Synthesis and 5-HT3 receptor affinity of new quinolinecarboxylic acid derivatives.

A series of quinolinecarboxylic acid amides and an ester with a quinuclidine moiety were synthesized and their in vitro affinities at 5-HT3, 5-HT4, and D2 receptors evaluated by radioligand binding assays. Highest affinity at 5-HT3 receptor corresponded to derivative 5 with Ki = 9.9 nM and with selectivity over 5-HT4 and D2 receptors. Compounds displayed moderate 5-HT3 antagonist activity (ED50 = 10.5-21.5 microg/kg i.v.). The obtained data suggest that the 5-HT3 receptor sites can accommodate the acyl group of the 2-quinoline derivatives. The results indicate the existence of an optimal distance between the lone electron pair of the quinoline nitrogen atom and the azabicyclic nitrogen atom, and a no-pharmacophoric pocket in the 5-HT3 receptor which would hold the fragment at the position 4 of the quinoline ring.