PSB SB 487

PSB-SB-487 is a coumarin derivative which is an antagonist at the former orphan receptor GPR55. Unlike older GPR55 antagonists such as O-1918, PSB-SB-487 has good selectivity over the related receptor GPR18, with an IC₅₀ of 113nM at GPR55 vs 12500nM at GPR18. However it has poorer selectivity over other related receptors, acting as a weak antagonist at CB₁ with a Ki of 1170nM, and a partial agonist at CB₂ with a Ki of 292nM.