U-77891

U-77891 is an opioid analgesic drug that was first synthesized in 1983 by the Upjohn company.[1] 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.[2] The original work found a mixture of agonists and antagonists.
wikipedia

trans-3,4-Dibromo-N-methyl-N-(1-methyl-1-azaspiro[4.5]dec-6-yl)-benzamide is a μ-opioid, δ-opioid and κ-opioid receptors agonist and an analgesic agent.