Structure/Activity Studies Related to 2-(3,4-Dichlorophenyl)-N-methyl-N-acetamides: A Novel Series of Potent and Selective κ-Opioid Agonists

Article abstract of DOI:10.1021/jm00115a001

This paper describes the synthesis of a series of N-<2-(1-pyrrolidinyl)ethyl>acetamides 1, variously substituted at the carbon adjacent to the amide nitrogen (C1), and related analogues, together with their biological evaluation as opioid κ agonists.In the first part of the study, the variants in N-acyl, N-alkyl, and amino functions were explored when the substituent at C1 was 1-methylethyl and the optimum was found to be exemplified by 2-(3,4-dichlorophenyl)-N-methyl-N-<(1S)-1-(1-methylethyl)-2-(1-pyrrolidinyl)ethyl>acetamide (13).Subsequently, racemic or chiral amino acids were used to introduce other alkyl and aryl substituents at C1 of the ethyl linking moiety.A series of potent compounds, bearing substituted-aryl groups at C1, were discovered, typified by 2-(3,4-dichlorophenyl)-N-methyl-N-<(1R,S)-1-(3-aminophenyl)-2-(1-pyrrolidinyl)ethyl>acetamide (48), which was 5-fold more active as the racemate than 13 in vitro and exhibited potent naloxone-reversible analgesic effects (ED50 = 0.04 mg/kg sc) in a mouse abdominal constriction model.