The azulene framework as a novel arene bioisostere: design of potent dopamine D4 receptor ligands inducing penile erection.

Blue makes it happen: The non-uniform charge distribution of the blue colored azulene framework is highly suitable for the bioisosteric replacement of bicyclic heteroarene moieties. Showing an analogous binding mode as heterocyclic dopamine D4 receptor-selective lead compounds, the induction of penile erection in rats over a greater range of doses indicates a putative advantage of the rationally developed azulene derivative 2 b over apomorphine.