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The Cardiac GlycosidesCardio-active Glycosides
A Group of steroidal glycosides act as cardiotonic agent. They increase tone, excitability and
contractility of cardiac muscles.
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Structural features:
-Steroidal nucleus must be present.
-3-OH group involved in glycosidic linkage.
-14-OH group at C-14.
- A/B ring junction cis –
- B/C ring junction trans-
-C/D ring junction cis-Additional OH groups at C-5, C-11 and C-16 may be
present.
-The presence of lactone ring:
R
OH
sug-O
R2
R1
3 5
12
16
17
R3
H
H
H
BA
CD
14
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• According to the type of lactone ring Cardiac Glycosides are classified into:– Cardinolides:They are C-23 containing 5-membered
unsaturated lactone ring
e.g. Digitalis & Strophanthus
– Bufadienolides:They are C-24 containing 6-membered
unsaturated lactone ring
e.g. Squill
OO
17
17
O
O
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The Sugar Part:
• The glycosides usually contain 3 to 4 sugars attached at C-3 OH.
• Beside Glucose and Rhamnose they usually contain deoxysugars.
CHO
CH
CH
CH
CH
CH2OH
OH
OH
HO
OH
Glucose
CHO
CH
CH
CH
CH
CH3
OH
OH
HO
Rhamnose
HO
CHO
CH2
CH
CH
CH
CH3
OH
OH
Digitoxose
OH
CHO
CH2
CH
CH
CH
CH3
OH
OH
Cymarose
OCH3
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The Cardinolides1- Digitalis Glycosides
• Digitalis is Known as “foxglove”
• The most important species includes:
• 1) Digitalis purpurea
• 2) Digitalis lanata
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OO
OH
HO
R2
R1
3 5
12
16
17R1=R2=H DigitoxigeninR1=H, R2=OH GitoxigeninR1=OH, R2=H Digoxigenin
Digitalis contain three major aglycones:
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Digitoxigenin derived Glycosides: (Glycosylation at 3 OH)
Lanatoside A DX-DX-DX(Ac)-Gl
Purpurea glycoside ADX-DX-DX-Gl
Acetyl-digitoxinDX-DX-DX(Ac)
DigitoxinDX-DX-DX
Gitoxigenin derived Glycosides: (Glycosylation at 3 OH)Lanatoside B
DX-DX-DX(Ac)-GlPurpurea glycoside B
DX-DX-DX-Gl
Acetyl-gitoxinDX-DX-DX(Ac)
GitoxinDX-DX-DX
Digoxigenin derived Glycosides: (Glycosylation at 3 OH)LanatosideC
DX-DX-DX(Ac)-GlDeacetyl lanatoside C (Deslanoside)
DX-DX-DX-Gl
Acetyl-digoxinDX-DX-DX(Ac)
DigoxinDX-DX-DX
-Ac (Alkaline hydr.)
-Ac (Alkaline hydr.)
-Gl (Enzymatic Hydr.)-Gl (Enzymatic Hydr.)
-Ac (Alkaline hydr.)
-Ac (Alkaline hydr.)
-Gl (Enzymatic Hydr.) -Gl (Enzymatic Hydr.)
-Ac (Alkaline hydr.)
-Ac (Alkaline hydr.)
-Gl (Enzymatic Hydr.) -Gl (Enzymatic Hydr.)
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2- Strophanthus Glycosides
• Obtained from Strophanthus kombé
• The used part is the seeds.
• The common aglycone is K-strophanthidin
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OO
OH
CHO
O
3 5
12
16
17
OH
Cymarose
-Glucose
-Glucose K-Strophanthoside
K-Strophanthin
Cymarin
K-Strophanthidin
10
14
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Bufadienolides1- Squill Glycosides
• They have 6-membered lactone ring.
• Obtained from Squill bulbs.
• Aglycone contains only two hydroxyl groups at C-3 and C-14.
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OH
O
3
5
12
16
17
Rhamnose
-Glucose
-Glucose Glucoscillarin A
Scillarin A
Proscillaridin A
Scillaridin A
O
O
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Physical and Chemical properties of cardiac glycosides:
• Solubility:– Glycosides are soluble in water and alcohols.– Increase number of sugars increase water
solubility.
– Aglycones soluble in CHCl3 and EtOAc.
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• Stability:– 1) Acid hydrolysis:
• Split sugars from the aglycone first.
– 2) Enzymatic hydrolysis:• Split sugars stepwise starting from the terminal
sugar.
– 3) Elevated temperature:• Cause dehydration by removal of C-14 OH group to
give inactive anhydro-form
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OO
OH
Sug-O
OO
Sug-O
High temperature
Anhydro-form
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Medicinal Importance:
• -They are Cardiotonics used to treat Congestive heart failure.
• -They increase force of contraction of cardiac muscles without increasing oxygen consumption.
• -Increase cardiac output.• The diastolic phase lasts longer, thus decreases
heart rate.• -Have diuretic effect due to increase amount of
blood passing through the kidney.
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Chemical Identification:
General test for steroids:Liebermann’s test:
Glycoside in acetic anhydride + Few drops of conc. H2SO4 Reddish violet Green
Test for Deoxysugars:Keller-Kiliani’s Test:
Glycoside in gl. acetic containing traces of FeCl3 + conc. H2SO4 on the wall of the tube
Acetic acid layer acquire Bluish-green colour (Digitalis)
Acetic acid layer acquire Red colour (Squill)
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• Test for 5-membered lactone ring:
– Legal’s test: • Cardenolide in pyridine + Na nitroprusside + NaOH
deep red colour.
– Kedde’s test : • Cardenolide + 3,5 dinitrobenzoic acid (Kedde’s reagent A) + NaOH
(Kedde’s reagent B) violet colour.COOH
NO2O2N