A new series of isoquinoline urea/thiourea derivatives (1-11) were synthesized, and their inhibitory effects on tyrosinase were evaluated. Isoquinoline urea/thiourea derivatives were obtained as a result of the reaction of 5-aminoisoquinoline with isocyanates or isothiocyanates. The result showed that all the synthesized compounds inhibited the tyrosinase enzyme activity. Among the compounds synthesized, 1-(4-chlorophenyl)-3-(isoquinolin-5-yl)thiourea (3) was found to be the most active one (Ki = 119.22 μM), and the inhibition kinetics analyzed using Lineweaver-Burk double reciprocal plots revealed that compound 3 was a competitive inhibitor. We also calculated HOMO-LUMO energy levels, some selected the synthesized compounds (1, 4, 11, 3, 6, 2) using Gaussian software.
Keywords: inhibition; thiourea; tyrosinase; urea.