Synthesis and tyrosinase inhibitory properties of some novel derivatives of kojic acid

Tyrosinase is a multifunctional oxidase that is widely distributed in nature. It is a key enzyme in melanin biosynthesis and is involved in determining the color of mammalian skin and hair. In addition it is responsible for the undesirable enzymatic browning that occurs in plant-derived foods, limiting the shelf -life of fresh-cut products with the resultant economic loss. In recent years there has been considerable interest to study the inhibitory activity of tyrosinase and a number of inhibitory compounds derived from natural sources or partly/fully synthetic have been described. However, the current conventional methods to control tyrosinase action are inadequate. Considering the significant industrial and economic impact of the inhibitors of tyrosinase, this study was set to seek new potent inhibitors of this enzyme. A series of 3-hydroxypyridine-4-one derivatives were prepared in high yield and evaluated for their inhibitory activity on tyrosinase enzyme using dopachrome method. Our results show that all synthesized compounds have inhibitory effect on tyrosinase activity for the oxidation of L-DOPA. Among compounds studied those containing two free hydroxyl group (ie Va and V'a) were more potent than their analogues with one hydroxyl group (ie Vb and V'b). Also substitution of a methyl group on position N-1 of the hydroxypyridinone ring seems to confer more inhibitory potency.