Inhibitory effect of synthetic aromatic heterocycle thiosemicarbazone derivatives on mushroom tyrosinase: Insights from fluorescence, 1H NMR titration and molecular docking studies

Three structurally similar aromatic heterocyclic compounds 2-thiophenecarboxaldehyde (a), 2-furaldehyde (b), 2-pyrrolecarboxaldehyde (c) were chosen and a series of their thiosemicarbazone derivatives(1a-3a, 1b-3b and 1c-3c) were synthesized to evaluate their biological activities as mushroom tyrosinase inhibitors. The inhibitory effects of these compounds on tyrosinase were investigated by using spectrofluorimetry, 1H NMR titration and molecular docking techniques. From the results of fluorescence spectrum and 1H NMR titration, it was found that forming complexes between the sulfur atom from thiourea and copper ion of enzyme center may play a key role for inhibition activity. Moreover, investigation of 1H NMR spectra further revealed that formation of hydrogen bond between inhibitor and enzyme may be helpful to above complexes formation. The results were well coincident with the suggestion of molecular docking and obviously showed that 2-thiophone N(4)-thiosemicarbazone (1a), 2-furfuran N(4)-thiosemicarbazone (1b) and 2-pyrrole N(4)-thiosemicarbazone (1c) are potential inhibitors which deserves further investigation.