SYNTHESIS AND INVITRO EVALUATION OF 5,6,7,8,9,10-HEXAHYDRO-7,10-IMINOCYCLOHEPT[B]INDOLES - HIGH-AFFINITY LIGANDS FOR THE N,N'-DI-O-TOLYLGUANIDINE-LABELED SIGMA BINDING-SITE

A series of 5,6,7,8,9,10-hexahydro-7,10-iminocyclo[b]indoles substituted at the 5 and/or 11 positions was synthesized from tropinone. Affinity for sigma binding sites was determined using [H-3]-N,N'-di-o-tolylguanidine ([H-3]DTG) and [H-3]-(+)-3-(3-hydroxyphenyl)-N-1-propylpiperidine ([H-3]-(+)-3-PPP) and for the dopamine D2 receptor labeled with [H-3]sulpiride. Nearly all compounds studied in this series possessed a higher affinity for [H-3]DTG than [H-3]-(+)-PPP-labeled sigma sites, suggesting that [H-3]DTG and [H-3]-(+)-3-PPP radioligands label pharmacologically distinct sigma binding sites, as reported previously. Substitution at the 11 position with side chains containing a four-carbon tether resulted in compounds having the highest affinity for the [H-3]DTG-labeled a site. The most potent and selective member of this series was 11-[4-(2-furanyl)butyl]-5,6,7,8,9, 10-hexahydro-7,10-iminocyclohept[b]indole(40). Enantioselectivity was investigated by preparing the (+)- and (-)-isomers of 40. These studies revealed that (+)-40 was more potent at the [H-3]-DTG-labeled sigma site whereas (-)-40 had a higher affinity at sigma sites labeled with [H-3]-(+)-PPP. Racemic 40 was observed to possess a higher affinity than either of its respective enantiomers at both the [H-3]DTG- and [H-3]-(+)-3-PPP-labeled sites, suggesting an allosteric interaction.