Two stereoisomeric imidazoline derivatives: synthesis and optical and alpha 2-adrenoceptor activities

Two eight-step pathways for synthesizing the stereoisomeric compounds (-)-2-[1-(2,6-dichlorophenoxy)ethyl]-2-imidazoline hydrochloride ("levlofexidine" hydrochloride; (-)-lofexidine hydrochloride) and (+)-2-[1-(2,6-dichlorophenoxy)ethyl]-2-imidazoline hydrochloride ("dexlofexidine" hydrochloride; (+)-lofexidine hydrochloride) and the optical resolution of (+/-)-lofexidine are described. (-)-Lofexidine, a stereoselective alpha 2-adrenoceptor agonist, due to its center of asymmetry, is demonstrated to be a potent drug for the treatment of hypertension (doses 0.561 microgram/kg) and to have the highest affinity and a concentration dependency for alpha 2-adrenoceptors in direct binding studies (0.36 nmol/L). (+)-Lofexidine is 10 times less potent.