Chalcones as promising pesticidal agents against diamondback moth (Plutella xylostella): Microwave-assisted synthesis and structure-activity relationship

Article abstract of DOI:10.1007/s00044-011-9602-8

A series of chalcones (A-CH=CH-CO-B) were synthesized under microwave irradiation, and for the first time their pesticidal activity against diamondback moth (Plutella xylostella) was evaluated to identify the promising lead structures. The structure-activity relationship (SAR) analysis revealed that electron-withdrawing substituents on ring A of chalcone provided good pesticidal agents, whereas, ring B can bear either electron-withdrawing or electron-releasing substituents. Moreover, compound 22 having para-Cl substitution on ring A as well on ring B showed maximum activity with LC ₅₀ value of 170.24 μg mL^-1. Springer Science+Business Media, LLC 2011.

Full text of DOI:10.1007/s00044-011-9602-8

MEDICINAL
CHEMISTRY
RESEARCH
Med Chem Res (2012) 21:922–931
DOI 10.1007/s00044-011-9602-8
ORIGINAL RESEARCH
Chalcones as promising pesticidal agents against diamondback
moth (Plutella xylostella): microwave-assisted synthesis
and structure–activity relationship
•
Rakesh Kumar Prabha Sharma Amit Shard
•
•
•
Dhananjay Kumar Tewary Gireesh Nadda
•
Arun Kumar Sinha
Received: 1 October 2010 / Accepted: 7 February 2011 / Published online: 20 February 2011
Ó Springer Science+Business Media, LLC 2011
Abstract A series of chalcones (A–CH=CH–CO–B)
were synthesized under microwave irradiation, and for the
first time their pesticidal activity against diamondback
moth (Plutella xylostella) was evaluated to identify the
promising lead structures. The structure–activity relation-
ship (SAR) analysis revealed that electron-withdrawing
substituents on ring A of chalcone provided good pesticidal
agents, whereas, ring B can bear either electron-with-
drawing or electron-releasing substituents. Moreover,
compound 22 having para-Cl substitution on ring A as well
on ring B showed maximum activity with LC50 value of
Control of P. xylostella has largely been dependent on use
of various pesticides such as substituted hydrocarbons
(Miyata et al., 1986), carbamates (Miyata et al., 1986),
organophosphates (Miyata et al., 1986), pyrethroids (Miy-
ata et al., 1986; Schuler et al., 1998), benzophenyl ureas
(Sun, 1990), emamectin benzoate (Zhao et al., 2006),
besides biopesticides such as Bacillus thuringiensis (Song,
1991; Sun, 1990; Tabashnik et al., 1990). However,
development of resistance for various classes of pesticides
is a major concern for the effective management of this
important crucifer defoliator (Miyata et al., 1986; Talekar
and Griggs, 1986; Sun, 1990; Tabashnik et al., 1990; Song,
1991; Shelton et al., 1993; Schuler et al., 1998; Zhao et al.,
2006). On the other side, adverse effects of some of the
above pesticides (Eskenazi et al., 1999) to humans, animals,
and environment besides difficulties associated with their
preparations have fostered the need for developing new
insect control agents with greater selectivity, better health,
and environmental profiles.
170.24 lg mL-1
.
Keywords Plutella xylostella ꢀ Chalcones ꢀ Pesticidal ꢀ
Structure–activity relationship ꢀ Microwave
Introduction
The diamondback moth, Plutella xylostella (L.) (Lepidop-
tera: Plutellidae), is one of the most destructive pests of
crucifers worldwide (Talekar and Shelton, 1993; Verkerk
and Wright, 1996). Larvae of P. xylostella, feed on the
foliage of the cruciferous plants from the seedling stage to
harvest and greatly reduce the yield and quality of produce.
Chalcones (1,3-diaryl-2-propen-1-ones) being structur-
ally simple class of natural products have assumed
importance because of their wide ranging biological pro-
files such as anti-inflammatory, antimalarial, antimicrobial,
and anticancer activity (Nowakowska, 2007; Go et al.,
2005; Liu et al., 2001; Dimmock et al., 1999; Mod-
zelewska et al., 2006). On the other side, their synthesis
with different substitution pattern on the two aryl rings
(A and B) further allow exploring a large number of
desired potential analogs. As a result, number of reports on
the structure–activity relationship (SAR) of the substituted
chalcones for various bioactivities still continue to appear
in the literature including a recent study on antimalarial
activity by our group (Kumar et al., 2010). Moreover,
insect antifeedant (Nalwar et al., 2009), nematicidal
(Awasthi et al., 2009; Gonza0lez and Braun, 1998), and
R. Kumar ꢀ A. Shard ꢀ A. K. Sinha (&)
Natural Plant Products Division, Institute of Himalayan
Bioresource Technology, Council of Scientific and Industrial
Research, Palampur, HP 176061, India
e-mail: aksinha08@rediffmail.com
P. Sharma ꢀ D. K. Tewary ꢀ G. Nadda
Hill Area Tea Science Division, Institute of Himalayan
Bioresource Technology, Council of Scientific and Industrial
Research, Palampur, HP 176061, India
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Med Chem Res (2012) 21:922–931
923
larvicidal (Das et al., 2005; Begum et al., 2010; Gautam
and Chourasia, 2010) activities have also been shown by
chalcone derivatives. However, to the best of our knowl-
edge, pesticidal activity of chalcones against one of the
most destructive crucifer defoliator, P. xylostella has not
yet been explored.
extract was washed with brine (2 9 5 mL), dried over
sodium sulfate, and concentrated under reduced pressure.
The obtained crude mixture was purified through column
chromatography (silica gel 60–120 mesh size) and recrys-
tallization with methanol to obtain the preferred pure
product.
In this study, for the first time, we have studied the
pesticidal SAR of chalcones against P. xylostella, wherein,
Cl substitution on ring A as well as on ring B of chalcone
was found to be an important feature for good activity. All
the chalcones were synthesized under microwave irradia-
tion which offered several advantages over conventional
techniques in terms of shorter reaction time, improvement
in the yield, besides reduction in consumption of solvent
(de la Hoz et al., 2005).
4-(2,4,5-Trimethoxyphenyl)but-3-en-2-one (1)
1
Deep yellow solid; yield 65%; m.p. 98–101°C. H-NMR:
(300 MHz, CDCl3): 7.94 (1H, d, J = 16.4 Hz), 7.10 (1H,
s), 6.69 (1H, d, J = 16.4 Hz), 6.56 (1H, s), 3.98 (3H, s),
3.94 (6H, s), and 2.42 (3H, s). 13C-NMR: (75.4 MHz,
CDCl3) 199.3, 154.4, 153.0, 143.9, 138.7, 125.7, 115.3,
110.8, 97.3, 56.9, 56.8, 56.5, and 27.4. HRMS-ESI: m/z
[M ? H]? for C13H16O4, calculated, 237.1121; observed,
237.1109.
Experimental
Synthesis of 4-(4-methoxyphenyl)but-3-en-2-one (2)
Materials and instruments
Compound 2 was prepared from anethole (Scheme 1)
employing a procedure similar to that described for com-
pound 1. Yellow solid; yield 61%; m.p. 67–71°C. 1H-
NMR: (300 MHz, CDCl3); 7.48–7.42 (3H, m), 6.90 (2H, d,
J = 8.3 Hz), 6.61 (1H, d, J = 16.4 Hz), 3.81 (3H, s), and
2.33 (3H, s); 13C-NMR: (75.4 MHz, CDCl3) 198.1, 161.5,
143.1, 129.8, 127.0, 124.9, 114.3, 55.2, and 27.2.
All the reagents/solvents were obtained from commercial
sources (Merck or Sigma–Aldrich) and used without fur-
ther purification. Column chromatography was performed
using silica gel (60–120 mesh size). CEM DiscoverÓ
focused microwave (2450 MHz, 300 W) was used for the
1
synthesis of chalcone derivatives. H (300 MHz) and 13C
(75.4 MHz) NMR spectra were recorded on a Bruker
Avance-300 spectrometer using tetramethylsilane (TMS)
as internal standard. HRMS-ESI spectra were determined
using micromass Q-TOF ultima spectrometer.
General procedure for microwave-assisted synthesis
of chalcones (4–24) using aqueous NaOH
as a condensing agent (Scheme 2)
Microwave-assisted synthesis of 4-(2,4,5-
trimethoxyphenyl)but-3-en-2-one (1) from natural b-
asarone of Acorus calamus oil (Scheme 1)
Compounds 4–24 were prepared by Claisen-Schmidt con-
densation (Batovska et al., 2009), wherein, equimolar
amounts of acetophenone (3 mmol) and benzaldehyde
(3 mmol) were taken in MeOH (5 mL). To this solution,
10% aqueous NaOH (6 mmol) was added, and the mixture
was irradiated under focused microwave irradiation
(110 W, 55°C) with continuous stirring for 20 min (or till
completion of the reaction). The obtained precipitates were
washed with dilute HCl, excess of water, methanol, dried in
air, and finally recrystallized from methanol to obtain pure
chalcones.
A mixture of b-asarone (0.31 g, 1.5 mmol), NaIO4 (1.17 g,
5.5 mmol), OsO4 (0.0004 g, 0.0015 mmol), and benzyl-
triethylammonium chloride (0.01 g, 0.04 mmol) were dis-
solved in H2O–THF (3 mL, 4:1) and irradiated under
focused microwave (150 W, 100°C) irradiation. After
completion of the reaction, the mixture was extracted with
ethyl acetate (3 9 15 mL) and vacuum evaporated to give
a crude mixture, which on column chromatography with
silica gel provided 2,4,5-trimethoxybenzaldehyde (Sinha
et al., 2003; Kumar et al., 2010) in 83% yield. Subse-
quently, the above benzaldehyde (0.24 g, 1.22 mmol) was
allowed to react with excess of acetone (3 mL) in the
presence of ionic liquid 1-methyl-3-butanesulfonic acid
imidazolium hydrogen sulfate ([MIMBSA]HSO4) (1 g)
under focused microwave irradiation (100 W, 75°C). The
reaction mixture was vacuum evaporated and extracted
with ethyl acetate (3 9 15 mL). The combined organic
For comparison purpose, the above reactions were also
accomplished at room temperature stirring where longer
reaction time (3 h versus 20 min) besides large amount of
solvent is required.
Compound 3 was prepared by Claisen-Schmidt con-
densation of 4-hydroxy-3-methoxybenzaldehyde (3 mmol)
with excess of acetone (3 mL) using 10% aqueous NaOH
(6 mmol) under microwave. The structures of synthesized
chalcones (3–24) were confirmed by NMR spectral data as
follows:
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Med Chem Res (2012) 21:922–931
O
Scheme 1 Synthesis of
chalcone derivatives 1 and 2
from natural phenylpropenes
under microwave irradiation
CHO
OsO4/NaIO4
M.W
CH3COCH3, M.W
[MIMBSA]HSO4
R
R
R
1-2
R = 2,4,5-tri-OCH3; β-Asarone
R = 4-OCH3; Anethole
Scheme 2 Synthesis of
chalcone derivatives 4–24 from
substituted acetophenones and
benzaldehydes under
O
O
CHO
10% aqueous NaOH
A
+
B
B
A
microwave irradiation
MeOH, M.W
(110W, 55°C)
R'
R
R'
R
4-24
R = OCH3, Cl, F, Br etc.
R' = OCH3, CH3, Cl, NO2, OH, OCH2CH=CH2, OCH2O etc.
4-(4-Hydroxy-3-methoxyphenyl)but-3-en-2-one (3)
(Sharma et al., 2006)
7.59 (1H, d, J = 15.3 Hz), 7.51–7.42 (3H, m), 6.94 (2H, d,
J = 8.4 Hz), and 3.81 (3H, s); 13C-NMR: (75.4 MHz,
CDCl3) 188.5, 163.5, 140.9, 133.7, 132.6, 131.8, 131.0,
130.9, 130.6, 128.7, 126.9, 126.3, 125.4, 125.0, 124.6,
123.6, 113.7, and 55.5.
Yellow solid; yield 56%; m.p.128–129°C. 1H-NMR:
(300 MHz, CDCl3); 7.48 (1H, d, J = 16.2 Hz), 7.10–7.05
(2H, m), 6.94 (1H, d, J = 8.2 Hz), 6.61 (1H, d,
J = 16.2 Hz), 3.92 (3H, s), and 2.37 (3H, s); 13C-NMR:
(75.4 MHz, CDCl3) 198.9, 148.7, 147.3, 144.2, 127.2,
125.3, 123.9, 115.2, 109.7, 56.3 and 27.6.
1,3-Bis(4-methoxyphenyl)prop-2-en-1-one (7) (Dong et al.,
2008)
Light yellow solid; yield 93%; m.p. 100–102°C. 1H-NMR:
(300 MHz, CDCl3); 8.04 (2H, d, J = 8.7 Hz), 7.80 (1H, d,
J = 16.1 Hz), 7.59 (2H, d, J = 8.2 Hz), 7.45 (1H, d,
J = 16.1 Hz), 6.97–6.89 (4H, m), 3.84 (3H, s), and 3.81
(3H, s); 13C-NMR: (75.4 MHz, CDCl3) 188.9, 163.5,
161.8, 144.0, 131.6, 130.9, 130.3, 128.1, 119.8, 114.6,
114.0, and 55.7.
1-(4-Nitrophenyl)-3-(thiophen-2-yl)prop-2-en-1-one (4)
Yellow solid; yield 75%; m.p. 171–173°C. 1H-NMR:
(300 MHz, DMSO); 8.34–8.30 (4H, m), 7.99 (1H, d,
J = 15.0 Hz), 7.83 (1H, s), 7.73 (1H, s), 7.57 (1H, d,
J = 15.0 Hz), and 7.21 (1H, s); 13C-NMR: (75.4 MHz,
DMSO) 188.3, 150.2, 142.8, 139.9, 138.7, 134.2, 131.8,
130.2, 129.3, 124.3 and 120.5. HRMS-ESI: m/z [M ? H]?
for C13H9O3NS, calculated, 260.0376; observed, 260.0372.
1-(4-Chlorophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one
(8) (Liu et al., 2001)
3-(Furan-2-yl)-1-(4-nitrophenyl)prop-2-en-1-one (5)
Creamy solid; yield 89%; m.p. 120–124°C. 1H-NMR:
(300 MHz, CDCl3); 8.02–7.97 (2H, m), 7.86 (1H, d,
J = 16.6 Hz), 7.66–7.62 (2H, m), 7.52–7.48 (2H, m), 7.44
(1H, d, J = 16.6 Hz), 7.00–6.96 (2H, m), and 3.89 (3H, s).
13C-NMR: (75.4 MHz, CDCl3) 189.4, 162.2, 145.5, 139.3,
137.2, 130.7, 130.2, 129.2, 127.8, 119.5, 114.8, and 55.7.
Yellow solid; yield 79%; m.p. 139–142°C. 1H-NMR:
(300 MHz, CDCl3); 8.27 (2H, d, J = 8.4 Hz), 8.09 (2H, d,
J = 8.8 Hz), 7.58–7.49 (2H, m), 7.35 (1H, d, J =
15.3 Hz), 6.73 (1H, d, J = 4.0 Hz), and 6.48 (1H, s); 13C-
NMR: (75.4 MHz, CDCl3) 188.1, 151.2, 150.0, 145.6,
142.9, 132.1, 129.3, 123.8, 118.3, 117.7 and 113.0. HRMS-
ESI: m/z [M ? H]? for C13H9NO4, calculated, 244.0604;
observed, 244.0615.
3-(4-Chlorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one
(9) (Dong et al., 2008)
Creamy solid; yield 88%; m.p. 128–131°C. 1H-NMR:
(300 MHz, CDCl3); 7.97 (2H, d, J = 9.2 Hz), 7.69 (1H, d,
J = 16.1 Hz), 7.50–7.41 (3H, m), 7.31 (2H, d,
J = 8.1 Hz), 6.92 (2H, d, J = 8.7 Hz), and 3.81 (3H, s).
13C-NMR: (75.4 MHz, CDCl3) 188.4, 163.5, 142.4, 136.1,
133.6, 130.8, 129.5, 129.2, 122.3, 113.9, and 55.5.
1-(4-Methoxyphenyl)-3-(naphthalene-1-yl)prop-2-en-1-one
(6) (Geyer et al., 2009)
Yellow solid; yield 90%; m.p. 127–133°C. 1H-NMR:
(300 MHz, CDCl3); 8.62 (1H, d, J = 15.3 Hz), 8.21 (1H, d,
J = 8.4 Hz), 8.04 (2H, d, J = 7.6 Hz), 7.85–7.80 (3H, m),
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Med Chem Res (2012) 21:922–931
925
3.90 (3H, s). 13C-NMR: (75.4 MHz, CDCl3) 188.3, 164.0,
141.3, 135.6, 134.5, 133.6, 131.2, 131.1, 130.0, 127.8,
123.8, 114.3, and 55.9. HRMS-ESI: m/z [M ? H]? for
C16H12Cl2O2, calculated, 307.0287; observed, 307.0280.
3-(4-Fluorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one
(10) (Liu et al., 2001)
White solid; yield 93%; m.p. 115–118°C. 1H-NMR:
(300 MHz, CDCl3); 8.07 (2H, d, J = 8.8 Hz), 7.81 (1H, d,
J = 15.6 Hz), 7.67–7.63 (2H, m), 7.52 (1H, d, J =
15.6 Hz), 7.15–7.09 (2H, m), 7.01 (2H, d, J = 8.1 Hz), and
3.91 (3H, s). 13C-NMR: (75.4 MHz, CDCl3) 188.6, 165.7,
163.6, 162.4, 142.7, 131.4, 130.9, 130.4, 121.7, 116.3,
116.0, 114.0, and 55.6. HRMS-ESI: m/z [M ? H]? for
C16H13O2F, calculated, 257.0972; observed, 257.0964.
3-(3,4-Dichlorophenyl)-1-(4-methylphenyl)prop-2-en-1-
one (15)
Light yellow solid; yield 86%; m.p. 137–138°C. 1H-NMR:
(300 MHz, CDCl3); 7.95 (2H, d, J = 6.9 Hz), 7.71–7.65
(2H, m), 7.53–7.42 (3H, m), 7.32 (2H, d, J = 7.1 Hz), and
2.41 (3H, s), 13C-NMR: (75.4 MHz, CDCl3) 189.5, 144.4,
141.7, 135.6, 135.5, 134.6, 133.6, 131.2, 130.1, 129.8,
129.0, 127.8, 123.9, and 22.0. HRMS-ESI: m/z [M ? H]?
for C16H12Cl2O, calculated, 291.0338; observed, 291.0335.
3-(4-Bromophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one
(11)
1
Off white solid; yield 91%; m.p. 149–152°C. H-NMR:
(300 MHz, CDCl3); 8.34–8.28 (2H, m), 8.05–7.96 (1H, m),
7.80–7.52 (5H, m), 7.29–7.23 (2H, m), and 4.19 (3H, s).
13C-NMR: (75.4 MHz, CDCl3) 189.2, 164.4, 143.3, 134.8,
133.0, 131.7, 130.5, 125.3, 123.2, 114.7, and 56.3. HRMS-
ESI: m/z [M ? H]? for C16H13BrO2, calculated, 317.0172;
observed, 317.0172.
3-(3,4-Dichlorophenyl)-1-(2-methoxyphenyl)prop-2-en-1-
one (16)
Yellow solid; yield 81%; m.p. 77–78°C. 1H-NMR:
(300 MHz, CDCl3); 7.72–7.69 (2H, m), 7.62–7.33 (5H, m),
7.15–7.05 (2H, m), and 3.99 (3H, s). 13C-NMR:
(75.4 MHz, CDCl3); dC (75.4 MHz, CDCl3) 192.4, 158.7,
140.2, 135.7, 134.3, 133.7, 133.5, 131.2, 130.9, 130.1,
129.2, 128.9, 127.7, 121.2, 112.1, and 56.2. HRMS-ESI: m/
z [M ? H]? for C16H12Cl2O2, calculated, 307.0287;
observed, 307.0284.
1-(3,4-Dioxymethylene)-3-(4-chlorophenyl)prop-2-en-1-
one (12)
White solid; yield 87%; m.p. 164–167°C. 1H-NMR:
(300 MHz, CDCl3); 7.68 (1H, d, J = 15.7 Hz), 7.57 (1H,
d, J = 8.0 Hz), 7.49–7.44 (3H, m), 7.40 (1H, d,
J = 15.7 Hz), 7.31 (2H, d, J = 8.4 Hz), 6.82 (1H, d,
J = 8.0 Hz), and 5.98 (2H, s). 13C-NMR: (75.4 MHz,
CDCl3) 187.9, 151.8, 148.3, 142.7, 136.2, 133.5, 132.8,
129.5, 129.2, 124.7, 122.1, 108.4, 107.9, and 101.9.
HRMS-ESI: m/z [M ? H]? for C16H11ClO3, calculated,
287.0470; observed, 287.0469.
3-(3,4-Dichlorophenyl)-1-(3-methoxyphenyl)prop-2-en-1-
one (17)
Light yellow solid; yield 79%; m.p. 105–107°C. 1H-NMR:
(300 MHz, CDCl3); 7.80–7.74 (2H, m), 7.69 (1H, d,
J = 7.3 Hz), 7.62–7.59 (2H, m), 7.56–7.47 (3H, m), 7.24
(1H, d, J = 8.6 Hz), and 3.97 (3H, s). 13C-NMR:
(75.4 MHz, CDCl3) 189.6, 160.1, 141.9, 139.2, 135.0,
134.5, 133.4, 131.0, 129.9, 129.8, 127.6, 123.6, 121.2,
119.7, 113.0, and 55.6. HRMS-ESI: m/z [M ? H]? for
C16H12Cl2O2, calculated, 307.0287; observed, 307.0272.
3-(2,4-Dichlorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-
one (13)
White solid; yield 88%; m.p. 134–137°C. 1H-NMR:
(300 MHz, CDCl3); 8.09–8.00 (3H, m), 7.67 (1H, d,
J = 8.4 Hz), 7.49 (1H, d, J = 15.8 Hz), 7.43 (1H, s), 7.28
(1H, d, J = 8.4 Hz), 6.98 (2H, d, J = 8.2 Hz), and 3.88
(3H, s); 13C-NMR: (75.4 MHz, CDCl3) 188.4, 164.0,
138.6, 136.5, 136.2, 132.4, 131.3, 131.0, 130.4, 128.8,
127.8, 125.2, 114.3, and 55.8.
3-(3,4-Dichlorophenyl)-1-(3,4-dimethoxyphenyl)prop-2-
en-1-one (18)
White solid; yield 87%; m.p. 122–123°C. 1H-NMR:
(300 MHz, CDCl3); 7.71–7.65 (3 H, m), 7.61 (1H, s),
7.55–7.45 (3H, m), 6.94 (1H, d, J = 8.6 Hz), and 3.97 (6H,
s). 13C-NMR: (75.4 MHz, CDCl3) 188.3, 154.0, 149.8,
141.5, 135.6, 134.6, 133.7, 131.4, 130.1, 128.0, 123.7,
111.2, 110.5, 56.6, and 56.5. HRMS-ESI: m/z [M ? H]?
for C17H14Cl2O3, calculated, 337.0393; observed,
337.0398.
3-(3,4-Dichlorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-
one (14)
1
Pale yellow solid; yield 89%; m.p. 129–131°C. H-NMR:
(300 MHz, CDCl3); 8.05 (2H, d, J = 9.3 Hz), 7.70–7.64
(2H, m), 7.54–7.42 (3H, m), 7.00 (2H, d, J = 9.1 Hz), and
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3-(3,4-Dichlorophenyl)-1-(3,4,5-trimethoxyphenyl)prop-2-
en-1-one (19)
3-(4-Chlorophenyl)-1-(4-hydroxyphenyl)prop-2-en-1-one
(24) (Batovska et al., 2009)
1
Pale yellow solid; yield 83%; m.p. 139–140°C. H-NMR:
White solid; yield 54%; m.p. 178–179°C. 1H-NMR:
(300 MHz, CDCl3); 9.31(1H, s), 8.10 (2H, s), 7.85–7.73
(4H, m), 7.48 (2H, s), and 6.98 (2H, s). 13C-NMR:
(75.4 MHz, CD3COCD3) 188.4, 163.4, 142.7, 136.7, 135.7,
132.5, 131.5, 130.4, 124.2, and 116.7.
(300 MHz, CDCl3); 7.72–7.67 (2H, m), 7.51–7.42 (3H, m),
7.20 (2H, s), and 3.95 (9H, s); 13C-NMR: (75.4 MHz,
CDCl3) 188.8, 153.6, 143.1, 142.2, 135.3, 134.7, 133.6,
133.4, 131.3, 130.1, 127.9, 123.5, 106.5, 61.4, and 56.8.
HRMS-ESI: m/z [M ? H]? for C18H16Cl2O4, calculated,
367.0498; observed, 367.0493.
Synthesis of 3-(4-chlorophenyl)-1-[4-(prop-2-en-1-
yloxy)phenyl]prop-2-en-1-one (25)
1-(4-Chlorophenyl)-3-(3,4-dichlorophenyl)prop-2-en-1-
one (20)
To a 50-mL round bottom flask containing 24 (0.5 g,
1.9 mmol) in dry acetone (20 mL), allyl bromide (0.46 g,
3.8 mmol), and anhydrous K2CO3 (0.52 g, 3.8 mmol) were
added. The mixture was refluxed for 6 h. After consump-
tion of starting chalcone (monitored on TLC), the mixture
was filtered to remove K2CO3. The filtrate was vacuum
evaporated and washed with hexane to remove excess of
allyl bromide. The obtained crude solid was recrystallized
with methanol to afford the desired pure product.
1
Off white solid; yield 92%; m.p. 135–137°C. H-NMR:
(300 MHz, CDCl3); 7.96–7.92 (2H, m), 7.70–7.63 (2H, m),
and 7.48–7.40 (5H, m), 13C-NMR: (75.4 MHz, CDCl3)
188.9, 142.8, 140.1, 136.6, 135.3, 135.1, 133.9, 131.5,
130.5, 130.3, 129.6, 128.1, and 123.4. HRMS-ESI: m/z
[M ? H]? for C15H9Cl3O, calculated, 310.9791; observed,
310.9786.
Spectral data of the product 25: White solid; yield 69%;
1
m.p.119–120°C. H-NMR: (300 MHz, CDCl3); 8.05 (2H,
1,3-Bis(3,4-dichlorophenyl)prop-2-en-1-one (21)
d, J = 8.0 Hz), 7.77 (1H, d, J = 16.2 Hz), 7.58–7.49 (3H,
m), 7.40 (2H, d, J = 8.9 Hz), 7.02 (2H, d, J = 8.0 Hz),
6.14–6.01 (1H, m), 5.48–5.31 (2H, m), and 4.64 (2H, d,
J = 5.1 Hz); dC (75.4 MHz, CDCl3) 188.7, 162.9, 142.7,
136.5, 134.0, 132.9, 131.4, 131.2, 129.8, 129.5, 122.7,
118.5, 115.0, and 69.3. HRMS-ESI: m/z [M ? H]? for
C18H15ClO2, calculated, 299.0833; observed, 299.0833.
1
Pale yellow solid; yield 88%; m.p. 164–167°C. H-NMR:
(300 MHz, CDCl3); 8.10 (1H, s), 7.87–7.70 (3H, m), and
7.62–7.40 (4H, m); 13C-NMR: (75.4 MHz, CDCl3) 187.7,
143.5, 138.1, 137.7, 135.2, 134.9, 133.8, 131.4, 131.2,
130.8, 130.3, 128.0, 127.9, and 122.7. HRMS-ESI: m/z
[M ? H]? for C15H8Cl4O, calculated, 344.9402; observed,
344.4444.
Biological evaluation
1,3-Bis(4-chlorophenyl)prop-2-en-1-one (22) (Santos
et al., 2006)
Test insect
1
Off white solid; yield 92%; m.p. 108–111°C. H-NMR:
Insects, P. xylostella, were obtained from infested field
crops and reared in the laboratory. Adult insects were
allowed to lay eggs on 1-week-old mustard plants grown in
the pots and encaged inside the wooden boxes. Second
instar larvae were removed from the mustard plants and
transferred on to the cabbage leaves encaged in other boxes
where the insect completed rest of the stages. The adults
emerged from the pupae were allowed to lay eggs on the
mustard plants placed in the cages. Insects were reared and
maintained at 25 1°C, 65 5% RH and a photoperiod
of 16:8 (L: D). Second instar larvae obtained from the
established colony maintained for [20 generations in the
laboratory were used in the experiments.
(300 MHz, CDCl3); 7.98 (2H, d, J = 7.6 Hz), 7.79 (1H, d,
J = 16.6 Hz), 7.59 (2H, d, J = 8.4 Hz), and 7.50–7.39
(5H, m). 13C-NMR: (75.4 MHz, CDCl3) 189.1, 144.1,
139.7, 137.0, 136.7, 133.6, 130.2, 130.0, 129.7, 129.4, and
122.3.
3-(4-Chlorophenyl)-1-(4-nitrophenyl)prop-2-en-1-one (23)
(Batovska et al., 2009)
Yellow solid; yield 73%; m.p. 158–161°C. 1H-NMR:
(300 MHz, CDCl3); 8.37 (2H, d, J = 7.2 Hz), 8.16 (2H, d,
J = 7.2 Hz), 7.82 (1H, d, J = 15.6 Hz), 7.61 (2H, d,
J = 8.2 Hz), and 7.49–7.41 (3H, m). 13C-NMR:
(75.4 MHz, CDCl3) 188.4, 149.8, 144.9, 142.5, 136.9,
132.5, 130.7, 129.1, 128.8, 123.6, and 121.4. HRMS-ESI:
m/z [M ? H]? for C15H10ClNO3, calculated, 288.0422;
observed, 288.0425.
Bioassays for preliminary screening
The larvicidal activity of the test compounds (1–25) was
evaluated by the leaf dip method against second instar
123

Med Chem Res (2012) 21:922–931
927
larvae. Larvicidal activity was evaluated on cabbage leaves
(*34 cm2). Known amounts of the test compounds was
dissolved in acetone and then diluted with water to obtain a
desired range of concentrations. The test compounds were
suspended in distilled water using Triton X-100 LR
spreader (s.d. Fine-Chem. Ltd; India) at 0.1 mL/L. Based
on our previous experiences, (Tewary et al., 2006) pre-
liminary screening of the test compounds were carried out
at two higher test dosages; 10000 lg mL-1 and
5000 lg mL-1. Three leaf disks were separately dipped in
each test solution for 30 s and allowed to dry at ambient
conditions. Second instar larvae (10 larvae in each repli-
cate), starved for 3–4 h, were transferred individually on
treated and control (disks treated with water mixed with
acetone: triton only) leaf disks placed in petri plates.
Moistures build up inside the petri plates was swabbed
after 24 h using tissue paper, and petri plates were resealed
using parafilm. Mortality was determined at 48 h after
larvae were placed on disks. Larvae, which did not show
movements when probed with camel hairbrush, were con-
sidered dead. All the treated samples were maintained at
25 1°C, 65 5% RH and a photoperiod of 16:8 (L:D)
in the laboratory.
pesticidal activities (Kumar et al., 2010; Bhardwaj et al.,
2010). In this study, initially we were interested in utilizing
natural phenylpropenes (Ar–CH=CH–CH3) for the syn-
thesis of chalcone derivatives (Ar–CH=CH–CO–CH3)
using ionic liquid under microwave irradiation. Conse-
quently, compounds 1 and 2 were prepared (Scheme 1)
from natural b-asarone and anethole, respectively (Sinha
et al., 2003). Chalcones 3–24 were prepared by Claisen-
Schmidt condensation (Batovska et al., 2009) between
benzaldehydes and acetophenone (acetone in case of 3)
under microwave irradiation (Scheme 2). Compound 25
was prepared by O-allylation of hydroxylated chalcone
(24) with allyl bromide. All the synthesized chalcone
derivatives (1–25) were tested against larvae of lepidop-
teron insect, P. xylostella. The % mortality and LC50 values
(only for those compounds which showed 100% mortality
at 5000 lg mL-1) are presented in Tables 1 and 2.
Preliminary screening of compounds 1–7 (Table 1) for
pesticidal activity did not show promising results (\30%
mortality) against the larvae after 48 h of exposure time.
Moreover, the presence of an OH group in 3 and the
naphthalene ring (6) created solubility problems.
In view of the well-known pesticidal potency of various
chlorinated compounds, chalcone 8 having Cl substitution
at ring B and OCH3 at ring A was synthesized which
showed 50% larval mortality at 10000 lg mL-1 dosage.
To our surprise, reversal of the substituents (Cl v/s OCH3)
of 8 resulted in compound 9 with 100% mortality even at
5000 lg mL-1. On the other side, replacement of Cl on
ring A with F (10) or Br (11) substituents caused dramatic
reduction in the larval mortality.
Dose–response experiment
Based on the review of preliminary screening results,
promising test compounds were selected and subjected to
dose–response bioassay. Test compounds of six concen-
trations each were prepared to provide dosage in the range
1 mg/mL and set for bioassay as mentioned above. Com-
mercial pesticide, deltamethrin, was estimated against P.
xylostella as positive control. Seven concentrations (400,
200, 100, 50, 25, 12.5, and 6.25 lg mL-1) of deltamethrin
were prepared in the tap water by serial dilutions. For
control set, leaf disks were treated with tap water only.
A comparison of the activities of compounds 7–12
indicates that electron-withdrawing substituents (particu-
larly Cl) on ring A and electron-releasing substituents
(particularly OCH3) on ring B of chalcone (/A–CH=CH–
CO–B/) increases the pesticidal potential while positional
interchange (?B–CH=CH–CO–A?) of these substituents
on both rings causes a decrease. Interestingly, above
observation is in contrast to our recent finding (Kumar
et al., 2010) on antimalarial activity, wherein, potent
chalcones were having electron-releasing substituents on
ring A and electron-withdrawing substituents on ring
B. Such findings would draw the attention of researchers in
future while designing chalcone-based novel compounds
with preferred activities.
Statistical analysis
Mortality was corrected by using Abbott’s formula
(Abbott, 1925). Lethal concentration to kill 50% of the
population relative to control values (LC50) was deter-
mined using (EPA PROBIT ANALYSIS PROGRAM used
for calculating LC/EC values version 1.5) (Finney, 1971).
Among the various tested chalcones (1–12, Table 1),
compound 9 (LC50: 356.45 lg mL-1) was selected as
prelude for further modification to improve and understand
the pesticidal SARs. As expected, compounds with more
electron-withdrawing substituents such as 2,4-dichloro (13,
Results and discussion
Our group has been working on the development of various
green synthetic methodologies using microwave (Sharma
et al., 2009), ionic liquids (Kumar et al., 2008) besides
utilization of abundantly available natural precursors
(Sinha et al., 2003, Sinha et al., 2007) for antimalarial and
LC50: 278.50 lg mL-1
) or 3,4-dichloro (14, LC50:
287.64 lg mL-1) on ring A exhibited better activity
compared to single chloro (9, LC50: 356.45 lg mL-1).
123

928
Med Chem Res (2012) 21:922–931
Table 1 Preliminary screening of chalcone derivatives against P. xylostella after 48 h
O
O
O
O
R
R
R
R'
R'
R'
(b;4-5)
(a;1-3)
(d; 7-12)
( c; 6)
Compound
Type
R
R0
Mortality [%]a SD
LC50 (lg mL-1 b
)
10000 lg mL-1
5000 lg mL-1
1
a
a
a
b
b
c
d
d
d
d
d
d
2,4,5-trimethoxy
4-methoxy
4-hydroxy-3-methoxy
sulfur
–
26.6 0.57
0
0
–
2
–
30
Solubility problem
30
0
26.6 0.57
–
–
3
–
–
4
4-nitro
0
23.3 0.57
16.6 0.57
–
–
5
oxygen
4-nitro
23 0.57
–
6
–
4-methoxy
4-methoxy
4-chloro
4-methoxy
4-methoxy
4-methoxy
3,4-methylenedioxy
Solubility problem
–
7
4-methoxy
4-methoxy
4-chloro
26.6
50 1.15
100
33.3 0.57
0
16.6 0.57
26.6 0.57
–
8
–
9
0
100
0
356.45
10
11
12
a
4-fluoro
26.6 0.57
3.3 0.57
13.3 0.57
–
–
–
4-bromo
10
23
0
0
4-chloro
Data represent the mean values of the three replicates and mortality in control accounted using Abbott’s formula
Only for those compounds which showed 100% larval mortality at 5000 lg mL-1
b
Although, pesticidal activities of both of the dichlorinated
derivatives with two Cl substituents might increase the
pesticidal potential.
chalcones 13 and 14 (Table 2) are comparable; however,
based on evaluation of dose–response data values, 14 could
be a better candidate if 100% kill is considered on bioef-
ficacy indicator parameter. Therefore, in further study,
effect of different substituents on ring B in association with
3,4-dichloro substitution on ring A was evaluated (15–21,
Table 2). Interestingly, replacement of OCH3 group of
compound 14 with another electron-releasing CH3 group
(15) induced less mortality.
Consequently, compound 22 possessing electron-with-
drawing Cl substituent on ring A as well as on ring B was
synthesized, and it showed good activity (22, LC50:
170.24 lg mL-1); however, introduction of polar NO2
group (23) on ring B caused drastic reduction in the larval
mortality. On the other side, replacement of Cl of 22 with
isosteric polar group i.e., OH provided 24 (LC50:
871.05 lg mL-1) with lower activity. These results indi-
cate the importance of both lipophilic as well as electron-
withdrawing substitution (such as Cl) on ring B for
enhanced pesticidal activity. The above assumption proved
correct when 25 (OCH2CH=CH2; both lipophilic- and
electron-releasing group) showed lesser activity than 22
but significantly improved activity than 24. In the same
vein, compound 9 (OCH3 group) showed better activity
than 24 (OH group) and marginally reduced activity than
25 (OCH2CH=CH2 group).
We next evaluated the positional importance of OCH3
group on ring B for the activity. However, introduction of
OCH3 group at meta position (17) met with the solubility
problem, whereas, its presence at ortho (16) position
showed drastic reduction in the activity (see comparison
between 14, 16 and 17, Table 2). Moreover, increase in the
electron density on ring B with 3,4-dimethoxy (18) or
3,4,5-trimethoxy groups (19) provided lower activity as
compared to 14.
From a structure–activity perspective, effect of electron-
withdrawing substituents on ring B was also evaluated.
However, compounds 20 and 21 possessing 4-chloro and
3,4-dichloro substituents, respectively, were found inac-
tive. A comparison of the % mortality of compounds 14, 20
and 21 (Table 2) indicated that as we increased the number
of Cl substituents from two to three or four, activity
reduced significantly. Hence, it was realized that chalcone
In order to develop dosages–response lines for the
identified potent chalcones i.e., 9, 13, 14, 22, 24, and 25,
their efficacy at different concentration were evaluated.
LC50 values and other statistical parameters generated by
linear regression analysis were compared and represented
in Table 3. Overall pesticidal activity of the above poten-
tial chalcone was found to obey the following order:
22 [ 25 [ 13 [ 14 [ 9 [ 24.
123

Med Chem Res (2012) 21:922–931
929
Table 2 Pesticidal activity of chloro-substituted chalcones against P. xylostella after 48 h
O
Ring B
Ring A
Compound
Substitution on
Mortality [%]a SD
LC50 (lg mL-1 b
)
Ring A
Ring B
10000 lg mL-1
5000 lg mL-1
13
14
15
16
17
18
19
20
21
22
23
24c
25
a
2,4-dichloro
3,4-dichloro
4-methoxy
4-methoxy
4-methyl
100
100
0
0
100
100
60
0
0
278.50
287.64
83.3 0.57
0
1
–
2-methoxy
3-methoxy
3,4-dimethoxy
3,4,5-trimethoxy
4-chloro
63.3 0.57
50
–
Solubility problem
68 0.57
–
–
46.6 0.57
–
–
Solubility problem
–
97.7
73.3 0.57
100
26.6 0.57
0
60
0
–
3,4-dichloro
4-chloro
46.6 0.57
–
4-chloro
0
100
20.0
100
100
0
170.24
–
4-nitro
0
4-hydroxy
4-allyl
100
100
0
0
0
0
871.05
268.20
Data represent the mean values of the three replicates and mortality in control accounted using Abbott’s formula
Only for those compounds which showed 100% mortality at 5000 lg mL-1
b
c
Compounds 24 and 22 showed 100% mortality at 5000 lg mL-1, whereas at lower concentration, compound 24 exhibited drastic reduction in
the larval mortality as compared with 22
Although, the identified potent compound 22 (LC50:
170.24 lg mL-1) is 27 times lesser active than the com-
mercial pesticide deltamethrin (LC50: 6.25 lg mL-1),
however, this study is the first report wherein a simple
moiety like chalcone has provided a promising lead for
pesticidal activity against P. xylostella. On the other hand,
deltamethrin is known to leave residual traces in the
environment which are quite harmful to humans (Villarini
et al., 1998), as compared with chalcones. Moreover, the
identified potent chalcone 22 is reported to be a hypolipi-
demic agent (Santos et al., 2006). Overall, this study will
pave out a new platform for the development of chalcone-
based economical pesticidal agents.
Proposed mode of action
A brief delving in the literature demonstrates the presence
of glutathione S-transferase (GST) isoenzymes and GST
Table 3 Insecticidal activity (LC50 values and regression parameters of probit analysis) of the promising compounds against P. xylostella after
48 h
Serial no.
Compound no
LC50 values and regression parameters of probit analysis after 48 h
LC50 [FL] in lg mL-1
v2
Intercept
LC50
Lower limit
Upper limit
1
2
3
4
5
6
7
9
356.45
278.50
287.64
170.24
871.05
268.20
6.25
307.8
213.2
221.3
130.2
552.7
197.3
2.21
417.1
367.8
377.8
222.08
1950.8
381.8
11.9
1.442
6.682
3.729
1.644
1.477
3.681
4.189
0.37623
0.07669
0.08344
1.91373
1.33189
1.04128
4.02511
13
14
22
24
25
Deltamethrin
123

930
Med Chem Res (2012) 21:922–931
Fig. 1 Proposed Michael type
addition of glutathione with
chalcone
GSH
GSH
O
O
glutathione S-transferase
OCH
A
B
A
B
Cl
OCH
3
3
Cl
(i) Electron withdrawing groups on ring A
(ii) Electron releasing groups on ring B
Stable GSH adduct
Palampur for providing the necessary infrastructure for conducting
this study.
genes in P. xylostella which helps in detoxification of
endogenous and xenobiotic compounds in vertebrates and
invertebrates (Rushmore and Pickett, 1993; Sonoda et al.,
2006). Mode of action of chalcone may be attributed to the
interaction of electrophilic b-position of a, b-unsaturated
ketone bridge (–CH=CH–CO–), with reduced glutathione
(GSH) to form its conjugate and consequent inhibition of
GST (Miyamoto and Yamamoto, 1994). In general, elec-
tron-withdrawing groups on ring A and electron-releasing
groups on ring B of chalcone would help increase the
stability of GSH conjugate (Fig. 1) and therefore accounts
for their pesticidal potential.
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