Conformational study of the cholinergic agonist pilocarpidine, isopilocarpidine, and related species

Abstract

A conformational study on the energies and geometries of the stable conformers of the cholinergic agonist pilocarpidine and of its inactive isomer, isopilocarpidine, has been carried out by molecular mechanics MM2 and by semiempirical quantum chemical AM1. The former predicts an envelope conformation of the γ-lactone nucleus, whereas AM1 predicts a planar conformation. The relative energies of the different conformations of both isomers are strongly dependent on the relative orientation of the imidazole moiety. Other related species, intermediate steps in their synthesis, and the anion intermediate in the epimerization are also discussed.