Structure of the flavonols and flavones and their mean Ki values (micromolar) as inhibitors of diclofenac 4′-hydroxylase activity in the CYP2C9 RECO system

Incubations performed using 0.3 pmol of RECO CYP2C9, 2.5 to 100 μM diclofenac, and a test compound with a concentration in the range 0 to approximately 6 times Ki. 4′-Hydroxydiclofenac/diclofenac was <1/20 in all assays. Global standard error for data fitting was less than 30% and γ2 > 0.90 for each effector.

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Flavonols K i Flavones K i
Galangin: 5,7=OH 0.15 Flavone 17
Fisetin: 7,3′,4′=OH 1.7 7-Hydroxyflavone: 7=OH 2.0
Kaempferol: 5,7,4′=OH 1.1 6-Hydroxyflavone: 6=OH 2.2a
Morin: 5,7,2′,4′=OH 1.8 Chrysin: 5,7=OH 1.0
Quercetin: 5,7,3′,4′=OH 2.0 Baicalein: 5,6,7=OH 0.91
Apigenin: 5,7,4′=OH 2.0
Luteolin: 5,7,3′,4′=OH 1.3
Scutellarein: 5,6,7,4′=OH 1.7
Wogonin: 5,7 = OH, 8=OCH3 1.0
Scutellarin (scutellarein 7-O-β-d-glucuronide) 75

Baicalin (baicalein 7-O-β-d-glucuronide)
  • a Noncompetitive inhibitor; all others are competitive inhibitors.