Hexosamine deamination

Both positional linkages (uronic acid to hexosamine and hexosamine to uronic acid) were established as being (1 — 4) by structural analysis of the previously mentioned (see Section IV), crystalline disaccharides containing D-glucuronic acid, isolated from an acid hydrolyzate of carboxyl-reduced heparin.128-129 Further evidence was obtained from the structure of the D-glucuronic acid-containing counterpart of disaccharides 6 and 8, obtained as minor products from pig-mucosal heparin following nitrous acid deamination,1110 136-138 and acid hydrolysis followed by N-acetylation,130 respectively. 

Deamination of the hexosamine molecule occurs on heating it with alkali,205 and determination of the ammonia evolved is the basis of one quantitative method for the determination of 2-amino-2-deoxy-D-glucose.206 Deamination of 2-amino-2-deoxy-D-glucose with nitrous acid leads to the formation of 2,5-anhydro-D-mannose ( chitose ), which can be isolated as the crystalline diphenylhydrazone.207 Reduction of 2,5-anhydro-o-man-... 

Recently, in seeking a colorimetric method more sensitive than the Elson-Morgan test (20y), Dische and Borenfreund88 have developed a technique needing only 5y of the amino sugar. The method is based on the deamination of the hexosamine to give the corresponding 2,5-anhydro-hexose with Walden inversion at C2. The anhydro derivatives yield stable characteristic colors when treated with indole in dilute hydrochloric acid, well suited to quantitative colorimetric estimation. 

The deamination reaction of 2-amino-2-deoxy aldonolactones is also of interest. 2,5-Anhydro-D-mannaric acid has been obtained from the treatment of 2-amino-2-deoxy-D-mannonolactone, epichitosaminic lactone, with nitrous acid and subsequent oxidation of the product with nitric acid. This indicates that the reaction proceeds with a net retention of configuration, as for the corresponding free acid discussed later (p. 56). Similar treatment of 2-amino-2-deoxy-D-idonolactone, d-dextro-xylo-hexosaminic lactone, provides 2,5-anhydro-D-gularic acid, which is the epimer of the product derived from the free acid. " ... 

Figure 4.83 Mechanism of deamination of equatorial hexosamines and derivatives, (a) Generation of diazonium ions (b) bond shift.

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