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Bioassay-directed fractionation of a medicinal plant, Polygonum cuspidatum (Polygonaceae), has led to the discovery of a hydroxystilbene, resveratrol 1, as an inhibitor of a protein-tyrosine kinase (p56lck) partially purified from bovine thymus. Both trans and cis isomers of resveratrol possess comparable protein-tyrosine kinase inhibitory activity. Comparison of the IC50 values of resveratrol for protein-tyrosine kinase inhibitory activity with those of piceid (resveratrol-O3-beta-glucoside) 2 and resveratrol-O4'-beta-glucoside 3 shows the requirement of free hydroxyl groups on both phenyl rings for the protein-tyrosine kinase inhibition. Protein kinase C inhibitory analysis suggests the requirements of two free hydroxyl groups on one phenyl ring only.
Jayatilake et al. (Fri,) studied this question.