Affinity Labels for β-Adrenoreceptors: Preparation and Properties of Alkylating β-Blockers Derived from Indole

Article abstract of DOI:10.1021/jm00387a005

New alkylating ligands derived from indole with high affinity for β-adrenoceptors were synthesized and their properties examined.N⁸-(Bromoacetyl)-N¹-<3-(4-indolyloxy)-2-hydroxypropyl>-(Z)-1,8-diamino-p-menthane (8) and its N¹,N⁸ isomer (9) were prepared by the reaction of bromoacetyl bromide with a product of the condensation of 4-indolyl glycidyl ether with (Z)-1,8-diamino-p-menthane.A similar reaction employing 2-cyano-4-indolyl glycidyl ether yielded the respective cyano derivatives 10 and 11.Apparent affinities (K_i, M) for β-adrenoreceptors on membrane preparations from rat heart and lung were 4.6*10^-10 and 1.34*10^-9 for 8, 2.3*10^-8 and 4.5*10^-9 for 9, 6.1*10^-10 and 1.49*10^-9 for 10, and 1.83*10^-9 and 2.78*10^-9 for 11, respectively.When membranes were preincubated with the above ligands (1*10^-8 M, 30 min, 30 deg C) and then washed extensively, reduction in the concentration of specific binding sites of <3H>dihydroalprenolol ranged from 7percent to 76percent and there was no change in K_D of the remaining binding sites. (+/-)-Alprenolol and (-)-isoproterenol, but not (+)-isoproterenol, when included with the alkylating ligands in the preincubation mixtures, prevented the reduction in concentration of <3H>dihydroalprenolol binding sites.Compounds 8-11 alone did not stimulate adenylate cyclase activity in rat heart homogenates.However, these compounds inhibited (-)-isoproterenol-stimulated adenylate cyclase activity with K_i values ranging between 5*10^-9 and 60*10^-9 M.These results suggest that high-affinity irreversible β-adrenergic antagonists were obtained that may be useful for in vivo studies of β-adrenoceptors.