Pharmacognosy Lecture No.1

Glycosides

Muhammad Tanveer Khan

Introduction

A glycoside is an organic compound, usually of plant origin, that is composed of a sugar portion linked to a non-sugar moiety.

Sugar portion ……….. Glycone

Non-sugar portion…... Aglycone / Genin

Linkage between sugar and non-sugar is usually an “oxygen linkage”

Types

Based on atoms involved in glycosidic linkage

O- glycosides

C- glycosides

S- glycosides

N- glycosides

Types

According to Sugar moiety

Glucosides

Ribosides

Rhamnosides

Classification

(a )Cardioactive glycosides: Digitalis, Strophanthus and white squill

(b )Anthraquinone glycosides: Cascara, Aloe, Rhubarb, Cochineal and Senna

(c )Saponin glycosides: Glycyrrhiza, Sarsaparilla(d )Cyanophore glycosides: Wild cherry

(e )Isothiocyanate glycosides: Black Mustard(f )Lactone glycosides: Cantharide

(g )Aldehyde glycosides: Vanilla(h )Miscellaneous glycosides: Gentian, Quassia, Dioscorea

Cardioactive GlycosidesUsed in treatment of CHF

Mechanism:These glycosides;

Increase the force of systolic contraction

Shorten length of systole

As a result

Heart have more time to rest between contraction.

Therapeutic activity depends upon;

1 .Chemical nature of aglycone

2 .Number of sugars

Aglycone is steroidal.

Aglycone may be;

Cardenolide (5-membered lactone at place of R)

Bufanolide (6-membered lactone at place of R)

a( DigitalisBotanical Origin:

Digitalis purpureaDigitalis lanata

Family:Plantigenaceae

Part used:Dried leaves

Collection:Leaves collected from 2nd year growth of plant in June before opening of flower.

Drying is done by applying artificial heat (temperature not more than 65°C).

Chemistry: Four aglycons in Digitalis

Digitoxigenin

Gitoxigenin

Gitatoxigenin

Digoxigenin (only in Digitalis lanata)

DerivativesD. purpureaD. lanata

DigitoxigeninDigitoxin

Glucodigitoxin

)Digitoxin + 1 glucose(

Acetyl digitoxin

Lanatoside A)Acetyl digitoxin + 1 glucose(

GitoxigeninGitoxin

Glucogitoxin)Gitoxin + 1 glucose(

Lanatoside B)Acetyl gitoxin + 1 glucose (

GitatoxigeninGitatoxinLanatoside E)Acetyl Gitatoxin + 1 glucose(

DigoxigeninDigoxin

Acetyl digoxin

Lanatoside C)Acetyl digoxin + 1 glucose(

Deslanoside)Digoxin + 1 glucose(

b( StrophanthusBotanical Origin:

Strophanthus kombe

Strophanthus hispidus

Family:Apocynaceae

Part used:Dried ripe seeds

Collection:Fruits are collected when fully ripen i.e. in June and July

Chemistry:

Active constituent is Strophanthin.

Upon hydrolysis it yields;

Strophanthidin

Sugars (alpha D-glucose + beta D-glucose + beta D-cymarose)

Apart from Strophanthin, there are;

30% fixed oils

Resin / Mucilage

Nitrogenous bases ( Trigonellin, Choline )

Uses:Cardiac stimulant

Diuretic

c( White squillBotanical Origin:

Urginea maritima

Family:Liliaceae

Part used:Dried fleshy scales of bulb

Collection:Bulbs are collected in August. Outer scale is removed and inner scale is divided into pieces and dried in sunlight.

Chemistry: Active constituent is Scillaren.

Upon hydrolysis it yields;

Scillarenin

Sugars (1 molecule of glucose + 1 molecule of rhamnose)

Uses: Emetic

Expectorant

Cardiac tonic

Diuretic