AR-A 2 is a selective 5-HT1B receptor antagonist with high affinity to guinea pig cortex 5-HT1B/1D and recombinant guinea pig 5-HT1B receptors (Ki: 0.24 and 0.47 nM), exhibiting a 10-fold lower affinity to guinea pig 5-HT1D receptor (Ki: 5 nM).

5-HT1B/1D receptor (rat cortical): 20 nM , D2: 330 nM , 5-HT1B receptor (guinea pig): 0.47 nM , 5-HT1B/1D (guinea pig cortex):（ki）0.24 nM , 5-HT1B receptor (guinea pig):（EC50）4.5 nM , α1-adrenoceptor: 490 nM , 5-HT1A receptor (rat hippocampus): 3070 nM , 5-HT2A receptor (rat cortex): 339 nM , 5-HT1D receptor (guinea pig): 5 nM

AR-A 2 (AR-A000002) is a selective 5-HT1B receptor antagonist, exhibiting an EC50 of 4.5 nM for the guinea pig 5-HT1B receptor. It also binds to the rat cortical 5HT1B/1D receptor (Ki: 20 nM), rat cortex 5-HT2A receptor (Ki: 339 nM), rat hippocampus 5-HT1A receptor (Ki: 3070 nM), and shows affinity for dopamine D2 (Ki: 330 nM) and α1-adrenoceptors (Ki: 490 nM).