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X.-Q. Liu et al. / Chinese Chemical Letters 27 (2016) 7–10
Fig. 1. Imidacloprid and representative neonicotinoids discovered in our group.
Fig. 2. Design strategy of tetrahydroimidazo[1,2-a]pyridin-5(1H)-one derivatives.
tetrahydroimidazo[1,2-a]pyridin-5(1H)-one derivatives were
designed and synthesized. Their insecticidal activities against
cowpea aphids (Aphis craccivora) and brown planthopper (Nila-
parvata lugens) were evaluated.
8.0 mmol), 6-Cl-PMNI (10.0 mmol), and hydrobromic acid
(10 mmol) in 50 mL acetonitrile at refluxing temperature was
stirred. The reaction progress was monitored by TLC. After
completion of the reaction, the organic solvent was extracted
thoroughly with CH2Cl2 (30 mL Â 3), washed with water, and dried
with anhydrous Na2SO4. The solvent was removed under reduced
pressure. The residue was purified by flash chromatography
eluting with dichloromethane/acetone (4:1, v/v) to afford target
products 10a–10r.
2. Experimental
2.1. Chemistry
Reagents and solvents were obtained from commercial sources
and used without further purification. Melting points (mp) were
determined on a Bu¨chi Melting Point B540 and were uncorrected.
Nuclear magnetic resonance spectra were recorded on a Bruker
Physical and spectroscopic characterization data of compounds
10a–10r were given in Supporting information.
2.2. Biological assay
AM-400 instruments in DMSO-d6 solvent (1H NMR at 400 MHz, 13
C
NMR at 100 MHz, and 19F NMR at 376 MHz). Chemical shifts are
given in parts per million (ppm) with tetramethylsilane as an
internal standard. High-resolution mass spectra (HRMS) were
determined on a MicroMass GCT CA 055 instrument. All MS
experiments were performed using electrospray ionization (ESI) in
positive ion mode. Reaction progress was determined by thin layer
chromatography (TLC) analysis on precoated plates (silica gel
60 F254), and spots were visualized with ultraviolet (UV) light.
Synthesis of benzoyl glycine 8: Glycine (0.1 mol) was dissolved
in 75 mL of 10% sodium hydroxide solution. To this, benzoyl
chloride (7, 0.115 mol) in five portions was added with stirring
until benzoyl chloride completely reacted. The solution was
transferred to beaker and rinsed the conical flask with a little
water. A few gram of crushed ice was added in the solution. Then
concentrated hydrochloric acid was added slowly with stirring
until the mixture was acidic. The crystalline precipitate of benzoyl
glycine was filtered, washed with carbon tetrachloride and then
with cold water. The solid product was collected, dried and
recrystallized in boiling water. Yield: 90%; mp: 85.1–85.6 8C.
General procedure for preparation of 9a–9r: A mixture of
aldehyde (0.1 mol), benzoyl glycine (8, 0.1 mol), acetic anhydride
(0.3 mol) and anhydrous potassium acetate (0.1 mol) was heated
to 90 8C till the mixture liquefied. Then the reaction mixture was
stirred on an oil bath and monitored by TLC. After 3 h, to this 10 mL
of ethanol was added slowly and allowed the mixture to stand
overnight at room temperature. The crystalline product was
separated by filtration, washed with 5 mL of ice-cold alcohol and
then finally washed with 5 mL of boiling water and recrystallized
using suitable solvent.
Bioassays were performed on representative test organisms
grown in the laboratory. The bioassay was repeated at (25 Æ 1) 8C
according to statistical requirements. All compounds were dissolved
in N,N-dimethylformamide (AP, Shanghai Chemical Reagent Co., Ltd.,
Shanghai, China) and diluted with distilled water containing Triton
X-100 (0.1 mg LÀ1) to obtain a series of concentrations of 500.0,
100.0 mg LÀ1 and others for bioassays. For comparative purposes,
avermectins and cycloxaprid as control was tested under the same
conditions.
Insecticidal test for cowpea aphids (A. craccivora): The activities
of insecticidal compounds against cowpea aphids were tested by
leaf-dip method. The leaves of the horsebean plant with 40–60
apterous adults were dipped in diluted solutions of the chemicals
containing Triton X-100 (0.1 mg LÀ1) for 5 s and the excess solution
was sucked out with filter paper, and the burgeons were placed in
the conditioned room ((25 Æ 1) 8C, 50% RH). Water containing Triton
X-100 (0.1 mg LÀ1) was used as a control. The mortality rates were
evaluated 48 h after treatment. Each treatment had three repetitions
and the data were adjusted and subjected to probit analysis as
before.
Insecticidal test for brown planthopper (N. lugens): The
insecticidal activity against brown planthopper was tested by
foliar application. Rice seedlings were placed on moistened pieces
of filter paper in Petri dishes. The dishes were infested with third
instar larvae and then sprayed with the compound solutions
(2.5 mL) using
a ;
Potter spray tower (pressure, 5 lb (in2)À1
settlement, 4.35 mg (cm2)À1). Samples were placed in the condi-
tioned room. The mortality rates were evaluated 48 h after
treatment. Each treatment had three repetitions, and the data
were adjusted and subject to probit analysis as before. The results
of bioassay are depicted in Table 1.
General procedure for preparation of 10a–10r: A solution
of 4-(substituted benzylidene)-2-phenyloxazole-5-ones (9a–9r,
Liu, Xuan-Qi
