Antihypertensive activity in a series of 1-piperazino-3-phenylindans with potent 5-HT2-antagonistic activity.

A series of trans-1-piperazino-3-phenylindans were synthesized with the goal of replacing their established neuroleptic profile with that of peripheral 5-hydroxytryptamine (5-HT2) antagonism. Compounds with an unsubstituted or fluoro-substituted 6-position in the indan ring, and which had a five- or six-membered heterocyclic ring attached by an ethylene chain to the piperazine ring, satisfied this objective. Some of the compounds had potent antihypertensive activity in conscious, spontaneously hypertensive rats (SHR). In pithed rats they antagonized the pressor effect induced by 5-HT in doses 100-1000 times lower than doses needed to antagonize the pressor effect of phenylephrine. The effect was stereoselective and associated with enantiomers with 1R,3S absolute configuration. 1S,3R enantiomers inhibited the uptake of dopamine and norepinephrine in vitro. The compound with the best antihypertensive activity was (+)-(1R,3S)-1-[2-[4-[3-(4-fluorophenyl)-1-indanyl]-1- piperazinyl]ethyl]-2-imidazolidinone (Lu 21-098, irindalone). Its pharmacological profile resembled that of the standard compound ketanserin. There was a close structural correspondence between ketanserin and irindalone in a conformation that we recently identified as a D-2 receptor-relevant configuration of its neuroleptic "parent" tefludazine. This suggests that the dopaminergic (D-2) and the serotonergic (5-HT2) pharmacophores are structurally closely related.