AR-A 2 is a selective 5-HT1B receptor antagonist, with a high affinity to guineapig cortex 5HT1B 1D and recombinant guineapig 5-HT1B receptors (Ki: 0.24 and 0.47 nM) and with 10-fold lower affinity to guineapig 5-HT1D receptor (Ki: 5 nM).
Axelopran(TD-1211) is potentially useful for the treatment of opioid-induced constipation, it is a potent, selective, and peripherally-restricted μ-, κ-, and δ-opioid receptor antagonist.