Synthesis of mono, bis-2-(2-arylideneaminophenyl) indole azomethines as potential antimicrobial agents

Article abstract of DOI:10.1007/s12272-011-0705-z

A series of mono and bis 2-2-(arylidineaminophenyl)indole azomethines have been synthesized by a condensation reaction of 2-(2-amino phenyl) indole with various mono and diketones R-CO-R^l /R-CO-X-CO-R^l (1:1/2:1 ratio) in ethanol medi

Full text of DOI:10.1007/s12272-011-0705-z

Arch Pharm Res Vol 34, No 7, 1077-1084, 2011
DOI 10.1007/s12272-011-0705-z
Synthesis of Mono, Bis-2-(2-Arylideneaminophenyl) Indole Azome-
thines as Potential Antimicrobial Agents
Rondla Rohini1,2, P. Muralidhar Reddy1,3, Kanne Shanker1,3, Kodipelli Kanthaiah1, Vadde Ravinder1, and Anren Hu2
2
1Department of Chemistry, Kakatiya University, Warangal 506009, A.P, India, Department of Laboratory Medicine and
3
Biotechnology, Tzu Chi University, Hualien 97004, Taiwan, and Department of Chemistry, National Dong Hwa Univer-
sity, Hualien 97441, Taiwan
(Received June 19, 2010/Revised October 29, 2010/Accepted October 31, 2010)
A series of mono and bis 2-2-(arylidineaminophenyl)indole azomethines have been synthesized
by a condensation reaction of 2-(2-amino phenyl) indole with various mono and diketones R-
CO-Rl /R-CO-X-CO-Rl (1:1/2:1 ratio) in ethanol media. The synthesized azomethines were
characterized via IR, 1H-NMR, 13C-NMR, MS and elemental analysis. The antimicrobial activ-
ity of these compounds against different bacteria and fungi was also evaluated.
Key words: Azomethines, Synthesis, Antibacterial activity, Antifungal activity
that combination of two or more moieties into one is a
common procedure for manipulation in medicinal
INTRODUCTION
Heterocycles play a central role in most bioactive chemistry and this can possibly result in augmenting
molecules and in their manifestation of bioactivity. the activity towards infectious microorganisms. More-
Despite the ever-increasing number of new bioactive over, the importance of the indole nucleus is well
compounds, nitrogen heterocycles and their derivatives established in the field of synthetic as well as medi-
have now developed into a major class which is cinal chemistry. Indole derivatives offer a high degree
fulfilling a seminal role in synthetic organic and of structural diversity and have proven to be broadly
medicinal chemistry (Kaplancikli et al., 2004; Jung et useful as therapeutic agents. Usually, indole and its
al., 2006; Habib et al., 2007; Mostafa et al., 2008). analogs constitute the active class of compounds pos-
Additionally, azomethines derived from various heter- sessing a wide spectrum of biological activities, such
ocycles have been well-recognized for their pharmaco- as antiinflammatory (Zheng et al., 2007), antimicro-
logical properties including anticonvulsant (Popp et al., bial (Gurkok et al., 2009), antibacterial (Sharma et al.,
1980; Küçükgüzel et al., 2004), analgesic (Sarangapani 2006), anticonvulsant (Gitto et al., 2009) and cardio-
and Reddy, 1996), cytotoxic (Tarafder et al., 2002), vascular (Yorikane et al., 1991). In fact, a number of
antiproliferative (Vicini et al., 2003), antidepressant drugs such as indolmycin (Hurdle et al., 2004), reser-
(Singh et al., 1997), anti-inflammatory (Andreani and pine (Krönig et al., 1997), vincristine (Mihelic et al.,
Maselli, 1977) and antimicrobial (Pignatello et al., 2007), the 5-HT3 receptor antagonist ondansetron
1994) activities. Consequently, development of new (Clavel et al., 1995) and 5HT1 receptor agonist suma-
beneficial azomethines is now attracting the attention triptan (Sakai et al., 2008) have an indole nucleus in
of the medicinal chemist. Literature surveys reveal their structures. In recent years, design and synthesis
of pharmacologically relevant heterocyclic molecules
having indole subunits have proven to be a promising
strategy in the search for new pharmaceutical lead
structures. In view of the above and in continuation of
our earlier work on the synthesis of new beneficial
azomethines (Reddy et al., 2009; Rohini et al., 2009;
Shanker et al., 2009a), finding indole-induced azome-
thines was under taken in the hope of getting better
Correspondence to: Vadde Ravinder, Department of Chemistry,
Kakatiya University, Warangal 506 009, A.P, India
Tel: 91-939-010-0594, Fax: 91-870-243-8800
E-mail: ravichemku@rediffmail.com
Anren Hu, Department of Laboratory Medicine and Biotechnol-
ogy, Tzu Chi University, Hualien 97004, Taiwan
Tel: 886-3-856-5301, Fax: 886-3-857-1917
E-mail: anren@mail.tcu.edu.tw
1077

1078
R. Rohini et al.
bioactive agents. Here, we present a convenient syn- resulting solution was refluxed for 3 h. After cooling,
thesis approach and antimicrobial screening of novel the deposited solid product was collected by filtration
indole azomethines.
and recrystalized with an ethanol/dichloromethane-
methanol mixture.
MATERIALS AND METHODS
Procedure for the preparation of bis-2-(2-ary-
lideneaminophenyl)indoles (Az7-13)
0.832 g, 4 mmol of 2-(o-aminophenyl)indole (A) was
All solvents used were of analytical grade. Melting
points were determined in open capillary tubes and
are uncorrected. TLC analysis was done using pre- dissolved in 20-40 mL of ethanol. To this solution, 30
coated silica gel plates and visualization was done mL of ethanolic RCO-X-COR1 solution (2 mmol) and a
using iodine vapors. Micro analytical (C, N, H) data few drops of acetic acid were added. The reaction mix-
was obtained by using a Perkin-Elmer 2400 CHN ture was refluxed for 2 h after which the compound
elemental analyzer. The IR spectra were recorded in was obtained. The product was collected and recry-
KBr pellets on a Perkin-Elmer-283 spectrophotometer stalized as indicated above.
1
(
ν
in cm−1). H-NMR spectra (at 400 MHz) and 13C-
NMR (at 100 MHz) spectra were acquired on a Bruker [2-(1H-Indol-2-yl)-phenyl]-(1-phenyl-ethylidene)-
NMR spectrometer. FAB mass spectra were recorded amine (Az1)
1
on a Finnigan-MAT 1020 instrument. MALDI Autoflex Yield 75%, m.p. 211-213oC; H-NMR (CDCl3):
δ
2.32
= 7.4 Hz), 7.08-7.16
Bacillus (4H, m, Ar), 7.29-7.42 (7H, m, Ar), 7.61 (1H, d, Ar,
Streptococcus pyogenes (Gram positive), Sal- 7.3 Hz), 7.94 (1H, d, Ar, = 7.3 Hz), 8.85 (1H, s,
monella typhimurium, Escherichia coli and Klebsiella indolyl-NH); 13C-NMR (CDCl3):
19.2 (1C, -CH3),
time-of-flight mass spectrometer (Bruker Daltonic) was (3H, S, -CH3), 6.82 (1H, t, Ar,
used for MS analyses. Staphylococcus aureus
subtilis
J
,
J =
,
J
δ
pneumonia (Gram negative) bacteria as well as Asper- 114.0, 118.1, 120.5, 123.2, 125.6, 130.5, 131.3, 132.2,
gillus niger, Candida albicans, Trichoderma viridae 136.5, 141.7, 142.6, 143.8, 146.3, 165.8 (21C, Ar-C). IR
fungi were used in the antimicrobial assays.
(KBr) cm−1: 3290, 2868, 1630, 1590, 1580, 1128. MS
m/z: 310. Anal. Calcd for C22H18N2: C, 85.13; H, 5.85;
N, 9.03%. Found: C, 85.18; H, 5.87; N, 9.05%.
General procedure for the preparation of 2-(o-
aminophenyl)indole (A)
The starting material, 2-(o-aminophenyl)indole (
A
,
2-{1-[2-(1H-Indol-2-yl)-phenylimino]-ethyl}-phenol
lit. m.p. 146oC) was obtained by Fischer indole cycliza- (Az2)
tion of phenylhydrazene and 2-aminoacetophenone Yield 79%, m.p. 205-207oC; H-NMR (CDCl3):
using a mixture of methane sulfonic acid and phos- (3H, S, -CH3), 6.85-7.20 (6H, m, Ar), 7.26-7.37 (5H, m,
phorus pentoxide at 85oC. Reactions were carried out Ar), 7.61 (1H, d, Ar,
= 7.3 Hz), 7.95 (1H, d, Ar,
according to a reported procedure (Billimoria and 7.3 Hz), 8.92 (1H, s, indolyl-NH), 10.21 (1H, s, OH);
δ 2.34
1
J
J =
Cava, 1994). Methanesulfonic acid (100 mL) by heating 13C-NMR (CDCl3):
δ 19.4 (1C, -CH3), 114.7, 117.5,
to 80oC, then phosphorus pentoxide (13.5 g) was 118.4, 123.8, 126.2, 130.6, 132.2, 133.6, 136.2, 141.2,
added to it with stirring until it dissolved completely. 142.6, 143.5, 145.4, 153.7, 167.8 (21C, Ar-C). IR (KBr)
The phenylhydrazone of 2-aminoacetophenone (10.0 g, cm−1: 3420, 3295, 2860, 1625, 1590, 1578, 1130. MS
44.4 mmol) (Kiang et al., 1956) was slowly added m/z: 326. Anal. Calcd for C22H18N2O: C, 80.96; H,
maintaining the temperature between 80 and 100oC. 5.56; N, 8.58%. Found: C, 80.95; H, 5.61; N, 8.55%.
The solution was then further heated at 85oC for 30
min. The reaction mixture was cooled to room temper- [2-(1H-Indol-2-yl)-phenyl]-(1-naphthalen-2-yl-ethy-
ature and poured over crushed ice containing sodium lidene)-amine (Az3)
1
hydroxide (65.0 g). The solid precipitate was filtered, Yield 80%, m.p. 215-217oC; H-NMR (CDCl3):
δ
2.31
washed with water and dried to afford the crude (3H, S, -CH3), 6.83 (1H, t, Ar,
J = 7.4 Hz), 7.08-7.18
product which was crystallized from ethanol.
(6H, m, Ar), 7.21-7.65 (8H, m, Ar), 7.95 (1H, d, Ar,
J
=
δ
7.3 Hz), 8.90 (1H, s, indolyl-NH); 13C-NMR (CDCl3):
19.5 (1C, -CH3), 114.4, 118.2, 123.1, 123.8, 126.2,
130.5, 130.8, 131.2, 132.5, 136.8, 141.6, 142,5, 143.8,
Procedure for the preparation of mono-2-(2-
arylideneaminophenyl) indoles (Az1-6)
To a solution of 2-(o-aminophenyl)indole (A
, 0.416 g, 146.3, 166.3 (25C, Ar-C). IR (KBr) cm−1: 3260, 2860,
2 mmol) in 20-40 mL of ethanol were added the 1635, 1590, 1575, 1126. MS m/z: 360. Anal. Calcd for
appropriate ketone (2 mmol of RCOR1 in ethanol) and C26H20N2: C, 86.64; H, 5.59; N, 7.77%. Found: C, 86.66;
a few drops of acetic acid with vigorous stirring. The H, 5.61; N, 7.81%.

Indole Azomethines as Potential Antimicrobial Agents
1079
Benzhydrylidene-[2-(1H-indol-2-yl)-phenyl]-amine N1-[1-(3-[2-(1H-2-indolyl)phenyl]ethanimidoyl-
(Az4) phenyl)ethylidene]-2-(1H-2-indolyl)aniline (Az8)
Yield 76%, m.p. 199-201oC; H-NMR (CDCl3):
(3H, S,-CH3), 6.82 (1H, t, Ar, = 7.4 Hz), 7.06-7.34 (6H, S, -CH3), 6.81-6.87 (4H, m, Ar), 7.08-7.41 (12H,
(9H, m, Ar), 7.57-7.65 (5H, m, Ar), 7.94 (1H, d, Ar,
7.3 Hz), 8.87 (1H, s, indolyl-NH); 13C-NMR (CDCl3):
1
1
δ
2.31 Yield 81%, m.p. 205-207oC; H-NMR (CDCl3):
δ 2.24
J
J
=
m, Ar), 7.61-7.96 (6H, m, Ar), 8.92 (2H, s, -NH); 13C-
δ
NMR (CDCl3): 21.2 (2C, -CH3), 113.5, 114.1, 122.6,
δ
19.2 (1C, -CH3), 113.4, 117.6, 123.0, 124.3, 126.5, 130.5, 124.2, 126.7, 128.2, 130.9, 132.1, 133.9, 136.1, 140.4,
131.8, 132.2, 136.9, 141.0, 142.2, 145.0, 150.8, 165.9 142.8, 145.5, 146.1, 165.4, 168.5 (36C, Ar-C). IR (KBr)
(26C, Ar-C). IR (KBr) cm−1: 3300, 2875, 1630, 1595, cm−1: 3290, 2878, 1648, 1620, 1580, 1324. MS m/z
:
1575, 1100. MS m/z: 372. Anal. Calcd for C27H20N2: C, 542. Anal. Calcd for C38H30N4: C, 84.10; H, 5.57; N,
87.07; H, 5.41; N, 7.52%. Found: C, 87.10; H, 5.45; N, 10.32%. Found: C, 84.11; H, 5.62; N, 10.35%.
7.55%.
N1-[1-(4-[2-(1H-2-indolyl)phenyl]ethanimidoyl-
[2-(1H-Indol-2-yl)-phenyl]-(1-pyridin-2-yl-ethyli-
phenyl)ethylidene]-2-(1H-2-indolyl)aniline (Az9)
1
dene)-amine (Az5)
Yield 79%, m.p. 236-238oC; H-NMR (CDCl3):
δ
2.23
1
Yield 78%, m.p. 221-223oC; H-NMR (CDCl3):
δ
2.34 (6H, S, -CH3), 6.81-6.84 (4H, m, Ar), 7.06-7.15 (6H, m,
= 7.3 Hz),
20.4 (2C, -CH3),
= 5.25 Hz), 8.90 (1H, s, indolyl-NH); 13C- 113.2, 114.5, 123.5, 125.6, 127.3, 128.3, 130.5, 131.2,
NMR (CDCl3): 19.6 (1C, -CH3), 113.3, 114.2, 119.4, 132.2, 137.4, 142,6, 144.2, 162.3, 168.6 (36C, Ar-C). IR
123.6, 125.1, 131.6, 137.2, 140.7, 142.4, 143.6, 147.0, (KBr) cm−1: 3300, 2865, 1625, 1608, 1590, 1128. MS m/
160.3, 167.1 (20C, Ar-C). IR (KBr) cm−1: 3290, 2870,
: 542. Anal Calcd for C38H30N4: C, 84.10; H, 5.57; N,
(3H, S, -CH3), 6.85-7.12 (3H, m, Ar), 7.16-7.33 (5H, m, Ar), 7.21-7.45 (10H, m, Ar), 7.95 (2H, d, Ar,
Ar), 7.61-7.86 (3H, m, Ar), 7.95 (1H, d, Ar,
= 7.3 Hz), 8.86 (2H, s, -NH); 13C-NMR (CDCl3):
8.71 (1H, d,
J
J
δ
J
δ
z
.
1635, 1615, 1585, 1125. MS m/z: 311. Anal. Calcd for 10.32%. Found: C, 84.15; H, 5.55; N, 10.33%.
C21H17N3: C, 81.00; H, 5.50; N, 13.49%. Found: C,
81.05; H, 5.55; N, 13.55%.
N1-[2-[2-(1H-2-indolyl)phenyl]imino-1,2-diphenyl-
ethylidene]-2-(1H-2-indolyl) aniline (Az10)
[2-(1H-Indol-2-yl)-phenyl]-[1-(6-methyl-pyridin-2- Yield 82%, m.p. 195-197oC; 1H-NMR (CDCl3):
δ
6.81-
7.14 (6H, m, Ar), 7.20-7.31 (12H, m, Ar), 7.42-7.60 (8H,
2.29 m, Ar), 7.92 (2H, d, Ar, = 7.3 Hz), 8.91 (2H, s,
114.6, 118.2, 123.3,
= 7.3 Hz), 123.4, 126.2, 130.4, 130.6, 131.2, 132.8, 136.6, 140.7,
= 7.3 Hz), 8.89 142,6, 143.9, 162.4, 165.6 (42C, Ar-C). IR (KBr) cm−1:
20.2 (2C, -CH3), 3295, 2875, 1620, 1606, 1578, 1125. MS m/z: 590.
Calcd for C42H30N4: C, 85.40; H, 5.12; N, 9.48%.
yl)-ethylidene]-amine (Az6)
Yield 75%, m.p. 228-230oC; H-NMR (CDCl3):
δ
J
1
(3H, S, -CH3), 2.34 (3H, S, -CH3), 6.70-7.21 (5H, m, indolyl-NH); 13C-NMR (CDCl3):
δ
Ar), 7.29-7.32 (3H, m, Ar), 7.62 (1H, d, Ar,
J
7.76-7.81 (2H, m, Ar), 7.93 (1H, d, Ar,
J
δ
(1H, s, indolyl-NH); 13C-NMR (CDCl3):
113.5, 114.2, 118.2, 123.4, 126.2, 130.7, 130.8, 131.7, Anal
.
132.7, 136.5, 140.1, 142,8, 143.6, 146.7, 149.4, 161.2, Found: C, 85.42; H, 5.15; N, 9.50%.
166.4 (20C, Ar-C). IR (KBr) cm−1: 3278, 2862, 1635,
1618, 1580, 1120. MS m/z: 325. Anal. Calcd for N1-[3-[2-(1H-2-indolyl)phenyl]imino-1,3-diphenyl-
C22H19N3: C, 81.20; H, 5.89; N, 12.91%. Found: C, 81.42; propylidene]-2-(1H-2-indolyl) aniline (Az11)
1
H, 5.87; N, 12.95%.
Yield 80%, m.p. 213-215oC; H-NMR (CDCl3):
δ
2.34
= 7.4 Hz), 7.10-7.16
(4H, m, Ar), 7.26-7.33 (12H, m, Ar), 7.38-7.80 (8H, m,
Ar), 7.94 (2H, d, Ar, = 7.3 Hz), 8.92 (2H, s, indzolyl-
35.5 (1C, -CH2-), 113.7,
(2H, S, -CH2-), 6.82 (2H, t, Ar,
J
N1-[1-(2-[2-(1H-2-indolyl)phenyl]ethanimidoyl-
phenyl)ethylidene]-2-(1H-2-indolyl)aniline (Az7)
J
Yield 80%, m.p. 243-245oC; H-NMR (CDCl3):
δ
2.25 NH); 13C-NMR (CDCl3):
δ
1
(6H, S, -CH3), 6.81-7.20 (10H, m, Ar), 7.26-7.45 (10H, 114.3, 118.6, 122.4, 125.2, 130.5, 132.6, 133.3, 136.5,
m, Ar), 7.94 (2H, d, Ar, = 7.3 Hz), 8.92 (2H, s, -NH); 141.9, 142.2, 143.5 160.3, 165.6 (42C, Ar-C). IR (KBr)
13C-NMR (CDCl3): 20.5 (2C, -CH3), 113.1, 114.6, cm−1: 3290, 2880, 1620, 1610, 1585, 1128. MS m/z
119.7, 123.2, 124.7, 125.2, 127.2, 128.3, 130.5, 131.2, 604. Anal Calcd for C43H32N4: C, 85.40; H, 5.33; N,
J
δ
:
.
133.9, 136.3, 141.5, 142.2, 144.8, 146.5, 165.8, 169.5 9.26%. Found: C, 85.45; H, 5.33; N, 9.25%.
1
(36C, Ar-C). IR (KBr) cm− : 3300, 2860, 1628, 1605,
1582, 1325, 1115. MS m/z: 542. Anal. Calcd for N1-[4-[2-(1H-2-indolyl)phenyl]imino-1,4-diphenyl-
C38H30N4: C, 84.10; H, 5.57; N, 10.32%. Found: C, butylidene]-2-(1H-2-indolyl)aniline (Az12)
1
84.16; H, 5.62; N, 10.37%.
Yield 76%, m.p. 222-224oC; H-NMR (CDCl3):
δ
2.32
(4H, S, -CH2-), 6.83 (2H, t, Ar,
J = 7.4 Hz), 7.08-7.15

1080
R. Rohini et al.
(6H, S, -CH3), 6.82-7.15 (5H, m, Ar), 7.21-7.32 (6H, m,
Ar), 7.36-7.41 (6H, m, Ar), 7.85-7.92 (4H, m, Ar), 8.86
(2H, s, -NH); 13C-NMR (CDCl3):
δ 20.2 (2C, -CH3), 113.2,
114.6, 121.3, 123.2, 124.6, 127.1, 128.4, 130.1, 132.6,
140.5, 142.6, 144.2, 146.2, 152.7, 164.1, 168.2 (35C, Ar-
C). IR (KBr) cm−1: 3290, 2865, 1630, 1610, 1578, 1126.
MS m/z: 543. Anal. Calcd for C37H29N5: C, 81.74; H,
5.38; N, 12.88%. Found: C, 81.75; H, 5.39; N, 12.95%.
RESULTS AND DISCUSSION
The key indole derivative (A, 2-o-aminophenylindole)
Fig. 1. Comparison of MIC values (in µg/mL) of indoloazo-
was obtained by the method described by Billimoria
and Cava. The target compounds were synthesized by
the condensation between 2-(o-aminophenyl)indole
methines and standards against different bacteria and fungi
(5H, m, Ar), 7.21-7.36 (9H, m, Ar), 7.32-7.65 (10H, m, and various mono, diketones R-CO-Rl /R-CO-X-CO-Rl
Ar), 7.95 (2H, d, Ar,
J
= 7.3 Hz), 8.92 (2H, s, indolyl- (in a 1:1/2:1 ratio). The general strategy for the syn-
31.2 (2C, -CH2-CH2-), 113.4, thesis of mono and bis-2-(2-arylideneaminophenyl)
NH); 13C-NMR (CDCl3):
δ
114.6, 118.2, 123.4, 124.1, 126.6, 130.4, 132.7, 136.1, indoles is illustrated in Scheme 1. All newly synthe-
141.8, 142.4, 143.2, 156.4, 165.9 (42C, Ar-C). IR (KBr) sized compounds were analyzed by different spectro-
cm−1: 3285, 2870, 1635, 1615, 1580, 1130. MS m/z
:
scopic technique such as IR, 1H-NMR, 13C-NMR, mass
618. Anal. Calcd for C44H34N4: C, 85.41; H, 5.54; N, spectroscopy and by elemental analysis.
9.05%. Found: C, 85.40; H, 5.56; N, 9.12%.
The IR spectrum of
A exhibited an absorption band
at 3380-3440 cm−1 assigned to -NH2 group and in the
N1-[1-(6-[2-(1H-2-indolyl)phenyl]ethanimidoyl-2-
spectra of A and azomethine derivatives Az1-13 two
pyridyl)ethylidene]-2-(1H-2-indolyl)aniline (Az13) absorption bands in the regions 3330-3400 cm−1 and
Yield 75%, m.p. 212-214oC; H-NMR (CDCl3):
δ
2.18 1540-1560 cm−1 were assigned to -NH stretching and
1
Scheme 1. Synthetic route of mono, bis-2-(2-arylideneaminophenyl) indoles

Indole Azomethines as Potential Antimicrobial Agents
1081
bending vibrations of the indolyl ring, respectively a cup-plate method (Reddy et al., 2009; Rohini et al.,
(Talbi et al., 1997). In all azomethines the character- 2009b). All the newly synthesized azomethines were
istic IR peaks for the -CHO and -NH2 groups at 1680- screened for antibacterial activity against S. aureus
1695 cm−1 and 3380-3440 cm−1 are absent and the char- B. subtilis
S. pyogenes (Gram positive); S. typhimurium,
E. coli and K. pneumonia (Gram negative) bacterial
,
,
1
acteristic peak for the CH=N around 1610-1635 cm−
is observed, which indicates effective condensation of strains in addition to their antifungal activities
the aldehyde group with the amino group of the key against A. niger, C. albicans and T. viridae. For this
indole derivative (2-o-aminophenylindole) (Amudha et study, ampicillin and ketoconazole were used as
al., 1999). The IR spectrum of an azomethine (Az8) is standards. Preliminary screening of all azomethines
presented in Fig. 2.
was performed at fixed concentrations of 1000 µg/mL.
The 1H-NMR spectra of all compounds were recorded One day prior to the experiment, the bacterial cultures
in CDCl3 using TMS as the internal standard. The were inoculated in nutrient broth and incubated
1H-NMR spectra of compound
6.4 ppm as a singlet for (-NH2),
A
showed signals at
δ
overnight at 37oC. The inoculated medium was poured
8.48 ppm as a singlet in sterile petri dishes and allowed to solidify and set
δ
for the (-NH) group, which confirmed the structure for 1 h. The cultures were swabbed on the surface of
(Billimoria and Cava, 1994). Formation of azomethines sterile nutrient agar plates using a sterile cotton swab
from was confirmed by disappearance of signals at Similarly, one and half days prior to the experiment,
6.4 ppm due to NH2 protons of compound and ap- the fungal cultures of A. niger, C. albicans and T.
pearance of signals around 7.9-8.1 ppm that cor- viridae were prepared in dextrose broth medium and
responded to -CH=N protons. The H-NMR spectrum incubated at 37oC for 36 h. Then, 50 mL of nutrient
of an azomethine (Az8) is presented in Fig. 3. broth cultures were swabbed on the surface of sterile
The 13C-NMR spectra of all the compounds showed sabouraud dextrose agar plates. Afterwards, 6 mm
signals at 141.1-169.5 ppm due to -C=N carbon atoms wide bores were made into the agar media using a
(Jung et al., 2008). The signals in the range of 113.1- sterile cork borer and the solutions of test compounds
158.2 ppm were attributed to the various aromatic were added into each of the bores using a sterile tip
ring carbon atoms. with a micropipette. Similar plates were prepared for
The final proof for the compounds was obtained by the positive controls ampicillin and ketoconazole. The
.
A
δ
A
δ
1
δ
δ
recording their mass spectral analysis.
plates were allowed to stand for an hour in order to
facilitate the diffusion of the drug solution. The plates
were then incubated at 37ºC for 24 h in the case of
Antimicrobial screening
The in vitro antimicrobial activity was performed by bacteria and at 28oC for 48-72 h in the case of fungi
Fig. 2. IR spectrum of azomethine (Az8)

1082
R. Rohini et al.
Fig. 3. 1H-NMR spectrum of azomethine (Az8)
and zones of inhibition formed were measured in mm. strains even against the standards.
Zone of inhibition values are summarized in Table I.
The minimum inhibitory concentration (Mallié et
The preliminary screening data revealed that all the al., 2005) of the potent azomethine derivatives were
tested compounds Az1-13 showed moderate to good also verified by the liquid dilution method: the effec-
inhibition towards all tested strains. Mainly, high tiveness was observed at lower concentrations. Stock
zone of inhibition values were observed for the Az5, solutions of test samples with 2.5, 5, 10, 15, 20, 25, 30,
Az6 azomethines for all tested strains. Furthermore, 35, 40, 45 and 50 µg/mL concentrations were used in
the majority of bis-azomethines (Az10-13) showed the this study. The minimum inhibitory concentration
most potent activity against all bacterial and fungal (MIC) which was defined no growth was recorded
Table I. Antimicrobial effects of 2-(2-arylidineaminophenyl)indoles (Az1-13) against different bacteria and fungi
Zone of inhibition (mm)
Compound
(1000 g/mL)
Gram-positive bacteria
Gram-negative bacteria
Fungi
µ
ATCC
ATCC
9372
ATCC
19615
ATCC
ATCC
25922
ATCC
3882
ATCC
16404
ATCC
10231
IAM
5061
25923
14028
Az1
18
15
16
25
52
50
25
26
36
52
51
55
55
a48a
16
13
13
16
45
42
22
35
22
50
55
48
52
a39a
11
19
18
20
46
51
26
28
25
52
50
52
50
a35a
18
12
13
15
50
48
35
35
28
46
48
50
55
a45a
12
20
15
19
42
41
30
30
31
50
48
51
52
a40a
16
15
20
14
45
46
25
25
35
46
51
52
51
a45a
16
16
13
18
50
48
32
32
30
50
51
52
55
a45b
10
15
12
16
46
45
35
30
26
45
48
51
52
a40b
11
20
14
11
45
42
26
30
25
48
50
52
50
a41b
Az2
Az3
Az4
Az5
Az6
Az7
Az8
Az9
Az10
Az11
Az12
Az13
Std
aAmpicillin, bKetoconazole: S. aureus (ATCC 25923), B. subtilis (ATCC 9372), S. pyogenes (ATCC 19615); S. typhimurium
(ATCC 14028), E. coli (ATCC 25922), K.pneumonia (ATCC 3882); A. niger (ATCC 16404); C. albicans (ATCC 10231) and
T. viridae (IAM 5061)

Indole Azomethines as Potential Antimicrobial Agents
1083
Table II. MIC values of potent 2-(2-arylidineaminophenyl) indoles and standards against bacteria and fungi
Range of concentration (µg/mL)
Gram-positive bacteria
Gram-negative bacteria
Fungi
Compound
ATCC
25923
ATCC
9372
ATCC
19615
ATCC
14028
ATCC
25922
ATCC
3882
ATCC
16404
ATCC
10231
IAM
5061
Az5
15
10
15
15
10
10
15
15
15
Az6
10
10
15
15
15
10
10
20
20
Az10
Az11
Az12
Az13
Std
12.5
15
12.5
12.5
10a
15
12.5
15
12.5
15
10
15
12.5
12.5
10a
15
10
12.5
12.5
15a
15
15
15
12.5
12.5
15b
20
15
15
10
15
12.5
12.5
15
12.5
15
12.5
15
12.5
12.5
20a
25a
10a
25b
20b
aAmpicillin, bKetoconazole: S. aureus (ATCC 25923), B. subtilis (ATCC 9372), S. pyogenes (ATCC 19615); S. typhimurium
(ATCC 14028), E. coli (ATCC 25922), K.pneumonia (ATCC 3882); A. niger (ATCC 16404); C. albicans (ATCC 10231) and
T. viridae (IAM 5061)
(Table II). Comparison of MIC values (in
µg/mL) of
Billimoria, A. D. and Cava, M. P., Chemistry of indolo[1,2-
c]quinazoline: an approach to the marine alkaloid hinck-
dentine A. J. Org. Chem., 59, 6777-6782 (1994).
Clavel, M., Bonneterre, J., d’Allens, H., and Paillarse, J. M.,
Oral ondansetron in the prevention of chemotherapy-
potent indole azomethines and standards against dif-
ferent strains are presented in Fig. 1. From this study,
it is clear that Az5, Az6 compounds (at MIC range 5-
20
µ
g/mL) and especially the bis indole azomethines
induced emesis in breast cancer patients. Eur. J. Cancer
,
(Az10-13) (MIC range 2.5-20
activity towards all bacterial and fungal strains.
µg/mL) showed superior
31A, 15-19 (1995).
Gitto, R., De Luca, L., Ferro, S., Citraro, R., De Sarro, G., Costa,
L., Ciranna, L., and Chimirri, A., Development of 3-sub-
In conclusion, we have synthesized thirteen novel
indole azomethines by using 2-(o-aminophenyl)indole
and diketones (R-CO-Rl /R-CO-X-CO-Rl). In fact, while
several synthetic routes have been published for a
variety of azomethines, there have been no attempts
to synthesis a mono and bis-2-(2-arylideneaminophen-
yl)indole azomethines; antimicrobial studies have also
not been reported. The compounds which contain pyri-
dyl substituents and two azo (-C=N) groups in their
structures (bis-azomethines) seem to be more potent
even compared to standards like ampicillin and keto-
conazole. However, the method of action of these com-
pounds is unknown. These observations may promote
an additional research in this field. Further develop-
stituted-1H-indole derivatives as NR2B/NMDA receptor
antagonists. Bioorg. Med. Chem., 17, 1640-1647 (2009).
Gurkok, G., Altanlar, N., and Suzen, S., Investigation of
antimicrobial activities of indole-3-aldehyde hydrazide/
hydrazone derivatives. Chemotherapy, 55, 15-19 (2009).
Habib, N. S., Soliman, R., El-Tombary, A. A., El-Hawash, S.
A., and Shaaban, O. G., Synthesis of thiazolo[4,5-d]pyri-
midine derivatives as potential antimicrobial agents.
Arch. Pharm. Res., 30, 1511-1520 (2007).
Hurdle, J. G., O’Neill, A. J., and Chopra, I., Anti-staphylococcal
activity of indolmycin, a potential topical agent for control
of staphylococcal infections. J. Antimicrob. Chemother.,
54, 549-552 (2004).
ment of this group of compounds may lead to com- Jung, H. J., Singh, N., and Jang, D. O., Highly Fe3+ selective
ratiometric fluorescent probe based on imine-linked
benzimidazole. Tetrahedron Lett., 49, 2960-2964 (2008).
Jung, J. K., Jung E. K., Nam-Goong, K., Cho, J. S., Kim, H.
M., Park, S. G., Yoo, Y. A., Kwon, J. H., and Lee, H. S.,
Synthesis and cytotoxic activities of 8-alkyl or 8-aryl-8,9-
dihydro-7H-isoindolo[5,6-g]quinoxaline-7,9-diones. Arch.
Pharm. Res., 29, 276-281 (2006).
Kaplancikli, Z. A., Turan-Zitouni, G., Revial, G., and Guven,
K., Synthesis and study of antibacterial and antifungal
activities of novel 2-[[(benzoxazole/benzimidazole-2-yl)
sulfanyl]acetylamino]thiazoles. Arch. Pharm. Res., 27,
1081-1085 (2004).
pounds with better pharmacological profiles than the
standards and serve as templates for the construction
of better drugs to combat bacterial and fungal infections.
REFERENCES
Amudha, P., Akilan, P., and Kandaswamy, M., Synthesis,
spectral, electrochemical and magnetic properties of new
symmetrical and unsymmetrical dinuclear copper(II) com-
plexes derived from binucleating ligands with phenol and
benzimidazole donors. Polyhedron, 18, 1355-1362 (1999).
Andreani, A. and Maselli, S., Anti-inflammatory activity of
N-benzoyl-isatinic acids and N-p-chlorobenzoyl isatinic
acids. Boll. Chim. Farm., 116, 493-495 (1977).
Kiang, A. K., Mann, F. G., Prior, A. F., and Topham, A., The
action of acyl cyanides on 2- and 1:2-substituted indoles.
Part II. Derivatives of 2-o-aminophenylindole. J. Chem.

1084
R. Rohini et al.
Soc., 1319-1331 (1956).
Sakai, Y., Dobson, C., Diksic, M., Aubé, M., and Hamel, E.,
Sumatriptan normalizes the migraine attack-related in-
crease in brain serotonin synthesis. Neurology, 70, 431-
439 (2008).
Sarangapani, M. and Reddy, V. M., Pharmacological evalu-
ation of 1-(N, N-disubstituted amino methyl)-3-imino-(2-
phenyl-3,4-dihydro-4-oxo-quinazolin-3-yl)indolin-2-ones.
Indian J. Pharm. Sci., 58, 147-149 (1996).
Krönig, B., Pittrow, D. B., Kirch, W., Welzel, D., and Weidinger,
G., Different concepts in first-line treatment of essential
hypertension. Comparison of a low-dose reserpine-thiazide
combination with nitrendipine monotherapy. Hyperten-
sion, 29, 651-658 (1997).
Küçükgüzel, I., Güniz Küçükgüzel,
G., Özdemir, O., Bayrak, I., Altu
S
g
., Rollas, S., Ötük-Sani
, T., and Stables, J. P.,
s,
Synthesis of some 3-(arylalkylthio)-4-alkyl/aryl-5-(4-ami-
nophenyl)-4H-1,2,4-triazole derivatives and their anticon-
vulsant activity. Farmaco, 59, 893-901 (2004).
Shanker, K., Rohini, R., Reddy, P. M., Ho, Y. P., and
Ravinder, V., Ru(II) complexes of N4 and N2O2 macrocyclic
Schiff base ligands: their antibacterial and antifungal
studies. Spectrochim. Acta A Mol. Biomol. Spectrosc., 73,
205-211 (2009).
Mallié, M., Bastide, J. M., Blancard, A., Bonnin, A., Bretagne,
S., Cambon, M., Chandenier, J., Chauveau, V., Couprie, B.,
Datry, A., Feuilhade, M., Grillot, R., Guiguen, C., Lavarde,
V., Letscher, V., Linas, M. D., Michel, A., Morin, O.,
Paugam, A., Piens, M. A., Raberin, H., Tissot, E., Toubas,
D., and Wade, A., In vitro susceptibility testing of candida
and aspergillus spp. to voriconazole and other antifungal
agents using Etest: results of a french multicentre study.
Int. J. Antimicrob. Agents, 25, 321-328 (2005).
Sharma, P., Kumar, A., and Pandey, P., A facile synthesis of
N
-phenyl-6-hydroxy-3-bromo-4-arylazo quinoline-2-ones
under phase transfer catalytic conditions and studies on
their antimicrobial activities. Indian J. Chem., 45B, 2077-
2082 (2006).
Singh, G. S., Singh, T., and Lakhan, R., Synthesis 13C-NMR
and anticonvulsant activity of new isatin-based spiroaze-
tidinones. Indian J. Chem., 36B, 951-954 (1997).
Mihelic, R., Kaufman, J., Lonial, S., and Flowers, C., Main-
tenance therapy in lymphoma. Clin. Lymphoma Myeloma
7, 507-513 (2007).
Mostafa, Y. A. H., Hussein, M. A., Radwan, A. A., and Kfafy,
A. E. H. N., Synthesis and antimicrobial activity of certain
new 1,2,4-triazolo[1,5-a]pyrimidine derivatives. Arch.
Pharm. Res., 31, 279-293 (2008).
,
Talbi, H., Humbert, B., and Billaud, D., Polyindole and poly
(5-cyanoindole): electrochemical and FT-IR spectroscopic
comparative studies. Synth. Met., 84, 875-876 (1997).
Tarafder, M. T. H., Kasbollah, A., Saravanan, N., Crouse, K.
A., Ali, A. M., and Tin, O. K., S-methyldithiocarbazate and
its Schiff bases: evaluation of bondings and biological
properties. J. Biochem. Mol. Biol. Biophys., 6, 85-91 (2002).
Vicini, P., Geronikaki, A., Incerti, M., Busonera, B., Poni, G.,
Cabras, C. A., and La Colla, P., Synthesis and biological
Pignatello, R., Panico, A., Mazzone, P., Pinizzotto, M. R.,
Garozzo, A., and Fumeri, P. M., Schiff bases of
N-hydroxy-
N'-aminoguanidines as antiviral, antibacterial and anti-
cancer agents. Eur. J. Med. Chem., 29, 781-785 (1994).
Popp, F. D., Parson, R., and Donigan, B. E., Potential
anticonvulsants. III. the condensation of isatin with cyclic
ketones. J. Heterocycl. Chem., 17, 1329-1330 (1980).
Reddy, P. M., Ho, Y. P., Shanker, K., Rohini, R., and Ravinder,
V., Physicochemical and biological characterization of
novel macrocycles derived from o-phthalaldehyde. Eur. J.
evaluation of benzo[d]isothiazole, benzothiazole and
thiazole Schiff bases. Bioorg. Med. Chem., 11, 4785-4789
(2003).
Yorikane, R., Mizuno, H., Itoh, Y., Koike, H., Miyake, S.,
Shiga, H., Kumakura, S., Fukami, M., Shimoji, Y., and
Hashimoto, T., Antiarrhythmic and cardiovascular profiles
of the fused indole compound (3aR,12R,12aR,12bS)-12-
amino-2,3,3a,4,11,12,12a,12b-octahydro-10-hydroxy isoquino
[2,1,8-lma]carbazol-5(1H)-one hydrochloride 1.5 hydrate.
Arzneimittelforschung, 41, 1130-1136 (1991).
Zheng, M., Zheng, M., Ye, D., Deng, Y., Qiu, S., Luo, X.,
Chen, K., Liu, H., and Jiang, H., Indole derivatives as
potent inhibitors of 5-lipoxygenase: design, synthesis, bio-
logical evaluation, and molecular modeling. Bioorg. Med.
Chem. Lett. 17, 2414-2420 (2007).
Med. Chem., 44, 2621-2625 (2009).
Rohini, R., Reddy, P. M., Shanker, K., and Ravinder, V.,
New mono, bis-2,2-(arylidineaminophenyl)benzimidazoles:
synthesis and antimicrobial investigation. Acta Chim.
Slov., 56, 900-907 (2009a).
Rohini, R., Shanker, K., Reddy, P. M., Ho, Y. P., and
Ravinder, V., Mono and bis-6-arylbenzimidazo[1,2-c]qui-
nazolines: a new class of antimicrobial agents. Eur. J. Med.
Chem., 44, 3330-3339 (2009b).