Synthetic strategies to lower affinity for CYP2D6

There are several models for the CYP2D6 active site with the characteristics of their substrates and inhibitors well defined (1-3). Imipramine possesses such characteristics and is both a substrate and an inhibitor of the CYP2D6 enzyme (4-6). Possible synthetic strategies to avoid interaction with the enzyme have been investigated, including: attenuation of basicity; and alteration of rigidity and length of the alkyl chain. Imipramine inhibited the 1'-hydroxylation of bufuralol (10 mu M), an in vitro marker of CYP2D6 activity, in a CYP2D6 cell line (IC50 = 2.4 mu M). Inhibitory potency was attenuated by the removal of the basic centre; imipramine N-oxide had no inhibitory effect on bufuralol 1'-hydroxylation. However, removal of this basic centre, as a strategy to decrease CYP2D6 interaction, may well have a detrimental effect on pharmacological efficacy. Both an increase and decrease in the N-N carbon chain length [2C,4C] caused a reduction in inhibitory potency. In addition, introduction of a carbonyl adjacent to the amino dibenzyl moiety into 2C, 3C and 4C compounds brought about a further reduction in inhibitory potency. These data demonstrate that changes to the molecule, distal to the basic centre, can attenuate the affinity of the molecule for CYP2D6 and are in keeping with the known characteristics of the enzyme.