Synthesis of β-ionone derived chalcones as potent antimicrobial agents

Article abstract of DOI:10.1016/j.bmcl.2012.08.084

A series of chalcones (3a-v) have been synthesized by condensation of β-ionone (1) with a variety of aldehydes (2a-v). The synthesized compounds have been screened for their in vitro antimicrobial activity against five bacterial and five fungal strains, using disc diffusion assay. The evaluated compounds display a wide range of activities, from completely inactive to the highly active compounds. Some of the compounds are also active against methicillin resistant staphylococcus aureus (MRSA).

Full text of DOI:10.1016/j.bmcl.2012.08.084

Bioorganic & Medicinal Chemistry Letters 22 (2012) 6343–6346
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of b-ionone derived chalcones as potent antimicrobial agents
Vishal Sharma a, Gurpreet Singh a, Harpreet Kaur c, Ajit K. Saxena b, Mohan Paul S. Ishar a,
⇑
a Bio-Organic and Photochemistry Laboratory, Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar-143 005, Punjab, India
b Indian Institute of Integrative Medicine, Pharmacology Division, Jammu 180 001, J & K, India
c Department of Microbiology, Guru Nanak Dev University, Amritsar-143 005, Punjab, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 May 2012
Revised 25 July 2012
Accepted 22 August 2012
Available online 30 August 2012
A series of chalcones (3a–v) have been synthesized by condensation of b-ionone (1) with a variety of alde-
hydes (2a–v). The synthesized compounds have been screened for their in vitro antimicrobial activity
against five bacterial and five fungal strains, using disc diffusion assay. The evaluated compounds display
a wide range of activities, from completely inactive to the highly active compounds. Some of the
compounds are also active against methicillin resistant staphylococcus aureus (MRSA).
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
b-Ionone
b-Ionone derived chalcones
Antibacterial activity
Antifungal activity
Life threatening infections caused by pathogenic fungi and bacte-
riaare becomingincreasinglycommonand widespreadepidemics in
the world, especially in individuals with suppressed immunesystem
that is, cancer, AIDS patients etc. Antimicrobial treatment used for
these infections is also a serious public health threat because of rapid
development of resistance by increasing number of pathogenic
microorganisms against multiple drugs.1–3 Therefore, efforts are
directed towards the design, synthesis and evaluation of the new
chemical therapeutics as alternative to existing antimicrobial ther-
apy. Chalcones represent an important group of natural products.
Both naturally occurring and synthetic chalcones (Fig. 1) exhibit
remarkable pharmacological activities such as antioxidant,4 tyrosi-
nase inhibition,5 antileishmanial,6 anticancer,7 antiangiogenic,8
anti-inflammatory,9 nitric oxide inhibition,10 antifungal,11 antibac-
terial12–15 etc. Recently, Liaras et al. have reported some thiazole
based chalcones displaying greater activity than reference drugs.12b
Chalcones such as 4-hydroxychalcone and 2,4-dihydroxychalcone
have been found to exhibit moderate activity against MRSA when
used alone and showed significant synergistic effect in combination
with non beta-lactam antibiotics.12c
single scaffold may result in formation of some potential antimi-
crobial molecules. Recently, some ionones based chalcones have
been reported as potential anticancer agents against prostate can-
cer cells.7b b-ionones derived chalcones (3a–v) were prepared by
condensing freshly distilled b-ionone (1, Scheme 1, Table 1) with
distilled/crystallized subsituted benzaldehydes (2a–v) in the
presence of 10% NaOH water-ethanol solution.19 The products
were purified through chromatography over silica gel (hexane,
hexane-benzene gradient) and/or by crystal1ization with diethyl-
ether and characterized through spectral data (IR, 1H NMR, 13C
NMR, mass) and elemental analysis.
The assigned structures of chalcones are based on detailed spec-
troscopic analysis. IR spectrum of compound 3i revealed a strong
band at 1650 cmÀ1, along with resonance in its 13C NMR at d
188.4 indicating the presence of a keto carbonyl function. Its 1H
NMR revealed, besides aromatic proton resonances in the region
d 7.27–7.15, two b-protons of
a,b-unsturated carbonyl moiety
showed up as doublets at d 7.97 and 7.43 with trans olefinic-H cou-
pling constant J = 15.9 Hz and two
at d 6.87 and 6.64 (J = 15.9 Hz).
a-protons appeared as doublets
On other hand, b-ionone is an important phytochemical present
in many fruits, vegetables and grains and known to exert diverse
biological activities including antibacterial and antifungal activ-
ity.16–18 Taking cognizance of wide range of biological activities
of both b-ionone and chalcones, particularly antibacterial and
antifungal, it was decided to synthesize some b-ionone derived
chalcones so that synergistic effect of both valuable moieties in
Antibacterial activity
In vitro antibacterial studies of various compounds (3a–v) were
carried out against Gram negative and gram positive bacterial
strains by disk-diffusion assay.20 The Gram positive strains used
were Staphylococcus aureus (MTCC 96), Bacillus subtilis (MTCC
2451) and gram negative bacteria were Escherichia coli (MTCC
82), Pseudomonas aeruginosa (MTCC 2642), Salmonella typhimurium
(MTCC 1251). The activity of compounds was determined in com-
⇑
Corresponding author. Tel.: +91 183 2258802x3321; fax: +91 183 2258820.
E-mail address: mpsishar@yahoo.com (M.P.S. Ishar).
0960-894X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2012.08.084

6344
V. Sharma et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6343–6346
Figure 1. Some biologically active chalcones.
Scheme 1. Synthesis of b-ionones derived chalcones (3a–v).
Table 1
Table 2
Time (min) and yield (%) of various b-ionones derived chalcones (3a–v).
MIC (lg/ml) of compounds 3a–v against various bacterial strains.
Comp. No.
Time (min)
(%) Yield
Comp. No.
Time (min)
(%) Yield
Comp. No.
B. subtilis
S. aureus
E. coli
P. aeruginosa
S. typhi
3a
3b
3c
3d
3e
3f
3g
3h
3i
45
40
40
40
40
50
55
40
40
50
40
90
90
85
90
90
85
80
80
90
90
80
3l
40
40
55
60
60
45
50
50
55
55
60
90
85
80
75
75
90
75
80
85
80
80
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
3p
3.12
6.25
—
25
>100
—
3.12
25
—
25.5
42
25
>100
25
1.56
22.2
6.25
25
>100
>100
—
19.5
32.5
6.25
—
1.56
3.12
>100
>100
37
12.5
12.5
>100
—
—
—
12.5
>100
>100
—
>100
>100
>100
>100
>100
>100
25
3m
3n
3o
3p
3q
3r
3s
3t
3u
3v
>100
—
25
65
3.12
0.78
25
3.12
40.2
—
6.25
1.56
31.5
12.5
—
>100
30.5
42
12.5
12.5
>100
3.12
>100
—
3j
3k
—
>100
55.5
>100
45
>100
>100
74
—
50
>100
0.9
—
25
—
22.5
>100
25
6.25
22.5
25
3.12
25
0.5
55.5
22.5
—
12.5
>100
—
>100
32.5
1.0
parison to standard antibiotic discs of Amoxicillin (5
floxacin (10
inoculated with 106 CFU/mL of test bacteria. Each compound was
dissolved in DMSO (1 mg/ml) and then 30 L of each was pipetted
l
g) and Cipro-
—
22
l
g). Pre-warmed Mueller–Hinton agar plates were
3q
3r
3s
3t
3u
3v
12.5
>100
55.5
6.25
>100
0.12
0.9
l
25
onto sterile paper discs (6 mm diameter) placed on the surface of
inoculated agar plates. Plates were incubated at 37 °C for 24 h.
Activity was expressed as the diameter of the inhibition zone
(mm) produced by the compounds. DMSO was used as negative
control. Minimum inhibitory concenteration (MIC) of compounds
exhibiting considerable activity (Table 2 and Fig. 2) was deter-
mined by using serial tube dilution method.21 The initial optical
density (OD) of the medium was measured by spectrophotometer
at 600 nm. The test strains were incubated in nutrient broth until
the OD reached 0.4–0.6. Different concentrations of compounds
6.25
>100
0.5
Amoxicillin
Ciprofloxacin
0.75
1.2
1.8
different concentration was observed and concentration showing
apparently no turbidity was considered to be the MIC of respective
compound.
Compound 3i showed highest antibacterial potential against
both Gram positive and Gram negative bacteria with MIC 0.78
against B. subtilis, followed by MIC 1.56 against both S. aureus
and E. coli and MIC 12.5 against P. aeruginosa. Compound 3a dis-
played valuable antibacterial activity with MIC 1.56 against
E. coli, followed by MIC 3.12 against both B. subtilis and S. aureus,
(0.78, 1.56, 3.12, 6.25, 12.5, 25, 50 lg/ml) were tested for the inhi-
bition of growth of these microbes in separate tubes. The 10 ml
tubes each containing 5 ml nutrient broth and 1 ml of different
concentrations of compounds were incubated for 24 h with shak-
ing at 180 rpm using a rotary shaker. Each tube corresponding to

V. Sharma et al. / Bioorg. Med. Chem. Lett. 22 (2012) 6343–6346
6345
Table 4
MIC (lg/ml) of active compounds against various fungal strains.
Comp. No.
A. niger S.
cerevisiae
C.
C.
M.
gypseum
albicans
gastricus
3a
3b
3d
3e
3g
3h
3i
3j
3k
3l
3m
3n
3r
3s
3t
>100
>100
15.6
52.4
>100
9.6
33.5
92.5
32.4
7.6
9.9
>100
3.9
61.4
55
25
61.5
12.5
15.6
>100
40.5
19.5
12.5
61.4
42.5
3.9
11.4
96
10.5
>100
>100
80
>100
>100
12.5
80
78
>100
>100
>100
90.5
>100
82
>100
>100
>100
>100
90.4
>100
>100
58.4
>100
>100
>100
>100
72.5
>100
55.5
19.5
31.2
1.9
46
11.2
11.5
>100
>100
31.2
44.5
72
35
74
71.5
>100
>100
3.9
94
88.5
>100
>100
>100
>100
>100
>100
98
Figure 2. Graphical representation of the antibacterial activity.
3u
3v
>100
71.5
1.9
80
34
1.9
1.9
Table 3
Fluconazole 1.9
Griseofulvin 1.9
MIC (mg/ml) of compounds against methecillin resistant staphylococcus aureus
(MRSA).
1.9
1.9
Comp. No.
3a
3b
3k
3n
3p
3u
3r
MRSA
9
10
9
5
20
4
5
MIC 12.5 against P. aeruginosa and S. typhimurium Compound 3b
exhibited significant activity with MIC 3.12 against E. coli, followed
by MIC 6.25 against B. subtilis and MIC 12.5 against P. aeruginosa.
Compound 3h showed good antibacterial activity with MIC 3.12
against B. subtilis, followed by MIC 6.25 against E. coli and MIC
12.5 against S. typhimurium Compound 3k showed promising
activity with MIC 3.12 against both B. subtilis and P. aeruginosa, fol-
lowed by MIC 6.25 against S. aureus and MIC 12.5 against E. coli.
Compound 3u possesses potential antibacterial activity with MIC
3.12 against B. subtilis, followed by MIC 6.25 against both S. aureus
and E. coli. Compound 3r was also endowed activity with MIC 6.25
against both B. subtilis and S. aureus, followed by MIC 12.5 against
E. coli and P. aeruginosa. Active compounds 3a, 3b, 3k, 3n, 3p, 3u, 3r
were further evaluated against bacterial resistant strains such as
methecillin resistant S. aureus (MRSA), a clinically isolate obtained
from PGIEMR-Chandigarh and Klebsiella pneumoniae (MTCC 530)
by using disk-diffusion assay.20 Compounds were found to be ac-
tive against MRSA and completely inactive against K. pneumoniae.
Minimum inhibitory concenteration (MIC) in mg/ml of compounds
exhibiting activity (Table 3) was determined by using serial tube
dilution method.21
Figure 3. Graphical representation of the antifungal activity.
say medium (Saboraud Dextrose agar with Chloramphenicol) at
40–45 °C and mixed well. The medium was poured into each of
the petridishes. Sterile discs of diameter 6 mm were placed on
the medium and 20 ll of each test solution was added to the pre-
viously marked discs and the media was allowed to stand for
5 min. The petridishes were kept aside for 1 h and then incubated
at 28 °C for 48 h. Zone of inhibition was measured and the average
of the three readings was calculated. DMSO was kept as negative
control. Minimum inhibitory concentration (MIC) of compounds
was determined by serial tube dilution method.21 Different dilu-
Structure–activity relationship can be established on the basis
of observed antibacterial activities. Compounds bearing electron
widhrawing lipophilic groups such as –Cl and –NO2 subsituents
on aromatic ring were endowed with valuable antibacterial activ-
ity as compared to compounds bearing electron releasing groups
at aromatic ring. However, replacement of aryl moiety with pyridyl
(3r) leads to enhancement of antibacterial activity.
tions of test compounds (1.9
lg/ml–500 lg/ml) were made from
stock solution and 1 ml nutrient broth was taken in each test tube
and 20
tubes.
ll of standard strains were added to previously marked test
The compounds evaluated were found to exert prominent anti-
fungal activity against various fungal strains, specially, against A.
niger, S. cerevisiae and C.albicans (Table 4, Fig. 3). Compounds 3h,
3l, 3m, and 3r showed significant inhibitory activity against A. ni-
ger with MIC < 10, whereas, compounds 3d showed inhibitory
activity with MIC 15.6. Compound 3l posses maximum inhibitory
potential against S. cerevisiae with MIC 3.9 whereas, compounds
3b, 3d, 3h, 3i, 3m and 3r displayed good inhibitory potential with
MIC < 20. Compounds 3d, 3h and 3i exhibit promising activity
against C. albicans with MIC < 15.
Antifungal activity
All synthesized compounds 3a–v were tested against five refer-
ence fungal strains such as Aspergillus niger (MTCC 1344), Saccharo-
myces cerevisiae (MTCC 172), Candida albicans (MTCC 3018),
Cryptococcus gastricus (MTCC 1715) and Microsporum gypseum
(MTCC 4490). by using disc diffusion method.20 The antifungal
activity of synthesized compounds was determined by observing
the zone of inhibition in comparison to the standard antifungal
discs (Fluconazole and Griseofulvin). Test compounds were dis-
solved in DMSO to make a stock solution of 1 mg/ml. The fresh
sub culture of strains in normal saline was added to the sterile as-
In conclusion, a series of b-ionone derived chalcones (3a–v)
were synthesize through condensation of b-ionone (1) with subsi-
tuted benzaldehydes (2a–v) in the presence of 10% NaOH water-

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in vitro antimicrobial activity against various pathogenic bacterial
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