Ascorbic acid esters

Ascorbic Acid and Ascorbic Acid Esters and Saits Vitamin C or ascorbic acid is widespread in nature but sparingly associated with fats of oils because of its hydrophilic nature (95). Ascorbic acid in the free form, salts of sodium and calcium, and esters of stearic and palmitic are commonly used as antioxidants in foods. Erythorbic acid is the D-isomer of naturally present L-ascorbic acid (Figure 10) and is often used as an antioxidant in dried fruits and a cure... 

Saika, S., Uenoyama, K., Hiroi, K., Tanioka, H., Takase, K., andHikita, M., 1993, Ascorbic acid ester and wound healing in rabbit corneal alkali bums Epithelial basement membrane and stroma, Graefe s Arch. Clin. Exp. Ophthalmol. 231 221-227. 

Sodium ascorbate and ascorbic acid esters, such as ascorbyl 6-palmitate (5-111) and ascorbyl 2-phosphate (5-113), are fully bioavailable, while ascorbyl 2-sulfate (5-114) is a completely inactive vitamin form. Phosphate and sulfate are about 20 times more stable to oxidation than the free acid. D-lsoascorbic acid (5-107) shows only 5-20% activity, 6-deoxy-L-ascorbic acid (5-115), found in fungi, has about 30% activity and the bound ascorbic acid form ascorbigen has 15-20% of the activity of ascorbic acid. Ascorbic acid 2-0-P-D-glucoside, systematic name 2-0-(P-D-glucopyranosyl)-L-ascorbic acid (5-116), has the same biological activity as ascorbic acid and is also stable against oxidation. 

Alcanoyl-6-0-ascorbic acid esters with different chain lengths (8-18) possess three free -OH groups in positions 2, 3 and 5 and behave as anionic single-chain surfactants. The... 

The cleavage of the intermediate osmate ester has presented problems in the past, and a variety of procedures have been developed, including the use of mannitol and strong aqueous base, refluxing aqueous alcoholic sodium bisulfite,formaldehyde and ascorbic acid. A much milder method involves simply bubbling hydrogen sulfide into a solution of the osmate ester osmium dioxide is precipitated rapidly, and the desired organic... 

A. Pentoses.—t-Ascorbic acid 2- and 3-phosphates, together with their phosphate esters, give a characteristic colour with ferric chloride and this colour reaction has been used in a study of the hydrolysis of L-ascorbic acid 3-phosphate (58). The acid-catalysed, pseudo-firsi-order hydrolysis proceeds with P—O bond fission, as does the bromine oxidation of its phenyl ester. Both of these observations can be rationalized if (58) is... 

This method, which utilizes 2-keto-3,4-dihydroxy acids or esters, is by far the best method for the preparation of ascorbic acids but it is dependent upon a successful process for the production of the 2-keto... 

These 2-keto esters can also be transformed into the corresponding ascorbic acids by heating them in aqueous solution with magnesium, iron, nickel, cobalt, manganese, cadmium and zinc.20 ... 

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 formation of this analog CXI of L-ascorbic acid containing one enolic hydroxy group is therefore responsible for the reducing properties displayed by the two dilactones CIX and CX and the two ester lactones CVII and CVIII of D-glucosaccharic acid. 

The methylated analog CXV of L-ascorbic acid, 2,5-dimethyl-A4-D-glucosaccharo-3,6-lactone methyl ester has been obtained by simultaneous enolization and methylation of a number of substances. For instance it is derivable by treatment, with silver oxide and methyl iodide, of D-glucosaccharo-1,5 3,6-dilactone (CIX), D-glucosaccharo-1,4 ... 

E 304 Fatty acid esters of ascorbic acid (i) Ascorbyl palmitate (ii) Ascorbyl stearate... 

E 304 esters of fatty acids with ascorbic acid (i) ascorbyl palmitate (ii) ascorbyl stearate quantum satis... 

The sequential Michael/Michael addition between 3-methoxymethoxycy-clopent-2-enone and the a,yS-unsaturated ester 70, which is accessible from ascorbic acid [41], afforded the tricycle 73 as a mixture of diastereomers (Scheme 10). The (li ) configuration was found to be kinetically favoured... 

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... 

Sodium, potassium, and calcium salts of ascorbic acids are called ascorbates and are used as food preservatives. These salts are also used as vitamin supplements. Ascorbic acid is water-soluble and sensitive to light, heat, and air. It passes out of the body readily. To make ascorbic acid fat-soluble, it can be esterified. Esters of ascorbic acid and acids, such as palmitic acid to form ascorbyl palmitate and stearic acid to form ascorbic stearate, are used as antioxidants in food, pharmaceuticals, and cosmetics. 

Ethanol, benzoic acid, sorbic acid, the hydroxybenzoate esters, phenylethyl alcohol, and glycerin Ascorbic acid, citric acid, sodium metabisulfite, and sodium sulfite... 

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