Saturday, 1 September 2018

Pharmacognosy of some important alkaloids: Pharmacy Notes


Pharmacognostical study of alkaloidal drugs is of utmost importance while preparing for the GPAT and other pharma exams. In this article, the most important alkaloids have been selected which must be studied while preparing for any pharma exam. Before going below, readers are suggested to have a brief on the general introduction of alkaloids.

PHARMACOGNOSY OF ERGOT
Ergot is obtained from the fungal sclerotium of claviceps purpurea (Clavicipitaceae) in ovary of rye plant secale serale (Graminae).
Sclerotium or dormant stage in the development of the fungus contains the maximum number of alkaloids.

Life Cycle of Ergot
  • Ovary of the rye plant is get infected by the ascospores of fungus.
  • Germination of ascospores lead to the formation hyphal strands which form mycelium over the ovary.
  • Mycelium secretes viscous sugary fluid known as honey-dew.
  • Hyphal strands also secrets asexual spores known as conidial spores.
  • The developmental stage of the fungus is sexual stage and called as sphaecelial stage.
  • For the collection of alkaloids, temperature range is of 20 to 30 degree Celsius and pH range from 4.6 to 6.3.
  • Sclerotia is fusifurm in shape.
Microscopic characters of alkaloids
  • Inner layer of sclerotium is made up of chittin.
  • Mycelial cells also contains fixed oils.
  • Starch grains and calcium oxalate is absent.
Chemical constiuents
  • Ergot alkaloids are derivatives of lysergic acid and these alkaloids are also known as peptide alkaloids.
  • Ergot alkaloids consists of six pairs of alkaloids out of which laevo form is medicinally active while dextro form is inactive.
The pair of  (-) ergometrine & (+) ergometrinine is water soluble while rest all are water insoluble. 
  • Ergometrine is used as oxytocic for uterus contraction where as ergotamine finds its use in the treatment of migraine.
Chemical tests
  1. Gives blue color with p-dimethylaminobenzaldehyde (Van-Urk's reagent).
  2. Gives blue fluroscence in water.
  3. In the mixture of glacial acetic acid and ethyl acetate, little quanity of ergotamine is mixed. This is treated with sulphuric acid by which blue color with red tinges appears. on further treatment with ferric chloride, the red color disappears whereas the blue color further deepens.


PHARMACOGNOSY OF NUX VOMICA
Nux vomica is obtained from the dried ripe seed of the Strychous nuxvomica (Loganiaceae).

Microscopy
  • Epidermis consist of lignified trichomes followed by a layer of collapsed cells.
  • Calcium oxalate & starch grains are absent.
  • Aleurone grains and globules are present in endosperm.
Chemical constituents
  • Chief constituents of nux vomica are strychinine and brucine.
  • Vomicine, alpha-colubrine, pseudostrychinine and strychnicine are also present in low amounts.
Chemical tests
  • TS of nux vomica with ammonium vanadate & H2SO4 manddin's reagent gives purple color to the endosperm.
  • TS of nux vomica with nitric acid gives yellow color to endosperm.
  • strychinine with sulphuric acid and potassium dichromate gives voilet color.
Adulterants

Strychnos nuxblanda and strychnos potatorum.

Allied drugs

Strychnos wallichana & Strychnos ignatii


PHARMACOGNOSY OF PHYSOSTIGMA
It is the dried ripe seed of Physostigma venenosum (Leguminosae).

Chemical Constituents
  • Main constituent is physostigmine (eserine) which is present in cotyledons.
  • Physostigmine is oxidized to rubeserine when exposed to air.
Uses
  •  It is used as parasympathomimetic for opthalmic purposes.

PHARMACOGNOSY OF RAUWOLFIA
Rauwolfia consist of dried roots of the plant known as Rauwolfia serpentina (Apocynaceae). The pH of the soil should be 3-4 and temperature should be maintained between 10 to 38 degree celsius. Rainfall should be of in the range of 250-500 cm. 

Microscopy

  • Cork of the roots is made up of stratified cells.
  • Both calcium oxalate & starch grains are present.
  • Stone cells phloem fibres are absent.
Chemical Constituents
  • Most of the alkaloids of the rauwolfia are found in the bark and root of the plants.
  • The alkaloids of rauwolfia are mainly classified into the following:
1. Indole alkaloids 2. Indoline alkaloids 3. Indolenine alkaloids 4. oxyindole alkaloids 
5. Pseudo indoxyl alkaloids 
  • Major alkaloids in rauwolfia are reserpine (ester of methyl reserpate & trimethoxybenzoic acid) & rescinnamine (esters of reserpine & trimethoxycinnamic acid). 
  • Reserpine determined colorimetrically by reaction between acidic solution of alkaloids and sodium nitrite.
Chemical tests
  • With nitric acid gives red color.
  • With solution of vanillin in acetic acid is treated with reserpine gives violet color.
Allied drugs

  • R. Vomitoria (African rauwolfia) 
  • R. densiflora (Contains sclerenchyma)
  • R. tetraphylla  (Uniform cork)
  • Catharanthus roses ( Contains ajmaliciline)
  • Pausinystalia yohimbia (Contains yohimbine)


PHARMACOGNOSY OF VINCA
Vinca is obtained from the catharanthus roseus (Apocynaceae).  

Microscopy
  • Consist of unicellular covering trichomes. 
  • Cruciferous stomata is present in lower epidermis.
  • Calcium oxalate crystals are absent.
Chemical constituents
  • Vincristine and vinblastine are most significant alkaloids.
  • Vinblastine: Indole part is called catharanthine and dihydroindole part is known as vindoline.

PHARMACOGNOSY OF OPIUM
Opium is obtained from the dried latex of of unripe capsules of papaver somniferum (papaveraceae). The opium collected is processed at Government opium factory at Ghazipur.

Chemical constituents

  • Chemically alkaloids obtained from poppy plant are classified as benzylisoquinoline (Narcotine, Narceine and papaverine) and phenathrene (Morphine, Codeine, Thebaine) types.
  • Morphine & Codeine is monoacidic and laevorotatry.
  • Papaverine is optically inactive.
  • Alkaloids are present as the salt of meconic acid.
Chemical tests
  1. Opium is dissolved in water and ferric chloride solutin is added to the filtrate. Reddish purple color is obtained.
  2. Morphine + Nitric acid: orange red color.
  3. Morhine + Potassium ferricyanide and ferric chloride: bluish green color.

PHARMACOGNOSY OF IPECACUANHA
It consists of the dried roots of either cephaelis ipecacuanha or cephaelis acuminata (Rubiaceae). 

Microscopy
  • Roots: Contains starch grains and calcium oxalate crystals.
  • Rhizomes: Pericycle is with thick walled scleroids, protoxylem and spiral vessels.
Chemical constituents

Main Chemical constituents are emetine, cephaeline, psychotrine, o-methyl psychotrine and emetamine.

Chemical tests
  1. 2.5 gm of drug + 20 ml HCl + 5 ml water. Shake and filter. To the filterate, add 0.5 potassium chlorate. Yellow color confirms the presence.
  2. Emetine + sulhuric acid + Na Molybedate (Frohde's reagent): bright green color.
Uses

Emetine is expectorant in small dose and as an emetic in higher doses.


PHARMACOGNOSY OF BELLADONA
European Belladona: Atropa belladona & Indian Belladona: Atropa acuminata (Solanaceae).

Microscopy
  • Anisocytic stomata & Uniseriate multicellular covering glandular trichomes. 
  • Palisade ratio is 5 to 7.
  • Anisocytic stomata

Chemical constituents
  • Main alkaloids of belladona are l-hyoscyamine and its racemic form atropine.
  • Atropine is trpoine (+/-)-tropate)
  • Other important alkaloid is hyoscine.
Chemical test (Vitali Morin reaction)
  • Tropanne alkaloid+ Nitric acid+ methanolic KOH: Violet Colour.
  • Hyoscine hydrobromide + Silver nitrate: Yellowish white precipitate.


Adulterants & Substitutes
  • Phytolacca americana (Idioblast & anomocytic stomata).
  • Solanum nigrum (Palisade ratio is 2-4).
  • Alianthus glandulosa (Crystals of calcium oxalate)


PHARMACOGNOSY OF CINCHONA
Cinchona is obtained from the dried barks of Cinchona Calisaya, C. ledgeriana, C. officinalis or C. succirubra (Rubiaceae)

Microscopy of Cinchona bark
  • Medullary rays are present.
  • one peculiar characterstic of cinchona bark is the presence of idioblast of calcium oxalate.
  • Parenchymatous tissues contain starch grains.

Chemical Constituents
  • Mainly cinchona bark contains around 25 alkaloids.
  • Medicinally important alkaloids are quinine, Quinidine, Cinchonine & Cinchonidine.
  • Quinine/Quinidine & Cinchonine/Cinchonidine are pairs of stereoisomers.


Chemical tests
  • Drug + Glacial acetic acid: purple vapours
  • Thalleoquin test: Drug + Bromine water & ammonia solution: Emerald green color.
  • Quinidine solution + Silver nitrate: white precipitate.


PHARMACOGNOSY OF EPHEDRA (Ma-Huang)
Dried young stem of Ephedra Gerdiana & E. nebrodensis (Gnetaceae/Ephederaceae)

Microscopy
  • Sunken stomata
  • Calcium oxalate is present in the cortex
  • Chlorenchymatous cortex.


Chemical constituents
  • Ephedra contains amino alkaloids (Ephedrine, Nor-ephedrine, n-methyl ephedrine & pseudo ephedrine).
  • Chemically ephedrine is 1-phenyl-1-hydroxy-2-methylaminopropane.


Chemical test
  • Ephedrine in water+ Dil HCl--------> treated separately with copper sulphate and NaOH: Violet color


PHARMACOGNOSY OF COLCHICUM
Dried seeds of colchicum luteum & C. automnale (Lililliaceae).

Microscopy
  • Endosperm contains aleurone grains & fixed oils.
  • Epidermis posses circular stomata.
  • Starch grains are present in the parenchyma.


Chemical constiuents (Amino alkaloids)
  • Colchicine & demecolcine (Tropolone/Cycloheptatrien-ol-one ring).
  • Colchicine is soluble in alcohol & chloroform.


Chemical tests
  1. Colchicine + 70 % sulfuric acid: yellow color
  2. Alcoholic solution of colchicine + Ferric Chloride: Red color


PHARMACOGNOSY OF KURCHI
Dried stem bark of Holarrhena antidysentrica (Apocynaceae).

Microscopy
  • Stone cells visible in the cortex.
  • Phloem fibres are absent.
  • Multiseriate medullary rays.
  • Calcium oxalate crystals in stone cells.


Chemical constituents (Steroidal Alkaloids)
  • Connesine, norconessine, isoconessine, dioxyconessine, conessimine & holarrhidine are the main active alkaloids.


PHARMACOGNOSY OF ASHAWGANDHA
dried roots of Withanis Somnifera (Solanaceae)

Chemical Constiuents (Alkaloids & Steroidal lactones)
  • Withanine is the main active constituent.
  • Steroids of Ashawgandha are known as withanolides.
  • Somnitol & Somnirol are two monohydric alcohols present in the Ashawgandha.


PHARMACOGNOSY OF VASAKA
Leaves of Adhatoda Vasika (Acanthaceae)

Microscopy
  • Caryophyllaceous stomata
  • Covering & Glandular trichomes
  • Dorsiventral leaves
  • Calcium oxalate crystals are present.


Chemical constituents
  • Basic ring of vasaka alkaloids is quinazoline (Vasicine, Vasicinone & 6-hydroxy vasicine).
  • Betain & Vasakin are two volatile oils present in the vasaka.



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