Medicinal Chemistry Research
atmosphere. After addition of water, the reaction mixture
was neutralized with saturated NaHCO3 solution and par-
titioned between ethyl acetate and water. The organic layer
was dried over anhydrous MgSO4, filtered and evaporated
under reduced pressure. The resulting residue was purified
by column chromatography (hexane:ethyl acetate = 7:1–
1:1) to give solids at yields of 17–86%.
2-(3,4-Dihydroxyphenyl)naphthalene-1,4-dione (1e)
1
Yield: 42%; H NMR (500 MHz, DMSO-d6) δ 9.33 (brs,
2H, OH), 8.06–8.04 (m, 1H, 6-H, or 7-H), 7.99–7.97 (m,
1H, 6-H, or 7-H), 7.88–7.84 (m, 2H, 5-, 8-H), 7.08 (d, 1H,
J = 1.5 Hz, 2′-H), 6.98 (dd, 1H, J = 8.0, 2.0 Hz, 6′-H), 6.97
(s, 1H, 3-H), 6.81 (d, 1H, J = 8.0 Hz, 5′-H); 13C NMR (100
MHz, CD3OD+CDCl3) δ 185.7, 185.2, 147.8, 147.4, 144.5,
133.9, 133.4, 132.7, 132.1, 127.1, 125.9, 125.3, 122.7,
120.6, 116.5, 115.3; LRMS (ESI-) m/z 265 (M-H)−
(Janeczko et al. 2016).
2-(2,4-Dihydroxyphenyl)naphthalene-1,4-dione (1a)
1
(Redaelli et al. 2015). Yield: 86%; H NMR (500 MHz,
DMSO-d6) δ 9.67 (s, 1H, OH), 9.66 (s, 1H, OH), 8.02–7.97
(m, 2H, 6-, 7-H), 7.86–7.84 (m, 2H, 5-, 8-H), 7.05 (d, 1H, J
= 8.5 Hz, 6′-H), 7.00 (s, 1H, 3-H), 6.37 (d, 1H, J = 1.5 Hz,
3′-H), 6.30 (dd, 1H, J = 8.5, 1.5 Hz, 5′-H); 13C NMR (100
MHz, DMSO-d6) δ 185.4, 184.5, 160.6, 157.5, 147.9,
135.4, 134.7, 134.6, 133.0, 132.9, 132.2, 127.1, 126.0,
112.7, 107.3, 103.3 (Redaelli et al., 2015).
2-(2,4-Dimethoxyphenyl)naphthalene-1,4-dione (1f)
1
Yield: 84%; H NMR (500 MHz, CDCl3) δ 8.15–8.10 (m,
2H, 6-, 7-H), 7.76–7.74 (m, 2H, 5-, 8-H), 7.21 (d, 1H, J =
8.5 Hz, 6′-H), 7.03 (s, 1H, 3-H), 6.58 (dd, 1H, J = 8.5, 2.0
Hz, 5′-H), 6.43 (d, 1H, J = 2.0 Hz, 3′-H), 3.86 (s, 3H, CH3),
3.78 (s, 3H, CH3); 13C NMR (100 MHz, DMSO-d6) δ
185.6, 184.2, 162.5, 158.8, 147.6, 136.5, 133.8, 133.7,
132.9, 132.4, 131.8, 127.1, 126.1, 116.0, 104.9, 99.2, 55.9,
55.7.
2-(4-Hydroxy-3-methoxyphenyl)naphthalene-1,4-dione (1b)
1
Yield: 37%; H NMR (500 MHz, CDCl3) δ 8.17–8.07 (m,
2H, 6-, 7-H), 7.76–7.74 (m, 2H, 5-, 8-H), 7.16 (m, 2H, 2′-,
6′-H), 7.03 (s, 1H, 3-H), 6.98 (d, 1H, J = 8.0 Hz, 5′-H),
3.94 (s, 3H, CH3); 13C NMR (100 MHz, CDCl3) δ 185.5,
185.1, 148.1, 147.7, 146.6, 133.9 (×2), 132.8, 132.3, 127.2,
126.1, 125.5, 123.6, 114.9, 112.4, 56.3; LRMS (ESI-) m/z
279 (M-H)−; HRMS (ESI-) m/z C17H12O4 (M-H)− calcd
279.0663, obsd 279.0660.
Biological evaluation
Mushroom tyrosinase inhibition assay
The mushroom tyrosinase-inhibitory assay for the synthe-
sized compounds 1a–1f was carried out according to the
known method with slight modifications (Hyun et al. 2008).
To a 96-well microplate, a total of 200 µL mixture was
added, containing 20 µL mushroom tyrosinase solution
(1000 U/mL), 10 µL of each test compounds (final con-
centration 30 µM) and 170 µL of substrate solution (293 µM
L-tyrosine solution and 14.7 mM potassium phosphate
buffer (pH 6.5) solution (1:1, v/v)). The microplate was
incubated for 30 min at 37 °C. A VersaMaxTM microplate
reader (Molecular Devices, Sunnylvale, CA, USA) was
used to measure the absorbance of dopachrome contents
produced during incubation at 450 nm. A volume of 50 µM
of kojic acid and 500 µM of arbutin were used as positive
controls, respectively. All experiments were repeated for
three times. Formula [Inhibition (%) = [1−(A/B)] × 100(A
= the absorbance of test compounds and B = the absor-
bance of the blank control with no test compound)] was
used for the calculation of tyrosinase inhibition. The IC50
value of compound 1c was determined in three different
concentrations.
2-(4-Hydroxy-2-methoxyphenyl)naphthalene-1,4-dione (1c)
Yield: 37%; 1H NMR (500 MHz, DMSO-d6) δ 9.88 (s, 1H,
OH), 8.02–7.98 (m, 2H, 6-, 7-H), 7.87–7.85 (m, 2H, 5-, 8-
H), 7.10 (d, 1H, J = 8.0 Hz, 6′-H), 6.95 (s, 1H, 3-H), 6.49
(s, 1H, 3′-H), 6.43 (d, 1H, J = 8.0 Hz, 5′-H), 3.66 (s, 3H,
CH3); 13C NMR (100 MHz, DMSO-d6) δ 185.3, 184.1,
161.0, 159.1, 148.2, 135.7, 134.6, 134.5, 132.8, 132.2,
132.1, 127.0, 126.0, 114.4, 107.8, 99.9, 55.9; LRMS (ESI-)
m/z 279 (M-H)−; HRMS (ESI-) m/z C17H11O4 (M-H)− calcd
279.0663, obsd 279.0665.
2-(2-Hydroxy-4-methoxyphenyl)naphthalene-1,4-dione (1d)
Yield: 17%; 1H NMR (500 MHz, DMSO-d6) δ 9.84 (s, 1H,
OH), 8.03–7.98 (m, 2H, 6-, 7-H), 7.87–7.85 (m, 2H, 5-, 8-
H), 7.16 (d, 1H, J = 8.0 Hz, 6′-H), 7.02 (s, 1H, 3-H), 6.48
(dd, 1H, J = 8.0, 2.0 Hz, 5′-H), 6.43 (d, 1H, J = 2.0 Hz, 3′-
H), 3.74 (s, 3H, CH3); 13C NMR (100 MHz, DMSO-d6) δ
185.4, 184.3, 162.1, 157.3, 147.7, 136.0, 134.7, 134.6,
133.0, 132.7, 132.2, 127.1, 126.1, 114.4, 105.5, 102.0,
55.8; LRMS (ESI-) m/z 279 (M-H)−; HRMS (ESI-) m/z
C17H11O4 (M-H)− calcd 279.0663, obsd 279.0664.
Kinetic analysis of tyrosinase inhibition
Kinetic analysis study was performed to determine the
nature of inhibition of compound 1c using mushroom