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.

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

B- Dimeric Anthracene derivatives: 1) Homo-Dianthrones: They are derived from two anthracene units connected by covalent C-C bond through C-10. 1) 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.

2) 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.

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

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. Barbaloin (aloin)

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

Mechanism of Action: The glycosides are absorbed from the small intestine and re-excreted in the large intestine where they cause irritation of colon mucosa increase the motility so produce laxation. Aglycones produce gripping effect so it is recommended to prescribe antispasmodic with them. Side effects: Urinary tract irritation, vomiting, diarrhea, uterine pain

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, mild antidepressant (MAO inhibitor) it has antiviral (anti-HIV) activity (in vitro). Side effects: allergic reaction in sensitive individuals