CARDIAC GLYCOSIDES
• The genins or aglycones of all cardiac
glycosides are steroidal in nature
• May be referred to as steroid glycosides
• They act as cardiotonic agents
• Enhance the tone of the heart
• Excitability
• Contractibility of the cardiac muscle
• Also the improved circulation tends to
improve renal secretion
• This relieves oedema often associated
with heart failure
Structural Characteristics of Cardiac Glycosides
• This is always involved in a glycosidic
linkage to a mono, di, tri, or tetra
saccharide
• Most sugars that are found in cardiac
glycosides are uncommon deoxy-sugars
• E.g Digitoxose, Cymarose, Thevetose
C
CHO
C
C
C
CH3
OH
OH
OH
H2 C
CHO
C
C
CH3
OH
OH
H2
CHO
C
C
CH OH
HC OCH3
OH
HCH3O
C OHH
CH3
Digitoxose Cyamarose Thevetose
O
R
OH
CH3
Sugar
Lactone ring
1
2
3
45
10
67
8
9
1112
13
1415
16
17
Types of cardiac glycosides
• The steroid aglycones or genins are of 2
types
• Cardenolides
• Bufadienolides
THE CARDENOLIDES• They are more prevalent in nature
• Cardenolides are C23 steroids
• These have α,β-unsaturated 5-membered
lactose ring in position C-17
2 main types:• Digitalis glycosides • Strophanthus glycosides
O
R
OH
CH3OH
Sugar
1
2
3
45
10
67
8
9
1112
13
1415
16
17
O OCardenolides
Digitalis glycosides R=CH3Strophanthus glycosides R=CHO OR CH2OH
The Digitalis group
These include:
• D. purpurea, D. dubia, D. ferruginea
• D. lanata, D. grandiflora, D. nervosa
• D. lutea D. mertonensis, D. subalpina
• D. thapsi
Chemical constituents
• digitoxin
• gitoxin
• digoxin
Digoxin
• Digoxin is the most widely used of
cardiotonic glycosides
• Obtained from the leaves of D. lanata
THE BUFADIENOLIDES
• This group of cardioactive agents includes
the following:
• Squill glycosides (scillarins)
• Toad poison (Bufotoxin)
Botanical source
• Obtained from the bulbs of varieties of
squill
• Family = Liliaceae
• Derives name from the generic name for
the toad (Bufo)
• Possesses doubly unsaturated 6-
membered lactone ring in position C-17
• Bufadienolides are C24 steroid
O
OH
R1R2
Sugar
1
2
3
45
10
67
8
9
1112
13
1415
16
17
O
O
Bufadienolides
Squill glycosides R1=OH, R2=H Bufotoxin R1 & R2 = ester group
Bufadienolides from Squill• These glycosides include the following:
• Scillarin A
• Scillarin B
Uses
• A potent cardiotonic
• As expectorant specially in chronic
bronchitis
• As stimulant
• It is used as a very effective expectotant
both in asthma and chronic bronchitis
• It may possess anticancer
• Produces diuresis
• It causes emesis in relatively higher doses
• Chemical colour reactions have been
evolved to be used as the qualitative tests
either for:
• the various glycosides
• or their corresponding aglycones
TEST FOR CARDIAC GLYCOSIDES
1 Kellar-Kiliani Test
The glycoside is dissolved in glacial acetic acid containing a trace of FeCl3, add conc. H2SO4 along the side of the test tube to settle at the bottom (for deoxy sugars e.g. digitoxose)
A reddish brown colour changing to bluish green colour appears at the junction of two reagents within 2-5 minutes spreading slowly into the acetic acid layer
2. Kedde’s Test A solution of glycosides is treated with a small amount of Kedde’s reagent (Cardenolides)
Development of a blue or violet colour that fades out in 1- 2 hours shows its presence
MEDICINAL IMPORTANCE OF CARDIAC GLYCOSIDES
• Cardiotonics
• Congestive heart failure
• Rheumatic heart disease
• Atherosclerosis
• Diuretics
Official Cardiac Drugs
• Digitalis leaf (digitalis tablets)
• Digitoxin tablets
• Digoxin injection