Solution-phase parallel synthesis of novel 1,2,3,4-tetrahydroisoquinolin-1- ones as anticonvulsant agents

Article abstract of DOI:10.1248/cpb.56.181

Following our previous studies in the field of anticonvulsant agents, we planned a one-pot solution-phase parallel synthesis (SPPS) of a small library of new 1,2,3,4-tetrahydroisoquinoline derivatives. The activity against audiogenic seizures in DBA/2 mice of the newly synthesized compounds has also been evaluated.

Full text of DOI:10.1248/cpb.56.181

February 2008
Notes
Chem. Pharm. Bull. 56(2) 181—184 (2008)
181
Solution-Phase Parallel Synthesis of Novel 1,2,3,4-Tetrahydroisoquinolin-
1-ones as Anticonvulsant Agents
Rosaria GITTO, ,a Eleonora FRANCICA,a Giovambattista De SARRO,b Francesca SCICCHITANO,b and
*
a
Alba CHIMIRRI
a Department of Medicinal Chemistry, Faculty of Pharmacy, Università di Messina; Viale Annunziata I-98168 Messina:
and b, Department of Experimental and Clinical Medicine, Faculty of Medicine and Surgery, University of Catanzaro; Via
T. Campanella, 115 I-88100 Catanzaro, Italy.
Received March 6, 2007; accepted November 29, 2007; published online November 30, 2007
Following our previous studies in the field of anticonvulsant agents, we planned a one-pot solution-phase
parallel synthesis (SPPS) of a small library of new 1,2,3,4-tetrahydroisoquinoline derivatives. The activity against
audiogenic seizures in DBA/2 mice of the newly synthesized compounds has also been evaluated.
Key words solution-phase parallel synthesis; isoquinolinone; anticonvulsant agent
The 2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)-propi- acids is extensively described. It is well known that the cy-
onate receptor (AMPAR) mediates fast glutamatergic synap- cloaddition of homophthalic anhydride with aldimines pro-
tic transmission in the mammalian central nervous system. vides a useful access to the preparation of this class of com-
Overactivation of AMPAR plays a pivotal role in epileptoge- pounds. This reaction produces a mixture of cis- and trans-
nesis and glutamate-induced neuronal death.1,2) On this basis, isomers and it has been observed that the reaction conditions
particular attention has been devoted to selective AMPAR (solvent polarity, temperature, etc.) and the nature of reagents
antagonists (e.g., GYKI 52466, 1, Fig. 1), as potential employed influence their stereochemistry.10—15)
neuroprotective agents against neurological pathologies such
as epilepsy, ischemia, Parkinson’s disease, and multiple scle- phase parallel synthesis (SPPS) of PD00735 and its ana-
rosis.1)
logues with the aim to obtain a small library of isoquinoli-
We report here a simple methodology for the solution-
Our previous studies reported chemical and pharmacologi- nonic acids for the evaluation in audiogenic seizure test and
cal data of some 2,3-benzodiazepine derivatives (e.g., 2, draw structure–activity relationship (SAR) considerations for
CFM-2, Fig. 1), that proved to be specific noncompetitive this class of compounds.
AMPAR antagonists and potent anticonvulsant agents.3—5)
Our challenge was also to decipher the main structural re- Results and Discussion
quirements for noncompetitive AMPAR antagonists and for
Using PD00735 (4) as a scaffold we performed some mod-
this reason we developed a suitable 3D ligand-based pharma- ifications with the aim to study their influence on anticonvul-
cophore model.6) This study allowed the identification of the sant activity. In particular, we inserted different substituents
2-acetyl-1-(4ꢀ-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahy- on the phenyl ring at C-3 to obtain SAR information. Fur-
droisoquinoline (3, Fig. 1) as a new very potent anticonvul- thermore, methyl ester and carboxamide derivatives of parent
sant agent acting as noncompetitive AMPAR antagonist.7,8)
compound PD00735 (4) have been prepared to clarify the
The model obtained was also used as a search query for importance of carboxylic function on pharmacological prop-
virtual screening on three dimensional databases and some erties.
molecules were selected and tested. Among the discovered
A simple solution-phase parallel methodology was set up
compounds, the trans isomer of 2-(4-chlorobenzyl)-3-(4- for the synthesis of 1-oxo-1,2,3,4-tetrahydroisoquinoline-4-
methoxyphenyl)-1-oxo-1,2,3,4-tetrahydroisoquinoline-4-car- carboxylic acids (Chart 1). The one-pot procedure was car-
boxylic acid (4, PD00735, Fig. 1) showed the most interest- ried out stirring the amine and the aldehyde at room tempera-
ing anticonvulsant efficacy6) encouraging us to explore some ture to give the corresponding imine intermediate that in the
structural modifications of PD00735.9)
same reactor was treated with homophthalic anhydride with-
Isoquinolinonic acids have previously been found to pos- out the isolation procedure. This protocol was particularly
sess a vast range of pharmacological properties including appropriate to perform a solution phase parallel synthetic ap-
psychotropic, antiallergic, antiinflammatory and estrogenic proach using a Buchi Syncore reactor. Starting from different
behaviour and for this reason the chemistry of isoquinolonic amines 5, aldehydes 6 and homophthalic anhydride, we ob-
Fig. 1. Noncompetitive AMPAR Antagonists
∗ To whom correspondence should be addressed. e-mail: rgitto@pharma.unime.it
© 2008 Pharmaceutical Society of Japan

182
Vol. 56, No. 2
Table 1. Anticonvulsant Activity of 1,2,3,4-Tetrahydroisoquinoline Deriv-
atives against Audiogenic Seizures in DBA/2 Mice
ED50 mmol/kga)
R1
R2
Clonus
Tonus
4b)
7a
7b
8
4-OMeC6H4
C6H5
OH
OH
19.7 (14.6—20.0) 16.3 (12.6—21.1)
ꢁ100
ꢁ100
21.8 (12.8—37.2)
C6H5
OH
ꢁ100
3-FC6H4
OH
76.2 (60.6—95.8) 31.7 (21.6—46.4)
50.4 (28.2—90.3) 18.2 (11.9—27.8)
9
4-FC6H4
OH
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4-ClC6H4
OH
ꢁ100
ꢁ100
ꢁ100
ꢁ100
ꢁ100
ꢁ100
4-BrC6H4
OH
ꢁ100
3-NO2C6H4
4-NO2C6H4
4-MeC6H4
4-CF3C6H4
3,4-F2C6H3
3,4-(OMe)2C6H3
3-NH2C6H4
4-NH2C6H4
4-OMeC6H4
4-OMeC6H4
4-OMeC6H4
4-OMeC6H4
4-OMeC6H4
4-OMeC6H4
OH
59.9 (38.7—92.7)
56.5 (38.0—84.0)
25.0 (14.1—44.6)
OH
Chart 1
OH
OH
43.3 (30.1—62.3) 15.0 (9.53—23.5)
ꢁ100 48.1 (29.4—78.8)
74.7 (60.4—92.4) 36.1 (24.5—53.4)
ꢁ100 ꢁ100
OH
OH
OH
OH
78.1 (55.1—110) 34.3 (21.4—54.8)
86.1 (67.3—110) 36.5 (24.5—54.2)
OCH3
NH2
ꢁ100
58.4 (39.6—86.2)
NHnC3H7
N(C2H4)2O
N(C2H4)2CH2
N(C2H4)2NCH3
95.9 (69.3—132) 49.6 (32.8—75.0)
ꢁ100
ꢁ100
ꢁ100
44.6 (32.4—61.5)
56.2 (42.2—75.0)
51.6 (36.2—73.7)
1, GYKI 52466
35.8 (24.4—52.4) 25.3 (16.0—40.0)
a) All data were calculated according to the method of Litchfield and Wilcoxon. At
least 32 animals were used to calculate each ED50, ꢂ95% confidence limits are given in
parentheses. b) Ref. 9.
Chart 2
tablished on the basis of the value of the vicinal coupling
constants between the H-3 and H-4 protons. In the cis config-
tained in good yields a large series of new 1,2,3,4-tetrahy- uration the J3,4 values were of ca. 6 Hz, while in the trans iso-
droisoquinolinone derivatives 7—17 according to previous mers the H3 and H4 hydrogens appear as two singlets for
procedure reported for this class of compounds16) with minor compounds 7—22 and 24, and ca. 3.5 Hz for carboxamides
modifications.
23 and 25.
The reaction between the benzylamine derivatives 5, alde-
In attempt to explore some structure–activity relationships
hydes 6 and homophthalic anhydride generally furnished the (SAR) for this class of compounds, the anticonvulsant effects
cycloadducts 7—17 as trans-disteroeisomers except for de- of new synthesized 1,2,3,4-tetrahydroisoquinolines were
rivative 7 which gave mixture of cis/trans-diastereoisomers evaluated after intraperitoneal (i.p.) administration against
7a, b resolved by fractional crystallization from ethyl acetate. audiogenic seizures in DBA/2 mice, which are considered an
In previous papers the cycloaddition of homophthalic an- excellent animal model for generalized epilepsy and for
hydrides with aldimine has been reported for the synthesis of screening new anticonvulsant drugs.3)
tetrahydroisoquinolinonic acids by using different reaction
In Table 1 we report the ED50 values of new synthesized
conditions and catalysts in attempt to obtain an isomer selec- compounds in comparison with the PD00735 (4). The results
tivity, but a definitive definition of the factors that control the pointed out that the replacement of 4ꢀ-methoxy group with
stereochemical outcomes of the reaction was not reached.
Aminophenyl analogues 18, 19 were obtained by reduction hydroisoquinoline scaffold was detrimental for the activity.
of the corresponding nitro derivatives 12, 13. Compounds 9 and 15 showed anticonvulsant effects compa-
other substituents on the 4-aromatic frame of 1,2,3,4-tetra-
By treatment of compound 4 with methyl iodide or suit- rable to those of GYKI 52466 (1), but their anticonvulsant
able amines, methyl ester 20 and carboxamides 21—25 were activity was lower than that of parent compound 4. When we
obtained respectively (Chart 2) as trans-diastereoisomers. In evaluated the activity of cis/trans 7 diastereoisomers we con-
particular, carboxamides 21—25 were easily prepared em- firmed that the trans-isomer 7a was more potent than cis-iso-
ploying S-(1-oxido-2-pyridinyl)-1,1,3,3-tetramethylthiouro- mer 7b in line with our virtual screening that selected only
nium tetrafluoroborate (TOTT) and N,Nꢀ-carbonyldiimida- PD00735 as lead compound and not its cis-isomer.9)
zole, as coupling agents, for amide 21 and N-substituted
amides 22—25 respectively.
As shown in Table 1 also the corresponding ester 20 and
amides 21—25, independently from the nature and bulk of
The configuration of the compounds synthesized was es- the substituent, lost activity thus suggesting that the car-

February 2008
183
CH2), 4.23 (1H, s, H-3), 5.53 (1H, s, H-4), 7.19—7.48 (9H, m, ArH), 7.84
(1H, s, ArH, H-2ꢄ), 7.98—8.04 (2H, m, ArH), 12.50 (1H, bs, COOH). 13C-
NMR (DMSO-d6) d: 49.22 (CH2), 50.38 and 60.88 (C-3 and C-4), 121.34,
122.64, 127.25, 128.14, 128.36, 128.75, 129.83, 130.27, 130.52, 131.96,
132.90, 133.31, 136.34, 141.80, 147.89, 163.00 (CO), 169.03 (COOH).
boxylic moiety is essential for anticonvulsant efficacy of the
parent compound 4.
In conclusion, by employing solution-phase parallel syn-
thesis we realized a small library of PD00735 (4) analogues
as potential anticonvulsant agents. Even if the above reported Anal. Calcd for C23H17ClN2O5 (436.86): C, 63.24; H, 3.92; N, 6.41. Found:
C, 63.28; H, 3.92; N, 6.42.
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-nitrophenyl)-1-oxo-1,2,3,4-tetrahydro-
structural modifications afforded derivatives less active than
lead compound 4, derivatives 9 and 15 showed anticonvul-
sant effects comparable to those of GYKI 52466 (1), the pro-
totype of non-competitive AMPA-antagonists.
isoquinoline-4-carboxylic Acid (13): 57% yield as yellow crystals, mp
234—236 °C. 1H-NMR (DMSO-d6) d: 4.06 and 5.15 (2H, 2d, Jꢃ15.11,
CH2), 4.20 (1H, s, H-3), 5.49 (1H, s, H-4), 7.18—7.34 (7H, m, ArH), 7.41—
7.44 (m, 2H, ArH), 7.96—7.99 (1H, m, H-8), 8.08 (2H, d, Jꢃ8.51, ArH),
12.50 (1H, bs, COOH). Anal. Calcd for C23H17ClN2O5 (436.86): C, 63.24;
Experimental
Melting points were determined on a STUART SPM10 hot stage appara- H, 3.92; N, 6.41. Found: C, 63.45; H, 3.91; N, 6.42.
tus and are uncorrected. Elemental analyses (C, H, N) were carried out on a
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-methylphenyl)-1-oxo-1,2,3,4-tetrahydro-
Carlo Erba Model 1106 Elemental Analyzer and the results are within isoquinoline-4-carboxylic Acid (14): 50% yield as white crystals, mp 253—
1
ꢂ0.4% of the theoretical values. Merck silica gel 60 F254 plates were used 255 °C. H-NMR (DMSO-d6) d: 2.79 (3H, s, CH3), 4.12 and 5.54 (2H, 2d,
1
for analytical TLC. H- and 13C-NMR spectra were measured with a Varian Jꢃ15.11, CH2), 4.36 (1H, s, H-3), 5.51 (1H, s, H-4), 7.22 (2H, d, Jꢃ8.24,
Gemini 300 spectrometer; chemical shifts are expressed in d (ppm) relative ArH), 7.35 (2H, d, Jꢃ7.97, ArH), 7.47—7.50 (1H, m, ArH), 7.61—7.70
to tetramethyl saline (TMS) as internal standard and coupling constants (J) (4H, m, ArH), 7.71—7.73 (2H, m, ArH), 8.25—8.28 (1H, m, H-8), 12.00
in Hz. All exchangeable protons were confirmed by addition of D2O.
(1H, bs, COOH). Anal. Calcd for C24H20ClNO3 (405.88): C, 71.02; H, 4.97;
General One-Pot Procedure for the Synthesis of 1,2,3,4-Tetrahydro- N, 3.45. Found: C, 71.18; H, 4.98; N, 3.46.
isoquinolinone-4-carboxylic Acid Derivatives (7—17) The mixtures of
trans N-(4ꢀ-Chlorobenzyl)-1-oxo-3-(4ꢄ-trifluoromethyphenyl)-1,2,3,4-
the suitable amine (6 mmol) and aldehyde (6 mmol) in 15 ml dichloro- tetrahydroisoquinoline-4-carboxylic Acid (15): 41% yield as white crystals,
1
methane were prepared into each reaction vessel then shaked overnight at mp 240—242 °C. H-NMR (DMSO-d6) d: 4.01 and 5.16 (2H, 2d, Jꢃ14.72,
200 rpm at room temperature in the presence of 1 ml trimethyl orthoformate
(9.6 mmol). Then, the homophthalic anhydride (6 mmol) was added to each
vessel and the reaction mixture was stirred at 200 rpm at room temperature
CH2), 4.17 (1H, s, H-3), 5.41 (1H, s, H-4), 7.21—7.30 (7H, m, ArH), 7.41—
7.43 (2H, m, ArH), 7.60 (2H, d, Jꢃ8.24, ArH), 7.96—7.99 (1H, m, H-8),
13.00 (1H, bs, COOH). 13C-NMR (DMSO-d6) d: 48.83 (CH2), 50.32 and
for 16 h; the desired products were collected by filtration and crystallized 60.88 (C-3 and C-4), 124.32, 125.36, 126.96, 127.06, 127.93, 128.04,
from ethyl acetate to give 7—17. The cis/trans mixture of 7a, b was solved 128.62, 129.60, 130.18, 131.75, 132.19, 133.28, 136.04, 136.21, 154.54,
by fractional crystallization from ethyl acetate.
162.98 (CO), 171.65 (COOH). Anal. Calcd for C24H17ClF3NO3 (459.84): C,
trans N-(4ꢀ-Chlorobenzyl)-1-oxo-3-phenyl-1,2,3,4-tetrahydroisoquino- 62.69; H, 3.73; N, 3.05. Found C, 62.73; H, 3.73; N, 3.05.
line-4-carboxylic Acid (7a): 57% yield as white crystals, mp 260—262 °C.
trans N-(4ꢀ-Chlorobenzyl)-1-oxo-3-(3ꢄ,4ꢄ-difluorophenyl)-1,2,3,4-
1H-NMR (DMSO-d6) d: 3.88 and 5.22 (2H, 2d, Jꢃ14.83, CH2), 4.10 (1H, s, tetrahydroisoquinoline-4-carboxylic Acid (16): 39% yield as white crystals,
1
H-3), 5.27 (1H, s, H-4), 7.03 (2H, m, ArH), 7.18—7.23 (8H, m, ArH),
7.39—7.43 (2H, m, ArH), 7.95—7.99 (1H, m, H-8), 11.50 (1H, bs, COOH).
mp 250—252 °C. H-NMR (DMSO-d6) d: 4.06 and 5.10 (2H, 2d, Jꢃ15.11,
CH2), 4.14 (1H, s, H-3), 5.33 (1H, s, H-4), 7.09 (1H, s, ArH), 7.13—7.47
Anal. Calcd for C23H18ClNO3 (391.86): C, 70.50; H, 4.63; N, 3.75. Found: (9H, m, ArH), 7.96 (1H, d, Jꢃ8.79, H-8,), 13.00 (1H, bs, COOH). Anal.
C, 70.58; H, 4.64; N, 3.75.
cis N-(4ꢀ-Chlorobenzyl)-1-oxo-3-phenyl-1,2,3,4-tetrahydroisoquinoline-
4-carboxylic Acid (7b): 38% yield as white crystals, mp 168—170 °C. H-
Calcd for C23H16ClF2NO3 (427.08): C, 64.57; H, 3.77; N, 3.24. Found: C,
64.70; H, 3.78; N, 3.24.
trans N-(4ꢀ-Chlorobenzyl)-3-(3ꢄ,4ꢄ-dimethoxyphenyl)-1-oxo-1,2,3,4-
1
NMR (DMSO-d6) d: 3.86 and 5.19 (2H, 2d, Jꢃ15.08, CH2), 4.72 (1H, d, tetrahydroisoquinoline-4-carboxylic Acid (17): 29% yield as white crystals,
1
Jꢃ6.32, H-3,), 4.99 (1H, d, Jꢃ6.04, H-4), 6.95—7.55 (m, 12H, ArH), 8.07 mp 252—253 °C. H-NMR (DMSO-d6) d: 3.61 (3H, s, OCH3), 3.64 (3H, s,
(1H, d, Jꢃ7.69, H-8,), 12.00 (1H, bs, COOH). Anal. Calcd for C23H18ClNO3 OCH3), 3.89 and 5.21 (2H, 2d, Jꢃ15.11, CH2), 4.11 (1H, s, H-3), 5.17 (1H,
(391.85): C, 70.50; H, 4.63; N, 3.57. Found: C, 70.53; H, 4.64; N, 3.58
trans N-(4ꢀ-Chlorobenzyl)-3-(3ꢄ-fluorophenyl)-1-oxo-1,2,3,4-tetrahydro- ArH, H-5ꢄ), 7.19—7.22 (m, 1H), 7.32 (bs, 4H, ArH), 7.38—7.47 (m, 2H),
isoquinoline-4-carboxylic Acid (8): 51% yield as white crystals, mp 277—
7.97 (1H, bs, H-8), 12.50 (bs, 1H, COOH). Anal. Calcd for C25H22ClNO5
278 °C. 1H-NMR (DMSO-d6) d: 3.99 and 5.16 (2H, 2d, Jꢃ14.83, CH2), 4.16 (451.12): C, 66.45; H, 4.91; N, 3.10. Found: C, 66.50; H, 4.92; N, 3.10.
s, H-4), 6.41 (1H, d, Jꢃ8.24, ArH), 6.76 (1H, d, Jꢃ8.51, ArH), 6.69 (1H, s,
(1H, s, H-3), 5.34 (1H, s, H-4), 6.83—7.47 (m, 11H, ArH), 7.97 (s, 1H, H-
8), 12.50 (1H, bs, COOH). Anal. Calcd for C23H17ClFNO3 (409.09): C,
67.40; H, 4.18; N, 3.42. Found: C, 67.50; H, 4.19; N, 3.42.
Synthesis of trans-3-Aminophenyl- and 4-Aminophenyl-N-(4ꢀ-chloro-
benzyl)-1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylic Acids (18, 19)
The solution of suitable trans 1,2,3,4-tetrahydroisoquinoline-4-carboxylic
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-fluorophenyl)-1-oxo-1,2,3,4-tetrahydro- acid (12 or 13) (0.5 mmol) in MeOH (30 ml) was stirred in a flask under a
isoquinoline-4-carboxylic Acid (9): 25% yield as white crystals, mp 280—
light stream of H2 in presence of Pd/C 5% as catalyst for 1 h; then the mix-
282 °C. 1H-NMR (DMSO-d6) d: 3.93 and 5.15 (2H, 2d, Jꢃ15.11, CH2), 4.08 ture was filtered off and the filtrate evaporated in vacuo to give an oil residue
(1H, s, H-3), 5.29 (1H, s, H-4), 7.04—7.07 (2H, m, ArH), 7.21—7.42 (9H, that was treated with AcOEt to afford desired products 18 or 19.
m, ArH), 7.97 (s, 1H, H-8), 12.00 (1H, bs, COOH). Anal. Calcd for
C23H17ClFNO3 (409.85): C, 67.40; H, 4.18; N, 3.42. Found: C, 67.45; H, isoquinoline-4-carboxylic Acid (18): 20% yield as pale crystals, mp 191—
4.19; N, 3.41.
193 °C. 1H-NMR (DMSO-d6) d: 3.50 (2H, bs, NH2), 3.83 and 5.27 (2H, 2d,
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-chlorophenyl)-1-oxo-1,2,3,4-tetrahydro- Jꢃ14.68, CH2), 4.08 (1H, s, H-3), 5.21 (1H, s, H-4), 6.73—6.87 (3H, m,
trans 3-(3ꢄ-Aminophenyl)-N-(4ꢀ-chlorobenzyl)-1-oxo-1,2,3,4-tetrahydro-
isoquinoline-4-carboxylic Acid (10): 47% yield as white crystals, mp 258—
ArH), 7.15—7.43 (8H, m, ArH), 7.98—7.99 (1H, m, H-8), 12.30 (1H, bs,
260 °C. 1H-NMR (DMSO-d6) d: 3.94 and 5.16 (2H, 2d, Jꢃ15.11, CH2), 4.10 COOH). Anal. Calcd for C23H19ClN2O3 (406.86): C, 67.90; H, 4.71; N, 6.89.
(1H, s, H-3), 5.29 (1H, s, H-4), 7.03—7.05 (2H, m, ArH), 7.21—7.42 (9H, Found: C, 67.85; H, 4.71; N, 6.90.
m, ArH), 7.97 (s, 1H, H-8), 12.00 (bs, 1H, COOH). Anal. Calcd for
C23H17Cl2NO3 (426.30): C, 64.08; H, 4.02; N, 3.39. Found: C, 63.98; H, isoquinoline-4-carboxylic Acid (19): 69% yield as pale crystals, mp 224—
4.00; N, 3.38.
226 °C. 1H-NMR (DMSO-d6) d: 4.00 (2H, bs, NH2), 4.36 and 5.73 (2H, 2d,
trans 3-(4ꢄ-Bromophenyl)-N-(4ꢀ-chlorobenzyl)-1-oxo-1,2,3,4-tetrahydro- Jꢃ14.83, CH2), 4.55 (1H, s, H-3), 5.68 (s, 1H, H-4), 7.30—7.43 (4H, m,
trans 3-(4ꢄ-Aminophenyl)-N-(4ꢀ-chlorobenzyl)-1-oxo-1,2,3,4-tetrahydro-
isoquinoline-4-carboxylic Acid (11): 56% yield as white crystals, mp 260—
ArH), 7.69—7.96 (8H, m, ArH), 12.32 (1H, bs, COOH). Anal. Calcd for
262 °C. 1H-NMR (DMSO-d6) d: 3.93 and 5.17 (2H, 2d, Jꢃ15.10, CH2), 4.10 C23H19ClN2O3 (406.86): C, 67.90; H, 4.71; N, 6.89. Found: C, 67.81; H,
(1H, s, H-3), 5.27 (1H, s, H-4), 6.96—6.99 (2H, m, ArH), 7.19—7.21 (m, 4.71; N, 6.88.
1H, ArH), 7.30—7.31 (4H, m, ArH), 7.41—7.44 (4H, m, ArH), 7.95—7.97
(1H, m, H-8), 12.00 (1H, bs, COOH). Anal. Calcd for C23H17BrClNO3
(470.75): C, 58.68; H, 3.64; N, 2.98. Found: C, 58.82; H, 3.65; N, 2.98.
Synthesis of trans Methyl N-(4ꢀ-Chlorobenzyl)-3-(4ꢁ-methoxyphenyl)-
1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylate (20) A mixture of
the appropriate 1-oxo-1,2,3,4-tetrahydroisoquinoline-4-carboxylic acid (1.6
trans N-(4ꢀ-Chlorobenzyl)-3-(3ꢄ-nitrophenyl)-1-oxo-1,2,3,4-tetrahydro- mmol), methyl iodide (3.2 mmol, 0.2 ml), K2CO3 (0.22 g) and dry acetone
isoquinoline-4-carboxylic Acid (12): 40% yield as yellow crystals, mp (20 ml) was refluxed for 4 h and filtered. The filtrate was cooled to room
254—256 °C. 1H-NMR (DMSO-d6) d: 4.19 and 5.04 (2H, 2d, Jꢃ15.11, temperature and evaporated under reduced pressure; the residual oil was

184
Vol. 56, No. 2
crystallized by treatment with Et2O to afford methyl carboxylate derivative.
58% yield as white crystals; mp 168—169 °C. 1H-NMR (CDCl3) d: 3.43
(3H, s, OCH3), 3.64 and 5.59 (2H, 2d, Jꢃ14.83, CH2), 3.74 (3H, s, OCH3),
3.85 (1H, s, H-3), 5.04 (1H, s, H-4), 6.75 (2H, d, Jꢃ8.8, ArH), 6.95 (2H, d,
Jꢃ8.8, ArH), 7.00—7.06 (1H, m, ArH), 7.21—7.30 (4H, m, ArH), 7.42—
7.46 (2H, m, ArH), 8.23 (1H, d, Jꢃ6.87, H-8). 13C-NMR (CDCl3): d 48.26
(CH2), 52.40 (COOCH3), 51.80 and 60.16 (C-3 and C-4), 55.00 (CH3O),
114.21, 124.00, 127.44, 128.16, 128.49, 129.00, 130.18, 130.45, 130.20,
132.10, 132.21, 134.40, 135.91, 159.00, 164.10 (CO), 170.10 (COOH).
Anal. Calcd for C25H22ClNO4 (435.91): C, 68.89; H, 5.09; N, 3.21. Found:
C, 69.00; H, 5.10; N, 3.21.
4.21 (1H, d, Jꢃ3.57, H-3), 4.57 (1H, d, Jꢃ3.57, H-4), 6.71—6.96 (4H, m,
ArH), 7.12—7.32 (5H, m, ArH), 7.40—7.48 (2H, m, ArH), 8.27—8.30 (1H,
m, H-8). Anal. Calcd for C29H30ClN3O3 (504.02): C, 69.11; H, 5.03; N, 8.34.
Found: C, 69.17; H, 5.04; N, 8.36.
Testing of Anticonvulsant Activity against Audiogenic Seizures in
DBA/2 Mice All experiments were performed with DBA/2 mice which are
genetically susceptible to sound-induced seizures. DBA/2 mice (8—12 g;
22—25-d-old) were purchased from Harlan Italy (Corezzano, Italy). Groups
of 10 mice of either sex were exposed to auditory stimulation 30 min follow-
ing administration of vehicle or each dose of drugs studied.17) 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). Individual mice were placed under a
hemispheric erspex dome (diameter 58 cm), and 60 s were allowed for habit-
uation and assessment of locomotor activity. Auditory stimulation (12—
16 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
and drug-treated mice were scored for latency to and incidence of the differ-
ent phases of the seizures. The experimental protocol and all the procedures
involving animals and their care were conducted in conformity with the in-
stitutional guidelines and the European Council Directive of laws and poli-
cies.
Synthesis of trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢁ-methoxyphenyl)-1-oxo-
1,2,3,4-tetrahydro-isoquinoline-4-carboxylamide (21) To a solution of
trans N-(4ꢀ-chlorobenzyl)-3-(4ꢄ-methoxyphenyl)-1-oxo-1,2,3,4-tetrahydro-
isoquinoline-4-carboxylic acid (4, 422 mg, 1 mmol) in N,N-dimethylform-
amide (DMF) (3 ml), diisopropylethylamine (DIEA) (0.17 ml), NH4Cl
(1 mmol) and TOTT (235 mg, 0.75 mmol) were added. The reaction mixture
was stirred for 30 min at room temperature; then brine was added and the
mixture was extracted with EtOAc. The organic layer was washed with HCl
(2 N), water, saturated aqueous NaHCO3 and water again; then dried, filtered
off and evaporated under reduced pressure to afford pure amide derivative
1
21 20% yield as as white crystals; mp 240—242 °C. H-NMR (CDCl3) d:
3.73 (3H, s, OCH3), 3.83 and 5.43 (2H, 2d, Jꢃ14.56, CH2), 5.41 (1H, s, H-
4), 5.57 (1H, s, H-3), 5.46 (2H, bs, NH2), 6.75 (2H, d, Jꢃ8.52, ArH, H-3ꢄ,
H-5ꢄ), 6.97 (2H, d, Jꢃ8.52, ArH, H-2ꢄ, H-6ꢄ), 7.13—7.19 (1H, m, H-5),
7.24—7.29 (4H, m, ArH), 7.51—7.54 (2H, m, H-6, H-7), 8.30—8.33 (1H,
m, H-8). Anal. Calcd for C24H21ClN2O3 (420.89): C, 68.49; H, 5.03; N, 6.66.
Found: C, 68.54; H, 5.05; N, 6.68.
Statistical Analysis Statistical comparisons between groups of control
and drug-treated animals were made using Fisher’s exact probability test (in-
cidence of the seizure phases). The ED50 values of each phase of audiogenic
seizures was determined for each dose of compound administered, and
dose–response curves were fitted using a computer program by Litchfield
and Wilcoxon’s method.18)
General Procedure for the Synthesis of 1,2,3,4-Tetrahydro-1-oxoiso-
quinoline-4-carboxamides (22—25) To
a solution of compound 4
(1.25 mmol) in anhydrous DMF (10 ml) N,Nꢀ-carbonyldiimidazole (CDI,
1.25 mmol) was added and under magnetic stirring in nitrogen atmosphere;
then a solution of the appropriate amine (1.25 mmol) in anhydrous DMF
(5 ml) was added dropwise and the reaction mixture was stirred at room tem-
perature for 3 h. The resulting mixture was evaporated to dryness leaving
oily residue; the residue was treated with saturated sodium hydrogen carbon-
ate aqueous solution and then with water. The organic layer was concen-
trated to dryness and the crude product was purified by column-chromatog-
raphy (CHCl3/MeOH 98 : 2 as eluant) to yield amides 22—25.
Acknowledgments Financial support for this research by Fondo Ateneo
di Ricerca (University of Messina, Italy) and FIRB2003 is gratefully ac-
knowledged.
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39, 229—236 (2002).
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-methoxyphenyl)-1-oxo-1,2,3,4-tetrahy-
droisoquinoline-4-propyl-carboxamide (22): 25% yield as white crystals; mp
1
173—174 °C. H-NMR (CDCl3) d: 0.70 (3H, Jꢃ7.40, t, CH3), 1.19—1.26
(2H, m, CH2), 2.93—3.02 (2H, m, CH2 ), 3.73 (3H, s, OCH3), 3.77 and 5.37
(2H, 2d, Jꢃ14.56, CH2), 3.75 (1H, s, H-3) , 5.35 (1H, s, H-4), 5.02 (1H, bs,
NH), 6.73 (2H, d, Jꢃ8.78, ArH), 6.97 (2H, d, Jꢃ8.51, ArH), 7.07—7.09
(1H, m, ArH), 7.24—7.26 (4H, m, ArH), 7.49—7.51 (2H, m, ArH), 8.27—
8.29 (1H, m, H-8). 13C-NMR (CDCl3) d: 17.2 (NHCH2CH2CH3), 22.35
(NHCH2CH2CH3), 41.62 (NHCH2CH2CH3), 47.50 (CH2), 49.38 and 61.78
(C-3 and C-4), 53.87 (OCH3), 114.14, 124.10, 127.35, 127.91, 128.12,
128.54, 129.11, 129.92, 132.00, 132.06, 132.10, 132.21, 132.83, 135.90,
159.00, 164.10 (CO), 168.41 (COOH). Anal. Calcd for C27H27ClN2O3
(462.97): C, 70.05; H, 5.88; N, 7.66. Found: C, 70.20; H, 5.90; N, 7.68.
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-methoxyphenyl)-1-oxo-1,2,3,4-tetrahy-
droisoquinoline-(4-piperidin-1-yl)carboxamide (23): 27% yield as white
1
crystals; mp 178—179 °C. H-NMR (CDCl3) d: 1.18—1.21 (6H, m, CH2),
3.12—3.22 (4H, m, CH2), 3.57 and 5.63 (2H, 2d, Jꢃ15.10, CH2), 3.77 (3H,
s, OCH3), 4.24 (1H, d, Jꢃ3.57, H-3), 4.61 (1H, d, Jꢃ3.57, H-4), 6.77 (2H, d,
Jꢃ8.79, ArH), 6.90—6.97 (3H, m, ArH), 7.13—7.45 (6H, m, ArH), 8.26—
8.29 (1H, m, H-8). Anal. Calcd for C29H29ClN2O3 (489.01): C, 71.23; H,
5.98; N, 5.73. Found: C, 71.28; H, 6.00; N, 5.75.
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-methoxyphenyl)-1-oxo-1,2,3,4-tetrahy-
droisoquinoline-4-(morpholin-4-yl)-carboxamide (24): 42% yield as white
crystals; mp 189—190 °C. 1H-NMR (CDCl3) d: 3.42—3.62 (8H, m,
(CH2)2), 3.67 and 5.69 (2H, 2d, Jꢃ15.11, CH2), 4.27 (1H, s, H-3), 4.65 (1H,
s, H-4), 6.83—6.86 (2H, m, ArH), 6.97—6.99 (3H, m, ArH ), 7.01—7.02
(2H, m, ArH), 7.17—7.20 (2H, m, ArH), 7.48—7.52 (2H, m, ArH), 8.33—
8.55 (1H, m, H-8). Anal. Calcd for C28H27ClN2O4 (490.98): C, 68.50; H,
5.54; N, 5.71. Found: C, 68.57; H, 5.56; N, 5.72.
15) Bonnaud B., Carlessi A., Bigg D. C. H., J. Heterocyclic Chem., 30,
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16) Yu N., Poulain R., Gesquiere J. C., Synlett, 2000, 355—356 (2000).
17) Chapman A. G., Croucher M. J., Meldrum B. S., Arzneim.-Forsch., 34,
1261—1264 (1984).
trans N-(4ꢀ-Chlorobenzyl)-3-(4ꢄ-methoxyphenyl)-1-oxo-1,2,3,4-tetrahy-
droisoquinoline-4-(4-methylpiperazin-1-yl)carboxamide (25): 30% yield as
1
white crystals; mp 173—174 °C. H-NMR (CDCl3) d: 10% yield as white
crystals; mp 145—146 °C. 1H-NMR (CDCl3) d: 1.58—1.76 and 1.80—1.96
(4H, 2m, CH2), 2.32—2.50 (2H, m, CH2), 2.24 (3H, s, CH3), 3.22—3.38
(2H, m, CH2), 3.55 and 5.66 (2H, 2d, Jꢃ15.10, CH2), 3.77 (3H, s, OCH3),
18) Litchfield J. T. J., J. Pharmacol. Exp. Ther., 97, 399—408 (1949).