Construction of Cholesterol Oxime Ether Derivatives Containing Isoxazoline/Isoxazole Fragments and Their Agricultural Bioactive Properties/Control Efficiency

Article abstract of DOI:10.1021/acs.jafc.1c01884

To explore natural-product-based pesticidal candidates and high value-added application of cholesterol in agriculture, oximinoether derivatives of cholesterol-containing isoxazoline/isoxazole fragments (I-1～I-16 and II-1～II-18) were semiprepared by structural optimization of cholesterol. Their structures were characterized by optical rotation, high-resolution mass spectrometry (HRMS), IR, and 1H NMR spectroscopy. Particularly, the Z configurations of oxime fragments at the C-7 position of target compounds were undoubtedly determined by X-ray crystallography. Against Mythimna separata Walker, compounds 3e, I-8, I-14, and II-3 showed 2.4-2.7-fold growth inhibitory activity of the precursor cholesterol. Against Plutella xylostella Linnaeus, compounds I-6, I-7, and I-9 showed 2.4-2.7-fold oral toxicity of cholesterol. Against Aphis citricola Van der Goot, compounds 2e and II-15 exhibited 4.9 and 5.8-fold aphicidal activity of cholesterol, respectively. Notably, they showed good control effects (3.0-5.0-fold promising control efficiency of 1) against A. citricola in the greenhouse. Structure-activity relationships (SARs) suggested that the C-3 hydroxyl group and the C-7 position of cholesterol are two important modification sites. It will pave the way for future structural optimization and application of cholesterol derivatives as potential pesticidal agents in agriculture.

Full text of DOI:10.1021/acs.jafc.1c01884

pubs.acs.org/JAFC
Article
Construction of Cholesterol Oxime Ether Derivatives Containing
Isoxazoline/Isoxazole Fragments and Their Agricultural Bioactive
Properties/Control Efficiency
Hui Xu,* Kong Zhang, Min Lv,* and Meng Hao
Cite This: J. Agric. Food Chem. 2021, 69, 8098−8109
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ABSTRACT: To explore natural-product-based pesticidal candidates and high value-added application of cholesterol in agriculture,
oximinoether derivatives of cholesterol-containing isoxazoline/isoxazole fragments (I-1∼I-16 and II-1∼II-18) were semiprepared by
structural optimization of cholesterol. Their structures were characterized by optical rotation, high-resolution mass spectrometry
1
(HRMS), IR, and H NMR spectroscopy. Particularly, the Z configurations of oxime fragments at the C-7 position of target
compounds were undoubtedly determined by X-ray crystallography. Against Mythimna separata Walker, compounds 3e, I-8, I-14,
and II-3 showed 2.4−2.7-fold growth inhibitory activity of the precursor cholesterol. Against Plutella xylostella Linnaeus, compounds
I-6, I-7, and I-9 showed 2.4−2.7-fold oral toxicity of cholesterol. Against Aphis citricola Van der Goot, compounds 2e and II-15
exhibited 4.9 and 5.8-fold aphicidal activity of cholesterol, respectively. Notably, they showed good control effects (3.0−5.0-fold
promising control efficiency of 1) against A. citricola in the greenhouse. Structure−activity relationships (SARs) suggested that the
C-3 hydroxyl group and the C-7 position of cholesterol are two important modification sites. It will pave the way for future structural
optimization and application of cholesterol derivatives as potential pesticidal agents in agriculture.
KEYWORDS: cholesterol, natural product, structural optimization, oximinoether derivatives, pesticidal activity
isoxazole derivatives (IV′) exhibited potential insecticidal
activity against Callosobruchus chinensis.23
INTRODUCTION
■
Aphis citricola Van der Goot (Hemiptera: Aphididae),1,2 Mythimna
separata Walker (Lepidoptera: Noctuidae),3,4 and Plutella xylostella
Linnaeus (Lepidoptera: Plutellidae)5,6 are three widespread
and threatening pests on fruit trees and crops. To effectively
control the damage of these pests, many agrochemicals were
extensively and unreasonably applied; however, pests resist-
ance and resurgence, as well as negative effects of pesticide
residues on human health and the ecological environment
simultaneously appeared.7−11 Due to the originality of their
chemical skeletons and the diversity of their biological acti-
vities, recently, the application of natural products that are
generated in the evolution of organisms over billions of years,
as pesticide alternatives have received much attention.12−14
When compared with those of traditional agrochemicals, but
in reality, the pesticidal activities of natural products are very
low, and generally they are not very popular in the market.
Recently, structural modifications of natural products as lead
compounds to improve their activities have been an important
approach to develop new effective pesticide candidates.15−19
Isoxazoline and isoxazole (Figure 1) are two important
moieties existing in a variety of bioactive products. As shown
in Figure 1, piperine derivatives containing the isoxazoline
scaffold (I′ and II′) showed more pronounced pesticidal acti-
vities than piperine;20 fluxametamide containing the isoxazoline
scaffold, a novel wide-spectrum insecticide as a ligand-gated
chloride channel (LGCC) antagonist, was discovered by Nissan
Chemical Industries, Ltd.;21 neonicotinoid-isoxazoles hybrids
(III′) displayed higher insecticidal activity than imidacloprid;22
Cholesterol (1, Figure 1), a waxy steroid in animals, plants,
and fungi, was used as a lead compound for the preparation of
cholesterol-type derivatives, which showed antiviral activity,24
anticancer activity,25,26 and antimicrobial activity.27,28 Pre-
viously, we studied cholesterol-based hydrazone derivatives
and found that some compounds exhibited more promising
insecticidal activity than toosendanin (a commercial botanical
insecticide registered in China) isolated from the plant Melia
azedarach; in particular, one intermediate 3-acetyloxy-7-
oxocholesterol (1′, Figure 1) also showed the potent
insecticidal activity.29 Based upon the above-mentioned results,
and to discover potent pesticide candidates from cholesterol,
herein, a series of oxime ethers derivatives of cholesterol (I and
II, Figure 1) were further designed by the introduction of
isoxazoline/isoxazole fragments via the oxime group at the C-7
position of cholesterol. Their agricultural activities were
evaluated against A. citricola, M. separata, and P. xylostella.
Their control efficiency was also tested against A. citricola in
the greenhouse.
Received: March 31, 2021
Revised: June 1, 2021
Accepted: July 7, 2021
Published: July 19, 2021
https://doi.org/10.1021/acs.jafc.1c01884
J. Agric. Food Chem. 2021, 69, 8098−8109
© 2021 American Chemical Society
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Article
Figure 1. Design of target compounds I and II.
phase was dried over anhydrous Na2SO4, concentrated, and purified
by silica gel column chromatography eluting with petroleum ether/
CH2Cl2 (v/v = 1:5) to give 3a−e in 62−98% yields. Exemplary data
for compound 3a are as follows.
MATERIALS AND METHODS
■
Synthesis of Compounds 2a−e. A mixture of cholesterol
(1, 1 mmol), substituted benzoyl chlorides (1.5 mmol), triethylamine
(2 mmol), and 4-dimethylaminopyridine (DMAP) (0.2 mmol) in dry
CH2Cl2 (10 mL) was stirred at room temperature for 12 h. Then,
CH2Cl2 (20 mL) was added to the mixture, which was washed with
brine (10 mL). The organic phase was dried over anhydrous Na2SO4,
concentrated, and purified by silica gel column chromatography
eluting with petroleum ether/CH2Cl2 (v/v = 5:1) to give 2a−e in
56−90% yields. Exemplary data for compound 2a are as follows.
Data for Compound 2a. Yield: 85%, white solid, mp 143−145 °C;
Data for Compound 3a. Yield: 63%, pale yellow solid, mp 205−
207 °C; [α]D25 = −40 (c 1.0 mg/mL, CHCl3); IR cm−1 (KBr): 3063,
2949, 2867, 1719, 1458, 1377, 1278, 1114, 939, 709; 1H NMR
(500 MHz, CDCl3) δ: 8.04 (d, J = 7.5 Hz, 2H, Ph-H), 7.58 (t, J =
7.5 Hz, 1H, Ph-H), 7.46 (t, J = 7.5 Hz, 2H, Ph-H), 5.75 (s,
1H, −CHC), 4.95−5.00 (m, 1H, −OCH), 2.68−2.71 (m, 1H),
2.60−2.65 (m, 1H), 2.38−2.44 (m, 1H), 2.28 (t, J = 11.5 Hz, 1H),
2.14 (d, J = 13.0 Hz, 1H), 2.01−2.06 (m, 2H), 1.87−1.91 (m, 1H),
1.79−1.85 (m, 1H), 1.50−1.59 (m, 5H), 1.32−1.37 (m, 5H), 1.24−
1.28 (m, 5H), 1.02−1.13 (m, 5H), 0.93 (d, J = 6.5 Hz, 3H), 0.85−
0.87 (m, 6H), 0.69 (s, 3H).
Synthesis of Compounds 4a−e. A mixture of 3a−e (1 mmol),
hydroxylamine hydrochloride (3.3 mmol), and NaOH (3.3 mmol) in
anhydrous ethanol (10 mL) was refluxed for 48 h. The mixture was
concentrated, to which brine (10 mL) was added. Then, the mixture
was extracted with ethyl acetate (20 mL × 3), and the combined
organic phase was dried over anhydrous Na2SO4, concentrated, and
purified by silica gel column chromatography eluting with petroleum
ether/ethyl acetate (v/v = 10:1) to give 4a−e in 66−87% yields.
Exemplary data for compound 4a are as follows.
25
[α]D = −14 (c 1.0 mg/mL, CHCl3); IR cm−1 (KBr): 3030, 2949,
1
2866, 1715, 1455, 1375, 1272, 1111, 949, 711; H NMR (500 MHz,
CDCl3) δ: 8.03−8.05 (m, 2H, Ph-H), 7.52−7.55 (m, 1H, Ph-H), 7.44
(t, J = 7.5 Hz, 2H, Ph-H), 5.42 (d, J = 4.0 Hz, 1H, −CHC), 4.83−
4.89 (m, 1H, −OCH), 2.47 (d, J = 7.5 Hz, 2H), 1.96−2.03 (m, 3H),
1.90−1.93 (m, 1H), 1.80−1.86 (m, 1H), 1.69−1.78 (m, 1H), 1.45−
1.57 (m, 7H), 1.21−1.35 (m, 5H), 1.07−1.17 (m, 9H), 0.99−1.03
(m, 2H), 0.93 (d, J = 6.5 Hz, 3H), and 0.86−0.87 (m, 6H), 0.69
(s, 3H).
Synthesis of Compounds 3a−e. A mixture of 2a−e (1 mmol),
CrO3 (1 mmol), t-BuOOH (10 mmol), and pyridine (2 mmol) in dry
CH2Cl2 (10 mL) was stirred at room temperature overnight. Then,
CH2Cl2 (20 mL) was added to the mixture, which was washed with
saturated NaHSO3 (10 mL × 3) and brine (10 mL). The organic
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Figure 2. Synthesis of intermediates 5a, 5c−e, and 6a−e.
Data for Compound 4a. Yield: 87%, white solid, mp 239−242 °C;
temperature for 24 h. The mixture was concentrated, to which brine
(10 mL) was added. Then, the mixture was extracted with CH2Cl2
(20 mL × 3), and the combined organic phase was dried over
anhydrous Na2SO4, concentrated, and purified by PTLC eluting with
petroleum ether/CH2Cl2 (v/v = 1:2) to give 6a−e in 53−98% yields.
Exemplary data for compound 6a are as follows.
25
[α]D = −101 (c 1.1 mg/mL, CHCl3); IR cm−1 (KBr): 2950, 2870,
1719, 1457, 1374, 1274, 1116, 954, 711; 1H NMR (500 MHz,
CDCl3) δ: 8.05 (d, J = 7.5 Hz, 2H, Ph-H) 7.57 (t, J = 7.0 Hz 1H,
Ph-H), 7.45 (t, J = 8.0 Hz, 2H, Ph-H), 6.62 (s, 1H, −CHC), 4.92−
4.98 (m, 1H, −OCH), 2.69−2.72 (m, 1H), 2.57−2.62 (m, 1H),
2.31−2.35 (m, 2H), 2.04−2.10 (m, 2H), 1.96−1.99 (m, 1H), 1.87−
1.93 (m, 1H), 1.76−1.82 (m, 1H), 1.49−1.59 (m, 3H), 1.22−1.42
(m, 8H), 1.11−1.19 (m, 9H), 0.99−1.05 (m, 1H), 0.94 (d, J = 6.5 Hz,
3H), 0.85−0.87 (m, 6H), 0.71 (s, 3H).
Synthesis of Compounds 5a,c−e. A mixture of 4a,c−e
(1 mmol), allyl bromide (2 mmol), potassium hydroxide (3 mmol),
and potassium iodide (0.5 mmol) in acetone (10 mL) was stirred at
room temperature for 24 h. The mixture was concentrated, to which
brine (10 mL) was added. Then, the mixture was extracted with
CH2Cl2 (20 mL × 3), and the combined organic phase was dried over
anhydrous Na2SO4, concentrated, and purified by preparative thin-
layer chromatography (PTLC) eluting with petroleum ether/CH2Cl2
(v/v = 1:1) to give 5a,c−e in 76−95% yields. Exemplary data for
compound 5a are as follows.
Data for Compound 6a. Yield: 67%, white solid, mp 155−156 °C;
25
[α]D = −88 (c 1.0 mg/mL, CHCl3); IR cm−1 (KBr): 3282, 3062,
2947, 2865, 1718, 1456, 1369, 1273, 1113, 882, 714; 1H NMR
(500 MHz, CDCl3) δ: 8.04 (d, J = 7.5 Hz, 2H, Ph-H), 7.57 (t, J =
7.5 Hz, 1H, Ph-H), 7.45 (t, J = 7.5 Hz, 2H, Ph-H), 6.52 (s, 1H,
−CHC), 4.90−4.94 (m, 1H, −OCH), 4.64 (d, J = 2.0 Hz, 2H),
2.64−2.68 (m, 1H), 2.54−2.59 (m, 1H), 2.42−2.49 (m, 2H), 2.34
(t, J = 11.5 Hz, 1H), 2.03−2.08 (m, 2H), 1.94−1.97 (m, 1H), 1.86−
1.90 (m, 1H), 1.75−1.82 (m, 1H), 1.52−1.56 (m, 3H), 1.27−1.44
(m, 7H), 1.11−1.19 (m, 9H), 1.02−1.05 (m, 1H), 0.94 (d, J = 6.5 Hz,
3H), 0.86−0.88 (m, 6H), 0.70 (s, 3H); HRMS [ESI]: calcd for
C37H52NO3 ([M + H]+), 558.3942; found, 558.3944.
General Procedure for the Preparation of Target Com-
pounds I-1 to I-16 and II-1 to II-18. A mixture of compounds
5a,c−e or 6a−e (1 mmol), different chloroximes (7a−e, 2.1 mmol),
and Et3N (1.1 mmol) in CH2Cl2 (10 mL) was stirred at room tem-
perature for 72−120 h. Then, the mixture was diluted with CH2Cl2
(20 mL). It was washed with brine (10 mL), dried over anhydrous
Na2SO4, and purified by PTLC eluting with petroleum ether/CH2Cl2
(v/v = 1:3 or 2:3) to afford target compounds I-1 to I-16 and II-1 to
II-18 in 9−59% yields. Exemplary data for compounds I-1 o I-3 and
II-1 to II-3 are as follows.
Data for Compound 5a. Yield: 92%, white solid, mp 126−127 °C;
25
[α]D = −85 (c 1.2 mg/mL, CHCl3); IR cm−1 (KBr): 3072, 2945,
1
2866, 1719, 1455, 1372, 1272, 1112, 926, 713; H NMR (500 MHz,
CDCl3) δ: 8.04 (d, J = 7.5 Hz, 2H, Ph-H), 7.56 (t, J = 7.5 Hz, 1H,
Ph-H), 7.45 (t, J = 7.5 Hz, 2H, Ph-H), 6.55 (s, 1H, −CH  C),
5.97−6.05 (m, 1H), 5.29 (d, J = 17.0 Hz, 1H), 5.19 (d, J = 10.5 Hz,
1H), 4.89−4.96 (m, 1H, −OCH), 4.50−4.58 (m, 1H, −OCH), 2.64−
2.68 (m, 1H), 2.54−2.59 (m, 1H), 2.41−2.46 (m, 1H), 2.31 (t, J =
11.5 Hz, 1H), 2.03−2.05 (m, 2H), 1.94−1.97 (m, 1H), 1.77−1.90
(m, 2H), 1.51−1.58 (m, 3H), 1.26−1.42 (m, 7H), 1.06−1.16
(m, 9H), 1.01−1.03 (m, 1H), 0.94 (d, J = 6.5 Hz, 3H), 0.86−0.88
(m, 6H), 0.70 (s, 3H).
Data for Compound I-1. Yield: 23%, pale yellow solid, mp 63−65
25
°C; [α]D = −86 (c 0.8 mg/mL, CHCl3); IR cm−1 (KBr): 3064,
2948, 2862, 1714, 1454, 1364, 1275, 1114, 889, 758; 1H NMR
(500 MHz, CDCl3) δ: 8.05 (d, J = 8.0 Hz, 2H, Ph-H), 7.66−7.69 (m,
2H, Ph-H), 7.58 (t, J = 7.0 Hz, 1H, Ph-H), 7.46 (t, J = 7.0 Hz, 2H,
Ph-H), 7.33−7.40 (m, 3H, Ph-H), 6.47 (d, J = 4.5 Hz, 1H, −CHC),
4.99−5.04 (m, 1H), 4.85−4.91 (m, 1H), 4.22−4.26 (m, 1H),
Synthesis of Compounds 6a−e. A mixture of 4a−e (1 mmol),
propargyl bromide (2 mmol), potassium hydroxide (3 mmol), and
potassium iodide (0.5 mmol) in acetone (10 mL) was stirred at room
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Figure 3. Synthetic route for target compounds I-1 to I-16 and II-1 to II-18.
4.10−4.14 (m, 1H), 3.31−3.42 (m, 2H), 2.48−2.59 (m, 2H), 2.37−
2.43 (m, 1H), 2.14−2.29 (m, 1H), 2.02−2.04 (m, 2H), 1.90−1.93
(m, 1H), 1.71−1.85 (m, 2H), 1.50−1.54 (m, 3H), 1.25−1.38
(m, 7H), 1.09−1.17 (m, 9H), 1.01−1.03 (m, 1H), 0.94 (d, J = 6.5 Hz,
3H), 0.86−0.88 (m, 6H), 0.69 (d, J = 9.5 Hz, 3H); HRMS [ESI]:
calcd for C44H58N2NaO4 ([M + Na]+), 701.4289; found, 701.4272.
Data for Compound I-2. Yield: 18%, white solid, mp 66−67 °C;
Data for Compound II-1. Yield: 40%, white solid, mp 129−
131 °C; [α]D25 = −72 (c 0.9 mg/mL, CHCl3); IR cm−1 (KBr): 3062,
2947, 2869, 1717, 1453, 1367, 1273, 1114, 913, 708; 1H NMR
(500 MHz, CDCl3) δ: 8.04 (d, J = 7.0 Hz, 2H, Ph-H), 7.82 (d, J =
4.5 Hz, 2H, Ph-H), 7.55 (s, 1H, Ph-H), 7.44 (s, 5H, Ph-H), 6.55
(d, J = 6.5 Hz, 2H), 5.18 (s, 2H), 4.94 (s, 1H, −OCH), 2.68 (d, J =
12.5 Hz, 1H), 2.55−2.59 (m, 1H), 2.40 (s, 1H), 2.32 (t, J = 11.0 Hz,
1H), 2.03−2.06 (m, 2H), 1.98 (d, J = 13.0 Hz, 1H), 1.75−1.86
(m, 2H), 1.53−1.56 (m, 3H), 1.24−1.40 (m, 7H), 1.12−1.17
(m, 9H), 1.01−1.03 (m, 1H), 0.94 (s, 3H), 0.86−0.87 (m, 6H), 0.69
(s, 3H); HRMS [ESI]: calcd for C44H56N2NaO4 ([M + Na]+),
699.4132; found, 699.4106.
Data for Compound II-2. Yield: 54%, yellow solid, mp 101−
103 °C; [α]D25 = −83 (c 1.4 mg/mL, CHCl3); IR cm−1 (KBr): 3058,
2944, 2867, 1716, 1454, 1371, 1274, 1114, 912, 710; 1H NMR
(500 MHz, CDCl3) δ: 8.04 (d, J = 8.0 Hz, 2H, Ph-H), 7.71 (d, J =
8.0 Hz, 2H, Ph-H), 7.57 (t, J = 7.5 Hz, 1H, Ph-H), 7.45 (t, J = 8.0 Hz,
2H, Ph-H), 7.25 (s, 2H, Ph-H), 6.54 (d, J = 6.5 Hz, 2H), 5.16 (s, 2H),
4.90−4.97 (m, 1H, −OCH), 2.65−2.68 (m, 1H), 2.54−2.59 (m, 1H),
2.39 (s, 4H), 2.32 (t, J = 11.5 Hz, 1H), 2.03−2.08 (m, 2H), 1.95−
1.97 (m, 1H), 1.72−1.86 (m, 2H), 1.51−1.57 (m, 3H), 1.25−1.43
(m, 7H), 1.10−1.17 (m, 9H), 1.01−1.05 (m, 1H), 0.94 (d, J = 6.5 Hz,
3H), 0.86−0.88 (m, 6H), 0.69 (s, 3H); HRMS [ESI]: calcd for
C45H58N2NaO4 ([M + Na]+), 713.4289; found, 713.4271.
25
[α]D = −78 (c 0.8 mg/mL, CHCl3); IR cm−1 (KBr): 3063, 2947,
1
2867, 1718, 1456, 1363, 1273, 1113, 902, 756; H NMR (500 MHz,
CDCl3) δ: 8.05 (d, J = 7.5 Hz, 2H, Ph-H), 7.58 (t, J = 8.0 Hz, 3H,
Ph-H), 7.46 (t, J = 7.5 Hz, 2H, Ph-H), 7.17−7.19 (m, 2H, Ph-H),
6.47 (s, 1H, −CHC), 4.96−5.01 (m, 1H), 4.86−4.92 (m, 1H),
4.22−4.25 (m, 1H), 4.08−4.12 (m, 1H), 3.29−3.41 (m, 2H), 2.49−
2.60 (m, 2H), 2.37−2.40 (m, 1H), 2.34 (d, J = 6.0 Hz, 3H), 2.15−
2.29 (m, 1H), 2.02−2.04 (m, 2H), 1.90−1.94 (m, 1H), 1.72−1.84
(m, 2H), 1.50−1.54 (m, 3H), 1.25−1.40 (m, 7H), 1.10−1.18
(m, 9H), 1.02−1.03 (m, 1H), 0.94 (d, J = 6.5 Hz, 3H), 0.86−0.88
(m, 6H), 0.69 (d, J = 7.5 Hz, 3H); HRMS [ESI]: calcd for
C45H60N2NaO4 ([M + Na]+), 715.4445; found, 715.4421.
Data for Compound I-3. Yield: 19%, white solid, mp 104−106 °C;
25
[α]D = −71 (c 0.8 mg/mL, CHCl3); IR cm−1 (KBr): 3065, 2947,
1
2868, 1718, 1457, 1366, 1274, 1111, 910, 748; H NMR (500 MHz,
CDCl3) δ: 8.05 (d, J = 7.5 Hz, 2H, Ph-H), 7.63 (t, J = 8.5 Hz, 2H,
Ph-H), 7.58 (t, J = 7.5 Hz, 1H, Ph-H), 7.46 (t, J = 8.0 Hz, 2H, Ph-H),
7.35−7.38 (m, 2H, Ph-H), 6.46 (d, J = 3.5 Hz, 1H, −CHC), 5.00−
5.06 (m, 1H), 4.87−4.91 (m, 1H), 4.23−4.26 (m, 1H), 4.09−4.13
(m, 1H), 3.27−3.41 (m, 2H), 2.48−2.59 (m, 2H), 2.36−2.41 (m,
1H), 2.13−2.29 (m, 1H), 2.02−2.05 (m, 2H), 1.91−1.94 (m, 1H),
1.73−1.84 (m, 2H), 1.50−1.55 (m, 3H), 1.24−1.38 (m, 7H), 1.10−
1.17 (m, 9H), 1.02−1.03 (m, 1H), 0.94 (d, J = 6.5 Hz, 3H), 0.86−
0.88 (m, 6H), 0.69 (d, J = 7.5 Hz, 3H); HRMS [ESI]: calcd for
C44H57ClN2NaO4 ([M + Na]+), 735.3899; found, 735.3873.
Data for Compound II-3. Yield: 51%, pale yellow solid, mp 78−
25
80 °C; [α]D = −72 (c 1.1 mg/mL, CHCl3); IR cm−1 (KBr): 3065,
2947, 2868, 1717, 1459, 1367, 1274, 1111, 836, 712; 1H NMR
(500 MHz, CDCl3) δ: 8.04 (d, J = 7.5 Hz, 2H, Ph-H), 7.76 (d, J =
8.5 Hz, 2H, Ph-H), 5.57 (t, J = 7.5 Hz, 1H, Ph-H), 7.45 (t, J = 8.5 Hz,
4H, Ph-H), 6.52 (s, 2H), 5.17 (s, 2H), 4.90−4.97 (m, 1H, −OCH),
2.65−2.69 (m, 1H), 2.54−2.59 (m, 1H), 2.35−2.41 (m, 1H), 2.32
(t, J = 11.5 Hz, 1H), 2.03−2.08 (m, 2H), 1.95−1.98 (m, 1H), 1.79−
1.87 (m, 2H), 1.52−1.56 (m, 3H), 1.25−1.40 (m, 7H), 1.10−1.17
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Figure 4. Chemical structures of isoxazoline derivatives I-1 to I-16.
(m, 9H), 1.01−1.03 (m, 1H), 0.94 (d, J = 6.5 Hz, 3H), 0.86−0.88
(m, 6H), 0.69 (s, 3H); HRMS [ESI]: calcd for C44H55ClN2NaO4
([M + Na]+), 733.3743; found, 733.3740.
culture plates for 2 days [conditions: 25 2 °C; 65−80% RH; 12/12 h
photoperiod (L/D)]. Their corrected MR values were calculated in the
same way as mentioned above.20
Aphicidal Activity against A. citricola Van der Goot. Acetone
solutions of compounds 1, 2a−e, 3a−e, 4a−e, 5a,c−e, 6a−e, I-1 to
I-16, and II-1 to II-18 were prepared at 1 mg/mL (acetone as CK).
Ninety apterous adults of A. citricola were used for each tested compound
(30 aphids in a Petri dish as one group). The corresponding solution
(0.04 μL) was added to the pronotum of aphids [conditions: 25 1 °C;
50 7% RH; 14/10 h photoperiod (L/D)]. Their 24 and 48 h corrected
MR values were calculated in the same way as mentioned above. Finally,
the 48 h LD50 values of some potent compounds were calculated.30
Control Efficiency against A. citricola in the Glasshouse.
Solutions of compounds 1, 2e, and II-15 were prepared at 1.0 mg/mL
in water containing 0.1‰ Tween-80 (0.1‰ aq Tween 80 as CK). The
corresponding solution (2 mL) was sprayed to each apple sapling, which
was infested with 70 apterous adults of A. citricola (one plant per
replicate; three replicates per treatment) [conditions: 25 1 °C; 50
7% RH; 14/10 h photoperiod (L/D)]. Their control effects after 1, 3, 5,
and 7 days were calculated in the same way as mentioned above.2
Agricultural Activities Assay. Growth Inhibitory Activity
against M. separata Walker. Acetone solutions of compounds 1,
2a−e, 3a−e, 4a−e, 5a,c−e, 6a−e, I-1 to I-16, and II-1 to II-18 were
prepared at 1 mg/mL (toosendanin as the positive control and
acetone as CK). Thirty early third-instar larvae of M. separata were
used for each tested compound (10 larvae in a Petri dish as one
group). Wheat leaf discs (1 × 1 cm2) were dipped into the solution
for 3 s, dried, and added to three corresponding dishes. Once the discs
were consumed, the additional ones were added. After 2 days, the rest
of the compound-soaked discs were cleaned and fresh ones were
added until pupation [conditions: 25
2 °C; 65−80% relative
humidity (RH); 12/12 h photoperiod (light (L)/dark (D))].
Corrected mortality rate (MR) (%) = (T − C) × 100/(100% − C),
where C is the MR of CK and T is the MR of the treated M. separata.2
Oral Toxicity against P. xylostella Linnaeus. Acetone solutions of
compounds 1, 2a−e, 3a−e, 4a−e, 5a,c−e, 6a−e, I-1 to I-16, and II-1
to II-18 were prepared at 20 mg/mL (toosendanin as the positive
control and acetone as CK). The corresponding solution (1 μL) was
added to a fresh Brassica oleracea leaf disc (0.5 × 0.5 cm2) and dried.
One piece of the above discs was added and eaten by each third-instar
larvae of P. xylostella, which was raised in each well of 12- or 24-well
RESULTS AND DISCUSSION
■
Preparation of Cholesterol Oxime Ether Derivatives
Containing Isoxazoline/Isoxazole Fragments. As depicted
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Figure 5. Chemical structures of isoxazole derivatives II-1 to II-18.
in Figure 2, at first, in the presence of Et3N, cholesterol (1)
reacting with substituted benzoyl chlorides gave 3-benzoylox-
ycholesterol derivatives (2a−e), which were further oxidized
by CrO3/t-BuOOH to give 3-benzoyloxy-7-oxocholesterol deriv-
atives (3a−e).29 By reaction with hydroxylamine, compounds 3a−
e were smoothly turned into 3-benzoyloxy-7-oximinocholesterol
derivatives (4a−e).15 3-Benzoyloxy-7-oximinoether derivatives of
cholesterol (5a,c−e and 6a−e) were prepared in 53−98% yields
by the reaction of compounds 4a−e with allyl and propargyl
bromides in the presence of KOH and KI.15 Finally, as described
in Figure 3, target compounds I-1 to I-16 and II-1 to II-18,
cholesterol oxime ethers derivatives containing isoxazoline/
isoxazole fragments, were produced in 9−59% yields by 1,3-
dipolar cycloaddition of the double bond of 5a,c−e or the
triple bond of 6a−e with the nitrile oxide dipoles, which were
in situ generated from chloroximes (7a−e) in the presence of
Et3N.31 Chemical structures of all target compounds I-1 to
I-16 and II-1 to II-18, which were characterized by mp, optical
showed that the benzoyloxy/2-bromobenzoyloxy groups at the
C-3 position of II-1, II-3, and II-18 were in β configuration, and
the substituents on the double bond of oximinoether fragments
at the C-7 position of II-1, II-3, and II-18 were in Z con-
figuration. According to Figure 6, if the substituents on the
double bond of oximinoether fragments at the C-7 position of
II-1, II-3, and II-18 are in E configuration, there may be a big
steric hindrance from the oximinoether fragments with the
hydrogen atoms at the C-8β and C-15 positions. So, the Z
configuration of the double bond at the C-7 position of II-1,
II-3, and II-18 is reasonable.
Pesticidal Properties. Growth Inhibitory Activity against
M. separata. The results of compounds 1, 2a−e, 3a−e, 4a−e,
5a,c−e, 6a−e, I-1 to I-16, and II-1 to II-18 at 1 mg/mL
against early third-instar larvae of M. separata are illustrated in
Table 1. The mortality rates (MRs) of tested compounds after
35 days were higher than those after 10 and 25 days, and it
suggested that these compounds exhibited growth inhibitory
activity. The corresponding bioassay symptoms of the treated
M. separata at three different growth stages (e.g., the larval,
pupation, and adult periods) were the same as our previous
reports;2,4,32,33 for instance, the thin and wrinkled larvae were
dead at the larval stage (Figure S1), different malformed pupae
1
rotation, HRMS, IR, and H NMR spectroscopy (see the
Supporting Information), are shown in Figures 4 and 5,
respectively. The steric structures of II-1 (CCDC: 2013589),
II-3 (CCDC: 2013591), and II-18 (CCDC: 2013590) were
further determined by X-ray crystallography (Figure 6). It clearly
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(R1 = 4-F, R2 = 2,4-diCl), I-14 (R1 = 2-Br, R2 = 4-Me), and
II-3 (R1 = H, R2 = 4-Cl) were 62.9, 70.3, 62.9, and 66.6%,
respectively; whereas, the FMRs of precursor 1 and toosendanin
were only 25.9 and 40.7%, respectively. That is, compounds 3e,
I-8, I-14, and II-3 showed 2.4−2.7-fold potent growth inhibitory
activity of 1. Obviously, compound I-8 exhibited the most
potent activity. To our delight, the growth inhibitory activity of
compounds 3e, I-8, I-14, and II-3 was higher than that of
cholesterol-based hydrazone derivatives.29 Figure 7 showed
the percentages of FMRs at three different growth stages of
M. separata treated with 3e, 5a, I-8, I-14, II-3, and TN
(toosendanin), respectively. The largest portion (>56%) of
FMRs of 3e, 5a, I-8, I-14, II-3, and TN was all at the larval
stage, and this phenomenon was similar to those of other natural
product derivatives, such as matrinic/oxymatrinic amides,32
fraxinellone oximinoesters,33 and 7β-oxycarbonylandrographolide
derivatives.2
3-Benzoyloxycholesterol derivatives (2a−e) showed a
potent growth inhibitory activity when compared with 1, and
it suggested that the free hydroxyl group at the C-3 position
of 1 is an important modification site. Introduction of the
carbonyl group at the C-7 position of 2e (R1 = 2-Br; FMR:
48.1%) led to the more pronounced compound 3e (R1 = 2-Br;
FMR: 62.9%); whereas the FMRs of 3a−d (R1 = H, 4-Me,
4-F, and 4-Cl) were 37.0−44.4%. Previously, the FMR of
3-acetyloxy-7-oxocholesterol (1′) against M. separata was
55.2%.29 Clearly, it demonstrated that the introduction of the
suitable acyloxy groups at the C-3 position of 7-oxocholesterol is
essential for the growth inhibitory activity. Once the oxime
group was introduced at the C-7 position of 3a−e to afford
4a−e, only 4b (R1 = 4-Me) showed the improved activity
when the activity of 4a−e was compared with that of their
corresponding precursors. To 7-oximinoether derivatives
5a,c−e and 6a−e, only allylethers series 5a,c−e showed
more potent activity than that of 4a,c−e, especially the FMR
of 5a (R1 = H) was increased from 44.4% (4a) to 59.2%.
To isoxazoline derivatives (I-1 to I-16), the relationship between
their chemical structures and insecticidal activity was obvious.
For example, the FMRs of I-5 to I-7 (R1 = 4-F; R2 = H, 4-Me,
and 4-Cl) were 37.0−40.7%, and the FMRs of I-4, I-12, and
I-16 (R1 = H, 4-Cl, and 2-Br; R2 = 2,4-diCl) were 40.7−51.8%,
whereas the FMR of I-8 (R1 = 4-F; R2 = 2,4-diCl) was 70.3%.
Similarly, the FMRs of I-13 to I-16 (R1 = 2-Br; R2 = H, 4-Cl,
and 2,4-diCl) were 48.1−51.8%, and the FMRs of I-2, I-6, and
I-10 (R1 = H, 4-F, and 4-Cl; R2 = 4-Me) were 33.3−40.7%,
whereas the FMR of I-14 (R1 = 2-Br, R2 = 4-Me) was 62.9%.
Notably, the introduction of R1 as 4-F and R2 as 2,4-diCl, or
R1 as 2-Br and R2 as 4-Me on the two phenyl moieties of I-1 is
very important for isoxazoline derivatives showing good growth
inhibitory activity. To isoxazole derivatives (II-1 to II-18), their
chemical structures and insecticidal activity relationship were
also observed. The FMRs of II-1, II-2, and II-4 (R1 = H;
R2 = H, 4-Me, and 4-NO2) were 44.4−51.8%, and the FMRs of
II-7, II-10, II-14, and II-18 (R1 = 4-Me, 4-F, 4-Cl, and 2-Br;
R2 = 4-Cl) were 33.3−48.1%, whereas the FMR of II-3 (R1 = H;
R2 = 4-Cl) was 66.6%. Evidently, for isoxazole derivatives,
the introduction of R1 as H and R2 as 4-Cl on the two phenyl
moieties is very vital for the growth inhibitory activity.
Figure 6. Three X-ray crystal structures of II-1 (top), II-3 (middle),
and II-18 (bottom).
appeared at the pupation stage (Figure S2), and different
malformed moths with vestigial wings emerged at the adult
stage (Figure S3). Among them, 12 derivatives 3e, 4b, 5a, 5e,
I-3, I-8, I-14, I-16, II-2, II-3, II-5, and II-16 showed potent
growth inhibitory activity with the final mortality rates (FMRs)
greater than 50%. Particularly, the FMRs of 3e (R1 = 2-Br), I-8
Oral Toxicity against P. xylostella. The results of oral
toxicity at 24 and 48 h of compounds 1, 2a−e, 3a−e, 4a−e,
5a,c−e, 6a−e, I-1 to I-16, and II-1 to I-18 against 3rd-instar
larvae of P. xylostella treated at 20 μg/larva are described in
Table 2. Compounds I-6 (R1 = 4-F, R2 = 4-Me), I-7 (R1 = 4-F,
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Table 1. Growth Inhibitory Activity of Compounds 1, 2a−e, 3a−e, 4a−e, 5a, c−e, 6a−e, I-1 to I-16, and II-1 to II-18 against
M. separata on Leaves Treated at a Concentration of 1 mg/mL
corrected mortality rate (mean SE, %)
corrected mortality rate (mean SE, %)
compound
10 days
25 days
35 days
compound
10 days
25 days
35 days
1
14.8 3.3
33.3 4.4
11.1 5.1
14.8 2.4
22.2 3.1
37.0 3.9
29.6 2.4
25.9 3.9
18.5 4.8
22.2 4.4
44.4 3.1
29.6 3.3
18.5 3.3
22.2 3.1
7.40 3.9
40.7 3.9
25.9 4.5
11.1 4.4
14.8 4.8
37.0 2.4
18.5 2.4
25.9 2.4
11.1 3.1
40.7 3.9
3.70 3.3
29.6 4.5
25.9 2.4
33.3 4.1
25.9 2.4
25.9 2.4
18.5 2.4
37.0 5.0
22.2 4.4
22.2 3.1
37.0 3.9
44.4 4.1
40.7 3.3
29.6 3.3
25.9 4.5
33.3 3.1
59.2 2.4
33.3 3.1
44.4 3.1
22.2 3.1
14.8 3.9
40.7 3.9
55.5 3.1
29.6 3.9
33.3 3.1
44.4 3.1
29.6 2.4
33.3 3.1
25.9 4.5
40.7 3.9
25.9 2.4
40.7 5.0
25.9 2.4
40.7 4.5
29.6 2.4
25.9 2.4
48.1 5.0
25.9 3.9
37.0 3.3
40.7 3.3
48.1 3.3
44.4 3.1
37.0 2.4
37.0 4.5
37.0 3.3
62.9 2.4
44.4 3.1
51.8 2.4
33.3 4.1
29.6 2.4
48.1 3.3
59.2 3.3
37.0 3.3
44.4 3.1
51.8 2.4
37.0 2.4
40.7 2.4
37.0 3.3
48.1 3.3
I-6
I-7
I-8
I-9
I-10
I-11
I-12
I-13
I-14
I-15
I-16
II-1
II-2
II-3
II-4
II-5
II-6
II-7
II-8
II-9
II-10
II-11
II-12
II-13
II-14
II-15
II-16
II-17
II-18
toosendanin
22.2 3.1
25.9 3.9
40.7 3.3
25.9 4.5
33.3 3.1
18.5 2.4
37.0 3.9
25.9 3.9
48.1 2.4
25.9 3.3
14.8 4.5
25.9 2.4
40.7 3.3
44.4 4.1
18.5 3.9
25.9 3.9
14.8 3.9
25.9 5.3
29.6 3.9
37.0 2.4
62.9 3.9
40.7 3.3
33.3 3.1
37.0 2.4
37.0 3.9
44.4 3.1
59.2 3.9
37.0 2.4
37.0 2.4
37.0 2.4
48.1 3.9
59.2 3.9
37.0 3.3
37.0 3.3
40.7 2.4
70.3 3.3
48.1 2.4
40.7 3.9
44.4 3.1
44.4 3.1
48.1 3.3
62.9 3.9
48.1 2.4
51.8 3.3
48.1 2.4
51.8 3.3
66.6 3.1
44.4 3.1
55.5 3.1
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
5a
5c
5d
5e
6a
6b
6c
6d
6e
I-1
I-2
I-3
I-4
I-5
44.4
0
22.2 3.1
33.3 5.1
33.3
0
44.4 4.1
37.0 2.4
29.6 3.3
33.3 4.1
44.4 3.1
48.1 3.3
44.4 3.1
40.7 3.9
40.7 4.5
55.5 3.1
44.4 4.1
48.1 2.4
40.7 2.4
11.1
0
33.3
0
11.1 3.1
18.5 3.3
25.9 4.5
33.3 3.1
25.9 3.9
22.2 3.1
18.5 4.5
37.0 4.8
22.2 3.1
14.8 2.4
22.2 3.1
14.8 3.9
25.9 3.9
33.3 4.4
40.7 3.3
33.3 3.1
33.3 4.4
29.6 5.5
48.1 3.9
40.7 3.9
37.0 3.3
29.6 2.4
33.3
0
44.4 4.4
33.3 3.1
51.8 3.9
40.7 3.9
40.7 2.4
33.3
0
(R1 = H; 48 h MR: 24.4%) or 2c (R1 = 4-F; 48 h MR: 35.5%),
the activity of the corresponding compounds 3a (R1 = H;
48 h MR: 4.4%) and 3c (R1 = 4-F; 48 h MR: 0%) was
decreased sharply. Except for 4d (R1 = 4-Cl; 48 h MR: 4.4%),
other 3-benzoyloxy-7-oximinocholesterols 4a−c,e showed the
improved insecticidal activity compared with that of 3a−c,e.
To 7-oximinoether derivatives 5a,c−e and 6a−e, except 5d
(R1 = 4-Cl; 48 h MR: 35.5%) and 6d (R1 = 4-Cl; 48 h MR:
31.1%), other derivatives did not show the improved insecticidal
activity when compared with that of 4a,c−e. To isoxazoline
derivatives (I-1 to I-16), the 48 h MRs of I-5 (R1 = 4-F;
R2 = H) and I-8 (R1 = 4-F; R2 = 2,4-diCl) were 35.5 and
33.3%, respectively, whereas the 48 h MRs of I-6 (R1 = 4-F,
R2 = 4-Me) and I-7 (R1 = 4-F, R2 = 4-Cl) were 51.1 and
53.3%, respectively. The 48 h MRs of I-10 to I-12 (R1 = 4-Cl;
R2 = 4-Me, 4-Cl and 2,4-diCl) were 11.1−33.3%, and the 48 h
MRs of I-1, I-5, and I-13 (R1 = H, 4-F, and 2-Br; R2 = H) were
28.8−35.5%, whereas the 48 h MR of I-9 (R1 = 4-Cl; R2 = H)
was 48.8%. Obviously, the introduction of R1 as 4-F and R2 as
4-Me/4-Cl, or R1 as 4-Cl and R2 as H, on the two phenyl
moieties of I-1 is very important for isoxazoline derivatives
showing good insecticidal activity against P. xylostella. Among
isoxazole derivatives (II-1∼II-18), like the growth inhibitory
activity against M. separata, compound II-3 (R1 = H, R2 =
4-Cl; 48 h MR: 42.2%) also showed the most potent oral toxicity
against P. xylostella. Additionally, the insecticidal activity of
isoxazoline compounds I-6, I-7, and I-9 was more pronounced
Figure 7. Percentages of FMRs at three different growth stages of
M. separata treated with compounds 3e, 5a, I-8, I-14, II-3, and TN
(toosendanin), respectively.
R2 = 4-Cl), and I-9 (R1 = 4-Cl, R2 = H) showed the good
insecticidal activity with 48 h MRs of 51.1, 53.3, and 48.8%,
respectively; whereas the 48 h MR of compound 1 was only
20.0%. That is, these three potent compounds displayed 2.4−
2.7-fold oral toxicity of 1. The structure−activity relationship
(SAR) was also observed. Except 2b (R1 = 4-Me; 48 h MR:
6.7%), other 3-benzoyloxycholesterols 2a,c−e showed
potent oral toxicity when compared with that of 1. However,
when the carbonyl was introduced at the C-7 position of 2a
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Table 2. Oral Toxicity of Compounds 1, 2a−e, 3a−e, 4a−e, 5a, c−e, 6a−e, I-1 to I-16, and II-1 to II-18 against P. xylostella
Treated at 20 μg/larva
corrected mortality rate (mean SE, %)
corrected mortality rate (mean SE, %)
compound
24 h
48 h
compound
24 h
48 h
1
15.5 1.9
24.4 2.7
2.2 1.9
20.0 3.6
20.0 2.5
24.4 2.7
6.7 2.5
35.5 2.7
37.7 3.1
28.8 3.7
4.4 2.7
33.3 3.3
I-6
I-7
I-8
I-9
I-10
I-11
I-12
I-13
I-14
I-15
I-16
II-1
II-2
II-3
II-4
II-5
II-6
II-7
II-8
II-9
II-10
II-11
II-12
II-13
II-14
II-15
II-16
II-17
II-18
toosendanin
22.2 3.1
31.1 2.7
24.4 4.3
37.7 1.9
24.4 3.9
6.7 2.5
24.4 2.7
20.0 2.5
4.4 1.9
31.1 3.9
15.5 3.7
24.4 1.9
13.3 3.6
17.7 3.1
51.1 2.7
53.3 2.5
33.3 3.6
48.8 1.9
33.3 4.1
11.1 3.1
26.6 2.5
33.3 3.3
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
5a
5c
5d
5e
6a
6b
6c
6d
6e
I-1
I-2
I-3
I-4
I-5
13.3
0
17.7 1.9
2.2 1.9
20.0 2.5
0
0
0
0
6.7
0
4.4 2.7
33.3 3.6
17.7 3.1
22.2 3.1
20.0 2.5
2.2 1.9
28.8 1.9
35.5 3.7
37.7 1.9
35.5 1.9
22.2 2.7
4.4 2.7
33.3 3.3
17.7 3.9
33.3 3.6
26.6 2.5
42.2 3.1
8.9 2.7
22.2 1.9
13.3 3.6
31.1 3.1
6.7 2.5
17.7 3.1
26.6 4.1
11.1 3.1
28.8 3.1
26.6 3.6
13.3 3.3
4.4 1.9
0
13.3
0
0
31.1 3.1
2.2 1.9
35.5 2.7
4.4 2.7
8.9 2.7
26.6 3.3
4.4 2.7
13.3 2.5
24.4 4.6
4.4 1.9
15.5 2.7
22.2 3.1
8.9 3.1
26.6 2.5
28.8 3.7
28.8 2.7
15.5 3.9
28.8 3.1
15.5 3.7
13.3 3.6
13.3 3.6
22.2 3.1
35.5 1.9
35.5 3.7
31.1 3.1
20.0 3.6
31.1 3.1
26.6 2.5
31.1 1.9
17.7 2.7
28.8 1.9
0
0
0
0
0
0
8.9 2.7
2.2 1.9
8.9 2.7
15.5 2.7
15.5 1.9
4.4 1.9
20.0 3.3
28.8 2.7
6.7 2.5
26.6 4.1
33.3 3.3
13.3 3.3
35.5 3.1
53.3
0
than that of corresponding isoxazole ones II-9 (R1 = 4-F,
R2 = 4-Me; 48 h MR: 17.7%), II-10 (R1 = 4-F, R2 = 4-Cl; 48 h
MR: 26.6%), and II-12 (R1 = 4-Cl, R2 = H; 48 h MR: 28.8%).
Therefore, the isooxazoline ring is also necessary for com-
pounds I-6, I-7, and I-9 having good insecticidal activity
against P. xylostella.
7-oximine of 4e was transformed to 7-oximinoethers 5e and
6e, their aphicidal activity was also decreased. Besides the
substituent R1, obviously, other functional groups changed on
the molecular skeleton of 1 can affect the activity; so it is suggested
that to obtain the potent compounds, their molecular skeleton
could be modified together. Considering compound II-15 as
an instance, the 48 h MRs of II-12 to II-14 (R1 = 4-Cl; R2 = H,
4-Me, and 4-Cl) were 26.5−41.4%, and the 48 h MRs of II-4
(R1 = H; R2 = 4-NO2) and II-11 (R1 = 4-F; R2 = 4-NO2) were
26.5 and 24.2%, respectively, whereas the 48 h MR of II-15
(R1 = 4-Cl; R2 = 4-NO2) was 55.2%. Therefore, the intro-
duction of R1 as 2-Br on the phenyl of 3-benzoyloxycholesterol,
and the introduction of R1 as 4-Cl and R2 as 4-NO2 on the two
phenyl moieties of II-1 are vital for the aphicidal activity
against A. citricola.
In Table 4, the 48 h LD50 values of two potent compounds
2e and II-15 were further evaluated against A. citricola, and
their 48 h LD50 values were 0.048 and 0.041 μg/nymph, respec-
tively; whereas the 48 h LD50 value of 1 was 0.237 μg/nymph.
Clearly, compounds 2e and II-15 exhibited 4.9- and 5.8-fold
potent aphicidal activity of 1, respectively. Moreover, the control
effects of compounds 2e and II-15 against A. citricola were
also tested in the glasshouse. In Table 5, the control effects
of 2e and II-15 on the 3rd, 5th, and 7th days after treatment
were 47.3/40.3, 50.0/54.5, and 53.8/59.8%, respectively,
but the corresponding results of 1 were only 9.5, 14.5, and
18.1%, respectively. So compounds 2e and II-15 generally
Aphicidal Activity and Control Efficiency against A. citricola.
The results of aphicidal activity at 24 and 48 h of compounds
1, 2a−e, 3a−e, 4a−e, 5a,c−e, 6a−e, I-1 to I-16, and II-1 to
II-18 against apterous adults of A. citricola treated at
0.04 μg/nymph are shown in Table 3. Interestingly, after modifi-
cation of 1, all derivatives displayed more promising aphicidal
activity than 1. Among them, 11 derivatives 2e, 3d, 4e, 5c, I-6,
I-7, I-12, II-2, II-3, II-14, and II-15 showed potent aphicidal
activity with the 48 h MRs greater than 40%, whereas the 48 h
MR of compound 1 against A. citricola was only 9.2%. That is,
these 11 compounds showed 4.4−6.0-fold aphicidal activity of
1. In particular, compounds 2e (R1 = 2-Br) and II-15 (R1 =
4-Cl, R2 = 4-NO2) exhibited the most potent aphicidal activity
with 48 h MRs of 54.0 and 55.2%, respectively. Among 2a−e,
compound 2e containing R1 as 2-Br showed the potent
aphicidal activity; however, when the carbonyl was introduced
at the C-7 position of 2e to give 3e, the 48 h MR of 3e was
sharply decreased from 54.0% (2e) to 15.0%. Interestingly,
once the carbonyl at the C-7 position of 3e was transformed to
7-oximine, the 48 h MR of the corresponding compound 4e
(R1 = 2-Br) was increased from 15.0% (3e) to 42.5%. When
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Table 3. Aphicidal Activity of Compounds 1, 2a−e, 3a−e, 4a−e, 5a, c−e, 6a−e, I-1 to I-16, and II-1 to II-18 against Apterous
Adults of A. citricola Treated at 0.04 μg/nymph
corrected mortality rate (mean SE, %)
corrected mortality rate (mean SE, %)
compound
24 h
48 h
compound
24 h
48 h
1
5.8 4.2
3.5 2.7
3.5 2.7
13.8 4.7
13.8 2.7
32.2 3.1
3.5 2.7
9.2 3.1
8.1 4.2
15.0 3.1
9.2 1.6
9.2 1.6
16.1 4.2
11.5 3.1
26.5 3.1
32.2 4.2
54.0 1.5
17.3 2.7
21.9 4.2
32.2 4.2
42.5 1.6
15.0 3.1
28.8 5.7
23.0 3.1
16.1 3.1
19.6 3.1
42.5 4.2
25.3 4.3
40.3 4.2
I-6
I-7
I-8
I-9
25.3 1.6
11.5 1.6
11.5 4.2
5.8 1.6
11.5 1.6
11.5 1.6
5.8 3.1
4.6 1.6
10.4 4.7
12.7 1.6
4.6 1.6
4.6 1.6
13.8 2.7
18.4 3.1
15.0 1.6
17.3 4.7
9.2 3.1
21.9 3.1
19.6 1.6
13.8 2.7
40.3 1.6
43.7 5.7
17.3 2.7
23.0 1.6
19.6 4.2
28.8 1.6
41.4 2.7
20.7 4.7
21.9 3.1
33.4 3.1
34.5 2.7
2a
2b
2c
2d
2e
3a
3b
3c
3d
3e
4a
4b
4c
4d
4e
5a
5c
5d
5e
6a
6b
6c
6d
6e
I-1
I-2
I-3
I-4
I-5
I-10
I-11
I-12
I-13
I-14
I-15
I-16
II-1
II-2
II-3
II-4
II-5
II-6
II-7
II-8
II-9
II-10
II-11
II-12
II-13
II-14
II-15
II-16
II-17
II-18
10.4
0
17.3
0
5.8 4.2
11.5 1.6
5.8 4.2
29.9 4.2
15.0 4.2
5.8 1.6
40.3 1.6
41.4 2.7
26.5 1.6
27.6 2.7
34.5 2.7
26.5 3.1
25.3 4.2
38.0 4.7
32.2 1.6
24.2 4.7
26.5 6.3
33.4 1.6
41.4 2.7
55.2 2.7
27.6 2.7
33.4 4.2
25.3 1.6
4.6 3.1
17.3
29.9 1.6
20.7
0
18.4 4.2
11.5 1.6
13.8 2.7
15.0 3.1
16.1 1.6
5.8 3.1
16.1 1.6
18.4 1.6
24.2 4.7
17.3 2.7
15.0 3.1
0
13.8
0
23.0 3.1
27.6 2.7
32.2 5.7
32.2 3.1
26.5 3.1
32.2 1.6
36.8 1.6
9.2 1.6
17.3 5.4
17.3 2.7
24.2 4.7
4.6 1.6
6.9 2.7
13.8 2.7
15.0 4.2
34.5
0
18.4 4.2
a
Table 4. LD50 Values of Some Potent Compounds at 48 h against A. citricola
compound
linear regression equation
LD50 (μg/nymph)
confidence interval 95% (μg/nymph)
r
1
2e
II-15
Y = 0.741 + 1.184X
Y = 1.454 + 1.100X
Y = 1.950 + 1.405X
0.237
0.048
0.041
0.185−0.328
0.035−0.062
0.031−0.050
0.965
0.946
0.974
a
Regression analysis by IBM SPSS Statistics 20.0, P < 0.05.
compounds I-6, I-7, and I-9 displayed 2.4−2.7-fold oral
toxicity of 1. Against A. citricola, compounds 2e and II-15
exhibited 4.9- and 5.8-fold aphicidal activity of 1, respectively.
Moreover, in the glasshouse, they showed 3.0−5.0-fold promising
control efficiency of 1 against A. citricola. This demonstrated that
the hydroxyl group at the C-3 and C-7 positions of 1 are two
important modification sites. These will lay the foundation for
future structural optimization and high-value-added application
of cholesterol derivatives as potentially pesticidal agents in
agriculture.
Table 5. Control Efficiency of Compounds 1, 2e, and II-15
against A. citricola in the Greenhouse Tests at 1.0 mg/mL
control efficiency (mean SE, %)
compound
first day
third day
fifth day
seventh day
1
2e
II-15
3.9 0.9
10.3 1.2
8.3 1.3
9.5 0.9
47.3 0.9
40.3 1.2
14.5 1.2
50.0 0.9
54.5 1.3
18.1 0.9
53.8 0.9
59.8 1.3
showed 3.0−5.0-fold promising control efficiency of 1 against
A. citricola.
In conclusion, a series of cholesterol oxime ethers derivatives
containing isoxazoline/isoxazole fragments were semiconstructed.
Three steric structures of target compounds were further
determined by X-ray crystallography, and the substituents on
the double bond of oximinoether fragments at the C-7 position
were undoubtedly in Z configurations. Against M. separata,
compounds 3e, I-8, I-14, and II-3 showed 2.4−2.7-fold growth
inhibitory activity of the precursor 1. Against P. xylostella,
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.jafc.1c01884.
1
Chemicals and instruments; H NMR spectra; data on
mp, 1H NMR, HRMS, optical rotation, and IR of target
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AUTHOR INFORMATION
■
Corresponding Authors
Hui Xu − College of Plant Protection, Northwest A&F
University, Yangling 712100 Shaanxi, China; School of
Marine Sciences, Ningbo University, Ningbo 315211
Zhejiang, China; orcid.org/0000-0002-3152-9922;
Phone: +86-29-87091952; Email: orgxuhui@
nwsuaf.edu.cn
Min Lv − College of Plant Protection, Northwest A&F
University, Yangling 712100 Shaanxi, China; Phone: +86-
29-87091952; Email: lvmin78@163.com
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address the sociobiological dilemma of pesticide resistance? Science
2018, 360, 728−732.
(12) Seiber, J. N.; Coats, J.; Duke, S. O.; Gross, A. D. Biopesticides:
state of the art and future opportunities. J. Agric. Food Chem. 2014, 62,
11613−11619.
Authors
Kong Zhang − College of Plant Protection, Northwest A&F
University, Yangling 712100 Shaanxi, China
Meng Hao − College of Plant Protection, Northwest A&F
University, Yangling 712100 Shaanxi, China
(13) Marrone, P. G. Pesticidal natural products-status and future
potential. Pest Manage. Sci. 2019, 75, 2325−2340.
(14) Duke, S. O.; Evidente, A.; Vurro, M. Natural products in pest
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Complete contact information is available at:
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Notes
The authors declare no competing financial interest.
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B.; Wang, Q. M. Various bioactivity and relationship of structure-
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ACKNOWLEDGMENTS
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This work was supported by the National Natural Science
Foundation of China (Nos. 31872013 and 31672071).
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