Cytochrome P450 2D6 (CYP2D6) is a critical pharmacogene involved in the metabolism of ~20% of commonly used drugs across a broad spectrum of medical disciplines including psychiatry, pain management, oncology and cardiology. Nevertheless, CYP2D6 is highly polymorphic with single-nucleotide polymorphisms, small insertions/deletions and larger structural variants including multiplications, deletions, tandem arrangements, and hybridisations with non-functional CYP2D7 pseudogenes. The frequency of these variants differs across populations, and they significantly influence the drug-metabolising enzymatic function of CYP2D6. Importantly, altered CYP2D6 function has been associated with both adverse drug reactions and reduced drug efficacy, and there is growing recognition of the clinical and economic burdens associated with suboptimal drug utilisation. To date, pharmacogenomic clinical guidelines for at least 48 CYP2D6-substrate drugs have been developed by prominent pharmacogenomics societies, which contain therapeutic recommendations based on CYP2D6-predicted categories of metaboliser phenotype. Novel algorithms to interpret CYP2D6 function from sequencing data that consider structural variants, and machine learning approaches to characterise the functional impact of novel variants, are being developed. However, CYP2D6 genotyping is yet to be implemented broadly into clinical practice, and so further effort and initiatives are required to overcome the implementation challenges and deliver the potential benefits to the bedside.

As a continuing part of our research program in search of novel compounds for the treatment of schizophrenia, we report the synthesis and preliminary receptor binding affinity for a series of bicyclic analogues of clozapine derived from a selection of promising tricyclic candidates published previously. These bicyclic compounds investigate some substituent effects and the length and nature of the linker between an ionizable nitrogen atom at physiological pH and the introduced aryl moiety. The chemistry, structural characterization, and in vitro evaluation are described. Preliminary findings on the effects on activity of the nature and length of the linker, degree of unsaturation, and selected substituents coupled to the bicyclic nucleus are discussed in relation to affinity for dopamine D4 and serotonin 5-HT2A receptors.