2.3- Diketo-L-gulonic acid

M. Otsuka, T. Kurata, and N. Arakawa, Isolation and characterization of an intermediate product in the degradation of 2,3-diketo-L-gulonic acid, Agric. Biol. Chem., 1986, 50, 531-533. 

L-threonic acid, and 2,3-diketo-L-gulonic acid. No oxalic acid can be detected in bread. 

In alkaline solutions the oxidation of 5-keto-D-gluconic acid, dehydro-L-ascorbic acid, and 2,3-diketo-L-gulonic acid are completely inhibited by borate which would indicate the reaction of these ligands with borate (54). 

The X-ray structure of the tetra-acetate of dimeric dehydro-ascorblc acid is referred to in Chapter 23, and the hydrolysis products of the acid (2,3-diketo-L-gulonic acid L—threo-hex-2,3-dlulosonlc acid) have been concluded to contain the 6-lactone... 

Oxalate is a terminal product of normal metabolism. When [ " C]oxalate is injected, most of the labeled compound is excreted, and only a small fraction of the radioactivity is recovered in bone and muscle. There are only two immediate precursors of oxalic acid in normal metabolic pathways glyoxylic acid and 2,3-diketo-L-gulonic acid. The first of these compounds is the product of amino acid oxidation (serine and glycine), and the second is derived from the oxidation of ascorbic acid (see Fig. 3-25). 

The intricacies of the metabolic pathway that leads from ascorbic acid to oxalate are not clear. Ascorbic acid is oxidized to yield dehydro-L-ascorbic add this compound is further hydrated to yield 2,3-diketo-L-gulonic acid. The intermediates between 2,3-diketo-L-gulonic acid and oxalate are not known. L-Xylulose, L-xylose, and L-xylosone have been eliminated. An enzyme was partially purified from rat kidney it catalyzes the decarboxylation of 2,3-diketo-L-gulonic acid to yield L-xylonic and L-lyxonic acids [105]. 

The 2,3-diketo-L-gulonic acid (XIV) is formed spontaneously on dissolution of dehydroascorbic acid I48). Dehydroascorbic acid may be stored as a methanol complex, which is far more stable than the parent substance 148a). 

Otsuka et al. (1986) used TLC to isolate and partially characterize degradation products of 2,3-diketo-L-gulonic acid (intermediates in the biosynthesis of ascorbic acid) the products were characterized by different spectrometric methods. Mandrou et al. (1988) devised a TLC procedure to determine ascorbic and dehydroascorbic acids in fruit juices and wine the sample was reacted with 2,4-dinitrophenylhydrazine to form the osazones the osazones were spotted on the TLC plate and quantified by. in situ densitometry at 494 nm. 

Polarographic studies of 2,3-diketo-L-gulonic acid (i.e. L-r/ireo-hex-2,3-diulosonic acid, the hydrolysis product of dehydroascorbic acid) and the 2,3- and 3,4-endiol forms of its 1,5-lactone have been reported. On condensation with a-phenylenediamine, these compounds form a single product, 2-(2-aminophenyl)-3-(L-f/ireo-triitol-l-yl)quinoxaline, that gives a well defined cathodic wave suitable for analytical purposes. "... 

About 3% of the body s vitamin C pool, which is 20-50 mg/kg body weight, is excreted in the urine as ascorbic acid, dehydroascorbic acid (a combined total of 25%) and their metabolites, 2,3-diketo-L-gulonic acid (20%) and oxalic acid (55%). An increase in excreted oxalic acid occurs only with a very high intake of ascorbic acid. Scurvy is caused by a dietary deficiency of ascorbic acid. 

Micromodifications. Click et al. (G4) described a method for the determination of L-ascorbic, dehydro-L-ascorbic, and diketo-L-gulonic acids in microgram quantities of tissue, such as adrenal tissue, with the phenylhydrazine method. They also found slightly lower values by incubation during coupling at 100°C for 5 minutes but false, high values at 100° C for ten minutes, as compared to the values obtained at 37°G for 6 hours. 

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