Rodger W. Stringham and David S. Teager

Org. Process Res. Dev., 2012, 16 (5), pp 764–768

DOI: 10.1021/op300037e

PAPER reports an improvement to the previously published manufacturing process for artemether, a key antimalarial drug, utilizing readily available reagents, easily controlled manufacturing conditions, and a greatly simplified workup and isolation. New analytical methods and in-process controls allow for optimization of yield through control of side product formation. A 70% overall yield from the two-step conversion of naturally or synthetically derived artemisinin to pure β-artemether is obtained. This corresponds to a usage factor of 1.35 kg of artemisinin needed to produce 1 kg of β-artemether, compared to the current industry average of 1.59 kg.

Correction to A Streamlined Process for the Conversion of Artemisinin toArtemether … The structure for β-artemether is shown above, with the correct stereochemistry shown at the anomeric (8a) position. … Assignments are correct for the α- and β-anomers of artemether and dihydroartemisinin as discussed in the text; only the structure drawings are in error. …

ACTs (Artemisinin) is extracted from the plant Artemisia annua out sesquiterpene lactones, is specific for malaria. With its discoverer Tu Yo Yo in 2011 received the Lasker Award for Clinical Medicine (Lasker Award), and because a number of the Lasker Award winners also won the Nobel Prize, artemisinin and its discoverer Tu Yo Yo won the Chinese public and widespread media attention.
The total synthesis of artemisinin from the Isopulegol ((-)-Isopulegol) began [JACS, 1983, 624].Contrast extracted from plants, is not an economical total synthesis method, but activity was found in the total synthesis of analogues are better practical significance of a thing. In this type of terpene total synthesis of natural products stereochemical conformation analysis is also very interesting. Hu menthol with MOMCl protected hydroxy, and get a double borohydride alcohol 1. Hydroboration Addition of anti-Markovnikov rule, which is replaced by hydrogen atoms added to the side of Quito, and the boron atoms added to the less substituted side. As the front side of the double bond MOM large steric hindrance, from the double rear borane adduct, resulting product1 . Compound 1 with a benzyl group protecting the primary alcohol, HCl removal of MOM protecting, PCC oxidation of the secondary alcohol to the ketone 3 . 3 with the hydrogen generating pull enolates LDA 4 , because of steric hindrance than hydrogen methyl, the nucleophilic reaction occurs in the torus , the form compound 5 . Ketone 5 and lithium reagent 6 an addition reaction, if one equivalent of lithium reagent, the resulting product was a 1:1 8 and 9 , if the 10-fold excess of lithium reagent, the resulting product was 8:1 8 and 9 . Lithium reagent 6 as a nucleophile large volume, its addition of cyclohexanone from the equatorial position to attack (such as an intermediate state 7 as shown), so that the generated key in an upright position hydroxyl group. Equivalent of lithium reagent no stereoselectivity of the reaction, but when a large excess of lithium, when chiral ketone 5 lithium reagent of the racemic 6 kinetic resolution becomes possible. Intermediate state 7 in, R configuration of the lithium reagent to Ketones speed is faster than its enantiomer S configuration lithium reagent. So generate eight faster than 9 , and finally get 8 and 9 of the ratio of 8:1. Lithium reagent 6, TMS air resistance maximum (A-value = 2.5 kcal / mol), OMe second air resistance (A-value = 0.75 kcal / mol), so that when the attack is downward TMS, OMe and H is determined by the relative position of cyclohexanone 2,6 substituent to the size and conformation of the decision, and should also be considered in the attack Burgi-Dunitz angle, so that the stereochemistry of the product unpredictable. Compound 8after removal of the benzyl protecting the primary alcohol with excess oxidized to carboxyl groups PCC automatically generate a macrolide 10 . 10 of the vinyl silane with m -CPBA and TFA into one11 , and then generate the enol methyl desilication TBAF ethers 12 , 12 and singlet oxygen reacts13 directly after treatment with acid artemisinin.