Vitamin reaction with

Chloroacetate esters are usually made by removing water from a mixture of chloroacetic acid and the corresponding alcohol. Reaction of alcohol with chloroacetyl chloride is an anhydrous process which Hberates HCl. Chloroacetic acid will react with olefins in the presence of a catalyst to yield chloroacetate esters. Dichloroacetic and trichloroacetic acid esters are also known. These esters are usehil in synthesis. They are more reactive than the parent acids. Ethyl chloroacetate can be converted to sodium fluoroacetate by reaction with potassium fluoride (see Fluorine compounds, organic). Both methyl and ethyl chloroacetate are used as agricultural and pharmaceutical intermediates, specialty solvents, flavors, and fragrances. Methyl chloroacetate and P ionone undergo a Dar2ens reaction to form an intermediate in the synthesis of Vitamin A. Reaction of methyl chloroacetate with ammonia produces chloroacetamide [79-07-2] C2H ClNO (53). 

X5lenol is an important starting material for insecticides, xylenol—formaldehyde resins, disinfectants, wood preservatives, and for synthesis of a-tocopherol (vitamin E) (258) and i7/-a-tocopherol acetate (USP 34-50/kg, October 1994). The Bayer insecticide Methiocarb is manufactured by reaction of 3,5-x5lenol with methylsulfenyl chloride to yield 4-methylmercapto-3,5-xylenol, followed by reaction with methyl isocyanate (257). Disinfectants and preservatives are produced by chlorination to 4-chloro- and 2,4-dich1oro-3,5-dimethylpheno1 (251). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Vitamin A palmitate [79-81-2] (3), a commercially important form of the vitamin, is produced from vitamin A acetate (2) via a transesterification reaction with methyl palmitate. En2ymatic preparation of the palmitate from the acetate has also been described (22). 

There are several comprehensive reviews of analytical methods for vitamin K (19,20). Owiag to the preseace of a aaphthoquiaoae aucleus, the majority of analytical methods use this stmctural feature as a basis for analysis. Several identity tests such as its reaction with sodium bisulfite or its uv spectmm exploit this characteristic. Although not specific, titrimetric, polarographic, and potentiometric methods have also been used (20). 

As practiced by Hoffmann-La Roche, the commercial synthesis of vitamin is outlined ia Figure 1. Oxidation of 2-methylnaphthalene (4) yields menadione (3). Catalytic reduction to the naphthohydroquinone (5) is followed by reaction with a ben2oating reagent to yield the bis-benzoate (6). Selective deprotection yields the less hindered ben2oate (7). Condensation of isophytol (8) (see Vitamins, vitamins) with (7) under acid-cataly2ed conditions yields the coupled product (9). Saponification followed by an air oxidation yields vitamin (1) (29). 

Vitamin E actually consists of a family of compounds, the most active of which is a-tocopherol. The mechanism of the vitamin s action is not completely certain, but it seems likely that it might undergo hydrogen atom transfer reactions with free radicals to give a stable radical (see also Chapter 17, Problem 7). 

Figure 45-6. Interaction and synergism between antioxidant systems operating in the lipid phase (membranes) of the cell and the aqueous phase (cytosol). (R-,free radical PUFA-00-, peroxyl free radical of polyunsaturated fatty acid in membrane phospholipid PUFA-OOH, hydroperoxy polyunsaturated fatty acid in membrane phospholipid released as hydroperoxy free fatty acid into cytosol by the action of phospholipase Aj PUFA-OH, hydroxy polyunsaturated fatty acid TocOH, vitamin E (a-tocopherol) TocO, free radical of a-tocopherol Se, selenium GSH, reduced glutathione GS-SG, oxidized glutathione, which is returned to the reduced state after reaction with NADPH catalyzed by glutathione reductase PUFA-H, polyunsaturated fatty acid.)...

Similarly, 2,3,5-trimethyl-1,4-hydroquinone (TMHQ), a key intermediate in the synthesis of vitamin E, is produced via oxidation of 2,3,6-trimethylphenol to the corresponding benzoquinone. Originally this was performed by reaction with chlorine followed by hydrolysis, but this process has now been superseded by oxidation with O2 in the presence of a Cu2Cl2/LiCl catalyst (see Fig. 2.20) (Mercier and Chabardes, 1994). Alternatively, this oxidation can also be cataly.sed by a heteropolyanion (Kozhevnikov, 1995). 

More than one hundred enzymes, and many of their coenzymes, have been recognized in animal mitochondria. Whether or not such an organization of enzymes is present in such a cell unit for performing a sequence of reactions with carbohydrates remains to be determined (see the Section on vitamin C). 

Antioxidant activity of flavonoids has already been shown about 40 years ago [90,91]. (Early data on antioxidant flavonoid activity are cited in Ref. [92].) Flavonoids are polyphenols, and therefore, their antioxidant activity depends on the reactivity of hydroxyl substituents in hydrogen atom abstraction reactions. As in the case of vitamins E and C, the most studied (and most important) reactions are the reactions with peroxyl radicals [14], hydroxyl radicals [15], and superoxide [16]. 

In the case of the synthesis of 10,19,19,19-2H4-vitamin A, the most useful for biological studies, three deuterium atoms were incorporated into /i-ionone 30, in >98% by deuterium exchange with excess D2O in the presence of Na02H (and pyridine). The tri-deuteriated 30, utilized in Wittig-Horner reaction with dideuterio triethyl phosphonate, provided tetradeuteriated ethyl /J-ionilidene acetate 31 with more than 98% 2H4 (by NMR). No deuterium loss in the subsequent synthetic steps was observed as evidenced by MS and NMR analysis. 

New isoxazoline derivatives of a-tocopherol, the main component of vitamin E, have been synthesized in a facile, two-step sequence consisting of nitration followed by 1,3-dipolar cycloaddition. 5-Nitromethyl-a-tocopheryl acetate, obtained from a-tocopheryl acetate by direct nitration in one step, act as the nitrile oxide precursor in the reaction with various alkenes. The facile conversion proceeds in the presence of equimolar amounts of PhNCO and catalytic amounts of triethylamine to give isoxazolines, 446 (489). 

The types of compounds that can be analyzed by fluorometry are rather limited. Benzene ring systems, such as the vitamins riboflavin (Figure 8.13) and thiamine, are especially highly fluorescent compounds and are analyzed in foods and pharmaceutical preparations by fluorometry. Metals can be analyzed by fluorometry if they are able to form complex ions by reaction with a ligand having a benzene ring system. 

The ability of cyanide to form complexes with some metallic ions such as cobalt is the basis for the reaction with hydroxocobalamin that yields cyanocobalamin. Cyanocobalamin (vitamin B12), which contains cyanide and cobalt, is essential for the health of mammalian organisms. 

The enhanced nucleophilicity in the cationic micelle is similarly expressed in the reaction with 2,4-dinitrofluorobenzene and vitamin B12 (Chaimovich et al., 1975 Nome and Fendler, 1977). In general, the extent of the rate increase observed in the thiolate reaction is somewhat smaller than that in oxyanionic reactions. This may be an important clue for elucidating the activation mechanism of the thiolate reaction. 

However, in the reaction of vitamin BjjS with primary halides and with benzyl chloride, where the 8 2 driving force can be calculated from the standard potential of the Co(ii)/Co(i) couple and from existing Co—C bond energy data, it appears that recasting the kinetic data point against DF Sf 2) instead of DF ET) brings it close to the ET line (Walder, 1989). 

Co Vitamin B12 rearrangements, reduction, and C and H transfer reactions with glycols and ribose... 

Orotic acid in the diet (usually at a concentration of 1 per cent) can induce a deficiency of adenine and pyridine nucleotides in rat liver (but not in mouse or chick liver). The consequence is to inhibit secretion of lipoprotein into the blood, followed by the depression of plasma lipids, then in the accumulation of triglycerides and cholesterol in the liver (fatty liver) [141 — 161], This effect is not prevented by folic acid, vitamin B12, choline, methionine or inositol [141, 144], but can be prevented or rapidly reversed by the addition of a small amount of adenine to the diets [146, 147, 149, 152, 162]. The action of orotic acid can also be inhibited by calcium lactate in combination with lactose [163]. It was originally believed that the adenine deficiency produced by orotic acid was caused by an inhibition of the reaction of PRPP with glutamine in the de novo purine synthesis, since large amounts of PRPP are utilized for the conversion of orotic acid to uridine-5 -phosphate. However, incorporation studies of glycine-1- C in livers of orotic acid-fed rats revealed that the inhibition is caused rather by a depletion of the PRPP available for reaction with glutamine than by an effect on the condensation itself [160]. 

Antioxidants are compounds that inhibit autoxidation reactions by rapidly reacting with radical intermediates to form less-reactive radicals that are unable to continue the chain reaction. The chain reaction is effectively stopped, since the damaging radical becomes bound to the antioxidant. Thus, vitamin E (a-tocopherol) is used commercially to retard rancidity in fatty materials in food manufacturing. Its antioxidant effect is likely to arise by reaction with peroxyl radicals. These remove a hydrogen atom from the phenol group, generating a resonance-stabilized radical that does not propagate the radical reaction. Instead, it mops up further peroxyl radicals. In due course, the tocopheryl peroxide is hydrolysed to a-tocopherylquinone. 

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