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general knowledge about Alkaloids

Therapeutic action
Group of natural products with potent physiological effects
Important therapeutic agents e.g. atropine, morphine & quinine
Treat many diseases from malaria to cancer.
Toxicity
 
Some are extremely poisonous e.g.:
1.Curare extract (tubocurarine alkaloid)  arrow poison.
2.Hemlock (Conium : coniine) Socrate’s suicide
3.Belladonna (atropine)  murdering.
4.Egyptian hembane (Hyoscyamus: hyoscyamine)  Cleopatra’s suicide.

Definition
Precise & general definition is difficult, as “alkaloids” are not a homogeneous group of compounds.
“Alkaloid” (alkali-like) = “basic nitrogenous compounds of plant origin that are physiologically active”.

Restrictions:
1.All alkaloids are nitrogenous, but not all nitrogenous compounds are alkaloids.
2.Some alkaloids are found in animals & fungi & almost all alkaloids are synthesized.
3.Most possess basic properties; but, certain are amphoteric (morphine) or acidic (colchicine).

Classification
May be based on:
Pharmacological action
Chemical structure
Biochemical origin
Taxonomical origin

Classification - According to chemical structure
1.Non-heterocyclic = “atypical alkaloids”
= “protoalkaloids”.
2. Heterocyclic = “typical alkaloids” [sub-classified into different groups according to the ring structure].

Alkaloids -Hegnauer’s classification
Based on type of nitrogen & biochemical origin 3 types:

Distribution
Major source : flowering plants (Angiosperms).
 Recently : in animals, fungi & marine organisms.
True alkaloids : rare in lower plants e.g. fungi (ergot alkaloids).

Angiosperms:
1.Orders almost free from alkaloids e.g. Salicales, Cucurbitales & Oleales.
2.Families rich in alkaloids:
Monocotyledons: Liliaceae & Amarylidaceae,
Dicotyledons: Solanaceae, Papaveraceae, Compositae & Loganiaceae.

Animal alkaloids:
Amphibians e.g. skin of certain frogs  potent neurotoxic alkaloids
Mammals : indole & isoquinoline derivatives & mammalian morphine.

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