Synthesis, 5-HT1A and 5-HT2A receptor activity of new 1-phenylpiperazinylpropyl derivatives with arylalkyl substituents in position 7 of purine-2,6-dione.

A series of new 1,3-dimethyl-7-phenylalkyl-8-[3-(4-phenyl-1-piperazinyl)propylamino]-purine-2,6-dione derivatives (10-16) was synthesized and their 5-HTIA and 5-HT2A receptor affinities were determined. It was found that compounds with the phenylpropyl substituent in position 7 of purine-2,6-dione (12, 14 and 16), or with phenylmethyl in position 7 and 2-OCH3 in the phenylpiperazine part (13) showed a distinct affinity for 5-HTIA receptors (Ki = 8-50 nM). No structural modifications resulted in 5-HT2A ligands, since the affinity of 10-16 for those receptors was insignificant (Ki = 115-550 nM). The new 5-HT1A receptor ligands (12-14, 16) were investigated in vivo to determine their functional activity at those receptors. In behavioral studies, 12-14 and 16 behaved like postsynaptic 5-HTIA receptor antagonists, since they reduced lower lip retraction and the behavioral syndrome induced by 8-OH-DPAT (5-HT1A receptor agonist) in rats. When given alone, none of the compounds investigated in vivo, mimicked 8-OH-DPAT activity in those tests. Derivative 12 did not affect the body temperature in mice, whereas 13, 14 and 16 decreased it. Furthermore, 12 did not change the hypothermia induced by 8-OH-DPAT, and the decrease in body temperature in mice induced by 13, 14 or 16 was not antagonized by WAY 100635 (5-HT1A receptor antagonist); hence in that model neither 12, 13, 14 nor 16 acted as antagonists or agonists, respectively, at presynaptic 5-HT1A receptors.