Design, Synthesis, and Biological Evaluation of Structurally Rigid Analogues of 4‑(3-Hydroxy­phenyl)­piperidine Opioid Receptor Antagonists

In order to gain additional information concerning the active conformation of the N-substituted trans-3,4-dimethyl-4-(3-hydroxy­phenyl)­piperidine (1) class of opioid receptor antagonists, procedures were developed for the synthesis of structurally rigid N-substituted-6-(3-hydroxy­phenyl)­3-azabicyclo­[3.1.0]­hexane and 3-methyl-4-(3-hydroxy­phenyl)-4-azabicyclo­[4.1.0]­heptanes. Evaluation of the conformationally constrained series in a [³⁵S]­GTPγS assay showed that structural rigid compounds having the 3-hydroxyphenyl group locked in the piperidine equatorial orientation had potencies equal to or better than similar compounds having more flexible structures similar to 1. The studies of the rigid compounds also suggested that the 3-methyl group present in compound 1 type antagonists may not be necessary for their pure opioid antagonist properties.