Pyridoxine compound

The related compounds pyridoxamine and pyridoxal, in which the CH2OH group in the 4-position is replaced by CH2NH2 and CHO respectively, also possess vitamin activity and for certain bacteria are much more active than pyridoxine. 

The ultraviolet spectrum of vitamin Be, or pyridoxine, measured in aqueous ethanol varies with the composition of the solvent indicating that this compound is in equilibrium with the zwitterion form 38. The equilibrium constant in pure water was obtained by extrapolation. Prior to this, equilibria which involved tautomers of type 39 had been suggested for vitamin Be, but see Section VI,A. In the case of pyridoxal, an additional equilibrium, 40 41, occurs (cf. Section VIII) other pyridoxal analogs have also been studied (Table II). 

Pyridoxal 157,158,253 Pyridoxamine 253 Pyridoxine 253 Pyrimidines 266,438, 439 Pyrocatechol see 1,2-Dihydroxybenzene I ocatecholsulfophthalein 398 I ocatechol violet reagent 398 Pyrolysis of organic compounds 92, 96 a,y-Pyrone derivatives 288 Pyrrole alkaloids 66 Pyrrole derivatives 266, 269, 270 Pyruvic acid 426... 

Six compounds have vitamin Bg activity (Figure 45-12) pyridoxine, pyridoxal, pyridoxamine, and their b -phosphates. The active coenzyme is pyridoxal 5 -phos-phate. Approximately 80% of the body s total vitamin Bg is present as pyridoxal phosphate in muscle, mostly associated with glycogen phosphorylase. This is not available in Bg deficiency but is released in starvation, when glycogen reserves become depleted, and is then available, especially in liver and kidney, to meet increased requirement for gluconeogenesis from amino acids. 

FIGURE 10.2 Structural formula of vitamin and related compounds. 1 — pyridoxine, 2 — pyridoxal, 3 — pyridoxamine, 4 — 4-pyridoxic acid 5 — pyridoxal-5 -phosphate. 

Vitamin B6 (pyridoxine) and its derivative pyridoxamine are apparently able to inhibit superoxide production, reduce lipid peroxidation and glycosylation in high glucose-exposed erythrocytes [353], It was suggested that the suppression of oxidative stress in erythrocytes may be a new mechanism by which these natural compounds inhibit the development of complication in diabetes mellitus. 

The usable range for T. pyriformis is from 0.3-300 mug/ml. The organism utilizes pyridoxal, pyridoxamine pyridoxine, and pyridoxal-5-phosphate. Pyridoxamine + pyridoxal yielded the best growth approximately 120 times more pyridoxine is required to yield the same growth as pyridoxamine (Fig. 4). As with nicotinic acid and its amide, when these compounds are added together in the same concentration, the increment of growth is less than the sum of the individual increments. Upon an intramuscular load dose of 100 mg of pyridoxine, peak vitamin Bs levels are reached 2 hours after injection. The curves for 4 normal individuals are illustrated in Fig. 5. 

Vitamin Be is again a small family of related compounds having the same biological activity. These include pyridoxine, pyridoxai, and pyridoxamine. In humans, these molecules are readily interconverted, accounting for their equivalence as vitamins. The stuff in your vitamin pill is likely to be pyridoxine. The actual molecule that functions as a coenzyme in metabolism is pyridoxai phosphate, in which a phosphate group has been added to pyridoxai in an ATP-dependent reaction. 

Where patients are at risk of Wernicke s encephalopathy - for example, because of chronic alcohol abuse, hyperemesis gravidarum, or malnutrition - they should be given thiamine. In many countries no intravenous preparation of thiamine alone is available, and the compound preparations that are available are prone to cause anaphylactoid reactions, so they should be given by slow infusion, and with adequate facilities for resuscitation. A high potency preparation (Pabrinex ) that contains thiamine 250 mg in 10 ml with ascorbic acid, nicotinamide, pyridoxine and riboflavin, can be given by intravenous infusion over 10 min. 

As aromatic compounds have been exhausted as building blocks for life science products, A-heterocyclic structures prevail nowadays. They are found in many natural products, such as chlorophyll hemoglobin and the vitamins biotin (H), folic acid, niacin (PP), pyridoxine HCl (Be), riboflavine (B2), and thiamine (Bi). In life sciences 9 of the top 10 proprietary drugs and 5 of the top 10 agrochemicals contain A-heterocycIic moieties (see Tables 11.4 and 11.7). Even modern pigments, such as diphenylpyrazolopyrazoles, quinacri-dones, and engineering plastics, such as polybenzimidazoles, polyimides, and triazine resins, exhibit an A-heterocydic structure. 

Vitamins are chemically unrelated organic compounds that cannot be synthesized by humans and, therefore, must must be supplied by the diet. Nine vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins (vitamins A, D, K, and E) are termed fat-soluble (Figure 28.1). Vitamins are required to perform specific cellular functions, for example, many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism. In contrast to the water-soluble vitamins, only one fat soluble vitamin (vitamin K) has a coenzyme function. These vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine, and significant quantities are stored in Die liver and adipose tissue. In fact, consumption of vitamins A and D in exoess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds. 

Vitamin B6 is a collective term for pyridoxine, pyridoxal, and pyridox amine, all derivatives of pyridine. They differ only in the nature of the functional group attached to the ring (Figure 28.10). Pyridoxine occurs primarily in plants, whereas pyridoxal and pyridoxamine are found in foods obtained from animals. All three compounds can serve as precur sors of the biologically active coenzyme, pyridoxal phosphate. Pyridoxal phosphate functions as a coenzyme for a large number of enzymes, par ticularly those that catalyze reactions involving amino acids. 

The most important derivatives of 2,5-dihydrofuran are the 2,5-dialkoxy and 2,5-diacetoxy compounds which are easily prepared from furans (Section 3.11.2.3). Their vast utility is as synthetic equivalents of malealdehyde and its derivatives (60MI31100). Suitable intermediates for Robinson-Schopf synthesis have been obtained in this way. Pyridazines are readily obtained (Scheme 121), and 3-pyridinols are available from 2-furylmethanamines (Scheme 122). This approach has been used in a synthesis of pyridoxine. The 2,5-diacetoxy... 

The two monoprotonated forms of pyridoxine are the tautomeric pair shown in Eq. 6-75 and whose concentrations are related by the tautomeric ratio, R = [neutral form]/[dipolar ion], a pH-independent equilibrium constant with a value of 0.204/0.796 = 0.26 at 25°C.75 Evaluation of microscopic constants for dissociation of protons from compounds containing non-identical groups depends upon measurement of the tautomeric ratio, or ratios if more than two binding sites are present. In the case of pyridoxine, a spectrophotometric method was used to estimate R. 

Corn inei ciaHy, the vitamin is available as a dietary supplement in the, compound pyridoxine hydrochloride. The compound can be synthesized by condensing ethoxy acetylacetone with cyanoacetamide (method of Harris and Folkers) or from oxazoles. 

Other compounds, not shown in Table VI, which are hydrolyzed by alkaline phosphatase are TPN (28), poly A (28), phosphocellulose (28), pyrophosphoserine (102, 103), phosphoserine (102-104), pyridoxine phosphate (104), pyridoxal phosphate (104), phosphothreonine (104), and phosphocholine (104) These compounds are all hydrolyzed at approximately the same rate. 

Pyridoxal-5 -phosphate is the coenzyme form of vitamin B6, and has the structure shown in figure 10.3. The name vitamin B6 is applied to any of a group of related compounds lacking the phosphoryl group, including pyridoxal, pyridoxamine, and pyridoxine. 

Shiroishi and Hayakawa (18) have described the effect of sunlight irradiation on pyridoxine and related compounds in aqueous solution at various pH s. Pyridoxine and pyTidoxamine are relatively stable in acidic medium, while pyridoxal decomposes independently of pH. The authors suggested that the aldehydic 0 participates in the photolysis of pyridoxal. The presence of Cu++ had no effect on the stability of these substances. A borate complex of pyridoxine is stable to sunlight irradiation, heating, or autoclaving. Acetic acid and a reddish brown substance were separated as the decomposition products from an irradiated solution of pyridoxine (18). 

Alkyl-substituted oxazoles have been found to react with maleic acid or its anhydride in a diene synthesis to yield substituted pyridine readily converted to pyridoxine (39). In this route, ethyl d, 1-alaninate hydrochloride is treated with formic-acetic anhydride to yield ethyl N-formyl d,1-alaninate (78%). This compound is refluxed in chloroform with phosphorous pentoxide (40), quenched with aqueous potassium hydroxide, and the organic layer distilled to give 4-methyl-5-ethoxyoxazole (I) (60%). The resulting oxazole (I) is condensed readily with a number of appropriate dienophiles to form 2-methyl-3-hydroxy-4,5-disubstituted-pyridines containing substituents (III, a, b, c) which could be converted to pyridoxine as follows ... 

Moller (57) has recognized pyridoxine, pyridoxal, pyridoxa-mine, and 4-pyridoxic acid as the excretion products of vitamin Bg. Complete balance studies have been made in pigs and in babies on all the known vitamin Bg metabolic compounds. In babies, the total output exceeded the intake. The assumption that a limited synthesis of vitamin Bg occurs seems justifiable. 

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