Conformational analysis of atropine.

The conformation of atropine was studied by nmr and dipole moment measurements. It was shown that there is a cis conformation between the C = O bond in the ester group and the tropanyl group. The nmr measurements indicated that the Ph--CH(CH2OH)--CO-- grouping assumes conformations I and II in equilibrium, while the conformational isomer III can be excluded. Consequently, the distance between the nitrogen atom and the carbonyl group is 4.5--5.0 A, and this determines the binding to the cholinergic receptor. This distance is substantially less than the 7 A presumed by other authors earlier.