3.1 Biosynthesis of Anthracene Glycosides
The biosynthesis of anthracene glycosides may be considered under the following two heads, namely:
(a) Emodin and Other Related Derivatives: The indepth knowledge with regard to the biosynthesis of anthracene aglycones has been duly established from an elaborated study with microorganisms, specifically Penicillium islandicum as shown below:
In this particular instance, an intermediate poly β-ketomethylene acid is assumed to have formed from 8 acetate units which on being subjected to intramolecular condensation gives rise to anthraquinones i.e.; emodin and other related derivatives.
(b) Alizarin: Another metabolic pathway for the formation of anthraquinone is established and recognised through the shikimic acid—mevalonic acid mediators as could be seen functional in certain plants belonging to the family Rubiaceae as given below:
The biosynthesis of alizarin reveals that the ring A in alizarin molecule has been derived from the shikimic acid, whereas the ring C in alizarin has been incorporated by the mevalonic acid component.
