Synthesis and insecticidal activity of some novel fraxinellone-based esters

Article abstract of DOI:10.1021/jf301734h

In continuation of a program aimed at the discovery and development of natural products-based insecticidal agents, two series of novel fraxinellone-based esters were synthesized by modification at the C-4 or C-10 position of fraxinellone and evaluated for their insecticidal activity against the pre-third-instar larvae of Mythimna separata in vivo. An efficient method for the stereoselective synthesis of 4α-hydroxyfraxinellone from fraxinellonone was developed, and the steric configuration of 6h was unambiguously confirmed by X-ray crystallography. Among 37 compounds, some derivatives displayed potent insecticidal activity; especially compounds 6h, 6q, 6t, and 7q showed more promising insecticidal activity than toosendanin, a commercial botanical insecticide derived from Melia azedarach. This suggested that introduction of the fluorine atom on the phenyl ring could lead to a more potent compound than one possessing chlorine or bromine. Meanwhile, introduction of the heterocyclic fragments at the C-4 or C-10 position of fraxinellone was essential for their insecticidal activity. This will pave the way for further design, structural modification, and development of fraxinellone as an insecticidal agent.

Full text of DOI:10.1021/jf301734h

Article
pubs.acs.org/JAFC
Synthesis and Insecticidal Activity of Some Novel Fraxinellone-Based
Esters
Yong Guo, Yuanyuan Yan, Xiang Yu, Yi Wang, Xiao-Yan Zhi, Ying Hu, and Hui Xu*
Laboratory of Pharmaceutical Design and Synthesis, College of Sciences, Northwest A&F University, Yangling 712100, Shannxi
Province, People′s Republic of China.
S
* Supporting Information
ABSTRACT: In continuation of a program aimed at the discovery and development of natural products-based insecticidal
agents, two series of novel fraxinellone-based esters were synthesized by modification at the C-4 or C-10 position of fraxinellone
and evaluated for their insecticidal activity against the pre-third-instar larvae of Mythimna separata in vivo. An efficient method for
the stereoselective synthesis of 4α-hydroxyfraxinellone from fraxinellonone was developed, and the steric configuration of 6h was
unambiguously confirmed by X-ray crystallography. Among 37 compounds, some derivatives displayed potent insecticidal
activity; especially compounds 6h, 6q, 6t, and 7q showed more promising insecticidal activity than toosendanin, a commercial
botanical insecticide derived from Melia azedarach. This suggested that introduction of the fluorine atom on the phenyl ring
could lead to a more potent compound than one possessing chlorine or bromine. Meanwhile, introduction of the heterocyclic
fragments at the C-4 or C-10 position of fraxinellone was essential for their insecticidal activity. This will pave the way for further
design, structural modification, and development of fraxinellone as an insecticidal agent.
KEYWORDS: fraxinellone, insecticidal activity, botanical insecticide, structural modification
INTRODUCTION
■
Nowadays, the increasing application of synthetic chemical
insecticides over the years has resulted in the development of
resistance in insect pest populations and environmental
problems. On the other hand, in many cases plants have a
history of usage as folk remedies and are still used to kill or
repel insects;1 therefore, botanical insecticides have long been
touted as attractive alternatives to synthetic chemical
insecticides for pest management because botanicals reputedly
pose little threat to the environment or to human health.2 Some
botanical insecticides such as nicotine, pyrethrum, and neem
extracts are made by plants as defenses against insects.3 The
discovery of new insecticidal compounds from plant secondary
metabolites and their use lead structures for further
Figure 1. Chemical structure of fraxinellone (1).
modification have been important approaches for the research
and development of new pesticides.3
insecticidal agents. Encouraged by the above-mentioned
interesting results, and in continuation of our program aimed
Fraxinellone (1, Figure 1), a well-known and significant
naturally occurring degraded limonoid, has been successfully
at the discovery and development of natural products-based
isolated and identified from many species of plants in Meliaceae
insecticidal agents,16−19 herein we designed and prepared two
series of novel fraxinellone-based esters as insecticidal agents.
and Rutaceae, including Dictamnus angustifolius,4 Fagaropsis
glabra,5 Melia azadarach,6,7 Raulinoa echinata,8,9 and Dictamnus
dasycarpus.10,11 Liu et al. found compound 1 exhibited
significant feeding deterrence against two stored-product
insects, Tribolium castaneum Herbst and Sitophilus zeamais
Motsch,10 and showed effects on the growth and digestive
MATERIALS AND METHODS
■
General. All reagents and solvents were of reagent grade or purified
according to standard methods before use. Analytical thin-layer
chromatography (TLC) and preparative thin-layer chromatography
(PTLC) were performed with silica gel plates using silica gel 60 GF254
(Qingdao Haiyang Chemical Co., Ltd.). Melting points were
physiology of Asian corn borer, Ostrinia furnacalis Guenee.11 Lu
̈
et al. described that the poisoned insects usually exhibited
typical stomach-poisoned symptoms (e.g., vomiting and
diarrhea) after treatment by compound 1, and compound 1
showed delayed insecticidal activity against Mythimna separa-
ta.12 Although total synthesis of compound 1 has been
reported,13−15 to the best of our knowledge, little attention
has been paid to structural modifications of 1 for use as
Received: April 23, 2012
Revised: June 22, 2012
Accepted: June 22, 2012
Published: June 22, 2012
© 2012 American Chemical Society
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Scheme 1. Synthetic Route for the Preparation of 6a−t and 7a−q
determined on a digital melting-point apparatus and were uncorrected.
Infrared spectra (IR) were recorded on a Bruker TENSOR 27
spectrometer. Optical rotation was measured on Rudolph Research
Analytical Autopol III automatic polarimeter. Nuclear magnetic
resonance spectra (NMR) were recorded on a Bruker Avance III
500 MHz instrument in CDCl3 (1H at 500 MHz and 13C at 125 MHz)
using tetramethylsilane (TMS) as the internal standard. High-
resolution mass spectra (HR-MS) and electrospray ion trap mass
spectrometry (ESI-MS) were carried out with an IonSpec 4.7 T FTMS
instrument and an Agilent 1100 LC/MSD SL instrument, respectively.
Microwave irradiation was performed in a CEM Discover Synthesis
Unit (CEM Corp., Matthews, NC, USA).
δ 7.51 (s, 1H, H-2′), 7.49 (s, 1H, H-5′), 6.36 (s, 1H, H-4′), 5.11 (s, 1H,
H-8), 2.62−2.64 (m, 2H, H-5), 2.18 (s, 3H, H-10), 2.14−2.21 (m, 1H,
H-6a), 2.06−2.09 (m, 1H, H-6b), 1.08 (s, 3H, H-11); 13C NMR (125
MHz, CDCl3) δ 198.01, 168.62, 145.17, 144.00, 140.12, 139.46,
119.27, 108.28, 82.82, 43.92, 32.92, 31.97, 18.91, 10.07; MS (ESI), m/
z (%) 244.94 ([M − H]+, 100).
Synthesis of 3-Formylfraxinellone (3). A mixture of fraxinellone (1,
92.8 mg, 0.4 mmol) and selenium dioxide (88.8 mg, 0.8 mmol) in 1,4-
dioxane (3 mL) was reacted at 110 °C for 2.5 h using a microwave
reactor at 150 W. After the mixture had cooled to room temperature,
the solvent was removed and the residue was dissolved in DCM and
filtered. The filtrate was concentrated in vacuo and purified by PTLC
to give 3 in 27% yield as a white solid. Rf = 0.26 (petroleum ether/
Fraxinellone was isolated from D. dasycarpus as a white solid in
0.118% yield, and its purity was >99% as measured with reverse phase
high-performance liquid chromatography (RP-HPLC). Rf = 0.62
(petroleum ether/acetone = 5:1); mp 113−115 °C; IR cm−1 3148,
ethyl acetate = 5:1); mp 118−120 °C; [α]23 = −50 (c 3.3 mg/mL,
D
acetone); IR cm−1 (KBr) 3125, 2990, 2975, 1754, 1680, 1193, 1156,
873, 692; 1H NMR (500 MHz, CDCl3) δ 10.68 (s, 1H, H-10), 7.52 (s,
1H, H-2′), 7.49 (s, 1H, H-5′), 6.37 (s, 1H, H-4′), 5.13 (s, 1H, H-8),
2.60−2.65 (m, 1H, H-4a), 2.24−2.32 (m, 1H, H-4b), 1.98−2.00 (m,
1H, H-5a), 1.87−1.90 (m, 1H, H-6a), 1.70−1.72 (m, 1H, H-5b),
1.47−1.53 (m, 1H, H-6b), 1.01 (s, 3H, H-11); 13C NMR (125 MHz,
CDCl3) δ 190.25, 167.46, 145.86, 143.89, 140.06, 119.45, 108.30,
83.70, 44.52, 30.42, 21.90, 20.11, 17.06; HRMS (ESI), calcd for
C14H15O4 ([M + H]+), 247.0965; found, 247.0963.
1
3130, 2930, 1741, 1671, 1607, 1503, 1202, 1022, 949, 870, 812; H
NMR (400 MHz, CDCl3) δ 7.44−7.47 (m, 2H, H-2′, 5′), 6.35 (s, 1H,
H-4′), 4.88 (s, 1H, H-8), 2.16−2.31 (m, 2H, H-7), 2.13 (s, 3H, H-10),
1.44−1.86 (m, 4H, H-5, 6), 0.85 (s, 3H, H-11); MS (ESI), m/z (%)
233.05 ([M + H]+, 58).
Synthesis of Fraxinellonone (2). To a mixture of CrO3 (40 mg, 0.4
mmol), pyridine (0.074 mL, 0.8 mmol), and 70% aqueous t-BuOOH
(0.55 mL, 4 mmol) in dried dichloromethane (DCM, 3 mL) was
added compound 1 (92.8 mg, 0.4 mmol). Then the above mixture was
reacted at 33 °C for 2.5 h using a microwave reactor at 25 W. When
the reaction was complete as checked by TLC analysis, the mixture
was diluted by DCM (40 mL), washed by saturated NaHSO3 (20 mL)
and brine (20 mL), dried over anhydrous Na2SO4, concentrated in
vacuo, and purified by PTLC to afford 2 in a 27% yield as a white solid.
Rf = 0.30 (petroleum ether/ethyl acetate = 5:1); mp 141−143 °C;
Synthesis of 4α-Hydroxyfraxinellone (4). To a stirred solution of
fraxinellonone (2, 1 mmol, 246.3 mg) in methanol at 0−5 °C was
slowly added NaBH4 (2 mmol, 75.7 mg). After the addition, the
reaction mixture was stirred at 0−5 °C for 1.5 h. The solvent was
removed, and the residue was dissolved in DCM (50 mL). The
mixture was then washed by brine (20 mL), and the organic phase was
dried over anhydrous Na2SO4, filtered, and concentrated under
reduced pressure. The crude product was purified by PTLC to give 4α-
hydroxyfraxinellone (4) as a white solid in 78% yield. Mp 112−114
[α]23 = −39 (c 3.0 mg/mL, acetone); IR cm−1 (KBr) 3138, 2950,
D
2928, 1754, 1672, 1214, 1146, 877, 773; 1H NMR (500 MHz, CDCl3)
°C; [α]20 = 16 (c 3.2 mg/mL, CHCl3); IR cm−1 3435, 2941, 2861,
D
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Figure 2. X-ray crystal structure of 6h.
1
1743, 1667, 1501, 1204, 1024, 980; H NMR (500 MHz, CDCl3) δ
added to the all of the dishes until adult emergence. The experiment
was carried out at 25 2 °C and a relative humidity (RH) of 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 with the formula
7.46 (s, 1H, H-2′), 7.44 (s, 1H, H-5′), 6.32 (s, 1H, H-4′), 4.91 (s, 1H,
H-8), 4.24 (t, J = 8.5 Hz, 1H, H-4), 2.19−2.25 (m, 4H, H-5a, 10),
1.72−1.82 (m, 4H, H-5b, 6, −OH), 0.95 (s, 3H, H-11); 13C NMR
(125 MHz, CDCl3) δ 169.42, 148.27, 143.61, 139.84, 130.02, 120.03,
108.37, 83.15, 71.64, 43.58, 31.39, 28.61, 20.40, 14.21; ESI-MS, m/z
271.0 ([M + Na]+, 100).
corrected mortality rate (%) = (T − C) × 100/(1 − C)
Synthesis of 10-Hydroxyfraxinellone (5). To a stirred solution of 3-
formylfraxinellone (3, 1 mmol, 246.3 mg) in methanol at 0−5 °C was
slowly added NaBH4 (2 mmol, 75.7 mg). The reaction mixture was
stirred at 0−5 °C for 1 h. The solvent was removed, and the residue
was dissolved in DCM (50 mL). The mixture was then washed by
brine (20 mL), and the organic phase was dried over anhydrous
Na2SO4, filtered, and concentrated under reduced pressure. The crude
product was purified by PTLC to give 10-hydroxyfraxinellone (5) as a
colorless liquid in 71% yield. [α]20D = −29 (c 3.0 mg/mL, CHCl3); IR
cm−1 3416, 2940, 2874, 1748, 1670, 1503, 1264, 1198, 1055, 1003,
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.
RESULTS AND DISCUSSION
■
Synthesis. As shown in Scheme 1, two key intermediates,
fraxinellonone (2) and 3-formylfraxinellone (3) were first
synthesized in 27% yields from compound 1 by regioselectively
allylic oxidation in the presence of chromium trioxide or
selenium dioxide under microwave irradiation. Then reduction
of 2 and 3 in the presence of NaBH4 afforded 4 and 5,
respectively. Finally, two series of novel fraxinellone-based
esters (6a−t and 7a−q) were smoothly obtained by reaction of
4 or 5 with the corresponding carboxylic acids in the presence
of DIC and DMAP. The steric configuration of 6h was
unambiguously confirmed by X-ray crystallography as illus-
trated in Figure 2. Crystallographic data (excluding structure
factors) for the structures of 6h has been deposited with the
Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC 876475. Copies of the data can be
obtained, free of charge, on application to CCDC, 12 Union
Road, Cambridge CB2 1EZ, U.K. [fax, +44 (0)1223 336033; or
e-mail, deposit@ccdc.cam.ac.uk]. This suggested that the 4-
fluorobenzoyloxy group of 6h adopted an α configuration; that
is, the configuration of 4-hydroxy of 4 was also α. Therefore, in
this paper we describe an efficient method for the stereo-
selective synthesis of 4 from 2 simply by the reducing agent
NaBH4.
1
875; H NMR (500 MHz, CDCl3) δ 7.48 (s, 1H, H-2′), 7.46 (s, 1H,
H-5′), 6.35 (s, 1H, H-4′), 5.01 (s, 1H, H-8), 4.50 (d, J = 14.0 Hz, 1H,
H-10a), 4.25 (d, J = 14.0 Hz, 1H, H-10b), 2.44−2.50 (m, 1H, H-4a),
2.21−2.29 (m, 1H, H-4b), 1.89−1.92 (m, 1H, H-5a), 1.74−1.83 (m,
2H, H-5b, 6a), 1.44−1.49 (m, 1H, H-6b), 0.90 (s, 3H, H-11); 13C
NMR (125 MHz, CDCl3) δ 170.84, 152.48, 143.65, 139.87, 129.86,
120.07, 108.45, 84.66, 62.54, 43.26, 31.13, 28.50, 20.47, 17.82; ESI-
MS, m/z 271.0 ([M + Na]+, 100).
General Procedure for the Synthesis of Fraxinellone-Based Esters
6a−t and 7a−q. A mixture of the corresponding acids RCO2H (0.28
mmol), diisopropylcarbodiimide (DIC, 0.28 mmol), 4-dimethylami-
nopyridine (DMAP, 0.04 mmol), and 4 or 5 (0.2 mmol) in dried
DCM (10 mL) was stirred at room temperature. When the reaction
was complete according to TLC analysis, the mixture was diluted by
DCM (40 mL), washed by aqueous HCl (0.1 mol/L, 20 mL), 5%
NaHCO3 (20 mL), and brine (20 mL), dried over anhydrous Na2SO4,
concentrated in vacuo, and purified by PTLC to give the pure target
products 6a−t and 7a−q. The data of 6a−t and 7a−q can be found in
the Supporting Information.
Biological Assay. The insecticidal activity of 6a−t and 7a−q
against the pre-third-instar larvae of M. separata Walker was assessed
by leaf-dipping method as described previously.20 For each compound,
30 larvae (10 larvae per group) were used. Acetone solutions of 6a−t,
7a−q, and toosendanin (used as a positive control) were prepared at
the 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
Insecticidal Activity. The insecticidal activity of 6a−t and
7a−q against the pre-third-instar larvae of M. separata in vivo
was tested by the leaf-dipping method at the concentration of 1
mg/mL. Toosendanin, a commercial insecticide derived from
M. azedarach, was used as the positive control and supplied by
the Research and Development Center of Biorational Pesticide,
Northwest A&F University, Shannxi province, China. Leaves
treated with acetone alone were used as a blank control group.
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As depicted in Table 1, the corresponding mortality rates after
35 days were generally higher than those after 10 and 25 days as
Table 1. Insecticidal Activity of 6a−t and 7a−q against M.
separata on Leaves Treated with a Concentration of 1 mg/
a
mL
corrected mortality rate (%)
compd
10 days
25 days
35 days
1
20.7 4.7
20.7 4.7
10.3 4.7
20.7 4.7
10.3 4.7
20.7 4.7
31.0 4.7
10.3 4.7
41.4 4.7
24.1 4.7
24.1 4.7
24.1 4.7
20.7 4.7
20.7 4.7
24.1 9.4
10.3 9.4
27.6 8.2
20.7 4.7
20.7 4.7
24.1 4.7
31.0 4.7
13.8 4.7
20.7 4.7
17.2 8.2
33.3
0
44.4
0
4
37.0 4.7
29.6 4.7
37.0 4.7
33.3 8.2
40.7 4.7
37.0 4.7
29.6 4.7
48.1 4.7
40.7 4.7
5
6a
6b
6c
6d
6e
6f
6g
6h
6i
6j
6k
6l
44.4
0
48.1 4.7
48.1 4.7
44.4
51.9 4.7
44.4
0
44.4
0
0
Figure 3. Representative abnormal larvae pictures of 4, 6f, 6o, 6t, and
7p during the larval period (CK, blank control group).
40.7 4.7
51.9 4.7
29.6 4.7
33.3 8.2
40.7 4.7
25.9 4.7
40.7 4.7
40.7 4.7
48.1 4.7
40.7 4.7
48.1 4.7
40.7 4.7
37.0 4.7
48.1 4.7
40.7 4.7
63.0 4.7
44.4
40.7 4.7
44.4
0
0
37.0 4.7
48.1 4.7
51.9 4.7
55.6 8.2
55.6 8.2
6m
6n
6o
6p
6q
66.7
0
6r
51.9 4.7
51.9 4.7
63.0 4.7
40.7 4.7
6s
6t
7a
33.3
0
7b
6.9
0
0
25.9 4.7
33.3 8.2
33.3 8.2
33.3 8.2
29.6 4.7
29.6 4.7
40.7 4.7
51.9 4.7
25.9 4.7
25.9 4.7
29.6 4.7
29.6 4.7
33.3
37.0 4.7
44.4
0
7c
27.6
7d
27.6 8.2
20.7 4.7
17.2 8.2
17.2 8.2
10.3 4.7
24.1 4.7
0
7e
48.1 4.7
29.6 4.7
29.6 4.7
51.9 4.7
7f
Figure 4. Representative malformed pupae pictures of 6e, 6q, 7c, 7i,
and 7q during the pupation period (CK, blank control group).
7g
7h
7i
55.6
0
treated groups (Figure 5). Eighteen compounds exhibited
insecticidal activity more pronounced than or comparable to
7j
6.9
0
40.7 4.7
7k
13.8 4.7
24.1 9.4
24.1 4.7
13.8 4.7
33.3
33.3
44.4
0
0
0
7l
7m
7n
33.3
0
40.7 4.7
44.4
7o
6.9
0
25.9 4.7
44.4 8.2
48.1 4.7
0
7p
27.6 8.2
24.1 4.7
27.6 8.2
51.9 4.7
59.3 4.7
48.1 4.7
7q
toosendanin
33.3
0
a
Values are the mean SD of three replicates.
Lu et al. reported;12 therefore, these compounds, in a time-
̈
dependent manner, are different from conventional neurotoxic
insecticides such as organophosphates, carbamates, and
pyrethroids in exhibiting delayed insecticidal activity. Mean-
while, the symptoms of the tested M. separata were also
characterized in the same way as in our previous papers.16−19
Due to feeding too much treated leaves during the first 48 h,
some larvae died slowly during the larval period (Figure 3). In
the meantime, many larvae of the treated groups molted to
malformed pupae and died during the stage of pupation (Figure
4). Malformed moths with imperfect wings also appeared in the
Figure 5. Representative malformed moth pictures of 6h, 6o, 6t, 7e,
and 7q during the emergence period (CK, blank control group).
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that of toosendanin. Especially compounds 6h, 6q, 6t, and 7q
showed more promising insecticidal activity than toosendanin.
Meanwhile, some interesting results of structure−activity
relationships of 6a−t and 7a−q were also observed. The
hydroxy at the C-4 or C-10 position of fraxinellone should not
be free. For example, the final mortality rates of 4 and 5 were
only 48.1 and 40.7%, respectively. In general, introduction of
the fluorine atom on the phenyl ring could lead to a more
potent compound than that possessing chlorine or bromine (6h
vs 6j, 6k, and 6l; 7h and 7i vs 7j, 7k, and 7l). Introduction of
the heterocyclic fragments at the C-4 or C-10 position of
fraxinellone improved insecticidal activity. For example, the
final mortality rates of 6p−t, 7p, and 7q were 55.6, 66.7, 51.9,
51.9, 63, 51.9, and 59.3%, respectively. However, alkylacyloxy,
benzoyloxy, p-methylbenzoyloxy, m-bromobenzoyloxy, or p-
bromobenzoyloxy introduced at the C-10 position of
fraxinellone in general decreased insecticidal activity (e.g., 7b,
7c, 7f, 7g, 7k, and 7l). Introduction of the ester groups at the
C-4 position of fraxinellone usually afforded more potent
compounds than those with the same groups at the C-10
position (e.g., 6m vs 7m; 6n vs 7n; 6o vs 7o). Interestingly, the
proper chain length of alkylacyloxy was important to the speed
of activity for 10 days. When the n-heptanoyloxy was
introduced at the C-4 or C-10 position of fraxinellone to give
6b and 7b, the mortality rates of 6b and 7b against M. separata
for 10 days were only 10.3 and 6.9%, respectively, whereas
when the acetyloxy or n-decanoyloxy was introduced at the C-4
or C-10 position of fraxinellone to give 6a, 6c, 7a, and 7c, the
mortality rates against M. separata for 10 days were 20.7, 20.7,
17.2, and 27.6%, respectively.
In conclusion, to improve the insecticidal activity of
fraxinellone, 37 novel fraxinellone-based esters were synthe-
sized by modification at the C-4 or C-10 position of
fraxinellone and evaluated for their insecticidal activity against
the pre-third-instar larvae of M. separata in vivo. Especially
compounds 6h, 6q, 6t, and 7q showed more promising
insecticidal activity than toosendanin. On the other hand, an
efficient method for the stereoselective synthesis of 4α-
hydroxyfraxinellone from fraxinellonone was developed. This
suggested that introduction of the fluorine atom on the phenyl
ring could lead to a more potent compound than that
possessing chlorine or bromine, and introduction of the
heterocyclic fragments at the C-4 or C-10 position of
fraxinellone was essential for their insecticidal activity. This
will pave the way for further design, structural modification, and
development of fraxinellone as a botanical insecticidal agent.
Colleges Basic Scientific Research Operating Expenses
(QN2009045).
Notes
The authors declare no competing financial interest.
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ASSOCIATED CONTENT
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S
* Supporting Information
1H NMR, 13C NMR, HRMS, optical rotation, melting point,
and IR data for the target compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Author
*Phone: +86(0)29-87091952. Fax: +86(0)29-87091952. E-
mail: orgxuhui@nwsuaf.edu.cn.
Funding
The present research was partly supported by National Natural
Science Foundation of China (No. 31071737, 31171896), the
Program for Changjiang Scholars and Innovative Research
Team in University (IRT1035), and Special Funds of Central
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Journal of Agricultural and Food Chemistry
Article
(20) Xu, H.; Wang, J. J.; Sun, H. J.; Lv, M.; Tian, X.; Yao, X. J.;
Zhang, X. Semisynthesis and quantitative structure-activity relationship
(QSAR) study of novel aromatic esters of 4′-demethyl-4-deoxypodo-
phyllotoxin as insecticidal agents. J. Agric. Food Chem. 2009, 57, 7919−
7923.
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dx.doi.org/10.1021/jf301734h | J. Agric. Food Chem. 2012, 60, 7016−7021