1. 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.

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

3. 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.

4. 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.

5. 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.

6. 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 > CH > COOH

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

8. 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.

9. 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.

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

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

12. 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.

13. 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.

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