This term “alkaloids” (alkali-like) is useful and commonly applied to basic nitrogenous
comounds of plant origin thatarephysiologically active. They areextremely difficult to define
becausethey do not represent ahomogenous group of compounds from either the chemical,
biochemical, or physiological viewpoint .
Alkaloids usually contain one nitrogen atom but some such asergotamine ,may contain five nitrogen atoms.
The nitrogen may exist as:
1- primary amine (RNH2)
2-Secondary amine (R2 NH)
3- Tertiaryamine (R2N)
4- quaternary ammonium compous(R4N+X- ) AS tubocurarine chloride or berberine chloride, these
compounds have four organic groups covalently bonded to nitrogen atom, and the positive charge of this ion
is balanced by negative charge ion.
types of alkaloids
There are three types of alkaloids:
1- Truealkaloids : these characterized by contain nitrogen atom in the heterocyclic ring and derived from
amino acids .ex :Atropine, nicotineand morphine .
2- Proto alkaloids : which contain nitrogen atom without aheterocyclic ring and also derived from amino
acids which lack one or more of the properties of typical alkaloids . ex:Adrenaline ,colchicine,mescaline
3- Psedoalkaloids: these characterized by heterocyclic ring with a nitrogen atom ,but are not derived from
amino acids .ex :caffeine,theobromine and theophylline.
Distribution of alkaloids
Plants havebeen rich source of alkaloids , but someare found in animals , fungi and
In theplants, theyare distributed in certainfamilies and genera:
1- Gymnosperms,thealkaloids are rarely found in them, exceptin taxaceae.
2- Angiosperms, whichincludetwo groups :
A- monocotyledons,thealkalois arenot produce in them,exceptin Liliaceae and
B-Dicotyledons, mainlyfound in the following families:Leguminosae,Papaveraceae,
Ranunucalaceae, Rubiaceae,Solanaceae andBerberidaceae.
While thelabiatae and rosaceae families arefree from alkaloids.
Distribution of alkaloid
In thefungi :thelysergic acid derivatives (e.g.ergotamineand the sulphur
containing alkaloids arethe best known.
In theanimals :
*nearly about 300 alkaloids belonging tomorethan 24classes are known to occur in
the skin of amphibians along with other toxine of frogsof the genus phyllobates.
*alkaloids derived frommammals include oneof indole and isoquinoline classes.
In thebacteria : pyocyanin alkaloids wich is : (toxin producedand secretedby
Parts of plants containing alkaloids
1- seed ;as in physostingma and areca
2- fruits ; asin conium.
3- leaves ; asin belladonna,and coca.
4- underground stems; asin sanguinaria.
5- root; asin belladonna roots.
6- rhizomes and roots; as in ipecacand hydrastis.
7- barks; as in cinchona .
8- alkaloids present in fungi asin ergot (e.g. ergotamine ). This fungus grows on rye and related
Names of alkaloids
The name of alkaloids can be obtained by various ways;
1- from the genus name of plants yielding them,examples,
a- Atropine from Atropa belladonna .
b- hydrastine from hydrastis Canadensis.
2- from the species name of plants yielding them, examples:
a- belladonnine from Atropa belladonna .
b- cocaine from Erythroxylum coca.
3- from the common name of the drug, example ergotamine that obtained from ergot.
4- from discoverer, example pelletrine from the name pelletier.
Names of alkaloids
*A suffixisaddedsometimesto designatethe alkaloidswhich are similarin structurebut
*A prefixis addedto designatealkaloidsfoundin the same plantexample hydroquinine.
* Alkaloidsnameshouldendwith (ine).
Physicochemical properties of alkaloids
In spite of the difficulty in precisely characterizing alkaloids by definition, they do have in common
asurprising numer of physical and chemical properties. For the most part, the alkaloids are insoluble or
sparingly soluble in water, but the salts formed on reaction with acids are usually freely soluble .
The free alkaloids are usually soluble in ether , chloroform, or other relatively nonpolar, immiscible solvents,
in which, however , the alkaloids salts are insoluble.
This permits areadily means for the isolation and purification of alkaloids as well as for their quantitative
estimation. Most of the alkaloids are crystalline solids, although a few are amorphous. An additional few ,
coniine, nicotine , and sparteine, which lack oxygen in their molecules, are liquids.
Alkaoids salts are crystalline , and their crystal form and habit are often a useful means of rapid microscopic