Beta-adrenergic blocking agents. 10. (3-amino-2-hydroxypropoxy)anilides

Quantitative structure-activity relationships of antianginal drugs

Quantitative structure-activity relationships (QSARs) of various classes of antianginal drugs, e.g. nitrates, beta-adrenergic blocking agents (beta-blockers), and calcium channel blockers (calcium antagonists), have been reviewed. This review gives an overall picture of the mode of action of each class of drugs and points out the specific physicochemical and structural properties that govern their activity. It is observed that in almost all kinds of antianginal drugs the lipophilic factor plays an important role and the next important factor seems to be the steric ones. The electronic factors are found to be occasionally important. In the case of beta-blockers, the most common factor that appeared to govern the activity remained the lipophilicity. In nitrates, too, the activity is observed to primarily depend upon the lipophilicity. In calcium channel blockers, however, the dominant effect is seen to be of steric factors. The steric roles may be essential in drug-receptor interactions, which seem to involve both hydrophobic, and to a lesser extent, electronic interactions.

Synthesis of oxypropanolamine derivatives of 3,4-dihydro-2H-1,4-benzoxazine, beta-adrenergic affinity, inotropic, chronotropic and coronary vasodilating activities

Aseries of oxypropanolamine derivatives of 3,4-dihydro-2H-1,4-benzoxazine were synthesized and evaluated for inotropic, chronotropic and coronary vasodilating activities in the canine heart, affinity to beta(1)-adrenergic receptor in turkey erythrocytes and affinity to the beta(2)-adrenergic receptor in the rat lung. Among these compounds, 4-acetyl-6-(3-tert-butylamino-2-hydroxy)propoxy-3,4-dihydro-2H-1,4-benzoxazine showed 2.1-fold more potent affinity to the beta(1) receptor than propranolol and 7-(3-tert-butylamino-2-hydroxy)propoxy-N-butyryl-3,4-dihydro-2H-1,4-benzoxazine showed 2.5-fold more potent affinity to the beta(2) receptor and furthermore 4386-fold more potent selectivity to the beta(2) receptor than propranolol. In addition, 4-acetyl-6-[3-(3,4-dimethoxybenzyl)amino-2-hydroxy]propoxy-3,4-dihydro-2H-1,4-benzoxazine showed 1.1-fold more potent affinity to the beta(1) receptor than propranolol and also 1147-fold more potent selectivity to the beta(1) receptor. With a few exceptions, negative inotropic and chronotropic actions of these compounds were dependent on the size of the 4-substituent obeying the order: unsubstituted < acetyl < propanoyl < butanoyl, while the benzoyl substituent conferred even stronger negative actions in the 6-oxypropanolamine derivatives. Neither negative inotropic and chronotropic actions related with affinity to beta(1)-adrenoceptor nor coronary vasodilator action related with affinity to beta(2)-adrenoceptor were observed. 4-acetyl-7-[3-(3,4-dimethoxybenzyl)amino-2-hydroxy]propoxy-3,4-dihydro-2H-1,4-benzoxazine exerted potent positive inotropic, chronotropic and coronary vasodilating actions. The inotropic and chronotropic actions of the latter compound may be attributed to the release of intrinsic catecholamines, as concluded by the absence of beta(1)-adrenoceptor affinity and disappearance of activity in the presence of a beta-blocker.

Further studies regarding the structure activity relationships of beta-adrenoceptor antagonists

1. The ortho (M66,527) and para (M66,368) analogues of 1-t-butylamino-3-(methoxyphenoxy)-2-propanol and para substituted tertiary butylphenoxy-1-N-isopropylamine-3 propanol-2 oxalate acid (L8429) were tested in dogs for their beta-adrenoceptor blocking activity.2. M66,527, which contains a methoxy group in the ortho position of the benzene ring, was found to be comparable to propranolol in blocking cardiac and peripheral vascular responses to isoprenaline. Like propranolol, M66,527 was more potent on peripheral receptors.3. Transference of the methoxy group to the para position (M66,368) reduced the overall potency; however, this compound was found to be relatively cardioselective in that it was 2 to 3.6 times more active in blocking cardiac responses to isoprenaline.4. The cardioselective properties of the short chain para methoxy substituent were less than those reported for compounds with longer para substitutions (i.e. practolol, para oxprenolol and para alprenolol).5. L8429, with a tertiary butyl group in the para position, was a weak beta-adrenoceptor antagonist without cardioselective properties. A longer, less bulky n-butyl group may provide for a more potent and selective antagonist.6. The results support the view that the size and site of the substituent on the benzene ring may be of importance in determining the cardioselective potency of beta-adrenoceptor antagonists.