1274
Vol. 57, No. 11
2-[(2,5-Dihydroxyphenyl)methylene]-thiosemicarbazone (2i): Yield 61%,
mp 237—239 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.30 (1H, s, NH),
9.15 (1H, s, OH), 8.76 (1H, s, OH), 8.27 (s, 1H, –HCꢂN–), 8.05 (1H, br s,
NH2), 7.76 (1H, br s, NH2), 7.20 (1H, s, phH), 6.66 (1H, d, Jꢂ7.8 Hz, phH),
6.73 (1H, d, Jꢂ8.1 Hz, phH). MS (ESI): m/z (100%)ꢂ212 (Mꢃ1). Anal.
Calcd for C8H9N3O2S: C, 45.49; H, 4.29; N, 19.89. Found: C, 45.31; H,
4.41; N, 20.08.
2-[(3,5-Dihydroxyphenyl)methylene]-thiosemicarbazone (2j): Yield 62%,
mp ꢄ250 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.27 (1H, s, NH), 9.34
(2H, s, OH), 8.11 (1H, br s, NH2), 7.83 (s, 1H, –HCꢂN–), 7.76 (1H, br s,
NH2), 6.56 (2H, d, Jꢂ2.1 Hz, phH), 6.25(1H, ‘t’, Jꢂ2.2 Hz, phH). MS
(ESI): m/z (100%)ꢂ212 (Mꢃ1). Anal. Calcd for C8H9N3O2S: C, 45.49; H,
4.29; N, 19.89. Found: C, 45.45; H, 4.40; N, 19.98.
2-[(3,4-Dihydroxyphenyl)methylene]-thiosemicarbazone (2k): Yield 73%,
mp 234—235 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.17 (1H, s, NH),
9.45 (1H, s, OH), 8.97 (1H, s, OH), 8.01 (1H, br s, NH2), 7.86 (s, 1H, –HCꢂ
N–), 7.70 (1H, br s, NH2), 7.15 (1H, s, phH), 7.01 (1H, d, Jꢂ8.1 Hz, phH),
6.73 (1H, d, Jꢂ8.1 Hz, phH). 13C-NMR (75 MHz, DMSO-d6) d: 177.9,
148.3, 146.1, 143.9, 126.2, 120.8, 116.2, 114.5. MS (ESI): m/z (100%)ꢂ212
(Mꢃ1). Anal. Calcd for C8H9N3O2S: C, 45.49; H, 4.29; N, 19.89. Found: C,
45.25; H, 4.43; N, 20.25.
phenylmethylenethiosemicarbazones.
Experimental
Chemistry Melting points (mp) were determined with WRS-1B melting
point apparatus and the thermometer was uncorrected. NMR spectra were
recorded on Mercury-Plus 300 spectrometers at 25 °C in deuterochloroform
(CDCl3) or dimethyl sulfoxide-d6 (DMSO-d6). All chemical shifts (d) are
quoted in ppm downfield from TMS and coupling constants (J) are given in
Hz. LC-MS spectra were recorded using the LCMS-2010A. All reactions
were monitored by TLC (Merck Kieselgel 60 F254) and the spots were visu-
alized under UV light. Elemental analyses were performed on a Vario EL in-
strument and were within ꢁ0.4% of the theoretical values. The benzylalde-
hydes, ketones, thiosemicarbazide and 4-methoxycinnamic acid were pur-
chased from Darui Chemical Co. (ShangHai, China). Mushroom tyrosinase
(specific activity of the enzyme is 6680 U/mg) and L-3,4-dihydroxyphenylala-
nine (L-DOPA) were purchased from Sigma Chemical Co. All commercially
available reagents and solvents were used without further purification.
Synthesis To the solution of appropriate aldehydes (10 mmol) in anhy-
drous ethanol (10 ml), thiosemicarbazide (10 mmol) and acetic acid (0.5 ml)
were added. The reaction mixture was refluxed for 24 h and cooled to room
temperature. The precipitate solid was filtered, washed with ether, and puri-
fied by recrystallization from 95% ethanol to afford compounds 2a—r.
2-(Phenylmethylene)-thiosemicarbazone (2a): Yield 76%, mp 153—154 °C.
1H-NMR (DMSO-d6, 300 MHz) d: 11.40 (1H, s, NH), 8.17 (1H, br s, NH2),
8.03 (s, 1H, –HCꢂN–), 7.96 (1H, br s, NH2), 7.77 (2H, m, phH), 7.38 (3H,
m, phH). MS (ESI): m/z (100%)ꢂ180 (Mꢃ1). Anal. Calcd for C8H9N3S: C,
53.61; H, 5.06; N, 23.44. Found: C, 53.25; H, 5.24; N, 23.21.
2-[(2-Hydroxyphenyl)methylene]-thiosemicarbazone (2b): Yield 66%, mp
219—220 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.33 (1H, s, NH), 9.84
(1H, s, OH), 8.34 (s, 1H, –HCꢂN–), 8.07 (1H, br s, NH2), 7.90 (1H, br s,
NH2), 7.87 (1H, d, Jꢂ7.5 Hz, phH), 7.18 (1H, ‘t’, Jꢂ8.1 Hz, phH), 6.83 (1H,
d, Jꢂ7.6 Hz, phH), 6.79 (1H, ‘t’, Jꢂ7.6 Hz, phH). MS (ESI): m/z
(100%)ꢂ196 (Mꢃ1). Anal. Calcd for C8H9N3OS: C, 49.21; H, 4.65; N,
21.52. Found: C, 49.04; H, 4.64; N, 21.61.
2-[(3-Hydroxyphenyl)methylene]-thiosemicarbazone (2c): Yield 83%, mp
168—170 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.34 (1H, s, NH), 9.50
(1H, s, OH), 8.15 (1H, br s, NH2), 7.95 (s, 1H, –HCꢂN–),7.86 (1H, br s,
NH2), 7.19 (1H, s, phH), 7.17 (1H, d, Jꢂ7.6 Hz, phH), 7.13 (1H, d, Jꢂ
7.3 Hz, phH), 6.79 (1H, m, phH). MS (ESI): m/z (100%)ꢂ196 (Mꢃ1). Anal.
Calcd for C8H9N3OS: C, 49.21; H, 4.65; N, 21.52. Found: C, 49.15; H, 4.82;
N, 21.28.
2-[(4-Hydroxyphenyl)methylene]-thiosemicarbazone (2d): Yield 52%, mp
218—219 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.21 (1H, s, NH), 9.83
(1H, s, OH), 8.03 (1H, br s, NH2), 7.93 (s, 1H, –HCꢂN–), 7.80 (1H, br s,
NH2), 7.59 (2H, d, Jꢂ8.3 Hz, phH), 6.75 (2H, d, Jꢂ8.3 Hz, phH). MS (ESI):
m/z (100%)ꢂ196 (Mꢃ1). Anal. Calcd for C8H9N3OS: C, 49.21; H, 4.65; N,
21.52. Found: C, 49.49; H, 4.66; N, 21.38.
2-[(4-Methoxyphenyl)methylene]-thiosemicarbazone (2e): Yield 75%, mp
166—168 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.28 (1H, s, NH), 8.08
(1H, br s, NH2), 7.97 (s, 1H, –HCꢂN–), 7.88 (1H, br s, NH2), 7.71 (2H, d,
Jꢂ8.7 Hz, phH), 6.94 (2H, d, Jꢂ8.7 Hz, phH), 3.78 (3H, s, CH3). 13C-NMR
(75 MHz, DMSO-d6) d: 178.1, 161.3, 142.9, 129.5, 127.4, 114.8, 56.1. MS
(ESI): m/z (100%)ꢂ210 (Mꢃ1). Anal. Calcd for C9H11N3OS: C, 51.65; H,
5.30; N, 20.08. Found: C, 51.78; H, 5.52; N, 19.93.
2-[(4-Bromophenyl)methylene]-thiosemicarbazone (2f): Yield 80%, mp
203—204 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.45 (1H, s, NH), 8.21
(1H, br s, NH2), 8.04 (1H, br s, NH2), 7.98 (s, 1H, –HCꢂN–), 7.73 (2H, d,
Jꢂ8.1 Hz, phH), 7.55 (2H, d, Jꢂ8.1 Hz, phH). 13C-NMR (75 MHz, DMSO-
d6) d: 178.6, 141.5, 134.1, 132.2, 129.8, 123.7. MS (ESI): m/z (100%)ꢂ258
(Mꢃ1). Anal. Calcd for C8H8BrN3S: C, 37.22; H, 3.12; N, 16.28. Found: C,
37.19; H, 3.26; N, 16.42.
2-[(2-Hydroxy-4-bromophenyl)methylene]thiosemicarbazone (2g): Yield
79%, mp 230—231 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.38 (1H, s,
NH), 10.19 (1H, s, OH), 8.27 (1H, s, –HCꢂN–), 8.17 (1H, s, phH), 8.13
(2H, br s, NH2), 7.30 (1H, dd, Jꢂ2.1, 8.5 Hz, phH), 6.80 (1H, d, Jꢂ8.8 Hz,
phH). MS (ESI): m/z (100%)ꢂ274 (Mꢃ1). Anal. Calcd for C8H8BrN3OS: C,
35.05; H, 2.94; N, 15.33. Found: C, 34.96; H, 2.88; N, 15.56.
2-[(3-Methoxy-4-hydroxyphenyl)methylene]-thiosemicarbazone
(2l):
Yield 85%, mp 194—195 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.21 (1H,
s, NH), 9.41 (1H, s, OH), 8.08 (1H, br s, NH2), 7.92 (1H, br s, NH2), 7.90 (s,
1H, –HCꢂN–), 7.44 (1H, s, phH), 7.01 (1H, d, Jꢂ8.3 Hz, phH), 6.75 (1H, d,
Jꢂ8.2 Hz, phH), 3.81 (3H, s, CH3). MS (ESI): m/z (100%)ꢂ226 (Mꢃ1).
Anal. Calcd for C9H11N3O2S: C, 47.99; H, 4.92; N, 18.65. Found: C, 48.13;
H, 4.88; N, 18.83.
2-[(3-Hydroxy-4-methoxyphenyl)methylene]-thiosemicarbazone
(2m):
Yield 88%, mp 176—177 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.23 (1H,
s, NH), 9.02 (1H, s, OH), 8.05 (1H, br s, NH2), 7.89 (s, 1H, –HCꢂN–), 7.78
(1H, br s, NH2), 7.23 (1H, s, phH), 7.08 (1H, d, Jꢂ7.8 Hz, phH), 6.90 (1H, d,
Jꢂ7.8 Hz, phH), 3.78 (3H, s, CH3). MS (ESI): m/z (100%)ꢂ226 (Mꢃ1).
Anal. Calcd for C9H11N3O2S: C, 47.99; H, 4.92; N, 18.65. Found: C, 48.15;
H, 4.81; N, 18.91.
2-[(2,5-Dimethoxyphenyl)methylene]-thiosemicarbazone (2n): Yield 82%,
1
mp 221—222 °C. H-NMR (DMSO-d6, 300 MHz) d: 11.36 (1H, s, NH), 8.35
(s, 1H, –HCꢂN–), 8.14 (1H, br s, NH2), 8.04 (1H, br s, NH2), 7.61 (1H, d,
Jꢂ2.8 Hz, phH), 6.93 (2H, m, phH), 3.75 (3H, s, CH3), 3.73 (3H, s, CH3).
13C-NMR (75 MHz, DMSO-d6) d: 178.4, 153.0, 152.9, 138.5, 123.5, 118.1,
113.8, 110.7, 57.0, 56.4. MS (ESI): m/z (100%)ꢂ240 (Mꢃ1). Anal. Calcd
for C10H13N3O2S: C, 50.19; H, 5.48; N, 17.56. Found: C, 50.41; H, 5.32; N,
17.79.
2-[(2,3,4-Trihydroxy)methylene]-thiosemicarbazone (2o): Yield 78%, mp
248—249 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.16 (1H, s, NH), 9.48
(1H, br s, OH), 8.94 (1H, br s, OH), 8.40 (1H, br s, NH2), 8.20 (s, 1H,
–HCꢂN–), 7.93 (1H, br s, OH), 7.72 (1H, br s, NH2), 7.11 (1H, d, Jꢂ8.4 Hz,
phH), 6.32 (1H, d, Jꢂ8.4 Hz, phH). MS (ESI): m/z (100%)ꢂ228 (Mꢃ1).
Anal. Calcd for C8H9N3O3S: C, 42.28; H, 3.99; N, 18.49. Found: C, 42.33;
H, 4.07; N, 18.31.
2-[(3,4,5-Trihydroxy)methylene]-thiosemicarbazone (2p): Yield 85%, mp
237—239 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.13 (1H, s, NH), 8.96
(2H, br s, OH), 8.62 (1H, br s, OH), 8.01 (1H, br s, NH2), 7.78 (s, 1H,
–HCꢂN–), 7.59 (1H, br s, NH2), 6.64 (2H, s, phH). 13C-NMR (75 MHz,
DMSO-d6) d: 177.9, 146.7, 144.4, 136.4, 125.0, 107.3. MS (ESI): m/z
(100%)ꢂ228 (Mꢃ1). Anal. Calcd for C8H9N3O3S: C, 42.28; H, 3.99; N,
18.49. Found: C, 42.19; H, 4.07; N, 18.65.
2-[(3,4,5-Trimethoxy)methylene]-thiosemicarbazone (2q): Yield 87%, mp
211—212 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.40 (1H, s, NH), 8.21
(1H, br s, NH2), 8.07 (1H, br s, NH2), 7.93 (s, 1H, –HCꢂN–), 7.06 (2H, s,
phH), 3.81 (6H, s, 2ꢅCH3), 3.66 (3H, s, CH3). 13C-NMR (75 MHz, DMSO-
d6) d: 178.3, 153.7, 142.8, 139.6, 130.3, 105.4, 60.8, 56.8. MS (ESI): m/z
(100%)ꢂ270 (Mꢃ1). Anal. Calcd for C11H15N3O3S: C, 49.06; H, 5.61; N,
15.60. Found: C, 48.99; H, 5.65; N, 15.87.
2-(2-Furanylmethylene)-thiosemicarbazone (2r): Yield 77%, mp 143—
145 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.39 (1H, s, NH), 8.18 (1H,
br s, NH2), 7.94 (s, 1H, –HCꢂN–), 7.78 (1H, d, Jꢂ1.8 Hz, furylH), 7.60
(1H, br s, NH2), 6.94 (1H, d, Jꢂ3.4 Hz, furylH), 6.59 (1H, m, furylH). MS
(ESI): m/z (100%)ꢂ170 (Mꢃ1). Anal. Calcd for C6H7N3OS: C, 42.59; H,
4.17; N, 24.83. Found: C, 42.86; H, 4.27; N, 24.42.
2-[(2,4-Dihydroxyphenyl)methylene]-thiosemicarbazone (2h): Yield 68%,
mp 228—230 °C. 1H-NMR (DMSO-d6, 300 MHz) d: 11.14 (1H, s, NH),
9.72 (2H, s, OH), 8.22 (s, 1H, –HCꢂN–), 7.93 (1H, br s, NH2), 7.72 (1H,
br s, NH2), 7.65 (1H, d, Jꢂ8.5 Hz, phH), 6.27 (1H, s, phH), 6.24 (1H, d,
Jꢂ8.8 Hz, phH). MS (ESI): m/z (100%)ꢂ212 (Mꢃ1). Anal. Calcd for
C8H9N3O2S: C, 45.49; H, 4.29; N, 19.89. Found: C, 45.60; H, 4.22; N,
20.22.
Tyrosinase Inhibition Assay Tyrosinase inhibition assays were per-
formed according to the developed method described earlier by Hearing.23)
Briefly, all the synthesized compounds were screened for the o-diphenolase
inhibitory activity of tyrosinase using L-DOPA as substrate. All the active in-