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Spiro[piperidine-4',1-(1,2,3,4-tetrahydro-beta-carboline)] (10), its derivatives 11-15 and its analogs 16 and 17 were examined as ligands of serotonin 5-HT1A receptors. It was shown that compounds 12 and 14 had essentially the same 5-HT1A affinity as 1-phenylpiperazine and its rigid analog 7, whereas there were substantial differences in the steric arrangement of their crucial pharmacophores, i.e. aromatic and protonation centers. On the basis of the existing models and using the (+)-LSD structure as a template, a new, extended three-point topographic model of 5-HT1A receptors has been proposed.

The 5-HT1A and 5-HT2A receptor affinity of model 1-(2-pyrimidinyl)-piperazine derivatives 15-21 and 23-32 has been determined. 2-(N-Methylpiperazino)-4,6-di(2-thienyl)pyrimidine 26 is a new, highly active and selective 5-HT2A receptor ligand. The topography of a molecule and the stereoelectronic effects of the thiophene rings are the major factors responsible for the high affinity and selectivity of 26 towards 5-HT2A sites.

The synthesis and the 5-HT1A and 5-HT2 receptor affinity of 2-substituted 1-[3-(4-aryl-1-piperazinyl)propyl]-imidazoles (1-8) has been described. It has been shown that both the N-3 imidazole atom and the N-1 piperazine one should be considered as possible protonation centers under physiological conditions. It has been found that the folded conformations of 1-8 exist predominantly in solution. Moreover, three different modes of interaction of the analyzed compounds with 5-HT1A and 5-HT2 receptor sites have been proposed.