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

With the aim to develop new ligands able to discriminate among the three subtypes of alfa1-adrenergic receptors (alfa1A-AR,alfa1B-AR, and alfa1D-AR), a series of new 1,2,3,9-tetrahydro-4H-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 isreminiscent of HEAT and RN5, two potent alfa1-AR antagonists which show high affinities for all three alfa1-AR subtypes. Some derivativesin which one ring of the tetrahydrocarbazolone system was opened were also prepared. Compounds were tested in radioligandbinding assays on human cloned alfa1A-AR, alfa1B-AR, and alfa1D-AR subtypes stably expressed in HEK293 cells. They showed moderateto good affinities, although their selectivity among the receptor subtypes hardly reached one order of magnitude.