Anthraquinone Glycosides

A number of glycosides with aglycones related to anthracene are present in such drugs as cascara sagrada, frangula, aloe, rhubarb and senna. These drugs are used as cathartics. The glycosides upon hydrolysis yield aglycones that are di-, tri-, or tetrahydroxy anthraquinones or modifications of these compounds.
Without sugar moiety, free anthraquinones exhibit little therapeutic activity. The sugar is essential because it serves to transport the aglycone to the site of action in the large intestine.
The anthracene derivatives occur in these medicinal plant substances in various forms at different oxidation levels as derivatives of anthraquinone, anthrone, or oxanthrone and of anthranol, as well as in a dimeric form (dianthrone) in some cases.
Biosynthesis of anthraquinone glycosides
Feeding of labeled acetate to penicillium islandicum, a species that produces several anthraquinone derivatives, have revealed that the distribution of radioactivity in these compounds is consistent with formation via a head to tail condensation of acetate units. A poly ?-ketomethylene acid intermediate is propably first produced and then gives rise to the various oxygenated aromatic compounds after intramolecular condensation. Emodin- like anthraquinones are formed in higher plants by similar pathway. Transglycosylation reaction, which create glycosides, occurs at a late stage in the pathway after the anthraquinone nucleus has been formed.
Numbering system and nomenclature
Drugs containing anthraquinone glycosides
1- Cascara Sagrada
Cascara sagrada or rhamnus purshiana is the dried bark of Rhamnus purshianus (Fam: Rhamnaceae). It should be aged for at least one year before use in medicinal preparations to lose its griping properties.
Active constituents
2- Frangula
Frangula or buchthorn bark is the dried bark of Rhamnus frangula. Its laxative effect is due to the presence of anthraquinone glycosides, principally frangulins A and B and the related glucofrangulins A and B.
3- Aloe
Aloe or aloes is the dried juice of the leaves of Aloe barbadensis (Fam:Liliaceae). Aloe is from the Arabic word Alloeh or the Hebrew halal, meaning a shining bitter substance. Barbadensis refers to the Barbados Island.
4-Rhubarb
Rhubarb ,rheum or Chinese rhubarb consists of the dried rhizome and root that are deprived of periderm tissues of rheum officinale (Fam: polygonaceae).
5-Senna
Senna or senna leaves consist of the dried leaflets of Cassia acutifolia, known in commerce as Alexandria senna (Fam:Fabaceae).