the cardiac glycosides
Post on 04-Feb-2016
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The Cardiac GlycosidesCardio-active GlycosidesGroup of steroidal glycosides act as cardiotonic agent. They increase tone, excitability and contractility of cardiac muscles.
Structure features:Steroidal nucleus must be present.3b-OH group involved in glycosidic linkage.14b-OH group at C-14.A/B ring junction cisB/C ring junction transC/D ring junction cisAdditional oH groups at C-5, C-11 and C-16 may be present.The presence of lactone ring:
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
The Sugar Part:The glycosides usually contain 3 to 4 sugars attached at C-3 OH.
Beside Glucose and Rhamnose they usually contain deoxysugars.
The Cardinolides1- Digitalis GlycosidesKnown as foxgloveThe most important species includes:
Digitalis contain three major aglycones:
2- Strophanthus GlycosidesObtained from Strophanthus kombThe used part is the seeds.The common aglycone is K-strophanthidin
Bufadienolides1- Squill GlycosidesThey have 6-membered lactone ring.Obtained from Squill bulbs.Aglycone contains only two hydroxyl groups at C-3 and C-14.
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.
Stability:Acid hydrolysis:Split sugars from the aglycone first.Enzymatic hydrolysis:Split sugars stepwise starting from the terminal sugar.Elevated temperature:Cause dehydration by removal of C-14 OH group to give inactive anhydro-form
Dehydration of Gitoxin with another OH at C-16 give a fluorescent compound used as test for Gitoxin
Medicinal Importance:They are Cardiotonics used to treat Congestive heart failure.They increase force of contraction of cardiac muscles without increase oxygen consumption.Increase cardiac output.The diastolic phse last longer so decrease heart rate.Have diuretic effect due to increase amount of blood passing through the kidney.
Chemical Identification:General test for steroids:Liebermanns test:Glycoside in acetic anhydride + Few drops of conc. H2SO4 Reddish violet GreenTest for Deoxysugars:Keller-Kilianis Test:Glycoside in acetic anhydride containing traces of FeCl3 + conc. H2SO4 on the wall of the tubeAcetic acid layer acquire Bluish-green colour (Digitalis)Acetic acid layer acquire Red colour (Squill)
Test for 5-membered lactone ring:
Legals test: Cardenolide in pyridine + Na nitroprusside + NaOH deep red colour.
Keddes test : Cardenolide+ 3,5 dinitrobenzoic acid (Keddes reagent A) + NaOH (Keddes reagent B) violet colour.