Synthesis, characterization, and antimicrobial activity of new benzofuran derivatives

Article abstract of DOI:10.1134/S107036321612046X

A novel series of (5-substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)methanones (4a–4i) have been prepared by the Knoevenagel condensation of (5-substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)methanone (3a–3i) with Meldrum’s acid. The structu

Full text of DOI:10.1134/S107036321612046X

ISSN 1070-3632, Russian Journal of General Chemistry, 2016, Vol. 86, No. 12, pp. 2827–2836. © Pleiades Publishing, Ltd., 2016.
Synthesis, Characterization, and Antimicrobial Activity
of New Benzofuran Derivatives1
R. Kenchappaa, Yadav D. Bodkea*, Sandeep Telkarb, M. Aruna Sindhea, and M. Giridhara
a Department of P. G. Studies and Research in Industrial Chemistry, Jnana Sahyadri,
Kuvempu University Shankaraghatta, Shivamogga, Karnataka, 577451 India
*e-mail: ydbodke@gmail.com
b Department of P. G. Studies and Research in Biotechnology and Bioinformatics, Jnana Sahyadri,
Kuvempu University, Shankaraghatta, Karnataka, 577451 India
Received May 27, 2016
Abstract—A novel series of (5-substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)methanones (4a–4i)
have been prepared by the Knoevenagel condensation of (5-substituted-1-benzofuran-2-yl)(2,4-substituted
phenyl)methanone (3a–3i) with Meldrum’s acid. The structures of the synthesized compounds were
characterized by different spectroscopic techniques. All newly synthesized compounds were screened for
antimicrobial activity.
Keywords: benzofuran, meldrums acid, Knoevenagel condensation, antimicrobial, molecular docking
DOI: 10.1134/S107036321612046X
INTRODUCTION
reported to have antiviral, antioxidant and antifungal
activities [6, 7]. Recently, 2-benzylbenzofuran
derivatives have been identified to possess antitumor
activity [8, 9]. Due to the pioneering work of Foster
and others [10] on the study of substituted benzo[b]-
furan there is an ever increasing number of synthetic
approaches towards the construction of the 2-
substituted benzo[b]furan compounds.
In recent years, the mounting threat of bacterial
resistance has heightened the urgency of discover and
develop anti-ineffective agents with novel mechanism
of action and enhanced activity profile. Clinical use of
potent drugs is limited in many cases due to their
systemic side effects. To overcome the clinical
limitation, considerable research efforts have been
directed to the discovery of high potency local
antimicrobial agents with reduced systemic adverse
effects [1].
Meldrum’s acid derivatives have attracted consider-
able attention as valuable reagents and intermediates in
organic synthesis [11, 12]. It has been reported that
derivatives of Meldrum’s acid possess wide range of
biological activities such as antibiotic [13], HIV-1
integrase inhibitory activity, phytotoxicity, cytotoxi-
city and mammalian DNA binding [14–16], anti-
malarial, anticancer, insect antifeedant properties, and
other activities [17].
Heterocyclic compounds are commonly presented
in a wide range of natural products and biologically
active building blocks [2]. Among them oxygenated
metabolites have attracted the attention of many
chemists due to their potent activities and structural
activity [3].
Literature review revealed that insertion of pharma-
cophore at position 2 of benzofuran moiety enhances
its antituberculosis and antimicrobial activity [18, 19].
Prompted by these observations, and as a part of our
ongoing research in developing new biologically active
heterocycles [20–22], we hereby report the synthesis of
some new substituted benzofuran derivatives coupled
with Meldrum’s acid nucleus. These compounds were
evaluated for their antimicrobial and antioxidant
properties.
Benzofuran as a highly valuable molecular motif is
not only ubiquitous in the realm of pharmaceutically
active agents and in natural products but also
frequently utilized as synthetic block [4]. In particular,
2-substituted benzofurans belong to one of the most
studied structural units in both the synthetic and
medicinal chemistry fields [5]. They have been
1 The text was submitted by the authors in English.
2827

2828
KENCHAPPA et al.
Scheme 1. Synthesis of (5-substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)methanone (4a–4i) derivatives.
O
Br
O
R2
R
CHO
OH
R
K2CO3
+
CH3CN reflux
O
R2
R1
R1
1a−1c
2a−2c
3a−3i
O
O
Reflux
AcOH
O
O
R1
R2
R
O
O
O
O
O
4a−4i
R = H, R1 = Br, R2 = H (4a), R = H, R1 = OCH3, R2 = H (4b), R = Br, R1 = Br, R2 = H (4c), R = Br, R1 = OCH3, R2 = H (4d),
R = OH, R1 = Br, R2 = H (4e), R = OH, R1 = OCH3, R2 = H (4f), R = H, R1 = H, R2 = Br (4g), R = Br, R1 = H, R2 = Br (4h),
R = OH, R1 = H, R2 = Br (4i).
RESULTS AND DISCUSSION
compound 4e showed singlet at δ = 1.22 ppm due to
(CH3)2 protons and another singlet at δ = 5.64 ppm
corresponding to OH proton. Multiplet, observed
between δ = 7.03–7.92 ppm is due to aromatic protons.
Further, the formation of compound 4e was confirmed
by 13C NMR spectrum. The compound 4e showed a
signal at δ = 166.7 ppm assigned the C=O group of
Meldrum’s acid nucleus. Signal appeared at δ 25.4 ppm
corresponds to the (CH3)2 carbon. Mass spectrum of
compound 4e displayed a molecular ion peak M+ at m/z
442.10 corresponding to the molecular mass of the
compound and isotopic peak at m/z 444.30 [M + 2].
Chemistry. The present study described the
Knoevenagel condensation of (5-substituted-1-benzo-
furan-2-yl)(2,4-substituted phenyl)methanone (3a–3i)
with Meldrum’s acid. Initially (5-substituted-1-benzo-
furan-2-yl)(2,4-substituted phenyl)methanone under-
goes protonation by acetic acid. The protonated form
of the methanone then facilitates the addition reaction
towards a nucleophile. The acetate ion which was
formed in the former step can accept a proton from the
methylene unit of barbituric/thiobarbituric acid and
generate a carbanion. The electron-rich carbanion
attacks on the electron deficient carbonyl carbon of (5-
substituted-1-benzofuran-2-yl)(2,4-substituted phenyl)-
methanone to form an adduct which upon dehydration
furnished the target compounds (Scheme 1).
Biological activity. In vitro antibacterial and
antifungal activity. All newly synthesized compounds
4a–4i in the present investigation were evaluated for
their antimicrobial activity as primary screening at
three different concentrations and the results are
displayed in Table 1.
The plausible mechanism is shown in Fig. 1.
The IR spectrum of compound 4e displayed the
absorption bands at 1702 and 552 cm–1 due to C=O
and C–Br stretching frequency.1H NMR spectrum of
Antimicrobial screening revealed that all tested
compounds showed varying degree of activity against
all tested microorganisms.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

SYNTHESIS, CHARACTERIZATION, AND ANTIMICROBIAL ACTIVITY
O
2829
O
Br
R2
R
O
R
CHO
OH
K2CO3
+
O
R2
R1
R1
H
1a−1c
2a−2c
R2
O
R1
O
R
H
OH
−H2O
R1
O
R
H
R
O
AcOH
O
R2
O
R2
O
R2
R1
O
3a−3i
O
OH
CH3COO−
R1
H
O
H
O
O
O
+
−H2O
O
O
O
O
O
O
R
O
R2
R1
4a−4i
Fig. 1. Proposed reaction mechanism of synthesized compounds 4a–4i. R = H, Br, OH; R1 = Br, OCH3, R2 = Br.
Further, the compounds which showed good
activity in primary screening were assessed to
determine minimum inhibitory concentration (MIC) to
quantify the antimicrobial potency of the compounds.
The resulted MIC values are given in Table 2.
The investigation of the MIC values indicates that
all the compounds exhibited a varied degree of MIC
(15.25–195.50 μg/mL) of antibacterial activity. Com-
pound 4c displayed excellent antibacterial activity
against all the tested bacterial strains at MIC 14.80–
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2830
KENCHAPPA et al.
Table 1. Zone of inhibition of antibacterial and antifungal activity of synthesized compounds 4a–4i
Zone of inhibition in mm (mean±S.D.) (n = 3)
Comp.
no.
Antibacterial
Antifungal
P.s±S.Da S.t±S.Da B.s±S.Da K.p±S.Da E.c±S.Da
A.f±S.Da C.a±S.Da M.g±S.Da A.t±S.Da
4a
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
1.0
0.5
09±0.3
07±0.1
07±0.2
06±0.3
12±0.2
10±0.3
10±0.2
08±0.3
11±0.2
08±0.3
09±0.2
06±0.3
10±0.2
08±0.3
11±0.2
08±0.3
08±0.2
07±0.3
15±0.2
13±0.3
–
10±0.2
09±0.3
06±0.1
05±0.2
12±0.1
10±0.2
10±0.1
07±0.2
11±0.1
08±0.2
08±0.1
06±0.1
09±0.1
08±0.2
12±0.1
09±0.2
07±0.1
06±0.2
16±0.1
15±0.2
–
12±0.1
10±0.3
07±0.2
05±0.2
15±0.2
13±0.1
10±0.2
08±0.1
12±0.2
10±0.1
09±0.2
06±0.2
10±0.2
07±0.1
13±0.2
11±0.1
08±0.2
06±0.2
18±0.2
16±0.1
–
13±0.1
11±0.1
07±0.3
05±0.1
16±0.3
14±0.1
11±0.3
10±0.1
13±0.3
12±0.1
08±0.3
–
10±0.3
08±0.1
06±0.2
04±0.2
13±0.2
11±0.3
10±0.2
08±0.3
11±0.2
09±0.3
07±0.2
06±0.3
09±0.2
07±0.3
12±0.2
09±0.3
06±0.2
04±0.3
16±0.2
14±0.3
–
12±0.2
10±0.1
07±0.2
06±0.3
12±0.2
11±0.3
10±0.2
09±0.3
11±0.2
09±0.3
09±0.2
08±0.3
10±0.2
08±0.3
11±0.2
09±0.3
09±0.2
07±0.3
–
17±0.1
16±0.2
09±0.1
06±0.2
18±0.3
17±0.1
15±0.1
14±0.2
16±0.1
14±0.2
12±0.1
10±0.3
14±0.1
13±0.2
17±0.1
15±0.2
11±0.1
09±0.2
–
17±0.2
15±0.1
09±0.2
06±0.1
18±0.2
16±0.1
15±0.2
13±0.1
15±0.2
14±0.1
13±0.2
11±0.1
14±0.2
12±0.1
16±0.2
15±0.1
12±0.2
09±0.1
–
19±0.3
16±0.1
10±0.3
–
4b
4c
20±0.3
17±0.2
16±0.3
15±0.1
17±0.3
16±0.1
14±0.3
12±0.3
15±0.3
14±0.1
18±0.3
15±0.1
13±0.3
11±0.1
–
4d
4e
4f
4g
09±0.3
09±0.1
14±0.3
13±0.1
08±0.3
05±0.1
19±0.3
17±0.1
–
4h
4i
Standardb
Standardc
–
–
–
–
14±0.2
12±0.3
20±0.1
19±0.2
19±0.2
17±0.1
22±0.3
19±0.1
–
–
–
–
–
a Each value is expressed as mean±SD of three replicates for zone of inhibition. b Streptomycin. c Fluconazole.
16.0 μg/mL. Compound 4a showed good ability to
inhibit Pseudomonas syringe and Escherichia coli at
MIC 15.50–16.0 μg/mL. In case of compounds 4b and
4f having electron donating OH and OCH3 substituent
on C5 of benzofuran and Br substituent on C4 position
of aryl ring exhibited less activity.
against all the tested fungal strains with MIC value of
6.30–12.75 µmol/L. Compounds 4h and 4e showed
very good activity against the tested organisms with
MIC value 6.40–13.70 μg/mL. Compounds 4d and 4g
exhibited moderate activity against the tested fungal
strains. This activity can be rationalized on the basis of
effect of structural changes in the target compounds
4a–4i. When Br group is in o-position of aryl ring 4g,
4i, we found decrease in activity, signifying that the
The MICs of title compounds indicated that, the
compounds 4c and 4a exhibited equipotent activity
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

SYNTHESIS, CHARACTERIZATION, AND ANTIMICROBIAL ACTIVITY
2831
Table 2. Minimum inhibitory concentration (MIC) of compounds 4a–4i
Minimum inhibitory concentration (MIC µg/mL)
Comp. no
4a
15.50
120.35
14.80
60.25
30.25
–
15.80
125.40
15.25
55.75
25.25
70.35
110.35
16.75
115.35
14.50
–
16.50
195.50
15.75
–
16.50
125.55
16.00
32.85
–
16.00
185.30
15.75
38.65
40.25
85.35
185.35
17.50
175.35
15.25
–
12.70
–
12.75
35.50
12.60
15.80
13.70
23.50
31.45
12.80
32.80
–
6.35
22.50
6.30
9.75
8.35
18.50
24.70
6.45
20.50
–
6.50
4b
25.55
6.35
7.55
8.55
21.55
24.75
6.40
28.50
–
4c
12.60
16.85
12.85
21.65
–
4d
4e
20.25
85.25
95.25
17.50
195.25
15.50
–
4f
75.35
155.35
17.25
120.35
15.25
–
4g
4h
105.35
16.25
125.35
14.50
–
12.75
35.75
–
4i
Streptomycin
Flucanazole
12.50
12.50
6.25
6.25
presence of substituent in the o-position of the aryl ring
could bring in important steric effects. Interestingly,
compound 4h exhibited moderate activity even though
substituent presented on the o-position, this could be
due to the influence of electron withdrawing group
presented at C5 of benzofuran ring. Compounds
containing electron donating groups 4f and 4i were
found to have reduced antimicrobial activity. However,
when bromine is introduced to o-position of aryl ring
4i, the activity did not change significantly.
conformation of the docked molecules. All the
molecules that were subjected for molecular docking
represented at least one H-bond except 4h.
Figure 3 represents the 3D interaction of 4c with
gyrase by using educational version of PyMol
software. The ligands are represented in green colour,
H-bonds with their respective distances are represented
with cyan colour, and the interacting residues are
represented in ball and stick model representation.
Compound 4a forms three hydrogen bonds with
Thr302 Val605 and Thr352 amino acids in the active
site of the target protein with bond length 3.07, 3.22
and 3.06 Å respectively, with the highest affinity and
hence is considered as the best dock conformation.
Compound 4c forms two hydrogen bonds with Thr352
and Thr302 amino acids with bond length 3.00 and
3.06 Å. Compound 4e exhibited two hydrogen bonding
with bond length 2.83 and 3.03 with Thr302 and
Thr352 amino acids respectively. In this study all the
docked molecules 4a, 4c, 4e, and 4h showed more
hydrophobic interaction than the standard Strepto-
mycin and Fluconazole drugs. RMSD has often been
used to measure the quality of reproduction of a known
binding pose by molecules with ligands. All docked
molecules have zero RMSD values, this indicates that
the true binding pose of molecules with protein.
Computational analysis. In correlation to in vitro
antimicrobial activity, it thought worthwhile to carry
out in silico studies to predict the binding affinity and
orientation at the active site of the receptor. The
molecular docking of ligand molecules 4a, 4c, 4e, and
4h with GlcN-6-P synthase revealed that all the tested
ligand molecules showed encouraging binding energy
and the compounds exhibited hydrogen bonding with
one or the other amino acids in the active pockets as
shown in Fig. 2. The docked compounds 4a, 4c, 4e,
and 4h were found best docked confirmation with least
binding affinity (–7.0, –7.0, –6.9, and –7.0 kJ/mol)
(Table 3).
The docked molecules were subjected to 2D and
3D protein-ligand interaction analysis. Figure 2
represents the further extrapolation of binding
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2832
KENCHAPPA et al.
(a)
(b)
(d)
(f)
(c)
(e)
Fig. 2. 2D representation of the interaction of the synthesized molecules (a) 4a, (b) 4c, (c) 4e, (d) 4h, and standards (e) fluconazole
and (f) streptomycin with glucosamine-6-phosphate synthase.
EXPERIMENTAL
All the reactions were carried out under nitrogen
atmosphere. The Meldrum’s acid and phenacyl
bromides with 98% purity were purchased from Sigma
Aldrich Company. Melting points were recorded on
electro thermal melting point apparatus and are
uncorrected. Column chromatography was performed
using silica gel (230-400mesh), silica gel GF254 plates
from Merck were used for TLC and spots were
identified under ultraviolet radiation. Ethyl acetate:
petroleum ether (1 : 4) was used as a mobile phase. FT-
IR spectra were taken in KBr pellets (100 mg) using
1
Shimadzu FT-Infrared spectrophotometer. H NMR
and 13C NMR spectra were recorded on a Bruker
Fig. 3. 3D representation of the interaction of the synthesized
molecules 4c with glucosamine-6-phosphate synthase.
400 MHz spectrometer and chemical shifts (δ) are
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

SYNTHESIS, CHARACTERIZATION, AND ANTIMICROBIAL ACTIVITY
2833
Table 3. In silico molecular docking results of synthesized compounds 4a, 4c, 4e, 4h and standard drugs
Affinity,
kcal/mol
H-Bond
length, Å
Ligand
H-Bonds
3
H-Bond between
Hydrophobic interactions
–7.0
3.07
3.22
3.06
3.00
3.06
4a : OAW :: Thr302:N
Ala400, Val399, Lys603,
Ser349, Ser604, Gln348,
Glu488, Leu601, Ser347,
Ala602, Gly301, Cys300
4a
4a : OAX :: Val605:N
4a : OG1 :: Thr352:N
4c : OAT :: Thr352:N
4c : OAY :: Thr302:N
–7.0
2
Lys603, Ala400, Ala602,
Leu601, Glu488, Pro598,
Val605, Cys300, Val309,
Ser303, Ser604, Gln348,
Ser347, Gly301
4c
4e
–6.9
–7.0
2
0
2.83
4e : OAX :: Thr302:N
Val399, Ser303, Ser604,
Leu601, Ala400, Lys603,
Glu488, Ser343, Ala602,
Gly301, Gln348, Cys300
3.03
–
4e : OAW :: Thr352:OG1
–
Asp354, Val605, Ala602,
Cys300, Leu601, Gly301,
Ser303, Lus603, Thr302,
Ser401, Gln348
4h
Fluconazole
Streptomycin
–7.0
–7.0
2
2.80
3.22
Flu : OAL :: Cys300: O
Flu : OAL :: Thr302 : N
Ala602, Glu488, Ser303,
Gly301, Thr352, Ser401,
Ser347, Gln348
12
2.80
3.01
2.81
2.76
2.45
2.80
2.73
2.70
2.70
3.09
3.15
3.31
Str : OAN :: Gln348 : N
Str : OAN :: Ser347 : OG
Str : NBH :: Ser303 : OG
Str : OAQ :: Ser303 : N
Str : OAQ:: Cys300 : O
Str: OAQ :: Thr302 : N
Str : NAY:: Val399 : O
Str : O6 :: Thr302 : OG1
Str : O6 :: Glu488 : OE2
Str : O4 :: Val399 : O
Ser401, Ala404, Ser604,
Gly301, Lys603, Val605,
Leu601
Str : O4 :: Ala602 : O
Str : N2 :: Ala602 : O
shown in ppm with tetramethylsilane (TMS) as
internal standard. LC-MS were obtained using C18
column on Shimadzu, LCMS 2010A.
none (3a–3i). The key intermediates, (5-substituted-1-
benzofuran-2-yl)(2,4-substituted phenyl)methanone (3a–
3i) were synthesized by a known method [23, 24].
General procedure for the synthesis of (5-substi-
tuted-1-benzofuran-2-yl)(2,4-substituted phenyl)metha-
General procedure for the synthesis of 5-[(2,4-
disubstituted phenyl)(5-disubstituted-1-benzofuran-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2834
KENCHAPPA et al.
2-yl)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione
derivatives (4a–4i). The mixture of (5-substituted-1-
benzofuran-2-yl)(2,4-disubstituted phenyl) methanone
3a–3i (0.01 mol) and Meldrum’s acid (0.01 mol) was
taken in acetic acid and refluxed on an oil bath for
about 8–10 h at 110–115°C. After the completion of
reaction, the reaction mass was cooled to room
temperature, poured into crushed ice and neutralized
with NaHCO3 solution. The product was filtered, dried
and recrystallized using ethyl acetate/ethanol.
(KBr), νmax, cm–1: 2918 (Ar-CH), 1717 (C=O), 590
(C–Br). 1H NMR spectrum (400 MHz, DMSO), δ, ppm:
7.7–8.0 m (Ar-H), 3.32 s (3H, OCH3), 1.61 s [6H,
(CH3)2]. 13C NMR spectrum (400 MHz, DMSO), δ,
ppm: 164.7 (C=O), 162.3, 159.4, 157.3, 133.7, 131.4,
129.3, 127.4, 124.2, 117.9, 116.5, 114.3, 112.0, 106.3,
104.1, 55.9 (OCH3), 25.4. Found, %: C 57.82, H 3.72,
Br 17.50, O 20.96. C22H17BrO6. Calculated, %: C 57.79,
H 3.75, Br 17.47, O 20.99. (LCMS): m/z: 456 [M] 458
[M + 2].
5-[1-Benzofuran-2-yl(2-bromophenyl)methylidene]-
2,2-dimethyl-1,3-dioxane-4,6-dione (4a). Yellow solid.
5-[(4-Bromophenyl)(5-hydroxy-1-benzofuran-2-
yl)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione
(4e). Off-white solid. Yield 85%, mp 169–171°C. IR
spectrum (KBr), νmax, cm–1: 3439 (Ar-OH), 2955 (Ar-
Yield 79%, mp 160–162°C. IR spectrum (KBr), νmax
,
cm–1: 3120 (Ar-CH), 1715 (C=O), 587 (C–Br). H
NMR spectrum (400 MHz, DMSO), δ, ppm: 7.37–8.0
m (9H, Ar-H), 1.21 s [6H, (CH3)2]; 13C NMR spectrum
(400 MHz, DMSO), δ, ppm: 163.5 (C=O), 162.3,
159.4, 157.2, 138.4, 132.2, 129.4, 128.3, 127.1, 125.7,
124.7, 121.0, 117.9, 116.1, 112.4, 107.0, 104.1, 24.2.
Found, %: C 59.04, H 3.54, Br 18.70, O 18.72.
C21H15BrO5. Calculated, %: C 59.09, H 3.49, Br 18.73,
O 18.69. MS (LCMS): m/z 426 [M] 428 [M + 2].
1
1
CH), 1702 (C=O), 552 (C–Br). H NMR spectrum
(400 MHz, DMSO), δ, ppm: 7.03–7.92 m (8H, Ar-H),
5.64 s (1H, OH), 1.22 s [6H, (CH3)2]. 13C NMR
spectrum (400 MHz, DMSO), δ, ppm: 166.7 (C=O),
161.4, 155.3, 153.4, 150.0, 140.1, 133.7, 130.8, 129.8,
129.4, 118.9, 114.6, 111.0, 105.7, 104.3, 25.4. Found,
%: C 56.93, H 3.38, Br 18.00, O 21.69. C21H15BrO6.
Calculated, %: C 56.90, H 3.41, Br 18.03, O 21.66.
(LCMS): m/z: 442 [M] 444 [M + 2].
5-[1-Benzofuran-2-yl(4-methoxyphenyl)methyl-
idene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4b). Off-
white solid. Yield 90%, mp 162–164°C. IR spectrum
(KBr), νmax, cm–1: 2920 (Ar-CH), 1705 (C=O). 1H NMR
spectrum (400 MHz, DMSO), δ, ppm: 7.19–7.86 m
(9H, Ar-H), 3.49 s (3H, OCH3), 1.49 s [6H, (CH3)2].
13C NMR spectrum (400 MHz, DMSO), δ, ppm: 167.8
(C=O), 161.3, 159.9, 155.7, 135.0, 130.9, 127.4, 124.4,
123.0, 121.0, 117.9, 114.5, 111.6, 106.9, 55.8 (OCH3),
24.8. Found, %: C 69.80, H 4.80, O 25.39.
C21H15BrO5. Calculated, %: C 69.83, H 4.79, O 25.37.
(LCMS): m/z: 378 [M].
5-[(5-Hydroxy-1-benzofuran-2-yl)(4-methoxyphenyl)-
methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4f).
Pale yellow solid. Yield 76%, mp 169–171°C. IR spec-
trum (KBr), νmax, cm–1: 3447 (Ar-OH), 2987 (Ar-CH),
1
1713 (C=O). H NMR spectrum (400 MHz, DMSO),
δ, ppm: 7.7–8.0 m (8H, Ar-H), 5.64 s (1H, OH), 3.32 s
(3H, OCH3), 1.61 s [6H, (CH3)2]. 13C NMR spectrum
(400 MHz, DMSO), δ, ppm: 163.7 (C=O), 161.3, 159.1,
157.1, 153.6, 150.5, 133.7, 132.1, 127.1, 117.5, 114.3,
112.3, 106.1, 105.7, 104.7, 55.9 (OCH3), 24.2. Found,
%: C 67.04, H 4.54, O 28.42. C22H18O7. Calculated, %:
C 67.00, H 4.60, O 28.40. (LCMS): m/z: 394 [M].
5-[(5-Bromo-1-benzofuran-2-yl)(4-bromophenyl)-
methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4c).
Off-white solid. Yield 83%, mp 158–160°C. IR spectrum
(KBr), νmax, cm–1: 2918 (Ar-CH), 1699 (C=O), 598
5-[1-Benzofuran-2-yl(2-bromophenyl)methyl-
idene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4g). Color-
less solid. Yield 91%, mp 76–78°C. IR spectrum (KBr),
1
(C–Br). H NMR spectrum (400 MHz, DMSO), δ,
ν
max, cm–1: 3128 (Ar-CH), 1709 (C=O), 587 (C–Br).
ppm: 7.37–8.0 m (8H, Ar-H), 1.21 s [6H, (CH3)2]. 13C
NMR spectrum (400 MHz, DMSO), δ, ppm: 163.5
(C=O), 161.4, 157.3, 139.0, 133.3, 131.6, 129.0, 127.3,
124.3, 122.3, 117.0, 115.2, 113.1, 106.0, 104.2, 24.5.
Found, %: C 49.86, H 2.76, Br 31.50, O 15.88. C21H14Br2
O5. Calculated, %: C 49.83, H 2.79, Br 31.57, O 15.81.
(LCMS): m/z : 504 [M] 506 [M + 2], 508 [M + 4].
1H NMR spectrum (400 MHz, DMSO), δ, ppm: 7.35–
8.0 m (9H, Ar-H), 1.27 s [6H, (CH3)2]; 13C NMR
spectrum (400 MHz, DMSO), δ, ppm: 165.5 (C=O),
162.3, 158.6, 157.2, 139.6, 133.1, 130.2, 128.3, 127.1,
125.7, 123.0, 121.4, 118.2, 115.2, 110.3, 107.0, 104.1,
25.2. Found, %: C 59.07, H 3.51, Br 18.72, O 18.70.
C21H15BrO5. Calculated, %: C 59.04, H 3.54, Br 18.70,
O 18.72; MS (LCMS): m/z 426 [M] 428 [M + 2].
5-[(5-Bromo-1-benzofuran-2-yl)(4-methoxyphenyl)-
methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4d).
Colorless solid. Yield 83%, mp 160–162°C. IR spectrum
5-[(5-Bromo-1-benzofuran-2-yl)(2-bromophenyl)-
methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione (4h).
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

SYNTHESIS, CHARACTERIZATION, AND ANTIMICROBIAL ACTIVITY
2835
Brown solid. Yield 75%, mp 155–157°C. IR spectrum
drawn in ChemBioDraw tool (ChemBioOffice Ultra
14.0 suite) assigned with proper 2D orientation and
structure of each compound was checked for structural
drawing error. Energy of each molecule was
minimized using ChemBio3D (Chem Bio Office Ultra
14.0 suite). The energy minimized ligand molecules
were then used as input for AutoDockVina, in order to
carry out the docking simulation [26]. The protein data
bank (PDB) coordinate file with the name “2VF5.pdb”
was used as receptor molecule. All the water molecules
were removed from the receptor and SPDBV Deep
view was used to automatically rebuild the missing
side chains in receptor. The Graphical User Interface
program “MGL Tools” was used to set the grid box for
docking simulations. The grid was set so that it
surrounds the region of interest in the macromolecule.
(KBr), νmax, cm–1: 2975 (Ar-CH), 1719 (C=O), 564
1
(Ar-Br). H NMR spectrum (400 MHz, DMSO), δ,
ppm: 7.37–8.0 m (8H, Ar-H), 1.21 s [6H, (CH3)2]. 13C
NMR spectrum (400 MHz, DMSO), δ, ppm: 165.7
(C=O), 162.1, 157.2, 138.2, 133.7, 130.4, 128.3, 126.1,
124.7, 118.9, 116.1, 114.3, 111.0, 106.1, 104.5, 24.2.
Found, %: C 49.80, H 2.82, Br 31.55, O 51.83.
C21H14Br2 O5. Calculated, %: C 49.83, H 2.79, Br
31.57, O 51.81. (LCMS): m/z: 504 [M] 506 [M + 2],
508 [M + 4].
5-[(2-Bromophenyl)(5-hydroxy-1-benzofuran-2-
yl)methylidene]-2,2-dimethyl-1,3-dioxane-4,6-dione
(4i). Green solid. Yield 83%, mp 95–97°C. IR
spectrum (KBr), νmax, cm–1: 3440 (Ar-OH), 2965(Ar-
1
CH), 1696 (C=O), 576 (C–Br). H NMR spectrum
The grid box volume was set to 20, 20, and 20 Å
for x, y, and z dimensions respectively, and the grid
center was set to 29.663, 15.499, and –2.754 for x, y,
and z center respectively, which covered all the
10 amino acid residues in the considered active pocket.
Auto Grid 4.0 Program, supplied with Auto Dock 4.0
was used to produce grid maps [27]. The docking
algorithm provided with Auto Dock Vina was used to
search for the best docked conformation between
ligand and protein. During the docking process, a
maximum of 10 conformers were considered for each
ligand. All the Auto Dock docking runs were
performed in Corei7 Intel processor CPU with 8 GB
DDR3l RAM. AutoDockVina was compiled and run
under Windows 8.0 professional operating system. Lig
Plot + (23) and PyMol were used to deduce the
pictorial representation of interaction between the
ligands and the target protein.
(400 MHz, DMSO), δ, ppm: 7.03–7.92 m (8H, Ar-H),
5.64 s (1H, OH), 1.22 s [6H, (CH3)2]. 13C NMR spec-
trum (400 MHz, DMSO), δ, ppm: 163.7 (C=O), 162.3,
157.3, 153.3, 139.2, 133.7, 131.4, 129.3, 127.1, 126.2,
118.9, 116.2, 114.3, 111.0, 106.3, 105.1, 103.4, 24.2.
Found, %: C 56.92, H 3.39, Br 18.05, O 21.64.
C21H15BrO6. Calculated, %: C 56.90, H 3.41, Br 18.03,
O 21.66. (LCMS): m/z :442 [M] 444 [M + 2].
Biological activity. Antimicrobial activity.
Antimicrobial activity of the synthesized compounds
was tested against five bacterial strains using agar well
diffusion method [25]. Dimethyl sulfoxide (DMSO)
was used as solvent control. The bacterial cultures
were inoculated on nutrient agar (Merck) and fungal
culture was inoculated on Potato Dextrose agar media
(20 mL). The test compounds were dissolved in
DMSO to get a concentration of 12.79 M and 100 µL
of this sample was directly loaded into the wells of
agar plates. Plates inoculated 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 (1.71 and 0.85 M) and
Fluconazole (3.26 and 1.6 M) were used as standard
drugs for antibacterial and antifungal activities respectively.
ACKNOWLEDGMENTS
The authors are thankful to the Chairman, Department
of Industrial Chemistry, Kuvempu University,
Shankaraghatta for providing the laboratory facilities.
One of the authors (R. Kenchappa) is thankful to the
UGC for the award of Post-Doctoral Fellowship.
The minimum inhibitory concentration (MIC)
studies were performed by serial broth-dilution method
(National committee for clinical laboratory standards,
1982) at different concentrations like 1, 10, 25, 50, and
100 mol/L. After the incubation period, the minimum
inhibition zone at which the microorganism growth
was inhibited was measured in M.
REFERENCES
1. Garudachari, M.N., Satyanarayana, B., Thippeswamy, C.K.,
Shivakumarc, K.N., Shivananda, G. H., and Arun, M.I.,
Eur. J. Med. Chem., 2012, vol. 54, p. 900. doi
org/10.1016/j.ejmech.2012.05.027
2. Gershon, H., Braun, R., Scala, A., and Rodin, R.,
J. Med. Chem., 1964, vol. 7, p. 808. doi 10.1021/
jm00336a032
In silico molecular docking studies. The structure
of synthesized molecules and the standards were
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016

2836
KENCHAPPA et al.
3. Nuria, O., Bernhard, B., Slawomir, U., and Frank, G.,
Tetrahedron, 2012, vol. 68, p. 5185. doi 10.1016/
j.tet.2012.03.109
16. Wheeler, M.H., Stipanovic, R.D., and Puckhaber, L.S.,
Mycol. Res., 1999, vol. 103, p. 967. doi 10.2307/
3756940
17. Okano, M., Fukamiya, N., and Lee, K.H., Stud. Nat.
Prod. Chem., 1990, vol. 7, p. 369. doi org/10.1016/
S1572-5995 (00)80132-5
4. Verma, G. K., Verma, R. K., Shukla, G., Anugula, N.,
Srivastava, A., and Singh, M.S., Tetrahedron, 2013,
vol. 69, p. 6612. doi org/10.1016/j.tet.2013.05.128
18. Reshma J.N., Santosh N.D., and Satish N.D., E. J. Med.
Chem., 2015, vol. 97, p. 561. doi org/10.1016/
j.ejmech.2014.10.085
19. Khanam, H. and Shamsuzzaman., E., J. Med. Chem.,
2015, vol. 97, p. 483. doi org/10.1016/
j.ejmech.2014.11.039
20. Kenchappa, R., Bodke, Y.D., Asha, B., Sandeep Telkar,
and Aruna Sindhe, M., Med. Chem. Res., 2014, vol. 23,
p. 3065. doi 10.1007/s00044-013-0892-x
21. Kenchappa, R., Bodke Y.D., Peethambar, S.K., Sandeep
Telkar, and Venkatesh, K.B., Med. Chem. Res., 2013,
vol. 22, p. 4787. doi 10.1007/s00044-013-0494-7
22. Kenchappa, R., Bodke, Y.D., Chandrashekar, A.,
Sandeep Telkar, Manjunatha, K.S., and Aruna Sindhe, M.,
Arab. J. Chem., 2013. doi 10.1016/j.arabjc.2013.03.020
23. Stille John, R., Ward, J.A., Leffelman, C., and Sulli-
van, K.A., Tetrahedron Lett., 1996, vol. 37(52), p. 9267.
doi org/10.1016/S0040-4039(97)82938-3
24. Mahboobi, S., Sellmer, A., Höcher, H., Garhammer, C.,
Pongratz, H., Maier, T., Ciossek, T., and Beckers, T.,
J. Med. Chem., 2007, vol. 50, p. 4405. doi 10.1021/
jm0703136
5. Wang, Y. and Zhang, A., Tetrahedron, 2009, vol. 65,
p. 6986. doi 10.1016/j.tet.2009.06.049
6. Fuganti, C. and Serra, S., Tetrahedron Lett., 1998,
vol. 39, p. 5609. doi 10.1016/S0040- 4039(98)01053-3
7. Abdel-Wahab, B.F., Abdel-Aziz, H.A., and Ahmed, E.M.,
Eur. J. Med. Chem., 2009, vol. 44, p. 2632. doi 10.1016/
j.ejmech.2008.09.029
8. Bissantz, C., Jablonski, P., Knust, H., Koblet, A.,
Limberg, A., Nettekoven, M., Ratni, H., and Riemer, C.,
US Patent, 2009, 312317 A1.
9. Hayakawa, I., Shioya, R., Agatsuma, T., Furukawa, H.,
Naruto, S., and Sugano, Y., Bioorg. Med. Chem. Lett.,
2004, vol. 14, p. 4383. doi 10.1016/j.bmcl.2004.06.067
10. Foster, R.T., Robertson, A., and Bushra, A., J. Chem.
Soc., 1948, p. 2254. doi 10.1039/JR9480002254
11. Oikawa, Y., Sugano, K., and Yonemitsu O., J. Org.
Chem., 1978, vol. 43, p. 2087. doi 0022326317811943-
2087$01.00
12. Pemberton, N., Jakobsson, L., and Almqvist, F., Org.
Lett., 2006, vol. 8, p. 935. 10.1021/ol052998e
13. Melillo, D.G., Shinkai, I., and Liu, T., Tetrahedron
Lett., 1980, vol. 21, p. 2783. doi org/10.1016/S0040-
4039(00)78606-0
14. Burmeister, H.R., Bennett, G.A., Vesonder, R.F., and
Hesseltine, C.W., Antimicrob. Agent. Chemother., 1974,
vol. 5, p. 634. doi 10.1128/AAC.5.6.634
25. Nasser Khalil, S.A.M., E. J. Med. Chem., 2010, vol. 45,
p. 5265. doi org/10.1016/j.ejmech.2010.08.046
26. Morris, G.M., Goodsell, D.S., and Halliday, R.S.,
J. Comput. Chem., 1998, vol. 19(14), p. 1639. doi
10.1002/(SICI)1096-987X(19981115)19
27. Laskowski, R.A. and Swindells, M.B., J. Chem. Inf.
Model., 2011, vol. 51(10), p. 2778. doi 10.1021/
ci200227u
15. Singh, S.B., Zink, D.L., Goetz, M.A., Dombrowski, A.W.,
Polishook, J.D., and Hazuda, D.J., Tetrahedron Lett.,
1998, vol. 39, p. 2243.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 86 No. 12 2016