KOR agonist 6 is a KOR agonist with a Ki value of 0.25 pM. In CHO cells, it exhibits agonistic activity on MOR and DOR and inhibits forskolin-stimulated cAMP accumulation. The compound stimulates KOR-mediated [35S]GTPγS binding in HEK293 cells expressing KOR and effectively suppresses cAMP accumulation as a potent agonist, showing lower β-arrestin recruitment efficacy. Additionally, KOR agonist 6 demonstrates analgesic effects in mice and can be employed in the study of analgesics with reduced central nervous system (CNS) side effects.

κ Opioid Receptor:0.25 pM (Ki)

KOR agonist 6 (Compound 5i) demonstrates an exceptionally high binding affinity for the κ-opioid receptor (KOR) (K i = 0.00025 nM) and exhibits outstanding subtype selectivity over the μ-opioid receptor (MOR) (K i = 14.1 nM) and δ-opioid receptor (DOR) (K i = 120.7 nM). In CHO cells, it shows agonistic activity on MOR (EC 50 = 44.78 nM, E max = 88.71%) and DOR (EC 50 = 15.26 nM, E max = 85.16%), while inhibiting forskolin-stimulated cAMP accumulation (EC 50 = 200.3 nM, E max = 99.51%). This compound exhibits potent stimulation of KOR-mediated [35S]GTPγS binding in KOR-expressing cell membranes (EC 50 = 0.024 nM, E max = 106.9%), and in HEK293 cells expressing KOR, it shows strong agonistic activity by inhibiting cAMP accumulation (EC 50 = 0.43 pM, E max = 63.63%). Additionally, KOR agonist 6 induces β-arrestin protein recruitment with moderate potency in HTLA cells transfected with KOR-Tango plasmid (EC 50 = 0.143 nM, E max = 42.89%).

KOR agonist 6 (Compound 5i), when administered via intraperitoneal injection at doses ranging from 0.4 to 8.0 mg/kg and evaluated 6 hours post-injection, demonstrated a dose-dependent analgesic effect in the mouse hot plate test (ED50 = 0.6 mg/kg). In the mouse abdominal constriction assay, this compound exhibited dose-dependent analgesic activity with an ED50 of 1.5 mg/kg, following similar injection parameters (0.08-8.0 mg/kg, monitored 6 hours post-administration). When tested in male CD1 mice, KOR agonist 6 (0.8-8.0 mg/kg, intraperitoneally injected, conditioned for 6 consecutive days, evaluated on day 8 with a 15-minute free exploration test) did not induce significant conditioned place aversion. Additionally, in male Kunming mice, administration of KOR agonist 6 (0.8-8.0 mg/kg, intraperitoneal injection, observed for 1 hour starting 6 hours post-injection) did not significantly reduce spontaneous locomotive activity (total movement distance).