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Syntheses of 5,6,7- and 5,7,8-trioxygenated 3',4'-dihydroxyflavones having alkoxy groups and their inhibitory activities against arachidonate 5-lipoxygenase.

Arachidonate 5-lipoxygenase plays a pivotal role in the biosynthesis of leukotrienes. Cirsiliol (3',4',5-trihydroxy-6,7-dimethoxyflavone), a selective inhibitor of the enzyme, was derivatized by introducing alkyl groups of various chain lengths at positions 5, 6, 7, and 8 of the A ring of the flavone skeleton. Modification of the positions 5 and 6 with an alkyl group of 5-10 carbons markedly decreased the IC50 values for 5-lipoxygenase inhibition to the order of 10 nM. As tested with 5- or 6-hexyloxy derivatives, a relatively selective inhibition of 5-lipoxygenase was shown. Inhibition of 12-lipoxygenase required much higher concentrations of these compounds, and cyclooxygenase was not inhibited. Modification of positions 7 and 8 did not increase the inhibitory effect of most flavone compounds.