Disaccharides reactions

Other extensions of this C-glycosylation methodology have been reported for the preparation of two C-linked 1,6-disaccharides. Reaction of the pyridyl sulfone of N-acetylglucosamine 54 with aldehyde 55 produced mainly the a-C- saccharide 56 (Scheme 13) [35]. The stereoselectivity at the anomeric center is explained in this case by internal coordination of the fV-acetyl group with the metal ion of the intermediate glycosyl samarium species 57, retarding anomerization to the ther-... 

For an elementary study of the sugars, it is not suggested that the student should remember the structure of the disaccharides their chief and clturactet-istic reactions will, ho. e er, be readily understood if the following facts arc borne in mind. 

Disaccharides, e.g., lactose, which yield galactose upon hydrolysis, will also give the sparingly-soluble mucic acid but in poorer 3deld. This reaction may be employed for the differentiation between certain disaccharides lactose — mucic + saccharic acids sucrose — saccharic acid only maltose — saccharic acid only. 

Reactions can also occur during chromatographic development. These can either be undesired reactions or planned derivatizations. Thus, Weicker and Brossmer [11] have reported, for example, that hexoses, pentoses and disaccharides can be ammated when ammonia-containing mobile phases are employed on silica gel G layers. On the other hand, fluorescamine or ninhydrin have been added to the... 

A disaccharide is added to a pyridine SO3 complex solution, which is prepared by reacting 5 to 6 times the molar amount of liquid SO3 as much as that of disaccharide with 5 to 10 times the amount of pyridine as that of the disaccharide at 0°C to 5°C, for sulfation at 50°C to 70°C for 3 to 7 hours. After the completion of sulfation, the greater part of pyridine Is removed by decantation. The obtained solution exhibits an acidity that is so strong that it is improper to apply the reaction with aluminum ion and, therefore, sodium hydroxide is added for neutralization. After the remaining pyridine is removed by concentration, 100 unit volumes of water per unit volume of the residue is added thereto. To the solution is then added aluminum ion solution mainly containing aluminum dihydroxychloride, the pH of which is 1.0 to 1.2, in such an amount that the aluminum ion Is present in an amount of 4 to 6 molar parts of the amount of disaccharide to provide a pH of 4 to 4.5. The mixture is reacted under stirring at room temperature and the formed disaccharide poly sulfate-aluminum compound is allowed to precipitate. After filtration, the residue is washed with water and dried. 

Application of the ring opening reaction to disaccharide derivatives such as 4,6 4, 6 -di-0-benzylidene-a,a-trehalose affords the corresponding 6,6 -dibromo-4,4 -dibenzoate in good yield. 

We saw in Section 25.6 that reaction of a monosaccharide with an alcohol yields a glycoside in which the anomeric -OH group is replaced by an -OR substituent. If the alcohol is itself a sugar, the glycosidic product is a disaccharide. 

An important metabolic reaction of disaccharides is the reverse of (5). Water, in the presence of H+(aq), reacts with sucrose to give glucose and fructose. This process is called hydrolysis, meaning reaction with water."... 

An important reaction of fats is the reverse of ester formation. They hydrolyze, or react with water, just as disaccharides do. Usually hydrolysis is carried out in aqueous Ca(OH)2, NaOH, or KOH solution. Because of long use in the preparation of soap from fats, the alkaline hydrolysis reaction (6) is called saponification. 

Disaccharides which can be regarded as formed by reaction of the two glycosidic (anomeric) hydroxy groups with one another are named, systematically, as glycosyl glycosides. The parent (cited as the glycoside component) is chosen according to 2-Carb-2.1. Both anomeric descriptors must be included in the name. 

C-Disaccharide analogs of trehalose were recently [20c] prepared by using as a key step an aqueous Diels-Alder reaction between the sodium salt of glyoxylic acid and the water soluble homochiral glucopyranosil-l,3-pentadiene 19 (Equation 6.1). A mixture of four diastereoisomers in a 41 24 21 14 proportion was obtained after esterification with methanol and acetylation. The main diaster-eoisomer 20 was isolated and characterized as benzoyl-derivative. 

The coupling of the protected disaccharides lactose and cellobiose with the pyrazinone scaffold via the 1,3-dipolar cycloaddition reaction was further investigated (Scheme 34). To run the reaction to completion, the use of 2 equiv... 

Hydrogenation of the carbonyl group of a mono- or disaccharide gives the corresponding sugar alcohol. On paper, this reaction is simple, and it can schematically be written as O... 

Figure 20 Post-column detection of mono- and disaccharides with 4-amino-benzoylbenzamide. Column CarboPac PA-1. Gradient 1-10 mm NaOH (0-20 min.), 10-20 mM NaOH (20-35 min). Flow rate 1 ml/min. Detection absorbance at 400 nm after reaction with 4-aminobenzoylhydrazide. (a) Standard mixture of fucose (1), arabinose (2), galactose (3), glucose (4), xylose and N-acetylglucosamine (5 and 6), allose (7), 3-fucosyllactose (8), fructose (9), lactose (10), Man-(3-(l,4)-GlcNac. (b) Normal urine, (c) Urine from a child with (3-mannosidosis. (Reproduced with permission of Academic Press from Peelen, G. O. H., de Jong, J. G. N., and Wever, R. A., Anal. Biochem., 198, 334, 1991.)...

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