Catalytic tritiations compounds

Catalytic tritiation of compounds containing vinylic protons under... 

When specifically labelled compounds are required, direct chemical synthesis may be necessary. The standard techniques of preparative chemistry are used, suitably modified for small-scale work with radioactive materials. The starting material is tritium gas which can be obtained at greater than 98% isotopic abundance. Tritiated water can be made either by catalytic oxidation over palladium or by reduction of a metal oxide ... 

When using, however, two-component catalysts alcohols also react with inactive metal-polymer (aluminium-polymer) bonds which are formed in the chain transfer reactions with a cocatalyst. It is expedient to use the alcohol method only for catalytic systems and polymerization conditions for which the number of inactive metal-polymer bonds is low. Such a case is the polymerization of 4-methyl-1-pentene on vanadium trichloride activated with various organoaluminium compounds. For this system the influence of catalyst composition and polymerization conditions on Cp and kp was determined by quenching the polymerization with tritiated alcohol. 

Hydroboration followed by protonolysis of the resulting alkylborane can be used as an alternative method for hydrogenation of alkenes, although catalytic hydrogenation (Section 7.12) is the more common procedure. Reaction of alkylboranes with deuterated or tritiated acetic acid also provides a very useful way to introduce these isotopes into a compound in a specific way. 

Conducting Pd/C- HjO labeling reactions in the presence of a small amount of hydrogen gas results in a more active catalyst , as can pretreatment of the catalyst with NaBH . Nevertheless, elevated temperatures are still required (110 C for nucleosides, 110-180 °C for N-heterocycles, > 140 °C for aU but the benzylic positions of aralkylic compounds) . The catalytic hydrogen gas rapidly becomes equilibrated with solvent deuterium . Very dilute tritiated water was used as proof of principle , but this method would not be practical in its current form for the preparation of high specific activity compounds because it requires neat water as solvent/labeling source. 

Tritiated tryptophan has been prepared by catalytic dehalogenation of the 5-bromo-derivative by Birkofer and Hempel 44). Labelling with tritium at the a- 62) and P-carbon 318) of tryptophan has been reported. Kirby and Varley 225) prepared tryptophan stereoselectively labelled with tritium and deuterium at the p-methylene group by using labelled 3-formyl indole as a starting compound (see also Section II.2.). 

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