Synthesis and biological evaluation of fragmented derivatives of tetrahydroisoquinolines. 2. Trimetoquinol studies

Cardiovascular effect of a naphthylmethyl substituted tetrahydroisoquinoline, YS 49, in rat and rabbit

A novel tetrahydroisoquinoline, 1-alpha-naphthylmethyl-6,7-dihydroxy-1,2,3,4- tetrahydroisoquinoline (YS 49) 1) increased heart rate and force in isolated rat atria; 2) relaxed PE- and KCl-contracted rat aorta, and 3) decreased blood pressure and increased heart rate in anesthetized rabbit. These effects were blocked by propranolol, a nonselective beta-antagonist, but not by phentolamine, an alpha-blocker, and/or depletion of catecholamine by reserpine. These results suggest that the mechanism of action of YS 49 is due, at least in part, to beta-adrenergic receptor stimulation.

Pharmacologic antagonism of thromboxane A2 receptors by trimetoquinol analogs in vitro and in vivo

Although (-)-(S)-trimetoquinol [1-(3,4,5-trimethoxy-benzyl)- 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline; TMQ] is recognized as a potent bronchodilator, (+)-(R)-TMQ is a selective antagonist of human platelet aggregation and serotonin secretion induced by thromboxane A2 (TXA2) agonists. To confirm the pharmacological actions of TMQ analogs, the interaction of the drugs with TXA2 receptors was examined in human platelets and in a mouse sudden death model. The inhibitory potencies of TMQ analogs (pIC50 values) for displacement of [3H]SQ 29,548 binding to platelets showed excellent correlation with the respective pIC50 (-log IC50) values for U46619-induced aggregation (r = 0.99, P less than 0.01) and serotonin secretion (r = 0.99, P less than 0.01) in human platelet-rich plasma and for whole blood aggregation (r = 0.99, P less than 0.01). In each system, the rank order of inhibitory potencies was rac-iodoTMQ greater than or equal to (+)-(R)-TMQ greater than rac-TMQ much greater than (-)-(S)-TMQ. Antithrombotic effects of TMQ analogs were evaluated in a mouse sudden death model. In vivo antithrombotic potencies of these compounds were consistent with the in vitro potencies as TXA2 receptor antagonists in platelet systems. Administration of rac-iodoTMQ, (+)-(R)-TMQ and rac-TMQ 15 min before the injection of U46619 (800 micrograms/kg, iv) protected mice against U46619-induced sudden death. On the other hand, (-)-(S)-TMQ did not protect animals against death. Protection of U46619-induced cardiopulmonary thrombosis by TMQ analogs was seen at doses of 3-100 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological properties of novel bicyclic isoquinoline analogs in isolated guinea pig atria, trachea and in human platelets: relationship to trimetoquinol

1. Antiplatelet and beta-adrenoceptor activities of a set of secondary and tertiary N-methyl substituted amine analogs of trimetoquinol (TMQ, I and II, respectively) and 5,8-ethano-l-(p-methoxybenzyl)-1,2,3,4,5,6,7,8-octahydroisoquin oline (bicyclic isoquinoline compounds III and IV, respectively) were examined. 2. Compounds III and IV induced relaxations of guinea pig trachea which were blocked by propranolol whereas neither compound acted as an agonist nor antagonist of beta-adrenoceptors (chronotropy) in guinea pig atria. TMQ analogs (I and II) were agonists in both beta-adrenoceptor systems. 3. When tested in human platelets, compounds III and IV, like the TMQ analogs, blocked several inducers of the prostaglandin-dependent and -independent pathways, and the alpha 2-adrenoceptor-mediated pathway of platelet activation. 4. The bicyclic isoquinoline analogs (III and IV) possessed more selective beta 2-adrenoceptor stimulatory activity and equal or greater inhibitory activity against inducers of the prostaglandin-independent pathways of platelet function than the corresponding TMQ analogs (I and II). 5. These chemically novel lipophilic bicyclic compounds provide a new lead to the development of agents useful for the treatment of asthma and thrombotic disorders.

Pharmacological evaluation of the beta-adrenoceptor agonist properties of N-benzyl substituted trimetoquinol analogues

The beta 1- and beta 2-adrenoceptor agonist properties of trimetoquinol (TMQ, I) and N-benzyl ring substituted TMQ analogues (II, 4'-methylbenzylTMQ; III, 4'-chloro-benzylTMQ; IV, 4'-methoxybenzylTMQ; V, 4'-nitrobenzylTMQ; VI, 3',4'-dichlorobenzylTMQ; and VII, 4'-aminobenzylTMQ) were studied in guinea pig atria and trachea. All compounds gave concentration-dependent responses in atria and trachea, and the rank order of beta-adrenoceptor agonist potency was I greater than VII greater than II greater than V greater than IV greater than VI greater than III and I greater than VII greater than IV = VI greater than V greater than III greater than II, respectively. Whereas the N-benzyl substitution reduced potency for beta-agonist activity, the beta 2/beta 1-selectivity ratio was enhanced by addition of groups to the N-benzyl ring, and the rank order of beta 2-selectivity was VI (10-fold) greater than III (8-fold) = IV (8-fold) greater than VII (3-fold) greater than V = I greater than II. The results show that varying the nature of substituents on the N-benzyl ring of TMQ produces compounds which retain greater beta 2-selectivity.

Pharmacological evaluation of the beta-adrenoceptor agonist and thromboxane receptor blocking properties of 1-benzyl substituted trimetoquinol analogues

The beta 1- and beta 2-adrenoceptor agonist and thromboxane A2 (TXA2) antagonist properties of trimetoquinol (TMQ, I) and 1-benzyl substituted TMQ analogues [3'-iodo-4',5'-dimethoxy TMQ, II; 3',5'-diiodo-4'-dimethoxy TMQ, III; 3',4'-dimethoxy-5'-nitro TMQ, IV; 3',4'-dimethoxy-5'-amino TMQ; V; and 3',4'-dimethoxy TMQ, VI] were studied in guinea pig atria (beta 1) and trachea (beta 2), and in rat thoracic aorta and human platelets, respectively. The rank order of agonist activities in beta 1- and beta 2-adrenoceptor tissues was IV greater than or equal to I greater than II greater than V greater than III greater than VI and I greater than II = IV = V greater than VI greater than III, respectively. An increase of beta 2/beta 1-selectivity (2- to 3-fold) was observed for analogues V and VI as compared to TMQ. The rank order of inhibitory potency against U46619-induced contraction of rat aorta and human platelet aggregation and secretion was the same (I = II = III greater than IV greater than V greater than VI). The results show that varying the substituents at the 3'- and 5'-positions of the trimethoxybenzyl group of TMQ produces compounds which give different profiles of biological activity for beta-adrenoceptor agonism versus TXA2 antagonism. Certain TMQ analogues, notably analogue V, showed a greater selectivity as beta 2-receptor agonists and TXA2 antagonists in vascular smooth muscle than the parent drug (TMQ), and the iodinated analogues (II and III) have promise as potential radioligands or photoaffinity probes for thromboxane A2 receptors.

Pharmacological evaluation of the beta-adrenoceptor agonist and thromboxane antagonist properties of N-substituted trimetoquinol analogues

The beta 1- and beta 2-adrenoceptor agonist and U46619 (a thromboxane A2 agonist) antagonist properties of trimetoquinol (TMQ, I) and its optical isomers, and N-substituted TMQ analogues (methyl, II; 2-hydroxyethyl, III; cyclic sulfite N-2-chloroethyl, IV; 2-chloroethyl, V; benzyl, VI) were studied in guinea pig atria and trachea and rat aorta, respectively. All compounds gave concentration-dependent responses in atria and trachea, and the rank order of beta-adrenoceptor agonist potency was I greater than II greater than III greater than IV greater than V greater than VI. Whereas N-substitution reduced potency for beta-agonism, the beta 2/beta 1-selectivity ratio was enhanced by increasing the size of the N-substituent. All analogues possessed equal or greater (up to 41-fold more) beta 2-selectivity than I. Propranolol was a competitive antagonist of selected TMQ analogues in guinea pig trachea and atria, thus confirming the beta-adrenoceptor actions of these drugs. The optical isomers of TMQ gave a rank order of agonist potency of S(-)-TMQ greater than R(+)-TMQ, and a beta 2/beta 1-selectivity equal to or greater than racemic-TMQ. Each TMQ analogue also blocked the contractile responses of U46619 in rat aorta in a competitive manner, and the rank order of inhibition of U46619-induced contraction in rat aorta was I greater than VI greater than II = III greater than IV greater than V. N-Benzyl TMQ (VI) possessed the greatest potency for U46619 blockade and beta 2/beta 1-selectivity ratio of the N-substituted analogues. The results show that varying the N-substituents on TMQ produces compounds which retain beta 2-selectivity and give a different activity profile for beta-adrenoceptor activation vs. endoperoxide/thromboxane A2 antagonism.

Stereoselective interaction of tetrahydroisoquinolines in beta-adrenoceptor systems

In selected beta1- (heart, lipolysis) and beta2-adrenoceptor (trachea) systems, the interaction of racemic-trimetoquinol (TMQ) and the erythro- and threo-diastereomers of 1-(3',4',5'-trimethoxy-alpha-hydroxybenzyl)-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (alpha-hydroxy TMQ) was investigated. Each tetrahydroisoquinoline possessed agonist activity in these beta-adrenoceptor systems. The rank order of potency observed for these compounds was racemic-TMQ greater than erythro-alpha-hydroxy TMQ greater than threo-alpha-hydroxy TMQ. Using isolated fat adipocytes, a favorable correlation was observed between the elevation in c-AMP and pharmacological response for the TMQ stereoisomers and diastereomers of alpha-hydroxy TMQ. The rise in intracellular c-AMP produced by (-)- and (+)-TMQ in fat cells was blocked by the presence of propranolol, and not in the presence of phentolamine. Since considerably higher concentrations (greater 10(-4) M) of these compounds were required to produce a significant inhibition of c-AMP phosphodiesterase activity in adipose tissue, it is proposed that the lipolytic response is a result of stereoselective interaction of these tetrahydroisoquinolines at the level of membrane-bound adenylate cyclase.