Glucose with alanine

The ESR spectra of reaction mixtures of glucose with a- and 3-alanine differed from each other in the complexity of their hyperfine structure, the former being split into 19 lines and the latter into 25 lines. This difference was shown to depend on... 

Figure 1. Free radical formation and browning in the reaction of D-glucose with a-alanine or fi-alanine (each 3 MJ, and ESR spectra of the reaction mixtures heated...

To confirm these relationships, the ability of these intermediates to generate the free radical was also examined. As shown in Fig. 8, the Amadori product did not provide any free radical on heating alone or with added sugar or amino acid. In contrast to this, glucosyl-8-alanine alone gave the free radical to an extent similar to that in the glucose-8-alanine system. In a separate run, the Schiff base, glucosyl-n-butylamine, alone in... 

Figure 7. Formation of free radical and other intermediates in the reaction of glucose with fi-alanine. The mixture (each 2 M) with aqueous alkali solution (0.1 N NaOH) was heated in a boiling water bath. Key , free radical O, browning A, 1-fl-alanino-l-deoxyfructose and , 3-deoxyglucosone. (Reproduced with...

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. 

Reviews by Ruderman (19) and Adibi (20,21) indicate that the branched-chain amino acids, particularly leucine, have an important role along with alanine in gluconeogenesis. Leucine and the other two branched-chain amino acids are catabolized in skeletal muscle. The nitrogen that is removed from the branched-chain amino acids in skeletal muscle is combined with pyruvate and returned to the liver as alanine. In the liver the nitrogen is removed for urea production and the carbon chain is utilized as substrate for synthesis of glucose. Adibi et al. (22) reported that during the catabolic conditions of starvation, oxidation of leucine and fatty acids increases in skeletal muscles. While glucose oxidation is reduced, the capacity for oxidation of the fatty acid palmltate more than doubled, and leucine oxidation increased by a factor of six. 

The mechanism that produces increased amino acid oxidation during exercise is unknown. White and Brooks (29) demonstrated a relationship of amino acid oxidation to use oT blood glucose. Concomitant with increases in the intensity of exercise and leucine oxidation, the oxidation of glucose and alanine increased. These data in combination with the earlier reports of increased flux of leucine to skeletal muscles and alanine from muscles to the liver suggest that the oxidation of amino acids may be linked to the need for glucose and to generation of substrates for gluconeogenesis. 

Fig. 21. Synthesis of alanine from glucose, with recovery of glutamate through a loop involving oxaloacetate, aspartate, fumarate, and malate.

One of the first researchers to study the aroma formation during the Maillard reaction was Ruckdeschel [21] in 1914. He described the reaction product of glucose with phenylalanine as rose-like, with leucine as bread-like, with valine as fine roasted and with alanine as similar to coloured malt. 

Fortunately, a host of methods is available for achieving this goal. They include resolution of a D,L-mixture [238] inversion of L-lactic acid derivatives (see Sections 1.2.1.2 and 1.2.2.2) asymmetric reduction of pyruvates catalytically [239], enzymatically [240], or with chiral boranes [241] and diazotization of D-alanine derivatives, which proceeds with net retention of configuration [242,243]. In addition, D-lactic acid can be obtained by the fermentation of glucose with Lactobacillus leichmannii in the presence of calcium carbonate [244],... 

Equimolar amounts of fmctose and P-alanine were heated in a heating block at 150 C for 4 min. Figure 2 shows the HPLC profiles of the methanol-water extracts from the reaction mixtures of fructose or glucose with P-alanine. The products from the reaction for 2 min gave... 

The volatile compounds from the reaction mixtures of fructose or glucose with P-alanine were extracted with dichloromethane and identified by GC and GC-MS using a fused silica capillary column (Figure 4). Eleven products were detected, and the major component, peak 5, was identified as DDMP (Table 1). 

Confirmation of Maltol in the Reactions of Fructose and Glucose with P-Alanine... 

Figure 9. Proposed mechanism of main compounds in the reaction of either fructose or glucose with P-alanine, identified by GC-MS.

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