To a solution of 55 (7.00 g, 33.6 mmol) in DMF (140 mL), NaH (674 mg, 28.0 mmol) was added portionwise under argon. The solution was stirred at 25 °C for 1.5 h. The mixture was then concentrated under reduced pressure, and the residue was solubilized in CH2Cl2. The solution was washed with saturated aqueous NH4Cl, water and brine, dried over anhydrous MgSO4, filtered, and the filtrate was concentrated under reduced pressure to afford 56 (1.10 g, 16%) as a yellow solid. MNT-1 Whole Cells Assay and Cytotoxicity. MNT-1 cells grown on 75 cm 2 flask were detached using trypsin-EDTA solution. Detached cells were then placed onto 96-wells plates at the initial density of 100,000 cells per cm 2 and incubated at 37 °C in a 5% CO2 incubator. After two to three days, when confluence was reached, cell medium was changed to fresh medium and MNT-1 cells were treated with increasing concentrations of test compounds (dissolved in DMSO), all wells (including negative controls) receiving the same amount of vehicle (i.e. 0.1% final concentration of DMSO (v/v)). Cells were then incubated for 96 h at 37 °C in a 5% CO2 incubator. At the end of the incubation, cells were washed three times with cold PBS and were then transferred to Eppendorf tubes. After centrifugation (at 1,200 rpm for 5 min), cell pellets were finally lysed by adding 0.5 mL of NaOH (2 M) and repeated sonication / vortexing until melanin was completely solubilized. The use of NaOH for extracting and solubilizing melanin has been heavily reported. Cell-associated melanin contents were measured at 600 nm using pure melanin (purchased from Sigma-Aldrich) diluted in 2 M NaOH as standard. Protein contents were also measured using the Lowry's procedure, bovine serum albumin (BSA) being used as standard. Protein quantification was performed to normalize melanin contents and also to estimate the toxicity of the compounds since protein contents reflect the number of cells present in the wells. supplemented with 10% heat-inactivated fetal bovine serum, 10,000 U/mL penicillin, 10 mg/mL streptomycin, 250 µg/mL amphotericin B and 1% non-essential amino acids (all from Biological Industries). Cells were counted to obtain 810 6 cells in each plate to reach 70% confluence at transfection. 18-24 hours after counting, the cells were transiently transfected with 6.8-7.5 μg of plasmid using CalFectin reagent (SignaGen Laboratories) following manufacturer's instructions. 18 hours post transfection, the cells were washed twice with fetal bovine serum (Biological Industries) and then cultured in expression media containing DMEM highglucose without phenol red and glutamine supplemented with 200 mM glutamine, 10,000 U/mL penicillin, 10 mg/mL streptomycin, 250 µg/mL amphotericin B, 1% non-essential amino acids (all from Biological Industries) and with 10 mM valproic acid (Sigma). After 5 days of incubation in the expression media, the supernatant containing secreted hsTYR was collected, concentrated in Centricon Plus-70, 30 kDa (Merck Millipore), equilibrated with binding buffer (20 mM Tris-HCl, pH 7.5, 500 mM NaCl, 20 mM imidazole) and purified by metal affinity chromatography on Ni 2+ -Sepharose column (GE Healthcare). hsTYR was eluted in one-step elution at 500 mM imidazole, and 0.54 mg of purified enzyme with a specific activity of 3.17 units/mg were collected from 200 mL media. One unit (U) is defined as the amount of enzyme that releases 1 µmol of L-dopachrome per minute under these assay conditions. Human Tyrosinase Activity Assay. The assay was performed as described previously for other TYR. In short, the assay was done in 96-well plates containing 1.2 µg of hsTYR, 0.01 mM CuSO4 and 1 mM L-DOPA in 50 mM sodium-phosphate buffer, pH 7.5-7.8. Absorbance was measured at 475 nm, following the formation of L-dopachrome (ε = 3,600 M -1 cm -1 ), in 18 s intervals for 1 hour in an EPOCH 2 microplate reader (BioTek) at 37 °C. Activity was deffered from the slopes of absorbance at 475 nm vs. time, and converted to units (U). Molecular Modeling. A homology model of hsTYR built from the crystal structure of hsTYRP1 was retrieved from Swiss Model Expasy. The docked compound and the protein were prepared using LePro tool. Compound 23 was then docked using LeDock software with standard settings, and a total of 20 poses were generated. Only poses with low energy conformations and plausible geometries were considered. UCSF Chimera 1.14 was used to display the small molecule ligand-protein docking results. The crystal structure of tyrosinase from Bacillus megaterium with bound tyrosine was retrieved from the Protein DataBank (PDB code 4p6r) and was superimposed with the best docking poses using UCSF Chimera 1.14.