Similar a Health benefits of plant alkaloids A Lecture By Mr Allah Dad Khan Former DG Agriculture Extension Khyber Pakhtun Khwa Province & Visiting Professor Agriculture University Peshawar Pakistan(20)
4. Alkaloids are low molecular weight natural organic substances derived from plant sources. Alkaloids are defined as
pharmacologically active nitrogen containing basic compounds of plant origin. The word alkaloid means alkali – like
or vegetable alkali. . The term ‘alkaloid’ was coined by the German pharmacist Carl Friedrich Wilhelm Meissner in
1819 to refer to plant natural products.
According to R.F. Raffauf (Plant Alkaloids: A Guide To Their Discovery and Distribution, 1996), more than 10,000
different alkaloids have been discovered in species from over 300 plant families.To date over 21,000 alkaloids have
been identified. About 20-30% plant species have been found to contain them. Many of the alkaloids are useful as
drugs. The drugs may be either purified natural alkaloids or chemically modified alkaloids. About 25% of the
drugs used today are of plant origin. The plant alkaloids usually have a marked physiological action on man or other
animals. The plants use alkaloids as defence chemical agents against herbivores and pathogens. Wink (1993) listed
183 alkaloids with antibacterial properties. The families Solanaceae and Apocynaceae are known for their alkaloid
production, 60-70% of their members producing alkaloids. Alkaloid bearing species have been found in nearly all
classes of organisms: frogs, ants, butterflies, bacteria, sponges, fungi, spiders, beetles and mammals. Some animals,
such as frogs produce toxic alkaloids in the skin or secretary glands.
6. Ancient phytotherapy
Alkaloids have been used throughout history in folk medicine in different regions of the
world. The alkaloids from plant extracts have been used as ingredients in potions (liquid
medicine) and poisons. Ancient people used plant extracts containing alkaloids for treating
a large number of ailments including: snakebite, fever and insanity. Humans have used
alkaloids as poisons in weapons. From the times of Hippocrates (460 – 377 BCE), medicinal
plants were used in Europe as herbal remedies for improving health. In ancient India and
China, herbs were known and used even since 770 BCE. India has a very long, safe and
continuous usage of many herbal drugs in the officially recognized alternative systems of
medicine viz. Ayurveda, Yoga, Unani, Siddha, Homeopathy and Naturopathy. In India more
than 70% of the population use herbal drugs for their health.Millions of Indians use herbal
drugs regularly, as spices, home-remedies, health foods, as self-medication or also as
drugs prescribed in the non-allopathic systems. The Indian medicinal plants are rich
sources of beneficial compounds including antioxidants and components that can be used
in functional foods.
9. Characteristics of alkaloids
The alkaloids are alkaline or basic in chemical reaction. They usually
taste bitter. They have complex ring structures (usually with
heterocyclic ring) and contain one or more nitrogen atoms. The dietary
intake of small doses have therapeutic effect as muscle relaxants,
tranquillizers, pain killers, antimicrobials in human beings. Intake of
large doses results in toxaemia or fatal. Many of the alkaloids are
synthesized from amino acids such as tyrosine, tryptophan, ornithine,
arginine and lysine.
10. Physico-chemical properties
Alkaloids (as bases) are not soluble or sparingly soluble in
water and soluble in apolar or only slightly polar organic
solvents. They are soluble in concentrated hydro-alcoholic
solutions. The alkaloids exist in plants in free states or as salts
or as N-oxides. Elementally alkaloids consist of carbon,
hydrogen and nitrogen. Most alkaloids also contain oxygen. A
few such as coniine from hemlock and nicotine from tobacco
are oxygen-free. Most alkaloids have well defined crystalline
structures which combine with acids to form salts. Most of the
alkaloids have complex molecular structures with significant
pharmacologic properties. An alkaloid never occurs alone;
alkaloids are usually present as a mixture of a few major and
several minor alkaloids of a particular biosynthetic unit, which
differ in functional groups (Wink 2005).
11. Functions of alkaloids in plants
As poisonous agents, alkaloids protect the plants against
insects and herbivores. Alkaloids form as end products of
detoxification reactions e.g., secondary metabolites. They serve
as regulatory growth factors in plants. They also serve as
reserve substances capable of supplying nitrogen or other
elements necessary to the plant’s economy.
13. Biosynthetic origin of alkaloids
Alkaloids are mainly derived from amino acids. The amino
acids that most often serve as alkaloidal precursors
include phenylalanine, tyrosine, tryptophan, histidine,
anthranilic acid, lysine and ornithine. Alkaloids also
derived from other precursors like terepenes or steroids.
Naming of alkaloids
The name of all alkaloids ends with the suffix ‘–ine’. In
addition the names of the alkaloids are based on various
1. From the generic name of the plant yielding them
e.g., atropine from Atropa bellodona.
2. From the specific name of the plant yielding them
3. From the common name of the drug yielding them
4. From their physiologic activity e.g., emetine.
5. From name of the discoverer e.g., pelletierine
14. Classification of alkaloids
Typical or true alkaloids have heterocyclic ring with
nitrogen derived from amino acids. They can be
categorised into 14 groups according to their ring
structures e.g., quinine, morphine, codeine etc.,
Atypical or protoalkaloids do not have heterocyclic ring
with nitrogen derived from amino acids e.g., colchicines.
Pesudoalkaloids have heterocyclic ring with nitrogen not
derived from amino acids. They can be derived from
terpenoids or purines.
15. Chemical classification
Alkaloids are usually classified by their common molecular
precursors based on the biological pathway used to
construct the molecule.
1. Pyridine group – e.g., piperine, coniine, pilocarpine,
2. Tropane group – e.g., atropine, cocaine.
3. Quinoline group – e.g., quinine, strychnine.
4. Isoquinoline group – e.g., opium alkaloids –morphine,
5. Phenylethylamine group – e.g., ephedrine, mescaline.
6. Indole group – e.g., reserpine, lysergic acid, emetine.
7. Purine group – e.g., caffeine.
8. Terpenoid group – e.g., aconitine.
9. Betaines – e.g., muscarine.
16. Health benefits
Alkaloids act on the central nervous system either as
depressants (morphine) or stimulants (caffeine). They also
act on the autonomic nervous system as
sympathomimetics ( e.g., ephedrine), sympatholytics (e.g.,
yohimbine), parasympathomimetics (e.g., pilocarpine),
anticholinergics (e.g., atropine) and ganglioplegics (e.g.,
nicotine). Alkaloids act as local anaesthetics (e.g.,
cocaine), agents to treat fibrillation (e.g., quinidine), anti-
tumour agents (e.g., vinblastine), anti-malarials (e.g.,
quinine), antibacterials (e.g., berberine), amoebicides
(e.g., emetine) and pain killer (e.g., codeine, morphine).