Synthesis of β-amino carbonyl derivatives of coumarin and benzofuran and evaluation of their biological activity

Article abstract of DOI:10.1007/s00044-013-0494-7

A series of β-amino carbonyl compounds containing coumarin (4a-h) and benzofuran (6a-i) moieties was synthesized by a three component Mannich reaction of 3-acetyl-2H-chromen-2-one (1) or 1-(1-benzofuran-2-yl) ethanone (5) with p-substituted aromatic aldehydes (2a-g) and aromatic amines (3a-b) in the presence of cerric ammonium nitrate as a catalyst. The newly synthesized compounds were screened for antimicrobial and antioxidant activities. Compounds 4b, 4e, 4f, 6f, 6g, and 6i showed microbial inhibition with minimal inhibition concentration ranging between 0.040 and 0.500 mg/mL, compounds 4b, 4c, 6c, 6e, and 6i showed promising free radical scavenging activity and compounds 4b, 4f, 6c, 6d, and 6h showed good chelating ability with Fe²⁺ ions. The synthesized compounds were studied for docking on the enzyme, glucosamine-6-phosphate synthase to predict the binding affinity and orientation at the active site of the receptor.

Full text of DOI:10.1007/s00044-013-0494-7

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res
DOI 10.1007/s00044-013-0494-7
ORIGINAL RESEARCH
Synthesis of b-amino carbonyl derivatives of coumarin
and benzofuran and evaluation of their biological activity
•
R. Kenchappa Yadav D. Bodke S. K. Peethambar
•
•
•
Sandeep Telkar Venkatesh K. Bhovi
Received: 1 September 2012 / Accepted: 11 January 2013
Ó Springer Science+Business Media New York 2013
Abstract A series of b-amino carbonyl compounds con-
taining coumarin (4a–h) and benzofuran (6a–i) moieties
was synthesized by a three component Mannich reaction of
3-acetyl-2H-chromen-2-one (1) or 1-(1-benzofuran-2-yl)
ethanone (5) with p-substituted aromatic aldehydes (2a–
g) and aromatic amines (3a–b) in the presence of cerric
ammonium nitrate as a catalyst. The newly synthesized
compounds were screened for antimicrobial and antioxi-
dant activities. Compounds 4b, 4e, 4f, 6f, 6g, and 6i
showed microbial inhibition with minimal inhibition con-
centration ranging between 0.040 and 0.500 mg/mL,
compounds 4b, 4c, 6c, 6e, and 6i showed promising free
radical scavenging activity and compounds 4b, 4f, 6c, 6d,
and 6h showed good chelating ability with Fe2? ions. The
synthesized compounds were studied for docking on the
enzyme, glucosamine-6-phosphate synthase to predict the
binding affinity and orientation at the active site of
the receptor.
Keywords Cerric ammonium nitrate ꢀ b-amino ketones ꢀ
Antimicrobial ꢀ Antioxidant ꢀ
Glucosamine-6-phosphate synthase
Introduction
Derivatives of coumarin and benzofuran have been found to
exhibit a variety of biological and pharmacological activities
and have raised considerable interest because of their
potential effects on human health (Kennedy and Thornes,
1997; Hoult and Paya, 1996). Coumarin, the potent basic
pharmacodynamic nucleus, has been reported to possess a
wide variety of biological properties, viz., antibacterial,
antifungal, antioxidant (Melagraki et al., 2009), anti-
inflammatory, analgesic, anticancer, anthelmintic, and anti-
convulsant (Sandhya et al., 2011). Benzo[b]furan deriva-
tives have been an important class of organic compounds
which are known to be present in many natural products and
possess physiological activity (Venkatesh et al., 2010). Most
of the compounds prepared from 2-acetylbenzofurans have
antimicrobial, antitumor, anti-inflammatory, fungicidal,
weed-killing activity, and were used for treatment of cardiac
arrhythmias (Basawaraj et al., 2001; Abdel-Wahab et al.,
2009; Dawood et al., 2006).
R. Kenchappa ꢀ Y. D. Bodke (&) ꢀ V. K. Bhovi
Department of P.G. Studies and Research in Industrial
Chemistry, Jnana Sahyadri, Kuvempu University
Shankaraghatta, Shivamogga 577451, Karnataka, India
e-mail: yd_bodke@yahoo.co.in; ydbodke@gmail.com
In recent years, cerium ammonium nitrate has been
employed as a multipurpose promoter for a wide range of
synthetically useful reactions (Hong-Juan Wang et al.,
2011). However, most examples require stoichiometric
quantities of CAN (Sridharan and Menendez, 2010). Ceric
ammonium nitrate has emerged as an important reagent for
the construction of carbon–carbon and carbon–heteroatom
bonds. In addition, many advantages such as solubility in
water, cost-effectiveness, eco-friendly nature, easy han-
dling, high reactivity, and facile work-up procedures made
S. K. Peethambar
Department of P.G. Studies and Research in Biochemistry, Jnana
Sahyadri, Kuvempu University, Shankaraghatta, Shivamogga
577451, Karnataka, India
S. Telkar
Department of P.G. Studies and Research in Biotechnology,
Jnana Sahyadri, Kuvempu University, Shankaraghatta,
Shivamogga 577451, Karnataka, India
123

Med Chem Res
CAN an efficient catalyst in organic synthesis. Besides,
CAN can catalyze various organic transformations not only
based on its electron transfer capacity but also with its Lewis
acidic property (Mazaahir et al., 2008). b-Amino carbonyl
compounds obtained from Mannich reaction have been
known to be crucial intermediates in the synthesis of phar-
maceutical ingredients and natural products (Muller et al.,
1999a, b). Therefore, much consideration has been drawn for
the development of new synthetic methods to prepare these
compounds. In view of the above facts and in continuation of
our work on the synthesis of biologically active compounds
(Sheelavanth et al., 2012; Chandrashekar et al., 2012), we
have made an attempt to synthesize a highly atom-economic
functionalized b-amino carbonyl compounds of coumarin
and benzofuran by one-pot, three component reaction using
CAN as an efficient catalyst. These compounds were eval-
uated for their pharmacological activity with the belief that
the assimilation of more than one bio-potent nucleus into a
single structure may furnish novel heterocycles with stim-
ulating antimicrobial and antioxidant activity.
presence of catalytic amount of CAN. In the initial studies,
this reaction was performed using common Lewis acid
such as ZnCl2, CuCl2, AlCl3, FeCl3 LaCl3, InCl3, and
CAN. Among these, CAN was found to be the most effi-
cient catalyst for this transformation resulting in the highest
conversion to the desired product.
Characterization data of the synthesized compounds
4a–h and 6a–i have been given in Table 1.
With the intention to optimize the reaction condition,
experiments were focused on the effect of solvents on
reaction time (Table 2, entries 1–5).Methonal, Ethanol,
acetonitrile, water, and solvent-free media were tried, and
ethanol was observed to be the preferred solvent in this
reaction.
We also studied the amount of CAN catalyst required to
get the desired compounds in good yield. In general, there
was no reaction in the absence of catalyst using 1 equivalent
of benzaldehyde, 1 equivalent of 3-acetyl-2H-chromen-2-
one, 1 equivalent of aniline, and variable amount of CAN,
the experiments showed that 10 mol% of CAN (based on
benzaldehyde) could effectively catalyze the reaction.
Increase in the amount of CAN (20 mol%) had no sub-
stantial improvement in the yield (Table 3). The optimum
ratio of benzaldehyde, 3-acetyl-2H-chromen-2-one, aniline,
and CAN was found to be 1:1:1:0.1, respectively. Encour-
aged from the above results, we extended this method for the
synthesis of 1-(1-benzofuran-2-yl)-3-phenyl-3-(phenylami-
no) propan-1-one (6a–i) derivatives. The optimum ratio of
benzaldehyde, 1-(1-benzofuran-2-yl) ethanone, aniline, and
CAN was found to be 1:1:1:0.07, respectively. Effects of
solvents and reaction conditions for the synthesis of 1-(1-
benzofuran-2-yl)-3-phenyl-3-(phenyl amino) propan-1-one
(6a–i) derivatives have been given in Table 3.
Based on the promising in vitro antimicrobial results,
comparative and automated docking studies with newly
synthesized compounds were performed to determine the
best in silico conformation. The molecular docking studies
were performed to compassionate coordination between in
silico studies with in vitro results considering GlcN6P
synthase as the target receptor.
Results and discussion
Chemistry
The synthetic pathways leading to the b-amino carbonyl
compounds have been described in the Scheme 1 and
Scheme 2. The starting material (1) was synthesized
according to the known method (Vijesh et al., 2010). Cou-
marin (4a–h) and benzofuran (6a–i) containing b-amino
carbonyl derivatives were synthesized through one-pot,
three component reaction between p-substituted aromatic
aldehydes, aromatic amines, and 3-acetyl-2H-chromen-2-
one (1) or 1-(1-benzofuran-2-yl) ethanone (5) in the
The structures of the newly synthesized compounds
were confirmed by IR, NMR, and LCMS spectral data.
Pharmacology
In vitro antibacterial and antifungal activity
The newly synthesized compounds were screened for their
antibacterial and antifungal activity by agar well diffusion
Scheme 1 Synthesis of 3-[3-
phenyl-3-(phenylamino)
propanoyl]-2H-Chromen-2-one
derivatives 4a–h
O
R1
O
EtOH, 10 mol% CAN
O
NH
+
+
60 oC
O
O
O
O
R1
R
NH2
3a-b
1
2a-g
4a-h
R
R = H, CH3, OCH3, Cl, F, NO2, N(CH3)2
R1 = H, COOH
123

Med Chem Res
Scheme 2 Synthesis of 1-(1-
benzofuran-2-yl)-3-phenyl-3-
(phenylamino) propan-1-one
derivatives 6a–i
R
R1
O
O
EtOH, 7mol% CAN
60 oC
+
+
O
NH
O
R1
O
NH2
R
5
2a-g
6a-i
3a-b
R = H, CH3, OCH3, Cl, F, NO2, N(CH3)2
R1 = H, COOH
Table 1 Characterization data of synthesized compounds 4a–h and 6a–i
Entry
Compd. no.
R
R1
Yield (%)
Color
m.p. (°C)
Mol. formula/Mol.wt.
C24H19NO3/369
1
4a
4b
4c
4d
4e
4f
H
H
79
90
86
83
85
76
91
75
83
79
89
77
84
76
81
75
87
Yellow solid
Colorless
160–163
162–165
158–162
160–164
165–169
161–164
75–80
2
H
COOH
COOH
COOH
COOH
COOH
COOH
COOH
H
C25H19NO5/413
3
CH3
OCH3
Cl
Off-white solid
Colorless
C26H21NO5/427
C26H21NO6/443
4
5
Off-white solid
Pale yellow solid
Colorless
C
25H18ClNO5/447
25H18FNO5/431
6
F
C
7
4g
4h
6a
6b
6c
6d
6e
6f
NO2
N(CH3)2
H
C25H18N2O7/458
C27H24N2O5/456
8
Brown solid
Green solid
155–158
95–98
9
C
23H19NO2/341
C24H21NO3/371
24H19NO4/385
10
11
12
13
14
15
16
17
OCH3
H
H
Brown solid
Yellow solid
Pale yellow solid
Brown solid
Colorless
101–105
90–95
COOH
COOH
COOH
COOH
COOH
COOH
COOH
C
OCH3
CH3
Cl
99–103
110–114
107–110
103–106
105–108
110–114
C25H21NO5/415
C25H21NO4/399
C
24H18ClNO4/419
24H18FNO4/403
6g
6h
6i
F
Brown solid
Pale yellow solid
Brown solid
C
NO2
N(CH3)2
C24H18N2O6/430
C26H24N2O4/428
active against E. coli; compound 6i against E. coli. and S.
aureus with MIC value 0.05 mg/mL; compounds 4e and 6i
were most active against P. aeruginosa with MIC value of
0.04 mg/mL, whereas compounds 4f, 6f, and 6 g were
active against E. coli, S. aureus, and P. aeruginosa with
MIC value ranging between 0.10 and 0.14 mg/mL.
Antifungal activity results indicated that compounds 4e,
6f, and 6i were active against A. flavus, C. keratinophilum,
C. albicanas with MIC ranging between 0.040 mg/mL and
0.050 mg/mL; compounds 4b, 4f, and 6 g showed varying
level of MIC ranging between 0.10 and 0.50 mg/mL
against the tested fungal strains. The compounds 4c and 4h
were inactive against C. keratinophilum, C. albicanas;
compound 6d was inactive against C. albicanas and com-
pounds 4d, 6b, and 6e are inactive against all the tested
organisms. The antimicrobial and MIC values have been
given in Table 4. The results of the antimicrobial screening
lead the following conclusion about the structural activity
relationship (SAR).
Table 2 Effect of solvent on the synthesis of compounds 4a–h and
6a–i
(4a–h) Derivatives
(6a–i) Derivatives
Entry Solvent Time Yield Entry Solvent Time Yield
(h)
(h)
(%)
(%)
1
2
3
4
5
MeOH
EtOH
15
7
55
91
63
45
38
1
2
3
4
5
MeOH
EtOH
16
7
52
89
60
42
39
CH3CN 12
H2O 18
CH3CN 13
H2O 17
Solvent 12
free
Solvent 14
free
method (Nasser Khalil et al., 2010). Furthermore, the
compounds which showed good zone of inhibition were
studied for minimum inhibitory concentration (MIC) to
quantify the antimicrobial potency of these compounds.
The investigation revealed that compounds 4b and 6i were
123

Med Chem Res
Table 3 Synthesis of compounds 4a and 6a at different molar ratio of catalyst and reactants
Compound 4a Compound 6a
Entry PhCOCH3 (mmol) PhNH2 (mmol) CAN (mmol) Yield % Entry PhCOCH3 (mmol) PhNH2 (mmol) CAN (mmol) Yield %
1
1.0
1.0
1.0
1.0
1.0
1.0
1.2
1.5
2.5
5.0
1.0
1.0
1.0
1.0
1.1
1.2
1.5
1.0
1.0
1.0
1.0
1.0
0.05
0.10
0.20
0.10
0.10
0.10
0.10
0.10
0.10
0.10
None
56
1
2
1.0
1.0
1.0
1.0
1.0
1.0
1.2
1.5
2.5
5.0
1.0
1.0
1.0
1.0
1.1
1.2
1.5
1.0
1.0
1.0
1.0
1.0
0.05
0.07
0.20
0.10
0.10
0.10
0.10
0.10
0.10
0.10
None
50
2
91
89
3
69
3
62
4
66
4
66
5
39
5
40
6
49
6
42
7
55
7
55
8
45
8
41
9
33
9
39
10
11
25
10
11
28
Trace
Trace
Table 4 Zone of inhibition and MIC values of compounds 4a–h and 6a–i
Zone of inhibition in mm (50 mg/mL)
Minimum inhibitory concentration (MIC mg/mL)
Comp E.c.
S.a.
P.a.
A.f.
C.k.
C.a.
E.c.
S.a.
P.a.
A.f.
C.k.
C.a.
4a
4b
4c
04 0.2 05 0.2 01 0.2 04 0.1 03 0.1 07 0.2 0.500
10 0.2 11 0.2 12 0.2 11 0.2 13 0.1 17 0.2 0.050
0.500
0.100
0.500
–
0.350
0.150
0.500
–
0.450
0.250
0.450
–
0.550
0.200
–
0.300
0.150
0.500
–
01 0.1 03 0.1 03 0.1 01 0.2
–
–
01 0.2 0.500
4d
4e
–
–
–
–
–
–
–
13 0.2 11 0.2 13 0.2 11 0.2 15 0.1 19 0.2 0.050
12 0.2 10 0.2 12 0.2 10 0.1 12 0.2 18 0.2 0.100
03 0.1 03 0.1 06 0.1 05 0.1 06 0.1 04 0.1 0.500
0.050
0.120
0.500
0.550
0.500
–
0.040
0.100
0.430
0.400
0.500
–
0.040
0.230
0.250
0.450
0.500
–
0.040
0.200
0.350
–
0.050
0.100
0.500
0.500
0.500
–
4f
4g
4h
6a
03 0.2 02 0.1 03 0.2 01 0.2
–
01 0.2 0.500
01 0.1 01 0.1 01 0.1 02 0.2 01 0.1 02 0.2 0.500
0.500
–
6b
6c
–
–
–
–
–
–
–
03 0.2 03 0.2 03 0.2 03 0.2 02 0.2 02 0.1 0.500
0.450
0.500
–
0.500
0.500
–
0.500
0.500
–
0.500
0.500
–
0.400
–
6d
6e
03 0.1 01 0.1 01 0.1 01 0.1 02 0.2
–
–
0.500
–
–
–
–
–
–
–
6f
09 0.2 08 0.1 07 0.1 07 0.2 13 0.1 17 0.2 0.120
05 0.2 06 0.2 09 0.2 09 0.1 12 0.1 18 0.1 0.300
03 0.2 03 0.2 03 0.2 03 0.2 02 0.2 02 0.1 0.500
13 0.1 11 0.2 10 0.1 10 0.2 12 0.8 19 0.1 0.050
0.130
0.140
0.400
0.060
0.030
–
0.140
0.140
0.500
0.040
0.030
–
0.040
0.130
0.550
0.040
–
0.040
0.150
0.500
0.100
–
0.050
0.100
0.450
0.050
–
6g
6h
6i
Stnda
Stndb
14 0.1 12 0.2 13 0.2
–
–
–
0.030
–
–
–
–
10 0.1 14 0.2 20 0.2
0.040
0.040
0.040
Each value is expressed as mean SD of three replicates for zone of inhibition
Stnda: Streptomycin, Stndb: Fluconazole
E.c Escherichia coli(NCTC 12923), S.a Staphylococcus aureus (NCTC10788), P.a Pseudomonas aeruginosa(ATCC 27853), A.f Aspergillus
flavus, C.k Chrysosporium keratinophilum, C.a Candida albicans (NCPF 3179)
The substituents where R=H, Cl, F, N (CH3)2 at the
p-position plays a key role in varying the efficacy of anti-
microbial activity (Ansari and Lal, 2009; Deepika et al.,
2009; Silvia et al., 2001; Yuefen et al., 2006). The cou-
marin and benzofuran moieties in the Mannich bases dis-
played good antimicrobial activity against the tested
123

Med Chem Res
Fig. 1 Interaction of ligand
molecules 4b, 4e, 4f, 6f, 6g, and
6i with GlcN-6-P. a interaction
of 4b with GlcN-6-P,
b interaction of 4e with GlcN-6-
P, c interaction of 4f with GlcN-
6-P, d interaction of 6f with
GlcN-6-P, e interaction of 6g
with GlcN-6-P, f interaction of
6i with GlcN-6-P, g interaction
of Fluconazole with GlcN-6-P,
h interaction of Streptomycin
with GlcN-6-P (in all images the
ligands are represented in green
color and the target protein
GlcN-6-P in Secondary
structure and secondary
colorization)
pathogens. The introduction of electron withdrawing group
Cl or F in the Mannich base led to a significant increase in
activity compared to an electron-donating CH3 group. The
role of electron-withdrawing group in improving antimi-
crobial activities had been reported in the literature
(Sharma et al., 2004). Interestingly, the presence of an
electron withdrawing group NO2 in both the series (4a–h,
6a–i) had no effect on antimicrobial activity.
ligand to substantiate the experimental results. Theoreti-
cally, all the tested ligand molecules showed encouraging
binding energy and the compounds have exhibited the
bonding with one or the other amino acids in the active
pockets as shown in Fig. 1.
The docking study of GlcN-6-P synthase with 4b, 4e, 4f,
6f, 6g, and 6i showed that compounds 4b, 4f, and 6i with
binding energy -6.8, -7.06, and -6.85 kJ mol-1
,
respectively, can be predicted as good bacterial inhibitors
and compounds 4b, 4e, and 6i with binding energy -6.8,
-6.05, and -6.85 kJ mol-1, respectively, as good fungal
inhibitors. Image 4e showing two hydrogen bonds between
carboxylic OH and ser 347, one hydrogen bond between
carboxylic OH and Cys300 amino acids in the active site of
the target protein with least binding energy
(6.05 kJ mol-1) has the highest affinity, and hence it has
In silico molecular docking studies
The newly synthesized Mannich bases 4b, 4e, 4f, 6f, 6g,
and 6i were analyzed for their mechanism of antimicrobial
action using GlcN-6-P synthase. The estimated binding
energy for each molecule was compared with the crucial
hydrogen and hydrophobic bonds between the protein and
123

Med Chem Res
Table 5 Binding energy (kJ mol-1) and inhibition constant (lM)
Compound
Binding energy (kJ mol-1
)
Inhibition constant lM
4b
-6.8
10.4
22.19
6.64
4e
-6.05
-7.06
-7.85
-7.1
4f
6f
5.75
6g
6.29
6i
-6.85
6.72
9.48
Streptomycin
Fluconazole
11.82
127.35
-5.31
Fig. 2 Ferrous ion chelating assay (%) of test compounds
the best dock conformation. Binding energy and inhibition
constants are given in Table 5.
6f, and 6g) on phenyl ring decreased the antioxidant
property, whereas they have shown better antimicrobial
activity.
Antioxidant activity
Free radical scavenging activity by DPPH method
The newly synthesized compounds were tested for 1,1-
diphenyl-picrylhydrazyl (DPPH) radical scavenging activ-
ity having Butylatedhydroxytoluene (BHT) as standard and
the results have been given in Table 6. Compounds 4b, and
6i with electron-donating N(CH3)2 group showed the
highest level of assay (64.6 and 67.2 %, respectively). The
incorporation of electron-withdrawing groups (4e, 4f, 4g,
Iron-chelating ability
The iron-chelating capacity test measures the ability of
antioxidants to compete with ferrozine in chelating ferrous
ion (Elmastas et al., 2006). It was reported that the com-
pounds containing two or more functional groups like OH,
SH, COOH, C=O, NR2, and O in a favorable structure–
function configuration can show the activity of metal
chelation (Yuan et al., 2005). The ferrous ion-chelating
activity of the newly synthesized compounds is represented
in Fig. 2. The range and mean of Fe?2 chelating capacities
varied significantly among the different compounds on the
basis of substitution on the phenyl ring. Compounds 4b and
6c showed good chelating ability (64.3 and 69.6 %,
respectively). Though compounds 4c, 6g, and 6i showed
relatively high free radical scavenging activity, they had
lower ferrous ion chelating capability compared to standard
(EDTA).
Table 6 DPPH assay of synthesized compounds 4a–h and 6a–i
Compounds
DPPH assay (%)
4a
4b
4c
4d
4e
4f
25.3 0.265
64.6 0.630
52.5 0.402
18.1 0.169
34.7 0.730
35.2 0.260
15.3 0.251
12.3 0.864
28.7 0.453
27.3 0.325
52.2 0.189
14.2 0.469
54.1 0.623
31.2 0.532
36.25 0.842
29.1 0.359
67.2 0.623
90.01 0.469
4g
4h
6a
6b
6c
6d
6e
6f
Experimental procedure
Chemistry
General procedure for the synthesis of compounds (4a–h)
An equimolar quantity of 3-acetyl-2H-chromen-2-one (1)
6g
6h
6i
(0.0026 mol),
p-substituted
aromatic
aldehyde
(0.0026 mol), and aromatic amine (0.0026 mol) in ethanol
(50 mL) was taken in 100-mL round bottom flask and
stirred at 60 °C. To this, 10 mol% of cerric ammonium
nitrate was added and the stirring was continued for 6 h.
BHT
Each value is expressed as mean SD of three replicates
BHT butylatedhydroxytoluene used as standard
123

Med Chem Res
The progress of reaction was monitored by TLC. After
completion of the reaction, the reaction mixture was cooled,
poured into crushed ice, and neutralized using 10 %
NaHCO3 solution. The precipitated product was filtered,
dried, and recrystallized from ethanol. The product was
further purified by silica gel column chromatography eluting
with petroleum ether, ethyl acetate mixture (80:20, v/v).
(C=O of carboxylic), 1678 (coumarin C=O), 1695 (free
1
C=O); H NMR (400 MHz, DMSO, d ppm): 10.76 (s, 1H,
OH), 7.86 (d, J = 9 Hz, 2H, Ar–H), 7.43–7.32 (m, 5H),
7.26 (d, J = 8.6 Hz, 2H), 7.24 (d, J = 8.5 Hz, 2H), 6.48 (d,
J = 7.56 Hz, 2H), 5.42 (t, J = 6.87 Hz, 1H, CH), 4.3 (br s,
1H, NH), 3.47 (dd, J1 = 6.5 Hz, J2 = 13.0 Hz), 2.27 (s,
3H); 13CNMR (300 MHz, DMSO, d ppm): 200.21 (C=O),
195.61, 175.78, 173.74, 171.54, 169.09 (C=O, carboxylic),
162.74, 155.61, 153.53, 142.00, 140.10, 136.00, 132.20,
130.78, 118.17, 114.06, 52.00, 45.03, 34.20; MS (LCMS):
m/z 444 [M ? 1].
3-[3-Phenyl-3-(phenyl amino) propanoyl]-2H-chromen-2-
one (4a) IR (KBr, t cm-1): 3290 (NH), 2850 (Ar–CH),
1677 (coumarin C=O), 1710 (C=O free ketone); H NMR
1
(400 MHz, DMSO, d ppm) 7.93 (d, J = 9.2 Hz, 2H, Ar–
H), 7.54–7.0 (m, 10H), 7.03 (t, J = 7.6 Hz, 2H), 6.63 (t,
J = 7.4 Hz, 1H), 4.43 (t, J = 6.64 Hz, 1H, CH), 4.3 (br s,
1H, NH), 3.42 (dd, J1 = 6.8, J2 = 13.3 Hz); 13CNMR
(300 MHz, DMSO, d ppm): 200.01 (C=O), 194.61, 174.78,
173.74, 172.54, 162.74, 158.61, 153.53, 151.17, 140.88,
140.10, 133.20, 130.78, 119.97, 118.17, 116.50, 108.20,
107.78, 64.00, 45.00; MS (LCMS): m/z 370 [M ? 1].
4-{[1-(4-Chlorophenyl)-3-oxo-3-(2-oxo-2H-chromen-3-yl)
propyl]amino}benzoic acid (4e) IR (KBr, t cm-1): 3327
(O–H), 3200 (NH), 2855 (Ar–CH), 1740 (C=O of car-
boxylic), 1677 (coumarin C=O), 1680 (free C=O); 1H
NMR (400 MHz, DMSO, d ppm): 10.68 (s, 1H, OH), 7.83
(d, J = 8.6 Hz, 2H, Ar–H), 7.41–7.29 (m, 5H), 7.28 (d,
J = 8.6 Hz, 2H), 7.24 (d, J = 8.5 Hz, 2H), 6.48 (d,
J = 7.56 Hz, 2H), 4.72 (t, J = 4.93 Hz, 1H, CH), 4.3 (br s,
1H, NH), 3.47 (dd, J1 = 6.5 Hz, J2 = 13.0 Hz); 13CNMR
(300 MHz, DMSO, d ppm): 200.40 (C=O), 194.61, 174.78,
173.74, 172.54, 170.09 (C=O, carboxylic), 162.74, 158.61,
153.53, 142.00, 140.10, 137.00, 133.20, 130.78, 129.06,
127.03, 114.17, 64.00, 45.00; MS (LCMS): m/z 449 [M],
451[M ? 2].
4-{[3-Oxo-3-(2-oxo-2H-chromen-3-yl)-1-phenylpropyl]
amino} benzoic acid (4b) IR (KBr, t cm-1): 3463 (O–H),
3280 (NH), 2850 (Ar–CH), 1773 (C=O of carboxylic),
1677 (coumarin C=O), 1695 (free C=O); 1H NMR
(400 MHz, DMSO, d ppm): 10.41 (s, 1H, OH), 7.87 (d,
J = 9 Hz, 2H, Ar–H), 7.41–7.30 (m, 5H), 7.21–7.01 (m,
5H), 6.48 (d, J = 7.56 Hz, 2H), 4.45 (t, J = 5.72 Hz, 1H,
CH), 4.2 (br s, 1H, NH), 3.41 (dd, J1 = 6.9 Hz,
J2 = 13.4 Hz); 13CNMR (300 MHz, DMSO, d ppm):
200.33 (C=O), 194.61, 174.78, 173.74, 172.54, 170.09
(C=O, carboxylic), 162.74, 158.61, 153.53, 142.00, 140.10,
137.00, 133.20, 130.78, 129.03, 119.97, 118.17, 107.78,
64.00, 45.00; MS (LCMS): m/z 413.
4-{[1-(4-Fluorophenyl)-3-oxo-3-(2-oxo-2H-chromen-3-yl)
propyl]amino}benzoic acid (4f) IR (KBr, t cm-1): 3325
(O–H), 3270 (NH), 2865 (Ar–CH), 1743 (C=O of car-
boxylic), 1683 (coumarin C=O), 1681 (free C=O); 1H
NMR (400 MHz, DMSO, d ppm): 10.65 (s, 1H, OH), 7.85
(d, J = 8.4 Hz, 2H, Ar–H), 7.41–7.26 (m, 5H), 7.27 (d,
J = 8.6 Hz, 2H), 7.26 (d, J = 8.5 Hz, 2H), 6.70 (d,
J = 7.56 Hz, 2H), 4.75 (t, J = 4.93 Hz, 1H, CH), 4.6 (br s,
1H, NH), 3.43 (dd, J1 = 6.4 Hz, J2 = 12.30 Hz); 13CNMR
(300 MHz, DMSO, d ppm): d 200.39 (C=O), 194.61,
174.78, 173.74, 172.54, 170.09 (C=O, carboxylic), 162.74,
157.61, 153.53, 142.00, 140.10, 137.021, 133.20, 130.78,
129.06, 127.05, 114.17, 64.00, 45.00; MS (LCMS): m/
z 431 [M].
4-{[1-(4-Methylphenyl)-3-oxo-3-(2-oxo-2H-chromen-3-yl)
propyl]amino}benzoic acid (4c) IR (KBr, t cm-1): 3459
(O–H), 3250 (NH), 2851 (Ar–CH), 1740 (C=O of car-
boxylic), 1679 (coumarin C=O), 1699 (free C=O); 1H
NMR (400 MHz, DMSO, d ppm): 10.41 (s, 1H, OH), 7.87
(d, J = 9 Hz, 2H, Ar–H), 7.41–7.30 (m, 5H), 7.28 (d,
J = 8.7 Hz, 2H), 7.26 (d, J = 8.6 Hz, 2H), 6.48 (d,
J = 7.56 Hz, 2H), 5.42 (t, J = 6.87 Hz, 1H, CH), 4.0 (br s,
1H, NH), 3.41 (dd, J1 = 6.6 Hz, J2 = 13.2 Hz), 2.261 (s,
3H); 13CNMR (300 MHz, DMSO, d ppm): 200.40 (C=O),
195.61, 174.78, 173.74, 172.54, 171.09 (C=O, carboxylic),
163.74, 158.61, 153.53, 142.00, 141.10, 137.00, 131.20,
130.78, 129.03, 118.17, 114.06, 64.00, 45.00, 22.10; MS
(LCMS): m/z 425.
4-{[1-(4-Nitrophenyl)-3-oxo-3-(2-oxo-2H-chromen-3-yl)
propyl]amino}benzoic acid (4g) IR (KBr, t cm-1): 3459
(O–H), 3260 (NH), 2865 (Ar–CH), 1746 (C=O of car-
boxylic), 1678 (coumarin C=O), 1682 (free C=O), 1557
(NO2); 1H NMR (400 MHz, DMSO, d ppm): 10.74 (s, 1H,
OH), 7.84 (d, J = 8.6 Hz, 2H, Ar–H), 7.43–7.28 (m, 5H),
7.25 (d, J = 8.3 Hz, 2H), 7.27 (d, J = 8.5 Hz, 2H), 6.72 (d,
J = 7.55 Hz, 2H), 4.80 (t, J = 4.93 Hz, 1H, CH), 4.6 (br s,
1H, NH), 3.47 (dd, J1 = 6.5 Hz, J2 = 11.20 Hz, 2H);
13CNMR (300 MHz, DMSO, d ppm): 200.35 (C=O),
194.61, 175.78, 173.74, 171.54, 170.09 (C=O, carboxylic),
4-{[1-(4-Methoxyphenyl)-3-oxo-3-(2-oxo-2H-chromen-3-yl)
propyl]amino}benzoic acid (4d) IR (KBr, t cm-1): 3439
(O–H), 3310 (NH), 2855 (Ar–CH), 2850 (C–O–CH3), 1740
123

Med Chem Res
162.74, 157.61, 153.53, 142.00, 139.10, 137.021, 133.20,
130.78, 129.06, 127.05, 113.17, 64.00, 45.00; MS (LCMS):
m/z 459 [M ? 1].
7.83 (d, J = 9.3 Hz, 2H, Ar–H), 7.56–7.10 (m, 10H), 7.03
(t, J = 7.6 Hz, 2H), 6.61 (t, J = 7.2 Hz, 1H), 5.32 (t,
J = 6.56 Hz, 1H, CH), 4.6 (br s, 1H, NH), 3.45 (dd,
J1 = 6.5, J2 = 11.3 Hz, 2H); 13CNMR (300 MHz, DMSO,
d ppm): 200.40 (C=O), 193.61, 175.78, 174.74, 172.54,
163.74, 157.61, 153.53, 151.17, 140.88, 140.10, 133.20,
127.78, 119.97, 118.17, 115.50, 108.78, 64.00, 41.00; MS
(LCMS): m/z 341.
4-{[1-(4-Dimethylaminophenyl)-3-oxo-3-(2-oxo-2H-chro-
men-3-yl) propyl] amino} benzoic acid (4h) IR (KBr, t
cm-1): 3455 (O–H), 3310 (NH), 2860 (Ar–CH), 1741 (C=O
of carboxylic), 1675 (coumarin C=O), 1685 (free C=O); 1H
NMR (400 MHz, DMSO, d ppm): 10.74 (s, 1H, OH), 7.83 (d,
J = 8.9 Hz, 2H, Ar–H), 7.49–7.35 (m, 5H), 7.26 (d,
J = 8.4 Hz, 2H), 7.21 (d, J = 8.53 Hz, 2H), 6.49 (d,
J = 7.55 Hz, 2H), 5.28 (t, J = 6.91 Hz, 1H, CH), 4.6 (br s,
1H, NH), 3.47 (dd, J1 = 6.5 Hz, J2 = 13.0 Hz), 2.75 (s, 6H,
H3C–N–CH3); 13CNMR (300 MHz, DMSO, d ppm): 200.26
(C=O), 194.61, 175.78, 173.74, 171.54, 170.09 (C=O, car-
boxylic), 162.74, 157.61, 153.53, 142.00, 139.10, 137.021,
133.20, 130.78, 129.06, 127.05, 37.51, 34.20, 32.50, 22.10
(H3C–N–CH3); MS (LCMS): m/z 457 [M ? 1].
1-(1-Benzofuran-2-yl)-3-(4-methoxyphenyl)-3-(phenylami-
no)propan-1-one (6b) IR (KBr, t cm-1): 3280 (NH),
2858 (Ar–CH), 1701 (free C=O); 1H NMR (400 MHz,
DMSO, d ppm): 7.84 (d, J = 9.3 Hz, 2H, Ar–H),
7.45–7.33 (m, 5H), 7.31–7.28 (m, 5H), 6.48 (d,
J = 7.56 Hz, 2H), 4.49 (t, J = 5.71 Hz, 1H, CH), 4.8 (br s,
1H, NH), 3.41 (dd, J1 = 6.9 Hz, J2 = 13.4 Hz, 2H), 2.25
(s, 3H); 13CNMR (300 MHz, DMSO, d ppm): 200.40
(C=O), 193.61, 175.78, 174.74, 172.54, 163.74, 157.61,
153.53, 151.17, 142.20, 140.10, 133.20, 127.78, 119.50,
118.17, 115.50, 108.78, 60.50, 52.10, 41.80; MS (LCMS):
m/z 372 [M ? 1].
General procedure for the synthesis of compound (5)
Salicylaldehyde (0.08 mol) was taken in 50 mL of absolute
ethanol. To this, KOH (0.08 mol) pellets were added and the
reaction mixture was stirred for 5 min. Then, chloroacetone
(0.08 mol) was added drop-wise for about 10 min and the
resulting reaction mixture was stirred for 20 min. Catalytic
amount of potassium iodide was used in the reaction. The
mass was poured into the crushed ice, the solid obtained was
filtered, and recrystallized from ethanol to get pale yellow
crystalline solid. Yield: 93 %, m.p: 120–122 °C.
4-{[3-(1-Benzofuran-2-yl)-3-oxo-1-phenylpropyl]amino}
benzoic acid (6c) IR (KBr, t cm-1): 3455 (O–H), 3230
(NH), 2855 (Ar–CH), 1773 (C=O of carboxylic), 1693
(free C=O); 1H NMR (400 MHz, DMSO, d ppm): 10.43 (s,
1H, OH), 7.89 (d, J = 9.2 Hz, 2H, Ar–H), 7.48–7.30 (m,
5H), 7.32–7.29 (m, 5H), 6.46 (d, J = 7.51 Hz, 2H), 4.50 (t,
J = 5.71 Hz, 1H, CH), 4.6 (br s, 1H, NH), 3.43 (dd,
J1 = 6.6 Hz, J2 = 10.4 Hz, 2H); 13CNMR (300 MHz,
DMSO, d ppm): 200.30 (C=O), 195.61, 174.58, 173.70,
172.64, 170.01 (C=O, carboxylic), 162.74, 158.61, 153.53,
142.00, 140.10, 137.00, 133.20, 130.78, 129.03, 121.58,
118.17, 63.00, 42.00; MS (LCMS): m/z 386[M ? 1].
General procedure for the synthesis of compounds (6a–i)
In 100-mL round bottom flask, 1-(1-benzofuran-2-yl)etha-
none (5) (0.003 mol), p-substituted aromatic aldehyde
(0.003 mol) and aromatic amine (0.003 mol), and absolute
ethanol (50 mL) were taken and heated 60 °C. To this,
7 mol% CAN (Cerric ammonium nitrate) was added and the
stirring was continued for 5–6 h at that temperature. The
progress of the reaction was monitored by TLC. After
completion of reaction, the reaction mixture was cooled
poured into crushed ice and neutralized using 10 % NaHCO3
solution. The precipitated product was filtered, dried, and
recrystallized using ethanol. The product was subjected to
further purification by silica gel column chromatography
eluting with petroleum ether and ethyl acetate mixture
(80:20, v/v) to yield the b-amino carbonyl compounds (6a–
i). The structure of all the compounds was unambiguously
established on the basis of their spectral analysis.
4-(3-(Benzofuran-2-yl)-1-(4-methylphenyl)-3-oxopropyl-
amin)benzoic acid (6d) IR (KBr, t cm-1): 3420 (O–H),
3285 (NH), 2849 (Ar–CH), 1735 (C=O of carboxylic),
1
1697 (free C=O); H NMR (400 MHz, DMSO, d ppm):
10.86 (s, 1H, OH), 7.9 (d, J = 9.3 Hz, 2H, Ar–H),
7.48–7.30 (m, 5H), 7.25 (d, J = 8.8 Hz, 2H), 7.21 (d,
J = 8.3 Hz, 2H), 6.45 (d, J = 7.46 Hz, 2H), 5.45 (t,
J = 6.87 Hz, 1H, CH), 4.7 (br s, 1H, NH), 3.45 (dd,
J1 = 6.7 Hz, J2 = 11.6 Hz, 2H), 2.21 (s, 3H); 13CNMR
(300 MHz, DMSO, d ppm): 200.40 (C=O), 196.61, 175.78,
173.74, 172.54, 171.09 (C=O, carboxylic), 162.74, 157.61,
153.53, 142.00, 141.10, 137.00, 131.20, 130.78, 125.03,
123.10, 119.17, 114.06, 61.80, 41.80, 22.10; MS (LCMS):
m/z 400[M ? 1].
4-(3-(Benzofuran-2-yl)-1-(4-methoxyphenyl)-3-oxopro-
pylamino)benzoic acid (6e) IR (KBr, t cm-1): 3415 (O–
H), 3200 (NH), 2859 (Ar–CH), 1776 (C=O of carboxylic),
1-(1-Benzofuran-2-yl)-3-phenyl-3-(phenyl amino) propan-
1-one (6a) IR (KBr, t cm-1): 3300 (NH), 2850 (Ar–CH),
1695 (free C=O); H NMR (400 MHz, DMSO, d ppm):
1
123

Med Chem Res
1
4-(3-(Benzofuran-2-yl)-1-(4-(dimethylamino)phenyl)-3-oxo-
propylamino)benzoic acid (6i) IR (KBr, t cm-1): 3431
(O–H), 3265 (NH), 2870 (Ar–CH), 1721 (C=O of car-
1698 (free C=O); H NMR (400 MHz, DMSO, d ppm):
10.69 (s, 1H, OH), 7.93 (d, J = 9.5 Hz, 2H, Ar–H),
7.56–7.43 (m, 5H), 7.35 (d, J = 8.5 Hz, 2H), 7.29 (d,
J = 8.3 Hz, 2H), 6.48 (d, J = 7.50 Hz, 2H), 5.31 (t,
J = 7.03 Hz, 1H, CH), 4.9 (br s, 1H, NH), 3.49 (dd,
J1 = 6.3 Hz, J2 = 9.6 Hz, 2H), 2.31 (s, 3H); 13CNMR
(300 MHz, DMSO, d ppm): 200.40 (C=O), 195.61, 175.78,
173.74, 171.54, 169.09 (C=O, carboxylic), 162.74, 158.61,
153.53, 141.00, 132.20, 127.30, 119.07, 114.06, 91.40,
89.50, 60.80, 41.80, 34.20; MS (LCMS): m/z 416 [M ? 1].
1
boxylic), 1659 (free C=O); H NMR (400 MHz, DMSO, d
ppm): 10.53 (s, 1H, OH), 7.89 (d, J = 8.68 Hz, 2H, Ar–H),
7.52–7.38 (m, 5H), 7.29 (d, J = 8.43 Hz, 2H), 7.23 (d,
J = 8.56 Hz, 2H), 6.52 (d, J = 7.65 Hz, 2H), 5.29 (t,
J = 6.92 Hz, 1H, CH), 4.72 (br s, 1H, NH), 3.50 (dd,
J1 = 6.45 Hz, J2 = 11.10 Hz), 2.73 (s, 6H, H3C–N–CH3);
13CNMR (300 MHz, DMSO, d ppm): 200.40 (C=O),
196.61, 176.68, 173.74, 171.54, 170.09 (C=O, carboxylic),
161.74, 156.61, 153.53, 142.00, 139.10, 137.20, 136.021,
132.20, 130.78, 129.06, 114.00, 64.00, 44.60 (H3C–N–
CH3), 41.76; MS (LCMS): m/z 429 [M ? 1].
4-(3-(Benzofuran-2-yl)-1-(4-chlorophenyl)-3-oxopropylamin)
benzoic acid (6f) IR (KBr, t cm-1): 3450 (O–H), 3210
(NH), 2855 (Ar–CH), 1739 (C=O of carboxylic), 1620
(free C=O); 1H NMR (400 MHz, DMSO, d ppm): 10.41 (s,
1H, OH), 7.90 (d, J = 8.50 Hz, 2H, Ar–H), 7.71–7.59 (m,
5H), 7.48 (d, J = 8.61 Hz, 2H), 7.37 (d, J = 8.42 Hz, 2H),
6.54 (d, J = 7.64 Hz, 2H), 5.22 (t, J = 7.90 Hz, 1H, CH),
4.76 (br s, 1H, NH), 3.53 (dd, J1 = 6.6 Hz, J2 = 9.70 Hz,
2H); 13CNMR (300 MHz, DMSO, d ppm): 200.40 (C=O),
194.61, 174.78, 173.74, 172.54, 170.69 (C=O, carboxylic),
162.74, 158.61, 153.53, 142.00, 140.10, 137.00, 134.50,
130.78, 129.06, 127.03, 121.17, 63.00, 41.00; MS (LCMS):
m/z 419 [M], 421[M ? 2].
Pharmacology
The newly synthesized compounds have been screened for
their antimicrobial and antioxidant properties.
Antimicrobial activity
The newly synthesized compounds have been screened for
their antibacterial and antifungal activity by agar well
diffusion method. Gram-positive bacteria, Staphylococcus
aureus-ATCC 25923, and Gram-negative bacteria Esche-
richia coli ATCC 25922 and Pseudomonas aeruginosa
ATCC 27853 were used for antibacterial activity evalua-
tion. Antifungal activity was screened against three fungal
strains, Aspergillus flavus, Chrysosporium keratinophilum,
and Candida albicans MTCC227. Dimethylsulfoxide
(DMSO) was used as solvent control. The bacterial cultures
were inoculated on nutrient agar (Merck) and fungal cul-
ture was inoculated on Potato Dextrose agar media
(20 mL).
4-{[3-(1-Benzofuran-2-yl)-1-(4-fluorophenyl)-3-oxopropyl]
amino}benzoic acid (6g) IR (KBr, t cm-1): 3470 (br, O–
H), 3305 (narrow strong, NH), 2875 (Ar–CH), 1743 (C=O
of carboxylic), 1659 (free C=O); 1H NMR (400 MHz,
DMSO, d ppm): 10.68 (s, 1H, OH), 7.88 (d, J = 8.82 Hz,
2H, Ar–H), 7.44–7.30 (m, 5H), 7.28 (d, J = 7.9 Hz, 2H),
7.27 (d, J = 8.30 Hz, 2H), 6.73 (d, J = 7.82 Hz, 2H), 4.78
(t, J = 4.93 Hz, 1H, CH), 4.51(br s, 1H, NH), 3.45 (dd,
J1 = 6.91 Hz, J2 = 10.30 Hz, 2H); 13CNMR (300 MHz,
DMSO, d ppm): 200.40 (C=O), 193.61, 174.78, 173.74,
171.54, 170.90 (C=O, carboxylic), 161.74, 157.61, 153.53,
142.00, 140.10, 137.02, 134.50, 130.78, 129.36, 127.05,
121.17, 62.00, 42.00; MS (LCMS): m/z 403 [M].
The test compounds were dissolved in DMSO to get a
concentration of 1 mg/mL and 100 lL of this sample was
loaded into the wells of agar plates directly. Plates inocu-
lated with the bacteria were incubated at 37 °C for 24 h
and the fungal culture was incubated at 25 °C for 72 h. All
determinations were done in triplicates. Streptomycin (1
and 0.5 mg/mL) and Fluconazole (1 and 0.5 mg/mL) were
used as standard drugs for antibacterial and antifungal
activities, respectively. MIC was performed by serial
broth-dilution method at different concentrations like 1, 10,
25, and 50 mg/mL. After the incubation period, the Mini-
mum Inhibition zone at which the microorganism growth
was inhibited was measured in mm.
4-(3-(Benzofuran-2-yl)-1-(4-nitrophenyl)-3-oxopropylamin)
benzoic acid (6h) IR (KBr, t cm-1): 3439 (NH), 3250
(O–H), 2873 (Ar–CH), 1726 (C=O of carboxylic), 1667
1
(free C=O), 1552 (NO2); H NMR (400 MHz, DMSO, d
ppm): 10.54 (s, 1H, OH), 7.87 (d, J = 8.54 Hz, 2H, Ar–H),
7.46–7.32 (m, 5H), 7.28 (d, J = 8.92 Hz, 2H), 7.26 (d,
J = 8.42 Hz, 2H), 6.75 (d, J = 7.53 Hz, 2H), 4.93 (t,
J = 4.93 Hz, 1H, CH), 4.82 (br s, 1H, NH), 3.43 (dd,
J1 = 7.5 Hz, J2 = 10.20 Hz, 2H); 13CNMR (300 MHz,
DMSO, d ppm): 200.30 (C=O), 194.61, 175.78, 173.74,
170.89 (C=O, carboxylic), 162.74, 157.61, 149.00, 139.10,
137.02, 133.20, 130.78, 129.06, 127.05, 114.17, 65.00,
42.00; MS (LCMS): m/z 430.
In silico molecular docking studies
The compounds in the present investigation were subjected
for molecular docking studies using AutoDock (version
123

Med Chem Res
4.2) by means of Lamarckian genetic algorithm. The syn-
thesized ligand molecules having 2D structure were con-
verted to energy minimized 3D structures and were further
used for in silico protein–ligand docking. The docking of
receptor GlcN-6-P with newly synthesized ligands exhib-
ited well established bonds with one or more amino acids
in the receptor active pocket. The active pocket was con-
sidered to be the site where glucosamine-6-phosphate
complexes with GlcN-6-P of 2VF5. The active pocket
consisted of 12 amino acid residues as Ala602, Val399,
Ala400, Gly301, Thr302, Ser303, Cys300, Gln348, Ser349,
Thr352, Ser347, and Lys603 (Wallace et al., 1995).
The crystal structure of GlcN-6-P synthase (PDB ID
2VF5) from the PDB (http://www.pdb.org/pdb/home/
home.do) was selected and edited by removing the het-
eroatoms and adding C-terminal oxygen (Binkowski et al.,
2003). The Graphical User Interface program ‘‘AutoDock
Tools’’ was used to prepare, run, and analyze the docking
simulations. Kollman united atom charges, solvation
parameters, and polar hydrogens were added to the receptor
for the preparation of protein in docking simulation. Since
ligands are not peptides, Gasteiger charge was assigned and
then non-polar hydrogens were merged.
methanol was added to a solution of 2 mM FeCl2
(0.05 mL) and the reaction was initiated by adding 5 mM
ferrozine (0.2 mL) and total volume was adjusted to 5 mL
with methanol. Then, the mixture was shaken vigorously
and left at room temperature for 10 min. The absorbance of
the solution was measured spectrophotometrically at
562 nm. The inhibition percentage of ferrozine–Fe2?
complex formations was calculated by the formula:
ÂÀ
Á
Ã
Metal chelating effect ð%Þ ¼ Acontrol ꢁ Asample =Acontrol
ꢂ 100
where Acontrol is the absorbance of control (control contains
FeCl2 ferrozine complex) and Asample is the absorbance of
test compounds. Ascorbic acid is used as control.
Conclusion
We have synthesized new functionalized coumarin (4a–h) and
benzofuran (6a–i) Mannich bases by a three component
Mannich reaction in the presence of CAN as catalyst and
evaluated their antimicrobial and antioxidant properties.
The study showed that some of these compounds exhibited
promising antimicrobial and antioxidant activity. From the
structure activity relationship (SAR) studies it is evident
that the electron-withdrawing groups substituted on aro-
matic ring, particularly at the para position, exhibited
potential antimicrobial activity. This was further proved by
docking studies on GlcN-6-P that the oxygen atom present
in coumarin and benzofuran nucleus is responsible for
binding with different amino acids.
Antioxidant activity
Free radical scavenging activity by DPPH method
Free radical scavenging capacities of synthesized com-
pounds were determined according to the reported proce-
dure (Braca et al., 2001). 2 mL of freshly prepared DPPH
solution (0.004 %) was taken in different test tubes and
1 mL of test compounds were added (100 lg/mL) to
respective test tubes so that the final volume of the test tube
would be 3 mL. After 10 min, the absorbance was recorded
at 517 nm using a UV–Visible spectrophotometer (Shi-
madzu UV-1800, Japan). Butylatedhydroxytoluene (BHT),
dissolved in distilled water, was used as a reference.
Control sample was prepared using the same volume
without any compound and BHT, 95 % methanol served as
blank. Test was performed in triplicate and the results were
averaged. Radical scavenging activity was calculated by
the formula: % of radical scavenging activity = [(Acontrol
- Atest)/Acontrol] 9 100, where Acontrol is the absorbance of
the control sample (DPPH solution without test sample)
and Atest is the absorbance of the test sample (DPPH
solution ? test compound).
Acknowledgments The authors are thankful to the Department
of Industrial Chemistry, Kuvempu University, Shankaraghatta, for
providing the laboratory facilities. One of the authors (Kenchappa R.)
is thankful to the UGC for the award of Rajiv Gandhi National
Fellowship (RGNF).
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