Tritium labelled compounds

The introduction of tritium into molecules is most commonly achieved by reductive methods, including catalytic reduction by tritium gas, PH2], of olefins, catalytic reductive replacement of halogen (Cl, Br, or I) by H2, and metal pH] hydride reduction of carbonyl compounds, eg, ketones (qv) and some esters, to tritium-labeled alcohols (5). The use of tritium-labeled building blocks, eg, pH] methyl iodide and pH]-acetic anhydride, is an alternative route to the preparation of high specific activity, tritium-labeled compounds. The use of these techniques for the synthesis of radiolabeled receptor ligands, ie, dmgs and dmg analogues, has been described ia detail ia the Hterature (6,7). 

This tritiated water can become incorporated into the normal bases of DNA and may contribute significantly to the overall apparent binding levels measured in DNA (4). Such problems are circumvented in the case of 14C labeled hydrocarbons. Tritium labeled compounds can be prepared at sufficiently high specific activities (often 20-80 Ci/mmole) that fentomole amounts of adduct may be detected. 

In the preparation of tritium-labeled compounds there are four stages ... 

The comprehensive dedicated research ultimately made it possible to decode the patterns of labelling in almost any type of tritium labelled compound at low isotopic abundance (e.g., 3 x 10 4 to 3 x 10 2 per cent. 3H per site) with the aid of 3H-NMR directly, rapidly, reliably and non-destructive analytical means. Since, 1971, the 3H-NMR spectroscopy, utilizing only millicurie (mCi) quantities of radioactivity, emerged as a most useful analytical tool for the study of tritium labelled compounds. 

Of all the elements, isotope effects see Isotope Effect) are greatest for hydrogen, justifying the use of distinctive names for the hydrogen isotopes protium, deuterium, and tritium. However, the chemical properties of H, D, and T are essentially identical, except in matters such as equilibrium constants. The isotopes of hydrogen are extensively used as tracers in deuterium- or tritium-labeled compounds. 

It is important to investigate the bioconcentration potential of natural hormones, such as 17 -estradiol, estrone (using or tritium labeled compounds) and synthetic hormones (e.g., mestranol, diethylstilbestrol etc.). However, the concentration in the water should be at environmental relevant concentrations (< 10 ng 1 ). 

Since the neat reagent is most effective, the solvent is usually removed before reduction of the ketone. Brown has reported a synthesis using neat a-pinene and solid 9-BBN. The deuterium- or tritium-labeled compound may be prepared by hydroboration with labeled 9-BBN. Alternatively B-methoxy-9-BBN may be reduced with LiAlD4 (see Lithium Aluminum Hydride) in the presence of a-pinene. ... 

The method can be applied to the synthesis of deuterium- " or tritium-labeled compounds by using Bu"sSnD or Bu"3SnT. The former reagent (Bu"3SnD) is commercially available (Aldrich) and the latter... 

In these examples labeling is said to be specific in that only one position in the compound contains radioactive nuclides. Alternatively, labeling may be general when all positions are labeled, which oft is the case for tritium-labeled compounds (cf. 15.6.2). 

Very recently, multiple tritium-labeled compounds have been synthesized by Cacace and co>vorkers via nuclear decay processes (51-54). The details of their studies will be described in the next section. 

Deuterium (and tritium) labelled compounds are not only useful for mechanistic studies but valuable information concerning both ground state and excited state properties of molecules has been obtained by the use of compounds containing isotopes of hydrogen. 

The introduction or substitution of tritium into organic molecules is much easier than substitution and tritium-labelled compounds are eonsequently more easily prepared. Conversely, the label is also more readily lost This aspect is particularly important in biological experiments, as the loss of tritium is not due to the biological system, even though there is some uncertainty regarding the ability of biological systems to replace the tritium with hydrogen without modification of the chemical stmcture. 

Tritium labelled compounds can also be used as true tracers for following the rates of homogeneous reactions. Thus, in the reaction of amines with epoxides, one can label the amine and by taking samples at fixed time intervals, quenching and subjecting them to radio-HPLC one can follow the disappearance of amine, the increase in the formation of a 1 1 complex and in some cases, the appearance of further complexes until reaction is complete (Fig. With so much information becoming available it is... 

Non-volatile tritium-labelled compounds have been produced, but the degree of polymerization has been found to be not very high since the intermediate carbocations participate also in other reactions which lead to shortening of the chain length (equation 132). Reaction 132c seems to be the most probable. No simple saturated aliphatic hydrocarbon has been formed in the system C H3 — CH2=CH2 . In a mixture consisting of C H3, CH2—CH2 and H2O no n-alcohols containing more than two carbon atoms have been detected. This means that the isomerization of the carbocations formed is a faster process than their reactions with water or with ethylene. The reaction... 

This results in an error not correctable by external standardization or by internal standardization unless the internal standard has a distribution coefficient identical with the labeled molecule in the sample. Further, since phase contact in some solgel scintillators varies with the aqueous sample concentration, the accuracy of the quench correction will vary with sample size. In short, phase contact in solgel scintillators is at present an undefined variable which Ccin result in large and unsuspected errors in experimental results in the radioassay of tritium-labeled compounds. 

The values of phase contact ratio are then plotted against the water sample concentration to give a curve where problem areas are readily apparent. Obviously a phase contact ratio of 1.00 at all concentrations represents ideal performance, showing perfect phase contact and equal counting efficiency for soluble tritium-labeled compounds at all concentrations regardless of partition coefficient. 

Assuming you have available propyne, a solution of sodium amide in liquid ammonia, and T2O, show how you would prepare the tritium-labeled compound CH3C = CT. 

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