Sugars from ascorbic acid

Although the action of acetic anhydride on sugar arylhydrazones gave only the respective per-acetyl derivatives, the hydrazones 20, derived from ascorbic acids, gave the pyrazole derivative 21 which can also be prepared xmder microwave irradiation (El Ashry et al., impubhshed results) [49,50]. 

Similarly, a C-aryl heptose sugar is prepared for the first time from the diol obtained from ascorbic acid. The epoxide (40), made from the diol (39), on reaction with acetylenic anion and further transformations gave the olefinic alcohol (42). Sharpless epoxidation of 42 and cyclization furnished the C-aryl heptose sugars (43a and 43b) in an efficient way (Scheme 22.10). 

Along with stomach, bile, and lactic acids, there are many other acids in the human body These include, but are not limited to, nucleic acids, amino acids, fatty acids, and vitamins such as folic and ascorbic acids. Nucleic acids, including RNA (ribonucleic acid) and DNA (deoxyribonucleic acid), are long chains of phosphates and sugar to which nucleotide bases are attached. The phosphate molecules in the backbone of RNA and DNA are derived from phosphoric acid. Therefore, DNA is very weakly acidic. 

Alpha hydroxy acids (AHAs) are water-soluble substances and thereby penetrate the outermost epidermal skin layers. In contrast, beta hydroxy acids (BHAs) are lipid (fat) soluble and are capable of penetrating to the underlying layers of skin (the dermis) located 1-5 mm below the surface of the skinJ2 Most AHAs are derived from plant materials and marine sources. Commonly used AHAs include malic acid (found in apples), ascorbic acid (a common ingredient in numerous fruits), glycolic acid (a constituent of sugar cane), lactic acid (a component of milk), citric acid (naturally abundant in citrus fruits), and tartatic acid (found in red wine). A common BHA is salicylic acid (an ingredient in aspirin). 

The nomenclature adopted in the designation of the analogs of L-ascorbic acid is based for convenience upon the name of the sugar from which the osone was prepared. For example, D-xylose (XVIII)... 

Ascorbic acid, which is closely related to the sugars and is no doubt derived from them in the metabolism of the cells of plants, has been shown to be identical with vitamin- C (Szent-Gyorgyi). It has the constitution of a lactone of a-keto-i-gulonic acid (W. N. Haworth, T. Reichstein) ... 

The nitriles can also be employed as intermediates in the condensation of ethyl glyoxylate with aJdehydo sugars under the influence of sodium methoxide, leading to the preparation of L-ascorbic acid and similar compounds. Helferich and Peters described the synthesis of D-ascorbic acid (XXVIII) from tetraacetyl-n-xylononitrile (XXVI) presumably the nitrile underwent a type of ZempMn degradation and the n-threose (XXVII) thus formed condensed with the glyoxylic ester. The method... 

Ascorbic acid, commonly known as vitamin C, is a sugar acid, biosynthesized in plants, and also found in the livers of most vertebrates, except human beings. Therefore, human beings need an external supply of this vitamin, mainly from fresh vegetables and fruits. In many pharmaceutical preparations ascorbic acid is used as an antioxidant preservative. Ascorbic acid is highly susceptible to oxidation, and oxidized easily to dehydroas-corbic acid. 

Composition. Scientific data concerning liquids washed with water from orange juice finisher pulp was first published by Olsen et al. (30). They studied Brix/acid ratios, sucrose, reducing sugars, pH, pectic constituents, turbidity, pulp content, ascorbic acid, viscosity, and flavonoid content of experimental and commercial samples. Characterization of pulp-wash continued with publication of quality data (31), examination of pectic substances (32), microbiology (33), and comparison of pulp-wash with orange concentrate (34). 

These adverse conditions have elicited considerable efforts to reduce the number of chiral centers as well as hydroxyl groups with the simultaneous introduction of useful functional groups (10, 13-15). One approach involves the shortening of the aldose carbon chain, or, more simply, its bisection, as exemplified by the use of D-mannitol-derived 2,3-Oisopropylidene-D-glyceraldehyde. Whilst this product and its L-ascorbic acid-derived enantiomer have developed into popular enantiopure three-carbon synthons (16), it may be objected that the photosynthetic achievement of Nature which graciously provides us with six-carbon compounds, is utilized rather inefficiently, clearly pointing towards elaboration of synthons from sugars with retention of the carbon chain. 

---