bu72 bu72 bu72 is an extremely potent opioid, with one of the highest known affinities for the μ-opioid receptor. in animal studies, it was found to be a potent analgesic, with a slow onset and long duration of action, but was not considered suitable to develop for medical use. it was used to produce the first crystal structure of the active μ-opioid receptor, and is now widely used to model the activation process. the stereochemistry has recently been revised, with the phenyl group in the (r) configuration, which has been accepted by the authors of the crystal structure. bu72 original proposed structure ((s)-phenyl epimer) bu72identifiers iupac name (2r,3s,3ar,5ar,6r,11br,11cs)-3a-methoxy-3,14-dimethyl-2-phenyl-2,3,3a,6,7,11c-hexahydro-1h-6,11b-(epiminoethano)-3,5a-methanonaphthoindol-10-ol cas number173265-76-4 ypubchem cid137348291iuphar/bps9363chemspider9662011uniikvn8rp2fqxchemblchembl4649916pdb ligandvf1 (pdbe, rcsb pdb)chemical and physical dataformulac28h32n2o2molar mass428.576 g·mol−13d model (jsmol)interactive image smiles co12c=c34c1(c)(n235ccn(c)4cc6ccc(o)cc56)c7ccccc7 inchi inchi=inchi=1s/c28h32n2o2/c1-25-17-26-11-12-28(25,32-3)24(29-23(25)18-7-5-4-6-8-18)27(26)13-14-30(2)22(26)15-19-9-10-20(31)16-21(19)27/h4-12,16,22-24,29,31h,13-15,17h2,1-3h3/t22-,23-,24+,25+,26-,27+,28+/m1/s1key:rgjhuvjqgaazlk-gktfkbbasa-n