Potent and selective A1 receptor inverse agonist. Exhibits high binding affinity at A1 receptor (Ki values are 0.07 and 0.96 nM for rat and human receptors respectively). Reduces basal [35S]-GTPγS binding 44.6% (IC50 = 0.19 nM). Antagonizes the effects of A1 agonist R-PIA (IC50 = 18.3 nM) and exhibits competitive antagonism on CCPA -induced tracheal contractions ex vivo. Displays 217- fold selectively over hA2A receptor and >1000-fold selectivity over hA3 receptor. Purity 98%. MW (observed): 350.39