Synthesis and comparative bioefficacy of N-(1-phenethyl-4-piperidinyl)propionanilide (fentanyl) and its 1-substituted analogs in Swiss albino mice

Abstract

Fentanyl [N-(1-phenethyl-4-piperidinyl)propionanilide] is a popular narcotic analgesic agent that is clinically used worldwide. However, fentanyl and its several analogs have caused abuse and fatalities in humans due to overdosing and narrow therapeutic index. The present study reports the synthesis and comparative bioefficacy of fentanyl and its four analogs, viz., N-(1-propyl-4-piperidinyl)propionanilide (1), N-(1-(2-phenoxyethyl)-4-piperidinyl)propionanilide (2), N-(1-(3-phenoxypropyl)-4-piperidinyl)propionanilide (3) and N-(1-(2-cyanoethyl)-4-piperidinyl)propionanilide (4), where the phenethyl chain of fentanyl was replaced by different functional groups, viz., alkyl, ethereal, and nitrile moieties. The median lethal dose (LD50) of the compounds was determined by three different routes and all the analogs were found to be safer than fentanyl. Observational assessment on spontaneous activities of the central nervous system, peripheral nervous system, and autonomic nervous system revealed that all the analogs were similar to fentanyl. Further, the neurotoxic effects of all the analogs were reversed by naloxone hydrochloride (opioid antagonist), confirming that their effects were mediated through opioid receptors. Antinociceptive activity was displayed by all the compounds and their median effective dose (ED50) and analgesic potency ratio were more or less similar to fentanyl. The lowest ED50 (23.7) and the highest potency ratio (1.18) was observed in the case of 2. However, the maximum therapeutic index was afforded by 4. The study indicates the promising role of some new opioid analgesics.