N-Nitrourea Derivatives as Novel Potential Fungicides against Rhizoctonia solani: Synthesis, Antifungal Activities, and 3D-QSAR

Authors


Corresponding author: Changshui Chen, caoxiufang@mail.hzau.edu.cn

Abstract

A series of N-nitrourea derivatives bearing various aryl substituents were conveniently obtained via three steps including nitration, carbamic chlorination, and aminolysis reactions. The structures of all newly synthesized compounds were characterized and confirmed by IR, 1H-NMR, MS, and elemental analysis. The preliminary bioassays indicate that five compounds possess sufficient fungicidal activity against Rhizoctonia solani. Structure–activity relationship (SAR) is also discussed based on the experimental data, and the further quantitative structure–activity relationship (QSAR) was analyzed using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA).

Rice sheath blight caused by Rhizoctonia solani is one of the most destructive rice diseases worldwide and severely impairs both rice yield and quality (1). Under conditions favorable for disease development, rice grain yield losses, ranging from 4% to 50%, have been attributed to sheath blight (2). In Japan, this disease causes a yield loss of as high as 20% and affects about 120 000–190 000 ha. In the United States, a yield loss of 50% is reported when susceptible cultivars are planted (3). In China, sheath blight disease affects about 15–20 million hectares and causes a yield loss of 6 million tons of rice grains per year (4). Therefore, the research on novel inhibitors controlling the Rhizoctonia solani becomes active, necessary, and meaningful.

Nowadays, urea derivatives have occupied a pivotal position in pesticide chemistry because of their significant activities (5–11), including herbicidal, antimicrobial, insecticidal activities, and so on. Many studies have proved that modification of both sides of carbamide bridge’s amines is an effective way to obtain new analogues with higher activity. On the other hand, N-nitro-substituted anilines displayed broad-spectrum biological activities including herbicidal properties (12), antifungal effects (13), and plant growth regulating activities (14). Keeping these considerations in mind, we proposed that the urea derivatives bearing a new group nitro in the NH-CO-NH bridge should display some interesting biological activities.

As a continuation of our ongoing project aimed, we report herein the detailed synthetic procedures of series of N-nitrourea derivatives and bioassay results, and the further quantitative structure–activity relationships of these synthesized compounds were also analyzed using comparative molecular field analysis (CoMFA) (15) and comparative molecular similarity indices analysis (CoMSIA) (16,17). Fortunately, some compounds with promising fungicidal activities were identified.

Experimental Section

Instrumentation and chemicals

All reagents were commercially available, and all solvents and liquid reagents were dried by standard methods and distilled before use. Melting points were determined with a digital melting point apparatus and are uncorrected. IR spectra were recorded on a Thermo Nicolet FT-IR Avatar 330 instrument. 1H-NMR spectra were measured on a Bruker AM spectrometer (Bruker, Fallanden, Switzerland) with tetramethylsilane as internal standard and DMSO-d6 as solvent. Elemental analysis was performed on a Vario EL III Elemental analysis instrument (Elementar Analysensysteme GmbH, Hanau, Germany). The progress of the reactions was monitored by TLC on silica gel plates visualized with UV light.

General procedure for the preparation of target compounds 4–41

Preparation of compound 4–41: Fuming nitric acid (16 mL) was slowly added dropwise to the stirred acetic anhydride (30 mL) for 30 min at 10–12 °C and kept stirring for 1 h. The formed crude product of acetyl nitrate 1 would be added dropwise to a solution of 2,4,6-trichloroaniline (50 g) in dry ethanoic acid (300 mL) and acetic anhydride (10 mL) for 1 h at 14 °C. The reaction mixture was stirred for another 1 h and then poured into ice water (2 L).The precipitate 2 was filtered and washed with water (1 L), which was recrystallized from ethanol and dried in vacuo. Precipitate 2 (10 mmol) with 2 mL triethylamine was added dropwise to the BTC (3.3 mmol) toluene solution. The mixture was stirred at −5 °C for 1 h and then heated to 50 °C and kept reacting for 2 h. The intermediate 3 was formed and without isolated. After quenching the unreacted phosgene with dry nitrogen, a series of substituted anilines (The structure of various anilines are shown in Table 1) with 2 mL triethylamine were added dropwise to the unseparated product 3, churned at 50–80 °C for 1–10 h, and then cooled to room temperature. The respective ureas 4–41 were precipitated, filtered, and washed with toluene, excess water, and acetone. Crude products were further purified by recrystallization (DMF/acetone).

Table 1.   Structures and biological activities of the compounds used in training and test sets
CompoundsArYeild (%)mp (°C)IC50 (μg/mL)
  1. aTest set compounds mp (melting point, °C).

 4aPhenyl63.7229–230448
 54-CH3Ph78.7232–233220
 63-CH3Ph83.4227–228193
 72-OCH3Ph70.6235–237567
 84-NO2Ph48.4286–288106
 92-NO2Ph46.1273–274149
104-OCH3Ph77.3245–246219
112-CH3Ph86.8241–243323
124-BrPh59.3244–245121
134-FPh69.7223–225170
141-Naphthyl54.9247–248227
152,6-di-CH3Ph73.7252–253978
164-OC2H5Ph57.1267–269239
172-OC2H5Ph68.2238–239287
183-BrPh53.6258–260119
193-Cl-4-FPh50.1242–245133
202,4-di-BrPh50.4241–24293
21a2,4-di-FPh62.6238–239104
223-F-4-CH3Ph76.6245–246107
233-Cl-4-CH3Ph72.5241–24272
243,4-di-CH3Ph76.8242–24484
253-NO2-4-CH3Ph59.1250–251132
263,4-di-OCH3Ph50.2237–238105
272-FPh69.4233–23444
28a3-FPh70.1231–23298
29a3,5-di-CH3Ph82.4242–24459
303,5-di-ClPh51.7260–26188
31a3-CH3-5-ClPh72.6259–261100
322,4-di-ClPh65.6236–23857
332-CH3-3-ClPh72.5246–24866
34a2,4-di-CH3Ph78.1249–251189
352,5-di-CH3Ph75.5236–238125
36a2,3-di-CH3Ph74.2245–24675
372,6-di-FPh66.7243–24429
384-ClPh58.5278–27930
393-ClPh47.8239–24169
40a2-ClPh52.6249–25055
412-NO2-4-ClPh54.5283–28532

N-nitro-N′-phenyl-N-(2,4,6-trichlorophenyl)urea (4): Ammonolysis at 50 °C for 4 h. Yield 63.7%, m.p. 229–230 °C; IR (KBr)/cm: 3267 (N-H), 3066 (Ar-H), 1646 (C=O), 1257 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.98 (s, 1H, NH), 7.76 (s, 2H, ArH), 7.45 (d, = 8.0 Hz, 2H, ArH), 7.29 (d, = 7.6 Hz, 2H, ArH), 6.99 (t, J = 7.6, 6.8 Hz, 1H, ArH). Anal. Calcd for C13H8Cl3N3O3: C, 43.30; H, 2.24; N, 11.65; Found: C, 43.23; H, 2.12; N, 11.80.

N′-(4-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (5): Ammonolysis at 50 °C for 1 h. Yield 78.7%, m.p. 232–233 °C; IR (KBr)/cm: 3280 (N-H), 3079 (Ar-H), 2919 (C-H), 1654 (C=O), 1283 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.85 (s, 1H, NH), 7.75 (s, 2H, ArH), 7.32 (d, J = 6.4 Hz, 2H, ArH), 7.07(d, J = 6.8 Hz, 2H, ArH), 2.24 (s, 3H, CH3). Anal. Calcd for C14H10Cl3N3O3: C, 44.89; H, 2.69; N, 11.22; Found: C, 45.01; H, 2.64; N, 11.35.

N′-(3-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (6): Ammonolysis at 50 °C for 2 h. Yield 83.4%, m.p. 227–228 °C; IR (KBr)/cm: 3280 (N-H), 3076 (Ar-H), 2916 (C-H), 1644 (C=O), 1284 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.89 (s, 1H, NH), 7.75 (s, 2H, ArH), 7.29 (s, 1H, ArH), 7.22 (d, = 8.4 Hz, 1H, ArH), 7.15 (t, = 7.2, 6.0 Hz, 1H, ArH), 6.79 (d, = 7.6 Hz, 1H, ArH), 2.26 (s, 3H, CH3). Anal. Calcd for C14H10Cl3N3O3: C, 44.89; H, 2.69; N, 11.22; Found: C, 44.99; H, 2.63; N, 11.34.

N′-(2-methoxyphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (7): Ammonolysis at 50 °C for 4 h. Yield 70.6%, m.p. 235–237 °C; IR (KBr)/cm: 3304 (N-H), 3079 (Ar-H), 2835 (C-H), 1660 (C=O), 1220 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.93 (s, 1H, NH), 8.05 (d, = 8.4 Hz, 1H, ArH), 7.74 (s, 2H, ArH), 7.01 (d, = 7.6 Hz, 1H, ArH), 6.90–6.98 (m, 1H, ArH), 6.86 (d, = 8.4 Hz, 1H, ArH), 3.88 (s, 3H, OCH3). Anal. Calcd for : C14H10Cl3N3O4 C, 43.05; H, 2.58; N, 10.76; Found: C, 43.14; H, 2.42; N, 10.88.

N-nitro-N′-(4-nitrophenyl)-N-(2,4,6-trichlorophenyl)urea (8): Ammonolysis at 80 °C for 10 h. Yield 48.4%, m.p. 286–288 °C; IR (KBr)/cm: 3281 (N-H), 3080 (Ar-H), 1656 (C=O), 1373 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 10.04 (s, 1H, NH), 8.02 (d, = 8.4 Hz, 2H, ArH), 7.69 (d, = 8.4 Hz, 2H, ArH), 7.28 (s, 2H, ArH). Anal. Calcd for C13H7Cl3N4O5: C, 38.50; H, 1.74; N, 13.81; Found: C, 38.43; H, 1.87; N, 13.62.

N-nitro-N′-(2-nitrophenyl)-N-(2,4,6-trichlorophenyl)urea (9): Ammonolysis at 80 °C for 10 h. Yield 46.1%, m.p. 273–274 °C; IR (KBr)/cm: 3295 (N-H), 3082 (Ar-H), 1658 (C=O), 1338 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 9.42 (s, 1H, NH), 8.52 (t, = 9.6, 2.4 Hz, 1H, ArH), 8.47 (d, = 8.6 Hz, 1H, ArH), 8.35 (d, = 3.2 Hz, 1H, ArH), 8.18 (t, = 8.8, 3.6 Hz, 1H, ArH), 7.77 (s, 2H, ArH). Anal. Calcd for C13H7Cl3N4O5: C, 38.50; H, 1.74; N, 13.81; Found: C, 38.44; H, 1.89; N, 13.65.

N′-(4-methoxyphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (10): Ammonolysis at 50 °C for 4 h. Yield 77.3%, m.p. 245–246 °C; IR (KBr)/cm: 3281 (N-H), 3078 (Ar-H), 2834 (C-H), 1645 (C=O), 1250 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 1H, NH), 7.72 (s, 2H, ArH), 7.33 (d, = 8.8 Hz, 2H, ArH), 6.84 (d, = 8.8 Hz, 2H, ArH), 3.69 (s, 3H, OCH3). Anal. Calcd for C14H10Cl3N3O4: C, 43.05; H, 2.58; N, 10.76; Found: C, 43.16; H, 2.44; N, 10.90.

N′-(2-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (11): Ammonolysis at 50 °C for 2 h. Yield 86.8%, m.p. 241–243 °C; IR (KBr)/cm: 3267 (N-H), 3067 (Ar-H), 2972 (C-H), 1647 (C=O), 1286 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.87 (s, 1H, NH), 7.75 (s, 2H, ArH), 7.21 (d, = 6.4 Hz, 1H, ArH), 7.13–7.20 (m, 1H, ArH), 6.96–7.08 (m, 1H, ArH), 6.81 (d, = 8.0 Hz, 1H, ArH), 2.23 (s, 3H, CH3). Anal. Calcd for C14H10Cl3N3O3: C, 44.89; H, 2.69; N, 11.22; Found: C, 45.01; H, 2.57; N, 11.32.

N′-(4-bromophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (12): Ammonolysis at 60 °C for 5 h. Yield 59.3%, m.p. 244–245 °C; IR (KBr)/cm: 3275 (N-H), 3078 (Ar-H), 1653 (C=O), 1278 (N-NO2); 1H NMR(400 MHz, DMSO-d6): δ 9.13 (s, 1H, NH), 7.86 (d, = 7.6 Hz, 2H, ArH), 7.75 (d, = 6.4 Hz,2H, ArH), 7.43 (s, 2H, ArH). Anal. Calcd for C13H7BrCl3N3O3: C, 35.53; H, 1.61; N, 9.56; Found: C, 35.64; H, 1.73; N, 9.82.

N′-(4-fluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (13): Ammonolysis at 60 °C for 4 h. Yield 69.7%, m.p. 223–225 °C; IR (KBr)/cm: 3314 (N-H), 3081 (Ar-H), 1669 (C=O), 1270 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.30 (s, 1H, NH), 7.73 (s, 2H, ArH), 7.30–7.47 (m, 2H, ArH), 7.08 (t, = 8.8 Hz, 2H, ArH). Anal. Calcd for C13H7Cl3FN3O3: C, 41.24; H, 1.86; N, 11.10; Found: C, 41.33; H, 1.94; N, 11.25.

N′-1-naphthyl-N-nitro-N-(2,4,6-trichlorophenyl)urea (14): Ammonolysis at 70 °C for 5 h. Yield 54.9%, m.p. 247–248 °C; IR (KBr)/cm: 3269 (N-H), 3049 (Ar-H), 1646 (C=O), 1267 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.04 (s, 1H, NH), 8.15 (d, = 8.0 Hz, 1H, ArH), 7.93 (t, = 6.4, 7.6 Hz, 2H, ArH), 7.67 (s, 2H, ArH), 7.50–7.66 (m, 3H, ArH), 7.47 (t, = 7.6, 8.0 Hz, 1H, ArH). Anal. Calcd for C17H10Cl3N3O3: C, 49.72; H, 2.45; N, 10.23; Found: C, 49.66; H, 2.38; N, 10.33.

N′-(2,6-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (15): Ammonolysis at 50 °C for 1 h. Yield 73.7%, m.p. 252–253 °C; IR (KBr)/cm: 3274 (N-H), 3070 (Ar-H), 2974 (C-H), 2921 (C-H), 1646 (C=O), 1264 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.33 (s, 1H, NH), 7.72 (s, 2H, ArH), 7.06 (d, = 4.0 Hz, 2H, ArH), 6.85 (t, = 6.8, 7.2 Hz, 1H, ArH), 2.23 (s, 6H, -CH3). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.44; H, 3.22; N, 10.95.

N′-(4-ethoxyphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (16): Ammonolysis at 60 °C for 2 h. Yield 57.1%, m.p. 267–269 °C; IR (KBr)/cm: 3273 (N-H), 3076 (Ar-H), 2977 (C-H), 1642 (C=O), 1246 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 1H, NH), 7.74 (s, 2H, ArH), 7.33 (d, = 9.2 Hz, 2H, ArH), 6.84 (d, = 8.8 Hz, 2H, ArH), 3.96 (m, 2H, -CH2), 1.30 (t, = 7.2, 6.8 Hz, 3H, -CH3). Anal. Calcd for C15H12Cl3N3O4: C, 44.52; H, 2.99; N, 10.38; Found: C, 44.61; H, 3.10; N, 10.48.

N′-(2-ethoxyphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (17): Ammonolysis at 60 °C for 2 h. Yield 68.2%, m.p. 238–239 °C; IR (KBr)/cm: 3291 (N-H), 3072 (Ar-H), 2979 (C-H), 1645 (C=O), 1263 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.08 (s, 1H, NH), 8.06 (d, = 7.6 Hz, 1H, ArH), 7.76 (s, 2H, ArH), 7.01 (d, = 8.0 Hz, 1H, ArH), 6.92 (q, = 1.2, 6.4, 8.0 Hz, 1H, ArH), 6.85 (t, = 8.0, 7.2 Hz, 1H, ArH), 4.14 (q, = 6.8, 7.2, 6.8 Hz, 2H, CH2), 1.42 (t, = 6.8, 7.2 Hz, 3H, CH3). Anal. Calcd for C15H12Cl3N3O4: C, 44.52; H, 2.99; N, 10.38; Found: C, 44.64; H, 3.11; N, 10.49.

N′-(3-bromophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (18): Ammonolysis at 60 °C for 5 h. Yield 53.6%, m.p. 258–260 °C; IR (KBr) cm-1: 3277 (N-H), 3075 (Ar-H), 1641 (C=O), 1274 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.19 (s, 1H, NH), 8.35 (s, 1H, ArH), 7.78 (s, 2H, ArH), 7.34 (d, = 7.6 Hz, 1H, ArH), 7.23 (t, = 8.0 Hz, 1H, ArH), 7.15 (d, = 7.2 Hz, 1H, ArH). Anal. Calcd for C13H7BrCl3N3O3: C, 35.53; H, 1.61; N, 9.56; Found: C, 35.62; H, 1.70; N, 9.81.

N′-(3-chloro-4-fluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea(19): Ammonolysis at 70 °C for 7 h. Yield 50.1%, m.p. 242–245 °C; IR (KBr)/cm: 3309 (N-H), 3084 (Ar-H), 1650 (C=O), 1263 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.20 (s, 1H, NH), 8.38 (s, 1H, ArH), 7.77 (s, 2H, ArH), 7.33 (d, = 7.2 Hz, 2H, ArH). Anal. Calcd for C13H6Cl4FN3O3: C, 37.80; H, 1.46; N, 10.17; Found: C, 37.89; H, 1.63; N, 10.31.

N′-(2,4-dibromophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (20): Ammonolysis at 80 °C for 6 h. Yield 50.4%, m.p. 241–242 °C; IR (KBr)/cm: 3288 (N-H), 3081 (Ar-H), 1650 (C=O), 1284 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.19 (s, 1H, NH), 8.01 (s, 1H, ArH), 7.90 (d, = 6.0 Hz, 1H, ArH), 7.87 (s, 2H, ArH), 7.54 (d, = 8.8 Hz, 1H, ArH). Anal. Calcd for C13H6Br2Cl3N3O3: C, 30.12; H, 1.17; N, 8.11; Found: C, 30.23; H, 1.09; N, 8.30.

N′-(3,4-difluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (21): Ammonolysis at 50 °C for 4 h. Yield 62.6%, m.p. 238–239 °C; IR (KBr)/cm: 3271 (N-H), 3084 (Ar-H), 1650 (C=O), 1250 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.20 (s, 1H, NH), 8.34 (s, 2H, ArH), 7.74 (s, 1H, ArH), 7.60 (d, = 6.8 Hz,1H, ArH), 7.27 (d, = 6.4 Hz,1H, ArH). Anal. Calcd for C13H6Cl3F2N3O3: C, 39.37; H, 1.53; N, 10.60; Found: C, 39.53; H, 1.62; N, 10.81.

N′-(3-fluoro-4-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (22): Ammonolysis at 50 °C for 2 h. Yield 76.6%, m.p. 245–246 °C; IR (KBr)/cm: 3280 (N-H), 3076 (Ar-H), 2921 (C-H), 1655 (C=O), 1274 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.10 (s, 1H, NH), 8.28 (s, 2H, ArH), 7.76 (s, 1H, ArH), 7.73 (d, = 6.0 Hz,1H, ArH), 7.04 (d, = 6.4 Hz, 1H, ArH), 2.16 (s, 3H, CH3). Anal. Calcd for C14H9Cl3FN3O3: C, 42.83; H, 2.31; N, 10.70; Found: C, 42.93; H, 2.18; N, 10.84.

N′-(3-chloro-4-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (23): Ammonolysis at 70 °C for 3 h. Yield 72.5%, m.p. 241–242 °C; IR (KBr)/cm: 3279 (N-H), 3080 (Ar-H), 2914 (C-H), 1652 (C=O), 1283 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.32 (s, 1H, NH), 8.55 (s, 2H, ArH), 8.00 (s, 1H, ArH), 7.91 (d, = 6.8 Hz,1H, ArH), 7.46 (d, = 6.0 Hz, 1H, ArH), 2.49 (s, 3H, CH3). Anal. Calcd for C14H9Cl4N3O3: C, 41.11; H, 2.22; N, 10.27; Found: C, 41.24; H, 2.12; N, 10.42.

N′-(3,4-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (24): Ammonolysis at 50 °C for 2 h. Yield 76.8%, m.p. 242–244 °C; IR (KBr)/cm: 3280 (N-H), 3074 (Ar-H), 2921 (C-H), 1654 (C=O), 1267 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 1H, NH), 7.74 (s, 2H, ArH), 7.22 (s, 1H, ArH), 7.14 (d, = 5.6 Hz,1H, ArH), 7.00 (d, = 4.8 Hz, 1H, ArH), 2.17 (s, 3H, CH3), 2.15 (s, 3H, CH3). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.27; H, 3.19; N, 10.98.

N′-(4-methyl-3-nitrophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (25): Ammonolysis at 80 °C for 5 h. Yield 59.1%, m.p. 250–251 °C; IR (KBr)/cm: 3313 (N-H), 3076 (Ar-H), 2989 (C-H), 1654 (C=O), 1310 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.40 (s, 1H, NH), 8.44 (s, 2H, ArH), 7.77 (s, 1H, ArH), 7.56 (d, = 7.2 Hz,1H, ArH), 7.41 (d, = 6.8 Hz, 1H, ArH), 2.45 (s, 3H, CH3). Anal. Calcd for C14H9Cl3N4O5: C, 40.07; H, 2.16; N, 13.35; Found: C, 40.16; H,2.10; N, 13.46.

N′-(3,4-dimethoxyphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (26): Ammonolysis at 80 °C for 5 h. Yield 50.2%, m.p. 237–238 °C; IR (KBr)/cm: 3283 (N-H), 3077 (Ar-H), 2993 (C-H), 1644 (C=O), 1238 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.24 (s, 1H, NH), 8.19 (s, 2H, ArH), 7.48 (s, 1H, ArH), 7.25 (d, = 7.6 Hz,1H, ArH), 7.06 (d, = 7.2 Hz, 1H, ArH), 4.05 (s, 3H, CH3), 4.03 (s, 3H, CH3). Anal. Calcd for C15H12Cl3N3O5: C, 42.83; H, 2.88; N, 9.99; Found: C, 42.94; H,2.98; N, 10.10.

N′-(2-fluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (27): Ammonolysis at 50 °C for 3 h. Yield 69.4%, m.p. 233–234 °C; IR (KBr)/cm: 3270 (N-H), 3076 (Ar-H), 1652 (C=O), 1273 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.85 (s, 1H, NH), 8.63 (s, 2H, ArH), 8.05 (d, = 7.2 Hz, 1H, ArH), 7.14–7.29 (m, 1H, ArH), 7.0–7.14 (m, 1H, ArH), 6.98 (d, = 6.0 Hz, 1H, ArH). Anal. Calcd for C13H7Cl3FN3O3: C, 41.24; H, 1.86; N, 11.10; Found: C, 41.31; H, 1.80; N, 11.22.

N′-(3-fluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (28): Ammonolysis at 50 °C for 3 h. Yield 70.1%, m.p. 231–232 °C; IR (KBr)/cm: 3277 (N-H), 3083 (Ar-H), 1655 (C=O), 1277 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.24 (s, 1H, NH), 8.33 (s, 2H, ArH), 7.76 (s, 1H, ArH), 7.43 (d, = 6.0 Hz, 1H, ArH), 7.28 (t, = 7.6, 6.4 Hz, 1H, ArH), 7.14 (d, = 7.2 Hz, 1H, ArH). Anal. Calcd for C13H7Cl3FN3O3: C, 41.24; H, 1.86; N, 11.10; Found: C, 41.32; H, 1.82; N, 11.24.

N′-(3,5-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (29): Ammonolysis at 50 °C for 1 h. Yield 82.4%, m.p. 242–244 °C; IR (KBr)/cm: 3276 (N-H), 3077 (Ar-H), 3014 (Ar-H), 2917 (C-H), 1648 (C=O), 1278 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.75 (s, 1H, NH), 8.14 (s, 2H, ArH), 7.74 (s, 2H, ArH), 7.02 (s, 1H, ArH), 2.17 (s, 6H, CH3). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.27; H, 3.19; N, 10.98.

N′-(3,5-dichlorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (30): Ammonolysis at 80 °C for 5 h. Yield 51.7%, m.p. 260–261 °C; IR (KBr)/cm: 3275 (N-H), 3079 (Ar-H), 1649 (C=O), 1268 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.39 (s, 1H, NH), 8.53 (s, 2H, ArH), 7.78 (s, 1H, ArH), 7.56 (s, 2H, ArH). Anal. Calcd for C13H6Cl5N3O3: C, 36.36; H, 1.41; N, 9.78; Found: C, 36.44; H, 1.52; N, 9.95.

N′-(3-chloro-5-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (31): Ammonolysis at 70 °C for 3 h. Yield 72.6%, m.p. 259–261 °C; IR (KBr)/cm: 3274 (N-H), 3079 (Ar-H), 1644 (C=O), 1267 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.59 (s, 1H, NH), 7.75 (s, 2H, ArH), 7.64 (s, 1H, ArH), 7.18 (s, 2H, ArH), 2.30 (s, 3H, CH3). Anal. Calcd for C14H9Cl4N3O3: C, 41.11; H, 2.22; N, 10.27; Found: C, 41.20; H, 2.14; N, 10.42.

N′-(2,4-dichlorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (32): Ammonolysis at 80 °C for 8 h. Yield 65.6%, m.p. 236–238 °C; IR (KBr)/cm: 3283 (N-H), 3080 (Ar-H), 1658 (C=O), 1279 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.55 (s, 1H, NH), 7.74 (s, 2H, ArH), 7.56 (s, 2H, ArH), 7.05 (d, = 6.4 Hz, 1H, ArH), 6.78 (d, = 8.0 Hz, 1H, ArH); GC-MS (DMSO) m/z(%): 427(1), 282(50). Anal. Calcd for C13H6Cl5N3O3: C, 36.36; H, 1.41; N, 9.78; Found: C, 36.42; H, 1.52; N, 9.96.

N′-(3-chloro-2-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (33): Ammonolysis at 60 °C for 4 h. Yield 72.5%, m.p. 246–248 °C; IR (KBr)/cm: 3279 (N-H), 3078 (Ar-H), 1650 (C=O), 1271 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.59 (s, 1H, NH), 7.75 (s, 2H, ArH), 7.56–7.69 (m, 1H, ArH), 7.10–7.19 (m, 2H, ArH), 2.30 (s, 3H, CH3); GC-MS (DMSO) m/z(%): 407 (1), 281(57), 91(72). Anal. Calcd for C14H9Cl4N3O3: C, 41.11; H, 2.22; N, 10.27; Found: C, 41.21; H, 2.33; N, 10.43.

N′-(2,4-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (34): Ammonolysis at 50 °C for 4 h. Yield 78.1%, m.p. 249–251 °C; IR (KBr)/cm: 3280 (N-H), 3078 (Ar-H), 2919 (C-H), 1651 (C=O), 1269 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.46 (s, 1H, NH), 7.73 (s, 2H, ArH), 7.53 (d, = 6.8 Hz, 1H, ArH), 6.99 (s, 1H, ArH), 6.93 (d, = 6.0 Hz, 1H, ArH), 2.22 (s, 3H, CH3), 2.21 (s, 3H, CH3); GC-MS (DMSO) m/z(%): 387(2), 359(4), 282(63), 91(28). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.26; H, 3.22; N, 10.97.

N′-(2,5-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (35): Ammonolysis at 50 °C for 4 h. Yield 75.5%, m.p. 236–238 °C; IR (KBr)/cm: 3284 (N-H), 3077 (Ar-H), 2921 (C-H), 1648 (C=O), 1283 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.55 (s, 1H, NH), 7.74 (s, 2H, ArH), 7.57 (s, 1H, ArH), 7.05 (d, = 6.4 Hz, 1H, ArH), 6.78 (d, = 6.0 Hz, 1H, ArH), 2.22 (s, 3H, CH3), 2.20 (s, 3H, CH3); GC-MS (DMSO) m/z(%): 387(2), 281(57), 91(42). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.24; H, 3.21; N, 10.99.

N′-(2,3-dimethylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (36): Ammonolysis at 50 °C for 4 h. Yield 74.2%, m.p. 245–246 °C; IR (KBr)/cm: 3288 (N-H), 3067 (Ar-H), 2956 (C-H), 1648 (C=O), 1273 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.44 (s, 1H, NH), 7.73 (s, 2H, ArH), 7.43 (d, = 7.2 Hz, 1H, ArH), 7.02 (t, = 6.4, 6.8 Hz, 1H, ArH), 6.92 (d, = 6.4 Hz, 1H, ArH), 2.25 (s, 3H, CH3), 2.15 (s, 3H, CH3); GC-MS (DMSO) m/z(%): 387(2), 282(85), 9(25). Anal. Calcd for C15H12Cl3N3O3: C, 46.36; H, 3.11; N, 10.81; Found: C, 46.25; H, 3.22; N, 10.97.

N′-(2,6-difluorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (37): Ammonolysis at 60 °C for 5 h. Yield 66.7%, m.p. 243–244 °C; IR (KBr)/cm: 3282 (N-H), 3071 (Ar-H), 1661 (C=O), 1243 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 8.50 (s, 1H, NH), 7.74 (s, 2H, ArH), 7.22–7.35 (m, 1H, ArH), 7.04–7.20 (m, 2H, ArH); GC-MS (DMSO) m/z(%): 395(1), 282(38), 45(100). Anal. Calcd for C13H6Cl3F2N3O3: C, 39.37; H, 1.53; N, 10.60; Found: C, 39.28; H, 1.59; N, 10.81.

N′-(4-chlorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (38): Ammonolysis at 80 °C for 5 h. Yield 58.5%, m.p. 278–279 °C; IR (KBr)/cm: 3293 (N-H), 3075 (Ar-H), 1655 (C=O), 1279 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.86 (s, 1H, NH), 7.77 (s, 2H, ArH), 7.47 (d, = 8.0 Hz, 2H, ArH), 7.32 (d, = 8.0 Hz, 2H, ArH). Anal. Calcd for C13H7Cl4N3O3: C, 39.53; H, 1.79; N, 10.64; Found: C, 39.43; H, 1.88; N, 10.82.

N′-(3-chlorophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (39): Ammonolysis at 80 °C for 5 h. Yield 47.6%, m.p. 239–241 °C; IR (KBr)/cm: 3273 (N-H), 3078 (Ar-H), 1641 (C=O), 1274 (N-NO2); 1H NMR (400 MHz, DMSO-d6): δ 9.31 (s, 1H, NH), 8.42 (s, 1H, ArH), 7.76 (s, 2H, ArH), 7.67 (d, = 5.6 Hz, 1H, ArH), 7.27 (d, = 7.2 Hz, 1H, ArH), 7.00–7.08 (m, 1H, ArH). Anal. Calcd for C13H7Cl4N3O3: C, 39.53; H, 1.79; N, 10.64; Found: C, 39.42; H, 1.89; N, 10.81.

N′-(2-methylphenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (40): Ammonolysis at 80 °C for 5 h. Yield 52.6%, m.p. 249–250 °C; IR (KBr)/cm: 3273 (N-H), 3077 (Ar-H), 1653 (C=O), 1290 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 8.86 (s, 1H, NH), 7.77 (t, = 8.8, 9.6 Hz, 1H, ArH), 7.65 (s, 2H, ArH), 7.37 (d, = 8.4 Hz, 1H, ArH), 7.22 (d, = 8.8 Hz, 1H, ArH), 7.13 (d, = 4.8, 5.2 Hz, 1H, ArH). Anal. Calcd for C14H10Cl3N3O3: C, 44.89; H, 2.69; N, 11.22; Found: C, 45.01; H, 2.80; N, 11.37.

N′-(4-chloro-2-nitrophenyl)-N-nitro-N-(2,4,6-trichlorophenyl)urea (41): Ammonolysis at 80 °C for 10 h. Yield 54.5%, m.p. 283–285 °C; IR (KBr)/cm: 3314 (N-H), 3081 (Ar-H), 1669 (C=O), 1270 (N-NO2). 1H NMR (400 MHz, DMSO-d6): δ 9.65 (s, 1H, NH), 8.75 (s, 1H, ArH), 8.30 (d, = 8.8 Hz, 1H, ArH), 8.13 (d, = 2.4 Hz, 1H, ArH), 7.77 (s, 2H, ArH). Anal. Calcd for C13H6Cl4N4O5: C, 35.48; H, 1.37; N, 12.73; Found: C, 35.37; H, 1.54; N, 12.89.

Antifungal activities

The in vivo fungicidal activities of N-nitrourea derivatives were tested against Rhizoctonia solani by the modified agar cup method according to the reported method in literature (18).

Molecular modeling

The 38 target compounds were divided into a training set and a testing set as shown in Table 1. The IC50 values were converted into pIC50 (-log IC50) for use in 3D-QSAR analysis. CoMFA and CoMSIA study was performed using sybyl 7.3 molecular modeling software (19). The 3D structures of all compounds were sketched by the Build/Edit module of SYBYL7.3. Partial atomic charges were calculated by the Gasteiger–Huckel method, and energy minimizations were performed by using the Tripos force and the Powell conjugate gradient algorithm with a convergence criterion of 0.05kcal/(mol Å) (20,21). The potent compound 41 was chosen as the template. The common substructure is displayed in Figure 1. Each compound in the training and testing sets was aligned to the template using the database alignment function because of its easy implementation and effectiveness. The aligned compounds are shown in Figure 1.

Figure 1.

 Structure of N-nitro urea derivatives: (A) General structure for title compounds; (B) 3D view of all the aligned molecules in training and test sets.

A grid that extends 4 Å units beyond the dimensions of aligned molecules was established (22). The CoMFA steric and electrostatic fields were calculated at grid points using Tripos Standard with a default energy cutoff of 30 kcal/mol. For CoMSIA, steric, electrostatic, hydrophobic, hydrogen-bond donor, and acceptor fields were evaluated using probe atom with +1 charge, radius of 1 Å, and +1 hydrophobicity on the same lattice as the CoMFA used. Each single and some possible combinations of fields were calculated. The relationship between activity data and fields of training set was analyzed by partial least squares (PLS) methods (23,24). The leave-one-out (LOO) cross-validation was performed to determine optimum number of components (N) and cross-validated coefficient q2, which indicates the consistency and prediction of models for the training set. Then, no validation was performed to derive the final PLS regression models, and the results were shown in Table 2.

Table 2.   CoMFA and CoMSIA results
FieldsLOONV
q2Nr2SEEF
  1. Note: N is the optimal number of components, NV is No-Validation, q2 is the leave-one-out (LOO) cross-validation coefficient, r2 is the non-cross-validation coefficient, SEE is the standard error of estimation, and F is the F-test value. The best models are marked in bold.

CoMFA
 Both steric and electrostatic0.77340.9590.077146.833
 Steric0.72930.9020.11779.975
 Electrostatic0.48020.7620.17943.160
CoMSIA
 Steric0.61560.8690.14325.488
 Electrostatic0.52260.8890.13230.758
 Hydrophobic0.26040.6690.21912.649
 H-bond donor0.49220.6290.22322.907
 H-bond acceptor0.35050.6590.2269.293
 Steric, electrostatic0.72060.9360.10056.051
 H-bond donor, H-bond acceptor0.49950.6940.21510.803

The external predictive ability of the models can be measured by inline image, inline image was according to the formula: inline image, where SD is the sum of the squared deviations between the biological activities of the test set compounds and mean activity of the training set compounds and PRESS is the sum of squared deviations between experimental and predicted activities of the test set compounds (25).

Results and Discussion

Synthesis

The synthetic route for target compounds 4–41 is outlined in Scheme 1. According to the reported procedures (26), 2,4,6-trichloroaniline was nitrified by acetyl nitrate 1 to give the N-nitro-N-(2, 4, 6-trichlorophenyl)amine 2 in yields of 75–86%. Then, at the presence of triethylamine as base (27), a subsequent reaction of BTC and intermediate 2 produced nitro (2,4,6-trichlorophenyl) carbamic chloride 3. Without further isolation, the key intermediate 3 reacted with the corresponding amine to afford the compounds 4–41 in the yields of 45–87%.

Figure Scheme 1:.

 Synthetic route for target compounds 4–41 and the structure of ArNH2 are shown in Table 1.

In vivo antifungal activities

Thirty-eight N-nitrourea derivatives 4–41 were synchronously tested the in vivo fungicidal activities against Rhizoctonia solani by agar cup method (18). As shown in Table 1, Compounds 20, 23, 24, 32, 33, and 39 display good activities, as the IC50 are less than 100 μg/mL. Compounds 27, 37, 38, 40, and 41 exhibit good antifungal activities with lower IC50 below 50 μg/mL.

For structure–activity relationship (SAR), the biological data obtained the various substituents on N′-benzene ring displayed different activities. For mono-substituted compounds, 27 (2-F) >40 (2-Cl) > 9 (2-NO2) > 17 (2-OC2H5) > 11 (2-CH3) > 7 (2-OCH3); 39 (3-Cl) > 28 (3-F) > 18 (3-Br) > 6 (3-CH3); 38 (4-Cl) > 8 (4-NO2) > 13 (4-F) > 10 (4-OCH3) > 5 (4-CH3) > 16 (4-OC2H5). Most of the disubstituted compounds displayed good antifungal activities. Their IC50 values are all under 150 μg/mL except compound 15 (2,6-di-CH3, 978 μg/mL) and 34 (2,4-di-CH3, 189 μg/mL). In addition, the compounds with optimal activity are 41 (2-NO2-4-Cl, 32 μg/mL) and 37 (2,6-di-F, 29 μg/mL).

Structure–activity relationships

The statistical results of the 3D-QSAR models are summarized in the Table 2, in which the best models are marked in bold. As seen, both the CoMFA (q2 = 0.773, r2 = 0.959) and CoMSIA (q2 = 0.720, r2 = 0.936) models show good prediction capability.

The predicted and residual pIC50 values for the training and testing set compounds are listed in Table 3. The relative plots of the predicted versus experimental pIC50 values for the two models are shown in Figure 2. The average residual values for the test set of two models were 0.14 and 0.16. The external testing set yields a predictive inline image of 0.662 and 0.568 for CoMFA and CoMSIA models. As seen, the values indicate that CoMFA and CoMSIA models possess a high predictive capacity, and the CoMFA model is considered more predictability with higher q2, r2, and inline image than the CoMSIA model. So we could predict that the hydrogen bond is not the key element for the activity of these inhibitors.

Table 3.   Observed and predicted activities for training and test sets’ compounds by 3D-QSAR models
CompoundsObserved pIC50CoMFA modelCoMSIA model
PredictedResidualPredictedResidual
  1. aThe selective compounds as test set compounds.

Training set
  53.663.660.003.61−0.05
  63.713.740.033.65−0.06
  73.243.280.043.23−0.01
  83.984.030.053.91−0.07
  93.833.73−0.103.860.03
 103.663.57−0.093.55−0.11
 113.493.550.063.560.07
 123.923.960.043.89−0.03
 133.763.770.013.890.13
 143.643.690.053.59−0.05
 153.012.94−0.072.98−0.03
 163.623.620.003.690.07
 173.553.53−0.023.600.05
 183.923.950.033.980.06
 193.883.86−0.023.990.11
 204.034.00−0.033.99−0.04
 223.973.970.004.050.08
 234.144.07−0.074.06−0.08
 244.084.120.044.170.09
 253.884.000.123.910.03
 263.984.020.044.020.04
 274.364.380.024.380.02
 304.054.110.064.130.08
 324.244.260.024.270.03
 334.184.10−0.083.98−0.20
 353.903.980.084.020.12
 374.544.51−0.034.48−0.06
 384.534.27−0.264.28−0.25
 394.164.160.004.230.07
 414.494.520.034.44−0.05
Test set
 4a3.353.600.253.580.23
 21a3.923.79−0.134.000.08
 28a4.104.240.144.350.25
 29a4.234.04−0.194.410.18
 31a4.004.030.034.210.21
 34a3.724.000.284.010.29
 36a4.124.160.044.06−0.06
 40a4.264.17−0.094.25−0.01
Average  0.14 0.16
Figure 2.

 Plot of the predicted versus observed pIC50 values for all the molecules based on CoMFA (q2 = 0.773, r2 = 0.959) model (A) and CoMSIA (q2 = 0.720, r2 = 0.936) model (B).

The steric and electrostatic contribution contour maps of the best models of CoMFA and CoMSIA are plotted in Figures 3 and 4. In the steric contour maps, the green contours (80% contribution) represent regions that bulky substituents would increase the inhibitory activity, while the yellow contours (20% contributions) represent regions that steric bukly group would be unfavorable. While in the electrostatic contour maps, the blue and red contours (80% and 20% contributions) signify the position where positively charged groups and negatively charged groups would be favorable, respectively.

Figure 3.

 CoMFA contour maps: (A) steric contour map; (B) electrostatic contour map.

Figure 4.

 CoMSIA contour maps: (A) steric contour map; (B) electrostatic contour map.

As shown in CoMFA steric map (Figure 3A), a bulky group in the region of the green contour on 4-position of N′-phenyl is favorable for activity. By comparing the structures and activities of 4-substituted compounds 4 (4-H), 5 (4-CH3), 8 (4-NO2), and 12 (4-Br), the activity order is: 8>12>5>4, which coincides with the model prediction. The yellow contours near 2-position suggests that the smaller substituents on this region would be advantageous. It can be proven by the compounds 7, 11, and 17 with lower activity.

In the CoMFA electrostatic contour map (Figure 3B), a red and blue contour are, respectively, distributed before and behind the N′-phenyl ring. On the 2-position, there is red contour before the ring and also blue contour behind it, which indicates that both electropositive and electronegative group here benefit activity, such as compounds 9 (2-NO2, pIC50 = 3.83), 11 (2-CH3, pIC50 = 3.49), 27 (2-F, pIC50 = 4.36), and 40 (2-Cl, pCI50 = 4.26) result better inhibitory activity than compound 4 (2-H, pIC50 = 3.35). There is a bulky blue contour near 4,5-position, which shows electropositive groups here would benefit activity. For example, compounds 8 (4-NO2), 13 (4-F), and 38 (4-Cl) possess significant inhibitory activity. And near 6-position, a red contour indicates electronegative groups are needed here. The CoMFA steric and electrostatic contour maps show that the linkers composed of small substituents on 2-position, bulky and electropositive groups on 4,5-region, electronegative groups on 6-position may increase the activity.

In Figure 4A, CoMSIA steric contour map, there is a big green contour covering all of the 2, 3, 4-position and two small yellow contours covering on the 2-region behind the ring and 6-position, respectively. So bulky groups linked to 3, 4-position of N′-phenyl ring may increase the activity, such as compounds 23 (3-Cl-4-CH3, pIC50 = 4.14), 24 (3,4-di-CH3, pIC50 = 4.08), 26 (3,4-di-OCH3, pIC50 = 3.98), 32 (2,4-di-Cl, pIC50 = 4.24), and 41 (2-NO2-4-Cl, pIC50 = 4.49). But near 2, 6-position suggests that substituents on this region would be small. It can be proven by compound 15(2, 6-di-CH3, pIC50 = 3.01) with lower activity.

Moreover, in the CoMSIA electrostatic contour map (Figure 4B), there are two bulky red contours near 2, 3-position before and behind the phenyl ring, which indicates that electronegative groups here benefits the activity, the CoMSIA steric and electrostatic contour maps indicate that linkers composed of small and electronegative groups on 2-position, bulky and electronegative substituents on 3-position, bulky groups on 4-region, small groups on 6-position may increase the activity.

Conclusions

Using a simple and convenient BTC one-pot synthetic method, we have prepared 38 N-nitrourea derivatives, and compounds 27, 37, 38, 40, and 41 exhibited excellent antifungal activities. Based on the experimental data, two best CoMFA and CoMSIA models with the cross-validated (LOO) q2 values of 0.773 and 0.72 and no validated r2 values of 0.959 and 0.936 were obtained, respectively. The testing set of compounds that gave a predictive inline image of 0.662 and 0.568 for CoMFA and CoMSIA models indicate that the two best models could be effectively used to predict the activity of new inhibitors and guide the further modification of these compounds, just as small and electronegative groups on 2-position (2-F), bulky and electronegative substituents on 3-position (3-CF3, 3-NO2), bulky and electropositive groups on 4,5-region, and small and electronegative groups on 6-position may increase the activity.

Acknowledgements

We gratefully acknowledge the support of this work by the Fundamental Research Funds for the Central Universities (2010JC001) and the National Natural Science Foundation of China (31101467).

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