3-amino-3,4-dihydro-2H-1-benzopyran derivatives as 5-HT1A receptor ligands and potential anxiolytic agents .2. Synthesis and quantitative structure-activity relationship studies of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans]

In continuation of our work on 3-amino-3,4-dihydro-2H-1-benzopyran derivatives with high affinity for 5-HT1A receptors, we have prepared rigid spirobenzopyran analogues designed from the pharmacophore models of Mellin and selected via a quantitative structure-activity relationship approach mainly based on similarity indices. A series of spiro[pyrrolidine- and piperidine-2,3'(2'H)-benzopyrans] with various substitutions on the aromatic ring as well as on the extracyclic spiranic nitrogen atom were then synthesized and evaluated for their serotonergic and dopaminergic activities. Good correlation between the predicted and the experimental binding values was observed with an average difference of 0.2 unit on log(ICE(50)). Affinities for the 5-HT1A receptors were in the nanomolar range for the best compounds ((+)-11a, 23) with a high selectivity versus other 5-HT (5-HT1B, 5-HT2, 5-HT3) or dopamine (D-1, D-2) receptor subtypes. As for the 3-amino-3,4-dihydro-2H-1-benzopyran series, the dextrorotatory enantiomer (+)-11a showed better affinity and selectivity for 5-HT1A receptors than its levorotatory analogue (-)-11a. Compound (+)-11a proved in vitro to be a full agonist and in vivo to be active in various comportmental tests predictive of psychotropic activity, such as the forced swim test and the tail suspension test, and is currently under complementary investigations.