Allosteric modulation of the adenosine A1 receptor.: Synthesis and biological evaluation of novel 2-amino-3-benzoylthiophenes as allosteric enhancers of agonist binding

Novel allosteric enhancers of agonist binding to the rat adenosine Al receptor are described. The lead compound for the new series was PD 81,723 ((2-amino-4,5-dimethyl-3-thienyl)[3(trifluoromethyl)phenyl]methanone), a compound previously reported by Bruns and co-workers (Mol. Pharmacol. 1990, 38, 950-958). The 4,5-dimethyl group and the benzoyl moiety were targets for further modifications, leading to series of 4,5-dialkyl (12a-g), of tetrahydrobenzo (12h-u), and of tetrahydropyridine (13a-g) derivatives. A number of compounds, in particular 12b, 12e, 12j, 12n, and 12u, proved superior to PD 81,723, Their EC50 values for enhancing the binding of the adenosine Al receptor agonist N-6-cyclopentyladenosine to the receptor were lower, and/or their antagonistic activity on the adenosine Al receptor was shown to be diminished.