Conformational structure of propranolol: A β‐adrenergic blocking drug studied by NMR and PCILO methods

The conformational structure of propranolol, a β‐adrenergic blocking drug, has been investigated by pcilo calculations and 270‐MHz proton nuclear magnetic resonance in D 2 O solution. The molecules coexist in at least two conformational states in solution with a low energy barrier. Both preferred conformations have extended structures which allow a three‐point drug‐receptor binding involving the aromatic moiety, the β‐hydroxyl group, and ‐NH + 2 groups of propranolol. The previously postulated “rigid” bicyclic structure does not exist to an appreciable extent in D 2 O solution.