Thiazoles from Other Heterocyclic Compounds

THIAZOLES FROM OTHER HETEROCYCLIC COMPOUNDS 

Closing this chapter on thiazoie synthetic methods, I would like to point out that it is possible to obtain thiazoles from other heterocyclic compounds. 

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VIII. THIAZOLES FROM OTHER HETEROCYCLIC COMPOUNDS... 

VIII. Thiazoles from Other Heterocyclic Compounds... 

Amino acids may also undergo thermal degradation, which is almost always coupled with some other food components, particular sugars. The major types of volatile compounds formed from amino-sugar interactions include Strecker degradation aldehydes, alkyl pyrazines, alkyl thiazolines and thiazoles and other heterocycles [35, 36]. As the subject has mainly relevance for baked and roasted vegetable food products, this subject will not be discussed in further detail. 

Thiols arising in the MaUlard reaction, mostly derived from heterocyclic compounds, such as furan, thiophene, thiazole and other heterocycles, are important flavour-active components of meat, coffee and many other foods. For example, 2-furanmethanethiol (furan-2-ylmethanethiol, furfuryl mercaptan) has an odour resembling roasted coffee, N- (2-mercaptoethyl) -1,3-thiazolidine (8-127), which is formed in the reaction of fructose with cysteamine, and has a very strong odour resembling popcorn. Its odour threshold is 0.005 ng/1 in air. 

Thiamine is present in cells as the free form 1, as the diphosphate 2, and as the diphosphate of the hydroxyethyl derivative 3 (Scheme 1) in variable ratio. The component heterocyclic moieties, 4-amino-5-hydroxymethyl-2-methylpyrimidine (4) and 4-methyl-5-(2-hydroxyethyl)thiazole (5) are also presented in Scheme 1, with the atom numbering. This numbering follows the rules of nomenclature of heterocyclic compounds for the ring atoms, and is arbitrary for the substituents. To avoid the use of acronyms, compound 5 is termed as the thiazole of thiamine or more simply the thiazole. This does not raise any ambiguity because unsubstituted thiazole is encountered in this chapter. Other thiazoles are named after the rules of heterocyclic nomenclature. Pyrimidine 4 is called pyramine, a well established name in the field. A detailed account of the present status of knowledge on the biosynthesis of thiamine diphosphate from its heterocyclic moieties can be found in a review by the authors.1 This report provides only the minimal information necessary for understanding the main part of this chapter (Scheme 2). 

Among the interaction products of alliin and IMP, acetol and acetoin were obviously derived from ribose, one of the degradation products of IMP. As an amino acid in nature, alliin would certainly catalyze the formation of these sugar degradation products. Other interaction products of IMP and alliin were heterocyclic compounds containing nitrogen and/or sulfur atoms such as pyrazines, thiazoles, pyrroles and thiophenes. 

Thiazine containing alkaloids are relatively rare in Nature, but they range in structural complexity from simple monocyclic derivatives such as chondrine and benzothiazines such as the aplidinones, to more complex tri- and polycyclic compounds exemplified by ansafhiazin and the shermilamines. On the other hand, the simplest N,S-heterocycle - the 5-membered thiazole - is relatively common in Nature, and, for example, plays a vital role in the function of thiamine (vitamin Bi). Thiazole rings also occur in important biologically active natural products such as the epothilones (Figure 1). 

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