Synthesis and pharmacological evaluation of novel cis and trans 3-substituted anilidopiperidines

4-Anilidopiperidine class of synthetic opioid analgesics, with it's representative fentanyl, are by far the most potent and clinically significant for the treatment of the severe chronic and surgical pain. However, side effects of μ-opioids are often quite serious. In order to improve the pharmacological profile of this class of opioid analgesics, a novel fentanyl analogs were designed, synthesized and evaluated in vivo for their antinociceptive activity.

The title compounds were prepared using known synthetic transformations, including N-bromoacetamide mediated Hofmann rearrangement, highly selective carbamate cleavage with trimethylsilyl iodide and dehydration of carboxamide group to nitrile in the presence of SOCl₂. The antinociceptive activity of the synthesized compounds was determined by tail-immersion and formalin test.

The scalable synthetic route towards novel fentanyl analogs bearing nitrogen groups in position C₃ of piperidine ring is designed. In addition, Hofmann rearrangement was substantially improved for the more efficient synthesis of previously published 3-substituted fentanyl analogs. The series of ten fentanyl analogs was tested in vivo for their antinociceptive activity. The most potent compound of the series was found to be cis-4, based on the determined ED₅₀ values in tail-immersion test.

Of ten compounds tested for their antinociceptive activity, compound cis-4 is characterized by high potency, rapid beginning and short duration of action and due to this might be incorporated in different pharmaceutical forms.