Benextramine-neuropeptide Y receptor interactions: contribution of the benzylic moieties to [3H]neuropeptide Y displacement activity

Abstract

Analogs of N,N'-bis[6-[(2-methoxybenzyl)amino]hex-1-yl]cystamine (benextramine, BXT, 2) were synthesized using solution-phase peptide synthesis methodology and analyzed for activity in displacing specifically bound 1 nM N-[propionyl-3H]neuropeptide Y([3H]NPY) from benextramine-sensitive neuropeptide Y (NPY) binding sites in rat brain. Our new synthetic approach to these analogs began with the acylation of cystamine with the N-hydroxysuccinimide ester of tert-butyloxycarbonyl (t-Boc) protected 6-aminohexanoic acid, followed by deprotection of the t-Boc groups with 4 N HCl in dioxane. Acylation of this symmetric diamine with N-hydroxysuccinimide esters of appropriately substituted benzoic acids, followed by reduction of the resultant tetraamides with diborane in refluxing THF, afforded the target compounds. The BXT analog lacking the benzylic group (i.e., compound 11) had no [3H]NPY displacement activity at concentrations up to 1.4 x 10(-3) M. The 9-fold range in activities observed for the ortho, meta, and para regioisomers of the methoxy, chloro, and hydroxy benextramine analogs at benextramine-sensitive NPY rat brain binding sites does not differ from the range of potencies observed at alpha-adrenoceptors. However, the order of potencies at [3H]NPY sites differs from the order of potencies at alpha-adrenoceptors, with the m-methoxyphenyl (9a), m-hydroxyphenyl (10b), and 2-naphthyl (9f) analogs being the most active at [3H]NPY binding sites. The present results demonstrate the importance of the benzylic moiety for BXT's NPY antagonist activity, and suggest that the BXT binding site on the NPY receptor is significantly distinct from that on the alpha-adrenoceptor.