• Alkaloids
are natural product that contains heterocyclic nitrogen
atoms, are
basic in character.
• The
name
of alkaloids derives from the “alkaline” and
it was used to describe any nitrogen-containing base.
• Alkaloids
are naturally
synthesis
by a large numbers of organisms,
including animals, plants, bacteria and fungi.
• Some
of
the fires natural products to be isolated from medicinal plants were alkaloids when they
first obtained from the plants materials
• In the
early years of 19th century, it
was found that they
were nitrogen containing bases which formed salts with acid. Hence they were known as the vegetable
alkalis or alkaloids and
these alkaloids
are
used as the local anesthetic and stimulant
as
cocaine.
• Almost
all
the alkaloids have
a bitter
taste. The alkaloid
quinine for example
is
one of the bitterest tasting substances known and is significantly bitter (1x10-5) at
a molar
concentration.
The
names
of individual members are, therefore, generally derived from the name of the
plant in which they occur, or from their characteristic physiological activity. the
various
classes of alkaloids according to the heterocyclic ring system they contain are
listed below:
1.Pyrrolidine
alkaloids: they
contain pyrrolidine ( tetrahydropyrrole)
ring system. E.g Hygrine
found in Erythroxylum coca
leaves.
2.Pyridine alkaloids: they
have piperidine (hexahydropyridine)
ring system. E.g
Coniine, piperine and isopelletierine.
3.Pyrrolidine-pyridine
alkaloids: the
heterocyclic ring system
present
in there alkaloids is Pyrrolidine-pyridine.E.g Myosmine,
Nicotine alkaloid found in tobacco (Nicotiana tabacum) plant.
4.Pyridine-piperidine
alkaloids:This
family of alkaloids contains
a
pyridine ring system join to a piperidine ring system the simplest member is Anabasine
alkaloid isolated
from
poisonous Asiatic plant anabasis aphyllan.
5.Quinoline
Alkaloids: These
have the basic heterocyclic ring system quinoline .E.g Quinine occurs in the bark of cinchona
tree.It has
been used for centuries for treatment of malaria.Synthetic
drugs such as primaquinine have
largely
replace
quinine as an anti-malarial.
6.Isoquinoline
alkaloids: They
contain heterocyclic rig system
isoquinoline. E.g
Opium alkaloids like narcotine, papaverine,
morphine, codeine, and heroine.
Activity of Alkaloids
• Alkaloids
are significant for the protecting and survival of plant because they ensure their survival
against
micro-organisms (antibacterial and antifungal activities),
insects and herbivores
(feeding
deterrens) and
also against other
plants
by means of allelopathically active chemicals.
•The
use of alkaloids
containing plants
as dyes, spices, drugs or
poisons can
be traced
back
almost to the beginning of civilization.
•Alkaloids
have
many pharmacological
activities
including antihypertensive effects ( many indole alkaloids), antiarrhythmic effect (quinidine, spareien), antimalarial activity
(quinine), and anticancer actions (dimeric indoles, vincristine, vinblastine).
•These
are
just a few example
illustrating
the great economic importance
of this
group of plant constituents.
Some
alkaloids have stimulant property as caffeine and nicotine,
morphine are used as the analgesic and
quinine as the antimalarial drug.
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