beta-funaltrexamine beta-funaltrexamine β-funaltrexamine (β-fna) is an irreversible (covalently bonding) opioid antagonist that was used to create the first crystal structure of the μ-opioid receptor. chemically, it is a naltrexone derivative with a methyl-fumaramide group in the 6-position. β-funaltrexamine names iupac name methyl (2e)-4--4-oxobut-2-enoate systematic iupac name methyl (2e)-4--4-oxobut-2-enoate identifiers cas number 72782-05-9 3d model (jsmol) interactive image abbreviations β-fna chebi chebi:81527 chembl chembl473136 chemspider 4470557 kegg c18127 pubchem cid 5311018 inchi inchi=1s/c25h30n2o6/c1-32-20(30)7-6-19(29)26-16-8-9-25(31)18-12-15-4-5-17(28)22-21(15)24(25,23(16)33-22)10-11-27(18)13-14-2-3-14/h4-7,14,16,18,23,28,31h,2-3,8-13h2,1h3,(h,26,29)/b7-6+/t16-,18-,23+,24+,25-/m1/s1key: pqkhesytskmwfp-wzjclrdwsa-n smiles coc(=o)/c=c/c(=o)n1cc2(3cc4ccc(c5c42(1o5)ccn3cc6cc6)o)o properties chemical formula c25h30n2o6 molar mass 454.523 g·mol−1 except where otherwise noted, data are given for materials in their standard state (at 25 °c , 100 kpa). infobox references