Download - Anthracene glycosides lecture-2012-2013(1)
ANTHRACENE GLYCOSIDES
• Contains anthraquinone derivatives as their
aglycone component
• Anthraquinones present either in their free
state or as glycosides
• They possess a laxative/cathartic effect
• They are present in:
• Senna /Cassia
• Cascara
• Aloes
DISTRIBUTIONMonocots
• Found in the Liliaceae family
• As C-glycosides
• E.g barbaloin
Dicots
• Occurs in the ff families:
• Rubiaceae
• Leguminosae
• Polygonaceae
• Rhamnaceae
• Ericaceae
• Euphorbiaceae
• Verbenaceae etc
Mode of Action
• Absorbed first in the small intestines
• Hydrolysed in the colon by enzymes to the
pharmacologically active free aglycones
• Released anthraquinones irritate and
stimulate the colon• This enhances its peristaltic movements
leading to purgation
• This usually produces their action in 8-12
hours after administration
• Causes appreciable griping effect
• Generally administered with carminatives
to counteract undesirable effects
Derivatives of anthraquinones
• Anthranols
• Anthrones
• Oxanthrones
• And dianthrones exist
Anthranols and anthrones
• They are reduced anthraquinone
derivatives
• May occur as free or combined as
glycosides
• The 2 are isomeric
• May be converted to the other in solution
Oxanthrones
• These are products obtained from
• Anthraquinones
• Present in cascara bark
• Oxidation of oxanthrones produce
anthraquinones
• Oxidising agents e.g H2O2 may be used
Test for Anthracene glycosides
Borntrager’s Test
• Boil powdered plant material in dil acid
• Filter hot
• Shake filtrate with organic solvent- e.g
chloroform, Ethylacetate, Ether
• Separate organic layer
• Shake with dil ammonia
• Rose pink colour in aqueous layer shows
the presence of free anthraquinones
• Borntrager’s test distinguishes
anthraquinones from anthrones and
anthranols
Modified Borntrager’s test
• Some C-glycosides eg Aloin/barbaloin
do not undergo hydrolysis using only acids or
bases
• Hydrolysis may be caused by using Ferric
chloride/HCl due to oxidative hydrolysis
• Heat powdered drug with solutions of
FeCl3 + HCl on water bath
• Filter whilst hot
• Extract liberated anthraquinone with
organic suitable solvent e.g CHCl3 etc
• Shake organic layer with ammonia
solution
• Rose-pink colour confirms its presence
• Anthrones and anthranols do not give the
test unless they are converted to
anthraquinone
• This is done by oxidation with mild
oxidants such as hydrogen peroxide
Drugs containing Anthracene derivatives
Senna
• Consists of the dried leaflet of Cassia
senna /Alexandrian senna, (C.acutifolia),
Tinnevelly senna (C.angustifolia)
• Family:Leguminosa
• Contains sennoside A & B, C, D
Cascara• The dried bark of Rhamnus purshiana
• Family Rhamnaceae
• Present as O-glycosides/C-glycoside
• Collection made at least one year before
bark is used
• Fresh bark contains emetic principles
• Possesses drastic cathartic action
i) Cascara contains the ff glycosides:
• Cascarosides A & B = barbaloin
• Cascarosides C & D = chrysaloin
Aloes• E.g Aloe vera, A. barbadensis etc
• Common in the liliaceae family
• Aloins are very resistance to hydrolysis
and are not easily hydrolysed to
corresponding anthraquinones
• Oxidative hydrolysis is employed
Effect of storage on the activities of Anthracene glycosides
• Prolonged storage causes oxidation of
anthranols and anthrones to give the
relatively less drastic anthraquinones
• Thus, the degree of the drastic activity of
drugs decreases with time
• Thus anthrones and anthranols are more
potent than their corresponding
oxanthrones
• Oxanthrones in turn are more active
than their corresponding anthraquinones
Activity of Anthraquinone derivatives
• Anthrones and anthranols > Dianthrones >
Anthraquinones