Thiamine thiazole

Thiamine can be considered to be the product of the quatemization of 4-methyl-5-(2-hydroxymethyl)thiazole (5) by an active derivative of 4-amino-5-(hydroxymethyl)-2-methyl pyrimidine (4) (Scheme 2). In living cells, pyramine can be activated by conversion into the diphosphate 7, via monophosphate 6, and the substrate of the enzyme responsible for the quatemization is not the thiamine thiazole, but its phosphate 8. The product of the condensation, thiamine phosphate (9), is finally converted into diphosphate 2—the biochemically active derivative—by hydrolysis to free thiamine, followed by diphosphorylation, or more directly, in some cases. Enzymes are known for all of the steps depicted in Scheme 2, and adenosine triphosphate (ATP) is, as usual, the phosphate donor. 

Scheme 10.—The assembly of precursors in the building of the thiamine thiazole in Enterobacteria.

An extract from the soluble stromal proteins of purified and intact spinach-leaf chloroplasts was prepared by lysis of the cells in buffer, centrifugation of the suspension of broken cells, and concentration of the supernatant with removal of insoluble material. This extract contained all of the enzymes involved in the condensation of the cyclic moieties of thiamine, thiazole, and pyramine. Thus, the synthesis of thiamine in this extract following the addition of pyramine and putative precursors was a proof that the system had the possibility of building the thiazole. It was found that L-tyrosine was the donor of the C-2 carbon atom of thiazole, as in E. coli. Also, as in E. coli cells, addition of 1 -deoxy-D-f/irco-pen-tulose permitted synthesis of the thiamine structure. The relevant enzymes were localized by gel filtration in a fraction covering the 50- to 350-kDa molecular-mass range. This fraction was able to catalyze the formation of the thiazole moiety of thiamine from 0.1 -mM 1-deoxy-D-t/ireo-pentulose at the rate of 220 pmol per mg of protein per hour, in the presence of ATP and Mg2+. 

Scheme 16.—Synthesis of the thiazole-glycol 39 from the thiamine thiazole and conversion to some derivatives useful for checking the specific radioactivity of a biosynthetic sample.

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. 

The significance of these metabolites in the biosynthesis of the thiamine thiazole in considered next. Although, from their constitution, and from the tracer experiments, the metabolites are undoubtedly the products of transformation of 1-deoxy-D-t/ireo-pentulose, their significance in the biosynthesis of the thiazole of thiamine is not clear. The thiazole glycol is not a product arising from a transformation of the thiazole (5) of thiamine. Reduction to this thiazole (5) occurs in dialyzed extracts of disrupted cells, in the presence of ATP, NADH, and NADPH, but only at 0.2% the rate of synthesis of the thiamine thiazole (5) by intact cells. The behavior of the thiazole glycol on plates is merely a consequence of the extreme sensitivity of the tetrazolium reagent. 

Scheme 22,—Proposal for the formation of the thiamine thiazole from a pentulose and glycine in yeast.

Chatteijee A, Jurgenson CT, Schroeder PC, Ealick SE, Begley TP. Biosynthesis of thiamin thiazole in eukaryotes conversion of NAD to an advanced intermediate. J. Am. Chem. Soc. 46. 2007 129 2914-2922. 

SuMur compounds compounds containing reduced or oxidized sulfur, seldom both (Table). Biochemically important S.a are the sulfur amino adds (see L-C eine, L-Methionine), biotin (thiophane ting) and thiamin (thiazole ting) (see Vitamins), sul-fatides (complex lipids of the nervous system see dy-colipids), and thiol peptides (see Glutathione, Vasopressin, Oxytodn, Insulin). S.c. also include Penicillin (see), and the sulfonamid which are important synthetic therapeutic agents. Hie mustard oil glycosides contain both oxidiz and reduced sulfur. Sulfate esters (see) are excreted by animals. 

Sulfur-containing flavor compounds in meat can be categorized into aliphatic, thiamines, thiazoles, and all others. Model studies have shown that cysteine reacts to produce thiazoles that have some meaty odors (15). However,... 

It is natutal to assume that the pjrriniidine moiety is dmved from orotic acid as are the pyrimidine bases of the nucleic adds. This has not, however, been shown. It is more difficult to qieculate on the biogenesis of the thiazole moiety. The limited experimental information on this matter comes again from experiments with pea roots (i). In this organ the thiamine thiazole requirement can be replaced by a mixture of thio formamide and acetopropyl alcohol and the vitamin thiazole is in fact synthesized from such a mixture [Eq. (3)]. 

Radioactive thiamine has been introduced into the animal body on a number of occasions (/ , IS) and, in fact, S Mabeled thiamine has been fed to humans (14) in an effort to learn the metabolic fate of the vitamin. More than half of the thiamine introduced was recovered intact in the urine which contained, in addition, a number of degradation products of thiamine such as thiamine disulfide, thiochrome, the thiamine thiazole moiety as well as significant amounts of SO7 from the oxidized thiazole ring. 

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