Binding of β-carbolines at imidazoline I2 receptors: a structure–affinity investigation

A series of ring-substituted (i.e., methoxy and bromo) 3,4-dihydro- and 1,2,3,4-tetrahydro-β-carbolines was examined at I2 imidazoline receptors, as was the effect of ring-opening, ring-expansion, and translocation of the piperidinyl nitrogen atom. Several analogues were identified that bind with Ki<20 nM at I2 sites and with reduced affinity at α2-adrenergic receptors, and 1,2,3,4-tetrahydro-γ-carbolines were identified as a novel class of I2 imidazoline receptor ligand.