115199-69-4

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This paper describes the synthesis of a series of N-acetamides (1), methylated at C1 and/or C2 of the ethyl linking group, and their biological evaluation as opioid κ agonists.Conformational analysis of corresponding desaryl analogues 2 suggested that only those compounds capable of occupying an energy minimum close to that of the known κ agonist N-acetamide U-50488 might possess κ agonist properties.Starting from chiral amino acids, other alkyl and aryl substituents were introduced at C1 of the ethyl-linking moiety, giving compounds capable of adopting the same conformation as U-50488.The most potent of these, 2-(3,4-dichlorophenyl)-N-methyl-N-acetamide (8), was 146-fold more active than U-50488 in vitro in the mouse vas deferens model and exhibited potent naloxone-reversible analgesic effects (ED50 = 0.004 mg/kg sc) in an abdominal constriction model.