Identification of novel C-2 symmetric Bis-Azo-Azamethine molecules as competitive inhibitors of mushroom tyrosinase and free radical scavengers: synthesis, kinetics, and molecular docking studies

Tyrosinase is a multi-copper enzyme found in plants, animals and microorganisms, plays a critical role in the melanogenesis and browning process critical to cosmetics and food industries. Many natural, semi-synthetic and synthetic inhibitors have been discovered. To this end, a small library of symmetrical Bis-Azo-Azamethine hybrids 5a–j was synthesized and characterized through spectroscopic and analytical data and explored for mushroom tyrosinase and free radical scavenging activity. All of the molecules 5a–j explicated better potential compared to the standard Kojic acid. On the whole, compound 5i having IC₅₀ value 0.002 ± 0.004 µM was found to be the most potent derivative. The Kinetic studies were performed for 5i and indicating the mode of inhibition in a competitive manner. Structure Activity Relationship (SAR) analysis and docking studies were carried out. Thus compound 5i bearing bulky naphthyl groups was most potent and, The molecular docking indicated formation of two hydrogen bonds with Arg268 and one hydrophobic interaction with Glu322. The carbonyl oxygen of 5i interacts with Arg268 and form two hydrogen bonds having lengths 2.44 and 2.62 Å, respectively. In the same way, compounds 5a–j were appraised for DPPH free radical scavenging ability and five of them 5d, 5e, 5h, 5i and 5j were found to exhibit higher % scavenging potency compared with vitamin C, as the standard. Interesting compound 5i was again the most potent in the series. The current investigation points towards the role of naphthyl group in design of new inhibitors of melanogenesis and the antioxidants with improved efficacy. Communicated by Ramaswamy H. Sarma.