Assignment of conformation and configuration to potassium permanganate oxidation products of quinidine

Two epimeric aldehydes [(R)- and (S)-quinidinals] and the corresponding acids[(R)- and (S)-norhydroquinidinoic acids] were prepared by the oxidation of quinidine. The alpha-alpha interactions of the carbonyl group and the aromatic moiety, as reflected in the NMR spectra, were compared with those of quinidine. NMR spectroscopic analyses made it possible to assign both the stable conformation and their configuration at C-3 to these molecules. The free hydroxyl group at C-9 must be present for the chemical shift values to be concentration dependent. These findings provide more information on association in the parent molecules.