Conformational Analysis of Epiquinine and Epiquinidine

The conformational potential energy surfaces for the epiquinine and epiquinidine molecules were analyzed in gas phase and water solution using semiempirical and ab initio levels of theory. The results obtained showed that the main conformation of the nonactive threo epimers is distinct from those observed for the active parent compounds quinine and quinidine. This result might be used, on a qualitative way, to understand the loss of activity of the threo epimers and allow selecting important conformations to be considered in molecular modeling quantitative studies addressing the drug–receptor interactions.