Thiamine and its derivatives

In an ice-cooled alkaline solution, thiamine (R = Me) reacts with COClj to give cyclocarbothiamine [1462]  

Hydroxyethylthiamine (R = MeCH(OH) reacts similarly. When the sodium salt of thiamine was treated with phosgene at -20 C in aqueous ethanol, S. -carbodithiamine was formed [1462]  

This material could also be obtained by treating the sodium salt of 0-(2-tetrahydropyranyl)-thiamine with phosgene, and eliminating the tetrahydropyranyl group with aqueous hydrochloric acid solution [1462]. 

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Normal phase chromatography using a Lichrosorb-NH2 stationary phase in combination with a post-column derivatisation procedure has been used for the resolution and detection of thiamine and its derivatives. Using a mobile phase of acetonitrile-90 mM potassium phosphate, pH 8.4 (60 40), good separations of thiochrome, thiochrome monophosphate, pyrophosphate and triphosphate were obtained (Ishii et al., 1979). The sensitivity of detection using mixtures of the thiochrome derivatives was approximately 1 pmol. 

Small amounts of thiamine and its derivatives can be satisfactorily separated by chromatography on paper. Location of the spots by applying the thiochrome procedure to the paper permits detection of 5 m g of thiamine. Naiman s potassium bismuth iodide reagent is less sensitive (limit o.i /ig). It imparts an orange-pink colour to the spots. ... 

Fig. 12. Circular dichroism spectra of mixtures of tryptophan and thiamine and its derivatives.

Scheme 1.—Thiamine and its two derivatives present in cells. The numbering of the atoms of pyra-mine (4) and thiazole (5) adopted in this chapter.

Acid dye method for the analysis of thiamin, 18A, 73 electrophoretic separation and fluorometric determination of thiamin and its phosphate esters, 18A, 91 catalytic polarography in the study of the reactions of thiamin and thiamin derivatives, 18A, 93 preparation of thiamin derivatives and analogs, 18A, 141 preparation of the mono- and pyrophosphate esters of 2-methyl-4-amino-5-hydroxymethylpyrimidine for thiamin biosynthesis, 18A, 162 formation of the pyrophosphate ester of 2-methyl-4-amino-5-hydroxymethylpyrimidine by enzymes from brewers yeast in thiamin biosynthesis, 18A, 203 resolution, reconstitution, and other methods for the study of binding of thiamin pyrophos-... 

The B-group is a heterogeneous collection of water-soluble vitamins, most of which function as co-enzymes or are precursors of co-enzymes. The B-group vitamins are thiamin, riboflavin, niacin, biotin, pantothenic acid, pyridoxine (and related substances, vitamin B6), folate and cobalamin (and its derivatives, vitamin B12). 

Thiamine shows a pH-dependent UV absorbance range of 230-270 nm. However, its UV absorbance is prone to interference by other endogenous UV absorbers in foods, such as nucleic acids (67,68). In a recent interlaboratory comparison of thiamine methods (42), the results obtained from an HPLC method using UV absorbance detection were rejected due to the presence of peaks that interfered with thiamine. In the interests of increased sensitivity and selectivity, the thiamine vitamers are generally converted to their thiochrome derivatives by alkaline oxidation and determined fluorimetrically (42,70). The thiochrome derivatives of thiamine and its phosphate esters all fluoresce at nearly identical excitation (365-375 nm) and emission (425-435 nm) maxima at pH over 8. The thiochrome derivatives are all relatively stable in alkaline solution at pH greater than 9 and room temperature. 

Small amounts of thiamine and its phosphates are present in most plant and animal tissue, but more abundant sources are unrefined cereal grains, liver, heart, kidney, and lean cuts of pork. The enrichment of flour and derived food products, particularly breakfast cereals, has considerably increased the availability of this vitamin. 

Under basic conditions thiamine degrades to 5-(2-hydroxyethyl)-4-methylthiazole (45, sulfurol) and the pyrimidine derivative 46 [71]. Sulfurol is used in compounded flavourings in the flavour industry. It is almost odourless as such [73] however, it can decompose giving rise to thiazole and its derivatives such as 4-methylthiazole (47), 4,5-dimethylthiazole (48), 4-methyl-5-ethylthiazole (49) and 4-methyl-5-vinylthia-zole (50) ]71, 74], which possess nutty, green notes [75]. 

Lonsdale, D. (2006). A review of the biochemistry, metabolism and clinical benefits of thiamin(e) and its derivatives. Evid. Based Complement. Alternat. Med. 3 49-59. 

The pathway as presented in Table I shows that it is linear for the first 10 steps with no branch points before the pivotal IMP is formed. However, a branch point does exist for the synthesis of the pyrimidine moiety (Bi-pyrimidine) of thiamine. Convincing evidence has been obtained to indicate that AIR also serves as a precursor to Bi-pyrimi-dine [27]. This explains the concomitant growth requirement for thiamine for most of the mutants blocked in any one of the first five enzymes [27-29]. A complication in regulatory control is thus introduced in that any attempt to control purine biosynthesis at the first five steps would have dire consequences on the formation of thiamine. This has indeed been found in the often-reported cases where inhibition of growth by adenine and its derivatives can be reversed by thiamine or its pyrimidine moiety [29-31]. The situation is more complicated in a special class of adenine-sensitive mutants where the sensitivity appears to be related to disturbances in folic acid metabolism [32]. Mutations in the AICAR formyltransferase complex (steps 9 and 10) also create a pleiotropic thiamine requirement which is not due to a deficiency in the synthesis of thiamine but rather to an unexplained phenotypic... 

Whereas thiamine is strongly adsorbed in some systems (Table 48), it is much more mobile on other layers and can be wholly separated from its esters, derivatives and degradation products. Information about such possibilities is available in Table 49. Waldi [143] has isolated thiamine and its phosphate esters on powdered paper. David and HmsH-FELD [24] have tried out 6 different types of cellulose for the same... 

Table 16.4 Thiamine measures in blood (free thiamine and its phosphate derivative).

As internal standard, either salicylamide or anthracene was used (17). These compounds, which are not related to thiamine in structure but have fluorescence characteristics comparable to those of thiochrome, were used only to compensate for variability in the volume injected into the column. In other studies, thiochrome compounds derived from authentic thiamine and its phosphates are used as calibration standards for the analysis of thiamine phosphates (4,17), since the fluorescence intensity of thiochrome phosphates varies considerably (see Fig. 2). 

Pyruvic acid and its derivative phosphoenol pyruvate have already appeared in Figure 1.1, and pyruvic acid was required in discussion of the action of thiamine diphosphate (Figures 2.12 to 2.14). They are important intermediates and will appear again. It is worth looking briefly at the origins of these compounds now. 

This volume is intended to present a comprehensive description of the chemistry of thiazole and its monocyclic derivatives, based on the chemical literature up to December, 1976. It is not concerned with polycyclic thiazoles, such as benzo- or naphthothiazole, nor with hydrogenated derivatives, such as thiazolines or thiazolidines later volumes in this series are devoted to these derivatives. The chemistry of thiamine has also been excluded from the present volume because of the enormous amount of literature corresponding to the subject and is developed in another volume. On the other hand, a discussion of selenazole and its monocyclic derivatives has been included, and particular emphasis has been given to the cyanine dyes derived from thiazolium salts. 

Physical Chemical Characterization. Thiamine, its derivatives, and its degradation products have been fully characterized by spectroscopic methods (9,10). The ultraviolet spectmm of thiamine shows pH-dependent maxima (11). H, and nuclear magnetic resonance spectra show protonation occurs at the 1-nitrogen, and not the 4-amino position (12—14). The H spectmm in D2O shows no resonance for the thiazole 2-hydrogen, as this is acidic and readily exchanged via formation of the thiazole yUd (13) an important intermediate in the biochemical functions of thiamine. Recent work has revised the piC values for the two ionization reactions to 4.8 and 18 respectively (9,10,15). The mass spectmm of thiamine hydrochloride shows no molecular ion under standard electron impact ionization conditions, but fast atom bombardment and chemical ionization allow observation of both an intense peak for the patent cation and its major fragmentation ion, the pyrimidinylmethyl cation (16). 

The thiazolecarboxylic acid structure (40) was also guessed in a similar way, from tracer experiments. The unknown compound was converted into the thiamine thiazole by heating at 100°C and pH 2. On paper electrophoresis, it migrated as an anion at pH 4. Tracer experiments indicated that it incorporated C-l and C-2 of L-tyrosine, and the sulfur of sulfate. The synthetic acid was prepared by carboxylation of the lithium derivative of the thiamine thiazole, and the derivatives shown in Scheme 19 were obtained by conventional methods. Again, the radioactivity of the unknown, labeled with 35S could not be separated from structure 40, added as carrier, and the molar radioactivity remained constant through several recrystallizations and the derivatizations of Scheme 17. 

Potentially tautomeric pyrimidines and purines are /V-alkylated under two-phase conditions, using tetra-n-butylammonium bromide or Aliquat as the catalyst [75-77], Alkylation of, for example, uracil, thiamine, and cytosine yield the 1-mono-and 1,3-dialkylated derivatives [77-81]. Theobromine and other xanthines are alkylated at N1 and/or at N3, but adenine is preferentially alkylated at N9 (70-80%), with smaller amounts of the N3-alkylated derivative (20-25%), under the basic two-phase conditions [76]. These observations should be compared with the preferential alkylation at N3 under neutral conditions. The procedure is of importance in the derivatization of nucleic acids and it has been developed for the /V-alkylation of nucleosides and nucleotides using haloalkanes or trialkyl phosphates in the presence of tetra-n-butylammonium fluoride [80], Under analogous conditions, pyrimidine nucleosides are O-acylated [79]. The catalysed alkylation reactions have been extended to the glycosidation of pyrrolo[2,3-r/]pyrimidines, pyrrolo[3,2-c]pyridines, and pyrazolo[3,4-r/]pyrimidines (e.g. Scheme 5.20) [e.g. 82-88] as a route to potentially biologically active azapurine analogues. 

The finding that thiamine, and even simple thiazolium ring derivatives, can perform many reactions in the absence of the host apoenzyme has allowed detailed analyses of its chemistry [33, 34]. In 1958 Breslow first proposed a mechanism for thiamine catalysis to this day, this mechanism remains as the generally accepted model [35]. NMR deuterium exchange experiments were enlisted to show that the thiazolium C2-proton of thiamine was exchangeable, suggesting that a carbanion zwitterion could be formed at that center. This nucleophilic carbanion was proposed to interact with sites in the substrates. The thiazolium thus acts as an electron sink to stabilize a carbonyl carbanion generated by deprotonation of an aldehydic carbon or decarboxylation of an a-keto acid. The nucleophilic carbonyl equivalent could then react with other electro-... 

Dwivedi and Arnold (89) determined the thiazole moiety in thiamine by derivatizing first to form the TMS analog. Samples were chromatographed on 3% OV-17 on Chromosorb G (DMCS treated) at 110°C. Vitamin D2 (calciferol) and its analog Vitamin have been the subject of many applications in GC analyses. The compounds have been derivatized as the TMS analog and chromatographed on OV-17 (90) and SE-30 (91) and on 3% silicone on Celite after treatment with antimony trichloride (92). Several references to vitamine E (oi-tocopherol) are included in the review by Kern et al. (39) on GLC determinations of pharmaceuticals and drugs. The acetate was determined on 3% OV-17 on Chrom W-HP at 280°C. Vecci and Kaiser (93) determined Vitamin C as the TMS derivative on 3% SE-30 or 10% XE-60 on Anachrom ABS. Column... 

Decarboxylation of an a-keto acid like pyruvate is a difficult reaction for the same reason as are the ketol condensations (see fig. 12.33) Both kinds of reactions require the participation of an intermediate in which the carbonyl carbon carries a negative charge. In all such reactions that occur in metabolism, the intermediate is stabilized by prior condensation of the carbonyl group with thiamine pyrophosphate. In figure 13.5 thiamine pyrophosphate and its hydroxyethyl derivative are written in the doubly ionized ylid form rather than the neutral form because this is the form that actually participates in the reaction even though it is present in much smaller amounts. 

As far as 2-methyl-3-furanthiol is concerned, it can be formed from cysteine, but thiamine constitutes its more important precursor by far.256 When the reaction is carried out in the presence of thiamine in an aqueous medium at 120 °C for 1 h, only about 8% of the thiol is derived from cysteine, and, in the absence of thiamine from the mix, no thiol was detected. The probable mechanism of formation from thiamine is shown in Scheme 5.16.257... 

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