Cardiac glycosides

The group includes several medicinal herbs like Digitalis purpurea, Thevetia nerifolia and Helleborus niger. The active constituents of the plants are powerful glycosides and due to a specific action on the heart, they are known as cardiac glycosides or heart tonic.

Cardiac glycosides are divided in two groups:

A. Bufadienolides (Fig. 5.143): They are C 24 steroids. Hellbrien is a bufadienolide cardiac glycoside. On hydrolysis, it yields aglycone, hellbrigenin, which is more active than hellebrin.

Cardiac Glycocide House Plants

B. Cardenolides (Fig. 5.144): They have C 17 position unsaturated lactone. They are cyclopentanophenantherne derivatives and have a hormonal nature. They act on the kidneys and heart. Digitalis glycosides belong to this group.

Digitalis glycosides deserve special mention. The glycosides are obtained from the leaves of Digitalis purpurea, when the medicinal plant is in the flowering stage. Then isolation of the glycosides in pure form is difficult and they are present in association with saponins. Stoll and Kries (1933) proved that the glycosides are of two types:

1. They are known as glycosides-A and digitoxin (Fig. 5.145) is the main glycoside. The aglycone for this group is digitoxigenin.

Fig. 5.144 Structure of cardenolides.

Fig. 5.144 Structure of cardenolides.

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Fig. 5.145 Structure of Digitoxin.

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Fig. 5.145 Structure of Digitoxin.

2. The second type is known as glycoside-B and gitoxin is the main glycoside. The aglycone for this group is gitaligenin.

The glycosides obtained from Digitalis lanata are of three types:

1. Digilanid-A

2. Digilanid-B

3. Digilanid-C.

Some species of Digitalis are known to contain pregnane glycosides like digipupurin, diginin and digitalonin. Three glycosides, digitoxin, gitoxin and gitalin have been isolated in pure form for pharmacological application. Digoxin is utilized clinically as a heart tonic (Fig. 5.146).

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Fig. 5.146 Structure of Digoxin.

Cardiac glycoside of Asclepias currassavica Asclepine

Glycosides of Terminalia arjuna

Arjunetin (Fig. 5.147) and fridelin (Fig. 5.148), new triterpene glycoside, arjunetoside and terminoside A, new cardenolide (16,17-dihydroneridienone 3-O-beta-D-glucopyranosyl-(1->6)-O-beta-D-galactopyranoside, a novel naphthanol glycoside, arjunaphthanoloside.

Fig. 5.147 Structure of Arjunetin.
Fig. 5.148 Structure of Fridelin.

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