Biological Material keto-acids

An efficient protocol for the synthesis of highly substituted a-pyrones 346 has been developed by Kim and co-workers.As shown in Scheme 4.109, a-pyrones 346 were synthesized via the sequential lactonization of 344 with TFAA and subsequent DBU-catalyzed isomerization of the intermediate 345. The starting materials, 8-keto acids 344, were easily synthesized from cinnamyl bromide 341 via S- 2 reaction and subsequent hydrolysis. This provides a synthetic route to multi-substituted a-pyrones, which have been used as important synthetic intermediates and are found in a wide variety of biologically active natural substances. ... 

As are most amino acids, branched amino acids are used through two main pathways the biosynthesis of proteins and polypeptides and their breakdown after oxidative deamination or transamination. The oxidative deamination is catalyzed by an amino acid oxidase and yields a-keto acids and ammonia. Monamine oxidases are widely distributed in biological material. 

For the determination of keto-acids, e.g. pyruvic, a-ketoglutaric and oxalacetic acids in mixtures and in biological materials, a method has been proposed employing paper electrophoretic separations of the 2,4-dinitrophenylhydrazones of these acids.< ) After elution, the polarographic wave corresponding to the reduction of the nitro-groups (in the 2,4-dinitrophenylhydrazone formed) was followed in 0-1 N HCl and the first wave at —0T4 V measured. 

As with other colorimetric methods, the thiobarbituric assay is subject to interference by a number of foreign substances in biological materials. In addition to the problem with 2-keto-3-deoxyaldonic acids... 

---