Hexahydrobenzo[a]phenanthridines: novel dopamine D₃ receptor ligands

We report that certain substituted hexathydrobenzo[a]phenanthridines are novel high affinity ligands selective for the dopamine D₃ receptor. These data demonstrate that substitutions on the heterocyclic nitrogen and the pendant phenyl ring of this nucleus cause a marked increase in both affinity and selectivity for dopamine D₃ vs. D₂ receptors. Thus, these compounds represent important new tools to study the pharmacology of dopamine D₃ receptors, and may also provide an opportunity for the synthesis of new radioligands for dopamine D₃ receptors.