1,2-Disaccharides

Disaccharides have an OH of one monosaccharide (the aglycone, denoted A) bonded to the anomeric C of a second monosaccharide, B. The disaccharide is a glycoside of B. 

Problem 22.36 Cellobiose, isolated from the polysaccharide cellulose, has the same chemistry as maltose except that it is hydrolyzed by emulsin. Give the structure of this disaccharide.  

Unlike maltose, cellobiose is a /3-glycoside. (The aglycone unit is turned 180° to permit a reasonable bond angle for the glycosidic linkage.) 

Problem 22.38 Use shorthand formulas to show how osazone formation establishes the glucose unit of lactose to have the hemiacetal linkage (Problem 22.37).  

Problem 22.39 (u) Give the structure of sucrose (cane and beet sugar) from the following information (1) It is hydrolyzed by maltase or emulsin to a mixture of d-( )-glucose and D-(-)-fructose. (2) It does not reduce Fehling s solution and does not mutarotate. (3) Methylation and hydrolysis gives 2,3,4.6-tetra-O-methyl-D-glucose and a tetramethyl-D-fructose. (b) What structural features are uncertain  

The influence of pyranose to furanose interconversion on the observed stability constants (iifobs) of boronic acid complexes can be effectively demonstrated in the fluorescence response of boronic acid appended sensors with disaccharides. In examining the stabilities of disaccharides with the 5-indolylboronic acid 38, Aoyama and co-workers noted that for non-reducing sugars the observed stability constants (Aiobs) were significantly reduced or zero. This phenomenon was ascribed to the lack of an anomeric hydroxyl, which inhibited the 

The same trend was observed for o-fructose and its disaccharide derivatives lactulose and leucrose. Strong fluorescence responses were observed with d-fructose and lactulose (saccharides which can interconvert between their pyranose and furanose forms). Conversely, only a weak fluorescence response was observed with leucrose, which is covalently bound at the 5-position (the fourth carbon as numbered from the anomeric centre) and as such cannot isomerise to adopt a furanose ring structure (but still allows approaching boronic acids unfettered access to the C2,C3-diol). 

From the pragmatic viewpoint of designing diboronic acid sensors with selectivity for D-glucose, many receptors have relied on an approximate spacing of the two boronic acid units such that the dimensions of the binding pocket mimic that of other established systems. 

I did not fail 1000 times the light bulb was developed in 1001 steps 

During recent years the use of a modular approach in the design and synthesis of new fluorescent PET sensors has been at the fore of the research undertaken towards molecular sensing within our research group. 

Add a tablespoon of sugar to a glass of water and stir. Taste. Add more sugar, stir, and taste. If you have other carbohydrates such as fructose, honey, cornstarch, arrowroot, or flour, add some of each to separate glasses of water and stir. If you have some artificial sweeteners, add a few drops of the sweetener or a package, if solid, to a glass of water. Taste each. 

Place the substances in order from the one that tastes least sweet to the sweetest. 

How does your list compare to the values in Table 13.2  

How does the sweetness of sucrose compare with that of the artificial sweeteners  

Check the labels of food products in your kitchen. Look for sugars such as sucrose or fructose, or artificial sweeteners such as aspartame or sucralose on the label. How many grams of sugar are in a serving of the food  

Using Mechanism 23.2 as a guide, write a stepwise mechanism for the acid hydroiysis of methyi a-o-giucopyranoside. 

Disaccharides are carbohydrates that yield two monosaccharide molecules on hydrolysis. Structurally, disaccharides are glycosides in which the alkoxy group attached to the ano-meric carbon is derived from a second sugar molecule. 

Maltose, obtained by the hydrolysis of starch, and cellobiose, by the hydrolysis of cellulose, are isomeric disaccharides. In both maltose and cellobiose two D-glucopyranose units are joined by a glycosidic bond between C-1 of one unit and C-A of the other. The two are diastereomers, differing only in the stereochemistry at the anomeric carbon of the glycoside bond maltose is an a-glycoside, cellobiose is a 3-glycoside. 

The stereochemistry and points of connection of glycosidic bonds are commonly designated by symbols such as a-(1 4) for maltose and 3-(l ) for cellobiose a and 3 designate the stereochemistry at the anomeric position the numerals specify the ring carbons involved. 

Both maltose and cellobiose have a free anomeric hydroxyl group that is not involved in a glycoside bond. The configuration at the free anomeric center is variable and may be either a or 3. Indeed, two stereoisomeric forms of maltose have been isolated one has its anomeric hydroxyl group in an equatorial orientation the other has an axial anomeric hydroxyl. 

PROBLEM 25.11 Methyl glycosides of 2-deoxy sugars have been prepared by the acid-catalyzed addition of methanol to unsaturated sugars known as glycals. 

The free anomeric hydroxyl group is the one shown at the far right of the preceding structural formula. The symbol is used to represent a bond of variable stereochemistry. 

FADH2 (Section 15-6C). Polynucleotides are polymers of nucleosides linked through phosphate ester bonds. Polynucleotides also are called nucleic acids (RNA and DNA) and are the genetic material of cells, as will be discussed in Chapter 25. 

Exercise 20-8 Work out a mechanism for the acid-induced hydrolysis of W-glyco-sides. Pay special attention as to where a proton can be added to be most effective in assisting the reaction. Would you expect that adenosine would hydrolyze more, or less, readily than /V-methyl-a-ribosylamine Give your reasoning. 

You should look at 22 and 23 carefully to be sure that you recognize the difference between them.5 In 22, sugar A is acting as a simple hydroxy compound, the aglycone of the sugar G to which it is linked by an O-glycoside 

Disaccharides of type 23 are different in that each sugar, G and G, is acting as both a glycoside sugar and as an aglycone. The linkage between 

In general, we find that the nonreducing disaccharides give none of the carbonyl reactions observed for glucose, such as mutarotation and osazone formation, except when the conditions are sufficiently acidic to hydrolyze the acetal linkage. 

Q2H22O11 + h2o c6h12o6 + c6h12o6 Sucrose, known as table sugar, is comprised of a-D-glucose and j8-D-fructose. The aldehyde group ( carbon) of glucose is linked 

A disaccharide is a compound that is formed from two monosaccharide units by elimination of one molecule of water. At least one carbon atom involved in the acetal bridge (called glycosidic linkage) 

FIGURE 2.41 The three possible nonreducing disaccharides of D-glucofuranose. 

The monosaccharide units can be present in both their furanose and pyranose forms, and the anomeric configuration can be both a and (3 in the case of nonreducing disaccharides. When both monosaccharides have the same configuration (e.g., D-glucose), there are several variations. When both monosaccharide units form furanose rings, three isomers — two symmetric 

FIGURE 2.45 Two possible depictions of the reducing disaccharide a-D-Glcp-(l - 3)-P-D-Glcp. 

The glycosidic bond is the key to understanding the structure of oligosaccharides and polysaccharides, as we will see in the following sections. 

Extracts of willow bark were used for medicinal purposes as early as the time of Hippocrates. 

The most common oligosaccharides are disaccharides. In a disaccharide, two monosaccharides are linked by a glycosidic bond between the anomeric carbon of one monosaccharide unit and a hydroxyl group on the other unit. In this section, we will describe the structure and properties of four important disaccharides. 

A disaccharide consists of two monosaccharides iinked by a giycosidic bond between the anomeric carbon of one unit and a hydroxyi group on the other unit. 

FIGURE 21.9 An overview of biosynthetic pathways for the eight essential monosaccharides. 

Show how iV-acetylneuraminic acid can arise by an aldol reaction of iV-acetyl-mannosamine with pyruvate, CH3C0C02.  

We saw in Section 21.6 that reaction of a monosaccharide with an alcohol yields a glycoside, in which the anomeric -OH is replaced hy an -OR group. If the alcohol is itself a sugar, the glycosidic product is a disaccharide. 

Disaccharides contain a glycosidic acetal bond between the anomeric carbon of one sugar and an -OH group at any position on the other sugar. A glycosidic bond between Cl of the first sugar and the -OH at C4 of the second sugar is particularly common. Such a bond is called a l— 4 link. 

The glycosidic bond to an anomeric carbon can be either a or j3. Maltose, the disaccharide obtained by enzyme-catalyzed hydrolysis of starch, consists of two a-D-glucopyranose units joined by a 1— 4-a-glycoside bond. Cellobiose, the disaccharide obtained by partial hydrolysis of cellulose, consists of two 8-D-glucopyranose units joined by a 1 4- 8-glycoside bond. 

Lactose must contain a free aldehyde group in the molecule, one that is not blocked by the linkage. 

Lactose is composed of one glucose and one galactose unit. Since it is hydrolyzed by P-galactosidase, we can conclude that the galactose is coupled at the anomeric carbon and that the linkage is equatorial. In combination with (i), this means that the glucose is not coupled at the anomeric carbon we have a ring that can open and close to mutaro-tate and for the aldehyde to be oxidized. 

So far, we can say we have the units as follows we know where the galactose (left) is bound, but for the glucose, we only know that it is not at Cl. 

These data allow us to complete the structure—the 4-position of glucose is unmethylated, so this is where the bond to galactose must have been. Note that although the anomeric hydroxyl of glucose will be methylated by dimethyl sulfate, this will be removed during the hydrolysis—it is an acetal, not an ether  

TABLE 16.6 Relative Sweetness of Various Nutritive and Nonnutritive Sweeteners 

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C,2H220ii,2H20. M.p. 9TC. A non-reducing disaccharide, which forms the principal carbohydrate of insect haemolymph. It comprises about 25% of trehala manna, the cocoons of a parasitic beetle. Trehalose also occurs in fungi, e.g. Amanita muscaria, generally replacing sucrose in plants lacking chlorophyll and starch. 

Kovacs H, Bagley S and Kowalewski J 1989 Motional properties of two disaccharides in solutions as studied by carbon-13 relaxation and NOE outside of the extreme narrowing region J. Magn. Reson. 85 530 1... 

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. 

Glucose and fructose (CeHijOj, monosaccharides) sucrose maltose and lactose (CiaHja n, disaccharides) starchy (CaHiflOs), a polysaccharide. 

Hydrolysis by acids. Place 15 ml. of starch solution in a boiling-tube, add I ml. of cone. HCl, mix well and place in a boiling water-bath for 20 minutes. Cool and add 2 drops of iodine solution to i ml. of the solution no blue coloration is produced. On the remainder, perform tests for glucose in particular show that glucosazone can be formed. Neutralise the excess of acid before carrying out these tests. (Note that a more concentrated acid is required to hydrolyse starch than to hydrolyse the disaccharides, such as sucrose.)... 

The weights of other monosaccharides and reducing disaccharides which will reduce i ml. of this standard Fehling s solution are galactose, 0 00511 g- fructose. 0 00514 g.. mannose, 0 00431 g. lactose, 0 00678 g. maltose, 0 00807 g. 

Carbohydrates may be divided into monosaccharides, disaccharides and polysaccharides. The monosaccharides under certain conditions react as polyhydroxy-aldehydes or polyhydroxy-ketones two important representatives are glucose CjHjjO (an aldose) and fructose (laevulose) CgHuO, (a ketose). Upon hydrolysis di- and polysaccharides 3deld ultimately monosaccharides. Common disaccharides are sucrose, lactose and maltose (all of molecular formula C,2H2. 0,), whilst starch, dextrin and cellulose, (CjHjoOj), in which n > 4, are typical polysaccharides. 

Disaccharides are sugars which yield two molecules of monosaccharides upon hydrolysis. The four of greatest practical interest are ... 

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. 

Of the common disaccharides sucrose does not reduce Fehling s solution. If the cane Sugar is hydrolysed by boiling it with dilute acid and the solution is neutralised with aqueous sodium hydroxide, the reduction of Fehling s solution occurs readily. 

D (+) Galactose is a constituent of numerous polysaccharides It is best obtained by acid hydrolysis of lactose (milk sugar) a disaccharide of d glucose and d galactose L (—) Galactose also occurs naturally and can be prepared by hydrolysis of flaxseed gum and agar The principal source of d (+) mannose is hydrolysis of the polysaccharide of the ivory nut a large nut like seed obtained from a South American palm... 

FIGURE 25 11 Diagram of a cell surface glycoprotein showing the disaccharide unit that IS recognized by an invading influenza virus... 

Maltose and cellobiose (Section 25 14) are examples of disaccharides denved from D glucopyranosyl units... 

Disaccharide (Sections 25 1 and 25 14) A carbohydrate that yields two monosaccharide units (which may be the same or different) on hydrolysis... 

Sucrose (Section 25 14) A disaccharide of glucose and fruc tose in which the two monosacchandes are joined at their anomenc positions... 

Lactulose. 4-O-P -D-Galactopyranosyl-4-D-fmctofuranose [4618-18-2] (Chronolac) (12) may be made from lactose using the method described in Reference 9. It is a synthetic disaccharide that is not hydroly2ed by gastrointestinal enzymes in the small intestine, but is metabolized by colonic bacteria to short-chain organic acids. The increased osmotic pressure of these nonabsorbable organic acids results in an accumulation of fluid in the colon. Lactulose may not be tolerated by patients because of an extremely sweet taste. It frequently produces flatulence and intestinal cramps. 

Rhamsan Gum. Rhamsan gum, produced y lcaligenes strain (ATCC 31961) (91), has the same backbone as geUan and welan gums, but it carries a disaccharide sidechain (92). 

Utilize the suciose-containing trisaccharide raffiaose [512-69-6] as a substrate for levan synthesis, releasing the disaccharide melihiose as a side-product. 

La.ctose, Lactose [63-42-3] (milk sugar), 20, makes up about 5% of cow s milk. Lactose is a disaccharide composed of D-glucose... 

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