Gluconic 3-keto-, lactone

D-Gluconic 7-lactone and potassium D-galactonate in methanol solution in the presence of phosphoric acid and V2O6 are oxidized by chloric acid to methyl 2-keto-D-gluconate and methyl 2-keto-D-galactonate, respectively 205). 

The process of lactonization and enolization of 2-keto esters under the influence of alkaline reagents has also been applied to the production of analogs of L-ascorbic acid containing a six-membered ring structure.22 For example, methyl 3,4,6-trimethyl-2-keto-D-gluconate (XLI) is treated... 

Aldonic and ketoaldonic acids may be difficult to separate. Norris and Campbell separated ketogluconic acid from gluconic acid by preparing the phenylhydrazone of the keto acid, which is then easily separable from gluconic acid. A methanol-ethanol-water solvent mixture was used.64 Another useful solvent developer is 1-butanol-formic acid-water.133 Macek and Tadra separated a series of ketoaldonic acids in a number of acidic solvent developers.134 Color reagents which may be used include ammoniacal silver nitrate,94 o-phenylenediamine dihydrochloride,84 and aniline acid oxalate.138 Lactones are detectable with hydroxylamine followed by ferric chloride.128... 

The oxidation of glucose to 5-p-ribulose involves in order phosphorylation by ATP oxidation of the sugar aldehyde to the lactone by TPN and finally oxidative decarboxylation of 6-p-gluconate to 5-p-ribulose again with TPN as specific electron acceptor. Phosphogluconate can be conceived of as a /3-hydroxy acid which serially is oxidized to the corresponding /3-keto acid and then decarboxylated to 5-p-ribulose. Both the oxidation and the corresponding decarboxylation appear to be catalyzed by the same enzyme. 

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