Inhibition of Adenosine 3', 5'-Cyclic Monophosphate Phosphodiesterase by Flavonoids. II

Thirty-eight flavones obtained from Scutellaria baicalensis and ninety six related flavones were tested for inhibitory activity against adenosine 3', 5'-cyclic monophosphate phosphodiesterase from beef heart. The most active inhibitor is 8-methoxy-5, 7, 2'-trihydroxyflavone from S. baicalensis. Its IC50 value is 0.6(× 10-5 M/l). The structure-activity relationships were investigated. a) O-Methylated flavones generally show lower inhibitory activity than the corresponding hydroxyflavones among the flavones having under four substituents. b) O-Methylated flavones generally show higher inhibitory activity than the corresponding hydroxyflavones in the flavones having over five substituents. (c) C-Glycosides are almost all poor inhibitors. (d) O-Glycosides are generally less potent than the corresponding flavones.