Reaction D Sugar Fragmentation

Because a-dicarbonyl compounds are particularly reactive, Weenen and Apeldoom57 specifically looked for these compounds by means of derivatisation with o-diaminobenzene among the butanol-soluble fragmentation products formed in 15 systems (glucose, fructose, xylose, 3-deoxyglucosone, or fructosylalanine without amine or with alanine or cyclohexylamine 1 h, 100 °C, phosphate buffer, pH 8). Four a-dicarbonyls were obtained glyoxal, 2-oxopropanal, butanedione, and 2,3-pentanedione. 

In the absence of added alanine, the Amadori compound gave the fust three in about equal amounts (ca 100 fig of each), but only ca 20 fig of 2,3-pentanedione. The four carbohydrates gave glyoxal and 2-oxopropanal only. This includes 3-deoxyglucosone, which also gave only a relatively poor yield of glyoxal, but somewhat more 2-oxopropanal, overall indicating rather modest reactivity. 

In the presence of alanine, all four a-dicarbonyls are formed in each system, glyoxal being produced in largest amounts by glucose and fructose and 2-oxopropanal by xylose and 3-deoxyglucosone. Fructosylalanine gave lower amounts of a-dicarbonyls (except 2,3-pentanedione) in the presence of alanine than in its absence. 

In the presence of cyclohexylamine, the yields were much higher in all cases, up to times 40, for 2-oxopropanal from fructose (1.10 mg), except for 2,3-pentanedione from glucose and 3-deoxyglucosone, where the increase was less than one-fifth. The largest yields were from xylose, fructose, and glucose, 2.23, 2.15, and 1.75 mg, respectively, each representing less than 0.1% of the carbohydrate used. 

Because of the importance of dicarbonyl compounds in the Maillard reaction, Meade and Gerrard58 are trying to elucidate their structure-activity relationships, using linear and cyclic dicarbonyls and RNase A, crosslinking being assessed by SDS PAGE. 

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Reaction C Sugar dehydration Reaction D Sugar fragmentation... 

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