A series of new derivatives of 4-aryl-pyrido[1,2-c]pyrimidine containing the 3-(4-piperidyl)-1H-indole residue or its 5-methoxy derivative were synthesized. They were characterized (i) in vitro by binding to 5-HT(1A) receptors and 5-HT transporter proteins in rat brain cortex membranes and (ii) in vivo in the mouse by induced hypothermia and forced swimming models for antagonist/agonist activity against the 5-HT(1A) autoreceptors and postsynaptic 5-HT(1A) receptors, respectively. Structure activity relationship evaluation indicated that the presence of the 3-(4-piperidyl)-1H-indole residue and ortho- or para-substituents with -F or -CH(3) groups in the aryl ring as well as an unsubstituted aryl in the 4-aryl-pyrido[1,2-c]pyrimidine moiety promoted low K(i) values for both receptors. In contrast, the presence of a 5-methoxy-3-(4-piperidyl)-1H-indole residue as well as -Cl or -OCH(3) substituents at the para position markedly reduced the receptor affinity.
A new series of chiral pyrido[1,2-a]pyrazine derivatives was synthesised and evaluated in in vivo animal models of epilepsy. A significant influence of the stereochemistry of the pyrido[1,2-a]pyrazine framework on the pharmacological activity was observed. Compounds with (4R,9aS) absolute configuration proved inactive, whereas other stereoisomers exhibited markedly dissimilar spectra of anti-seizure efficacy in the maximal electroshock seizure (MES), subcutaneous Metrazol seizure (scMET) and Pilocarpine-induced status prevention (PISP) tests. Importantly, the investigated agents revealed high potency in the 6Hz model, with the ED(50) values comparable to the reference drug Levetiracetam. Derivatives (4S,9aR)-6 and (4R,9aR)-6 emerged as promising new lead structures, the former having a broad spectrum of anticonvulsant activity and the latter showing high potency in 6Hz and PISP models.
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