Tritium labeling rearrangements

However, 1,2 migration of alkyl groups has been shown to occur in certain diradicalsFor example, the following rearrangement has been established by tritium labeling. 

Sharpless and Flood682 observed reactions characteristic of monooxygenases, such as stereospecific epoxidation of olefins and arene hydroxylation, with oxotransition metal (M=0) oxidants. For example, Cr02X2 (X=C1, OAc) oxidized tritium labeled naphthalene to naphthoquinone accompanied by tritium migration. Rearrangement is suggestive of arene oxide transients. 

The acid-catalysed conversion into phenols is achieved in the same way. Deuterium and tritium labeling experiments have established that this rearrangement involves a 1,2-hydride shift from carbon to oxygen (the NIH shift, named after the National Institute of Health, Bethesda,USA, where it was discovered) ... 

A third and most significant study involves tracer experiments with Papaver rhoeas L. Both 135- and 13/ -tritium labeled scoulerines were incorporated into rhoeadine, but the rhoeadine isolated from plants fed with 135-labeled scoulerine had lost 19% of the tritium present in the precursor, whereas the 13/ -Iabeled scoulerine afforded rhoeadine which had retained 74% of the original tritium. A stereospecific loss of the pro-5 hydrogen must, therefore, have occurred from the C-13 of scoulerine at some specific stage of its biotransformation into rhoeadine. It seems likely that scoulerine is converted first into stylopine which is oxidized to 42. A-Methylation and rearrangement then provide the correct skeleton from which rhoeadine can arise... 

This mechanism was challenged by Palm and Simon [18c, 27]. Employing tritium-labeled substrates these workers showed that the 1,1-bis-amino derivative 22 is not necessarily an intermediate of the rearrangement. The rate-determining step was found to be the abstraction of the proton at C-2 in the initially formed glycosylamine, supporting the observed general base and acid catalysis. 

The stereospecificity of the uranediol rearrangement is further exemplified by predominant formation of different products in the formolysis of the epimeric 20a-tosylate (359-OTs) (443, 444). That olefin (360) is formed by 1,2-hydrogen and methyl rearrangements (rather than elimination and secondary acid-catalyzed rearrangement) was demonstrated by introduction of deuterium and tritium label at C20. A substantial... 

The adduct, which presumably is enzyme-bound, is thought to imdergo an intramolecular rearrangement to form thymidylate and dihydrofolate, which then leave the enzyme. Experiments with H4-folate, labeled with tritium exclusively in the 6-position hydrogen, have shown that the chick embryo synthetase also forms tritiated thymidylate (7) evidently an intramolecular transfer of a hydride ion is involved because no dilution of radioactivity occurs during introduction of the isotope into the methyl group. 

Tritium ( H) and with half-lives of 12.26 years and 5600 years respectively, are the most commonly used radioactive isotopes. They are used extensively to monitor the uptake of precursors into metabolites and to determine the fates of individual hydrogens or carbons in a precursor during biosynthesis. Tritium finds particular application in this latter regard because any number of proton additions/removals and rearrangements may occur in the course of the biotransformation of precursor into metabolite. (Tritium loss is normally measured by reference to a label in the precursor which is known not to be lost during biosynthesis.)... 

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