• They are either C23 or C24 steroids, because of either five membered or six membered lactone ring respectively.

• Those with five membered lactone ring are called as cardenolides, while with six membered lactone ring and two double bond which is attached at the 17 α-position are termed as bufadienolides.

• The lactone of cardenolide contain only one double bond and is attached to steroidal nucleus through C - 17 α-position.

• The term bufadienolide has been derived from bufalin, obtained from skin of toads.

• The presence and attachment through a specific position to steroidal nucleus of the lactone is essential for proper cardiac activity.

• The steroid nucleus has hydroxyls at 3- and 14-positions of which the sugar attachment uses the 3-OH group. 14-OH is normally unsubstituted.

• Many genins have OH groups at 12- and 16-positions.

• These additional hydroxyl groups influence the partitioning of the cardiac glycosides into the aqueous media and greatly affect the duration of action.

• The size and degree of unsaturation varies with the source of the glycoside.

• The sugar part is attached through C - 3, β OH-linkage. Various types of sugars have been reported to be present in cardiac glycosides, such as glucose, fucose, rhamnose, digitoxose, digitalose, cymarose, sarmentose, thevatose, etc.

• Though, the sugars do not potentiate the medicinal activity of aglycone part, they are useful in solubilization of aglycone thereby, beneficial in absorption and distribution in the body.

• These sugars predominantly exist in the cardiac glycosides in the β-conformation.

• The presence of acetyl group on the sugar affects the lipophilic character and the kinetics of the entire glycoside.

• It has been also shown that increase in number of OH groups on aglycone leads to quicker onset of action and enhanced metabolism.

• Though, the number of plants contain cardiac glycosides, they are broadly restricted to angiosperms. Leguminosae, Sterculiaceae, Cruciferae, Scrophulariaceae, Euphorbiaceae etc. show presence of cardenolides.

• Very few families like Liliaceae and Ranunculaceae contain bufadienolides.

• The cardenolides have an unsaturated butyrolactone ring while the bufadienolides have a pyrone ring.

Chemical Tests for Cardiac Glycosides

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. Biren shah, A. K. Seth; Text Book of Pharmacognosy; Elsevier Publishers, Haryana.

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.