Alkaloids (Pharmacognosy) MANIK

Alkaloids: Distribution, properties, tests, extraction, structural types and classification.

1. Pharmacognosy-I

2. Aprecisedefinitionoftheterm'alkaloid'((alk=alkaliandoid=likei.e.alkali-
like)issomewhatdifficultbecausethereisnoclearcutboundarybetween
alkaloidsandnaturallyoccurringcomplexamines
Introduction
Coniine Md. Imran Nur Manik

3. Distribution Md. Imran Nur Manik

4. Plant Part Drug ( Alkaloids) Plants
Whole aerial plant Lobeline, Tylophorine, EphedrineLobelia. Tylophora. Ephedra
Seeds Strychnine, Physostigmine,
Colchicine
Nuxvomica. Physostigma,
Colchicum
Rhizomes & RootsEmetine, Reserpine, AconitineIpecac, Rauwolfia, Aconite
Bark Conessine, Cinchonine Kurchi, Cinchona
Fruit Piperine Black pepper
Leaves Scopolamine, Atropine, EcgonineDatura, Belladonna, Coca
Stem Anaferine Withania
Flowering buds Hyoscyamine Hyoscyamus Md. Imran Nur Manik

5. Properties of alkaloid
Alkaloids exhibit a variety of physical and chemical properties Md. Imran Nur Manik

6. Chemical Properties of alkaloid
Alkaloids possess carbon, hydrogen and nitrogen and in
most cases oxygen as elements.
Alkaloidsusuallycontainonenitrogenatom,although
some,likeergotamine,maycontainupto5.
Thenitrogenmayexistasaprimaryamine(RNH),as
asecondaryamine(R
2NH),orasatertiaryamine(R
3NH).
Likebasiccompoundstheyformtheircrystallinesaltswith
acidslikehydrochloricacid,sulphuricacid,citricacid,and
tartaricacid.
Ontreatmentwithphosphotungsticacid,phosphomolybdic
acid,picricacid,potassiummercuri-iodideandtannic
acid,theyyieldinsolubleprecipitates(doublesalts) Md. Imran Nur Manik

7. Pharmacological Action of Alkaloid
Activity Alkaloids
Analgesic & Narcotic Morphine and Codeine
CNS-stimulant Caffeine, Strychnine & Brucine
Cardiac depressant Qinidine
Mydriatic Atropine & Hematropine
Miotic Physostigmine, Pilocarpine
Hypertensive (BP) Ephedrine
Anti-Hypertensive Reserpine
Anti cancer Vincristine, Vinblastine
Antimalarial Quinine
Diuretic Theobromine, Theophylline
Antiamoebic& Emetic Emetine, Sanguinine
Anticholinergic Atropine, hyoscyamine
Antitussive Codeine, Noscapine Md. Imran Nur Manik

8. Why alkaloids occur in the plants?
Inplantsalkaloidsactaspoisonousandstimulatingagents.
1.Theymayactasprotectiveagainstinsectsandherbivoresduetotheir
bitternessandtoxicity.Fore.g.Nicotineandanabasineactaspowerfulrepellentsfor
manyinsectgroupsandthusprotectsplantsfrominsectsandherbivorous.
2.Theyfunctionasreservesubstancesfornitrogenandsupplyitaswellas
otherelementsnecessaryfortheplant'seconomy.
3.Theysometimes,actasgrowthregulatorsincertainmetabolicsystems.
4.Theyareendproductofdetoxificationreactionsrepresentingametabolic
lockingupofharmfulsubstancesfortheplant.
5.Theyoccuraspigments,suchaspteridineandbetalains,andattract
animalsforpollination.Md. Imran Nur Manik

9. Classification of Alkaloids
There are various schemes for the classification of alkaloids. Widely accepted
classification system is as:Md. Imran Nur Manik

10. Based on the ring structure or nucleus of the chief alkaloid group in the plant
drug are classified as follows: (1) , (2)
Alkaloids Ring Examples
Pyridine-piperidine
The alkaloids in this group
contain Pyridine or
Piperidine in the
molecule
Pyridine-piperidine
Nicotine Coniine
Tropane
Tropane is a dicyclic
compound where both
Pyrrolidine and Piperidine
ring systems are presentPyrrolidine-piperidine-Tropane
Atropine
+e.g.lobelia alkaloids, lupine alkaloids,
+e.g.hyoscyamine and scopolamine,Md. Imran Nur Manik

11. On the basis of nucleus/ Ring structure(3) , (4)
Alkaloids Ring Examples
Quinoline
The alkaloids in this group
contain Quinoline ring as
the principal nucleus
Quinoline
Quinine
Isoquinoline
The Isoquinolinering
occurs in a number of
alkaloids in widely
separated plant familiesIsoquinoline
Papaverine
+e.g.Quinidine, Cinchonine, Cinchonidine,
+e.g.Morphine, Emetine ,Md. Imran Nur Manik

12. On the basis of nucleus/ Ring structure (5) , (6)
Alkaloids Ring Examples
Indole
A number of important
alkaloids possess an
indole ring in their
structure
Indole
Reserpine
Imidazole
The Imidazole ring occurs
in the alkaloids.
Imidazole
Pilocarpine
+e.g.Strychnine, Brucine, Vinblastine, Vincristine
+e.g.Isopilocarpine,
ReserpineMd. Imran Nur Manik

13. On the basis of nucleus/ Ring structure (7) , (8)
Alkaloids Ring Examples
Steroidal
The steroidal alkaloids
are characterized by the
cyclopentanoperhydro
phenanthrene (CPP)
nucleus.
CPP
Conessine
Lupinane
The alkaloids in the group
contain a dicyclic
Lupinanestructure/ring.
Lupinane Lupinine
+e.g.solanine, Protoveratrine A & B, Aconitine
+e.g.Sparteine
ConessineMd. Imran Nur Manik

14. On the basis of nucleus/ Ring structure (9) , (10)
Alkaloids Ring Examples
Alkaloidal amino
group
The alkaloids in this group
do not contain
heterocyclic nitrogen
atoms. Some are
derivatives of
Phenylethylamine.
Phenylethylamine
Ephedrine
Purine
The alkaloids in this group
contain the Purine
nucleus which consists of
the six membered
Pyridine ring fused to the
five membered
Imidazole ring. . Purine
Caffeine
+e.g.Mescaline ,Colchicine
+e.g.TheobromineMd. Imran Nur Manik

15. Basic ring structuresMd. Imran Nur Manik

16. Chemical Tests for Alkaloids
Most alkaloids are precipitated from neutral or slightly acid solutions by various re-agents. The precipitate may
be amorphous or crystalline and are of various colourssuch as:-
Reagents ( Chemical composition) Cloursof PPT
Mayer’s Reagents (Potassium mercuric iodide
solution)
Creamy ( Pale yellow) precipitate with True alkaloid
Exception: Alkaloids of the purine group and few others.
Wagner’s Reagent (solution of iodine in KI)Reddish brown ( or brown) precipitate with alkaloids
Hager's Reagents (a saturated solution of
picric acid)
Yellow (characteristic crystalline) precipitate (with many
alkaloids)
Dragendorff’sReagents (Solution of
potassium bismuth iodide)
Reddish brown (Orange coloured) precipitate with
alkaloids
Tannic Acid Test (A freshly prepared aqueous
solution of tannic acid (5%, w/v))
Gives recipitatewith most of the alkaloids which is soluble
in dilute acid or ammonia solution.
Ammonia ReineckateTest (A saturated aqueous solution
of ammonia retneckateslightly acidified with HCl)
Pink flocculent precipitate with most of the
alkaloids.Md. Imran Nur Manik

17. Extraction of Alkaloid
Powdered material
Free alkaloid & other plant constituents
.
Moisture with aqueous alkali ( e.g. NaCO
3, NaHCO
3or Lime-Ca(OH)
2
Extract with organic solvent such as Benzene, Chloroform etc
Organic layer (alkaloid & other plant constituents)Aqueous layer (water soluble components)
Extract (shaken) with dilute ( aqueous) Acid
Aqueous layer (Containing alkaloidal salts)Organic layer (Other organic components e.g. impurities )
Precipitate of free alkaloid
(crude alkaloidal mixture)
Finally purification is accompanied by crystallization method
Add aqueous alkaliMd. Imran Nur Manik

18. Description:
Thepowderedmaterialismoistenedwithaqueousalkali[water
andmixedwithlimewhichcombineswithacids,tanninsandother
phenolicsubstancesandsetsfreethealkaloids(iftheyexistinthe
plantassalts)].Thealkaloidsaresetfreewithotherplant
constituents.Extractionisthencarriedoutwithorganicsolvents
suchasBenzeneorchloroform(etherorpetroleumspirit).
Theconcentratedorganicliquidwhichcontainsalkaloidsandother
plantconstituentsisthenshakenwithdiluteacid(aqueousacid)
andallowedtoseparate.Alkaloidsaltsarenowintheaqueous
liquid,whilemanyimpuritiesremainbehindintheorganicliquid.
Aqueousalkaliisaddedtotheaqueouslayergivingprecipitationof
freealkaloids.Md. Imran Nur Manik

19. Pharmacological Action of Alkaloid
Activity Alkaloid
Analgesic & Narcotic Morphine and Codeine
CNS-stimulant Caffeine, Strychnine & Brucine
Cardiac depressant Qinidine
Mydriatic Atropine & Hematropine
Miotic Physostigmine, Pilocarpine
Hypertensive (BP) Ephedrine
Anti-Hypertensive Reserpine
Anti cancer Vincristine, Vinblastine
Myotic Pilocarpine
Antiamoebic& Emetic Emetine, Sanguinine
Anticholinergic Atropine, hyoscyamine
Antimalarial Quinine
Diuretic Theobromine, Theophylline
Antitussive Codeine, Noscapine
Thealkaloidshaveawide
rangeofpharmacological
actions:Md. Imran Nur Manik