Methods for incorporating tritium

Methods for Incorporating Tritium into Organic Compounds... 

The incorporation of 14C into compounds at a suitable site often requires extensive and complicated syntheses, and thus a relatively long time. This usually means that 14C-labeled compounds are unsuitable for studies to be carried out during discovery. There are however, very rapid methods for incorporating 3 H into compounds. The newer methods, generally involving metal-catalyzed exchange reactions [15-18], in our experience, mean that suitable labels can often be prepared in 2 or 3 weeks. These time scales make the approach viable for discovery support. Additionally, and importantly, these methods can lead to specific incorporation of tritium. 

The first stage of the synthesis is the preparation of the substrate for enzymatic polymerization, the polyprenyl pyrophosphate-galactosy1-rhamnosy1-mannose XXI. Since the most convenient way to control the polycondensation reaction is the use of isotopic methods, a procedure for incorporation of tritium into trisaccharide I was developed (2 5). Labelled trisaccharide was then converted into the glycosyl phosphate XIX through interaction of its peracetate III with anhydrous phosphoric acid (26). Conditions were found under which the reaction is accompanied by minimal destruction and yields the Ot-phosphate of the trisaccharide. 

A mixture of (35,45)-[4— H]-mevalonate and (3/ ,4/ )-[4— H]-mevalonate and ( )-[2— C]-mevalonate [( )-463 ] was fed to whole plants of C. japonica by the cotton-wick method (Scheme 62). The ratio of to T of the labelled tutin (11 ) showed that one of the three tritium atoms survived the biosynthetic pathway, with the other two tritium atoms lost to oxidation. For the tritium at position C(4) it is only possible for it to remain if the hydrogen transfer occurs in a one-step reaction. In the case of a double 1,2-hydrogen transfer, the tritium atom would be incorporated in the isopropyl group and vanish with the dehydrogenation to the... 

When the acidities of hydrocarbons are compared in terms of the relative stabilities of neutral and anionic forms, the appropriate data are equilibrium acidity measurements, which relate directly to the relative stability of the neutral and anionic species. For compounds with pA > 35, it is difficult to obtain equilibrium data. In such cases, it may be possible to compare the rates of deprotonation, i.e., the kinetic acidity. These comparisons can be made between different protons in the same compound or between two different compounds by following an isotopic exchange. In the presence of a deuterated solvent, the rate of incorporation of deuterium is a measure of the rate of carbanion formation. Tritium ( H)-NMR spectroscopy is also a sensitive method for direct measurement of kinetic acidity. ... 

A general method for the synthesis of dialdoses and nucleoside 5 -aldehydes has been described, and their asymmetric reaction with nucleophiles discussed. The reversible interconversion of GDP-D-mannose and -L-galactose which is brought about by a Chorella enzyme system was proposed to occur as shown in Scheme 2 following the observation that tritium incorporation from the solvent occurred equally at C-3 and C-5. Epimerizations at positions a to the carbonyl groups can also be photoinduced, and compound (1) has now been isolated in... 

The pungent principle of Capsicum, capsaicin, was isolated by Thresh et al. in 1876 [1]. Afterward, several synthetic methods for capsaicin were reported [2,3]. According to reports concerning the biosynthesis of capsaicin [4], when tritium-labeled precursors were administered to immature red pepper (C. annuum), it was demonstrated that DT-[3phenylalanine, L-[3, 5 - H2]tyrosine, [5 - H]vaniUylamine, and various cinnamic acids (labeled in the aromatic ring) were incorporated. It was also shown that the rate of uptake of phenylalanine was better than that of tyrosine. 

Biosynthetic methods for direct introduction of tritium from a tritiated-water medium into a drug or intermediate can Involve specific Incorporation of tritium in the compound, using a particular enzyme system, or nonspecific incorporation, involving growth of an organism. 

Despite the paucity of data for orientation studies with substituted heterocyclics labeled by the Wilzbach method, extensive work has been done with analogous aromatic compounds and, thus, by extrapolation, a number of general predictions can be made for heterocyclic systems. For example, in toluene34 tritium incorporation in the ring predominates over side-chain labeling. 

Samples of the same batch were tested for the absence of any cytotoxic contaminations in a highly sensitive in vitro test [81]. The recombinant proteins were added to EBV-transformed cytotoxic T cells in a concentration range from 0.001 to 10 [xg/ml. No change in viability or tritium incorporation was seen in the treated cells. In contrast, cells treated under the same conditions with the toxic allergen Asp f 1 were effectively killed. We conclude that our preparation of Alt a 1 is nontoxic. Based on this and on earlier observations with other allergens purified using the same method, Alt a 1 and Altemaria enolase (see below) were approved by the local ethics committee for clinical testing. 

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