Drug Containing Tannins PDF - Classification, Uses

Drug Containing Tannins By Abyot E. (B.Pharm, MSc.)  Learning objectives After compliting this unit, you will be able to – Define and classify tannins – State physical and chemical properties of tannins – Discuss the use of tannins – Categorize drug containing tannins  Tannins ar...

Drug Containing Tannins By Abyot E. (B.Pharm, MSc.)  Learning objectives After compliting this unit, you will be able to – Define and classify tannins – State physical and chemical properties of tannins – Discuss the use of tannins – Categorize drug containing tannins  Tannins are – Complex organic, non-nitrogenous plant products. – Derivatives of polyhydroxy benzoic acid (polyphenols). – Ability to precipitate proteins – Having high molecular weight (500 to > 20000) – Historically, tannin containing drugs are related to their tanning property i.e. their ability to transform fresh hides into imputrescible leather  Properties and tests of tannins Tannins are soluble in water, dilute alkalis, alcohol, glycerol and acetone, but generally only sparingly soluble in other organic solvents Solutions precipitate heavy metals, alkaloids, glycosides and gelatin With ferric salts, gallitannins and ellagitannins give blue-black precipitates and condensed tannins brownish-green ones. Chemical test  Goldbeater's skin test Soak a small piece of goldbeater's skin in 2% hydrochloric acid; rinse with distilled water and place in the solution to be tested for 5 min – Wash with distilled water and transfer to a 1% solution of ferrous sulphate. » A brown or black colour on the skin denotes the presence of tannins Goldbeater's skin is a membrane prepared from the intestine of the ox and behaves similarly to an untanned hide  Phenazone Test: – To 5 ml of aqueous solution of tannin containing drug, add 0.5 g of sodium acid phosphate. Warm the solution, cool and filter. Add 2 % phenazone solution to the filtrate. – All tannins are precipitated as bulky, colored precipitate. Gelatin Test: – To a 1% gelatin solution, add little 10% sodium chloride. If a 1% solution of tannin is added to the gelatin solution, tannins cause precipitation of gelatin from solution Bromine water: – only condensed tannin gives ppt. with bromine water  Uses of Tannins Industrially – in leather tanning, ink manufacture Medicinally – astringent, haemostatic, antidiarrheal, antidote in alkaloid and heavy metals toxicity In labs – reagent for detection of proteins, alkaloids and heavy metals because of their precipitating properties.  Classification of tannins based on Goldbeaters skin test positive negative tanning test tanning test True tannin Psedutannin  True tannins Hydrolysable Non Hydrolysable tannins tannins  Hydrolysable tannins These are ester of sugars and phenolic acid molecules Phenolic acid Mineral acids Tannase Sugar part  Phenolic acid either Gallic acid or Ellagic acid Gallotannins e.g: Ellagitannins rhubarb Gall e.g: Clove pomegranate eucalyptus  on dry distillation are converted to pyrogallol derivatives. The hydrolysable tannins are soluble in water and their solution produces blue color with ferric chloride.  Condensed tannins Proanthocyanidins They consist of flavan-3-ol units linked together by carbon-carbon bonds most often 4 8 or 4 6  Condensed tannins occur due to polymerization (condensation) reactions between flavonoids. The polymers may include up to 50 monomer units. On treatment with acids or enzymes condensed tannins are converted into red insoluble compounds known as phlobaphenes. Phlobaphenes give the characteristic red colour to many drugs such as red cinnamon bark.  On dry distillation, they yield catechol derivatives. Condensed tannins are also soluble in water and produces green color with ferric chloride.  Pseudotannins They are compounds of lower molecular weight than true tannins and they do not respond to the goldbeater's skin test. Examples of drugs containing Pseudotannins are: Gallic acid: Rhubarb Catechins: Guarana, Cocoa Chlorogenic acid: Mate, Coffee Ipecacuanhic acid: ipecacuanha  OH COOH HO O OH HO OH OH OH OH Gallic acid Catechin HOOC OH OH O HO O OH OH Chlorogenic acid  Tannins Hydrolysable containing drugs – Myrobalan It is the mature dried fruits of Terminalia chebula (Combretaceae)  Chemical Constituents: – Myrobalan contains about 30 % of the hydrolysable tannins, which consists of chebulinic acid, chubulagic acid and D- galloyl glucose. – It contains free tannic acid, gallic acid, ellagic acid and resin myrobalanin  Uses: – Because of antiseptic and healing properties of tannins, it is used externally in chronic ulcers, wounds, piles and as stomachic. – Fine powder of myrobalan is used in dental preparations  Nutgalls – Nutgall consists of the excrescence obtained from the young twigs of the dyers oak, Quercus infectoria Olivier (Fagaceae). Excrescence is caused by the puncture of ovums of insect Cynips tinctoria or Adleria gallaetinctoriae Olivier (Cynipidae) obtained principally from Asiatic Turkey.  Chemical Constituents: – Nutgalls contains about 50 %-70% tannin mainly gallotannic acid which is official tannic acid. Uses: – Nutgall is the major source of tannic acid, which is largely used in tanning and dyeing industry and for the manufacture of ink. – It is used medicinally as a local astringent in ointments and suppositories.  Pomegranate rind This consists of the dried pericarp of the fruit of Punica granatum (Punicaceae Pomegranate rind is used in India as a herbal remedy for non- specific diarrhea. It is very astringent It contains about 28% of tannin (ellagitannins) and coloring matters It should be distinguished from the root bark which contains alkaloids Drug with condensed tannins – Pale Catechu (Gambier) Gambier or Pale catechu is a dried aqueous extract produced from the leaves and young twigs of Uncaria gambier Roxburgh (Rubiaceae) native to Malaya and cultivated in Indonesia, Malaysia, Sumatra, Bornea and Singapore  Chemical Constituents – Pale catechu contain from about 7 % to 30 % of pseudotannin catechin and 22 % to 55 % of a phlobatannin catechutannic acid  Uses – Pale catechu is medicinally used as local astringent. – In diarrhoea, it is used as general astringent – Large proportion of gambier is used in dyeing and tanning industries. It is used for tanning of animal hides to convert it to leather  Black Catechu – Black catechu is the dried aqueous extract prepared from the heart wood of Acacia catechu Willdenow (Fabaceae/Leguminosae) native to India.  Chemical constituents – Cutch or black catechu resembles pale catechu or gambier in its composition. It contains about 2 % -12 % of catechin and about 25 % to 33 % of phlobatannin catechutannic acid.. Uses – Cutch is used in medicine as astringent – It cures troubles of mouth, diseases of the throat and diarrhoea – It also increases appetite – In dyeing industries, cutch is used for dyeing fabrics brown or black  Exercise Categorize the following as hydrolysale, condenssed or psuedo tannins – Tannic acid – Catechin – Cinchotannic acid – Chlorogenic acid – Chebulinic acid – Gallotannic acid