New n-substituted (E)-4-arylidene isoquinoline-1,3-dione derivatives: NMR spectroscopic investigation and antibacterial activity

Article abstract of DOI:10.1080/00397911.2011.581792

New N-substituted 4-arylidene-isoquinoline-1,3-dione derivatives were obtained as one geometrical isomer by aldol condensation of the appropriate aldehyde and the corresponding N-substituted homophthalimides. The structural elucidation of compounds 3a-h w

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New N-Substituted (E)-4-Arylidene
Isoquinoline-1,3-dione Derivatives:
NMR Spectroscopic Investigation and
Antibacterial Activity
Nafâa Jegham a , Najeh Tka a , Yakdhane Kacem a & Béchir Ben
Hassine a
a Laboratoire de Synthèse Organique Asymétrique et Catalyse
Homogène, Faculté des Sciences , Monastir , Tunisia
Accepted author version posted online: 12 Jan 2012.Published
online: 18 Jul 2012.
To cite this article: Nafâa Jegham , Najeh Tka , Yakdhane Kacem & Béchir Ben Hassine (2012) New N-
Substituted (E)-4-Arylidene Isoquinoline-1,3-dione Derivatives: NMR Spectroscopic Investigation and
Antibacterial Activity, Synthetic Communications: An International Journal for Rapid Communication
of Synthetic Organic Chemistry, 42:22, 3328-3336, DOI: 10.1080/00397911.2011.581792
To link to this article: http://dx.doi.org/10.1080/00397911.2011.581792
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Synthetic Communications1, 42: 3328–3336, 2012
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.581792
NEW N-SUBSTITUTED (E)-4-ARYLIDENE
ISOQUINOLINE-1,3-DIONE DERIVATIVES: NMR
SPECTROSCOPIC INVESTIGATION AND
ANTIBACTERIAL ACTIVITY
ˆ
Nafaa Jegham, Najeh Tka, Yakdhane Kacem, and
Bechir Ben Hassine
´
`
Laboratoire de Synthese Organique Asymetrique et Catalyse Homogene,
Faculte des Sciences, Monastir, Tunisia
´
`
´
GRAPHICAL ABSTRACT
Abstract New N-substituted 4-arylidene-isoquinoline-1,3-dione derivatives were obtained
as one geometrical isomer by aldol condensation of the appropriate aldehyde and the corre-
sponding N-substituted homophthalimides. The structural elucidation of compounds 3a–h
was established by infrared and NMR spectroscopy including 1H, 13C, CH CORR, and
distortionless enhancement by polarization transfer measurements. Compounds 3d–h were
evaluated for their antibacterial activity against some strains of bacteria using the disc
diffusion method and microdilution tests.
Keywords Antibacterial activity; ASIS effect; (E)-4-arylidene-N-methyl-(2H)-isoquino-
line-1,3-diones; (E)-4-arylidene-N-phenyl-(2H)-isoquinoline-1,3-diones; IR and NMR
spectra
INTRODUCTION
Synthetic and natural a,b-unsaturated carbonyl compounds are of great interest
from both biological and chemical points of view.[1–4] In particular, exocyclic a,b-
unsaturated ketones have been used as starting materials for the synthesis of new
nitrogen-containing spiroheterocyclic ring systems[5–10] by 1,3-dipolar cycloaddition
Received January 19, 2011.
Address correspondence to Bechir Ben Hassine, Laboratoire de Synthese Organique Asymetrique
´
et Catalyse Homogene (01uR1201), Faculte des Sciences, Avenue de l’Environment, 5019 Monastir,
`
´
`
Tunisia. E-mail: bechirbenehassine@yahoo.fr
´
3328

(E)-4-ARYLIDENE ISOQUINOLINE-1,3-DIONE DERIVATIVES
3329
Figure 1. Isoquinoline 4-ylidene derivatives exhibiting antiproliferative activity.
reaction with different dipoles. Moreover, they have a good reactivity with dinucleo-
philes leading to polycyclic fused ring systems such as tricyclic pyrazolines,[11,12] tetra-
cyclic benzothiazepines, tetracyclic benzodiazepines, thiazines,[13,14] pyrimidines,[15]
and quinazolines.[16]
Among exocyclic a,b-enones, isoquinolinone 4-ylidene derivatives have been
reported to possess important biological activity[17] (Fig. 1). However, few studies
reporting the stereochemistry of these compounds have been mentioned in the litera-
ture. As far as we know, no pure isoquinoline-1,3-dione-4-ylidene stereoisomer has been
isolated and no attempt has been made to determine their isomeric configuration.[18]
Herein, we report the synthesis and stereochemistry study of new isoquinoline-1,3-
dione-4-ylidene derivatives. Because the aim of our work is drug discovery,[19,20] we
have conducted some biological tests on the prepared (E)-4-arylidene isoquinoline-1,3-
diones to evaluate their antibacterial activity.
RESULTS AND DISCUSSION
Synthesis and Spectroscopic Investigation
The (E)-4-arylideneisoquinoline-1,3-diones derivatives 3a–h were obtained by
condensation of aromatic aldehydes 2a–e with N-methylhomophthalimide 1a or
N-phenylhomophthalimide 1b in dry chloroform using piperidine as catalyst
(Scheme 1).The chemical yields and the melting points of the novel compounds
3a–h are summarized in Table 1.
Based on the infrared (IR) and NMR studies, we have proved that the 4-ary-
lidene isoquinoline-1,3-dione derivatives 3a–h were formed in a trans configuration
Scheme 1. Synthesis of N-substituted 4-arylidene-isoquinoline-1,3-diones derivatives 3a–h.

3330
N. JEGHAM ET AL.
Table 1. Chemical yields and melting points of compounds 3a–h
Compound
R
R0
Yielda (%)
Mp (ꢀC)
3a
3b
3c
3d
3e
3f
Me
Me
Me
Ph
Ph
Ph
Ph
Ph
H
70
75
68
72
80
70
65
75
89
119
194
183
173
168
179
189
Me
NO2
H
Me
NO2
Br
3g
3h
OMe
aYields of isolated products after crystallization.
in all cases. The (E)-configuration was proved by aromatic solvent-induced shift
1
(ASIS) effect.[21,22] We have found that the H NMR spectra of compounds 3a–h,
recorded in CDCl3 and C6D6, present a negative solvent effect for proton H-9
(Dd < 0; Dd (H-9) ¼ d (H-9) CDCl3-d (H-9) C6D6 and positive (Dd > 0;
Dd ¼ dCDCl3-dC6D6) for aromatic protons H-20,60 and H-30,50 (Table 2), which
places the proton H-9 cis to the carbonyl group. The signal of the proton H-9 of
compound 3 h appears as singlet at 8.15 ppm in CDCl3 and at 8.31 ppm in C6D6
(Fig. 2).
Table 2. Aromatic solvent-induced shift effect (Dd ¼ dCDCl3-dC6D6)
Compounds
Dd (H-9)
Dd (H-20,6)
Dd (H-30,50)
3a
3b
3c
3d
3e
3f
ꢁ0.08
ꢁ0.12
ꢁ0.09
ꢁ0.15
ꢁ0.13
ꢁ0.17
ꢁ0.14
ꢁ0.16
0.25
0.23
0.20
0.29
0.21
0.22
0.26
0.36
0.28
0.35
0.27
0.30
0.43
0.33
0.20
0.17
3g
3h
Figure 2. Signals of proton H9 of compound 3h recorded in (a) CDCl3 and (b) C6D6.

3331

3332
N. JEGHAM ET AL.
Table 4. 13C NMR chemical shiftsa (in ppm) of compounds 3a–h
Product
3a
3b
3c
3d
3e
3f
3g
3h
R
Me
H
Me
Me
Me
NO2
Ph
Ph
Me
Ph
NO2
Ph
Br
Ph
OMe
R0
H
—
dR
dR0
27.84
—
27.82
21.87
27.67
—
—
21.64
—
—
—
—
—
55.47
—
=
dC O
166.52
164.83
125.96
135.99
127.45
129.96
132.52
129.19
126.24
144.61
132.32
—
166.62
164.86
125.16
132.84
127.33
129.04
132.44
129.24
126.16
144.87
132.55
129.28
130.02
140.32
166.58
164.11
126.18
130.85
127.14
129.80
132.60
129.54
128.24
140.46
142.54
129.64
124.41
147.93
166.09
164.42
126.18
135.86
127.66
129.44
132.97
129.75
126.36
144.81
131.26
—
166.22
164.48
125.04
135.57
127.21
129.40
132.55
129.76
125.95
145.07
131.53
128.92
130.08
140.27
165.81
164.36
126.68
135.44
127.68
129.85
133.32
130.13
128.93
141.27
142.70
129.97
124.80
148.37
166.24
164.61
124.29
135.70
127.53
129.70
133.10
129.70
126.46
143.34
132.28
129.76
130.78
126.75
166.34
164.53
123.86
135.62
127.30
129.06
132.88
129.06
125.93
144.77
126.94
128.93
114.39
161.08
=
dC O
dC4
dC4a
dC5
dC6
dC7
dC8
dC8a
b
dC9
0
dC1
0
0
0
dC2 ,6
0
dC3 ,5
—
128.28
—
128.01
0
dC4
aThe assignments were supported by DEPT and 2D-XH CORR measurement.
bSide chain.
1
The IR and H and 13C NMR data (Tables 3 and 4) proved the expected
structures of 4-arylidene isoquinoline-1,3-dione derivatives. As shown in Table 3,
the chemical shift values of the H-8 proton of the condensed benzene ring, in peri
position to the carbonyl groups, were measured in series a and b, ranging from
8.16 to 8.29 ppm. The anisotropic effect of the carbonyl causes an even larger down-
field shift on the H-8 signal.[23]
From this data and the IR frequency characteristics, it may be remarked that
=
the wave numbers (mean values) of the C O band reveal higher frequencies (Table 3)
due to the ring strain[24] in compounds 3a-h. The deshielding effect resulting from the
diamagnetic anisotropy of the carbonyl group leads to the vinyl proton in the trans
isomer (with the proton cis to the carbonyl group), giving a signal at a greater
chemical shift than in the cis isomer. As result, the (Z) configuration may be highly
unfavorable because of strong steric interaction between the aryl and carbonyl
groups.
Biological Activity
Compounds 3d–h were tested at concentrations ranging from 1 to 0.25 mg mLꢁ1
for antibacterial activity against bacterial strains. The strains of microorganisms
employed were Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC
25923, Echerichia coli ATCC 35218, Salamonelia typhimurium ATCC 1408, and
Enterococcus faecalis ATCC 29212. Antibacterial activity was studied along with
an antibacterial drug named penicillin. Table 5 summarizes the results obtained by
the disc diffusion method showing that the tested products have a moderate antibac-
terial activity compared to the controlled antibiotic (penicillin). Reported compound

(E)-4-ARYLIDENE ISOQUINOLINE-1,3-DIONE DERIVATIVES
3333
Table 5. Antibacterial activity of compounds 3d–h (DD: mm; MIC, MBC: mg mLꢁ1
)
P. aeruginosa
ATCC27853
S. aureus E. coli
ATCC25923 ATCC35218
S. typhimurim
ATCC1408
E. feacalis
ATCC29212
Compound Parameter
3d
DDa
MIC
MBC
DDb
MIC
MBC
DDb
MIC
MBC
DDb
MIC
MBC
DDb
MIC
MBC
DDc
11
0.2
>0.2
7
9
0.4
>0.4
11
10
0.2
11
0.4
>0.4
9
14
0.2
0.2
8
>0.2
10
3e
0.1
0.2
7
0.1
0.2
11
0.1
0.1
12
0.1
0.1
5
0.1
0.1
12
3f
0.8
>0.8
8
0.2
>0.2
6
0.2
>0.2
9
0.18
0.3
9
0.2
0.2
7
3g
0.2
>0.2
11
0.3
>0.3
12
0.05
0.1
>0.1
7
0.1
0.1
12
0.05
9
3h
0.04
0.08
24
0.1
0.1
53
0.1
0.1
0.1
0.1
6
0.1
0.1
25
Penicillin
11
Note. DD, diameter of zone of inhibition (mm) including disc diameter of 6 mm; MIC, minimum inhibi-
tory concentrations; MBC, minimum bactericidal concentrations values given as mg mL1.
aTested at a concentration of 1 mg mLꢁ1
.
bTested at a concentration of 0.5 mg mLꢁ1
.
cTested at a concentration of 6 mg=disc.
3 h was found to be more active than the other products against most of the tested
bacterial strains. These results were confirmed by the determination of the minimum
inhibitory concentrations (MIC) and the minimum bactericidal concentrations
(MBC) values of the tested compounds (Table 5). Compound 3 h shows good antibac-
terial activity against P. aeruginosa at a concentration (MIC) of 0.04 mg mLꢁ1 and
minimum bactericidal concentration (MBC) of 0.08 mg mLꢁ1. Compounds 3e and
3 g exhibit acceptable antibacterial activity at low concentrations (MIC and MBC),
0.05 and 0.1 mg mLꢁ1 respectively, against E. coli.
CONCLUSION
In this article, we have described a simple method for the synthesis of new
(E)-4-arylidene isoquinoline-1,3-dione derivatives. Spectroscopic study was affected
to confirm the structure and the configuration of obtained compounds. Some of the
reported compounds were screened for their antibacterial activity against a spectrum
of microbial organisms and show moderate antibacterial activity.
EXPERIMENTAL
All chemicals were purchased commercially and used without further purifi-
cation. Solvents were purified by standard methods, freshly distilled under nitrogen,
and dried before use. N-Phenylhomophthalimide or N-methylhomophthalimide were
prepared according to the reported method.[25] Melting points were determined on a

3334
N. JEGHAM ET AL.
Kofler bank and were uncorrected. Elemental analyses were carried out by the
service of Microanalyse of the Institut National de Recherche et d’Analyse Physico-
Chimique de Tunis. IR spectra were recorded at room temperature in the region of
1800–1600 cmꢁ1 on a Perkin-Elmer 197 spectrometer and were taken in KBr discs.
The concentrations of the measured solutions were chosen to reach a transmittance
ranging from 25% and 30% for the investigated bands. The 1H and 13C NMR spectra
were recorded in a CDCl3 solution on a Bruker-Spectrospin AC 300 spectrometer,
operating at 300 MHz for 1H and 75.5 MHz for 13C, using tetramethylsilane
(TMS) as internal standard. Distortionless enhancement by polarization transfer
(DEPT) spectra[26] were run in a standard manner,[27] using only the h ¼ 135ꢀ pulse.
The 2D-XH CORR spectra[28] were obtained by using the standard Bruker pulse
program HXCO.AU.
General Procedure for the Synthesis of (E)-4-Arylidene
Isoquinoline-1,3-dione Derivatives 3a–h
N-Substituted homophthalimide (0.01 mol) was dissolved in dry chloroform
(20 mL), then the aromatic aldehyde (0.01 mol) and the piperidine (0.2 mL) were
added, and the reaction mixture was stirred and refluxed for 5 h under an argon
atmosphere. After cooling to room temperature, the solution was washed with
10 mL of water. After separation, the aqueous layer was extracted with chloroform
(2 ꢂ 10 mL). The combined organic layers were dried with sodium sulfate and filtered,
and the solvent was evaporated in vacuum. The obtained product was crystallized in
ethanol. The purity of the samples was checked by thin-layer chromatography (TLC)
using Merck silica gel 60 F254 aluminum sheets and cyclohexane–ethyl acetate (9:1).
Biological Activity Testing
Disc diffusion method. The agar disc method[29] was used as preliminary
assay for testing antibacterial effects of compounds 3d–h. A suspension of the tested
bacterial (2 ꢂ 106 cfu=mL) was spread on the solid media plates. Filter paper discs
(6 mm in diameter) were individually impregnated with 10 mL of the products 3d–h
and then placed on the previously inoculated agar plates. The Petri dishes were kept
at 4 ꢀC for 2 h and then incubated at 37 ꢀC for 24 h. The diameters of the inhibition
zones were measured in millimeters. Penicillin was used as positive control.
Microwell dilution assays. MIC and MBC values were determined by a
micro-titre plate dilution method described by Sahin et al.[30] All tests were performed
in Mueller–Hinton broth (MHB). The inoculums of the bacteria were prepared from
12 h broth cultures, and suspensions were adjusted to 0.5 McFarland standard tur-
bidity. The synthesized compounds were first dissolved in 10% dimethylsulfoxide
(DMSO) and then diluted to be tested. In brief, the 96-well plates were prepared by
dispensing into each well 100 mL of nutrient broth and 5 mL of the inoculums. A
200-mL stock solution of the compound initially prepared at the concentration of
1 mg mLꢁ1 was added into the first well. Then, 100 mL from their serial dilutions
was transferred into nine consecutive wells. The last well containing 100mL of nutrient
broth without compound and 5mL of the inoculums on each strip was used as negative

(E)-4-ARYLIDENE ISOQUINOLINE-1,3-DIONE DERIVATIVES
3335
control. The plate was covered with a sterile plate sealer and then incubated for 18 h at
37 ꢀC. The MIC was defined as the lowest concentration of the compounds 3d–h to
inhibit the growth of microorganisms, after incubation. To determine MBC, broth
was taken from each well and inoculated in Mueller–Hinton agar for 24 h at 37 ꢀC.
The MBC was defined as the lowest concentration of the compounds 3d–h at which
inoculated bacteria were totally killed. The results were expressed in milligram per
milliliter.
ACKNOWLEDGMENT
´ ´
The authors are grateful to Direction Generale de la Recherche Scientifique of
the Tunisian Ministry of Higher Education Scientific Research and Technology for
the financial support of this research.
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