WB 4101-related compounds.: 2.: Role of the ethylene chain separating amine and phenoxy units on the affinity for α1-adrenoreceptor subtypes and 5-HT1A receptors

WB 4101 (1)-related benzodioxanes were synthesized by replacing the ethylene chain separating the amine and the phenoxy units of 1 with a cyclopentanol moiety, a feature of 6,7-dihydro-5-[[(cis-2-hydroxy-trans-3-phenoxycyclopentyl)amino]methyl]-2-methylbenzo[b]thiophen-4(5H)-one that was reported to display an intriguing selectivity profile at alpha(1)-adrenoreceptors, This synthesis strategy led to 4 out of 16 possible stereoisomers, which were isolated in the case of (-)-3, (+)-3, (-)-4, and (+)-4 and whose absolute configuration was assigned using a chiral building block for the synthesis of (-)-3 starting from (+)-(2R)-2,3-dihydro-1,4-benzodioxine-2-carboxylic acid ((+)-9) and (1S,2S,5S)-2-amino-5-phenoxycyclopentan-1-ol ((+)-10). The aim of this project was to further investigate whether it is possible to differentiate between these compounds with respect to their affinity for alpha(1)-adrenoreceptor subtypes and the affinity for 5-HT1A receptors, as 1 binds with high affinity at both receptor systems. The biological profiles of reported compounds at alpha(1)-adrenoreceptor subtypes were assessed by functional experiments in isolated rat vas deferens (alpha(1A)), spleen (alpha(1B)), and aorta (alpha(1D)) and by binding assays in CHO and HeLa cells membranes expressing the human cloned alpha(1)-adrenoreceptor subtypes and 5-HT1A receptors, respectively. Furthermore, the functional activity of(-)-3, (+)-3, (-)-4, and (+)-4 toward 5-HT1A receptors was evaluated by determining the induced stimulation of [S-35]-GTP gamma S binding in cell membranes from HeLa cells transfected with human cloned 5-HT1A receptors. The configuration of the cyclopentane unit determined the affinity profile: a 1R configuration, as in (+)-3 and (-)-4, conferred higher affinity at alpha(1)-adrenoreceptors, whereas a 1S configuration, as in (-)-3 and (+)-4, produced higher affinity for 5-HT1A receptors. For the enantiomers (+)-4 and (-)-4 also a remarkable selectivity was achieved. Functionally, the stereoisomers displayed a similar alpha(1)-selectivity profile, that is alpha(1D) > alpha(1B) > alpha(1A), which is different from that exhibited by the reference compound 1. The epimers (-)-3 and (+)-4 proved to be agonists at the 5-HT1A receptors, with a potency comparable to that-of 5-hydroxytryptamine.