Design, synthesis, acaricidal activity, and mechanism of oxazoline derivatives containing an oxime ether moiety

Article abstract of DOI:10.1021/jf500461a

Two series of novel 2,4-diphenyl-1,3-oxazolines containing an oxime ether moiety were designed and synthesized via the key intermediate N-(2-chloro-1-(p-tolyl)ethyl)-2,6-difluorobenzamide. The bioassay results showed that the target compounds with an oxime ether substituent at the para position of 4-phenyl exhibited excellent acaricidal activity against Tetranychus cinnabarinus in the laboratory. Moreover, all of the target compounds had much higher activities than etoxazole, as the ovicidal and larvicidal activities of the target compounds I-a-I-l and II-a-II-n against T. cinnabarinus were all over 90% at 0.001 mg L^-1, but etoxazole gave only 30% and 40% respectively at the same concentration. The activity order of compounds with regard to acaricidal activity in vivo was almost consistent with their affinity activity with sulfonylurea receptor (SUR) of Blattella germanica in vitro, hence, it was supposed that the acaricidal mechanism of action of the target compounds was that they can bind with the site of SUR and therefore inhibit chitin synthesis. Moreover, the eminent effect of the compound II-l, [2-(trifluoromethyl)benzaldehyde O-(4-(2-(2,6-difluorophenyl)-4,5-dihydrooxazol- 4-yl)benzyl) oxime], against Panonychus citri and T. cinnabarinus in the field indicated that II-l exhibited a promising application prospect as a new candicate for controlling spider mites in the field.

Full text of DOI:10.1021/jf500461a

Article
pubs.acs.org/JAFC
Design, Synthesis, Acaricidal Activity, and Mechanism of Oxazoline
Derivatives Containing an Oxime Ether Moiety
Yongqiang Li,†,‡ Chaojie Li,† Yanlong Zheng,† Xingcun Wei,† Qiaoqiao Ma,† Peng Wei,† Yuxiu Liu,*,†
Yaoguo Qin,‡ Na Yang,† Yufeng Sun,‡ Yun Ling,‡ Xinling Yang,*,‡ and Qingmin Wang*,†
†State Key Laboratory of Elemento-Organic Chemistry, Research Institute of Elemento-Organic Chemistry, Nankai University,
Tianjin 300071, The People’s Republic of China
‡Key Laboratory of Pesticide Chemistry and Application, MOA, Department of Applied Chemistry, College of Science, China
Agricultural University, The People’s Republic of China
ABSTRACT: Two series of novel 2,4-diphenyl-1,3-oxazolines containing an oxime ether moiety were designed and synthesized
via the key intermediate N-(2-chloro-1-(p-tolyl)ethyl)-2,6-difluorobenzamide. The bioassay results showed that the target
compounds with an oxime ether substituent at the para position of 4-phenyl exhibited excellent acaricidal activity against
Tetranychus cinnabarinus in the laboratory. Moreover, all of the target compounds had much higher activities than etoxazole, as
the ovicidal and larvicidal activities of the target compounds I-a−I-l and II-a−II-n against T. cinnabarinus were all over 90% at
0.001 mg L−1, but etoxazole gave only 30% and 40% respectively at the same concentration. The activity order of compounds
with regard to acaricidal activity in vivo was almost consistent with their affinity activity with sulfonylurea receptor (SUR) of
Blattella germanica in vitro, hence, it was supposed that the acaricidal mechanism of action of the target compounds was that they
can bind with the site of SUR and therefore inhibit chitin synthesis. Moreover, the eminent effect of the compound II-l, [2-
(trifluoromethyl)benzaldehyde O-(4-(2-(2,6-difluorophenyl)-4,5-dihydrooxazol-4-yl)benzyl) oxime], against Panonychus citri and
T. cinnabarinus in the field indicated that II-l exhibited a promising application prospect as a new candicate for controlling spider
mites in the field.
KEYWORDS: 2,4-diphenyl-1,3-oxazoline, oxime ether, acaricidal activity, mechanism, sulfonylurea receptor
equal to those in Drosophila melanogaster that was treated with
the benzoylphenylurea diflubenzuron. Furthermore, Leeuwen
et al. demonstrated that etoxazole inhibited chitin biosynthesis
in T. urticae utilizing the technology of calcofluor white (CFW)
staining. Therefore, it was strongly suggested that the acaricidal
mechanism of action of etoxazole was similar, if not identical, to
that of the known benzoylphenylureas.
The structure−activity relationship studies (SARs) also
showed that 2,4-diphenyl-1,3-oxazolines and benzoylphenylur-
eas had an intimate relationship. 2,4-Diphenyl-1,3-oxazoline
derivatives containing 2,6-difluorophenyl group at the 2-phenyl
moiety (part A) always exhibited better acaricidal activity
against T. urticae, as did the benzoylphenylureas.8 With respect
to the 4-phenyl moiety (part C) of 2,4-diphenyl-1,3-oxazolines,
the quantitative structure−activity relationship studies
(QSARs) showed that the substituent modification at the
ortho and meta positions of the 4-phenyl moiety was
unfavorable for ovicidal activity. Moreover, the effects of
groups at the para position of the 4-phenyl moiety were also
similar to the para-substituent effects at the anilide moiety (part
C) of benzoylphenylurea.9−11
INTRODUCTION
■
With the improvement of living standards and the enhance-
ment of people’s awareness of environment protection, the
direction of plant protection today is obliged to turn to the
rational control of harmful organisms instead of simply “kill
(-cide)”. The process of chitin synthesis exists only in insect
cuticle and fungal cell wall but not in higher plants and
mammals, so insect chitin synthesis inhibitors (CSIs),1 which
especially emphasize controlling the pest populations, exhibit
high potential on target pests and low toxicity to nontarget
organisms, and are therefore safe to humans, livestocks, insects’
natural enemies, and the ecological environment.2 Benzoylphe-
nylureas (Figure 1) are such successful CSIs; in the past 40
years, over twenty benzoylphenylureas were commercialized.3
3,4-Diphenyl-1,3-oxazoline derivatives are another class of
novel CSIs, of which etoxazole4,5 is the only commercial
ovicide/larvicide with higher efficiency and faster ovicidal/
larvicidal action against phytophagous mites than the conven-
tional benzoylphenylureas.
It was reported that similar poisoning symptoms and changes
in the chitin content were observed when the larvae of
Spodoptera frugiperda were exposed to benzoylphenylurea
triflumuron and etoxazole, and both compounds could inhibit
the incorporation of [14C]GlcNAc into the pieces of isolated
integuments in vitro.6 Likewise, in 2012, Leeuwen and co-
workers reported that etoxazole had high bioactivity against the
eggs and the nymphs of the two-spotted spider mite,
Tetranychus urticae, and the offspring of the treated female
adults failed to hatch,7 and the observed symptoms were almost
Based on the similarity in the mechanism of action and
QSAR for the 2,4-diphenyl-1,3-oxazolines and benzoylpheny-
lureas,12,13 a series of compounds I containing an oxime ether
Received: January 27, 2014
Revised: March 12, 2014
Accepted: March 13, 2014
Published: March 27, 2014
© 2014 American Chemical Society
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Figure 1. Design of the target compounds I and II.
Scheme 1. Synthetic Route of 6
group at the 4-phenyl moiety of 2,4-diphenyl-1,3-oxazoline
were designed by referring to benzoylphenylurea NK-17, which
was discovered by our research group and showed excellent
larvicidal activity.3 Similarly, another series of compounds II
were designed by referring to the commercial benzoylphenylur-
ea flucycloxuron which was created by Solvay-Duphar B.V. as a
CSI and also contained an oxime ether group.14 The acaricidal
activity of all the target compounds (I-a−I-l and II-a−II-n)
against T. cinnabarinus was assayed in the laboratory.
Furthermore, the effects of the II-l on T. cinnabarinus and
Panonychus citri (P. citri) were evaluated in the field.
In 2004, diflubenzuron, a CSI belonging to benzoyphenylur-
ea, was testified to act on the target site of sulfonylurea receptor
(SUR) protein by means of the isotope labeling technology,15
and later the mechanism of NK-17 was also proposed to bind
to the same site of SUR by fluorescence polarization (FP)
method in our previous report.16 Since numerous experimental
data had indicated that the action mechanism of etoxazole was
similar to that of the benzoylphenylureas, we would like to
know if etoxazole and the target compounds (I-a−I-l and II-a−
II-n) that we synthesized in this paper can also bind to the
same site of SUR. To raise awareness to the mode of action of
the target compounds and help to discover some superior
compounds, in this paper, we preliminarily determined the
affinity activity of all the target compounds binding to the SUR
in vitro by FP method, and the results were discussed.
MATERIALS AND METHODS
■
1
Instruments and Chemicals. H NMR spectra were recorded at
300 or 400 MHz by respectively using a Bruker AV300 spectrometer
or a Bruker AV400 spectrometer with CDCl3 or DMSO-d6 as solvent
and tetramethylsilane as the internal standard. Chemical shift values
(δ) are reported in parts per million (ppm). High-resolution mass
spectrometry (HRMS) was obtained by means of FTICR-MS
(Ionspec 7.0T). The melting points were obtained utilizing an X-4
binocular microscope melting point apparatus (Beijing Tech Instru-
ments Co., Beijing, China) and are uncorrected. Yields were not
optimized. The values of the FP were obtained by CARY eclipse
fluorescence spectrophotometer (Agilent Technologies, Santa Clara,
CA, USA). All of the reaction reagents were analytically or chemically
pure, which were dried and distilled according to standard methods
before use when necessary. All other biochemical reagents used in the
FP determination were of the highest purity grade from Sigma-Aldrich
Chemical Co., Ltd.
General Synthetic Procedure for Compound 6 (Scheme 1).
Synthesis of Ethyl 2-p-Tolyl-2-oxoacetate (2). To a solution of ethyl
chloroglyoxylate (4.5 g, 33 mmol) in anhydrous dichloromethane (50
mL) was added anhydrous AlCl3 (4.40 g, 33 mmol), and the mixture
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Scheme 2. General Synthetic Route of the Target Compounds I-a−I-l
was stirred at room temperature until AlCl3 was dissolved. The
mixture was cooled to −10 °C, toluene (2.76 g, 30 mmol) in
dichloromethane (50 mL) was added dropwise over a period of 2 h,
and then the reaction mixture was stirred at room temperature for
another 5 h until the reaction was complete, indicated by TLC. The
mixture was poured to ice−water (80 mL), and the value of the pH
was adjusted to 2. After the organic phase was separated, the aqueous
phase was extracted with dichloromethane. The combined organic
phase was washed with saturated brine, dried over anhydrous sodium
sulfate, filtered, and concentrated in vacuo to give 2 as a yellow liquid
mmol) in tetrahydrofuran (60 mL) over a period of 2.5 h, and then the
reaction mixture was warmed to room temperature for 5 h until the
reaction was complete. The mixture was filtered, concentrated, and
purified by recrystallization using ethyl acetate and petroleum ether to
give 5 as a solid (4.57 g). The mother liquid was concentrated and
purified by flash chromatography on silica gel with petroleum ether
and ethyl acetate (v/v = 2:1) to give another portion of 5 (2.89 g).
Overall yield: 77%. Mp: 125−127 °C. 1H NMR (400 MHz, CDCl3): δ
7.43−7.35 (m, 1H), 7.28 (d, J = 8.0 Hz, 2H), 7.20 (d, J = 8.0 Hz, 2H),
6.97 (t, J = 8.0 Hz, 2H), 6.55 (d, J = 6.8 Hz, 1H), 5.55 (dd, J = 12.8,
5.2 Hz, 1H), 4.02−3.91 (m, 2H), 2.35 (s, 3H).
1
(5.08 g, yield 88%). H NMR (400 MHz, CDCl3): δ 7.91 (d, J = 8.0
Hz, 2H), 7.31 (d, J = 8.0 Hz, 2H), 4.45 (q, J = 7.2 Hz, 2H), 2.45 (s,
3H), 1.42 (t, J = 7.2 Hz, 3H).
Synthesis of N-(2-Chloro-1-(p-tolyl)ethyl)-2,6-difluorobenzamide
(6). To a solution of 5 (41.7 g, 140 mmol) in chloroform (120 mL)
was added dropwise thionyl chloride (19.59 g, 165 mmol) in
chloroform (60 mL) over a period of 70 min. The reaction mixture
was refluxed for 100 min until the reaction was complete. After the
value of the pH of the mixture was adjusted to 8 with saturated sodium
bicarbonate solution, the organic phase was separated, washed with
saturated brine, dried with magnesium sulfate, filtered and
concentrated to give 6 as a white solid (41.7 g, yield 94%). Mp:
Synthesis of Ethyl 2-(Hydroxyimino)-2-(p-tolyl)acetate (3). To a
solution of 2 (86.21 g, 450 mmol) in ethanol (400 mL) was added
hydroxylamine hydrochloride (52.98 g, 760 mmol), and the mixture
was refluxed for 8 h and monitored by TLC. After removal of ethanol,
the solid residue obtained was redissolved in ethyl acetate. The
mixture was washed twice with water, dried with anhydrous sodium
sulfate, filtered, and concentrated in vacuo to give a crude product,
which was purified by recrystallization using carbon tetrachloride and
petroleum ether to give 3 (45.80 g). The mother liquid was purified by
flash chromatography on silica gel with petroleum ether and ethyl
acetate (v/v = 20:1, 10:1) to give another portion of 3 (21.5 g).
Overall yield: 72%. Mp: 116−117 °C. 1H NMR (300 MHz, CDCl3): δ
8.65 (s, 1H), 7.42 (d, J = 8.1 Hz, 2H), 7.25 (d, J = 8.1 Hz, 2H), 4.35
(q, J = 7.2 Hz, 2H), 2.39 (s, 3H), 1.36 (t, J = 7.2 Hz, 3H).
Synthesis of 2-Amino-2-(p-tolyl)ethanol (4). To a solution of
compound 3 (25.25 g, 120 mmol) in anhydrous tetrahydrofuran (200
mL) under stirring was added sodium borohydride (13.83 g, 370
mmol). Iodine (46.37 g, 180 mmol) in THF (180 mL) was added
dropwise over a period of 6.5 h at 0 °C. Afterward, the reaction
mixture was refluxed for 5 h. The excess reducing agent was quenched
with methanol at 0 °C, and then the solvent was removed. After the
residue was added to a solution of 5% sodium hydroxide in water, the
mixture was refluxed for 5 h. When it was complete, indicated by TLC,
the reaction mixture was cooled to room temperature and extracted by
dichloromethane. Then, the organic layer was dried by sodium sulfate,
filtered, and concentrated to give 4 as a yellow solid (17.45 g, yield
94%). Mp: 68−70 °C. 1H NMR (400 MHz, CDCl3): δ 7.22 (d, J = 8.0
Hz, 2H), 7.16 (d, J = 8.0 Hz, 2H), 4.01 (dd, J = 8.4, 4.4 Hz, 1H), 3.72
(dd, J = 10.8, 4.4 Hz, 1H), 3.53 (dd, J = 10.8, 8.4 Hz, 1H), 2.34 (s,
3H).
1
62−63 °C. H NMR (300 MHz, CDCl3): δ 7.44−7.37 (m, 1H), 7.29
(d, J = 8.1 Hz, 2H), 7.21 (d, J = 8.1 Hz, 2H), 6.97 (t, J = 8.1 Hz, 2H),
6.53 (d, J = 6.0 Hz, 1H), 5.56 (dd, J = 12.9, 5.1 Hz, 1H), 4.03−3.91
(m, 2H), 2.36 (s, 3H).
General Synthetic Procedure for the Target Compounds I-
a−I-l (Scheme 2). Synthesis of N-(2-Chloro-1-(4-formylphenyl)-
ethyl)-2,6-difluorobenzamide (7). To a solution of 6 (10.0 g, 32
mmol) in glacial acetic acid (60 mL) was added dropwise concentrated
sulfuric acid (7 mL) over a period of 1 h at the temperature range of
−10 °C to −5 °C. Then powdered CrO3 was added, after which the
reaction mixture was stirred for 6 h. The reaction mixture was poured
to ice−water (300 mL) and extracted by ethyl acetate (100 mL × 5).
The combined organic phase was successively washed with water,
saturated sodium bicarbonate, and saturated brine and dried with
anhydrous magnesium sulfate. After filtration, the solvent was removed
under reduced pressure to give a crude black residue. The residue was
added to a mixture of methanol (30 mL) and concentrated
hydrochloric acid (10 mL), and then the reaction was stirred under
tepidity for 5 h. The reaction mixture was cooled to room temperature,
concentrated under reduced pressure, and then extracted by ethyl
acetate (50 mL × 3). The organic layer was washed with saturated
sodium bicarbonate solution and saturated brine successively, dried
with anhydrous magnesium sulfate, filtered and concentrated under
reduced pressure. The residue was purified by flash chromatography
on silica gel with petroleum ether and ethyl acetate (v/v = 3:1) to give
Synthesis of 2,6-Difluoro-N-(2-hydroxy-1-(p-tolyl)ethyl)-
benzamide (5). To a mixture of 4 (5.0 g, 33 mmol) and triethylamine
(5.51 g, 40 mmol) in anhydrous tetrahydrofuran (70 mL) at 0 °C was
added dropwise a solution of 2,6-difluorobenzoyl chloride (6.14 g, 35
1
7 as a yellow oil (4.1 g, yield 41%). H NMR (400 MHz, CDCl3): δ
10.03 (s, 1H), 7.93 (d, J = 8.4 Hz, 2H), 7.59 (d, J = 8.4 Hz, 2H), 7.47−
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Scheme 3. General Synthetic Route of the Target Compounds II-a−II-n
7.40 (m, 1H), 7.00 (t, J = 8.4 Hz, 2H), 6.73 (d, J = 7.6 Hz, 1H), 5.71−
5.67 (m, 1H), 4.05 (dd, J = 11.6, 4.4 Hz, 1H), 3.97 (dd, J = 11.6, 4.4
Hz, 1H).
1H), 5.48 (dd, J = 10.4, 8.4 Hz, 1H), 5.36 (dd, J = 17.2, 1.6 Hz, 1H),
5.26 (dd, J = 10.4, 1.2 Hz, 1H), 4.83 (dd, J = 10.4, 8.4 Hz, 1H), 4.68
(d, J = 5.6 Hz, 2H), 4.28 (t, J = 8.0 Hz, 1H). HRMS (ESI): calcd for
C19H16F2N2O2Na [M + Na]+ 365.1072, found 365.1075.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-Prop-2-yn-1-yl Oxime (I-c). Oil; yield 47%. 1H
NMR (300 MHz, CDCl3): δ 8.13 (s, 1H), 7.62 (d, J = 8.1 Hz, 2H),
7.49−7.39 (m, 1H), 7.36 (d, J = 8.1 Hz, 2H), 7.01 (t, J = 8.1 Hz, 2H),
5.49 (dd, J = 10.2, 8.2 Hz, 1H), 4.83 (dd, J = 10.2, 8.2 Hz, 1H), 4.78
(d, J = 2.1 Hz, 2H), 4.27 (t, J = 8.1 Hz, 1H), 2.51 (t, J = 2.4 Hz, 1H).
HRMS (ESI): calcd for C19H14F2N2O2Na [M + Na]+ 363.0916, found
363.0912.
Synthesis of N-(2-Chloro-1-(4-((hydroxyimino)methyl)phenyl)-
ethyl)-2,6-difluorobenzamide (8). To a mixture of 7 (2.43 g, 8
mmol), triethylamine (1.90 g, 19 mmol), and hydroxylamine
hydrochloride (1.30 g, 19 mmol) in anhydrous tetrahydrofuran (50
mL) were added molecular sieves (4 Å), and then the mixture was
refluxed for 4 h and monitored with TLC. After the reaction was
complete, the mixture was filtered to remove molecular sieves,
concentrated in vacuo, and purified by flash chromatography on silica
gel with petroleum ether and ethyl acetate (v/v = 3:1) to give 8 as a
1
white solid (1.93 g, yield 76%). H NMR (400 MHz, DMSO-d6): δ
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
1
11.26 (s, 1H), 9.47 (d, J = 8.4 Hz, 1H), 8.14 (s, 1H), 7.61 (d, J = 8.4
Hz, 2H), 7.61−7.57 (m, 1H), 7.49 (d, J = 8.4 Hz, 2H), 7.22−7.13 (m,
2H), 5.34−5.29 (m, 1H), 3.95 (dd, J = 11.2, 4.8 Hz, 1H), 3.80 (dd, J =
11.2, 9.6 Hz, 1H).
benzaldehyde O-Cyclohexylmethyl Oxime (I-d). Oil; yield 44%. H
NMR (400 MHz, CDCl3): δ 8.07 (s, 1H), 7.59 (d, J = 8.0 Hz, 2H),
7.47−7.42 (m, 1H), 7.34 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H),
5.48 (dd, J = 10.0, 8.8 Hz, 1H), 4.82 (dd, J = 10.0, 8.8 Hz, 1H), 4.27 (t,
J = 8.0 Hz, 1H), 3.98 (d, J = 6.4 Hz, 2H), 1.82−1.72 (m, 5H), 1.31−
1.21 (m, 6H). HRMS (ESI): calcd for C23H24F2N2O2Na [M + Na]+
421.1698, found 421.1693.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-Benzyl Oxime (I-e). Yellow oil; yield 50%. 1H
NMR (400 MHz, CDCl3): δ 8.14 (s, 1H), 7.60 (d, J = 8.0 Hz, 2H),
7.47−7.31 (m, 8H), 7.01 (t, J = 8.0 Hz, 2H), 5.48 (dd, J = 12.0, 8.0 Hz,
1H), 5.21 (s, 2H), 4.83 (dd, J = 12.0, 8.0 Hz, 1H), 4.27 (t, J = 8.0 Hz,
1H). HRMS (ESI): calcd for C23H19F2N2O2 [M + H]+ 393.1409,
found 393.1402.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(2-Fluorobenzyl) Oxime (I-f). Oil; yield 63%. 1H
NMR (400 MHz, CDCl3): δ 8.13 (s, 1H), 7.60 (d, J = 8.0 Hz, 2H),
7.49−7.41 (m, 2H), 7.34 (d, J = 8.0 Hz, 2H), 7.32−7.28 (m, 1H),
7.16−7.12 (m, 1H), 7.10−7.05 (m, 1H), 7.01 (t, J = 8.0 Hz, 2H), 5.48
(dd, J = 10.4, 8.0 Hz, 1H), 5.28 (s, 2H), 4.83 (dd, J = 10.4, 8.0 Hz,
1H), 4.27 (t, J = 8.0 Hz, 1H). HRMS (ESI): calcd for
C23H17F3N2O2Na [M + Na]+ 433.1134, found 433.1129.
Synthesis of 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-Ethyl Oxime (I-a). To a mixture of 8 (0.82 g, 2.4
mmol) in N,N-dimethylformamide (DMF) (30 mL) stirred for 10 min
at 0 °C was added sodium hydride (0.23 g, 10 mmol), and the reaction
mixture was stirred for 1 h. After ethyl iodide (0.57 g, 4 mmol) was
added, the reaction mixture was stirred for another 2 h. When the
reaction was complete, as indicated by TLC, ethyl acetate (150 mL)
was added. The mixture was washed with a large amount of water
three times and saturated brine once, dried with anhydrous magnesium
sulfate, filtered, and concentrated under reduced pressure. The residue
was purified by flash chromatography on silica gel with petroleum
ether and ethyl acetate (v/v = 12:1) to give the target compound I-a as
1
an oil (0.51 g, yield 64%). H NMR (400 MHz, CDCl3): δ 8.07 (s,
1H), 7.60 (d, J = 8.4 Hz, 2H), 7.48−7.40 (m, 1H), 7.35 (d, J = 8.4 Hz,
2H), 7.00 (t, J = 8.0 Hz, 2H), 5.48 (dd, J = 10.4, 8.4 Hz, 1H), 4.83 (dd,
J = 10.4, 8.4 Hz, 1H), 4.28 (t, J = 8.4 Hz, 1H), 4.23 (q, J = 7.2 Hz,
2H), 1.33 (t, J = 7.2 Hz, 3H). HRMS (ESI): calcd for
C18H16F2N2O2Na [M + Na]+ 353.1072, found 353.1073.
Compounds I-b−I-l were synthesized according to a method similar
to that for I-a using the corresponding alkyl bromide instead of ethyl
iodide.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
1
benzaldehyde O-(3-Fluorobenzyl) Oxime (I-g). Oil; yield 53%. H
NMR (400 MHz, CDCl3): δ 8.15 (s, 1H), 7.60 (d, J = 8.0 Hz, 2H),
7.48−7.40 (m, 1H), 7.35 (d, J = 8.0 Hz, 2H), 7.32−7.30 (m, 1H),
7.19−7.11 (m, 1H), 7.03−6.98 (m, 3H), 5.48 (dd, J = 10.4, 8.4 Hz,
1H), 5.19 (s, 2H), 4.83 (dd, J = 10.4, 8.4 Hz, 1H), 4.27 (t, J = 8.4 Hz,
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
1
benzaldehyde O-Allyl Oxime (I-b). Oil; yield 58%. H NMR (400
MHz, CDCl3): δ 8.12 (s, 1H), 7.60 (d, J = 8.0 Hz, 2H), 7.48−7.41 (m,
1H), 7.35 (d, J = 8.0 Hz, 2H), 7.01 (t, J = 8.0 Hz, 2H), 6.10−6.00 (m,
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1
1H). HRMS (ESI): calcd for C23H17F3N2O2Na [M + Na]+ 433.1134,
found 433.1130.
69%). H NMR (400 MHz, CDCl3): δ 7.49−7.31 (m, 1H), 7.38 (d, J
= 8.0 Hz, 2H), 7.32 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.47
(dd, J = 10.0, 8.4 Hz, 1H), 5.07 (s, 2H), 4.81 (dd, J = 10.0, 8.4 Hz,
1H), 4.30 (t, J = 8.4 Hz, 1H), 2.44 (t, J = 6.8 Hz, 2H), 2.36 (t, J = 6.8
Hz, 2H), 1.77−1.71 (m, 4H). HRMS (ESI): calcd for C21H21F2N2O2
[M + H]+ 371.1566, found 371.1570.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(4-Fluorobenzyl) Oxime (I-h). White solid; mp
97−100 °C; yield 69%. 1H NMR (400 MHz, CDCl3): δ 8.12 (s, 1H),
7.59 (d, J = 8.0 Hz, 2H), 7.48−7.38 (m, 3H), 7.34 (d, J = 8.0 Hz, 2H),
7.07−6.99 (m, 4H), 5.48 (dd, J = 10.4, 8.0 Hz, 1H), 5.16 (s, 2H), 4.83
(dd, J = 10.4, 8.0 Hz, 1H), 4.27 (t, J = 8.0 Hz, 1H). 13C NMR (100
MHz, CDCl3): δ 163.8, 162.5, 162.5, 161.4, 160.0, 159.9, 157.8, 148.7,
143.6, 133.3, 133.3, 132.6, 132.5, 132.4, 131.6, 130.3, 130.3, 127.6,
127.0, 115.4, 115.2, 112.1, 112.1, 112.1, 111.9, 111.9, 75.7, 74.7, 70.0.
HRMS (ESI): calcd for C23H17F3N2O2Na [M + Na]+ 433.1134, found
433.1130.
Compounds II-a and II-c−II-n were synthesized according to a
method similar to that for II-b.
Data for Propan-2-one O-(4-(2-(2,6-Difluorophenyl)-4,5-dihy-
drooxazol-4-yl)benzyl) Oxime (II-a). Yellow oil; yield 52%. 1H
NMR (400 MHz, CDCl3): 7.41−7.46 (m, 1H), 7.37 (d, J = 7.6 Hz,
2H), 7.32 (d, J = 7.6 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.49−5.44 (m,
1H), 5.06 (s, 2H), 4.83−4.79 (m, 1H), 4.32−4.28 (m, 1H), 1.88 (s,
3H), 1.87 (s, 3H). HRMS (ESI): calcd for C19H19F2N2O2 [M + H]+
367.1229, found 367.1224.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(4-(Trifluoromethoxy)benzyl) Oxime (I-i). White
1
solid; mp 102−103 °C; yield 65%. H NMR (400 MHz, CDCl3): δ
Data for Cyclohexanone O-(4-(2-(2,6-Difluorophenyl)-4,5-dihy-
1
8.13 (s, 1H), 7.59 (d, J = 8.4 Hz, 2H), 7.47−7.42 (m, 3H), 7.35 (d, J =
8.0 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.48
(dd, J = 10.4, 8.0 Hz, 1H), 5.20 (s, 2H), 4.82 (dd, J = 10.4, 8.0 Hz,
1H), 4.27 (t, J = 8.0 Hz, 1H). HRMS (ESI): calcd for
C24H17F5N2O3Na [M + Na]+ 499.1052, found 499.1050.
drooxazol-4-yl)benzyl) Oxime (II-c). Yellow oil; yield 40%. H NMR
(400 MHz, CDCl3): 7.46−7.41(m, 1H), 7.36 (d, J = 8.0 Hz, 2H), 7.32
(d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.4 Hz, 2H), 5.52−5.42 (m, 1H), 5.05
(s, 2H), 4.85−4.78 (m, 1H), 4.32−4.28 (m, 1H), 2.50 (t, J = 6.2 Hz,
2H), 2.24−2.15 (m, 2H), 1.64−1.66 (m, 4H), 1.59−1.61(m, 2H).
HRMS (ESI): calcd for C22H23F2N2O2 [M + H]+ 385.1722, found
385.1722.
Data for 4-(2-(2,6-difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(4-(Trifluoromethyl)benzyl) Oxime (I-j). White
1
solid; mp 91−93 °C; yield 56%. H NMR (400 MHz, CDCl3): δ
Data for Cycloheptanone O-(4-(2-(2,6-Difluorophenyl)-4,5-dihy-
1
8.15 (s, 1H), 7.62 (d, J = 8.0 Hz, 2H), 7.59 (d, J = 8.0 Hz, 2H), 7.52
(d, J = 8.0 Hz, 2H), 7.47−7.40 (m, 1H), 7.35 (d, J = 8.0 Hz, 2H), 7.00
(t, J = 8.0 Hz, 2H), 5.48 (dd, J = 10.4, 8.0 Hz, 1H), 5.25 (s, 2H), 4.82
(dd, J = 10.4, 8.0 Hz, 1H), 4.27 (t, J = 8.0 Hz, 1H). HRMS (ESI):
calcd for C24H17F5N2O2Na [M + Na]+ 483.1102; 483.1104.
drooxazol-4-yl)benzyl) Oxime (II-d). Yellow oil; yield 46%. H NMR
(400 MHz, CDCl3): δ 7.46−7.41 (m, 1H), 7.37 (d, J = 8.0 Hz, 2H),
7.32 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.47 (dd, J = 10.4,
8.0 Hz, 1H), 5.06 (s, 2H), 4.81 (dd, J = 10.4, 8.4 Hz, 1H), 4.30 (t, J =
8.4 Hz, 1H), 2.59−2.54 (m, 2H), 2.38−2.34 (m, 2H), 1.73−1.56 (m,
8H). HRMS (ESI): calcd for C23H25F2N2O2 [M + H]+ 399.1879,
found 399.1875.
Data for 4-(2-(2,6-Difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(4-Chlorobenzyl) Oxime (I-k). Yellow solid; mp
1
77−80 °C; yield 83%. H NMR (400 MHz, DMSO-d6): δ 8.33 (s,
Data for Benzaldehyde O-(4-(2-(2,6-Difluorophenyl)-4,5-dihy-
drooxazol-4-yl)benzyl) Oxime (II-e). Yellow oil; yield 68%. 1H
NMR (400 MHz, CDCl3): 8.13 (s, 1H), 7.64−7.54 (m, 2H), 7.45−
7.41(m, 3H), 7.41−7.30 (m, 5H), 7.00 (t, J = 8.4 Hz, 2H), 5.53−5.42
(m, 1H), 5.21 (s, 2H), 4.88−4.76 (m, 1H), 4.27−4.31(m, 1H). HRMS
(ESI): calcd for C23H19F2N2O2 [M + H]+ 393.1409, found 393.1408.
Data for 2-Fluorobenzaldehyde O-(4-(2-(2,6-Difluorophenyl)-4,5-
1H), 7.72−7.62 (m, 3H), 7.44 (s, 4H), 7.37 (d, J = 8.0 Hz, 2H), 7.30
(t, J = 8.0 Hz, 2H), 5.52 (t, J = 9.2 Hz, 1H), 5.17 (s, 2H), 4.86 (t, J =
9.2 Hz, 1H), 4.20 (t, J = 8.4 Hz, 1H), HRMS (ESI): calcd for
C23H18ClF2N2O2 [M + H]+ 427.1019, found 427.1020.
Data for 4-(2-(2,6-difluorophenyl)-4,5-dihydrooxazol-4-yl)-
benzaldehyde O-(4-tert-Butylbenzyl) Oxime (I-l). Yellow solid; mp
1
1
70−73 °C; yield 75%. H NMR (300 MHz, CDCl3): δ 8.13 (s, 1H),
dihydrooxazol-4-yl)benzyl) Oxime (II-f). Yellow oil; yield 61%. H
7.60 (d, J = 8.1 Hz, 2H), 7.49−7.33 (m, 7H), 7.01 (t, J = 8.1 Hz, 2H),
5.48 (dd, J = 10.2, 8.4 Hz, 1H), 5.18 (s, 2H), 4.83 (dd, J = 10.2, 8.7
Hz, 1H), 4.27 (t, J = 8.4 Hz, 1H), 1.32 (s, 9H). HRMS (ESI): calcd for
C27H26F2N2O2Na [M + Na]+ 471.1855, found 471.1858.
NMR (300 MHz, CDCl3): δ 8.38 (s, 1H), 7.81 (t, J = 6.6 Hz, 1H),
7.45−7.32 (m, 6H), 7.15−6.96 (m, 4H), 5.48 (dd, J = 10.2, 8.1 Hz,
1H), 5.22 (s, 2H), 4.82 (dd, J = 10.2, 8.4 Hz, 1H), 4.31 (t, J = 8.1 Hz,
1H). 13C NMR (100 MHz, CDCl3): δ 164.1, 162.6, 162.5, 161.7,
160.0, 157.6, 147.93, 147.90, 141.6, 136.8, 134.5, 134.4, 132.5, 132.4,
132.33, 130.28, 130.2, 129.0, 126.8, 123.2, 123.2, 116.9, 116.7, 113.4,
113.2, 112.1, 112.1, 111.8, 76.3, 74.8, 70.1. HRMS (ESI): calcd for
C23H18F3N2O2 [M + H]+ 411.1315, found 411.1307.
General Synthetic Procedure for the Target Compounds II-
a−II-n (Scheme 3). Synthesis of N-(1-(4-(Bromomethyl)phenyl)-2-
chloroethyl)-2,6-difluorobenzamide (9).17,18 To a solution of 6 (5.0
g, 16.1 mmol) in dichloromethane (40 mL) were successively added
water (40 mL), potassium bromide (1.9 g, 16.1 mmol), and potassium
bromate (1.33 g, 8.05 mmol), and then a solution of concentrated
hydrochloric acid (6.1 mL) in water (14 mL) was added dropwise at 0
°C. The reaction mixture was stirred for 25 h until reaction was
complete. The organic phase was separated and washed with saturated
sodium carbonate. The water phase was extracted with dichloro-
methane. Then the combined organic phase was washed with brine,
dried over anhydrous magnesium sulfate, and concentrated to give a
white solid, which was purified by recrystallization using toluene and
petroleum ether to give 9 as crystals (3.5 g, yield 56%). Mp: 127−128
Data for 3-Fluorobenzaldehyde O-(4-(2-(2,6-Difluorophenyl)-4,5-
1
dihydrooxazol-4-yl)benzyl) Oxime (II-g). Yellow oil; yield 32%. H
NMR (300 MHz, CDCl3): δ 8.08 (s, 1H), 7.47−7.26 (m, 8H), 7.09−
6.93 (m, 3H), 5.47 (dd, J = 10.2, 8.1 Hz, 1H), 5.20 (s, 2H), 4.80 (dd, J
= 10.2, 8.4 Hz, 1H), 4.28 (t, J = 8.1 Hz, 1H). 13C NMR (100 MHz,
CDCl3): δ 164.1, 162.6, 162.5, 161.7, 160.0, 157.6, 147.93, 147.90,
141.6, 136.8, 134.5, 134.4, 132.5, 132.4, 132.3, 130.3, 130.2, 129.0,
126.8, 123.25, 123.22, 116.9, 116.7, 113.4, 113.2, 112.1, 112.1, 111.8,
76.3, 74.8, 70.1. HRMS (ESI): calcd for C23H18F3N2O2 [M + H]+
411.1315, found 411.1315.
1
°C. H NMR (400 MHz, CDCl3): δ 7.45−7.36 (m, 5H), 6.97 (t, J =
Data for 4-Fluorobenzaldehyde O-(4-(2-(2,6-Difluorophenyl)-4,5-
8.0 Hz, 2H), 6.62 (d, J = 7.6 Hz, 1H), 5.61−5.57 (m, 1H), 4.49 (s,
2H), 4.04−3.91 (m, 2H).
dihydrooxazol-4-yl)benzyl) Oxime (II-h). Yellow solid; mp 85−87 °C;
1
yield 33%. H NMR (400 MHz, CDCl3): δ 8.10 (s, 1H), 7.60−7.52
Synthesis of Cyclopentanone O-(4-(2-(2,6-Difluorophenyl)-4,5-
dihydrooxazol-4-yl)benzyl) Oxime (II-b). To a mixture of cyclo-
pentanone oxime (0.51 g, 5.15 mmol) in DMF (50 mL) was added
sodium hydride (0.49 g, 20.59 mmol). The mixture was stirred for 40
min, and then 9 (1.00 g, 2.57 mmol) was added. The reaction mixture
was stirred at 0 °C until TLC showed that the reaction was finished.
The reaction mixture was extracted with ethyl acetate, and the organic
layer was dried over anhydrous magnesium sulfate, filtered, and
concentrated to give a reddish brown oil. The crude was purified by
flash chromatography on silica gel with petroleum ether and ethyl
acetate (v/v = 10:1) to give the target II-b as a yellow oil (0.65 g, yield
(m, 2H), 7.47−7.39 (m, 3H), 7.35 (d, J = 8.0 Hz, 2H), 7.07−6.98 (m,
4H), 5.48 (dd, J = 10.4, 8.0 Hz, 1H), 5.19 (s, 2H), 4.82 (dd, J = 10.4,
8.4 Hz, 1H), 4.29 (t, J = 8.0 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ
147.9, 141.6, 137.0, 132.5, 132.4, 132.3, 128.9, 126.8, 115.9, 115.7,
112.1, 111.8, 76.1, 74.8, 70.1. HRMS (ESI): calcd for C23H18F3N2O2
[M + H]+ 411.1315, found 411.1313.
Data for 4-Methoxybenzaldehyde O-(4-(2-(2,6-Difluorophenyl)-
4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-i). Yellow oil; yield 46%. 1H
NMR (400 MHz, CDCl3): δ 8.08 (s, 1H), 7.51 (d, J = 8.8 Hz, 2H),
7.46−7.39 (m, 3H), 7.34 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H),
6.88 (d, J = 8.8 Hz, 2H), 5.50− 5.46 (m, 1H), 5.18 (s, 2H), 4.84−4.79
3068
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Journal of Agricultural and Food Chemistry
Article
Table 1. Acaricidal Activities of the Target Compounds against T. cinnabarinus in the Laboratory
acaricidal act. (%) at concn (mg L−1
)
eggs of T. cinnabarinus
larvae of T. cinnabarinus
compd
I-a
10
1
0.1
0.01
0.001
0.0001
10
1
0.1
0.01
0.001
0.0001
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
78
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
56
100
100
100
100
95
90
88
95
85
57
75
85
75
100
100
60
80
78
0
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
80
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
65
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
40
80
95
I-b
I-c
95
I-d
90
I-e
75
I-f
100
100
100
100
100
90
80
I-g
75
I-h
85
I-i
100
100
70
I-j
I-k
I-l
100
100
100
97
96
II-a
II-b
II-c
II-d
II-e
II-f
II-g
II-h
II-i
II-j
II-k
II-l
II-m
II-n
etoxazole
85
90
75
0
80
100
100
100
100
100
100
100
100
100
100
100
30
95
90
100
90
85
85
86
75
100
100
95
0
96
100
100
100
90
85
100
100
100
100
0
(m, 1H), 4.31−4.27 (m, 1H), 3.82 (s, 3H). HRMS (ESI): calcd for
C24H21F2N2O3 [M + H]+ 445.1334, found 445.1335.
7.74 (d, J = 7.6 Hz, 1H), 7.61 (d, J = 7.6 Hz, 1H), 7.51−7.39 (m, 4H),
7.36 (d, J = 8.0 Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.48 (dd, J = 10.0,
8.4 Hz, 1H), 5.23 (s, 2H), 4.82 (dd, J = 10.0, 8.4 Hz, 1H), 4.30 (t, J =
8.4 Hz, 1H). 13C NMR (100 MHz, CDCl3): δ 164.1, 162.6, 162.5,
161.7, 160.0, 157.6, 147.93, 147.90, 141.6, 136.8, 134.5, 134.4, 132.5,
132.4, 132.33, 130.28, 130.2, 129.0, 126.8, 123.25, 123.22, 116.9,
116.7, 113.4, 113.2, 112.1, 112.1, 111.8, 76.3, 74.8, 70.1. HRMS (ESI):
calcd for C24H18F5N2O2 [M + H]+ 461.1283, found 461.1282.
Data for 4-(Trifluoromethyl)benzaldehyde O-(4-(2-(2,6-difluor-
ophenyl)-4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-n). Yellow oil;
yield 53%. 1H NMR (400 MHz, CDCl3): 8.15 (s, 1H), 7.69 (d, J = 8.0
Hz, 2H), 7.61 (d, J = 8.0 Hz, 2H), 7.44−7.42 (m, 3H), 7.36 (d, J = 8.0
Hz, 2H), 7.00 (t, J = 8.0 Hz, 2H), 5.52−5.44 (m, 1H), 5.23 (s, 2H),
4.87−4.78 (m, 1H), 4.27−4.32 (m, 1H). HRMS (ESI): calcd for
C24H18F5N2O2 [M + H]+ 461.1283, found 461.1285.
Biological Assay. All biological assays were performed on
representative test organisms prepared in the laboratory. Each bioassay
was replicated three times at 25 1 °C for the statistical requirements.
Percentage mortalities were evaluated according to a percentage scale
of 0−100, in which 0 indicates no activity and 100 indicates total kill.
When the percentage mortality of the blank control was less than 5%,
the results of the treats were directly used. However, if the percentage
mortality of the blank control was less than 20% and more than 5%,
the results were corrected by means of V = ((X − Y)/X) × 100 (V =
value of corrected mortality, X = livability of the blank control, Y =
livability of the treat). Etoxazole was evaluated using the entirely same
procedure as contrast.19
Data for 4-Chlorobenzaldehyde O-(4-(2-(2,6-Difluorophenyl)-
4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-j). Yellow solid; mp 78−
80 °C; yield 58%. 1H NMR (400 MHz, CDCl3): 8.07 (s, 1H), 7.50 (d,
J = 8.0 Hz, 2H), 7.42 (d, J = 7.6 Hz, 3H), 7.38−7.28 (m, 4H), 6.98 (t,
J = 9.2 Hz, 2H), 5.49−5.44 (m, 1H), 5.19 (s, 2H), 4.83−4.78 (m, 1H),
4.30−4.26 (m, 1H). HRMS (ESI): calcd for C23H18ClF2N2O2 [M +
H]+ 427.1019, found 427.1026.
Data for 4-(tert-Butyl)benzaldehyde O-(4-(2-(2,6-Difluorophen-
yl)-4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-k). Yellow oil; yield
58%. 1H NMR (400 MHz, CDCl3): δ 8.11 (s, 1H), 7.50 (d, J = 8.0 Hz,
2H), 7.43−7.36 (m, 5H), 7.33 (d, J = 7.6 Hz, 2H), 6.97 (t, J = 8.4 Hz,
2H), 5.45 (t, J = 9.2 Hz, 1H), 5.19 (s, 2H), 4.79 (t, J = 9.2 Hz, 1H),
4.27 (t, J = 8.2 Hz, 1H), 1.31 (s, 9H). 13C NMR (100 MHz, CDCl3): δ
162.6, 162.5, 160.02, 159.96, 157.6, 153.2, 149.0, 141.5, 137.2, 132.5,
132.4, 132.3, 129.4, 128.9, 126.9, 126.7, 125.7, 112.1, 111.8, 107.5,
107.3, 107.1, 75.9, 74.8, 70.1, 34.8, 31.2. HRMS (ESI): calcd for
C27H27F2N2O2 [M + H]+ 449.2035, found 449.2032.
Data for 2-(Trifluoromethyl)benzaldehyde O-(4-(2-(2,6-Difluor-
ophenyl)-4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-l). Yellow oil;
1
yield 70%. H NMR (400 MHz, CDCl3): δ 8.51 (d, J = 2.0 Hz, 1H),
8.02 (d, J = 7.6 Hz, 1H), 7.61 (d, J = 7.6 Hz, 1H), 7.50−7.31 (m, 7H),
6.94 (t, J = 8.4 Hz, 2H), 5.46 (dd, J = 10.0, 8.0 Hz, 1H), 5.23 (s, 2H),
4.78 (dd, J = 10.0, 8.4 Hz, 1H), 4.26 (t, J = 8.4 Hz, 1H). 13C NMR
(100 MHz, CDCl3): δ 164.1, 162.6, 162.5, 161.7, 160.0, 157.6, 147.93,
147.90, 141.6, 136.8, 134.5, 134.4, 132.5, 132.4, 132.33, 130.28, 130.2,
129.0, 126.8, 123.25, 123.22, 116.9, 116.7, 113.4, 113.2, 112.1, 112.1,
111.8, 76.3, 74.8, 70.1. HRMS (ESI): calcd for C24H18F5N2O2 [M +
H]+ 461.1283, found 461.1287.
Acaricidal Activity against Eggs and Larvae of Spider Mite
(Tetranychus cinnabarinus). The acaricidal activities of all the target
compounds and the contrast etoxazole against eggs and larvae of
spider mite (T. cinnabarinus) were measured on the basis of previously
reported procedure.20,21
Data for 3-(Trifluoromethyl)benzaldehyde O-(4-(2-(2,6-Difluor-
ophenyl)-4,5-dihydrooxazol-4-yl)benzyl) Oxime (II-m). Yellow oil;
yield 54%. 1H NMR (400 MHz, CDCl3): δ 8.15 (s, 1H), 7.84 (s, 1H),
3069
dx.doi.org/10.1021/jf500461a | J. Agric. Food Chem. 2014, 62, 3064−3072

Journal of Agricultural and Food Chemistry
Article
Table 2. Effect of Acaricidal Program on Spider Mite in the Field in 2013
% effect of II-l
% effect of etoxazole
a
b
trial sites
treatments
3 days
P. citri
7 days
14 days
3 days
7 days
14 days
c
Jingzhou, Hubei Province
10
15
22
10
15
22
10
15
22
64
74
74
70
77
82
79
79
83
81
87
88
84
88
91
82
86
91
88
91
94
55
81
85
80
90
87
93
d
Changsha, Hunan Province
e
f
g
Guilin, Guangxi Autonomous Region
95
97
f
g
95
98
f
g
f
g
98
99
99
97
T. cinnabarinus
h
Tianjin City
10
15
85
88
90
91
92
93
89
91
92
22
91
94
92
a
b
c
Treatments: the unit of concentration is mg kg−1. The number of days between spraying insecticides and investigating the effects. The amount
d
e
f
g
h
sprayed is about 1000 g ha−1. The amount sprayed is about 2000 g ha−1. The amount sprayed is about 900 g ha−1. 10 days. 15 days. The
amount sprayed is about 750 g ha−1.
Affinity of the Target Compounds and Etoxazole Binding to
SUR. Preparation of SUR. According to our previous reported
method, the buffer of SUR was prepared from German cockroach
(Blattella germanica, B. germanica) through the process of chopping,
homogenization, centrifugation, etc.15
Assay of Binding to SUR. The affinity of the target compounds and
etoxazole to SUR was tested using a method similar to our previously
published method. After the superior concentration of N-phenyl-1-
naphthylamine (1-NPN) that acted as fluorescence probe was
determinated, ligands such as etoxazole and the target compounds
in different concentrations were respectively added to a mixture
solution containing SUR, buffer, and 1-NPN. After the mixture was
incubated for 1 h at room temperature, the binding affinity was tested
by FP.16
Evaluation of Acaricidal Activity in the Field. The field trials
were carried out between April and June in 2013. The trial against T.
cinnabarinus in tomato field was performed in the trial area of Institute
of Plant Protection, Tianjin Academy of Agricultural Science, Tianjin
City, China. Moreover, the trials against Panonychus citri (P. citri) in
orange orchard were performed in the trial area of Institute of Plant
Protection, Hunan Academy of Agricultural Science, Changsha City;
Citrus Institute of Guangxi, Guilin City; and College of Agricuture,
Yangtze University, Jingzhou City. The treated plots of tomatoes or
oranges were designed in a random block array with four replicates.
The untreated plots served as a blank control. The formulation of
compound II-l and etoxazole (2.5% emulsifiable concentrates (EC))
was prepared in our research group. They were diluted to 10, 15, or 22
mg kg−1 before use. The amount sprayed on the field area varied from
750 to 2000 g ha−1 at different sites. The control effects expressed as
percentages were arcsine transformed to homogenize variances before
analysis, which of different spraying treatments were examined using
analysis of variance (ANOVA).22
chloro group in 6 by thionyl chloride using chloroform as
solvent.
The target compounds I-a−I-l were synthesized from 6 as
shown in Scheme 2. The methyl group in 6 was oxidized with
CrO3 in the presence of concentrated sulfuric acid and glacial
acetic acid to give aldehyde 7, which was further reacted with
hydroxylamine hydrochloride to afford 8 containing an oxime
moiety. 8 was treated with sodium hydride and reacted with a
series of alkyl or substituted-benzyl bromide to give 2,4-
diphenyl-1,3-oxazolines I-a−I-l containing oxime ether moiety
after nucleophilic cyclization and substitution.
The target compounds II-a−II-n were also synthesized from
compound 6 as shown in Scheme 3. The key intermediate 9
was obtained through bromination of 6 according to the
reported method using water as solvent, in which the reaction
temperature was strictly maintained between 0 °C and 5 °C to
minimize the formation of byproduct. A series of oximes were
successfully reacted with 9 in the presence of sodium hydride to
give the target compounds II-a−II-n via cyclization and
substitution.
Acaricidal Activity against Eggs and Larvae of T.
cinnabarinus in the Laboratory. Table 1 shows acaricidal
activities of the target compounds I-a−I-l and II-a−II-n against
eggs and larvae of T. cinnabarinus, with etoxazole, the only 2,4-
diphenyl-1,3-oxazoline acaricide widely used in China, as a
contrast. The result showed that all of the target compounds
had much higher activities than etoxazole, as the ovicidal and
larvicidal activities of the target compounds I-a−I-l and II-a−
II-n against T. cinnabarinus were all over 90% at 0.001 mg L−1,
but etoxazole gave only 30% and 40% respectively at the same
concentration. Therefore, the modification at the para site of
the 4-phenyl moiety of 2,4-diphenyl-1,3-oxazolines was
favorable to the acaricidal activity, which was in accordance
with our design ideas. Especially, I-i and I-j, respectively bearing
trifluoromethoxyl and trifluoromethyl group at the para
position of the benzyl moiety, showed the highest ovicidal
and larvicidal activities at 0.0001 mg L−1. Compounds II-l and
II-m, that bear a trifluoromethyl at the ortho and meta
positions of the benzene ring, respectively, had obviously higher
ovicidal and larvicidal activities than the others.
RESULTS AND DISCUSSION
■
Synthesis. N-(2-Chloro-1-(p-tolyl)ethyl)-2,6-difluorobenza-
mide (6), as a critical intermediate for all the target compounds,
was synthesized from toluene (1) as shown in Scheme 1. Ethyl
2-oxo-2-(p-tolyl)acetate (2) was obtained by Friedel−Crafts
acylation of toluene with ethyl 2-chloro-2-oxoacetate. 2 was
reacted with hydroxylamine hydrochloride to afford hydrox-
yimino compound 3, which was further reduced by sodium
borohydride and iodine to give α-amino alcohol 4. After 4 was
reacted with 2,6-difluorobenzoyl chloride to give the corre-
sponding benzamide 5, the hydroxyl in 5 was converted to
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Evaluation of Acaricidal Activity of II-l in the Field.
Based on the comprehensive analysis of bioactivity, physical
properties, synthetic procedure, and so on, compound II-l,
which had exhibited excellent acaricidal activity in the
laboratory, was chosen to evaluate the acaricidal activity in
the field. 2.5% EC of II-l and etoxazole were separately
prepared and evaluated for the control of P. citri in Jingzhou
City (Hubei Province, South China), Changsha City (Hunan
Province, South China), and Guilin City (Guangxi Zhuang
Autonomous Region, South China) and T. cinnabarinus in
Tianjin City (North China). Part of the result of the field trials
is shown in Table 2. It was shown that II-l at the concentration
of 22 mg kg−1 had a better control effect than etoxazole at the
same concentration. The data of the field trial in Jingzhou
showed that, 3 days after the spray, the control efficiency of II-l
against P. citri at 22 mg L−1 was 75%, whereas that of etoxazole
was 55% at the same condition; this phenomenon suggested
that the speed of action of II-l was faster than that of etoxazole.
Fourteen days after the spray, the control efficiency of II-l and
etoxazole was respectively 91% and 87%. The control efficiency
of II-l and etoxazole against P. citri in Changsha and Guilin was
similar, if not identical, to that in Jingzhou. In Tianjin, the
control efficiency of both II-l and etoxazole against T.
cinnabarinus at 22 mg L−1 was 92% when tested 14 days after
the spray. Therefore, it was suggested that II-l could be
considered as an alternative to the excessively employed
acaricide for further development on the basis of the field trials.
Affinity of the Target Compounds Binding to SUR.
The binding affinity of each series of the target compounds to
the isolated SUR were tested by FP method with etoxazole as a
contrast.23 Since the accurate determination of concentration
and stability of the SUR have not been realized up to now, in
order to make the data comparable and minimize the errors, the
binding affinity was assayed within the same set of experiments
and containing 5 replicates. In the paper, that is to say, the
target compounds I-a−I-l and etoxazole were tested with the
same vesicle prepared, and so were compounds II-a−II-n.
In the buffer solution having the most proper concentration
of 1-NPN-SUR, each of the target compounds I-a−I-l and
etoxazole in different concentrations was separately added, and
the FP data were recorded (Figure 2). From the figure we could
find all the FP data were related to the concentration of the
added compounds, which meant all these compounds could
replace 1-NPN and then bind with SUR by themselves. The
affinity with SUR is relevant to the value of the FP: the more
decreased polarization was tested, the stronger affinity was
exhibited. Thus from the figure, the order of affinity of these
compounds was approximately deduced as I-i > I-j > I-d > I-f >
I-b > I-c > I-l > I-a > I-e > I-g > I-h > I-k > etoxazole. The
result indicated that the binding affinity to SUR of the target
compounds I-a−I-l in vitro was almost consistent with their
acaricidal activity against T. cinnabarinus in vivo, since I-i and I-j
showed the strongest acaricidal activity against eggs and larvae
of T. cinnabarinus in vivo, and I-k exhibited the lowest activity
among the target compounds I-a−I-l.
Figure 2. Binding curves of compounds I-a−I-l and etoxazole to
sulfonylurea receptor.
Figure 3. Binding curves of the compounds II-a−II-n and etoxazole to
sulfonylurea receptor.
the target compounds and etoxazole could act on the site of
SUR to suppress the chitin synthesis in mite body.
In summary, two series of novel 2,4-diphenyl-1,3-oxazoline
compounds both containing an oxime ether group were
designed and synthesized on the basis of etoxazole,
flucycloxuron, and NK-17. The bioassay results indicated that
all of the target compounds exhibited considerable acaricidal
activities against T. cinnabarinus in the laboratory. Especially,
compound II-l, 2-(trifluoromethyl)benzaldehyde O-(4-(2-(2,6-
difluorophenyl)-4,5-dihydrooxazol-4-yl)benzyl) oxime, showed
100% ovicidal activities and 100% larvicidal activities at 0.0001
mg L−1, much higher than etoxazole, thus it was selected to
proceed to field trial. The field trial results from four sites in
different parts of China clearly showed that II-l had nearly
equivalent activity with etoxazole against T. cinnabarinus and P.
citri at the same doses. Furthermore, when the fluorescence
polarization method was employed to study the action
mechanism, the target compounds and etoxazole were all
Likewise, the FP data against the concentration of II-a−II-n
and etoxazole are shown in Figure 3, from which the affinity
order was deduced as II-m > II-l > II-f > II-g > II-k > II-n > II-
h > II-j > II-e > II-i > II-a > II-c > II-d > II-b > etoxazole. The
result was also almost consistent with the acaricidal activity
against T. cinnabarinus in vivo, supported by the fact that II-m
and II-l had the highest acaricidal activity, and II-a−IId had
relatively lower activity in vivo. Therefore, it was verified that
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: liuyuxiu@nankai.edu.cn (Yuxiu Liu); yangxl@cau.edu.
cn (Xinling Yang); wangqm@nankai.edu.cn (Qingmin Wang).
(17) Adimurthy, S.; Ghosh, S.; Patoliya, P. U.; Ramachandraiah, G.;
Agrawal, M.; Gandhi, M. R.; Upadhyay, S. C.; Ghosh, P. K.; Ranu, B.
C. An alternative method for the regio- and stereo selective
bromination of alkenes, alkynes, toluene derivatives and ketones
using a bromide/bromate couple. Green Chem. 2008, 10, 232−237.
(18) Kikuchi, D.; Sakaguchi, S.; Ishii, Y. An alternative method for
the selective bromination of alkylbenzenes using NaBrO3/NaHSO3
reagent. J. Org. Chem. 1998, 63, 6023−6026.
Author Contributions
Yongqiang Li, Chaojie Li, Yanlong Zheng, Xingcun Wei,
Qiaoqiao Ma, and Peng Wei contributed equally to this work.
Funding
This work was supported by the National Key Project for Basic
Research (2010CB126100) and the National Natural Science
Foundation of China (21132003, 21372131, 21102077) and
the National 12th Five-year Key Technology R&D Program
(2011BAE06B08-04).
(19) Abbott, W. S. A method of computing the effectiveness of an
insecticide. J. Econ. Entomol. 1925, 18, 265−267.
(20) Kuhn, D. G.; Kameswaran, V. Insecticidal, acaricidal and
molluscicidal 1-(substituted)thioalkylpyrroles. U.S. Patent 5,302,383,
1993.
Notes
The authors declare no competing financial interest.
(21) Wang, Y. J.; Ou, X. M.; Pei, H.; Lin, X. M.; Yu, K. Toxicities of
novel insecticide chlorfenpyr against several insects in lab. Agrochem.
Res. Appl. 2006, 10, 20−23.
(22) Siegel, S.; Castellan, N. J., Jr. Nonparametric statistics for the
behavioral sciences; McGraw-Hill Book Co.: Singapore, 1988.
(23) Harris, A.; Cox, S.; Burns, D.; Norey, C. Miniaturization of
fluorescence polarization receptor-binding assays using CyDye-labeled
ligands. J. Biomol. Screen. 2003, 8410−8420.
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