Extraction of artemisinin and artemisinic acid: preparation of artemether and new analogues.

The preparation of artemether from artemisinin is reviewed. Firstly, the extraction of artemisinin from Artemisia annua is described and an estimation of the yield per hectare based on literature data is given. Artemisinin is reduced with sodium borohydride to produce dihydroartemisinin as a mixture of epimers. The mixture is treated with methanol and an acid catalyst to provide artemether. Increasing demand for use of artemether places pressure on the supply of artemisinin, and an alternative means of preparing the drug from artemisinic acid, an abundant constituent of A. annua, which could triple current yields, is described. In anticipation of problems of drug resistance emerging with the continued use of artemether and artesunate to treat malaria, development of new derivatives of artemisinin which have enhanced stability is required. Examples of such derivatives which have been prepared in our laboratories, or proposed, are described.