2. Alkaloid - Introduction
Alkaloids are a group of molecules with a relatively large
occurrence in nature around the globe.
They are very diverse chemicals and biomolecules, but they
are all secondary compounds and are derived from amino
acids or from the transamination process.
The most common precursor of alkaloids are aminoacids.
Alkaloids are nitrogen containing compounds having at leave some basicity.
They are usually heterocyclic and occur primarily in higher plants and some
They usually exhibit significant physicological activity in humans and
animals and represent one of the largest and most diverse groups of secondary
Poisons – conine
Narcotics – morphine
Stimulants – caffeine
Medicine – Taxol
4. Alkaloids - Classification
Alkaloids are broadly classified into
True alkaloids – possess heterocyclic ring and are derived
from amino acids. Eg. Nicotine, Quinine.
Protoalkaloids – Do not possess heterocyclic ring but are
derived from amino acids. Eg. Colchicine.
Pseudoalkaloids – Not derived from amino acids. Eg.
5. Alkaloids - Classification
There are many other classification systems, which are based
on taxonomy, pharmacological properties and their
The chemical classification of alkaloids universally adopted
depends on the heterocyclic ring structure present and is
6. Sl.no. Class Heterocyclic Example
1. Pyrrolidine Stachydirn
2. Pyridine Nicotine
3. Piperidine Conine
4. Tropane Atropine
5. Indole Reserpine
7. 6. Quinoline Quinine
7. Isoquinoline Emetine
8. Quinolizidine Lupinine
9. Pyrrolizidine Hellotridine
10. Quinazoline Peganine
Sl.no. Class Heterocyclic Example
8. Alkaloids - Function
Alkaloids play a defense role in plants against insects other
arthropods and vertebrates.
Some alkaloids function as antimicrobial compounds.
Some alkloids have allelopathic effects.
Many alkaloids possess physicoloigcal actions in humans. For
example vinblastine and vincristine are potent anticancer drugs.
Alkaloids act as reserve substances able to supply nitrogen.
They are end products of detoxification meachanisms.
9. Alkaloids - Pharmaceutiacal uses of
Many alkaloids exhibit marked pharmacological activity, and some
fine important uses in medicine.
Atropine, present in Datura species is used widely in medicine as
anticholinergic drug. It is also used to dilate the pupil eye surgery.
Morphine and codeine are narcotic analgesics, and codeine is also
an antitussive agent, less toxic and less habit-forming than
Colchicines, from the corms and seeds of the autumn crocus, is used
as a gout suppressant.
10. Alkaloids - Function
Caffenine, which occurs in coffee, tea, and cocoa is a central
nervous system stimulant; it is used as an antidote to barbiturate
and morphine poisoning.
Emetine, the key alkaloid is used in the treatment of amebic
dysentery and other protozoal infections.
Ephedrine and related alkaloids occur in the genus Ephedra.
Ephedrine acts at the nerve-nerve spaces. Since it causes peripheral
contraction of arterioles it is used to correct low blood pressure
conditions and also to dilate the pupil of the eye. As a broncho-
dilator it is used in allergic conditions like asthma.
11. Alkaloids - Function
The leaves of coca contain cocaine. Cocaine is the oldest local anesthetic
known. Because of its systemic effect and the danger of addiction, its use is
now restricted to ophthalimic surgery and surgery of the ear, nose and
Quninne, cinchonine, quindine and a number of other alkaloids are
present in the barks of cinchona. Cinchona alkaloids have been used for the
treatment of malaria for many years.
12. Alkaloids - Function
Reserpine extracted from the roots and rhizomes of the genus Rauvolfia has been
used as a sedative and hypnotic and for reducing blood pressure. The drug is
now largely used in insanity and high blood pressure. It is more suitable for cases of
mild anxiety or patients of chronic mental illness.
Vinblastine and vincristine are alkaloids found in Catharanthusroseus. Vinblastine
is mainly useful for treating Hodgkin’s disease, advanced testicular cancer and
advanced breast cancer. Vincristine is mainly used to treat acute leukemia and
Digitoxin and digoxin are cardiac glycodiesobtrained from digitals. These
alkaloids are used to treat congestive heart failure.
13. Review questions
Choose the correct answer
1. Monomeric unit of terpenes
a) Isoprene b) amino acid c) Benzene
2. Which one of the following is an alkaloid?
a) Geraniol b) Caffeic acid c) Azadirachtin d) Quinine
3. Shikimic acid pathway is involved in the synthesis of
a) Phenolics b) Terpenes c) Alkaloids d) Steroids
4. β-Carotene is a
a) Monoterpene b) Diterpene c) Triterpene d) Tetraterpene
5. Azadirachtin is used for the control of
a) Bacterial disease b) Insect c) Fungal disease d) Rodents
14. Review questions
6. Compounds containing aromatic ring with one or more hydroxyl groups
a) Terpenes b) Alkaloids c) Phenolics
7. Juglone is an example of compounds producing ------ effect that affects the growth
of another species of plant.
a) Amphipathic b) Amphoteric c) allelopathic
8. Sesquiterpenes contain ----- carbon atoms
a) 5 b) 10 c) 15 d) 20
9. The diterpene plant hormone is
a) Auxin b) Giberellins c) Cytokinins d) Ethylene
10. The sesquiterpene plant hormone
a) Auxin b) Giberellins c) Cytokinins d) Abscisic acid
16. Review questions
Write in detail
1.What are phenolics? Explain their occurance, classification and functions.
2.What are terpenes? Explain their occurance, classification and functions.
3.Define alkaloids? Explain their occurrence, classification and