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.

Impact of stable conformation of cinchona alkaloids on protonation site.

NMR analyses of quinidine and other cinchona alkaloids and their monoprotonated salts in deuterium oxide and in deuterochloroform revealed that the molecules assume new conformations in polar and nonpolar media, affecting the protonation site and hydrophilic-lipophilic characteristics. The ion-pair feature of the salts is lost and the molecules assume a neutral feature when they are transferred from an aqueous to a lipoid phase. Hydrophobic bonds between the molecules and their environment and within the molecule itself may affect the binding of cinchona alkaloids to membranes in biological fluids.