Charge and Substituent Effects on Affinity and Metabolism of Benzbromarone-Based CYP2C19 Inhibitors

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Abstract
Human cytochrome P450 (CYP) 2C19 is one of the most important CYP2C family members responsible for metabolizing commonly prescribed drugs. This research describes synthetic modifications to benzbromarone (Bzbr) to create the most potent CYP2C19 inhibitor ever reported. The most important features enabling analogues of Bzbr to bind to CYP2C19 with high affinity are low acidity (high pKa or nonionizability) and hydrophobic substituents adjacent to the phenol moiety. Though CYP2C19 was known to prefer neutral substrates, the extent was perhaps not realized until the anionic, parent compound Bzbr (Ki = 3.7 μM) was compared to a less acidic dimethyl analogue (Ki = 0.033 μM). However, differences in affinity for anionic and neutral Bzbr analogues did not appear to affect the regiospecificity of their metabolism by CYP's 2C19 and 2C9. In addition, some Bzbr analogues were metabolized both on the phenol and benzofuran rings. By using a substrate with a methyl ether in place of the Bzbr phenol, it was shown that some Bzbr analogues must be able to freely reposition after binding and oxidize the more energetically favorable position. Normally, O-demethylation of this methyl ether is favored over benzofuran hydroxylation based on ion current from LC/MS. Deuterium substitution of the methyl ether results in an inverse isotope effect on benzofuran hydroxylation (i.e. increased oxidation of this less favorable site). Likewise, Bzbr-based CoMFA models of CYP2C19 demonstrated no clear preference for any one ligand alignment. This suggests results from this modeling method must be interpreted carefully for each CYP isoform. In summary, Bzbr analogues have demonstrated they can be adapted to other CYP2C enzymes in order to probe isoform-specific properties.

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