Alkylating prazosin analogue: irreversible label for alpha 1-adrenoceptors.

A series of prazosin analogues comprised of N-acyl derivatives of N'-(4-amino-6,7-dimethoxyquinazolin-2-yl)piperazine was prepared and the nature of their binding to alpha 1-adrenoceptors was investigated. Derivatives with alpha, beta-unsaturated acyclic acyls had some affinity but no irreversible action at the receptor. Other potent compounds, also without irreversible activity, contained cinnamoyl or (phenylamino)thiocarbonyl residues. High affinity and irreversible binding were obtained with a bicyclo[2.2.2]octa-2,5-dien-2-ylcarbonyl derivative. The conjugated double bond in this compound was in about the same position and distance from the pharmacophore as in some of the above compounds of high affinity but with no irreversible action. Two consecutive recognition steps were thought to be involved in irreversible blockade: reversible binding of the pharmacophore part of the molecule to the binding site of the receptor, followed by reaction of the chemoreactive part with an adjacent nucleophile of the receptor. The present results suggest that for the second step to occur efficiently, some affinity for the receptor must be present even in the chemoreactive part of the molecule; simple spanning of the binding and nucleophile sites of the receptor was insufficient.

Affinity labels for beta-adrenoceptors: preparation and properties of alkylating beta-blockers derived from indole.

New alkylating ligands derived from indole with high affinity for beta-adrenoceptors were synthesized and their properties examined. N8-(Bromoacetyl)-N1-[3-(4-indolyloxy)-2-hydroxypropyl]-(Z)-1,8-dia mino-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 (Ki, M) for beta-adrenoceptors on membrane preparations from rat heart and lung were 4.6 X 10(-10) and 1.34 X 10(-9) for 8, 2.3 X 10(-8) and 4.5 X 10(-9) for 9, 6.1 X 10(-10) and 1.49 X 10(-9) for 10, and 1.83 X 10(-9) and 2.78 X 10(-9) for 11, respectively. When membranes were preincubated with the above ligands (1 X 10(-8) M, 30 min, 30 degrees C) and then washed extensively, reduction in the concentration of specific binding sites of [3H]dihydroalprenolol ranged from 7% to 76% and there was no change in KD 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 Ki values ranging between 5 X 10(-9) and 60 X 10(-9) M. These results suggest that high-affinity irreversible beta-adrenergic antagonists were obtained that may be useful for in vivo studies of beta-adrenoceptors.