Synthesis and evaluation of 3-aryl piperidine analogs as potent and efficacious dopamine D4 receptor agonists

A series of 3-aryl piperidine analogs with 2-piperidinoalkylamino or 2-piperidinoalkyloxy fused bicyclic rings were prepared and found to be potent and efficacious human dopamine D4 agonists. The synthesis and structure-activity relationship (SAR) studies that led to the identification of these compounds are discussed.

Synthesis and Structure−Activity Studies on N-[5-(1H-Imidazol-4-yl)-5,6,7,8-tetrahydro-1-naphthalenyl]methanesulfonamide, an Imidazole-Containing α1A-Adrenoceptor Agonist

Structure-activity studies were performed on the alpha(1A)-adrenoceptor (AR) selective agonist N-[5-(1H-imidazol-4-yl)-5,6,7,8-tetrahydro-1-naphthalenyl]methanesulfonamide (4). Compounds were evaluated for binding activity at the alpha(1A), alpha(1b), alpha(1d), alpha(2a), and alpha(2B) subtypes. Functional activity in tissues containing the alpha(1A) (rabbit urethra), alpha(1B) (rat spleen), alpha(1D) (rat aorta), and alpha(2A) (rat prostatic vas deferens) was also evaluated. A dog in vivo model simultaneously measuring intraurethral pressure (IUP) and mean arterial pressure (MAP) was used to assess the uroselectivity of the compounds. Many of the compounds that were highly selective in vitro for the alpha(1A)-AR subtype were also more uroselective in vivo for increasing IUP over MAP than the nonselective alpha(1)-agonists phenylpropanolamine (PPA) (1) and ST-1059 (2, the active metabolite of midodrine), supporting the hypothesis that greater alpha(1A) selectivity would reduce cardiovascular side effects. However, the data also support a prominent role of the alpha(1A)-AR subtype in the control of MAP.

Dopamine D4 Ligands and Models of Receptor Activation: 2-(4-Pyridin-2-ylpiperazin-1-ylmethyl)-1H-benzimidazole and Related Heteroarylmethylarylpiperazines Exhibit a Substituent Effect Responsible for Additional Efficacy Tuning

A series of subtype selective dopamine D(4) receptor ligands from the hetroarylmethylphenylpiperazine class have been discovered that exhibit a remarkable structure-activity relationship (SAR), revealing a substituent effect in which regiosubstitution on the terminal arylpiperazine ring can modulate functional or intrinsic activity. Other structure-dependent efficacy studies in the dopamine D(4) field have suggested a critical interaction of the heteroarylmethyl moiety with specific protein microdomains in controlling intrinsic activity. Our studies indicate that for some binding orientations, the phenylpiperazine moiety also plays a key role in determining efficacy. These data also implicate a kinetic or efficiency term, contained within measured functional affinities for agonists, which support a sequential binding and conformational stabilization model for receptor activation. The structural similarity between partial agonist and antagonist, within this subset of ligands, and lack of bioisosterism for this substituent effect are key phenomena for these hypotheses.

Discovery of inhibitors of cell adhesion molecule expression in human endothelial cells. 1. Selective inhibition of ICAM-1 and E-selectin expression

A critical early event in the inflammatory cascade is the induced expression of cell adhesion molecules on the lumenal surface of vascular endothelial cells. These adhesion molecules include E-selectin, ICAM-1, and VCAM-1, which serve to recruit circulating leukocytes to the site of the inflammation. These adhesive interactions allow the leukocytes to firmly adhere to and cross the vascular endothelium and migrate to the site of tissue injury. Pharmaceutical agents which would prevent the induced expression of one or more of the cell adhesion molecules on the endothelium might be expected to provide a novel mechanism to attenuate the inflammatory responses associated with chronic inflammatory diseases. A thieno[2,3-d]pyrimidine, A-155918, was identified from a whole-cell high-throughput assay for compounds which inhibited the tumor necrosis factor-alpha (TNFalpha)-induced expression of E-selectin, ICAM-1, or VCAM-1 on human vascular endothelial cells. Traditional medicinal chemistry methods were applied to this low-micromolar inhibitor, resulting in the 2,4-disubstituted thieno[2,3-c]pyridine A-205804, a potent and selective lead inhibitor of E-selectin and ICAM-1 expression (IC(50) = 20 and 25 nM, respectively). The relative position of the nitrogen atom in the thienopyridine isomer was shown to be critical for activity, as was a small amide 2-substituent.

Structure-activity relationships of N-hydroxyurea 5-lipoxygenase inhibitors

The discovery of second generation N-hydroxyurea 5-lipoxygenase inhibitors was accomplished through the development of a broad structure-activity relationship (SAR) study. This study identified requirements for improving potency and also extending duration by limiting metabolism. Potency could be maintained by the incorporation of heterocyclic templates substituted with selected lipophilic substituents. Duration of inhibition after oral administration was optimized by identification of structural features in the proximity of the N-hydroxyurea which correlated to low in vitro glucuronidation rates. Furthermore, the rate of in vitro glucuronidation was shown to be stereoselective for certain analogs. (R)-N-[3-[5-(4-Fluorophenoxy)-2-furyl]-1-methyl-2-propynyl]-N-hydroxyure a (17c) was identified and selected for clinical development.

5-Lipoxygenase inhibitors: synthesis and structure-activity relationships of a series of 1-aryl-2H,4H-tetrahydro-1,2,4-triazin-3-ones

Synthetic routes were developed to access a variety of novel 1-aryl-2H,4H-tetrahydro-1,2,4-triazin-3-one analogs which were evaluated as 5-lipoxygenase (5-LO) inhibitors. The parent structure, 1-phenylperhydro-1,2,4-triazin-3-one (4), was found to be a selective inhibitor of 5-LO in broken cell, intact cell, and human blood assays with IC50 values of 5-21 microM. In a rat anaphylaxis model, 4 blocked leukotriene formation with an ED50 = 7 mg/kg when administered orally. Compound 4 exhibited selectivity for inhibition of 5-LO with little activity against related enzymes: 12-LO from human platelets, 15-LO from soybean, and cyclooxygenase (COX) from sheep seminal vesicle. In pilot subacute toxicity testing, 4 did not produce methemoglobinemia in rats (400 mg/kg po daily for 9 days) or in dogs (200 mg/kg po daily for 28 days). These results indicated that the triazinone structure provided a 5-LO inhibitor template devoid of the toxicity problems observed in the related phenidone (1) and pyridazinone (3) classes of 5-LO inhibitors. The parent compound 4 is a selective, orally bioavailable 5-LO inhibitor which can serve as a useful reference standard for in vivo pharmacological studies involving leukotriene-mediated phenonmena.