Deoxy sugars acid decomposition

The first question concerns the nature and relative proportions of constituent monosaccharides. In principle, this is obtained by acidic hydrolysis (Biermann 1988) but, in practice, it must be carefully applied as there are a certain number of important specific cases. Hydrochloric, sulfuric, and trifluoroacetic acids are used whose 1 N solutions have a pH of 0.1, 0.3, and 0.7, respectively. When hydrolysis liberates monosaccharides fragile in an acidic medium, a delicate balance between the risk of incomplete hydrolysis and partial destruction of the hydrolysis product must be maintained. The fragile sugars are pentoses, deoxy sugars, and uronic and aldonic acids. When sialic acid is kept for 30 min at 90°C in 0.01 M HCl, 20% decomposition occurs. With neutral polysaccharides, decomposition can be limited to less than 9%. The acetyl groups of acetamides are hydrolysed and relatively stable protonated amino sugars are obtained. 

In the Lobry de Bruyn-Alberda van Ekenstein transformation (reviewed by Speck ) of a ketose to the epimeric aldoses, formation of the 3-deoxy-uloses is normally considered to be a side reaction, and both reactions are considered to proceed through a common intermediate, the 1,2-enediol of the sugar. Under the conditions used for preparation of the 3-deoxy-hexos-uloses from the diketose-(amino acids), the former were, however, the main products and the epimeric aldoses only minor products. Furthermore, under these conditions, both reactions were irreversible and the products so stable that the amounts of the two t3rpes of compound were a measure of their rates of formation. The rapid rate of decomposition of the diketose-(amino acids) was probably due to their ready enolization, even in the absence of strong alkali or acid, to give the 1,2-enolammonium compound... 

Sugar degradation products were determined as benzimidazole derivatives after reaction with o-phenylenediamine. More than 120 amino-acid specific Maillard products have been isolated and identified from the reaction of L-proline, hydixn roline, < teine and methionine with monosaccharides at 150° for 1-1.5 h, in connection with studies of thermally generated aromas. Proline derived components were important constituents of bread, malt and beer, and cysteine and methionine derived components were predominant in roasted coffee and meat flavours. The effects of temperature, pH, and the relative concentration of rhamnose and proline on the quantity of specific volatiles produced in the Maillard reaction of these substrates have been studied, and the data have been analysed 1 computer methodology. The glucosylated cyclopentenone (44) was one of the products of decomposition of the Amadori product 1-deoxy-l-piperidino-maltulose in warm water. ... 

---