Melanogenesis of Natural Depigmenting Ingredients Structurally Modified via CAMD Method

Abstract

Kojic acid and rucinol are well known depigmenting agents. Both compounds have strong inhibitory activities against tyrosinase which is rate-limiting enzyme in melanin synthesis. We established a synthetic method for the preparation of ester of kojic acid without any side products. We synthesized various cinnamate or benzoate derivatives of kojic acid. We also synthesized hydroxyl benzamide derivative of which structure is very much similar to that of rucinol. We evaluated depigmenting activities of synthetic compounds on tyrosinase and on melan-a cells. After screening kojic acid derivatives and hydroxyl benzamide derivatives, we proposed N-adamantyl-3,4-dihydroxybenzamide (14c) as a class of desirable candidates for depigmenting agent. The inhibitory effects of N-adamantyl-3,4-dihydroxybenzamide 14c on the melanogenesis were studied. We found that compound 14c exhibited a potent inhibitory effect on melanin production in melan-a cells. To investigate the depigmenting mechanism of compound 25, both tyrosinase assays such as cell tyrosinase activity and in situ tyrosinase activity were utilized. Compound 14c showed inhibitory activity only in situ assay condition. From these results, we supposed that inhibition pathway of compound 14c may be related with expression of tyrosinase. We investigated the effects of compound 14c on the expression of melanin biosynthesis enzymes such as tyrosinase, TRP-1 and TRP-2. Compound 25 down-regulated the expression of tyrosinase as well as TRP-1 and TRP-2. Down-regulation of these enzymes may be caused potent decrease in the synthesis of melanin (IC50 = 1.25 M). Its activity was more potent than that of hydroquinone. Over all these results suggest that compound 14c can be used as an effective skin depigmenting agent.