SPECIFIC 3H-LABELLING BY DIIMIDE REDUCTION OF UNSATURATED BONDS .2. METHODS AND APPLICATIONS OF LABELLING

Methods for specific labelling of alkyl groups on a mCi/mmole level are described, in which double bonds are hydrogenated with labelled diimide and in which tritiated water is used as the source of the label. In one method, labelled diimide is obtained by exchange labelling and oxidation of hydrazine in acetonitrile and in the other, potassium azodicarboxylate is decomposed with labelled hydrogen ions in a pyridine medium. Molar specific activities of 8 and 20 % of the original water are obtained. The latter method is preferred for reproducible quantitative conversions of unsaturated fatty acids and methyl esters on a 10–100 mg scale. By partial oxidation with permanganate in acetone, both the specificity of diimide labelling and the usefulness of permanganate degradation for the localization of tritium labels in fatty acids were demonstrated. The possible application of a combination of diimide labelling and oxidative degradation for the determination of the structure of polyunsaturated acids is illustrated for arachidonic acid. Copyright © 1969 John Wiley & Sons, Ltd.