Glycosides Flashcards
What are glycosides
These are compounds which yield one or more sugars and other non-sugar products on hydrolysis
• The sugar unit is called the ‘glycone’
• The non-sugar unit is called ‘aglycone’ or ‘genin’ • Commonest sugar is β-D-glucose
What unit of glycone is responsible for its pharmacological activity
Agylcone unit or genin unit
How do glycosides form
• A REVERSIBLE condensation reaction occurs between OH of the
sugar unit and the H from the non-sugar unit with the natural enzyme glycosidasis
All NATURAL glycosides are beta forms true/false
True
What are the three physical properties of glycosides
1.Glycosides are soluble in water but the aglycone is insoluble
- Glycosides are hydrolysed by enzymes or boiling with dilute mineral acids
- The sugars helps to transfer the aglycone to it site of action
What can enhance the solubility of agylcosides
Sugar moelty
What therapeutically active compounds are glycosides a source of
Cardiac function (cardiac glycosides) ➢Laxatives (anthraquinones) ➢Analgesics (salicylates)
What are the four classification of glycosides according to the linkage between the sugar moiety and the aglycone
➢O-glycosides: linkage is through an oxygen bridge (the most common glycosides)
➢C-glycosides: linkage is through a carbon bridge (very difficult to hydrolyse)
- N-glycosides: linkage is through the nitrogen bridge (nucleosides)
- S-glycosides: linkage is through a sulphur bridge (glucosinolates)
What does the type of linkage in glycosides determine
the stability of the glycoside during extraction
WhaT are the five ways glycosides May be classified
Based on linkage Based on pharmacological activity • according to the sugar moiety • according to the number of sugar moieties • according to the aglycones
What are the two experiments to test for glycosides
General test: reducing sugar test
• Hydrolysis of the glycoside using mineral acids or enzymes
How are gycosides named
According to the sugar moiety
Eg: Glucose glucosides
-galactose galactoside
Old systems were named with ‘in’ eg Salicin, strophanthin, aloin
But now ‘oside is used’
What derivatives of hesperidin gycosides are used as drugs(cardiac gylcosides
Diosmine
Sennosides A and B(2mg)
The others are in the genus Digitalis, Scilla and Strophantus groups
What are the flavonoid glycosides ( bioflavonoids used as drugs
Hesperidin
Rutin
Querciten
HRQ
What is he common nature of the sugars of cardiac glycosides
Genin and aglycons
They are steroidal and act as cardiotonic agents
How do cardiac glycosides work
Enhance tone of heart by improving excitability and contractibility
This improved circulation will improve renal secretion that relieves odema associated with heart failure
What are the two structural characteristics of glycosides
They are always in a glycosidic bond with mono di tri tetra sugars
Most sugars found in glycosides are uncommon deoxy-sugars
What are the uncommon deoxy-sugars
Cymarose, Thevetose Digitoxose
Learn the diagrams and structures in the slides
Yes boss
What are the two types of cardiac glycosides
The steroid aglycones or genins are of 2 types
• Cardenolides
• Bufadienolides
What are cardenosides
C23steriods that have alpha,beta-unsaturated 5 membered lactose ring on C17
They are more prevalent in nature
What are the two types of cardenolides
Digitalis glycosides
Strophantus glycosides
What plant are cardenolides found
Lily if the valley
Convallaria majalis (Likiaceae)
The Digitalis group
• D. purpurea, D. dubia, D. ferruginea • D. lanata, D. grandiflora, D. nervosa • D. lutea D. mertonensis, D. subalpina • D. thapsi
What are the two chemical constituents of cardenolides
Digoxin
Gitoxin
What are digoxin and which Digitalis leaves are they derived
Digoxin is the most widely used of cardiotonic glycosides
• Obtained from the leaves of D. lanata
What are bufadienolides
Possesses doubly unsaturated 6-membered lactone ring in position C-17
• Bufadienolides are C24 steroid
What is Botanical source of bufadienolides
Obtained from the bulbs of varieties of squill
Family = Liliaceae
What are the two groups of cardioactive agents in bufadienolides
• Squill glycosides (scillarins) • Toad poison (Bufotoxin)
What is the difference btn squill and toad glycosides in terms of structure
Squill
R1=OH, R2=H R1
Bufotoxin
R1= ester R2 =ester
What are the two components of squill glycosides
Scillarin A
Scillarin B
What are the 7 uses of squill glycosides
- 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
What are the MEDICINAL IMPORTANCE OF CARDIAC GLYCOSIDES
- Cardiotonics
- Congestive heart failure
- Rheumatic heart disease
- Atherosclerosis
- Diuretics
What are the three official cardiac drugs
Digitalis leaf (digitalis tablets) Digitoxin tablets Digoxin injection
What are the two qualitative test for cardiac glycosides
Kedde’s test
Keller-Kiliani test
How is the Keller-Kiliani test conducted
Method, re agent, test purpose(aim) and observation for positive test
Re agents- H2SO4, FeCl3, glacial acetic acid
To test for de oxygen sugars
Method
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)
+ve test
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 laye
What is Kedde’s test Method, re agent, test purpose(aim) and observation for positive test
To test for cardenolides
Reagent- Kedde’s reagent
Method
A solution of glycosides is treated with a small amount of Kedde’s reagent
+ve test
Development of a blue or violet colour that fades out in 1- 2 hours shows its presence
