Tetrahydrobenzothiophenone Derivatives as a Novel Class of Adenosine Receptor Antagonists
作者:A. Michiel van Rhee、Suhaib M. Siddiqi、Neli Melman、Dan Shi、William L. Padgett、John W. Daly、Kenneth A. Jacobson
DOI:10.1021/jm9504823
日期:1996.1.1
A novel class of non-nitrogen-containing heterocycles, the tetrahydrobenzothiophenones, was found to bind to adenosine receptors as antagonists in the micromolar range. Affinity was determined in radioligand-binding assays at rat brain A(1) and A(2a) receptors. A structure-activity analysis indicated that a 3-thioether group is favored and affinity at A(2a), but not at AL, receptors is highly dependent on this thioether substituent. A carboxylic acid-derived substituent is required at the 1-position of the thiophene ring, with esters being more potent in binding at A(1) receptors than the corresponding carboxyl hydrazide or carboxylic acid derivatives. The methyl (15) and ethyl (16) esters are about equipotent at A(1) but not at A(2a) receptors. A 4-keto group on the saturated ring is favored for receptor affinity. Dimethyl substitution at the B-position of the saturated ring is allowed. One of the most potent derivatives was the nonselective compound ethyl 3-(benzylthio)-4-oxo-4,5,6,7-tetrahydrobenzo[c]thiophene-1-carboxylate (BTH4, 7; Figure 1), which antagonized adenosine agonist-induced inhibition of adenylyl cyclase in rat adipocyte membranes with a K-B value of 1.62 +/- 0.73 mu M and adenosine agonist-induced stimulation of adenylyl cyclase in pheochromocytoma cell membranes with a K-B value of 9.19 +/- 0.98 mu M. Displacement of radioligand binding by BTH4 (7) at cloned human A(3) receptors was negligible, but one slightly A(3) selective compound (11, 3.9-fold over A(1) and >7.5-fold over A(2a)) was found. A 1-methylpropyl thioether (17) was 29-fold selective for A(1) vs A(2a) receptors. BTH4 (7) alone, at 10 mg/kg, stimulated locomotor activity in mice but paradoxically acted, under certain circumstances, synergistically with an A(1) selective agonist to depress locomotor activity. A pharmacophore model relating structural features of xanthine and non-xanthine adenosine antagonists to BTH4 (7) suggests a high degree of similarity in electrostatic surfaces, assuming that the thiophene ring superimposes the region of the uracil ring of xanthines.