BU72

BU72 is an extremely potent opioid used in pharmacological research.

Pharmacology
BU72 is an agonist for the μ-opioid receptor with exceptionally high binding affinity and potency, comparable to carfentanil. It also has extremely high efficacy, giving a stronger maximal effect than the standard full agonist DAMGO. In animal studies, it was found to be a potent analgesic, with a slow onset and long duration of action.

Chemistry
BU72 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. In the crystal structure, BU72 appears to bond to the receptor covalently, but this seems not to occur in vivo, since the compound binds reversibly, and preventing bond formation has no effect on affinity.