u-77891 u-77891 u-77891 is an opioid analgesic drug that was first synthesized in 1983 by the upjohn company. it was originally synthesized to prove that the removal of a single methylene spacer of the benzamide would alter a κ-opioid receptor agonist such as u-50488 into an μ-opioid receptor agonist, as well as producing a semi-rigid derivative of u-47700. this would help elucidate the relative positions of the hydrogen-bond acceptors and substituted aromatic system to find the compound with the lowest ki value in a series of benzamide opioids dating back to the 1970s. the original work found a mixture of agonists and antagonists. u-77891clinical dataroutes ofadministrationby mouth, parenteralidentifiers iupac name 3,4-dibromo-n-methyl-n-decan-6-yl]benzamide cas number119878-31-8 ypubchem cid117071705chemspider23120785unii7p6974d7rxchemblchembl279065chemical and physical dataformulac18h24br2n2omolar mass444.211 g·mol−13d model (jsmol)interactive image smiles cn1ccc12cccc2n(c)c(=o)c3ccc(br)c(br)c3 inchi inchi=1s/c18h24br2n2o/c1-21-11-5-10-18(21)9-4-3-6-16(18)22(2)17(23)13-7-8-14(19)15(20)12-13/h7-8,12,16h,3-6,9-11h2,1-2h3/t16-,18+/m1/s1key:xhbtzwgphrhwqz-aefflsmtsa-n u-77891 acts as an agonist of the μ-opioid, δ-opioid and κ-opioid receptors with ki values of 2, 105 and 2300 nm, respectively. the compound has ed50 values of 0.02 mg/kg and 0.21 mg/kg in mouse phenylquinone writhing and tail-flick assays. one reason for the high potency is the logp of 4.57, allowing it to accumulate in fatty tissue such as the brain.