L-654284 is an α2-adrenergic receptor antagonist characterized by its notable selectivity. It competes with 3H-clonidine and 3H-rauwolscine for binding in vitro, exhibiting Ki values of 0.8 nM and 1.1 nM, respectively. L-654284 effectively blocks the pre-ejaculatory effects of clonidine in isolated rat vas deferens, with a pA2 value of 9.1. The compound demonstrates significant selectivity for α2 over α1 adrenergic receptors, with a Ki value of 110 nM against 3H-prazosin binding. In vivo, L-654284 significantly increases the turnover of norepinephrine in the rat cerebral cortex, indicating its activity in blocking α2-adrenergic receptors within the central nervous system.