Anthraquinones

For the parent molecule 9,10-antraquinone, see here

Chemical structure of Aloe emodin.

Anthraquinones (also known as anthraquinonoids) are a class of naturally occurring phenolic compounds based on the 9,10-anthraquinone skeleton.

Biosynthesis

A type II polyketide synthase is responsible for anthraquinone biosynthesis in the bacterium Photorhabdus luminescens.^[1] Chorismate, formed by isochorismate synthase in the shikimate pathway, is an important precursor of anthraquinones in Morinda citrifolia. ^[2]

Test for anthraquinones in natural extracts

0.5g of plant extract is shaken with 10 ml of benzene and filtered. 5ml of 10% ammonia is added to the filtrate. The mixture is shaken and the presence of pink, red or violet colour indicates the presence of anthraquinones.^[3]

Derivatives

Hypericin and fagopyrin are naphthodianthrones, anthraquinone-derivatives.

Applications

Many quinones are stable in multiple redox states; as such they can absorb electrons when appropriate counterions are available to maintain the bulk neutrality of the material. As such, 2,6-dihydroanthraquinone can be used as a negative electrolyte reservoir in an alkaline flow battery (opposite ferrocyanide) to store electrons when a current is applied at an ion-selective membrane.^[4]

Anthraquinones are also used as laxatives such as in the drug Senna glycoside.

References