Acetic acid, labeled with

Administration203 to chicks of acetic acid labeled with C14 (in the carboxyl group) gave D-glucose (from the glycogen) labeled equally at C3 and C4, but the D-ribose (from nucleic acids) had more label at C3 than at C2, indicating that in vivo D-ribose does not arise exclusively from hexose by loss of Cl. The 20-30% isotope content of D-ribose formed from D-glucose-l-C14 by Escherichia coli indicates that direct conversion is the major pathway but that a part is probably derived from transketolase action.204 206... 

B-6. What is the distribution of radioactive carbon (14C) in isopentenyl pyrophosphate biosynthesized from acetic acid labelled with 14C at its carboxyl carbon (CH3C02H) 14C is indicated by an asterisk ( ) in the structures. 

Long has prepared oxalic acid in 50% yield by introducing C 02 into an evacuated flask containing molten potassium and sand. Acetic acid labelled with C in both carbons has been prepared by Barker and... 

Four reports describe investigations of the incorporation of various isotopo-mers of acetic acid labeled with stable isotopes into the tropane alkaloids. The first of these, by Sankawa and Noguchi [42], reported the regiochemistry of [ 1,2- C2] acetate incorporation into hyoscyamine (3) in Hyoscyamus albus. Surprisingly at the time, it was found that the resonances due C-2 and C-4 both showed coupling to the resonance assigned to C-3. The authors concluded that two labeled species were present in the sample, one in which an intact bond from acetate was introduced in such a fashion that C-2 and C-3 were bond-labeled and another one in which C-4 and C-3 were bond-labeled. The analysis of the C NMR spectra of other alkaloids, the 6)3- hydroxy derivatives of (3), isolated from this experiment indicated an identical pattern of incorporation of acetate into these substances as well. 

Newman lA (1965) Distribution of indolyl-3-acetic acid labelled with carbon-14 in Avena. Nature 205 1336-1337... 

Most naturally occurring fatty acids have even numbers of carbon atoms. Therefore, it was natural for biochemists to postulate that they were formed by condensation from two-carbon units. This suggestion was confirmed in 1944 when Rittenberg and Bloch isolated fatty acids from tissues of rats which had been fed acetic acid labelled with C in the carboxyl group and in the methyl group. The two kinds of atoms were located at alternate positions along the chain, showing that the complete chain could be derived from acetic acid. 

In the experiments with acetic acid labelled radioisotopically and fed to ani-mals, it has been established that the cholesterol carbon framework is made up entirely of the acetic acid carbon. 

Carboxylic acids are thermally stable. Decarboxylation of carboxylic acids is observed at 600 K and higher in the absence of dioxygen [4], At the same time, the decarboxylation of fatty acids in oxidized cumene was observed at 350 K [71]. The study of C02 production from oxidized acetic, butanoic, isobutanoic, pentanoic, and stearic acids labeled with 14C in the... 

Electrical Conductivity, (a) Pure Substances. Note that the lamp does not glow when air fills the space between the electrodes. Then raise successively between electrodes B distilled water, alcohol, pure acetic acid (labeled glacial acetic acid ), and place in contact with electrodes A lumps of any two dry salts found in the laboratory, for example, common salt, NaCl, and blue vitriol, CuS04 5H20. 

This mechanism was tested by use of C-labeled carbon dioxide (Barker, 1943 Buswell and Sollo, 1948 Stadtman and Barker, 1949, 1951 Pine and Barker, 1956 Baresi et al, 1978). Essentially none of the methane was found to be derived from carbon dioxide. Methane is derived entirely from the methyl carbon atoms and carbon dioxide is derived exclusively from carboxyl carbon atoms. Van Neil s mechanism is clearly not valid because the methyl carbon atom is not oxidized to carbon dioxide. Other work has been done to ascertain whether hydrogen atoms are removed during the fermentation of acetic acid, and whether the methyl group is incorporated intact into methane (Pine and Barker, 1954). Water and heavy water were used with deuterated and nondeuterated acetic acid. Acetic acid labeled in the methyl group, when used as the substrate, showed that the isotopic content of acetic acid and methane are the same. Unlabeled acetic acid fermented in the presence of heavy water indicated that about one atom of deuterium per molecule of methane formed is derived from heavy water. It was concluded that the methyl group is transferred from acetic acid to methane as a unit without the loss of attached hydrogen or deuterium atoms. 

Collins (p. 899) prepared 1,1,2-triphenylethyl acetate triply labeled with C (indicated as C ) and studied reactions (l)-(3) in ordinary acetic acid. The equilibrium... 

Experimental evidence for such nucleophilic catalysis is sununarized in Figure 7.27. Hydrolysis of 2,4-dinitrophenyl benzoate catalyzed by acetate ion labeled with on both oxygen atoms led to product in which both benzoic acid and acetic acid were labeled with 0, but about 75% of the label derived from one 0 in the reactant was found in the benzoate ion. The data were interpreted as evidence for the intermediacy of the mixed anhydride CH3CO2COC6H5. 

The focus is changed to the carboxyl unit of an amino acid, and the conjugate base of a carboxylic acid, the carboxylate anion (Chapter 6, Section 6.2.4). The conjugate base formed when acetic acid reacts with NaOH is sodium acetate (NaOAc). If sodium acetate is treated with aqueous acid, acetate is a base and its conjugate acid is acetic acid. Zwitterion 45 reacts with aqueous acid in a similar manner to give 46. These are acid-base reactions, so an equilibrium is shown between 46, 45, and 47. Each equilibrium will have an equilibrium constant (K), labeled for conversion of 39 to 40 and K2 for conversion of 39 to 41. 

When a suitably labelled precursor is administered to an animal, the label appears in the glycerophosphatides of most tissues. This is true for a wide variety of precursors, including orthophosphate labelled with fatty acid labelled with H, or elaidic acid acetate labelled with or glycerol labelled with... 

Further experiments using acetic acid labeled in the carboxyl group with and in the methyl group with deuterium showed conclusively that both carbon atoms of acetate participate in cholesterol biosynthesis (Rittenberg and Bloch, 1944,1945). Subsequent experiments by Little and Bloch (1950) carried out with CHg COOH and iscHgi COOH showed that all 27 carbon atoms of cholesterol could be derived from acetate and that the ratio of incorporation of methyl/ carboxyl was 15/12. Separate analysis of nucleus and side chain showed... 

Shanorellin (48). Previous studies with C-labelled precursors indicated that acetate and the S-methyl group of methionine were efficiently incorporated into shanorellin (48), which is a benzoquinone pigment obtained from Shanorella spirotricha Benjamin. Oxidation with chromic add of shanorellin labelled by [l- C]acetate yielded an inactive acetic acid, whereas quinone samples labelled by [Afe- C]methionine and [2- C]acetate gave, after oxidation, acetic acid labelled at the methyl and carboxy-groups, respectively. On this basis, the biosynthetic route in Scheme 14 was proposed. 

Malonic acid labeled with carbon-14 at C2 or at Cl,3 and the corresponding mono- and diesters have become important and highly versatile building blocks for the synthesis of a broad range of labeled compounds, such a,/3-unsaturated acids and esters, cycloalkanes, 8-keto esters, a-amino acids, phenols, dihydropyridines/pyridines, pyrimidines and quinolines. In addition, they are widely used as acetic acid synthons ( CH2COOR CHCOOR) for the extension of carbon chains of alkyl, allyl and benzyl halides as well as of saturated and a,)8-unsaturated carbonyl compounds. This Section discusses aU malonates, wherever labeled, and unlabeled malonates used with carbon-14-labeled reaction partners. However, it is the [2- " C]malonates that have been most often used in radiochemical synthesis. 

Now, let s draw out the forward scheme. This multi-step synthesis uses three equivalents of ethylene (labeled A, B, C in the scheme below) and one equivalent of acetic acid (labeled D). Ethylene (A) is converted to 1,2-dibromoethane upon treatment with bromine. Subsequent reaction with excess sodium amide produces an acetylide anion which is then treated with bromoethane [made tfom ethylene (B) and HBr] to produce 1-butyne. Deprotonation with sodium amide, followed by reaction with an epoxide [prepared by epoxidation of ethylene (C)] and water workup, produces a compound with an alkyne group and an alcohol group. Reduction of the alkyne to the cis alkene is accomplished with H2 and Lindlar s catalyst, after which the alcohol is converted to a tosylate with tosyl chloride. Reaction with the conjugate base of acetic acid [produced by treating acetic acid (D) with NaOH] allows for an Sn2 reaction, thus yielding the desired product, Z-hexenyl acetate. 

How many carbon atoms of citronellal would be radioactively labeled if the acetic acid used in the experiment were enriched with at C 1 instead of at C 2 Identify these carbon atoms... 

Nucleophilic substitution in cyclohexyl systems is quite slow and is often accompanied by extensive elimination. The stereochemistry of substitution has been determined with the use of a deuterium-labeled substrate (entry 6). In the example shown, the substitution process occurs with complete inversion of configuration. By NMR amdysis, it can be determined that there is about 15% of rearrangement by hydride shift accon any-ing solvolysis in acetic acid. This increases to 35% in formic acid and 75% in trifiuoroacetic acid. The extent of rearrangement increases with decreasing solvent... 

Mechanism I was ruled out by an isotopic labeling experiment. The mixed anhydride of salicylic acid and acetic acid is an intermediate if nucleophilic catalysis occurs by mechanism 1. This molecule is known to hydrolyze in water with about 25% incorporation of solvent water into the salicylic acid. 

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