Maltose

Some common disaccharides are maltose, cellobiose, lactose, and sucrose. 

The systematic name for maltose, shown beneath the common name, describes the structure fully, including the name of each unit (D-glucose), the ring sizes (pyra-nose), the configuration at each anomeric carbon (a or /3), and the location of the hydroxyl group involved in the glycosidic link (4-0). 

The anomeric carbon of the right glucose unit in maltose is a hemiacetal. Naturally, when maltose is in solution, this hemiacetal function will be in equilibrium with the open-chain aldehyde form. Maltose, therefore, gives a positive Tollens test and other reactions similar to those of the anomeric carbon in glucose. 

PROBLEM 16.13 When crystalline maltose is dissolved in water, the initial specific rotation changes and gradually reaches an equilibrium value. Explain. 

Before going straight on to Lipid A, we wanted to check disaccharides on the way, and chose first p-maltose, 4-0-a D-glucopy-ranosyl-p-D-glucopyranose, for which structural data were available. We found all conformers in PEP300 there are four those of lowest energy compared well with crystal conformations. 

We also found the path in conformational space between the two most populated conformers, the barrier height, and the rate of interchange, which is fast on the NMR time scale. The weighted average of a specific proton-proton distance across the glycosidic linkage agreed with NMR measurements. 

The conformers were redetermined when PEP400 was ready a 

A thorough x-ray investigation of p-maltose octaacetate lends support to our calculations. The crystal conformation is close to our middle conformer in the minimum valley, see Table 5-1 The C5-C6 conformation is g g in the reducing sugar and alternateley ga and ag in the nonreducing, confirming our calculated possibilities. For 

In connection with the crystallographic work a primitive conformational analysis was carried out, with results inferior to our 16 S 215 

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Lactose on hydrolysis gives glucose and an isomeric monosaccharide galactose, which may be given the symbol Ga-r. The lactose molecule may be represented as Ga-r-G-r, and it has therefore also a free potential aldehyde group and is a reducing sugar like maltose. 

Both maltose and lactose, being reducing sugars, give osazones which differ from one another and from glucosazone in crystalline form. Sucrose (G-r-r-F), having no potential aldehyde or ketone grouping, does not form an osazone. 

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

Action of sodium hydroxide. Boil about 0 2 g. of glucose with 5 of 10% NaOH solution the mixture turns yellow, then brown, and emits the odour of caramel. Fructose, maltose, lactose and soluble starch behave similarly sucrose and ordinary starch do not give colorations. 

Rapid furfural test." Violet coloration after about i minute s boiling, as for glucose and maltose. 

TEST Glucose F ructose Sucrose Maltose Lactose... 

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. 

They are highly specific in their reactions, e.g., maltose attacks the a glucosidic link (which occurs in maltose), but is without action on the 3-glucosidic links. 

Diastase (or amylase) liver, etc., malt starch (amylum) maltose and dextrin 6-0 (liver) 5-2 (malt)... 

Maltase pancreas, small intes tine, yeast maltose glucose 6-1 (gut) 6 6 (yeast)... 

Diastase or amylase is formed when malt is produced by the germination of barley grains. Malt is therefore a good source of the enzyme. Diastase is also secreted by the salivary glands (when it is known as ptyalin), and also by the pancreas. Its function is to hydrolysef starch to a mixture of maltose and dextrin ... 

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. 

CijHjjOii Maltose + HjO CgHjjO, d-Olucose + CgHjjO, d-Glucose... 

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. 

For practice, the student should apply tests (iii) and (iv) to glucose, lactose, maltose and sucrose. 

The approximate times of osazone formation in minutes are given in Table 111,139. The product from mannose is the simple hydrazone and is practically white. Arabinose osazone separates first as an oil, whilst that from galactose is highly crystalline. Lactose and maltose give no precipitate from hot solution. 

Maltose obtained by the hydrolysis of starch and cellobiose by the hydrolysis of cellulose are isomenc disaccharides In both maltose and cellobiose two d glucopyra nose units are joined by a glycosidic bond between C 1 of one unit and C 4 of the other The two are diastereomers differing only m 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(l 4) for maltose and (3(1 4) for cellobiose a and (3 designate the stereochemistry at the anomeric position the numerals specify the ring car bons involved... 

FIGURE 25 6 Molecu lar models of the disaccha rides maltose and cellobiose Two D glucopyranose units are connected by a glycoside linkage between C 1 and C 4 The glycosidic bond has the a orientation in maltose and IS p in cellobiose Mai tose and cellobiose are diastereomers... 

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 iso lated one has its anomeric hydroxyl group m an equatorial orientation the other has an axial anomeric hydroxyl... 

The two stereoisomeric forms of maltose just mentioned indergo mutarotation when dissolved in water What is the structure of the key intermediate in this process ... 

Lactose is a disacchande constituting 2-6% of milk and is known as milk sugar It differs from maltose and cellobiose m that only one of its monosaccharide units is D glucose The other monosaccharide unit the one that contributes its anomeric carbon to the glycoside bond is d galactose Like cellobiose lactose is a (3 glycoside... 

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

Maltose (Section 25 14) A disacchande obtained from starch in which two glucose units are joined by an a(l 4) glyco sidic link... 

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