Anthracene (Anthraquinone) Glycosides Anthracene glycosides are oxygenated derivatives of pharmacological importance that are used as laxatives or cathartics, anti-inflammatory, antibacterial, antifungal and also as natural dyes.

The activity decreases as oxidation level increase. Forms of Anthracene derivatives in Plants: Aglycones:

Dimeric Anthracene derivatives: They are derived from two anthracene unites connected by covalent C-C bond through C-10. Homo-Dianthrones: The two anthrone moieties are similar. e.g. Sennidins A&B and their corresponding glycosides Sennosides A&B. They are all formed of two Rhein monomers. The A group are (l)-form while the B group are meso compounds with zero optical rotation.

Hetero-Dianthrones: The two anthrone moieties are different. e.g. Sennidins C&D and their corresponding glycosides Sennosides C&D. They are all formed of one Rhein and one Aloe-emodin monomers. The C group are (l)-form while the D group are meso compounds with zero optical rotation.

Glycosides: O-glycosides: e.g. Cascarosides A & B. They are both O- and C-glycosides. Each one contain two sugar unites. C-glycosides: e.g. Barbaloin it is formed from the removal of one sugar from Cascarosides.

Structure-Activity Relationship: Glycosylation is essential for activity. Hydroxylation at C-1 and C-8 is essential for activity. Oxidation level at C-9 and C-10 is important: Highest level of oxidation (anthraquinones) have the lowest activity. Oxanthrones are less active than anthrones. Complete reduction of C-9 and C-10 eliminates the activity. Substitution at C-3 have great impact on activity: CH2OH > CH3 > COOH

Some Drugs containing Anthracene derivatives: Senna: Leaves and pods contain Sennosides A-D. The C-C bond protect the anthrone from oxidation.

Cascara bark: Contain Cascarosides A- D. Barbaloin present as a secondary glycoside in Cascara. They are O- and C-glycosides. The C-linked glucose at C-10 protect anthrones from oxidation.

Aloes: The major glycoside in Aloes is the C-glycoside Barbaloin. Barbaloin is primary glycoside in Aloes. The C-linked glucose at C-10 protect anthrones from oxidation.

Rhubarb: It is purgative only in large doses. It contains high amount of tannins that have astringent effect.

Frangula bark: Contain anthraquinone derivatives the most oxidized and least active.

Mechanism of Action: The glycosides are absorbed from the small intestine and re-excreted in the large intestine where they increase the motility so produce laxation. Aglycones produce griping effect so it is recommended to prescripe antispasmodic with them.

Chemical test: Borntrager’s and Modified Borntrager’s test: For Aglycones: Extract plant material with organic solvent. Shake with NH4OH OR KOH. For O-Glycosides: Boil plant material with dil. HCl for 10 min, filter and shake with organic solvent (Ether or Benzene). Separate the organic solvent. For C-Glycosides: Boil plant material with dil. HCl/FeCl3, filter and shake with organic solvent (Ether or Benzene). Positive result indicated by Rose Red colour in the aqueous alkaline layer.

Hypericin Sources: Dried flowering tops of Hypericum perforatum. Structure: Aromatic polycyclic dianthrones. Uses: Tranquilizer, antidepressant (MAO inhibitor), and antiviral (anti-HIV).