PSB-SB-487 is a coumarin derivative which is an antagonist at the former orphan receptorGPR55. 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.
^Rempel V, Volz N, Hinz S, Karcz T, Meliciani I, Nieger M, et al. (September 2012). "7-Alkyl-3-benzylcoumarins: a versatile scaffold for the development of potent and selective cannabinoid receptor agonists and antagonists". Journal of Medicinal Chemistry. 55 (18): 7967–77. doi:10.1021/jm3008213. PMID22916707.