SYNTHESIS AND BIOCHEMISTRY OF ASCORBIC ACID ANALOGUES

抗坏血酸（维生素C）是人体健康所需的一种饮食

Ascorbic acid (vitamin C), a dietary requirement for human health, is an electron donor for several enzymatic actions, functions as an antioxidant, and is implicated in host defense mechanisms, endocrine function and the visual process (lens). Recent renewed interest in the biochemistry of ascorbic acid has been prompted by the realization that relatively little is known concerning the concentrations of the vitamin required for optimum functioning of these several roles. In the case of enzymatic reactions, optimal rate of a process is defined as that concentration that allows the reaction to reach Vmax without toxicity. As part of a program to determine these concentrations, in situ kinetic measurements have been carried out for certain vitamin C- linked reactions. In addition to examination of functional roles of vitamin C, recent characterization of efficient transport mechanisms that translocate vitamin C across cellular membranes has emphasized the importance of the vitamin to biological processes. Kinetic parameters of these transport mechanisms are also being determined. Kinetic measurements of transport inhibition of 6-deoxy-6-haloascorbic acid analogues have clearly demonstrated the presence of separate pathways for the translocation of ascorbic acid and dehydroascorbic acid. Using our route to 6-aryloxy-ascorbic acid analogues, we have prepared radiolabeled functionalized analogues having the potential for irreversible binding to the ascorbic acid transporter. This incluces 6-(4-benzoylphenoxy)-6-deoxyascorbic acid, a potential photoaffinity label. This analogue is transported by the ascorbic acid carrier. To investigate the importance of the 2-hydroxyl group on ascorbic acid activity, we have prepared 2-deoxy-ascorbic acid. This analogue is being used as a starting material for the preparation of the previously unreported 2-deoxy-2-halo ascorbic acids, including 2- deoxy-2-fluoro-ascorbic acid, an isosteric and isopolar, non- oxidizable, analogue.