Synthesis and biological activity of the putative metabolites of the atypical antipsychotic agent tiospirone.

Putative oxidative metabolites of the lead antipsychotic agent tiospirone (1) were synthesized to assist in the identification of the authentic metabolic products found in human urine samples. Thus far, six authentic metabolites have been correlated to the synthetic species. The putative metabolites were further examined in vitro to assess their central nervous system therapeutic potential. SAR analysis of these derivatives indicates that hydroxyl substitution, particularly in the azaspirodecanedione region of the molecule, diminishes the dopamine D-2 affinity of the species without significantly altering the serotonin type-1A and type-2 interactions. In addition, an increase in alpha 1-adrenergic affinity appears to be linked to the attenuation of effects at the dopamine receptors. The biological profile of the 6-hydroxytiospirone metabolite 42 was exemplary in these respects and the in vivo actions of this compound suggest potent antipsychotic potential with a minimal liability for extrapyramidal side effects (EPS). While compound 42 has been unambiguously characterized as an actual human metabolite of tiospirone, the role of 42 in the observed antipsychotic activity of the parent drug, if any, has not yet been determined.