Chemical transformations of oxyresveratrol (trans-2,4,3′,5′-tetrahydroxystilbene) into a potent tyrosinase inhibitor and a strong cytotoxic agent

From oxyresveratrol (trans-2,4,3′,5′-tetrahydroxystilbene 1), seven derivatives were prepared, including trans-2-methoxy-4,3′,5′-trihydroxystilbene (2), trans-2,3′-dimethoxy-4,5′-dihydroxystilbene (3), trans-4,3′-dimethoxy-2,5′-dihydroxystilbene (4), trans-2,4,3′,5′-tetramethoxystilbene (5) and cis-2,4,3′,5′-tetramethoxystilbene (6), 2,4,3′,5′-tetrahydroxybibenzyl (7), and 2,4,3′,5′-tetramethoxybibenzyl (8). The tetrahydroxybibenzyl 7, a hydrogenation product of 1, exhibited more potent tyrosinase inhibitory activity than the parent compound, without cytotoxicity. A kinetic study revealed that 7 was a reversible and non-competitive inhibitor of mushroom tyrosinase with l-dopa as the substrate. Analysis of the Ki values indicated that 7 has a slightly higher affinity to the enzyme than 1. Compound 6, a tetra-O-methylated analogue of 1 with cis-configuration, was deprived of inhibitory effect on the enzyme tyrosinase, but showed very strong cytotoxicity against the human cancer cells KB, BC, and NCI-H187, with potency comparable to those of the anticancer agents ellipticine and doxorubicin. Data on the tyrosinase inhibitory activity and cytotoxicity of 1–8 indicated that O methylation on stilbene 1 destroyed anti-tyrosinase activity but generated cytotoxicity. Thus, facile preparations of a potent tyrosinase inhibitor (7) and a strong cytotoxic agent (6) from the natural product 1 were achieved through simple chemical reactions.

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