Synthesis, characterization and antimicrobial activities of chalcones and their post transformation to pyrazole derivatives

Article abstract of DOI:10.14233/ajchem.2017.20561

An efficient procedure for the synthesis of trisubstituted pyrazoles was developed. Claisen-Schmidt condensation of 2,4,5-trimethoxybenzaldehyde and substituted acetophenone in the presence of aqueous alkaline bases produced chalcones. The cyclocondensati

Full text of DOI:10.14233/ajchem.2017.20561

Asian Journal of Chemistry; Vol. 29, No. 7 (2017), 1538-1542
ASIAN JOURNAL OF CHEMISTRY
https://doi.org/10.14233/ajchem.2017.20561
Synthesis, Characterization and Antimicrobial Activities of
Chalcones and Their Post Transformation to Pyrazole Derivatives
1
2
1
1
1,*
D. RAMYASHREE , K.R. RAGHAVENDRA , A. DILEEP KUMAR , C.B. VAGISH and K. AJAY KUMAR
1Department of Chemistry, Yuvaraja’s College, Mysuru-570 006, India
2Department of Chemistry, S.B.R.R. Mahajana First Grade College, Mysuru-570 012, India
*Corresponding author: E-mail: ajaykumar@ycm.uni-mysore.ac.in
Received: 1 February 2017;
Accepted: 31 March 2017;
Published online: 13 May 2017;
AJC-18389
An efficient procedure for the synthesis of trisubstituted pyrazoles was developed. Claisen-Schmidt condensation of 2,4,5-
trimethoxybenzaldehyde and substituted acetophenone in the presence of aqueous alkaline bases produced chalcones. The cyclocondensation
reaction of chalcones and phenyl hydrazine hydrochloride catalyzed by an acid produced trisubstituted pyrazolines in good yields. The
synthesized new compounds were characterized by spectral studies and elemental analysis and some of the intermediate chalcones by
single crystal X-ray diffraction studies. The compounds were screened in vitro for their antimicrobial susceptibilities against different
bacteria and fungi species.
Keywords: Antibacterial, Antifungal, Cyclocondensation, Inhibition, Pyrazoline, Spectral.
diamine oxidase (SKDAO) and bovine serum amine oxidase
(BSAO) [7]. Pyrazoles have known to exhibit antifungal, anti-
bacterial, antioxidant [8,9], antitubercular [10] and anticancer
[11] activities.
INTRODUCTION
Chalcones and their derivatives demonstrate a wide range
of biological activities and constitutes the central core for the
construction of a wide range of bioactive compounds [1,2].
Five membered nitrogen heterocycles, particularly pyrazoles
and their derivatives are regarded as important molecules in
organic synthesis. They serve as building blocks for the cons-
truction of biologically potent molecules. Numerous methods
have been developed for synthesis of substituted pyrazoles
viz. by (i) the reaction of 1,3-diketones with hydrazines, (ii)
the reaction of α,β-unsaturated aldehyde and ketones with
hydrazines. However, the classical method employed for the
synthesis of pyrazolines and pyrazoles involves 1,3-dipolar
cycloaddition reactions of nitrile imines to alkenes and alkynes
[3,4]. An efficient regioselective synthetic route to multi-
substituted pyrazoles by cyclocondensation of β-thioalkyl-α,β-
unsaturated ketones with hydrazines was developed by Jin et al.
[5]. A convenient and efficient synthesis of a series of 1,3-
diaryl-4-halo-1H-pyrazoles in moderate to excellent yields by
1,3-dipolar cycloaddition of 3-aryl sydnones and 2-aryl-1,1-
dihalo-1-alkenes was reported [6].
The enormous pharmacological applications associated
with pyrazoles prompted us to work in this area. In continuation
of our work on pyrazoles and in search of new potential anti-
fungal and antibacterial agents, we herein report the synthesis
of a series of new pyrazoles via Claisen Schmidt condensation
of aromatic aldehydes and aromatic ketones and their in vitro
antimicrobial susceptibilities against different bacteria and
fungi organisms.
EXPERIMENTAL
Melting points were determined by an open capillary tube
method and are uncorrected. Purity of the compounds was
checked on thin layer chromatography (TLC) plates pre-coated
with silica gel using the solvent system ethyl acetate:dichloro-
methane (1:4 v/v). The spots were visualized under UV light.
1H NMR and 13C NMR spectra were recorded onAgilent-NMR
400 MHz and 100 MHz spectrometer respectively. The solvent
CDCl3 with TMS as an internal standard was used to record
the spectra. The chemical shifts are expressed in δ ppm. Mass
spectra were obtained on Mass Lynx SCN781 spectrometer
TOF mode. Elemental analyses was obtained on a Thermo
Finnigan Flash EA 1112 CHN analyzer. Purification of com-
Pyrazole derivatives have been used as important pharma-
cores and synthons in the field of organic chemistry and drug
designing. For instance, a series of 1-acetyl-3,5-diphenyl-4,5-
dihydro-(1H)-pyrazoles synthesized were investigated for their
ability to inhibit selectively monoamine oxidases, swine kidney

Vol. 29, No. 7 (2017)
Synthesis and Antimicrobial Activities of Chalcones 1539
pounds was done by column chromatography on silica gel
(70-230 mesh Merck).
(E)-1-(4-Chlorophenyl)-3-(2,4,5-trimethoxyphenyl)-
prop-2-en-1-one (3c): By reaction of 2,4,5-trimethoxybenzal-
dehyde (1, 10 mmol) and 4-chloroacetophenone (2c, 10 mmol)
The synthetic method involves the synthesis of a series of
chalcones (3a-g) by the reaction of 2,4,5-trimethoxybenzal-
dehyde (1) with substituted acetophenone (2a-g) in the
presence of base in alcohol medium. The cyclocondensation
reaction of chalcones (3a-g) with phenyl hydrazine hydro-
chloride (4) and a few drops of concentrated hydrochloric acid
in methyl alcohol to obtain pyrazole derivatives (5a-g) in good
yields. The schematic diagram for the synthesis of chalcones
and pyrazolines is outlined in Fig. 1.
1
in 94 % yield, m.p. 158–159 °C; H NMR: δ 3.848 (s, 9H,
OCH3), 6.718–6.751 (m, 2H, Ar–H), 7.316 (d, 1H, C=CH),
7.452–7.778 (m, 4H,Ar–H), 8.116 (d, 1H, CH=C);Anal. calcd.
(%) for C18H17O4Cl(m/z: 332): C, 64.97; H, 5.15; Found (%):
C, 64.86; H, 5.08.
(E)-1-(4-Methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)-
prop-2-en-1-one [12] (3d): By reaction of 2,4,5-trimethoxy-
benzaldehyde (1, 10 mmol) and 4-methoxyacetophenone (2d,
10 mmol) in 91 % yield, m.p. 104-105 °C; 1H NMR: δ 3.850
(s, 12H, OCH3), 6.726–6.744 (m, 2H, Ar–H), 7.324 (d, 1H,
C=CH), 7.458–7.781 (m, 4H, Ar–H), 8.184-8.222 (d, 1H,
CH=C);Anal. calcd. (%) for C19H20O5 (m/z: 328): C, 69.50; H,
6.14; Found (%): C, 69.39; H, 6.05.
Synthesis of chalcones (3a-g): A mixture of 2,4,5-tri-
methoxybenzaldehyde (1, 5 mmol), substituted acetophenone
(2a-g, 5 mmol) and sodium hydroxide (5 mmol) in 95 % ethyl
alcohol (25 mL) was stirred at room temperature for 3 h. The
progress of the reaction was monitored by TLC. After the
completion of the reaction, the mixture was poured in to ice
cold water and kept in the refrigerator for overnight. The solid
formed was filtered and washed with cold hydrochloric acid
(5 %). Crude products obtained were crystallized from methyl
alcohol to obtain pure chalcones (3a-g).
(E)-1-(3-Methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)-
prop-2-en-1-one (3e): By reaction of 2,4,5-trimethoxybenzal-
dehyde, 1 (10 mmol) and 3-methoxyacetophenone (2e, 10
mmol) in 82 % yield, m.p. 158–159 °C; 1H NMR: δ 3.852 (s,
12H, OCH3), 6.732–6.752 (m, 2H, Ar–H), 7.330 (d, 1H,
C=CH), 7.460–7.787 (m, 4H, Ar–H), 8.202 (d, 1H, CH=C);
Anal. calcd. (%) for C19H20O5 (m/z: 328): C, 69.50; H, 6.14;
Found (%): C, 69.41; H, 6.08.
(E)-1-Phenyl-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-
one (3a): By reaction of 2,4,5-trimethoxybenzaldehyde (1,
10 mmol) and acetophenone (2a, 10 mmol) in 82 % yield,
1
m.p. 141-142 °C; H NMR: δ 3.845 (s, 9H, OCH3), 6.718–
(E)-1-(2-Methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)-
prop-2-en-1-one (3f): By reaction of 2,4,5-trimethoxybenzal-
dehyde (1, 10 mmol) and 2-methoxyacetophenone (2f,
10 mmol) in 85 % yield, m.p. 140–141 °C; 1H NMR: δ 3.850
(s, 12H, OCH3), 6.730–6.754 (m, 2H, Ar–H), 7.311 (d, 1H,
C=CH), 7.455–7.788 (m, 4H, Ar–H), 8.172 (d, 1H, CH=C);
Anal. calcd. (%) for C19H20O5 (m/z: 328): C, 69.50; H, 6.14;
Found (%): C, 69.37; H, 6.04.
6.752 (m, 2H, Ar–H), 7.322 (d, 1H, C=CH), 7.458–7.766 (m,
5H,Ar–H), 8.112 (d, 1H, CH=C);Anal. calcd. (%) for C18H18O4
(m/z: 298): C, 72.47; H, 6.08; Found (%): C, 72.37; H, 5.98.
(E)-1-(4-Fluorophenyl)-3-(2,4,5-trimethoxyphenyl)-
prop-2-en-1-one (3b): By reaction of 2,4,5-trimethoxybenzal-
dehyde (1, 10 mmol) and 4-fluoroacetophenone (2b, 10 mmol)
1
in 88 % yield, m.p. 126-127 °C; H NMR: δ 3.848 (s, 9H,
OCH3), 6.720–6.749 (m, 2H, Ar–H), 7.310 (d, 1H, C=CH),
7.440–7.780 (m, 4H,Ar–H), 8.120 (d, 1H, CH=C);Anal. calcd.
(%) for C18H17O4F (m/z: 316): C, 68.35; H, 5.42; Found (%):
C, 68.22; H, 5.28.
(E)-1-(Benzo[d][1,3]dioxol-5-yl)-3-(2,4,5-trimethoxy-
phenyl)prop-2-en-1-one (3g) [13]: By reaction of 2,4,5-
trimethoxybenzaldehyde (1, 10 mmol) and 1-(benzo[d][1,3]-
dioxol-5-yl)ethanone (2g, 10 mmol) in 89 % yield, m.p. 126-
COCH3
CHO
H3CO
H3CO
OCH3
R
R2
OCH3
MeOH/KOH
+
R1
R1
H3CO
R2
O
R
OCH3
3a-g
1
2
NHNH2·HCl
MeOH/HCl
4
a) R=H, R1=H, R2=H;
OCH3
2
H3CO
b) R=F, R1=H, R2=H;
R
c) R=Cl, R1=H, R2=H;
d) R=OCH3, R1=H, R2=H;
e) R=H, R1=OCH3, R2=H;
f) R=H, R1=H, R2=OCH3;
g) R=R1=OCH2O, R2=H.
H3CO
R1
N
N
R2
5a-g
Fig. 1. Schematic diagram for the synthesis of pyrazolines (5a-g)

1540 Ramyashree et al.
Asian J. Chem.
1
128 °C; H NMR: δ 3.848 (s, 9H, OCH3), 6.031 (s, 2H,
149.22 (1C), 153.04 (1C, C-4); MS m/z: 424 (M+, 37Cl), 422
(M+, 35Cl); Anal. calcd. (%) for C24H23ClN2O3 (%): C, 68.16;
H, 5.48; N, 6.62; Found (%): C, 68.10; H, 5.36; N, 6.54.
3-(4-Methoxyphenyl)-1-phenyl-5-(2,4,5-trimethoxy-
phenyl)-4,5-dihydro-1H-pyrazole (5d): By reaction of (E)-
1-(4-methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-
1-one (3d, 10 mmol) and phenyl hydrazine hydrochloride (4,
10 mmol) in 96 % yield, m.p. 133–134 °C; 1H NMR: δ 2.992-
3.133 (dd, 1H, J = 7.2 Hz, 14.5 Hz, C3-Ha), 3.841 (s, 3H,
OCH3), 3.864 (s, 9H, OCH3), 3.688-3.732 (dd, 1H, J = 8.2
Hz, 15.6 Hz, C3-Hb), 5.430-5.483 (dd, 1H, J = 6.8 Hz, 13.3
Hz, C2-H), 7.012–7.725 (m, 11H, Ar–H); 13C NMR: δ 39.56
(1C, C-2), 53.08 (1C, C-3), 55.62 (3C), 55.74 (1C), 99.86 (1C),
112.60 (1C), 114.56 (2C), 115.88 (2C), 120.10 (1C), 122.48
(1C), 128.30 (2C), 128.74 (1C), 129.14 (2C), 140.35 (1C),
142.22 (1C), 147.70 (1C), 148.20 (1C), 152.66 (1C, C-4),
161.82 (1C); MS m/z: 418 (M+); Anal. calcd. (%) for
C25H26N2O4 (%): C, 71.75; H, 6.26; N, 6.69; Found (%): C,
71.64; H, 6.13; N, 6.54.
OCH2O), 6.740–6.768 (m, 2H, Ar–H), 7.308 (d, 1H, C=CH),
7.448–7.750 (m, 3H,Ar–H), 8.190 (d, 1H, CH=C);Anal. calcd.
(%) for C19H18O6 (m/z: 342): C, 66.66; H, 5.30; Found (%): C,
66.52; H, 5.22.
General procedure for the synthesis of pyrazolines (5a-
g): To a stirred solution of chalcones (3a-g, 0.01 mol) and
phenyl hydrazine hydrochloride (4, 0.01 mol) in methyl alcohol
(15 mL), concentrated hydrochloric acid (7-8 drops) were
added. The mixture was refluxed for 3-4 h and the progress of
the reaction was monitored by TLC. After completion, the
reaction mixture was poured in to ice cold water; solid sepa-
rated was filtered, washed with ice cold water and dried. The
products were purified column chromatography using silica
gel (60-120 mesh) and ethyl acetate:dichloromethane (1:4 v/v)
as eluent.
1,3-Diphenyl-5-(2,4,5-trimethoxyphenyl)-4,5-dihydro-
1H-pyrazole (5a): By reaction of (E)-1-phenyl-3-(2,4,5-
trimethoxyphenyl)prop-2-en-1-one (3a, 10 mmol) and phenyl-
hydrazine hydrochloride (4, 10 mmol) in 81 % yield, m.p.
3-(3-Methoxyphenyl)-1-phenyl-5-(2,4,5-trimethoxy-
phenyl)-4,5-dihydro-1H-pyrazole (5e): By reaction of (E)-
1-(3-methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-
1-one (3e, 10 mmol) and phenyl hydrazine hydrochloride (4,
1
112–114 °C; H NMR: δ 2.990.3.147 (dd, 1H, J = 6.7 Hz,
13.6 Hz, C3-Ha), 3.852 (s, 9H, OCH3), 3.660-3.738 (dd, 1H, J
= 6.8 Hz, 14.8 Hz, C3-Hb), 5.432-5.502 (dd, 1H, J = 7.6 Hz,
15.2 Hz, C2-H), 7.218–7.965 (m, 12H, Ar–H); 13C NMR: δ
40.44 (1C, C-2), 53.48 (1C, C-3), 55.75 (3C), 99.98 (1C),
112.95 (1C), 115.92 (2C), 120.80 (1C), 122.50 (1C), 128.37
(2C), 128.90 (2C), 129.44 (2C), 131.20 (1C), 135.56 (1C),
140.26 (1C), 142.88 (1C), 147.71 (1C), 148.94 (1C), 154.12
(1C, C-4); MS m/z: 388 (M+, 24), 387(100); Anal. calcd. (%)
for C24H24N2O3 (%): C, 74.21; H, 6.23; N, 7.21; Found (%): C,
74.10; H, 6.12; N, 7.08.
1
10 mmol) in 83 % yield, m.p. 1127–129 °C; H NMR: δ
2.998.3.201 (dd, 1H, J = 7.0 Hz, 14.6 Hz, C3-Ha), 3.848 (s,
3H, OCH3), 3.871 (s, 9H, OCH3), 3.656-3.718 (dd, 1H, J =
8.0 Hz, 15.0 Hz, C3-Hb), 5.416-5.485 (dd, 1H, J = 9.1 Hz,
15.2 Hz, C2-H), 6.992–7.754 (m, 11H, Ar–H); 13C NMR: δ
39.80 (1C, C-2), 53.26 (1C, C-3), 55.62 (3C), 55.70 (1C),
100.06 (1C), 112.44 (1C), 114.60 (2C), 115.80 (2C), 120.24
(1C), 122.53 (1C), 128.28 (2C), 128.70 (1C), 129.34 (2C),
140.60 (1C), 142.76 (1C), 147.92 (1C), 148.40 (1C), 152.84
(1C, C-4), 161.77 (1C); MS m/z: 418 (M+); Anal. calcd. (%)
for C25H26N2O4 (%): C, 71.75; H, 6.26; N, 6.69; Found (%): C,
71.62; H, 6.18; N, 6.60.
3-(4-Fluorophenyl)-1-phenyl-5-(2,4,5-trimethoxyphenyl)-
4,5-dihydro-1H-pyrazole (5b): By reaction of (E)-1-(4-
fluorophenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-one
(3b, 10 mmol) and phenyl hydrazine hydrochloride (4, 10
1
mmol) in 92 % yield, m.p. 124–125 °C; H NMR: δ 2.998-
3-(2-Methoxyphenyl)-1-phenyl-5-(2,4,5-trimethoxy-
phenyl)-4,5-dihydro-1H-pyrazole (5f): By reaction of (E)-
1-(2-methoxyphenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-
1-one (3f, 10 mmol) and phenyl hydrazine hydrochloride (4,
10 mmol) in 83 % yield, m.p. 144–146 °C; 1H NMR: δ 3.028-
3.210 (dd, 1H, J = 7.5 Hz, 14.2 Hz, C3-Ha), 3.850 (s, 3H, OCH3),
3.882 (s, 9H, OCH3), 3.640-3.696 (dd, 1H, J = 8.6 Hz, 15.3
Hz, C3-Hb), 5.430-5.462 (dd, 1H, J = 9.0 Hz, 15.0 Hz, C2-H),
6.997–7.760 (m, 11H, Ar–H); MS m/z: 418 (M+); Anal. calcd.
(%) for C25H26N2O4 (%): C, 71.75; H, 6.26; N, 6.69; Found
(%): C, 71.70; H, 6.15; N, 6.57.
3.142 (dd, 1H, J = 7.7 Hz, 13.0 Hz, C3-Ha), 3.863 (s, 9H,
OCH3), 3.648-3.710 (dd, 1H, J = 6.8 Hz, 13.4 Hz, C3-Hb),
5.454-5.501 (dd, 1H, J = 8.3 Hz, 15.8 Hz, C2-H), 6.986–7.624
(m, 11H, Ar–H); 13C NMR: δ 40.37 (1C, C-2), 53.16 (1C, C-
3), 55.65 (3C), 100.08 (1C), 112.44 (1C), 115.82 (2C), 116.42
(2C), 119.16 (1C), 122.34 (1C), 128.95 (2C), 129.66 (2C),
133.22 (1C), 140.78 (1C), 142.10 (1C), 148.55 (1C), 149.14
(1C), 153.99 (1C, C-4), 164.95 (1C); MS m/z: 406 (M+);Anal.
calcd. (%) for C24H23N2O3F (%): C, 70.92; H, 5.70; N, 6.89;
Found (%): C, 70.80; H, 5.56; N, 6.75.
3-(4-Chlorophenyl)-1-phenyl-5-(2,4,5-trimethoxy-
phenyl)-4,5-dihydro-1H-pyrazole (5c): By reaction of (E)-
1-(4-chlorophenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-
one (3c, 10 mmol) and phenyl hydrazine hydrochloride (4, 10
mmol) in 90 % yield, m.p. 99–101 °C;1H NMR: δ 3.008.3.166
(dd, 1H, J = 7.9 Hz, 13.8 Hz, C3-Ha), 3.850 (s, 9H, OCH3),
3.672-3.744 (dd, 1H, J = 8.0 Hz, 14.9 Hz, C3-Hb), 5.442-5.496
(dd, 1H, J = 9.0 Hz, 16.1 Hz, C2-H), 7.006–7.624 (m, 11H,
Ar–H); 13C NMR: δ 40.30 (1C, C-2), 53.33 (1C, C-3), 55.68
(3C), 99.95 (1C), 112.98 (1C), 115.76 (2C), 119.92 (1C),
122.50 (1C), 128.30 (2C), 128.84 (2C), 129.72 (2C), 134.15
(1C), 136.80 (1C), 142.17 (1C), 143.52 (1C), 148.34 (1C),
3-(Benzo[d][1,3]dioxol-5-yl)-1-phenyl-5-(2,4,5-trime-
thoxyphenyl)-4,5-dihydro-1H-pyrazole (5g): By reaction
of (E)-1-(benzo[d][1,3]dioxol-5-yl)-3-(2,4,5-trimethoxy-
phenyl)prop-2-en-1-one (3g, 10 mmol) and phenyl hydrazine
hydrochloride (4, 10 mmol) in 78 % yield, m.p. 1106–108 °C;
1H NMR: δ 3.016.3.202 (dd, 1H, J = 7.0 Hz, 14.7 Hz, C3-Ha),
3.862 (s, 9H, OCH3), 3.655-3.698 (dd, 1H, J = 8.1 Hz, 14.5
Hz, C3-Hb), 5.445-5.478 (dd, 1H, J = 9.0 Hz, 15.0 Hz, C2-H),
6.050 (s, 2H, OCH2O), 6.984–7.746 (m, 10H, Ar–H); 13C
NMR: δ 40.12 (1C, C-2), 53.40 (1C, C-3), 55.85 (3C), 99.50
(1C), 102.26 (1C), 110.55 (1C), 112.96 (1C), 113.70 (1C),
115.82 (2C), 119.90 (1C), 121.22 (1C), 122.73 (1C), 126.12

Vol. 29, No. 7 (2017)
Synthesis and Antimicrobial Activities of Chalcones 1541
(1C), 129.65 (2C), 141.00 (1C), 142.88 (1C), 147.22 (1C),
148.84 (1C), 149.66 (1C), 152.20 (1C), 153.24 (1C, C-4); MS
m/z: 434 (M+); Anal. calcd. (%) for C25H24N2O5 (%): C, 69.43;
H, 5.59; N, 6.48; Found (%): C, 69.32; H, 5.45; N, 6.37.
In 13C NMR spectrum, compound 3d showed a signal at
δ 39.56, 53.08 and 152.66 ppm due to C-2, C-3 amd C-4 carbons
of the pyrazole ring. A signal appeared for three carbons at δ
55.75 ppm was assigned to three OCH3 carbons. An array of
signals appeared at δ 99.98, 112.95, 115.92, 120.80, 122.50,
128.37, 128.90, 129.44, 131.20, 135.56, 140.26, 142.88, 147.71,
148.94 and 154.12 ppm were ambiguously assigned to aromatic
carbons. Compound 3d showed M+ ion peak corresponding
to its molecular mass and a base peak corresponds to m/z (M-1).
Further elemental analysis showed that the analytical data
obtained for the compound were in good agreement with theore-
tically calculated values. Similar and consistent pattern signals
were observed in the 1H NMR, 13C NMR and Mass spectra of
the synthesized series of compounds 3b-g, which strongly
supports the structure proof for the synthesized compounds.
Antimicrobial activity:Antimicrobial studies of synthe-
sized compounds 3a-g and 5a-g were assessed by minimum
inhibitory concentration (MIC) by serial dilution method
[14,15]. The compounds were screened for their antimicrobial
activities against Gram-negative bacteria Escherichia coli,
Gram-positive bacteria Staphylococcus aureus, fungi species
Aspergillus nigar and Aspergillus flavus. The experiments were
carried out in triplicate; the results were taken as a mean of
three determinations. The antibiotics ciprofloxacin and nystatin
were used as standard drugs for antibacterial and antifungal
studies respectively. The results of MIC’s were tabulated in
Table-1.
RESULTS AND DISCUSSION
1H NMR, elemental analysis and X-ray diffraction crystallo-
graphic studies provide the structural proof of the compounds
3a-g. The structural assignments were made by NMR analysis
by considering compound, 3d as the representative compound
among the series. In 1H NMR spectra, the alkenyl proton each
for C=CH and CH=C appeared as doublets at δ 6.726–6.744
and 8.184-8.222 ppm respectively. The signals appeared as
singlet for twelve protons at δ 3.850 were assigned to OCH3
protons, while as multiplet for two and four protons each at δ
6.726–6.744 and δ 7.458–7.781 ppm were due to aromatic
protons. The analytical data obtained for the compound 3d were
in good agreement with theoretically calculated data. Further,
the structure was confirmed by single crystal X-ray diffraction
studies and was depicted in ORTEP diagram (Fig. 2) [12]. All
the compounds of the series 3a-g showed similar spectral and
analytical data, among them the structure of 3g was confirmed
by single crystal X-ray diffraction studies and was depicted in
ORTEP diagram (Fig. 2) [13].
The structural elucidation of the compounds, 3a-g were
1
provided by H NMR, 13C NMR, Mass spectral studies and
elemental analysis. The structural assignments were made by
NMR analysis by considering compound, 5a as the represen-
The synthesized chalcones (3a-g) and pyrazoles (5a-g)
exerted a wide range of in vitro antimicrobial activities against
the tested organisms. Results of the study reveal that the target
pyrazole derivatives (5a-g) exerted increased antimicrobial
susceptibilities in comparison to their intermediate chalcones
(3a-g) against all the tested organisms.Among the synthesized
series, compounds 3c and 5c having chloro substitution showed
a greater activity against all the tested species. Compounds
3d, 3e, 3f, 5d, 5e and 5f with methoxy substitutions in the
aromatic ring found moderately active; while compounds 3g,
5b and 5g showed good activities and compounds 3a and 3b
exhibited promising inhibitory activities against the tested
organisms.
1
tative compound among the series. In H NMR spectra, two
methylene protons designated as C3-Ha and C3-Hb of the newly
formed pyrazoline ring is diastereotopic. The C3-Ha, C3-Hb and
C2-H protons appeared as a doublet of doublets. The doublet
of doublet for C3-Ha appeared in the region δ 2.990.3.147 (J =
6.7, 13.6 Hz) ppm; doublet of doublet for C3-Hb appeared in
the region δ 3.660-3.738 (J = 6.8, 14.8 Hz) ppm and that of
C2-H in the region δ 5.432-5.502 (J = 7.6, 15.2Hz) ppm.
Among C3-Ha, C3-Hb and C2-H protons, C2-H is the most
deshielded due to its close proximity to benzene ring and elec-
tronegative nitrogen. C2-H couples not only with C3-Ha but
also with C3-Hb and appears as doublet of doublet instead of a
triplet.A collection of signal observed singlet for nine protons
at δ 3.852 ppm and as multiplet for twelve protons in the region
δ 7.218–7.965 ppm were assigned to OCH3 and aromatic
protons respectively.
Conclusion
The simple easy accessible procedure for the synthesis of
pyrazoles via Claisen-Schimidt condensation of aromatic
aldehydes and ketones and their in vitro antimicrobial activity
3g
3d
Fig. 2. ORTEP diagram of 3d and 3g with 50 % probability ellipsoids

1542 Ramyashree et al.
Asian J. Chem.
TABLE-1
ANTIMICROBIAL ACTIVITIES OF THE COMPOUNDS 3a-g AND
5a-g AGAINST BACTERIAL AND FUNGAL STAINS
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One of the authors (D. Ramyashree) is grateful to the
Institution of Excellence, University of Mysore, Mysuru, India
for spectral analysis.