PF-514273 is a drug developed by Pfizer, which acts as an extremely selective antagonist for the CB1receptor, with approximately 10,000x selectivity over the closely related CB2 receptor. This very high selectivity makes it useful for scientific research into these receptors, as many commonly used cannabinoid receptor antagonists also block the CB2 receptor to some extent.
^Dow RL, Carpino PA, Hadcock JR, Black SC, Iredale PA, DaSilva-Jardine P, Schneider SR, Paight ES, Griffith DA, Scott DO, O'Connor RE, Nduaka CI. Discovery of 2-(2-chlorophenyl)-3-(4-chlorophenyl)-7-(2,2-difluoropropyl)-6,7-dihydro-2H-pyrazolo[3,4-f][1,4]oxazepin-8(5H)-one (PF-514273), a novel, bicyclic lactam-based cannabinoid-1 receptor antagonist for the treatment of obesity. Journal of Medicinal Chemistry. 2009 May 14;52(9):2652-5. PMID 19351113