Carbon-14 labelling of biomolecules induced by 14CO ionized gas

Ionized 14CO gas provides a rapid method for producing 14C-labelled biomolecules. The apparatus consists of a high vacuum system in which a small amount of 14CO is ionized by electron impact. The resulting species drift towards a target where they interact with the molecule of interest to produce 14C-labelled compounds. Since the reaction time is only 2 minutes, the method is particularly promising for producing tracer biomolecules with short-lived 11C at high specific activities. The applicability of the method to various classes of compounds of biological importance, including steroids, alkaloids, prostaglandins, nucleosides, amino acids and proteins has been studied. All compounds treated gave rise to 14C addition and degradation products. Furthermore, for some compounds, chromatographic analysis in multiple systems followed by derivatization and crystallization to constant specific activity, indicated that carbon exchange may occur to produce the labelled, but otherwise unaltered substrate in yields of the order of 10-100 mCi/mol. More conclusive proof of radiochemical identity must await production of larger quantities of material and rigorous purification including at least two different chromatographic techniques. (author)