Dehydroascorbic Acid

Dehydroascorbic acid (DHA) is the first stable oxidation product of L-ascorbic acid (AA). DHA can be easily and quantitatively prepared by air oxidation of AA over charcoal in ethanol. DHA is stable for days in aqueous solution of pH 2-4. 1H NMR and 13C NMR studies show that the principle species of DHA is the bicyclic hydrate, 3,6-anhydro-L-xylo-hexalono-1,4-lactone hydrate. This finding is confirmed by synthesis and spectral studies of related compounds. DHA contains equilibrium concentrations of various dehydrated and open side-chain forms, but these species are too small to detect using NMR spectroscopy. The DHA dimer is converted to the monomer when it is dissolved in water. The chemistry of DHA is reviewed, including the hydrolysis to diketogulonic acid and the reactions of the 2- and 3-oxo groups. DHA readily forms Schiff bases and undergoes a Strecker reaction with amino acids. The known enzymatic reactions of DHA are reviewed.