Lecture 5: Pharmacognosy I (PHCG 111) - PDF

For First year Pharmacy Students By  VIII- SECONDARY PLANT METABOLITES (Active Constituents) ▪The secondary metabolites act, as protective agents. They are the waste (detoxification) product of metabolism. They are biosynthesized to aid the producers' survival. ▪Thus they are...

For First year Pharmacy Students By  VIII- SECONDARY PLANT METABOLITES (Active Constituents) ▪The secondary metabolites act, as protective agents. They are the waste (detoxification) product of metabolism. They are biosynthesized to aid the producers' survival. ▪Thus they are energy producer and physiologically active. ▪Secondary metabolites are divided into several classes of various organic compounds: 1. CARBOHYDRATES and related compounds: ▪Compounds composed of carbon, hydrogen, and oxygen as polyhydroxy aldehydes or ketone alcohols: sucrose, lactose, starch, gums, mucilage and pectin. Gums, mucilage and pectins Gums: ▪Polysaccharides or salts of Polysaccharides ▪Produced in higher plants as protective after injury ▪Gums give arabinose, galactose, glucose, mannose and various uronic acids (uronic acids may form salts with Ca, Mg and other cations) on hydrolysis ▪Example gum acacia and gum tragacanth. Mucilage: ▪Polysaccharide complexes. ▪Insoluble in alcohol, form viscous, non-adhesive colloidal solution with water. They don’t form jelly. 1. Pectose type (red colour with ruthenium red e.g. Senna, Buchu and Henna leaves) 2. Callose type (red colour with corallin soda, e.g. squill) 3. Neutral (blue with methylene blue e.g. Foenugreek). Pectin: 1. Purified carbohydrate (CHO) obtained from dilute Acid extract of the inner part of the rind of Citrus fruit or apple pomace ‫تفل‬. 2. Soluble in 20 parts water it forms stiff gel. 3. Used as protecting and suspending agent and as ingredient in antidiarrheal preparation. 2. GLYCOSIDES: Aglycone Glycone C S (genin) (sugar) CN ▪Glycosides are non-reducing organic compounds that yield one or more sugars among the product of hydrolysis by dilute acids, alkalis or enzymes. The non-sugar part of the molecule is called the aglycone (genin), and the sugar component (glycone). ▪Chemically glycosides are considered as sugar ethers. The condensation may occur by loss of water and formation of O- (oxygen glycosides or ether linkage), C- (carbon glycosides), S-(sulphur glycosides or thio-glycosides) and CN-(cyanophore glycosides). ▪Glycosides are generally soluble in water and hydro alcoholic solvents due to the hydrophilic nature of the sugar. The higher the sugar content the less soluble in organic solvent. The aglycones are soluble in organic solvent. Classification of Glycosides: According to the nature of the aglycone (genin) into the following: A. PHENOLIC GLYCOSIDES i. Simple Phenolic Glycosides: e.g. Arbutin present in Uva ursi leaf. It is a hydroquinone glycosides used in urethritis and cystitis. ii. Flavonoid Glycosides: ▪Flavonoids are the largest group of naturally occurring phenols. ▪They occur in the plant in both free aglycone and /or as glycosides. e.g. Diosmin glycoside of Buchu and Hesperidin glycoside of Citrus species. ▪The flavonoid glycosides are yellow compounds. ▪They dissolve in aqueous alkali and give canary-yellow color. iii. Anthocyanin Glycosides: ▪They are structurally related to flavonoids and are colored. They constitute the pigment of the colored petals of the flowers. ▪Their color changes are affected by the pH of the cell sap and ranges from red - violet to blue e.g. KarKadeh. iv. Anthraquinones Glycosides: ▪They occur as pharmacologically active constituents of several laxatives and purgatives of plant origin e.g. Senna. ▪They give positive Borntrager's and modified Borntrager's' tests. B. ALCOHOLIC GLYCOSIDES: i. Cardiac glycosides: ▪ They exert a special powerful action on cardiac muscles. ▪ A very small amount can exert a beneficial stimulation on a diseased heart, but excessive dose may cause death. ▪ These drugs are used in medicine as mainly to increase the tone, excitability and contractility of the cardiac muscle. Also as diuretic effects due to the increased renal circulation. ▪ Example Digitalis 12:10 AM  (SAR) example: Digitoxose 12:10 AM Detection of cardiac glycosides: ▪ Several chemical tests could be used for identification of cardiac glycosides. 1. Keller-killiani's test for steroidal neucleus and 2-deoxy sugars. 2. Kedde's reagent specific for cardinolides (5-membered lactone ring). 3. Baljet's test for cardinolides (5- membered lactone ring). 12:10 AM ii. Saponin glycosides: This group of plant glycosides is characterized by the following: 1. It foams in aqueous solution forming froth 2. It causes haemolysis of red blood cells, so they are highly toxic when injected into the blood stream. 3. Drugs containing saponins are usually sternutatory and irritating to the mucous membrane of the eyes and nose. 4. They are used in cleaning industrial equipment and fine fabrics and as a powerful emulsifier of certain resins, fats and fixed oils. 12:10 AM C. Cyanophore Glycosides: ( -C≡N / Cyanogenic) ▪ They yield HCN as one of the products of hydrolysis. ▪ They don't have wide applications in pharmacy or medicine due to the poisonous properties of HCN. ▪ Detection of cyanophore glycosides in vegetable drugs is by reaction with sodium picrate paper (Grignard Reaction). 12:10 AM D. Thioglycosides: (thiocyanate S-C=N or sulphur glycosides): ▪ Among these glycosides are Sinigrin from Black Mustard seeds (mustard irritant gas) ▪ Sinalbin from white Mustard seeds (non volatile). 12:10 AM III. TANNINS: ▪ Large group of complex substances. ▪ They are non-crystalline compounds ▪ With water form colloidal solutions and a sharp astringent taste. ▪ They cause precipitation of solutions of gelatin as well as alkaloids. ▪ They precipitate proteins from solution and can combine with proteins. ▪ Uses of drugs containing tannins: 1. Astringents in the gastrointestinal tract and on skin abrasions (hemostatic). 2. In the treatment of burns, form a protective coat. 3. Antidote for alkaloidal and heavy metals poisoning. 4. Tanning of leather. 5. Preparation of ink. 12:10 AM Types of Tannins: Hydrolysable Tannins (Pyrogallol Condensed Tannins (Catechol tannins) tannins): ▪ hydrolyzed by acids or enzymes such ▪ not readily hydrolyzed to simpler as tannase molecules and they do not contain a sugar moiety ▪ formed from several molecules of ▪ on hydrolysis they yield catechin phenolic acids such as gallic acid ▪ give blue-black color with FeCl3 ▪ give green color with FeCl3 ▪ Give no precipitate with bromine ▪ give precipitate with Br2 water water ▪ Examples clove and Galls. ▪ Examples Tea and Henna leaves. IV. ALKALOIDS: ▪ Alkaloids, which mean alkali-like, ▪ They are basic nitrogenous compounds of biological origin. ▪ They are physiologically active. ▪ All alkaloids contain nitrogen, but not all compounds, which contain nitrogen, are classified as alkaloids. ▪ Generally, alkaloidal bases are insoluble in water but soluble in organic solvents. While alkaloidal salts are soluble in water, sparingly soluble or insoluble in organic solvents. 12:10 AM Detection of alkaloids: ▪ Alkaloids can be detected by two groups of reagents: 1. Alkaloidal precipitants: ▪ e.g. Mayer's reagent (potassium mercuric iodide solution) give a creamy white precipitate with most alkaloids except caffeine. 2. Alkaloidal color reagents: ▪ The most common is Dragendorff's reagent give orange color. 12:10 AM Chemical composition Occurrence Effect of steam steam Saponification Stain on filter paper Bad storage Uses Example Test 12:10 AM