Design and synthesis of thiourea derivatives with sulfur-containing heterocyclic scaffolds as potential tyrosinase inhibitors.

Tyrosinase is a key enzyme during the production of melanins in plants and animals. A class of novel N-aryl-N'-substituted phenylthiourea derivatives (3a-i, 6a-k) were designed, synthesized and their inhibitory effects on the diphenolase activity of mushroom tyrosinase were evaluated. The results showed some 4,5,6,7-tetrahydro-2-[[(phenylamino)thioxomethyl]amino]-benzo[b]thiophene-3-carboxylic acid derivatives (3a-i) exhibited moderate inhibitory potency on diphenolase activity of tyrosinase. When the scaffold of 4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylic acid was replaced with 2-(1,3,4-thiadiazol-2-yl)thio acetic acid, the inhibitory activity of compounds (6a-k) against tyrosinase was improved obviously; especially, the inhibitory activity of compound 6h (IC50=6.13 μM) is significantly higher than kojic acid (IC50=33.3 μM). Moreover, the analysis on inhibition mechanism revealed that compound 6h might plays the role as a noncompetitive inhibitor.