Effect of modifications of the Alkylpiperazine moiety of trazodone on 5HT2A and α1 receptor binding affinity

A series of triazolopyridine derivatives (compounds 2a-I) were synthesized in order to-explore the effect of modifications of the alkylpiperazine moiety of trazodone (fragment A) on binding affinity for 5HT(2A) and alpha(1) receptors. All of the synthesized compounds show a decrease of affinity for both 5HT(2A) and alpha(1) receptors, as compared to trazodone, with the exception of compounds 2b,c which bear a methyl group in an alpha position to the aliphatic nitrogen atom N-1. These compounds showed a decrease of affinity only for the alpha(1) receptor. The stereochemical influence of the piperazine moiety of compound 2c was also evaluated. Enantiomer (S)-2c showed the most significant differences between 5HT(2A) and alpha(1) receptor affinity (IC50 values) and among the corresponding functional properties (pA(2) values). Since (S)-2c cannot generate the metabolite 4-(3-chlorophenyl)piperazine this product was selected for further pharmacological studies.