New 1,2,3,9-tetrahydro-4H-carbazol-4-one derivatives: Analogues of HEAT as ligands for the α1-adrenergic receptor subtypes

Abstract With the aim to develop new ligands able to discriminate among the three subtypes of α 1 -adrenergic receptors (α 1A -AR, α 1B -AR, and α 1D -AR), a series of new 1,2,3,9-tetrahydro-4 H -carbazol-4-ones bearing a 3-[[[2-(4-hydroxyphenyl)ethyl]amino]methyl] or a 3-[[4-(2-substitutedphenyl)piperazin-1-yl]methyl] side chain were synthesized. The general structure of the new compounds is reminiscent of HEAT and RN5, two potent α 1 -AR antagonists which show high affinities for all three α 1 -AR subtypes. Some derivatives in which one ring of the tetrahydrocarbazolone system was opened were also prepared. Compounds were tested in radioligand binding assays on human cloned α 1A -AR, α 1B -AR, and α 1D -AR subtypes stably expressed in HEK293 cells. They showed moderate to good affinities, although their selectivity among the receptor subtypes hardly reached one order of magnitude.