Although the correlation between the binding affinities of the two ligands and their abilities to inhibit mushroom tyrosinase was not perfect, both derivatives had much stronger binding affinities (?7

Although the correlation between the binding affinities of the two ligands and their abilities to inhibit mushroom tyrosinase was not perfect, both derivatives had much stronger binding affinities (?7.3?~??7.5?kcal/mol) than the kojic acid (?5.7?kcal/mol) (Fig. triplet of doublets by coupling to the fluorine atoms and vicinal hydrogen atoms. The results of characteristic coupling by fluorine atoms were observed in 13C NMR spectrum of 1p. All carbon peaks alpha-hederin of -phenyl rings attached to fluorine atoms appeared as doublet of doublets and the -carbon of the PUSC scaffold was also split into a doublet by the 2-fluorine atom. 2.2. Inhibitory activities of thioxazolidinedione derivatives 1aC1p against mushroom tyrosinase To select derivatives for cell-based assays of anti-melanogenic and tyrosinase-inhibitory effects, the inhibitory activities of the sixteen synthesized ((a species of mushroom) was utilized as the 3D-structure [Protein Data Bank (PDB) ID: 2Y9X] for docking simulation. Although the correlation between the binding affinities of the two ligands and their abilities to inhibit mushroom tyrosinase was not perfect, both derivatives had much stronger binding affinities (?7.3?~??7.5?kcal/mol) than the kojic acid (?5.7?kcal/mol) (Fig. 4d). LigandScout 4.3 software was utilized to determined which amino acid residues of tyrosinase interacted with 1c and 1j. Three amino acids (His259, His263, and Met280) of tyrosinase were found to interact with kojic acid (Fig. 4c). The branched hydroxyl group of kojic acid formed two hydrogen bonds with amino acid residues His259 and His263 and the ring hydroxyl formed a hydrogen bond with Met280. Both hydroxyl groups of kojic acid acted as hydrogen bonding donors. Compounds 1c and 1j both interacted hydrophobically with five amino acid residues (Val248, Met257, Phe264, Smcb Val283, and Ala286) (Fig. 4a and b) without hydrogen bonding. Docking simulation results suggested although the amino acids that interacted with kojic acid and those that interacted with 1c and 1j differed all three ligands bind to the active site of tyrosinase. However, LigandScout results based on AutoDock Vina docking simulations showed kojic acid appeared to bind more strongly to the active site of tyrosinase than 1c or 1j, which was contrary to the results of the binding affinity obtained from AutoDock Vina. Open in a separate window Fig. 4 Docking simulation of the (tyrosinase using AutoDock Vina and pharmacophore analysis. (a-c) Pharmacophore results for 1c, 1j, alpha-hederin and kojic acid obtained using LigandScout 4.3 showed possible hydrophobic (yellow), – stacking (violet arrow), and hydrogen bonding (green arrow) interactions between tyrosinase amino acid residues and the three ligands. Docking simulation 3D-results indicated hydrophobic (yellow sphere), – stacking (violet ring), and hydrogen bonding (green sphere) regions on the ligands. (d) Docking scores for interactions between tyrosinase and 1c, 1j, and kojic acid (PDB code: 2Y9X). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) Two more docking simulation software packages, that is, AutoDock 4 and Dock 6, were utilized to increase the reliability alpha-hederin of docking simulation results. The same tyrosinase species used for the AutoDock Vina simulation were used. According to AutoDock 4 and Dock 6, the binding affinities of 1c were ?7.41 and ?30.70?kcal/mol and for 1j were ?7.19 and ?32.42?kcal/mol, respectively (Fig. 5b), which were greater than those of kojic acid (?4.2 and ?27.59?kcal/mol, respectively). Furthermore, these results were consistent with experimental data for mushroom tyrosinase inhibition. However, according to Dock 6, 1j had greater binding affinity than 1c, while in AutoDock 4, the reverse was the case. Compound 1c which showed greater inhibitory activity against mushroom tyrosinase than 1j showed higher binding affinity to tyrosinase than 1j in AutoDock 4. Thus, LigandScout results based on AutoDock 4 were examined (Fig. 5a). These results showed kojic acid formed one hydrogen connection with Met280 which its band interacted with His263 by – stacking. Substance 1c which demonstrated more powerful binding affinity than substance 1j produced two alpha-hederin hydrogen bonds with Asn260 and Met280 which consists of two hydroxyls and interacted hydrophobically with Val248, Val283, and Ala286 through its two phenyl bands. Alternatively, substance 1j interacted hydrophobically with Val 248, Met257, Phe264,.