Ascorbic acid analogs structure

The second route to an ascorbic acid analog consisted in oxidation by bromine to a 2-ketoacid with the same number of carbon atoms, enoliza-tion, and lactonization. The product was not crystallized, but the optical rotation of the sirup, [ ]d —20° (in water), was in fair agreement with that for the expected D-arabo-ascorbic acid. The sirup was strongly reducing and gave the absorption peak at 2450 A. characteristic of the ascorbic-acid structure. 

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... 

The variation in the antiscorbutic activity displayed by the various analogs of L-ascorbic acid makes it abundantly clear that the activity is dependent upon the stereochemical configuration of the molecule as a whole, and it would appear that the more closely the structure of a particular analog approaches that of the natural Vitamin C the greater will be the antiscorbutic power. Support for this view is illustrated by 6-desoxy-L-ascorbic acid which is obtained from L-sorbose.2 -80 Condensation of L-sorbose with acetone gives a mixture of 2,3-isopropylidene-L-sorbose (LII) and the diisopropylidene derivative. Treatment of LII with p-toluenesulfonyl chloride yields l,6-ditosyl-2,3-isopropylidene-L-sorbose (LIII). The greater reactivity of the tosyl group at C6 enables... 

Other ketones and aldehydes have been used for preparing protected derivatives of L-sorbose that are structurally analogous to 26. These include cyclohexanone,113-115 formaldehyde,81,118 acetone,81, 118,117 benzaldehyde,81,118 and 1-methylcyclohexanone.115 The resulting acetals have been converted into L-ascorbic acid. 

Reichstein and Griissner also prepared di-O-benzylidene and di-O-(2-butylidene) acetals of L-sorbose, and found them to be useful intermediates in synthesis of L-ascorbic acid. By analogy, therefore, their structures are 2,3 4,6-di-0-benzylidene-a-L-sorbofuranose (30) and 2,3 4,6-di-0-(2-butylidene)-a-L-sorbofuranose (102). 

Recent studies in biological systems have revealed the presence of a variety of compounds of many structural types that appear to function as antioxidants. The plant kingdom is especially rich in these materials (Larson, 1988). They include flavonoids and other phenolic compounds, alkaloids and other amines, reduced sulfur compounds, uric acid, ascorbic acid. Vitamin E, carotenoids, and many other substances. Often, their principal mechanism of action appears to be the quenching of peroxy radicals, removing them from the autooxidation chain. Vitamin E, for example, reacts with these radicals in a manner entirely analogous to that of BHT ... 

Inspired by the success of PB-modified electrodes, different HCFs [54] have been more recently proposed for electroanalytical applications. Amongst others, Cu, Co, and Ni HCF have been the most frequently studied. In analogy to PB-modified electrodes, they have been proposed for the development of electrochemical sensors for H2O2 detection [55-57]. However, the performance of these materials was found to be definitely lower than that of PB or, as very recently demonstrated [58], only attributable to the presence of PB impurities in the structure of HCF films. On the other hand, non-iron HCF coatings, quite interestingly, demonstrate electrocatalytic properties in oxidation reactions involving, for instance, hydrazine [59], dopamine [60], and ascorbic acid [61, 62]. 

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