Drugs Containing Carbohydrates and Derived Products

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Chapter: Pharmacognosy and Phytochemistry : Drugs Containing Carbohydrates and Derived Products

Carbohydrates, as the name suggest, were defined as a group of compounds composed of carbon, hydrogen and oxygen in which the latter two elements are in the same proportion as in water and were expressed by a formula (CH2O)n, that is, hydrates of carbon.


Drugs Containing Carbohydrates and Derived Products

 

INTRODUCTION

 

 

Carbohydrates, as the name suggest, were defined as a group of compounds composed of carbon, hydrogen and oxygen in which the latter two elements are in the same proportion as in water and were expressed by a formula (CH2O)n, that is, hydrates of carbon.

 

The term ‘carbohydrates’ arose from the mistaken belief that substances of this kind were hydrates of carbon, because the molecular formula of many substances could be expressed in the form CX(H2O)Y, for example, glucose (C6 H12 O6), sucrose (C12 H22 O11), etc. In these examples, the hydrogen and oxygen are present in the same ratio

as in water. But this definition has certain drawbacks as given below:

 

·  It should be kept in mind that all organic compounds containing hydrogen and oxygen in the proportion found in water are not carbohydrates. For example, formaldehyde HCHO for the present purpose written as C(H2O); acetic acid CH3COOH written as C3(H2O)2; and lactic acid CH3CHOHCOOH written as C3(H2O)3 are not carbohydrates.

 

·  Also, a large number of carbohydrates such as rhamnose (C6H12O5), cymarose (C7H14O4), digitoxose (C6H12O4), etc., are known which do not contain the usual propor-tions of hydrogen to oxygen.

 

·  Finally, certain carbohydrates are also known which contain nitrogen or sulphur in addition to carbon, hydro-gen and oxygen.

 

From the above discussion, it can be concluded that the definitions described above are not correct; however, carbohydrates are now defined chemically as polyhydroxy aldehyde or polyhydroxy ketones or compound that on hydrolyses produce either of the above.

 

Carbohydrates are among the first products to arise as a result of photosynthesis. They constitute a large proportion of the plant biomass and are responsible, as cellulose, for the rigid cellular framework and, as starch, for providing an important food reserve. Of special pharmacognostical importance is the fact that sugars unites with a wide variety of other compounds to form glycosides and secondary metabolites. Mucilage, as found in marshmallow root and psyllium seeds, act as water-retaining vehicles, where as gums and mucilage, which are similar in composition and properties, are formed in the plant by injury or stress and usually appear as solidified exudates; both are typically composed of uronic acid and sugar units. The cell walls of the brown seaweeds and the middle lamellae of higher plant tissues contain polysaccharides consisting almost entirely of uronic acid components.

 

Low molecular weight carbohydrates are crystalline, soluble in water and sweet in taste, for example, glucose, fructose, sucrose, etc. The high molecular weight carbohydrates (polymers) are amorphous, tasteless and relatively less soluble in water, for example, starch, cellulose, inulin, etc.

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