The aim of this work was to improve the oral bioavailability of a recently discovered, novel structural class of 5-HT 1A receptor agonists: aryl-{[4-(6-R-pyridin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl-methanone. Incorporation of a fluorine atom in the -position to the amino function in the side chain led to analogues that exhibited, in general, enhanced and longlasting 5-HT 1A agonist activity in rats after oral administration. Location of the fluorine atom at the C-4 position of the piperidine ring was the most favorable, and among the various substituents tested, the ability of the fluorine was unique in improving the oral activity of this family of ligands. Thus, the derivatives 39, 46, and 61 bound with higher affinity and selectivity to 5-HT 1A receptors (versus dopaminergic D 2 and adrenergic R 1 receptors) and displayed more potent 5-HT 1A agonist activity in vitro and in vivo than their C-4 desfluoro analogues. To examine the relationship between the conformation of the pharmacophore and the level of agonistic activity of this type of ligand, we synthesized a series of 3-chloro-4-fluorophenyl-(4-fluoro-4{[(5-(H or CH 3 )-6-R-pyridin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl-methanone derivatives and found that the combination of a 5-methyl and a 6-methylamino substituent on the pyridine ring synergistically affected their 5-HT 1A agonist properties. Thus, the 3-chloro-4-fluorophenyl-(4-fluoro-4{[(5-methyl-6-methylamino-pyridin-2-ylmethyl)-amino]-methyl}-piperidin-1-yl-methanone 40 behaved as a more potent 5-HT 1A receptor agonist in vitro and in vivo than its 5-unsubstituted analogue 38. The antidepressant potential of the lead compounds 40, 45, and 54 was examined by means of the forced swimming test (FST) in rats. The results indicated that, after a single oral administration, these compounds inhibited immobility in the FST more potently and more extensively than the clinically used antidepressant imipramine. Thus, 40, 45, and 54 are potent, orally active 5-HT 1A receptor agonists with marked antidepressant potential.

We report the discovery of novel 5-HT1A receptor agonists and describe the process that led to the antidepressant candidate 9 (F 15599). 9 has nanomolar affinity for 5-HT1A binding sites and is over 1000-fold selective with respect to the other 5-HT1 receptor subtypes, 5-HT2-7 receptor families, and also numerous GPCRs, transporters, ion channels, and enzymes. In a cellular model of signal transduction, 9 activates h5-HT1A receptors with an efficacy superior to that of the prototypical 5-HT1A agonist (+/-)-8-OH-DPAT and comparators undergoing clinical trials. After acute oral administration in rats, 9 totally reverses immobility in the forced swimming test and produces behaviors characteristic of 5-HT1A receptor activation. However, these effects occurred at widely separated doses, suggesting that 9 discriminates between distinct populations of 5-HT1A receptors. While the clinical relevance of these observations is still unknown, this opens new perspectives for the treatment of depressive disorders.

A search for novel, selective agonists with high intrinsic activity at the 5-HT1A subtype of serotonin (5-HT) receptors was undertaken. Mechanistic and thermodynamic considerations led to the design of 6-substituted-2-pyridinylmethylamine as a potential 5-HT1A pharmacophore. Various adducts derived from the 6-substituted-2-pyridinylmethylamine moiety were tested for their affinity at 5-HT1A, alpha1-adrenergic, and D2-dopaminergic receptors. Compounds with high affinity for 5-HT1A receptors (pKi >/= 8) were examined for agonist properties by measuring their ability to inhibit forskolin-stimulated cAMP production in HA7 cells (i.e., HeLa cells permanently transfected with the h5-HT1A receptor gene and expressing the h5-HT1A receptor protein). Several compounds of the type aryl¿4-[(6-substituted-pyridin-2-ylmethylamino)methyl]piperidin -1-yl¿ methanone had nanomolar affinity for 5-HT1A binding sites and were more than 500-fold selective with respect to alpha1 and D2 sites. Importantly, their 5-HT1A agonist properties were demonstrated in HA7 cells where they behaved as potent inhibitors of cAMP accumulation. In particular, (3, 4-dichlorophenyl)¿4-[(6-oxazol-5-ylpyridin-2-ylmethylamin o)methyl]pip eridin-1-yl¿methanone (70) and (3, 4-dichlorophenyl)¿4-[(6-azetidinopyridin-2-ylmethylamino)met hyl]piper idin-1-yl¿methanone (36) appeared to be more potent than, and at least as efficacious as, the prototypical 5-HT1A agonist (+/-)-8-OH-DPAT. SAR studies revealed that the pyridine nitrogen atom and the nature and the position of the substituents on the pyridine ring were critically involved in the ability of the compounds to recognize and activate 5-HT1A receptors. Structural modifications of the nonpharmacophoric part of the molecule showed, however, that the entire structure was required for affinity at 5-HT1A binding sites.

The aim of the research was to discover antagonists at α 2 receptor subtypes potentially more selective than known compounds. We focused on new, conformationally restricted analogues of atipamezole. The key step in the synthetic sequences leading to target compounds relied on a rhodiumcatalyzed intramolecular cyclopropanation reaction, the outcome of which varied with the nature of the diazo styrene precursor. Thus, depending on the substitution pattern of the double bond and the electronic properties of the diazo pre-

We report the discovery of a new family of α(2) adrenergic receptor antagonists derived from atipamezole. Affinities of the compounds at human α(2) and α(1b) receptors as well as their functional activities at hα(2A) receptors were determined in competition binding and G-protein activation assays, respectively. Central α(2) antagonist activities were confirmed in mice after oral administration. Further studies on a selected example: (+)-4-(1a,6-dihydro-1H-cyclopropa[a]inden-6a-yl)-1H-imidazole, (+)-1 (F 14805), were undertaken to probe the potential of the series. On the one hand, (+)-1 increased the release of noradrenaline in mouse frontal cortex following acute systemic administration, the magnitude of this effect being much larger than that obtained with reference agents. On the other, (+)-1 produced minimal cardiovascular effects in intact, anesthetized rat, a surprising outcome that might be explained by its differential action at peripheral and central α(2) receptors. A strategy for improving the therapeutic window of α(2) antagonists is put forward.