Synthesis and structure-activity relationships of a new model of arylpiperazines .1. 2-[[4-(o-methoxyphenyl)piperazin-1-yl]methyl]-1,3-dioxoperhydroimidazo[1,5-a]pyridine: A selective 5-HT1A receptor agonist

A series of new bicyclohydantoin-arylpiperazines was prepared and evaluated for affinity at 5-HT1A, alpha(1), and D-2 receptors. Most of the compounds showed very low affinity for D-2 receptors, and most of them demonstrated moderate to high affinity for 5-HT1A and alpha(1) receptor binding sites. SAR observations indicated that the length of the alkyl chain between the arylpiperazine and the hydantoin moiety is of great importance for 5-HT1A/alpha(1) affinity and selectivity, n = 1 being the optimal value. Compound 1h, 2-[[4-(o-methoxyphenyl)piperazin-1-yl]methyl]-1,3-dioxoperhydroimidazo[1,5-a]pyridine, bound at 5-HT1A sites with nanomolar affinity (K-i = 31.7 nM) and high selectivity over alpha(1), D-2, and 5-HT2A receptors (K-i > 1000, > 10 000, and > 1000 nM, respectively). Preliminary studies showed that this agent is probably functioning as a partial to full 5-HT1A agonist, and it displayed anxiolytic activity on the social interaction test in mice.