LIU Wen-Rui HUA Xue-Wen② ZHOU Sh YUAN Feng-Ying WANG Gui-Qing②LIU Yi XING Xio-Rn

a (College of Agriculture, Liaocheng University, Liaocheng 252000, China)

b (Collaborative Innovation Center of Zhejiang Province for Green Pesticide, School of Forestry and Bio-technology, Zhejiang A&F University, Hangzhou 311300, China)

c (Liaocheng Center for Disease Control and Prevention, Liaocheng 252000, China)

ABSTRACT Fifteen novel N-sulfonyl aromatic amide derivatives were designed and synthesized, and the structures were characterized by 1H- and 13C-NMR, EA and HRMS. The crystal structures of compounds I-8 and I-9 were obtained from X-ray diffraction: I-8 is of triclinic system, Mr = 372.35, space group P21/n with a =7.9151(10), b = 8.5637(11), c = 12.2022(15) Å, β = 86.865(2)º, V = 807.09(18) Å3, Z = 2, F(000) = 384, Dc = 1.532 g/cm3, the final R = 0.0408 and wR = 0.1068 for 2836 unique reflections with 2435 observed ones (I > 2σ(I)). I-9 belongs to triclinic system, Mr = 407.39, space group P21/n, with a = 8.4911(8), b = 8.6053(9), c = 14.5808(15) Å,β = 77.1190(10)º, V = 995.44(17) Å3, Z = 2, F(000) = 416, Dc = 1.359 g/cm3, the final R = 0.0567 and wR = 0.1779 for 3475 unique reflections with 2392 observed ones (I > 2σ(I)). The preliminary bioassay results indicated that the target compounds showed weak nematicidal activity, while compound I-5 displayed good fungicidal activity against Colletotrichum capsici with the inhibition rate of 61.7%.

Keywords: heterocyclic amide, synthesis, crystal structure, fungicidal activity, nematicidal activity;

1 INTRODUCTION

Pesticides play an important role in improving the yield and quality of crops[1-3]. However, with the long-term and large-scale use of pesticides, problems such as drug resistance have become increasingly prominent[4,5]. The development of new and efficient pesticide active molecules can effectively alleviate the problems caused by drug resistance, and the discovery of lead compounds is the basis of innovative drug research[6,7].

Fluopyram successfully developed by Bayer company is a new broad-spectrum amide fungicide acting on succinate dehydrogenase (SDH)[8,9]. At the same time, it has been widely used in the control of soil nematodes in recent years due to its high efficiency and novel mechanism of action[10].At present, researches on the tri-factor relationship among fluopyram structural modification, fungicidal activity and nematicidal activity are relatively lacking.

In our previous work, combined with the newly reported structures of new active ingredients in fungicide and nematicide[11-20], four series of amide derivatives with fluopyram as the molecular skeleton were designed and synthesized by introducing sulfide and sulfone substructures into the amide bridge (Fig. 1). Subsequently, the nematicidal and fungicidal activities of the target compounds were measured, and compound h-I-9 displayed excellent fungicidal activity and compounds h-I-11, h-II-6 and h-IV-1～h-IV-6 exhibited good nematicidal activity (Fig.2)[21-23]. The structure-activity relationships indicated that theN-sulfonyl amide containing aromatic sulfide substructure showed good nematicidal activity[21-23]. On this basis, in order to explore the effect of structural modification of the N-sulfonyl amide on nematicidal and fungicidal activities, a series of N-sulfonyl amide compounds directly connected to the aromatic rings was designed and synthesized by shortening the amide bridge (Fig. 2). The preliminary molecular docking simulation indicated that the designed molecules could interact with the receptorAscaris suumSDH (PDB ID: 3VRB)(Fig. 2).

Fig. 1. Structural modification of the amide bridge in our previous work

Fig. 2. Design strategy of the target compounds

2 EXPERIMENTAL

2. 1 Materials and methods

All reaction reagents were of analytical grade. Melting points for target compounds were determined on an X-4 binocular microscope (Gongyi Tech. Instrument Co., Henan,China). Proton (1H)- and carbon-13 (13C)-nuclear magnetic resonance (NMR) were obtained on a Bruker-500 MHz spectrometer, and chemical-shift values (δ) were reported as parts per million (ppm) with tetramethylsilane as the internal standard. Elemental analyses (EA) were determined on an Elementar Vario EL elemental analyzer. High resolution mass spectrometry (HRMS) was recorded using a high resolution mass spectrometer (Varian 7.0T FTMS). The X-ray single-crystal structure was determined on a Bruker D8 Venture diffractometer with Mo-Kαradiation (λ= 0.71073 Å).Column chromatography purification was carried out using silica gel (200～300 mesh).

2. 2 Synthesis of the target compounds

2. 2. 1 General synthetic procedure for the target compounds I-1～I-4, I-6～I-9 and I-11～I-14

N-((2-Methoxycarbonylphenyl)sulfonyl)-2-(trifluoromethyl)benzamide (I-1) was synthesized as follows. A mixture of 2-(trifluoromethyl)benzoic acid (0.40 g, 2.1 mmol), 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride(EDCI, 0.48 g, 2.5 mmol) and 4-dimethylaminopyridine(DMAP, 0.62 g, 5.0 mmol) in N,N-dimethylformamide (DMF,10 mL) was stirred for 30 min at room temperature, followed by the addition of methyl 2-sulfamoylbenzoate (0.50 g, 2.3 mmol). The reaction was continued to stir for 8 h, and the progress was monitored by TLC. After completion, the mixture was poured into the dilute hydrochloric acid aqueous solution. The resulting precipitate was filtered to provide the product, which was purified by using ethyl acetate to recrystallize. The products could also be purified by dissolving in potassium carbonate aqueous solution, washing with ethyl acetate and using the dilute hydrochloric acid aqueous solution to acidize the water layer to produce the white precipitate, yield 78%.

N-((2-Methoxycarbonylphenyl)sulfonyl)-2-(trifluoromethyl)benzamide (I-1): White granules, yield 78%, m.p. 140～141 ℃.1H NMR (500 MHz, DMSO-d6)δ12.99 (s, 1H,CONHSO2), 8.22 (dd,J= 7.7, 1.0 Hz, 1H, Ph-H), 7.89～7.70(m, 6H, Ph–H), 7.64 (d,J= 7.5 Hz, 1H, Ph–H), 3.89 (s, 3H,COOCH3).13C NMR (126 MHz, DMSO-d6)δ167.4, 165.9,136.3, 134.6, 133.3, 133.0, 132.8, 131.7, 131.2, 129.6, 129.0,127.1 (q,J= 3.8 Hz), 126.6 (q,J= 32.8 Hz), 123.8 (q,J=273.4 Hz), 53.6. Anal. Calcd. (%) for C16H12F3NO5S: C, 49.62;H, 3.12; N, 3.62. Found (%): C, 49.53; H, 3.30; N, 3.51.

N-((2-Methoxycarbonylphenyl)sulfonyl)-2-chloro-4-(methylsulfonyl)benzamide (I-2): White granules, yield 79%, m.p.213～214 ℃.1H NMR (500 MHz, DMSO-d6)δ13.10 (s, 1H,CONHSO2), 8.23 (d,J= 7.4 Hz, 1H, Ph–H), 8.09 (d,J= 1.3 Hz, 1H, Ph–H), 7.98 (dd,J= 8.0, 1.4 Hz, 1H, Ph-H), 7.84 (pd,J= 7.5, 1.5 Hz, 2H, Ph-H), 7.79～7.73 (m, 2H, Ph-H), 3.87 (s,3H, COOCH3), 3.33 (s, 3H, SO2CH3).13C NMR (126 MHz,DMSO-d6)δ167.3, 164.4, 144.3, 138.7, 136.5, 134.7, 132.8,131.5, 131.4, 130.4, 129.7, 128.7, 126.3, 53.7, 43.5. Anal.Calcd. (%) for C16H14ClNO7S2: C, 44.50; H, 3.27; N, 3.24.Found (%): C, 44.39; H, 3.44; N, 3.11.

N-((2-Methoxycarbonylphenyl)sulfonyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide (I-3): White granules, yield 82%, m.p. 190～191 ℃.1H NMR (500 MHz,DMSO-d6)δ12.40 (s, 1H, CONHSO2), 8.60 (s, 1H,pyrazole-H), 8.18～8.13 (m, 1H, Ph-H), 7.82～7.75 (m, 2H,Ph–H), 7.73～7.68 (m, 1H, Ph–H), 7.09 (t,J= 53.7 Hz, 1H,CHF2), 3.95 (s, 3H, pyrazole-CH3), 3.88 (s, 3H, OCH3).13C NMR (126 MHz, DMSO-d6)δ167.3, 159.7, 146.4 (t,J= 23.9 Hz), 137.1, 135.4, 134.3, 132.6, 131.3, 131.3, 129.6, 113.5,109.8 (t,J= 235.6 Hz), 53.6, 40.1. H RMS (ESI) m/z: calcd.for C14H14F2N3O5S+374.0617, found 374.0612 [M + H]+.

N-((2-Methoxycarbonylphenyl)sulfonyl)-2-methyl-4-(trifluoromethyl)thiazole-5-carboxamide (I-4): White needle,yield 77%, m.p. 141～142 ℃.1H NMR (500 MHz, DMSO-d6)δ8.14 (d, J = 7.5 Hz, 1H, Ph-H), 7.84～7.75 (m, 2H, Ph-H),7.70 (dd,J= 7.1, 1.5 Hz, 1H, Ph-H), 3.86 (s, 3H, OCH3), 2.73(s, 3H, thiazole-CH3).13C NMR (126 MHz, DMSO-d6)δ169.2, 167.4, 158.9, 141.2, 140.9, 137.1, 134.1, 132.7, 131.3,131.1, 129.5, 120.4 (q,J= 272.2 Hz), 53.5, 19.2. Anal. Calcd.(%) for C14H11F3N2O5S2: C, 41.18; H, 2.72; N, 6.86. Found(%): C, 41.03; H, 3.02; N, 6.71.

N-((4-Acetamidophenyl)sulfonyl)-2-(trifluoromethyl)benzamide (I-6): White granules, yield 81%, m.p. 234～236 ℃.1H NMR (500 MHz, DMSO-d6)δ12.72 (s, 1H, CONHSO2),10.42 (s, 1H, CONH), 7.96～7.90 (m, 2H, Ph–H), 7.87～7.82(m, 2H, Ph–H), 7.81～7.68 (m, 3H, Ph–H), 7.57 (d,J= 7.4 Hz, 1H, Ph–H), 2.12 (s, 3H, COCH3).13C NMR (126 MHz,DMSO-d6)δ169.7, 165.9, 144.5, 133.6, 133.1, 132.6, 131.5,129.6, 128.9, 127.0 (q,J= 5.0 Hz), 126.3 (q,J= 31.5 Hz),123.7 (q,J= 274.7 Hz), 118.8, 24.7. HRMS (ESI) m/z: calcd.for C16H14F3N2O4S+387.0621, found 387.0619 [M + H]+.

N-((4-Acetamidophenyl)sulfonyl)-2-chloro-4-(methylsulfonyl)benzamide (I-7): White granules, yield 75%, m.p.256～258 ℃.1H NMR (500 MHz, DMSO-d6)δ12.89 (s, 1H,CONHSO2), 10.43 (s, 1H, CONH), 8.06 (d,J= 1.5 Hz, 1H,Ph–H), 7.98～7.91 (m, 3H, Ph–H), 7.85 (d,J= 8.9 Hz, 2H,Ph-H), 7.74 (d,J= 8.0 Hz, 1H, Ph–H), 3.32 (s, 3H, SO2CH3),2.12 (s, 3H, COCH3).13C NMR (126 MHz, DMSO-d6)δ169.7, 164.3, 144.7, 144.2, 138.9, 132.5, 131.3, 130.4, 129.6,128.6, 126.3, 118.9, 43.5, 24.7. Anal. Calcd. (%) for C16H15ClN2O6S2: C, 44.60; H, 3.51; N, 6.51. Found (%): C,44.52; H, 3.72; N, 6.39.

N-((4-Acetamidophenyl)sulfonyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide (I-8): White needle, yield 83%, decomposed at 228 ℃.1H NMR (500 MHz, DMSO-d6)δ12.26 (s, 1H, CONHSO2), 10.39 (s, 1H, CONH), 8.53 (s, 1H,pyrazole-H), 7.92 (d,J= 8.8 Hz, 2H, Ph–H), 7.81 (d,J= 8.8 Hz, 2H, Ph–H), 7.11 (t,J= 53.8 Hz, 1H, CHF2), 3.93 (s, 3H,pyrazole-CH3), 2.10 (s, 3H, COCH3).13C NMR (126 MHz,DMSO-d6)δ169.6, 159.7, 146.3 (t,J= 23.9 Hz), 144.4, 135.4,133.2, 129.5, 118.9, 113.6, 109.8 (t,J= 235.6 Hz), 24.6. Anal.Calcd. (%) for C14H14F2N4O4S: C, 45.16; H, 3.79; N, 15.05.Found (%): C, 45.03; H, 3.95; N, 14.91.

N-((4-Acetamidophenyl)sulfonyl)-2-methyl-4-(trifluoromethyl)thiazole-5-carboxamide (I-9): White granules, yield 63%,m.p. 215～216 ℃.1H NMR (500 MHz, DMSO-d6)δ10.41 (s,1H, CONH), 7.90 (d,J= 8.9 Hz, 2H, Ph-H), 7.82 (d,J= 8.9 Hz, 2H, Ph–H), 2.73 (s, 3H, thiazole-CH3), 2.11 (s, 3H,COCH3).13C NMR (126 MHz, DMSO-d6)δ169.7, 169.5,158.4, 144.6, 140.9 (q,J= 36.5 Hz), 132.5, 132.3, 129.6,120.3 (q,J= 272.2 Hz), 118.9, 24.6, 19.2. HRMS (ESI) m/z:calcd. for C14H13F3N3O4S2+408.0294, found 408.0291 [M +H]+.

N-((3-(Dimethylcarbamoyl)pyridin-2-yl)sulfonyl)-2-(trifluoromethyl)benzamide (I-11): White needle, yield 71%, m.p.190～192 ℃.1H NMR (500 MHz, DMSO-d6)δ13.15 (s, 1H,CONHSO2), 8.80 (dd,J= 4.6, 1.4 Hz, 1H, pyridine-H), 8.04(dd,J= 7.8, 1.4 Hz, 1H, pyridine-H), 7.87～7.79 (m, 3H,Ph–H and pyridine-H), 7.75 (dd,J= 12.4, 7.6 Hz, 2H, Ph–H),3.02 (s, 3H, CH3), 2.87 (s, 3H, CH3).13C NMR (126 MHz,DMSO-d6)δ166.9, 166.1, 151.3, 150.0, 137.6, 133.6, 133.1(q,J= 1.3 Hz), 133.0, 131.8, 129.4, 128.3, 127.1 (q,J= 5.0 Hz), 126.6 (q,J= 32.8 Hz), 123.7 (q,J= 274.7 Hz), 38.7,34.9. Anal. Calcd. (%) for C16H14F3N3O4S: C, 47.88; H, 3.52;N, 10.47. Found (%): C, 47.75; H, 3.79; N, 10.33.

N-((3-(Dimethylcarbamoyl)pyridin-2-yl)sulfonyl)-2-chlor-4-(methylsulfonyl)benzamide (I-12): White needle, yield 69%,m.p.: 231～232 ℃.1H NMR (500 MHz, DMSO-d6)δ13.08 (s,1H, CONHSO2), 8.81 (dd,J= 4.6, 1.4 Hz, 1H, pyridine-H),8.11 (s, 1H, Ph-H), 8.06 (dd,J= 7.8, 1.3 Hz, 1H, pyridine-H),8.00 (dd,J= 8.0, 1.5 Hz, 1H, Ph–H), 7.85～7.80 (m, 2H,pyridine-H and Ph-H), 3.35 (s, 3H, SO2CH3), 3.02 (s, 3H,CH3), 2.87 (s, 3H, CH3).13C NMR (126 MHz, DMSO-d6)δ166.1, 165.5, 151.2, 150.1, 144.4, 138.4, 137.7, 133.6, 131.5,130.7, 128.8, 128.5, 126.3, 43.5, 38.7, 34.9. HRMS (ESI) m/z:calcd. for C16H17ClN3O6S2+446.0242, found 446.0240 [M +H]+.

N-((3-(Dimethylcarbamoyl)pyridin-2-yl)sulfonyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide (I-13):Transparent needle, yield 72%, m.p. 200～201 ℃.1H NMR(500 MHz, DMSO-d6)δ12.63 (s, 1H, CONHSO2), 8.70 (dd,J= 4.6, 1.3 Hz, 1H, pyridine-H), 8.61 (s, 1H, pyrazole-H), 8.01(dd,J= 7.8, 1.3 Hz, 1H, pyridine-H), 7.76 (dd, J = 7.8, 4.7 Hz,1H, pyridine-H), 7.03 (t,J= 53.7 Hz, 1H, CHF2), 3.96 (s, 3H,pyrazole-CH3), 3.00 (s, 3H, CH3), 2.87 (s, 3H, CH3).13C NMR (126 MHz, DMSO-d6)δ166.2, 160.7, 151.7, 149.9,146.3 (t,J= 235.6 Hz), 137.6, 135.6, 133.2, 128.2, 113.4,109.7 (t,J= 235.6 Hz), 40.1, 38.7, 34.8. HRMS (ESI) m/z:calcd. for C14H16F2N5O4S+388.0886, found 388.0881 [M +H]+.

N-((3-(Dimethylcarbamoyl)pyridin-2-yl)sulfonyl)-2-methyl-4-(trifluoromethyl)thiazole-5-carboxamide (I-14): White granules, yield 68%, m.p. 193～195 ℃.1H NMR (500 MHz,DMSO-d6)δ8.78～8.70 (m, 1H, pyridine-H), 8.07～7.98 (m,1H, pyridine-H), 7.82～7.74 (m, 1H, pyridine-H), 3.00 (s, 3H,CH3), 2.84 (s, 3H, CH3), 2.75 (s, 3H, thiazole-H).13C NMR(126 MHz, DMSO-d6)δ169.6, 166.1, 159.7, 151.6, 149.8,141.2, 137.6, 133.3, 132.4, 128.3, 120.3 (q,J= 272.2 Hz),38.7, 34.8, 19.3. HRMS (ESI) m/z: calcd for C14H14F3N4O4S2+423.0403, found 423.0401 [M + H]+.

2. 2. 2 General synthetic procedure for the target compounds I-5, I-10 and I-15

N-((2-Methoxycarbonylphenyl)sulfonyl)-3,4-dichloroisothiazole-5-carboxamide (I-5) was prepared according to the following method. A solution of 3,4-dichloroisothiazole-5-carboxylic acid (0.40 g, 2.0 mmol) and 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU,0.78 g, 2.4 mmol) in N,N-dimethylformamide (10 mL) was stirred for 1 h at 40 ℃, followed by the addition of methyl 2-sulfamoylbenzoate (0.47 g, 2.2 mmol) and N,N-diisopropylethylamine (DIEA, 0.57 g, 4.4 mmol). The mixture was reacted for 8 h at 40 ℃, and the progress was monitored by TLC. After completion, the reaction was poured into the dilute hydrochloric acid aqueous solution. The resulting precipitate was filtered to provide the product, which was purified by dissolving in potassium carbonate aqueous solution, filtration and acidizing with the dilute hydrochloric acid aqueous solution to produce the white pure precipitate,yield 47%.

N-((2-Methoxycarbonylphenyl)sulfonyl)-3,4-dichloroisothiazole-5-carboxamide (I-5): White granules, yield 47%, m.p.135～136 ℃.1H NMR (500 MHz, DMSO-d6)δ8.07 (d,J=7.7 Hz, 1H, Ph–H), 7.66～7.58 (m, 2H, Ph–H), 7.51～7.45(m, 1H, Ph–H), 3.77 (s, 3H, COOCH3).13C NMR (126 MHz,DMSO-d6)δ168.5, 159.9, 159.5, 148.0, 141.2, 132.6, 131.8,130.2, 130.1, 128.3, 120.8, 52.9. Anal. Calcd. (%) for C12H8Cl2N2O5S2: C, 36.47; H, 2.04; N, 7.09. Found (%): C,36.40; H, 2.25; N, 6.93.

N-((4-Acetamidophenyl)sulfonyl)-3,4-dichloroisothiazole-5-carboxamide (I-10): White needle, yield 42%, decomposed at 209 ℃.1H NMR (500 MHz, DMSO-d6)δ10.30 (s, 1H,CONH), 7.90～7.84 (m, 2H, Ph–H), 7.78～7.72 (m, 2H,Ph–H), 2.09 (s, 3H, COCH3).13C NMR (126 MHz, DMSO-d6)δ169.4, 158.5, 157.0, 147.9, 143.6, 135.1, 129.3, 121.7, 118.7,24.6. HRMS (ESI) m/z: calcd. for C12H10Cl2N3O4S2+393.9484, found 393.9482 [M + H]+.

N-((3-(Dimethylcarbamoyl)pyridin-2-yl)sulfonyl)-3,4-dichloroisothiazole-5-carboxamide (I-15): White granular, yield 41%, m.p. 219～220 ℃.1H NMR (500 MHz, DMSO-d6)δ8.72 ～8.68 (m, 1H, pyridine-H), 7.93 ～7.88 (m, 1H,pyridine-H), 7.71～7.67 (m, 1H, pyridine-H), 3.01 (s, 3H,CH3), 2.89 (s, 3H, CH3).13C NMR (126 MHz, DMSO-d6)δ167.0, 160.1, 158.3, 154.6, 149.2, 148.1, 137.3, 132.4, 126.7,121.3, 38.8, 34.8. HRMS (ESI) m/z: calcd. for C12H11Cl2N4O4S2+408.9593, found 408.9589 [M + H]+.

2. 3 X-ray crystal structure determination

The crystals of the target compounds I-8 and I-9 were cultivated from a mixed solvent of methanol, dichloromethane andn-hexane, respectively. All measurements were made on a Bruker D8 Venture diffractometer with Mo-Kαradiation (λ=0.71073 Å). The crystal data of compound I-8 were collected at 296.15 K and the colorless crystal is of triclinic system,space groupP21/nwitha= 7.9151(10),b= 8.5637(11),c=12.2022(15) Å,α= 87.740(2)º,β= 86.865(2)º,γ= 77.869(2)º,V= 807.09(18) Å3,Z= 2,F(000) = 384, density (calculated) =1.532 g/cm3, and linear absorption coefficient 0.251 mm-1. All of the non-H atoms were refined anisotropically by full-matrix least-squares to give the finalR= 0.0408 andwR=0.1068 (w= 1/[σ2(Fo2) + (0.0547P)2+ 0.4910P], whereP=(Fo2+ 2Fc2)/3) with (Δ/σ)max= 0.000 andS= 1.070 by using the SHELXL program. The crystal data of compound I-9 were collected at 298 K and the colorless crystal is of triclinic system, space groupP21/nwitha= 8.4911(8),b= 8.6053(9),c= 14.5808(15) Å,α= 80.745(2)º,β= 77.1190(10)º,γ=74.6030(10)º,V= 995.44(17) Å3,Z= 2,F(000) = 416, density(calculated) = 1.359 g/cm3, and linear absorption coefficient 0.317 mm-1. All of the non-H atoms were refined anisotropically by full-matrix least-squares to give the finalR= 0.0567 andwR= 0.1779 (w= 1/[σ2(Fo2) + (0.2000P)2],whereP= (Fo2+ 2Fc2)/3) with (Δ/σ)max= 0.001 andS= 0.723 by using the SHELXL program. The crystal structures were solved by direct methods with SHELXS-2014/6 program.

2. 4 Biological activity screening

2. 4. 1 Fungicidal activity

2. 4. 2 Nematicidal activity

The stock solution with a concentration of 100 μgmL-1was prepared by dissolving the target compounds (5.0 mg) in dimethyl sulfoxide and diluting with sterilized water, and then 50 μL of the test solution was introduced into the wells of 24-well tissue culture plates. In each well, 50 μL of the third-stage juvenile suspension ofBursaphelenchus xylophiluswas added, and the final concentration of nematodes was approximately 50 juveniles per 100 μL of water. The plates were covered and maintained at 25 ± 1 ℃, and each treatment was replicated three times. Nematode mortality was observed under a stereomicroscope after 24 h, and fluopyram and avermectin were used as the positive controls.

3 RESULTS AND DISCUSSION

3. 1 Synthetic chemistry

Herein, the target compounds I-1～I-15 were synthesized according to the procedures in Scheme 1. Firstly, EDCI and DMAP were adopted as condensing agents to prepare the target compounds I-1 ～I-4, I-6 ～I-9 and I-11 ～I-14.Subsequently, considering the low reactivity of 3,4-dichloroisothiazole-5-carboxylic acid, the target compounds I-5, I-10 and I-15 were synthesized by using the stronger condensing agents TBTU and DIEA. Finally, fifteen novel N-sulfonyl aromatic amide derivatives were identified and characterized by1H-NMR,13C-NMR, EA and HRMS. In addition, the polarity of the target compounds was high so that it could only use dichloromethane and methanol as eluent for column chromatography to purify the products. For the purification methods of the target compounds, it would be more convenient to be dissolved in potassium carbonate aqueous solution, filtered and acidified with dilute hydrochloric acid to produce precipitation. On the other hand, column chromatography was not recommended due to wasting time and solvents.

Scheme 1. Synthetic route for the target compounds

3. 2 Crystal structures and packing

The crystal structures and packing of the target compounds I-8 and I-9 are shown in Fig. 3, respectively. The selected bond lengths and bond angles are listed in Table 1, and the dihedral angles in Table 2. From the data, the sum of bond angles O(4)–C(13)–N(4), O(4)–C(13)–C(14) and N(4)–C(13)–C(14) in compound I-8 is 360º, indicating thesp2hybridization state of atom C(13). Similarly, the atoms C(1) in I-8 and I-9 and C(13) in I-9 also adoptsp2hybridization state. In compound I-8, the bond angles of O(2)–S(1)–C(7), O(2)–S(1)–N(3), O(2)–S(1)–O(3),O(3)–S(1)–C(7), O(3)–S(1)–N(3) and C(7)–S(1)–N(3) are 109.56(10)°, 108.49(10)°, 119.29(10)°, 108.26(10)°,103.54(10)° and 106.93(10)°, respectively, revealing that the atom S(1) is at the center of a tetrahedron. On this basis, the entire molecular configuration forms an "L" shape due to the planar structures of benzene ring, pyrazole ring and amide bond (O=C–N). Likewise, the entire molecular configuration of compound I-9 also forms an "L" shape. However, due to the difference in molecular structure, the configuration of the amide bonds in crystals I-8 and I-9 is completely opposite.The torsion angles of O(1)–C(1)–N(3)–H(3) and O(4)–C(13)–N(4)–H(4) in compound I-8, and O(1)–C(1)–N(2)–H(2) and O(4)–C(13)–N(3)–H(3) in compound I-9 are –130.4(2)°, –174.2(2)°, –169.7(2)° and 176.8(8)°, respectively, implying that the amide bond O(1)–C(1)–N(2)–H(2) is apparently non-planar. In addition,the dihedral angles between the amide plane(O(1)–C(1)–N(3)) and pyrazole ring and between the amide plane (O(1)–C(1)–N(2)) and thiazole ring are 16.95(0.14)°and 65.11(0.19)°, respectively, which indicates that a weak conjugation effect maybe exist between the amide plane(O(1)–C(1)–N(3)) and pyrazole ring. Therefore, under the combined influence of conjugation and induction effects, the bond lengths of O(1)=C(1) (1.210(3) Å) and O(4)=C(13)(1.223(3) Å) in compound I-8 are longer than those correspondingly in compound I-9. At the same time, owing to the direct connection to the sulfonyl group and pyrazole or thiazole ring, the corresponding amide bond length of O(1)=C(1) (1.210(3) Å for I-8 and 1.200(4) Å for I-9) is shorter than that of O(4)=C(13) (1.223(3) Å for I-8 and 1.218(4) Å for I-9). From Table 2, the planes between amide bond (O(4)–C(13)–N(4)) and benzene ring in I-8, between amide bond (O(1)–C(1)–N(3)) and pyrazole ring in I-8, and between amide bond (O(4)–C(13)–N(3)) and benzene ring in I-9, are approximately coplanar. On the other hand, the planes among the amide bonds O(1)–C(1)–N(2) and O(4)–C(13)–N(3) and between amide bond (O(1)–C(1)–N(2))and benzene ring in I-9 are nearly vertical with the dihedral angles of 86.84(0.11)° and 87.99(0.15)°, respectively.Furthermore, from the crystal configurations of compounds I-8 and I-9, it could be found that there may be an electronic repulsion between the trifluoromethyl group and the carbonyl oxygen atom in compound I-9, while the presence of hydrogen atom in the difluoromethyl group reduced this repulsion effect. Based on the above reasons, the dihedral angle between the amide bond (O(1)–C(1)–N(3)) and the pyrazole ring in compound I-8 is smaller than that between the amide bond (O(1)–C(1)–N(2)) and the thiazole ring in I-9,with the corresponding dihedral angles of 16.95(0.14)° and 65.11(0.19)°, respectively (Fig. 3a and 3b). From the crystal packing,π-πinteractions occur between the benzene rings,between the pyrazole rings and between the thiazole rings of the adjacent molecules, thus strengthening the integration of the crystal molecules (Figs. 3c and 3d).

Fig. 3. Crystal structures of I-8 (a), I-9 (b), and crystal packing of I-8 (c), I-9 (d)

Table 1. Selected Bond Lengths (Å) and Bond Angles (°) for the Target Compounds I-8 and I-9

Table 2. Selected Dihedral Angles (°) for the Target Compounds I-8 and I-9

3. 3 Biological activity

The nematicidal activity of the target compounds againstBursaphelenchus xylophilus, with fluopyram and avermectin as the positive controls, was first screened at the test concentration of 50. The results showed that the mortality rates of the positive controls were 100%, while the corresponding mortality rates of the target compounds were less than 30%. Combined with the structure-activity relationships obtained in the previous work, theN-sulfonyl amide directly connected to the aromatic rings was unbeneficial to the nematicidal activity, which may be related to the strong polarity of the target compounds. Subsequently,the fungicidal activity of the target compounds was evaluated and the results are displayed in Table 3. From the data,compared with the positive controls, the target compounds exhibited weak fungicidal activity. From the structural characteristics, there was no obvious regularity among the fungicidal activities of the target compounds. Interestingly,compound I-5 showed good fungicidal activity againstColletotrichum capsiciwith the inhibition rate of 61.7%. In a given category, compounds I-6 ～I-10 exhibited higher inhibition rates againstGibberella zeaethan other target compounds in the preliminary activity screening. In addition,compounds I-11 and I-13～I-15 displayed better fungicidal activity againstAlternaria sp.than other target compounds.

Table 3. Nematicidal and Fungicidal Activities of the Target Compounds at 50-1

Table 3. Nematicidal and Fungicidal Activities of the Target Compounds at 50-1

GZ, Gibberella zeae; RS, Rhizoctonia solani; PP, Physalospora piricola; AK,Alternaria kikuchiana Tanaka; CC, Colletotrichum capsici; AS, Alternaria sp

Compounds Mortality of B. xylophilus (%)Fungicidal inhibition rate (%)GZ RS PP AK CC AS I-1 21.3 ± 1.37 18.4 ± 0.47 12.9 ± 0.32 13.3± 0.86 8.7 ± 0.39 15.4 ± 0.62 8.9 ± 0.90 I-2 12.4 ± 0.88 20.1 ± 0.26 11.3 ± 0.81 12.4 ± 0.29 10.0 ± 0.52 8.5 ± 0.29 17.2 ± 0.43 I-3 8.9 ± 0.67 21.3 ± 0.37 5.8 ± 0.39 36.6 ± 0.41 7.8 ± 0.63 11.1 ± 0.24 11.6 ± 0.41 I-4 13.3 ± 1.01 8.9 ± 0.71 12.7 ± 0.93 8.5 ± 0.40 9.4 ± 0.86 19.5 ± 0.62 16.7 ± 0.30 I-5 17.8 ± 0.76 17.9 ± 0.78 11.6 ± 0.22 19.9 ± 0.59 9.3 ± 0.48 61.7 ± 0.58 8.1 ± 0.43 I-6 19.4 ± 1.11 30.1 ± 0.42 10.9 ± 0.98 6.2 ± 0.29 6.2 ± 0.24 4.1 ± 0.24 2.9 ± 0.55 I-7 25.8 ±1.34 26.7 ± 0.46 5.4 ± 0.66 3.5 ± 0.63 10.8 ± 0.58 5.0 ± 0.41 3.1 ± 0.70 I-8 14.6 ± 0.93 22.0 ± 0.21 9.2 ± 0.98 7.8 ± 0.71 9.8 ± 0.53 9.7 ± 0.33 6.2 ± 0.60 I-9 5.6 ± 0.55 32.1 ± 0.73 6.7 ± 0.53 5.4 ± 0.54 11.5 ± 0.75 9.0 ± 0.29 13.0 ± 0.49 I-10 23.2 ± 1.42 20.1 ± 1.29 4.7 ± 0.39 10.6 ± 0.71 9.7 ± 0.48 9.2 ± 0.51 2.4 ± 0.49 I-11 11.7 ± 0.79 16.5 ± 0.70 3.0 ± 0.59 5.6 ± 0.66 13.0 ± 0.29 12.6 ± 0.75 29.8 ± 0.85 I-12 15.4 ± 0.92 15.8 ± 0.52 11.6 ± 0.78 4.3 ± 0.52 12.7 ± 0.82 15.7 ± 0.62 6.7 ± 0.25 I-13 10.1 ± 0.37 8.6 ± 0.47 8.4 ± 0.55 22.1 ± 0.90 6.3 ± 0.48 20.6 ± 0.82 20.6 ± 0.65 I-14 18.7 ± 0.78 13.4 ± 0.95 5.6 ± 0.50 3.9 ± 0.24 10.8 ± 0.41 16.7 ± 0.58 24.3 ± 1.20 I-15 13.4 ± 0.66 17.1 ± 0.56 11.8 ± 0.27 12.2 ± 0.63 7.3 ± 0.29 3.6 ± 0.29 19.6 ± 0.90 Carbendazim -- 100 100 100 53.6 ± 0.44 100 19.7 ± 0.52 Fluopyram 100 92.3 ± 0.23 54.2 ± 0.47 56.9 ± 0.33 97.3 ± 0.53 50.5 ± 0.55 98.8 ± 0.66 Avermectin 100 -- -- -- -- -- --

4 CONCLUSION

In summary, fifteen novelN-sulfonyl aromatic amide derivatives were designed and synthesized, and their structures were characterized by1H- and13C-NMR, EA and HRMS. The crystal structures of compounds I-8 and I-9 were obtained from X-ray diffraction, and the corresponding crystal configurations were discussed. The preliminary bioassay results indicated that the target compounds showed weak namaticidal activity, while compound I-5 displayed good fungicidal activity againstColletotrichum capsiciwith the inhibition rate of 61.7%.