Uronic Acids Uronic acid is formed when glucose is oxidised such that its primary alcohol group is converted to COOH group, without the oxidation of the aldehyde group. Examples D-glucose D-glucuronic acidD-galactose D-galacturonic acid In the body, glucuronic acid is formed from glucose in the uronic acid pathway in the liver.
Glycosides are present in many drugs and spices. They are also the chief constituents of animal tissues. Aglycones are methanol, glycerol, sterol, or phenol. Glycosides play a very important role in medicine because of their action in heart (cardiac glycosides). Examples are the derivatives of digitals and ouabain. Ouabain is a very good inhibitor of Na+—K+—ATPase…
Glycosides are produced by the interaction of monosaccharide residue with the hydroxyl group of a second compound, which may be a monosaccharide or some other compound. The non-carbohydrate compound is called an aglycone. The glycosidic bond is formed as an acetal link between a hemiacetal and a —OH group. Sugar—H + R—OH Sugar—R (Glycoside) +…
Osazone reaction is possible only when a free carbonyl (aldehyde or ketone) group is present. A monosaccharide or reducing disaccharide is first mixed and heated with phenylhydrazine in acetic acid to form sugar-phenylhydrazine, which then reacts with more reagents to form particular osazone-forming characteristic crystals of specific shapes. This test is very important to distinguish…
Monosaccharides are reduced to their corresponding alcohols by reducing agents such as sodium amalgam or by hydrogen under high pressure in the presence of a catalyst. For example, aldoses yield the following alcohols: D-glucose D-sorbitolD-galactose D dulucitolD-mannose D-mannitol Similarly, ketoses also yield two alcohols due to the formation of a new asymmetric carbon in the C-2 position.…
Aldoses are oxidised to different compounds based upon the reactants. The following are a few examples: Glucoses produce glucuronic acid, whereas galactose and mannose yield galacturonic acid and mannuronic acid, respectively.
When sugars react with strong mineral acids, they undergo dehydration and form furfurals. Furfurals condense with phenolic compounds such as α-napthol, thymol, and resorcinol to produce coloured complexes. This property of the sugars helps in the identification of sugars. Note: This test is used for distinguishing between glucose and fructose. If boiled for a long time,…
Reducing Properties Sugars that are oxidised at C-1 are known as reducing sugars. Sugars can react with the chemical agents due to the presence of free carbonyl (aldehyde or ketone) groups. In the alkaline medium, they form enediols, which reduce Cu2+, Ag+, Fe3+, and Bi+3 and oxidise to the corresponding sugar acids. Such sugars are known…
The phenomenon of mutarotation appears to be due to the changes of α- and β-forms and vice versa via the straight chain aldo to keto form. It is generally accepted that the mechanism of mutarotation involves opening and closing of the hemiacetal ring structure of monosaccharides to form traces of aldehyde and α- to β-ring…
Explanation Mutarotation means changing of optical rotation. Tamet explained that when a solution of freshly prepared crystalline glucose of α-D-form is observed in a polariscope, its initial specific rotation of +121.1° gradually decreases and finally becomes steady at + 52.5°. If, however, a solution of pure crystals of β-D-glucose is observed in a polariscope, the initial specific…