NEW KAPPA-RECEPTOR AGONISTS BASED UPON A 2-((ALKYLAMINO)METHYL)PIPERIDINE NUCLEUS

The syntheses of some 1-[(3,4-dichlorophenyl)acetyl]2-[(alkylamino)methyl]peperidines and their activities as kappa-opioid receptor agonists are described. Selected structural modifications are made to the basic moiety and at the 2-, 3-, 4-, 5-, and 6-positions on the piperidine nucleus to enable structure-activity relationships to be delineated. As a result, some highly potent and selective kappa-receptor agonists have been identified. In particular, this has been achieved by introduction of oxygen-containing functionality into the 4-position of the piperidine nucleus or the 3-position of the pyrrolidinylmethyl side chain. Thus, 1-[(3,4-dichlorophenyl)acetyl]2-[[1-(3-oxopyrrolidinyl)methyl]?? piperidine (10) possesses high activity in the rabbit vas deferens (LCD, kappa-specific tissue) (IC50 = 0.20 nM) and is a potent antiociceptive agent, as determined by the mouse acetylcholine-induced abdominal constriction test (MAC) (ED50 = 0.06 mg/kg sc). The spirocyclic analogue 8-[3,4-dichlorophenyl)acetyl]7-(1-pyrrolidinylmethyl)-1,4-dioxa-8-azaspiro[4.5]decane (39) showed exceptionally potent activity: LVD, IC50 = 0.10 nM; MAC, ED50 = 0.001 mg/kg, sc. Both 10 and 39 displayed high selectivity for kappa-opioid receptors over both mu- and delta-opioid receptor subtypes.