Synthesis, molecular docking and kinetic studies of novel quinolinyl based acyl thioureas as mushroom tyrosinase inhibitors and free radical scavengers

The enzyme tyrosinase plays a vital role in melanin biosynthesis and enzymatic browning of vegetables and fruits. A series of novel quinolinyl thiourea analogues (11a-j) were synthesized by reaction of 3-aminoquinoline and corresponding isothiocyanates, in moderate to excellent yields with different substitutions and their inhibitory effect on mushroom tyrosinase and free radical scavenging activity were evaluated. The compound N-(quinolin-3-ylcarbamothioyl) hexanamide (11c) exhibited the maximum tyrosinase inhibitory effect (IC50 = 0.0070 +/- 0.0098 mu M) compared to other derivatives and the reference Kojic acid (IC50 = 16.8320 +/- 0.0621 mu M). The docking studies were carried out and the compound (11c) showed most negative estimated free energy of -7.2 kcal/mol in mushroom tyrosinase active site. The kinetic analysis revealed that the compound (11c) inhibits the enzyme tyrosinase non-competitively to form the complex of enzyme and inhibitor. The results revealed that 11c could be identified as putative lead compound for the design of efficient tyrosinase inhibitors.