Beta-adrenoceptor antagonist activity of bivalent ligands. 1. Diamide analogues of practolol.

Two series of bivalent ligands (P-X-P) containing the (R,S)-3-[(4-aminoaryl)oxy]-1-(isopropylamino)propan-2-ol pharmacophore and a connecting alpha,omega-dicarbonylpoly(methylene) [X = -OC(CH2)nCO-] or alpha,omega-N,N'-bis(carbonylmethylene) polymethylenediamine [X = -OCCH2NH(CH2)nNHCH2CO-] spanner were synthesized and evaluated for beta-adrenoceptor antagonist activity in rat heart and lung membrane preparations. The target compounds were obtained as a mixture of stereoisomers in modest yields by using a three to four step sequence beginning with N-benzylpractolol. The results from the competitive binding studies indicated that binding affinity increased by a factor of up to 160 by increasing the length of the group spanning the pharmacophore moieties. Modest increases in cardioselectivity were also obtained. The data suggest that further increases in spanner length and lipophilicity and optical resolution may improve the potential of a labeled bivalent beta 1-adrenoceptor antagonist to function as a myocardial imaging agent.