Abstract
The existing ambiguity regarding the configurations of quinine, quanidine, cinchonine, cinchonidine, and their C-9 epimers has been resolved by stereospecifically converting quaternary salts of the dihydro derivatives of quinine, quinidine, quinidine-9 d, and epiquinidine to derivatives containing the conformationally rigid oxirane ring. The configurations of the oxiranes were determined by NMR spectroscopy, and the stereochemistry of the alkaloid percursors was deduced on the basis of the known stereochemical course of the reactions used in the preparation of the oxiranes. In this way, it has unequivocally been demonstrated that the natural cinchona alkaloids are all of the erythro configuration with respect to their C-8, C-9 systems and that the epi-bases are threo.
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