Tritium catalytic tritiations

Tracers used in this study were 24,28-tritiated castasterone and brassinolide, which were prepared by tritium catalytic reduction of dohchosterone and dolicholide, respectively (7). Figure 4 shows a reverse phase HPLC profile of tritiated products of dolicholide, in which brassinolide was a major component but, in addition, its 24-epimer was also present in the product. Tritiated brassinolide was separated from its 24 epimer by this HPLC technique. In the case of castasterone, die product was likewise purified by HPLC to separate tritiated castasterone from its 24-epimer. 

There is a much wider variety of indirect replacement approaches. In most cases these approaches introduce the labels at structurally predefined positions generated by (formally) oxidative processes, which are then followed in a second step by reductive operations. Examples of such approaches preferentially designed for the introduction of tritium include halogenation followed by tritiodehalogenation, the introduction of carbon-carbon multiple bonds followed by catalytic tritiation, the oxidation of carbon-heteroatom bonds followed by reduction using tritide reagents, etc. These approaches, which do not alter the skeleton of the target in the process, are discussed in Chapter 4, Sections 1-3 and Chapter 10, Sections 10.1.1.2. ... 

Of even more practical relevance is the incorporation of excess tritium during the catalytic tritiation of 4,5-dehydroleucine (A -Leu) and of peptides containing this precursor of [ HJleucine, leading to specific activities of up to 200 Ci/mmol. N-Boc-A -Leu (5) has been subjected to catalytic tritiation using palladium catalysts then the... 

Since ivermectin (= 22,23-dihydroavermectin B ) is obtained by catalytic reduction of avermectin B, the same procedure using tritium gas convenientiy affords tritiated ivermectin (22,23- [JT]-22,23-dihydroavermectin B ). The preparation of a tritiated derivative containing a 22,23-double bond starts with the readily available 5-ketone, which is reduced with [JT]-sodium borohydride stereospecificaHy to a 5- [JT]-derivative (40). Carbon-14 labeled avermectins can be obtained by a biosynthetic process using sodium (l- C)propionate as labeled precursor (48). 

Properties of T2O. Some important physical properties of T2O are Hsted in Table 2. Tritium oxide [14940-65-9] can be prepared by catalytic oxidation of T2 or by reduction of copper oxide using tritium gas. T2O, even of low (2—19% T) isotopic abundance, undergoes radiation decomposition to form HT and O2. Decomposition continues, even at 77 K, when the water is fro2en. Pure tritiated water irradiates itself at the rate of 10 MGy/d (10 rad/d). A stationary concentration of tritium peroxide, T2O2, is always present (9). AH of these factors must be taken into account in evaluating the physical constants of a particular sample of T2O. 

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 ... 

Two di-tritiated isocarbacyclin methyl esters 116 and 117 in the title have been synthesized95 from (Z)-olefinic precursors 118 and 119 at the >-side chain by catalytic hydrogenation with tritium gas (equations 44 and 45). The therapeutic candidates for cardiovascular deseases96, 116 and 117, were required for preclinical studies and for use in RIA analysis. 

H]GR 168320 was developed as a (stably labelled) tritiated H3 antagonist and evaluated for its in vitro use as a radioligand for the H3 receptor [29], As has been shown for thioperamide, the tritium labels at the 2 and 5 position of the imidazole moiety and at the 4 position of the piperidine moiety are sensitive to exchange with hydrogen from the storage solution. [3H]GR 168320 is labelled at the cyclohexane, by a catalytic reduction with 3H2, no details about the synthesis have been published (scheme 11). [3H]GR 168320 was isolated with a specific activity of 4.8 Ci/mmol. 

Tritiated cabergoline ([3H]cabergoline), 354, has been obtained by catalytic reduction with tritium gas of the 6-propargyl derivative 355 employing 10% Pd/C, poisoned with 16% quinoline in dioxane, as catalyst (equation 151) in order to minimize the production of the fully saturated 6-propyl derivative 356. 

Tosti, S. et al., Catalytic membrane reactors for tritium recovery from tritiated water in the ITER fuel cycle, Fus. Eng. Design, 49-50, 953, 2000. 

CCPA is now available in the market also in the tritiated form, obtained by catalytic reduction in a tritium atmosphere of the corresponding cyclopentenyl derivative [15]. 

Several routes applicable to the large scale conversion of testosterone into 4,5a-dihydrotestosterone have been investigated. The method of choice appears to be via catalytic reduction of a 17-acyloxy-3,3-ethylenedioxyandrost-5-ene. Platinum-catalysed hydrogenation of 19-acetoxy, hydroxy-, or methoxy-cholestan-3-ones affords higher proportions of 3a-alcohols than does the 19-unsubstituted steroid. Tritiation of 17)S-hydroxyandrosta-l,4-dien-3-one affords testosterone having a tritium ratio of 1 3.4 (a P) at C-1 and 1 1.4 at C-2 implying that reduction must proceed, in part, by 1,4-addition. ... 

Tosti S, Violante V, Basile A, Chiappetta G, CastelU S, De Francesco M, Scaglione S, Sarto F (2000) Catalytic memlnane reactors Tot tritium recovery fiom tritiated water in the ITER fuel cycle. Fusion Eng Des 49-50 953-958... 

Ganglioside Gdi has also been tritiated. The method involves catalytic addition of tritium gas to the unsaturated centres of the ganglioside which had been isolated from beef brain. Because this results in a... 

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