B. Pagano, L. De Luca, R. Citraro, E. Russo, G. De
Sarro, A. Chimirri, Novel potent anticonvulsant agent containing a tetra-
hydroisoquinoline skeleton, J. Med. Chem. 49 (2006) 5618e5622.
[11] E. Arstad, R. Gitto, A. Chimirri, R. Caruso, A. Constanti, D. Turton,
S.P. Hume, R. Ahmad, L.S. Pilowsky, S.K. Luthra, Closing in on the
AMPA receptor: Synthesis and evaluation of 2-acetyl-1-(40-chloro-
phenyl)-6-methoxy-7-[(11)C]methoxy-1,2,3,4-tetrahydro isoquinoline as
a potential PET tracer, Bioorg. Med. Chem. 14 (2006) 4712e4717.
[12] G. Ferreri, A. Chimirri, E. Russo, R. Gitto, P. Gareri, A. De Sarro, G. De
Sarro, Comparative anticonvulsant activity of N-acetyl-1-aryl-6,7-dime-
thoxy-1,2,3,4-tetrahydroisoquinoline derivatives in rodents, Pharmacol.
Biochem. Behav. 77 (2004) 85e94.
[13] G. DeSarro, A. Chimirri, A. DeSarro, R. Gitto, S. Grasso, P. Giusti,
A.G. Chapman, GYKI 52466 and related 2,3-benzodiazepines as
anticonvulsant agents in DBA/2 mice, Eur. J. Pharmacol. 294 (1995)
411e422.
3.2.2. Statistical analysis
[14] S.D. Donevan, M.A. Rogawski, GYKI 52466, a 2,3-benzodiazepine, is
a highly selective, noncompetitive antagonist of AMPA/kainate receptor
responses, Neuron 10 (1993) 51e59.
[15] R. Gitto, M.L. Barreca, L. De Luca, A. Chimirri, New trends in the de-
velopment of AMPA receptor antagonists, Expert Opin. Ther. Pat. 14
(2004) 1199e1213.
[16] A.G. Chapman, M.J. Croucher, B.S. Meldrum, Evaluation of anticonvul-
sant drugs in DBA/2 mice with sound-induced seizures, Arzneimittelfor-
schung 34 (1984) 1261e1264.
Statistical comparisons between groups of control and
drug-treated animals were made using Fisher’s exact probabil-
ity test (incidence of the seizure phases). The ED50 values of
each phase of audiogenic seizures were determined for each
dose of compound administered, and dose-response curves
were fitted using a computer program by Litchfield and Wil-
coxon’s method [21].
[17] K.K. Borowicz, A.M. Duda, Z. Kleinrok, S.J. Czuczwar, Interaction of
GYKI 52466, a selective non-competitive antagonist of AMPA/kainate
receptors, with conventional antiepileptic drugs in amygdala-kindled sei-
zures in rats, Pol. J. Pharmacol. 53 (2001) 101e108.
Acknowledgment
Financial support for this research by Fondo di Ateneo per
`
[18] R. Jakus, M. Graf, R.D. Ando, B. Balogh, I. Gacsalyi, G. Levay,
S. Kantor, G. Bagdy, Effect of two noncompetitive AMPA receptor an-
tagonists GYKI 52466 and GYKI 53405 on vigilance, behavior and
spike-wave discharges in a genetic rat model of absence epilepsy, Brain
Res. 1008 (2004) 236e244.
la Ricerca (PRA 2004 e Universita di Messina) and Fondo per
gli Investimenti della Ricerca di Base (FIRB 2003) is grate-
fully acknowledged.
[19] E. Donato Di Paola, P. Gareri, A. Davoli, S. Gratteri, F. Scicchitano,
C. Naccari, G. De Sarro, Influence of levetiracetam on the anticonvulsant
efficacy of conventional antiepileptic drugs against audiogenic seizures
in DBA/2 mice, Epilepsy Res. 75 (2007) 112e121.
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