Synthesis and antimicrobial evaluation of some heterocyclic chalcone derivatives

Article abstract of DOI:10.3390/molecules16032304

Some new heterocyclic compounds containing isoxazole, pyrazole and oxadiazole ring systems were prepared from various chalcones. The synthesized compounds have been characterized by elemental analysis and spectral methods. These compounds were screened fo

Full text of DOI:10.3390/molecules16032304

Molecules 2011, 16, 2304-2312; doi:10.3390/molecules16032304
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Synthesis and Antimicrobial Evaluation of Some Heterocyclic
Chalcone Derivatives
Nagwa Mohamed Mahrous Hamada 1 and Essam Mohamed Sharshira 2,*
1
Department of Chemistry, Faculty of Education, Alexandria University, Alexandria, Egypt; E-Mail:
nagwahamada2002@yahoo.com (N.M.M.H.)
2
Department of Chemistry, Faculty of Science, Alexandria University, Alexandria, Egypt
* Author to whom correspondence should be addressed; E-Mail: dressamsharshira@yahoo.com.
Received: 13 December 2010; in revised form: 12 February 2011 / Accepted: 21 February 2011 /
Published: 9 March 2011
Abstract: Some new heterocyclic compounds containing isoxazole, pyrazole and oxadiazole
ring systems were prepared from various chalcones. The synthesized compounds have
been characterized by elemental analysis and spectral methods. These compounds were
screened for their antimicrobial activities.
Keywords: chalcones; isoxazoles; pyrazoles; oxadiazoles; antimicrobial
1. Introduction
Chalcones are synthesized by condensing ketones with aromatic aldehydes in the presence of
suitable bases. They are very useful intermediates for the synthesis of five- [1,2], six- [1,3] and
seven-membered [4] heterocyclic compounds. Chalcone derivatives exhibit diverse pharmacological
activities [5-14]. It is therefore, not surprising that many synthetic methods have been developed for
the preparation of heterocycles starting from chalcone precursors that have been tested for their
antimicrobial activities.
2. Results and Discussion
All of our results are shown in Scheme 1. The starting chalcones 1a–c were obtained in good yields by a
base catalyzed condensation [15-16] of appropriately substituted benzaldehydes and cyclopropylmethyl
ketone [17]. The method is attractive since it specifically generates the (E) isomer [18].

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Scheme 1. Synthesis of 2a–f, 3a–f, 4a–f and 5a–f.
X
H
C C
H
O
1a, X = NO
1b, X = H
2
1c, X = OMe
O
NH OH.HCl /
2
Y
C
/
H NNH
2
CH CO Na/EtOH
3
2
Y = H, Me, NO
2
O
H
N C
N
Y
X
N
X
C
O
CH CH
5a-c
2a-f
Ac O / reflux
30% HCl / 
2
O
N
H
C
X
N
C
Y
C
H C
3
H
C
N
O
O
N
X
3a-f
Y
4a-f
The hydrazones 2a–f were prepared by the reaction of chalcones 1a–c with benzoyl hydrazine
derivatives and were subsequently used for the syntheses of various pyrazoles 3a–f and oxadiazoles 4a–f.
The IR spectra of these hydrazones revealed the characteristic bands for vinyl CH=CH at 1582–1617,
1
C=N at 1616–1647, C=O at 1664–1698 and NH at 3330–3420 cm−1. The H-NMR spectra showed the
presence of a singlet at  = 9.97–10.82 ppm for the NH proton, a multiplet at  = 7.17–8.45 ppm
characteristic for the aromatic protons and the olefinic =C–CH=CH, a doublet at  = 6.60–6.95 ppm

Molecules 2011, 16
2306
characteristic for the olefinic =C–CH=CH proton. The cyclopropyl ring protons appeared as two
multiplets in the range  = 1.56–2.64 ppm (CH) and  = 0.70–1.46 ppm (2CH2), respectively.
The pyrazole derivatives 3a–f were obtained by treatment of hydrazones 2a–f with 30%
hydrochloric acid. The IR of 3a–f showed the characteristic bands for C=C–Ar at 1519–1596, C=N at
1623–1644 and amide carbonyl band at 1660–1686 cm−1, while the 1H-NMR spectra showed a singlet
at  = 6.64–7.12 ppm for the pyrazole–C4–H. On the other hand, refluxing of hydrazones 2a–f with
acetic anhydride gave the corresponding dihydro-1,3,4-oxadiazole derivatives 4a–f. The mechanism of
cyclization reaction has been well studied [19-20]. The IR spectra of the dihydro-oxadiazoles 4a–f
lacked the NH, but showed a carbonyl absorption at 1667–1677 cm−1 for the acetyl group. Their
structures were further confirmed from the 1H-NMR spectra which does not reveal the presence of NH
1
signal present in the starting hydrazone 2, moreover, the H-NMR of 4 exhibited a singlet of three
protons intensity at  = 2.10–2.16 ppm for the COCH3. Finally, treatment of chalcones 1a–c with
hydroxylamine hydrochloride in presence of sodium acetate produced isoxazoles 5a–c in moderate
yield. The structure of 5 was fully confirmed by spectral method. For example, the IR of 5 does not
1
show the presence of carbonyl band characteristic for the starting chalcone 1. The H-NMR of 5
exhibited a singlet of one proton intensity at  = 5.42–5.69 ppm characteristic for the isoxazole–C4–H.
Melting points, elemental analysis and spectral methods are outlined in Tables 1 and 2.
2.1. Antimicrobial Activity
All the synthesized heterocyclic derivatives, pyrazoles 3a–f oxadiazoles 4a–f and isoxazoles 5a–c
were assayed for their antimicrobial activity against four test organisms: Staphylococcus aureus
ATCC6538P, Escherichia coli ATCC8739, Pseudomonas aeruginosa ATCC9027 and Candida
albicans ATCC2091 using rifampicin (5 g/disc) and ampicillin (10 g/disc) as standard drugs
following agar well-diffusion method [21].
The tested heterocyclic compounds showed no significant effect against Pseudomonas aeruginosa
and Candida albicans, whereas they showed a potent activity against Staphylococcus aureus and
Escherichia coli. The maximum activity (+ + +) (MIC = 25 g/mL) was indicated for compounds 3a,
3b, 4a, 4b and 5a. These results suggest that the electron-withdrawing nitro group plays a crucial role
in enhancing the observed activity.
Compounds 3e, 4c, 4e and 4f showed a moderate activity (+ +) (MIC = 50 g /mL) against
Staphylococcus, while these compounds exhibited slight activity (+) (MIC = 75 g/mL) against
Escherichia coli. All other compounds were inactive towards the different strains of bacteria. The
results are summarized in Table 3.

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Table 1. Physical and analytical data of compounds, 2a–f, 3a–f, 4a–f and 5a–c.
Calculated %
Found %
H N
Yield
(%)
72
79
66
65
69
74
81
92
62
66
64
59
83
97
59
58
67
80
54
49
74
Mp
(ºC)
181
201
166
180
190
160
183
197
159
164
171
180
201
210
177
179
189
162
165
159
161
Molecular
Formula
Compound
X
Y
C
H
N
C
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
4a
4b
4c
4d
4e
4f
5a
5b
5c
NO2
NO2
H
Me
NO2
H
Me
Me
H
Me
NO2
H
Me
Me
H
Me
NO2
H
Me
Me
H
C20 H19 N3 O3
C19 H16 N4 O5
C19 H18 N2 O
C20 H20 O N2
C21 H22 O2 N2
C20 H20 O2 N2
C20 H17 O3 N3
C19 H14 O5 N4
C19 H16 O N2
C20 H18 O N2
C21 H20 O2 N2
C20 H18 O2 N2
C22 H21 O4 N3
C21 H18 O6 N4
C21 H20 O2 N2
C22 H22 O2 N2
C23 H24 O3 N2
C22 H22 O3 N2
C12 H10 O3 N2
C12 H11 O N
C13 H13 O2 N
68.77
60.00
78.62
78.95
75.45
75.00
69.16
60.32
79.17
79.47
75.90
75.47
67.52
59.72
57.90
76.30
73.40
72.93
62.61
77.84
72.56
5.44 12.03 68.71 5.39 12.09
4.21 14.74 60.06 4.19 14.77
6.21 9.66
6.58 9.21
6.59 8.38
6.25 8.75
4.90 12.10 69.22 4.87 12.08
3.70 14.81 60.33 3.69 14.77
5.56 9.72
5.96 9.27
6.02 8.43
5.66 8.81
5.37 10.74 67.52 5.43 10.80
4.27 13.27 59.69 4.26 13.22
6.02 8.43
6.36 8.09
6.38 7.45
6.08 7.73
4.35 12.17 62.66 4.29 12.21
5.95 7.57
6.05 6.51
78.59 6.19 9.62
H
79.01 6.49
75.49 6.62
74.97 6.26
9.28
8.44
8.77
OMe
OMe
NO2
NO2
H
79.21 5.53
79.51 5.91
75.93 6.06
75.52 5.60
9.71
9.27
8.51
8.86
H
OMe
OMe
NO2
NO2
H
57.84 5.99
76.28 6.31
73.44 6.39
72.91 6.01
8.44
8.12
7.49
7.76
H
OMe
OMe
NO2
H
―
―
―
77.90 5.99 7.62
72.60 6.01 6.48
OMe

Molecules 2011, 16
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Table 2. IR and 1H-NMR spectral data of compounds 2a–f, 3a–f, 4a–f and 5a–c.
IR cm−1 (KBr) 1H NMR ( / ppm)a
Pyrazole-
Ar–CH3
(s)
Ar–OCH3
and
CH3CO–
2.21
Cyclopropyl ring H’s
Ar–H’s and
C=C C=N C=O NH =C–CH=CH
(m)
C4–H (s)
or
isoxazole–
C4–H (s)
―
Compound
=C–CH=CH
(d), J =12 Hz
NH
(s)
CH
(m)
2 (CH2)
(m)
2a
2b
2c
2d
2e
2f
3a
3b
3c
3d
3e
3f
4a
4b
4c
4d
4e
4f
5a
5b
5c
1592 1629 1678 3420
1617 1647 1698 3390
1582 1616 1664 3330
1587 1636 1669 3336
1601 1628 1687 3411
1617 1644 1681 3332
7.36–7.91
7.23–8.45
7.19–7.63
7.29–7.82
7.20–7.71
6.72
6.93
6.60
6.71
6.75
6.95
―
10.66 1.91–2.55 0.75–1.37
10.45 1.80–2.64 0.71–1.40
9.97 1.82–2.49 0.78–1.29
10.82 1.71–2.36 0.70–1.40
10.73 1.63–2.40 0.77–1.46
9.99 1.56–2.59 0.78–1.16
―
―
―
―
―
―
2.10
2.19, 3.49
3.42
7.17–7.49
―
1519 1629 1670
1586 1633 1684
1556 1641 1660
1590 1644 1678
1571 1623 1686
1596 1633 1664
1587 1645 1669
1610 1646 1667
1602 1626 1669
1594 1630 1670
1600 1633 1677
1615 1646 1671
―
―
―
―
―
―
―
―
―
―
―
―
―
―
―
7.26–7.92 b
7.24–8.33 b
7.22–7.71 b
7.24–7.77 b
7.21–7.68 b
7.11–7.62 b
7.18–7.79 b
7.22–8.22 b
7.16–7.75 b
7.33–7.76 b
7.26–7.72 b
7.25–7.51 b
7.19–7.99 b
7.22–7.62 b
7.26–7.70 b
6.85
7.12
6.78
6.64
6.69
6.74
―
―
―
―
―
―
―
―
―
―
―
―
―
―
―
―
1.90–2.48 0.69–1.21
1.76–2.66 0.80–1.36
1.73–2.40 0.71–1.28
1.75–2.41 0.77–1.33
1.66–2.39 0.71–1.33
1.49–2.55 0.77–1.19
1.92–2.41 0.67–1.32
1.70–2.66 0.71–1.40
1.68–2.39 0.75–1.26
1.73–2.44 0.71–1.38
2.13
―
―
2.11
―
―
―
―
―
―
2.10,3.44
3.39
2.01, 2.16
2.13
2.11
1.99, 2.13
―
―
―
―
―
―
―
―
1.60–2.47 0.71–1.26 2.13,3.32,2.15
―
―
―
―
―
1.47–2.61 0.76–1.33
1.82–2.51 0.71–1.36
1.43–2.45 0.69–1.27
1.57–2.41 0.67–1.29
3.34,2.10
―
1580 1627
1571 1629
1569 1633
―
―
―
5.69
5.42
5.46
―
3.30
a Solution in DMSO-d6; b The chemical shift only indicates Ar–H’s.

Molecules 2011, 16
Table 3. Antibacterial activities of newly synthesized compounds 3–5.
2309
Compound
X
NO2
NO2
NO2
NO2
NO2
OMe
H
OMe
OMe
H
H
OMe
H
Y
Me
NO2
Me
NO2
―
Me
H
Me
H
H
Me
H
Me
―
―
Staphylococcus aureus
Escherichia coli
3a
3b
4a
4b
5a
3e
4c
4e
4f
3c
3d
3f
4d
5b
5c
+ + +
+ + +
+ + +
+ + +
+ + +
+ +
+ +
+ +
+ +
―
+ + +
+ + +
+ + +
+ + +
+ + +
+
+
+
+
―
―
―
―
―
―
―
―
―
H
OMe
―
―
+ + + for maximum activity, MIC = 25 μg/mL; + + for moderate activity, MIC = 50 μg/mL; +for
slight activity, MIC = 75 μg/mL and – for inactive.
3. Experimental
3.1. General
Melting points were taken in open capillary tubes using Electrothermal apparatus 9100 ( UK ) and
are uncorrected. Microanalyses were performed at Faculty of Science, Cairo University, Cairo, Egypt,
using a Elementary Vario el III C, H, N, S Analyzer (Germany). IR spectra were recorded using
potassium bromide disks on a Perkin-Elmer 1650 spectrophotometer (Faculty of Science, Alexandria
University, Alex, Egypt). 1H-NMR spectra were determined on a Varian EM-390 MHz
spectrophotometer, using TMS as internal standard.
3.2. General Procedure for Preparation of E-l-Cyclopropyl-3-(p-substituted-phenyl)-2-
propenenones 1a–c
To a cold solution of sodium hydroxide (3 g) in aqueous ethanol (50 mL, 60%), cyclopropylmethyl
ketone (10 mmol), was added dropwise (30 min), while rapidly stirring and the temperature kept below
20 °C, then the desired p-substituted benzaldehyde (10 mmol) was added dropwise (30 min). After five
hours, the mixture was left overnight in refrigerator. The separated solid was filtered, washed with
water and dried, then recrystallized from ethanol as colorless needles. The physical properties and all
the spectral data were as reported in the literature [17].

Molecules 2011, 16
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3.3. General Procedure for Preparation of 1-Cyclopropyl-3-(p-substituted-phenyl)-2-
propene-l-aroyl hydrazones 2a–e
A solution of chalcones 1a–c (10 mmol) in ethanol (10 mL) was refluxed with the appropriate aroyl
hydrazines (10 mmol) in glacial acetic acid (2 mL) for about six hours, then the reaction mixture was
poured onto crushed ice and was kept overnight at room temperature, the separated solid was filtered
off, washed successively with water and dried, then recrystallized from methanol. IR and NMR data:
see Tables 1 and 2.
3.4. General Procedure for Preparation of 1-Aroyl-3-cyclopropyl-5-(p-substituted-phenyl)-
pyrazoles 3a–e
A solution of the appropriate hydrazone 3a–e (10 mmol) in 30% hydrochloric acid (15 mL) was
refluxed for about two hours, the reaction mixture was concentrated, separated solid was filtered off,
washed with water, dried and recrystallized from methanol. IR and NMR data: see Tables 1 and 2.
3.5. General Procedure for Preparation of 3-Acetyl-2-cyclopropyl-2-(p-substituted styryl)-5-(p-
substituted phenyl)-1,3,4-oxadiazoles 4a–e
A mixture of the appropriate hydrazone 2a–e (10 mmol) and acetic anhydride (15 mL) was heated under
reflux for three hours. After the reaction mixture attained room temperature, it was poured into crushed ice
and the oily product deposited was decanted from water and extracted with ether. The ether layer was
washed with sodium bicarbonate, followed by water, dried over anhydrous sodium sulphate and evaporated
to give the corresponding oxadiazoles 4a–e as needles. IR and NMR data: see Tables 1 and 2.
3.6. General Procedure for Preparation of 3-Cyclopropyl-5-(p-substituted Phenyl)isoxazole 5a–c
A mixture of chalcone 1a–c (20 mmol), hydroxylamine hydrochloride (20 mmol) and sodium
acetate (20 mmol) in ethanol (25 mL) was refluxed for six hours. The mixture was concentrated by
distilling out the solvent under reduced pressure and poured into ice-water. The precipitate obtained
was filtered, washed and recrystallized from ethanol to give isoxazole 5 as needles. IR and NMR data:
see Tables 1 and 2.
3.7. Determination of Antimicrobial Activity
All the synthesized heterocyclic compounds 3a–f, 4a–f and 5a–f were tested against four different
microorganisms: Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida
albicans. The agar well-diffusion method was applied for the determination of inhibition zone and
minimum inhibitory concentration (MIC). Briefly, 0.75 mL of broth culture containing ca. 106
colon-forming units (CFU) per mL of the test strain was added to 75 mL of nutrient agar medium at 45 ºC,
mixed well, and then poured into a 15 cm sterile metallic Petri plate. The medium was allowed to
solidify, and 8 mm wells were dug with a sterile metallic borer. Then, a DMSO solution of the test
sample (1 mL) at 1 mg/mL was added to the respective wells. DMSO served as negative control, and
the standard antimicrobial drugs rifampicin (5 g/disc) and ampicillin (10 g/disc) were used as

Molecules 2011, 16
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positive controls. Triplicate plates of each microorganism strain were prepared and were incubated
aerobically at 37 ºC for 24 h. The activity was determined by measuring the diameter of zone showing
complete inhibition (mm), thereby, the zones were precisely measured with the aid of a Vernier
Caliper (precision 0.1 mm).The growth inhibition was calculated with reference to the positive control.
4. Conclusions
In summary, this work demonstrates a rapid, efficient method for synthesis of new heterocyclic
compounds of pharmacological interest.
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Sample Availability: Samples of all the compounds are available from the authors.
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