Glycosides

Question 1

What are glycosides

Answer 1

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

Question 2

What unit of glycone is responsible for its pharmacological activity

Answer 2

Agylcone unit or genin unit

Question 3

How do glycosides form

Answer 3

• A REVERSIBLE condensation reaction occurs between OH of the
sugar unit and the H from the non-sugar unit with the natural enzyme glycosidasis

Question 4

All NATURAL glycosides are beta forms true/false

Answer 4

True

Question 5

What are the three physical properties of glycosides

Answer 5

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

Question 6

What can enhance the solubility of agylcosides

Answer 6

Sugar moelty

Question 7

What therapeutically active compounds are glycosides a source of

Answer 7

Cardiac function (cardiac glycosides)
➢Laxatives (anthraquinones)
➢Analgesics (salicylates)

Question 8

What are the four classification of glycosides according to the linkage between the sugar moiety and the aglycone

Answer 8

➢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)

Question 9

What does the type of linkage in glycosides determine

Answer 9

the stability of the glycoside during extraction

Question 10

WhaT are the five ways glycosides May be classified

Answer 10

Based on linkage
Based on pharmacological activity 
• according to the sugar moiety
• according to the number of sugar
moieties
• according to the aglycones

Question 11

What are the two experiments to test for glycosides

Answer 11

General test: reducing sugar test

• Hydrolysis of the glycoside using mineral acids or enzymes

Question 12

How are gycosides named

Answer 12

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’

Question 13

What derivatives of hesperidin gycosides are used as drugs(cardiac gylcosides

Answer 13

Diosmine

Sennosides A and B(2mg)
The others are in the genus Digitalis, Scilla and Strophantus groups

Question 14

What are the flavonoid glycosides ( bioflavonoids used as drugs

Answer 14

Hesperidin
Rutin
Querciten

HRQ

Question 15

What is he common nature of the sugars of cardiac glycosides

Genin and aglycons

Answer 15

They are steroidal and act as cardiotonic agents

Question 16

How do cardiac glycosides work

Answer 16

Enhance tone of heart by improving excitability and contractibility

This improved circulation will improve renal secretion that relieves odema associated with heart failure

Question 17

What are the two structural characteristics of glycosides

Answer 17

They are always in a glycosidic bond with mono di tri tetra sugars

Most sugars found in glycosides are uncommon deoxy-sugars

Question 18

What are the uncommon deoxy-sugars

Answer 18

Cymarose, Thevetose Digitoxose

Question 19

Learn the diagrams and structures in the slides

Answer 19

Yes boss

Question 20

What are the two types of cardiac glycosides

Answer 20

The steroid aglycones or genins are of 2 types
• Cardenolides
• Bufadienolides

Question 21

What are cardenosides

Answer 21

C23steriods that have alpha,beta-unsaturated 5 membered lactose ring on C17
They are more prevalent in nature

Question 22

What are the two types of cardenolides

Answer 22

Digitalis glycosides

Strophantus glycosides

Question 23

What plant are cardenolides found

Answer 23

Lily if the valley

Convallaria majalis (Likiaceae)

Question 24

The Digitalis group

Answer 24

• D. purpurea, D. dubia, D. ferruginea • D. lanata, D. grandiflora, D. nervosa • D. lutea D. mertonensis, D. subalpina • D. thapsi

Question 25

What are the two chemical constituents of cardenolides

Answer 25

Digoxin Gitoxin

Question 26

What are digoxin and which Digitalis leaves are they derived

Answer 26

Digoxin is the most widely used of cardiotonic glycosides | • Obtained from the leaves of D. lanata

Question 27

What are bufadienolides

Answer 27

Possesses doubly unsaturated 6-membered lactone ring in position C-17 • Bufadienolides are C24 steroid

Question 28

What is Botanical source of bufadienolides

Answer 28

Obtained from the bulbs of varieties of squill | Family = Liliaceae

Question 29

What are the two groups of cardioactive agents in bufadienolides

Answer 29

• Squill glycosides (scillarins) • Toad poison (Bufotoxin)

Question 30

What is the difference btn squill and toad glycosides in terms of structure

Answer 30

Squill R1=OH, R2=H R1 Bufotoxin R1= ester R2 =ester

Question 31

What are the two components of squill glycosides

Answer 31

Scillarin A Scillarin B

Question 32

What are the 7 uses of squill glycosides

Answer 32

* 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

Question 33

What are the MEDICINAL IMPORTANCE OF CARDIAC GLYCOSIDES

Answer 33

* Cardiotonics * Congestive heart failure * Rheumatic heart disease * Atherosclerosis * Diuretics

Question 34

What are the three official cardiac drugs

Answer 34

``` Digitalis leaf (digitalis tablets) Digitoxin tablets Digoxin injection ```

Question 35

What are the two qualitative test for cardiac glycosides

Answer 35

Kedde’s test Keller-Kiliani test

Question 36

How is the Keller-Kiliani test conducted | Method, re agent, test purpose(aim) and observation for positive test

Answer 36

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

Question 37

What is Kedde’s test Method, re agent, test purpose(aim) and observation for positive test

Answer 37

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