Tyrosinase-catalyzed l-tyrosine oxidation is a key step in melanogenesis, and intense melanin formation is often a problem in chemotherapies or food preservation. Here we report that methyl cinnamate one of the constituents characterized from mycelium and sporocarp of American matsutake mushroom Tricholoma magnivelare inhibits both enzymatic and cellular melanin formation. Methyl cinnamate inhibits mushroom tyrosinase-catalyzed l-tyrosine oxidation while the oxidation of l-3,4-dihydroxyphenylalanine (l-DOPA) was not inhibited. In subsequent cellular assays, methyl cinnamate significantly suppressed melanogenesis of murine B16-F10 melanoma cells without affecting cell growth. However, methyl 3-phenylpropionate, a dihydro-derivative of methyl cinnamate, did not possess melanogenesis, indicating that the double bond in the enone moiety is a key Michael reaction acceptor to elicit the activity. In addition, a rather rare chlorinated benzaldehyde derivative, 3,5-dichloro-4-methoxybenzaldehyde isolated from the same source, was found to show potent cytotoxicity, and the chlorine atom reduced a tyrosinase inhibitory activity but enhanced cytotoxicity. Our findings suggest that methyl cinnamate is a novel melanogenesis inhibitor from natural sources.
Keywords: 3,5-Dichloro-4-methoxybenzaldehyde; Matsutake mushroom; Melanogenesis; Methyl cinnamate; Murine B16-F10 melanoma cells; Tyrosinase.
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