GR103545

**GR103545** is a selective and potent **kappa opioid receptor (KOR) agonist** and serves as the active enantiomer of the racemic compound GR89696. It is widely used in research as a radiolabeled ligand, most notably as **[11C]GR103545**, for positron emission tomography (PET) imaging to quantify and map kappa opioid receptors in the brain. The compound exhibits high affinity for KOR (Ki ≈ 0.02–0.13 nM) and excellent selectivity over mu opioid receptor (MOR, 2.1 nM) and delta opioid receptor (DOR, 80.6 nM) targets[1][3][4][9]. In functional assays, GR103545 acts as a full agonist at KOR with much lower activity at MOR and negligible activity at DOR. It demonstrates good brain penetration and washout in PET studies, and its receptor binding profile allows its use in imaging and neuropharmacological research of disorders involving KOR, such as addiction, affective disorders, and pain[1][3][7][9]. The inactive enantiomer (+)-GR103545 binds negligibly to receptors.

Other names

(-)-GR103545active enantiomer of GR89696