Questions and Answers
What is the effect of higher number of -OH groups on the steroidal nucleus?
What is the result of replacing -OH groups at C3 and/or C14 by H atoms?
What is the orientation of the C17 side chain required for activity?
What is the effect of the sugar moiety on cardiac glycosides?
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Which of the following is more potent?
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What is the trend in potency with increasing number of sugar units in oligosaccharide moieties?
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Which plant is a source of cardiac glycosides?
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What is the commercial source of Digitalis lanata?
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What is the principal glycoside of the wood of the African Acokanthera schimperi?
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What is the cardiac effect of Thevetia peruviana glycosides?
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What is the result of partial hydrolysis of Thevetia peruviana glycosides?
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What is the family of plants that Calotropis spp belongs to?
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What is the use of Bufadienolides as cardioactive drugs?
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What is the reagent used in Legal's test for cardiac glycosides?
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What is the result of Keller-Killiani's test for cardiac glycosides?
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What is the name of the glycoside isolated from Urginea maritima?
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Study Notes
Oxygen Substitution on Steroidal Nucleus
- Higher number of -OH groups results in more rapid onset of action and elimination from the body.
- Replacement of -OH groups at C3 and/or C14 by H atoms results in slight reduction of potency.
Structure Activity Relationship
- β-orientation of C17 side chain is necessary for activity, 17α-cardenolides (allocardenolides) are inactive.
- Sugar moiety has no cardiac activity, but when attached to C3 -OH group of steroidal moiety, activity is modified and influences pharmacokinetic behavior.
- Free aglycones are less potent than their glycosides.
- Type and number of sugar units may affect potency.
- Cardiac glycosides with 6-deoxy sugars (6-CH3) are more potent than their 6-CH2OH analogs.
- For oligosaccharide moieties, potency decreases with increase in number of sugar units.
Distribution in Nature
- Scrophulariaceae (Digitalis purpurea leaves - foxglove, Digitalis lanata leaves - white flowers)
- Apocyanaceae (Strophanthus kombe vine seeds - Africa)
- Liliceae (Urginea bulbs - squill, Europe, India)
- In toads (cardiac glycosides are also found in animals only in exceptional cases)
Digitalis
- Digitalis spp (Scrophulariaceae)
- D. lanata: Mediterranean/White, commercially produced in Ecuador, USA, and Holland (total glycosides, 1.5%) with major: Lanatosides A-E (primary glycosides) and digoxin.
- D. purpurea: British/Purple, commercially produced in Holland and Eastern Europe (total 0.5%) with major: Purpurea glycosides A, B, and E, digitoxin, gitoxin, and gitaloxin.
Strophanthidin
- Seeds of East African Strophanthus kombé were formerly official in the BP.
- Principal glycosides: K-strophanthoside, K-strophanthin, and cymarin, all based on the genin strophanthidin.
- Also found in Strophanthus hispidus.
Ouabain
- The principal glycoside of the wood of the African Acokanthera schimperi (A. ouabaio).
- Strophanthus gratus seeds contain 4-8% of ouabain (G-strophanthin), a rhamnose glycoside more stable than those present in other species.
Oleander Glycosides
- Thevetia peruviana (T. neriifolia) - yellow oleander, are a rich source of the glycoside thevetin A.
- Partial hydrolysis and the loss of two glucose units yields peruvoside.
- Peruvoside consists of L-thevetose linked to the aglycone cannogenin.
Other Sources
- Calotropis spp
- Asclepiadaceae
- Convallaria majalis (Liliaceae) - Lily of the Valley
Bufadienolides
- Found in some Liliaceae and Ranunculaceae, and in the toad venoms.
- The genins are partly free and partly combined with suberyl arginine.
- Therapeutically, they find little use as cardioactive drugs because of their low therapeutic index and their production of side effects.
Urginea maritima
- Squill
- Scillaren A, and an amorphous mixture of glycosides, scillaren B isolated.
- Scillaren A is the most important cardiac glycoside.
Chemical Testing
- Colour tests based on the aglycone:
- Legal's test: deep red color.
- Raymond's test: violet color - blue color.
- Kedde's test: violet color.
- Baljet's test: orange or red.
- Liebermann's test and Antimony test will give a positive reaction.
- Colour tests based on the glycone:
- Keller-Killiani's test (for 2-deoxy sugar): a blue ring between the 2 layers is a positive reaction.
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Description
This quiz covers the effects of oxygen substitution on the steroidal nucleus on distribution, metabolism, and potency, as well as the importance of β-orientation of the C17 side chain and sugar moiety on cardiac activity. Learn how structural changes impact the activity of steroids.