These are medicinally and commercially important.
Soap like action shown by the aglycone part of these glycosides.
They exhibit some physical properties like foaming action by shaking with water and yielding colloidal solutions.
They cause haemolysis of erythrocytes because of this they are generally considered as haemotoxic.
Due to this activity, some of them are used as fish poisons.
Saponins have a bitter and acrid taste.
They cause irritation of mucous membrane.
They are mostly non-crystalline substances soluble in water and alcohol; but insoluble in non-polar organic solvent Chemically
They contain aglycone called as sapogenin.
Sapogenins are high molecular weight substances which by acetylation give crystalline forms.
The harmful sapogenins are called as sapotoxins.
Depending on the nature of aglycone, saponins are categorized into 2 groups viz.
(i) Steroidal saponins (Tetracyclic triterpenoid saponins)
(ii) Pentacyclic triterpenoid saponins Both types of aglycones are linked with different types of sugars and uronic acids .
Steroid Pattern of Saponins .(Tetracyclic Triterpenoids)
Pentacyclic Triterpenoid
Steroidal saponins are used as raw material for the synthesis of various medicinally useful steroids
Like vitamin D, cardiac glycosides, corticoids like betamethasone and cortisone acetate, sex hormones like progesterone, testosterone and oestradiol, oral contraceptives such as mestranol and norethisterone; and spironolactone which is a diuretic steroid, Steroidal sapogenins viz. diosgenin and hecogenin can be considered as a representative example of this group of saponins.
Due to their pharmaceutical importance, many plants have been screened for the detection of steroidal saponins.
Their distribution is limited to plant kingdom, In dicot plants, important sources are from Leguminosae, Solanaceae, Apocynaceae, etc.
They are mainly obtained from monocot plants like Liliaceae, Dioscoreaceae and Amaryllidaceae.
β - amyrin
α- amyrin
lupeol.
Pentacylic Triterpenoid Saponins
This group contains the sapogenin with pentacyclic triterpenoid nucleus, which is linked with sugars or uronic acids.
The sapogenin is further differentiated into
(a) α- amyrin type;
(b) β - amyrin type; and
(c) lupeol.
An important derivative of this group is triterpenoid acids.
These acids are present in various drugs formed by substitution of carboxylic group at C4 , C7 and C20 .
Besides the chemical structure, these types of saponins differ from steroidal saponins by way of their distribution.
Pentacyclic triterpenoid saponins are available from various families of dicot plants like Polygalaceae, Caryophyllaceae, Berberidaceae, Umbelliferae, Rubiaceae, Compositae, Primulaceae, Rutaceae, Chenopodiaceae, etc.
They are however scarcely found in monocot plants.
References:
1. Trease D. & Evans W.C.: Text Book of Pharmacognosy: W.B. Saunders.
2. Tyler V. E. Brady L. R. & Robbers J. E.: Pharmacognosy; Lea Feibger, USA.
3. Wallis T. E.; Text Book of Pharmacognosy; CBS Publishers, Delhi.
4. Kokate C. K., Purohit A. P. & Gokhale S. B.: Pharmacognosy; Nirali Publications, Pune.
5. Harbone J. B.: Phytochemical Methods: A guide to modern techniques Analysis: Chapman & Hall, London.
6. Bruneton J.: Pharmacognosy, Phytochemistry, Medicinal Plants: Intercept Limited.