4,5-Dehydroascorbate 2-sulfate

The 2-sulfate ester of 4Z-2,3,4,6-tetrahydroxyhexa-2,4-dienoate-8-lac-tone (4,5-dehydroascorbate 2-sulfate) was characterized largely by NMR and H NMR. The data in Table V show that the signals of C4 and C5 were shifted downfield 70 and 38 ppm, respectively, compared to their positions in the spectrum of L-ascorbate at pH 7. In addition, the resonances of Cl and C3 moved upheld approximately 5 ppm upon introduction of the 4,5-double bond. 

Vascular fragility may also result from reduced sulfation of proteoglycans in connective tissue, as may also occur in hyperhomocysteinemia (Section 10.3.4.2). Dehydroascorbate catalyzes the oxidation of homocysteine to ho-mocysteic acid, which is the precursor of PAPS, the sulfate donor for sulfation reactions (McCuUy, 1971). 

Dehydroascorbate catalyzes the oxidation of homocysteine to ho-mocysteic acid, which is the precursor of PAPS, the sulfate donor for sulfation reactions (McCully, 1971). 

Stuber and Tolbert (61) utilized the oxidative stability of the 2-0-sulfate in a short synthesis of both saccharoascorbic acid and saccharoascorbic acid 2-0-sulfate. Oxidation of ascorbic acid 2-0-sulfate, 18, with platinum and oxygen afforded good yields of acid 34 under conditions in which ascorbic acid itself is oxidized to dehydroascorbic acid. Hydrolysis of the sulfate in acid afforded saccharoascorbic acid, 35, in good yield. 

The main metabolites of ascorbate in the human body are oxalate, dehydroascorbic acid, 2,3-diketogulonic acid, and ascorbic acid 2-sulfate. Of these, oxalate has attracted the most attention because of the potential hazard for renal complications by precipitation of oxalate stones. The above-mentioned metabolic turnover for ascorbate, which appears saturable, indicates that in normal humans the amount of oxalate that can be formed is limited. Therefore, the overall risk of inducing oxalate precipitation by increasing the intake of ascorbate probably is minute. 

There is formation of dehydroascorbic acid (see direct iodometry, Chap. 18) by direct titration with ceric sulfate ... 

---