Oxidation of vitamins

Further side-chain oxidation of vitamin metabohtes may be necessary for phosphate transport (188,189). 24,25-Dihydtoxycholecalcifetol is... 

Work in the mid-1970s demonstrated that the vitamin K-dependent step in prothrombin synthesis was the conversion of glutamyl residues to y-carboxyglutamyl residues. Subsequent studies more cleady defined the role of vitamin K in this conversion and have led to the current theory that the vitamin K-dependent carboxylation reaction is essentially a two-step process which first involves generation of a carbanion at the y-position of the glutamyl (Gla) residue. This event is coupled with the epoxidation of the reduced form of vitamin K and in a subsequent step, the carbanion is carboxylated (77—80). Studies have provided thermochemical confirmation for the mechanism of vitamin K and have shown the oxidation of vitamin KH2 (15) can produce a base of sufficient strength to deprotonate the y-position of the glutamate (81—83). 

Sparrow LG, PPK Ho, TK Sundaram, D Zach, EJ Nyns, EE Snell (1969) The bacterial oxidation of vitamin Bg. VII. Purification, properties, and mechanism of action of an oxygenase which cleaves the 3-hydroxypyridine ring. J Biol Chem 244 2590-2660. 

Rosenau, T. Ebner, G. Stanger, A. Perl, S. Nuri, L. From a theoretical concept to biochemical reactions strain-induced bond localization (SIBL) in oxidation of vitamin E. Chem. Eur. j. 2005, 11(1), 280-287. 

Mechanism of Action An antioxidant that prevents oxidation of vitamins A and C, protects fatty acids from aff ack by free radicals, and protects RBCs from hemolysis by oxidizing agents. Therapeutic Effect Prevents and treats vitamin E deficiency. Pharmacokinetics Variably absorbed from the GI tract (requires bile salts, dietary fat, and normal pancreatic function). Primarily concentrated in adipose tissue. Metabolized in the liver. Primarily eliminated by biliary system. 

The determination of vitamins in pharmaceutical preparations continues to receive considerable attention. The voltammetric oxidation of vitamin A at a carbon paste electrode in the presence of vitamin E, a potential source of error in the assay, has been described [142,143]. Other assays involve the polaro-graphic determination of niacinamide [144-146], menadione (vitamin K3) [147], riboflavin (vitamin B2) [148], thiamine, riboflavin, and nicotinamide in multivitamin preparations [149], and multivitamins [150]. 

Active manganese dioxide was used by Canonica in 19472 for the oxidation of oximes into nitrocompounds before the seminal publication of Ball et al. on the oxidation of vitamin A (76). Canonica prepared active manganese dioxide by reacting MnCb with KMn04. In fact the oxidation power of precipitated manganese dioxide is known since the 1870 s.3... 

The oxidation of vitamin K hydroquinone monoanion (17) with labelled, 802 in THF leads to vitamin K oxide (18) in which the epoxide oxygen is fully labelled, hi addition, partial incorporation of 180 at the carbonyl oxygen is observed (on the basis of the mass spectrum).215 This is most readily explained by invoking a dioxetane intermediate (19) as opposed to the alternative intermediacy of a 2-hydroperoxide (20), where only the epoxide oxygen would be expected to be labelled. 

Fujino (142) has improved a method for the determination of vitamin Bg, by utilising the fluorescence of 4-pyridoxic acid which is produced by oxidation of vitamin Bg with permanganate. This method is applied for the determination of vitamin Bg in biological fluids (86, 143-144). 

In other words, the oxidation of vitamin E may generate problems. 

BHT is used to prevent the oxidation of vitamins A and E in foods. It carries the E-number E321. There has been some controversy over its use because it is a cancer suspect agent, but it is used in some foods like chewing gum. BHT stands for Butylated HydroxyToluene you can call it 2,6-di-t-butyl-4-methylphenol if you want to, but you may prefer to look at the structure and just call it BHT, You met BHT briefly in Chapter 2 when you were introduced to the tertiary butyl group. 

Retinal] (carotene) Oxidation of Vitamin A (Retinol), in turn derived from pro-vitamin A carotenes PKC... 

Chemical instability reactions appear with or without microbiological contribution through reactions such as hydrolysis, oxidation, isomerization, and epi-merization. Interactions between ingredients and ingredients with container closure materials are established as the principal causes of these reactions [1], for instance, the hydrolysis of cefotaxime sodium, the oxidation of vitamin C, the isomerization of epinephrine, and the epimerization of tetracycline [7],... 

An alternative approach to determining requirements is to measure the fractional rate of catabolism of the vitamin by use of a radioactive tracer, then determine the intake that would be required to maintain an appropriate level of liver reserves. As discussed in Section2.2.1.1, when the liver concentration rises above 70 /rmol per kg, there is increased activity of the microsomal oxidation of vitamin A and biliary excretion of retinol metabolites. The fractional catabolic rate is 0.5% per day assuming 50% efficiency of storage of dietary retinol, this gives a mean requirement of 6.7 /rg per kg of body weight and a reference intake of 650 to 700 /rg for adult men (Olson, 1987a). Reference intakes for vitamin A are shown in Table 2.4. 

As shown in Figure 5.2, the initial reaction is oxidation of vitamin K hydro-quinone to the epoxide, linked to y -deprotonation of the glutamate residue to yield a carbanion, catalyzed by vitamin K epoxidase. 

Oxidatioa of vitamin A mkahol. Oxidation of vitamin A alcohol (I) with peracetic... 

In addition to its reactivity toward reducing agents, vitamin is also reactive toward oxidising agents. Chromic acid oxidation of vitamin gives... 

Liebler, D., and Burr, J. (1992). Oxidation of vitamin E during iron-catalyzed lipid peroxi-dationi Evidence for eiectron-lransfer reactions of the tocopherOxyi radical. Bftviwwiisfry 31,8278-8284. 

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