PT  - JOURNAL ARTICLE
AU  - JAMES E. FERRELL, JR.
AU  - PETER D. G. CHANG SING
AU  - GILDA LOEW
AU  - ROY KING
AU  - JOAN M. MANSOUR
AU  - TAG E. MANSOUR
TI  - Structure/Activity Studies of Flavonoids As Inhibitors of Cyclic AMP Phosphodiesterase and Relationship to Quantum Chemical Indices
DP  - 1979 Sep 01
TA  - Molecular Pharmacology
PG  - 556--568
VI  - 16
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/16/2/556.short
4100  - http://molpharm.aspetjournals.org/content/16/2/556.full
SO  - Mol Pharmacol1979 Sep 01; 16
AB  - A series of 45 flavonoids and related compounds were tested as inhibitors of liver fluke cyclic nucleotide phosphodiesterase. Many were found to be potent inhibitors; seven were as potent or more potent than any inhibitor previously tested. The kinetics of six compounds spanning a wide range of activities were investigated and found to be competitive. The most potent inhibitors, cyanidin chloride and quercetin, had Ki values of 10 ± 3 µM and 13 ± 6 µM, respectively, approaching the Km for CAMP (8 µM). Structure/ activity studies showed that adding exocyclic substituents to the basic flavonoid skeleton affected activity only slightly, while changing the planarity of the heterocyclic ring greatly decreased activity. This observation, taken with the competitive kinetics, suggests that flavonoids compete with cAMP for a nucleotide binding site at which stacking occurs, perhaps similar to the binding sites of bovine pancreatic ribonuclease A and lobster glyceraldehyde-3-phosphate dehydrogenase. Quantum chemical calculations further suggest that the competition arises from the mimicking of the pyrimidine ring in cAMP by the pyranone ring of the flavonoids. If the flavonoids are comparably potent inhibitors of other phosphodiesterases, several reported pharmacological effects of the flavonoids might be explained. ACKNOWLEDGMENTS The cooperation of Dr. Martin Apple of the University of California, San Francisco, in providing many of the flavonoids and in helpful discussions is gratefully acknowledged. Also acknowledged are helpful discussions with Dr. Fred Fuhrman, Hopkins Marine Laboratory, and Drs. John Thomas and Oleg Jardetzky of Stanford University.