PolysaccharidesGlycans pharmacognosy II2 nd lecture PolysaccharidesGlycans CLASSIFICATION the

Polysaccharides(Glycans) pharmacognosy II/2 nd lecture

Polysaccharides(Glycans) CLASSIFICATION: the polysaccharides or glycans may be classified into two major groups, namely: (a) Homoglycans, and (b) Heteroglycans (a) Homoglycan: The polysaccharide is termed as homoglycan when it contains only one type of monosaccharide unit, and (b) Heteroglycan: The polysaccharide is known as heteroglycan when it involves more than one kind of monosaccharide unit. Homoglycan A large number of plant products belonging to this particular category are like : honey, starch, inulin, dextran, cellulose, cotton, and dextrin.

1. Honey: is a viscid and sweet secretion stored in the honey comb by various species of bees. The average composition of honey ranges as follows: Moisture 14 -24%, Dextrose 23 -36%, Fructose 30 -47%, Sucrose 0. 4 -6%, Dextrin and Gums 0 -7% , Besides, it is found to contain small amounts of essential oil, beeswax, pollen grains, formic acid, acetic acid, succinic acid, maltose, dextrin, colouring pigments, vitamins and an admixture of enzymes eg; diastase, invertase and inulase. Uses 1. It is used as a sweetening agent. 2. Being a demulcent, it helps to relieve dryness and is, therefore, recommended for coughs, colds, sore-throats and constipation. 3. Because of its natural content of simple sugars, it is employed as a good source of nutrient for infants, and elderly persons.

2. Starch: (Corn starch, Potato Starch, Rice Starch) Hydrolysis of starch in acidic medium yields glucose. Uses: 1. It is used in the formulation of tablets and pills as a vital disintegrating agent and a binder. 2. It is employed as a diluent in the preparation of capsules. 3. It is an antidote of choice for iodine poisoning. 4. ‘Glycerine of starch’ is used not only as an emollient but also as a base for the suppositories. 5. It possesses nutrient properties as a food and in cereal based foods for babies e. g. , Farex (Glaxo) and Cerelac (Nestle). 6. It is the starting material for the large scale production of liquid glucose, and glucose syrup. 7. It is used topically and externally to allay itching.

3. Inulin is a starchy substance found in a wide variety of fruits, vegetables, and herbs, including wheat, onions, and bananas. The inulin that is used for medicine is most commonly obtained by soaking roots in hot water. 1. Inulin used to measure the GFR of kidneys. 2. Used to enhance the growth of lactobacilli , the beneficial bacteria in the colon and enhance the immunity of the body. 3. Used to decrease the cholestrol and triglycerides. 4. for treatment of constipation.

4. Dextran Is a carbohydrate substance made up predominantly of Dglucose units i. e. (C 6 H 10 O 5)n. It is α– 1, 6 linked polyglucan. the clinical dextrans have variable molecular weights, for example ; Dextran 40 (Baxter); Dextran 70 and Dextran 75. Uses: 1. . Dextrans as a whole helps in minimizing platelet adhesiveness, which property is gainfully exploited in their usage for prophylaxis of thrombosis and thromo embolism both during and after surgery.

2. Dextrans are employed in the formulation of fat-soluble vitamins (. Vitamin A, D, E, K). 3. It is also used in preparing sustained released tablets. 4. Dextrans find their abundant applications in various types of confectionaries, for instance: ice creams, candies, jellies, syrups and cake–topings ﺳﻜﺮﻳﺎﺕ. 5. Dextran 70 and Dextran 75 are used extensively in 6% solutions as plasma extender for the control and management of hypovolemic shock caused by hemorrhage, trauma, and severe burns.

5. Cellulose Represents one of the most widely distributed and abundantly available organic matter on this planet ﻛﻮﻛﺐ. It is, in-fact, the most important structural element of higherplant-cell walls. wood (40 -50% cellulose) is the major source of cellulose for industrial purposes , whereas cotton (98% cellulose) provides the balance requirement. Cellulose is comprised of chains of D-glucose units, whereby each unit is joined by a glycosidic linkage to C-4 of the next unit.

6. Absorbent Cotton • Synonyms: Purified cotton; Cotton wool; Surgical cotton. • Chemical Constituents : Absorbent cotton is mostly cellulose 93 -94% and moisture 6 -7%.

7. Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Uses: 1. As an excipient for dry extracts and pills. 2. It is used for preparing emulsions. 3. It is used for preparing printer’s inks, glues and mucilage. Heteroglycans Gums represent a heterogenous group of substances, that essentially possess in common the characteristic property of swelling in water to form either gels or viscous, sticky, solutions. It has also been advocated that gums are the resulting products obtained from normal plant metabolism.

In actual practice, the natural gums may be classified into many different groups, namely: (a) Exudate Gums (b) Seed Gums and (c) Marine Gums Exudate Gums 1. Acacia Synonyms : Indian Gum; Gum Acacia; Gum Arabic. Gum after collection is freed from small bits of bark and other foreign organic matter, dried in the sun directly that helps in the bleaching of the natural gum to a certain extent. Chemical Constituents : Acacia was originally thought to be composed only of four chemical constituents, namely : ( –) arabinose; (+) – galactose; (–)–rhamnose and (+) glucuronic acid.

Uses: 1. The mucilage of acacia is employed as a demulcent. 2. It is used extensively as a vital pharmaceutical aid for emulsification and to serve as a thickening agent. 3. It is used in the process of ‘granulation’ for the manufacture of tablets. 4. It finds its enormous application as a binding agent for tablets e. g. , cough lozenges.

2. Tragacanth: Synonym : Gum Tragacanth comprises of two vital fractions: first, being water soluble and is termed as ‘tragacanthin’ and the second, being water-insoluble and is known as ‘bassorin’. Both are not soluble in alcohol. Uses: 1. It is used as a demulcent in throat preparations. 2. It is employed as an emolient in cosmetics (e. g. , hand lotions). 3. It is used as a pharmaceutical aid as a suspending agent for insoluble and heavy powders in mixtures. 4. It is effectively employed as a binding agent for the preparation of tablets and pills. 5. It is also used as an emulsifying agent for oils and waxes.

Seed Gums are hydrocolloids contained in some seed embryos where they actually play the role as polysaccharide food reserves. 1. Pectin: in general, is a group of polysaccharides found in nature in the primary cell walls of all seed bearing plants. It has been observed that these specific polysaccharides actually function in combination with both cellulose and hamicellulose as an intercellular cementing substance. Pectin is naturally found in a number of plants namely: lemon peel, orange peel, carrots, sunflower-heads Pectin is the purified admixture of polysaccharides, obtained by carrying out the hydrolysis in an acidic medium of the inner part of the rind of citrus peels, for instance: Citrus limon (or Lemon).

Uses 1. It is employed mostly as an intestinal demulcent. producing a protective action along with Kaolin to prevent and control diarrhoea. 2. As a pharmaceutical aid pectin is used frequently as an emulsifying agent and also as a gelling agent preferably in an acidic medium. 2. Guar Gum Uses 1. It is used therapeutically as a bulk laxative. 2. It is also used as a thickner and its thickening property is 5 to 8 times more than starch. 3. It finds its use in peptice ulcer therapy. 4. It is employed both as a binding and a disintegrating agent in tablet formulations. 5. It is widely used in suspensions, emulsions, lotions, creams and toothpastes.

Marine Gums A variety of algae and seaweeds comprise of marine gums as components of cell walls and membranes or present in the intracellular regions where they actually serve as reserve food material. Algin: Synonyms : Sodium alginate; Alginic acid sodium. Uses: 1. It is extensively used in the manufacture of ice-creams where it serves as a stabilizing colloid, ensuring creamy texture. 2. It is employed as a stabilizing and thickening agent in food and pharmaceutical industry. 3. It is employed as a binding and distintegrating agent for tablets and lozenges.