Molecular design of tyrosinase inhibitors: A critical review of promising novel inhibitors from synthetic origins

The enzyme tyrosinase is known to be a multifunctional copper-containing enzyme from the oxidase superfamily, which is the key protein involved in the biosynthesis of the large biological pigment, melanin. The enzyme catalyzes two distinct reactions of melanin biosynthesis, the hydroxylation of a monophenol and the conversion of an o-diphenol to the corresponding o-quinone. Inhibitors of this protein have a huge impact on industry and economy. So a number of research groups around the world are engaged and are expending much effort in the discovery of these inhibitors. In this report, we review the importance and applications of the recently designed synthetic tyrosinase inhibitors from our and other leading laboratories of the world, which have been published in recent years. In our continuing search for tyrosinase inhibitors from natural resources to semi- and full synthetic approaches, until now we discovered and reported a large number of mild to potent inhibitors of several classes, such as phenolics, terpenes, steroids, chalcones, flavonoids, alkaloids, long-chain fatty acids, coumarins, sildenafil analogs, bipiperidines, biscoumarins, oxadiazole, tetraketones, etc. The structure-activity relationships (SARs) of different classes of synthetic tyrosinase inhibitors have also been discussed in this review.