General
The starting materials which include 4-(1-adamantyl)benzaldehyde was prepared according to procedure described previously and other required chemicals were purchased from different commercial sources and used without purification unless otherwise stated. The progress of reactions was monitored by using thin layer chromatography (TLC) with silica gel 60 aluminium-backed plates and the 1H NMR and 13C NMR spectra were recorded via Bruker spectrometer 400 MHz as dilute solutions in suitable deuterated solvent at 25°C. The chemical shifts were recorded on the δ-scale (ppm) using residual solvents as an internal standard (DMSO; 1H 2.50, and CHCl3; 1H 7.26,). Coupling constant were calculated in Hertz (Hz) and multiplicities were labelled as s (singlet), d (doublet), t (triplet), q (quartet), quint (quintet) and the prefixes br (broad) or app (apparent) were used. IR spectra were recorded on a Specord 2000 spectrometer. Mass spectra were taken on the AB Sciex 6500 QTAP mass spectrometer. Melting points of synthesized compounds were determined by means of a Stuart™ melting point SMP3 apparatus.
Chemistry
General procedure for synthesis of derivatives 6a-h
The anilines (1.0 mmol) was dissolved in 20 mL of DMF, and NaOH (1.2 mmol) and CS2 (1.0 mmol) were added. After reaction at room temperature for 2 h, hydrazine hydrate (3.0 mmol) was added, and the reaction was continued for 1 h. Cool to room temperature, pour the solution into crushed ice, filter with suction, and recrystallize the filter cake with ethanol to obtain intermediates 6a-h.
N-(2-Fluorophenyl)hydrazinecarbothioamide (6a)
1H NMR (400 MHz, DMSO-d6) δ 9.34 (s, 1H), 8.08 (s, 1H), 7.19 (dq, J = 22.4, 7.7 Hz, 3H); 13C NMR (100 MHz, DMSO-d6) δ 180.44, 156.88, 154.46, 127.82, 127.72, 127.13, 126.39, 126.32, 124.16, 115.56; FT-IR (KBr, cm-1): v(N-H) 3265.31, 3193.09, v(C-N) 1481.12, v(C=S) 1226.07.
N-(2-Methoxyphenyl)hydrazinecarbothioamide (6b)
1H NMR (400 MHz, DMSO-d6) δ 9.94 (s, 1H), 9.18 (s, 1H), 8.74 (s, 1H), 7.04 (s, 2H), 6.90 (s, 1H), 4.83 (s, 2H), 3.84 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 178.87, 149.87, 128.63, 124.26, 121.63, 120.16, 111.28, 56.3; FT-IR (KBr, cm-1): v(N-H) 3313.47, 3193.43, v(C-N) 1457.01, v(C=S) 1238.42.
N-(3-Fluorophenyl)hydrazinecarbothioamide (6c)
1H NMR (400 MHz, DMSO-d6) δ 9.29 (s, 1H), 7.86 (s, 1H), 7.45 (s, 1H), 7.32 (s, 1H), 6.91 (s, 1H); 13C NMR (100 MHz, DMSO-d6) δ 179.70, 141.72, 129.94, 119.24, 40.29; FT-IR (KBr, cm-1) : v(N-H) 3291.84, 3193.52, v(C-N) 1456.99, v(C=S) 1224.76.
N-(3-Methoxyphenyl)hydrazinecarbothioamide (6d)
1H NMR (400 MHz, DMSO-d6) δ 9.14 (s, 1H), 7.49 (s, 1H), 7.20 (d, J = 7.1 Hz, 2H), 6.67 (d, J = 6.2 Hz, 1H), 4.78 (s, 2H), 3.73 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 159.55, 140.90, 129.28, 115.64, 109.96, 109.21, 55.54; FT-IR (KBr, cm-1) : v(N-H) 3266.26, 3190.51, v(C-N) 1457.42, v(C=S) 1228.66.
N-Phenylhydrazinecarbothioamide (6e)
1H NMR (400 MHz, DMSO-d6) δ 9.11 (s, 1H), 7.66 (s, 2H), 7.42-7.22 (m, 2H), 7.17-7.05 (m, 1H), 4.81 (s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 180.05, 139.79, 128.52, 124.49, 123.78; FT-IR (KBr, cm-1) 3300.04, 3156.12, 1635.80, 1524.39, 1488.93, 1282.00, 1217.49, 1068.07, 971.13, 894.88, 735.19, 609.89.
N-(4-Fluorophenyl)hydrazinecarbothioamide (6f)
1H NMR (400 MHz, DMSO-d6) δ 9.72 (s, 1H), 9.12 (s, 1H), 7.55 (d, J = 37.9 Hz, 2H), 7.14 (dt, J = 17.5, 8.8 Hz, 2H), 4.78 (s, 2H); 13C NMR (100 MHz, DMSO-d6) δ 180.34, 136.14, 126.33, 115.13, 114.91; FT-IR (KBr, cm-1) 3307.96, 3108.03, 1636.04, 1493.81, 1284.91, 1208.69, 905.59, 813.48, 502.85.
N-(4-Methoxyphenyl)hydrazinecarbothioamide (6g)
1H NMR (400 MHz, DMSO-d6) δ 9.40 (s, 1H), 8.96 (s, 1H), 7.37 (dd, J = 53.0, 8.5 Hz, 2H), 6.88 (t, J = 10.1 Hz, 2H), 4.70 (s, 2H), 3.73 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 180.45, 156.69, 132.72, 126.03,113.76,55.71; FT-IR (KBr, cm-1) 3312.45, 3158.14, 1635.19, 1508.62, 1489.55, 1240.97, 1031.78, 829.78, 509.71.
N-(p-Tolyl)hydrazinecarbothioamide (6h)
1H NMR (400 MHz, DMSO-d6) δ 9.54 (s, 1H), 9.04 (s, 1H), 7.49 (d, J = 6.1 Hz, 2H), 7.10 (d, J = 8.1 Hz, 2H), 4.76 (s, 2H), 2.27 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 180.09 , 137.18 , 133.68 , 128.99 , 124.02 , 20.96; FT-IR (KBr, cm-1) 3291.18, 3191.53, 1615.95, 1537.23, 1060.91, 806.74, 726.66, 441.48.
Synthesis of target compound 7a-h
4-(1-adamantyl)benzaldehyde (1.0 mmol) and thiosemicarbazone (6a-h) (1.2 mmol) were dissolved in ethanol (6 mL). Then two drops of acetic acid was added and the solution was refluxed for 3 h.
2-[4-(Adamantan-1-yl)benzylidene]-N-phenylhydrazine-1-carbothioamide (7a)
Light yellow solid, yield 62 %, m.p.178-180 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.91 (s, 1H), 9.93 (s, 1H), 8.13 (s, 1H), 7.80 (d, J = 8.3 Hz, 2H), 7.55 (t, J = 7.5 Hz, 1H), 7.41 (d, J = 8.3 Hz, 2H), 7.26 (dd, J = 24.5, 9.3 Hz, 3H), 2.06 (s, 3H), 1.88 (s, 6H), 1.74 (s, 6H). 13C NMR (100 MHz, DMSO-d6) δ 127.92, 125.50, 124.39, 55.35, 42.91, 36.65, 28.79. FT-IR (KBr, cm-1) 3298.94, 3141.85, 2899.12, 2846.27, 1621.21, 1545.86, 1221.97, 805.11,745.76; MS, m/z (%): 408.3 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(2-methoxyphenyl)hydrazine-1-carbothioamide (7b)
Light yellow solid, yield 60 %, m.p.187-189 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.89 (s, 1H), 10.00 (s, 1H), 8.36 (d, J = 7.3 Hz, 1H), 8.17 (d, J = 16.8 Hz, 1H), 7.72 (d, J = 8.3 Hz, 2H), 7.46 (d, J = 8.3 Hz, 2H), 7.24-6.89 (m, 3H), 3.91 (s, 3H), 2.07 (s, 3H), 1.90 (d, J = 12.0 Hz, 6H), 1.75 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 151.41, 143.06, 127.53, 125.78, 123.50, 120.35, 56.56, 42.86, 39.44, 36.60, 28.74; FT-IR (KBr, cm-1) 3154.70, 2899.16, 1599.45, 1235.88, 1193.39, 1031.00, 743.44; MS, m/z(%): 420.3 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(3-methoxyphenyl)hydrazine-1-carbothioamide(7c)
Light yellow solid, yield 79 %, m.p. 175-177 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.89 (s, 1H), 10.12 (s, 1H), 8.15 (s, 1H), 7.82 (d, J = 8.2 Hz, 2H), 7.63 (d, J = 11.3 Hz, 1H), 7.51-7.42 (m, 2H), 7.40 (d, J = 10.2 Hz, 1H), 7.03 (t, J = 8.8 Hz, 1H), 2.07 (s, 3H), 1.88 (s, 6H), 1.75 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 163.19, 153.66, 143.93, 128.05, 125.46, 121.50, 112.57, 42.86, 36.60; FT-IR (KBr, cm-1) 3135.56, 2987.81, 2900.50, 2847.06, 1599.16, 1541.58, 1272.83, 1064.02, 548.94; MS, m/z (%): 408.3 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(4-methoxyphenyl)hydrazine-1-carbothioamide (7d)
Light yellow solid, yield 53 %, m.p.174-176 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.77 (s, 1H), 9.99 (s, 1H), 8.14 (s, 1H), 7.82 (d, J = 8.0 Hz, 2H), 7.41 (d, J = 8.0 Hz, 2H), 7.34-7.15 (m, 3H), 6.78 (d, J = 7.9 Hz, 1H), 3.77 (s, 3H), 2.07 (s, 3H), 1.88 (s, 6H), 1.74 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 159.49, 143.52, 129.18, 127.98, 125.46, 118.01, 111.53, 111.17, 55.64, 42.87, 36.60, 28.74; FT-IR (KBr, cm-1) 3125.97, 2899.24, 2845.76, 1597.70, 1546.41, 1463.44, 1288.53, 767.71, 546.23, 448.62; MS, m/z (%): 420.3 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(2-fluorophenyl)hydrazine-1-carbothioamide (7e)
Light yellow solid, yield 49 %, m.p.170-171 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.68 (s, 1H), 9.95 (s, 1H), 8.11 (s, 1H), 7.81 (d, J = 8.4 Hz, 2H), 7.40 (d, J = 8.6 Hz, 4H), 6.93 (d, J = 8.9 Hz, 2H), 5.75 (s, 1H), 3.77 (s, 3H), 2.06 (s, 3H), 1.86 (d, J = 12.9 Hz, 6H), 1.74 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 176.31, 143.43, 128.48, 127.96, 126.07, 125.44, 42.88, 36.62, 28.76; FT-IR (KBr, cm-1) 3138.58, 1198.23,803.73, 744.39, 493.02; MS, m/z (%): 390.1 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(3-fluorophenyl)hydrazine-1-carbothioamide (7f)
Light yellow solid, yield 50 %, m.p.188-190 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.79 (s, 1H), 10.06 (s, 1H), 8.13 (s, 1H), 7.82 (d, J = 8.3 Hz, 2H), 7.55 (dd, J = 8.8, 5.1 Hz, 2H), 7.41 (d, J = 8.4 Hz, 2H), 7.20 (t, J = 8.8 Hz, 2H), 2.07 (s, 3H), 1.89 (d, J = 9.0 Hz, 6H), 1.74 (s,6H); 13C NMR (100 MHz, DMSO-d6) δ 176.72, 158.89, 143.56, 135.95, 128.49, 127.97, 125.44, 115.01, 42.87, 36.61, 28.75; FT-IR (KBr, cm-1) 3155.17, 2900.14, 2845.94, 1526.22, 1508.51, 1196.02, 928.48, 836.46, 553.47, 499.03; MS, m/z (%): 408.3 [M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(4-fluorophenyl)hydrazine-1-carbothioamide (7g)
Light yellow solid, yield 57 %, m.p.177-179 °C; 1H NMR (400 MHz,DMSO-d6) δ 11.68 (s, 1H), 9.95 (s, 1H), 8.11 (s, 1H), 7.80 (s, 2H), 7.41 (s, 4H), 6.94 (s, 2H), 3.77 (s, 3H); 13C NMR (100 MHz, DMSO-d6) δ 157.42, 143.23, 131.91, 127.90, 125.41, 113.78, 55.77, 42.92, 36.64, 28.78; FT-IR (KBr, cm-1) 3135.42, 2980.90, 2899.64, 1608.72, 1532.53, 1510.61, 1233.24, 1014.33, 804.52, 548.38; MS, m/z (%): 420.3[M+H]+.
2-[4-(Adamantan-1-yl)benzylidene]-N-(p-tolyl)hydrazine-1-carbothioamide (7h)
Light yellow solid, yield 89 %, m.p.196-197 °C; 1H NMR (400 MHz, DMSO-d6) δ 11.71 (s, 1H), 9.97 (s, 1H), 8.12 (s, 1H), 7.81 (d, J = 8.2 Hz, 2H), 7.42 (t, J = 9.5 Hz, 4H), 7.17 (d, J = 8.0 Hz, 2H), 2.31 (s, 3H), 2.06 (s, 3H), 1.88 (s, 6H), 1.74 (s, 6H); 13C NMR (100 MHz, DMSO-d6) δ 143.30, 131.86, 128.96, 127.93, 126.09, 125.44, 42.87, 36.6, 28.75; FT-IR (KBr, cm-1) 3132.79, 2896.53, 2845.57, 1532.84, 1492.85, 1264.08, 1201.14, 1176.71, 835.84, 449.53; MS, m/z (%): 404.4 [M+H]+.
In vitro antibacterial activity evaluation
Minimum Inhibitory Concentration (MIC) assays using standard microdilution methods were carried out in 96-well microplates based on a modified procedure described previously according to the guidelines of the Clinical and Laboratory Standards Institute [30-31]. All compounds were prepared as 5 mg/mL solutions in dimethyl sulfoxide (DMSO) and were tested in a final concentration range of 1-8 μg/mL. MICs for the reference antibiotic Ampicillin against quality control strains were used to confirm the validity of the screen.
All experiments were performed in duplicate and repeated three times.