Design, synthesis, and antimelanogenic effects of (2-substituted phenyl-1,3-dithiolan-4-yl)methanol derivatives

Figures & data

Figure 1 Rationale used to design PDTM derivatives as tyrosinase inhibitors.

Abbreviation: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol.

Table 1 Substitution patterns and tyrosinase-inhibitory activities by the synthesized compounds PDTM1–PDTM17, kojic acid, and arbutin

Compound	R^1	R^2	R^3	R^4	Tyrosinase inhibition (%)
Kojic acid					65.71±1.9
Arbutin					51.46±3.25
PDTM1	H	H	OH	H	NI
PDTM2	H	OH	OH	H	NI
PDTM3	OH	H	OH	H	77.99±0.34
PDTM4	H	OMe	OH	H	7.44±2.41
PDTM5	H	OEt	OH	H	7.8±2.45
PDTM6	H	OH	OMe	H	56.23±1.48
PDTM7	H	H	OMe	H	77.95±0.96
PDTM8	H	OMe	OMe	H	73.76±0.97
PDTM9	OMe	H	OMe	H	74.6±0.68
PDTM10	OH	H	H	H	35.59±2.65
PDTM11	H	OMe	OMe	OMe	65.2±3.12
PDTM12	H	OMe	OH	OMe	38.7±3.14
PDTM13	H	Br	OH	H	75.27±0.97
PDTM14	H	Br	OH	Br	52.44±2.47
PDTM15	H	Me	OH	H	60.64±1.61
PDTM16	H	Me	OH	Me	50.1±1.81
PDTM17	H	t-Bu	OH	t-Bu	61.11±2.26

Notes: Results shown as mean ± standard error of the mean (n≥3) at a concentration of 50 μM (with the exception of arbutin, at 500 μM). R¹–R⁴, substituents on phenyl ring in the chemical structure of PDTMs.

Abbreviations: NI, no inhibition; PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl) methanol; t-Bu, tertiary butyl.

Table 2 Kinetic parameters of mushroom tyrosinase in the presence of PDTM3

Concentration (µM)	Vmax (mM⋅min^−1)	Km (mM)	Ki (M)
0	0.0123	0.229
5	0.0123	2.973	4.17×10^−7
10	0.0123	5.676	4.20×10^−7
25	0.0123	11.005	5.31×10^−7

Notes: Data are representative of three independent experiments using different concentrations of l-tyrosine as a substrate. V_max was obtained by measuring the increase in the optical density at 475 nm per minute.

Abbreviations: V_max, maximum velocity; K_m, Michaelis constant; K_i, inhibition constant.

Figure 2 Mode of mushroom tyrosinase inhibition by PDTM3.

Notes: Lineweaver–Burk plots were used to determine the nature of tyrosinase inhibition by PDTM3. The results shown are mean 1/V values, ie, the inverse of the increase in absorbance per minute at 0.5, 1, 2, and 4 mM of l-tyrosine. The modified Michaelis–Menten equation was used: 1/V_max = 1/K_m(1+ [S]/K_i), where V is velocity of the reaction, S is concentration of the l-tyrosine, K_m is Michaelis constant, and K_i is inhibition constant.
Abbreviation: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol.

Figure 3 Docking simulation of PDTM derivatives and kojic acid with tyrosinase.

Notes: (A) Tyrosinase docking scores of the five PDTM analogues and kojic acid. (B) Docking result between (2S,4S)-PDTM3 and mushroom tyrosinase. (C) The pharmacophore model obtained by the LigandScout 3.1.2 program indicated possible hydrophobic (yellow), hydrogen-bonding (green arrow), and π–π stacking (violet arrow) interactions between the amino acid residues of tyrosinase and the ligands tested.
Abbreviation: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol.

Figure 4 Effect of PDTM3 on B16F10 cell viability.

Notes: Cell viability after treatment with PDTM3 at different concentrations for 24 hours presented as mean percentage viability against untreated controls. All experiments were independently conducted in triplicate. Bars represent standard error of the mean.
Abbreviation: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol.

Figure 5 Antimelanogenic effect of PDTM3 in α-MSH-stimulated B16F10 cells.

Notes: B16F10 cells were treated with 1 μM α-MSH and then exposed to kojic acid (25 μM) or PDTM3 (0, 5, 10, or 25 μM) for 24 hours. Inhibitions of melanin production are indicated as mean percentage inhibitions to that of the α-MSH only-treated control cells. Results expressed as mean ± standard error of three independent experiments. One-way analysis of variance followed by Dunnett’s test was used to determine whether group means differed significantly from those of controls. Unpaired Welch’s t-test was used to determine whether the effects of PDTM3 and kojic acid were significantly different. *P<0.05; ***P<0.001.
Abbreviations: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol; MSH, melanocyte-stimulating hormone.

Figure 6 Effect of PDTM3 on tyrosinase activity in B16F10 cells.

Notes: B16F10 cells were prestimulated with 1 μM α-MSH and then treated with PDTM3 (0, 5, 10, or 25 μM) or kojic acid (25 μM) for 24 hours. Tyrosinase-activity inhibition is indicated as mean percentages compared to that of the α-MSH only-treated control cells. Results expressed as mean ± standard error of three independent experiments. One-way analysis of variance followed by Dunnett’s test was used to determine whether group means differed significantly from those of controls. Unpaired Welch’s t-test was used to determine whether the effects of PDTM3 and kojic acid were significantly different. *P<0.05; ***P<0.001.
Abbreviations: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol; MSH, melanocyte-stimulating hormone.

Figure 7 The effect of PDTM derivatives on DPPH radical scavenging activity.

Notes: After 30 minutes in the dark, the radical scavenging activity of each compound was assayed at a concentration of 1 mM. Asterisks indicate a significant difference between PDTMs and l-ascorbic acid. Results expressed as mean ± standard error of three independent experiments. One-way analysis of variance followed by Dunnett’s test was used to determine whether group means differed significantly from those of controls. **P<0.01; ***P<0.001.
Abbreviations: PDTM, (2-substituted phenyl-1,3-dithiolan-4-yl)methanol; DPPH, 2,2-diphenyl-1-picrylhydrazyl.

Scheme 1 Structures of (2-substituted phenyl-1,3-dithiolan-4-yl)methanol (PDTM) derivatives, kojic acid, and arbutin, and reagents and conditions.

Notes: a, H₂SO₄ in 1,4-dioxane at 70°C. t-Bu, tertiary butyl (group).