Monosaccharides reaction model

De Bruijn et al.26 30 used chromatographic and spectroscopic techniques to analyze the effect of reaction variables (such as pH and monosaccharide concentration) on the product profile and developed a reaction model (see Fig. 9) that emphasized the role of a-dicarbonyl compounds. Some of the features of the model shown in Fig. 9 are ... 

Equatorially positioned methyl-branched derivatives may be obtained by reductive cleavage of spiro epoxides [94], Thus the Peterson olefination of 188gives the exocyclic 3 -methylene function in 189. By means of a Sharpless epoxidation the allylic 4"-hydroxy group should determine the chirality of the resulting epoxide. However, the Sharpless method does not show any reaction neither in a monosaccharide model system nor in this trisaccharide precursor [95]. Amazingly, the classical epoxidation with m-chloroperbenzoic acid is employed to give exclusively the desired (3"R) epoxide 190 in excellent yield. These results may be associated with a sufficient chiral induction of the stereochemical information at C-l", C-4", and C-5". A subsequent reduction furnishes the original E-D-C trisaccharide sequence 191 of mithramycin [95, 96]. 

Many studies of nonenzymatic browning have been carried out using model systems of monosaccharides and amino acids. Given the ease of release of arabinose from the pentosan, there is the possibility that Maillard reactions could take place if the temperature is appropriate. 

As demonstrated in previous publications, model reactions of L-proline and monosaccharides result in complex mixtures of proline specific compounds (J —4 ) During the Maillard reaction of L-proline and reducing sugars more than 120 proline specific compounds were identified by MS-, IR-, 1H- and 13c-NMR-spectroscopy (among them ... 

C. M. Brands and M. A. J. S. van Boekel, Reactions of monosaccharides during heating of sugar-casein systems building a reaction network model, J. Agric. Food Chem., 2001, 49, 4661-4615. 

Titanium-based catalysts, would seem particularly attractive candidates, but the pore size of e.g. TS-1, is much too small to admit even a monosaccharide. Recently a number of synthetic approaches towards mesoporous titanium containing catalysts of the MCM-41 type have appeared in the literature . In the present paper we will deseribe the use of Ti-MCM-41 materials in the oxidation of the model mono- and disaccharides methyl a-D-glucopyranoside, sucrose and a,a-trehalose, and we will discuss the effect of the zeolite synthesis on the effectiveness in these reactions. Several preparative approaches of Ti-MCM-41 have been compared in the oxidation of these model carbohydrates. 

Space-filling models, whose dimensions are proportional to the radius of the atoms, also give useful structural information. (See Figures 7.19,7.20, and 7.21.) Monosaccharides undergo most of the reactions that are typical of aldehydes, ketones, and alcohols. The most important of these reactions in living organisms are described. 

Related to the cyclic carbonates are the cyclic imidocarbonates produced by the action of cyanogen bromide on polysaccharides. " In terms of a monosaccharide model, " the major derivative of the reaction from a (1- 4)- or (I->6)-glucan is the trans-2,3-imidocarbonate, small proportions of the 2,3-carbonate, 2- and 3-carbamate, and, possibly, triazinyl groups also being formed. Cyclic imidocarbonate derivatives of Sephadex and 0-(2-aminoethyl)- and 0-[3-(p-aminophenoxy)-2-hydroxypropyl]-Sephadex have been prepared, " and the derivatization occurs equally well... 

Many of the early studies were conducted with enzymes from fermentation, particularly invertase, which catalyzes the hydrolysis of sucrose to monosaccharides D-glucose and D-fmctose. With the introduction of the concept of hydrogen ion concentration, expressed by the logarithmic scale of pH (Sorensen, 1909), Michaelis and Menten (1913) realized the necessity for carrying out definitive experiments with invertase. They controlled the pH of the reaction medium by using acetate buffer, allowed for the mutarotation of the product and measured initial reaction rates at different substrate concentrations. Michaelis and Menten described their experiments by a simple kinetic law which afforded a foundation for a subsequent rapid development of numerous kinetic models for enzyme-catalyzed reactions. Although the contribution of previous workers, especially Henri (1902, 1903), was substantial, Michaelis and Menten are regarded as the founders of modern enzyme kinetics due to the definitive nature of their experiments and the viability of their kinetic theory. 

Volatile components formed from the reaction of monosaccharides or disaccharides with P-alanine were investigated in a dry condition as a model system of cookie processing. Maltol is a common compound formed in the Maillard reaction, but it was very difficult to detect it in previous experiments using actual cookie materials. In this work, we investigated the principal compounds and maltol formation from the reaction of monosaccharides or disaccharides with P-alanine at 150 °C for 10 min. Neither the reaction of monosaccharides nor the disaccharides with P-alanine resulted in the formation of maltol. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one (DDMP) was detected as a principal product from the reaction of monosaccharides with P-alanine. 5-Hydroxymethyl-2-furfural was also confirmed as being a major product in both reactions. 

For the model system of cookies baking, the reaction mixtures consisted of equimolar amounts of a sugar (either 180 mg of monosaccharides or 360 mg of disaccharides) and P-alanine (89 mg). The components were placed in test tubes, and the mixtures were heated in a heating block at 150 for 2-10 min. On cooling, the samples were extracted with methanol-water (3 1 v/v) or dichloromethane, and the extract with dichloromethane was concentrated to 100 mL under a stream of nitrogen. 

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