5-HT1B receptor antagonist properties of novel arylpiperazide derivatives of 1-naphthylpiperazine.

A new series of arylpiperazide derivatives of 1-naphthylpiperazine of general formula 4 has been prepared and evaluated as 5-HT1B antagonists. Binding experiments at cloned human 5-HT1A, 5-HT1B, and 5-HT1D receptors show that these derivatives are potent and selective ligands for 5-HT1B/1D subtypes with increased binding selectivity versus the 5-HT1A receptor when compared to 1-naphthylpiperazine (1-NP). Studies of inhibition of the forskolin-stimulated cAMP formation mediated by the human 5-HT1B receptor demonstrate that the nature of the arylpiperazide substituent modulates the intrinsic activity of these 1-NP derivatives. Among them, 2-[[8-(4-methylpiperazin-1-yl)naphthalen-2-yl]oxy] -1-(4-o-tolylpiperazin-1-yl)ethanone (4a) was identified as a potent neutral 5-HT1B antagonist able to antagonize the inhibition of 5-HT release induced by 5-CT (5-carbamoyltryptamine) in guinea pig hypothalamus slices. Moreover, 4a was found to potently antagonize the hypothermia induced by a selective 5-HT1B/1D agonist in vivo in the guinea pig following oral administration (ED50 = 0.13 mg/kg).

Dimers of 5HT1 ligands preferentially bind to 5HT1B/1D receptor subtypes.

New dimers of known 5HT1 ligands (5HT, 1-NP or 8-OH-DPAT) have been prepared and evaluated at human cloned 5HT1B, 5HT1D and 5HT1A receptors. Binding experiments show that all these dimers have better affinities at 5HT1B/1D receptors than their corresponding monomeric ligands. Studies of inhibition of the forskolin-stimulated c-AMP formation mediated by the human 5HT1B receptor show that hetero-bivalent ligands [combining an agonist (5HT) with an antagonist (1-NP)] behave as partial agonists while the intrinsic activity of bivalent antagonists (combining two 1-NP residues) was found to be spacer dependent. Surprisingly enough, the dimer of 8-OH-DPAT 6 binds to 5HT1A, 5HT1B and 5HT1D receptors with similar high affinity.