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Phytochem > Glycosides > Flashcards

Glycosides Flashcards

1
Q

What are glycosides

A

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

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2
Q

What unit of glycone is responsible for its pharmacological activity

A

Agylcone unit or genin unit

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3
Q

How do glycosides form

A

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

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4
Q

All NATURAL glycosides are beta forms true/false

A

True

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5
Q

What are the three physical properties of glycosides

A

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
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6
Q

What can enhance the solubility of agylcosides

A

Sugar moelty

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7
Q

What therapeutically active compounds are glycosides a source of

A 
Cardiac function (cardiac glycosides)
➢Laxatives (anthraquinones)
➢Analgesics (salicylates)
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8
Q

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

A

➢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)
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9
Q

What does the type of linkage in glycosides determine

A

the stability of the glycoside during extraction

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10
Q

WhaT are the five ways glycosides May be classified

A 
Based on linkage
Based on pharmacological activity 
• according to the sugar moiety
• according to the number of sugar
moieties
• according to the aglycones
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11
Q

What are the two experiments to test for glycosides

A

General test: reducing sugar test

• Hydrolysis of the glycoside using mineral acids or enzymes

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12
Q

How are gycosides named

A

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’

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13
Q

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

A

Diosmine

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

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14
Q

What are the flavonoid glycosides ( bioflavonoids used as drugs

A

Hesperidin
Rutin
Querciten

HRQ

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15
Q

What is he common nature of the sugars of cardiac glycosides

Genin and aglycons

A

They are steroidal and act as cardiotonic agents

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16
Q

How do cardiac glycosides work

A

Enhance tone of heart by improving excitability and contractibility

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

17
Q

What are the two structural characteristics of glycosides

A

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

Most sugars found in glycosides are uncommon deoxy-sugars

18
Q

What are the uncommon deoxy-sugars

A

Cymarose, Thevetose Digitoxose

19
Q

Learn the diagrams and structures in the slides

A

Yes boss

20
Q

What are the two types of cardiac glycosides

A

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

21
Q

What are cardenosides

A

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

22
Q

What are the two types of cardenolides

A

Digitalis glycosides

Strophantus glycosides

23
Q

What plant are cardenolides found

A

Lily if the valley

Convallaria majalis (Likiaceae)

24
Q

The Digitalis group

A

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

25
Q

What are the two chemical constituents of cardenolides

A

Digoxin

Gitoxin

26
Q

What are digoxin and which Digitalis leaves are they derived

A

Digoxin is the most widely used of cardiotonic glycosides

• Obtained from the leaves of D. lanata

27
Q

What are bufadienolides

A

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

28
Q

What is Botanical source of bufadienolides

A

Obtained from the bulbs of varieties of squill

Family = Liliaceae

29
Q

What are the two groups of cardioactive agents in bufadienolides

A

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

30
Q

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

A

Squill
R1=OH, R2=H R1

Bufotoxin
R1= ester R2 =ester

31
Q

What are the two components of squill glycosides

A

Scillarin A

Scillarin B

32
Q

What are the 7 uses of squill glycosides

A
  • 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

33
Q

What are the MEDICINAL IMPORTANCE OF CARDIAC GLYCOSIDES

A
  • Cardiotonics
  • Congestive heart failure
  • Rheumatic heart disease
  • Atherosclerosis
  • Diuretics
34
Q

What are the three official cardiac drugs

A 
Digitalis leaf (digitalis tablets) Digitoxin tablets
Digoxin injection
35
Q

What are the two qualitative test for cardiac glycosides

A

Kedde’s test

Keller-Kiliani test

36
Q

How is the Keller-Kiliani test conducted

Method, re agent, test purpose(aim) and observation for positive test

A

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

37
Q

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

A

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

Phytochem (9 decks)

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