Flavonoids from Koelreuteria henryi and other sources as protein-tyrosine kinase inhibitors.

The EtOH extract of Koelreuteria henryi was investigated in a search for natural products with potential protein-tryrosine kinase (PTK) inhibitory activity. The PTK inhibitory activity of the crude fractions was determined by measuring their inhibition of p56lck partially purified from bovine thymus using angiotensin I as a substrate. Analysis of those fractions that exhibited significant activity led to the isolation of kaempferol and quercetin, in addition to two kaempferol glycosides, kaempferol-O3-alpha-rhamnopyranoside [1] and kaempferol-O3-alpha-arabinopyranoside [2]. This study represents the first report on the isolation of flavonols and their PTK inhibitory activities from the genus Koelreuteria. Eight other flavonoids were also examined to study the role of the hydroxy groups on the B ring on PTK inhibitory activity.