Structure--activity relationships among novel phenoxybenzamine-related beta-chloroethylamines.
A series of beta-chloroethylamines 5--18, structurally related to the irreversible alpha(1)-adrenoceptor antagonist phenoxybenzamine [PB, N-benzyl-N-(2-chloroethyl)-N-(1-methyl-2-phenoxyethyl)amine hydrochloride, 1] and the competitive antagonist WB4101 [N-(2,3-dihydro-1,4-benzodioxin-2-ylmethyl)-N-[2-(2,6-dimethoxyphenoxy)ethyl]amine hydrochloride, 2], were synthesized and evaluated for their activity at alpha-adrenoceptors of the epididymal and the prostatic portion of young CD rat vas deferens. All compounds displayed irreversible antagonist activity. Most of them showed similar antagonism at both alpha(1)- and alpha(2)-adrenoceptors, whereas compounds 13 and 18, lacking substituents on both the phenoxy group and the oxyamino carbon chain, displayed a moderate alpha(1)-adrenoceptor selectivity (10--35 times), which was comparable to that of PB. Compounds 14 and 15, belonging to the benzyl series and bearing, respectively, a 2-ethoxyphenoxy and a 2-i-propoxyphenoxy moiety, were the most potent alpha(1)-adrenoceptor antagonists with an affinity value similar to that of PB (pIC(50) values of 7.17 and 7.06 versus 7.27). Interestingly, several compounds were able to distinguish two alpha(1)-adrenoceptor subtypes in the epididymal tissue, as revealed by the discontinuity of their inhibition curves. A mean ratio of 24:76 for these alpha(1)-adrenoceptors was determined from compounds 8--10, 12, and 15--17. Furthermore, compounds 9, 10, 12, 16a, and 16b showed higher affinity towards the minor population of receptors, whereas compounds 8, 15, and 17 preferentially inhibited the major population of alpha(1)-adrenoceptors. In addition, selected pharmacological experiments demonstrated the complementary antagonism of the two series of compounds and their different, preferential affinity for one of the two alpha(1)-adrenoceptor subtypes. In conclusion, we found beta-chloroethylamines that demonstrate a multiplicity of alpha(1)-adrenoceptors in the epididymal portion of young CD rat vas deferens and, as a consequence, they are possible useful tools for alpha(1)-adrenoceptor characterization.
Giardinà
Dario
D
Department of Chemical Sciences, University of Camerino, Italy. giardina@camserv.unicam.it
Crucianelli
Mauro
M
Angeli
Piero
P
Buccioni
Michela
M
Gulini
Ugo
U
Marucci
Gabriella
G
Sagratini
Gianni
G
Melchiorre
Carlo
C
D000317:Adrenergic alpha-Antagonists / Q000138:chemical synthesis* / Q000494:pharmacology; D000818:Animals; D004146:Dioxanes; D004305:Dose-Response Relationship, Drug; D005021:Ethylamines / Q000138:chemical synthesis* / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008297:Male; D010643:Phenoxybenzamine / Q000138:chemical synthesis* / Q000494:pharmacology; D011485:Protein Binding; D051381:Rats; D013329:Structure-Activity Relationship; D014649:Vas Deferens / Q000187:drug effects
D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D005021:Ethylamines; D010643:Phenoxybenzamine; C010654:(2-(2',6'-dimethoxy)phenoxyethylamino)methylbenzo-1,4-dioxane; C010076:2-chloroethylamine