Tritiated formates

Alkynyl cations are so unstable that they cannot be generated even with very good leaving groups. However, one way in which they have been generated was by formation of a tritiated substrate. 

Hydrogenation reactions in which H2/D2/T2 gases are replaced by various formates proceed very rapidly under MW irradiation conditions (Scheme 6.54) [182]. The pattern of labeling can be easily modified and the advantages are especially noteworthy in the case of tritium where high specific activity tritiated water is hazardous to use. 

Under the experimental conditions dehalogenation proved to be extremely rapid and was complete within 1 min. This contrasts with the 90-270 min at 100 °C required for thermal debromination of 2-bromonapthalene. No dehalogenation takes place in the absence of the formate donor and when the deuterium is located in the cosolvent rather than the donor (i. e. HCOOK + D20) hardly any deuterium incorporation takes place. Another interesting observation was that the amount (%) deuterium incorporation was always lower when protic solvents such as alcohols were used than aprotic solvents such as dimethyl sulfoxide (DMSO). These are both interesting and useful findings which are valuable for proposed tritiation studies. 

Recently, the enzymatic formation of folinic acid has been utilized to synthesize radioactively labeled products.34 The preparation of 5-formyl tetrahydrofolate, 9,3, 5 -3H and 5-formyl-14C-tetrahydrofolate starts with tritiated folic acid, which is reduced to dihydrofolate, incubated in the presence of formaldehyde, dihydrofolate reductase, and NADPH, and finally incubated with 5,10-methylenetetrahydrofolate dihydrogenase. The product,... 

Group VIII transition metal catalyzed hydrogen exchange reactions are important in providing useful information concerning the fundamental processes of bond rupture and bond formation on catalyst surfaces. The reactions are also a convenient source of deuterated and tritiated compounds for chemical and biological research (i). 

The formation of surface oxides on the prism faces of graphite single crystals was shown by Hennig (67). The experiments have been described on page 191. Adsorption studies with tritiated water by Montet (68) confirmed this result. 

The most direct route towards functionalized aliphatic polyesters is based on the functionalization of polyester chains. This approach is a very appealing because a wide range of functionalized aliphatic polyesters could then be made available from a single precursor. This approach was implemented by Vert and coworkers using a two-step process. Eirst, PCL was metallated by lithium diisopropylamide with formation of a poly(enolate). Second, the poly(enolate) was reacted with an electrophile such as naphthoyl chloride [101], benzylchloroformate [101] acetophenone [101], benzaldehyde [101], carbon dioxide [102] tritiated water [103], ot-bromoacetoxy-co-methoxy-poly(ethylene oxide) [104], or iodine [105] (Fig. 26). The implementation of this strategy is, however, difficult because of a severe competition between chain metallation and chain degradation. Moreover, the content of functionalization is quite low (<30%), even under optimized conditions. 

The normal cell cycle consists of a definable sequence of evenfs fhaf characferize fhe growfh and division of cells and can be observed by morphological and biochemical means. The cell cycle is depicfed in Fig. 55.1. Two of the four phases of the cell cycle can be studied directly the M-phase, or mitosis, is easily visible using light microscopy because of chromosomal condensation, spindle formation, and cell division. The S-phase is the period of DNA synthesis and is observed by measuring the incorporation of tritiated thymidine into cell nuclei. 

The formation of 76a is essential, as the enol 76 would not be expected to be decarboxylated. When allowed to react in tritiated water, both L-ascorbic acid and D-amfomo-hexulosonic acid produced 2-furaldehyde having an activity approximately 60% of that of the solvent most of the activity was situated at the a-carbon atom. The failure to detect any pentose is probably ascribable to the high reactivity of the 1,2-enediol (77). 

The original work on wet chemical functionalization of germanium was reported as early as 1962 by Cullen et al. (researchers in RCA labs) [105]. They exposed ethyl Grignard to a chloride-terminated Ge(lll) surface and used radiotracer studies with tritiated ethyl groups to show that ethylation of the surface occurs via formation of Ge—C bonds in a one-to-one ratio with surface atoms. Because the chlorination procedure used by the authors can lead to formation of mono-, di-, and trichloride species, there may be some uncertainty as to the Ge/C ratio. However, these surfaces did demonstrate hydrophobic behavior and stability in both atmosphere and aqueous solution. 

Bromobiphenyl produced a major metabolite (4% of the dose) identified as either 3-bromo-4-biphenylol or 5-bromo-2-biphenylol a minor dihydroxylated metabolite was also detected. 4-Bromobiphenyl yielded two metabolites 4 -bromo-4-biphenylol (2% of the dose) and 4 -bromo-3,4-biphenyldiol (1.5% of the dose). Experiments witli tritiated 4-bromobiphenyl suggest that the metabolism of this congener involves the formation of an arene oxide. 

The results of Alizade and Simon (37) also indicate the formation of NADH during the decarboxylation of L-malic acid in Leuconostoc mesen-teroides. During growth on glucose and in the presence of L-malic acid tritiated at the C2 position, tritium was recovered in the C2 position of L-lactic acid, as would be expected from a first decarboxylation. Surprisingly, a significant amount of label was recovered in D-lactic acid which indicated the intermediate formation of tritiated NADH from malic acid. 

Kenny (1973) recommends a Soy peptone-yeast dialysate medium (Appendix 4) for culture of mycoplasma. Inclusion of arginine (16 mM) and 0.4 mg% phenol red indicates the presence of arginine deaminase by formation of alkali (purple coloration). Alternatively, incubation with tritiated thymidine and analysis of the culture medium for tritiated thymine can be used to detect thymidine phosphorylase (House and Waddell, 1967). 

The present work was undertaken in an attempt to shed light on the mechanism of hydroxyproline formation in collagen biosynthesis and on the site of action of ascorbate. It was recognized that these phenomena were very likely to be closely interrelated. Proline labeled with tritium was used because it was anticipated that tritium released from proline during hydroxylation would appear in the tissue water as tritiated water. The use of tritiated proline in such a system might then provide a new parameter for following the hydroxylation reaction, provided that the formation of tritiated water was stoichiometrically related to the formation of hydroxyproline. Such an approach might conceivably permit the demonstration of hydroxylation and peptide bond formation as separate chemical steps. 

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