Antinociceptive effects of 1-acyl-4-dialkylaminopiperidine and 1-alkyl-4-dialkylaminopiperidine in mice: structure-activity relation study of matrine-type alkaloids.

We previously reported that (+)-matrine and (+)-allomatrine have antinociceptive properties mediated mainly through the activation of kappa-opioid receptors. 1-Acyl-4-dialkylaminopiperidines were synthesized as the simplest derivatives of matrine, and the structure-activity relations were examined by the acetic acid-induced abdominal contraction test. The antinociceptive potencies of 1-alkyl-4-dialkylaminopiperidines were significantly lower than those of the corresponding 1-acyl-4-dialkylaminopiperidines. These findings suggest that the amide group of (+)-matrine is an essential functional group that influences antinociceptive potency.