Thiazole ring 4-hydroxy

In this chapter we intend to outline the general methods by which the thiazolic ring is synthetized from open-chain compounds. The conversion of one thiazole compound to another is not discussed here, but in appropriate later chapters. Thus the conversion of thiazole carboxylic acids, halogeno-, amino-, hydroxy-, and mercaptothiazoles, to the corresponding unsubstituted thiazoles is treated in Chapters IV through VII, respectively. 

An unexpected reaction occurred when an attempt was made to convert 2-chloromethyl-5-methoxypyran-4-one (512) into its isothiuronium salt. Opening of the pyran ring and recyclization to a benzene ring followed by thiazole ring formation accounts for the formation of 2-amino-5-hydroxy-6 methoxybenzothiazole hydrochloride (513) (80JHC817). 

Anthraquinoneazoles. In contrast to the older yellow Algol dyes, which contain two thiazole rings (e g., 2,2-bisanthra [2,1 d thiazole-6,11-quinonyl), the red to blue oxazoles and thiazoles derived from l-aminoanthraquinone-2-carboxylic acid and 3-amino-2-hydroxy- or -mercaptoanthraquinones exhibit good lightfastness. The good fastness to atmospheric conditions and chlorine of the blue deriv-... 

Unsubstituted thiazole does not react with chlorine or bromine in an inert solvent. Of the monomethylthiazoles only the 2-isomer undergoes bromination giving the 5-bromo derivative. When the 5-position is not free, as in 2,5-dimethylthiazole, no reaction occurs. 2-Hydroxy and 2-amino groups strongly activate the 5-position. However, bromination of 2-amino-4-(2-furyl)thiazole under mild conditions occurs successively on the furan and thiazole rings (Scheme 16). 

JCS(C)2094). In the thiazolopyrimidine (382) the hydroxy group protects the pyrimidine ring, and it is the thiazole ring which is cleaved with loss of C-2 (70JCS(C)2478). 

Thiazoles react readily with alkyl halides to form the corresponding thiazolium salts. Many examples exist in the literature and studies of the effect of thiazole ring substituents upon the rate of reaction have been well reviewed < 1984CHEC(6)235>. Thiazoles and benzothiazoles substituted with a hydroxy, thio, or amino group can undergo alkylation equally at either the endo- or exocyclic heretoatom. This reactivity has been discussed elsewhere < 1996CHEC-II(3)373>. 

The same transformations occur with 2-methyl-4-hydroxy-5-(amino-methyl) pyrimidines. These special substituents on the thiazole ring have been studied especially in connection with vitamin and its analogs. 

Wahrscheinlich ist die erfolgreiche 1-Hydroxy-alkylierung einer 4- oder 5-Methyl-Gruppe wie-derum auf Falle begrenzt, in denen sich eine Carboxy-Gruppe am 1,3-Thiazol-Ring befindetl496 ... 

Als Sonderfall ist die Oxidation von 2-Amino-6-hydroxy-l,3-benzothiazol - als 2-Phenylsul-fenylamino-6-phenylsulfenyloxy-l,3-benzothiazol- anzusehen, bei der, unter Einbeziehung des 1,3-Thiazol-Ringes in das chinoide System, 6-Oxo-2-phenylthioimino-2,6-dihydro-1,3-benzothiazol erhalten wird1077 ... 

Enzymes which degrade a-keto acids to COg and aldehydes contain thiamine pyrophosphate (D 10.4.5) as coenzyme. The keto acid is added in a reversible reaction to carbon atom 2 of the thiazole ring of thiamine pyrophosphate giving an oc-hydroxy acid derivative. This compound is decarboxylated and split to an aldehyde and thiamine pyrophosphate. Figure 25 shows this sequence of reactions for the enzyme pyruvate decarboxylase which splits pyruvate to acetaldehyde and COg. 

Halipeptins A-C are strongly anti-inflammatory depsipeptides, isolated from another sponge of the genus Haliclona harvested in Vanuatu. These three products have the characteristic of a thiazole ring included in the cyclic part of the depsipeptide and atypical a-amino acids, such as N-methyl-8-hydroxy-isoleucine (Randazzo et al, 2001 Della Monica et al, 2002). 

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