Deuterium oxide carboxylic acid derivatives

The formation of 2-furaldehyde on acid-catalysed dehydration, etc., of 1-benzyl-amino-l-deoxy-D-f/ireo-pentulose and l-benzylamino-l-deoxy-o-fructuronic acid has been studied in isotopically labelled water (either acidified deuterium oxide or tritiated water).The pattern of labelling of the 2-furaldehyde derived from the latter compound is consistent with a mechanism involving the decarboxylation of a Py-unsaturated carboxylic acid intermediate (see also p. 136). 

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. 

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