Synthesis, Acaricidal Activity, and Structure–Activity Relationships of

Article pubs.acs.org/JAFC

Synthesis, Acaricidal Activity, and Structure−Activity Relationships of Pyrazolyl Acrylonitrile Derivatives Haibo Yu, Yan Cheng, Man Xu, Yuquan Song, Yanmei Luo, and Bin Li* State Key Laboratory of the Discovery and Development of Novel Pesticide, Shenyang Sinochem Agrochemicals R&D Company Ltd., Shenyang 110021, People’s Republic of China ABSTRACT: A series of novel pyrazolyl acrylonitrile derivatives was designed, targeting Tetranychus cinnabarinus, and synthesized. Their structures were identified by combination of 1H NMR, 13C NMR, and MS spectra. The structures of compounds 18 and 19 were further confirmed by X-ray diffraction. Extensive greenhouse bioassays indicated that compound 19 exhibits excellent acaricidal activity against all developmental stages of T. cinnabarinus, which is better than the commercialized compounds cyenopyrafen and spirodiclofen. It was shown that the acute toxicity of compounds 19 to mammals is quite low. The structure−activity relationships are also discussed. KEYWORDS: pyrazolyl, acrylonitrile, synthesis, spider mite, acaricidal activity, structure−activity relationship

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INTRODUCTION Nowadays, spider mite pests are becoming a major threat to many important agricultural and horticultural cropping systems worldwide, particularly cotton, tea, vegetables, fruits, and ornamentals.1−4 Due to their extremely short life cycle, as well as resistance development resulting from frequent applications of acaricides, the control of spider mites has demonstrated to be a significant problem.5,6 As a consequence, the continuous development of new acaricides that would have an excellent insecticidal activity, novel modes of action, and a lower impact on nontarget organisms is highly required.7 Cyenopyrafen and cyflumetofen are complex II inhibitors, which were recently developed for the control of spider mites.8,9 Cyenopyrafen was initially launched in 2009 in Japan and South Korea for use on fruits and vegetables. Both compounds are highly effective in controlling spider mites (Tetranychus sp., Oligonychus sp., Panonychus sp.) during all their life stages, although some highly multiresistant Tetranychus urticae strains might still show cross-resistance to some extent.10 Importantly, they have an excellent safety profile for most nontarget arthropods. This characteristic has promoted their usage in IPM programs.11−14 In the past few years, much attention has been paid to the pyrazole derivatives due to their predominant application as intermediates in the synthesis of novel pesticidal compounds.15 As an example, the pyrazole moiety as the key active pharmacophore is present in many crop protection compounds, such as tebufenpyrad, cyenopyrafen, pyflubumide, and fenpyroximate.16 It is widely accepted that, through modifying the pharmacophore of a model bioactive molecular, bioactivities can be improved.17 Given that the moiety of pyrazolyl acrylonitrile has proven to be an important pharmacophore for cyenopyrafen, to develop novel acaricidal compounds with low resistance, a series of derivatives was thus synthesized from the lead compound cyenopyrafen, and new functional groups were introduced into pyrazole moiety for improved pesticidal activity. This study investigated the syntheses and bioactivities of a number of pyrazolyl acrylonitrile derivatives. The structure− activity relationships (SARs) are also discussed. © XXXX American Chemical Society

MATERIALS AND METHODS

Instruments. Melting points were determined by using an RY-1 melting-point apparatus (TaiKe, Beijing, China). 1H NMR and 13C NMR spectra were recorded utilizing an AV 300 spectrometer (Bruker, Karlsruhe, Germany) in CDCl3 solution using tetramethylsilane as an internal standard. Mass spectra were obtained with a JMA-700 mass spectrometer (JEOL, Kyoto, Japan). X-ray single-crystal diffraction was determined on a P4 diffractometer (Siemens, Bonn, Germany). Elemental analyses were determined using a Vario EL III elemental analysis instrument (Elementar, Hanau, Germany). Reaction progress was monitored by thin-layer chromatography (TLC) on silica gel GF254 (Tianzhe, Qingdao, China), and spots were visualized with ultraviolet (UV) light (Gongyi, Zhengzhou, China). Chemicals. All chemical reagents were commercially available. The solvents (dichloromethane (99%), methanol (99%), ethyl acetate (99%), heptane (99%), and toluene (99%)) were purchased from Sinopharm Chemical Reagent Co. Ltd. and were used directly without further purification. Syntheses of 6, 6a, and 6b. Compound 6 was synthesized according to Figure 1 and the literature.18−21 Pyrazol-5-carboxylic acid methyl ester 6a was synthesized according to Figure 2 and the literature.21 1-Vinyl-1H-pyrazole-5-carboxylate 6b was prepared according to Figure 3 and the literature.22,23 General Procedure for the Preparation of Compound 7. 4-tert-Butylphenylacetonitrile (18.0 g, 107.02 mmol), pyrazol-5carboxylic acid methyl ester 6 (117.72 mmol), and diethylene glycol dimethyl ether (10 mL) were dissolved in heptane (200 mL). The reaction mixture was refluxed under N2 for 1 h. At this temperature, a 28% sodium methoxide methanol solution (30.97 g, 160.53 mmol) was added dropwise to the mixture over 3 h, and then the resulting mixture was further reacted for another 5 h. When the reaction was complete, water (200 mL) was added to separate the heptane phase. After the addition of ethyl acetate (250 mL) to the aqueous phase, concentrated hydrochloric acid (16.70 g, 160.53 mmol) was added dropwise to be neutralized. After separation of the aqueous phase, the organic layer was dried over anhydrous magnesium sulfate and filtered. Received: Revised: Accepted: Published: A

September 21, 2016 November 28, 2016 December 2, 2016 December 2, 2016 DOI: 10.1021/acs.jafc.6b04221 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

Article

Journal of Agricultural and Food Chemistry

Figure 1. Synthetic route of compound 6. Reagents and conditions: (a) EtOCOCOOEt, MeONa, MeOH; (b) NH2NH2 H2O, CH2Cl2; (c) R1 = Me, (MeO)2SO2, CH2Cl2; R1 = Et, (EtO)2SO2, CH2Cl2; R1 = CH3CH2CH2, CH3CH2CH2I, K2CO3, DMF; R1 = (CH3)2CH2, (CH3)2CH2Br, K2CO3, DMF; (d) R3 = F, Selectfluor, CH3CN; R3 = Cl or Br, NCS, or NBS, DMF; R3 = CN, NIS, CuCN, DMF. reaction mixture was heated to 65 °C. After 1 h of stirred at this temperature, pivaloyl chloride (1.33 g, 11.00 mmol) was added dropwise at 65−67 °C over 1 h. Stirring at this temperature was continued until TLC monitoring indicated total consumption of intermediate compound 7. The reaction mixture was then evaporated to dryness, and the residue was chromatographed, eluting with 1:10 ethyl acetate/ petroleum ether, yielding the title compound. The physical properties and elemental analyses of compounds 8−23 are listed in Table 1. Their 1H NMR, 13C NMR, and MS spectra analyses are given in Tables 2 and 3, respectively. Acaricidal Assay. Test against Spider Mite (Tetranychus cinnabarinus). According to the procedures in the literature,24 the activities against adults, nymphs, and eggs of T. cinnabarinus were tested.

Figure 2. Synthetic route of compound 6a. Reagents and conditions: (a) (HCHO)n, HCl(g), 1,4-dioxane; (b) H2, Pd/C (cat), methol.

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RESULTS AND DISCUSSION Synthesis. 2-(4-tert-Butylphenyl)-3-hydroxy-3-(1H-pyrazol5-yl)acrylonitrile 7 was prepared according to Figure 4.25 2-(4tert-Butylphenyl)acetonitrile is condensed with pyrazole-5carboxylate 6 to give 3-hydroxyacrylonitrile 7 in good yield. The target compounds were synthesized by the reaction of pivaloyl chloride with the intermediate 3-hydroxyacrylonitrile 7 (Figure 4).25,26 The configuration of product is influenced by the base and solvent used. When the organic base pyridine and a polar aprotic solvent dioxane were employed in the reaction, the configuration of major product was E-form. To synthesize the product with Z-form, the inorganic base K2CO3 and a low polar solvent toluene play an important role. The configurations of compound 18 and its isomer 19 were confirmed by X-ray diffraction analyses, as shown in Figure 5. Structure−Activity Relationship. The bioactivities are shown in Table 4. Some compounds showed excellent acaricidal

Figure 3. Synthetic route of compound 6b. Reagents and conditions: (a) BrCH2CH2Br, NaH; (b) MeONa, MeOH; (C) NCS, DMF. The filtrate was evaporated under reduced pressure to afford target compound 7. General Procedure for the Preparation of Compounds 8−23. Method A. Pivaloyl chloride (1.33 g, 11.00 mmol) was added dropwise to a stirred solution of compound 7 (10.00 mmol) and pyridine (0.87 g, 11.00 mmol) in dioxane (20 mL) at 25−30 °C. Stirring at this temperature was continued until TLC monitoring indicated total consumption of intermediate compound 7. The reaction mixture was then evaporated to dryness, and the residue was chromatographed, eluting with 1:10 ethyl acetate/petroleum ether, yielding the title compound. Method B. K2CO3 (1.52 g, 11.00 mmol) was added to a stirring solution of compound 7 (10.00 mmol) in toluene (20 mL), and the

Table 1. Physical Properties and Elemental Analyses of Compounds 8−23 elemental analysis (%, calcd) compound

appearance/mp (°C)

yield (%)

8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

yellow oil yellow oil yellow oil yellow oil yellow oil yellow oil white solid/94−95 yellow oil yellow oil yellow oil white solid/121−123 white solid/92−93 yellow oil white solid/124−125 yellow oil yellow oil

66 62 60 61 62 60 75 60 56 56 75 60 66 62 66 62

C 66.82 67.42 67.98 68.52 68.55 68.30 67.39 67.99 67.99 67.72 73.30 73.31 73.69 70.10 61.03 71.75 B

(66.74) (67.35) (67.93) (68.48) (68.48) (68.25) (67.35) (67.93) (67.93) (67.67) (73.25) (73.25) (73.68) (70.05) (61.02) (71.74)

H 6.88 7.11 7.35 7.55 7.53 6.92 7.01 7.35 7.38 6.65 7.88 7.90 8.20 7.36 6.45 7.27

N

(6.82) (7.07) (7.30) (7.52) (7.52) (6.87) (7.07) (7.30) (7.30) (6.63) (7.94) (7.94) (8.16) (7.35) (6.40) (7.22)

10.12 9.83 9.47 9.18 9.20 9.52 9.80 9.47 9.57 9.79 10.67 10.70 10.33 10.28 8.83 13.40

(10.15) (9.82) (9.51) (9.21) (9.21) (9.55) (9.82) (9.51) (9.51) (9.87) (10.68) (10.68) (10.31) (10.21) (8.89) (13.39)

DOI: 10.1021/acs.jafc.6b04221 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry Table 2. 1H NMR of Compounds 8−23 H NMR (CDCl3, δ)

1

compound 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

1.21 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 2.25 (s, 3H, Me), 3.98 (s, 3H, NCH3), 7.50 (q, 4H, Ar−H) 1.25 (t, J = 7.5 Hz, 3H, Me), 1.28 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 2.63 (q, J = 7.5 Hz, 2H, CH2), 3.29 (s, 3H, NCH3), 7.06 (d, J = 8.4 Hz, 2H, Ar−H), 7.32 (d, J = 8.4 Hz, 2H, Ar−H) 1.21 (s, 9H, t-Bu), 1.30 (d, J = 6.9 Hz, 6H, CH(CH3)2), 1.34 (s, 9H, t-Bu), 3.00−3.10 (m, 1H, CH), 3.99 (s, 3H, NCH3), 7.50 (q, 4H, Ar−H) 1.21 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.39 (s, 9H, t-Bu), 3.98 (s, 3H, Me), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.55 (d, J = 8.4 Hz, 2H, Ar−H) 0.94 (d, J = 6.9 Hz, 6H, CH(CH3)2), 1.21 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 2.00−2.10 (m, 1H, CH), 2.50 (d, 2H, CH2), 4.00 (s, 3H, NCH3), 7.51 (q, 4H, Ar−H) 0.939 (d, J = 7.5 Hz, 4H, CH2CH2), 1.21 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.80−1.90 (m, 1H, CH), 3.94 (s, 3H, NCH3), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.54 (d, J = 8.4 Hz, 2H, Ar−H) 1.20 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.55 (t, J = 7.5 Hz, 3H, Me), 2.27 (s, 3H, Me), 4.21 (q, J = 7.2 Hz, 2H, CH2), 7.50 (q, 4H, Ar−H) 0.96 (t, J = 6.6 Hz, 3H, Me), 1.20 (s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 1.90−2.10 (br, 2H, CH2), 2.29 (s, 3H, Me), 4.09 (t, J = 7.5 Hz, 2H, CH2), 7.55 (d, J = 8.6 Hz, 2H, Ar−H), 7.65 (d, J = 8.6 Hz, 2H, Ar−H) 1.22 (s, 9H, t-Bu), 1.37 (s, 9H, t-Bu), 1.57 (m, 6H, CH(CH3)2), 2.31 (s, 3H, Me), 4.63 (q, 1H, CH(CH3)2), 7.48 (d, J = 8.4 Hz, 2H, Ar−H), 7.56 (d, J = 8.4 Hz, 2H, Ar−H) 1.20 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 2.32 (s, 3H, Me), 4.97 (d, J = 8.1 Hz, 1H, CH), 5.82 (d, J = 15.9 Hz, 1H, CH), 7.04 (q, J = 6.3 Hz, 1H, CH), 7.50 (dd, J1 = 8.7 Hz, J2 = 8.7 Hz, 4H, Ar−H) 1.14 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.54 (t, J = 7.2 Hz, 3H, Me), 2.31 (s, 3H, Me), 4.25 (q, J = 7.2 Hz, 2H, CH2), 6.36 (s, 1H, Ar−H), 7.45 (d, J = 8.4 Hz, 2H, Ar−H), 7.46 (d, J = 8.4 Hz, 2H, Ar−H) 1.01 (t, J = 7.2 Hz, 3H, Me), 1.27 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 2.28 (s, 3H, Me), 3.57 (q, J = 7.2 Hz, 2H, CH2), 6.18 (s, 1H, Ar−H), 7.07 (d, J = 8.4 Hz, 2H, Ar−H),7.32 (d, J = 8.4 Hz, 2H, Ar−H) 1.15 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.48 (t, J = 7.2 Hz, 3H, Me), 2.12 (s, 3H, Me), 2.23 (s, 3H, Me), 4.20−4.10 (m, 2H, CH2), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.48 (d, J = 8.4 Hz, 2H, Ar−H) 1.18 (s, 9H, t-Bu), 1.36 (s, 9H, t-Bu), 1.51 (t, J = 7.2 Hz, 3H, Me), 2.26 (s, 3H, Me), 4.18 (q, J = 7.2 Hz, 2H, CH2), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.49 (d, J = 8.4 Hz, 2H, Ar−H) 1.20 (s, 9H, t-Bu), 1.34 (s, 9H, t-Bu), 1.56 (t, J = 7.2 Hz, 3H, Me), 2.28 (s, 3H, Me), 4.24 (q, J = 7.2 Hz, 2H, CH2), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.54 (d, J = 8.4 Hz, 2H, Ar−H) 1.25 (s, 9H, t-Bu), 1.35 (s, 9H, t-Bu), 1.61 (t, J = 7.2 Hz, 3H, Me), 2.42 (s, 3H, Me), 4.30 (q, J = 7.2 Hz, 2H, CH2), 7.46 (d, J = 8.4 Hz, 2H, Ar−H), 7.55 (d, J = 8.4 Hz, 2H, Ar−H)

Table 3. 13C NMR (CDCl3, δ) and MS of Compounds 14 and 18−22 13

compound 14 18 19 20 21 22

11.03, 14.30, 26.58, 29.46, 34.64, 132.00, 145.22, 146.83, 153.40, 13.34, 14.87, 26.41, 30.96, 34.61, 135.30, 147.82, 149.29, 153.02, 13.47, 13.79, 26.69, 30.96, 34.63, 134.53, 148.49, 148.81, 152.87, 11.10, 13.31, 26.80, 30.98, 34.67, 146.79, 153.26, 174.48 11.94, 14.23, 26.61, 30.87, 34.58, 133.79, 146.83, 147.27, 153.35, 11.99, 13.21, 26.78, 31.34, 34.61, 132.77, 147.26, 147.32, 153.19,

39.17, 45.93, 174.77 38.92, 45.36, 174.62 38.92, 44.71, 175.43 39.25, 45.36,

C NMR (CDCl3, δ)

MS (EI)

110.29, 111.29, 115.81 (CN), 125.42, 125.63, 126.53, 127.99, 128.12,

m/z 429.1 ([M + 1]+, 40)

107.73, 109.10, 116.49 (CN), 125.46, 125.62, 126.99, 127.90, 128.13,

m/z 394.2 ([M + 1]+, 100)

106.97, 108.40, 115.33 (CN), 125.96, 126.75, 127.80, 127.81, 127.84,

m/z 394.2 ([M + 1]+, 100)

110.14, 110.73, 114.93 (CN), 126.02, 126.39, 127.68, 130.99, 145.63,

m/z 408.2 ([M + 1]+, 100)

39.11, 45.93, 95.99, 111.55, 115.71 (CN), 125.45, 125.54, 126.45, 128.01, 128.12, 174.73 39.19, 45.31, 95.68, 110.77, 114.85 (CN), 125.86, 125.99, 126.11, 126.33, 128.15, 175.45

m/z 412.1 ([M + 1]+, 100) m/z 473.1 ([M + 1]+, 100)

Figure 4. Synthetic route of compounds 8−23. Reagents and conditions: (a) MeONa, ethylene glycol ether, heptane; (b) 2,2-dimethylpropionyl chloride, Et3N, THF or 2,2-dimethylpropionyl chloride, K2CO3, toluene.

1-position of the pyrazole ring (R1) (14) exhibited a better acaricidal activity compared with the corresponding methyl substitution (compound 8). Propyl (15) and isopropyl (16) derivatives showed no activity, and replacement of the ethyl (14) by a vinyl group (17) caused a clear decrease of activity. Compounds with H (18) and Cl (14) groups at the 4-position of the pyrazole ring (R3) exhibited acaricidal activity similar to that of the compound with a methyl (20) group. Replacement of H (18) by Br (22) or a cyano group (23) clearly diminished the activity.

activities such as compounds 18 and 19, which have a better acaricidal activity when compared to the commercialized compound cyenopyrafen. A summary of results against adults of T. cinnabarinus is outlined in Figure 6. With regard to the substitution at the 3-position of the pyrazole ring (R2), the methyl group was intrinsic for the activity. Elongation of the alkyl chain and replacement of the methyl group by ethyl (9), isopropyl (10), tert-butyl (11), isobutyl (12), or cyclopropyl (13) caused an obvious decrease of activity. Compounds with ethyl at the C

DOI: 10.1021/acs.jafc.6b04221 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry

Figure 5. Crystal structures of compounds 18 and 19.

Table 4. Acaricidal Activity of Substituted Pyrazole Derivatives against Adults of T. cinnabarinus

Detailed Studies of Compound 19. Anticipating agricultural utilization, compound 19 was selected as a candidate for extensive laboratory bioassays and field trials. Compound 19 showed excellent activity against all developmental stages of T. cinnabarinus but was more effective against adults and nymphs than eggs, as shown in Table 5. Table 5. Acaricidal Activities of Compound 19, Cyenopyrafen, and Spirodiclofen against T. cinnabarinus LC50 (mg/L)

Figure 6. Structure−activity relationships for pyrazolyl acrylonitrile derivatives against adults of T. cinnabarinus. D

compound

adults

nymphs

eggs

19 cyenopyrafen spirodiclofen

0.22 0.41 12.52

0.12 >0.2 0.55

1.16 >2.5 4.87

DOI: 10.1021/acs.jafc.6b04221 J. Agric. Food Chem. XXXX, XXX, XXX−XXX

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Journal of Agricultural and Food Chemistry Table 6. Field Trial Results for Compound 19 in Fuzhou and Guilin against P. citri mortality at x days after spraying (%) trail 1 in Fuzhou compound

rate (g ai/ha)

x=1

x=3

x=7

x = 14

x = 21

x=1

x=3

x=7

x = 14

x = 21

100 50 50

46.4 23.8 49.2

79.2 73.5 64.5

88.8 88.0 70.1

89.7 89.7 72.7

100 91.2 91.2

99.4 99.7 48.4

99.9 99.7 69.1

99.6 99.4 82.2

99.8 99.4 98.1

99.6 99.3 97.9

19 (30%, SC) spirodiclofen (24%, SC)

(5) Sugimoto, N.; Osakabe, M. Cross-resistance between cyenopyrafen and pyridaben in the two spotted spider mite Tetranychus urticae (Acari: Tetranychidae). Pest Manage. Sci. 2014, 70, 1090−1096. (6) Khalighi, M.; Dermauw, W.; Wybouw, Y.; Bajda, S.; Osakabe, M.; Tirry, L.; Van leeuwen, T. Molecular analysis of cyenopyrafen resistance in the two-spotted spider mite Tereanychus urticae. Pest Manage. Sci. 2016, 72, 103−112. (7) Takahashi, N.; Nakagawa, H.; Sasama, Y.; Ikemi, N. Development of a new acaricide, cyflumetofen. J. Pestic. Sci. (Tokyo, Jpn.) 2012, 37, 263−264. (8) Nakahira, K. Strategy for discovery of a novel miticide cyenopyrafen which is one of electron transport chain inhibitors. J. Pestic. Sci. (Tokyo, Jpn.) 2011, 36, 511−515. (9) Sparks, T. C.; DeAmicis, C. V. Inhibitors of mitochondrial electron transport: acaricides and insecticides. In Modern Crop Protection Compounds; Kramer, W., Schirmer, U., Jeschke, P., Witschel, M., Eds.; Wiley-VCH Verlag: Weinheim, Germany, 2011; pp 1078−1108. (10) Kahalighi, M.; Tirry, L.; Van leeuwen, T. Cross-resistance risk of the novel complex II inhibitors cyenopyrafen and cyflumetofen in resistant strains of the two-spotted spider mite Tetranychus urticae. Pest Manage. Sci. 2014, 70, 365−368. (11) Hayashi, N.; Sasama, Y.; Takahashi, N.; Ikemi, N. Cyflumetofen, a novel acaricide its mode of action and selectivity. Pest Manage. Sci. 2013, 69, 1080−1084. (12) Paik, C. H.; Kim, S. S. Susceptibility of tea red spider mite, Tetranychus kanzawai (Acari: Tetranychidae) to cyenopyrafen. Korean J. Pestic. Sci. 2010, 14, 170−174. (13) Gotoh, T.; Fujiwara, S.; Kitashima, Y. Susceptibility to acaricides in nine strains of the tomato red spider mite Tetranychus evansi (Acari: Tetranychidae). Int. J. Acarol. 2011, 37, 93−102. (14) Kramer, T.; Nauen, R. Monitoring of spirodiclofen susceptibility in field populations of European red mites, Panonychus ulmi (Koch) (Acari: Tetranychidae), and the cross-resistance pattern of a laboratory-selected strain. Pest Manage. Sci. 2011, 67, 1285−1293. (15) Murakami, H.; Masuzawa, S.; Takii, S.; Ito, T. Preparation of phenyl- and heterocyclyl-substituted acrylonitriles as insecticides, acaricides, nematocides, and marine antifouling agents. JP Patent 2003201280, 2003. (16) Furuya, T.; Suwa, A.; Nakano, M.; Fujioka, S.; Yasokawa, N.; Machiya, K. Synthesis and biological activity of a novel acaricide, pyflubumide. J. Pestic. Sci. (Tokyo, Jpn.) 2015, 40, 38−43. (17) Fustero, S.; Roman, R.; Sanz-Cervera, J. F.; Simon-Fuentes, A.; Bueno, J.; Villanova, S. Synthesis of new fluorinated tebufenpyrad analogs with acaricidal activity through regioselective pyrazole formation. J. Org. Chem. 2008, 73, 8545−8552. (18) Zhang, D. Q.; Xu, G. F.; Fan, Z. J.; Wang, B. Q.; Yang, X. L.; Yuan, D. K. Synthesis and anti-TMV activity of novel N-(3-alkyl-1Hpyrazol-4-yl)-3-alkyl-4-substituted-1H-pyrazole-5-carboxamides. Chin. Chem. Lett. 2012, 23, 669−672. (19) Player, M. R.; Calvo, R.; Chen, J. S.; Meegalla, S.; Parks, D.; Parsons, W.; Ballentine, S.; Branum, S. Preparation of substituted azabicyclic imidazole derivatives useful as therapeutic TRPM8 receptor modulators. U.S. Patent 20110218197, 2011. (20) Tabrizi, M. A.; Baraldi, P. G.; Preti, D.; Romagnoli, R.; Saponaro, G.; Baraldi, S.; Moorman, A. R.; Zaid, A. N.; Varani, K.; Borea, P. A. 1,3-Dipropyl-8-(1-phenyl acetamide-1H-pyrazol-3-yl)xanthine derivatives as highly potent and selective human A2B

The bioassays revealed that compound 19 exhibited a clearly better acaricidal activity than cyenopyrafen and spirodiclofen. Field trials with a 30% SC formulation of compound 19 at an application rate of 50−100 g ai/ha provided an effective control of Panonychus citri for 21 days, as shown in Table 6. A summary of the mammalian toxicology data is provided in Table 7. The results show that its acute toxicity to mammals is quite low. Table 7. Toxicity Results for Compound 19 acute toxicity test

species

oral LD50 (mg/kg)

rat

dermal

rat

skin irritation eye irritation skin sensitization Ames

rabbit rabbit guinea pig

results >4600 (male) >4600 (female) >2150 (male) >2150 (female) nonirritating minimally irritating nonsensitizing negative

Because of the excellent efficacy and low toxicity to mammals, as an acaricidal candidate, compound 19 is in development for controlling P. citri in citrus.

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AUTHOR INFORMATION

Corresponding Author

*(B.L.) Phone: +86-24-85869218. Fax: +86-24-85869137. E-mail: [email protected]. ORCID

Bin Li: 0000-0003-4862-7921 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Liang Lv and Pengfei Liu for assistance with manuscript preparation. The toxicity test was carried out by the National Safety and Evaluation Centre of New Drug (Shenyang).

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trail 2 in Guilin

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DOI: 10.1021/acs.jafc.6b04221 J. Agric. Food Chem. XXXX, XXX, XXX−XXX