Benzisothiazoles and beta-adrenoceptors: synthesis and pharmacological investigation of novel propanolamine and oxypropanolamine derivatives in isolated rat tissues.
In an attempt to examine the ability of benzisothiazole-based drugs to interact with beta-adrenoceptors, a series of 1,2-benzisothiazole derivatives, which were substituted with various propanolamine or oxypropanolamine side chains in the 2 or 3 position, were synthesised and tested. The pharmacological activity of these compounds at the beta-adrenoceptors was examined using isolated rat atria and small intestinal segments, which preferentially express the beta1- and beta3-adrenoceptor-mediated responses, respectively. None of these products showed any beta-adrenoceptor agonistic activity. In contrast, the 2- and 3-substituted isopropyl, tert-butyl, benzyl, and piperonyl derivatives 2a-d and 3a-d elicited surmountable inhibition of the isoprenaline-induced chronotropic effects in the atria, suggesting competitive antagonism at the beta1-recognition site. The pA2 values revealed tert-butyl 3b and the isopropyl substituted piperonyl derivatives 3a to be the most effective. Remarkably, many of the 2-substituted propanolamines were less active than the corresponding 3-substituted oxypropanolamines. With the exception of compound 3b, none of these drugs antagonised the muscle relaxant activity of isoprenaline in the intestine, suggesting no effect on the beta3-adrenoceptors. These results confirm the ability of the benzisothiazole ring to interact with the beta-adrenoceptors, and demonstrate that 2-substitution with propanolamine or 3-substitution with oxypropanolamine groups yields compounds with preferential antagonistic activity at the cardiac beta1-adrenoceptors. The degree of antagonism depends strongly on both the nature of the substituent and its position on the benzisothiazole ring.
Morini
Giovanni
G
University of Parma, School of Pharmacy, Pharmaceutical Department, Italy.
Poli
Enzo
E
Comini
Mara
M
Menozzi
Alessandro
A
Pozzoli
Cristina
C
D058671:Adrenergic beta-1 Receptor Antagonists; D058672:Adrenergic beta-2 Receptor Antagonists; D058673:Adrenergic beta-3 Receptor Antagonists; D000319:Adrenergic beta-Antagonists / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006325:Heart Atria / Q000187:drug effects; D007082:Ileum / Q000187:drug effects / Q000502:physiology; D007545:Isoproterenol / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009200:Myocardial Contraction / Q000187:drug effects; D011412:Propanolamines / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D013844:Thiazoles / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*
D058671:Adrenergic beta-1 Receptor Antagonists; D058672:Adrenergic beta-2 Receptor Antagonists; D058673:Adrenergic beta-3 Receptor Antagonists; D000319:Adrenergic beta-Antagonists; D011412:Propanolamines; D013844:Thiazoles; C466948:benzisothiazole; C507551:oxypropanolamine; D011433:Propranolol; D007545:Isoproterenol