RESUMEN
A series of 2,3-dihydro-2-oxo-1H-benzimidazole-1-carboxamide derivatives bearing a piperazine moiety was synthesized. Their in vitro 5-HT(4), 5-HT(3), and D(2) receptors affinities were evaluated by radioligand binding assay. For selected compounds functional studies at the 5-HT(4) receptor were made by using precontracted (by carbachol) preparations of rat esophageal tunica muscularis mucosae (TMM). The influence of the 3-substituent of the benzimidazole ring, the 4-substituent of the piperazine moiety, and the alkylene spacer was studied. Compounds with an ethyl or a cyclopropyl substituent in the 3-position of the benzimidazole ring showed moderate to high affinity (K(i) = 6.7-75.4 nM) for the 5-HT(4) receptor with selectivity over 5-HT(3) and D(2) receptors and moderate antagonist activity (pK(b) = 6.19-7.73). Compounds with an isopropyl substituent in the 3-benzimidazole position exhibited moderate and selective 5-HT(4) affinity (K(i) >/= 38.9 nM) and a partial agonist activity (5a, i.a. = 0.94) higher than that of the reference compound BIMU 8 (i.a. = 0.70). This reversal of the pharmacological activity due only to a small structural difference might confirm the existence of two binding sites on the 5-HT(4) receptor. In the alkylene spacer, a two-methylene chain is favorable to optimize the affinity and the antagonist or the partial agonist activity. In the ethyl and cyclopropyl series, 5-HT(4) antagonist activity seems to be unrelated to the size of the 4-substituent of the piperazine moiety, whereas a methyl group is optimal for high partial agonist activity in the isopropyl series; however, the presence of a butyl substituent is a favorable pattern for 5-HT(4) antagonism and even causes a reversal of the pharmacological profile in the isopropyl series (5h, pK(b) = 7.94). N-Butyl quaternization of 5a led to an improvement in affinity for the 5-HT(4) receptor and mantained the high partial agonist activity (5r, K(i) = 66.3 nM, i.a. = 0.93).
Asunto(s)
Amidas/síntesis química , Bencimidazoles/síntesis química , Receptores de Serotonina/efectos de los fármacos , Antagonistas de la Serotonina/síntesis química , Agonistas de Receptores de Serotonina/síntesis química , Amidas/química , Amidas/metabolismo , Amidas/farmacología , Animales , Bencimidazoles/química , Bencimidazoles/metabolismo , Bencimidazoles/farmacología , Cuerpo Estriado/metabolismo , Corteza Entorrinal/metabolismo , Esófago/efectos de los fármacos , Esófago/fisiología , Cobayas , Técnicas In Vitro , Masculino , Músculo Liso/efectos de los fármacos , Músculo Liso/fisiología , Ensayo de Unión Radioligante , Ratas , Ratas Wistar , Receptores de Dopamina D2/efectos de los fármacos , Receptores de Serotonina/metabolismo , Receptores de Serotonina 5-HT3 , Receptores de Serotonina 5-HT4 , Antagonistas de la Serotonina/química , Antagonistas de la Serotonina/farmacología , Agonistas de Receptores de Serotonina/química , Agonistas de Receptores de Serotonina/farmacología , Relación Estructura-ActividadRESUMEN
New 4-(diphenylmethyl)-1-piperazine derivatives with a terminal heteroaryl or cycloalkyl amide fragment were synthesized and evaluated for their antihistaminic, anticholinergic and antiallergic activities. Tested compounds were found to be moderate to potent in vitro (guinea-pig ileum) histamine H(1)-receptor antagonists. Derivatives with a four methylene chain (1e-1h) were as potent in vivo (capillary permeability in rats) as cetirizine; the heteroaryl derivatives 1e and 1h were found to be the most active agents. These compounds displayed only weak in vitro (guinea-pig ileum) muscarinic M(3)-receptor antagonist activity. Compounds 1e and 1g were about 100 times more potent than ketotifen in preventing the compound 48/80-induced histamine release from rat peritoneal mast cells. Derivatives 1e, 1f and 1h did not modify the spontaneous motor activity in rats at 100 mg/kg po. Compound 1e has been selected for further studies.
RESUMEN
A series of 8-beta-acyloxy-3-phenethyl-3-azabicyclo[3.2.1]octane and its N-endo methiodides were synthesized and studied by 1H and 13C NMR spectroscopy, and the crystal structure of 8-beta-p-chlorobenzoyloxy-3-phenethyl-3-azabicyclo[3.2.1]octane methiodide (2c) was determined by X-ray diffraction. In CDCl3 solution, 1b-1e display the same preferred conformation. The cyclopentane and piperidine rings adopt an envelope conformation flattened at C-8 and a distorted chair conformation puckered at C-8 and flattened at N-3, respectively, with the N-substituent in the equatorial position with respect to the piperidine ring. In all cases, methylation takes place from the endo position. The ability of the title compounds to antagonize the acetylcholine-induced contraction of guinea pig ileum is also reported. An initial structure-activity relationship is proposed.