A series of new derivatives of sulfaphenazole (SPA), in which the NH(2) and phenyl substituents of SPA are replaced by various groups or in which the sulfonamide function of SPA is N-alkylated, were synthesized in order to further explore CYP 2C9 active site and to determine the structural factors explaining the selectivity of SPA for CYP 2C9 within the human P450 2C subfamily. Compounds in which the NH(2) group of SPA was replaced with R(1) = CH(3), Br, CH = CH(2), CH(2)CH = CH(2), and CH(2)CH(2)OH exhibited a high affinity for CYP 2C9, as shown by the dissociation constant of their CYP 2C9 complexes, K(s), which was determined by difference visible spectroscopy (K(s) between 0.1 and 0.4 microM) and their constant of CYP 2C9 inhibition (K(i) between 0.3 and 0.6 microM). This indicates that the CYP 2C9-iron(III)-NH(2)R bond previously described to exist in the CYP 2C9-SPA complex does not play a key role in the high affinity of SPA for CYP 2C9. Compounds in which the phenyl group of SPA was replaced with various aryl or alkyl R(2) substituents only exhibited a high affinity for CYP 2C9 if R(2) is a freely rotating and sufficiently electron-rich aryl substituent. Finally, compounds resulting from a N-alkylation of the SPA sulfonamide function (R(3) = CH(3), C(2)H(5), or C(3)H(7)) did not retain the selective inhibitory properties of SPA toward CYP 2C9. However, they are reasonably good inhibitors of CYP 2C8 and CYP 2C18 (IC(50) approximately 20 microM). These data allow one to better understand the structural factors that are important for selective binding in the CYP 2C9 active site. They also provide us with clues towards new selective inhibitors of CYP 2C8 and CYP 2C18.
Copyright 2001 Academic Press.