Biosynthesis of artemisinin - revisited

Artemisinin is a well-known antimalarial drug isolated from the Artemisia annua plant. The biosynthesis of this well-known molecule has been reinvestigated by using [1-C-13] acetate, [2-C-13] acetate, and [1,6-C-13(2)] glucose. The C-13 peak enrichment in artemisinin was observed in six and nine carbon atoms from [1-C-13] acetate and [2-C-13] acetate, respectively. The C-13 NMR spectra of C-13-enriched artemisinin suggested that the mevalonic acid (MVA) pathway is the predominant route to biosynthesis of this sesquiterpene. On the other hand, the peak enrichment of five carbons of C-13-artemisinin including carbon atoms originating from methyls of dimethylallyl group of geranyl pyrophosphate (GPP) and farnesyl pyrophosphate (FPP) was observed from [1,6-C-13(2)] glucose. This suggested that GPP which is supposed to be biosynthesized in plastids travels from plastids to cytosol through the plastidial wall and combines with isopentenyl pyrophosphate (IPP) to form the (E,E)-FPP which finally cyclizes and oxidizes to artemisinin. In this way the DXP pathway also contributes to the biosynthesis of this sesquiterpene.