O and N sulfation

The simultaneous sulfation of several hydroxyls has been accomplished with the same reagents discussed above, that is, sulfur trioxide pyridine90 or sulfur trioxide- trialkylamine complexes.91 Prolonged reaction times or repeated treatment with the sulfating agent may be needed to achieve complete sulfation. 

The regioselective sulfation of a 6-hydroxyl of a partially protected saccharide can be achieved by employing the above-mentioned reagents, albeit at lower reaction temperatures.89 11 1 92 

The acidity of sulfates may cause hydrolysis of glycosidic linkages and therefore the products are usually isolated as salts. 

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Sulfotransferases917 920a transfer sulfo groups to O and N atoms of suitable acceptors (reaction type ID, Table 10-1). Usually, transfer is from the "active sulfate," 3 -phosphoadenosine 5 -phosphosuIfate (PAPS),921 whose formation is depicted in Eq. 17-38. Sulfatases catalyze hydrolysis of sulfate esters. The importance of such enzymes is demonstrated by the genetic mucopolysaccharidoses. In four of these disease-specific sulfatases that act on iduronate sulfate, heparan N-sulfate, galactose-6-sulfate, or N-acetylglu-cosamine-4-sulfate are absent. Some of these, such as heparan N-sulfatase deficiency, lead to severe mental retardation, some cause serious skeletal abnormalities, while others are mild in their effects.922... 

Subsequent modifications of the polymers involve extensive formation of O-sulfate esters,1903 193 197 N-deacetylation and N-sulfation,198/199 and epimerization at C5.10 In some tissues almost all GluA is epimer-ized.200 The modifications are especially extensive in dermatan, heparan sulfates, and heparin (see also p. 177).196 201 203b The modifications are not random and follow a defined order. N-Deacetylation must precede N-sulfation, and O-sulfation is initiated only after N-sulfation of the entire chain is complete. The modifications occur within the Golgi (see Fig. 20-7) but not all... 

The complete sequences of the carbohydrate chains of Bik are known to change during disease progression [31-33]. Both O- and N-linked glycoside chains are connected to Bik in domain I (Fig. 2). A key feature of the O-linked glycoside is the sulfated chondroitin chain. The O-linked chondroi-tin sulfate glycoconjugate is essential for cell membrane stability and is also involved in cell membrane binding. 

It is important to note that the foregoing, biosynthetic-polymer modification is usually incomplete. In fact, only a fraction of the heparin precursor undergoes all of the transformations shown in Scheme 1. However, as the product of each enzymic reaction constitutes the specific substrate for the succeeding enzyme, the biosynthesis of heparin is not a random process. Thus, sulfation occurs preferentially in those regions of the chain where the amino sugar residues have been N-deacetylated and N-sulfated, and where o-glucuronic has been epimerized to L-iduronic acid. °... 

This approach was first used for sulfate ester protection in carbohydrates by Flitsch and co-workers. Once the sulfo groups have been protected, the free hydroxyl and carboxyl groups could be protected in organic solvents used in standard carbohydrate synthesis. This chemistry has been successfully used to selectively protect primary and secondary O- and N sulfo groups in unprotected sulfated mono- and di-saccharides in high yields. ... 

Pyridones, alkylation, 745 O- and N-alkylation with dialkyl sulfates, 752 alkylation with diazomethane, 754... 

Chitosan-6-0- sulfate, N-sulfated chitosan O-sulfation and N-sulfation of amino groups of chitosan Imparts anticoagulant property [177] [178]... 

Whistler RL, Kosik M (1971) Anticoagulant activity of oxidized and N-sulfated and O-sulfated chitosan. Arch Biochcan Biophys 142 106-110... 

Although gravimetric methods have been used traditionally for the determination of large amounts of tellurium, more accurate and convenient volumetric methods are favored. The oxidation of teUurium(IV) by ceric sulfate in hot sulfuric acid solution in the presence of chromic ion as catalyst affords a convenient volumetric method for the determination of tellurium (32). Selenium(IV) does not interfere if the sulfuric acid is less than 2 N in concentration. Excess ceric sulfate is added, the excess being titrated with ferrous ammonium sulfate using o-phenanthroline ferrous—sulfate as indicator. The ceric sulfate method is best appHed in tellurium-rich materials such as refined tellurium or tellurium compounds. 

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