Natural-product-based insecticidal agents 14. Semisynthesis and insecticidal activity of new piperine-based hydrazone derivatives against Mythimna separata Walker in vivo

Article abstract of DOI:10.1016/j.bmcl.2013.08.053

In continuation of our program aimed at the discovery and development of natural-product-based insecticidal agents, twenty-six new piperine-based hydrazone derivatives were synthesized from piperine, an alkaloid isolated from Piper nigrum Linn. The single-crystal structures of 6c, 6q and 6w were unambiguously confirmed by X-ray crystallography. Their insecticidal activity was evaluated against the pre-third-instar larvae of Mythimna separata Walker in vivo. Especially compounds 6b, 6i and 6r, the final mortality rates of which, at the concentration of 1 mg/mL, were 62.1%, 65.5% and 65.5%, respectively, exhibited more pronounced insecticidal activity compared to toosendanin at 1 mg/mL, a commercial botanical insecticide isolated from Melia azedarach. It suggested that introduction of the substituents at the C-2 position on the phenyl ring of the hydrazone derivatives was important for their insecticidal activity.

Full text of DOI:10.1016/j.bmcl.2013.08.053

Bioorganic & Medicinal Chemistry Letters 23 (2013) 5552–5557
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Natural-product-based insecticidal agents 14. Semisynthesis
and insecticidal activity of new piperine-based hydrazone
derivatives against Mythimna separata Walker in vivo
Huan Qu a, Xiang Yu a, Xiaoyan Zhi a, Min Lv b, Hui Xu a,
⇑
a Laboratory of Pharmaceutical Design & Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, PR China
b College of Plant Protection, Northwest A&F University, Yangling 712100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
In continuation of our program aimed at the discovery and development of natural-product-based insec-
ticidal agents, twenty-six new piperine-based hydrazone derivatives were synthesized from piperine, an
alkaloid isolated from Piper nigrum Linn. The single-crystal structures of 6c, 6q and 6w were unambigu-
ously confirmed by X-ray crystallography. Their insecticidal activity was evaluated against the pre-third-
instar larvae of Mythimna separata Walker in vivo. Especially compounds 6b, 6i and 6r, the final mortality
rates of which, at the concentration of 1 mg/mL, were 62.1%, 65.5% and 65.5%, respectively, exhibited
more pronounced insecticidal activity compared to toosendanin at 1 mg/mL, a commercial botanical
insecticide isolated from Melia azedarach. It suggested that introduction of the substituents at the C-2
position on the phenyl ring of the hydrazone derivatives was important for their insecticidal activity.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 8 April 2013
Revised 30 July 2013
Accepted 12 August 2013
Available online 20 August 2013
Keywords:
Piperine
Hydrazone
Insecticidal activity
Botanical insecticide
Structural modification
Mythimna separata Walker
Although synthetic chemical insecticides have played a signifi-
cant role in modern agricultural pest management, repeat applica-
tion of those agrochemicals over the years has led to the
development of resistance in insect pest populations and environ-
mental problems.1–3 On the other hand, as plant secondary metab-
olites result from the interaction between plants and environment
(life and non-life) during the long period of evolution, pesticides
originated from plant secondary metabolites may lead to less or
slower resistance development and lower pollution.4 Recently,
the discovery of new pesticidal agents from plant secondary
metabolites, or by using them as the lead compounds for further
structural modification, have been one of the important procedures
for research and development of new insecticides.5
Piperine (1, Fig. 1), a simple alkaloid isolated from Piper nigrum
Linn., has been found many medicinal activities such as mono-
amine oxidase (MAO) inhibitors,6,7 liver CYP3A4 enzymatic
inhibitors,8 antiadipogenic activity,9 antimicrobial activity,10 anti-
inflammatory activity,11 positive allosteric GABA(A) receptor
modulators,12,13 Staphylococcus aureus NorA efflux pump inhibitor
(EPI),14 trypanocidal agents,15,16 and cytochrome P450 (CYP) inhib-
itor.17 Additionally, compound 1 and its related derivatives also
exhibited the interesting insecticidal activity.18,19 More recently,
we have synthesized a series of fraxinellone-based hydrazone
O
O
O
N
1
Figure 1. The chemical structure of piperine (1).
derivatives and found some compounds displayed the potent
insecticidal activity.20 In continuation of our program aimed at
the discovery and development of natural-product-based insecti-
cidal agents,20–23 therefore, in the present Letter we prepared a ser-
ies of piperine-based hydrazone derivatives as insecticidal agents
(Scheme 1). Their insecticidal activity was evaluated against the
pre-third-instar larvae of Mythimna separata Walker in vivo.
As shown in Scheme 1, the piperic acid (2) was obtained from 1
by the basic hydrolysis,24 and methyl piperate (3) was smoothly
prepared by reaction of 2 with methanol in the presence of
concd sulfuric acid. Then reduction of 3 with LiAlH4 and AlCl3
gave (2E,4E)-5-(1,3-benzodioxol-5-yl)-2,4-pentadien-1-ol (4),25
which was subsequently oxidized by MnO2 to produce
(2E,4E)-5-(1,3-benzodioxol-5-yl)-2,4-pentadienal (5).16 Finally,
compound 5 reacted with hydrazides or hydrazines to afford piper-
ine-based hydrazone derivatives (6a–z), which were characterized
by 1H NMR, IR, HRMS and mp (see Supplementary data). Due to the
steric hindrance, the substituents on the C N double bond of all
⇑
@
Corresponding author. Tel./fax: +86 29 87091952.
E-mail address: orgxuhui@nwsuaf.edu.cn (H. Xu).
@
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.08.053

H. Qu et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5552–5557
5553
O
O
O
O
O
O
O
OH
a
N
b
OCH3
O
O
1
2
3
H
N
N
CHO
O
O
d
O
O
O
OH
R
c
e
O
4
6a-z
5
R
O
O
O
CH3
a
h
i
t
n
NO2
79%
NO2
86%
C2H5O
(E/Z = 9:1)
77%
(E/Z = 9:1)
O
O
72%
(E/Z = 5:1)
O
b
NO2
68%
u
O2N
F
82%
o
H3C
(E/Z = 4:1)
O
70%
F
71%
F
O
c
d
O
O
F
v
j
F
p
67%
N
83%
F
OH
81%
O
O
61%
Cl
O
w
q
r
(E/Z = 1.6:1)
k
70%
N
S
77%
O
O
O
OCH3
76%
76%
x
y
e
CN
O
O
O
74%
Cl
(E/Z = 3:1)
77%
OCH3
64%
l
S
O
Cl
f
(E/Z = 2.4:1)
(E/Z = 1.9:1)
75%
82%
O
O
m
33%
O
Cl
S
z
s
g
OCH3
Br
OCH3
71%
CH3
64%
76%
Cl
Cl
63%
(E/Z = 2.3:1)
Scheme 1. Synthetic route for the preparation of 6a–z. Reagents and conditions: (a) KOH, 95% ethanol, reflux, 16 h, 93%; (b) methanol, H2SO4, reflux, 16 h, 91%; (c) LiAlH4/
AlCl3, THF, 0 °C, 4 h, 58%; (d) MnO2, THF, reflux, 4 h, 75%; (e) hydrazides or hydrazines, ethanol, HOAc, reflux, 1–3 h, 33–86%.
Figure 2. The X-ray crystal structure of 6c.
compounds (except 6a, 6d, 6e, 6i, 6n, 6r, 6t, 6y and 6z) adopted E
configuration. The ratios of E/Z of 6a, 6d, 6e, 6i, 6n, 6r, 6t, 6y and 6z
were 9/1, 1.6/1, 3/1, 4/1, 5/1, 1.9/1, 9/1, 2.4/1, and 2.3/1, respec-
tively.26 To obtain the precise three-dimensional structural infor-
mation of 6a–z, the single-crystal structures of 6c, 6q and 6w
were well determined by X-ray crystallography (Figs. 2–4).27 The
@
substituents on the C N double bond of 6c, 6q and 6w all adopted
@
E configuration, which is found during crystal packing.

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H. Qu et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5552–5557
Figure 3. The X-ray crystal structure of 6q.
Figure 4. The X-ray crystal structure of 6w.
The insecticidal activity of 6a–z was tested against the pre-
Table 1
Insecticidal activity of 6a–z against M. separata on leaves treated with a concentration
third-instar larvae of Mythimna separata Walker in vivo by the
leaf-dipping method at the concentration of 1 mg/mL.23,28 Too-
sendanin, a commercial botanical insecticide isolated from Melia
azedarach, was used as the positive control at 1 mg/mL, and leaves
treated with acetone alone were used as a blank control group.
Analysis of variance (ANOVA) was followed by Duncan’s post test,
which was conducted using SPSS 20 for Windows 7.
As described in Table 1, the corresponding mortality rates of
6a–z after 34 days were usually higher than those after 10 and
20 days. Therefore, these piperine-based hydrazone derivatives,
in a time-dependent manner, different from those conventional
neurotoxic insecticides such as organophosphates, carbamates,
and pyrethroids, exhibited delayed insecticidal activity. Mean-
while, the symptoms of the tested M. separata were also character-
ized by the same way as our previous reports.20–23 Due to feeding
too much treated leaves during the first 48 h, some larvae died
slowly as evidenced from slim and wrinkled bodies during the lar-
val period (Fig. 5). In the meantime, many larvae of the treated
groups moulted to malformed pupae, and died during the stage
of pupation (Fig. 6). Malformed moths with imperfect wings were
also appeared in the treated groups (Fig. 7). According to the symp-
toms of the tested M. separata, the above derivatives possibly dis-
played the anti-molting hormone effect.
of 1 mg/mLa
Compounds
Corrected mortality rate (%)
20 days
10 days
34 days
1
2
3
4
5
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
6m
6n
6o
6p
6q
6r
23.3 efgb
6.7 ab
10.0 abc
6.7 ab
37.9 fgh
24.1 bcd
34.5 efg
20.7 abc
27.6 cde
41.4 gh
37.9 fgh
27.6 cde
20.7 abc
27.6 cde
20.7 abc
24.1 bcd
31.0 def
41.4 gh
27.6 cde
20.7 abc
37.9 fgh
27.6 cde
17.2 ab
41.4 gh
24.1 bcd
20.7 abc
44.8h
48.3 fgh
37.9 cde
51.7 ghi
34.5 bcd
48.3 fgh
55.2 hij
62.1 jk
48.3 fgh
41.4 def
37.9 cde
34.5 bcd
41.4 def
44.8 efg
65.5k
34.5 bcd
34.5 bcd
44.8 efg
48.3 fgh
34.5 bcd
58.6 ijk
44.8 efg
34.5 bcd
65.5k
20.0 def
10.0 abc
10.0 abc
13.3 bcd
16.7 cde
23.3 efg
3.3 a
20.0 def
16.7 cde
23.3 efg
10.0 abc
10.0 abc
13.3 bcd
10.0 abc
3.3 a
30.0g
13.3 bcd
6.7 ab
30.0g
As shown in Table 1, if the amide group of 1 was substituted by
a carboxyl, ester, alcohol, or aldehyde moiety, the corresponding
derivatives such as 2, 3, 4, and 5 did not exhibit the more potent
insecticidal activity compared to their precursor piperine. Interest-
ingly, when 5 reacted with hydrazides or hydrazines to afford pip-
erine-based hydrazone derivatives 6a–z, some compounds such as
6a, 6b, 6i, 6o and 6r showed the more potent insecticidal activity
than their precursor piperine. Especially compounds 6b, 6i and
6r displayed the most promising and pronounced insecticidal
activity compared to toosendanin. For example, the final mortality
rates of 6b, 6i and 6r were 62.1%, 65.5% and 65.5%, respectively;
6s
6t
6u
6v
6w
6x
6y
6z
10.0 abc
3.3 a
6.7 ab
6.7 ab
26.7fg
6.7ab
3.3a
6.7 ab
20.0 def
24.1 bcd
31.0 def
20.7 abc
17.2 ab
31.0 def
24.1bcd
17.2ab
48.3 fgh
44.8 efg
37.9 cde
44.8 efg
44.8 efg
31.0abc
24.1a
13.8 a
41.4 gh
27.6 ab
51.7 ghi
Toosendanin
a
Values are means SD of three replicate.
Multiple range test using Duncan’s test (p <0.05). The same letters denote
treatments not significantly different from each other.
b

H. Qu et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5552–5557
5555
Figure 5. The representative abnormal larvae pictures of 6h, 6i, 6o, 6r, and 6w during the larval period (CK: blank control group).
Figure 6. The representative malformed pupae pictures of 6a, 6i, 6k, 6r, and 6y during the pupation period (CK: blank control group).

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H. Qu et al. / Bioorg. Med. Chem. Lett. 23 (2013) 5552–5557
Figure 7. The representative malformed moth pictures of 6a, 6b, 6i, 6o, and 6r during the emergence period (CK: blank control group).
whereas the final mortality rates of toosendanin was 51.7%. Intro-
duction of the substituents at the C-2 position on the phenyl ring of
the hydrazone derivatives was important to their insecticidal
activity. For example, the final mortality rates of 6g (containing
4-methyl on the phenyl ring) and 6h (containing 3-methyl on
the phenyl ring) were 41.4% and 44.8%, respectively; whereas the
final mortality rate of 6i (containing 2-methyl on the phenyl ring)
was 65.5%. Similarly, the final mortality rates of 6q (containing 3-Cl
on the phenyl ring) and 6s (containing 2,4,6-trichloro on the phe-
nyl ring) were 34.5% and 48.3%, respectively; whereas the final
mortality rate of 6r (containing 2-Cl on the phenyl ring) was
65.5%. However, introduction of the substituents R as the alkylcar-
bonyl (e.g., 6d and 6e) or the heterocyclylcarbonyl groups
(e.g., 6v–z) could not lead to the more potent compounds
compared to their precursor piperine.
In summary, a series of new piperine-based hydrazone deriva-
tives (6a–z) were prepared by structural modification of piperine.
Their insecticidal activity was evaluated against the pre-third-in-
star larvae of M. separata in vivo. Among them, especially 6b, 6i
and 6r exhibited the more pronounced insecticidal activity com-
pared to toosendanin. It suggested that introduction of the substit-
uents at the C-2 position on the phenyl ring of the hydrazone
derivatives was necessary for their insecticidal activity.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.bmcl.2013.08.
053.
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Acknowledgments
This work was supported by National Natural Science Founda-
tion of China (No. 31171896), and the Special Funds of Central Col-
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Mythimna separata Walker was assessed by leaf-dipping method. For each
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1H NMR spectra (see Supplementary data).
27. Crystallographic data (excluding structure factors) for the structures of 6c, 6q
and 6w in this Letter have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication number CCDC 932634, 932635, and
932633, respectively. Copies of the data can be obtained, free of charge, on
concentration of 1 mg/mL. Fresh wheat leaves were dipped into the
corresponding solution for 3 s, then taken out and dried in a room. Leaves
treated with acetone alone were used as a control group. Several treated leaves
were kept in each dish, where every 10 larvae were raised. If the treated leaves
were consumed, the corresponding ones were added to the dish. After 48 h,
untreated fresh leaves were added to the all dish until the adult emergence.
The experiment was carried out at 25 2 °C and relative humidity (RH)
65–80%, and on 12 h/12 h (light/dark) photoperiod. The insecticidal activity of
the tested compounds against the pre-third-instar larvae of M. separata was
calculated by the following formula:
Corrected mortality rate (%) = (TÀC) Â 100/(1ÀC)
where T is the mortality rate in the treated group expressed as a percentage,
and C is the mortality rate in the untreated group expressed as a percentage.