Pharmacognosy Notes PDF CH. 5 - CHEMICAL NATURE OF DRUGS
Glycosides are non-reducing organic substances which on hydrolysis give an aglycon and glycon. The aglycon portion called as non-sugar and glycon portion known as sugar.
- Cardiac glycosides : Digitalis, Arjuna Bark.
- Anthracene Glycosides: Senna, Rhubarb.
- Cyanogenetic Glycosides: Bitter Almond
- Flavone Glycosides : Senna Leaves.
- Saponin Glycosides : Dioscorea, Shataveri.
- Is othiocynate Glycosides : Mustard.
Cardiac glycosides are steroids or cyclopentenephenantherene derivatives.
- At position number, 3 and 14 they have an OH group.
- At position number, 10 and 13, they have a CH3 group
- All Cardiac glycosides have at position number 17 a Lactones ring.
- The Lactone ring is an important for the cardiac activity.
- If the Lactone ring is 5 numbered, they are called C 23 glycosides cardenolides.
- If the Lactone ring is 6 numbers they are called C24 Glycosides Bufadienolides.
Ex. Stropanthus and squill. It can be identified by:
Baljet Test: Take the glycoside and add sodium picrate reagent. A yellow to orange Colour is obtained.
Legal Test: Sample is dissolved in pyridine and sodium Nitroprus side solution makes it alkaline, a pink Colour is obtained.
These constitute a major class of glycosides. These are mainly found in the dicot plant. Anthracene glycosides contain an aglycon, which is a poly hydroxyl anthraquinone derivative. These are the derivatives of Anthracene.
These Anthracene derivatives occur in two forms they are:
Oxidation form: Ex. Anthraquinones.
Reduced form: Ex. Anthrones, anthranols & diathrones
Use: Purgative Ex. Senna, Aloes, Rhubarb.
MODIFIED BORNTRAGER TEST:
This test is done for Anthracene glycosides:
- 1gm of sample is taken, to this 5ml of ferric chloride
- Add 5ml dilute HCl is added
- Heated on a water bath and cooled.
- This is then extracted with benzene.
- An equal volume of ammonia is added to benzene extract.
- A pinkish red colour is obtained in the ammonia layer.
Isolation of Glycosides
The finely powdered plant part is extracted with water or alcohol in soxhlet apparatus. The enzymes present in plant tissues are destroyed by heating at suitable temperature specialcare should be taken in case of thermoliable glycosides and they should be extracted at low temperatures. The non glycosides impurities are precipitated with lead acetate solution and excess of latter is removed by passing hydrogen sulphide gas through the extract. The concentration of extract gives crude glycoside, which is further purified using suitable solvent and chromatography, according to the chemical nature and prosperities of glycosides.
- Phenolic glycosides are used as urinary antiseptic effects
- Alcohol glycosides used as analgesic, antpyretic, anti-inflammatory action
- Cardiac glycosides used in treatment of heart disease
- Antraquinone glycosides are used as laxative action
Alkaloids are defined as basic Nitrogenous Compounds of plant origin and have marked physiological activity. The name alkaloid derived from Alkali. They are highly poisonous but in low dose give therapeutic activities.
- They are basic in nature, they form salt with acids.
- They are Colourless, crystalline solids.
- They are insoluble in water but soluble in organic solvents.
- They are extremely bitter.
- They contain C, H, N, O and sometimes sulphur.
- These are optically active compounds.
- They have molecular weight between 100-900 daltrons.
Ex.Ephedrine (Ephedra), Colchinine (Colchicum)
Pyrrole & Pyrrolidine
Ex. Tea & Caffeine
Pyrine & Pyridine & PiperiAdine
Identification test for alkaloids
Mayer’sTest : Alkaloids+Mayer’sreagent ———— Whiteppt.
DragandroffsTest :Alkaloids+Dragandroff’sReagent ——- Orangered ppt.
Hager’sTest :Alkaloids +Hager’s Reagent ——- YellowColour.
Extraction method of alkaloid
The alkaloids can be isolatedby either of the two methods:
Methods A: It consists of the following steps:
- The powder material is moisted with water and mixed with lime. This lime combines with the acids. Tannins and phenolic substances. Therefore, they can be removed.
- The above mixture is extracted with organic solvents like ether or petroleum ether.
- The organic liquid which is obtained is shaken with aqueous acid and allowed to separate .The separated aqueous layer contains the alkaloids salts.
- Powder materials extracted with water or aqueous alcohol containing diluteacid.
- The above extract is shaken with chloroform or other organic solvents this helps in removing pigments and other unwanted materials.
- Excess of sodium bicarbonate or ammonia is added which precipitates the freealkaloids.
- This alkaloids are then removed by filtration or extraction with organic solvents.
- Many alkaloids used as local anesthetic properties like cocaine.
- Vincristine and Vinblastine are alkaloid used as anticancer.
- Ephedrine obtained from ephedra used in bronchial asthama.
- Morphine is strong analgesic.
- Atropine from belladonna plant is used to treat bradycardia in injection form.
Tannins are complex organic, non-nitrogenous phenolic compounds of high molecular weight.
- Tannins are dark brown or reddish brown.
- They combine with the proteins of animals hide and skin to give leather.
- They have an astringent taste.
- They are soluble in water and alcohol.
- They show acidic reaction.
- They precipitate protein, alkaloids and heavy metals.
- Tannins give precipitate with anti-pyrine.
- They are insoluble in either and chloroform.
- They are amourphous and non-crystalline in nature.
Classification: They are classified as:
- Condensed Tannins: These are formed by condensation of catechol units. They are called Phlobaphenes. On dry distillation they yield catechol tannin. On reaction with ferric chloride solution they produce brownish green Colour.
Example: Pale Catechu and Black Catechu.
- Hydrolysable Tannins: On hydrolysis they giveeither gallic acid or ellagic acid.On dry distillation they yield pyrogalol. On reaction with ferric chloride solution they produce blue colour.Example: Clove, Rhubarb and Tannic acid.
- Tannins + Ferric Chloride ——– Dark blue or Green Colour.
- Tannins + Lead acetate solution ————— White ppt.
- Tannins + Anti-pyrine or gelatin —————- White ppt.
Extraction and Isolation
- Both hydrolyzable and condense tannins are water and alcohol soluble but insoluble in organic solvents (e.g. ether, chloroform, and benzene).
- Hence, tannin containing compound (Gallic acid, ellagic acid, other tannins) are extracted with using water or alcohol as solvent…
- Collected aqueous layer and concentrated to get crude extract of tannins.
- Then the free acids such as Gallic and ellagic acid go along with ether, whereas true tannin gets extracted in water.
- Chlorophyll or pigment containing substances are removed by ether.
- After extraction the aqueous and ethereal layers are separately concentrated, dried, and finally various separation techniques of chromatography.
Pharmaceutical and Therapeutic Application
- They used as preservatives.
- They use in ink manufacturing industries.
- They are used to treat tonsillitis, Pharyngitis, Hemorrhoids,
- They used for vegetable tanning
- They are used to convert animal hide into leather.
- They used for lipolysis in fat cells
Resins are plant exudates, amorphous, solid or semisolid in nature and normal or abnormal metabolic products.
- They are transparent, translucent. Solids Semi-solids or Liquid substances.
- On heating they soften, melt and form clear liquids.
- They have specific gravity more than one.
- They are insoluble in water but soluble in organic solvents like alcohol.
- They form a thin layer on smooth surfaces which on drying from a hard transparent film.
- They are mixture of essential oils.
- Resins do not contain nitrogen element.
- Oleo Resins: Resins are present in combination with volatile oils. Ex: Copaiba.
- Oleo Gum Resin: Resins are in combination with volatile oil and gums. Ex: Myrrh.
- Balsams: It is the resin which contains cinnamic and benzoic and then they are called as balsam. Ex. Tolu balsam.
- Acid Resin: It is the resin contains greater proportion of acid they called acid resin.
Isolation of resins:
Resins are extracted with alcohol and precipitating resins present in concentrated extract by addition of large amount of water
Pharmaceutical and Therapeutic Applications
a) They are also used as stimulant.
b) Resins act in bronchial asthma.
c) Resins used in treatment of cancer.
Volatile oils are odours volatile principles of plant and animal so which are easily evaporable.
Classification of Volatile Oils
- Alcohol containing volatile oils, e.g. peppermint, cardamom
- Aldehyde containing volatile olls, eg. cinnamon, lemon, orange.
- Hydrocarbon containing volatile oils e.g. turpentine.
- Ketone containing volatile oils, e.g. caraway.
- Oxide containing volatile oils, e.g. eucalyptus.
- Phenolic-ester containing volatile oils, e.g. fennel, Nutmeg
- Phenol containing volatile oils, e.g. clove.
General Properties of Volatile Oils
- They have characteristic odour.
- They have high refractive index.
- Most of volatile oills are optically active,
- They are either colourless rarely coloured.
- They have aromatic taste.
- They are insoluble in water and soluble in ether, alcohol, etc.
- They have good essence. The oils are called essence oils.
Isolation of volatile oils
- Hydro-distillation: This methods comprising of water distillation, water and
steam distillation and steam distillation are used for extraction of volatile oll
from herbal drugs. The fresh material is subjected to hydro distillation in case of
the leaf drugs. Air -dried subterranean parts are extracted by steam distillation.
- Adsorption in purified Fats:
This method is also known as Effleurage. This method is used for extraction of
dellcate perfumes. The fat is spreaded on glass plates and warmed to about 50°C
of fatty materials, then its surface is covered with flower petals and it is allowed
to keep several days. The exhausted petals are replaced by fresh material. The
process is continued till the fatty layer is saturated with volatile principles
which are then extracted with lipid solvent.
- Ecuelle methods: method is used for extraction of citrus olls, wherein ol cells
in ring areruptured mechanically using pointed projections by twisting raw
material over them in clockwise direction either mechanically or manually.
and therapeutic activity
a) As flavoring agents and perfumes.
b) As carminatives.
c) As stomachic.
d) Externally, counter irritant.
e) As aspices.
f) As a localanesthetics.
The term terpene represent hydrocarbons (CsHa) while terpeniods include hydrocarbons. As well as their oxygenated derivatives. Terpenes and terpenoids are found in all volatile oils (essential oils) of plant and animal origin.
Examples of volatile oils along with their terpenoids:
Classification of terpeniods:
These are classified on the basis of isoprene units i.e.(C5H8) they contain:
Name of the class ofterpenoids
No. of isoprene units
Monoterpenes or terpenes
Depends upon typeandno. of rings interpenoids they are classified as
Isolation of terpenoids:-
Terpenoids are physically extracted by fractional distillation method which carried under reduce pressure.
Pharmaceutical and therapeutic activity
- Terpenoids are potent antioxidant
- They serve as anti-inflammatory agent
- They have wound healing property