Conformational analysis of epiquinine and epiquinidine

The conformational potential energy surfaces for the epiquinine and epiquin idine molecules were analyzed in gas phase and water solution using semiemp irical and ab initio levels of theory. The results obtained showed that the main conformation of the nonactive threo epimers is distinct from those ob served for the active parent compounds quinine and quinidine. This result m ight be used, on a qualitative way, to understand the loss of activity of t he threo epimers and allow selecting important conformations to be consider ed in molecular modeling quantitative studies addressing the drug-receptor interactions.